JPS63275678A - Thermoset coating composition - Google Patents

Abstract

PURPOSE:To provide a thermoset coating composn. which is excellent in decorativeness, weather resistance, water resistance, etc., and suited for use in application of a coating to an automobile body, by the wet-on-wet coating of a particular thermosetting compsn. for base coating and a particular thermosetting composn. for clear coating, and performing simultaneous heat curing thereof. CONSTITUTION:A composn. comprising 60-90wt.% acrylic copolymer obtd. by copolymn. of a hydroxyl-contg. vinyl monomer, a carboxyl-contg. vinyl monomer and a (meth)acrylic ester and 40-10wt.% amino resin is compounded with a pigment, thereby producing a thermosetting composn. for base coating. Separately, 50-90wt.% acrylic copolymer obtd. by copolymn. of t-butyl methacrylate, a (meth)acrylic ester, a hydroxyl-contg. vinyl monomer and a carboxyl-contg. vinyl monomer is mixed with 50-10wt.% amino resin, thereby producing a thermosetting composn. for clear coating. Both of the composn. are applied by the wet-on-wet-method, followed by simultaneous heat curing of both of the composn.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a thermosetting coating composition, and more particularly to a thermosetting coating composition suitable for coating films that require a high degree of cosmetic properties and performance, such as coatings for automobile bodies. Thermosetting coating compositions.

[Summary of the invention]

The present invention is an excellent thermosetting coating composition because it is formed by overcoating a base coat paint of a specific composition and a clear coat paint of a specific composition in a wet-on-wet method and curing the composition by heating. It is designed to have both cosmetic properties and performance.

[Prior art and problems to be solved by the invention] In the painting of automobile bodies, after electrodeposition painting and intermediate coating, a base coat paint containing a color pigment and/or metallic pigment and a top clear coat are applied. A so-called 2-coat/1-bake method is generally used, in which a paint is applied wet-on-wet and both paints are heated and cured at the same time.

In recent years, amidst international competition as automakers expand overseas, the demand for cosmetic products has become increasingly strong. Therefore, thickening of the clear coat has been implemented as a measure to improve the cosmetic appearance of the clear coat. However, this thickening is not preferable in terms of workability because it tends to cause the problem of paint dripping on vertical parts. As a solution to this problem, attempts have been made to use two clear coats, but in this case there are problems such as complicated processes and peeling between the two clear coats. On the other hand, attempts have been made to improve cosmetic properties by lowering the molecular weight of the acrylic copolymer that constitutes the clear coat, but in this case, there is a problem that the performance of the cured film, such as solvent resistance and weather resistance, deteriorates. occurs.

The object of the present invention is to solve the above-mentioned problems in a 2-coat/1-bake coating method, maintain the weather resistance, water resistance, etc. of an acrylamine thermosetting coating film, and provide a thermal coating with excellent cosmetic properties. An object of the present invention is to provide a cured coating composition.

[Means for solving problems]

According to the present invention, a pigment-containing thermosetting base coat paint and a thermosetting clear coat paint are overcoated in a wet-on-wet manner, and then both paints are heated and cured at the same time. In the thermosetting coating composition, the base coat paint contains (1) ('a) 10 to 40% by weight of a hydroxyl group-containing vinyl monomer (b) 0.2 to 10% by weight of a carboxyl group-containing vinyl monomer.
% by weight (C) 10 to 70% by weight of (meth)acrylic acid ester of general formula (1) % formula % (1) (in the formula, R1 represents H or CH, , n represents an integer of 1 to 4) (d) Hydroxyl value 40-80 mgKO obtained by copolymerizing 0-30% by weight of other copolymerizable vinyl monomers
H/g and an acid value of 0.5 to 25 mgK OH/g, a composition consisting of 60 to 90% by weight of an acrylic copolymer (I) and 10 to 40% by weight of (2) an amino resin, in which a pigment is blended. (3) (e) 15 to 50% by weight of t-butyl methacrylate (f) General formula (n) R,0 CHz = CCOC-H2-+I (II) (in the formula R
2 represents H or C'H3, and m represents an integer of 8 or more. ) (meth)acrylic acid ester 15-50% by weight (g) water M! Containing vinyl monomer 10-50% by weight (h) Carboxyl group-containing vinyl monomer 1-10% by weight (i) Other copolymerizable vinyl monomer 0-30% by weight Obtained by copolymerizing, hydroxyl value 50 ~150mgK
A thermosetting coating comprising 50 to 90% by weight of an acrylic copolymer (II) having an OH/g and an acid value of 2 to 40 mgK OH/g and (4) an amino resin of 10 to 50% by weight. A composition is provided.

In the present invention, the acrylic copolymer (1) used in the base coat paint has a hydroxyl value of 40 to 80 mgK from the viewpoint of interlayer adhesion between the base coat and the clear coat.
Contains a hydroxyl group-containing vinyl monomer so that the OH/H ratio is within the range of OH/H. If the hydroxyl group-containing vinyl monomer is less than 10% by weight, the crosslinking density of the cured coating film due to the crosslinking reaction between the acrylic copolymer (1) and the amino resin will be low, and sufficient coating performance will not be obtained; If the hydroxyl group-containing vinyl monomer is exceeded, the solution viscosity of the acrylic copolymer (I) becomes too high and the water resistance of the cured coating film decreases, which is undesirable.
acrylate, hydroxyalkyl (meth)acrylates such as 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, [Cardura El (synthetic fatty acid manufactured by Shell Chemical)] monoepoxy compounds and (meth) represented by glycidyl esters)
Examples include esterification reaction products with acrylic acid, fumaric acid, or maleic acid, and low molecular weight polyester resins having polymerizable unsaturated groups.

The carboxyl group-containing vinyl monomer described in (1) and (b) above is important for improving the affinity between the acrylic copolymer (1) and the pigment and as a catalyst for the crosslinking reaction when the base coat paint contains a curing agent. A polymerizable monomer having one or more carboxyl groups, such as α,
β-monoethylenically unsaturated carboxylic acids, specifically acrylic acid, methacrylic acid, itaconic acid, maleic acid and fumaric acid, and monoalkyl esters of these acids (e.g. monomethyl ester, monoethyl ester, monobutyl ester, etc.) can be mentioned. If the amount of these α,β-monoethylenically unsaturated carboxylic acids is less than 0.2% by weight, the above effects will be insufficient, and if it exceeds 10% by weight, the solution viscosity of the acrylic copolymer (1) will decrease. This is not preferable because it increases the water resistance and reduces water resistance. The preferred range for this amount is 0.5-5% by weight.

The (meth)acrylic acid ester of general formula (1) described in item (1)(c) above is an essential component from the viewpoint of mineral collecting property, weather resistance, and flexibility, and specific examples include methyl (meth) Acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate,
Isobutyl (meth)acrylate, t-butyl (meth)
Examples include acrylate.

Other copolymerizable vinyl monomers mentioned in (1) and (d) above include styrene derivatives such as styrene, α-methylstyrene, and vinyltoluene; polymerizable unsaturated nitrites such as acrylonitrile and methacrylate; vinyl acetate;
Vinyl esters such as vinyl propionate; N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide, N-butoxymethyl (meth)
N-alkoxy-substituted amides such as acrylamide; epoxy group-containing monomers such as glycidyl (meth)acrylate, (meth)acrylic glycidyl ether, and metaglycidyl (meth)acrylic acid ester; dimethylaminoethyl (meth)acrylic acid, diethylaminoethyl ( Meta)
Basic monomers such as acrylic acid can be mentioned, and these can be used as necessary.

In the present invention, the acrylic copolymer (1) contained in the base coat paint can be obtained by any known method such as solution polymerization, bulk polymerization, emulsion polymerization, etc., but especially by solution polymerization. Preferably, it is a polymer. In the case of solution polymerization, the mixture of monomers is copolymerized in the presence of an organic solvent and a polymerization initiator. The organic solvent used may be a commonly used organic solvent such as isopropyl alcohol, n-butanol, toluene, or xylene, and the polymerization initiator may be a commonly used polymerization initiator such as azobisisobutyronitrile, benzoyl peroxide, or cumene hydroperoxide. A drug is sufficient. Furthermore, a chain transfer agent such as 2-mercaptoethanol or n-octylmercaptan can be used if necessary.

In the base coat paint of the present invention, if the amine resin content is less than 10% by weight, the crosslinking density of the cured coating film will be low and sufficient performance will not be obtained, and if it exceeds 40% by weight, the water resistance and flexibility of the cured coating film will deteriorate. This is not preferable because it lowers the temperature. The preferred range for the amount of amino resin is 15-30% by weight. This amino resin is, for example, a methylolated aminotriazine, urea, dicyandiamide or N,N-ethylene urea,
Preferred are melamine resins obtained by alkyl etherification with cyclohexanol or alkanols having 1 to 6 carbon atoms, particularly obtained from aminotriazine, such as methyl etherified melamine resins and butyl etherified melamine resins.

In the acrylic copolymer (II) used in the clear coat paint of the present invention, if the amount of t-butyl methacrylate is less than 15% by weight, the characteristic of improving the bran collectability of the present invention cannot be fully exhibited. Moreover, if this amount exceeds 50% by weight, the cured coating film becomes brittle, which is not preferable. The preferred range for the amount of t-butyl methacrylate is 20-40% by weight.

Examples of the (meth)acrylic ester of general formula (n) described in item (3)(f) above include 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and (meth)acrylate.
Examples include tridecyl acrylate and stearyl (meth)acrylate. If the amount of this (meth)acrylic acid ester is less than 15% by weight, the characteristic of improving the bran collection property of the present invention cannot be fully exhibited, and if it exceeds 50% by weight, the hardness, solvent resistance, etc. of the cured coating film will deteriorate. descend.

The hydroxyl group-containing vinyl monomer in item (3) (g) above is contained in an amount such that the hydroxyl value of the acrylic copolymer (n) constituting the clear coat paint is 50 to 150 KOH/g', and is 10% by weight. If it is less than acrylic copolymer (n
) and the amino resin, the crosslinking density of the cured coating film is too low and satisfactory coating performance cannot be obtained, and if it exceeds 50% by weight, the solution viscosity of the acrylic copolymer becomes too high. Moreover, it is not preferable because the water resistance of the cured coating film decreases. Examples of this hydroxyl group-containing vinyl monomer are 2
-Hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (
Hydroxyalkyl (meth)acrylates such as meth)acrylate; adducts of 2-hydroxyethyl (meth)acrylate and ethylene oxide and adducts of 2-hydroxyethyl (meth)acrylate and propylene oxide; ) Adducts of 2-hydroxyethyl (meth)acrylate and organic lactones, such as adducts of acrylate and γ-butyrolactone and adducts of 2-hydroxyethyl (meth)acrylate and ε-caprolactone, can be mentioned. .

When a curing agent such as a melamine resin is included as in the present invention, the carboxyl group-containing vinyl monomer in item (3) (h) plays an important role as a catalyst, and the acid value of the acrylic copolymer (II) is contained in an amount of 2 to 40 ■KOH/g. If the amount of this carboxyl group-containing vinyl monomer is less than 1% by weight, the above-mentioned curing will be insufficient and the coating performance will deteriorate, and if it exceeds 10% by weight, the solution viscosity of the acrylic copolymer will become too high. Therefore, the cosmetic properties of the cured coating film are reduced and the water resistance is also reduced, which is not preferable. Specific examples of this carboxyl group-containing vinyl monomer include (meth)acrylic acid, itaconic acid, fumaric acid,
Examples include crotonic acid, maleic acid, monomethyl itaconate, monobutyl itaconate, monomethyl maleate, monobutyl maleate, 2-sulfoethyl (meth)acrylate, and the like.

The other copolymerizable vinyl yarn threads mentioned in item (3)(i) may be used as necessary in an amount within a range that does not impair the cosmetic properties that are a feature of the present invention. Specific examples include styrene, α- Styrene derivatives such as methylstyrene and vinyltoluene; Polymerizable unsaturated nitrites such as acrylonitrile and methacrylonitrile; Vinyl esters such as vinyl acetate and vinyl propionate; N-methoxymethyl (meth)acrylamide, N-ethoxymethyl ( meth) acrylamide, N
-N-alkoxy substituted amides such as butoxymethyl (meth)acrylamide; Epoxy group-containing monomers such as glycidyl (meth)acrylate, (meth)allyl glycidyl ether, metaglycidyl (meth)acrylic acid ester; dimethylaminoethyl (meth) Basic monomers such as acrylic acid, diethylaminoethyl (meth)acrylic acid; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, amyl (meth)acrylate , cyclohexyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, and the like.

The polymerization method for the acrylic copolymer (n) contained in the clear coat paint is similar to the polymerization method for the acrylic copolymer (1) contained in the base coat paint, but especially solution polymerization. The method is preferred.

The clear coat paint of the present invention contains an amino resin as a curing agent in order to satisfy the quality performance in the automotive paint, which is the main application. If the amount of amino resin is less than 10% by weight, the crosslinking density of the cured coating will be low, resulting in insufficient weather resistance, solvent resistance, water resistance, etc., and if it exceeds 50% by weight, the cured coating will be poor. It is not preferable because it deteriorates the physical and chemical properties such as the glossy window and metallic appearance. Specific examples of this amino resin are the same as those described for the amino resin contained in the base coat paint.

Furthermore, when an amino resin is used as a curing agent, an external acid catalyst such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, or their amine neutralized products is added to the clear coat paint. can be used.

The base coat paint of the present invention contains pigments such as aluminum paste, mica, scaly iron oxide, titanium oxide, carbon black, quinacridone, and cyanine blue, which are commonly used in the preparation of paints. Resins other than acrylic resins such as polyester resins, epoxy resins, and cellulose resins; and auxiliary additives such as surface conditioners, ultraviolet absorbers, antioxidants, and pigment anti-settling agents are selected as necessary, and general It can be added by any combination method.

〔Example〕

The present invention will be explained below with reference to Examples.

40 parts by weight of toluene and 10 parts by weight of n-butanol were charged into a container equipped with a stirrer, a temperature control device, and a condenser. Heat the contents of the container while stirring to bring the temperature to 100℃.
The temperature was raised to ℃. Next, a solution of composition (1) shown in Table 1 was added dropwise over 4 hours, and then benzoyl peroxide 0.6
A solution consisting of parts by weight and 20 parts by weight of toluene was added dropwise over 30 minutes. The reaction solution was further stirred and heated at 100° C. for 2 hours to increase the conversion rate to resin, and then 30 parts by weight of toluene was added to terminate the reaction. The obtained acrylic copolymer solution (non-volatile content: 50% by weight) is designated as acrylic resin varnish (I). The acrylic copolymer contained in this varnish is the acrylic copolymer (1) in the present invention.
meets the requirements. The weight average molecular weight of this coelectric material was 70,000.

Next, in place of the composition (1), the composition shown in Table 1 (
Perform the reaction using the solution of 2) in exactly the same manner as above,
An acrylic copolymer solution (nonvolatile content: 50% by weight) was obtained. This solution is referred to as acrylic resin varnish (n). The acrylic copolymer contained in this varnish does not meet the requirements for the acrylic copolymer (1). The weight average molecular weight of this copolymer was also 70,000.

(The following margins are continued on the next page) 1.Pour each material in the proportions shown in Table 2 into a stainless steel container, stir thoroughly, adjust the viscosity with a diluent mixed solvent, and prepare base coat paint B-1. ~B-3 was produced.

Table 2 * Aromatic petroleum derivative clear coat manufactured by Shell Chemical ■ Acrylic U listed in Table 2 A polymerization reaction was carried out using the following procedure for each mixture having the nine types of 7-mer compositions shown in Table 3. .

First, 53.3 parts by weight of Tsurupetz #100 (aromatic petroleum derivative manufactured by Shell Kagaku 01) was charged into a container equipped with a stirrer, a temperature control device, and a condenser, and heated while stirring to raise the temperature 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 listed in Table 3, and the mixture was allowed to drip over 3 hours. Next, 0.1 part by weight of azobisisobutyronitrile was added four times at 30 minute intervals.

After further stirring and heating at 120° C. for 2 hours to increase the conversion rate to resin, 13.3 parts by weight of n-butanol was added to terminate the reaction. The viscosity and nonvolatile content of the nine types of acrylic copolymer solutions obtained and the acid value of each acrylic copolymer were as shown in Table 3.

Clear coat paint P-1 to P-1 using the above nine types of acrylic copolymer solutions and the paint formulations shown in Table 3.
-9 was produced.

Among these clear coat paints, the acrylic copolymer is the acrylic copolymer (II
) The paints P-1 to P-4 meet the requirements.

(Margins continue on next page) 1-5 ″ 1-8 A zinc phosphate-treated steel plate (30 x 45 cm) was coated with an automotive cationic electrodeposition paint and baked at 180°C for 30 minutes. An intermediate paint consisting of an alkyd resin and an amino resin was applied, baked at 160°C for 30 minutes, and the paint film was sanded, water-sanded, and dried. The base coat paint and the clear coat paint listed in Table 3 above were coated in combinations shown in Examples 1 to 5 in Table 4 using a wet-on-wet method.This layer coating was carried out as follows. First, a base coat paint was applied to the medium 12 film to a dry film thickness of 15 μm, and after being left for 3 minutes, a clear coat paint was applied to a dry film thickness of 30 μm. After drying the layered coating film, leave it at room temperature for 10 minutes, then bake it in a hot air dryer at 140°C for 25 minutes.
Thermosetting coating compositions of Examples 1-5 were obtained.

Using exactly the same procedure, base coat paints and clear coat paints were overcoated using the combinations shown in Comparative Examples 1 to 8 in Table 4 to obtain thermosetting coating compositions of Comparative Examples 1 to 8.

Table 4 shows the results of evaluating the appearance and performance of each of the thermoset coatings of the Examples and Comparative Examples.

As is clear from this result, when either the base coat or the clear coat contains an acrylic copolymer that does not meet the requirements for an acrylic copolymer in the present invention, the thermosetting coating as the object of the present invention Unable to obtain composition.

(The following margin continues on the next page) [Effects of the Invention] As mentioned above, the thermosetting coating composition of the present invention has excellent bran collection properties and performance, and therefore is extremely useful as a coating film for automobile bodies. It can become a thing.

Claims (1)

[Scope of Claims] A pigment-containing thermosetting base coat paint and a thermosetting clear coat paint are overcoated in a wet-on-wet manner, and then both paints are heated and cured at the same time. In the thermosetting coating composition, the base coat paint comprises (1) (a) 10 to 40% by weight of a hydroxyl group-containing vinyl monomer (b) 0.2 to 10% by weight of a carboxyl group-containing vinyl monomer (c) General formula ▲ There are mathematical formulas, chemical formulas, tables, etc.▼ (In the formula, R_1 represents H or CH_3, and n represents an integer from 1 to 4.) 10 to 70% by weight of (meth)acrylic ester (d) Other copolymerizable Hydroxyl value 40-80mgKO obtained by copolymerizing vinyl monomer 0-30% by weight
H/g and acid value 0.5-25 mgKOH/g acrylic copolymer 60-90% by weight and (2) amino resin 10
A pigment is blended into a composition consisting of ~40% by weight, and the clear coat paint has the following properties: (3) (e) 15 to 50% by weight of t-butyl methacrylate (f) General formula (In the formula, R_2 represents H or CH_3, and m represents an integer of 8 or more.) 15-50% by weight of (meth)acrylic acid ester (g) 10-50% by weight of hydroxyl group-containing vinyl monomer (h) Hydroxyl group value 50-150 mgK obtained by copolymerizing 1-10% by weight of a carboxyl group-containing vinyl monomer (i) 0-30% by weight of another copolymerizable vinyl monomer
OH/g and acid value 2-40 mgKOH/g acrylic copolymer 50-90% by weight and (4) amino resin 10-90% by weight
50% by weight of a thermosetting coating composition.