JPH0637601B2 - Resin composition for electrodeposition coating - Google Patents

Description

TECHNICAL FIELD The present invention relates to a resin composition for electrodeposition coating. For more information,
The present invention relates to a resin composition for electrodeposition coating, which is excellent in various properties such as heat resistance, weather resistance, and transparency of a coating film, and further forms a coating film having excellent adhesion to an object to be coated.

(Prior Art) Conventionally, electrodeposition coating has been widely used for anticorrosion and surface finishing of automobiles, aluminum building materials, home appliances, office equipment, etc.
It is applied to various base materials.

However, automotive parts, lighting equipment, etc. are required to have both weather resistance and heat resistance as coating film performance, as well as chemical resistance, stain resistance, etc. There is nothing that can form a satisfactory coating film, and the present situation is that a fluororesin coating material having excellent coating film performance is spray-coated or electrostatically coated.

With this fluororesin coating, it is difficult to form a uniform coating film on the surface, and in order to improve the light reflectivity, electrodeposition coating can be applied, and excellent weather resistance and heat resistance performance is exhibited. There has been a demand for the development of a resin composition for electrodeposition coating.

(Problems to be Solved by the Invention) An object of the present invention is to eliminate the drawbacks of the above-mentioned conventional methods, and has both weather resistance and heat resistance, and further has excellent chemical resistance and stain resistance. It is intended to provide a resin composition for electrodeposition coating capable of forming a coating.

(Means for Solving the Problem) When the present invention is outlined, a film-forming component is A. (a) α, β
0.5 to 5% by weight of ethylenically unsaturated carboxylic acid, (b)
Alkyl ester of α, β-ethylenically unsaturated carboxylic acid 40 to 94% by weight, (c) Hydroxyalkyl-containing ester of α, β-ethylenically unsaturated carboxylic acid 0.5 to 2
5% by weight, (d) 0 to 60% by weight of other copolymerizable monomer, and (e) 5 to 30% by weight of a monomer represented by the following structural formula, which has an acid value of 5 to 100. 40 to 95% by weight of a polycarboxylic acid resin and B. A resin composition for electrodeposition coating, which comprises 5 to 60% by weight of a melamine-formaldehyde resin.

R represents a cyclohexyl group or a cyclohexyl group substituted with an alkyl group having 1 to 6 carbon atoms.

According to the research conducted by the present inventors, by using maleimides having a specific structural formula in combination during the synthesis of α, β-ethylenically unsaturated polycarboxylic acid resin, various properties such as heat resistance, weather resistance, and coating transparency can be obtained. The inventors have found that a polycarboxylic acid resin having excellent performance can be obtained, and completed the present invention.

The present invention will be described in more detail. In the resin composition for electrodeposition coating, the coating film forming component is A. A specific polycarboxylic acid resin and B.I. It is composed of a curing agent. A. The specific polycarboxylic acid resin of is prepared by reacting the following monomer compositions.

(a) 0.5 to 5% by weight of α, β-ethylenically unsaturated carboxylic acid, (b) 40 to 94% by weight of alkyl ester of α, β-ethylenically unsaturated carboxylic acid, (c) α, β- Hydroxyalkyl-containing ester of ethylenically unsaturated carboxylic acid 0.5 to 25% by weight, (d) other copolymerizable monomer 0 to 6
0% by weight and (e) 5 to 30 monomers represented by the following structural formula
Obtained by reacting wt%. (However, the total amount of the monomers is 100% by weight.) R represents a cyclohexyl group or a cyclohexyl group substituted with an alkyl group having 1 to 6 carbon atoms.

When the blending amount of the α, β-ethylenically unsaturated carboxylic acid as the component (a) is less than 0.5% by weight, it is not possible to impart sufficient water dispersibility to the polycarboxylic acid, and when it exceeds 5% by weight. However, performance such as water resistance and alkali resistance is deteriorated, which is not preferable.

The hydroxyalkyl-containing ester of the α, β-ethylenically unsaturated carboxylic acid, which is the component (c), is an important component for imparting crosslinking reactivity to the polycarboxylic acid resin, and its content is less than 0.5% by weight. In the case of, the cross-linking density of the coating film is insufficient and the coating strength and heat resistance are deteriorated. On the other hand, when it is more than 25% by weight, the coating film becomes brittle and cracks easily occur, which is not preferable.

In order to impart excellent heat resistance, weather resistance and transparency to the electrodeposition coating film, it is necessary to use the component (e) at least 3% by weight of the total monomer composition.

On the other hand, if it exceeds 30% by weight, gelation tends to occur in the reaction, which is not preferable.

The alkyl ester of α, β-ethylenically unsaturated carboxylic acid as the component (b) provides the resin composition according to the present invention as a stable aqueous liquid, and also improves the film-forming property during electrodeposition. , Used to efficiently achieve electrodeposition. If the blending amount is less than 40% by weight, the stability as an aqueous liquid is inferior, and almost no film-forming property is exhibited under the electrodeposition conditions usually performed, while if it is more than 94% by weight, the main component of the polycarboxylic acid resin is Performance such as heat resistance and electric insulation based on the maleimide-based monomer forming the skeleton cannot be sufficiently obtained, which is not preferable.

This A. The polycarboxylic acid resin is synthesized by heating and mixing a composition composed of the following monomers in the presence of an organic solvent and a polymerization catalyst, and controlling the reaction by adding a polymerization regulator.

Suitable (a) α, β-ethylenically unsaturated carboxylic acids include acrylic acid, α-chloroacrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid,
Citraconic acid, mesaconic acid and the like, or a functional derivative thereof having at least one carboxyl group, such as unsaturated polymerizable di- or polycarboxylic acid partial ester or amide.

(b) Examples of the alkyl ester of α, β-ethylenically unsaturated carboxylic acid include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl. Acrylate, butyl methacrylate, lauryl acrylate, lauryl methacrylate,
Stearyl acrylate, stearyl methacrylate,
There are hexyl acrylate, 2-ethylhexyl methacrylate, heptyl acrylate, heptyl methacrylate, and the like, and similar esters having up to about 20 carbon atoms in the alkyl group can be used. (c) Hydroxyalkyl-containing esters of α, β-ethylenically unsaturated carboxylic acids include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate. , 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, diethylene glycol monoacrylate, diethylene glycol monomethacrylate and the like.

(d) Other copolymerizable monomers include acrylamide, methacrylamide, methylolacrylamide, methylolmethacrylamide, alkoxymethylolacrylamide, alkoxymethylolmethacrylamide,
Examples include α, β-ethylenically unsaturated carboxylic acid amides or amide derivatives such as diacetone acrylamide and diacetone methacrylamide, styrene, α-alkylstyrene, α-chlorostyrene, vinyltoluene, acrylonitrile, vinyl acetate and the like. (e) structural formula, R represents a cyclohexyl group or a cyclohexyl group substituted with an alkyl group having 1 to 6 carbon atoms.

Examples of the monomer represented by: N-cyclohexylmaleimide, N-2-methylcyclohexylmaleimide, N-
There are 2-ethylcyclohexylmaleimide, N-2-chlorocyclohexylmaleimide and the like.

The polycarboxylic acid resin is prepared by emulsion polymerization, suspension polymerization, or solution polymerization at a polymerization temperature of 40 to 130 ° C. using a hydrophilic solvent such as water or isopropyl alcohol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether. At this time, if necessary, ammonium persulfate, potassium persulfate, α. Polymerization initiators such as α'-azobisisobutyronitrile, 4.4'-azobis-4-cyanovaleric acid, benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxybenzoate , A reducing agent such as ferric chloride, and a surfactant such as sodium alkylbenzene sulfonate and alkyl ether sulfonate. The compound can be used alone or as a mixture of two or more kinds.

The acid value of the polycarboxylic acid resin is 5 to 100 mgKOH, preferably 10 to 50 mgKOH, and the hydroxyl value is 10 to 150 mgKOH.
Is appropriate. When the acid value is less than 5 mgKOH, sufficient dispersibility in water as an electrodeposition coating cannot be obtained, and the electrophoretic property is poor, which is not preferable. On the other hand, when it is more than 100 mgKOH, the chemical properties such as water resistance and alkali resistance of the coating film remarkably deteriorate, which is not preferable. When the hydroxyl value is less than 10, a sufficient crosslink density cannot be obtained and the coating film strength becomes insufficient, and when the hydroxyl value exceeds 150, the chemical resistance becomes poor and the coating film becomes brittle, which is not preferable.

In the resin composition of the present invention, the proportion of the polycarboxylic acid resin as the component A and the melamine-formaldehyde resin as the component B is 40 to 95% by weight for the component A and 5 to 60 for the component B.
It is suitable to use in the range of weight%.

As the melamine-formaldehyde resin, a melamine resin, particularly methanol, ethanol, propanol,
Preference is given to using methylolmelamine at least partially etherified with one or more lower alcohols such as butanol.

When the content of the melamine-formaldehyde resin is less than 5% by weight, the coating film is not sufficiently crosslinked and the coating film performance is deteriorated. On the other hand, when it is more than 60% by weight, the coating film becomes brittle, which is not preferable.

The resin composition for electrodeposition coating of the present invention is prepared, for example, by the following method.

A polycarboxylic acid resin, a melamine-formaldehyde resin and an organic solvent are charged into a reaction vessel equipped with a stirrer and a thermometer, and then stirred and sufficiently mixed. As the organic solvent, for example, methanol, ethanol, n-
Propanol, isopropanol, n-butanol, isobutanol, secondary butanol, tertiary butanol,
Alcohols such as pentanol and the like, cellosolves such as methyl cellosolve, ethyl cellosolve, isopropyl cellosolve, butyl cellosolve, secondary butyl cellosolve and the like are used.

As a method for producing an electrodeposition coating liquid from the resin composition for electrodeposition coating thus prepared, a basic compound is added to the resin composition, and at least the carboxyl group present in the polycarboxylic acid resin molecule is added. A part of the solution is neutralized to make it dispersible in water, and deionized water is added to this to dilute it to an appropriate resin solid content concentration to obtain an electrodeposition coating solution.

The basic compound that can be used may be one that is normally used, for example, ammonia, or monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monoisopropylamine, diisopropylamine, triisopropylamine, monoamine. Primary to tertiary alkylamines such as butylamines, dibutylamines and tributylamines, monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, dimethylaminoethanol and Alkanolamines such as diethylaminoethanol, ethylenediamine, propylenediamine, diethylenetriamine and triethylene Alkylene polyamines such as tetramine, alkylene imine such as ethylene imine and propylene imine, piperazine, Horumorin, there is pyrazine and pyridine, and the like.

The electrodeposition coating liquid usually has a resin solid content of 3 to 50% by weight.
It is preferably prepared and used in the range of about 7 to 30% by weight.

At this time, if necessary, a reaction catalyst such as paratoluenesulfonic acid or dibutyltin dilaurate, an antioxidant such as paramethoxyphenol, dibutylthiodipropionate or tertiary butylcatechol, or an ultraviolet absorber, an antifoaming agent, a leveling agent. A coating additive such as an anti-settling agent, a pigment such as titanium oxide, talc, or carbon black can be mixed and used.

A conductive article in the electrodeposition coating solution prepared in this manner as an anode, after applying a direct current voltage between the counter electrode, pulling up the conductive article, and after heating or baking without washing, A uniform electrodeposition coating film is formed on the surface of the conductive article.

In the resin composition for electrodeposition coating of the present invention, for example, the coating film is heated and baked at 130 to 250 ° C, preferably 140 to 230 ° C.
Is achieved under the condition of 15 to 60 minutes.

(Example) In order to more specifically describe the present invention, an example will be shown below.

[Preparation of Polycarboxylic Acid Resin A] Into a four-necked flask equipped with a thermometer, a stirrer and a reflux condenser, ethylene glycol monobutyl ether 2
Charge 50 g and tertiary butyl peroxy-2-ethylhexanoate 7.5 g, and raise the temperature to 80 ° C. To this, 131 g of methyl methacrylate and n-methacrylic acid were added.
Butyl 90 g, ethyl acrylate 110 g, 2-hydroxyethyl methacrylate 80 g, acrylic acid 14 g, N
A mixture of 75 g of cyclohexylmaleimide and 1.0 g of 2,4-diphenyl-4-methyl-1-pentene in the monomer composition was added dropwise into the flask over 240 minutes, followed by stirring for another 240 minutes. Then, a mixture of 30 g of ethylene glycol monobutyl ether and 1.5 g of tertiary butyl peroxy-2-ethylhexanoate is added 3 times every 60 minutes. Then, at 80 ℃ 24
Stirring was continued for 0 minutes to prepare polycarboxylic acid resin A.

[Preparation of Polycarboxylic Acid Resins B to L] In the method for preparing the polycarboxylic acid resin A, the same method was used except that the monomer composition was changed to those shown in Table 1, and the polycarboxylic acid resins B were respectively prepared. ~ L was prepared.

Example 1 In a container, 120 g of polycarboxylic acid resin A and melamine resin (trade name Cymel HM-6 manufactured by Mitsui Cyanamid Co., Ltd.) 3
0 g was sampled and sufficiently stirred to prepare a resin composition for electrodeposition coating.

Examples 2 to 5 and Comparative Examples 1 to 6 In the same manner as in Example 1, the same method was used except that the kind of polycarboxylic acid resin was changed to that shown in Table 2 to obtain a resin composition for electrodeposition coating. Was prepared.

Experimental Example The resin compositions prepared in Examples 1 to 7 and Comparative Examples 1 to 7 were used, triethylamine and 2-ethylhexyl alcohol were added thereto, and the mixture was sufficiently stirred. Deionized water was gradually added while stirring to prepare an electrodeposition coating solution having a resin solid content of about 15% by weight.

Next, using each of the electrodeposition coating solutions, an aluminum plate degreased with toluene by a conventional method was used as an anode, and a stainless plate was connected to the cathode to perform DC electrodeposition coating. The electrodeposition coating conditions are as follows.

Aluminum material: JIS A-1100 Voltage: 80 V Current duration: 2 minutes Coating baking: 180 ° C. × 30 minutes As a result, an electrodeposition coating having the performance shown in Table 1 was obtained.

(Effects of the Invention) As is clear from the above description, the resin composition for electrodeposition coating of the present invention is a coating film showing various properties such as excellent heat resistance, weather resistance, alkali resistance, acid resistance, and transparency. Is formed.

Claims (1)

[Claims] 1. A coating film forming component is A. (a) α, β-ethylenically unsaturated carboxylic acid 0.5 to 5% by weight, (b) α, β-
Alkyl ester of ethylenically unsaturated carboxylic acid 40-
94% by weight, (c) 0.5 to 25% by weight of hydroxyalkyl-containing ester of α, β-ethylenically unsaturated carboxylic acid, (d) 0 to 60% by weight of other copolymerizable monomer, and (e) below. Polycarboxylic acid resin 4 having an acid value of 5 to 100 obtained by reacting 5 to 30% by weight of the monomer represented by the structural formula
0 to 95% by weight and B.I. A resin composition for electrodeposition coating, comprising 5 to 60% by weight of a melamine-formaldehyde resin. However, the structural formula of (e) is R represents a cyclohexyl group or a cyclohexyl group substituted with an alkyl group having 1 to 6 carbon atoms.