JPH07196982A - Thermosetting coating composition - Google Patents

Abstract

PURPOSE:To obtain a thermosetting coating composition, containing an acrylic copolymer prepared by copolymerizing specific components and a polyisocyanate curing agent and capable of providing a film, excellent in durability, weather resistance for a long period and beautiful decorativeness and further nonsanding adhesion. CONSTITUTION:This thermosetting coating composition contains (A) an acrylic copolymer prepared by copolymerizing (i) 3-60wt.% (meth)acrylic acid ester having a 5-10C hydroxyalkyl [e.g. 2-hydroxypentyl (meth)acrylate] with (ii) 0.1-10wt.% vinyl monomer containing carboxyl (e.g. methacrylic acid), (iii) 10-96.9wt.% (meth)acrylic acid ester having a 6-20C hydrocarbon substituent group [e.g. n-hexyl (meth)acrylate] and (iv) 0-70wt.% other vinylic monomers copolymerizable with the components (i) to (iii) [e.g. methyl (meth)acrylate] and (B) a polyisocyanate curing agent. Furthermore, the component (A) is preferably produced by a solution polymerization method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosetting coating composition which provides a coating film which is excellent in durability, weather resistance, beauty, and non-sanding adhesion.

[0002]

2. Description of the Related Art Paints used for coating metals such as automobiles and metals, plastics, etc., have a great influence on their commercial value due to their coating film performance represented by their beauty, weather resistance and chipping resistance. In order to provide such coatings, the demands on the performance of these coatings are becoming stricter year by year. In the case of a coating film consisting of a single layer, there is a limit to the choice of coating color, and it is difficult to maintain the coating film performance at a high level. However, since a multilayer coating film is a laminate of coating films having chemically and physically different properties, adhesion between coating film layers tends to be insufficient, and peeling may occur between coating film layers at the initial stage or with time. In some cases, the intended multilayer coating film may not be formed. In order to improve the adhesion between coating layers, some coating performance is sacrificed, or the dried or cured coating is sanded with a great deal of time and effort and then repainted. Therefore, there is a strong demand for a thermosetting coating composition having good non-sanding adhesion and good coating performance.

[0003]

SUMMARY OF THE INVENTION The object of the present invention is to solve the drawbacks of the prior art, to shorten the process by a non-sanding method, to contribute to labor saving and cost reduction.
It is an object of the present invention to provide a thermosetting coating composition for obtaining a coating film excellent in durability represented by scratch resistance, weather resistance and beauty.

[0004]

In view of the above-mentioned problems of the prior art, the present inventor diligently studied an acrylic copolymer as a thermosetting coating composition, and as a result, it has a specific hydroxyalkyl group (meth). We have found a thermosetting coating composition that provides a coating film that is excellent in durability, weather resistance, cosmetics and non-sanding adhesion by using an acrylic ester.

That is, the thermosetting coating composition of the present invention comprises (a) a (meth) acrylic acid ester having a hydroxyalkyl group having 5 to 10 carbon atoms in an amount of 3 to 60% by weight, and (b) a vinyl group containing a carboxyl group. Monomer 0.1 to 10% by weight (c) 10 to 96.9% by weight of (meth) acrylic acid ester having a hydrocarbon substituent having 6 to 20 carbon atoms (d) (a) to ( Other heat-curable coating composition comprising an acrylic copolymer obtained by copolymerizing 0 to 70% by weight of another vinyl monomer copolymerizable with component c) and a polyisocyanate curing agent. It is characterized by containing.

The acrylic copolymer used in the thermosetting coating composition of the present invention is obtained by copolymerizing the above-mentioned monomers (a) to (d) in a specific ratio, and has a hydroxyl value. Is 40 to 180 mg KOH / g, acid value is 0.5 to 40 m
It is preferably gKOH / g. This is because when the hydroxyl value of the acrylic copolymer is less than 40 mgKOH / g, the hardness and solvent resistance of the cured coating film tend to decrease,
If it exceeds 180 mgKOH / g, the water resistance of the cured coating film,
This is because the impact resistance tends to decrease. More preferably, it is in the range of 60 to 150 mgKOH / g. In addition, the acid value of the acrylic copolymer is 0.5 mgKOH / g
If the amount is less than 40%, the solvent resistance of the cured coating film tends to decrease, and if it exceeds 40 mgKOH / g, the water resistance and weather resistance of the cured coating film tend to decrease, such being undesirable. More preferably, it is in the range of 2 to 20 mgKOH / g.

The weight average molecular weight of the acrylic copolymer of the present invention is preferably 2,000 to 50,000.
When the weight average molecular weight is less than 2000, the solvent resistance, hardness and weather resistance of the formed coating film tend to be lowered, and when it exceeds 50,000, the cosmetic properties and solvent volatility at the time of coating are lowered. This is because there is a tendency.

The (meth) acrylic acid ester (a) having a hydroxyalkyl group having 5 to 10 carbon atoms, which is used in the acrylic copolymer of the present invention, is, for example,
2-hydroxypentyl (meth) acrylate, 4-hydroxypentyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, 1-methyl-4-hydroxybutyl (meth) acrylate, 5-hydroxyhexyl (meth) acrylate, 6 -Hydroxypentyl (meth) acrylate, 1-methyl-4-hydroxypentyl (meth) acrylate, 7-hydroxyheptyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, 3-ethyl-3-hydroxyhexyl (meth) Acrylate, 9-hydroxynonyl (meth) acrylate, 2-hydroxydecyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate are mentioned, and these may be used alone or in combination of two or more kinds. Kill.

In the present invention, it is important that the hydroxyalkyl group of the (meth) acrylic acid ester (a) having the hydroxyalkyl group has 5 to 10 carbon atoms. This is because the hydroxyalkyl group has 4 carbon atoms.
If the number is less than the number, the scratch resistance of the cured coating film becomes insufficient,
This is because when the hydroxyalkyl group has 11 or more carbon atoms, the solvent resistance of the cured coating film is reduced. These have a hydroxyalkyl group having 5 to 10 carbon atoms (meth)
The acrylic ester (a) is used in the range of 3 to 60% by weight. If the (meth) acrylic acid ester (a) having a hydroxyalkyl group having 5 to 10 carbon atoms is less than 3% by weight, the non-sanding adhesion of the cured coating film and the scratch resistance tend to be lowered, and 60% by weight. If it exceeds%, the cured coating film tends to have insufficient water resistance and hardness, which is not preferable. The preferred range is 5 to 30% by weight.

Examples of the carboxyl group-containing vinyl monomer used as the component (b) of the present invention include methacrylic acid, acrylic acid, fumaric acid, itaconic acid, maleic acid, crotonic acid, vinylbenzoic acid and maleic acid. Examples thereof include acid monobutyl ester, itaconic acid monomethyl ester and itaconic acid butyl ester, and these may be used alone or in combination of two or more kinds.

The carboxyl group-containing vinyl monomer (b) is used in the range of 0.1 to 10% by weight. If the carboxyl group-containing vinyl monomer (b) is less than 0.1% by weight, the solvent resistance and hardness of the cured coating film will tend to decrease, and if it exceeds 10% by weight, the water resistance and weather resistance will be poor. It tends to decrease, which is not preferable. Preferably 0.5 to 5
% By weight.

The component (c) of the present invention has 6 to 2 carbon atoms.
Examples of the (meth) acrylic acid ester having 0 hydrocarbon substituents include n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, Lauryl (meth) acrylate, tridecyl (meth) acrylate, cetyl (meth) acrylate, stearyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth)
Acrylate, cycloheptyl (meth) acrylate,
Examples include adamantyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, dihydrodicyclopentadienyl (meth) acrylate, and tricyclodecanyl (meth) acrylate, which may be used alone or in combination of two or more. Can be used.

The (meth) acrylic acid ester (c) having a hydrocarbon substituent must have 6 to 20 carbon atoms. This is because when the number of carbon atoms of the hydrocarbon substituent is 5 or less, it becomes difficult to form an excellent coating film by the wet-on-wet method when the thermosetting coating composition of the present invention is used as a clear coat, This is because if the number of carbon atoms in the hydrogen substituent is 21 or more, the hardness and solvent resistance of the cured coating film decrease. The (meth) acrylic acid ester (c) having a hydrocarbon substituent having 6 to 20 carbon atoms is used in the range of 10 to 96.9% by weight. If the (meth) acrylic acid ester (c) having a hydrocarbon substituent having 6 to 20 carbon atoms is less than 10% by weight, the weather resistance and cosmetic properties of the cured coating film tend to be deteriorated, and 96.9% by weight. If it exceeds%, the hardness and solvent resistance of the cured coating film tend to decrease, which is not preferable. It is preferably 10 to 70% by weight.

In the acrylic copolymer of the present invention, other vinyl-based monomer (d) copolymerizable with the above-mentioned components (a) to (c) can be used if necessary. Examples of the other vinyl-based monomer (d) include methyl (meth) acrylate, ethyl (meth) acrylate, and n-.
Carbon number of propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, Sec-butyl (meth) acrylate, n-pentyl (meth) acrylate, etc. (Meth) acrylic acid esters having 1 to 5 hydrocarbon substituents, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2
-Hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate and other (meth) acrylic acid esters having a hydroxyalkyl group having 2 to 4 carbon atoms, and γ to 2-hydroxyethyl methacrylate
-Butyrolactone ring-opening adduct, ε-caprolactone ring-opening adduct to 2-hydroxyethyl acrylate, ethylene oxide ring-opening adduct to methacrylic acid, propylene oxide ring-opening adduct to methacrylic acid, 2-hydroxyethyl ( (Meth) acrylate or 2-hydroxypropyl (meth) acrylate dimer or trimer having a hydroxyl group at the terminal (meth) acrylic acid ester, styrene, vinyltoluene, styrene derivatives such as α-methylstyrene, acrylonitrile , Ethylenically unsaturated nitriles such as methacrylonitrile, N-methoxymethylacrylamide, N-ethoxymethylacrylamide, N-
N-alkoxy substituted amides such as butoxymethyl acrylamide, glycidyl (meth) acrylate, epoxy group-containing ethylenically unsaturated monomers such as methallyl glycidyl ether, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate And the like, such as ethylenically unsaturated basic monomers, and these can be used alone or in combination of two or more kinds. These other vinyl-based monomers (d) are used in the range of 0 to 70% by weight. Other vinyl-based monomer (d)
If it exceeds 70% by weight, the non-sanding adhesion of the coating film and the scratch resistance tend to decrease, which is not preferable.

The acrylic copolymer of the present invention can be produced by subjecting the copolymerization components (a) to (d) to known polymerization methods such as a solution polymerization method, a bulk polymerization method and an emulsion polymerization method. It is preferably produced by a solution polymerization method. When producing the acrylic copolymer by a solution polymerization method,
Component (a) -in the presence of an organic solvent and a polymerization initiator
The mixture of (d) is copolymerized. As the organic solvent, general ones such as isopropanol, n-butanol, toluene and xylene can be selected. As the polymerization initiator,
It can be selected from commonly used polymerization initiators such as azobisisobutyronitrile, benzoyl peroxide and cumene hydroperoxide. If necessary, a chain transfer agent such as 2-mercaptoethanol or n-octyl mercaptan can be used.

The acrylic copolymer of the present invention can be used as a thermosetting coating composition together with a polyisocyanate curing agent. The polyisocyanate curing agent is not particularly limited and can be appropriately selected depending on the application, for example, tetramethylene diisocyanate, hexamethylene diisocyanate, aliphatic diisocyanates such as trimethylhexane diisocyanate,
Aliphatic diisocyanates such as isophorone diisocyanate and 4,4′-methylenebis (cyclohexyl isocyanate), aromatic diisocyanates such as xylylene diisocyanate and tolylene diisocyanate, ethylene glycol, propylene glycol, neopentyl glycol, trimethylol propane, etc. , A low molecular weight polyester resin having a functional group that reacts with a polyhydric alcohol or an isocyanate group, or an adduct such as water or a bullet, a polymer of diisocyanates, a lower monohydric alcohol with them, and known blocking such as methyl ethyl ketoxime Examples include those blocked with agents.

These polyisocyanate curing agents are preferably used in the range of 10 to 60% by weight of the thermosetting coating composition. If the amount of the curing agent is less than 10% by weight, the solvent resistance and hardness of the cured coating film tend to decrease, and if it exceeds 60% by weight, the cured coating film becomes brittle and the impact resistance and weather resistance of the coating film decrease. It tends to be unfavorable. More preferably, 15
~ 50% by weight.

In these polyisocyanate curing agents, the ratio of the OH group equivalent of the acrylic copolymer of the present invention to the NCO group equivalent of the polycyanate curing agent is OH / NCO = 1.
It is preferably used in the range of /0.5 to 1/2. More preferably, OH / NCO = 1 / 0.8 to 1 /
The range is 1.3.

When preparing the thermosetting coating composition, a curing accelerator represented by dibutyltin dilaurate or the like and a curing catalyst (amine-based or the like) can be used if necessary.

When the thermosetting coating composition of the present invention is made into a coating material, an inorganic pigment such as titanium oxide, an organic pigment such as cyanine blue, a diluent containing a volatile organic solvent, and a surface preparation agent. Additives such as an ultraviolet absorber, a light stabilizer, an antioxidant, and an anti-sagging agent can be appropriately blended using known means, if necessary.

The thermosetting coating composition of the present invention can be used as a clear coat layer or a solid color coat layer of a multilayer coating film. The clear coat layer is a single-layer clear coat layer consisting of only the thermosetting coating composition of the present invention or a known thermosetting coating composition, preferably a multilayer clear coat layer containing a clear coating layer consisting of a thermosetting acrylic resin. Either may be used, and these can be appropriately selected depending on the application.

The solid color coat layer is a single-layer solid color coat layer consisting of only the thermosetting coating composition of the present invention or a known thermosetting coating composition, preferably a solid color coating layer consisting of a thermosetting acrylic resin. It may be either a multi-layer solid color coat layer containing, and these can be appropriately selected according to the application.

For the base coat layer in contact with the clear coat layer, known curable resins can be appropriately used, if necessary, and among them, thermosetting resins such as thermosetting acrylic resins and thermosetting alkyd resins are preferable. . These thermosetting resins include diluents composed of volatile organic solvents, curing agents composed of amino resins or polyisocyanate compounds, aluminum pastes, mica, brightening agents such as flake iron oxide, titanium oxide, carbon black. , Inorganic pigments such as quinacridone and organic pigments, polyester resins, epoxy resins, addition resins such as cellulose resins, surface modifiers, ultraviolet absorbers, antioxidants and other additives using known means as necessary. It can be blended appropriately.

The curable resin composition used in the intermediate coating layer in contact with the base coat layer or the solid color coating layer and the undercoat layer in contact with the intermediate coating layer can be appropriately selected according to the intended use of the multilayer coating film.

[0025]

EXAMPLES The present invention will be specifically described below with reference to examples. All parts and percentages in the examples are by weight. Definition of physical properties of copolymer Viscosity: Value measured by Gardner-Holt foam viscometer (25
Nonvolatile content: 1g of resin is sampled on an aluminum dish and dried at 150 ° C for 1 hour. Nonvolatile content ratio (%) Hydroxyl value: Acrylic copolymer 1g of acetic anhydride is used to completely remove hydroxyl groups. Number of mg of potassium hydroxide required for acetylation and neutralization Acid value: Number of mg of potassium hydroxide required for neutralizing 1 g of acrylic copolymer Weight average molecular weight: Measured by gel permeation chromatography Definition of physical properties of paint Coating viscosity: No. 4 Seconds until all the paint in the Ford cup falls and flows out (20 ° C) ・ Definition of coating film performance Metallic feeling, color unevenness: visual judgment Coating surface: visual judgment Gloss: Digital change made by Suga Test Instruments Co., Ltd. Square gloss meter uGV
-4D measurement (60 ° G) Image clarity: Measured using a portable sharpness gloss meter made by Tokyo Koden Co., Ltd. (PGD value) Hardness: Using Mitsubishi Pencil Uni (Coating at an angle of 45 degrees Scratch the film to measure hardness) Gasoline resistance: Visually judge appearance by dipping in Nisseki Regular Gasoline at room temperature for 24 hours. Warm resistance: Visually judge appearance by dipping in hot water at 50 ° C for 10 hours. Weather resistance: Suga After 1000 hours of evaluation with a sunshine weatherometer manufactured by a tester, the appearance of a coating film immersed in warm water at 50 ° C for 24 hours is visually determined. Scratch resistance: using a friction fastness tester manufactured by Daiei Kagaku Seiki Co., Ltd. Gauze is applied to the area where the surfaces come into contact, and the load is 1 kg.
10 reciprocating friction test and visually inspecting for scratches ・ Visual judgment criteria 4: The coating quality after the performance test did not change from that before the test and it was determined that excellent coating performance was maintained 3: Performance The coating quality after the test is slightly lower than that before the test, but it is judged that it has sufficient practical performance. 2: It is judged that the coating quality after the performance test is lower than before the test and there is a problem in practical use. 1: The coating film quality after the performance test was significantly lower than that before the test,
Determined to be practically unusable

Method for evaluating non-sanding adhesion (in the case of Examples 1 to 7 and Comparative Examples 1 to 7) A zinc phosphate-treated steel plate (30 cm × 45 cm) was coated with a cationic electrodeposition coating composition for automobiles at 180 ° C. Bake for 30 minutes. Furthermore, an amino alkyd resin-based intermediate coating material is applied, baked at 160 ° C. for 30 minutes, and then the coating film is water-polished,
Dried. First, a base coat paint and a clear coat paint are applied over the coating film by a wet-on-wet method, and then baked in a hot air dryer at 160 ° C for 25 minutes, and after being left to cool, the same base coat paint and clear coat paint are further applied without sanding. Was repeatedly applied by a wet-on-wet method and baked for 25 minutes with a hot air dryer at 120 ° C. to form a multilayer coating film for evaluation. 1 of this laminated coating film
Cm squares were scratched at intervals of 1 mm to form 100 cross-cuts, cellophane tape was stuck on this, and then peeled off at once, and the adhesiveness was evaluated from the area remaining without peeling.

(Example 8 and Comparative Example 8) A zinc phosphate-treated steel plate (30 cm x 45 cm) was coated with a cationic electrodeposition paint for automobiles and baked at 180 ° C for 30 minutes. Further, an amino alkyd resin-based intermediate coating material was applied and baked at 160 ° C. for 30 minutes, and then the coating film was water-polished and dried. First, apply a solid color coat paint on this coating film, bake it in a hot air dryer at 160 ° C for 25 minutes, and after cooling it, apply the same solid color coat paint without sanding, and dry it with a hot air dryer at 120 ° C. And baked for 25 minutes to form a multilayer coating film for evaluation. The 1 cm square of this laminated coating film was scratched at 1 mm intervals to form 100 cross-cuts, and cellophane tape was adhered onto it, and then peeled off at once, and the adhesiveness was evaluated from the area remaining without peeling.

Criteria for evaluation of non-sanding adhesion 4: Area remaining without peeling is 90/100 or more,
Judged to be excellent in non-sanding adhesion 3: Area remaining without peeling was 70/100 or more 90/1
It is less than 00 and judged to have practically usable non-sanding adhesiveness 2: The area remaining without peeling is 50/100 or more and 70/1
It is less than 00, and it is judged that the non-sanding adhesion is insufficient. 1: The area remaining without peeling is less than 50/100,
Non-sanding adhesion is low and judged to be practically unusable

(1) Synthesis of acrylic copolymer (P-1) 59.9 parts of Solvesso # 100 (produced by Esso Co., aromatic petroleum derivative) was used as a solvent in a container equipped with a stirrer, a temperature controller and a condenser. In addition, after heating to 120 ° C. with stirring, 5-hydroxypentyl acrylate 10
Parts, methacrylic acid 2 parts, n-butyl methacrylate 41
Parts, 15 parts of 2-ethylhexyl acrylate, 12 parts of 2-hydroxyethyl acrylate, 20 parts of styrene, 2 parts of azobisisobutyronitrile, and 4 parts of t-butylperoxoisopropyl carbonate. The mixture is submerged in the solvent for 2 hours,
Furthermore, after adding 0.5 part of azobisisobutyronitrile and polymerizing at the same temperature for 2 hours, 6.7 parts of n-butanol was added to terminate the reaction, and the acrylic copolymer (P-
1) was synthesized. The obtained acrylic copolymer has a nonvolatile content of 59.9%, a Gardner viscosity of Y, and an acid value of 13 mg.
KOH / g, hydroxyl value was 93 mg KOH / g, and weight average molecular weight was 9000.

(2) Acrylic copolymer (P-2)
Synthesis of (P-12) The vinyl-based monomer shown in Table 1 was polymerized by using the polymerization initiator shown in Table 1 by the same operation as in the method of synthesizing the acrylic copolymer (P-1) to obtain The characteristic values of the obtained copolymer are shown in Table 1.

[0031]

[Table 1]

* 1) Propylene oxide ring-opening adduct of methacrylic acid manufactured by NOF CORPORATION (3) Preparation of clear coat paints (C-1) to (C-14) Acrylic copolymer (P- 1) to (P-12),
Clear coat paints (C-1) to (C-14) were prepared according to the paint formulations shown in Tables 2 and 3.

[0033]

[Table 2]

[0034]

[Table 3]

* 1) Nippon Polyurethane Industry Co., Ltd., polyisocyanate compound (nonvolatile content 100%) * 2) Sumitomo Bayer Urethane Co., Ltd., polyisocyanate compound (nonvolatile content 100%) * 3) Monsanto Surface conditioner * 4) Ciba Geigy, UV absorber * 5) Sankyo Co., Ltd., light stabilizer * 6) Esso, aromatic petroleum derivative * 7) Esso, aromatic petroleum derivative (4) Solid color coat paint (S-1), (S-
Preparation of 2) Solid color coat paints (S-1) and (S-2) were prepared by using acrylic copolymers (P-1) and (P-7) and blending the paints shown in Table 4. .

[0036]

[Table 4]

* 1) Polyisocyanate compound (100% non-volatile content), manufactured by Nippon Polyurethane Industry Co., Ltd. * 2) Ishihara Sangyo Co., Ltd., chlorinated titanium oxide * 3) Surface modifier, Monsanto * 4 ) Ciba Geigy, UV absorber * 5) Sankyo Co., Ltd., light stabilizer * 6) Esso, aromatic petroleum derivative * 7) Esso, aromatic petroleum derivative (5) Heat curing for base coat paint Of Resin (D-1) 50 parts of toluene as solvent and 10 parts of methyl isobutyl ketone in a container equipped with a stirrer, a temperature controller and a condenser
After adding parts by weight and heating to 100 ° C. with stirring, from 5 parts of styrene, 2 parts of methacrylic acid, 35 parts of methyl methacrylate, 46 parts of ethyl acrylate, 12 parts of 2-hydroxyethyl acrylate, 1.5 parts of benzoyl peroxide. The mixture of the vinyl-based monomer and the polymerization initiator is placed in a solvent for 4 hours, 0.6 part of benzoyl peroxide is further added, and the mixture is polymerized for another hour at the same temperature.
Was added to terminate the reaction, and a thermosetting resin (D-1) for base coat paint was synthesized. The resulting acrylic copolymer has a nonvolatile content of 50% and a weight average molecular weight of 5000.
It was 0.

(6) Base coat paints (B-1) to (B
Preparation of -3) Using the thermosetting resin (D-1) for base coat paint and blending the paints shown in Table 5, the base coat paint (B-
1) to (B-3) were prepared.

[0039]

[Table 5]

* 1) Mitsui Toatsu Chemical Co., Ltd., butyl etherified melamine resin (nonvolatile content 60%) * 2) Nippon Polyurethane Co., Ltd., polyisocyanate compound (nonvolatile content 100%) * 3) Sumitomo Bayer Urethane Co., Ltd., polyisocyanate compound (nonvolatile content 100%) * 4) Degussa, black pigment * 5) Toyo Aluminum Co., Ltd., aluminum paste (nonvolatile content 65%) * 6) Esso, aromatic Petroleum Derivatives Examples 1 to 7 and Comparative Examples 1 to 7 A zinc phosphate treated steel sheet (30 cm x 45 cm) was coated with a cationic electrodeposition coating for automobiles and baked at 180 ° C for 30 minutes. Further, an amino alkyd resin-based intermediate coating material was applied and baked at 160 ° C. for 30 minutes, and then the coating film was water-polished and dried. First, a base coat paint is applied on this coating film so that the dry film thickness is 20 to 30 μm.
After leaving for a minute, apply clear coat paint to a dry film thickness of 30.
Overcoating was performed by the wet-on-wet method so that the thickness became μm. After leaving the undried coating film for 10 minutes at room temperature,
Bake for 25 minutes in a 140 ° C hot air dryer to coat 2 coats
A multilayer coating film was formed by the baking method. The multilayer coating films obtained are shown in Tables 6 and 7.

[0041]

[Table 6]

[0042]

[Table 7]

Example 8 and Comparative Example 8 A zinc phosphate-treated steel plate (30 cm × 45 cm) was coated with an automotive cationic electrodeposition coating and baked at 180 ° C. for 30 minutes. Further, an amino alkyd resin-based intermediate coating material was applied and baked at 160 ° C. for 30 minutes, and then the coating film was water-polished and dried. First, a solid color coat paint was spray-coated on this coating film so that the dry film thickness was 40 μm, and baked for 25 minutes by a hot air dryer at 140 ° C. The coating performance of the obtained multilayer coating is shown in Table 8.

[0044]

[Table 8]

Acrylic copolymer (P-1) of the present invention
The multilayer coating film having a clear coat layer or a solid color coat layer containing (P-6) has an excellent appearance, weather resistance, non-sanding adhesion, as shown in Examples 1 to 8. The coating film performance such as scratch resistance was also excellent.

On the other hand, acrylic copolymers (P-7) to (P-12) which do not satisfy the conditions specified by the present invention.
As shown in Comparative Examples 1 to 8, the multilayer coating film having a clear coat layer or a solid color coat layer containing was poor in appearance and coating film performance.

[0047]

As is clear from the above examples, when the thermosetting coating composition containing the acrylic copolymer and the polyisocyanate curing agent of the present invention is used, durability,
It is possible to provide a coating film which is excellent in long-term weather resistance and beauty, and is also excellent in non-sanding adhesion, which is very useful industrially.

Claims (1)

[Claims] 1. (a) (meth) acrylic acid ester having a hydroxyalkyl group having 5 to 10 carbon atoms 3 to 60% by weight (b) carboxyl group-containing vinyl monomer 0.1 to 10% by weight (C) (Meth) acrylic acid ester having a hydrocarbon substituent having 6 to 20 carbon atoms 10 to 96.9% by weight (d) Other copolymerizable with the components (a) to (c) A thermosetting coating composition comprising an acrylic copolymer obtained by copolymerizing 0 to 70% by weight of a vinyl monomer and a polyisocyanate curing agent.