JPH06107765A - Production of aqueous blocked isocyanate and coating material composition containing the same aqueous blocked isocyanate - Google Patents

Abstract

PURPOSE:To produce the subject compound capable of preparing an aqueous coating material capable of forming a coating film excellent in low-temperature physical properties by synthesizing a polyisocyanate using a specified polyol and reacting NCO groups of the resultant polyisocyanate with a thermally eliminable blocking agent and a compound having a hydrophilic group and an active hydrogen. CONSTITUTION:The objective compound is obtained by reacting (A) NCO groups of a polyisocyanate synthesized through a reaction between a polyol (preferably polycaprolactone polyol having two or three hydroxyl groups and exhibiting 500 to 1600 number-average molecular weight and an aliphatic or alicyclic diisocyanate (preferably hexamethylene diisocyanate) with (B) a thermally eliminable blocking agent (preferably acetoxime or methyl ethyl ketoxime) and (C) a compound (e.g. an oxyacid such as glycolic acid) having a hydrophilic group or a functional group convertible into a hydrophilic group and an active hydrogen reactive with NCO. In addition, the reaction between the components (A) and (B) is carried out preferably at 0 to 100 deg.C.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a non-yellowing type water-based block isocyanate. More specifically, it can provide excellent coating properties at low temperatures in addition to weather resistance, chemical resistance, etc. The present invention relates to a block isocyanate extremely useful as a paint for electric appliances and the like, and an aqueous paint composition using the same.

[0002]

2. Description of the Related Art Conventionally, polyurethane resin paints have very excellent wear resistance, chemical resistance, and stain resistance.
Polyurethane resin coatings derived from non-yellowing polyisocyanates made from aliphatic and alicyclic diisocyanates have excellent weather resistance, and their demand tends to increase. In addition, automobiles and building exteriors are exposed to all environments and must withstand them. In particular, even at low temperatures below 0 ° C, the above-mentioned automobiles and building exterior paints have extensibility,
Excellent coating film physical properties such as impact resistance and adhesiveness are required, and improvements thereof are described in JP-B-64-10023, JP-A-1-92276 and JP-A-2-1718.
It is proposed in Japanese Patent Publication.

On the other hand, in recent years, water-based paints have attracted particular attention from the viewpoints of global environment, safety, hygiene and the like. From building exteriors to industrial products, it has come to be used for industrial paints such as food cans and coil coatings. Furthermore, there are many proposals for automobile coatings that require high quality such as weather resistance, chemical resistance, and impact resistance, and are disclosed in JP-A-56-157358, JP-A-63-175079, and JP-A-63-175079. -1
Aqueous paints are disclosed in Japanese Patent Publication No. 93968 and the like. However, these have problems in coating film physical properties such as excellent flexibility at low temperatures.

[0004]

Accordingly, in the field of water-based paints, there has been a demand for the appearance of an aqueous polyurethane paint having excellent weather resistance, chemical resistance, etc., and particularly excellent low-temperature physical properties.

[0005]

The present invention is achieved by reacting a compound having a blocking agent, a hydrophilic group and an active hydrogen with an isocyanate group of polyisocyanate which is a reaction product of a polyol and a diisocyanate. In the method for producing the obtained block isocyanate, it was found that the block isocyanate can be made water-based by using a polyol having a specific number average molecular weight and a hydroxyl group as the polyol, and the above-mentioned problems have been solved.

That is, according to the present invention, the isocyanate group of the polyisocyanate obtained by reacting a polyol with an aliphatic or alicyclic diisocyanate is added to the [A] heat dissociable blocking agent and [B] hydrophilic group. Alternatively, in a method for producing a block isocyanate composition obtained by reacting a compound having at least one active hydrogen capable of reacting with a hydrophilic group with a functional group capable of converting to a hydrophilic group in one molecule,
The above polyol has a number average molecular weight of 500 to 1600 and a hydroxyl group of 2 to 3, and a method for producing an aqueous block isocyanate, and a hydroxyl value of a resin component of 10.
A water-soluble coating composition comprising a water-affinity polyol having a number average molecular weight of 2,000 to 50,000 and a number average molecular weight of 2,000 to 50,000 and the water-based block isocyanate obtained by the above-described method for producing a water-based block isocyanate.

The present invention will be described in detail below. The polyol, which is one component of the raw material of the polyisocyanate of the present invention, has an average hydroxyl value of 2 to 3 in one molecule and a number average molecular weight of 500 to 1600. When a polyol having a number average molecular weight of less than 500 is used as one component of the raw material, the elongation of the formed coating film at low temperature is insufficient.
Further, when a polyol having a number average molecular weight of more than 1600 is used as one component of the raw material, the obtained polyisocyanate has a low isocyanate content and low compatibility with the main agent, resulting in poor practicability. Examples of such polyols include aliphatic hydrocarbon polyols, polyether polyols, polyester polyols, epoxy resins, polycarbonate polyols and the like.

Examples of the aliphatic hydrocarbon polyols include terminally hydroxylated polybutadiene and hydrogenated products thereof. Examples of the polyether polyols include polyether polyols and polytetramethylene obtained by adding alkylene oxide such as ethylene oxide or propylene oxide to a single or mixture of polyhydric alcohol such as glycerin or propylene glycol. There are glycols and polyether polyols obtained by reacting alkylene oxide with a polyfunctional compound such as ethylenediamine and ethanolamine.

As the polyester polyols, for example, a dibasic acid alone selected from the group of carboxylic acids such as succinic acid, adipic acid, sebacic acid, dimer acid, maleic anhydride, phthalic anhydride, isophthalic acid and terephthalic acid. Or polyester polyol resins obtained by a condensation reaction of a mixture and a polyhydric alcohol selected from the group of ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, trimethylolpropane, glycerin, etc., alone or in a mixture, and, for example, ε Examples thereof include polycaprolactone polyols of polycaprolactones obtained by ring-opening polymerization of caprolactone using a polyhydric alcohol.

The polycarbonate polyols include
Examples thereof include those obtained by a conventional method using aromatic polyhydric alcohols such as bisphenol A and aliphatic / alicyclic polyhydric alcohols such as 1,6-hexanediol as raw materials. Examples of epoxy resins include novolac type,
β-methyl epichloro type, cyclic oxirane type, glycidyl ether type, glycol ether type, epoxy type of aliphatic unsaturated compound, epoxidized fatty acid ester type, polycarboxylic acid ester type, aminoglycidyl type, halogenated type, resorcin type, etc. Epoxy resins of

Among the above polyols, polycaprolactone polyol is particularly preferable. In commercial products, for example,
For polycaprolactone polyols, Praxel 3
03, PLAXEL 305, PLAXEL 308, PLAXEL 312, PLAXEL 205, PLAXEL 212 (all manufactured by Daicel Chemical Industries, Ltd., trade names). You may use these individually or in mixture of 2 or more types.

The diisocyanates of the invention which are reacted with such polyols are aliphatic and cycloaliphatic diisocyanates. The aliphatic diisocyanate preferably has 4 to 30 carbon atoms, and the alicyclic diisocyanate preferably has 8 to 30 carbon atoms. For example, 1,4-tetramethylene diisocyanate and 1,5 -Pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, lysine diisocyanate, 3
-Isocyanatomethyl-3,3,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate), 1,3-bis (isocyanatomethyl) -cyclohexane, 4,4'-dicyclohexylmethane diisocyanate and the like. I can. Among them, weather resistance,
Hexamethylene diisocyanate (hereinafter referred to as HMDI) is preferable because of its industrial availability.

The reaction between the polyol and diisocyanate is carried out at room temperature to 200 ° C, preferably 80 to 140 ° C. When the reaction temperature is low, it takes too long to complete the reaction. On the contrary, when the reaction temperature is high, undesired side reactions occur to increase the viscosity of the reaction product or cause coloration, which is not practical. A solvent may be used in the reaction. As usable solvents, for example, toluene, xylene,
Those which are inert to isocyanates such as ethyl acetate and butyl acetate are preferable. If necessary, an organic tin compound, a tertiary amine compound or the like may be used to accelerate the reaction between the isocyanate group and the hydroxyl group.

When the reaction is completed, the unreacted diisocyanate and the solvent in the reaction mixture can be removed to obtain the desired polyisocyanate. Examples of such polyisocyanates include JP-B-64-10023 and JP-A-2-1718. The order of the reaction of the isocyanate group of the polyisocyanate thus obtained and the compound containing a blocking agent and a hydrophilic group having an active hydrogen or a functional group convertible to a hydrophilic group is not particularly limited, If the functional group can be active hydrogen, the reaction with the blocking agent should be preferred.

Examples of the blocking agent of the present invention include:
There are phenol-based, alcohol-based, active methylene, mercaptan-based, acid amide-based, acid imide-based, imidazole-based, urea-based, oxime-based, amine-based, imide-based compounds, etc., which may be used alone or in combination. Good.
Examples of more specific blocking agents are: (1) phenol-based; phenol, cresol, ethylphenol, butylphenol, etc. (2) alcohol-based; butyl cellosolve, propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol, ethanol, 2-Ethylhexanol, etc. (3) Active methylene type; dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, acetylacetone, etc. (4) Mercaptan type; Butyl mercaptan, dodecyl mercaptan, etc. (5) Acid amide type; acetanilide , Acetic acid amide, ε-
Caprolactam, δ-valerolactam, γ-butyrolactam, etc. (6) Acid imide type; succinimide, maleic acid imide, etc. (7) Imidazole type; imidazole, 2-methylimidazole, etc. (8) Urea type; urea, thiourea, Ethylene urea, etc. (9) Oximes; formaldoxime, acetoaldoxime, acetoxime, methylethylketoxime, cyclohexanone oxime, etc. (10) Amines; diphenylamine, aniline, carbazole, etc. (12) Imines; ethyleneimine, polyethyleneimine, etc. Of these, oxime-based, acid amide-based, and active methylene-based are preferable, and acetoxime and methylethylketoxime are particularly preferable.

The blocking reaction can be carried out with or without the presence of a solvent. When using a solvent, it is necessary to use a solvent which is inactive to the isocyanate group. In the blocking reaction, an organic metal salt of tin, zinc, lead or the like, a tertiary amine or the like may be used as a catalyst. The reaction can be generally carried out at -20 to 150 ° C, preferably 0 to 100 ° C. If the temperature is 100 ° C. or higher, a side reaction may occur. On the other hand, if the temperature is too low, the reaction rate becomes slow, which is disadvantageous. 10 to 100 of isocyanate groups
It is preferable to block%.

The hydrophilic group of the present invention means a carboxyl group,
Examples include sulfone group, sulfonium group, phosphonium group, amino group, hydroxyl group, alkoxy group, ether group and the like. These hydrophilic groups may be used alone or in combination of two or more. The method of introducing a hydrophilic group of the present invention is a method of reacting a compound having both active hydrogen and a hydrophilic group with an isocyanate. After reacting a compound having both active hydrogen and a tertiary nitrogen with an isocyanate, an organic acid is added. Method of forming salt, inorganic acid salt, and quaternary ammonium salt After reacting a compound having both active hydrogen and an epoxy group with an isocyanate, (1) a method of reacting with a dibasic acid (2) hydroxyl group, mercapto Group, a method of reacting with a compound having both a methyl group and a carboxyl group, and then hydrolyzing (3) a method of reacting with a compound having both a carboxyl group and / or a sulfone group and an amino group ( 4) There is a method of reacting an onium salt-forming substance in combination with an organic acid or an inorganic acid.

The above-mentioned active hydrogen is capable of reacting with an isocyanate, and examples of the compound containing active hydrogen include phenol-based compounds, lactam-based compounds, oxime-based compounds, active methylene-based compounds, alcohol-based compounds, mercaptan-based compounds, acid amide-based compounds, There are imide type, amine type, imidazole type, urea type compounds and the like. Examples of the compound containing both active hydrogen and a hydrophilic group in the molecule used in the above reaction include, for example, oxy acid, polycarboxylic acid, mercaptocarboxylic acid, sulfonic acid, mercapto alcohol, aminomercaptan, amino alcohol, ethylene oxide polymer. , Ethylene oxide-propylene oxide copolymer, acrylic acid polymer, acrylic acid amide polymer, methacrylic acid polymer,
Methacrylic acid amide polymer, polyvinyl alcohol,
Examples include carboxymethyl cellulose, methyl cellulose and the like, and polymers composed of these. A specific example is shown below.

Examples of the oxyacid include glycolic acid,
Examples thereof include lactic acid, tartaric acid, citric acid, hydroxyacrylic acid, oxybutyric acid, oxyvaleric acid, oxystearic acid, glyceric acid, tartronic acid, salicylic acid, and dihydroxycarboxylic acid, such as dimethylolpropionic acid and polymers thereof. Examples of the polycarboxylic acid include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid and sebacic acid.

Examples of the mercaptocarboxylic acid include mercaptoacetic acid and mercaptosuccinic acid. Examples of the sulfonic acid include isethionic acid, sulfoacetic acid, phenolsulfonic acid, phenoldisulfonic acid, aminophenolsulfonic acid, methanilic acid, sulfanilic acid and the like.

Examples of the mercapto alcohol include mercaptoethanol and dimercaptopropanol. Examples of amino mercaptans include aminoethyl mercaptan. Examples of amino alcohols include 2-aminoethanol, 2-amino-1-butanol, and 2-amino-2-methyl-1,3-propanediol.

Examples of the compound having both active hydrogen and tertiary nitrogen used in the above reaction include dimethylaminopropanol, N-isobutylethanolamine, dimethylaminoethylamine, diethylaminoethylamine, dimethylaminopropylamine, diethylaminopropylamine and dibutyl. Examples include aminopropylamine, dimethylaminoethoxypropylamine, N-aminoethylpiperidine, N-aminopropylmorpholine, 2- (dimethylaminomethyl) phenol, and 2-hydroxypyridine. To convert at least a part of the introduced tertiary nitrogen atom into an organic acid salt, an inorganic acid salt, or a quaternary ammonium salt, formic acid, acetic acid, propionic acid,
Organic acids such as oxalic acid and p-toluenesulfonic acid; inorganic acids such as hydrochloric acid, sulfuric acid, boric acid and phosphoric acid; and quaternary agents such as dialkyl sulfuric acid such as methyl chloride and benzyl chloride are used.

Examples of the compound having both active hydrogen and an epoxy group used in the above reaction include glycidol and the like. Examples of the dibasic acid used in the reaction (1) above include oxalic acid, malonic acid, succinic acid, glutaric acid, and terephthalic acid. Examples of the compound containing a methyl ester of a carboxyl group and a hydroxyl group, a mercapto group, or an amino group used in the reaction (2) above include p-hydroxybenzoic acid methyl ester and mercaptoacetic acid methyl ester. . Examples of the compound containing a compound having both an amino group and a carboxyl group include aminoacetic acid methyl ester.

Examples of the compound having both a carboxyl group and / or a sulfone group and an amino group used in the reaction (3) above include alanine. Above-
As the onium salt-forming substance used in the reaction (4),
There are basic amino compounds, tertiary phosphines, secondary sulfides, etc., and quaternary ammonium, phosphonium,
A sulfonium base can be generated. Examples of the basic amino compound include diethylamine, dipropylamine, N
-Methylethanolamine, diethanolamine, ethylenediamine, diethylenetriamine, dimethylcyclohexylamine, dimethylethanolamine, methyldiethanolamine, triethanolamine, diethylenetriamine and the like. When a polyamine is used, its primary amino group is preferably a ketimine derivative obtained by previously reacting it with a ketone such as acetone, methyl ethyl ketone or isobutyl ketone. Examples of the third phosphine include trimethylphosphine, triethylphosphine, phenyldimethylphosphine, phenyldiethylphosphine, and the like. Examples of the second sulfide include diethyl sulfide, dipropyl sulfide, dibutyl sulfide, diphenyl sulfide, thiodiethanol and thiodipropanol. Examples of the organic acid include formic acid, acetic acid, lactic acid, propionic acid, oxalic acid, acrylic acid, p-toluenesulfonic acid and the like, and examples of the inorganic acid include boric acid, hydrochloric acid, sulfuric acid, phosphoric acid and the like.

In the present invention, the molar ratio [A] / [B] of [A] the heat dissociable blocking agent and [B] the compound having both a hydrophilic group or active hydrogen capable of being converted into a hydrophilic group is 1.5 to. 1
It is 5. If this ratio is less than 1.5, crosslinking is not sufficiently performed and the coating film physical properties are not sufficient. On the other hand, if this ratio exceeds 15, the water-solubilizing ability will be insufficient. The acidic group introduced by these methods is preferably neutralized. Examples of the neutralizing agent include ammonia, diethylamine, triethylamine, morpholine, N, N-dimethylethanolamine, 2-dimethylamino-2-methyl-1-propanol, monoisopropanol, N, N diethylethanolamine, 2-amino. -2-methyl-1-propanol,
Examples include monoethanolamine, N-methyldiethanolamine, diisopropylamine, N-ethyldiethanolamine, triethanolamine, caustic soda and caustic potash.

The aqueous block isocyanate thus prepared is mixed with a water-affinitive polyol to form an aqueous paint. The water-affinity polyol used in the present invention can be used without particular limitation as long as it is one usually used for water-based paints, and it can be anionic, cationic, zwitterionic, or has no ionicity. In addition, alkyd, polyester, epoxy, fluorine, acrylic, etc. may be used.

The resin has a hydroxyl value of 10 to 300 and a number average molecular weight of 2,000 to 50,000, and is dissolved or dispersed in a dispersion medium containing water as a main component. If the resin component has a hydroxyl value of less than 10, the density of urethane crosslinks due to the reaction with the isocyanate component decreases,
If the physical properties of the present invention cannot be achieved and the hydroxyl value of the resin exceeds 300, the crosslinking density is increased, and the mechanical properties of the coating film deteriorate, which is not preferable.

Dissolvable polyols include those disclosed in JP-A-63 / 1988.
-295680, JP-A-63-175059, JP-A-62-216671, JP-A-2-19
The manufacturing method is disclosed in Japanese Patent No. 1692. Dispersion type polyols include those disclosed in JP-A-56-157358.
The publication discloses the manufacturing method.

As a fluorine polyol which is a fluorine copolymer having a hydroxyl group, there is known Japanese Patent Application Laid-Open No. 57-3410.
7, JP-A-61-231044, JP-A-3
The manufacturing method is disclosed in Japanese Patent Publication No. 37252/1997. The present invention is disclosed in JP-A-63-295680, JP-A-63-175059, and JP-A-56-157358.
It is suitable for the acrylic resin disclosed in Japanese Patent Publication No.

When only the aqueous block isocyanate is used as the curing agent in the aqueous coating composition of the present invention, the molar ratio of the latent isocyanate group to the resin component hydroxyl group of the water-affinity polyol is usually 0.5 to 2.5. The melamine-based curing agent can be used together as a curing agent.
Typical examples of the melamine-based curing agent include hexamethoxymethylol melamine and methyl-butylated melamine.

If desired, an antioxidant, an ultraviolet absorber, a pigment, a metal powder pigment, a crosslinking accelerator, a solvent, a rheology control agent, etc. may be added. The water-based paint prepared in this way is applied to metals, plastics, etc. by spray coating, roll coating, shower coating, electrodeposition coating, dip coating, etc., and is also useful as a chipping-resistant coating, precoat metal coating, etc. is there.

[0032]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to the following examples. All% in the examples are shown by weight. The evaluation was performed according to the following. (Gel Fraction) The value of the undissolved part weight when the cured coating film was immersed in acetone at 20 ° C. for 24 hours was expressed as a percentage.

(Low temperature impact resistance) JIS 3141 (S
PCC-SB) 0.8 × 70 × 150 mm (manufactured by Japan Test Panel Co., Ltd.) steel plate coated with a coating film having a film thickness of 30 μm, DuPont type 1/2 inch × 500 g × 50
It was performed in accordance with JIS 5400 under the condition of cm (-20 ° C). The evaluation criteria are as follows.

No crack: ○ Slight cracking: △ Cracking: × (low temperature flexibility) A coating film having a thickness of 30 μm applied to a tin plate of 0.3 × 50 × 150 mm at −20 ° C. , JIS 5400. The evaluation criteria are as follows.

No crack: ○ Slightly cracked: △ Cracked: × [Production Example 1 (production of block isocyanate)] In a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen blowing tube. In a nitrogen atmosphere, 792.4 g of 1,6-hexamethylene diisocyanate, and 115.3 g of polycaprolactone polyol "Placcel 305" (trade name of Daicel Chemical Industries, Ltd.) were charged and stirred,
The reaction was carried out at a reaction temperature of 100 ° C. for 1 hour. The reaction solution thus obtained was distilled at a temperature of 160 ° C. and a vacuum degree of 0.2 mmHg using a thin film distillation apparatus to remove unreacted 1,6-hexamethylene diisocyanate to obtain polyisocyanate. As a result of measuring the isocyanate concentration of this polyisocyanate, it was 11.5%.

[Production Examples 2 to 3 (Production of Block Isocyanate)] The same procedure as in Production Example 1 was carried out except that the polyols and the reaction conditions were changed as shown in Table 1. The isocyanate concentration of the obtained prepolymer is shown in Table 1.

[0037]

Examples 1 to 3 (Production of Aqueous Blocked Isocyanate) A 4-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen blowing tube was placed in a nitrogen atmosphere, and then 100 g of polyisocyanate shown in Table 2 was used. , Ethyl acetate 28
Then, the blocking agent shown in Table 2 was added while controlling the reaction temperature at 50 ° C. or lower under stirring. Next, the temperature in the flask was raised to 60 ° C., the water performance-imparting agent shown in Table 2 was added, and the mixture was kept for 10 hours. The infrared spectrum of this reaction product confirmed the absence of isocyanate.

Further, a neutralizing agent shown in Table 2 was added,
Mix well. 10 g of the obtained reaction product and 10 g of ion-exchanged water were mixed to check the water-solubilizing ability.
As a result, it was confirmed that a transparent liquid was obtained and the blocked isocyanate was made water-based.

[0039]

[Examples 4 to 5 (Production of aqueous block isocyanate)] A four-necked flask equipped with a stirrer, a thermometer, a reflux cooling tube, and a nitrogen blowing tube was placed in a nitrogen atmosphere, and then the polyisocyanate shown in Table 2 was used. Nart 100 g, ethyl acetate 28
Then, the blocking agent shown in Table 2 was added while controlling the reaction temperature at 50 ° C. or lower under stirring. Next, the temperature in the flask was raised to 60 ° C., the water performance-imparting agent glycidol shown in Table 2 was added, and the mixture was kept for 10 hours. The infrared spectrum of this reaction product confirmed the absence of isocyanate. Further, diethylamine shown in Table 2 was added and the mixture was maintained for 1 hour with stirring. The temperature in the flask was lowered by 30 ° C., acetic acid shown in Table 2 was added, and the mixture was kept under stirring. 10 g of the obtained reaction product and 10 g of ion-exchanged water were mixed to check the water-solubilizing ability. As a result, it was confirmed that a transparent liquid was obtained and the blocked isocyanate was made water-based.

[0040]

[Comparative Examples 1 and 2 (Production of aqueous block isocyanate)] Example 1 was repeated except that the raw materials shown in Table 2 were used.

[0041]

[Examples 6 to 10 and Comparative Examples 3 and 4 (evaluation of coating film)] A water-affinity acrylic polyol neutralized with dimethylethanolamine (trade name "ALMATEX WA of Mitsui Toatsu Co., Ltd."
911 "), the aqueous block isocyanates obtained in Examples 1 to 5 and Comparative Examples 1 to 2 are used in Table 3 in solid content ratio.
Formulated as shown in Fig. 3, and water was added, and the paint viscosity was Ford Cup No. 4 was adjusted to 30 seconds. This paint was applied with an applicator, set at room temperature for 30 minutes, and then baked at 160 ° C. for 20 minutes. Table 3 shows the result of the evaluation method.

[0042]

[Example 11 (melamine combination system)] A water-soluble acrylic polyol neutralized with dimethylethanolamine (trade name "ALMATEX WA911" manufactured by Mitsui Toatsu Co., Ltd.) was used to obtain the product in Example 1. Aqueous block isocyanate has a solid content ratio of 100: 22, and a melamine resin (Mitsui Toatsu Co., Ltd., trade name "Cymel 350" has a solid content ratio of 100.
Mixed to make a pair 13. Furthermore, water is added to make the viscosity of the Ford Cup No. 4 was adjusted to 30 seconds. This paint is applied with an applicator, 160 ℃, 20
Cure for minutes. The coating film evaluation results are shown in Table 3.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

[Table 3]

[0046]

As compared with the conventional water-based paint, the water-based paint using the water-based blocked isocyanate according to the present invention can obtain good flex resistance and impact resistance at low temperature.

Claims (3)

[Claims] 1. An isocyanate group of a polyisocyanate obtained by reacting a polyol with an aliphatic or alicyclic diisocyanate has [A] a heat dissociable blocking agent and [B] a hydrophilic group or a hydrophilic group. In the method for producing a block isocyanate composition obtained by reacting a compound having at least one active hydrogen capable of reacting with a group and a functional group capable of reacting with an isocyanate in one molecule, the number average molecular weight of the polyol is 500. ˜1600 and having 2 to 3 hydroxyl groups, a process for producing an aqueous block isocyanate. 2. The method for producing an aqueous block isocyanate according to claim 1, wherein the molar ratio [A] / [B] is 1.5 to 15. 3. A water-based coating composition comprising a water-affinity polyol having a resin component hydroxyl value of 10 to 300 and a number average molecular weight of 2,000 to 50,000 and the water-based block isocyanate obtained by the production method according to claim 1.