JPH09125000A - Topcoat coating and top coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a topcoat coating which can form a coating film having excellent finishing appearance, weather resistance, and acid resistance by using a particular acrylic copolymer having a low acid value. SOLUTION: This topcoat coating comprises: a hydroxyl-contg. acrylic copolymer (A) having an acid value of not more than 4mg KOH/g resin, pref. a hydroxyl value of 50 to 170mg KOH/g resin, a wt.-average mol.wt. of 3,000 to 30,000, and a glass transition temperature of -40 to 100 deg.C; an aliphatic and/or alicyclic blocked polyisocyanate (B) in such an amt. that the blocked isocyanato group is equivalent to the hydroxyl group of the component (A); and an organotin compd. and/or an organozinc compound (C) win an amt. of 0.005 to 10wt.% of the total amt. of the resin components of the coating (component (A) content + component (B) content).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a topcoat and a coating method using the topcoat. More specifically,
Acid resistance, weather resistance, scratch resistance, it is possible to form a coating film excellent in finished appearance, suitable for automotive coating topcoat, and after coating a thermosetting base coating containing a pigment on the surface to be coated, The present invention relates to a two-coat / one-bake system coating method in which two layers of uncured coating films obtained by applying the above-mentioned top coating composition as a clear coating material are heated and cured at the same time.

[0002]

2. Description of the Related Art In addition to forming a coating film excellent in finished appearance such as smoothness, gloss and sharpness, and weather resistance as a performance required for a top coating for automobiles, a recent trend is to further improve acid resistance. It is possible to form a coating film that also has properties such as scratch resistance and scratch resistance. At present, the topcoat paints for automobiles, which are mainly composed of a hydroxyl group-containing acrylic copolymer and an amino resin, are mainly used for acid coating, although a coating film excellent in finished appearance and weather resistance can be obtained. Depending on the case, the coating film may be etched, whitening, stains, etc. may occur, and a coating film having good acid resistance is strongly desired. JP-A-2-242867, JP-A-4-246
Japanese Patent Laid-Open No. 483 discloses that acid resistance is improved by using an amino resin and a blocked polyisocyanate together as a curing agent component. In addition, JP-A-5-32056
No. 2 discloses the use of an acrylic copolymer having a styrene content of 45% by weight to 55% by weight and a block polyisocyanate, but suggests any description about the effect of the resin acid value on the acid resistance. Not even done. Thus, the acid resistance was improved by replacing the curing agent component from the amino resin with the blocked polyisocyanate, but further improvement was desired.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a top coating composition which is excellent in finished appearance and weather resistance and can form a coating film excellent in acid resistance.

[0004]

As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by using a specific acrylic copolymer. It came to completion. That is, the present invention
Mainly (A) hydroxyl group-containing acrylic copolymer having an acid value of 4 mgKOH / g resin or less, (B) aliphatic and / or alicyclic block polyisocyanate, (C) organotin compound and / or organozinc compound A top coating composition comprising the composition as a component, an automotive top coating composition comprising the composition,
A top coat clear coating for automobiles and a thermosetting base paint containing a pigment on the surface to be coated, and then two layers of uncured coating obtained by coating the clear coating on top of it at the same time by heat curing. In the method, the clear coating material is the above-mentioned top coating material.

The present invention will be described in more detail below. The hydroxyl group-containing acrylic copolymer used in the present invention has an acid value of 4
It is less than or equal to mgKOH / g resin. Preferably 3 mg KO
It is H / g resin or less, more preferably 2 mgKOH / g resin or less. If the acid value is greater than 4 mgKOH / g resin, it will act as a catalyst poison for the curing catalyst and cause curing failure.
As a result, the acid resistance and the scratch resistance are adversely affected. The hydroxyl value of the acrylic copolymer is 50 to 170 mgKOH / g
Resin is preferred, more preferably 80-160 mg KO
It is in the range of H / g resin. Weight average molecular weight is 3,000
To 30,000 are preferable, and 5,000 are more preferable.
Is in the range of 20,000. If the hydroxyl value is less than 50, the crosslink density will be low, and the coating properties such as acid resistance and scratch resistance will be poor. On the other hand, if the hydroxyl value is greater than 170, the shrinkage of the coating film during curing will be large, resulting in a finished appearance. It is not preferable because it adversely affects it. When the weight average molecular weight is less than 3,000, the coating performance such as weather resistance is poor, and when it exceeds 30,000, the viscosity is high, the amount of the diluting solvent at the time of coating is increased, and the finished appearance of the coating is poor. It is not preferable. The glass transition temperature of the acrylic copolymer is preferably -40 to 100 ° C, more preferably -20 to 80 ° C, further preferably 0 to 60.
It is in the range of ° C.

The acrylic copolymer can be obtained by copolymerizing a polymerizable monomer having one or more active hydrogens in one molecule with another monomer copolymerizable therewith. For example, acrylic acid esters having active hydrogen such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxymethacrylic acid. Methacrylic acid esters having active hydrogen such as propyl and 2-hydroxybutyl methacrylate, or polyvalent acrylic acid monoester or methacrylic acid monoester of glycerin, acrylic acid monoester or methacrylic acid monoester of trimethylolpropane, etc. Monomers or mixtures of monomers selected from the group of (meth) acrylic acid esters having active hydrogen, methyl acrylate,

Acrylic esters such as ethyl acrylate, isopropyl acrylate, -n-butyl acrylate, 2-ethylhexyl acrylate; methyl methacrylate, ethyl methacrylate, isopropyl methacrylate,
-N-butyl methacrylate, isobutyl methacrylate,
Methacrylic acid esters such as methacrylic acid-n-hexyl, cyclohexyl methacrylate, lauryl methacrylate, glycidyl methacrylate; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid; acrylamide, N-methylol acrylamide, Unsaturated amides such as diacetone acrylamide; other polymerizable monomers such as styrene, vinyltoluene, vinyl acetate, and acrylonitrile; and are exemplified in JP-A-1-261409 and JP-A-3-6273. For example, 4- (meth) acryloyloxy-2,2,6,6
-Tetramethylpiperidine, 4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 1
-Crotonoyl-4-crotonoyloxy-2,2,
6,6-Tetramethylpiperidine, 2-hydroxy-4
It is obtained by copolymerizing a monomer selected from the group of polymerizable UV-stable monomers such as-(3-methacryloxy-2-hydroxypropoxy) benzophenone with a single monomer or a mixture thereof.

Above all, it is preferable that 10 to 60% by weight of the monomer constituting the acrylic copolymer is styrene, and the more preferable amount of styrene is in the range of 15 to 40% by weight. When the amount of styrene is less than 10% by weight, the hardness of the coating film is low, the acid resistance is adversely affected, and the gloss is lowered, which is not preferable. On the other hand, if it exceeds 60% by weight, the weather resistance is adversely affected, which is not preferable.

The copolymerization reaction of these monomers can be carried out in the same manner as a usual method for polymerizing acrylic resin or vinyl resin. For example, it can be carried out by dissolving or dispersing the above-mentioned monomer in an organic solvent, and heating it for about 1 to 10 hours while stirring at a temperature of 60 to 180 ° C in the presence of a radical polymerization initiator.

Examples of the organic solvent include benzene, toluene, xylene, cyclohexane, heptane,
Hydrocarbons such as octane and mineral spirits; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; esters such as ethyl acetate, -n-butyl acetate, isobutyl acetate, propylene glycol monomethyl ether acetate and butyl carbitol acetate;
Alcohols such as methanol, ethanol, isopropanol, n-butanol, sec-butanol, and isobutanol; ethers such as n-butyl ether, dioxane, and ethylene glycol monoethyl ether can be used.

As the radical polymerization initiator, any of those usually used can be used. For example, peroxides such as benzoyl peroxide and t-butylperoxy-2-ethylhexanoate; azobisisobutyrate. Azo compounds such as ronitrile and azobisdimethylvaleronitrile are used. The blocked polyisocyanate used in the present invention is obtained by a known reaction between a polyisocyanate and a blocking agent.

The polyisocyanates are derived from aliphatic and / or cycloaliphatic diisocyanates. The aliphatic diisocyanate preferably has 4 to 30 carbon atoms, and the alicyclic diisocyanate preferably has 8 to 30 carbon atoms. For example, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (hereinafter referred to as HDI), 2,2,4 (or 2,4,4) -trimethyl-1,6-diisocyanate hexane, lysine diisocyanate, isophorone diisocyanate (hereinafter referred to as IPDI), 1,3-bis (isocyanatomethyl) -cyclohexane, 4,4 Examples include'-dicyclohexylmethane diisocyanate and the like. These may be used alone or in combination of two or more. Among them, HDI, because of its weather resistance and industrial availability,
IPDI is preferred and HDI is most preferred.

Polyisocyanates derived from these aliphatic or alicyclic diisocyanates include, for example, isocyanurate type polyisocyanates, burette type polyisocyanates, urethane type polyisocyanates and alohanate type polyisocyanates. Preferably,
It is an isocyanurate type polyisocyanate with excellent weather resistance and heat resistance. The average value of the number of isocyanate groups bonded to one molecule of polyisocyanate (hereinafter referred to as the average number of functional groups) is a value obtained by dividing the product of the number average molecular weight and the isocyanate concentration by the formula weight of the isocyanate (42), and is 3 to 12
Is preferred. It is more preferably 4.5 to 10, and even more preferably 5 to 8. If the average number of functional groups is less than 3, the crosslinkability is poor, and baking is required at high temperature or for a long time in order to obtain sufficient acid resistance, weather resistance and the like, which is disadvantageous. While 1
If it exceeds 2, it is necessary to add a large amount of a leveling agent or the like in order to obtain the smoothness of the coating film.

When synthesizing isocyanurate type polyisocyanate, for example, JP-A-57-47321, JP-A-61-111371 and JP-A-6-31296 are used.
As disclosed in Japanese Patent No. 9 or the like, modification, that is, urethanization, can be carried out by using a hydroxyl compound before, during and / or after the isocyanurate-forming reaction. Examples of the hydroxyl compound used for modification include, for example, monohydroxyl compounds such as methanol, ethanol, isopropanol and phenol; ethylene glycol, propylene glycol, 1,3-butanediol, pentanediol, hexanediol, cyclohexanediol, dimethylolcyclohexane, Neopentyl glycol,
Dihydroxyl compounds such as 2,2,4-trimethyl 1,3-pentanediol; polyhydric hydroxy compounds such as trimethylolpropane, glycerin, pentaerythritol; acrylic polyols, polyester polyols, polyether polyols, aliphatic carbonization Examples include polyols such as hydrogen polyols, epoxy resins, and fluorine polyols.

Specific examples of the aliphatic hydrocarbon polyols include terminal hydroxylated polybutadiene and hydrogenated products thereof. Examples of the polyether polyols include polyether polyols obtained by adding alkylene oxides such as ethylene oxide and propylene oxide to a single or mixture of polyhydric alcohols such as glycerin and propylene glycol, and a polytetraol. Polyethylene polyols obtained by reacting methylene glycols and alkylene oxides with polyfunctional compounds such as ethylenediamine and ethanolamine, and so-called polymer polyols obtained by polymerizing acrylamide and the like using these polyethers as a medium. Etc. are included.

As the polyester polyols, for example, a dibasic acid alone selected from the group of carboxylic acids such as succinic acid, adipic acid, sebacic acid, dimer acid, maleic anhydride, phthalic anhydride, isophthalic acid and terephthalic acid. Or a mixture with a polyhydric alcohol selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane and glycerin, alone or in a mixture. Examples thereof include polyester polyol resins obtained by the condensation reaction of 1) and polycaprolactones obtained by ring-opening polymerization of ε-caprolactone using a polyhydric alcohol.

Examples of the epoxy resins include novolac type, β-methyl epichloro type, cyclic oxirane type, glycidyl ether type, glycol ether type, epoxy type of unsaturated aliphatic compound, epoxidized fatty acid ester type,
Examples thereof include polycarboxylic acid ester type, aminoglycidyl type, halogenated type and resorcin type epoxy resins. Preferably, trimethylolpropane, polyether polyols, polyester polyols are used. These hydroxyl compounds, even when used alone,
Two or more kinds may be used in combination. The modification amount is such that the amount of the hydroxyl group of the modifier with respect to the isocyanate group is 0.1 to 2
0 equivalent% is preferred. It is more preferably in the range of 0.5 to 15 equivalent%, and even more preferably in the range of 1 to 10 equivalent%.

The modification with a hydroxyl compound can generally be carried out at -20 to 150 ° C, preferably 0-1.
It is in the range of 00 ° C. If the temperature becomes too high, side reactions may occur, while if the temperature becomes too low, the reaction rate becomes slow, which is disadvantageous. A catalyst is usually used for the isocyanurate-forming reaction. The catalyst used here is generally preferably one having basicity, for example, tetramethylammonium, tetraethylammonium, tetraalkylammonium hydroxide such as tetrabutylammonium, or its acetate, octylate, myristate,
Organic weak acid salts such as benzoate, trimethylhydroxyethylammonium, trimethylhydroxypropylammonium, triethylhydroxyethylammonium, hydroxyalkylammonium hydroxide such as triethylhydroxypropylammonium, and its acetate, octylate, myristate, Organic weak acid salts such as benzoate, alkali metal salts of alkylcarboxylic acids such as acetic acid, caproic acid, octylic acid and myristic acid, and metal salts of the above alkylcarboxylic acids such as tin, zinc and lead, hexamethylene disilazane, etc. Aminosilyl machine-containing compounds and the like.

The catalyst concentration is usually selected from the range of 10 ppm to 1.0% based on the isocyanate compound.
The reaction can be performed with or without a solvent. When a solvent is used, it is necessary to use a solvent inert to isocyanate groups. The reaction temperature is usually in the range of 20 to 160 ° C, preferably 40 to 130 ° C. When the reaction reaches the target yield, the catalyst is deactivated by, for example, sulfonic acid, phosphoric acid, etc. to stop the reaction. Unreacted materials and solvent are removed to obtain polyisocyanate. Examples of the blocking agent for obtaining the blocked polyisocyanate used in the present invention include alcohol, phenol, active methylene, mercaptan, acid amide, acid imide, imidazole, urea, oxime, amine System, imide system, pyridine system, pyrazole system compounds and the like, and these may be used alone or in combination. Examples of more specific blocking agents are shown below.

Alcohols such as methanol, ethanol, propanol, butanol, 2 ethylhexanol, methyl cellosolve, butyl cellosolve, methyl carbitol, benzyl alcohol, cyclohexanol, etc., and phenols such as phenol, cresol, ethylphenol, butylphenol, nonylphenol. , Dinonylphenol, styrenated phenol, hydroxybenzoic acid ester, etc., as active methylene type, dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, acetylacetone, etc., as mercaptan type,

Acid amides such as butyl mercaptan and dodecyl mercaptan are acetanilide, acetic amide, ε-caprolactam, δ-valerolactam, γ-butyrolactam and the like. Acid imides are succinimide,
Maleic imide, imidazole-based, imidazole, 2-methylimidazole, urea-based, urea, thiourea, ethylene urea, etc., oxime-based, formaldoxime, acetoaldoxime, acetoxime, methylethylketoxime, cyclohexanone oxime, etc. As amines, diphenylamine, aniline, carbazole, diisopropylamine, etc., as imines, ethyleneimine, polyethyleneimine, etc., as bisulfites, sodium bisulfite, etc., as pyridines,
2-hydroxypyridine, 2-hydroxyquinoline, etc.
Examples of the pyrazole type include pyrazole, 3-methylpyrazole, and 3,5-dimethylpyrazole.

Among them, oxime type, active methylene type, phenol type and acid amide type are preferable, and acetoxime and methyl ethyl ketoxime are particularly preferable. The blocking reaction can be performed regardless of the presence or absence of a solvent.
When a solvent is used, it is necessary to use a solvent inert to isocyanate groups. A catalyst may be used in the blocking reaction. As the catalyst, for example, dibutyltin diacetate, dibutyltin dilaurate, tetrabutyldiacetoxystannoxane, organotin compounds such as tin octylate, organozinc compounds such as zinc octylate, organolead compounds such as lead octylate, etc. Examples of the organic metal compounds, metal alcoholates such as sodium methylate, triethylenediamine, and tertiary amines such as 1,8-diazabicyclo [5,4,0] undecene-7.

The blocking reaction is generally -20 to 150.
It can be carried out at a temperature of 0 ° C, but is preferably in the range of 0 to 100 ° C. If the temperature is 150 ° C or higher, a side reaction may occur. On the other hand, if the temperature is too low, the reaction rate becomes low, which is disadvantageous. It is preferably blocked so as to be substantially free of isocyanate groups.

The equivalence ratio of the blocked isocyanate group in the blocked polyisocyanate to the hydroxyl group in the polyol in the present invention is determined by the required physical properties of the coating film, but is selected from the range of 0.1 to 2. Is normal. As the organic tin compound used in the present invention, any organic tin compound can be used, but a tetravalent tin compound is particularly preferable. Particularly, a tetravalent organotin compound represented by the following general formula (1) or (2) is preferable.

[0025]

Embedded image

[0026]

Embedded image

[In the formulas (1) and (2), R ₁ and R ₃ are each an alkyl group or an aryl group having 1 to 12 carbon atoms, and R ₂ is a hydrogen atom or an alkyl group having 1 to 21 carbon atoms. It is an alkyl group, an alkenyl group, an aralkyl group, an alkoxyalkyl group or an aryl group, and these groups may be the same or different from each other. X and Y are OCOR ₂ , O
H, halogen, O _1/2 or S _1/2 , which may be the same or different. Z is O, S or a divalent carboxylic acid residue, and p is an integer of 0 or 1. ]

The organotin compound represented by the general formula (1) or (2) will be specifically described. Examples of R ₁ and R ₃ of the organotin compound of the general formula (1) or (2) are, for example, , Methyl group, butyl group, octyl group, lauryl group, phenyl group and the like. Particularly, a butyl group and an octyl group are preferable. The —OCOR ₂ group is a carboxylic acid residue having 1 to 22 carbon atoms, and examples of the carboxylic acid include formic acid, acetic acid, caproic acid, octylic acid, lauric acid, myristic acid, palmitic acid, behenic acid, neopentanoic acid. ,
Neodecanoic acid, acrylic acid, crotonic acid, isocrotonic acid, undecylenic acid, oleic acid, erucic acid, sorbic acid, linoleic acid, linolenic acid, phenylacetic acid, phenylbutyric acid, phenylpropionic acid, cyclopentanecarboxylic acid, acetoacetic acid, benzoic acid , Methoxybenzoic acid, tert-butylbenzoic acid, hydroxybenzoic acid and the like, and acetic acid, octylic acid, lauric acid and benzoic acid are preferable.

Further, a plurality of R _{2 s} may form the same ring. In that case, R ₂ is a divalent carboxylic acid residue, and examples thereof include divalent aliphatic and aromatic carboxylic acids such as adipic acid, maleic acid and phthalic acid, and sulfur-containing divalent aliphatic carboxylic acids such as thiodipropionic acid. Examples thereof include residues such as acids. X and Y halogens include, for example, chlorine. Examples of the divalent carboxylic acid residue of Z include, for example,
Sulfur-containing compounds such as divalent aliphatic and aromatic carboxylic acids such as adipic acid, maleic acid and phthalic acid, and thiodipropionic acid 2
Residues such as a valent aliphatic carboxylic acid may be mentioned. Particularly preferred organic tin compounds include dibutyltin diacetate, dibutyltin dioctoate, dibutyltin dilaurate, bis (dibutyltin monoacetate) oxide, bis (dibutyltin monolaurate) oxide, bis (dioctyltin monooctylate). It is an oxide. As the organozinc compound used in the present invention, any organozinc compound can be used, but the organozinc compound represented by the following general formula (3) is particularly preferred.

[0030]

Embedded image R ₄ COO—Zn— (O—Zn—) _q —OCOR ₄ ... (3) [wherein R ₄ is a hydrogen atom or an alkyl group having 1 to 21 carbon atoms, It is an alkenyl group, an aralkyl group, an alkoxyalkyl group or an aryl group, and these groups may be the same or different from each other. q is an integer of 0 or 1. ]

The organic zinc compound represented by the general formula (3) will be described in detail. The —OCOR ₄ group has 1 to 22 carbon atoms.
Carboxylic acid residue, and as the carboxylic acid,
For example, formic acid, acetic acid, caproic acid, octylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, neopentanoic acid, neoheptanoic acid, neodecanoic acid, acrylic acid, crotonic acid, isocrotonic acid, undecylenic acid, oleic acid. , Erucic acid, sorbic acid, linoleic acid, linolenic acid, phenylacetic acid, phenylbutyric acid, phenylpropionic acid, cyclopentanecarboxylic acid, acetoacetic acid, benzoic acid, tert-butylbenzoic acid methoxybenzoate, hydroxybenzoic acid, etc. Preferred are acetic acid, octylic acid, lauric acid and benzoic acid.

The amount of the tin compound and / or zinc compound used in the present invention is not particularly limited, but is usually
It is in the range of 0.005 to 10% by weight, preferably 0.2 to 4% by weight, based on the coating resin content. In the composition used in the present invention, the following additives, pigments, solvents and the like which are commonly used in the technical field can be used. For example,
UV absorbers such as hindered amine type, benzotriazole type, benzophenone type, hindered phenol type,
Phosphorus-based and sulfur-based antioxidants, amine-based urethane conversion catalysts, leveling agents, additives such as rheology control agents, and for applications other than clear paints, quinacridone-based, azo-based, phthalocyanine-based, etc. Organic pigments, titanium oxide, barium sulfate, calcium carbonate, inorganic pigments such as silica, other carbon-based pigments, metal foil pigments,
Pigments such as anticorrosion pigments can also be used.

In addition, when mixing the components, if necessary, a suitable solvent such as benzene, toluene, xylene, cyclohexane, heptane, octane, hydrocarbons such as mineral spirit, acetone, methyl ethyl ketone, methyl isobutyl ketone, etc. Ketones, ethyl acetate, n-butyl acetate, isobutyl acetate, esters such as propylene glycol monomethyl ether acetate, butyl carbitol acetate, alcohols such as methanol, ethanol, isopropanol, n-butanol, sec-butanol, isobutanol, etc. , Ethers such as n-butyl ether, dioxane, and ethylene glycol monoethyl ether can be appropriately selected and used according to the purpose and application. These solvents may be used alone or in combination of two or more.

Next, the coating method for 2 coats and 1 bake will be described. The thermosetting paint containing a pigment used in the present invention, that is, the base paint may be any paint as long as it is a paint whose main component is a resin which is conventionally known to be cured and crosslinked by heating, such as an acrylic resin or Examples include paints containing polyester resin and the like, melamine resin, blocked isocyanate and the like as main components. As the pigment used for the base paint, a usual paint pigment can be used, for example, quinacridone-based, azo-based, phthalocyanine-based organic pigments, titanium oxide, barium sulfate, calcium carbonate,
Inorganic pigments such as silica, carbon-based pigments, metal foil pigments, rust preventive pigments and the like can be mentioned.

This coating method is carried out in the same manner as the conventional coating method using a coating liquid type coating as the top clear coating.
As an example, first, the base paint is diluted with a solvent for dilution to 10
The viscosity is adjusted to -30 seconds (Ford cup # 4/20 ° C), and this is directly or directly applied to the object to be coated to form a primer coating film, and then dried so that the dry film thickness is in the range of about 10 to 30 µm. Spray, airless spray, rotary atomizer,
Paint using an electrostatic coating machine etc. and leave at room temperature for several minutes.
Then dilute solvent for 15-40 seconds (Ford Cup # 4/2
(0 ℃) Adjust the viscosity of the top clear paint to dry film thickness 2
The coating is applied in the same manner as the base coating so as to be in the range of 0 to 60 μm, and left at room temperature for several minutes. Then 120-1
The base coating and the clear top coating are simultaneously cured by heating at 60 ° C. for 10 to 30 minutes.

[0036]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples and the like. The measuring methods in Examples and Comparative Examples are shown below. “Parts” are based on weight. Molecular weight: Determined from a polystyrene standard calibration curve using the following gel permeation chromatography. (Apparatus used) -Device: Shimadzu LC-3A-Column: Tosoh Corporation TSKgel G-5000HXL TSKgel G-4000HXL TSKgelG-2000HXL-Detector: Shimadzu RID-6A-Carrier: Tetrahydrofuran hydroxyl value, acid value: JISK-0070 It was measured according to.

Resin content: The residual weight ratio when the resin liquid was dried at 105 ° C. for 3 hours was defined as the resin content (%). Glass transition temperature: The crossing point of the tangent line of the inflection point of the DSC curve and the extrapolation of the baseline, that is, the extrapolation start temperature when the temperature is increased by 5 ° C./min with a differential scanning calorimeter DSC200 manufactured by Seiko Instruments Inc. The glass transition temperature was used. Coating gloss: 6 with a digital automatic colorimeter of Suga Test Instruments Co., Ltd.
It was measured at 0 °. 95 or more was represented by O, 90 or more and less than 95 was represented by Δ, and less than 90 was represented by X. Curability: The value of the undissolved part weight when the cured coating film is immersed in acetone at 20 ° C. for 24 hours compared to before immersion (gel fraction)
Was calculated.

Coating acid resistance: 0.2 ml of pH 2 sulfuric acid and 0.3 wt% calcium sulfate aqueous solution was spotted as artificial acid rain on the cured coating film. This is dried at 70 ° C for 30 minutes (pass time), washed with water, polished with a compound, and the etching depth is measured by a three-dimensional surface roughness meter (Surfcom 570).
A: Tokyo Seimitsu Co., Ltd.), less than 1 μ: ○, 1 μ or more: 1.
Less than 5 μ was evaluated as Δ, and 1.5 μ or more was evaluated as x. Storage stability: A coating solution of 20 seconds / 20 ° C in Ford cup # 4 was stored at 40 ° C for 1 month, and then 25 seconds / 20 ° C or less in Ford cup # 4.

Preparation of test plate: A cation electrodeposition plate manufactured by Nippon Test Panel Co., Ltd. was wiped with acetone to degrease it, and the following base paint was coated on it with an air spray gun to a dry film thickness of 30 μm. The test plate was left at room temperature for 30 minutes. However, the gel fraction was measured by using a polypropylene plate wiped with acetone as a test plate. Base paint: Acrydic 44 of acrylic polyol
100 parts of -179 (manufactured by Dainippon Ink and Chemicals), 50 parts of titanium oxide TITANIX JR701 (manufactured by TAYCA Corporation), and 50 parts of xylene were dispersed together with 1 mmφ ceramic beads for 30 minutes using a sand mill. To 100 parts of the coating solution from which the ceramic beads have been removed, 12.5 parts of melamine resin Super Beckamine J-820-60 (manufactured by Dainippon Ink and Chemicals, Inc.) is added, and as a thinner, ethyl acetate / toluene / butyl acetate / xylene / A mixed solution of propylene glycol monomethyl ether acetate (weight ratio = 30/30/20/15/5) was added, and the temperature was adjusted to 15 seconds / 20 ° C. with Ford cup # 4 to obtain a base paint.

Production Example 1 (Synthesis of Acrylic Copolymer) Xylene 51.5 was placed in a four-necked flask equipped with a stirrer, a thermometer, a reflux cooling tube, a nitrogen blowing tube, and a dropping funnel.
And 51.5 parts of butyl acetate were charged, the flask was made a nitrogen atmosphere, heated and stirred, and after reaching 80 ° C., the following monomer mixture was added dropwise over 3 hours. Styrene 25 parts n-butyl methacrylate 33 parts n-butyl acrylate 20 parts 2-hydroxyethyl methacrylate 12 parts 2-hydroxyethyl acrylate 10 parts Azobisisobutyronitrile 3 parts

After the dropping was completed, the mixture was kept at 80 ° C. for another 30 minutes, and then a mixture of 0.3 parts of azobisisobutyronitrile, 1.5 parts of xylene and 1.5 parts of butyl acetate was added,
After that, stirring was continued while maintaining the temperature at 80 ° C. for 2 hours and then cooled to obtain an acrylic copolymer A. This acrylic copolymer has a weight average molecular weight of 15,000 as shown in Table 1.
0, acid value 0.3 mg KOH / g resin, hydroxyl value 100 m
The content of gKOH / g resin was 50.5%.

[Production Examples 2 to 7] (Synthesis of Acrylic Copolymer) Acrylic copolymers having the monomer compositions shown in Table 1 were synthesized in the same manner as in Production Example 1 to prepare acrylic copolymers B to G. Got The characteristic values of the obtained acrylic copolymer are shown in Table 1. [Production Example 8] (Synthesis of Block Polyisocyanate) A 4-necked flask equipped with a stirrer, a thermometer, a reflux condenser tube, a nitrogen blowing tube, and a dropping funnel was placed in a HDI-based urethane-modified isocyanurate polyisocyanate "Duranate MFA-". 90X "(trade name of Asahi Kasei Corporation, isocyanate content 16.4%, resin content 90%, average functional group number 5.4) 100 parts and xylene 71 parts were charged, and a nitrogen atmosphere was created in the flask. 36 parts of methyl ethyl ketoxime was added dropwise thereto so that the reaction temperature did not exceed 60 ° C. Confirmed disappearance of characteristic absorption of isocyanate in infrared spectrum, resin content 60%, effective isocyanate amount 7.9
% Blocked polyisocyanate solution was obtained.

Example 1 The acrylic copolymer A obtained in Production Example 1 and the blocked polyisocyanate obtained in Production Example 8 were blended so that the blocked isocyanate groups and hydroxyl groups would be equivalent. To this, dibutyltin dilaurate was added as a catalyst to the coating resin content (the sum of the acrylic copolymer and the block polyisocyanate resin content) at 0.5%, and as a thinner, ethyl acetate / toluene / acetic acid was added. Butyl / xylene / propylene glycol monomethyl ether acetate (weight ratio = 30/30/2
(0/15/5) was added and the temperature was adjusted to 20 seconds / 20 ° C. with Ford cup # 4. The obtained coating solution was coated on the test plate shown above with an air spray gun so that the dry film thickness would be 50 microns, and baked for 30 minutes in an oven maintained at 140 ° C to measure the physical properties of the coating film. It was In addition, a storage stability test was conducted using a part of the coating solution.
Table 2 shows the obtained results.

(Examples 2 to 5) A coating material was prepared in the same manner as in Example 1 except that the acrylic copolymer shown in Table 2 was used, and the coating film physical properties were measured. Table 2 shows the obtained results. (Comparative Examples 1 and 2) A coating material was prepared and coating film physical properties were measured in the same manner as in Example 1 except that the acrylic copolymer shown in Table 2 was used. Table 2 shows the obtained results.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

According to the present invention, by lowering the resin acid value of the acrylic copolymer, the curability is enhanced, and as a result, excellent acid resistance is obtained, and the coating is excellent in weather resistance and appearance. A film is obtained. This coating composition exhibits excellent performance as a top coating for automobile coatings and the like.

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Claims (6)

[Claims] 1. A hydroxyl group-containing acrylic copolymer having an acid value of 4 mgKOH / g resin or less, (B) an aliphatic and / or alicyclic block polyisocyanate, (C) an organotin compound and / or A top coating composition comprising a composition containing an organozinc compound. 2. The hydroxyl value of the acrylic copolymer is 50 to 1
70 mg KOH / g resin, weight average molecular weight 3,000-
Topcoat paint according to claim 1, characterized in that it is 30,000. 3. Styrene accounts for 10 to 60% by weight of the monomer constituting the acrylic copolymer.
The topcoat paint according to claim 1. 4. A topcoat paint for automobiles comprising the composition according to claim 1. 5. A topcoat clear coating material for automobiles, which comprises the composition according to claim 1. 6. A coating method in which a thermosetting coating material containing a pigment is applied to the surface to be coated, and then a clear coating material is applied over the coating material to simultaneously heat cure two layers of uncured coating film. A clear coating is the coating according to claim 1, which is a coating method.