JP2654120B2 - Thermosetting coating composition - Google Patents

Description

The present invention relates to a thermosetting coating composition, and more specifically, the present invention relates to a coating composition such as a coating film for an automobile body, which requires a high degree of aesthetics and performance. The present invention relates to a thermosetting coating composition suitable for use in a thermosetting clear coat paint of a top coat for forming a film.

[Prior Art] In the coating of an automobile body, after performing electrodeposition coating and intermediate coating, a base coat paint and a clear coat paint containing a pigment such as a color pigment or a metallic pigment are wet-on-wet. The two coatings are applied simultaneously by coating and then curing both paints at the same time.
A bake method is generally employed.

2. Description of the Related Art In recent years, demands for long-term durability including weather resistance have been more and more increased due to international competition accompanying overseas production by automobile manufacturers. As a measure for improving the durability, a method of adding an ultraviolet absorber and / or a light stabilizer to the clear coat paint is very common.

[Problems to be Solved by the Invention] However, since these ultraviolet absorbers and / or light stabilizers are used as additives, they fall off from the surface of the thermosetting coating film during outdoor exposure, and their There is a problem that the effect is lost. Also, since the light stabilizer used in the thermosetting resin has an amine structure, when used in a large amount, yellowing during overbaking and water resistance may occur. When a methylated melamine resin is used as a curing agent, there is a problem that a curing failure occurs and sufficient performance is obtained.

SUMMARY OF THE INVENTION An object of the present invention is to provide a two-coat, one-bake system in which the above-mentioned problems have been solved, that is, an acrylic amino-based thermosetting coating film has excellent cosmetic properties, water resistance, and excellent weather resistance. The purpose of the present invention is to provide a thermosetting coating composition suitable for use in forming a coating.

[Means for Solving the Problems] The thermosetting coating composition of the present invention comprises (i) (a) a hydroxyl group-containing vinyl monomer: 10 to 60% by weight, and (b) a carboxyl group-containing vinyl monomer: 0.2 to 10% by weight. , (C) general formula (Wherein, R ¹ is a hydrogen atom or a methyl group, and R ² is a hydrogen atom or a methyl group): (meth) acrylate: 0.5 to 10% by weight; (Wherein, R ³ is a hydrogen atom or a methyl group, and R ⁴ is an alkyl group having 4 or more hydrogen atoms): (meth) acrylate: 15 to 50% by weight; ) Other copolymerizable vinyl monomers: Acrylic copolymer (A) 50 to 90 obtained by copolymerizing 0 to 50% by weight
% By weight, and (ii) 10 to 50% by weight of the amino resin (B).

The thermosetting coating composition of the present invention is obtained by applying a thermosetting basecoat paint and a thermosetting clearcoat paint each containing a pigment in a wet-on-wet manner, and then simultaneously heating and curing both paints. It is suitable for use as a thermosetting clear coat paint used for a top coat.

The acrylic copolymer (A) used in the thermosetting coating composition of the present invention contains 10 to 60% by weight of at least one hydroxyl group-containing vinyl monomer as a monomer unit. Examples of the hydroxyl group-containing vinyl monomer include hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxypropyl (meth) acrylate, and 6-hydroxyhexyl (meth) acrylate. Hydroxyalkyl (meth) acrylates; adducts of 2-hydroxyethyl (meth) acrylate with ethylene oxide and adducts of 2-hydroxyethyl (meth) acrylate with propylene oxide; 2-hydroxyethyl (meth) acrylate Adduct of γ-butyrolactone with 2-hydroxyethyl (meth) acrylate and ε-
Examples include adducts of 2-hydroxyethyl (meth) acrylate and organic lactones, such as adducts of caprolactone. Further, an esterification reaction product of a monoepoxy compound and (meth) acrylic acid, fumaric acid or maleic acid, represented by "Kajura E" (glycidyl ester of a synthetic fatty acid manufactured by Shell Chemical Co., Ltd.), a polymerizable unsaturated group And a low molecular weight polyester resin having the following formula:

In the present invention, when the amount of the hydroxyl group-containing vinyl monomer is less than 10% by weight, the cross-linking density of the cured coating film due to the cross-linking reaction between the acrylic copolymer (A) and the amino resin (B) is low. No film performance, 60% by weight
If the ratio exceeds the above range, the water resistance of the cured coating film is undesirably reduced.

The carboxyl group-containing vinyl monomer (i) or (b), which is a monomer unit, improves the affinity between the acrylic copolymer (A) and the pigment, and plays an important role as a catalyst for a crosslinking reaction with an amino resin. Fulfill. Examples of the carboxyl group-containing vinyl monomer include polymerizable monomers having one or more carboxyl groups, for example, α, β-monoethylenically unsaturated carboxylic acids, specifically, acrylic acid, methacrylic acid, itacone Acids, maleic acid and fumaric acid, and monoalkyl esters of these acids (eg, monomethyl ester, monoethyl ester, monobutyl ester, etc.) can be mentioned.

In the present invention, the carboxyl group-containing vinyl monomer is
It is used in an amount of 0.2 to 10% by weight, preferably 0.5 to 5% by weight. If the amount is less than 0.2% by weight, the above effect is insufficient. If the amount is more than 10% by weight, the solution viscosity of the acrylic copolymer (A) is increased, and the water resistance is undesirably lowered.

Formula (I) of the above (i) and (c) which is a monomer unit
The (meth) acrylate improves weather resistance.
Examples of this (meth) acrylate are 2,2,6,6-
Tetramethylpiperidinyl methacrylate, 2,2,6,6-
Tetramethylpiperidinyl acrylate, N-methyl-
2,2,6,6-tetramethylpiperidinyl methacrylate,
N-methyl-2,2,6,6-tetramethylpiperidinyl acrylate can be mentioned.

In the present invention, the (meth) acrylate of the general formula (I) is used in an amount of 0.5 to 10% by weight, preferably 0.5 to 4% by weight. If the amount is less than 0.5% by weight, the effect of improving the weather resistance is not sufficiently exhibited, and if it exceeds 10% by weight, there is a problem of yellowing of the coating film, which is not preferable.

General formula (II) of the above (i) and (d) which is a monomer unit
The (meth) acrylic acid ester improves aesthetics, weather resistance and flexibility. Examples of the (meth) acrylic ester include n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 6-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, and 2-ethylhexyl. Examples thereof include (meth) acrylate, 8-octyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, cetyl (meth) acrylate, and stearyl (meth) acrylate.

In the present invention, the (meth) acrylate of the general formula (II) is used in an amount of 15 to 50% by weight. If the amount is less than 15% by weight, the coating properties such as sufficient aesthetics and weather resistance will be out of balance, while if it exceeds 50% by weight, the solvent resistance will be reduced, which is not preferable.

Styrene derivatives such as styrene, α-methylstyrene and vinyltoreene as other copolymerizable vinyl monomers of the above (i) and (e) which are monomer units; polymerizable unsaturated nitriles such as acrylonitrile and methacrylonitrile; acetic acid Vinyl esters such as vinyl and vinyl propionate; N-methoxymethyl (meth) acrylamide;
N-alkoxy-substituted amides such as N-ethoxymethyl (meth) acrylamide and N-butoxymethyl (meth) acrylamide; epoxy such as glycidyl (meth) acrylate, (meth) allyl glycidyl ether, and metaglycidyl (meth) acrylate Group-containing monomers;
Basic monomers such as dimethylaminoethyl (meth) acrylic acid and diethylaminoethyl (meth) acrylic acid;
Examples thereof include (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, and propyl (meth) acrylate.

In the present invention, the other copolymerizable vinyl monomer is an optional component and can be used in an amount of 0 to 50% by weight.

The acrylic copolymer (A) used in the thermosetting coating composition of the present invention can be obtained by any known polymerization method such as a solution polymerization method, a bulk polymerization method, and an emulsion polymerization method.
In particular, a copolymer obtained by a solution polymerization method is desirable. In the case of the solution polymerization method, a mixture of the monomers is copolymerized in the presence of an organic solvent and a polymerization initiator. The organic solvent used is isopropyl alcohol, n-
A commonly used organic solvent such as butanol, toluene and xylene may be used, and the polymerization initiator may be a commonly used polymerization initiator such as azobisisobutyronitrile, benzoyl peroxide and cumene hydroperoxide. Furthermore,
If necessary, a chain transfer agent such as 2-mercaptoethanol and n-octylmercapta can be used.

The thermosetting coating composition of the present invention satisfies the above-mentioned quality performance in automotive coatings, which is a main application,
An amino resin (B) is contained as a curing agent in addition to the acrylic copolymer (A). Amino resin (B) is 10
Used in an amount of 5050% by weight. If the amount is less than 10% by weight, the crosslinked density of the cured film is low, so that the weather resistance, solvent resistance and water resistance of the film become insufficient. Physical and chemical properties such as a feeling and a metallic feeling are deteriorated. As a specific example of the amino resin (B), aminotriazine, urea, dicyandiamine or N, N-ethyleneurea is methylolated, and then alkyl etherified with cyclohexanol or an alkanol having 1 to 6 carbon atoms. In particular, there are those obtained from aminotriazine, and for example, methyletherified melamine resin, butyletherified melamine resin and the like are preferable.

Furthermore, in the thermosetting coating composition of the present invention, in order to promote curing, an external acid catalyst represented by paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid or an amino-neutralized product thereof is used. Can be used.

The thermosetting coating composition of the present invention comprising the acrylic copolymer (A) and the amino resin (B) is usually diluted with an organic solvent for dilution so as to have an appropriate viscosity. Used. Examples of the organic solvent for dilution include xylene as an aromatic petroleum derivative, Solevesso # 100 (manufactured by Esso), and ketone-based 2-heptanone (manufactured by Eastman).

Thermosetting acrylic melamine resin or thermosetting alkyd melamine resin as a resin system serving as a vehicle of a thermosetting base coat coating used together with the thermosetting clear coat coating which is the thermosetting coating composition of the present invention. Can be mentioned. For example, in the case of an acrylic melamine resin base coat paint, a film-forming acrylic resin having a functional group capable of reacting with an amino resin, a volatile organic liquid diluent, and a curing agent dissolved in the organic liquid diluent. A composition comprising a certain amino resin, if necessary, a luminous agent such as selected aluminum paste, mica, and flaky iron oxide; titanium oxide; carbon black; an organic pigment such as quinacridone; an ethoxy resin; Such as non-acrylic resins; surface conditioners, UV absorbers,
Auxiliary additives such as an antioxidant and a pigment settling inhibitor; and the like are blended by a general method.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.

Production Example of Acrylic Copolymer Contained in Base Coating Paint (Reference Example) A container equipped with a stirrer, a temperature controller and a condenser was charged with 40 parts by weight of toluene and 10 parts by weight of n-butanol. Heat the contents of the container while stirring to a temperature of 100 ° C.
Was raised. Then, after a solution of the composition (1) shown in Table 1 was added dropwise for 4 hours, a solution composed of 0.6 parts by weight of benzoyl peroxide and 20 parts by weight of toluene was added dropwise for 30 minutes. The reaction solution was stirred and heated at 100 ° C. for another 2 hours to increase the conversion to resin, and then 30 parts by weight of toluene was added to terminate the reaction. The resulting acrylic copolymer solution (nonvolatile content 50% by weight) is referred to as acrylic resin varnish (I). The weight average molecular weight of this copolymer was 70,000.

Production example of base coat paint (Reference example) Each material in the ratio shown in Table 2 was placed in a stainless steel container,
After sufficiently stirring, adjust the viscosity with a mixed solvent for dilution,
Base coat paints B-1 to B-3 were produced.

Production Example of Acrylic Copolymer Included in Clear Coating Paint A polymerization reaction was carried out using the respective mixtures having the six types of monomer compositions shown in Table 3 in the following procedure.

First, 53.3 parts by weight of Solvesso # 100 (an aromatic petroleum derivative manufactured by Esso) is charged into a vessel equipped with a stirrer, a temperature control device and a condenser, and heated while stirring to reduce the temperature.
Increased to 120 ° C. Next, 2 parts by weight of azobisisobutyronitrile and 4 parts by weight of t-butylperoxyisopropyl carbonate were added to 100 parts by weight of the monomer mixture shown in Table 3, and the mixture was dropped into the container over 3 hours. Then, 0.1 parts by weight of azobisisobutyronitrile was added four times at 30 minute intervals. After stirring and heating at 120 ° C. for another 2 hours to increase the conversion to resin, 13.3 parts by weight of n-butanol was added to terminate the reaction. The viscosity and nonvolatile content of the resulting six types of acrylic copolymer solutions and the acid value of each acrylic copolymer were as shown in Table 3.

Production Examples of Clear Coating Paints The clear coating paints P-1 to P-1 were prepared by using the six types of acrylic copolymer solutions and by formulating the coatings shown in Table 3.
P-6 was produced.

Among these paints for a car coat, it is paints P-1 to P-4 that the acrylic copolymer satisfies the requirements of the acrylic copolymer (A) in the present invention.

Examples 1-5 and Comparative Examples 1-2 A cationic electrodeposition paint for automobiles was applied to a steel plate (30 × 45 cm) treated with zinc phosphate, and baked at 180 ° C. for 30 minutes. Next, an intermediate coating composed of an alkyd resin and an amino resin was applied and baked at 160 ° C. for 30 minutes, then the coating was sanded, polished and dried. On this coating film, the second
The base coat paints shown in the table and the clear coat paints shown in the above Table 3 were overcoated with the combinations shown in Examples 1 to 5 of Table 4 by a wet-on-wet method. This recoating was performed as follows. First, a base coat paint was applied on the intermediate coating film so as to have a dry film thickness of 15 μm, and after standing for 3 minutes, a clear coat paint was applied so as to have a dry film thickness of 30 μm. After leaving the undried coating film at room temperature for 10 minutes, it was baked with a hot air dryer at 140 ° C. for 25 minutes to obtain the heat-cured topcoat films of Examples 1 to 5.

In exactly the same procedure, the base coat paint and the clear coat paint were overcoated with the combinations shown in Comparative Examples 1 and 2 in Table 4 to obtain the thermosetting overcoat films of Comparative Examples 1 and 2. In Comparative Example 1, curing was inhibited, primary physical properties were low, gloss was significantly reduced, and in Comparative Example 2, cracks occurred.

The appearance and performance of each of the heat-cured coatings of the above Examples and Comparative Examples were evaluated. The results are shown in Table 4.

As is apparent from the results, when the clear coat paint contains an acrylic copolymer that does not satisfy the requirements of the acrylic copolymer (A-5) in the present invention,
It is not possible to obtain a heat-cured topcoat film intended for the present invention.

[Effects of the Invention] As described above, by using the thermosetting coating composition of the present invention, it is possible to obtain a top coat having excellent aesthetics and performance, and particularly excellent weather resistance. The coating is extremely useful as a coating for automobile bodies.

Claims (1)

(57) [Claims] (1) (i) (a) a hydroxyl group-containing vinyl monomer: 1
0 to 60% by weight, (b) carboxyl group-containing vinyl monomer: 0.2 to 10% by weight, (c) general formula (Wherein, R ¹ is a hydrogen atom or a methyl group, and R ² is a hydrogen atom or a methyl group): (meth) acrylate: 0.5 to 10% by weight; (Wherein, R ³ is a hydrogen atom or a methyl group, and R ⁴ is an alkyl group having 4 or more hydrogen atoms): (meth) acrylate: 15 to 50% by weight; ) Other copolymerizable vinyl monomers: Acrylic copolymer (A) 50 to 90 obtained by copolymerizing 0 to 50% by weight
A thermosetting coating composition comprising: (ii) 10 to 50% by weight of an amino resin (B).