JP2009165980A - Method for forming multi-layer coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a multi-layer coating film, which is capable of forming a coating film excellent in scratch resistance, acid resistance, surface finish appearance, etc., and capable of reducing the number of processes and the emission amount of a solvent. <P>SOLUTION: The method for forming a multi-layer coating film includes: simultaneously curing a base coating material (A) comprising a carboxyl-containing and hydroxyl-containing resin, a specified tertiary amino-containing resin, and a hydroxyl-reactive crosslinking agent, a water-based coloring coating material (B), and a clear coating material (C) to form a three-layer coating film; coating the three-layer coating film with a clear coating material (D) comprising a specified hydroxyl-containing acrylic resin, a trifunctional HMD isocyanurate compound, and a specified low-molecular-weight polyester-polyol; and curing the clear coating material by heating. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for forming a multilayer coating film that can form a coating film excellent in scratch resistance, acid resistance, finished appearance, and the like, and that can reduce the coating process.

  A paint to be applied to an object such as an automobile body is required to have excellent coating film performance such as scratch resistance, acid resistance, stain resistance, and finished appearance.

  Conventionally, melamine cross-linking paints have been widely used as paints for articles such as automobile bodies. A melamine cross-linking paint is a paint containing a hydroxyl group-containing resin as a base resin and a melamine resin as a cross-linking agent, and has a high cross-linking density at the time of heat curing and excellent in film performance such as scratch resistance and finish. Form. However, this paint has a problem that the crosslinked coating film is easily hydrolyzed by acid rain, and the acid resistance of the coating film is poor.

  Patent Document 1 discloses a two-pack type urethane crosslinked coating composition comprising a hydroxyl group-containing acrylic resin, a hydroxyl group-containing oligoester and an isocyanate prepolymer. The coating film formed from this paint is excellent in acid resistance because urethane crosslinks are hardly hydrolyzed, but has a problem of insufficient scratch resistance.

  Further, for the purpose of improving the finished appearance quality, for example, in Patent Document 2, after applying the clear paint and the first clear paint in sequence, which employs double clear coating, and heating both the coating films simultaneously, In a method for forming a multi-layer coating film by a 3-coat 2-bake method, which comprises applying a second clear paint to the coated surface and curing by heating, a hydrolyzate of a specific silicon compound is contained as the second clear paint A method for forming a hard overcoat film characterized by being a clear paint is disclosed. According to this method, it is possible to form a multi-layer coating film with improved scratch resistance, finished appearance, etc., but if an intermediate coating process usually performed in automobile coating is included, a 4-coat 3-bake system is adopted. However, the process load is large, and it does not satisfy the demand for reducing the painting process from the viewpoint of energy saving and environmental response.

Japanese Patent Laid-Open No. 6-220397 Japanese Patent Laid-Open No. 10-272414

  An object of the present invention is to provide a method for forming a multilayer coating film that can form a coating film excellent in scratch resistance, acid resistance, finished appearance, etc., and that can reduce the coating process and the amount of solvent discharged. That is.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have now obtained a base comprising a carboxyl group- and hydroxyl group-containing resin, a specific tertiary amino group-containing resin, and a crosslinking agent capable of reacting with a hydroxyl group. A three-layer coating film obtained by simultaneously curing the paint (A), the water-based coloring paint (B) and the clear paint (C) is formed, and a specific hydroxyl group-containing acrylic resin, 3 It has been found that the above object can be achieved by a multilayer coating film forming method in which a clear coating (D) comprising a functional HMDI isocyanurate compound and a specific low molecular weight polyester polyol is applied and cured by heating. The invention has been completed.

Thus, in the present invention, the base paint (A) is applied to the object to be coated, the water-colored paint (B) and the clear paint (C) are sequentially applied to the uncured coating surface, and then heated to the paint (A ), (B) and (C) are simultaneously cured, then the clear coating (D) is applied on the three-layer coating, and then heated and cured to form a multilayer coating. In the film forming method,
The base paint (A) is a carboxyl group- and hydroxyl group-containing resin (a-1), a tertiary amino group-containing unsaturated monomer (a-2-1), a polyoxyalkylene group-containing nonionic unsaturated monomer (a-2). -2) and a tertiary amino group-containing resin (a-2) obtained by copolymerizing other unsaturated monomer (a-2-3), and a crosslinking agent (a-3) capable of reacting with a hydroxyl group A paint consisting of
The clear paint (D) contains a hydroxyl group having a hydroxyl value of 100 to 200 mg KOH / g and a number average molecular weight of 5,000 to 10,000, obtained by copolymerizing a monomer mixture containing an aromatic vinyl monomer and a monomer having a cyclohexyl ring. The hydroxyl value obtained by esterifying an acrylic resin (d-1), a trifunctional HMDI isocyanurate compound (d-2), and a diol having 3 to 6 carbon atoms and a dicarboxylic acid having a cyclohexyl ring is 250 to 350 mgKOH. The present invention provides a method for forming a multilayer coating film characterized by being a two-component clear coating composition comprising a polyester polyol (d-3) having a / g and a number average molecular weight of 350 to 550.

  The clear paint (D) to be applied to the uppermost layer in the multilayer coating film forming method of the present invention has a relatively high concentration of hydroxyl group as a cross-linking functional group and an aromatic vinyl monomer and a cyclohexyl ring as hard monomer components. Using a hydroxyl group-containing acrylic resin as a base resin, and a trifunctional HMDI polyisocyanurate compound having a hard isocyanurate structure as compared with HMDI having a linear structure as a crosslinking agent. Because it is a composition comprising a polyester polyol with a low molecular weight and a structure having a cyclohexyl ring, which is useful for improving the properties, it forms a coating film having a urethane cross-linking structure with a high cross-linking density and excellent balance between hardness and scratch resistance. This makes it possible to produce a multi-layer coating film with excellent scratch resistance, acid resistance and stain resistance. Rukoto can.

  In addition, a base paint (A) comprising a carboxyl group- and hydroxyl group-containing resin (a-1), a tertiary amino group-containing resin (a-2), and a crosslinking agent (a-3) capable of reacting with a hydroxyl group is applied. Since it has the effect of developing viscosity in the coating film, it is possible to suppress the mixed layer with the water-based colored paint (B) applied to the upper layer, and the base paint (A), water-based colored paint (B) and clear paint (C ) Can be cured at the same time, so that in the conventional double clear coating of automobiles, the 4-coat 3-bake method including the intermediate coating process is used. According to the multilayer coating film forming method, the 4-coat 2-bake method is adopted, and the baking process can be reduced.

  Thus, according to the present invention, a method for forming a multilayer coating film that can form a coating film excellent in scratch resistance, acid resistance, finished appearance, etc., and can reduce the amount of the process and the amount of solvent discharged. Can provide a remarkable effect.

BEST MODE FOR CARRYING OUT THE INVENTION

  Hereinafter, the multilayer coating film forming method of the present invention (hereinafter sometimes referred to as “the present method”) will be described in more detail.

Base paint (A)
According to this method, the base paint (A) is first applied to the article to be coated. The base paint (A) is a paint comprising a carboxyl group- and hydroxyl group-containing resin (a-1), a tertiary amino group-containing resin (a-2), and a crosslinking agent (a-3) capable of reacting with a hydroxyl group. is there.

Carboxyl group and hydroxyl group-containing resin (a-1)
The carboxyl group- and hydroxyl group-containing resin (a-1) is not particularly limited as long as it contains a carboxyl group and a hydroxyl group. Specific examples of the resin include acrylic resins and polyesters. Examples thereof include resins, polyether resins, polycarbonate resins, polyurethane resins and the like.

  The coating film of the base paint (A) is formed by forming a pseudo-crosslinked structure by the acid-base interaction between the carboxyl group in the resin (a-1) and the tertiary amino group in the resin (a-2). The viscous development effect is brought about.

  The carboxyl group- and hydroxyl group-containing resin (a-1) is generally 2 to 100 mgKOH / g, preferably 5 to 80 mgKOH / g, from the viewpoint of the effect of developing viscosity due to the interaction with the tertiary amino group-containing resin (a-2). More preferably, it can have an acid value in the range of 5 to 65 mgKOH / g.

  The carboxyl group- and hydroxyl group-containing resin (a-1) is also generally 20 to 200 mgKOH / g, preferably 35 to 180 mgKOH / g, more preferably 50 to 50 from the viewpoints of curability and water resistance of the obtained coating film. It can have a hydroxyl value in the range of 150 mg KOH / g.

  Preferred examples of the carboxyl group and hydroxyl group-containing resin (a-1) include a carboxyl group and a hydroxyl group-containing acrylic resin, a carboxyl group and a hydroxyl group-containing polyester resin, a carboxyl group and a hydroxyl group-containing polyurethane resin, etc. The preferred resin will be described more specifically.

Carboxyl group and hydroxyl group-containing acrylic resin Carboxyl group and hydroxyl group-containing acrylic resin are carboxyl group-containing unsaturated monomer (M-1), hydroxyl group-containing unsaturated monomer (M-2) and other copolymerizable unsaturated monomers (M -3) can be synthesized by copolymerization by a conventional method.

  The carboxyl group-containing unsaturated monomer (M-1) includes a compound having at least one carboxyl group and one unsaturated bond in one molecule. For example, acrylic acid, methacrylic acid, crotonic acid, itacone An acid, maleic acid, maleic anhydride, etc. can be mentioned. These can be used alone or in combination of two or more.

  The hydroxyl group-containing unsaturated monomer (M-2) includes a compound having at least one hydroxyl group and one unsaturated bond in one molecule, and the hydroxyl group mainly includes a carboxyl group and a hydroxyl group-containing acrylic resin. It acts as a functional group that reacts with a crosslinking agent that reacts with a hydroxyl group. As the monomer (M-2), a monoester product of (meth) acrylic acid and a dihydric alcohol having 2 to 10 carbon atoms is suitable. For example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl ( Examples include meth) acrylate and 4-hydroxybutyl (meth) acrylate.

  In the present specification, “(meth) acrylate” means acrylate or methacrylate, “(meth) acrylic acid” means acrylic acid or methacrylic acid, and “(meth) acryloyl” means acryloyl or Means methacryloyl.

In addition to the above, the monoesterified product of (meth) acrylic acid and a polyhydric alcohol may be a monoesterified product of (meth) acrylic acid and a dihydric alcohol having 2 to 10 carbon atoms. Compounds obtained by ring-opening polymerization of caprolactone and the like, for example, “Placcel FA-1”, “Placcel FA-2”, “Placcel FA-3”, “Placcel FA-4”, “Placcel FA-5”, “Placcel FM” -1 "," Placcel FM-2 "," Placcel FM-3 "," Placcel FM-4 "," Placcel FM-5 "(all of which are trade names, manufactured by Daicel Chemical Co., Ltd.) be able to. Further, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2-hydroxy-3-butoxypropyl (meth) acrylate, monohydroxyethyl phthalate ( A (meth) acrylate etc. can also be used.

  The other copolymerizable unsaturated monomer (M-3) is one unsaturated per molecule other than the carboxyl group-containing unsaturated monomer (M-1) and the hydroxyl group-containing unsaturated monomer (M-2). Including compounds having a bond, specific examples thereof include those described in the following (1) to (6).

  (1) Monoesterified product of (meth) acrylic acid and C1-C20 monohydric alcohol: for example, methyl (meth) acrylate, ethyl acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, lauryl (meth) acrylate, isobornyl (meth) acrylate, Tridecyl (meth) acrylate, stearyl (meth) acrylate, butoxyethyl (meth) acrylate and the like.

  (2) Aromatic unsaturated monomer: For example, styrene, α-methylstyrene, vinyltoluene and the like.

  (3) Glycidyl group-containing unsaturated monomer: A compound having one glycidyl group and one unsaturated bond in each molecule is included, and specific examples thereof include glycidyl acrylate and glycidyl methacrylate.

  (4) Unsaturated bond-containing amide compound: For example, acrylic acid amide, methacrylic acid amide, dimethylacrylamide, N, N-dimethylpropylacrylamide, N-butoxymethylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, di Acetone acrylamide and the like.

  (5) Other unsaturated compounds: For example, vinyl acetate, vinyl propionate, vinyl chloride, versatic acid vinyl ester Veova 9, Veova 10 (above, Japan Epoxy Resin, trade name), and the like.

  (6) Unsaturated bond-containing nitrile compound: For example, acrylonitrile, methacrylonitrile and the like.

  These other unsaturated monomers (M-3) can be used alone or in combination of two or more.

  The carboxyl group- and hydroxyl group-containing acrylic resin can generally have an acid value in the range of 5-100 mg KOH / g, preferably 20-80 mg KOH / g, more preferably 35-65 mg KOH / g. If the acid value of the acrylic resin is less than 5 mgKOH / g, the effect of developing the viscosity due to the interaction with the tertiary amino group-containing resin (a-2) may be reduced, and if it exceeds 100 mgKOH / g, The water resistance of the coating film may decrease.

  The carboxyl group- and hydroxyl group-containing acrylic resin can also generally have a hydroxyl value in the range of 20 to 150 mgKOH / g, preferably 35 to 120 mgKOH / g, more preferably 50 to 100 mgKOH / g. When the hydroxyl value of the acrylic resin is less than 20 mgKOH / g, the curability may be insufficient, and when it exceeds 150 mgKOH / g, the water resistance of the coating film may be lowered.

  The carboxyl group- and hydroxyl group-containing acrylic resin can further have a number average molecular weight generally in the range of 2000-100000, preferably 3000-50000, more preferably 4000-20000. When the number average molecular weight of the acrylic resin is less than 2,000, the weather resistance of the coating film may be insufficient, and when it exceeds 100,000, the smoothness of the coating surface may be deteriorated.

  In addition, in this specification, a number average molecular weight is the value which converted the number average molecular weight measured with the gel permeation chromatograph (The Tosoh company make, brand name "HLC8120GPC") on the basis of the number average molecular weight of polystyrene.

Carboxyl group and hydroxyl group-containing polyester resin The carboxyl group and hydroxyl group-containing polyester resin can be synthesized by esterifying a polybasic acid and a polyhydric alcohol according to a method known per se.

  The polybasic acid is a compound having at least two carboxyl groups in one molecule. For example, phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, hexa Hydrophthalic acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid, pyromellitic acid and their anhydrides, and the like. The polyhydric alcohol has at least two hydroxyl groups in one molecule. For example, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-diethyl-1,3 -Propanediol, neopentyl glycol, 1,9-nonanediol, 1,4-cyclohexanedio Hydroxypivalic acid neopentyl glycol ester, 2-butyl-2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethylpentanediol, hydrogenated bisphenol A, etc. Diols of trimethylolpropane, trimethylolethane, glycerin, pentaerythritol and other trivalent or higher polyols; 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolpentane Examples thereof include polyhydroxycarboxylic acids such as acid, 2,2-dimethylolhexanoic acid and 2,2-dimethyloloctanoic acid. These compounds may form an ether with a lower alcohol.

  In addition, α-olefin epoxides such as propylene oxide and butylene oxide; monoepoxy compounds such as Cardura E10 (product name, glycidyl ester of synthetic hyperbranched saturated fatty acid) such as Cardura E10 are reacted with acid, and these are reacted. The compound may be introduced into the polyester resin.

  The introduction of the carboxyl group into the polyester resin is, for example, a method of reacting a polybasic acid such as trimellitic acid or trimellitic anhydride or an anhydride thereof after the esterification reaction of the polybasic acid and the polyhydric alcohol. It is also possible to do so.

In addition, carboxyl group-containing polyester resins include oil fatty acids, coconut oil fatty acids, safflower oil fatty acids, soybean oil fatty acids, sesame oil fatty acids, eno oil fatty acids, hemp oil fatty acids, tall oil fatty acids, dehydrated castor oil fatty acids, etc. ) Fatty acid-modified polyester resin modified with drying oil fatty acid may be used. In general, the modified amount of these fatty acids is preferably 30% by mass or less in terms of oil length. Furthermore, the carboxyl group-containing polyester resin may be obtained by partially reacting a monobasic acid such as benzoic acid.

  The carboxyl group- and hydroxyl group-containing polyester resin can generally have an acid value in the range of 5-70 mgKOH / g, preferably 15-55 mgKOH / g, more preferably 25-45 mgKOH / g. If the acid value of the polyester resin is less than 5 mgKOH / g, the effect of developing the viscosity due to the interaction with the tertiary amino group-containing resin (a-2) may be reduced, and if it exceeds 70 mgKOH / g, The water resistance of the coating film may decrease.

  The carboxyl group- and hydroxyl group-containing polyester resin can also generally have a hydroxyl value in the range of 30 to 200 mg KOH / g, preferably 50 to 180 mg KOH / g, more preferably 70 to 150 mg KOH / g. If the hydroxyl value of the polyester resin is less than 30 mgKOH / g, the curability may be insufficient, and if it exceeds 200 mgKOH / g, the water resistance of the coating film may be lowered.

  Furthermore, the carboxyl group- and hydroxyl group-containing polyester resin can generally have a number average molecular weight in the range of 300 to 50000, preferably 500 to 20000, and more preferably 1000 to 10,000. When the number average molecular weight of the polyester resin is less than 300, the weather resistance of the coating film may be insufficient, and when it exceeds 50,000, the smoothness of the coating surface may be deteriorated.

Carboxyl group and hydroxyl group-containing polyurethane resin The carboxyl group and hydroxyl group-containing polyurethane resin can be obtained by a conventional method, for example, by reacting a polyol containing a carboxyl group-containing polyol with a diisocyanate.

  Examples of the carboxyl group-containing polyol include 2,2-dimethylolpropionic acid and 2,2-dimethylolbutanoic acid, and 2,2-dimethylolpropionic acid is particularly preferable. When these are used, a small amount of a solvent such as N-methylpyrrolidone can be used in order to allow the reaction to proceed rapidly.

  Examples of polyols that do not contain a carboxyl group include divalent alcohols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, and hexamethylene glycol; trivalent compounds such as trimethylolpropane, glycerin, and pentaerythritol. Alcohol etc. can be mentioned. Examples of high molecular weight materials include polyether polyol, polyester polyol, acrylic polyol, and epoxy polyol. Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like. Examples of the polyester polyol include alcohols such as the above divalent alcohols, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, and neopentyl glycol, and dibasic acids such as adipic acid, azelaic acid, and sebacic acid. And lactone ring-opening polymer polyols such as polycaprolactone; polycarbonate diols and the like.

Examples of the polyisocyanate to be reacted with the above polyol include aliphatic polyisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, lysine diisocyanate, and burette type adducts of these polyisocyanates. , Isocyanurate cycloadduct; isophorone diisocyanate, 4,4′-methylenebis (cyclohexyl isocyanate), methylcyclohexane-2,4- (or-2,6-) diisocyanate, 1,3- (or 1,4-) diisocyanate (Isocyanatomethyl) cycloaliphatic diisocyanates such as cyclohexane, 1,4-cyclohexane diisocyanate, 1,3-cyclopentane diisocyanate, 1,2-cyclohexane diisocyanate And burette type adducts, isocyanurate cycloadducts of these polyisocyanates; xylylene diisocyanate, metaxylylene diisocyanate, tetramethyl xylylene diisocyanate, tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 1,5- Naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, (m- or p-) phenylene diisocyanate, 4,4'-biphenylene diisocyanate, 3,3'-dimethyl- Aromatic diisocyanates such as 4,4′-biphenylene diisocyanate, bis (4-isocyanatophenyl) sulfone, isopropylidenebis (4-phenylisocyanate) Compounds and burette-type adducts of these polyisocyanates, isocyanurate cycloadducts; triphenylmethane-4,4 ′, 4 ″ -triisocyanate, 1,3,5-triisocyanatobenzene, 2,4 , 6-triisocyanatotoluene, 4,4′-dimethyldiphenylmethane-2,2 ′, 5,5′-tetraisocyanate and the like, and polyisocyanates having three or more isocyanate groups in one molecule, and these polyisocyanates Burette type adducts, isocyanurate ring adducts, and the like.

  The carboxyl group- and hydroxyl group-containing polyurethane resin generally has an acid value in the range of 2-50 mgKOH / g, preferably 5-40 mgKOH / g, more preferably 5-20 mgKOH / g. When the acid value of the polyurethane resin is less than 5 mgKOH / g, the viscosity expression effect due to the interaction with the tertiary amino group-containing resin (a-2) may be reduced, and when it exceeds 50 mgKOH / g, The water resistance of the coating film may decrease.

  The carboxyl group- and hydroxyl group-containing polyurethane resin can generally have a number average molecular weight in the range of 1000 to 3000000, preferably 10000 to 2000000, and more preferably 20000 to 1000000. When the number average molecular weight of the polyurethane resin is less than 1000, the weather resistance of the coating film may be insufficient, and when it exceeds 3000000, the coated surface smoothness may be deteriorated.

  The carboxyl group in the carboxyl group- and hydroxyl group-containing resin (a-1) is preferably neutralized. The neutralization is preferably performed using a basic substance before mixing with the tertiary amino group-containing resin (a-2), the crosslinking agent (a-3) and the like.

  Examples of basic substances used for neutralization include ammonia; primary monoamines such as ethylamine, propylamine, butylamine, benzylamine, monoethanolamine, neopentanolamine, 2-aminopropanol, and 3-aminopropanol; diethylamine , Secondary monoamines such as diethanolamine, di-n- or diisopropanolamine, N-methylethanolamine, N-ethylethanolamine; N, N-dimethylethanolamine, trimethylamine, triethylamine, triisopropylamine, methyldiethanolamine, etc. Tertiary amines; polyethylenes such as diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, methylaminopropylamine, etc. Al may be used alone or in combination of two or more thereof.

  The amount of the basic substance used for neutralization is suitably in the range of 0.1 to 1 equivalent, particularly 0.2 to 0.8 equivalent, relative to the carboxyl group in the resin (a-1). Yes.

Tertiary amino group-containing resin (a-2)
The tertiary amino group-containing resin (a-2) includes a tertiary amino group-containing unsaturated monomer (a-2-1), a polyoxyalkylene group-containing nonionic unsaturated monomer (a-2-2), and other A tertiary amino group-containing acrylic resin obtained by copolymerizing an unsaturated monomer (a-2-3).

Tertiary amino group-containing unsaturated monomer (a-2-1)
The tertiary amino group-containing polymerizable unsaturated monomer (a-2-1) is a monomer component for introducing a tertiary amino group into the tertiary amino group-containing resin (a-2). Monomers having secondary amino groups and unsaturated groups are included.

  Specifically, for example, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-di-t- N, N-dialkylaminoalkyl (meth) acrylates such as butylaminoethyl (meth) acrylate and N, N-dimethylaminobutyl (meth) acrylate; N, N-dimethylaminoethyl (meth) acrylamide, N, N-diethylamino Examples include N, N-dialkylaminoalkyl (meth) acrylamides such as ethyl (meth) acrylamide and N, N-dimethylaminopropyl (meth) acrylamide. These monomers can be used alone or in combination of two or more.

  Of these monomers, N, N-dialkylaminoalkyl (meth) acrylate, particularly N, N-dimethylaminoethyl (meth) acrylate, is preferred.

  The tertiary amino group introduced into the tertiary amino group-containing resin (a-2) by the tertiary amino group-containing polymerizable unsaturated monomer (a-2-1) is a carboxyl in the resin (a-1). It interacts with the group and contributes to the development of the viscosity of the coating material due to the pseudo-crosslinking formation effect due to the acid-base interaction.

Nonionic unsaturated monomer containing polyoxyalkylene group (a-2-2)
The polyoxyalkylene group-containing nonionic unsaturated monomer (a-2-2) imparts hydrophilicity to the tertiary amino group-containing resin (a-2) and the resin (a-1) and the resin (a-2). ) Is a monomer component for introducing a polyoxyalkylene group for suppressing excessive interaction into the tertiary amino group-containing resin (a-2), and includes a polyoxyalkylene group and an unsaturated group in one molecule. It is a monomer having

  Examples of the polyoxyalkylene group include a polyoxyethylene group, a polyoxypropylene group, a group having a block structure of polyoxyethylene and polyoxypropylene, and the like. The polyoxyalkylene group preferably has a molecular weight in the range of usually 200 to 3,000, particularly 300 to 2,500.

As a representative example of the monomer (a-2-2), for example, the following formula (1)
^{_{CH 2 = C (R 1)}} COO (C n H 2n O) m -R 2 (1)
(Wherein R ¹ represents a hydrogen atom or a methyl group, R ² represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, m is an integer of 4 to 60, preferably 6 to 50, and n is An integer of 2 or 3, preferably 2, where m oxyalkylene units (C _n H _2n O) may be the same or different from each other)
The compound shown by can be mentioned.

Specific examples of such a monomer (a-2-2) include, for example, tetraethylene glycol (meth) acrylate, methoxytetraethylene glycol (meth) acrylate,
Ethoxytetraethylene glycol (meth) acrylate, n-butoxytetraethylene glycol (meth) acrylate, tetrapropylene glycol (meth) acrylate, methoxytetrapyrene glycol (meth) acrylate, ethoxytetrapropylene glycol (meth) acrylate, n-butoxy Examples include tetrapropylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, and ethoxypolyethylene glycol (meth) acrylate. Of these, polyethylene glycol (meth) acrylate and polypropylene glycol (meth) acrylate are particularly preferable. These monomers can be used alone or in combination of two or more.

  Resin (a-1) and resin (a-) are introduced into the tertiary amino group-containing resin (a-2) by the monomer (a-2-2) due to the steric hindrance of the side chain portion of the polyoxyethylene group. Excessive pseudo-crosslinked structure formation with 2) is suppressed, smoothness due to aggregation does not occur, and a coating film having an excellent finished appearance can be obtained.

Other unsaturated monomers (a-2-3)
The other unsaturated monomer (a-2-3) is copolymerizable with the monomer (a-2-1) and the monomer (a-2-2) described above, and these monomers (a-2-1) ) And the monomer (a-2-2), and can be appropriately selected and used depending on the properties desired for the tertiary amino group-containing resin (a-2).

Specific examples of such a monomer (a-2-3) include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) ) Acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate , isobornyl (meth) acrylate, tridecyl (meth) linear or cyclic alkyl of _C 1 _{-C 24} acrylate such as (meth) acrylate monomers; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth Hydroxyl group-containing unsaturated monomers such as acrylate and 4-hydroxybutyl (meth) acrylate (typically hydroxyalkyl (meth) acrylate monomers); acrylamide, methacrylamide; 3-ethyl-3- (meth) acryloyloxymethyloxetane, Oxetane ring-containing (meth) acrylates such as 3-methyl-3- (meth) acryloyloxymethyloxetane and 3-butyl-3- (meth) acryloyloxymethyloxetane; aromatics such as styrene, α-methylstyrene and vinyltoluene Vinyl compounds; (meth) acrylonitrile, vinyl acetate and the like can be mentioned, and these can be used alone or in combination of two or more.

  The tertiary amino group-containing resin (a-2) preferably has a functional group that reacts with the crosslinking agent (a-3) from the viewpoint of coating film performance and the like. As the functional group capable of reacting with the cross-linking agent (a-3), a hydroxyl group can be mentioned as a preferable one. In this case, the monomer (a-2-3) preferably contains a hydroxyl group-containing unsaturated monomer as at least a part of its components.

Specific examples of the hydroxyl group-containing unsaturated monomer include 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 2,3-dihydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, Monoesterified product of polyhydric alcohol such as polyethylene glycol mono (meth) acrylate and (meth) acrylic acid; Compound obtained by ring-opening polymerization of ε-caprolactone to monoesterified product of polyhydric alcohol and (meth) acrylic acid, etc. Can be mentioned. Among them, ε-caprolapton is ring-opening polymerized to 4-hydroxybutyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, and monoesterified product of polyhydric alcohol and (meth) acrylic acid from the viewpoint of reactivity and the like. The compound obtained by doing is suitable. These exemplified compounds can be used alone or in combination of two or more. The hydroxyl group-containing unsaturated monomer is generally 3 to 30% by mass, preferably 5 to 5%, based on the total amount of monomers (a-2-1), (a-2-2) and (a-2-3). It is preferable to use within the range of 25% by mass.

  The tertiary amino group-containing resin (a-2) includes the above-mentioned tertiary amino group-containing unsaturated monomer (a-2-1), polyoxyethylene group-containing nonionic unsaturated monomer (a-2-2), and others. The unsaturated monomer (a-2-3) is copolymerized.

  The proportion of the monomers (a-2-1), (a-2-2) and (a-2-3) used in the copolymerization is not strictly limited and is desirable for a tertiary amino group-containing resin. Specifically, the monomer (a-2-1), (a-2-2) and (a-2-3) can be used as a reference based on the total amount of the monomers (a-2-1), (a-2-2) and (a-2-3). 2-1) is generally 1-25% by weight, preferably 3-20% by weight, more preferably 5-15% by weight; monomer (a-2-2) is generally 5-40% by weight, preferably 7- 35 mass%, more preferably 10-30 mass%, and the monomer (a-2-3) is generally in the range of 35-94 mass%, preferably 45-90 mass%, more preferably 55-85 mass%. Can be used.

  The copolymerization of the monomers (a-2-1), (a-2-2) and (a-2-3) is performed by a method known per se, for example, a method such as solution polymerization in an organic solvent. be able to. Specifically, the copolymerization by the solution polymerization method is performed, for example, by mixing a mixture of the monomers (a-2-1), (a-2-2) and (a-2-3) and a radical polymerization initiator with an organic solvent. It can be carried out by dissolving or dispersing in a solvent and polymerizing by heating with stirring at a temperature of about 80 ° C. to about 200 ° C. for about 1 to 10 hours. As the organic solvent that can be used for the solution polymerization, for example, a hydrophilic organic solvent such as a propylene glycol type or a dipropylene glycol type is preferable.

  The tertiary amino group-containing resin (a-2) generally has an amine value in the range of 3 to 100 mgKOH / g, preferably 10 to 80 mgKOH / g, more preferably 15 to 60 mgKOH / g, from the viewpoint of the effect of developing viscosity. It is suitable to have. The tertiary amino group-containing resin (a-2) is generally 10 to 130 mgKOH / g, preferably 20 to 100 mgKOH / g, more preferably 30 to 70 mgKOH, from the viewpoint of water resistance and curability of the resulting coating film. It preferably has a hydroxyl value in the range of / g. Further, the tertiary amino group-containing resin (a-2) is generally in the range of 500 to 20000, particularly 1000 to 10000, more particularly 3000 to 7000, from the viewpoint of coating surface smoothness and weather resistance of the resulting coating film. It is preferred to have a number average molecular weight of

  The monomer (a-2-1) unit constituting the tertiary amino group-containing resin (a-2) is used to develop the viscosity of the coating material due to the pseudo-crosslinking effect with the carboxyl group- and hydroxyl group-containing resin (a-1). Contributing and the monomer (a-2-2) unit constituting the tertiary amino group-containing resin (a-2) suppresses excessive formation of the pseudo-crosslinked structure, and forms a coating film with an excellent finished appearance. Will contribute.

Crosslinker capable of reacting with hydroxyl group (a-3)
The crosslinking agent (a-3) capable of reacting with a hydroxyl group is not particularly limited as long as it is a compound having a functional group capable of reacting with a hydroxyl group. For example, melamine resin, block polyisocyanate compound, water listed below A dispersible block polyisocyanate compound or the like can be preferably used.

The melamine resin melamine resins, specifically, di -, tree, tetra -, penta -, hexa - The methylol melamine and alkyl etherified product (alkyl by their alcohols, e.g., methyl, ethyl, propyl, isopropyl, Butyl, isobutyl, 2-ethylhexyl and the like) and condensates thereof.

  Specific examples of the melamine resin include, for example, Cymel 303, Cymel 323, Cymel 325, Cymel 327, Cymel 350, Cymel 370, Cymel 380, Cymel 385, Cymel 212, Cymel 251, Cymel 254, Mymel manufactured by Nippon Cytec Industries, Ltd. Coat 776; Resin 735, Resimin 740, Resimin 741, Resimin 745, Resimin 746, Resimin 747 manufactured by Monsanto; Sumitomo Chemical Co., Ltd. Sumimar M55, Sumimar M30W, Sumimar M50W; Series etc. (all are trade names) can be mentioned.

  The melamine resin preferably has a mononuclear content of at least 30 mass%, preferably at least 40 mass%, more preferably at least 45 mass%. Further, from the viewpoint of finish, storage stability, etc., in the alkyl etherified melamine resin, the ratio of methoxy group to butoxy group (methoxy group / butoxy group) is usually 100/0 to 60/40 mol%, particularly 100/0 to Preference is given to methyl / butyl (mixed) etherified melamine resins which are in the range of 70/30 mol% and have a high methoxy group ratio.

  As a particularly preferred melamine resin, a methyl / butyl (mixed) etherified melamine resin having a mononuclear content of 30% by mass or more and a ratio of methoxy group to butoxy group of 100/0 to 60/40 mol% is used. Can be mentioned. Specific examples of such a melamine resin include Cymel 325, Cymel 327, Cymel 350, Cymel 212, Cymel 251, My Coat 212, My Coat 776 (named above) (manufactured by Nihon Cytec Industries). .

  When a melamine resin is used as a crosslinking agent, sulfonic acids such as paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, and salts of these acids and amines can be used as catalysts.

  The melamine resins described above can be used alone or in combination of two or more.

Block Polyisocyanate Compound A block polyisocyanate compound is a compound obtained by blocking the isocyanate group of a polyisocyanate compound having at least two free isocyanate groups in one molecule with a blocking agent.

Examples of the polyisocyanate compound in the block polyisocyanate compound include aliphatic polyisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, lysine diisocyanate, and burette-type adducts of these polyisocyanates, isocyanurate rings. Adducts: isophorone diisocyanate, 4,4′-methylenebis (cyclohexyl isocyanate), methylcyclohexane-2,4- (or-2,6-) diisocyanate, 1,3- (or 1,4-) di (isocyanatomethyl) ) Alicyclic rings such as cyclohexane, 1,4-cyclohexane diisocyanate, 1,3-cyclopentane diisocyanate, 1,2-cyclohexane diisocyanate Diisocyanates and burette-type adducts, isocyanurate cycloadducts of these polyisocyanates; xylylene diisocyanate, metaxylylene diisocyanate, tetramethyl xylylene diisocyanate, tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 1, 5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4′-toluidine diisocyanate, 4,4′-diphenyl ether diisocyanate, (m- or p-) phenylene diisocyanate, 4,4′-biphenylene diisocyanate, 3,3 ′ -Dimethyl-4,4'-biphenylene diisocyanate, bis (4-isocyanatophenyl) sulfone, isopropylidenebis (4-phenylisocyanate), etc. Aromatic diisocyanate compounds and burette type adducts of these polyisocyanates, isocyanurate cycloadducts; triphenylmethane-4,4 ′, 4 ″ -triisocyanate, 1,3,5-triisocyanatobenzene, 2 , 4,6-triisocyanatotoluene, 4,4′-dimethyldiphenylmethane-2,2 ′, 5,5′-tetraisocyanate and the like, and polyisocyanates having at least three isocyanate groups in one molecule, and the like Polyisocyanate burette type adducts, isocyanurate cycloadducts; ethylene glycol, propylene glycol, 1,4-butylene glycol, dimethylolpropionic acid, polyalkylene glycol, trimethylolpropane, hexanetriol Urethanization adduct sulfonate groups obtained by reacting a polyisocyanate compound in a ratio to be excess and biuret type adducts of these polyisocyanate can include an isocyanurate ring adducts. These polyisocyanate compounds can be used alone or in combination of two or more.

The blocking agent is a compound that temporarily blocks a free isocyanate group by reacting with an isocyanate group of a polyisocyanate compound, and the block polyisocyanate compound is usually, for example, 100 ° C or higher, preferably 130 ° C or higher. When heated, the blocking agent is released and the free isocyanate group is regenerated, so that the blocked polyisocyanate compound can react with the hydroxyl group. Examples of such blocking agents include phenols such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and hydroxybenzoic acid methyl; ε-caprolactam, δ-valerolactam, lactams such as γ-butyrolactam, β-propiolactam; aliphatic alcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, lauryl alcohol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono Butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, pro Len glycol monomethyl ether, ether systems such as methoxymethanol; benzyl alcohol; glycolic acid; glycolic acid ester systems such as methyl glycolate, ethyl glycolate, and butyl glycolate; lactic acid; lactate esters such as methyl lactate, ethyl lactate, and butyl lactate System; alcohol system such as methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate; formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, cyclohexane oxime, etc. Active methyl such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, acetylacetone Mercaptans such as butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, ethylthiophenol; Acid amides such as acetic acid amide, stearic acid amide, benzamide; imides such as succinimide, phthalic acid imide, maleic acid imide; diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine Amines such as dimethyl, dibutylamine and butylphenylamine; imidazoles such as imidazole and 2-ethylimidazole; 3,5-dimethyl Pyrazoles such as razole; ureas such as urea, thiourea, ethylene urea, ethylene thiourea and diphenyl urea; carbamates such as phenyl N-phenylcarbamate; imines such as ethyleneimine and propyleneimine; sodium bisulfite And sulfites such as potassium bisulfite. These blocking agents can be used alone or in combination of two or more.

Blocked polyisocyanate compound imparted with water dispersibility In addition, by blocking the isocyanate group of the above polyisocyanate compound with a blocking agent containing hydroxymonocarboxylic acid, the hydroxymonocarboxylic acid is introduced into the blocked polyisocyanate compound, and hydroxymonocarboxylic acid A block polyisocyanate compound imparted with water dispersibility by a carboxyl group derived from a carboxylic acid can also be used as the crosslinking agent (a-3).

  As the blocking agent, the same ones as described above can be used, and examples of the hydroxy monocarboxylic acids include 2-hydroxyacetic acid, 3-hydroxypropanoic acid, 12-hydroxy-9-octadecanoic acid (ricinoleic acid). ), 3-hydroxy-2,2-dimethylpropanoic acid (hydroxypivalic acid), dimethylolpropionic acid (DMPA) and the like, among others, 3-hydroxy-2,2-dimethylpropanoic acid (hydroxypivalic acid) ) Is preferred.

  The reaction of the blocking agent containing a polyisocyanate compound and hydroxymonocarboxylic acid can be usually carried out in a solvent inert to the isocyanate group. Examples of the solvent include ketones such as acetone and methyl ethyl ketone, and ethyl acetate. And esters such as N-methylpyrrolidone (NMP).

  Moreover, when using a block polyisocyanate compound as a crosslinking agent, the catalyst for promoting urethanation reaction, such as an organotin compound, can be used.

  The base paint (A) is generally composed of 20 to 20 resins (a-1) based on the total solid content (total amount) of the resin (a-1), the resin (a-2) and the crosslinking agent (a-3). 80% by weight, in particular 30-70% by weight, the resin (a-2) in general 5-35% by weight, in particular 10-30% by weight, and the cross-linking agent (a-3) 15-45% by weight, in particular 20- It is preferable to comprise within the range of 40 mass%.

  The base coating material (A) can further contain polymer fine particles (a-4) from the viewpoint of improving the thickening effect and improving the anti-moisture resistance.

Polymer fine particles (a-4)
In the polymer fine particles (a-4), for example, a monomer (a-4-1) containing at least two unsaturated groups in the molecule and another unsaturated monomer (a-4-2) are allyl groups. Examples thereof include polymer fine particles obtained by emulsion polymerization in the presence of a contained reactive emulsifier. As such polymer fine particles, for example, those described in JP-A-3-66770 can be used. Can do.

Examples of the monomer (a-4-1) containing at least two unsaturated groups in the molecule include an unsaturated monocarboxylic acid ester of a polyhydric alcohol, an unsaturated alcohol ester of a polybasic acid, and at least two An aromatic compound substituted with an unsaturated group can be exemplified. Specifically, for example, ethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 1,4-butanediol diacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol dimethacrylate, pentaerythritol trimethacrylate, penta Erythritol tetramethacrylate, glycerol dimeta Relate, glycerol diacrylate, glycerol allyloxy dimethacrylate, 1,1,1-trishydroxymethylethane diacrylate, 1,1,1-trishydroxymethylethane triacrylate, 1,1,1-trishydroxymethylethanedi Methacrylate, 1,1,1-trishydroxymethylethane trimethacrylate, 1,1,1-trishydroxymethylpropane diacrylate, 1,1,1-trishydroxymethylpropane triacrylate, 1,1,1-trishydroxymethyl Propane dimethacrylate, 1,1,1-trishydroxymethylpropanetrimethacrylate, triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, diallyl terephthalate, diallyl Can be mentioned rate and divinylbenzene, these monomers can be used either alone or in combination of two or more.

  The other unsaturated monomer (a-4-2) is the remaining component constituting the fine particle polymer, and the carboxyl group-containing unsaturated monomer (M-) exemplified in the carboxyl group- and hydroxyl group-containing resin (a-1). 1) A hydroxyl group-containing unsaturated monomer (M-2) and other copolymerizable unsaturated monomers (M-3) can be used in the same manner. Nitrogen-containing alkyl (meth) acrylates such as dimethylaminoethyl (meth) acrylate; diene compounds such as butadiene and isoprene; vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane, γ-methacryloxy Alkoxysilyl group-containing monomers such as propyltrimethoxysilane and vinyltriacetoxysilane can also be used, and these monomers can be used alone or in combination of two or more.

  The proportion of the monomers (a-4-1) and (a-4-2) used in the copolymerization is not strictly limited and can be changed according to the physical properties desired for the polymer fine particles. Specifically, the monomer (a-4-1) is generally 1 to 60% by mass, preferably 1 to 50% by mass, based on the total amount of the monomers (a-4-1) and (a-4-2). %, More preferably 1 to 40% by weight, and the monomer (a-4-2) is generally in the range of 40 to 99% by weight, preferably 50 to 99% by weight, more preferably 60 to 99% by weight. Can do.

  The copolymerization of the monomers (a-4-1) and (a-4-2) can be carried out by emulsion polymerization known per se using a polymerization initiator in the presence of a reactive emulsifier containing an allyl group. .

  As the allyl group-containing reactive emulsifier, any anionic, cationic or nonionic reactive emulsifier can be used as long as it is an allyl group-containing reactive emulsifier. A contained reactive emulsifier can be preferably used.

  Examples of the anionic allyl group-containing reactive emulsifier include ammonium salts of sulfonic acid compounds having an allyl group. Specifically, for example, an anionic emulsifier having a polyoxyethylene alkyl ether sulfate ester salt as a basic structure and a radically polymerizable allyl group introduced as a part of the hydrophobic group can be used.

  As a commercial item of the said emulsifier, for example, Aqualon KH-10 (Daiichi Kogyo Seiyaku Co., Ltd., trade name), Latemul S-180A (Kao Co., trade name), SR-1025 (Asahi Denka Kogyo Co., Ltd., commercial product) Name).

  The amount of the reactive emulsifier used is usually 0.1 to 10% by mass, preferably 1 to 5% by mass, based on the total amount of the monomers (a-4-1) and (a-4-2). It is suitable.

  If necessary, anionic surfactants, nonionic surfactants, zwitterionic surfactants and the like other than the reactive emulsifiers can be used in combination as emulsifiers. Specifically, examples of the anionic surfactant include fatty acids, alkyl sulfate esters, alkylbenzene sulfonates, and alkyl phosphates. Nonionic surfactants include, for example, polyoxyethylene alkyl. Examples include ethers, polyoxyethylene alkyl allyl ethers, polyoxyethylene derivatives, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkyl amines, alkyl alkanol amides, and the like. Examples of the zwitterionic surfactant include alkylbedine.

  The emulsifier used in combination as necessary is usually 0.1 to 10% by weight, preferably 1 to 5% by weight, based on the total amount of monomers (a-4-1) and (a-4-2). It is suitable to use at a concentration within the range.

  Examples of the polymerization initiator include peroxides represented by ammonium persulfate, potassium persulfate, ammonium peroxide, and the like; these peroxides, and reducing agents such as sodium bisulfite, sodium thiosulfate, Rongalite, and ascorbic acid. And so-called redox initiators in combination with azo compounds such as 4,4′-azobis (4-cyanobutanoic acid). Of these, azo compounds, particularly water-soluble azoamide compounds, can be preferably used. Water-soluble azoamide compounds are known (see JP-A-61-218618 and JP-A-61-63643). As specific examples of commercially available products, the VA series (trade name, Wako Pure Chemical Industries, Ltd.) Manufactured).

  The polymerization initiator is usually 0.01 to 10% by mass, preferably 0.1 to 5% by mass, based on the total amount of the monomers (a-4-1) and (a-4-2). Can be used.

  Moreover, the density | concentration of all the unsaturated monomers in emulsion polymerization reaction is 0.1-50 mass% normally, Preferably it can be in the range of 0.5-30 mass%.

  The reaction temperature during the emulsion polymerization varies depending on the polymerization initiator used, but is usually 60 to 90 ° C., and the reaction time is usually 5 to 10 hours.

  The polymer fine particles (a-4) are generally hydroxyl groups within the range of 0 to 70 mgKOH / g, preferably 0 to 60 mgKOH / g, more preferably 0 to 50 mgKOH / g, from the viewpoint of the water resistance of the resulting coating film. Can have a valence. The polymer fine particles (a-4) generally have an acid value in the range of 0 to 90 mgKOH / g, preferably 0 to 70 mgKOH / g, more preferably 0 to 50 mgKOH / g, from the viewpoint of water dispersibility and the like. Can have. Furthermore, the polymer fine particles (a-4) can generally have a particle diameter in the range of 10 to 500 nm, preferably 20 to 250 nm, more preferably 30 to 150 nm.

In the present specification, the particle diameter can be measured using a COULTER N4 type submicron particle analyzer (trade name, manufactured by Nikkaki Co., Ltd.).

  The polymer fine particles (a-4) can be neutralized with a basic compound as necessary. As the neutralizing agent for the polymer fine particles (a-4), the basic substances mentioned for the carboxyl group- and hydroxyl group-containing resin (a-1) can be used in the same manner.

  The polymer fine particles (a-4) are generally 0 to 40% by mass, particularly 0 to 40% by mass, based on the total solid content of the resin (a-1), the resin (a-2) and the crosslinking agent (a-3). It is preferable to use within a range of 30% by mass, more particularly 0 to 20% by mass.

  A base coating material (A) can be prepared by mixing said resin (a-1), resin (a-2), and a crosslinking agent (a-3) with a solvent.

  The base paint (A) may be of any type, water-based or hydrophilic organic solvent type.

  In the present specification, the hydrophilic organic solvent means an organic solvent that dissolves 20 g or more with respect to 100 g of water at 20 ° C.

  Examples of the hydrophilic organic solvent include solvents that satisfy the above-mentioned solubility conditions such as ester, ether, alcohol, amide, and ketone. These hydrophilic organic solvents can be used alone or in combination of two or more. In particular, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, Diethylene glycol monobutyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, methyl alcohol, ethyl alcohol, allyl alcohol, n-propyl alcohol, isopropyl alcohol, tertiary butyl alcohol, ethylene glycol, 1,2-propylene group Call, 1,3-butylene glycol, 2,3-butylene glycol, hexylene glycol, hexanediol, dipropylene glycol, acetone, can be preferably used a hydrophilic organic solvent such as diacetone alcohol.

  The hydrophilic organic solvent type includes a mode in which a part of the hydrophilic organic solvent is replaced with water such as deionized water to form a mixed system of the hydrophilic organic solvent and water. In the mixed system of the hydrophilic organic solvent and water, it is suitable that the hydrophilic organic solvent is 50 to 100% by mass and the water is 0 to 50% by mass with respect to the total solvent in the base paint (A). .

  When the polymer fine particles (a-4) are contained in the base paint (A), the polymer fine particles (a-4) can be added in the form of an aqueous dispersion, but a hydrophilic organic solvent type base paint ( In the case of A), it can be added after being converted into a form dispersed in a hydrophilic organic solvent. The conversion from the aqueous dispersion of polymer fine particles (a-4) to the hydrophilic organic solvent dispersion includes, for example, xylene, butyl alcohol, butyl acetate, methyl ethyl ketone in the aqueous dispersion of polymer fine particles (a-4). A method of adding a solvent such as toluene, removing water by azeotropic distillation of water and those solvents, and dispersing the polymer fine particles (a-4) in a hydrophilic organic solvent; polymer fine particles (a-4) ) After the water is evaporated by a spray-drying method or simple drying and then re-dispersed in a hydrophilic organic solvent.

A pigment can be mix | blended with a base coating material (A). The pigment is not particularly limited, and for example, titanium dioxide, zinc white, carbon black, brown, phthalocyanine blue, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, isoindoline pigment, selenium pigment Inorganic and organic pigments such as perylene pigments; body pigments such as talc, clay, kaolin, barita, barium sulfate, barium carbonate, calcium carbonate, silica, alumina white; aluminum powder, mica powder, titanium oxide Bright pigments such as coated mica powder, mica-like iron oxide, silver-plated glass flakes, titanium-coated graphite, metal titanium flakes, and phthalocyanine flakes can be suitably used. The above pigments can be used alone or in combination of two or more.

  The blending amount of the pigment is generally 0 to 250% by mass, particularly 0.1% based on the total solid content of the resin (a-1), the resin (a-2) and the crosslinking agent (a-3). It is preferable to be within a range of ˜150 mass%.

  If necessary, the base coating material (A) further contains a curing catalyst, a dispersant, an anti-settling agent, an antifoaming agent, a thickening agent, an ultraviolet absorber, a light stabilizer, a surface conditioner, an antioxidant, and the like. Can be used.

  The non-volatile content concentration during the coating of the base paint (A) can usually be 20 to 65% by mass, but the base paint (A) has a reduced amount of organic solvent from the viewpoint of air pollution prevention and resource saving. For example, a high solid type that is generally adjusted in the range of 30 to 60% by mass, particularly 40 to 60% by mass is preferable.

  The single paint film of the base paint (A) is usually a colored opaque or colored transparent solid or metallic paint film. Here, the opaque coating means a coating having a light transmittance of less than 5% in the cured coating of 20 μm of the base coating coating alone, and the transparent coating refers to the transmission of light in the cured coating of 20 μm. It means a coating film with a rate of 5% or more.

The coated material to which the present method is applied is not particularly limited. For example, a cold-rolled steel plate, a galvanized steel plate, a zinc alloy-plated steel plate, a stainless steel plate, a tin-plated steel plate, etc., an aluminum plate, aluminum Metal substrates such as alloy plates; various plastic materials are preferred. Moreover, the vehicle body etc. of various vehicles, such as a motor vehicle, a two-wheeled vehicle, and a container formed from these, may be sufficient.

  The object to be coated may be a metal substrate or a metal surface of the vehicle body or the like subjected to surface treatment such as phosphate treatment, chromate treatment, or complex oxide treatment.

  In addition, these objects to be coated may have been previously subjected to undercoating (for example, cationic electrodeposition coating) and optionally further intermediate coating.

  In this method, first, the base paint (A) is applied to the article to be coated.

  The base paint (A) has a coating viscosity, for example, Ford Cup No. 4 at 20 ° C., adjusted to within a range of 13 to 60 seconds, preferably 15 to 40 seconds, using a diluting solvent, etc., for example, by air spray, airless spray, rotary atomization coating, etc. The film can be applied so that the film thickness based on the cured coating film is generally 5 to 25 μm, particularly 10 to 20 μm. Without heating and curing the coating film of this base paint (A), it is allowed to stand at room temperature for 1 to 20 minutes as necessary, and further at a temperature of about 60 to 80 ° C. for about 3 to 10 minutes as necessary. After the preliminary drying, an aqueous coloring paint (B) is applied to the uncured coating surface.

Water-based coloring paint (B)
The aqueous colored paint (B) is an aqueous liquid paint applied to the uncured coating surface of the base paint (A). Generally, the base resin (B-1), the cross-linking agent (B-2) and the color pigment (B -3) can be prepared by mixing and dispersing in an aqueous medium.

  Examples of the base resin (B-1) include an acrylic resin containing a carboxyl group and a hydroxyl group, and a polyester resin containing a carboxyl group and a hydroxyl group.

  The base resin (B-1) preferably has an acid value in the range of usually 10 to 150 mgKOH / g, particularly 30 to 100 mgKOH / g, from the viewpoint of water dispersibility and the like. Moreover, it is preferable that base resin (B-1) has a hydroxyl value in the range of normally 10-150 mgKOH / g, especially 30-100 mgKOH / g from viewpoints of curability. Furthermore, the base resin (B-1) is usually in the range of 3000 to 100000, particularly 5000 to 50000 in the acrylic resin, and usually in the range of 500 to 50000, particularly 3000 to 30000 in the polyester resin from the viewpoint of weather resistance and the like. Preferably having a number average molecular weight of

  As the base resin (B-1), the same resin as the carboxyl group- and hydroxyl group-containing resin (a-1) in the base paint (A) can be used. Moreover, as an acrylic resin, what is manufactured by emulsion polymerization in presence of dispersion stabilizer aqueous solution can also be used.

  In the case of the acrylic resin produced by the emulsion polymerization, those having a number average molecular weight in the range of usually 100,000 or more, particularly 200000 to 2000000 are preferable.

  Examples of the dispersion stabilizer used in the emulsion polymerization include nonionic surfactants and anionic surfactants, and aqueous resins such as acrylic resins having an acid value of about 10 to 150 mgKOH / g and a number average molecular weight of about 5000 to 30000. Can be preferably used.

  The emulsion polymerization can be carried out by a method known per se.

  Especially as base resin (B-1), since the acrylic emulsion manufactured by the multistage polymerization method using a carboxyl group-containing unsaturated monomer can obtain the water-colored coating material excellent in coating workability | operativity, it is preferable. That is, first, a polymerization reaction is carried out using a monomer mixture having a composition containing no or almost no carboxyl group-containing unsaturated monomer (usually 3% by mass or less in all monomers), and then containing a carboxyl group-containing unsaturated monomer ( Usually, the acrylic emulsion obtained by performing a polymerization reaction using a monomer mixing part having a composition of 5 to 30% by mass in all monomers has a viscous expression effect by neutralization with a basic substance, It is preferable because an aqueous colored paint excellent in coating workability such as sagging resistance can be obtained. As the basic substance used for neutralization, the basic substance exemplified for the resin (a-1) of the base paint (A) can be used. The amount used is preferably 0.1 to 1.5 equivalents, particularly preferably 0.3 to 1.2 equivalents, based on the carboxyl group of the acrylic emulsion produced by the multistage polymerization method. .

  As a crosslinking agent (B-2), at least 1 sort (s) chosen from the crosslinking agent which can react with the hydroxyl group illustrated by the crosslinking agent (a-3) of the said base coating material (A) can be used.

  The blending ratio of the base resin (B-1) and the crosslinking agent (B-2) in the water-based colored paint (B) is generally 50 to 90 mass for the base resin (B-1) based on the total amount of both components. %, In particular 65 to 80% by weight, and the crosslinking agent (B-2) is generally in the range of 10 to 50% by weight, in particular 20 to 35% by weight.

  The color pigment (B-3) is for coloring the coating film of the water-based coloring paint (B), and the coating film may be either colored transparent or colored opaque. As the color pigment (B-3), the color pigments exemplified for the base paint (A) can be used in the same manner. The color pigments (B-3) can be used alone or in combination of two or more.

  The blending amount of the color pigment (B-3) is generally 0.1 to 200% by mass, particularly 1 to 100% by mass, based on the total solid content of the base resin (B-1) and the crosslinking agent (B-2). % Is preferable.

  The water-based colored paint (B) can be prepared by mixing and dispersing the base resin (B-1), the crosslinking agent (B-2) and the color pigment (B-3) in water.

  Similarly to the base paint (A), an anti-settling agent, an extender pigment, and the like can be appropriately blended in the water-based colored paint (B) as necessary. Further, if necessary, a curing catalyst, a dispersant, an anti-settling agent, an antifoaming agent, a thickener, an ultraviolet absorber, a light stabilizer, a surface conditioner, an antioxidant and the like can be used as appropriate. .

  The non-volatile content concentration during application of the water-based colored paint (B) is usually preferably 15 to 65% by mass, and the single coating film can be an opaque or transparent solid or metallic coating film. Here, the opaque coating means a coating having a light transmittance of less than 5% in a 20 μm cured coating of a single aqueous colored coating, and the transparent coating refers to a light beam in the cured coating of 20 μm. It means a coating film having a transmittance of 5% or more.

  The water-based coloring paint (B) is allowed to stand at room temperature for 1 to 20 minutes, if necessary, and further subjected to preliminary drying at a temperature of about 60 ° C. to 80 ° C. for about 3 to 10 minutes as necessary. Is applied to the surface of the uncured base paint (A).

  The water-based colored paint (B) has a coating viscosity, for example, Ford Cup No. 4 at 20 ° C., usually 15 to 60 seconds, preferably adjusted to 20 to 50 seconds. For example, by air spray, airless spray, rotary atomization coating, etc., electrostatic application is performed as necessary, The coating can be applied so that the film thickness based on the cured coating is generally 5 to 40 μm, particularly 10 to 35 μm.

  In this method, the water-colored paint (B) is applied to the uncured surface of the base paint (A), and then the clear paint (C) is applied. If necessary, the clear paint (C) is applied. Prior to this, a two-layer coating film composed of the base paint (A) and the water-based colored paint (B) may be preliminarily dried at a temperature of about 50 to 100 ° C. By this preliminary drying, most of the volatile components such as the organic solvent and water in both coating films can be evaporated.

  Since the volatile components are volatilized by the preliminary drying and the coating film is dried and solidified, when the clear paint (C) is applied onto the coated surface, the solvent and low molecular resin components contained in the coating film Even if it permeates and diffuses into the two-layer coating film, it can suppress a decrease in viscosity of the two-layer coating film, can suppress reflow of the metallic pigment, etc. when using a metallic pigment, metal unevenness, etc. Can be prevented.

Clear paint (C)
As the clear paint (C), those usually used in automobile painting can be used, and examples thereof include an organic solvent-type or water-based clear paint mainly composed of a thermosetting resin composition. . Examples of the thermosetting resin composition used in the clear paint (C) include base resins such as acrylic resins, polyester resins, and urethane resins having a crosslinkable functional group such as a hydroxyl group, melamine resins, and (blocks). Examples thereof include a composition comprising a crosslinking agent such as a polyisocyanate compound; an acid / epoxy crosslinking resin composition comprising an acid group-containing resin and an epoxy group-containing resin as main components. As the clear paint, a water-based paint can be suitably used from the viewpoint of reducing the amount of solvent.

  As the clear paint (C), a clear paint (C-1) containing an acrylic resin having a hydroxyl value of 100 to 200 mg KOH / g and an acid value of 10 to 50 mg KOH / g and a crosslinking agent can be preferably used. When the clear paint (C-1) is used, interlayer adhesion between the paint film of the water-colored paint (B) and the paint film of the clear paint (D) described below can be improved.

  As the acrylic resin that can be used in the paint (C-1), the carboxyl group- and hydroxyl group-containing acrylic resins exemplified for the base paint (A) can be used in the same manner. In particular, from the viewpoint of interlayer adhesion, ring-opening polymerization of ε-caprolactone or the like to a monoester product such as hydroxybutyl acrylate, hydroxybutyl methacrylate, 2-hydroxyethyl (meth) acrylate, etc. as a hydroxyl group-containing unsaturated monomer A compound etc. can be used conveniently.

  The acrylic resin used in the paint (C-1) preferably has a number average molecular weight in the range of 2000 to 20000, particularly 3000 to 10,000 from the viewpoint of smoothness of the coating surface.

  As the crosslinking agent for the paint (C-1), a crosslinking agent (a-3) capable of reacting with the hydroxyl group of the base paint (A) can be used in the same manner.

  In the clear paint (C-1), the blending ratio of the acrylic resin and the crosslinking agent is generally 50 to 90% by mass, particularly 60 to 80%, based on the total solid content (total amount) of the two components. The mass% and the crosslinking agent are generally preferably in the range of 50 to 10 mass%, in particular 40 to 20 mass%.

  If necessary, the clear paint (C) can be blended with color pigments, extender pigments and the like to such an extent that transparency is not impaired. As a coloring pigment and an extender, what was illustrated by the base coating material (A) can be used, for example. The color pigment and extender can be used alone or in combination of two or more.

  For the clear paint (C), if necessary, a curing catalyst, an antifoaming agent, a thickener, an ultraviolet absorber, a light stabilizer, an antioxidant, a surface conditioner, a dispersing agent, Additives such as anti-settling agents can be added as appropriate.

  Moreover, the non-volatile content concentration at the time of the application of the clear paint (C) is usually preferably in the range of 30 to 70% by mass.

  The clear paint (C) is applied on the two-layer coating film composed of the base paint (A) and the water-colored paint (B). The clear paint (C) is coated with a solvent and / or water at an appropriate coating viscosity (for example, a viscosity of 20 to 50 seconds, preferably 25 to 40 seconds at 20 ° C. using Ford Cup No. 4). After the adjustment, it can be applied by a method known per se, for example, airless spray, air spray, rotary atomization coating, or the like. During painting, electrostatic application can also be performed. The coating film thickness is preferably in the range of usually 15 to 35 μm, particularly 20 to 30 μm, based on the cured coating film.

After applying the clear paint (C), the base paint (A), the water-colored paint (B) and the clear paint (
A three-layer coating film is formed by simultaneously heat-curing the three-layer coating film comprising C).

  In order to promote evaporation of volatile components in the coating film of the clear paint (C) after the application of the clear paint (C) and before heat curing, the temperature is about 50 to 100 ° C. as necessary. The three-layer coating film can be pre-dried for about 1 to 10 minutes. By this preliminary drying, most of the volatile components such as the organic solvent and water in the three-layer coating film can be evaporated.

  The heat curing of the three-layer coating film can be carried out at a temperature of usually 100 to 180 ° C., preferably 120 to 170 ° C. for 5 to 60 minutes, preferably 10 to 40 minutes.

  A clear paint (D) is applied on the three-layer coating film after heat curing.

Clear paint (D)
The clear paint (D) contains a hydroxyl group having a hydroxyl value of 100 to 200 mg KOH / g and a number average molecular weight of 5,000 to 10,000 obtained by copolymerizing a monomer mixture containing an aromatic vinyl monomer and a monomer having a cyclohexyl ring. The hydroxyl value obtained by esterifying an acrylic resin (d-1), a trifunctional HMDI isocyanurate compound (d-2), and a diol having 3 to 6 carbon atoms and a dicarboxylic acid having a cyclohexyl ring is 250 to 350 mgKOH. / G and a two-component clear paint comprising a polyester polyol (d-3) having a number average molecular weight of 350 to 550.

Hydroxyl group-containing acrylic resin (d-1)
In the clear paint (D), the hydroxyl group-containing acrylic resin (d-1) used as the base resin has a hydroxyl value obtained by copolymerizing a monomer mixture containing an aromatic vinyl monomer and a monomer having a cyclohexyl ring. It is a hydroxyl group-containing acrylic resin having a number average molecular weight of 5,000 to 10,000 and a 100 to 200 mg KOH / g.

  The hydroxyl group-containing acrylic resin (d-1) includes, for example, a hydroxyl group-containing monomer (d-1-1), an aromatic vinyl monomer, a monomer having a cyclohexyl ring (d-1-2), and other unsaturated monomers (d 1-3) can be produced by copolymerization by a conventional method.

  The hydroxyl group-containing monomer (d-1-1) is a compound having one hydroxyl group and one polymerizable unsaturated bond in one molecule. Examples of the monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and 3-hydroxybutyl (meth). Monoesterified product of (meth) acrylic acid such as acrylate, 4-hydroxybutyl (meth) acrylate and dihydric alcohol having 2 to 10 carbon atoms; adduct of (meth) acrylic acid and epoxy group-containing compound (for example, “Cardura E10”, manufactured by Yuka Shell Epoxy Co., Ltd., trade name); and compounds obtained by ring-opening polymerization of ε-caprolactone. As the compound obtained by ring-opening polymerization of ε-caprolactone, a commercially available product can be used. Examples of the commercially available product include “Placcel FA-1”, “Placcel FA-2”, “Placcel FA-3”, “ “Plaxel FA-4”, “Plaxel FA-5”, “Plaxel FM-1”, “Plaxel FM-2”, “Plaxel FM-3”, “Plaxel FM-4”, “Plaxel FM-5” (above, Any of them may include Daicel Chemical Co., Ltd., trade name). These hydroxyl group-containing monomers can be used alone or in combination of two or more, and the amount used thereof is such that the hydroxyl value of the hydroxyl group-containing acrylic resin (d-1) is about 100 to 200 mgKOH / g. It can be.

The aromatic vinyl monomer and the monomer (d-1-2) having a cyclohexyl ring are respectively a compound having one aromatic ring and one vinyl group in one molecule, and a cyclohexyl ring and a polymerizable non-polymerizable in one molecule. The aromatic vinyl monomer can include, for example, styrene, α-methylstyrene, vinyltoluene and the like, and the monomer having a cyclohexyl ring includes, for example, Examples thereof include cyclohexyl (meth) acrylate.

  In the hydroxyl group-containing acrylic resin (d-1), the aromatic vinyl monomer and the monomer (d-1-2) having a cyclohexyl ring are intended to improve both the hardness and weather resistance of the crosslinked coating film. An aromatic vinyl monomer and a monomer having a cyclohexyl ring are used in combination, and it is particularly preferable to use styrene and cyclohexyl methacrylate in combination.

  The amount of the aromatic vinyl monomer and the monomer having a cyclohexyl ring (d-1-2) is generally 5% based on the total amount of monomers constituting the hydroxyl group-containing acrylic resin (d-1). The monomers having -25% by weight, in particular 10-20% by weight, and cyclohexyl rings are generally preferably in the range of 5-25% by weight, in particular 10-20% by weight.

  The other unsaturated monomer (d-1-3) is present in one molecule other than the hydroxyl group-containing monomer (d-1-1), the aromatic vinyl monomer, and the monomer (d-1-2) having a cyclohexyl ring. A compound having one polymerizable unsaturated bond, and specific examples thereof are as follows.

  (1) Acid group-containing monomer: a compound having one or more acid groups and one polymerizable unsaturated bond in one molecule, such as (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid And carboxyl group-containing monomers such as maleic anhydride; sulfonic acid group-containing monomers such as vinyl sulfonic acid and sulfoethyl (meth) acrylate; 2- (meth) acryloyloxyethyl acid phosphate, 2- (meth) acryloyloxypropyl acid phosphate, Examples thereof include acidic phosphoric acid ester monomers such as 2- (meth) acryloyloxy-3-chloropropyl acid phosphate and 2-methacryloyloxyethylphenyl phosphoric acid.

  (2) Monoesterified product of acrylic acid or methacrylic acid and a monohydric alcohol having 1 to 20 carbon atoms: For example, methyl (meth) acrylate, ethyl acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, lauryl (meth) acrylate, isobornyl (meth) acrylate, Tridecyl (meth) acrylate, stearyl (meth) acrylate and the like.

  (3) Glycidyl group-containing vinyl monomer: A compound having one glycidyl group and one polymerizable unsaturated bond in one molecule, such as glycidyl acrylate and glycidyl methacrylate.

  (4) Polymerizable unsaturated bond-containing amide compound: For example, acrylic acid amide, methacrylic acid amide, dimethylacrylamide, N, N-dimethylpropylacrylamide, N-butoxymethylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide , Diacetone acrylamide and the like.

(5) Other vinyl compounds: For example, vinyl acetate, vinyl propionate, vinyl chloride, versatic acid vinyl ester and the like. Examples of the versatic acid vinyl ester include “Veoba 9” and “Veoba 10” (trade names, manufactured by Japan Epoxy Resin Co., Ltd.), which are commercially available products.

  (6) Polymerizable unsaturated bond-containing nitrile compounds: for example, acrylonitrile, methacrylonitrile and the like.

  These monomers can be used alone or in combination of two or more.

  The hydroxyl group-containing acrylic resin (d-1) can generally have a hydroxyl value in the range of 100 to 200 mgKOH / g, preferably 120 to 180 mgKOH / g. If the hydroxyl value of the hydroxyl group-containing acrylic resin (d-1) is less than 100 mgKOH / g, the curability of the composition may be insufficient. On the other hand, if it exceeds 200 mgKOH / g, the water resistance of the coating film decreases. There is a case.

  The hydroxyl group-containing acrylic resin (d-1) can generally have a number average molecular weight in the range of 5000 to 10000, preferably 6000 to 9000. When the number average molecular weight of the hydroxyl group-containing acrylic resin (d-1) is less than 5,000, the coating performance such as acid resistance may be deteriorated, and when it exceeds 10,000, the smoothness of the coating surface may be deteriorated. is there.

  The hydroxyl group-containing acrylic resin (d-1) also preferably has a glass transition temperature generally in the range of about -30 ° C to about 30 ° C, particularly about -20 to about 20 ° C. When the glass transition temperature of the hydroxyl group-containing acrylic resin (d-1) is less than −30 ° C., the coating film hardness may be insufficient, and when it exceeds 30 ° C., the coating surface smoothness of the coating film is lowered. There is a case.

  In producing the hydroxyl group-containing acrylic resin (d-1), a hydroxyl group-containing monomer (d-1-1), an aromatic vinyl monomer, a monomer having a cyclohexyl ring (d-1-2), and other unsaturated monomers ( The use ratio of d-1-3) is generally 15 to 55% by mass, preferably 20 to 50% by mass of the hydroxyl group-containing monomer (d-1-1), based on the total amount of all monomers, and aromatic. The vinyl monomer and the monomer (d-1-2) having a cyclohexyl ring are generally 10 to 40% by mass, preferably 15 to 35% by mass, and the other unsaturated monomer (d-1-3) is generally 10 to 10% by mass. It can be in the range of 75% by weight, preferably 20-60% by weight.

  The copolymerization of a hydroxyl group-containing monomer (d-1-1), an aromatic vinyl monomer, a monomer having a cyclohexyl ring (d-1-2), and other unsaturated monomers (d-1-3) is known per se. These methods, for example, a solution polymerization method, an emulsion polymerization method, a suspension polymerization method and the like can be performed, and among these, a solution polymerization method performed in the presence of a polymerization initiator in an organic solvent is preferable.

Examples of the organic solvent that can be used in the solution polymerization method include aromatic solvents such as toluene, xylene, and Swazol 1000 (trade name, high-boiling petroleum solvent) manufactured by Cosmo Oil; ethyl acetate, 3-methoxybutyl Ester solvents such as acetate, ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone; propyl propionate, butyl propionate, ethoxy ethyl propionate, etc. Can be mentioned. These organic solvents can be used alone or in combination of two or more, but the hydroxyl group-containing acrylic resin used in the present paint has a relatively high hydroxyl value, so from the viewpoint of the solubility of the resin, It is preferable to use a high boiling ester solvent or ketone solvent. In addition, aromatic solvents having higher boiling points can be suitably used in combination.

  Examples of the polymerization initiator that can be used in the copolymerization include 2,2′-azobisisobutyronitrile, benzoyl peroxide, di-t-butyl peroxide, di-t-amyl peroxide, and t-butyl. Examples thereof include radical polymerization initiators known per se such as peroctoate and 2,2′-azobis (2-methylbutyronitrile).

Trifunctional HMDI isocyanurate compound (d-2)
In the clear paint (D), the trifunctional HMDI isocyanurate compound (d-2) used as a crosslinking agent has 3 isocyanate groups in one molecule having an isocyanurate ring obtained by trimerizing hexamethylene diisocyanate. This is a compound having one (ie, trifunctional) compound.

  The trifunctional HMDI isocyanurate compound is, for example, isocyanurated (trimerized) by a method known per se, for example, hexamethylene diisocyanate at a temperature of about 60 ° C. in the presence of a catalyst such as a quaternary ammonium salt. ).

  The trifunctional HMDI isocyanurate compound is polyfunctional and has a cyclic isocyanurate ring portion and a linear hexamethylene chain portion in the molecular structure, thereby reacting with the hydroxyl group-containing acrylic resin (d-1). Thus, a crosslinked coating film having a high-density network structure can be formed, and elasticity and flexibility can be imparted to the network structure in a well-balanced manner, which is extremely suitable as a crosslinking agent for the clear paint (D). .

  As the trifunctional HMDI isocyanurate compound, a commercially available product can be used. Specifically, for example, Sumidur N-3300 (trade name, manufactured by Sumika Bayer Urethane Co., Ltd.), Duranate TPA-100 (trade name, Asahi Kasei) And Duranate THA-100 (trade name, manufactured by Asahi Kasei Co., Ltd.).

Polyester polyol (d-3)
The polyester polyol (d-3) is obtained by esterifying a diol having 3 to 6 carbon atoms with a dicarboxylic acid having a cyclohexyl ring, and has a hydroxyl value of 250 to 350 mgKOH / g and a number average molecular weight of 350 to 550. The polyester polyol.

  The polyester polyol can be produced by an esterification reaction of a diol having 3 to 6 carbon atoms and a dicarboxylic acid having a cyclohexyl ring by a conventional method.

  The diol having 3 to 6 carbon atoms is a compound having 3 to 6 carbon atoms having two hydroxyl groups in one molecule. For example, 1,3-propanediol, 1,4-butanediol, 1,5-pentane Diols such as diol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanediol, 3-methyl-1,5-pentanediol; 2,2-dimethylolpropionic acid, 2,2-dimethylolbutane Examples thereof include hydroxycarboxylic acids such as acids. Of the diols, 1,3-propanediol is particularly preferable. These can be used alone or in combination of two or more.

  A dicarboxylic acid having a cyclohexyl ring is a compound having two carboxyl groups and at least one cyclohexyl ring in one molecule. For example, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1, Examples include 2-cyclohexanedicarboxylic acid. Of these dicarboxylic acids, 1,4-cyclohexanedicarboxylic acid is particularly preferable. These can be used alone or in combination of two or more.

  The polyester polyol can generally have a hydroxyl value in the range of 250 to 350 mg KOH / g, preferably 270 to 330 mg KOH / g. When the hydroxyl value of the polyester polyol is less than 250 mgKOH / g, the scratch resistance may be insufficient, and when it exceeds 350 mgKOH / g, the water resistance of the coating film may be lowered.

  The polyester polyol can generally have a number average molecular weight in the range of 350 to 550, preferably 400 to 500. When the number average molecular weight of the polyester polyol is less than 350, the coating performance such as acid resistance may be lowered, and when it exceeds 550, the coated surface smoothness of the coating may be lowered.

  The proportion of both of these in the case of esterification reaction of a diol having 3 to 6 carbon atoms and a dicarboxylic acid having a cyclohexyl ring is not particularly limited as long as the above hydroxyl value and number average molecular weight can be achieved. The dicarboxylic acid having a cyclohexyl ring can be used in the range of usually 0.5 to 0.7 mol, preferably 0.53 to 0.67 mol, with respect to 1 mol of the diol of several 3 to 6.

  In the clear paint (D), the hydroxyl group-containing acrylic resin (d-1), the polyester polyol (d-3), and the polyester polyol (d-3) contain a hydroxyl group from the viewpoint of the curability and scratch resistance of the coating film. The equivalent ratio (NCO / OH) of the hydroxyl groups of the acrylic resin (d-1) and the polyester polyol (d-3) and the isocyanate group of the trifunctional HMDI isocyanurate compound (d-2) is preferably 0.5 to 2.0. More preferably, it can be used at such a ratio that it falls within the range of 0.7 to 1.4.

  The mixing ratio of the hydroxyl group-containing acrylic resin (d-1), trifunctional HMDI isocyanurate compound (d-2) and polyester polyol (d-3) in the clear coating (D) is 100 parts by mass in total of the solid content of these three components. As a non-volatile content, the hydroxyl group-containing resin (d-1) is generally 30 to 75% by mass, preferably 40 to 65% by mass, and the trifunctional HMDI isocyanurate compound (d-2) is generally 20 to 60% by mass. The polyester polyol (d-3) is generally in the range of 3 to 30% by weight, preferably 5 to 25% by weight, more preferably 10 to 20% by weight. Yes.

  The clear paint (D) usually contains an organic solvent in addition to the three components of the hydroxyl group-containing acrylic resin (d-1), the trifunctional HMDI isocyanurate compound (d-2) and the polyester polyol (d-3). In addition, if necessary, other curing catalysts, leveling agents, ultraviolet absorbers, light stabilizers, plasticizers, and the like can be used.

  Examples of the curing catalyst include tin octylate, dibutyltin di (2-ethylhexanoate), dioctyltin di (2-ethylhexanoate), dioctyltin diacetate, dibutyltin dilaurate, dibutyltin oxide, and dioctyl. Examples thereof include organometallic catalysts such as tin oxide and lead 2-ethylhexanoate, and tertiary amines.

  These compounds described above as the curing catalyst can be used alone or in combination of two or more. Although the usage-amount of a curing catalyst changes with kinds etc., it is 0-5 mass normally with respect to 100 mass parts of total solid content of three components of (d-1), (d-2), and (d-3). Parts, preferably 0.1-4 parts by mass.

As the UV absorber, conventionally known UV absorbers can be used, and examples thereof include UV absorbers such as benzotriazole absorbers, triazine absorbers, salicylic acid derivative absorbers, and benzophenone absorbers. The content of these ultraviolet absorbers in the clear paint (D) is usually 0 to 10 parts by mass, particularly 0.2 to 10 parts by mass with respect to 100 parts by mass of the total resin solid content in terms of weather resistance and yellowing resistance. It is preferably 5 parts by mass, more preferably in the range of 0.3 to 2 parts by mass.

  A conventionally well-known thing can be used as said light stabilizer, For example, a hindered amine light stabilizer can be mentioned. The content of the light stabilizer in the clear paint (D) is usually 0 to 10 parts by mass, particularly 0.2 to 5 parts per 100 parts by mass of the total amount of resin solids in terms of weather resistance and yellowing resistance. It is preferable to be in the range of parts by mass, more particularly 0.3-2 parts by mass.

  The clear paint (D) is stored in the hydroxyl group-containing acrylic resin (d-1) and the polyester polyol (d-3) because the hydroxyl group of the trifunctional HMDI isocyanurate compound (d-2) reacts at room temperature. From the viewpoint of stability, it is in the form of a two-component paint in which the hydroxyl group-containing acrylic resin (d-1) and polyester polyol (d-3) and the trifunctional HMDI isocyanurate compound (d-2) are separated, immediately before use. It is desirable to use both in combination.

  The coating method of the clear paint (D) is not particularly limited, but the wet coating film can be formed by methods such as air spray coating, airless spray coating, rotary atomization coating, curtain coat coating, and the like. In these coating methods, electrostatic application may be performed as necessary. Of these, air spray coating and rotary atomization coating are particularly preferred. The coating amount of the clear paint (D) is preferably an amount that is usually about 20 to 50 μm, particularly about 25 to 40 μm, as a cured film thickness.

  When the clear paint (D) is applied by air spray painting, airless spray paint or rotary atomization paint, the viscosity of the clear paint (D) is adjusted to a viscosity range suitable for the paint, usually Ford Cup #No. In a 4-viscosity meter, it is preferable to adjust appropriately using a solvent such as an organic solvent at 20 ° C. so that the viscosity is usually about 15 to 60 seconds, particularly about 20 to 45 seconds.

  Curing of the clear paint (D) is performed by heating, and the heating temperature is usually in the range of 60 to 180 ° C, preferably 90 to 150 ° C. The heating time is not particularly limited, but is usually preferably about 15 to 30 minutes.

  In this method, heating and preliminary drying performed as necessary are performed by using a known heating means, specifically, a drying furnace such as a hot air furnace, an electric furnace, or an infrared induction heating furnace. It can be carried out.

  According to the multilayer coating film forming method of the present invention described above, a multilayer coating film excellent in any of scratch resistance, acid resistance, stain resistance and finished appearance can be formed, and the amount of solvent Since reduction and process shortening are also possible, it can be particularly suitably used as a method for forming a multilayer coating film applied to the intermediate coating and top coating processes in automobile painting.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited only to a following example. In the following, “part” and “%” are both based on mass, and the film thickness of the coating film is based on the cured coating film.

Production of carboxyl group- and hydroxyl group-containing acrylic resin (a-1) Production Example 1
Into a four-necked flask equipped with a stirrer, a thermometer, a cooling tube and a nitrogen gas inlet, 37.5 parts of isopropanol was charged, and the temperature was raised to 85 ° C. under nitrogen gas flow. After reaching 85 ° C., the nitrogen gas flow was stopped, and a monomer mixture composed of a monomer and a polymerization initiator (styrene 25 parts, n-butyl acrylate 46 parts, 4-hydroxybutyl acrylate 10 parts, Plaxel FM-3 12.5 Parts, 6.5 parts of acrylic acid and 2 parts of 2,2-azobis (2,4-dimethylvaleronitrile) were added dropwise over 3 hours (the initial stage of addition was weakly refluxed, but for a while after starting the monomer mixture addition) Then it will not be in a reflux state). After aging for 2 hours while ventilating nitrogen gas at 85 ° C., the mixture was cooled to 60 ° C. and diluted with 29 parts of methoxypropanol, whereby each carboxyl group and hydroxyl group-containing acrylic resin (a -1) A solution was obtained. The obtained resin (a-1) had a number average molecular weight of 10,000, a hydroxyl value of 53.8 mgKOH / g, and an acid value of 50 mgKOH / g.

  “Plexel FM-3” is a trade name (manufactured by Daicel Chemical Industries), and is ε-caprolactone-modified hydroxyethyl methacrylate (modified at a ratio of 3 mol of ε-caprolactone to 1 mol of hydroxyethyl methacrylate). is there.

Production of tertiary amino group-containing resin (a-2) Production Example 2
In a four-necked flask equipped with a stirrer, a thermometer, a cooling pipe and a nitrogen gas inlet, 20 parts of ethylene glycol monobutyl ether was charged and heated to 95 ° C. under nitrogen gas flow. After reaching 95 ° C., the nitrogen gas flow was stopped, and a monomer mixture composed of a monomer, a solvent and a polymerization initiator (10 parts of styrene, 10 parts of n-butyl acrylate, 40 parts of methyl methacrylate, 2-hydroxyethyl acrylate) 10 parts, 10 parts of dimethylaminoethyl methacrylate, 40 parts of MPEG2000MA (trade name), 45 parts of ethylene glycol monobutyl ether, 1 part of α, α'-azobisisobutylnitrile) were added dropwise over 3 hours. After aging for 2 hours while ventilating nitrogen gas at 95 ° C., the mixture was cooled to 60 ° C. and diluted with 15 parts of ethylene glycol monobutyl ether to obtain a tertiary amino group-containing resin (a-2 having a solid content of 50% by mass). ) A solution was obtained. The obtained resin (a-2) had a number average molecular weight of 6,500, a hydroxyl value of 48.4 mgKOH / g, and an amine value of 35.5 mgKOH / g.

  MPEG2000MA (trade name) is methoxypolyethylene glycol 2000 methacrylate, a monomer manufactured by Degussa Japan. The active ingredient concentration of MPEG2000MA is 50%.

Production of polymer fine particles (a-4) Production Example 3
A four-necked flask equipped with a stirrer, a thermometer, a condenser tube and a mantle heater was added to 355 parts of deionized water and Latemul S-120A (sulfosuccinic acid-based anionic reactive emulsifier, manufactured by Kao Corporation, solid content 50 %) 4 parts were charged and the temperature was raised to 90 ° C. with stirring. VA-086 (water-soluble azoamide polymerization initiator, 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) -propionamide], manufactured by Wako Pure Chemical Industries, Ltd., trade name) 20% of an aqueous solution in which 25 parts were dissolved in 50 parts of deionized water was added. After 15 minutes, 5% of the monomer mixture (a mixture of 48 parts styrene, 22 parts methyl methacrylate, 22 parts n-butyl acrylate and 8 parts 1,6-hexanediol diacrylate) was added. Then, after stirring for 30 minutes, dropping of the remaining monomer mixture and the remaining aqueous polymerization initiator solution was started. The monomer mixture was dropped for 3 hours and the aqueous polymerization initiator solution was dropped for 3.5 hours, and the polymerization temperature was maintained at 90 ° C. during that time. After completion of the dropwise addition of the polymerization initiator aqueous solution, aging at 90 ° C. for 30 minutes, cooling to room temperature, and filtering with a 200 mesh nylon cloth, a polymer fine particle (a-4) aqueous dispersion having a solid content of 20% is obtained. Obtained.

  Further, the obtained polymer fine particle (a-4) aqueous dispersion was dried at 60 ° C. on a stainless steel vat in an electric hot air drier to remove water to obtain a solid, and then heated to 60 ° C. The dispersion was again dispersed in warm ethylene glycol monomethyl ether to obtain a polymer fine particle (a-4) dispersion having a solid content of 20%.

Production of acrylic resin (a) aqueous dispersion for water-based colored paint (B) Production Example 4
As a resin dispersion used for the water-based colored paint (B), an acrylic resin (A) aqueous dispersion was prepared as follows.

  A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and dropping device was charged with 145 parts of deionized water and 1.2 parts of Newcol 562SF (Note 1), stirred and mixed in a nitrogen stream, and heated to 80 ° C. The temperature rose. Next, 5% of the total amount of the following monomer emulsion (1) and 5.2 parts of a 3% ammonium persulfate aqueous solution were introduced into the reaction vessel and maintained at 80 ° C. for 20 minutes.

  Then, the remaining monomer emulsion (1) was dripped in reaction container over 3 hours, and it age | cure | ripened for 30 minutes after completion | finish of dripping. Subsequently, the following monomer emulsion (2) was added dropwise over 1.5 hours, and after aging for 2 hours, the mixture was gradually aged for 2 hours, and then gradually added 89 parts of a 1.5% N, N-dimethylethanolamine aqueous solution to 30 ° C. It cooled and discharged | emitted, filtering with a 100 mesh nylon cloth, and obtained acrylic resin (ii) water dispersion liquid of solid content 25%. The obtained acrylic resin (I) had a hydroxyl value of 22 mgKOH / g, an acid value of 30 mgKOH / g, and an average particle size of 100 nm.

(Note 1) Newcol 562SF; manufactured by Nippon Emulsifier Co., Ltd., trade name, ammonium polyoxyethylene alkylbenzenesulfonate, active ingredient 60%.
Monomer emulsion (1): 94.3 parts of deionized water, 17 parts of methyl methacrylate, 80 parts of n-butyl acrylate, 3 parts of allyl methacrylate and 1.2 parts of Newcol 562SF were mixed and stirred to obtain a monomer emulsion (1). It was.
Monomer emulsion (2): 37.3 parts of deionized water, 15.4 parts of methyl methacrylate, 2.9 parts of n-butyl acrylate, 5.9 parts of hydroxyethyl acrylate, 5.1 parts of methacrylic acid, Newcol 562SF 0.5 And 1.7 parts of a 3% aqueous solution of ammonium persulfate were mixed and stirred to obtain a monomer emulsion (2).

Production of acrylic resin (b) for clear paint (C) Production example 5
A four-necked flask equipped with a stirrer, thermometer, cooling pipe and nitrogen gas inlet was charged with 50 parts of Swazol 1000 (petroleum solvent, manufactured by Maruzen Petrochemical Co., Ltd.) and heated to 95 ° C. under nitrogen gas flow. did. After reaching 95 ° C., the nitrogen gas flow was stopped, and a monomer mixture composed of a monomer, a solvent and a polymerization initiator (styrene 50 parts, lauryl methacrylate 9 parts, 4-hydroxybutyl acrylate 25.5 parts, Plaxel FA -2 12.5 parts, acrylic acid 3 parts, swazol 1000 15 parts, n-butyl alcohol 10 parts and α, α'-azobisisobutylnitrile 4 parts) were added dropwise over 3 hours. After aging for 2 hours while ventilating nitrogen gas at 95 ° C., the mixture was cooled to 60 ° C. and diluted with 10 parts of Swazol 1000 to obtain an acrylic resin (B) solution having a solid content of 55% by mass. The obtained acrylic resin (b) had a number average molecular weight of 5000, a hydroxyl value of 120 mgKOH / g, and an acid value of 24 mgKOH / g.

“Placcel FA-2” is a trade name (manufactured by Daicel Chemical Industries), which is ε-caprolactone-modified hydroxyethyl acrylate (modified at a ratio of 2 mol of ε-caprolactone to 1 mol of hydroxyethyl acrylate). is there.

Production examples of hydroxyl group-containing acrylic resin (d-1) Production Examples 6 to 17
In a four-necked flask equipped with a stirrer, a thermometer, a condenser tube and a nitrogen gas inlet, 31 parts of ethoxyethyl propionate was charged, and the temperature was raised to 155 ° C. under nitrogen gas flow. After reaching 155 ° C., the flow of nitrogen gas was stopped, and a dropping monomer mixture composed of a monomer and a polymerization initiator shown in Table 1 below was dropped over 4 hours. After aging for 2 hours while ventilating nitrogen gas at 155 ° C., the mixture was cooled to 100 ° C. and diluted with 32.5 parts of butyl acetate to obtain a hydroxyl group-containing acrylic resin having a solid content of 60%. The solid content concentration (%) and the resin property value of each hydroxyl group-containing acrylic resin obtained are shown in Table 1 below.

  In addition, the glass transition temperature (degreeC) in Table 1 was computed by the following formula.

1 / Tg (K) = (W1 / T1) + (W2 / T2) +
Tg (° C.) = Tg (K) -273
In each formula, W1, W2,... Are the mass fractions of the monomers used for copolymerization, and T1, T2,... Are the Tg (K) of the homopolymer of each monomer. T1, T2,... Are values according to Polymer Handbook (Second Edition, edited by J. Brandup, E. H. Immergut).

  In addition, Production Examples 12 to 17 are for comparative examples.

Production example of polyester polyol (d-3) Production examples 18 to 23
A four-necked flask equipped with a heating device, a stirrer, a thermometer, a reflux condenser, and a water separator was charged with a dicarboxylic acid and a diol having a molar ratio shown in Table 2 below, from 160 ° C to 230 ° C over 3 hours. After raising the temperature, the produced condensed water was kept at 230 ° C. while being distilled off by a water separator, and the reaction was continued until the acid value became 5 mgKOH / g or less. The resin property values of the obtained polyester polyol (d-3) are shown in Table 2 below. Production Examples 22 and 23 are for comparative examples.

Production of base paint (A) Production Example 24
33.3 parts of the acrylic resin (a-1) solution obtained in Production Example 1, 1 part of carbon MA-100 (carbon black, manufactured by Mitsubishi Chemical Co., Ltd., trade name), JR-806 (titanium white, manufactured by Teika Co., Ltd., product) Name) 40 parts, BARIACE B-32 (barium sulfate, manufactured by Sakai Chemical Industry Co., Ltd., trade name) 25 parts, N, N-dimethylethanolamine 1.6 parts and ethylene glycol monobutyl ether 24.1 parts Then, pigment dispersion paste 1 was obtained by dispersing for 30 minutes with a paint shaker.

Production Examples 25-27
A solution of the acrylic resin (a-1) obtained in Production Example 1, a solution of the tertiary amino group-containing resin (a-2) obtained in Production Example 2, the pigment dispersion paste 1 obtained in Production Example 24, Cymel 325 (Mitsui Cytec Co., Ltd., methylated melamine resin, solid content 80%, trade name), polymer fine particles (a-4) dispersion obtained in Production Example 3 and N, N-dimethylethanolamine are shown in the table below. The mixture shown in FIG. 3 was mixed and stirred, and ethylene glycol monomethyl ether was further added. The base coating materials (A-1) to (A-3) were obtained by adjusting the viscosity to 4 for 30 seconds. In addition, in each base coating material, the neutralization equivalent by N, N- dimethylethanolamine with respect to the carboxyl group of acrylic resin (a-1) is all 0.5.

  In addition, Production Example 27 is a paint for a comparative example.

Production of water-based colored paint (B) Production Example 28
While stirring to 37.5 parts of Cymel 325, 50 parts of SETAL 6306 (water-soluble polyester resin, manufactured by Akzo, trade name, solid content 60%) and the acrylic resin (A) aqueous dispersion 160 obtained in Production Example 4 were used. Parts were added in order. Thereafter, 4 parts of carbon black was added with mixing and dispersed, and N, N-dimethylethanolamine and deionized water were added to adjust the pH to 8.0, Ford Cup No. The viscosity was 30 seconds at 20 ° C. as measured by 4 to obtain an aqueous colored paint (B-1).

Production of clear paint (C) Production example 29
136 parts (solid part 75 parts) of the acrylic resin (b) solution obtained in Production Example 5, 42 parts (Uban 20SE-60) (solid part 25 parts) and 20 parts of n-butanol were mixed, and further swazol. The clear coating material (C-1) was obtained by adjusting the viscosity to 1000 for 20 seconds (Ford cup # 4/20 ° C.) and the solid content during coating to 40%.

Production of clear paint (D) Production examples 30 to 52
Using the hydroxyl group-containing acrylic resin obtained in Production Examples 6 to 17, the polyester polyol obtained in Production Examples 18 to 23 and the raw materials described in Table 4 below, a rotary vane stirrer with the composition shown in Table 4 below The mixture was stirred and mixed to form a paint, and each clear paint was obtained. In addition, the mixing | blending of the clear coating material shown in Table 4 is solid content mass ratio of each component.

  (* 1) to (* 4) in Table 4 below have the following meanings.

(* 1) N-3300: manufactured by Sumika Bayer Urethane Co., Ltd., trade name, trifunctional hexamethylene diisocyanate (HMDI) isocyanurate compound, solid content 100%, NCO content 21.8%.
(* 2) Takenate D160N: manufactured by Takeda Pharmaceutical Company Limited, trade name, hexamethylene diisoisocyanate and trimethylolpropane adduct, solid content 75%, NCO content 12.6%.
(* 3) UV1164: UV absorber manufactured by Ciba Geigy.
(* 4) HALS292: Ciba Geigy's light stabilizer.

  Each coating composition obtained in Examples 1 to 13 and Comparative Examples 1 to 10 was added with butyl acetate, and Ford Cup #No. 4 was adjusted to a viscosity of 25 seconds at 20 ° C.

  In addition, Production Examples 43 to 52 are paints for comparative examples.

Formation of multilayer coating (preparation of test plate)
Examples 1-14 and Comparative Examples 1-14
As the base paint (A), each of the base paints (A-1) to (A-3) obtained in Production Examples 25 to 27 and as the aqueous colored paint (B), the aqueous colored paint obtained in Production Example 28 ( B-1) Using the clear paint (C-1) obtained in Production Example 29 and the clear paints (D-1) to (D-23) obtained in Production Examples 30 to 52, the following: A test plate was prepared as described above.

  Electrocolon-coated ELECRON NT-200 (trade name, cationic electrodeposition paint, manufactured by Kansai Paint Co., Ltd.) on a cold-rolled steel sheet to which Palbond # 3020 (Nihon Parkerizing Co., trade name, zinc phosphate treatment) was applied. The coating was heated at 30 ° C. for 30 minutes to form a coating film having a thickness of 20 μm.

  Next, under the conditions of a temperature of 25 ° C. and a humidity of 80%, each of the above base paints (A-1) to (A-3) is a minibell G (rotary atomizing electrostatic coating machine, manufactured by Nippon Landsburg, (Trade name) is applied to a film thickness of 20 μm and left for 7 minutes, then water-based colored paint (B-1) is applied to REA (electrostatic air spray coating machine, manufactured by Nippon Landsberg Co., Ltd., trade name). The film was coated to a thickness of 25 μm and allowed to stand for 3 minutes, followed by preheating at 70 ° C. for 5 minutes. Further, after being left for 6 minutes, a clear paint (C-1) was applied using a minibell G so that the film thickness was 35 μm. Next, after leaving for 10 minutes, the three-layer coating film consisting of the base paint (A), the water-colored paint (B-1) and the clear paint (C) was heated and cured at 140 ° C. for 30 minutes in an electric hot air drying oven. It was.

  On the coating film, each of the clear paints (D-1) to (D-23) was applied using a minibell G so as to have a film thickness of 35 μm. Then, after leaving at room temperature for 7 minutes, it heated at 140 degreeC for 20 minutes, and each test board (multilayer coating film) was obtained by hardening the coating film of clear coating material (D).

  In Comparative Examples 2 and 3, Amirak KPX-70 (Note 3) (trade name, polyester / melamine resin-based automotive intermediate coating) manufactured by Kansai Paint Co., Ltd. was used instead of the base coating (A-1). Then, after the paint was applied, it was cured by heating at 140 ° C. for 20 minutes, and then the aqueous colored paint (B-1) was applied. Therefore, the multilayer coating film forming method of the present invention has a 4-coat 2-bake specification, while Comparative Examples 2 and 3 have a 4-coat 3-bake specification.

  In Comparative Examples 3 and 4, KINO # 2300 (Note 4) (trade name, acid / epoxy curable acrylic resin clear paint manufactured by Kansai Paint Co., Ltd.) is used instead of the clear paint (D-1). did.

  Each of the obtained test plates was allowed to stand at room temperature for 7 days and then subjected to the following coating film performance test.

Finishing performance of coating film performance test : Measured with a Wave Scan (trade name) manufactured by BYK Gardner. Long Wave value (LW) and Short Wave value (SW) are measured by Wave Scan. The Long Wave value is an index of the amplitude of the surface roughness having a wavelength of about 1.2 to 12 mm, and can evaluate the condition of the medium wave skin of the coated surface. The Short Wave value is an index of the amplitude of the surface roughness having a wavelength of about 0.3 to 1.2 mm, and the condition of the minute skin on the coated surface can be evaluated. Each Wave Scan value indicates that the smaller the measured value, the higher the coated surface smoothness.

  Gloss: The 20-degree specular reflectance (20 ° gloss value) of the test plate was measured and evaluated.

  Scratch resistance: The test plate was fixed to a test stand, and the 20-degree specular reflectance (20 ° gloss value) of the test plate after measuring 15 times with a car wash machine at 20 ° C. was measured. The gloss retention (%) relative to the 20 ° gloss value before the test was evaluated. The higher the gloss retention, the better the scratch resistance. As a car wash machine, “PO20 FWRC” (trade name) manufactured by Yasui Industry Co., Ltd. was used.

  Acid resistance: 0.4 cc of 40% sulfuric acid was dropped on the coating film of each test plate, heated for 15 minutes on a hot plate heated to 60 ° C., and then the test plate was washed with water. The etching depth (μm) of the sulfuric acid dropping portion was cut off with a surface roughness meter (manufactured by Tokyo Seimitsu Co., Ltd., surface roughness shape measuring instrument “Surfcom 570A”, trade name) 0.8 mm (scanning speed 0.3 mm). / Sec, magnification 5000 times), and acid resistance was evaluated. The smaller the etching depth, the better the acid resistance.

Results The performance test results are shown in Table 5.

Claims (5)

The base paint (A) is applied to the object to be coated, the water-colored paint (B) and the clear paint (C) are sequentially applied to the uncured coating surface, and then heated to paint (A), (B) and In the method for forming a multi-layer coating film comprising simultaneously curing the three-layer coating film comprising (C), coating the clear coating (D) on the three-layer coating film, and then curing by heating.
The base paint (A) is a carboxyl group- and hydroxyl group-containing resin (a-1), a tertiary amino group-containing unsaturated monomer (a-2-1), a polyoxyalkylene group-containing nonionic unsaturated monomer (a-2). -2) and a tertiary amino group-containing resin (a-2) obtained by copolymerizing other unsaturated monomer (a-2-3), and a crosslinking agent (a-3) capable of reacting with a hydroxyl group A paint consisting of
The clear paint (D) contains a hydroxyl group having a hydroxyl value of 100 to 200 mg KOH / g and a number average molecular weight of 5,000 to 10,000, obtained by copolymerizing a monomer mixture containing an aromatic vinyl monomer and a monomer having a cyclohexyl ring. The hydroxyl value obtained by esterifying an acrylic resin (d-1), a trifunctional HMDI isocyanurate compound (d-2), and a diol having 3 to 6 carbon atoms and a dicarboxylic acid having a cyclohexyl ring is 250 to 350 mgKOH. / G and a two-component clear coating composition comprising a polyester polyol (d-3) having a number average molecular weight of 350 to 550.   Presence of an allyl group-containing reactive emulsifier in which the base paint (A) comprises a monomer (a-4-1) containing at least two unsaturated groups in the molecule and another unsaturated monomer (a-4-2). The method for forming a multilayer coating film according to claim 1, which is a paint further containing polymer fine particles (a-4) obtained by emulsion polymerization under pressure.   Based on the total amount of the resin (a-1), the resin (a-2) and the cross-linking agent (a-3), the base paint (A) contains 20-80% by mass of the resin (a-1), The method for forming a multilayer coating film according to claim 1 or 2, comprising 5 to 35% by mass of a-2) and 15 to 45% by mass of a crosslinking agent (a-3).   The method for forming a multilayer coating film according to any one of claims 1 to 3, wherein the polyester polyol (d-3) is obtained by using 1,4-cyclohexanedicarboxylic acid as a dicarboxylic acid component.   The method for forming a multilayer coating film according to any one of claims 1 to 4, wherein the polyester polyol (d-3) is obtained using 1,3-propanediol as a diol component.