JP5464575B2 - 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.

  Industrial products such as automobiles are generally provided with a laminated coating film to give an aesthetic appearance. In particular, an intermediate coating film, a base coating film, and a clear coating film are sequentially formed on a substrate on which an electrodeposition coating has been applied in order to give a high-quality appearance to an automobile. Previously, the three-layer laminated coating film of the intermediate coating film, the base coating film, and the clear coating film was formed by baking and curing each coating film one after another. However, in recent years where resource saving and energy saving are required, the so-called two-coat one-bake is applied in which a clear coating is applied without baking and curing after the base coating is applied, and then both the base coating and the clear coating are baked and cured at once. The method of forming a multilayer coating film by the method, and further developing it to form not only the base coating film but also the intermediate coating film without baking and curing after application, three layers (intermediate coating film, base coating film) A method of forming a multilayer coating film by a so-called three-coat one-bake method for baking and curing a film and a clear coating film at a time has been proposed.

  Such a film-forming method that reduces the number of times of baking and curing is not necessarily an ideal multilayer film-forming method, but the appearance of the film due to physical or chemical changes during curing, such as inter-layer mixing and familiarity. Increased chance of impact. In particular, in the case of a so-called metallic coating film in which a bright pigment such as aluminum flake is blended in the base coating film, more careful control is required.

  For example, in the method of forming a multi-layer coating film of 3 coats and 1 bake, many improvements such as adjustment of paints for each of the 3 layers have been proposed. JP 2007-75791 A (Patent Document 1) describes the coating film appearance of a multilayer coating film formed by 3 coats and 1 bake by defining all compositions of the intermediate coating, base coating and clear coating, In particular, a technique for improving the appearance of a coating film on a vertical surface has been proposed.

JP 2007-75791 A

  An object of this invention is to improve the coating-film external appearance of the laminated coating film obtained by improving the multi-layer coating-film formation method by the 2 coat 1 baking method or the 3 coat 1 baking method.

  In the formation of a multilayer coating film by the 2-coat 1-bake method or the 3-coat 1-bake method, the present inventors have found that the solvent that volatilizes from the uncured coating film below is the cause of the coating film defect on the surface of the cured coating film. We found out that it was caused by leaving traces of solvent. The present invention proposes a method for improving coating film defects in the formation of a multilayer coating film by the 2-coat 1-bake method or the 3-coat 1-bake method.

The present invention comprises a step of coating an object to be coated with a melamine curable base coating composition containing 5% by mass or more of a melamine resin based on the solid content of the coating to form an uncured base coating film,
A step of applying a two-part clear coating composition on the uncured base coating to form an uncured clear coating; and the resulting uncured base coating and uncured clear coating A process of baking and curing the film;
A method for forming a laminated coating film comprising:
The two-part clear coating composition is
A main component containing a hydroxyl group-containing acrylic resin (A) 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 curing agent comprising an isocyanate compound (B);
A two-component clear coating composition comprising:
The present invention provides a method for forming a laminated coating film, whereby the above object is achieved.

  The melamine curable base coating composition is obtained by polymerizing a monomer mixture containing a dicarboxylic acid group-containing unsaturated monomer selected from the group consisting of maleic acid, fumaric acid, itaconic acid and their monoalkyl esters. What contains the acrylic resin which is 1-80 mgKOH is preferable.

  The melamine curable base coating composition 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. And a monomer mixture (b) containing a core part having a crosslinked structure and a dicarboxylic acid group-containing unsaturated monomer selected from the group consisting of maleic acid, fumaric acid, itaconic acid and their monoalkyl esters. A core-shell type acrylic resin emulsion (A) having an acid value of 1 to 80 mg KOH / g, a polyether polyol (I), and a melamine resin (U). What is a composition is preferable.

  Furthermore, the melamine curable base coating composition is obtained by polymerizing a monomer mixture containing a dicarboxylic acid group-containing unsaturated monomer selected from the group consisting of maleic acid, fumaric acid, itaconic acid and their monoalkyl esters. Also preferred is a solvent-based melamine curable base coating composition comprising an acrylic resin having an acid value of 1 to 80 mg KOH / g; a melamine resin (ki); and a polymerized fine particle (ku).

  In the step of forming the uncured base coating film, the coating object to which the melamine curable base coating composition is applied is a coating object having an uncured intermediate coating film, and the baking is performed. In the step of curing, the uncured intermediate coating film, the uncured base coating film and the uncured clear coating film are preferably baked and cured.

  The present invention also provides a coated article having a multilayer coating film obtained by the method for forming a multilayer coating film described above.

  The present invention further provides a two-component clear coating composition used in the method for forming a laminated coating film described above.

  According to the study by the present inventors, an uncured base coating film and a clear coating film are formed, and then baking and curing is performed. The solvent present in the film (base coating film) is volatilized through the upper layer (that is, the clear coating film layer). It was found that the trace of the film was generated and the trace was a coating film defect. In the present invention, the clear coating composition is designed to cure slowly so as not to cause traces of the solvent. Specifically, the clear coating composition is a two-pack type clear coating comprising a combination of an isocyanate compound and a hydroxyl group-containing acrylic resin, and a part or all of the hydroxyl groups of the acrylic resin are replaced with secondary hydroxyl groups, and the curing agent is caused by steric hindrance. It was designed to delay the reaction with (isocyanate compound). It is understood that if the curing reaction of the uppermost clear coating layer becomes slow, even if the solvent is volatilized, coating defects such as traces are less likely to occur and the coating appearance is improved.

  The laminated coating film obtained by sequentially applying the base coating composition and the clear coating composition, which are the methods of the present invention, by wet-on-wet has high coating film smoothness and an excellent coating film appearance. . In addition, the two-component clear coating composition used in the present invention has a high storage stability after mixing the main agent and the curing agent, and thus has an advantage of excellent coating workability.

  In the method for forming a laminated coating film of the present invention, a melamine curable base coating composition and a two-component clear coating composition are used. Hereinafter, each coating composition will be described.

Melamine curable base coating composition In the method for forming a laminated coating film of the present invention, a melamine curable base coating composition containing 5% by mass or more of melamine resin with respect to the solid content of the coating is used as the base coating composition. By forming a laminated coating film using this melamine curable base coating composition and the two-component clear coating composition described below, it can be designed so that the curing reaction rate of the clear coating film becomes slow, Thereby, there exists an advantage that the laminated coating film which has a favorable coating-film external appearance is obtained.

  The melamine curable base coating composition used in the present invention is obtained by polymerizing a monomer mixture containing a dicarboxylic acid group-containing unsaturated monomer selected from the group consisting of maleic acid, fumaric acid, itaconic acid and their monoalkyl esters. It is preferable that an acrylic resin having an acid value of 1 to 80 mgKOH is obtained. The melamine curable base coating composition may be an aqueous melamine curable base coating composition or a solvent melamine curable base coating composition.

  An acid value obtained by polymerizing a monomer mixture containing a dicarboxylic acid group-containing unsaturated monomer selected from the group consisting of maleic acid, fumaric acid, itaconic acid and their alkyl esters, on a melamine curable base coating composition By including the acrylic resin of 1 to 80 mgKOH, there is an advantage that the base coating film can be quickly cured when the uncured base coating film and the clear coating film are baked and cured at a time. The reason why the acrylic coating can be accelerated by including the acrylic resin in the melamine curable base coating composition is as follows.

  The melamine curable base coating composition includes a hydroxyl group and / or an acid group of an acrylic resin (emulsion) and a melamine resin in both the aqueous melamine curable base coating composition and the solvent type melamine curable base coating composition. It is a curing system that cures by reaction. In such a curing system, the acrylic resin (emulsion) has a carboxylic acid group derived from a dicarboxylic acid group-containing unsaturated monomer selected from the group consisting of maleic acid, fumaric acid, itaconic acid, and alkyl esters thereof. By being contained, a carboxyl group derived from maleic acid, fumaric acid or itaconic acid, which is a stronger acid compared to an acid group derived from an acrylate group contained in a general acrylic resin emulsion, is a base coating composition. It will exist inside. And the presence of this stronger acid lowers the curing start temperature of the base coating composition, whereby the base coating composition cures faster during the bake curing. 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 of a laminated coating film will improve.

  Hereinafter, specific embodiments of the aqueous melamine curable base coating composition and the solvent melamine curable base coating composition will be described.

Aqueous melamine curable base coating composition Examples of the aqueous melamine curable base coating composition that can be used in the method for forming a laminated coating film of the present invention include an aqueous coating composition containing an acrylic resin emulsion and a melamine resin. Here, the acrylic resin emulsion is obtained by polymerizing a monomer mixture containing a monoalkyl ester of a dicarboxylic acid group-containing unsaturated monomer selected from the group consisting of maleic acid, fumaric acid and itaconic acid, with an acid value of 1 to 80 mg KOH A certain acrylic resin is preferable.

  Specific examples of such an aqueous melamine curable base coating composition include, for example, an aqueous coating composition containing an acrylic resin emulsion (A); a polyether polyol (I); and a melamine resin (U). The aqueous melamine curable base coating composition may contain other coating film forming resins, glitter pigments, color pigments and the like as necessary in addition to the components (a) to (c).

Acrylic resin emulsion (A)
The acrylic resin emulsion (A) contained in the aqueous melamine curable 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 monoalkyl ester of a dicarboxylic acid group-containing unsaturated monomer selected from the group consisting of maleic acid, fumaric acid and itaconic acid,
A core-shell type acrylic resin emulsion is preferred.

  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 5-15 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, solvent resistance can be improved by using a polymerizable amide compound in preparation of a core part.

  In the present invention, the monomer mixture (b) used for the preparation of the shell part includes a monoalkyl ester of a dicarboxylic acid group-containing unsaturated monomer. Here, the dicarboxylic acid group-containing unsaturated monomer constituting the monoalkyl ester of the dicarboxylic acid group-containing unsaturated monomer is maleic acid, fumaric acid or itaconic acid.

  The alkyl group constituting the monoalkyl ester of the dicarboxylic acid group-containing unsaturated monomer contained in the monomer mixture (b) used for the preparation of the shell part is a linear or branched alkyl group having 1 to 6 carbon atoms. preferable. Specific examples of the linear or branched alkyl group having 1 to 6 carbon atoms include, for example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, pentyl group, hexyl group and the like.

  The amount of the monoalkyl ester of the dicarboxylic acid group-containing unsaturated monomer used in the preparation of the acrylic resin emulsion (a) is used in such an amount that the acid value of the resulting acrylic resin emulsion (a) is in the range of 1 to 80 mgKOH / g. It is done. The content of the monoalkyl ester of the dicarboxylic acid group-containing unsaturated monomer in the monomer mixture (b) used for the preparation of the shell part is preferably 0.2 to 30% by mass. When the acid value of the core-shell type acrylic resin emulsion is less than 1 mgKOH / g, the smoothness of the laminated coating film decreases, and when it exceeds 80 mgKOH / g, the water resistance of the resulting laminated coating film is inferior.

  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.

  In the acrylic resin emulsion (a) in the present invention, the monomer mixture (a) and the monomer mixture (b) preferably contain a hydroxyl group-containing unsaturated monomer. In this case, the hydroxyl value of the resulting acrylic resin emulsion (a) is preferably 10 to 150, more preferably 20 to 100. If the hydroxyl value is less than 10, sufficient curability may not be obtained. Moreover, when it exceeds 150, there exists a possibility that the various performance 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), but the monomer mixture (a) and the monomer mixture (b). It can obtain | require by calculation from the compounding quantity of various unsaturated monomers in. In the present specification, the acid value, hydroxyl value and Tg of the acrylic resin emulsion (a) are values obtained by calculating the acid value, hydroxyl value and Tg from the blending amounts of various unsaturated monomers in the monomer mixture (b). It is.

  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.), Adekari 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 melamine curable 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, More preferably, it is 10-85 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 resins The aqueous melamine curable base coating composition used in the method for forming a laminated coating film of the present invention contains other coating film-forming resins as required in addition to the acrylic resin emulsion (a). May be. 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 melamine curable 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. 0.0 or more is preferable. When the aqueous melamine curable base coating composition contains this polyether polyol, 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 may be 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 3 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 may be 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 may be lowered. Preferably it is 400-2000. In the present specification, the number average 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 polyether polyol is less than 2.0, the water dispersibility is lowered, and the coating film appearance may be deteriorated. 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.

Melamine resin (U)
The melamine resin (c) contained in the aqueous melamine curable base coating composition is a component that functions as a curing agent. The melamine resin (c) 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 (c) 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 (trade name, manufactured by Mitsui Cytec Co., Ltd.), Uban 20N60, Uban 20SE (both trade names, manufactured by Mitsui Chemicals, Inc.), and the like. These may be used alone or in combination of two or more.

  The content of the melamine resin (c) in the aqueous melamine curable base coating composition is 5% by mass or more with respect to 100 parts by mass of the coating resin solid content. It is preferable that content of a melamine resin (u) is 5-60 mass parts from a sclerosing | hardenable viewpoint.

Brilliant pigment (D), etc. The water-based melamine curable base coating composition used in the automobile body finishing method of the present invention can contain a bright pigment and a colored 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 coloring pigment may be included. 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. , Isoindolinone pigments, metal complex pigments and the like. It does not specifically limit as an inorganic coloring pigment, For example, a yellow lead, yellow iron oxide, a bengara, carbon black, titanium dioxide etc. can be mentioned.

  The total pigment concentration (PWC) in the aqueous melamine curable base coating composition, that is, the total pigment concentration including the glitter pigment and the colored pigment is 0.1 parts by mass with respect to 100 parts by mass of the coating resin solid content. The upper limit is preferably in the range of 50 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 melamine curable base coating composition used in the present invention contains a scale-like glitter 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, It is preferable to contain a phosphoric acid group-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 melamine curable 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 water-based melamine curable base coating composition used in the present invention contains a metallic glitter material, as a corrosion inhibitor for the glitter material or improving the wettability of the glitter material, the physical properties of the resulting multilayer coating film In order to improve this, 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 10-14. 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 melamine curable 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 with respect to the coating resin solid content. It is preferable to be within the range of mass%. 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 gas generation or discoloration of the glittering material occurs, and when it exceeds 5% by mass, the water resistance may be lowered.

Other components In the aqueous melamine curable base coating composition in the present invention, in addition to the above-mentioned components, additives usually added to the coating, for example, surface conditioners, thickeners, antioxidants, UV inhibitors, You may mix | blend an antifoamer etc. These compounding amounts are within the range known to those skilled in the art.

Production of aqueous melamine curable base coating composition The production method of the aqueous melamine curable base coating composition is not particularly limited, and the above components are kneaded using a kneader or a roll, using a sand grind mill or a disper. Any method known to those skilled in the art, such as dissolving and / or dispersing in water, can be used.

Solvent-type melamine curable base coating composition Solvent-type melamine curable base coating composition that can be used in the method for forming a laminated coating film of the present invention includes, for example, a solvent-based coating composition containing an acrylic resin and a melamine resin. . Here, the acrylic resin has an acid value of 1 to 80 mgKOH obtained by polymerizing a monomer mixture containing a monoalkyl ester of a dicarboxylic acid group-containing unsaturated monomer selected from the group consisting of maleic acid, fumaric acid and itaconic acid. An acrylic resin is preferred.

  As a specific example of such a solvent-type melamine curable base coating composition, for example, a solvent type containing an acrylic resin (F) having an acid value of 1 to 80 mgKOH / g; a melamine resin (KI); A coating composition is mentioned.

  As described above, the acrylic resin (F) is a resin obtained by polymerizing a monomer mixture containing a monoalkyl ester of a dicarboxylic acid group-containing unsaturated monomer selected from the group consisting of maleic acid, fumaric acid and itaconic acid. Is preferred.

Components other than the monoalkyl ester of the dicarboxylic acid group-containing unsaturated monomer contained in the monomer mixture used for the preparation of the acrylic resin (f) are not particularly limited.
Methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, (meth) acrylic acid t -Butyl, 2-ethylhexyl (meth) acrylate, lauryl methacrylate, phenyl acrylate, isobornyl (meth) acrylate, cyclohexyl methacrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentadi (meth) acrylate (Meth) acrylic acid esters such as enil, (meth) acrylic acid dihydrodicyclopentadienyl;
Hydroxyl-containing unsaturated monomers such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, allyl alcohol, methacrylic alcohol, and ε-caprolactone adduct of hydroxyethyl (meth) acrylate ;
(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 Polymerizable amide compounds such as N-monooctyl (meth) acrylamide 2,4-dihydroxy-4′-vinylbenzophenone, N- (2-hydroxyethyl) acrylamide, N- (2-hydroxyethyl) methacrylamide;
Polymerizable aromatic compounds such as styrene, α-methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene and vinylnaphthalene;
Polymerizable nitriles such as acrylonitrile and methacrylonitrile;
Α-olefins such as ethylene and propylene;
Vinyl esters such as vinyl acetate and vinyl propionate;
Dienes such as butadiene and isoprene;
Etc. The monomer mixture is provided with a hydroxyl group-containing monomer.

  When the acid value of the acrylic resin (f) is less than 1 mgKOH / g, the physical properties of the coating film may be inferior, and when it exceeds 80 mgKOH / g, the water resistance of the coating film may be easily retreated. More preferably, it is 10-45 mgKOH / g.

  The acrylic resin (f) preferably has a number average molecular weight of 1000 to 20000. If it is less than 1000, the coating film properties such as weather resistance may be inferior. On the other hand, if it exceeds 20000, the viscosity of the resin increases and a large amount of solvent may be required.

  The acrylic resin (f) preferably has a hydroxyl value (solid content) of 10 to 200. If it is less than 10, curing may be insufficient and physical properties of the coating film may be inferior. Moreover, when it exceeds 200, there exists a possibility that the flexibility and water resistance of a coating film may fall.

  It does not specifically limit as a manufacturing method of the said acrylic resin (f), For example, it can carry out by solution polymerization, such as normal radical polymerization.

  The content of the acrylic resin (f) in the solvent-based melamine curable base coating composition is such as acrylic resin (f), melamine resin (ki) and polymerized fine particles (ku) in the solvent-type melamine curable base coating composition. It is preferable that it is 10-90 mass% with respect to solid content of coating-film formation resin. If it is less than 10% by mass, the physical properties of the coating film may be inferior, for example, the fastness may be reduced. is there.

  The melamine resin (g) contained in the solvent-based melamine curable base coating composition of the present invention is not particularly limited, and is exemplified by the melamine resin (c) contained in the aqueous melamine curable base coating composition. Melamine resin or the like can be used.

  The content of the melamine resin (ki) in the solvent-based melamine curable base coating composition is such as acrylic resin (ka), melamine resin (ki) and polymerized fine particles (ku) of the solvent melamine curable base coating composition. It is 5 mass% or more with respect to solid content of film forming resin. The content of the melamine resin (ki) is preferably 5 to 60 parts by mass, and more preferably 15 to 45% by mass. If the content of the melamine resin (ki) is below the lower limit, the curability may be insufficient, and if it exceeds the upper limit, the cured film becomes stiff and the chipping property may be lowered when it is formed into a coating film.

  The polymer fine particles (ku) contained in the solvent-based melamine curable base coating composition of the present invention preferably contain crosslinked polymer fine particles (ku-1) and a non-aqueous dispersion resin (ku-2). The content of polymerized fine particles (ku) in the solvent-based melamine curable base coating composition is such as acrylic resin (f), melamine resin (ki) and polymerized fine particles (ku) of the solvent-based melamine curable base coating composition. It is preferable that it is 1-30 mass parts with respect to solid content of coating-film formation resin.

The crosslinked polymer fine particles (K-1) blended in the solvent-based melamine curable base coating composition of the present invention are insoluble in an organic solvent and have an average particle size (D ₅₀ ) of 0.01 to 1 μm. Use. If the average particle size exceeds the upper limit, the stability may decrease, and if the average particle size is less than the lower limit, the difficulty in production equipment is high, and it may be difficult to maintain the particle shape. The crosslinked polymer fine particles can be prepared by emulsion polymerization of a polymerizable monomer in an aqueous medium in the presence of a resin having an emulsifying ability and a polymerization initiator. Examples of the resin having emulsifying ability include resins such as alkyd resins and polyester resins synthesized using a monomer having a zwitterionic group and two or more hydroxyl groups in the molecule as one of the polyhydric alcohol components. .

As the zwitterionic group, for example, —N ⁺ —R—COO ^— or —N ⁺ —R—SO ₃ ^— (wherein R represents a C _{1 to} C ₆ linear or branched alkylene group) is, for example, Can be mentioned. By using a monomer having such an amphoteric group and two or more hydroxyl groups, a resin having an emulsifying ability can be suitably prepared. As such a monomer, a hydroxyl group-containing aminosulfonic acid type zwitterionic compound is preferably used for resin synthesis. Specific examples of the monomer include bishydroxyethyl taurine.

  The resin having an amphoteric group in the molecule and having an emulsifying ability synthesized using the above monomer has an acid value of 30 to 150 mgKOH / g, preferably 40 to 150 mgKOH / g, and a number average molecular weight of 500. More preferred is a polyester resin of ˜5000, preferably 700 to 3,000. When these acid values and number average molecular weights exceed the upper limit, the handling properties of the resin may be lowered. Moreover, when these acid values and number average molecular weights are less than the lower limit, there is a possibility that the resin having emulsifying ability may be detached or the solvent resistance may be lowered when a coating film is formed.

  Moreover, as the polymerizable monomer to be emulsion polymerized used in the synthesis of the crosslinked polymer fine particles, a monomer having two or more radically polymerizable ethylenically unsaturated groups in the molecule is used. The monomer having two or more radically polymerizable ethylenically unsaturated groups in the molecule is preferably contained in the range of 0.1 to 70% by mass in the total monomers. This amount is selected to the extent that sufficient crosslinking is provided so that the particulate polymer does not dissolve in the solvent.

  Examples of monomers having two or more radically polymerizable ethylenically unsaturated groups in the molecule include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, trimethylolpropane di (meth) acrylate, and trimethylol. Examples thereof include propane tri (meth) acrylate and glycerin di (meth) acrylate.

  The crosslinked polymer fine particle (K-1) used in the present invention does not contain a low-molecular emulsifier or protective colloid that degrades the performance when formed into a coating film, and more than one radically polymerizable ethylene in the molecule. Crosslinking is carried out by copolymerizing a monomer having a polymerizable unsaturated group. Therefore, it has the advantage that the water resistance, solvent resistance, and gloss of the resulting coating film can be improved.

  The non-aqueous dispersion resin (K-2) can be prepared as resin particles insoluble in the mixed solution by copolymerizing a polymerizable monomer in the mixed solution of the dispersion stabilizing resin and the organic solvent. The “non-aqueous dispersion” means a non-aqueous dispersion type resin, and is obtained by dispersing and stabilizing a resin using an organic solvent as a medium.

  The resin particles in the non-aqueous dispersion resin (K-2) are preferably prepared as non-crosslinked resin particles. The monomer to be copolymerized in the presence of the dispersion-stable resin to obtain non-crosslinked resin particles is not particularly limited as long as it is a radical polymerizable unsaturated monomer.

  However, it is preferable to use a polymerizable monomer having a functional group in the synthesis of the dispersion stabilizing resin and the non-aqueous dispersion resin (K-2). This is because the non-aqueous dispersion resin (K-2) having a functional group can react with a post-curing agent together with the dispersion stabilizing resin containing the functional group to form a three-dimensionally crosslinked coating film.

  The dispersion stable resin is not particularly limited as long as it can stably synthesize the non-aqueous dispersion resin (K-2) in an organic solvent. Specifically, as the dispersion stable resin, the hydroxyl value (solid content) is 10 to 250, preferably 20 to 180, and the acid value (solid content) is 0 to 100 mgKOH / g, preferably 0 to 50 mgKOH / g, It is preferable to use an acrylic resin, polyester resin, polyether resin, polycarbonate resin or polyurethane resin having a number average molecular weight of 800 to 100,000, preferably 1000 to 20,000. If these upper limits are exceeded, the handling properties of the resin may be reduced, and the handling of the non-aqueous dispersion itself may also be reduced. If the lower limit is not reached, the resin may be detached or the stability of the particles may be reduced when the coating film is formed.

  The method for synthesizing the dispersion stable resin is not particularly limited, and preferred examples include a method obtained by radical polymerization in the presence of a radical polymerization initiator and a method obtained by condensation reaction or addition reaction. Furthermore, the monomer used to obtain the dispersion-stable resin can be appropriately selected according to the properties of the resin, but has a hydroxyl group that a polymerizable monomer used to synthesize a non-aqueous dispersion described later has. Those having a functional group such as an acid group are preferably used, and those having a functional group such as a glycidyl group or an isocyanate group may be used as necessary.

  The non-aqueous dispersion resin (K-2) can be obtained by polymerizing a polymerizable monomer in the presence of a dispersion stable resin. As the polymerizable monomer, a radical polymerizable monomer can be used.

  The polymerizable monomer used for the synthesis of the non-aqueous dispersion resin (K-2) preferably has a functional group. Typical examples of the polymerizable monomer having a functional group are as follows. Examples of the polymerizable monomer having a hydroxyl group include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxymethyl methacrylate, allyl alcohol, and hydroxyethyl (meth) methacrylate. Examples include adducts with ε-caprolactone.

  On the other hand, the polymerizable monomer having an acidic group includes a polymerizable monomer having a carboxyl group, a sulfonic acid group, or the like. Examples of those having a carboxyl group include (meth) acrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, maleic anhydride, fumaric acid and the like. Examples of the polymerizable monomer having a sulfonic acid group include t-butylacrylamide sulfonic acid. When using the polymerizable monomer which has an acidic group, it is preferable that a part of acidic group is a carboxyl group.

  In addition, glycidyl group-containing unsaturated monomers such as glycidyl (meth) acrylate, isocyanate group-containing unsaturated monomers such as m-isopropenyl-α, α-dimethylbenzyl isocyanate, isocyanatoethyl acrylate, and the like are functional groups. As a polymerizable monomer having

  Other polymerizable monomers include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, T-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, methacrylic acid (Meth) acrylic acid alkyl ester such as tridecyl, addition reaction product of oil fatty acid and acrylic acid or methacrylic acid ester monomer having oxirane structure (for example, addition reaction product of stearic acid and glycidyl methacrylate), having 3 or more carbon atoms Oxirane compounds containing alkyl groups and acrylic acid or methacrylate Addition product with phosphoric acid, styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, pt-butylstyrene, benzyl (meth) acrylate, itaconic acid ester (itaconic acid Dimethyl, etc.), maleic acid esters (dimethyl maleate, etc.), fumarate esters (dimethyl fumarate, etc.), acrylonitrile, methacrylonitrile, methyl isopropenyl ketone, vinyl acetate, Veova monomer (trade name, manufactured by Shell Chemical Co., Ltd.) ), Vinyl propionate, vinyl pivalate, ethylene, propylene, butadiene, N, N-dimethylaminoethyl acrylate, N, N-dimethylaminoethyl methacrylate, acrylamide, vinyl pyridine and the like.

  In the preparation of the non-aqueous dispersion resin (K-2), the composition ratio of the dispersion stable resin and the polymerizable monomer can be arbitrarily selected according to the purpose. For example, the dispersion stable resin is based on the total mass of the two components. Is preferably 3 to 80% by mass, particularly 5 to 60% by mass, and the polymerizable monomer is preferably 97 to 20% by mass, and particularly preferably 95 to 40% by mass. Furthermore, the total concentration of the dispersion stabilizing resin and the polymerizable monomer in the organic solvent is preferably 30 to 80% by mass, particularly 40 to 60% by mass, based on the total mass.

  The polymerization reaction for obtaining the non-aqueous dispersion is preferably performed in the presence of a radical polymerization initiator. Examples of the radical polymerization initiator include azo initiators such as 2,2′-azobisisobutyronitrile and 2,2′-azobis (2,4-dimethylvaleronitrile), benzoyl peroxide, lauryl peroxide, Examples include t-butyl peroctoate. The amount of these initiators used is 0.2 to 10 parts by mass, preferably 0.5 to 5 parts by mass, per 100 parts by mass of the polymerizable monomers. In general, the polymerization reaction for obtaining a non-aqueous dispersion in an organic solvent containing a dispersion-stable resin is preferably performed in a temperature range of about 60 to 160 ° C. for about 1 to 15 hours.

The non-aqueous dispersion resin (K-2) thus obtained has a hydroxyl value (solid content) of 50 to 400, preferably 100 to 300, and an acid value (solid content) of 0 to 200 mgKOH / g, preferably 0. ˜50 mg KOH / g, average particle size (D ₅₀ ) is 0.05 to 10 μm, preferably 0.1 to 2 μm. If it is below the lower limit, the particle shape cannot be maintained, and if it exceeds the upper limit, the stability when dispersed in the coating composition is lowered.

  Further, the non-aqueous dispersion is different from the crosslinked polymer fine particles, and is a particle component in the coating composition, but has a characteristic that a particle structure is not formed in the coating film. That is, the non-aqueous dispersion is different from the crosslinked polymer fine particles in that there are no cross-linked sites in the particles, so that the particle shape changes during the baking process and can become a resin component.

Further, as the non-aqueous dispersion resin (K-2), for example, NAD (Non Aqueous Dispersion, non-aqueous polymer used in the NAD paint described in Color Materials, Vol. 48 (1975), pages 686 to 692 is used. Resin particles referred to as (dispersion liquid) can also be used. The non-aqueous dispersion resin (K-2) used in the solvent-based melamine curable base coating composition has an average particle size (D ₅₀ ) of 0.05 to 10 μm among the non-aqueous dispersion resins described above. It is preferable to use one.

  The “average particle size” in the present specification is generally used to represent the particle size (whether the particle size is coarse or fine), and is a median diameter or arithmetic average diameter corresponding to 50% by mass. , Surface area average diameter, volume area average diameter, etc. are used. The average particle diameter shown in the present specification is a value measured by a laser method. The laser method is a method of measuring an average particle size, a particle size distribution, and the like by dispersing particles in a solvent, applying a laser beam to the dispersion solvent, and capturing and calculating the obtained scattered light.

  The mixed solid mass ratio of the crosslinked polymer fine particles (K-1) contained in the solvent-based melamine curable base coating composition and the non-aqueous dispersion resin (K-2) having a core-shell structure is 40/60 to The range is 60/40. When outside the above range, a sufficient viscosity control effect cannot be imparted to the solvent-based melamine curable base coating composition. That is, by using the crosslinked polymer fine particles (K-1) and the non-aqueous dispersion resin (K-2) having a core-shell structure in the above range, a larger structural viscosity can be expressed.

  The solvent-based melamine curable base coating composition may contain a film-forming resin other than the acrylic resin (f). The film-forming resin is not particularly limited, and examples thereof include film-forming resins such as polyester resins, alkyd resins, epoxy resins, and urethane resins. These resins are used in combination with a curing agent such as an amino resin and / or a blocked isocyanate resin. From the viewpoint of pigment dispersibility or workability, a combination of acrylic resin and / or polyester resin and melamine resin is preferred.

  The solvent-based melamine curable base coating composition may further contain a luster pigment or a color pigment. As the glitter pigment and the color pigment, those mentioned in the glitter pigment and the color pigment that can be contained in the aqueous melamine curable base coating composition can be used. The solvent-based melamine curable base coating composition may further contain extender pigments.

  The total pigment concentration (PWC) in the solvent-based melamine curable base coating composition including the glitter pigment and the color pigment is 1 to 50%, preferably 1 to 40%, more preferably. Is from 1% to 30%. If the upper limit is exceeded, the coating film appearance may be reduced.

  The solid content during coating of the solvent-based melamine curable base coating composition used in the present invention is preferably 15 to 70% by mass, and more preferably 20 to 50% by mass. When the upper limit is exceeded, the viscosity is too high and the appearance of the coating film may deteriorate. On the other hand, if the value is below the lower limit, the viscosity is too low and there is a risk of appearance defects such as familiarity and unevenness. Further, outside the above range, the paint stability tends to decrease.

  The solvent melamine curable base coating composition may be either an organic solvent type or a non-aqueous dispersion type as long as it is a solution type. In addition to the above components, solvent-based melamine curable base coating compositions contain additives that are usually added to coatings, such as surface conditioners, thickeners, antioxidants, UV inhibitors, and antifoaming agents. May be. These compounding amounts are within the range known to those skilled in the art.

Production of solvent- based melamine curable base coating composition The method for producing the solvent-based melamine curable base coating composition is not particularly limited, and a composition such as a pigment is kneaded and dispersed using a kneader or a roll. All methods known to those skilled in the art can be used.

Two-component clear coating composition The two-component clear coating composition used in the present invention is:
A main component containing a hydroxyl group-containing acrylic resin (A) 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 curing agent comprising an isocyanate compound (B);
Is a two-component clear coating composition. The clear coating composition may be a solvent type or an aqueous type.

  The hydroxyl group-containing acrylic resin (A) 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 this hydroxyl value is 20 to 100%. Acrylic resin. This hydroxyl group-containing acrylic resin (A) can be prepared by copolymerizing a hydroxyl group-containing acrylic monomer and another ethylenically unsaturated group-containing monomer by an ordinary method. However, it is necessary to use an acrylic monomer having a secondary hydroxyl group as the hydroxyl group-containing acrylic monomer.

  Examples of the secondary hydroxy acid-containing acrylic monomer used for the synthesis of the hydroxyl group-containing acrylic resin (A) 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 (A) has a number average molecular weight (Mn) of 1,500 to 6,000. The number average molecular weight (Mn) is preferably 2,000 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 (A) has a hydroxyl value of 100 to 200. The hydroxyl value is preferably 110 to 180. When the hydroxyl value exceeds the upper limit, the water resistance of the coating film decreases, and when it falls below the lower limit, the curability of the coating film decreases. Furthermore, in the hydroxyl group-containing acrylic resin (A) in the present invention, the ratio of secondary hydroxyl groups in the hydroxyl value is 20 to 100%. The proportion of secondary hydroxyl groups in the hydroxyl value is preferably 30 to 100%. If it is 20% or less of the secondary hydroxyl group, the curing reaction rate cannot be delayed, and the appearance defects tend to increase. 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 (A), 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 (A) 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 (B) 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 (A) contained in the main agent and the isocyanate compound (B) 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 (B) to the hydroxyl group (OH) of the hydroxyl group-containing acrylic resin (A) is 1 / 1.5 to 1.5 / 1. It is preferable to use it in an amount that falls within the range. When the content of the isocyanate compound (B) 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 an amount ranging from 1 / 1.2 to 1.2 / 1.

  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, 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. 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.

Multilayer coating formation
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.

Laminate film formation method
A so-called two-coat one-bake method in which an uncured base coating film and an uncured clear coating film are formed on an object to be coated, and these two uncured coating films are baked and cured. A so-called three-coat one-bake method in which an intermediate coating film, an uncured base coating film and an uncured clear coating film are formed, and these three uncured coating films are baked and cured,
There are two modes.

Formation of multilayer coating film by 2-coat 1-bake method The formation of a multilayer coating film by 2-coat 1-bake method can use the above-mentioned substrate as an object to be coated. Next, if necessary, an intermediate coating film is formed on this substrate. Examples of the intermediate coating composition that can be used to form the intermediate coating film include an aqueous or solvent-type intermediate coating composition containing an intermediate coating resin component, a pigment, and an aqueous solvent and / or an organic solvent. . Here, the intermediate coating resin component is composed of an intermediate coating resin and, if necessary, an intermediate curing agent. Examples of the intermediate coating resin include acrylic resin, polyester resin, polyurethane resin, alkyd resin, fluororesin, epoxy resin, and polyether resin. Of these resins, acrylic resins, polyester resins, and polyurethane resins are preferably used. These resins may be used alone or in combination of two or more.

  Examples of the method for forming the intermediate coating film include a method of applying the intermediate coating composition using a spray method, a roll coater method, or the like. Specifically, as a painting method, an air electrostatic spray called “react gun” or a rotary atomization type called “micro / micro (μμ) bell”, “micro (μ) bell”, “metabell”, etc. It is preferable to apply using an electrostatic coating machine. Among these, it is particularly preferable to perform the coating using a rotary atomizing electrostatic coating machine. A preferable dry film thickness of the intermediate coating film is 5 to 80 μm, and more preferably 10 to 50 μm.

  The intermediate coating film can be formed by applying an intermediate coating composition and then baking at a curing temperature of 100 to 180 ° C., preferably 120 to 160 ° C. for 10 to 30 minutes.

  In the method of forming a multilayer coating film by the 2-coat 1-bake method, a base coating film is formed on a substrate by a melamine curable base coating composition, a clear coating film is formed by a two-component clear coating composition, and wet on wet. The two coating films are then baked and cured at once.

  The melamine curable base coating composition can be applied by air electrostatic spray coating or a rotary atomizing electrostatic coating machine such as Metabell, μμ Bell, 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.

  After forming the base coating film in this way, the process proceeds to the next step of forming a clear coating film without curing the obtained coating film. Here, before the two-component clear coating composition is applied, preheating may be performed at a temperature lower than the temperature used in the heat curing (baking) treatment.

  In the method for forming a laminated coating film of the present invention, a clear coating material is applied wet-on-wet on an uncured base coating film to form an uncured clear coating film. In the present invention, various kinds of so-called main agents containing a hydroxyl group-containing acrylic resin (A) as a component for forming a coating film and other components and so-called curing agents mainly containing an isocyanate compound (B) are used. A two-pack type clear coating composition that is preliminarily mixed and adjusted to the coating viscosity by the above method is used.

  In the method for forming a coating film according to the present invention, the clear coating film that is applied after the base coating film is formed smoothes and protects irregularities caused by the base coating film and flickering that occurs when a bright pigment is included. Formed to do. Specifically, as a coating method of the two-pack type clear coating composition, it is preferable to form a coating film using a rotary atomizing electrostatic coating machine such as the μμ bell or μbell described above.

  The two-component clear coating composition is an organic solvent that is a dilution medium having a coating viscosity determined empirically based on the above-described factors such as the atomization method of the electrostatic coating machine or the coating environment such as temperature and humidity. To adjust viscosity. Generally, it is preferable that the coating viscosity in a range of 10 ° C. to 40 ° C. and a humidity of 10 to 98% is 15 to 60 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 50 seconds (/ 20 ° C., No. 4 Ford Cup).

  The dry film thickness of the clear coating film formed from the two-component 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 peeling or sagging during painting. On the other hand, if the lower limit is not reached, the underlying irregularities may not be concealed.

  Two types of uncured coating films obtained as described above are formed simultaneously by so-called two-coat one-bake. This method can omit the baking and drying furnace for the base coating film, and is preferable from the viewpoint of economy and environment.

  By setting the curing temperature for curing the multilayer coating film to, for example, 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 10 to 60 minutes at 120-160 degreeC.

  In many cases, the film thickness of the laminated coating film formed in the present invention is 20 to 150 μm, preferably 20 to 100 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.

Formation of a multilayer coating film by the 3-coat 1-bake method In the formation of a multilayer coating film by the 3-coat 1-bake method, first, an uncured intermediate coating film is formed using the substrate as an object to be coated, and then an uncured base coating film And a clear coating is formed, followed by baking and curing three uncured coatings at once.

  In the 3-coat 1-bake method, first, an intermediate coating composition is applied in the same manner as described above to form an uncured intermediate coating film. Next, the process proceeds to a base coating film forming step in the next step without heating and curing the uncured intermediate coating film. Here, before the base coating film is formed, preheating may be performed at a temperature lower than the temperature used in the heat curing (baking) process.

  The melamine curable base coating composition and the two-component clear coating composition can be applied in the same manner as described above. A laminated coating film is obtained by baking and curing the thus-obtained laminated coating film comprising an intermediate coating film, a base coating film and a clear coating film in the same manner as described above.

  In the present invention, a specific two-component clear coating composition is used as the clear coating composition, and 20 to 100% of the hydroxyl groups of the hydroxyl group-containing acrylic resin used in the coating composition are converted to secondary hydroxyl groups. By using 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 appearance is improved.

  In the present invention, as described above, an acid value of 1 obtained by polymerizing a monomer mixture containing a monoalkyl ester of a dicarboxylic acid group-containing unsaturated monomer selected from the group consisting of maleic acid, fumaric acid and itaconic acid By using a melamine curable base coating composition containing an acrylic resin of -80 mg KOH, the curing start temperature of the melamine curable base coating composition can be lowered, whereby the reaction of the melamine curable base coating composition You can speed up.

  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 Production of aqueous melamine curable base coating composition
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 a monomer mixture (b) used for the preparation of the shell part, ethyl acrylate 15.84 parts, 2-hydroxyethyl methacrylate 1.86 parts , monobutyl maleate 6.4 parts, Aqualon HS-100.2 parts, And a monomer emulsion consisting of 10 parts of deionized water and 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 hour. . 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 acrylic resin emulsion (a) having a solid content acid value of 20 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.

Production Example 1-4 275 parts of the acrylic resin emulsion resin (A) obtained in Production Example 1-1 of the manufacturer of the aqueous melamine curable base coating composition (I) , 10 parts of a 10% by mass dimethylethanolamine aqueous solution, 33 parts of acrylic resin of Production Example 1-2, Prime Pol PX-1000 as polyether polyol (a) (bifunctional polyether polyol manufactured by Sanyo Chemical Industries, number average molecular weight 400, hydroxyl value 278, primary / secondary 10 parts of hydroxyl value ratio = 63/37, water tolerance infinite), 25 parts of Cymel 204 (mixed alkylated melamine resin made by Mitsui Cytec, water tolerance 3.6 ml) as melamine resin (U), glitter 21 parts of Alpaste MH8801 (Alumina Pigment made by Asahi Kasei Co., Ltd.) An aqueous melamine curable base coating composition (I) was obtained by adding 5 parts of a resin and 0.3 part of lauryl acid phosphate and uniformly dispersing.

Production Example 1-5 Production of aqueous melamine curable base coating composition (II) Production Example except that 6.4 parts of monobutyl maleate was replaced with 2.6 parts of acrylic acid and 19.64 parts of ethyl acrylate. In the same manner as in 1-1, after obtaining an acrylic resin emulsion (A) having an average particle size of 150 nm, a non-volatile content of 20%, a solid content acid value of 20, and a hydroxyl value of 40, an acrylic resin is used instead of the acrylic resin emulsion (A). An aqueous melamine curable base coating composition (II) was obtained in the same manner as in Production Example 1-4 except that the emulsion (I) was used.

Production Example 2 Production of solvent-based melamine curable base coating composition
Production Example 2-1 Production of Acrylic Resin ( F ) 50 parts of xylene and 25 parts of n-butanol were charged in a container equipped with a stirrer, a temperature controller, and a reflux condenser. Next, 5.0 parts of solution styrene having the following composition, 3.2 parts of monobutyl maleate, 20.0 parts of methyl methacrylate, 45.0 parts of ethyl acrylate, 6.6 parts of 2-hydroxyethyl acrylate, and 5. 0 parts, 17.6 parts of Plaxel FM-2 (Daicel Chemical Industries hydroxyl group-containing monomer), and 20 parts of 7.0 parts of azobisisobutyronitrile were added and heated with stirring to raise the temperature. While refluxing, the remaining 87.7 parts of the mixed solution was added dropwise over 3 hours, and then a solution consisting of 0.2 parts of azobisisobutyronitrile and 8 parts of xylol was added dropwise over 30 minutes. The reaction solution was further stirred and refluxed for 1 hour to increase the rate of conversion to resin, and the reaction was terminated to obtain an acrylic resin varnish (ka) having a solid content of 55% and a number average molecular weight of 3800.

Production Example 2-2 Production of Crosslinked Polymer Fine Particles (K-1)
Production of polyester resin having amphoteric groups 2 L Kolben equipped with a stirrer, nitrogen inlet tube, temperature controller, condenser and decanter, 134 parts of bishydroxyethyl taurine, 130 parts of neopentyl glycol, 236 parts of azelaic acid, phthalic anhydride 186 parts of acid and 27 parts of xylene were charged and the temperature was raised. The water produced by the reaction was removed by azeotropy with xylene. About 2 hours from the start of refluxing, the temperature was raised to 190 ° C., stirring and dehydration were continued until the acid value corresponding to carboxylic acid reached 145, and then cooled to 140 ° C. Subsequently, the temperature of 140 ° C. was maintained, and 314 parts of “Cardura E-10” (Versatic acid glycidyl ester manufactured by Shell) was dropped in 30 minutes, and then the stirring was continued for 2 hours to complete the reaction. The polyester resin thus obtained had an acid value of 59, a hydroxyl value of 90, and a number average molecular weight of 1054.

Production of crosslinked polymer fine particles In a 1 L reaction vessel equipped with a stirrer, a cooler, and a temperature control device, 232 parts of deionized water, 10 parts of polyester resin obtained by the production of the above-mentioned polyester resin having an amphoteric group, and dimethyl A solution prepared by dissolving 0.75 parts of ethanolamine while maintaining the temperature at 80 ° C. with stirring, and dissolving 4.5 parts of azobiscyanovaleric acid in 45 parts of deionized water and 4.3 parts of dimethylethanolamine was added thereto. Added. Next, a mixed solution consisting of 130 parts of methyl methacrylate, 40 parts of styrene and 140 parts of ethylene glycol dimethacrylate was dropped over 60 minutes. After the dropwise addition, 1.5 parts of azobiscyanovaleric acid dissolved in 15 parts of deionized water and 1.4 parts of dimethylethanolamine were added and stirring was continued at 80 ° C. for 60 minutes. As a result, the solid content was 45%, pH 7 An emulsion having a viscosity of 92 cps (25 ° C.) and a particle size of 0.1 μm was obtained. This emulsion was replaced with a xylol solution by using azeotropy to obtain a xylol dispersion having a crosslinked polymer fine particle diameter of 0.07 μm and a crosslinked polymer fine particle content of 20% by mass.

Production Example 2-3 Production of non-aqueous dispersion (K-2)
Production of Dispersion Stabilizing Resin 90 parts of butyl acetate was charged in a vessel equipped with a stirrer, temperature controller, and reflux condenser. Next, 20 parts of a solution composed of 38.9 parts of methyl methacrylate, 38.8 parts of stearyl methacrylate, 22.3 parts of 2-hydroxyethyl acrylate and 5.0 parts of azobisisobutyronitrile were added and stirred. While heating, the temperature was raised. The remaining 85 parts of the above mixed solution was added dropwise at 110 ° C. over 3 hours, and then a solution consisting of 0.5 parts of azobisisobutyronitrile and 10 parts of butyl acetate was added dropwise over 30 minutes. The reaction solution was further stirred and refluxed for 2 hours to increase the rate of conversion to resin, and then the reaction was terminated to obtain an acrylic resin having a solid content of 50%, a number average molecular weight of 5600 and an SP value of 9.5.

Production of non-aqueous dispersion In a vessel equipped with a stirrer, a cooler and a temperature control device, 90 parts of butyl acetate, 120 parts of acrylic resin obtained in the production of the above (2-1) dispersion stable resin (60 parts as solid content) Was charged. Next, 7.0 parts of styrene, 1.8 parts of methacrylic acid, 12.0 parts of methyl methacrylate, 8.5 parts of ethyl acrylate, 40.7 parts of 2-hydroxyethyl acrylate, and 1.4 parts of azobisisobutyronitrile. Then, a solution consisting of 0.1 parts of azobisisobutyronitrile and 1 part of butyl acetate was added dropwise over 30 minutes. When the reaction solution was further stirred for 1 hour, an emulsion having a solid content of 60% and a particle size of 180 nm was obtained. This emulsion was diluted with butyl acetate to obtain a core-shell type butyl acetate dispersion having a viscosity of 300 cps (25 ° C.) and a particle diameter of 180 nm and a non-aqueous dispersion content of 40% by mass. The non-aqueous dispersion resin had a Tg of 23 ° C. and a hydroxyl value of 162.

Production Example 2-4 Production of Solvent-type Melamine Curing Base Coating Composition (III) In a stainless steel container, 70 parts of acrylic resin (f) of Production Example 2-1 and Uban 20N60 (Mitsui Chemicals' melamine resin, solid content 60) %) 30 parts, 5 parts of crosslinked polymer fine particles (K-1) of Production Example 2-2, 5 parts of non-aqueous dispersion resin (K-2) having a core-shell structure of Production Example 2-3, aluminum paste 91- 15 parts of 0562 (aluminum pigment manufactured by Toyo Aluminum Co., Ltd.) were weighed and stirred with a desktop stirrer to prepare a solvent-based melamine curable base coating composition (III).

Production Example 2-5 Production of Solvent Type Melamine Curing Base Coating Composition (IV) Instead of 3.2 parts monobutyl maleate, 0.8 parts acrylic acid, 20.74 parts methyl methacrylate, 46.67 ethyl acrylate In the same manner as in Production Example 2-1, except that the acrylic resin varnish (ki) having a nonvolatile content of 55% and a number average molecular weight of 4000 was obtained, the acrylic resin varnish (ka) was used instead of the acrylic resin varnish (ka). A solvent-based melamine curable base coating composition (IV) was obtained in the same manner as in Production Example 2-4 except that (g) was used.

Production Example 3-1 Production of hydroxyl group-containing acrylic resin (A-1) 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 (A-1) was obtained.

Production Example 3-2 Production of hydroxyl group-containing acrylic resin (A-2) Similar to Production Example 3-1, except that 32.4 parts of 2-hydroxypropyl acrylate was used instead of 36 parts of 2-hydroxypropyl methacrylate. To obtain a varnish of a hydroxyl group-containing acrylic resin (A-2) having a solid content of 70%, a number average molecular weight of 3800, a hydroxyl value of 140 (of which the secondary hydroxyl group ratio is 100%) and an acid value of 6.2 mg / KOH. It was.

Production Example 3-3 Production of hydroxyl group-containing acrylic resin (A-3) Production Example 3 except that 27 parts of 2-hydroxypropyl methacrylate and 9 parts of hydroxybutyl acrylate were used instead of 36 parts of 2-hydroxypropyl methacrylate. -1, a hydroxyl group-containing acrylic resin (A-3) having a solid content of 70%, a number average molecular weight of 3800, a hydroxyl value of 140 (including a secondary hydroxyl group ratio of 75%), and an acid value of 6.2 mg / KOH The varnish was obtained.

Production Example 3-4 Production of hydroxyl group-containing acrylic resin (A-4) Production Example 3 except that 18 parts of 2-hydroxypropyl methacrylate and 18 parts of hydroxybutyl acrylate were used instead of 36 parts of 2-hydroxypropyl methacrylate. The hydroxyl group-containing acrylic resin (A-4) having a solid content of 70%, a number average molecular weight of 3800, a hydroxyl value of 140 (of which 50% is a secondary hydroxyl group), and an acid value of 6.2 mg / KOH. The varnish was obtained.

Production Example 3-5 Production of hydroxyl group-containing acrylic resin (A-5) Production Example 3 except that 9 parts of 2-hydroxypropyl methacrylate and 27 parts of hydroxybutyl acrylate were used instead of 36 parts of 2-hydroxypropyl methacrylate. The hydroxyl group-containing acrylic resin (A-5) having a solid content of 70%, a number average molecular weight of 3800, a hydroxyl value of 140 (of which the ratio of secondary hydroxyl group is 25%), and an acid value of 6.2 mg / KOH. The varnish was obtained.

Comparative Production Example 1 Production of Hydroxyl-Containing Acrylic Resin (Ratio-1) The same procedure as in Production Example 3-1 was conducted except that 32.4 parts of hydroxyethyl methacrylate was used instead of 36 parts of 2-hydroxypropyl methacrylate. A varnish of a hydroxyl group-containing acrylic resin (ratio-1) having a solid content of 70%, a number average molecular weight of 3800, a hydroxyl value of 140 (of which the ratio of secondary hydroxyl group was 0%) and an acid value of 6.2 mg / KOH was obtained.

Comparative Production Example 2 Production of hydroxyl group-containing acrylic resin (ratio-2) Instead of 36 parts 2-hydroxypropyl methacrylate, Plaxel FM-1 (trade name, adduct of 2-hydroxyethyl (meth) acrylate and polycaprolactone, Except having used 61 parts of Daicel Chemical Industries Ltd.), it carried out similarly to manufacture example 3-1, solid content 70%, number average molecular weight 3800, hydroxyl value 140 (of which the ratio of secondary hydroxyl group is 0%), acid A varnish of a hydroxyl group-containing acrylic resin (ratio-2) having a value of 6.2 mg / KOH was obtained.

Comparative Production Example 3 Production of Hydroxyl-Containing Acrylic Resin (Ratio-3) Performed in the same manner as in Production Example 3-1, except that 36 parts of 4-hydroxybutyl acrylate was used instead of 36 parts of 2-hydroxypropyl methacrylate, A varnish of a hydroxyl group-containing acrylic resin (ratio-3) having a solid content of 70%, a number average molecular weight of 3800, a hydroxyl value of 140 (of which the ratio of secondary hydroxyl groups was 0%), and an acid value of 6.2 mg / KOH was obtained.

Example 1
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 (A-1) of Production Example 3-1, UV absorber “Tinuvin 384” 5 manufactured by Ciba Geigy .6 parts, 5.6 parts of Ciba Geigy's light stabilizer “Tinubin 123”, 5.6 parts of acrylic surface conditioner, 37.0 parts of toluene and 37.0 parts of xylene were added in order, and stirred thoroughly with a disper The main component of the two-pack type clear coating composition was obtained.

  To another metal container, add 100.0 parts of “DISMODULE N-3300” (NCO active ingredient 22%) manufactured by Sumitomo Bayer Urethane Co., Ltd. and 2-ethylethoxypropanol in order, stir 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. On the resulting coated plate, a gray intermediate coating “Olga P-2” (polyester / melamine based paint manufactured by Nippon Paint Co., Ltd.) diluted beforehand in 25 seconds (measured at 20 ° C. using a No. 4 Ford cup). Two-stage coating was performed by air spray so that the dry film thickness was 35 μm, and baking was performed at 140 ° C. for 30 minutes.

  After cooling, the solvent-based melamine curable base coating composition (III) prepared in Production Example 2-4 comprises 50 parts of Solvesso 150 (a hydrocarbon solvent manufactured by Exxon Petroleum), 25 parts of ethyl acetate, and 25 parts of toluene. In dilution thinner, no. The dilution was adjusted to 12.5 seconds / 20 ° C. with a 4 Ford cup. The obtained diluted base coating composition was applied with “Metabell” (rotary atomization type electrostatic coating machine manufactured by Landsburg) on two stages at intervals of 1.5 minutes so that the dry film thickness was 15 μm. A base coating film was prepared by allowing to stand at room temperature for 10 minutes.

  The main agent and the curing agent obtained by the production of the above two-component clear coating composition were mixed at 3/1 (mass ratio (%)) to obtain a clear coating composition. 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.

Example 2
Except having changed the varnish of the hydroxyl-containing acrylic resin (A-1) of manufacture example 3-1 into the varnish of the hydroxyl-containing acrylic resin (A-2) of manufacture example 3-2, it carried out similarly to Example 1, and changed. A main component of a two-pack type clear coating composition was obtained. A curing agent for the two-component clear coating composition was prepared in the same manner as in Example 1, and a laminated coating film was formed in the same manner as in Example 1.

Example 3
Except having changed the varnish of the hydroxyl-containing acrylic resin (A-1) of manufacture example 3-1 to the varnish of the hydroxyl-containing acrylic resin (A-3) of manufacture example 3-3, it carried out similarly to Example 1, and changed. A main component of a two-pack type clear coating composition was obtained. A curing agent for the two-component clear coating composition was prepared in the same manner as in Example 1, and a laminated coating film was formed in the same manner as in Example 1.

Example 4
Except having changed the varnish of the hydroxyl-containing acrylic resin (A-1) of manufacture example 3-1 into the varnish of the hydroxyl-containing acrylic resin (A-4) of manufacture example 3-4, it carried out similarly to Example 1, and changed. A main component of a two-pack type clear coating composition was obtained. A curing agent for the two-component clear coating composition was prepared in the same manner as in Example 1, and a laminated coating film was formed in the same manner as in Example 1.

Example 5
Except having changed the varnish of the hydroxyl-containing acrylic resin (A-1) of manufacture example 3-1 into the varnish of the hydroxyl-containing acrylic resin (A-5) of manufacture example 3-5, it carries out similarly to Example 1. A main component of a two-pack type clear coating composition was obtained. A curing agent for the two-component clear coating composition was prepared in the same manner as in Example 1, and a laminated coating film was formed in the same manner as in Example 1.

Example 6
In Example 1, except that the base coating composition was formed as described in the next paragraph using the aqueous melamine-curable base coating composition (I) obtained in Production Example 1-4. A laminated coating film was formed in the same manner as in Example 1.

  The aqueous melamine curable base coating composition (I) produced according to Production Example 1-4 was diluted with deionized water for 30 seconds (measured at 20 ° C. using a No. 4 Ford cup). Two-stage coating was performed with a metallic bell (manufactured by ABB Industries) to a dry film thickness of 20 μm under conditions of room temperature of 25 ° C. and humidity of 85%. 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 to prepare a base coating film.

Example 7
In the multilayer coating film formation of Example 1 employed in Example 2, the solvent-based melamine curable base coating composition was used as the aqueous melamine curable base coating composition (I) obtained in Production Example 1-4. A laminated coating film was formed in the same manner as in Example 2 except that a base coating film was formed as described in the next paragraph.

  The aqueous melamine curable base coating composition (I) produced according to Production Example 1-4 was diluted with deionized water for 30 seconds (measured at 20 ° C. using a No. 4 Ford cup). Two-stage coating was performed with a metallic bell (manufactured by ABB Industries) to a dry film thickness of 20 μm under conditions of room temperature of 25 ° C. and humidity of 85%. 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 to prepare a base coating film.

Example 8
In the formation of the multilayer coating film of Example 1 employed in Example 3, the solvent-based melamine curable base coating composition was prepared using the aqueous melamine curable base coating composition (I) obtained in Production Example 1-4. A laminated coating film was formed in the same manner as in Example 3 except that a base coating film was formed as described in the next paragraph.

  The aqueous melamine curable base coating composition (I) produced according to Production Example 1-4 was diluted with deionized water for 30 seconds (measured at 20 ° C. using a No. 4 Ford cup). Two-stage coating was performed with a metallic bell (manufactured by ABB Industries) to a dry film thickness of 20 μm under conditions of room temperature of 25 ° C. and humidity of 85%. 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 to prepare a base coating film.

Example 9
In Example 1, a solvent-based melamine curable base coating composition was prepared using the aqueous melamine curable base coating composition (II) obtained in Production Example 1-5 as described in the next paragraph. A laminated coating film was formed in the same manner as in Example 1 except that it was formed.

The aqueous melamine curable base coating composition (II) produced according to Production Example 1-4 was diluted with deionized water for 30 seconds (measured at 20 ° C. using a No. 4 Ford cup). Two-stage coating was performed with a metallic bell (manufactured by ABB Industries) to a dry film thickness of 20 μm under conditions of room temperature of 25 ° C. and humidity of 85%. 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 to prepare a base coating film.
Example 10
A laminated coating film as in Example 1 except that the aqueous melamine curable base coating composition (IV) obtained in Production Example 2-5 was used as the solvent type melamine curable base coating composition in Example 1. Formed.

Comparative Example 1
Except that the varnish of the hydroxyl group-containing acrylic resin (A-1) of Production Example 3-1 was changed to the varnish of the hydroxyl group-containing acrylic resin (Ratio-1) of Comparative Example Production Example 1, the procedure was the same as in Example 1. A main component of a two-pack type clear coating composition was obtained. A curing agent for the two-component clear coating composition was prepared in the same manner as in Example 1, and a laminated coating film was formed in the same manner as in Example 1.

Comparative Example 2
Except having changed the varnish of the hydroxyl group-containing acrylic resin (A-1) of Production Example 3-1 to the varnish of the hydroxyl group-containing acrylic resin (Ratio-2) of Comparative Example Production Example 2, the same procedure as in Example 1 was performed. A main component of a two-pack type clear coating composition was obtained. A curing agent for the two-component clear coating composition was prepared in the same manner as in Example 1, and a laminated coating film was formed in the same manner as in Example 1.

Comparative Example 3
Except having changed the varnish of the hydroxyl-containing acrylic resin (A-1) of manufacture example 3-1 into the varnish of the hydroxyl-containing acrylic resin (ratio-3) of comparative example manufacture example 3, it carried out similarly to Example 1, and changed. A main component of a two-pack type clear coating composition was obtained. A curing agent for the two-component clear coating composition was prepared in the same manner as in Example 1, and a laminated coating film was formed in the same manner as in Example 1.

  The varnish of the hydroxyl group-containing acrylic resin (A-1) of Production Example 3-1 used in Example 1 employed in Example 6 is changed to the varnish of the hydroxyl group-containing acrylic resin (Ratio-1) of Comparative Example Production Example 1. Except for this, a main component of a two-pack type clear coating composition was obtained in the same manner as in Example 1. A curing agent for the two-component clear coating composition was prepared in the same manner as in Example 1, and a laminated coating film was formed in the same manner as in Example 6.

  The following evaluation was performed using the coating composition obtained by the said Example and comparative example. The evaluation results are shown in the following table.

Pot Life Measurement The main component and curing agent of the two-component clear coating composition obtained were mixed at 3/1 (mass ratio (%)), and a dilution solvent consisting of 2-ethylethoxypropanol / xylene = 1/1 was used. And diluted for 30 seconds (measured at 20 ° C. using a No. 4 Ford cup). In this diluted state, the viscosity at the time when a certain period of time passed at 20 ° C. was measured to determine the rate of increase in viscosity. Using this viscosity increase rate, the following criteria were used for evaluation.
Time to thicken for 5 seconds or more A: Over 3 hours.
○: 2 hours or more and less than 3 hours.
Δ: 1 hour or more and less than 2 hours.
X: Less than 1 hour.

Acid resistance test A 40% aqueous sulfuric acid solution was prepared using ion-exchanged water and reagent-grade sulfuric acid. Next, 0.5 ml of the sulfuric acid aqueous solution was dropped on the multilayer coating film obtained in the above examples and comparative examples, and then kept in a heating oven at 80 ° C. for 30 minutes, and then washed with water. Thereafter, the spot marks on the multilayer coating film were visually observed and evaluated based on the following criteria.
◎: No trace at all ○: Slight trace △: The ring is clearly visible ×: The coating is whitened and the ring is clearly visible

Appearance evaluation of multi- layer coating For the overall coating after top coating, measure the overall appearance using “Wave scan-DOI” (BYK-Gardner GmbH), and measure the Wc and Wb values. Both the Wc value and the Wb value indicate that the smaller the numerical value, the better the appearance.

As is clear from the examples in the above table, the curing start temperature of the clear coating film was determined as a comparative example by using a hydroxyl group-containing acrylic resin containing a predetermined amount of secondary hydroxyl group as the two-component clear coating composition. It will be set higher than what (acrylic resin which does not contain a predetermined amount of secondary hydroxyl groups). Accordingly, the curing start temperature is in the order of clear coating film> base coating film, and the coating film appearance of the obtained multilayer coating film is improved. In the examples, the storage stability (pot life) after mixing the main agent and the curing agent is also improved, indicating that the coating workability is excellent. Moreover, in an Example, it can confirm that acid resistance is also favorable and it is excellent also in the chemical resistance of a laminated coating film. Examples 6 to 8 show examples in which a water-based melamine curable base coating composition is used. In this example as well, good performance is obtained. Examples 9 and 10 are examples in which a conventional dicarboxylic acid group-containing unsaturated monomer is not used as the melamine curable base coating composition, but although high performance is shown, the appearance is slightly inferior.
On the other hand, in the comparative example (the one using a conventional acrylic resin containing no secondary hydroxyl group), the curing start temperature of the clear coating film is low, and accordingly, the coating film appearance of the laminated coating film is deteriorated. In the comparative example, it can also be confirmed that the pot life is short and the painting workability is inferior.

  As apparent from the above experimental example, in the method for forming a multilayer coating film of 2 coats and 1 bake, the outermost layer clear film begins to cure later than the lower layer coating film. I can understand that it will decrease.

In the present invention, there is an economic advantage because the baking step is omitted, and there is an advantage that CO ₂ emission can be reduced. It is possible to provide an excellent multilayer coating film.

Claims (7)

A step of coating a melamine curable base coating composition containing 5% by mass or more of melamine resin with respect to the solid content of the coating on an object to form an uncured base coating;
A step of applying a two-part clear coating composition on the uncured base coating to form an uncured clear coating; and the resulting uncured base coating and uncured clear coating A process of baking and curing the film;
A method for forming a laminated coating film comprising:
The two-part clear coating composition is
A main component containing a hydroxyl group-containing acrylic resin (A) 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 curing agent comprising an isocyanate compound (B);
A two-component clear coating composition comprising:
Laminated coating film forming method.   The melamine curable base coating composition is obtained by polymerizing a monomer mixture containing a dicarboxylic acid group-containing unsaturated monomer selected from the group consisting of maleic acid, fumaric acid, itaconic acid and their monoalkyl esters. The method for forming a laminated coating film according to claim 1, which is a melamine curable base coating composition containing an acrylic resin having a value of 1 to 80 mgKOH. The melamine curable 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 dicarboxylic acid group-containing unsaturated monomer selected from the group consisting of maleic acid, fumaric acid, itaconic acid and their monoalkyl esters,
A core-shell type acrylic resin emulsion (A) having an acid value of 1 to 80 mgKOH / g;
Polyether polyol (a);
Melamine resin (U);
The method for forming a laminated coating film according to claim 1, which is an aqueous melamine curable base coating composition. The melamine curable base coating composition is
An acrylic resin having an acid value of 1 to 80 mg KOH / g, obtained by polymerizing a monomer mixture containing a dicarboxylic acid group-containing unsaturated monomer selected from the group consisting of maleic acid, fumaric acid, itaconic acid and monoalkyl esters thereof (F);
Melamine resin (ki);
Polymerized fine particles (ku);
The method for forming a laminated coating film according to claim 1, which is a solvent-based melamine curable base coating composition. In the step of forming the uncured base coating film, the coating object to which the melamine curable base coating composition is applied is a coating object having an uncured intermediate coating film, and the baking and curing process And bake and cure the uncured intermediate coating film, the uncured base coating film, and the uncured clear coating film,
The laminated coating film formation method in any one of Claims 1-4.   A coated article having a multilayer coating film obtained by the method for forming a multilayer coating film according to any one of claims 1 to 5.   A two-component clear coating composition used in the method for forming a laminated coating film according to any one of claims 1 to 5.