JP7474125B2 - Blocked polyisocyanate composition, resin composition, resin film and laminate - Google Patents

Description

The present invention relates to a blocked polyisocyanate composition, a resin composition, a resin film, and a laminate.

Conventionally, polyurethane resin paints have excellent abrasion resistance, chemical resistance, and stain resistance. In particular, polyurethane resin paints using polyisocyanates obtained from aliphatic diisocyanates or alicyclic diisocyanates have even better weather resistance, and demand for them is increasing. However, polyurethane resin paints are generally two-liquid, making them extremely inconvenient to use. That is, ordinary polyurethane resin paints consist of two components, polyol and polyisocyanate, and it is necessary to store the polyol and polyisocyanate separately and mix them when painting. In addition, once the two are mixed, the paint gels in a short time and becomes unusable. Because polyurethane resin paints have such problems, it is extremely difficult to use them for automatic painting in fields where line painting is performed, such as automobile painting or weak electric painting. In addition, since isocyanates easily react with water, it is impossible to use them with water-based paints such as electrocoating paints. Furthermore, when paints containing isocyanates are used, it is necessary to thoroughly clean the painter and paint tank at the end of work, which significantly reduces work efficiency.

To improve the above-mentioned problems, it has been proposed to use blocked polyisocyanates in which all active isocyanate groups are blocked with a blocking agent. These blocked polyisocyanates do not react with polyols at room temperature. However, by heating, the blocking agent dissociates, and the active isocyanate groups are regenerated and react with polyols to cause a crosslinking reaction, thereby improving the above-mentioned problems. Therefore, many blocking agents have been investigated, and representative examples include phenol and methyl ethyl ketoxime.

However, when using blocked polyisocyanates that use these blocking agents, a high baking temperature of 140°C or higher is generally required. The need for baking at high temperatures is not only disadvantageous in terms of energy, but also requires the substrate to be heat resistant, which limits its applications.

On the other hand, research has been conducted into low-temperature baked blocked polyisocyanates using active methylene compounds such as acetoacetate esters and malonic acid diesters. For example, Patent Documents 1 and 2 propose blocked polyisocyanate compositions that cure at 90°C.

JP 2002-322238 A JP 2006-335954 A

However, in recent years, from the perspective of protecting the global environment and in light of the strong demand for adaptation to plastics with low heat resistance, there is a strong demand for blocked polyisocyanate compositions that cure at temperatures below 90°C. Under these circumstances, there is still no known composition that has good dispersibility when mixed with aqueous polyols (water-dispersible polyols) that have hydroxyl groups, does not gel or excessively thicken during storage, and has good curing properties at 80°C or less.

The present invention has been made in consideration of the above circumstances, and provides a blocked polyisocyanate composition that has good storage stability when made into a resin composition and good curing properties at a low temperature of about 80°C when made into a resin film, as well as a resin composition and a resin film using the blocked polyisocyanate composition.

That is, the present invention includes the following aspects .

The blocked polyisocyanate composition according to a first aspect of the present invention is a blocked polyisocyanate composition comprising a blocked polyisocyanate derived from a polyisocyanate, a malonic acid ester having one or more types of tertiary alkyl groups, and a malonic acid ester having one or more types of secondary alkyl groups, wherein the molar ratio of the constituent units derived from the malonic acid ester having a secondary alkyl group to the constituent units derived from the malonic acid ester having a tertiary alkyl group is greater than 5/95 and less than 95/5.

In the blocked polyisocyanate composition related to the first aspect, the malonate ester having a tertiary alkyl group includes di-tert-butyl malonate, and the malonate ester having a secondary alkyl group includes diisopropyl malonate.

In the blocked polyisocyanate composition according to the first aspect, the polyisocyanate may have an average number of isocyanate functional groups of 2 or more.

In the blocked polyisocyanate composition according to the first aspect, the polyisocyanate may be a polyisocyanate derived from one or more diisocyanates selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates.

The weight average molecular weight Mw of the blocked polyisocyanate composition according to the first embodiment is 2.0×10 ³ It may be more than that.

In the blocked polyisocyanate composition according to the first aspect, the blocked polyisocyanate may have an isocyanurate group.

A resin composition according to a second aspect of the present invention contains the blocked polyisocyanate composition according to the first aspect and a polyvalent hydroxy compound.

The resin film according to the third aspect of the present invention is obtained by curing the resin composition according to the third aspect. The resin composition is heated at 80° C. for 30 minutes to cure the resin film having a thickness of 40 μm. The gel fraction of the resin film may be 82% by mass or more when the resin composition is stored at 23° C. for 1 week and then immersed in acetone at 23° C. for 24 hours.

The resin composition may be heated on glass at 80° C. for 30 minutes to cure the resin composition, resulting in a resin film having a thickness of 40 μm, which has a Konig hardness at 23° C. of 38 times or more.
The resin composition may be heated at 80°C for 30 minutes to harden the resin film, which has a thickness of 40 µm, a width of 10 mm and a length of 40 mm. The resin film is set so that the chuck distance is 20 mm, and a tensile test is performed at 23°C and at a speed of 20 mm/min, and the maximum stress is 5 MPa or more.

A laminate according to a fourth aspect of the present invention is a laminate including two or more layers of the resin film according to the third aspect having different compositions,
The thickness of each layer of the laminate is 1 μm or more and 50 μm or less.

The blocked polyisocyanate composition of the above embodiment can provide a blocked polyisocyanate composition that has good storage stability when made into a resin composition and has good curing properties at a low temperature of about 80°C when made into a resin film. The resin composition of the above embodiment has good storage stability. The resin film of the above embodiment has good curing properties at a low temperature of about 80°C.

The following describes in detail the form for carrying out the present invention (hereinafter, referred to as the "present embodiment"). Note that the present invention is not limited to the present embodiment. The present invention can be carried out with appropriate modifications within the scope of its gist.

In this specification, the term "polyol" refers to a compound having two or more hydroxyl groups (-OH).
As used herein, the term "polyisocyanate" refers to a reaction product in which multiple monomer compounds having one or more isocyanate groups (--NCO) are bonded together.

In this specification, the term "structural unit" refers to a structure resulting from one molecule of a monomer in the structure that constitutes a polyisocyanate or a blocked polyisocyanate. For example, a structural unit derived from a malonic acid ester refers to a structure resulting from one molecule of a malonic acid ester in a blocked polyisocyanate. The structural unit may be a unit formed directly by a (co)polymerization reaction of a monomer, or may be a unit in which a portion of the unit is converted into a different structure by processing the (co)polymer.

<Blocked polyisocyanate composition>
The polyisocyanate composition of the present embodiment contains a blocked polyisocyanate derived from a polyisocyanate and one or more blocking agents.
The polyisocyanate composition of the present embodiment contains a structural unit represented by the following general formula (I) (hereinafter may be referred to as "structural unit (I)") and a structural unit represented by the following general formula (II) (hereinafter may be referred to as "structural unit (II)"), and the molar ratio of the structural unit represented by the following general formula (II) to the structural unit represented by the following general formula (I) (hereinafter may be abbreviated as "molar ratio of structural unit (II)/(I)") is greater than 5/95 and less than 95/5.

(In general formula (I), R ¹¹ , R ¹² and R ¹³ each independently represent an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group. R ¹⁴ , R ¹⁵ and R ¹⁶ each independently represent a hydrogen atom or an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group. The dashed lines represent bonds.)

(In general formula (II), R ²¹ , R ²² , R ²³ and R ²⁴ each independently represent a hydrogen atom or an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxyl group and an amino group. The dashed lines represent bonds.)

In the polyisocyanate composition of the present embodiment, the molar ratio of the structural units (II)/(I) is more than 5/95 and less than 95/5, preferably 7/93 or more and 93/7 or less, more preferably 10/90 or more and 93/7 or less, even more preferably 20/80 or more and 93/7 or less, particularly preferably 30/70 or more and 93/7 or less, and most preferably 35/65 or more and 93/7 or less. By having the molar ratio be equal to or more than the lower limit, the storage stability of the resin composition can be improved, and by having the molar ratio be equal to or less than the upper limit, the low-temperature curing property of the resin film can be improved.
The molar ratio of the structural unit (II) to the structural unit (I) can be calculated, for example, by evaporating the blocked polyisocyanate composition at ⁵⁰ ° C. or less to remove the solvent and other components, drying the composition under reduced pressure, and then measuring the composition ratio of the structural unit (II) to the structural unit (I) by ¹ H-NMR and 13 C-NMR.

It is preferred that the structural unit (I) is derived from a malonic acid ester having a tertiary alkyl group, which is a blocking agent, and that the structural unit (II) is derived from a malonic acid ester having a secondary alkyl group, which is a blocking agent, or a malonic acid ester having a primary alkyl group.
That is, the polyisocyanate composition of the present embodiment preferably contains a polyisocyanate, a malonic acid ester having one or more tertiary alkyl groups, and a blocked polyisocyanate derived from a malonic acid ester having one or more secondary alkyl groups or a malonic acid ester having one or more primary alkyl groups. At this time, the molar ratio of the structural unit derived from a malonic acid ester having a secondary alkyl group to the structural unit derived from a malonic acid ester having a tertiary alkyl group, and the molar ratio of the structural unit derived from a malonic acid ester having a primary alkyl group to the structural unit derived from a malonic acid ester having a tertiary alkyl group are in the same range as the molar ratio of the structural unit (II)/(I). By the molar ratio being equal to or greater than the lower limit, the storage stability of the resin composition can be improved, and by the molar ratio being equal to or less than the upper limit, the low-temperature curing property of the resin film can be improved.
The molar ratio can be calculated, for example, from the molar amounts of the malonic acid ester having a tertiary alkyl group, the malonic acid ester having a secondary alkyl group, and the malonic acid ester having a primary alkyl group used as the blocking agent. Alternatively, the molar ratio can be calculated, for example, by removing the solvent and other components from the blocked polyisocyanate composition at ^{50 °} C. or less using an evaporator, drying under reduced pressure, and then measuring the composition ratio of the structural units derived from a malonic acid ester having a secondary alkyl group to the structural units derived from a malonic acid ester having a tertiary alkyl group, or the composition ratio of the structural units derived from a malonic acid ester having a primary alkyl group to the structural units derived from a malonic acid ester having a tertiary alkyl group, by 1 H-NMR and 13 C-NMR.

In a further preferred embodiment, the blocked polyisocyanate composition of this embodiment contains a blocked polyisocyanate derived from a polyisocyanate, a malonic acid ester having one or more tertiary alkyl groups, and a malonic acid ester having one or more secondary alkyl groups.

In the blocked polyisocyanate composition of the present embodiment, the molar ratio of the structural units derived from the malonic acid ester having a secondary alkyl group to the structural units derived from the malonic acid ester having a tertiary alkyl group (structural units derived from the malonic acid ester having a secondary alkyl group/structural units derived from the malonic acid ester having a tertiary alkyl group) is more than 5/95 and less than 95/5, preferably 7/93 or more and 93/7 or less, more preferably 10/90 or more and 93/7 or less, even more preferably 20/80 or more and 93/7 or less, particularly preferably 30/70 or more and 93/7 or less, and most preferably 35/65 or more and 93/7 or less. By having the molar ratio be equal to or more than the lower limit, the storage stability of a resin composition can be improved, and by having the molar ratio be equal to or less than the upper limit, the low-temperature curing property of a resin film can be improved.
The molar ratio can be calculated, for example, from the molar amounts of the malonic acid ester having a tertiary alkyl group and the malonic acid ester having a secondary alkyl group used as the blocking agent. Alternatively, the molar ratio can be calculated, for example, by evaporating the blocked polyisocyanate composition at ⁵⁰ ° C. or less to remove ^the solvent and other components, drying the composition under reduced pressure, and then measuring the composition ratio of the structural units derived from the malonic acid ester having a secondary alkyl group to the structural units derived from the malonic acid ester having a tertiary alkyl group by 1 H-NMR and 13 C-NMR.

It has been known for some time that blocked polyisocyanates blocked with malonic acid esters having a tertiary alkyl group have excellent curing properties at low temperatures of about 80°C. However, there is a problem that the reaction with the hydroxyl groups of polyhydric hydroxy compounds such as polyols is high, and when a resin composition containing a base agent and a curing agent is stored, a significant increase in viscosity and gelation are likely to occur. Therefore, there has been no resin composition that combines curing properties at low temperatures of about 80°C and storage stability when made into a resin composition. In addition, there is a method of improving storage stability by adding alcohols to the resin composition, but adding a large amount of alcohols may affect the compatibility with the polyol solution and the physical properties of the resin film produced, making it difficult to combine low-temperature curing properties and storage stability. In addition, from the viewpoint of design freedom, a composition that does not contain alcohol or contains a small amount of alcohol is desired.

In contrast, the blocked polyisocyanate composition of the present embodiment uses a combination of a malonic acid ester having a tertiary alkyl group and a malonic acid ester having a secondary alkyl group or a malonic acid ester having a primary alkyl group as a blocking agent, and the molar ratio of the constituent units derived from the malonic acid ester having a secondary alkyl group to the constituent units derived from the malonic acid ester having a tertiary alkyl group, or the molar ratio of the constituent units derived from the malonic acid ester having a primary alkyl group to the constituent units derived from the malonic acid ester having a tertiary alkyl group, is within the above range, thereby improving the above problem, effectively suppressing the increase in viscosity and gelation during storage of the mixed liquid of the blocked polyisocyanate composition and the polyhydric hydroxy compound, and exhibiting good storage stability. At the same time, a resin film with excellent curing properties at a low temperature of about 80°C is obtained.

Below, each component contained in the blocked polyisocyanate composition of this embodiment will be described in detail.

<Blocked polyisocyanate>
A blocked polyisocyanate is a reaction product of a polyisocyanate and a blocking agent, i.e., at least a part of the isocyanate groups in the polyisocyanate is blocked with a blocking agent.

The polyisocyanate composition of the present embodiment contains a structural unit (structural unit (I)) represented by the following general formula (I) and a structural unit (structural unit (II)) represented by the following general formula (II). That is, in the polyisocyanate composition of the present embodiment, the blocked polyisocyanate may contain both structural unit (I) and structural unit (II) in the molecule, or may be a mixture of a blocked polyisocyanate containing structural unit (I) and a blocked polyisocyanate containing structural unit (II).

(In general formula (I), R ¹¹ , R ¹² and R ¹³ each independently represent an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group. R ¹⁴ , R ¹⁵ and R ¹⁶ each independently represent a hydrogen atom or an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group. The dashed lines represent bonds.)

(In general formula (II), R ²¹ , R ²² , R ²³ and R ²⁴ each independently represent a hydrogen atom or an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxyl group and an amino group. The dashed lines represent bonds.)

[Structural unit (I)]
In formula (I), R ¹¹ , R ¹² and R ¹³ are each independently an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxyl group and an amino group, and R ¹⁴ , R ¹⁵ and R ¹⁶ are each independently a hydrogen atom or an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxyl group and an amino group.

The alkyl group in R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ and R ¹⁶ preferably has 1 or more and 30 or less carbon atoms, more preferably has 1 or more and 8 or less carbon atoms, further preferably has 1 or more and 6 or less carbon atoms, and particularly preferably has 1 or more and 4 or less carbon atoms. Specific examples of the alkyl group having no substituent include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a tert-butyl group, a sec-butyl group, an isobutyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a 1-methylbutyl group, an n-hexyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 2,2-dimethylbutyl group, a 2,3-dimethylbutyl group, an n-heptyl group, a 2-methylhexyl group, a 3-methylhexyl group, a 2,2-dimethylpentyl group, a 2,3-dimethylpentyl group, a 2,4-dimethylpentyl group, a 3,3-dimethylpentyl group, a 3-ethylpentyl group, a 2,2,3-trimethylbutyl group, an n-octyl group, an isooctyl group, a 2-ethylhexyl group, a nonyl group, and a decyl group.

Furthermore, when R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ and R ¹⁶ are alkyl groups having a substituent, the substituent is a hydroxy group or an amino group.
Examples of the alkyl group containing a hydroxy group as a substituent include a hydroxymethyl group, a hydroxyethyl group, and a hydroxypropyl group.
Examples of the alkyl group containing an amino group as a substituent include an aminomethyl group, an aminoethyl group, an aminopropyl group, and an aminobutyl group.
Examples of the alkyl group containing a hydroxy group and an amino group as a substituent include a hydroxyaminomethyl group, a hydroxyaminoethyl group, and a hydroxyaminopropyl group.

Among these, the alkyl group in R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , and R ¹⁶ is preferably an alkyl group having 1 to 4 carbon atoms and no substituents, more preferably a methyl group, an ethyl group, or a propyl group, and even more preferably a methyl group, because it has excellent low-temperature curing properties when made into a resin film.
When R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ and R ¹⁶ are all methyl groups, the structural unit (I) is a structural unit derived from di-tert-butyl malonate. Of these, it is particularly preferable that R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ and R ¹⁶ are all methyl groups, that is, the structural unit (I) is a structural unit derived from di-tert-butyl malonate.

[Structural unit (II)]
In general formula (II), R ²¹ , R ²² , R ²³ and R ²⁴ each independently represent a hydrogen atom or an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group.

Examples of the alkyl group which may have one or more substituents selected from the group consisting of a hydroxy group and an amino group in ^R21 , ^R22 , ^R23 , and ^R24 include the same as those exemplified in " ^R11 , ^R12 , ^R13 , ^R14 , ^R15 , and ^R16 " above.

Among these, R ²¹ , R ²² , R ²³ and R ²⁴ are preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms and no substituents, because they have excellent storage stability when made into a resin composition, more preferably a hydrogen atom, a methyl group or an ethyl group, and even more preferably a methyl group or an ethyl group, because they have excellent low-temperature curing properties.
When R ²¹ , R ²² , R ²³ and R ²⁴ are all methyl groups, the structural unit (II) is a structural unit derived from diisopropyl malonate. When one of R ²¹ and R ²² is a hydrogen atom and the other is a methyl group, and when one of R ²³ and R ²⁴ is a hydrogen atom and the other is a methyl group, the structural unit (II) is a structural unit derived from diethyl malonate. Among them, it is particularly preferable that R ²¹ , R ²² , R ²³ and R ²⁴ are all methyl groups, that is, the structural unit (II) is a structural unit derived from diisopropyl malonate.

The blocking agent preferably contains a malonic acid ester having a secondary alkyl group or a malonic acid ester having a primary alkyl group, and a malonic acid ester having a tertiary alkyl group, and more preferably contains a malonic acid ester having a secondary alkyl group and a malonic acid ester having a tertiary alkyl group. The blocked polyisocyanate contained in the blocked polyisocyanate composition of this embodiment may be a blocked polyisocyanate in which at least a part of the isocyanate groups in the molecule of the blocked polyisocyanate are blocked with a malonic acid ester having a secondary alkyl group or a malonic acid ester having a primary alkyl group, and a malonic acid ester having a tertiary alkyl group. Alternatively, the blocked polyisocyanate may be a mixture of a blocked polyisocyanate in which at least a part of the isocyanate groups in the polyisocyanate are blocked with a malonic acid ester having a secondary alkyl group, or a blocked polyisocyanate in which at least a part of the isocyanate groups in the polyisocyanate are blocked with a malonic acid ester having a primary alkyl group, and a blocked polyisocyanate in which at least a part of the isocyanate groups in the polyisocyanate are blocked with a malonic acid ester having a tertiary alkyl group.

The blocked polyisocyanate may have one or more functional groups selected from the group consisting of an allophanate group, a uretdione group, an iminooxadiazinedione group, an isocyanurate group, a urethane group, and a biuret group. Of these, it is preferable to have an isocyanurate group because it has excellent weather resistance.

[Polyisocyanate]
The polyisocyanate used in the production of the blocked polyisocyanate is a reaction product obtained by reacting multiple monomer compounds having one or more isocyanate groups (-NCO) (hereinafter, sometimes referred to as "isocyanate monomers").
The isocyanate monomer is preferably one having a carbon number of 4 to 30. Specific examples of the isocyanate monomer include the following. These isocyanate monomers may be used alone or in combination of two or more.
(1) Aromatic diisocyanates such as diphenylmethane-4,4'-diisocyanate (MDI), 1,5-naphthalene diisocyanate, tolylene diisocyanate (TDI), xylylene diisocyanate, and m-tetramethylxylylene diisocyanate (TMXDI).
(2) Aliphatic diisocyanates such as 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (hereinafter sometimes referred to as "HDI"), 2,2,4-trimethyl-1,6-diisocyanatohexane, 2,4,4-trimethyl-1,6-hexamethylene diisocyanate, 2-methylpentane-1,5-diisocyanate (MPDI), and lysine diisocyanate (hereinafter sometimes referred to as "LDI").
(3) Alicyclic diisocyanates such as isophorone diisocyanate (hereinafter sometimes referred to as "IPDI"), 1,3-bis(diisocyanatemethyl)cyclohexane, 4,4'-dicyclohexylmethane diisocyanate, diisocyanatenorbornane, and di(isocyanatemethyl)norbornane.
(4) Triisocyanates such as 4-isocyanatomethyl-1,8-octamethylene diisocyanate (hereinafter sometimes referred to as "NTI"), 1,3,6-hexamethylene triisocyanate (hereinafter sometimes referred to as "HTI"), bis(2-isocyanatoethyl) 2-isocyanatoglutarate (hereinafter sometimes referred to as "GTI"), and lysine triisocyanate (hereinafter sometimes referred to as "LTI").

Among them, the isocyanate monomer is preferably one or more diisocyanates selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates, because they have excellent weather resistance. Moreover, the isocyanate monomer is more preferably HDI or IPDI, because they are easily available industrially. Moreover, the isocyanate monomer is even more preferably HDI, because it reduces the viscosity of the blocked polyisocyanate component.

As the isocyanate monomer used in the production of polyisocyanate, either an aliphatic diisocyanate or an alicyclic diisocyanate may be used alone or in combination, but it is preferable to use an aliphatic diisocyanate and an alicyclic diisocyanate in combination, and it is particularly preferable to use HDI and IPDI. By using an aliphatic diisocyanate and an alicyclic diisocyanate, the toughness and hardness of the coating film can be further improved.

In the polyisocyanate, from the viewpoint of improving the coating hardness and strength, the mass ratio of the constituent units derived from an aliphatic diisocyanate to the constituent units derived from an alicyclic diisocyanate (constituent units derived from an aliphatic diisocyanate/constituent units derived from an alicyclic diisocyanate) is preferably from 50/50 to 95/5, more preferably from 55/45 to 93/7, even more preferably from 60/40 to 91/9, and even more preferably from 65/35 to 90/10.
By setting the mass ratio of the constituent units derived from an aliphatic diisocyanate to the constituent units derived from an alicyclic diisocyanate to be equal to or greater than the above lower limit, it is possible to more effectively prevent a decrease in flexibility when the coating film is formed, whereas by setting the mass ratio to be equal to or less than the above upper limit, it is possible to more effectively improve the hardness when the coating film is formed.
The mass ratio of the constituent units derived from the aliphatic diisocyanate to the constituent units derived from the alicyclic diisocyanate can be calculated, for example, by the following method. First, the mass of the unreacted aliphatic diisocyanate and the mass of the unreacted alicyclic diisocyanate are calculated from the mass of the unreacted diisocyanate after the reaction and the aliphatic diisocyanate concentration and the alicyclic diisocyanate concentration in the unreacted diisocyanate obtained by gas chromatography measurement. Next, the mass of the unreacted aliphatic diisocyanate and the mass of the unreacted alicyclic diisocyanate calculated above are subtracted from the mass of the charged aliphatic diisocyanate and the mass of the alicyclic diisocyanate, respectively, and the obtained difference is the mass of the constituent units derived from the aliphatic diisocyanate and the mass of the constituent units derived from the alicyclic diisocyanate, respectively. Next, the mass of the constituent units derived from the aliphatic diisocyanate is divided by the mass of the constituent units derived from the alicyclic diisocyanate to obtain the mass ratio of the constituent units derived from the aliphatic diisocyanate to the constituent units derived from the alicyclic diisocyanate.

(Polyol)
The polyisocyanate is preferably derived from the above-mentioned diisocyanate monomer and a polyol having an average hydroxyl functional group number of 3.0 to 8.0. This allows the average number of isocyanate groups in the resulting polyisocyanate to be larger. In the polyisocyanate, urethane groups are formed by the reaction between the hydroxyl groups of polyol B and the isocyanate groups of the diisocyanate monomer.

The average number of hydroxyl functional groups of the polyol is preferably 3.0 or more and 8.0 or less, more preferably 3 or more and 6 or less, even more preferably 3 or more and 5 or less, and particularly preferably 3 or 4. The average number of hydroxyl functional groups of the polyol referred to here is the number of hydroxyl groups present in one molecule of the polyol.

From the viewpoint of improving the coating hardness and strength, the number average molecular weight of the polyol is preferably from 100 to 1,000, more preferably from 100 to 900, more preferably from 100 to 600, still more preferably from 100 to 570, even more preferably from 100 to 500, still more preferably from 100 to 400, particularly preferably from 100 to 350, and most preferably from 100 to 250.
When the number average molecular weight of the polyol is within the above range, the blocked polyisocyanate composition has excellent low-temperature curing properties when formed into a coating film, and is particularly excellent in hardness and strength. The number average molecular weight Mn of the polyol is, for example, the number average molecular weight based on polystyrene standards measured by GPC.

Examples of such polyols include trimethylolpropane, glycerol, and polycaprolactone polyols derived from trihydric or higher polyhydric alcohols and ε-caprolactone.
Commercially available polycaprolactone polyols include, for example, Daicel Corporation's "PLACCEL 303" (number average molecular weight 300), "PLACCEL 305" (number average molecular weight 550), "PLACCEL 308" (number average molecular weight 850), and "PLACCEL 309" (number average molecular weight 900).

(Method for producing polyisocyanate)
The method for producing polyisocyanate will be described in detail below.
The polyisocyanate can be obtained by, for example, carrying out an allophanate reaction to form an allophanate group, a uretdione reaction to form a uretdione group, an iminooxadiazinedione reaction to form an iminooxadiazinedione group, an isocyanurate reaction to form an isocyanurate group, a urethanization reaction to form a urethane group, and a biuret reaction to form a biuret group all at once in the presence of an excess of isocyanate monomer, and removing the unreacted isocyanate monomer after the reaction is completed. That is, the polyisocyanate obtained by the above reaction is a reaction product in which a plurality of the above-mentioned isocyanate monomers are bonded, and which has one or more types selected from the group consisting of an allophanate group, a uretdione group, an iminooxadiazinedione group, an isocyanurate group, a urethane group, and a biuret group.
Alternatively, the above reactions may be carried out separately and the resulting polyisocyanates may be mixed in a specific ratio.
From the viewpoint of ease of production, it is preferable to carry out the above reaction at one time to obtain a polyisocyanate, and from the viewpoint of freely adjusting the molar ratio of each functional group, it is preferable to produce them separately and then mix them.

(1) Method for Producing Allophanate Group-Containing Polyisocyanate Allophanate group-containing polyisocyanate can be obtained by adding an alcohol to an isocyanate monomer and using an allophanate reaction catalyst.
The alcohol used to form the allophanate group is preferably an alcohol formed only from carbon, hydrogen and oxygen.
Specific examples of the alcohol include, but are not limited to, monoalcohols, dialcohols, etc. These alcohols may be used alone or in combination of two or more.
Examples of monoalcohols include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, and nonanol.
Examples of the dialcohol include ethylene glycol, 1,3-butanediol, neopentyl glycol, and 2-ethylhexanediol.
Among them, as the alcohol, a monoalcohol is preferable, and a monoalcohol having a molecular weight of 200 or less is more preferable.

Examples of the allophanate reaction catalyst include, but are not limited to, alkyl carboxylates of tin, lead, zinc, bismuth, zirconium, zirconyl, and the like.
Examples of tin alkylcarboxylates (organotin compounds) include tin 2-ethylhexanoate and dibutyltin dilaurate.
An example of the alkyl carboxylate of lead (organic lead compound) is lead 2-ethylhexanoate.
Examples of zinc alkylcarboxylates (organic zinc compounds) include zinc 2-ethylhexanoate.
An example of the alkyl carboxylate of bismuth is bismuth 2-ethylhexanoate.
An example of the zirconium alkylcarboxylate is zirconium 2-ethylhexanoate.
An example of the zirconyl alkylcarboxylate is zirconyl 2-ethylhexanoate. These catalysts can be used alone or in combination of two or more.
In addition, an isocyanurate reaction catalyst described later can also serve as an allophanate reaction catalyst. When an allophanate reaction is carried out using an isocyanurate reaction catalyst described later, an isocyanurate group-containing polyisocyanate (hereinafter, sometimes referred to as an "isocyanurate-type polyisocyanate") is naturally produced.
Among these, it is preferable from the viewpoint of economical production to carry out the allophanate formation reaction and the isocyanurate formation reaction using an isocyanurate formation catalyst described below as the allophanate formation reaction catalyst.

The lower limit of the amount of the allophanate reaction catalyst used is preferably 10 ppm by mass, more preferably 20 ppm by mass, further preferably 40 ppm by mass, and particularly preferably 80 ppm by mass, based on the mass of the charged isocyanate monomer.
The upper limit of the amount of the allophanate reaction catalyst used is preferably 1000 ppm by mass, more preferably 800 ppm by mass, further preferably 600 ppm by mass, and particularly preferably 500 ppm by mass, based on the mass of the charged isocyanate monomer.
That is, the amount of the allophanate reaction catalyst used is preferably 10 ppm by mass or more and 1,000 ppm by mass or less, more preferably 20 ppm by mass or more and 800 ppm by mass or less, even more preferably 40 ppm by mass or more and 600 ppm by mass or less, and particularly preferably 80 ppm by mass or more and 500 ppm by mass or less, relative to the mass of the charged isocyanate monomer.

The lower limit of the allophanate formation reaction temperature is preferably 40°C, more preferably 60°C, further preferably 80°C, and particularly preferably 100°C.
The upper limit of the allophanate reaction temperature is preferably 180°C, more preferably 160°C, and even more preferably 140°C.
That is, the allophanate reaction temperature is preferably 40° C. or higher and 180° C. or lower, more preferably 60° C. or higher and 160° C. or lower, even more preferably 80° C. or higher and 140° C. or lower, and particularly preferably 100° C. or higher and 140° C. or lower.
By setting the allophanate formation reaction temperature to the above lower limit or higher, it is possible to further increase the reaction rate. By setting the allophanate formation reaction temperature to the above upper limit or lower, it is possible to more effectively suppress coloration of the polyisocyanate.

(2) Method for Producing Uretdione Group-Containing Polyisocyanate When deriving a polyisocyanate having uretdione groups from an isocyanate monomer, the polyisocyanate can be produced, for example, by polymerizing the isocyanate monomer using a uretdione reaction catalyst or by heat.
The uretdione reaction catalyst is not particularly limited, but examples thereof include tertiary phosphines such as trialkylphosphines, tris(dialkylamino)phosphines and cycloalkylphosphines, Lewis acids, and the like.
Examples of the trialkylphosphine include tri-n-butylphosphine and tri-n-octylphosphine.
An example of the tris(dialkylamino)phosphine is tris-(dimethylamino)phosphine.
The cycloalkylphosphine includes, for example, cyclohexyl-di-n-hexylphosphine.
Examples of Lewis acids include boron trifluoride and zinc oxychloride.

Many of the uretdione reaction catalysts can also simultaneously promote the isocyanurate reaction.
When a uretdione-forming reaction catalyst is used, it is preferable to add a deactivator for the uretdione-forming reaction catalyst such as phosphoric acid or methyl paratoluenesulfonate to terminate the uretdione-forming reaction when a desired yield is achieved.
When one or more diisocyanates selected from the group consisting of the aliphatic diisocyanates and the alicyclic diisocyanates are heated to obtain a polyisocyanate having a uretdione group without using a uretdione reaction catalyst, the heating temperature is preferably 120° C. or higher, and more preferably 150° C. or higher and 170° C. or lower. The heating time is preferably 1 hour or longer and 4 hours or shorter.

(3) Method for Producing Iminooxadiazinedione Group-Containing Polyisocyanate When deriving an iminooxadiazinedione group-containing polyisocyanate from an isocyanate monomer, an iminooxadiazinedione reaction catalyst is usually used.
Examples of the iminooxadiazinedione catalyst include the following 1) and 2).
1) (Poly)hydrogen fluoride represented by the general formula M[F _n ] or M[F _n (HF) _m ] (wherein m and n are integers satisfying the relationship m/n>0. M is an n-charged cation (mixture) or one or more radicals having a valence of n in total).
2) Compounds comprising a compound represented by the general formula R ¹ --CR' ₂ --C(O)O-- or R ² ═CR'--C(O)O-- and a quaternary ammonium cation or a quaternary phosphonium cation.
(In the formula, ^R1 and ^R2 are each independently a linear, branched or cyclic, saturated or unsaturated perfluoroalkyl group having from 1 to 30 carbon atoms. Each of the multiple R's is independently a hydrogen atom, or an alkyl or aryl group having from 1 to 20 carbon atoms which may contain a heteroatom.)

Specific examples of the compound 1) ((poly)hydrogen fluoride) include tetramethylammonium fluoride hydrate, tetraethylammonium fluoride, and the like.
Specific examples of the compound 2) include 3,3,3-trifluorocarboxylic acid, 4,4,4,3,3-pentafluorobutanoic acid, 5,5,5,4,4,3,3-heptafluoropentanoic acid, and 3,3-difluoroprop-2-enoic acid.
Among them, as the iminooxadiazinedione reaction catalyst, 1) is preferred from the viewpoint of availability, and 2) is preferred from the viewpoint of safety.

The lower limit of the amount of the iminooxadiazinedione catalyst used is not particularly limited, but from the viewpoint of reactivity, the amount is preferably 5 ppm by mass, more preferably 10 ppm, and even more preferably 20 ppm, relative to the raw material isocyanate monomer such as HDI.
The upper limit of the amount of the iminooxadiazinedione catalyst used is preferably 5000 ppm, more preferably 2000 ppm, and even more preferably 500 ppm by mass relative to the raw material isocyanate monomer such as HDI, from the viewpoint of suppressing coloration and discoloration of the product and controlling the reaction.
That is, the amount of the iminooxadiazinedione catalyst used is preferably 5 ppm or more and 5000 ppm or less, more preferably 10 ppm or more and 2000 ppm or less, and even more preferably 20 ppm or more and 500 ppm or less, by mass ratio relative to the raw material isocyanate monomer such as HDI.

The lower limit of the reaction temperature for the iminooxadiazinedione formation is not particularly limited, but from the viewpoint of the reaction rate, it is preferably 40°C, more preferably 50°C, and even more preferably 60°C.
The upper limit of the reaction temperature for the iminooxadiazinedione formation is preferably 150° C., more preferably 120° C., and even more preferably 110° C., from the viewpoint of suppressing coloration and discoloration of the product.
That is, the reaction temperature for the iminooxadiazinedione formation is preferably 40° C. or higher and 150° C. or lower, more preferably 50° C. or higher and 120° C. or lower, and even more preferably 60° C. or higher and 110° C. or lower.

When the iminooxadiazinedione reaction reaches the desired iminooxadiazinedione group content, the iminooxadiazinedione reaction can be stopped. The iminooxadiazinedione reaction can be stopped, for example, by adding an acidic compound to the reaction solution. Examples of acidic compounds include phosphoric acid, acidic phosphate esters, sulfuric acid, hydrochloric acid, and sulfonic acid compounds. This neutralizes the iminooxadiazinedione reaction catalyst, or inactivates it by thermal decomposition or chemical decomposition. After the reaction is stopped, filtration is performed if necessary.

(4) Method for Producing Isocyanurate Group-Containing Polyisocyanate As a catalyst for deriving an isocyanurate group-containing polyisocyanate from an isocyanate monomer, a commonly used isocyanurate reaction catalyst can be mentioned.

The isocyanurate reaction catalyst is not particularly limited, but is preferably a catalyst having basicity in general. Specific examples of the isocyanurate reaction catalyst include the following.
1) Hydroxides of tetraalkylammonium such as tetramethylammonium, tetraethylammonium, and tetrabutylammonium, and organic weak acid salts such as acetates, propionates, octylates, caprates, myristates, and benzoates of the above tetraalkylammonium.
2) Hydroxides of aryltrialkylammonium such as benzyltrimethylammonium and trimethylphenylammonium, and organic weak acid salts such as acetates, propionates, octylates, caprates, myristates, and benzoates of the above aryltrialkylammonium.
3) Hydroxyalkylammonium hydroxides such as trimethylhydroxyethylammonium, trimethylhydroxypropylammonium, triethylhydroxyethylammonium, and triethylhydroxypropylammonium, and organic weak acid salts such as acetates, propionates, octylates, caprates, myristates, and benzoates of the above hydroxyalkylammoniums.
4) Metal salts, such as tin, zinc, lead, etc., of alkyl carboxylic acids, such as acetic acid, propionic acid, caproic acid, octylic acid, capric acid, and myristic acid.
5) Metal alcoholates such as sodium and potassium.
6) Aminosilyl group-containing compounds such as hexamethylenedisilazane.
7) Mannich bases.
8) Mixtures of tertiary amines and epoxy compounds.
9) Phosphorus compounds such as tributylphosphine.

Among these, from the viewpoint of preventing the generation of unnecessary by-products, the isocyanurate reaction catalyst is preferably a quaternary ammonium hydroxide or an organic weak acid salt of a quaternary ammonium, and more preferably a tetraalkylammonium hydroxide, an organic weak acid salt of a tetraalkylammonium, an aryltrialkylammonium hydroxide, or an organic weak acid salt of an aryltrialkylammonium.

The upper limit of the amount of the isocyanurate reaction catalyst used is preferably 1000 ppm by mass, more preferably 500 ppm by mass, and even more preferably 100 ppm by mass, based on the mass of the charged isocyanate monomer.
On the other hand, the lower limit of the amount of the isocyanurate reaction catalyst used is not particularly limited, and may be, for example, 10 ppm by mass.

The isocyanurate reaction temperature is preferably 50°C or higher and 120°C or lower, and more preferably 60°C or higher and 90°C or lower. By keeping the isocyanurate reaction temperature below the upper limit, coloration of the polyisocyanate tends to be more effectively suppressed.

When a desired conversion rate (the ratio of the mass of polyisocyanate produced in the isocyanuration reaction to the mass of the charged isocyanate monomer) is reached, the isocyanuration reaction is stopped by adding an acidic compound (e.g., phosphoric acid, an acidic phosphoric acid ester, etc.).
In order to obtain polyisocyanate, it is necessary to stop the reaction at an early stage. However, since the reaction rate of the isocyanurate reaction is very fast at the early stage, it is difficult to stop the reaction at an early stage, and therefore the reaction conditions, particularly the amount and method of adding the catalyst, must be carefully selected. For example, a method of adding the catalyst in portions at regular intervals is recommended as a suitable method.
Therefore, the conversion rate of the isocyanurate reaction to obtain a polyisocyanate is preferably 10% or more and 60% or less, more preferably 15% or more and 55% or less, and even more preferably 20% or more and 50% or less.
By setting the conversion rate of the isocyanurate reaction to the upper limit or less, the viscosity of the blocked polyisocyanate component can be made lower. By setting the conversion rate of the isocyanurate reaction to the lower limit or more, the reaction terminating operation can be more easily carried out.

When deriving a polyisocyanate containing an isocyanurate group, a monohydric to hexahydric alcohol can be used in addition to the above-mentioned isocyanate monomer.
Examples of alcohols having a valence of 1 to 6 that can be used include non-polymerizable alcohols and polymerizable alcohols. The term "non-polymerizable alcohol" used herein means an alcohol that does not have a polymerizable group. On the other hand, the term "polymerizable alcohol" means an alcohol obtained by polymerizing a monomer having a polymerizable group and a hydroxyl group.
Examples of the non-polymerizable alcohol include polyhydric alcohols such as monoalcohols, diols, triols, and tetraols.
Examples of monoalcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, n-pentanol, n-hexanol, n-octanol, n-nonanol, 2-ethylbutanol, 2,2-dimethylhexanol, 2-ethylhexanol, cyclohexanol, methylcyclohexanol, and ethylcyclohexanol.
Examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,2-propanediol, 1,5-pentanediol, 2-methyl-2,3-butanediol, and 2-methyl-2,3-butanediol. Examples of the hexanediol include hexanediol, 1,6-hexanediol, 1,2-hexanediol, 2,5-hexanediol, 2-methyl-2,4-pentanediol, 2,3-dimethyl-2,3-butanediol, 2-ethyl-hexanediol, 1,2-octanediol, 1,2-decanediol, 2,2,4-trimethylpentanediol, 2-butyl-2-ethyl-1,3-propanediol, and 2,2-diethyl-1,3-propanediol.
Examples of triols include glycerin and trimethylolpropane.
An example of the tetraols is pentaerythritol.

Polymerizable alcohols include, but are not limited to, polyester polyols, polyether polyols, acrylic polyols, polyolefin polyols, etc.

The polyester polyols are not particularly limited, but examples thereof include products obtained by a condensation reaction between a dibasic acid alone or a mixture of dibasic acids and a polyhydric alcohol alone or a mixture of polyhydric alcohols.
The dibasic acid is not particularly limited, but examples thereof include at least one dibasic acid selected from the group consisting of carboxylic acids such as succinic acid, adipic acid, sebacic acid, dimer acid, maleic anhydride, phthalic anhydride, isophthalic acid, and terephthalic acid.
The polyhydric alcohol is not particularly limited, but examples thereof include at least one polyhydric alcohol selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, trimethylolpropane, and glycerin.
Examples of polyester polyols include polycaprolactones obtained by ring-opening polymerization of ε-caprolactone using the above polyhydric alcohols.

The polyether polyols are not particularly limited, but examples thereof include polyether polyols obtained by adding an alkylene oxide or a mixture of an alkylene oxide to a polyhydric alcohol or a mixture of an alkylene oxide using an alkali metal hydroxide or a strong basic catalyst, polyether polyols obtained by reacting an alkylene oxide with a polyamine compound, and so-called polymer polyols obtained by polymerizing acrylamide or the like using the above-mentioned polyethers as a medium.
Examples of the alkali metal include lithium, sodium, and potassium.
Examples of the strong basic catalyst include alcoholates and alkylamines.
Examples of the polyhydric alcohol include the same ones as those exemplified for the polyester polyols above.
Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, cyclohexene oxide, and styrene oxide.
Examples of the polyamine compound include ethylenediamines.

The acrylic polyols are not particularly limited, but examples thereof include copolymers of a single or mixture of ethylenically unsaturated bond-containing monomers having a hydroxyl group and a single or mixture of other ethylenically unsaturated bond-containing monomers copolymerizable therewith.
The ethylenically unsaturated bond-containing monomer having a hydroxyl group is not particularly limited, but examples thereof include hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate.
The other ethylenically unsaturated bond-containing monomer copolymerizable with the ethylenically unsaturated bond-containing monomer having a hydroxyl group is not particularly limited, and examples thereof include acrylic acid esters, methacrylic acid esters, unsaturated carboxylic acids, unsaturated amides, vinyl-based monomers, and vinyl-based monomers having a hydrolyzable silyl group.
Examples of acrylic esters include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, benzyl acrylate, and phenyl acrylate.
Examples of methacrylic acid esters include methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, benzyl methacrylate, and phenyl methacrylate.
Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, and itaconic acid.
Examples of the unsaturated amide include acrylamide, methacrylamide, N,N-methylenebisacrylamide, diacetone acrylamide, diacetone methacrylamide, maleic acid amide, and maleimide.
Examples of the vinyl monomer include glycidyl methacrylate, styrene, vinyl toluene, vinyl acetate, acrylonitrile, and dibutyl fumarate.
Examples of vinyl monomers having a hydrolyzable silyl group include vinyltrimethoxysilane, vinylmethyldimethoxysilane, and γ-(meth)acryloxypropyltrimethoxysilane.

Examples of polyolefin polyols include hydroxyl-terminated polybutadiene and its hydrogenated products.

(5) Method for Producing Urethane Group-Containing Polyisocyanate When deriving a polyisocyanate containing a urethane group from an isocyanate monomer, it can be produced by, for example, mixing an excess of the isocyanate monomer, the polyol, and, if necessary, an alcohol other than the polyol, and, if necessary, adding a urethanization reaction catalyst.
Examples of the polyol include those exemplified in the above "polyol".
Examples of the alcohol other than the polyol include those exemplified in the above "Method for producing an isocyanurate group-containing polyisocyanate" except for those exemplified in the above "Polyol".
The urethanization reaction catalyst is not particularly limited, but examples thereof include tin-based compounds, zinc-based compounds, and amine-based compounds.
The urethanization reaction temperature is preferably from 50°C to 160°C, and more preferably from 60°C to 120°C.
By controlling the urethane-forming reaction temperature to be equal to or lower than the above upper limit, coloration of the polyisocyanate tends to be more effectively suppressed.
The urethane reaction time is preferably from 30 minutes to 4 hours, more preferably from 1 hour to 3 hours, and even more preferably from 1 hour to 2 hours.
The molar ratio of the isocyanate group of the isocyanate monomer to the molar amount of the hydroxyl group of the polyol (and, if necessary, the alcohol other than the polyol) is preferably 2/1 or more and 50/1 or less. When the molar ratio is equal to or more than the lower limit, the viscosity of the polyisocyanate can be made lower. When the molar ratio is equal to or less than the upper limit, the yield of the urethane group-containing polyisocyanate can be increased.

(6) Method for Producing Biuret Group-Containing Polyisocyanate The biuret-forming agent for deriving a biuret group-containing polyisocyanate from an isocyanate monomer is not particularly limited, and examples thereof include water, a monohydric tertiary alcohol, formic acid, an organic primary monoamine, and an organic primary diamine.
The amount of isocyanate groups per mole of the biuretizing agent is preferably 6 moles or more, more preferably 10 moles or more, and even more preferably 10 moles or more and 80 moles or less. When the amount of molar isocyanate groups per mole of the biuretizing agent is equal to or more than the lower limit, the viscosity of the polyisocyanate becomes sufficiently low, and when it is equal to or less than the upper limit, the low-temperature curing property of the resin film is further improved.

A solvent may be used in the biuretization reaction. The solvent may be any solvent that dissolves the isocyanate monomer and the biuretization agent such as water and forms a homogeneous phase under the reaction conditions.
Specific examples of the solvent include ethylene glycol-based solvents and phosphoric acid-based solvents.
Examples of ethylene glycol solvents include ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol mono-n-propyl ether acetate, ethylene glycol monoisopropyl ether acetate, ethylene glycol mono-n-butyl ether acetate, ethylene glycol diacetate, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol di-n-propyl ether, ethylene glycol diisopropyl ether, ethylene glycol di-n-butyl ether, ethylene glycol methyl ethyl ether, ethylene glycol methyl isopropyl ether, ethylene glycol methyl-n-butyl ether, ethylene glycol ethyl-n-propyl ether, ethylene glycol ethyl isopropyl ether, ethylene glycol ethyl-n-butyl ether, ethylene glycol-n-propyl-n-butyl ether, ethylene glycol isopropyl-n-butyl ether, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol mono-n-propyl ether acetate, diethylene glycol monoisopropyl ether acetate, diethylene glycol mono-n-butyl ether acetate, diethylene glycol diacetate, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol di-n-propyl ether, diethylene glycol diisopropyl ether, diethylene glycol di-n-butyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl isopropyl ether, diethylene glycol methyl-n-propyl ether, diethylene glycol methyl-n-butyl ether, diethylene glycol ethyl isopropyl ether, diethylene glycol ethyl-n-propyl ether, diethylene glycol ethyl-n-butyl ether, diethylene glycol-n-propyl-n-butyl ether, diethylene glycol isopropyl-n-butyl ether, and the like.
Examples of the phosphoric acid-based solvent include trimethyl phosphate, triethyl phosphate, tripropyl phosphate, and tributyl phosphate.
These solvents may be used alone or in combination of two or more.
Among these, the ethylene glycol solvent is preferably ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol diacetate, or diethylene glycol dimethyl ether.
As the phosphoric acid-based solvent, trimethyl phosphate or triethyl phosphate is preferred.

The biuretization reaction temperature is preferably 70°C or higher and 200°C or lower, and more preferably 90°C or higher and 180°C or lower. By keeping the temperature below the upper limit, discoloration of the polyisocyanate tends to be more effectively prevented.

The above-mentioned allophanate formation reaction, uretdione formation reaction, iminooxadiazinedione formation reaction, isocyanurate formation reaction, urethanization reaction, and biuret formation reaction may be carried out successively, or some of them may be carried out in parallel.
After the reaction is completed, unreacted isocyanate monomer is removed from the reaction solution by thin-film distillation, extraction, or the like to obtain a polyisocyanate.

Furthermore, an antioxidant or an ultraviolet absorber may be added to the obtained polyisocyanate, for example, for the purpose of suppressing coloration during storage.
Examples of the antioxidant include hindered phenols such as 2,6-di-tert-butyl-p-cresol. Examples of the ultraviolet absorber include benzotriazole and benzophenone. These antioxidants and ultraviolet absorbers may be used alone or in combination of two or more. The amount of these added is preferably 10 ppm by mass or more and 500 ppm by mass or less based on the mass of the polyisocyanate.

(Average number of isocyanate functional groups of polyisocyanate)
The average number of isocyanate functional groups of the polyisocyanate is preferably 2 or more from the viewpoint of improving the low-temperature curing property when formed into a resin film, and from the viewpoint of both the low-temperature curing property when formed into a resin film and the compatibility with the polyhydric alcohol compound, it is more preferably 3 to 20, even more preferably 3.3 to 10, particularly preferably 3.8 to 9, and most preferably 4.2 to 8.
The average number of isocyanate functional groups of the polyisocyanate can be measured by the method described in the Examples below.

[Blocking agent]
The blocking agent used in the production of the blocked polyisocyanate preferably contains a malonic acid ester having a secondary alkyl group or a malonic acid ester having a primary alkyl group, and a malonic acid ester having a tertiary alkyl group, and more preferably contains a malonic acid ester having a secondary alkyl group and a malonic acid ester having a tertiary alkyl group. The blocking agent may contain one type each of the malonic acid ester having a secondary alkyl group, the malonic acid ester having a primary alkyl group, and the malonic acid ester having a tertiary alkyl group, or may contain two or more types in combination.

Malonic acid esters having a primary alkyl group are not particularly limited, but examples include dimethyl malonate, diethyl malonate, dipropyl malonate, dibutyl malonate, dicyclohexyl malonate, diphenyl malonate, etc. Among these, diethyl malonate is preferred as a malonic acid ester having a primary alkyl group.

Malonic acid esters having a secondary alkyl group are not particularly limited, but examples include di-sec-butyl malonate, diisopropyl malonate, and isopropylethyl malonate. Of these, diisopropyl malonate is preferred as a malonic acid ester having a secondary alkyl group.

Malonic acid esters having a tertiary alkyl group are not particularly limited, but examples include di-tert-butyl malonate, di-tert-pentyl malonate, and tert-butylethyl malonate. Of these, di-tert-butyl malonate is preferred.

Among them, it is preferable that the blocking agent contains diisopropyl malonate as a malonic acid ester having a secondary alkyl group, and di-tert-butyl malonate as a malonic acid ester having a tertiary alkyl group.

(Other blocking agents)
The blocking agent used in the production of the blocked polyisocyanate may further contain other blocking agents in addition to the malonic acid ester having a secondary alkyl group and the malonic acid ester having a tertiary alkyl group, within the range that does not impair the storage stability when made into a resin composition and the low-temperature curing property when made into a resin film.
The content of the malonic acid ester having a secondary alkyl group and the malonic acid ester having a tertiary alkyl group relative to the total molar amount of all blocking agents used in the production of the blocked polyisocyanate is preferably 50 mol % or more, more preferably 70 mol % or more, even more preferably 90 mol % or more, particularly preferably 95 mol % or more, and most preferably 100 mol % or more.
By ensuring that the content of the malonic acid ester having a secondary alkyl group and the malonic acid ester having a tertiary alkyl group is within the above range, the low temperature curing property of the resin film formed can be further improved.

Other blocking agents include, for example, 1) alcohol-based compounds, 2) alkylphenol-based compounds, 3) phenol-based compounds, 4) active methylene-based compounds other than malonic acid esters having a secondary alkyl group and malonic acid esters having a tertiary alkyl group, 5) mercaptan-based compounds, 6) acid amide-based compounds, 7) acid imide-based compounds, 8) imidazole-based compounds, 9) urea-based compounds, 10) oxime-based compounds, 11) amine-based compounds, 12) imide-based compounds, 13) bisulfites, 14) pyrazole-based compounds, 15) triazole-based compounds, etc. More specifically, the following blocking agents can be used:

1) Alcohol compounds: alcohols such as methanol, ethanol, 2-propanol, n-butanol, sec-butanol, 2-ethyl-1-hexanol, 2-methoxyethanol, 2-ethoxyethanol, and 2-butoxyethanol.
2) Alkylphenol compounds: mono- and di-alkylphenols having an alkyl group having 4 or more carbon atoms as a substituent. Specific examples of the alkylphenol compounds include monoalkylphenols such as n-propylphenol, iso-propylphenol, n-butylphenol, sec-butylphenol, tert-butylphenol, n-hexylphenol, 2-ethylhexylphenol, n-octylphenol, and n-nonylphenol; and dialkylphenols such as di-n-propylphenol, diisopropylphenol, isopropyl cresol, di-n-butylphenol, di-tert-butylphenol, di-sec-butylphenol, di-n-octylphenol, di-2-ethylhexylphenol, and di-n-nonylphenol.
3) Phenolic compounds: phenol, cresol, ethylphenol, styrenated phenol, hydroxybenzoic acid esters, etc.
4) Active methylene compounds: methyl acetoacetate, ethyl acetoacetate, methyl isobutanoylacetate, ethyl isobutanoylacetate, acetylacetone, etc.
5) Mercaptan compounds: butyl mercaptan, dodecyl mercaptan, etc.
6) Acid amide compounds: acetanilide, acetic acid amide, ε-caprolactam, δ-valerolactam, γ-butyrolactam, etc.
7) Acid imide compounds: succinimide, maleimide, etc.
8) Imidazole compounds: imidazole, 2-methylimidazole, etc.
9) Urea compounds: urea, thiourea, ethyleneurea, etc.
10) Oxime compounds: formaldoxime, acetaldoxime, acetoxime, methyl ethyl ketoxime, cyclohexanone oxime, etc.
11) Amine compounds: diphenylamine, aniline, carbazole, di-n-propylamine, diisopropylamine, isopropylethylamine, etc.
12) Imine compounds: ethyleneimine, polyethyleneimine, etc.
13) Bisulfite compounds: sodium bisulfite, etc.
14) Pyrazole compounds: pyrazole, 3-methylpyrazole, 3,5-dimethylpyrazole, etc.
15) Triazole compounds: 3,5-dimethyl-1,2,4-triazole, etc.

[Hydrophilic Compound]
At least a portion of the blocked polyisocyanate may have a structural unit derived from a hydrophilic compound, that is, a hydrophilic group.

The hydrophilic compound is a compound having a hydrophilic group. In addition to the hydrophilic group, the hydrophilic compound preferably has at least one active hydrogen group per molecule of the hydrophilic compound, which reacts with at least one isocyanate group of the polyisocyanate. Specific examples of active hydrogen groups include hydroxyl groups, mercapto groups, carboxylic acid groups, amino groups, and thiol groups.

Examples of hydrophilic compounds include nonionic compounds, cationic compounds, and anionic compounds. These hydrophilic compounds may be used alone or in combination of two or more. Among them, nonionic compounds are preferred as hydrophilic compounds from the viewpoints of availability and resistance to electrical interaction with the compound, and anionic compounds are preferred from the viewpoints of suppressing a decrease in the hardness and strength of the resulting resin film and improving emulsifiability.

(Nonionic compounds)
Specific examples of nonionic compounds include monoalcohols and compounds in which ethylene oxide is added to the hydroxyl group of an alcohol. Examples of monoalcohols include methanol, ethanol, butanol, etc. Examples of compounds in which ethylene oxide is added to the hydroxyl group of an alcohol include ethylene glycol, diethylene glycol, polyethylene glycol, etc. These nonionic compounds also have active hydrogen groups that react with isocyanate groups.
Among these, as the nonionic compound, polyethylene glycol monoalkyl ether in which ethylene oxide is added to the hydroxyl group of a monoalcohol is preferred, since it can improve the water dispersibility of the blocked polyisocyanate composition with a small amount of use.

The number of ethylene oxide additions in the compound to which ethylene oxide is added is preferably 4 or more and 30 or less, more preferably 4 or more and 25 or less. When the number of ethylene oxide additions is equal to or more than the above lower limit, water dispersibility tends to be more effectively imparted to the blocked polyisocyanate composition, and when the number of ethylene oxide additions is equal to or less than the above upper limit, precipitation of the blocked polyisocyanate composition during low-temperature storage tends to be less likely to occur.

The lower limit of the amount of nonionic hydrophilic groups added to the blocked polyisocyanate (hereinafter, may be referred to as the "content of nonionic hydrophilic groups") is preferably 0.1 mass%, more preferably 0.15 mass%, further preferably 0.2 mass%, and particularly preferably 0.25 mass%, relative to the mass of the solid content of the hydrophilic polyisocyanate composition, from the viewpoint of the aqueous dispersion stability of the blocked polyisocyanate composition.
In addition, the upper limit of the content of the nonionic hydrophilic group is preferably 55 mass%, more preferably 50 mass%, even more preferably 48 mass%, and particularly preferably 44 mass%, relative to the mass of the solid content of the blocked polyisocyanate composition, from the viewpoint of the water resistance of the obtained resin film.
That is, the content of the nonionic hydrophilic group is preferably 0.1 mass % or more and 55 mass % or less, more preferably 0.15 mass % or more and 50 mass % or less, even more preferably 0.20 mass % or more and 48 mass % or less, and particularly preferably 0.25 mass % or more and 44 mass % or less, based on the mass of the solid content of the blocked polyisocyanate composition.
When the content of the nonionic hydrophilic group is within the above range, the blocked polyisocyanate composition tends to be more dispersible in water, and a homogeneous film tends to be obtained.

From the viewpoint of suppressing a decrease in the hardness and strength of the resulting resin film, the amount of nonionic hydrophilic groups added to the blocked polyisocyanate, expressed as a molar ratio, is preferably 0.05 mol% to 15 mol% relative to 100 mol% of the isocyanate groups in the raw material polyisocyanate, more preferably 0.10 mol% to 12 mol%, even more preferably 0.10 mol% to 8 mol%, even more preferably 0.10 mol% to 6 mol%, even more preferably 0.15 mol% to 4 mol%, particularly preferably 0.15 mol% to 3 mol%, and most preferably 0.15 mol% to 2 mol%.

(Cationic Compound)
As the cationic compound, specifically, a compound having both a cationic hydrophilic group and an active hydrogen group can be mentioned.In addition, a compound having an active hydrogen group such as a glycidyl group and a compound having a cationic hydrophilic group such as sulfide or phosphine can be combined to form a hydrophilic compound.In this case, a compound having an isocyanate group and a compound having an active hydrogen group are reacted in advance, a functional group such as a glycidyl group is added, and then a compound such as sulfide or phosphine is reacted.From the viewpoint of ease of production, a compound having both a cationic hydrophilic group and an active hydrogen group is preferred.

Specific examples of compounds having both a cationic hydrophilic group and an active hydrogen group include dimethylethanolamine, diethylethanolamine, diethanolamine, and methyldiethanolamine. Tertiary amino groups added using these compounds can also be quaternized with, for example, dimethyl sulfate or diethyl sulfate.

The reaction between the cationic compound and the alicyclic polyisocyanate can be carried out in the presence of a solvent. In this case, the solvent is preferably one that does not contain an active hydrogen group, and specific examples include ethyl acetate, propylene glycol monomethyl ether acetate, and dipropylene glycol dimethyl ether.

The cationic hydrophilic group added to the blocked polyisocyanate is preferably neutralized with a compound having an anionic group, such as a carboxy group, a sulfonic acid group, a phosphoric acid group, a halogen group, or a sulfate group.
Specific examples of compounds having a carboxyl group include formic acid, acetic acid, propionic acid, butyric acid, and lactic acid.
A specific example of a compound having a sulfonic acid group is ethanesulfonic acid.
Specific examples of compounds having a phosphoric acid group include phosphoric acid and acidic phosphate esters.
A specific example of the compound having a halogen group is hydrochloric acid.
Specific examples of compounds having a sulfate group include sulfuric acid.
Among them, as the compound having an anionic group, a compound having a carboxy group is preferable, and acetic acid, propionic acid or butyric acid is more preferable.

(Anionic Compounds)
Specific examples of the anionic hydrophilic group include a carboxy group, a sulfonic acid group, a phosphoric acid group, a halogen group, and a sulfate group.
Specific examples of the anionic compound include compounds having both an anionic group and an active hydrogen group, and more specific examples of the anionic compound include compounds having a carboxy group of a monohydroxycarboxylic acid or polyhydroxycarboxylic acid as the anionic group.
Examples of monohydroxycarboxylic acids include 1-hydroxyacetic acid, 3-hydroxypropanoic acid, 12-hydroxy-9-octadecanoic acid, hydroxypivalic acid, and lactic acid.
Examples of compounds having a carboxy group of a polyhydroxycarboxylic acid as an anionic group include dimethylol acetic acid, 2,2-dimethylol butyric acid, 2,2-dimethylol pentanoic acid, dihydroxysuccinic acid, and dimethylol propionic acid.
Further, compounds having both a sulfonic acid group and an active hydrogen group are also included, and more specifically, for example, isethionic acid is included.
Among these, hydroxypivalic acid or dimethylolpropionic acid is preferred as a compound having both an anionic group and an active hydrogen group.

The anionic hydrophilic group added to the blocked polyisocyanate is preferably neutralized with an amine compound, which is a basic substance.
Specific examples of the amine compound include ammonia and water-soluble amino compounds.
Specific examples of water-soluble amino compounds include monoethanolamine, ethylamine, dimethylamine, diethylamine, triethylamine, propylamine, dipropylamine, isopropylamine, diisopropylamine, triethanolamine, butylamine, dibutylamine, 2-ethylhexylamine, ethylenediamine, propylenediamine, methylethanolamine, dimethylethanolamine, diethylethanolamine, and morpholine. Tertiary amines such as triethylamine and dimethylethanolamine can also be used. These amine compounds may be used alone or in combination of two or more.

<Other components>
The blocked polyisocyanate composition of the present embodiment may further contain additives such as a solvent, in addition to the blocked polyisocyanate.

Examples of solvents include 1-methylpyrrolidone, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether, 3-methoxy-3-methyl-1-butanol, ethylene glycol diethyl ether, diethylene glycol diethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether (DPDM), propylene glycol dimethyl ether, methyl ethyl ketone, and acetonitrile. Examples of the solvent include ethanol, methyl isobutyl ketone, propylene glycol monomethyl ether acetate, ethanol, methanol, iso-propanol, 1-propanol, iso-butanol, 1-butanol, tert-butanol, 2-ethylhexanol, cyclohexanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, ethyl acetate, isopropyl acetate, butyl acetate, toluene, xylene, pentane, iso-pentane, hexane, iso-hexane, cyclohexane, solvent naphtha, and mineral spirits. These solvents may be used alone or in combination of two or more. From the viewpoint of dispersibility in water, the solvent is preferably one having a solubility in water of 5% by mass or more, and specifically, DPDM is preferred.

<Method for producing blocked polyisocyanate composition>
The blocked polyisocyanate composition is not particularly limited, but examples thereof include the following two methods.
1) A method of reacting the polyisocyanate with the malonic acid ester having a tertiary alkyl group, and the malonic acid ester having a secondary alkyl group or the malonic acid ester having a primary alkyl group;
2) A method in which the above polyisocyanate is reacted with at least one blocking agent selected from the group consisting of the above malonic acid ester having a tertiary alkyl group, the above malonic acid ester having a secondary alkyl group, and the above malonic acid ester having a primary alkyl group, and an alcohol having a chain alkyl group is added to the obtained reaction product to introduce an alkyl group derived from the alcohol by transesterification of the terminal ester site of the reaction product, and then the remaining alcohol is removed by distillation under reduced pressure or the like.

As the alcohol having a chain alkyl group used in the method 2), a monoalcohol is preferable, and examples thereof include monoalcohols having a linear alkyl group such as methanol, ethanol, propanol, and butanol; and monoalcohols having a branched alkyl group such as isopropanol, isobutanol, and tert-butanol. The chain alkyl group of the alcohol may have the same chain alkyl group as that of the blocking agent, or may have a different chain alkyl group. When the chain alkyl group is different from that of the blocking agent, it is preferable to use a monoalcohol having a chain alkyl group with a different number of alkyl substitutions from that of the blocking agent. Specifically, for example, when a single malonic acid ester having a secondary alkyl group is used as the blocking agent, a monoalcohol having a tertiary alkyl group can be used.

Of the above two methods, method 1) is preferred, taking into consideration the ease of the process and the ease of controlling the molar ratio of structural unit (II)/structural unit (I).

The blocking reaction between the polyisocyanate and the blocking agent can be carried out regardless of the presence or absence of a solvent, to give a blocked polyisocyanate.
The blocking agent may be one of malonic acid esters having a primary alkyl group, one of malonic acid esters having a secondary alkyl group, and one of malonic acid esters having a tertiary alkyl group, or a combination of two or more of them.
The amount of the blocking agent added may usually be 80 mol % or more and 200 mol % or less, and preferably 90 mol % or more and 150 mol % or less, based on the total molar amount of isocyanate groups.

In addition, in the blocking agent to be added, the molar ratio of the structural units derived from malonic acid ester having a secondary alkyl group to the structural units derived from malonic acid ester having a tertiary alkyl group [(malonic acid ester having a secondary alkyl group)/(malonic acid ester having a tertiary alkyl group)], and the molar ratio of the structural units derived from malonic acid ester having a primary alkyl group to the structural units derived from malonic acid ester having a tertiary alkyl group [(malonic acid ester having a primary alkyl group)/(malonic acid ester having a tertiary alkyl group)] are each more than 5/95 and less than 95/5, preferably 7/93 or more and 93/7 or less, more preferably 10/90 or more and 93/7 or less, even more preferably 20/80 or more and 93/7 or less, particularly preferably 30/70 or more and 93/7 or less, and most preferably 35/65 or more and 93/7 or less. By having the molar ratio be equal to or more than the lower limit, the storage stability of the resin composition can be improved, and by having the molar ratio be equal to or less than the upper limit, the low-temperature curing property of the resin film can be improved.

In addition, when a solvent is used, it is sufficient to use a solvent that is inactive to an isocyanate group.
When a solvent is used, the content of non-volatile matters derived from the polyisocyanate and the blocking agent per 100 parts by mass of the blocked polyisocyanate composition may usually be 10 parts by mass or more and 95 parts by mass or less, preferably 20 parts by mass or more and 80 parts by mass or less, and more preferably 30 parts by mass or more and 75 parts by mass or less.

In the blocking reaction, an organic metal salt of tin, zinc, lead or the like, a tertiary amine compound, an alcoholate of an alkali metal such as sodium, or the like may be used as a catalyst.
The amount of catalyst added varies depending on the temperature of the blocking reaction, etc., but is usually from 0.05 to 1.5 parts by mass, and preferably from 0.1 to 1.0 part by mass, per 100 parts by mass of polyisocyanate.

The blocking reaction can generally be carried out at −20° C. or higher and 150° C. or lower, preferably at 0° C. or higher and 100° C. or lower, and more preferably at 10° C. or higher and 80° C. or lower. When the temperature of the blocking reaction is equal to or higher than the above lower limit, the reaction rate can be increased, and when the temperature is equal to or lower than the above upper limit, side reactions can be suppressed.
After the blocking reaction, a neutralization treatment may be carried out by adding an acidic compound or the like.
The acidic compound may be an inorganic acid or an organic acid. Examples of the inorganic acid include hydrochloric acid, phosphorous acid, and phosphoric acid. Examples of the organic acid include methanesulfonic acid, p-toluenesulfonic acid, dioctyl phthalate, and dibutyl phthalate.

When a hydrophilic compound is used, the polyisocyanate is reacted with the blocking agent and the hydrophilic compound to obtain the resin.

The reaction between the polyisocyanate and the hydrophilic compound and the reaction between the polyisocyanate and the blocking agent can be carried out simultaneously, or one of the reactions can be carried out in advance before the second or subsequent reaction is carried out. In particular, it is preferable to carry out the reaction between the polyisocyanate and the hydrophilic compound first, obtain a hydrophilic compound-modified polyisocyanate modified with the hydrophilic compound, and then react the obtained hydrophilic compound-modified polyisocyanate with the blocking agent.

The reaction between the polyisocyanate and the hydrophilic compound may be carried out using an organic metal salt, a tertiary amine compound, or an alcoholate of an alkali metal as a catalyst. Examples of the metal constituting the organic metal salt include tin, zinc, and lead. Examples of the alkali metal include sodium.

The reaction temperature between the polyisocyanate and the hydrophilic compound is preferably -20°C or higher and 150°C or lower, and more preferably 30°C or higher and 130°C or lower. When the reaction temperature is equal to or higher than the lower limit, the reactivity tends to be higher. Also, when the reaction temperature is equal to or lower than the upper limit, side reactions tend to be more effectively suppressed.

It is preferable to completely react the hydrophilic compound with the polyisocyanate so that no unreacted hydrophilic compound remains. This tends to more effectively suppress the deterioration of the aqueous dispersion stability of the blocked polyisocyanate composition and the low-temperature curing properties when made into a resin film.

The reaction between the hydrophilic compound-modified polyisocyanate and the blocking agent can be carried out using the method described above as the blocking reaction.

<Characteristics of Blocked Polyisocyanate Composition>
[Weight average molecular weight Mw]
The weight average molecular weight Mw of the blocked polyisocyanate composition of this embodiment is preferably 2.0 x 10 ³ or more, more preferably 2.0 x 10 ³ or more and 2.0 x 10 ⁵ or less, even more preferably 4.0 x 10 ³ or more and 1.5 x 10 ⁵ or less, particularly preferably 4.0 x 10 ³ or more and 1.0 x 10 ⁵ or less, and most preferably 4.0 x 10 ³ or more and 7.0 x 10 ⁴ or less. By having the weight average molecular weight Mw within the above range, the viscosity of the blocked polyisocyanate composition can be maintained better. The weight average molecular weight Mw can be measured, for example, by gel permeation chromatography (hereinafter sometimes abbreviated as "GPC").

<Resin composition>
The resin composition of the present embodiment includes the above-mentioned blocked polyisocyanate composition and a polyvalent hydroxy compound. The resin composition of the present embodiment can also be said to be a one-liquid type resin composition including a curing agent component and a base component.

The resin composition of the present embodiment can provide a resin film that has excellent storage stability and low-temperature curing properties.
The components of the resin composition of the present embodiment will be described in detail below.

<Polyhydroxy Compound>
In this specification, the term "polyhydric hydroxy compound" refers to a compound having at least two hydroxy groups (hydroxyl groups) in one molecule, and is also called a "polyol."
Specific examples of the polyhydric hydroxy compound include aliphatic hydrocarbon polyols, polyether polyols, polyester polyols, epoxy resins, fluorine-containing polyols, and acrylic polyols.
Among these, the polyhydric hydroxy compound is preferably a polyester polyol, a fluorine-containing polyol or an acrylic polyol.

[Aliphatic Hydrocarbon Polyols]
Examples of the aliphatic hydrocarbon polyols include hydroxyl-terminated polybutadiene and hydrogenated products thereof.

[Polyether polyols]
Examples of the polyether polyols include those obtained by any one of the following methods (1) to (3).
(1) Polyether polyols or polytetramethylene glycols obtained by adding an alkylene oxide, either alone or in a mixture, to a polyhydric alcohol, either alone or in a mixture.
(2) Polyether polyols obtained by reacting alkylene oxides with polyfunctional compounds.
(3) Polymer polyols obtained by polymerizing acrylamide or the like using the polyether polyols obtained in (1) or (2) as a medium.
Examples of the polyhydric alcohol include glycerin and propylene glycol.
Examples of the alkylene oxide include ethylene oxide and propylene oxide.
Examples of the polyfunctional compound include ethylenediamine and ethanolamines.

[Polyester polyols]
Examples of the polyester polyols include the following polyester polyols (1) and (2).
(1) Polyester polyol resins obtained by a condensation reaction between a dibasic acid alone or a mixture of two or more kinds and a polyhydric alcohol alone or a mixture of two or more kinds.
(2) Polycaprolactones obtained by ring-opening polymerization of ε-caprolactone with polyhydric alcohols.
Examples of the dibasic acid include carboxylic acids such as succinic acid, adipic acid, dimer acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid, and 1,4-cyclohexanedicarboxylic acid.
Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, trimethylpentanediol, cyclohexanediol, trimethylolpropane, glycerin, pentaerythritol, 2-methylolpropanediol, and ethoxylated trimethylolpropane.

[Epoxy resins]
Examples of the epoxy resins include novolac type epoxy resins, β-methylepicrotype epoxy resins, cyclic oxirane type epoxy resins, glycidyl ether type epoxy resins, glycol ether type epoxy resins, epoxy type aliphatic unsaturated compounds, epoxidized fatty acid esters, ester type polycarboxylic acids, aminoglycidyl type epoxy resins, halogenated type epoxy resins, and resorcinol type epoxy resins, as well as resins obtained by modifying these epoxy resins with amino compounds, polyamide compounds, or the like.

[Fluorine-containing polyols]
Examples of the fluorine-containing polyols include copolymers of fluoroolefins, cyclohexyl vinyl ethers, hydroxyalkyl vinyl ethers, and monocarboxylic acid vinyl esters, which are disclosed in Reference Document 1 (JP-A-57-34107) and Reference Document 2 (JP-A-61-275311), etc.

[Acrylic polyols]
The acrylic polyols can be obtained, for example, by polymerizing a polymerizable monomer having one or more active hydrogens in one molecule, or by copolymerizing a polymerizable monomer having one or more active hydrogens in one molecule with another monomer copolymerizable with the polymerizable monomer, as necessary.

Examples of the polymerizable monomer having one or more active hydrogens in one molecule include the following (i) to (iii). These may be used alone or in combination of two or more.
(i) Acrylic esters having active hydrogen, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-hydroxybutyl acrylate.
(ii) Methacrylic acid esters having active hydrogen, such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and 2-hydroxybutyl methacrylate.
(iii) (meth)acrylic acid esters having polyvalent active hydrogen, such as acrylic acid monoesters or methacrylic acid monoesters of glycerin, and acrylic acid monoesters or methacrylic acid monoesters of trimethylolpropane.

Examples of other monomers copolymerizable with the polymerizable monomer include the following (i) to (v). These may be used alone or in combination of two or more.
(i) Acrylic acid esters such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate.
(ii) Methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, and glycidyl methacrylate.
(iii) Unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, and itaconic acid.
(iv) Unsaturated amides such as acrylamide, N-methylol acrylamide, and diacetone acrylamide.
(v) Styrene, vinyl toluene, vinyl acetate, acrylonitrile, etc.

Other examples include acrylic polyols obtained by copolymerizing polymerizable ultraviolet-stable monomers, as disclosed in Reference 3 (JP Patent Publication 1-261409 A) and Reference 4 (JP Patent Publication 3-006273 A).

Specific examples of the polymerizable ultraviolet-stable monomer include 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, and 2-hydroxy-4-(3-methacryloxy-2-hydroxypropoxy)benzophenone.

For example, the above monomer components can be solution polymerized in the presence of a known radical polymerization initiator such as a peroxide or an azo compound, and then diluted with an organic solvent, etc., as necessary, to obtain an acrylic polyol.

Water-based acrylic polyols can be produced by known methods such as a method of solution polymerization of an olefinic unsaturated compound and converting it into an aqueous phase, or emulsion polymerization. In this case, water-solubility or water-dispersibility can be imparted by neutralizing the acidic moieties of carboxylic acid-containing monomers such as acrylic acid and methacrylic acid, and sulfonic acid-containing monomers, with amines or ammonia.

[Hydroxyl value and acid value of polyhydric hydroxy compound]
The hydroxyl value of the polyhydric hydroxy compound contained in the resin composition of this embodiment is preferably 5 mgKOH/g or more and 300 mgKOH/g or less.
When the hydroxyl group of the polyhydric hydroxy compound is equal to or greater than the lower limit, the crosslink density of the urethane due to the reaction with the polyisocyanate is increased, and the function of the urethane bond is more easily exhibited. On the other hand, when the hydroxyl group of the polyhydric hydroxy compound is equal to or less than the upper limit, the crosslink density does not increase too much, and the mechanical properties of the resin film are improved.

[NCO/OH]
The molar equivalent ratio (NCO/OH) of the isocyanate groups of the blocked polyisocyanate composition to the hydroxyl groups of the polyvalent hydroxy compound contained in the resin composition of the present embodiment is determined depending on the required physical properties of the resin film, but is usually 0.01 or more and 22.5 or less.

<Other additives>
The resin composition of the present embodiment may further contain other additives.
Examples of other additives include curing agents capable of reacting with crosslinkable functional groups in the polyhydric hydroxy compound, curing catalysts, solvents, pigments (extender pigments, colored pigments, metallic pigments, etc.), ultraviolet absorbers, light stabilizers, radical stabilizers, yellowing inhibitors that suppress coloring during the baking process, coating surface conditioners, flow conditioners, pigment dispersants, defoamers, thickeners, film-forming assistants, and the like.

Examples of the curing agent include melamine resins, urea resins, epoxy group-containing compounds or resins, carboxyl group-containing compounds or resins, acid anhydrides, alkoxysilane group-containing compounds or resins, and hydrazide compounds.

The curing catalyst may be a basic compound or a Lewis acid compound.
Examples of the basic compound include metal hydroxides, metal alkoxides, metal carboxylates, metal acetylacetinates, hydroxides of onium salts, onium carboxylates, halides of onium salts, metal salts of active methylene compounds, onium salts of active methylene compounds, aminosilanes, amines, phosphines, etc. As the onium salts, ammonium salts, phosphonium salts, or sulfonium salts are preferable.
Examples of the Lewis acid compound include an organotin compound, an organozinc compound, an organotitanium compound, and an organozirconium compound.

The solvent may be the same as those exemplified in the blocked polyisocyanate composition above.

In addition, known pigments (extender pigments, color pigments, metallic pigments, etc.), ultraviolet absorbers, light stabilizers, radical stabilizers, yellowing inhibitors that suppress coloring during the baking process, coating surface conditioners, flow conditioners, pigment dispersants, defoamers, thickeners, and film-forming aids can be appropriately selected and used.

<Method of producing resin composition>
The resin composition of the present embodiment can be used as either a solvent-based or aqueous-based resin composition, but since no aqueous-based resin composition having good storage stability has been known to date, it is preferably used as an aqueous-based resin composition.

When producing a water-based resin composition (water-based resin composition), first, additives such as a curing agent capable of reacting with a crosslinkable functional group in the polyhydroxy compound, a curing catalyst, a solvent, pigments (body pigments, coloring pigments, metallic pigments, etc.), an ultraviolet absorber, a light stabilizer, a radical stabilizer, an anti-yellowing agent for suppressing coloring during the baking process, a coating surface conditioner, a flow conditioner, a pigment dispersant, an antifoaming agent, a thickener, and a film-forming aid are added to the polyhydroxy compound or its water dispersion or water solution as necessary. Next, the above-mentioned blocked polyisocyanate composition or its water dispersion is added as a curing agent, and water or a solvent is further added as necessary to adjust the viscosity. Next, the mixture is forcedly stirred with a stirring device to obtain a water-based resin composition (water-based resin composition).

When producing a solvent-based resin composition, first, additives such as a curing agent capable of reacting with the crosslinkable functional group in the polyhydroxy compound, a curing catalyst, a solvent, pigments (body pigments, coloring pigments, metallic pigments, etc.), UV absorbers, light stabilizers, radical stabilizers, yellowing inhibitors for suppressing coloring during the baking process, coating surface conditioners, flow conditioners, pigment dispersants, defoamers, thickeners, and film-forming aids are added to the polyhydroxy compound or its solvent dilution as necessary. Next, the above-mentioned blocked polyisocyanate composition is added as a curing agent, and a solvent is further added as necessary to adjust the viscosity. Next, the solvent-based resin composition can be obtained by stirring by hand or using a stirring device such as a mixer.

<Resin film>
The resin film of the present embodiment is formed by curing the above-mentioned resin composition. The resin film of the present embodiment has good low-temperature curing properties.

The resin film of this embodiment is obtained by applying the resin composition to a substrate using a known method such as roll coating, curtain flow coating, spray coating, bell coating, or electrostatic coating, and then curing the composition by heating.

From the viewpoints of energy saving and heat resistance of the substrate, the heating temperature is preferably from about 70° C. to about 120° C., more preferably from about 70° C. to about 110° C., and even more preferably from about 75° C. to about 100° C.
From the viewpoints of energy saving and heat resistance of the base material, the heating time is preferably from about 1 minute to about 60 minutes, and more preferably from about 2 minutes to about 40 minutes.

The substrate is not particularly limited, and examples thereof include the outer panels of automobile bodies such as passenger cars, trucks, motorcycles, and buses; automobile parts such as bumpers; the outer panels of household electrical appliances such as mobile phones and audio equipment; and various films, among which the outer panels of automobile bodies or automobile parts are preferred.

The material of the substrate is not particularly limited, and examples thereof include metal materials such as iron, aluminum, brass, copper, tinplate, stainless steel, zinc-plated steel, zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.) plated steel; resins such as polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy resin, and various plastic materials such as FRP; inorganic materials such as glass, cement, and concrete; wood; and fibrous materials such as paper and cloth, among which metal materials and plastic materials are preferred.

The substrate may be the surface of the above-mentioned metal material, or the metal surface of a car body or the like formed from the above-mentioned metal material, which has been subjected to a surface treatment such as phosphate treatment, chromate treatment, complex oxide treatment, or the like, and further may be one on which a coating film has been formed. The substrate on which a coating film has been formed may be one on which a surface treatment has been performed as necessary and on which a primer coating film has been formed, for example, a car body on which a primer coating film has been formed by electrochemical paint. The substrate may be the surface of the above-mentioned plastic material, or the plastic surface of an automobile part or the like formed from the above-mentioned metal material, which has been subjected to a surface treatment as desired. The substrate may also be one in which a plastic material and a metal material are combined.

As shown in the examples described later, the resin film of this embodiment is a 40 μm thick resin film obtained by heating the resin composition at 80° C. for 30 minutes to cure the resin composition, and when the resin film is stored at 23° C. for one week and then immersed in acetone at 23° C. for 24 hours, the gel fraction is preferably 82% by mass or more, more preferably 85% by mass or more, and even more preferably 86% by mass or more. By having a gel fraction equal to or greater than the above lower limit, the low-temperature curing property can be improved. On the other hand, the upper limit of the gel fraction is not particularly limited, but can be, for example, 100% by mass. A specific method for measuring the gel fraction can be, for example, the method shown in the examples described later.

As shown in the examples described later, the resin film of this embodiment is a 40 μm thick resin film formed by heating the above resin composition on glass at 80° C. for 30 minutes to harden the resin composition, and the Konig hardness at 23° C. is preferably 38 or more, more preferably 40 or more, even more preferably 50 or more, and particularly preferably 55 or more. By having the Konig hardness at 23° C. be equal to or greater than the above lower limit, a resin film with better hardness can be obtained. On the other hand, the upper limit of the Konig hardness at 23° C. is not particularly limited, but can be, for example, 140. A specific method for measuring the Konig hardness at 23° C. can be, for example, the method shown in the examples described later.

As shown in the examples described later, the resin film of this embodiment is a resin film having a thickness of 40 μm, a width of 10 mm, and a length of 40 mm, which is obtained by heating and curing the resin composition at 80° C. for 30 minutes. The resin film is set so that the chuck distance is 20 mm, and the maximum stress in a tensile test performed at a speed of 20 mm/min in a 23° C. environment is preferably 5 MPa or more, more preferably 10 MPa or more, even more preferably 15 MPa or more, and particularly preferably 20 MPa or more. By having the maximum tensile stress be equal to or greater than the above lower limit, a resin film with better strength can be obtained. On the other hand, the upper limit of the maximum tensile stress is not particularly limited, but can be, for example, 100 MPa. A specific method for measuring the maximum tensile stress can be, for example, the method shown in the examples described later.

The resin film of this embodiment has excellent low-temperature curing properties, making it suitable for use in products in various fields where energy conservation is required, and as a coating for materials with low heat resistance.

<Laminate>
The laminate of the present embodiment includes two or more layers of the resin film having different compositions. The thickness of each resin film is 1 μm or more and 50 μm or less. The laminate of the present embodiment includes the resin film, and thus has excellent low-temperature curing properties.

The laminate of this embodiment can also contain two or more layers of the above resin film of the same composition.

The laminate of the present embodiment is formed by laminating various coating films including the above-mentioned resin film on an adherend.
Examples of the adherend include glass, various metals, porous members, members with various coatings, cured sealants, rubbers, leathers, fibers, nonwoven fabrics, resin films and plates, ultraviolet-cured acrylic resin layers, and layers made of inks. Examples of the various metals include aluminum, iron, galvanized steel sheets, copper, and stainless steel. Examples of the porous members include wood, paper, mortar, and stone. Examples of the various coatings include fluorine coatings, urethane coatings, and acrylic urethane coatings. Examples of the cured sealants include silicone-based, modified silicone-based, and urethane-based. Examples of the rubbers include natural rubber and synthetic rubber. Examples of the leathers include natural leather and artificial leather. Examples of the fibers include plant-based fibers, animal-based fibers, carbon fibers, and glass fibers. Examples of the resins that are the raw materials for the resin films and plates include polyvinyl chloride, polyester, acrylic, polycarbonate, triacetyl cellulose, and polyolefin. Examples of the inks include printing inks and UV inks.

The laminate of this embodiment can be obtained by applying different layers of the above resin composition to an adherend using known methods such as roll coating, curtain flow coating, spray coating, bell coating, and electrostatic coating, and then heating and curing each layer, or by applying all layers and then heating and curing them together.

The laminate of this embodiment may include, in addition to the resin film, layers made of other known components, such as a primer layer, an adhesive layer, a decorative layer, etc.

Hereinafter, the present embodiment will be described in more detail based on examples and comparative examples, but the present embodiment is not limited to the following examples in any way.
In the following, Examples 21 to 23 and 25 are considered as reference examples.

<Test items>
For the blocked polyisocyanate compositions obtained in the examples and comparative examples, the physical properties were measured and evaluated according to the methods described below.

[Physical Properties 1]
(Isocyanate group (NCO) content)
In order to measure the NCO content of the polyisocyanate, the polyisocyanate before being blocked with a blocking agent was used as a measurement sample.

First, 2 g to 3 g of the measurement sample was weighed out (Wg) into a flask. Next, 20 mL of toluene was added to dissolve the measurement sample. Next, 20 mL of a 2N toluene solution of di-n-butylamine was added, mixed, and left at room temperature for 15 minutes. Next, 70 mL of isopropyl alcohol was added and mixed. Next, this liquid was titrated with a 1N hydrochloric acid solution (Factor F) as an indicator. The titration value obtained was V2 mL. Next, the titration value obtained without the polyisocyanate sample was V1 ml. Next, the isocyanate group (NCO) content (mass%) of the polyisocyanate was calculated from the following formula.

Isocyanate group (NCO) content (mass%) = (V1-V2) x F x 42/(W x 1000) x 100

[Physical Properties 2]
(Number average molecular weight and weight average molecular weight)
The number average molecular weight and weight average molecular weight are polystyrene-based number average molecular weight and weight average molecular weight measured by gel permeation chromatography (GPC) using the following equipment. To measure the number average molecular weight of the polyisocyanate, the polyisocyanate before blocking with a blocking agent was used as the measurement sample. For the weight average molecular weight, the blocked polyisocyanate composition was used as it was as the measurement sample. The measurement conditions are shown below.

(Measurement condition)
Apparatus: Tosoh Corporation, HLC-802A
Column: Tosoh Corporation, G1000HXL x 1
G2000HXL x 1
G3000HXL x 1 Carrier: Tetrahydrofuran Detection method: Differential refractometer

[Physical Properties 3]
(Average number of isocyanate functional groups)
The average number of isocyanate functional groups (average NCO number) of the polyisocyanate was calculated by the following formula. In the formula, "Mn" is the number average molecular weight of the polyisocyanate before blocking with a blocking agent, and the value measured in the above "Physical Properties 2" was used. "NCO content" is the isocyanate group content of the polyisocyanate measured before blocking with a blocking agent, and the value calculated in the above "Physical Properties 1" was used.

Average number of isocyanate functional groups = (Mn x NCO content x 0.01)/42

[Physical Properties 4]
(Solid content of blocked polyisocyanate composition)
The solids content of the blocked polyisocyanate composition was determined as follows.
First, an aluminum dish with a bottom diameter of 38 mm was precisely weighed. Next, about 1 g of the blocked polyisocyanate composition produced in the Examples and Comparative Examples was precisely weighed on the aluminum dish (W1). Next, the blocked polyisocyanate composition was adjusted to a uniform thickness. Next, the blocked polyisocyanate composition placed on the aluminum dish was kept in an oven at 105°C for 1 hour. Next, after the aluminum dish reached room temperature, the blocked polyisocyanate composition remaining on the aluminum dish was precisely weighed (W2). Next, the solid content (mass%) of the blocked polyisocyanate composition was calculated from the following formula.

Solid content of blocked polyisocyanate composition (mass%) = W2/W1 x 100

[Physical Properties 5]
(Molar ratio of structural unit (II)/structural unit (I))
The molar ratio of the structural unit (II) to the structural unit (I) (the molar ratio of (II)/(I)) was calculated by evaporating the blocked polyisocyanate composition at 50° C. or less to remove the solvent and other components, drying the composition under reduced pressure, and then measuring the composition ratio of the structural unit (II) to the structural unit (I) by ¹ H-NMR and ¹³ C-NMR.

[Preparation of resin composition]
An acrylic polyol ("Setalux 1152" (product name) manufactured by Allnex Corporation, OH% (on solids) = 4.2, Acid value (mg KOH/g) = 4.8, solid content 61 mass%) and each blocked polyisocyanate composition were blended so that the ratio of the molar amount of isocyanate groups to the molar amount of hydroxyl groups (isocyanate groups/hydroxyl groups) was 1, and butyl acetate was further blended to adjust the solid content to 33 mass%, thereby obtaining a resin composition.

[Evaluation 1]
(Storage Stability)
For 20 g of the obtained resin composition, the initial viscosity and the viscosity after storage in a 20 mL glass bottle at 23° C. for 24 hours were measured (viscometer: RE-85R manufactured by Toki Sangyo Co., Ltd.). The ratio of the viscosity after storage to the initial viscosity was calculated. Note that a viscosity ratio after storage of 5.0 or less to the initial viscosity and no gelation or precipitation was observed was evaluated as good, and the difference in the good level was expressed according to the following evaluation criteria.

(Evaluation criteria)
◎: Very good, the ratio of viscosity after storage to the initial viscosity is 2.0 or less. 〇〇: Good, the ratio of viscosity after storage to the initial viscosity is more than 2.0 and less than 3.0. 〇: Generally good, the ratio of viscosity after storage to the initial viscosity is more than 3.0 and less than 5.0.

[Evaluation 2]
(Low temperature curing)
The obtained resin composition was applied to a polypropylene (PP) plate so that the dry film thickness was 40 μm, and then heated and dried at 80 ° C for 30 minutes to obtain a resin film. The obtained resin film was stored at room temperature (23 ° C) for one week, and the gel fraction was measured. The gel fraction was calculated as a percentage (mass %) of the value obtained by dividing the undissolved mass of the resin film when it was immersed in acetone at 23 ° C for 24 hours by the mass before immersion. In addition, a gel fraction of 82 mass % or more was evaluated as good.

[Evaluation 3]
(Konig hardness)
A resin film was obtained on a glass plate using the same method as in "Evaluation 2" above. The obtained resin film was measured for Konig hardness (times) in a 23°C environment using a Konig hardness tester (Pendulum hardness tester from BYK Gardner). A Konig hardness of 38 times or more was evaluated as good.

[Evaluation 4]
(Maximum tensile stress)
The obtained resin composition was applied to a polypropylene (PP) plate so that the dry film thickness was 40 μm, and then heated and dried at 80 ° C for 30 minutes to obtain a resin film. The obtained resin film was cut to a width of 10 mm and a length of 40 mm, set so that the chuck distance was 20 mm, and a tensile test was performed at a speed of 20 mm / min in a 23 ° C environment. The maximum point stress at that time was taken as the maximum tensile stress. In addition, a maximum tensile stress of 5 MPa or more was evaluated as good.

<Synthesis of Polyisocyanate>
[Synthesis Example 1]
(Synthesis of Polyisocyanate P-1)
In a four-neck flask equipped with a thermometer, a stirring blade, and a reflux condenser, 100 parts by mass of HDI and 5.2 parts by mass of a polyester polyol derived from a trihydric alcohol and ε-caprolactone (manufactured by Daicel Chemical Industries, Ltd., "Placcel 303" (trade name), average number of hydroxyl groups: 3, number average molecular weight: 300) were charged under a nitrogen gas flow, and the temperature inside the reactor was kept at 88°C for 1 hour under stirring to carry out a urethane reaction. Thereafter, the temperature inside the reactor was kept at 62°C, and an isocyanurate catalyst tetramethylammonium caprylate was added, and when the yield reached 51% by mass, phosphoric acid was added to stop the reaction. After filtering the reaction liquid, unreacted HDI was removed using a thin-film evaporator to obtain an isocyanurate-type polyisocyanate (hereinafter, sometimes referred to as "polyisocyanate P-1"). The NCO content of the obtained polyisocyanate P-1 was 18.8% by mass, the number average molecular weight was 1180, and the average number of isocyanate groups was 5.3. Furthermore, the obtained polyisocyanate P-1 was subjected to ¹ H-NMR analysis, which confirmed the presence of isocyanurate groups.

[Synthesis Example 2]
(Synthesis of Polyisocyanate P-2)
In a four-neck flask equipped with a thermometer, a stirring blade, and a reflux condenser, 80 parts by mass of HDI, 20 parts by mass of IPDI, and 5.2 parts by mass of a polyester polyol derived from a trihydric alcohol and ε-caprolactone (manufactured by Daicel Chemical Industries, Ltd., "Placcel 303" (trade name), average number of hydroxyl groups: 3, number average molecular weight: 300) were charged under a nitrogen gas flow, and the temperature inside the reactor was kept at 88°C for 1 hour under stirring to carry out a urethane reaction. Thereafter, the temperature inside the reactor was kept at 62°C, and an isocyanurate catalyst tetramethylammonium caprylate was added, and when the yield reached 51% by mass, phosphoric acid was added to stop the reaction. The reaction liquid was filtered, and unreacted HDI and IPDI were removed using a thin-film evaporator to obtain an isocyanurate-type polyisocyanate (hereinafter, sometimes referred to as "polyisocyanate P-2"). The obtained polyisocyanate P-2 had an NCO content of 18.0% by mass, a number average molecular weight of 1200, and an average number of isocyanate groups of 5.1. Furthermore, the obtained polyisocyanate P-2 was subjected to ¹ H-NMR analysis, and it was confirmed that an isocyanurate group was present.

[Synthesis Example 3]
(Synthesis of Polyisocyanate P-3)
In a four-neck flask equipped with a thermometer, a stirring blade, and a reflux condenser, 70 parts by mass of HDI, 30 parts by mass of IPDI, and 3.2 parts by mass of trimethylolpropane (average number of hydroxyl functional groups: 3, molecular weight: 134), which is a trihydric alcohol, were charged under a nitrogen gas flow, and the temperature inside the reactor was kept at 85° C. for 1 hour under stirring to carry out a urethane reaction. Thereafter, the temperature inside the reactor was kept at 78° C., and 0.012 parts by mass of an isocyanurate catalyst tetramethylammonium caprylate was added, and when the yield reached 45% by mass, phosphoric acid was added to stop the reaction. After filtering the reaction liquid, unreacted HDI and IPDI were removed using a thin-film evaporator to obtain an isocyanurate-type polyisocyanate (hereinafter, sometimes referred to as "polyisocyanate P-3"). The NCO content of the obtained polyisocyanate P-3 was 18.9% by mass, the number average molecular weight was 1200, and the average number of isocyanate groups was 5.4. Furthermore, the obtained polyisocyanate P-3 was subjected to ¹ H-NMR analysis, which confirmed the presence of isocyanurate groups.

[Synthesis Example 4]
(Synthesis of Polyisocyanate P-4)
In a four-neck flask equipped with a thermometer, a stirring blade, and a reflux condenser, 70 parts by mass of HDI, 30 parts by mass of IPDI, and 2.6 parts by mass of trimethylolpropane (average number of hydroxyl functional groups: 3, molecular weight: 134), which is a trihydric alcohol, were charged under a nitrogen gas flow, and the temperature inside the reactor was kept at 91° C. for 1 hour under stirring to carry out a urethane reaction. Thereafter, the temperature inside the reactor was kept at 77° C., and 0.012 parts by mass of an isocyanurate catalyst tetramethylammonium caprylate was added, and when the yield reached 45% by mass, phosphoric acid was added to stop the reaction. After filtering the reaction liquid, unreacted HDI and IPDI were removed using a thin-film evaporator to obtain an isocyanurate-type polyisocyanate (hereinafter, sometimes referred to as "polyisocyanate P-4"). The NCO content of the obtained polyisocyanate P-4 was 19.1% by mass, the number average molecular weight was 1070, and the average number of isocyanate groups was 4.9. Furthermore, the obtained polyisocyanate P-4 was subjected to ¹ H-NMR analysis, which confirmed the presence of isocyanurate groups.

[Synthesis Example 5]
(Synthesis of Polyisocyanate P-5)
In a four-neck flask equipped with a thermometer, a stirring blade, and a reflux condenser, 69 parts by mass of HDI, 31 parts by mass of IPDI, and 2.56 parts by mass of trimethylolpropane (average number of hydroxyl functional groups: 3, molecular weight: 134), which is a trihydric alcohol, were charged under a nitrogen gas flow, and the temperature inside the reactor was kept at 91° C. for 1 hour under stirring to carry out a urethane reaction. Thereafter, the temperature inside the reactor was kept at 78° C., and 0.0124 parts by mass of an isocyanurate catalyst tetramethylammonium caprylate was added, and when the yield reached 45% by mass, phosphoric acid was added to stop the reaction. After filtering the reaction liquid, unreacted HDI and IPDI were removed using a thin-film evaporator to obtain an isocyanurate-type polyisocyanate (hereinafter, sometimes referred to as "polyisocyanate P-5"). The NCO content of the obtained polyisocyanate P-5 was 18.3% by mass, the number average molecular weight was 1420, and the average number of isocyanate groups was 6.2. Furthermore, the obtained polyisocyanate P-5 was subjected to ¹ H-NMR analysis, which confirmed the presence of isocyanurate groups.

[Synthesis Example 6]
(Synthesis of Polyisocyanate P-6)
In a four-neck flask equipped with a thermometer, a stirring blade, and a reflux condenser, 80 parts by mass of HDI, 20 parts by mass of IPDI, and 3.5 parts by mass of trimethylolpropane (average number of hydroxyl functional groups: 3, molecular weight: 134), which is a trihydric alcohol, were charged under a nitrogen gas flow, and the temperature inside the reactor was kept at 92°C for 1 hour under stirring to carry out a urethane reaction. Thereafter, the temperature inside the reactor was kept at 77°C, and 0.012 parts by mass of an isocyanurate catalyst tetramethylammonium caprylate was added, and when the yield reached 45% by mass, phosphoric acid was added to stop the reaction. After filtering the reaction liquid, unreacted HDI and IPDI were removed using a thin-film evaporator to obtain an isocyanurate-type polyisocyanate (hereinafter, sometimes referred to as "polyisocyanate P-6"). The NCO content of the obtained polyisocyanate P-6 was 19.0% by mass, the number average molecular weight was 1240, and the average number of isocyanate groups was 5.6. Furthermore, the obtained polyisocyanate P-6 was subjected to ¹ H-NMR analysis, which confirmed the presence of isocyanurate groups.

[Synthesis Example 7]
(Synthesis of Polyisocyanate P-7)
Polyisocyanate P-1: 100 parts by mass, methoxypolyethylene glycol (MPG-081, ethylene oxide repeating unit: 15, manufactured by Nippon Nyukazai Co., Ltd.) in an amount of 0.5 mol % relative to 100 mol % of isocyanate groups in Polyisocyanate P-1, 2-ethylhexyl acid phosphate (JP-508T, manufactured by Johoku Chemical Industry Co., Ltd.) : 0.08 parts by mass, and dipropylene glycol dimethyl ether (DPDM) were mixed in a four-neck flask equipped with a thermometer, a stirring blade, and a reflux condenser under a nitrogen stream, and the mixture was stirred at 120°C for 2 hours to obtain Polyisocyanate P-7.

[Synthesis Example 8]
(Synthesis of Polyisocyanate P-8)
In a four-neck flask equipped with a thermometer, a stirring blade, and a reflux condenser, 100 parts by mass of polyisocyanate P-4, methoxypolyethylene glycol (MPG-081, ethylene oxide repeating units: 15, manufactured by Nippon Nyukazai Co., Ltd.): 0.5 mol % relative to 100 mol % of isocyanate groups in polyisocyanate P-4, 0.08 parts by mass of 2-ethylhexyl acid phosphate (JP-508T, manufactured by Johoku Chemical Industry Co., Ltd.), and dipropylene glycol dimethyl ether (DPDM) were mixed under a nitrogen stream and stirred at 120° C. for 2 hours to obtain polyisocyanate P-8.

[Synthesis Example 9]
(Synthesis of Polyisocyanate P-9)
In a four-neck flask equipped with a thermometer, a stirring blade, and a reflux condenser, 100 parts by mass of polyisocyanate P-1, 6.0 parts by mass of methoxypolyethylene glycol (MPG-081, ethylene oxide repeating unit: 15, manufactured by Nippon Nyukazai Co., Ltd.) (amount equivalent to 2.0 mol % relative to 100 mol % of isocyanate groups in polyisocyanate P-1), 0.08 parts by mass of 2-ethylhexyl acid phosphate (JP-508T, manufactured by Johoku Chemical Industry Co., Ltd.), and dipropylene glycol dimethyl ether (DPDM) were mixed under a nitrogen stream and stirred at 120° C. for 2 hours to obtain polyisocyanate P-9.

<Production of Blocked Polyisocyanate Composition>
[Example 1]
(Production of blocked polyisocyanate composition BL-a1)
In a four-neck flask equipped with a thermometer, a stirring blade, and a reflux condenser, 100 parts by mass of the polyisocyanate P-1 obtained in Synthesis Example 1, 6.8 parts by mass of diisopropyl malonate (20 mol% relative to 100 mol% of NCO groups), and 74.9 parts by mass of di-tert-butyl malonate (80 mol% relative to 100 mol% of NCO groups) were charged under a nitrogen stream, and dipropylene glycol dimethyl ether (DPDM) was further added to adjust the solid content to 60% by mass. Next, while stirring, 1.0 part by mass of a methanol solution containing sodium methylate (28% by mass relative to the total mass of the solution) was dropped, and the external bath was adjusted so that the solution temperature was 55°C, and the blocking reaction was carried out at 55°C for 5 hours to obtain a blocked polyisocyanate composition BL-a1. The obtained blocked polyisocyanate composition BL-a1 had a solid content of 60.1% by mass and a weight average molecular weight of 5.39 x 10 ³ .

[Examples 2 to 10 and Comparative Examples 1 to 3]
(Production of blocked polyisocyanate compositions BL-a2 to BL-a10 and BL-b1 to BL-b3)
Blocked polyisocyanate compositions BL-a2 to BL-a10 and BL-b1 to BL-b3 were produced in the same manner as in Example 1, except that the types and blending ratios of the blocking agents shown in Tables 1 to 3 were used.

[Example 11]
(Blocked polyisocyanate composition BL-a11)
In a four-neck flask equipped with a thermometer, a stirring blade and a reflux condenser, 100 parts by mass of polyisocyanate P-3 obtained in Synthesis Example 3, diisopropyl malonate: 60 mol% relative to 100 mol% of NCO groups, and di-tert-butyl malonate: 40 mol% relative to 100 mol% of NCO groups were charged under nitrogen gas flow, and dipropylene glycol dimethyl ether (DPDM) was further added to adjust the solid content to 60% by mass. Next, while stirring, 1.2 parts by mass of a methanol solution containing sodium methylate (28% by mass relative to the total mass of the solution) was dropped, and the outer bath was adjusted so that the solution temperature was 55 ° C., and the blocking reaction was carried out at 53 ° C. for 8 hours or more to obtain a blocked polyisocyanate composition BL-a11. The obtained blocked polyisocyanate composition BL-a11 had a solid content of 60.1% by mass and a weight average molecular weight of 7.94 × 10 ³ .

[Examples 12 to 23]
(Blocked polyisocyanate compositions BL-a12 to BL-a23)
Blocked polyisocyanate compositions BL-a12 to BL-a23 were produced in the same manner as in Example 11, except that the types of polyisocyanates and the types and blending ratios of blocking agents were as shown in Tables 4 to 6.

[Example 24]
(Blocked polyisocyanate composition BL-a24)
In a four-neck flask equipped with a thermometer, a stirring blade and a reflux condenser, 100 parts by mass of polyisocyanate P-1 obtained in Synthesis Example 1, diisopropyl malonate: 80 mol% relative to 100 mol% of NCO groups, and di-tert-butyl malonate: 20 mol% relative to 100 mol% of NCO groups were charged under nitrogen gas flow, and dipropylene glycol dimethyl ether (DPDM) was further added to adjust the solid content to 60% by mass. Next, while stirring, 1.0 part by mass of a methanol solution containing sodium methylate (28% by mass relative to the total mass of the solution) was dropped, and the external bath was adjusted so that the solution temperature was 53 ° C., and the blocking reaction was carried out at 53 ° C. for 6 hours or more, and the disappearance of the peak of the isocyanate group was confirmed by infrared spectroscopy (IR) method. Thereafter, tert-butanol was added in an amount equivalent to 100 mol% relative to 100 mol% of the initial NCO groups (NCO groups before the blocking reaction) of polyisocyanate P-1, and the mixture was allowed to react at 80°C for 2 hours. Thereafter, the tert-butanol remaining in the reaction solution and the isopropanol produced by the transesterification reaction were removed by distillation under reduced pressure, and dipropylene glycol dimethyl ether (DPDM) removed during the distillation under reduced pressure was added to obtain a blocked polyisocyanate composition BL-a24. The obtained blocked polyisocyanate composition BL-a24 had a solid content of 60.2 mass% and a weight average molecular weight of 8.31 x ¹⁰³ .

[Example 25]
(Blocked polyisocyanate composition BL-a25)
In a four-neck flask equipped with a thermometer, a stirring blade and a reflux condenser, 100 parts by mass of polyisocyanate P-1 obtained in Synthesis Example 1, 84.2 parts by mass of diisopropyl malonate (amount equivalent to 100 mol% relative to 100 mol% of NCO groups) were charged under nitrogen gas flow, and dipropylene glycol dimethyl ether (DPDM) was further added to adjust the solid content to 60% by mass. Next, while stirring, 1.0 part by mass of a methanol solution containing sodium methylate (28% by mass relative to the total mass of the solution) was dropped, and the outer bath was adjusted so that the solution temperature was 48 ° C., and the blocking reaction was carried out at 48 ° C. for 6 hours or more, and the disappearance of the peak of the isocyanate group was confirmed by the IR method. Thereafter, 66.4 parts by mass of tert-butanol (amount equivalent to 200 mol% relative to 100 mol% of the initial NCO groups of polyisocyanate P-1) was added, and the reaction was carried out at 80 ° C. for 4 hours. Thereafter, the tert-butanol remaining in the reaction solution and the isopropanol produced by the transesterification reaction were removed by vacuum distillation, and further, dipropylene glycol dimethyl ether (DPDM) removed during the vacuum distillation was added to obtain a blocked polyisocyanate composition BL-a25. The obtained blocked polyisocyanate composition BL-a25 had a solid content of 60.1% by mass and a weight average molecular weight of 6.83 × ¹⁰³ .

[Example 26]
(Blocked polyisocyanate composition BL-a26)
A blocked polyisocyanate composition BL-a26 was produced in the same manner as in Example 1, except that the types of polyisocyanate and the types and blending ratios of blocking agents were as shown in Table 6.

The blocked polyisocyanate composition BL-a26 was prepared as a resin composition by the following method.
A water-based acrylic polyol base agent (Nuplex Corporation, "Setaqua (registered trademark) 6515" (trade name), OH (%) (on solids) = 3.3, Acid value (mg KOH / g) = 9.9, solid content 45 mass%) and blocked polyisocyanate composition BL-a26 were mixed so that the ratio of the molar amount of isocyanate groups to the molar amount of hydroxyl groups (isocyanate group / hydroxyl group) was 0.80. Further, ion exchange water was mixed, and a trace amount of dimethylaminoethanol was added to adjust the pH to about 8.0 to 8.5 and the solid content to 45 mass%. Next, the solution was stirred at 1000 rpm using a homodisper for 15 minutes, and after defoaming, a resin composition was obtained. The obtained resin composition was evaluated for low temperature curing property using the same method as above.

In addition, various evaluations were performed using the above-mentioned methods on the blocked polyisocyanate compositions obtained in the examples and comparative examples. The results are shown in Tables 1 to 6 below.

In Tables 1 to 6, the types of blocking agents are as follows:
(Blocking agent)
B-1: Diisopropyl malonate B-2: Di-tert-butyl malonate B-3: Diethyl malonate

As can be seen from Tables 1 to 6, the blocked polyisocyanate compositions BL-a1 to BL-a26 (Examples 1 to 26), in which the molar ratio of the structural unit (II)/structural unit (I) was 20/80 or more and 92/8 or less, had good storage stability when made into a resin composition, and also had good low-temperature curing properties, Konig hardness, and maximum tensile stress when made into a resin film.
In addition, in the blocked polyisocyanate compositions BL-a1 to BL-a9 and BL-a11 to BL-a15 (Examples 1 to 9 and 11 to 15) having different molar ratios of the structural unit (II)/structural unit (I), the smaller the molar ratio of the structural unit (II)/structural unit (I), i.e., the higher the proportion of B-2, the better the Konig hardness when formed into a resin film. On the other hand, the larger the molar ratio of the structural unit (II)/structural unit (I), i.e., the higher the proportion of B-1, the better the storage stability when formed into a resin composition. Furthermore, in the blocked polyisocyanate compositions BL-a1 to BL-a8 and BL-a11 to BL-a15 (Examples 1 to 8 and 11 to 15) in which the molar ratio of the structural unit (II)/structural unit (I) is 90/10 or less, the resin composition tended to have a better maximum tensile stress.
In addition, in the blocked polyisocyanate compositions BL-a10 to BL-a18 and BL-a20 (Examples 10 to 18 and 20) using polyisocyanates containing structural units derived from HDI and IPDI, the Konig hardness and maximum tensile stress when formed into a resin film tended to be particularly excellent.
Block polyisocyanate composition BL-a19 (Example 19) using a polyisocyanate containing a structural unit derived from a hydrophilic compound tended to be superior in low-temperature curing properties, Konig hardness, and maximum tensile stress when made into a resin film, compared with block polyisocyanate composition BL-a6 (Example 6) using a polyisocyanate not containing a structural unit derived from a hydrophilic compound.
Among the blocked polyisocyanate compositions BL-a2, BL-a4, BL-a6, and BL-a21 to BL-a23 (Examples 2, 4, 6, and 21 to 23) which used different combinations of blocking agents, the blocked polyisocyanate compositions BL-a2, BL-a4, and BL-a6 (Examples 2, 4, and 6) which used a malonic acid ester having a tertiary alkyl group and a malonic acid ester having a secondary alkyl group tended to have better low-temperature curing properties, Konig hardness, and maximum tensile stress when formed into a resin film.

On the other hand, in the blocked polyisocyanate composition BL-b1 (Comparative Example 1) in which diisopropyl malonate (B-1) was used alone, the storage stability was excellent when made into a resin composition, but the low-temperature curing property and Konig hardness were poor when made into a resin film.
In addition, in the blocked polyisocyanate composition BL-b2 (Comparative Example 2) in which di-tert-butyl malonate (B-2) was used alone, the low-temperature curing property and Konig hardness were kept good when made into a resin film, but the storage stability was poor when made into a resin composition.
In the blocked polyisocyanate composition BL-b3 (Comparative Example 3) in which the molar ratio of the structural unit (II)/structural unit (I) was 5/95, the low-temperature curing properties and Konig hardness were excellent when made into a resin film, but the storage stability was poor when made into a resin composition.

The blocked polyisocyanate composition of this embodiment can provide a blocked polyisocyanate composition that has good storage stability when made into a resin composition and has good curing properties at a low temperature of about 80°C when made into a resin film. The resin composition of this embodiment contains the blocked polyisocyanate composition and has good storage stability. In addition, the resin composition of this embodiment can provide a resin film that has excellent low-temperature curing properties, and is therefore suitable for use in coating materials with low heat resistance.

Claims (11)

A blocked polyisocyanate composition comprising a blocked polyisocyanate derived from a polyisocyanate, a malonic acid ester having one or more tertiary alkyl groups, and a malonic acid ester having one or more secondary alkyl groups,
a molar ratio of the structural units derived from a malonic acid ester having a secondary alkyl group to the structural units derived from a malonic acid ester having a tertiary alkyl group is greater than 5/95 and less than 95/5;
The blocked polyisocyanate composition , wherein the malonic acid ester having a tertiary alkyl group comprises di-tert-butyl malonate, and the malonic acid ester having a secondary alkyl group comprises diisopropyl malonate . 2. The blocked polyisocyanate composition according to claim 1 , wherein the polyisocyanate has an average isocyanate functionality of 2 or greater. 3. The blocked polyisocyanate composition according to claim 1 or 2 , wherein the polyisocyanate is a polyisocyanate derived from one or more diisocyanates selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates. The blocked polyisocyanate composition according to any one of claims 1 to 3 , wherein the blocked polyisocyanate composition has a weight average molecular weight Mw of 2.0 x ¹⁰³ or more. The blocked polyisocyanate composition according to any one of claims 1 to 4 , wherein the blocked polyisocyanate has an isocyanurate group. A resin composition comprising the blocked polyisocyanate composition according to any one of claims 1 to 5 and a polyvalent hydroxy compound. A resin film obtained by curing the resin composition according to claim 6 . The resin film according to claim 7, wherein the resin composition is heated at 80°C for 30 minutes to cure the resin film having a thickness of 40 µm, and the resin film is stored at 23°C for 1 week and then immersed in acetone at 23°C for 24 hours. 9. The resin film according to claim 7 or 8 , wherein the resin composition is heated on a glass plate at 80° C. for 30 minutes to cure the resin film, the resin film having a thickness of 40 μm, has a Konig hardness at 23° C. of 38 or more. The resin film according to any one of claims 7 to 9, wherein the resin composition is heated at 80°C for 30 minutes to harden the resin film, which has a thickness of 40 µm, a width of 10 mm and a length of 40 mm, and is set so that the chuck distance is 20 mm. A tensile test is performed at 23°C and at a speed of 20 mm/min, and the maximum stress is 5 MPa or more. A laminate comprising two or more layers of the resin film according to any one of claims 7 to 10 , each layer having a different composition,
The laminate has a thickness of 1 μm or more and 50 μm or less per layer.