JPH0525433A - Extensible low-temperature-curable one-component polyurethane coating composition - Google Patents

Abstract

PURPOSE:To provide the subject compsn. which cures at low temp., exhibits an improved extensibility, and gives a coating film improved in weatherability and low-temp. properties by compounding a specific blocked polyisocyanate, a polyol, and a cure accelerator. CONSTITUTION:A diol and/or a triol having a number-average mol.wt. of 500-1,600 and a mean hydroxyl functionality of 2-3 is allowed to react with an alph. or alicyclic diisocyanate at from room temp. to 200 deg.C to give a polyisocyanate compd., of which isocyanate groups are blocked with a blocking agent to give a blocked polyisocyanate. A mixture of the blocked polyisocyanate with a polyol having a hydroxyl value of 10-30mgKOH/g in a molar ratio of NCO group to OH group of 0.4-2 is mixed with 0.01-10wt.% at least one cure accelerator selected from the group consisting of metal chelate compds. of Co, Zn, Ni, Sn, Mn, and Cu.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a low temperature crosslinkable one-part polyurethane thermosetting coating composition having extensibility.

[0002]

2. Description of the Related Art Conventionally, polyurethane resin paints have extremely excellent wear resistance, chemical resistance and stain resistance, and
Polyurethane resin coatings derived from non-yellowing polyisocyanates using aliphatic and alicyclic diisocyanates as raw materials have further excellent weather resistance, and their demand tends to increase.

However, since the polyurethane resin paint is generally a two-part type, it is very inconvenient to use it. That is, a usual urethane resin coating consists of two components, a polyol and a polyisocyanate, and it is necessary to store them separately and mix them at the time of coating. In addition, under the present circumstances, once mixed, the paint gels in a short time and cannot be used. This makes it extremely difficult to perform automatic painting in the field of line painting such as automobiles or weak electric painting.

Further, since it is necessary to sufficiently wash the coating machine and the coating tank at the end of the work, the work efficiency is remarkably reduced. In order to improve the above-mentioned drawbacks, it has been conventionally proposed to use a block isocyanate in which all active isocyanate groups are blocked with a blocking agent. This block isocyanate does not react with the polyol at room temperature, but at a high temperature, it has the property of dissociating the blocking agent and regenerating the active isocyanate group to react with the polyol to cause a crosslinking reaction, so that the above-mentioned drawbacks are temporarily improved. You can

However, the above crosslinking reaction requires a high baking temperature. A high baking temperature is not only an increase in energy cost, but also an accompanying increase in air pollution, and a fatal drawback in coating a heat-sensitive object such as plastics. In addition, automobiles and building exteriors are exposed to all environments and must withstand them. Particularly, even at a low temperature of 0 ° C. or less, excellent flexibility, impact resistance, adhesion, and other excellent coating film physical properties are required.

Therefore, in the field of polyurethane resin coatings, it has been desired to develop a one-component polyurethane resin coating having excellent weather resistance, a low crosslinking temperature and excellent low-temperature physical properties. Several proposals have been made to reduce the crosslinking temperature. In JP-B-44-18877, JP-A-53-138434, JP-A-56-84714 and JP-A-57-8217, a specific organotin compound is added as a catalyst for promoting curing. JP 62-
In 199609 publication, a lead compound and an inorganic zinc compound are added as catalysts for hardening promotion.

However, even if the above curing accelerator is added to the block isocyanate in which the isocyanate group of the polyisocyanate derived from the non-yellowing diisocyanate is masked, the crosslinking temperature of the coating does not decrease so much, Moreover, the excellent coating film physical properties at low temperature were not obtained, and the use was limited.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a coating composition having excellent weather resistance, a low coating crosslinking temperature, and excellent coating properties at low temperatures. It is in.

[0009]

Means for Solving the Problems As a result of intensive investigations by the present inventors, by combining a curing accelerator composed of a specific block polyisocyanate, a specific polyol and a specific metal chelate compound, the above-mentioned object can be achieved. The inventors have succeeded in finding out what has been achieved and have reached the present invention. That is, the present invention is
(1) A block obtained by blocking an isocyanate group of a polyisocyanate comprising a diol and / or triol having a number average molecular weight of 500 to 1600 and a diisocyanate which is an aliphatic or alicyclic diisocyanate alone or as a mixture with a blocking agent. Polyisocyanate, (2) polyol having a hydroxyl value of resin component of 10 to 300 mg KOH / g,
And (3) a low temperature curable one having extensibility, which comprises, as a main component, one or more curing accelerators selected from chelate compounds of cobalt, zinc, nickel, tin, manganese and copper. It is a liquid polyurethane coating composition.

The diols and triols, which are one component of the raw material for the polyisocyanate of the present invention, have an average hydroxyl value of 2 and 3 in one molecule and a number average molecular weight of 500 to 160.
Must be in the 0 range. When a diol or triol having a number average molecular weight of less than 500 is used as one component of the crude raw material, the elongation of the formed coating film at low temperature is not sufficient. When a diol or triol 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 a low solubility in a solvent, resulting in poor practicability. Examples of such diols and triols include aliphatic hydrocarbon polyols, polyether polyols, polyester polyols, epoxy resins and polycarbonate polyols.

Specific examples of the aliphatic hydrocarbon polyols include terminally hydroxylated polybutadiene and hydrogenated products thereof. Further, as the polyether polyols, for example, polyether polyols obtained by adding alkylene oxide such as ethylene oxide or propylene oxide alone or in mixture to polyhydric alcohol such as glycerin or propylene glycol, alone or in mixture, There are methylene 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 a polyester polyol resin 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 ε- Examples thereof include polycaprolactones obtained by ring-opening polymerization of caprolactone using a polyhydric alcohol.

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

Polytetramethylene glycol and polycaprolactone polyol are particularly preferable. In the case of commercially available products, for example, in the case of polytetramethylene glycol, PTG
Examples of commercially available 65 Liols include:
If it is polytetramethylene glycol, PTG65
0, PTG1000, PTG1500, PTG1800
(Both are trade names of Hodogaya Chemical Co., Ltd.), polycaprolactone polyol, Praxel 30
3, PLAXEL 305, PLAXEL 308, PLAXEL 312, PLAXEL 205, PLAXEL 212 (all manufactured by Daicel Chemical Industries, Ltd., trade name). You may use these individually or in mixture of 2 or more types.

The diisocyanates of the present invention which are reacted with such diols and triols are aliphatic and alicyclic diisocyanates. The aliphatic diisocyanate preferably has 4 to 30 carbon atoms, and the alicyclic diisocyanate preferably has 8 to 30 carbon atoms.
1,4-tetramethylene diisocyanate, 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4-trimethyl-1,6
-Hexamethylene diisocyanate, lysine isocyanate, 3-isocyanatomethyl-3,3,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate), 1,3-bis (isocyanatomethyl)
-Cyclohexane, 4,4'-dicyclohexylmethane diisocyanate and the like can be mentioned. Above all,
1,6-hexamethylene diisocyanate (hereinafter referred to as HMDI) is preferable from the viewpoint of weather resistance and industrial availability.

The reaction between the diol, triol and diisocyanate is from room temperature to 200 ° C., preferably 80 to
It is carried out at 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. Examples of usable solvents include toluene,
Those which are inactive to isocyanates such as xylene, ethyl acetate and butyl acetate are preferable. Also, if necessary,
Organotin compounds, tertiary amine compounds and the like may be used to accelerate the reaction between the isocyanate group and the hydroxyl group. Further, an isocyanurate reaction may be further performed. The reaction temperature in this case is 40 to 120 ° C., and a catalyst is usually used.

Examples of the catalyst include hydroxides of tetraalkylammonium such as tetramethylammonium, tetraethylammonium, tetrabutylammonium and weak organic acid salts, trimethylhydroxypropylammonium, trimethylhydroxyethylammonium, triethylhydroxypropylammonium and triethylhydroxyethyl. Hydroxyalkyl ammonium salts such as ammonium and weak organic acid salts, alkali salts of alkylcarboxylic acids such as acetic acid, caproic acid, octylic acid and myristic acid, metal salts such as tin, zinc and lead, aminosilyl groups such as hexamethyldisilazane Examples include contained compounds. When stopping the isocyanurate-forming reaction, sulfuric acid, phosphoric acid, sulfonic acid, etc. are added to deactivate the catalyst. 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 polyisocyanate include, for example, Japanese Examined Patent Publication No. 64-10023.
And Japanese Patent Application Laid-Open No. 2-1718.

The isocyanate group of the polyisocyanate thus obtained is blocked by the blocking agent. As the blocking agent of the present invention, for example, phenol-based, alcohol-based, active methylene, mercaptan-based,
There are acid amide-based, acid imide-based, imidazole-based, urea-based, oxime-based, amine-based, and imide-based compounds, and these may be used alone or in combination. Examples of more specific blocking agents are shown below.

Phenolic type; phenol, cresol,
Ethylphenol, butylphenol, etc. Alcohol type; butyl cellosolve, propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol, ethanol, 2-ethylhexanol, etc., active methylene type; dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate ,
Acetylacetone, etc., mercaptans; butylmercaptan, dodecylmercaptans, etc., acid amides; acetanilide, acetic amide, ε-caprolactam, δ-valerolactam, γ-butyrolactam, etc., acid imides; succinimide, maleic imide, etc., imidazole System; imidazole, 2-methylimidazole, etc., urea system; urea,
Oximes such as thiourea and ethylene urea; formaldoxime, acetaldoxime, acetoneoxime,
Among the above blocking agents, oxime type and acid amide type are preferable, and acetone oxime and methyl ethyl ketoxime are preferable, such as methyl ethyl ketoxime, cyclohexanone oxime and the like, amine type; diphenylamine, aniline, carbazole and the like, imine type; Particularly preferred. A coating film using such a block isocyanate as a crosslinking agent has extensibility.

As the polyol in the present invention, aliphatic hydrocarbon polyols, polyether polyols,
Examples thereof include polyester polyols, epoxy resins, fluorine polyols and acrylic polyols.
Specific examples of the aliphatic hydrocarbon polyols include, for example, terminally hydroxylated polybutadiene and hydrogenated products thereof. Further, as polyether polyols,
For example, polyether polyols, polytetramethylene glycols, and alkylene oxides obtained by adding a single or mixture of alkylene oxides such as ethylene oxide and propylene oxide to a single or mixture of polyhydric alcohols such as glycerin and propylene glycol. Polyether polyols obtained by reacting a polyfunctional compound such as ethylenediamine and ethanolamine, and so-called polymer polyols obtained by polymerizing acrylamide and the like using these polyethers as a medium are included.

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 a polyester polyol resin 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 ε- Examples thereof include polycaprolactones obtained by ring-opening polymerization of caprolactone using a polyhydric alcohol.

The epoxy resins include, for example, 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,
Examples thereof include polycarboxylic acid ester type, aminoglycidyl type, halogenated type and resorcin type epoxy resins.

Examples of the fluoropolyols include fluoroolefins, cyclohexyl vinyl ethers, hydroxyalkyl vinyl ethers, monocarboxylic acid vinyl esters, etc. disclosed in, for example, JP-A-57-34107 and JP-A-61-275311. There are polymers and the like. Examples of the acrylic polyol include acrylic acid ester having active hydrogen such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-hydroxybutyl acrylate, or acrylic acid monoester of glycerin or methacrylic acid. Monoesters, acrylic acid monoesters of trimethylolpropane are methyl acrylate, ethyl acrylate, isopropyl acrylate, -n-butyl acrylate, acrylic acid-, alone or a mixture selected from the group of methacrylic acid monoesters. Acrylic ester such as 2-ethylhexyl, methyl methacrylate, ethyl methacrylate,
An isopropyl methacrylate, -n-butyl methacrylate, isobutyl methacrylate, -n-hexyl methacrylate, a single or a mixture selected from the group of methacrylic acid esters such as lauryl methacrylate as an essential component,
Unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid and itaconic acid, unsaturated amides such as acrylamide, N-methylol acrylamide, diacetone acrylamide, and glycidyl methacrylate, styrene, vinyltoluene, vinyl acetate, acrylonitrile, fumar Acrylic polyol resin obtained by polymerization in the presence or absence of a single compound or a mixture selected from the group of other polymerizable monomers such as dibutyl acid and JP-A-1-261409 and JP-A-3-6273. Acrylic polyol resins obtained by copolymerizing polymerizable UV-stable monomers as exemplified in the publications and the like.

Particularly preferred among these polyols are the above-mentioned acrylic polyols. The polyol of the present invention has a resin component hydroxyl value of 10 to 300 mgKOH / g. When the hydroxyl value of the resin component is less than 10, the crosslinking density of the urethane due to the reaction with the isocyanate component is reduced, and the function of the urethane bond cannot be exhibited. When the hydroxyl value of the resin component exceeds 300, the crosslinking is reversed. The density increases and the mechanical properties of the coating film deteriorate, which is not preferable, and in some cases, the hydroxyl group and the isocyanate group do not react completely.

In the block isocyanate and the polyol thus obtained, the molar ratio of the blocked isocyanate group in the block isocyanate to the hydroxyl group in the polyol is in the range of 0.4: 1 to 2: 1. Is preferred. Further, various blocked polyisocyanates and melamine-based curing agents can be used in combination depending on the application. As the block polyisocyanate, a buret-type polyisocyanate block (for example, JP-A-55)
No. 144021), a block of isocyanurate type polyisocyanate (for example, JP-A-55-383).
80), urethane-modified isocyanurate-modified isocyanurate-type polyisocyanurate block (for example, JP-A-60-149572) and the like. Typical examples of the melamine-based curing agent include hexamethoxymethylol melamine and methyl-butylated melamine.

The curing accelerator used in the present invention will be described. The metal chelate compound used in the present invention is a chelate compound of cobalt, zinc, nickel, tin, manganese, and copper. In these metal chelate compounds, at least one of the metal atoms is an alkoxy group having 1 to 14 carbon atoms, and examples thereof include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy and s.
ce-butoxy, n-pentoxy, isoamyloxy,
A compound such as n-heptyloxy, n-octyloxy, n-stearyloxy or an alkoxyalkoxy group having 2 to 10 carbon atoms, to which, for example, methoxymethoxy, methoxyethoxy, ethoxybutoxy, butoxypentoxy and the like are bonded is preferable. Is.

The remaining group bonded to the above metal is, for example, an alkyl group having 1 to 8 carbon atoms, such as methyl, ethyl, n-butyl, isobutyl, sec.
-Butyl, tert-butyl, amyl, etc., aryl groups such as phenyl, toluyl, etc., alkenyl groups such as vinyl, allyl, etc., alkyl groups having 1 to 8 carbon atoms substituted with a mercapto group or amino group, such as γ-mercaptopropyl, amino Examples include ethyl, aminopropyl and aminobutyl.

Examples of the chelating agent include lower alkanolamines such as triethanolamine, diethanolamine, dimethylaminoethanol and dimethylaminoethanol, acetoacetic acid esters such as methyl acetoacetate and ethyl acetoacetate, and diketone alcohols such as diacetone alcohol. , Diketones such as acetylacetone, glycols such as ethylene glycol and octylene glycol, oxycarboxylic suns such as lactic acid and tartaric acid, dicarboxylic acids such as maleic acid and ethyl malonate or their esters, other salicylic acid, catechol, pyrogallol Etc., and diketones and acetoacetic acid esters are preferable.

Typical examples of the metal chelate compound used in the present invention include dibutyl bis (acetylacetone) tin, butyl tris (acetylacetonato) tin,
Dipropyl bis (acetylacetonate) tin, propyl tris (acetylacetonate) tin, dioctyl
Bis (acetylacetonate), dibutyl bis (ethylacetoacetate) tin, propyl tris (ethylacetoacetate) tin, propoxy tris (ethylacetoacetate) tin, bis (acetylacetone) zinc, bis (ethylacetoacetate) zinc , Dipropoxy bis (acetylacetonato) cobalt, dipropoxy
Examples thereof include bis (ethylacetoacetate) cobalt, bis (acetylacetone) cobalt, bis (acetylacetone) nickel, and bis (ethylacetoacetate) nickel. These may be used alone or in combination of two or more. Preferred is a bis (acetylacetone) salt. The addition amount is not particularly limited, but usually,
It is 0.01 to 10% by weight, preferably 0.5 to 5% by weight, based on the resin solid content.

In addition, in the composition of the present invention, a suitable solvent, such as benzene, toluene, xylene, cyclohexane, mineral spirits, hydrocarbons such as naphtha, acetone, methyl ethyl ketone, etc., may be added as necessary when mixing the components. It can be appropriately selected and used from the group of ketones such as methyl isobutyl ketone, esters such as ethyl acetate, -n-butyl acetate and cellosolve acetate according to the purpose and application. These solvents may be used alone or in combination of two or more.

If necessary, an antioxidant, an ultraviolet absorber, a pigment, a metal powder pigment, a rheology control agent, etc. may be added.

[0032]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited thereto. In addition, in the examples, the blending ratio of buflock isocyanate and polyol is shown in parts by weight. Further, the curing accelerator is shown in% by weight based on the solid content of these block isocyanate and polyol. The evaluation was performed according to the following.

The physical properties of the coating film were measured and evaluated by the following methods. (Gel fraction) The coating film after baking and curing was added to acetone at 20 ° C.
The gel fraction is the value of the weight of the undissolved portion after being immersed for 24 hours under the condition of before the immersion. This value was used as an index of the coating film forming ability. If this value is less than 50%, it cannot be used as a paint, if it is 50 to less than 85%, it is not satisfactory as another paint, and if it is 85% or more, it is sufficiently satisfactory. .. (Low temperature impact resistance) JIS3141 (SPCC-SB)
DuPont 1/2 inch x 500 g of coating film with a thickness of 30μ applied to 0.8 x 70 x 150 mm steel plate
It was performed in accordance with JIS 5400 under the condition of × 50 cm (-10 ° C). In the evaluation, no cracks were evaluated as O, slight cracks were evaluated as Δ, and cracks were evaluated as X.

[0034]

Reference Example 1 (Production of Block Isocyanate) A 4-necked flask equipped with a stirrer, a thermometer, a reflux cooling tube, and a nitrogen blowing tube was placed in a nitrogen atmosphere, and 1,6-hexamethyldiisocyanate (HMDI) was added. 1008 g, number average molecular weight 100
0 polytetramethylene glycol PTG100
400 (manufactured by Hodogaya Chemical Co., Ltd.) was charged, and the mixture was reacted with stirring at a reaction temperature of 100 ° C. for 1 hour. The reaction solution thus obtained was heated at a temperature of 160 ° C. using a thin film distillation apparatus.
Distillation was performed at a vacuum degree of 0.2 mmHg to remove unreacted HMDI to obtain polyisocyanate. After the inside of a 4-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen blowing tube was made to have a nitrogen atmosphere, the resulting polyisocyanate 10 was obtained.
Charged with 00g and 284g of ethyl acetate, 135g of butanone oxime while stirring and controlling the reaction temperature at 50 ° C or lower.
Was dripped. It was confirmed by infrared spectrum that the absorption of the isocyanate group had disappeared.

[0035]

Reference Example 2 (Production of Block Isocyanate) Using the same apparatus as in Reference Example 1, the inside of the flask was made a nitrogen atmosphere, and then HMDI was used.
792 g and Praxel 305 (manufactured by Daicel Chemical Industries, Ltd., trade name, number average molecular weight 550) which is a polycaprolactone polyol were charged and reacted at 100 ° C. for 1 hour under stirring. 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 HMDI to obtain polyisocyanate.
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 1000 g of the obtained polyisocyanate and 314 g of ethyl acetate were charged, and the reaction temperature was 50 ° C or lower with stirring. 254 g of butanone oxime was added dropwise while controlling the above. It was confirmed by infrared spectrum that the absorption of the isocyanate group had disappeared.

[0036]

Reference Example 3 (Production of Block Isocyanate) The same apparatus as in Reference Example 1 was used, and the inside of the flask was made into a nitrogen atmosphere, and then HMDI was used.
300 g and Praxel 205 (manufactured by Daicel Chemical Industries, Ltd., trade name, number average molecular weight 550), which is a polycaprolactone polyol, were charged and reacted at 100 ° C. for 1 hour under stirring. 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 HMDI to obtain polyisocyanate.
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 1000 g of the obtained polyisocyanate and 300 g of ethyl acetate were charged, and the reaction temperature was kept at 50 ° C or lower with stirring. 205 g of butanone oxime was added dropwise while controlling. It was confirmed by infrared spectrum that the absorption of the isocyanate group had disappeared.

[0037]

Reference Example 4 (Production of Block Isocyanate) Using a device similar to that of Reference Example 1, the flask was filled with a nitrogen atmosphere, and then HMDI was used.
Duranate 2 which is a polyisocyanate made from
1000 g of 4A (trade name of Asahi Kasei Co., Ltd.) and 380 g of ethyl acetate were charged, and 511 g of butanone oxime was added dropwise under stirring while controlling the reaction temperature at 50 ° C. or lower. It was confirmed by infrared spectrum that the absorption of the isocyanate group had disappeared.

[0038]

Examples 1 to 9 Examples 1 to 6, 8 and 9 were prepared using Dainippon Ink and Chemicals, Inc. as a polyol using the block isocyanate synthesized in Reference Example as a non-volatile content 50% hydroxyl value 50 mgKOH / g of acrylic polyol. Example 7 is manufactured by Dainippon Ink and Chemicals, Inc. Acrylic polyol non-volatile content 50%
A hydroxyl value of 17.5 mgKOH / g was used and compounded as shown in Table 1 to obtain a composition of the present invention. Applicator coating was performed using this composition. After setting at room temperature for 30 minutes, baking was performed at 120 ° C. for 30 minutes. The results of the evaluation method are shown in Table 1.

[0039]

Comparative Examples 1 to 5 Comparative Examples 1 to 3 and 5 are acrylic polyol non-volatile components 50 manufactured by Dainippon Ink and Chemicals, Inc. as a polyol using the block isocyanate synthesized in Reference Example.
% Hydroxyl value 50 mg KOH / g, Comparative Example 4 Asahi Denka Co., Ltd. polyaceter polyol Hydroxyl value 450 mg
A composition was obtained by compounding as shown in Table 2 using KOH / g. Applicator coating was performed using this composition. After setting at room temperature for 30 minutes, baking was performed at 120 ° C. for 30 minutes. Table 2 shows the results of the evaluation method.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

EFFECTS OF THE INVENTION According to the present invention, a specific block polyisocyanate, a specific polyol, and a specific metal are provided as compared with a yellowing-free one-component polyurethane paint mainly composed of a conventional polyol and a block isocyanate. By combining a chelate compound, the crosslinking temperature of the coating can be lowered. That is, not only low temperature curing is possible, but also good coating properties, especially at low temperature, which are excellent in flexibility, impact resistance and adhesion can be obtained.

Claims (1)

Claims: (1) A polyisocyanate comprising a diol and / or triol having a number average molecular weight of 500 to 1600 and a diisocyanate which is an aliphatic or alicyclic diisocyanate alone or as a mixture. 1 selected from a block polyisocyanate blocked with a blocking agent, (2) a polyol having a resin component hydroxyl value of 10 to 300 mg KOH / g, and (3) a metal chelate compound of cobalt, zinc, nickel, tin, manganese, and copper. A low temperature curable one-component polyurethane coating composition having extensibility, which comprises one or more curing accelerators as a main component.