JP5230518B2 - LAMINATED COATING FORMATION METHOD AND COATED PRODUCT - Google Patents

Description

  The present invention relates to a method for forming a laminated coating film formed on an automobile body and the like, and a coated article having a laminated coating film obtained by the method.

  Conventionally, a coating composition using an organic solvent as a diluent solvent, which is called a solvent-type coating composition, has been widely used as a coating used for industrial coatings. However, this solvent-based coating composition contains a large amount of organic solvent in the coating. For this reason, reduction in the organic solvent contained in the coating composition is required due to the recent increase in environmental awareness. In response to the demand for reducing the organic solvent content, the development of an aqueous coating composition is required.

  The base coating composition used in the coating of automobile bodies and the like is a coating composition that includes a color pigment and / or a luster pigment and greatly affects the design of the resulting coated product. Therefore, the finish of the coating film obtained by this base coating composition has a great influence on the coating film appearance of the obtained multilayer coating film. Conventionally, solvent-based base coating compositions have been widely used as the base coating composition. However, the use of aqueous base coating compositions is being demanded in response to the demand for reducing the content of organic solvents.

As an aqueous base coating composition, for example, JP 2001-311035 A (Patent Document 1) describes an aqueous base coat coating containing a polyether polyol and an emulsion resin. This Patent Document 1 further describes a method for forming a composite coating film by a so-called two-coat one-bake method in which this aqueous base coat paint is applied, a clear top coat paint is applied thereon, and then both are cured simultaneously. ing. This coating film forming method can omit the baking step of the base coating composition. Therefore, there is an economic advantage, and there is also an advantage that CO ₂ emission can be reduced.

  However, the laminated coating film obtained by the two-coat one-bake method using the aqueous base coating composition generally has a glitter and gloss feeling as compared with the laminated coating film obtained using the solvent-based base coating composition. There is a problem of being inferior. In general, it can be said that an important factor is that the coating film imparts a high-class feeling to the object to be coated, and that the coating film has high smoothness and has a mirror-like gloss. In particular, in the field of automobile painting and the like, the level required for the appearance of such a coating film is increasing year by year.

By the way, in the field of automobile painting and the like, generally, an electrodeposition coating film, an intermediate coating film, a base coating film, and a clear coating film are formed in this order. However, due to recent demands for energy saving, CO ₂ emission reduction and cost reduction, a method of omitting not only the baking process but also a part of the coating process itself is being adopted. As one aspect of the simplification of the coating process, there is a method of omitting the intermediate coating. However, by omitting the intermediate coating, there is a high possibility that the chipping resistance of the intermediate coating film in the obtained multilayer coating film is lowered. Moreover, the intermediate coating film provided between the electrodeposition coating film and the base coating film also has an effect of improving the coating film adhesion of these electrodeposition coating film and base coating film. Therefore, when the intermediate coating is omitted, the adhesion between the electrodeposition coating film and the base coating film may be inferior.

JP 2001-311035 A

  The present invention relates to an interlayer adhesion and chipping resistance of a coating film obtained in a coating method in which a laminated coating film comprising a base coating film and a clear coating film is formed on an electrodeposition coating film, omitting the intermediate coating process. It aims at improving the coating-film external appearance of the laminated coating film obtained while ensuring coating-film performance, such as property.

  The present invention eliminates the intermediate coating process in which an aqueous base coating composition and a specific clear coating composition are sequentially coated on an electrodeposition coating, and then two uncured coatings are baked and cured. In the conventional method for forming a laminated coating film, the problem of securing coating film performance such as interlayer adhesion and chipping resistance of the obtained coating film has been solved. As a result of intensive studies, the inventors have found that the above problem can be solved by using a specific block polyisocyanate in the aqueous base coating composition.

That is, the present invention
An aqueous base coating composition and a clear coating composition are sequentially applied on a substrate on which an electrodeposition coating is formed by wet-on-wet, and two uncured coatings that have been applied are coated at once. Baking and curing,
A method for forming a laminated coating film comprising:
The aqueous base coating composition comprises an acrylic resin emulsion (A); a polyether polyol (A); an active methylene type block polyisocyanate (U);
The acrylic resin emulsion (a) is obtained by emulsion polymerization of a monomer mixture (a) containing 1 to 20% by mass of a polyfunctional unsaturated monomer containing two or more (meth) acrylate groups in one molecule. A core portion having a crosslinked structure;
A shell part obtained by emulsion polymerization of a monomer mixture (b) containing a carboxylic acid group-containing unsaturated monomer and a hydroxyl group-containing unsaturated monomer,
A core-shell type acrylic resin emulsion having a hydroxyl value of 10 to 200 and an acid value of 1 to 80 mgKOH / g,
The polyether polyol (I) is a polyether polyol having an average of 0.02 or more primary hydroxyl groups in one molecule, a number average molecular weight of 300 to 3000, and a water tolerance of 2.0 or more.
An aqueous base coating composition, wherein the clear coating composition further comprises:
A one-component clear coating composition comprising: a carboxyl group-containing acrylic resin (A); a carboxyl group-containing polyester resin (B); and an epoxy group-containing acrylic resin (C).
Laminated coating film forming method,
This achieves the above object.

  In the present invention, the clear coating composition is a two-component clear coating composition comprising: a main agent containing a hydroxyl group-containing acrylic resin (D); and a curing agent containing an isocyanate compound (E); Hydroxyl group-containing acrylic resin (D) having a number average molecular weight (Mn) of 1500 to 6000, a hydroxyl value of 100 to 200, and a ratio of secondary hydroxyl groups of the hydroxyl value of 20 to 100%. A resin is preferred.

  The present invention further provides a coated product having a multilayer coating film obtained by the above-described method for forming a multilayer coating film.

  By using a specific aqueous base coating composition in a coating method that omits the intermediate coating step, which forms a laminated coating consisting of a base coating and a clear coating on the electrodeposition coating in the present invention, It is possible to ensure coating film performance such as interlayer adhesion and chipping resistance of the obtained coating film. Furthermore, the multilayer coating film obtained by this method for forming a multilayer coating film has a feature that it has high smoothness and an excellent coating film appearance.

In the coating method in which the intermediate coating process is omitted, the coating and baking curing procedures of the intermediate coating composition are omitted, and thus the method is very economical. In addition, the 2-coat 1-bake method can eliminate the baking and drying furnace for the base coating composition, and is therefore economical and advantageous in that it can reduce CO ₂ emissions and reduce the burden on the environment. Have Moreover, the amount of the organic solvent discharged | emitted in coating-film formation can be reduced by using a water-based base coating composition in a 2 coat 1 baking method. According to the present invention, it is possible to form a laminated coating film by a 2-coat 1-bake method that omits the intermediate coating process without deteriorating the physical properties of the coating film or the appearance of the coating film. By the laminated coating film forming method of the present invention, a laminated coating film having excellent coating film performance and coating film appearance can be formed by an industrially excellent method having economic advantages and environmental advantages.

Aqueous base paint composition The aqueous base paint composition used in the coating film forming method of the present invention comprises an acrylic resin emulsion (A); a polyether polyol (A); an active methylene type block polyisocyanate (U). It is a thing. In addition, the said water-based base coating composition may contain other coating-film-forming resin, a color pigment, etc. other than the said component (A)-(U) as needed.

Acrylic resin emulsion (A)
The acrylic resin emulsion (a) contained in the aqueous base coating composition is
A core part having a cross-linked structure obtained by emulsion polymerization of a monomer mixture (a) containing 1 to 20% by mass of a polyfunctional unsaturated monomer containing two or more (meth) acrylate groups in one molecule;
A shell part obtained by emulsion polymerization of a monomer mixture (b) containing a carboxylic acid group-containing unsaturated monomer and a hydroxyl group-containing unsaturated monomer,
It is a core-shell type acrylic resin emulsion having a hydroxyl value of 10 to 200 and an acid value of 1 to 80 mgKOH / g.

  It does not specifically limit as said polyfunctional unsaturated monomer contained in the monomer mixture (a) used for preparation of a core part, For example, ethylene glycol dimethacrylate, divinylbenzene, etc. can be mentioned. When the content of the polyfunctional unsaturated monomer is less than 1% by mass, the design properties of the obtained coating film are reduced, and when it exceeds 20% by mass, the smoothness of the obtained coating film is reduced. Preferably it is 1-15 mass%. When the polyfunctional unsaturated monomer is contained in the monomer mixture (a) used for the preparation of the core part, the core part has a crosslinked structure.

The monomer mixture (a) used for the preparation of the core part may further contain other α, β-ethylenically unsaturated monomers. Other α, β-ethylenically unsaturated monomers include, for example:
Hydroxyl group-containing unsaturated monomer (for example, ε-caprolactone addition of hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, allyl alcohol, methacrylic alcohol, hydroxyethyl (meth) acrylate More preferable among these are hydroxyethyl (meth) acrylate, hydroxybutyl (meth) acrylate, and ε-caprolactone adduct of hydroxyethyl (meth) acrylate.)
(Meth) acrylic acid ester (for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, (meth) 2-ethylhexyl acrylate, lauryl methacrylate, phenyl acrylate, isobornyl (meth) acrylate, cyclohexyl methacrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentadienyl (meth) acrylate, (meth) acryl Acid dihydrodicyclopentadienyl),
Polymerizable amide compounds (for example, (meth) acrylamide, N-methylol (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-dibutyl (meth) acrylamide, N, N-dioctyl (meth) acrylamide, N-monobutyl (meth) acrylamide, N-monooctyl (meth) acrylamide 2,4-dihydroxy-4′-vinylbenzophenone, N- (2-hydroxyethyl) acrylamide, N- (2-hydroxyethyl) methacrylamide, etc.) ,
Polymerizable aromatic compounds (for example, styrene, α-methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene, vinylnaphthalene, etc.),
Polymerizable nitriles (eg, acrylonitrile, methacrylonitrile, etc.),
α-olefin (for example, ethylene, propylene, etc.),
Vinyl esters (eg, vinyl acetate, vinyl propionate, etc.),
Dienes (eg, butadiene, isoprene, etc.),
Etc. These can be variously selected according to the desired performance.
As other α, β-ethylenically unsaturated monomers, a mode in which a hydroxyl group-containing unsaturated monomer and a polymerizable amide compound such as (meth) acrylamide are included is more preferable.
Curability can be ensured by using a hydroxyl group-containing unsaturated monomer in the preparation of the core part. Moreover, the solvent resistance of the coating film obtained can be improved by using a polymerizable amide compound in preparation of a core part.

  In this invention, the monomer mixture (b) used for preparation of a shell part contains a carboxylic acid group containing unsaturated monomer and a hydroxyl group containing unsaturated monomer.

  The carboxylic acid group-containing unsaturated monomer is not particularly limited. For example, acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, 2-acryloyloxyethylphthalic acid, 2-acryloyloxyethyl succinic acid, 2-acryloyl Oxyethyl acid phosphate, 2-acrylamido-2-methylpropanesulfonic acid, ω-carboxy-polycaprolactone mono (meth) acrylate, isocrotonic acid, α-hydro-ω-[(1-oxo-2-propenyl) oxy] Poly [oxy (1-oxo-1,6-hexanediyl)], maleic acid, fumaric acid, itaconic acid, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid and the like can be mentioned.

  As the hydroxyl group-containing unsaturated monomer, the hydroxyl group-containing unsaturated monomer described in the monomer mixture (a) used for the preparation of the core portion can be used in the same manner.

  The monomer mixture (b) used for the preparation of the shell part may further contain other α, β-ethylenically unsaturated monomers. Examples of other α, β-ethylenically unsaturated monomers include, for example, the hydroxyl group-containing unsaturated monomers exemplified in the monomer mixture (a), (meth) acrylic acid esters having 3 or more carbon atoms in the ester portion, and polymerizable aromatic compounds. , Polymerizable nitriles, α-olefins, vinyl esters, dienes and the like. These can be variously selected according to the desired performance.

  The hydroxyl value of the acrylic resin emulsion (a) in the present invention is 10 to 200. The hydroxyl value is preferably 20 to 150. If the hydroxyl value is less than 10, sufficient curability may not be obtained. Moreover, when it exceeds 200, there exists a possibility that the various performance of the coating film obtained may fall.

  Moreover, the acid value of the acrylic resin emulsion (a) in this invention is 1-80 mgKOH / g. The acid value is preferably 3 to 50 mgKOH / g. If the acid value is less than 1 mgKOH / g, the coating workability may be insufficient. Moreover, when it exceeds 80 mgKOH / g, there exists a possibility that the water resistance of the coating film obtained may fall.

  Moreover, it is preferable that the glass transition temperature (Tg) of an acrylic resin emulsion (a) is -20-80 degreeC from a viewpoint of the physical property of the coating film obtained.

  The acid value, hydroxyl value and Tg of the obtained acrylic resin emulsion (a) can be determined by actually measuring the acrylic resin emulsion (a). In the present specification, the monomer mixture (a) And a value obtained by calculation from the blending amount of various unsaturated monomers in the monomer mixture (b).

  The acrylic resin emulsion (a) is prepared by two-stage emulsion polymerization. That is, first, emulsion polymerization of the monomer mixture (a) is performed to obtain a core part having a crosslinked structure, and then the monomer mixture (b) is further added to carry out emulsion polymerization to obtain a shell part.

  Emulsion polymerization performed here can be performed using the normal method used by those skilled in the art. Specifically, an emulsifier is dissolved in water or an aqueous medium containing an organic solvent such as alcohol as necessary, and the monomer mixture (a) or the monomer mixture (b) and a polymerization initiator are heated and stirred. It can be performed by dropping. The monomer mixture (a) or the monomer mixture (b) emulsified in advance using an emulsifier and water may be similarly dropped.

  Examples of the polymerization initiator include azo oily compounds (for example, azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 2,2′-azobis (2,4-dimethylvalero). Nitrile), etc.) and aqueous compounds (eg anionic 4,4′-azobis (4-cyanovaleric acid), cationic 2,2′-azobis (2-methylpropionamidine)); and redox Oily peroxides (for example, benzoyl peroxide, parachlorobenzoyl peroxide, lauroyl peroxide, t-butyl perbenzoate, etc.) and aqueous peroxides (for example, potassium persulfate, ammonium peroxide, etc.) are preferred.

  As said emulsifier, what is usually used by those skilled in the art can be mentioned. In particular, reactive emulsifiers such as Antox MS-60 (manufactured by Nippon Emulsifier Co., Ltd.), Eleminol JS-2 (manufactured by Sanyo Kasei Kogyo Co., Ltd.), Adekaria Soap NE-20 (manufactured by Asahi Denka Co., Ltd.) and Aqualon HS -10 (Daiichi Kogyo Seiyaku Co., Ltd.) is preferable. In order to adjust the molecular weight, a mercaptan such as lauryl mercaptan and a chain transfer agent such as α-methylstyrene dimer may be used as necessary.

  The reaction temperature is determined by the polymerization initiator, and for example, it is preferably 60 to 90 ° C. for an azo initiator and 30 to 70 ° C. for a redox system. In general, the reaction time is 1 to 8 hours. The content of the polymerization initiator relative to the total mass of the monomer mixture (a) and the monomer mixture (b) is generally 0.1 to 5% by mass, and preferably 0.2 to 2% by mass.

  The average particle size of the acrylic resin emulsion (a) thus obtained is preferably in the range of 0.01 to 1.0 μm. When the average particle diameter is less than 0.01 μm, the improvement in coating workability is small, and when it exceeds 1.0 μm, the appearance of the resulting coating film may be deteriorated. This average particle size can be adjusted, for example, by adjusting the monomer composition and emulsion polymerization conditions.

  The acrylic resin emulsion (A) can be used at pH = 5 to 10 by neutralizing with a base as necessary. This is because the stability in this pH region is high. This neutralization is preferably carried out by adding a tertiary amine such as dimethylethanolamine or triethylamine to the system before or after emulsion polymerization.

  The content of the acrylic resin emulsion (a) in the aqueous base coating composition used in the method for forming a multilayer coating film of the present invention is preferably 5 to 95% by mass in the solid content of the coating, and 10 to 85. More preferably, it is mass%, and it is still more preferable that it is 20-70 mass%. When the said content is outside the said range, there exists a possibility that coating workability | operativity and the external appearance of the coating film obtained may fall.

Other coating film forming resin The aqueous base coating composition used in the coating film forming method of the present invention may contain other coating film forming resin, if necessary, in addition to the acrylic resin emulsion (a). . Although it does not specifically limit as such a thing, Coating film forming resin, such as an acrylic resin, a polyester resin, an alkyd resin, an epoxy resin, a urethane resin, can be utilized.

  The other film-forming resin has a number average molecular weight of 3,000 to 50,000, preferably 6,000 to 30,000. If it is less than 3000, the coating workability and curability are not sufficient, and if it exceeds 50000, the non-volatile content at the time of coating becomes too low, and the coating workability deteriorates.

  The other film-forming resin preferably has an acid value of 10 to 100 mgKOH / g, and more preferably 20 to 80 mgKOH / g. If the upper limit is exceeded, the water resistance of the coating film may be reduced, and if it is lower than the lower limit, the water dispersibility of the resin may be reduced. Moreover, it is preferable that a hydroxyl value is 20-180 mgKOH / g, and it is more preferable that it is 30-160 mgKOH / g. If the upper limit is exceeded, the water resistance of the coating film may be reduced, and if it is less than the lower limit, the curability of the coating film may be reduced.

  The coating film-forming resin is preferably a polyester resin or an alkyd resin from the viewpoint of flip-flop properties and chipping resistance of the resulting coating film.

  The polyester resin is obtained by condensation polymerization of an acid component and an alcohol component. The acid component is not particularly limited, and examples thereof include polyvalent carboxylic acid compounds such as adipic acid, sebacic acid, isophthalic acid, and phthalic anhydride, and anhydrides thereof. Furthermore, as the acid component, a compound having a carboxylic acid group and a hydroxyl group in one molecule such as dimethylolpropionic acid can be used. Moreover, it does not specifically limit as said alcohol component, Polyhydric alcohol compounds, such as ethylene glycol, a trimethylol propane, neopentyl glycol, can be mentioned.

  The alkyd resin is not particularly limited, and can be obtained by condensation polymerization of the acid component, the alcohol component, and oils and fats such as coconut oil and linseed oil. Furthermore, the coating film-forming resin may be neutralized with a base such as a tertiary amine such as dimethylethanol or triethylamine, if necessary, and dissolved or dispersed in water.

  Among the resin components in the aqueous base paint, the blending ratio of the acrylic resin emulsion (A) and the other film-forming resin is 5 to 5 based on the total resin solid content. 95% by mass, more preferably 10-85% by mass, particularly preferably 20-70% by mass, and other film-forming resins are 95-5% by mass, more preferably 90-15% by mass, particularly preferably. 80 to 30% by mass. If the ratio of the acrylic resin emulsion (a) is less than 5% by mass, the suppression of sagging and the appearance of the coating film are lowered, and if it is more than 95% by mass, the coating film appearance may be deteriorated.

Polyether polyol (I)
The polyether polyol (I) contained in the aqueous base coating composition has an average of 0.02 or more primary hydroxyl groups in one molecule, a number average molecular weight of 300 to 3000, and a water tolerance of 2.0 or more. It is. By including this polyether polyol in the aqueous base coating composition, the flip-flop property, water resistance and chipping resistance of the coating film can be improved.

  When the average number of primary hydroxyl groups in one molecule of the polyether polyol is less than 0.02, the water resistance and chipping resistance of the coating film are lowered. Moreover, it is preferable to have 0.04 or more primary hydroxyl groups in one molecule. In particular, it is more preferable to have one or more primary hydroxyl groups in one molecule. In addition to the primary hydroxyl group, the number of hydroxyl groups including secondary and tertiary hydroxyl groups is preferably at least 2 in one molecule from the viewpoint of the water resistance and chipping resistance of the coating film. In view of the hydroxyl value, the hydroxyl value is preferably 30 to 700. When the hydroxyl value is below the lower limit, curability is lowered, and the water resistance and chipping resistance of the coating film are lowered. If the upper limit is exceeded, the paint stability and the water resistance of the coating film will decrease. Especially preferably, it is 50-500.

  Further, when the number average molecular weight of the polyether polyol is less than 300, the water resistance of the coating film is lowered, and when it exceeds 3000, the curability and chipping resistance of the coating film are lowered. Preferably it is 400-2000. In the present specification, the molecular weight is determined by a GPC method using a styrene polymer as a standard.

  On the other hand, when the water tolerance of the said polyether polyol is less than 2.0, water dispersibility will fall and a coating-film external appearance will worsen. In particular, it is preferably 3.0 or more.

  The water tolerance used here is for evaluating the degree of hydrophilicity, and the higher the value, the higher the hydrophilicity. In this specification, the water tolerance value is measured by mixing 0.5 g of the above polyether polyol in 10 ml of acetone in a 100 ml beaker under the condition of 25 ° C., and using a burette in this mixture, deionized water. Is gradually added, and the amount of deionized water (ml) required for the mixture to become cloudy is measured. This amount of deionized water (ml) is taken as the water tolerance value.

  In this method, for example, when the polyether polyol is hydrophobic, the polyether polyol and acetone were in good compatibility at first, but became incompatible with the addition of a small amount of deionized water. The system becomes cloudy. Conversely, when the polyether polyol is hydrophilic, the higher the hydrophilicity of the polyether polyol, the more deionized water is required before white turbidity occurs. Therefore, the degree of hydrophilicity / hydrophobicity of the polyether polyol can be measured by this method.

  The polyether polyol is preferably contained in an amount of 1 to 40% by mass, more preferably 3 to 30% by mass in the solid content of the coating resin. When the upper limit is exceeded, the water resistance and chipping resistance of the coating film are reduced, and when the lower limit is exceeded, the appearance of the coating film is reduced.

  As said polyether polyol, the compound which alkylene oxide added to active hydrogen containing compounds, such as a polyhydric alcohol, polyhydric phenol, polyhydric carboxylic acids, is mentioned. Examples of the active hydrogen atom-containing compound include water, polyhydric alcohols (ethylene glycol, diethylene glycol, trimethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4 -Dihydric alcohols such as dihydroxymethylcyclohexane and cyclohexylene glycol, glycerin, trioxyisobutane, 1,2,3-butanetriol, 1,2,3-pentanetriol, 2-methyl-1,2,3-propane Triol, 2-methyl-2,3,4-butanetriol, 2-ethyl-1,2,3-butanetriol, 2,3,4-pentanetriol, 2,3,4-hexanetriol, 4-propyl- 3,4,5-heptanetriol, 2,4-dimethyl 2,3,4-pentanetriol, pentamethylglycerin, pentaglycerin, 1,2,4-butanetriol, trivalent alcohol such as 1,2,4-pentanetriol, trimethylolethane, trimethylolpropane, pentaerythritol, 1,2,3,4-pentanetetrol, 2,3,4,5-hexanetetrol, 1,2,4,5-pentanetetrol, 1,3,4,5-hexanetetrol, diglycerin , Tetrahydric alcohols such as sorbitan, pentahydric alcohols such as adonitol, arabitol, xylitol, triglycerin, hexavalent alcohols such as dipentaerythritol, sorbitol, mannitol, iditol, inositol, dulcitol, talose, allose, octavalents such as sucrose Alcohol, polyglycerin Polyhydric phenols [polyhydric phenols (pyrogallol, hydroquinone, phloroglucin, etc.), bisphenols (bisphenol A, bisphenol sulfone, etc.)]; polycarboxylic acids [aliphatic polycarboxylic acids (succinic acid, adipic acid, etc.), Aromatic polycarboxylic acids (phthalic acid, terephthalic acid, trimellitic acid, etc.)] and the like; and mixtures of two or more of these. Particularly preferred as trihydric or higher alcohols used to form a polyether polyol having at least 3 or more hydroxyl groups in one molecule are glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, sorbitan, sorbitol, etc. It is.

  The polyether polyol is usually obtained by subjecting an alkylene oxide to the active hydrogen-containing compound in the presence of an alkali catalyst and subjecting it to an addition reaction at a temperature of 60 to 160 ° C. under normal pressure or pressure. Examples of the alkylene oxide include alkylene oxides such as ethylene oxide, propylene oxide, and butylene oxide, and these can be used alone or in combination of two or more. When two or more types are used in combination, the addition format may be either block or random.

  In addition, the said polyether polyol can use what is marketed, for example, Primepole PX-1000, Sannix SP-750, PP-400 (all the above are manufactured by Sanyo Chemical Industries), PTMG- 650 (manufactured by Mitsubishi Chemical Corporation).

  Furthermore, the above-mentioned polyether polyol is used to improve the pigment dispersibility, as described in JP-A-59-138269, for example, amino resin and hydroxyethylethyleneimine (for example, “HEA” of Mutual Pharmaceutical Company) described later. , 2-hydroxypropyl-2-aziridinylethylcarboxylate (for example, mutual drug “HPAC”). The amount of the modifier is preferably 1 to 10% by mass relative to the polyether polyol. If it is less than 1% by mass, a sufficient modification effect cannot be obtained, and if it exceeds 10% by mass, the stability of the modified polyether polyol is deteriorated.

Active methylene type block polyisocyanate (U)
The aqueous base coating composition contains an active methylene type block polyisocyanate (U). The active methylene type block polyisocyanate (c) contained in the aqueous base coating composition is a component that functions as a curing agent. In this active methylene type block polyisocyanate (U), the blocking agent is dissociated by heating to generate an isocyanate group. The generated isocyanate groups react with the functional groups of the acrylic resin emulsion (A) and other coating film forming resins, and the coating film is cured.

  This active methylene type block polyisocyanate (U) is prepared by addition reaction of a compound having an active methylene group with polyisocyanate. The polyisocyanate used for the preparation of the active methylene type block polyisocyanate (U) is not particularly limited, and examples thereof include trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), and trimethylhexamethylene diisocyanate. Aliphatic isocyanates; aliphatic cyclic isocyanates such as 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,2-cyclohexane diisocyanate; xylylene diisocyanate (XDI), 2,4-tolylene diisocyanate (TDI) Aromatic isocyanates such as 2,6-tolylene diisocyanate; isophorone diisocyanate (IPDI), norbornane diisocyanate Alicyclic isocyanates such as Netomechiru; and their biuret body, can be used multimers and mixtures such as isocyanurate body. Examples of the compound having an active methylene group include active methylene compounds such as alkyl acetoacetate (for example, methyl acetoacetate and ethyl acetoacetate), alkyl malonate (for example, methyl malonate and ethyl malonate), and acetylacetone. It is done.

  The conditions under which the compound having an active methylene group is added to the polyisocyanate can be used without particular limitations on the conditions usually used by those skilled in the art.

A commercial item can also be used as said active methylene type block polyisocyanate (U). Examples of commercially available products include active methylene type blocked isocyanates such as Duranate ^(trademark) series (for example, 17B-60PX, TPA-B80E, MF-B60X, MF-K60X, E402-B80T, K-6000, etc.) manufactured by Asahi Kasei Corporation. It is done.

  The content of the active methylene type block polyisocyanate (U) is 10 to 60% by mass based on the mass of the coating resin solid content. This content is more preferably 10 to 40% by mass. When the content of the active methylene type block polyisocyanate (c) is less than 10% by mass, the adhesion between the base coating film and the electrodeposition coating film is inferior. Moreover, when content is 60 mass%, the storage stability of a coating material falls.

Melamine resin The aqueous base coating composition in the present invention may further contain a melamine resin. This melamine resin is a component that functions as a curing agent, like the active methylene type block polyisocyanate (U). The melamine resin is not particularly limited, and a water-soluble melamine resin or a water-insoluble melamine resin can be used. From the viewpoint of the stability of the paint, it is preferable to use a melamine resin having a water tolerance value of 3.0 or more. The water tolerance value can be measured in the same manner as described for the polyether polyol.

  Specific examples of the melamine resin include alkyl etherified melamine resins and the like. Among these, a melamine resin substituted with a methoxy group and / or a butoxy group can be used more preferably. As the melamine resin substituted with the methoxy group and / or butoxy group, those having a methoxy group alone, Cymel 325, Cymel 327, Cymel 370, Mycoat 723; As a mixed type of methoxy group and butoxy group, Cymel 202, Cymel 204, Cymel 232, Cymel 235, Cymel 236, Cymel 238, Cymel 254, Cymel 266, Cymel 267 (all trade names, manufactured by Mitsui Cytec Co., Ltd.); Mycoat 506 as having a butoxy group alone , My Coat 723, My Coat 2677 (trade name, manufactured by Mitsui Cytec Co., Ltd.) and the like. These may be used alone or in combination of two or more.

  The content when the melamine resin is contained in the aqueous base coating composition is preferably 5 to 40% by mass based on the solid content of the coating resin. In addition, it is preferable that the total content of active methylene type block polyisocyanate (U) and a melamine resin which function as a hardening | curing agent is 10-60 mass% on the basis of coating-resin solid content mass.

Pigment component The water-based base coating composition used in the automobile body paint finishing method of the present invention may contain pigment components such as a luster pigment and a color pigment in addition to the above components.

The shape of the glitter pigment is not particularly limited, and may be colored. For example, the average particle diameter (D ₅₀ ) is in the range of 2 μm lower limit and 50 μm upper limit, and the thickness is lower than 0. It is preferable to be within a range of 1 μm and an upper limit of 5 μm. Moreover, it is more preferable that the average particle size is in the range of 10 μm as the lower limit and 35 μm as the upper limit because the glitter is excellent.

  The luster pigment is not particularly limited, and examples thereof include non-colored or colored metal luster materials such as aluminum, copper, zinc, iron, nickel, tin, aluminum oxide, and the like, and mixtures thereof. be able to. Further, interference mica pigments, white mica pigments, graphite pigments and the like can also be used as the glitter pigment.

  The color pigment is not particularly limited, and examples thereof include organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, and quinacridone pigments. Examples thereof include pigments, isoindolinone pigments, and metal complex pigments. The inorganic coloring pigment is not particularly limited, and examples thereof include chrome lead, yellow iron oxide, bengara, carbon black, and titanium dioxide.

  The total pigment concentration (PWC) in the aqueous base coating composition, that is, the total pigment concentration including the luster pigment and the colored pigment, is lower limit of 0.1 part by weight and upper limit of 50 part with respect to 100 parts by weight of the solid content of the coating resin. It is preferably within the range of parts by mass. The upper limit is more preferably 40 parts by weight and even more preferably 30 parts by weight. When the total pigment concentration exceeds 50 parts by mass, the coating film appearance is deteriorated, which is not preferable. The lower limit is more preferably 0.5 parts by mass and even more preferably 1.0 part by mass.

When the aqueous base coating composition used in the present invention contains a scaly glittering pigment such as a thin film aluminum pigment having an average thickness of 0.05 to 0.20 μm and an average particle diameter of 10 to 20 μm, a phosphate group It is preferable to contain a containing acrylic resin. This phosphoric acid group-containing acrylic resin has the following general formula (I):
CH ₂ = CXCO (OY) _n OPO (OH) ₂ (I)
[Wherein, X represents a hydrogen atom or a methyl group, Y represents an alkylene group having 2 to 4 carbon atoms, and n represents an integer of 3 to 30. ]
It is an acrylic resin obtained by copolymerizing the monomer represented by the above and other ethylenic monomers.

  The phosphoric acid group-containing acrylic resin is used for satisfactorily dispersing the scaly glittering pigment. This resin preferably has an acid value of 15 to 200 mgKOH / g, an acid value of 10 to 150 mgKOH / g based on a phosphoric acid group, and a number average molecular weight of 1,000 to 50,000. When the acid value is less than 15 mgKOH / g, the scaly glitter pigment may not be sufficiently dispersed. Moreover, when an acid value exceeds 200 mgKOH / g, the storage stability of an aqueous | water-based base coating composition may worsen. Among the acid values of 15 to 200 mgKOH / g, the acid value due to the phosphoric acid group is more preferably 15 to 100 mgKOH / g.

  When the aqueous base coating composition used in the present invention contains a metallic glitter material, it improves the physical properties of the resulting multilayer coating film as a corrosion inhibitor for the glitter material or improves the wettability of the glitter material. Therefore, it is preferable to include a phosphate group-containing compound having an alkyl group.

  The number of carbon atoms in the alkyl group is preferably 8-18, and more preferably 8-14. When the number of carbon atoms is less than 8, the wettability decreases and the adhesion decreases, and when it exceeds 18, the crystal of the compound may be precipitated in the paint, which may cause a problem.

  The phosphate group-containing compound having an alkyl group is not particularly limited, and examples thereof include mono- or dialkyl acid phosphate. The mono- or dialkyl acid phosphate is not particularly limited, and examples thereof include 2-ethylhexyl acid phosphate, mono- or di-isodecyl acid phosphate, mono- or di-tridecyl acid phosphate, mono- or di-lauryl acid phosphate. Mono- or di-nonylphenyl acid phosphate and the like.

  When the aqueous base coating composition used in the present invention contains the phosphate group-containing compound, the content of the phosphate group-containing compound is a lower limit of 0.1% by mass and an upper limit of 5% by mass with respect to the solid content of the coating resin. It is preferable to be within the range. The lower limit is more preferably 0.2% by mass, and the upper limit is more preferably 2% by mass. When the content is less than 0.1% by mass, the corrosion prevention effect is not sufficient, and there is a possibility that gas generation or discoloration of the glittering material may occur. Moreover, when it exceeds 5 mass%, there exists a possibility that water resistance may fall.

Other components In the aqueous base coating composition according to the present invention, in addition to the above-mentioned components, additives usually added to the coating, for example, surface conditioners, thickeners, antioxidants, UV inhibitors, antifoaming agents Etc. may be blended. These compounding amounts are within the range known to those skilled in the art.

Production of water-based base coating composition The method for producing the water-based base coating composition is not particularly limited, and the above components are kneaded using a kneader or a roll, dissolved in water using a sand grind mill or a disper and / or the like. Alternatively, any method known to those skilled in the art, such as dispersion, can be used.

  The aqueous base coating composition contains an active methylene type block polyisocyanate (U). Then, the active methylene type block polyisocyanate (U) is contained in the aqueous base coating composition, thereby improving the chipping resistance of the obtained base coating film. This is considered to be because the cohesive force of the urethane bond is high and the stress relaxation ability of the coating film is improved.

  Further, the active base methylene type block polyisocyanate (U) is contained in the aqueous base coating composition, so that the adhesion between the electrodeposition coating film and the base coating film is improved even when the intermediate coating film is not provided. The effect that will be obtained. This is presumably because the presence of an isocyanate component derived from the active methylene type block polyisocyanate (U) in the base coating film causes a crosslinking reaction with the electrodeposition coating film, thereby improving the adhesion.

Clear coating composition The clear coating composition used in the method of the present invention comprises:
Carboxyl group-containing acrylic resin (A); carboxyl group-containing polyester resin (B); and epoxy group-containing acrylic resin (C);
Or a one-part clear coating composition comprising
A main agent containing a hydroxyl group-containing acrylic resin (D); and a curing agent containing an isocyanate compound (E);
A two-part clear coating composition comprising:
It is.

One-pack type clear coating composition In the coating film forming method of the present invention, a one-pack type clear resin containing a carboxyl group-containing acrylic resin (A), a carboxyl group-containing polyester resin (B) and an epoxy group-containing acrylic resin (C). A coating composition can be used. This one-component clear coating composition is crosslinked by forming an ester bond by a reaction between a carboxyl group and an epoxy group by heating.

  The carboxyl group-containing acrylic resin (A) contained in the clear coating composition has an average of two or more carboxyl groups in one molecule, and has an acid value of 5 to 300 mgKOH / g (solid content) and a number average molecular weight. The thing which is (Mn) 500-8000 is mentioned.

  As the carboxyl group-containing acrylic resin (A), a carboxyl group and a carboxylic ester group obtained by reacting (1) an acrylic polyanhydride and (2) a monoalcohol are bonded to adjacent carbon. It is more desirable to use a carboxyl group-containing acrylic resin. The (1) acrylic polyanhydride can be obtained by copolymerizing an acid anhydride group-containing ethylenically unsaturated monomer and an ethylenically unsaturated monomer having no acid anhydride group.

  Examples of the acid anhydride group-containing ethylenically unsaturated monomer include itaconic anhydride, maleic anhydride, and citraconic anhydride.

  Examples of the ethylenically unsaturated monomer having no acid anhydride group include styrene, α-methylstyrene, pt-butylstyrene, various (meth) acrylic esters, VeoVa-9 and VeoVa-10 manufactured by Shell. And Versatic acid glycidyl ester. Further, as an ethylenically unsaturated monomer having no acid anhydride group, a monomer having a carboxyl group such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, and an ethylenically unsaturated monomer having a hydroxyl group and an acid anhydride group Adducts with containing compounds can also be used.

  As said (2) monoalcohol, it is preferable to use a C1-C12 thing, especially 1-8 thing. This is because alcohol easily volatilizes during the reaction with the acrylic polyanhydride described above, which is suitable for regenerating the acid anhydride group. As such (2) monoalcohol, methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, n-hexyl alcohol, lauryl alcohol, methyl cellosolve, ethyl cellosolve, methoxy Examples include propanol, ethoxypropanol, furfuryl alcohol, dimethylaminoethanol, diethylaminoethanol, acetol, allyl alcohol, propargyl alcohol and the like.

  The carboxyl group-containing acrylic resin (A) is used in an amount of 10 to 70 mass%, preferably 15 to 50 mass%, more preferably 20 to 45 mass%, based on the total nonvolatile content in the resin composition. If this blending amount is less than the lower limit, the weather resistance of the resulting coating film may be lowered, and if it exceeds the upper limit, the coating film may be too hard.

  As the carboxyl group-containing polyester resin (B) contained in the clear coating composition, an acid value of 50 obtained by reacting (1) a polyester polyol having 3 or more hydroxyl groups and (2) an acid anhydride. -350 mgKOH / g (solid content), number average molecular weight 400-3500, and a weight average molecular weight / number average molecular weight are 1.8 or less.

  The carboxyl group-containing polyester resin (B) can be obtained by (1) half-esterifying a polyester polyol having 3 or more hydroxyl groups and (2) an acid anhydride. Polyester polyol refers to a polyhydric alcohol having two or more ester bond chains, which reacts with an acid anhydride group and has two or more acid functionalities per molecule and the following characteristics.

  Such (1) polyester polyol is a low molecular polyhydric alcohol having 3 to 16 carbon atoms having at least three hydroxyl groups, or a chain obtained by adding a lactone compound such as ε-caprolactone to this low molecular polyhydric alcohol. It can also be synthesized by extending. By introducing a linear aliphatic group into the low-molecular polyhydric alcohol, flexibility is imparted to the resulting coating film and impact resistance is improved.

  Examples of the low molecular weight polyhydric alcohol used include trimethylolethane, trimethylolpropane, 1,2,4-butanetriol, ditrimethylolpropane, pentaerythritol, dipentaerythritol, glycerin and mixtures thereof.

  Examples of the acid anhydride (2) include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 4-methylhexahydrophthalic anhydride, trimellitic anhydride, and succinic anhydride.

  The half esterification reaction of the above (1) polyester polyol and (2) acid anhydride can be carried out under ordinary reaction conditions such as room temperature to 150 ° C. and normal pressure. However, it is not necessary to modify all the hydroxyl groups of the polyester polyol to carboxyl groups, and the hydroxyl groups may remain. According to the above-mentioned method, since the molecular weight distribution becomes sharp, further solidification is possible, and a coating film excellent in weather resistance and water resistance can be formed.

  The carboxyl group-containing polyester resin (B) component is blended in an amount of 5 to 70% by mass, preferably 5 to 50% by mass, more preferably 10 to 40% by mass, based on the mass of the total nonvolatile content in the paint. be able to. If the amount of the carboxyl group-containing polyester resin (B) is less than the lower limit, the nonvolatile content concentration of the paint may be lowered, and if it exceeds the upper limit, the weather resistance of the coating film may be lowered.

  The epoxy group-containing acrylic resin (C) contained in the clear coating composition used in the present invention has an average of 2 or more, preferably 2 to 10, more preferably 3 to 8 epoxy groups in one molecule. It is an epoxy group-containing acrylic resin.

  What is preferable as the epoxy group-containing acrylic resin (C) is obtained by copolymerizing (1) an epoxy group-containing ethylenically unsaturated monomer 1 and (2) an ethylenically unsaturated monomer having no epoxy group. It is an epoxy group-containing acrylic resin.

  Examples of the (1) epoxy group-containing ethylenically unsaturated monomer include glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, 3,4-epoxycyclohexanyl (meth) acrylate, and the like. In order to ensure balanced curability and storage stability, it is preferable to use glycidyl (meth) acrylate.

  As said (2) ethylenically unsaturated monomer which does not have an epoxy group, what does not influence an epoxy group among the ethylenically unsaturated monomers which do not have the above-mentioned acid anhydride group can be used similarly.

  Further, (2) a hydroxyl group-containing ethylenically unsaturated monomer can be used as the ethylenically unsaturated monomer having no epoxy group. Specific examples of the hydroxyl group-containing ethylenically unsaturated monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and (meth) acrylic acid 4- Hydroxybutyl, 6-hydroxyhexyl (meth) acrylate, and their reactants with ε-caprolactone, (meth) acrylic acid and a large excess of diols (eg, 1,4 butanediol, 1,6 hexanediol, polyethylene glycol) , Polypropylene glycol) and the like are exemplified.

  The epoxy group-containing acrylic resin (C) comprises an ethylenically unsaturated monomer having a hydroxyl group-containing ethylenically unsaturated monomer, (1) an epoxy group-containing ethylenically unsaturated monomer, and a hydroxyl group and an epoxy group that are used as necessary. It can be obtained by copolymerizing with a saturated monomer. In this case, the epoxy group-containing acrylic resin (C) to be obtained has an average of 2 to 12, more preferably 3 to 10, and an average of 0.5 to 10 hydroxyl groups in one molecule, more preferably 0.5 to 10 hydroxyl groups. Have 1-8.

  The epoxy group-containing acrylic resin (C) component is 10 to 80% by mass, preferably 20 to 70% by mass, more preferably 30 to 65% by mass, based on the total solid content in the curable resin composition. It can mix | blend in quantity. If the amount of the epoxy group-containing acrylic resin is below the lower limit, the curability may be lowered, and if it exceeds the upper limit, the yellowing resistance may be deteriorated.

  The clear coating composition can be produced by mixing the carboxyl group-containing acrylic resin (A), the carboxyl group-containing polyester resin (B), and the epoxy group-containing acrylic resin (C). In particular, when the carboxyl group-containing acrylic resin (A) having a carboxyl group and a carboxylic ester group is used, and the epoxy group-containing acrylic resin (C) having a hydroxyl group and an epoxy group is used, the acid resistance is particularly excellent. A clear coating composition that forms a coating film is obtained.

  The curing mechanism of the clear coating composition obtained in this way is as follows. First, the carboxyl group in the carboxyl group-containing acrylic resin (A) reacts with the carboxylate ester group by heating to cause the carboxyl group-containing acrylic resin (A) to react. An acid anhydride group is formed, and a free monoalcohol is formed. The produced monoalcohol is evaporated and removed out of the system. And the acid anhydride group produced | generated in carboxyl group-containing acrylic resin (A) forms a crosslinking point by reacting with the hydroxyl group contained in carboxyl group-containing polyester resin (B) and epoxy group-containing acrylic resin (C). Then, a carboxyl group is formed again. The carboxyl group and the carboxyl group present in the carboxyl group-containing polyester resin (B) react with the epoxy group present in the epoxy group-containing acrylic resin (C) to form a crosslinking point. In this way, the three types of polymers react with each other, so that curing proceeds and a coating film crosslinked at a high density is formed.

  The clear coating composition may contain a curing catalyst usually used in an esterification reaction between an acid such as a quaternary ammonium salt and an epoxy. Examples of the curing catalyst include benzyltriethylammonium chloride or bromide, tetrabutylammonium chloride or bromide, salicylate or glycolate, paratoluenesulfonate, and the like.

  In addition, a known tin-based compound described in JP-A-2-151651 can be mixed in the clear coating composition. Examples of such a tin-based catalyst include dimethyltin bis (methyl maleate), dimethyltin bis (ethyl maleate), dimethyltin bis (butyl maleate), dibutyltin bis (butyl maleate), and the like.

  A blocked isocyanate can be added to the clear coating composition in order to increase the crosslinking density and improve the water resistance. Moreover, you may add a well-known ultraviolet absorber, light stabilizer, antioxidant, etc. Furthermore, known rheology control agents and other surface conditioners may be added, and solvents such as alcohol solvents, aromatic hydrocarbon solvents, ester solvents and ketone solvents are used for viscosity adjustment and the like. You can also.

Two-component clear coating composition In the coating film forming method of the present invention, a two-component clear coating composition comprising: a main agent containing a hydroxyl group-containing acrylic resin (D); and a curing agent containing an isocyanate compound (E); Can also be used to form a clear coating film. This two-component clear coating composition may be a solvent type or an aqueous type.

  The hydroxyl group-containing acrylic resin (D) contained in the main component of the two-pack type clear coating composition has a number average molecular weight (Mn) of 1500 to 6000, a hydroxyl value of 100 to 200, and the ratio of secondary hydroxyl groups in the hydroxyl value. It is preferable that it is a hydroxyl-containing acrylic resin (D) which is 20 to 100%.

  The hydroxyl group-containing acrylic resin (D) can be prepared by copolymerizing a hydroxyl group-containing acrylic monomer and another ethylenically unsaturated group-containing monomer by an ordinary method. Here, it is more preferable to use an acrylic monomer having a secondary hydroxyl group as the hydroxyl group-containing acrylic monomer.

  Examples of the secondary hydroxyl-containing acrylic monomer that can be used for the synthesis of the hydroxyl group-containing acrylic resin (D) include 2-hydroxypropyl (meth) acrylate and 2-hydroxybutyl (meth) acrylate. An acrylic monomer having a primary hydroxyl group instead of a secondary hydroxyl group can also be used. Examples thereof include hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl methacrylate; Plaxel FM -1 (trade name, adduct of 2-hydroxyethyl (meth) acrylate and polycaprolactone, manufactured by Daicel Chemical Industries); polyalkylene glycol mono (meth) acrylates, and the like. These may be used alone or in combination of two or more. In the present specification, (meth) acrylate represents acrylate and / or methacrylate.

  It does not specifically limit as said other ethylenically unsaturated group containing monomer, For example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meta) ) Alkyl (meth) acrylates such as acrylate, t-butyl acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate; aromatic vinyl monomers such as styrene and vinyltoluene; glycidyl (meth) acrylate, etc. Epoxy group-containing monomers; amino group-containing monomers such as dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate; (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-butoxymethyl (meta Acrylamide, acrylamide monomer such as N- methylacrylamide; acrylonitrile, vinyl acetate, acrylic acid and methacrylic acid. These may be used alone or in combination of two or more.

  The hydroxyl group-containing acrylic resin (D) preferably has a number average molecular weight (Mn) of 1,500 to 6,000, more preferably 2000 to 5,000. When the number average molecular weight is less than 1,500, workability and curability are not sufficient, and when it exceeds 6,000, the non-volatile content during coating becomes too low, and workability may be deteriorated.

  The hydroxyl group-containing acrylic resin (D) preferably has a hydroxyl value of 100 to 200. The hydroxyl value is preferably 110 to 180. If the hydroxyl value exceeds the upper limit, the water resistance of the coating film decreases, and if it falls below the lower limit, the curability of the coating film may decrease. Furthermore, the hydroxyl group-containing acrylic resin (D) in the present invention preferably has a ratio of secondary hydroxyl groups in the hydroxyl value of 20 to 100%. The proportion of secondary hydroxyl groups in the hydroxyl value is more preferably 30 to 100%. When the secondary hydroxyl group is less than 20%, the curing reaction rate cannot be delayed, the internal stress of the coating film increases, and the chipping resistance tends to be lowered. Even if the secondary hydroxyl group is 100%, there is no significant drop in the curing reaction rate, and the workability and the degree of curing are not adversely affected.

  Moreover, in the hydroxyl group-containing acrylic resin (D), the storage stability (pot life) after mixing the main agent and the curing agent is improved by the proportion of the secondary hydroxyl group in the hydroxyl value being 20 to 100%. There are also advantages.

  The hydroxyl group-containing acrylic resin (D) preferably has an acid value of 1 to 45 mgKOH / g. The acid value is more preferably 2 to 30 mgKOH / g. When the acid value exceeds the upper limit, the water resistance of the coating film may be reduced, and when the acid value is lower than the lower limit, the curability of the coating film may be reduced.

  The isocyanate compound (E) contained in the curing agent is not particularly limited as long as it is an isocyanate compound used as a curing agent for paints. Typical isocyanate compounds include aliphatic isocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate, 1,3-cyclopentane diisocyanate, 1,4-cyclohexane. Aliphatic cyclic isocyanates such as diisocyanate, 1,2-cyclohexane diisocyanate, aromatic isocyanates such as xylylene diisocyanate (XDI), 2,4-tolylene diisocyanate (TDI), 2,6-tolylene diisocyanate, isophorone diisocyanate ( IPDI), alicyclic isocyanates such as norbornane diisocyanate methyl, these burettes, It can be used multimers and mixtures such as body.

  In the two-component clear coating composition used in the present invention, the mixing ratio of the hydroxyl group-containing acrylic resin (D) contained in the main agent and the isocyanate compound (E) contained in the curing agent can be variously selected depending on the purpose. In the present invention, the equivalent ratio (NCO / OH) of the isocyanate group (NCO) of the isocyanate compound (E) to the hydroxyl group (OH) of the hydroxyl group-containing acrylic resin (D) is in the range of 0.6 to 1.5. It is preferable to use it in an amount. When the content of the isocyanate compound (E) is less than the above lower limit, the curability may be insufficient. On the other hand, when the content exceeds the upper limit, the cured film may become hard and brittle. It is particularly preferable that the equivalent ratio (NCO / OH) of the isocyanate group (NCO) to the hydroxyl group (OH) is in the range of 0.7 to 1.3.

  The above-described two-component clear coating composition may further contain a viscosity control agent. By including the viscosity control agent, the coating workability can be improved. As the viscosity control agent, those generally showing thixotropy can be used, for example, those already described in the aqueous base coating composition can be used. Further, if necessary, it may contain a curing catalyst, a surface conditioner and the like. Furthermore, you may contain a well-known ultraviolet absorber, light stabilizer, antioxidant, etc. Furthermore, a known surface conditioner or the like may be added, and a solvent such as an alcohol solvent, an aromatic hydrocarbon solvent, an ester solvent, or a ketone solvent may be used for the purpose of adjusting the viscosity. These additives can be included in the main agent and / or the curing agent.

  Regarding the mixing timing of the main agent and the curing agent in the two-pack type clear coating composition, the main agent and the curing agent may be mixed before use and coated by a normal coating method. Moreover, you may paint by the method of sending each liquid to a gun with a 2 liquid mixing gun, and mixing with a gun tip.

Laminate coating formation method
Substrate The method for forming a laminated coating film of the present invention can be advantageously used for various substrates such as metals, plastics, foams, etc., particularly metal surfaces, and castings. Especially, it can use especially suitably with respect to the metal product which can be cationic electrodeposition coating.

  Examples of the metal products include iron, copper, aluminum, tin, zinc, and the like and alloys containing these metals. Specific examples include automobile bodies and parts such as passenger cars, trucks, motorcycles, and buses. These metals are particularly preferably those subjected to chemical conversion treatment with phosphate, chromate, zirconium salt or the like in advance.

  Moreover, as for the to-be-coated article used for the laminated coating film formation method of this invention, an electrodeposition coating film is formed on the base material by which chemical conversion treatment was carried out as needed. As the electrodeposition paint for forming the electrodeposition coating film, a cation type and an anion type can be used. However, the cationic electrodeposition coating composition is preferable because it provides a laminated coating film excellent in corrosion resistance. Examples of the cationic electrodeposition coating composition that can be preferably used include a cationic electrodeposition coating composition containing an amine-modified epoxy resin, a blocked isocyanate curing agent, and an optional pigment. Cationic electrodeposition coating is performed by immersing a base material in an electrodeposition coating composition, and then applying a voltage between the base material as a cathode and an anode to deposit a film. The energization time varies depending on the electrodeposition conditions, but is generally about 2 to 4 minutes. The applied voltage is, for example, a voltage of 50 to 450 V between the base material as the cathode and the anode. In this way, after electrodeposition coating, washing with water as necessary is performed. Subsequently, an electrodeposition coating film is usually formed by baking at 140 to 180 ° C. for 10 to 30 minutes.

  In the formation of the multilayer coating film of the present invention, the base coating film and the clear coating film are sequentially formed without providing the intermediate coating film using the substrate on which the electrodeposition coating film is formed in this manner as an object to be coated.

Laminated coating film formation The coating film forming method of the present invention comprises applying a water-based base coating composition and a clear coating composition in order on a substrate to be coated by wet-on-wetting to form an uncured base coating film and a clear coating film. Form.

  The aqueous base coating composition can be applied by air electrostatic spray coating or a rotary atomizing electrostatic coating machine such as a metabell, μμ bell, or μ bell. The dry film thickness of a base coating film can be set to 5-35 micrometers, Preferably it is 7-30 micrometers. If the film thickness of the base coating film exceeds 35 μm, the sharpness may be deteriorated, or unevenness or flow may occur in the coating film. Neither of these is preferable because a discontinuous state of the film may occur.

  In the method for forming a coating film according to the present invention, the clear coating film to be applied after the base coating film is formed smoothes the unevenness caused by the base coating film and the unevenness caused by the base coating film. Formed to protect. Specifically, as a coating method, it is preferable to form a coating film by a rotary atomizing electrostatic coating machine such as the μμ bell or μbell described above.

  The clear coating composition uses an organic solvent as a dilution medium for the above-described coating viscosity determined based on the atomization method of the electrostatic coating machine or the coating environment such as temperature and humidity. Dilute and adjust the viscosity before painting. Generally, it is preferable that the coating viscosity in the range of 10 ° C. to 40 ° C. and humidity of 10 to 98% is 15 to 80 seconds (/ 20 ° C. No. 4 Ford cup). Outside this range, defects such as sagging and armpits are likely to occur. More preferably, it is 18 to 60 seconds (/ 20 ° C., No. 4 Ford Cup).

  The dry film thickness of the clear coating film formed from the clear coating composition is generally preferably about 10 to 80 μm, more preferably about 20 to 60 μm. Exceeding the upper limit may cause problems such as armpits or sagging. If the lower limit is not reached, the underlying irregularities may not be concealed.

  The two types of coating films thus obtained are cured by so-called two-coat one-bake that is baked and cured at a time. This method can omit the baking and drying furnace for the base coating film, and is preferable from the viewpoint of economy and environmental protection.

  By setting the curing temperature for curing the multilayer coating film to 100 to 180 ° C., preferably 120 to 160 ° C., a multilayer coating film having good hardness can be obtained. If the upper limit is exceeded, the coating film may become hard and brittle, and if the lower limit is not reached, sufficient curing may not be obtained. Although hardening time changes with hardening temperature, it is about 10 to 60 minutes at 120 to 160 degreeC.

  The film thickness of the laminated coating film formed in the present invention is 10 to 150 μm in many cases, and preferably 30 to 150 μm. If the upper limit is exceeded, film physical properties such as cooling and cooling cycles will decrease, and if it falls below the lower limit, the strength of the film itself may decrease.

  In the laminated coating film forming method of the present invention, there is an advantage that the coating film smoothness of the obtained laminated coating film is improved by including the active methylene type block polyisocyanate (U) in the aqueous base coating composition. .

  As a method for improving the coating film appearance of a multilayer coating film obtained by a two-coat one-bake method in which a base coating composition and a clear coating composition are sequentially applied by wet-on-wet and then baked and cured, Studies are underway to control the cure rate. For example, the rate of cure during baking of uncured base and clear coatings can be reduced from lower coatings by assembling the coating composition such that the base coating cures faster and the clear coating cures slower. As a result, it is possible to prevent the occurrence of "waks" due to the formation of a hole when the solvent in the coating film evaporates and escapes, thereby improving the smoothness of the coating film. Conceivable.

  The aqueous base coating composition used in the present invention contains active methylene type block polyisocyanate (U). This active methylene type block polyisocyanate (U) has a higher reactivity than a melamine resin contained in a general aqueous base coating composition, and reacts at a lower temperature during baking and curing. For this reason, the curing start temperature of the aqueous base coating composition is lowered, whereby the curing of the uncured base coating proceeds faster than the curing of the clear coating. For this reason, when forming a laminated coating film, volatilization of the solvent contained in a base coating film is performed smoothly, and the coating film smoothness in a laminated coating film will improve.

  As the hydroxyl group-containing acrylic resin contained in the two-component clear coating composition, those in which 20 to 100% of the hydroxyl groups are secondary hydroxyl groups are preferably used. By using a hydroxyl group-containing acrylic resin containing a secondary hydroxyl group in this way, the curing reaction of the clear coating composition is delayed. More specifically, the curing start temperature of the clear coating composition increases. When the curing start temperature of the clear coating composition increases, the solvent that volatilizes from the lower layer, that is, the base coating, volatilizes while the clear coating does not start curing. For this reason, no trace of the solvent remains on the clear coating film, so that no coating film defect occurs and the coating film appearance is further improved.

  In the present invention, preferably, the curing start temperatures of the respective coating materials are in the order of clear coating composition (or clear coating film)> base coating composition (or base coating film).

  The following examples further illustrate the present invention, but the present invention is not limited thereto. In the examples, “parts” and “%” are based on mass unless otherwise specified.

Production Example 1-1 Production of Acrylic Resin Emulsion (A) 126.5 parts of deionized water was added to a reaction vessel, and the temperature was raised to 80 ° C. while mixing and stirring in a nitrogen stream. Next, as a monomer mixture (a) used for preparing the core part, 33.70 parts of methyl acrylate, 34.88 parts of ethyl acrylate, 7.42 parts of 2-hydroxyethyl methacrylate, 4.00 parts of acrylamide, Aqualon HS -10 (polyoxyethylene alkylpropenyl phenyl ether sulfate ester, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 0.5 part, Adekalya soap NE-20 (α- [1-[(allyloxy) methyl] -2- (nonylphenoxy) Ethyl] -ω-hydroxyoxyethylene (manufactured by Asahi Denka Co., Ltd., 80% aqueous solution) 0.5 part and deionized water 80 parts monomer emulsion, ammonium persulfate 0.24 parts, and deionized water 10 parts The resulting initiator solution was added dropwise to the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.

  Then, as monomer mixture (b) used for the preparation of the shell part, ethyl acrylate 15.84 parts, 2-hydroxyethyl methacrylate 1.86 parts, methacrylic acid 2.30 parts, Aqualon HS-100.2 parts, and A monomer emulsion consisting of 10 parts of deionized water, 0.06 part of ammonium persulfate and an initiator solution consisting of 10 parts of deionized water were added dropwise to the reaction vessel in parallel at 80 ° C. for 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.

  Next, after cooling to 40 ° C. and filtering through a 400 mesh filter, 67.1 parts of deionized water and 0.32 part of dimethylaminoethanol were added to adjust the pH to 6.5, an average particle diameter of 190 nm, a non-volatile content of 20%, An acrylic resin emulsion (a) having a solid content acid value of 15 and a hydroxyl value of 40 was obtained.

Production Example 1-2 Production of acrylic resin 23.89 parts of dipropylene glycol methyl ether and 16.11 parts of propylene glycol methyl ether were added to a reaction vessel, and the mixture was heated to 105 ° C. while being mixed and stirred in a nitrogen stream. Next, 13.1 parts of methyl methacrylate, 68.4 parts of ethyl acrylate, 11.6 parts of 2-hydroxyethyl methacrylate, 6.9 parts of methacrylic acid, 10.0 parts of dipropylene glycol methyl ether and t-butyl An initiator solution consisting of 1 part of peroxy 2-ethylhexanoate was dropped into the reaction vessel in parallel over 3 hours. After completion of the dropping, aging was performed at the same temperature for 0.5 hours.

  Further, an initiator solution consisting of 5.0 parts of dipropylene glycol methyl ether and 0.3 part of t-butylperoxy 2-ethylhexanoate was added dropwise to the reaction vessel over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.

  After removing 11.11 parts of the solvent at 110 ° C. under reduced pressure (70 torr) with a solvent removal apparatus, 204 parts of deionized water and 7.14 parts of dimethylaminoethanol were added to obtain an acrylic resin B-1 solution. The obtained acrylic resin solution had a non-volatile content of 30.0%, a solid content acid value of 40, a hydroxyl value of 50, and a viscosity of 140 poise (E-type viscometer 1 rpm / 25 ° C.).

Production Example 1-3 Production of Phosphoric Acid Group-Containing Acrylic Resin 40 parts of ethoxypropanol was charged into a 1 liter reaction vessel equipped with a stirrer, temperature controller, and condenser, and 4 parts of styrene and 35.96 of n-butyl acrylate were added thereto. Parts, ethyl hexyl methacrylate 18.45 parts, 2-hydroxyethyl methacrylate 13.92 parts, methacrylic acid 7.67 parts, ethoxypropanol 20 parts, Phosmer PP (Acid phosphooxyhexa (oxypropylene) monomethacrylate manufactured by Unichemical Co., Ltd.) ) 40 parts of a solution in which 20 parts were dissolved and 121.7 parts of a monomer solution consisting of 1.7 parts of azobisisobutyronitrile were added dropwise at 120 ° C. for 3 hours, and stirring was further continued for 1 hour.

  The obtained resin was an acrylic varnish (nonvolatile content: 63%) having an acid value of 105 mgKOH / g, of which an acid value of 55 mgKOH / g based on a phosphate group, a hydroxyl value of 60 mgKOH / g, and a number average molecular weight of 6000.

Comparative Production Example 1 Production of block polyisocyanate (ratio-1) Hexamethylene diisocyanate (Desmodur H, manufactured by Sumitomo Bayer Urethane Co., Ltd.) in a flask equipped with a stirrer, cooler, nitrogen injection tube, thermometer and dropping funnel 168. 0 parts, 73.2 parts of methyl isobutyl ketone, and 0.2 part of dibutyltin dilaurate were weighed. While stirring and bubbling nitrogen, 34.6 parts of trimethylolpropane was dropped from a dropping funnel, and then 106.7 parts of methyl isobutyl ketone oxime was dropped from the dropping funnel over 1 hour. The temperature was increased from 50 ° C. to 70 ° C. Thereafter, the reaction was continued for 1 hour, and the reaction was continued until the absorption of the NCO group disappeared with an infrared spectrometer. Thereafter, methyl isobutyl ketone was added to obtain a non-volatile content of 78% to obtain a block polyisocyanate (ratio-1).

Production Example 2-1 Production of hydroxyl group-containing acrylic resin (D) 30 g of butyl acetate was charged in a container equipped with a stirrer, a temperature controller, and a reflux condenser, and the temperature was raised to 120 ° C. Next, a solution having the following composition (20 parts of styrene, 15.3 parts of n-butyl acrylate, 27.9 parts of n-butyl methacrylate, 36 parts of 2-hydroxypropyl methacrylate, 0.8 parts of acrylic acid) and Kayaester O 12 And 6 parts of butyl acetate were added dropwise over 3 hours, then left for 30 minutes, a solution of 0.5 part of Kayaester O and 4 parts of butyl acetate was added dropwise over 30 minutes, and the reaction solution was stirred for 1 hour. After increasing the rate of change to the resin, the reaction was terminated, and the solid content was 70%, the number average molecular weight was 3800, the hydroxyl value was 140 (of which the secondary hydroxyl group ratio was 100%), and the acid value was 6.2 mg / KOH. A varnish of a hydroxyl group-containing acrylic resin (D) was obtained.

Example 1
55 parts of the acrylic resin emulsion resin (A) obtained in Production Example 1-1 of the manufacturer of the aqueous base coating composition , 10 parts of a 10% by mass dimethylethanolamine aqueous solution, and 10 parts of the acrylic resin of Production Example 1-2. Part, Prime Pol PX-1000 (Sanyo Kasei Kogyo Co., Ltd., bifunctional polyether polyol, number average molecular weight 400, hydroxyl value 278, primary / secondary hydroxyl value ratio = 63/37) as polyether polyol (I) 10 Part, Duranate ^(trademark) MFK60X as an active methylene type block polyisocyanate (Asahi Kasei Co., Ltd., active methylene type block polyisocyanate (hexafunctional)) (U-1) 41.7 parts, glitter pigment (D) 21 parts of Alpaste MH8801 (aluminum pigment manufactured by Asahi Kasei Co., Ltd.), phosphoric acid group-containing acrylic of Production Example 1-3 An aqueous base coating composition was obtained by adding 5 parts of resin and 0.3 part of lauryl acid phosphate and dispersing uniformly.

Laminated coating film formation Zinc phosphate treated 0.8 mm thick, 30 cm long, 40 cm wide steel plate with cationic electrodeposition paint “Power Top U-50” (manufactured by Nippon Paint Co., Ltd.), resulting in a dry film thickness of 20 μm Electrodeposition coating was performed and baked at 160 ° C. for 30 minutes.

  To the resulting coated plate, the aqueous base coating composition produced as described above was diluted with deionized water for 30 seconds (measured at 20 ° C. using a No. 4 Ford cup). Under the conditions of room temperature of 25 ° C. and humidity of 85%, two-stage coating was performed with “μμ Bell COPES-IV type” (manufactured by ABB Industry) for water-based paint coating so that the dry film thickness was 15 μm. An interval setting of 1 minute was performed between the two coatings. After the second application, setting was performed with an interval of 5 minutes. Thereafter, preheating was performed at 80 ° C. for 5 minutes.

  Next, in advance, no. Uncured intermediate coating and base coating with 1-pack type clear coating composition “McFlow O-600” (manufactured by Nippon Paint Co., Ltd.) diluted to 25 seconds / 20 ° C. in a 4 Ford cup. Once coated with “METABELL” (rotary atomization type electrostatic coating machine manufactured by Lansburg), the coated film on which the film is formed is wet-on-wet so that the dry film of the clear film becomes 35 μm. Painted.

  An object on which a two-layer uncured coating film was formed was left standing at room temperature for 7 minutes in a vertical state, and then baked in a dryer at 140 ° C. for 20 minutes in the vertical state. A laminated coating film by coating 1 baking was obtained.

Example 2
Production of water-based base coating composition and laminated coating film formation As active methylene type block polyisocyanate, Duranate ^(trademark) MFK60X (manufactured by Asahi Kasei Co., Ltd., active methylene type block polyisocyanate (hexafunctional)) (U-1) An aqueous base coating composition was prepared in the same manner as in Example 1 except that 31.3 parts and 8.1 parts of Cymel 204 (manufactured by Nippon Cytec Co., Ltd., mixed alkylated melamine) were used as the melamine resin. .
A laminated coating film was formed in the same manner as in Example 1 using the obtained aqueous base coating composition.

Example 3
Production of water-based base coating composition and laminated coating film formation As active methylene type block polyisocyanate, Duranate ^(trademark) MFK60X (manufactured by Asahi Kasei Co., Ltd., active methylene type block polyisocyanate (hexafunctional)) (U-1) An aqueous base coating composition was prepared in the same manner as in Example 1 except that 20.8 parts and 29.2 parts of Cymel 204 as a melamine resin were used.
A laminated coating film was formed in the same manner as in Example 1 using the obtained aqueous base coating composition.

Example 4
Production of water-based base coating composition and laminated coating film formation As active methylene type block polyisocyanate, Duranate ^(trademark) MFK60X (manufactured by Asahi Kasei Co., Ltd., active methylene type block polyisocyanate (hexafunctional)) (U-1) An aqueous base coating composition was prepared in the same manner as in Example 1 except that 10.4 parts and 24.3 parts of Cymel 204 as a melamine resin were used.
A laminated coating film was formed in the same manner as in Example 1 using the obtained aqueous base coating composition.

Example 5
Production of water-based base coating composition and laminated film forming active methylene type block polyisocyanate, instead of Duranate ^(trademark) MFK60X, Duranate ^(trademark) K-6000 (manufactured by Asahi Kasei Corporation, active methylene type block polyisocyanate) (Trifunctional)) An aqueous base coating composition was prepared in the same manner as in Example 1 except that 41.7 parts of (U-2) was used.
A laminated coating film was formed in the same manner as in Example 1 using the obtained aqueous base coating composition.

Example 6
Manufacture of two-pack type clear coating composition In a 1 L metal container, 245.3 parts of the varnish of the hydroxyl group-containing acrylic resin (D) of Production Example 2-1 and Ciba Geigy UV absorber “Tinuvin 384” 5.6 5.6 parts of a light stabilizer “Tinuvin 123” manufactured by Ciba Geigy Co., 5.6 parts of an acrylic surface conditioner, 37.0 parts of toluene and 37.0 parts of xylene were sequentially added, and the mixture was sufficiently stirred with a disper. Next, 0.5 parts of an organic carboxylic acid ammonium salt “BYK-ES80” and 6.0 parts of methanol manufactured by Big Chemie Company were added and further stirred to obtain a main component of a two-pack type clear coating composition.

  To another metal container, 100.0 parts of “Dismodule N-3300” (NCO active ingredient 22%) manufactured by Sumitomo Bayer Urethane Co., Ltd. and 2-ethylethoxypropanol are sequentially added, stirred well, and a two-component clear paint. A curing agent for the composition was obtained.

Formation of Laminate Coating Film Cathode electrodeposition paint “Power Top U-50” (manufactured by Nippon Paint Co., Ltd.) on a dull steel plate of 0.8 mm thickness, 30 cm length and 40 cm width treated with zinc phosphate, with a dry film thickness of 20 μm Electrodeposition coating was performed and baked at 160 ° C. for 30 minutes.

To the resulting coated plate, the aqueous base coating composition produced in Example 1 was diluted with deionized water for 50 seconds (measured at 20 ° C. using a No. 4 Ford cup). Under the conditions of room temperature of 25 ° C. and humidity of 85%, two-stage coating was performed with “μμ Bell COPES-IV type” (manufactured by ABB Industry) for water-based paint coating so as to have a dry film thickness of 15 μm. An interval setting of 1 minute was performed between the two coatings. After the second application, setting was performed with an interval of 5 minutes. Thereafter, preheating was performed at 80 ° C. for 5 minutes.
I did the setting. Thereafter, preheating was performed at 80 ° C. for 5 minutes.

  62/38 (mass ratio (%), equivalent ratio of isocyanate group (NCO) and hydroxyl group (OH) (NCO / OH) = the main component and the curing agent of the two-component clear coating composition obtained from the above) 1.1 / 1) to obtain a clear coating composition (organic solvent content: 64% by mass). The resulting clear coating composition was diluted with a diluent solvent consisting of 2-ethylethoxypropanol / xylene = 1/1 (measured at 20 ° C. using a No. 4 Ford cup) for 30 seconds. The clear coating of the above production example was applied in one stage with “Microbell” so that the dry film thickness was 40 μm.

  An object on which a two-layer uncured coating film is formed is allowed to stand at room temperature for 10 minutes in a vertical state and then baked in a dryer at 140 ° C. for 20 minutes in the vertical state. A laminated coating film by coating 1 baking was obtained.

Comparative Example 1
Preparation of water-based base coating composition and laminated coating film formation A water-based base is the same as in Example 1 except that no active methylene type block polyisocyanate is used, while 32.5 parts of Cymel 204 is used as the melamine resin. A coating composition was prepared.
A laminated coating film was formed in the same manner as in Example 1 using the obtained aqueous base coating composition.

Comparative Example 2
Production of water-based base coating composition and laminated coating film formation Active methylene type block polyisocyanate was not used, while 41.7 parts of Uban 20N60 (Mitsui Chemicals, methyl isobutyl imino type melamine) was used as a melamine resin. Except for this, an aqueous base coating composition was prepared in the same manner as in Example 1.
A laminated coating film was formed in the same manner as in Example 1 using the obtained aqueous base coating composition.

Comparative Example 3
Production of water-based base coating composition and laminated coating film formation Active methylene-type block polyisocyanate was not used, while on the other hand 31.3 parts of Cymel 254 (manufactured by Nippon Cytec Co., Ltd., methylisobutyl-based imino-type melamine) was used. Except for this, an aqueous base coating composition was prepared in the same manner as in Example 1.
A laminated coating film was formed in the same manner as in Example 1 using the obtained aqueous base coating composition.

Comparative Example 4
Production of water-based base coating composition and laminated coating film formation Example 1 except that 32.1 parts of the block polyisocyanate (ratio-1) of Comparative Production Example 1 was used instead of the active methylene type block polyisocyanate. Similarly, an aqueous base coating composition was prepared.
A laminated coating film was formed in the same manner as in Example 1 using the obtained aqueous base coating composition.

  The following evaluation was performed using the coating film obtained by the said Example and comparative example.

Adhesiveness to the electrodeposition coating film A 0.8mm thickness, 30cm length, 40cm width dull steel plate treated with zinc phosphate is coated with a cationic electrodeposition paint "Power Top U-50" (manufactured by Nippon Paint Co., Ltd.). Electrodeposition coating was performed to 20 μm and baking was performed at 190 ° C. for 1 hour.

The obtained base plate was coated with the aqueous base coating composition used in each Example and Comparative Example so as to have a dry film thickness of 15 μm according to each Example and Comparative Example. Next, the clear coating composition used in each Example and Comparative Example was applied to a dry film thickness of 30 μm according to each Example and Comparative Example, and baked and cured at 140 ° C. for 20 minutes.
Using a cutter knife (NT cutter S type or A type) on the coating film surface of the laminated coating film obtained from the above, the coating plate base material penetrates 11 vertical x 11 horizontal coatings at an interval of 2 mm. 100 squares were formed in the coating. On this cross-cut coating film, a cellophane adhesive tape (manufactured by Nichiban Co., Ltd.) having a width of 24 mm was uniformly pressed with a fingertip so as not to generate bubbles. Immediately holding one end of the adhesive tape, the adhesive tape was peeled off from the surface of the coated plate by pulling it rapidly at an angle of about 45 ° to the coated plate. The interlayer adhesion of the coating film was evaluated under the following criteria based on the area ratio of the coating film peeled off with the adhesive tape. The adhesiveness was evaluated by visually measuring [number of peeled eyes] / [number of goofy eyes = 100] at this time.

Evaluation of chipping resistance The test plate having the laminated coating film obtained in each Example and Comparative Example was tested using the Gralove Tester KSS-1 (manufactured by Suga Test Instruments Co., Ltd., Diamond Shot System) under the following conditions. Went.
<Test conditions>
Stone size: 6-8mm
Stone amount: 0.7-0.8g / piece Distance: 35cm
Shot pressure: 0.6kg / cm2
Shot angle: 45 °
Test temperature: -20 ° C

The test plate after the stepping stone test was evaluated according to the following criteria.
5: Peeling is hardly seen.
4: Although the peeling area is small, slight peeling is observed at the interface between the electrodeposition coating film and the base coating film.
3: The peeling area is slightly large, and peeling is observed at the interface between the electrodeposition coating film and the base coating film.
2: The peeling area is large, and peeling is observed at the interface between the electrodeposition coating film and the base coating film.
1: The peeling area is large, and the electrodeposition coating film is broken.

Appearance Evaluation of Laminated Coating Film About the surface of the laminated coating film obtained as described above, the finished appearance was evaluated by measuring the Wa value using “Wave Scan DOI” manufactured by BYK-Gardner GmbH. The Wa value is an index for evaluating the gloss and fine skin of the coating film. The lower the value, the higher the coating film smoothness and the better the finished appearance.

  The composition and evaluation results of the above examples and comparative examples are summarized in the following table. In addition, the numerical value of the column of the water-based base coating composition in the following table | surface shows each component compounding quantity (solid content mass with respect to coating resin solid content).

  In the examples according to the blending of the present invention, both chipping resistance and appearance evaluation of the laminated coating film are excellent. Comparative Examples 1 to 3 are examples in which the active methylene type block polyisocyanate was not used and the type of melamine resin was changed. As is apparent from Comparative Examples 1 to 3, when no active methylene type block polyisocyanate is used, the chipping resistance is poor and the Wa value of the appearance evaluation is also poor. Comparative Example 4 is an example using the block polyisocyanate of Comparative Production Example 1 which is not an active methylene type block polyisocyanate, but both the chipping resistance and the appearance evaluation of the laminated coating film were also poor.

  In the present invention, the multilayer coating film obtained by the coating method in which the multilayer coating film composed of the base coating film and the clear coating film is formed on the electrodeposition coating film without the intermediate coating process is not subjected to the intermediate coating. Nevertheless, it has a characteristic that it has good coating film performance in terms of interlayer adhesion and chipping resistance of the coating film. According to the present invention, it is possible to form a laminated coating film by a two-coat one-bake method on an electrodeposition coating film without performing an intermediate coating process without deteriorating coating film properties or coating film appearance. By the method for forming a multilayer coating film of the present invention, a multilayer coating film having an excellent coating film appearance can be formed by an industrially excellent method.

Claims (3)

An aqueous base coating composition and a clear coating composition are sequentially applied on a substrate on which an electrodeposition coating is formed by wet-on-wet, and two uncured coatings that have been applied are coated at once. Baking and curing,
A method for forming a laminated coating film comprising:
The aqueous base coating composition comprises an acrylic resin emulsion (A); a polyether polyol (A); an active methylene type block polyisocyanate (U);
The acrylic resin emulsion (a) is obtained by emulsion polymerization of a monomer mixture (a) containing 1 to 20% by mass of a polyfunctional unsaturated monomer containing two or more (meth) acrylate groups in one molecule. A core portion having a crosslinked structure;
A shell part obtained by emulsion polymerization of a monomer mixture (b) containing a carboxylic acid group-containing unsaturated monomer and a hydroxyl group-containing unsaturated monomer,
A core-shell type acrylic resin emulsion having a hydroxyl value of 10 to 200 and an acid value of 1 to 80 mgKOH / g,
The polyether polyol (I) is a polyether polyol having an average of 0.02 or more primary hydroxyl groups in one molecule, a number average molecular weight of 300 to 3000, and a water tolerance of 2.0 or more.
An aqueous base coating composition, wherein the clear coating composition further comprises:
A one-component clear coating composition comprising: a carboxyl group-containing acrylic resin (A); a carboxyl group-containing polyester resin (B); and an epoxy group-containing acrylic resin (C);
A two-component clear coating composition comprising: a main agent comprising a hydroxyl group-containing acrylic resin (D); and a curing agent comprising an isocyanate compound (E).
Laminated coating film forming method. The clear coating composition is a two-component clear coating composition comprising: a main agent containing a hydroxyl group-containing acrylic resin (D); and a curing agent containing an isocyanate compound (E);
The hydroxyl group-containing acrylic resin (D) contained in the main agent has a number average molecular weight (Mn) of 1500 to 6000, a hydroxyl value of 100 to 200, and the proportion of secondary hydroxyl groups in the hydroxyl value is 20 to 100%. A hydroxyl group-containing acrylic resin,
The method for forming a laminated coating film according to claim 1.   A coated article having a multilayer coating film obtained by the method for forming a multilayer coating film according to claim 1.