JP5113439B2 - Multi-layer coating formation method - Google Patents

Description

  The present invention relates to a method for forming a multilayer coating film having an excellent appearance.

  As a method of forming a coating film on an automobile body, an electrodeposition coating film is formed on an object to be coated, and then an intermediate coating paint → baking cure → base coat paint coating → clear paint coating → baking cure 3 coat 2 bake ( 3C2B) The method of forming a multilayer coating film by the method has been widely adopted. However, in recent years, from the viewpoint of energy saving, the baking and curing step after coating the intermediate coating is omitted, and the electrodeposition coating is applied to the object to be coated. Then, a method of forming a multi-layer coating film by a 3-coat 1-bake (3C1B) system is attempted (for example, coating of an intermediate coating, coating of a base coating, coating of a clear coating, and baking curing) (for example, Patent Document 1).

  However, in the 3C1B system, since a mixed layer of the intermediate coating film and the base coat coating film is likely to occur, there is a drawback in that the smoothness and sharpness of the resulting coating film are reduced, which is a problem.

  Conventionally, as a countermeasure, after applying the intermediate coating, the intermediate coating film to be formed is brought as close to the cured state as possible, and then the base coat coating is applied to form a mixed layer of the intermediate coating film and the base coating film. For example, Patent Document 2 discloses that a water-based first paint is applied to an object to be coated, and the gel fraction of a formed coating film is adjusted to 5% by weight or more. When the paint is applied and the moisture in the coating film formed is volatilized, the clear paint is applied, and then the resulting three-layer coating film is heated and cured at the same time. It is described that it is possible to form a multi-layer coating film excellent in hiding the film (underlying hiding property). However, even in this coating method, a multilayer coating film having sufficient smoothness and sharpness may not be obtained, which is a problem.

Japanese Patent Laid-Open No. 10-216617 JP 2001-327911 A

  An object of the present invention is to provide a multilayer coating film forming method capable of forming a coating film excellent in smoothness and sharpness in the 3C1B system.

  As a result of intensive studies to achieve the above object, the inventors of the present invention have, as a first colored paint, a relatively low acid value having a specific structure in the coating process of a multilayer coating film by the 3C1B method. When a paint containing a hydroxyl group-containing polyester resin and a polyisocyanate compound is used, the first colored paint is adjusted to a relatively low gel fraction, and then the aqueous second colored paint is applied. The present inventors have found that an excellent multilayer coating film can be formed and have completed the present invention.

Thus, the present invention includes the following steps (1) to (5),
Step (1): A step of forming an uncured first colored coating film by coating the first colored paint (X) on an object to be coated;
Step (2): a step of setting the gel fraction of the uncured first colored coating film formed in the step (1) to 5% by mass or more and less than 40% by mass,
Step (3): a step of applying an aqueous second colored paint (Y) on the uncured first colored coating film formed in the step (2) to form an uncured second colored coating film,
Step (4): a step of applying a clear paint (Z) on the uncured second colored coating film formed in the step (3) to form an uncured clear coating film, and a step (5) : A step of simultaneously baking and curing the first colored coating film, the second colored coating film and the clear coating film formed in the steps (1) to (4),
In the method of forming a multilayer coating film by sequentially performing the steps, the first colored paint (X) is obtained by the reaction of the acid component (a1) and the alcohol component (a2), and the fat in the acid component (a1) The hydroxyl group-containing polyester resin (A) in which the content of the group polybasic acid (a1-1) is in the range of 20 to 70 mol% based on the total amount of the acid component (a1) and the acid value is 15 mgKOH / g or less And a coating composition comprising a polyisocyanate compound (B) is provided.

  According to the present invention, a multilayer coating film excellent in smoothness and sharpness can be easily formed by the 3C1B method.

  Hereinafter, the multilayer coating film forming method of the present invention will be described in more detail.

Process (1)
In this step, the first colored paint (X) is applied on the object to be coated, and an uncured first colored coating film is formed.

Coating material The coating material to which the water-based first colored coating material (X) can be applied according to the present invention is not particularly limited. For example, an outer plate portion of an automobile body such as a passenger car, a truck, a motorcycle, or a bus; Automobile parts: The outer plate part of home electric products such as mobile phones and audio equipments can be mentioned. Of these, the outer plate part of the automobile body and the automobile parts are preferable.

  In addition, the material of the object to be coated is not particularly limited. For example, iron, aluminum, brass, copper, stainless steel, tinplate, galvanized steel, alloyed zinc (Zn-Al, Zn-Ni, Zn-Fe, etc.) Metal materials such as plated steel; polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy resin, etc. Various plastic materials such as FRP; inorganic materials such as glass, cement, and concrete; wood; fiber materials (paper, cloth, etc.), and the like, among which metal materials and plastic materials are suitable.

  The object to be coated may be one in which a surface treatment such as a phosphate treatment, a chromate treatment, or a complex oxide treatment is performed on a metal surface of the metal material or a vehicle body formed from the metal material. Further, the object to be coated may be one in which an undercoat film such as various electrodeposition paints is formed on the metal material or the vehicle body, and in particular, the undercoat film is formed by a cationic electrodeposition paint. The body is particularly suitable.

First colored paint (X)
In the present invention, the first colored paint (X) is obtained by the reaction of the acid component (a1) and the alcohol component (a2), and contains the aliphatic polybasic acid (a1-1) in the acid component (a1). A hydroxyl group-containing polyester resin (A) having an amount in the range of 20 to 70 mol% based on the total amount of the acid component (a1) and having an acid value of 15 mgKOH / g or less, and a polyisocyanate compound (B) Is used (hereinafter referred to as the coating composition of the present invention).

Hydroxyl-containing polyester resin (A)
The hydroxyl group-containing polyester resin (A) used as the base resin in the coating composition of the present invention has at least one hydroxyl group in one molecule and is obtained by the reaction of the acid component (a1) and the alcohol component (a1). And the content of the aliphatic polybasic acid (a1-1) in the acid component (a1) is 20 to 70 mol%, preferably 25 to 60 mol%, more preferably based on the total amount of the acid component (a1) The polyester resin is in the range of 30 to 50 mol% and has an acid value of 15 mgKOH / g or less, preferably 1 to 12 mgKOH / g, and more preferably 3 to 10 mgKOH / g.

Acid component (a1)
In the present invention, the acid component (a1) is an aliphatic polybasic acid (a1-1) based on the total amount of the acid component (a1), 20 to 70 mol%, preferably 25 to 60 mol%, more preferably 30. Contains ~ 50 mol%.

  The aliphatic polybasic acid (a1-1) is generally an aliphatic compound having two or more carboxyl groups in one molecule, an acid anhydride of the aliphatic compound, and an esterified product of the aliphatic compound. Aliphatic polycarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, octadecanedioic acid, citric acid; An anhydride of the aliphatic polyvalent carboxylic acid; a lower alkyl esterified product of the aliphatic polyvalent carboxylic acid, and the like. The above aliphatic polybasic acids can be used alone or in combination of two or more.

  As the aliphatic polybasic acid (a1-1), it is preferable to use a dicarboxylic acid having an alkyl chain having 4 to 18 carbon atoms. Examples of the dicarboxylic acid having an alkyl chain having 4 to 18 carbon atoms include adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassic acid, and octadecanedioic acid. Among them, adipic acid can be preferably used.

  When the acid component (a1) contains a dicarboxylic acid having an alkyl chain having 4 to 18 carbon atoms as the aliphatic polybasic acid (a1-1), the dicarboxylic acid having an alkyl chain having 4 to 18 carbon atoms The content of is preferably 20 to 70 mol%, preferably 25 to 60 mol%, more preferably 30 to 50 mol%, based on the total amount of the acid component (a1). Moreover, when an acid component (a1) contains adipic acid as said aliphatic polybasic acid (a1-1), content of adipic acid is 20-70 mol% on the basis of the total amount of an acid component (a1). , Preferably 25 to 60 mol%, more preferably 30 to 50 mol%.

  In addition to the aliphatic polybasic acid (a1-1), an alicyclic polybasic acid (a1-2) and an aromatic polybasic acid (a1-3) are preferably used as the acid component (a1). can do.

  The alicyclic polybasic acid (a1-2) is generally a compound having one or more alicyclic structures (mainly 4 to 6 membered rings) and two or more carboxyl groups in one molecule, Acid anhydrides and esterified products of the compounds, for example, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, Cycloaliphatic polyvalents such as 3-methyl-1,2-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, 1,3,5-cyclohexanetricarboxylic acid, etc. Carboxylic acid; anhydride of the alicyclic polyvalent carboxylic acid; lower alkyl esterified product of the alicyclic polyvalent carboxylic acid, and the like. Rhohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic anhydride, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, 4-cyclohexene-1,2- Dicarboxylic acid anhydride can be preferably used. The said alicyclic polybasic acid (a1-2) can be used individually or in combination of 2 or more types.

  When the acid component (a1) contains the alicyclic polybasic acid (a1-2), the content of the alicyclic polybasic acid (a1-2) is based on the total amount of the acid component (a1). As for it, it is suitable in the range of 20-70 mol%, Preferably it is 25-60 mol%, More preferably, it is in the range of 30-50 mol%.

  Moreover, as said alicyclic polybasic acid (a1-2), the alicyclic polybasic acid which has a carboxyl group in 1st-position and 2nd-position from a smoothness of a multilayer coating film obtained and a vividness viewpoint It is preferable to use (a1-2-1) and an alicyclic polybasic acid (a1-2-2) having a carboxyl group at the 1-position and the 4-position in combination.

  As the alicyclic polybasic acid (a1-2), the alicyclic polybasic acid (a1-2-1) having the carboxyl group at the 1-position and the 2-position and the fat having the carboxyl group at the 1-position and the 4-position When the cyclic polybasic acid (a1-2-2) is used in combination, the amount used is based on the total amount of the acid component (a1) and the content of the alicyclic polybasic acid (a1-2-1) is 5 to 50 mol%, preferably 8 to 40 mol%, more preferably 12 to 30 mol%, and the alicyclic polybasic acid (a1-2-2) content is 5 to 50 mol%, preferably It is suitable to be in the range of 8-40 mol%, more preferably 12-30 mol%. The molar ratio of the alicyclic polybasic acid (a1-2-1) to the alicyclic polybasic acid (a1-2-2) is 20/80 to 80/20, preferably 30/70 to 70 /. It is suitable that it is in the range of 30, more preferably 40/60 to 60/40.

  Examples of the alicyclic polybasic acid (a1-2-1) having the carboxyl groups at the 1-position and 2-position include alicyclic rings such as 1,2-cyclohexanedicarboxylic acid and 4-cyclohexene-1,2-dicarboxylic acid. An aliphatic polycarboxylic acid; an anhydride of the alicyclic polyvalent carboxylic acid; a lower alkyl esterified product of the alicyclic polyvalent carboxylic acid, and the like. Among them, 1,2-cyclohexanedicarboxylic acid, 1,2 -Cyclohexanedicarboxylic acid anhydride, 4-cyclohexene-1,2-dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid anhydride, preferably 1,2-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid anhydride Can be preferably used. The said alicyclic polybasic acid (a1-2-1) can be used individually or in combination of 2 or more types.

  Examples of the alicyclic polybasic acid (a1-2-2) having a carboxyl group at the 1-position and the 4-position include alicyclic polyvalent carboxylic acids such as 1,4-cyclohexanedicarboxylic acid; Examples thereof include lower alkyl esterified products of monovalent carboxylic acids, among which 1,4-cyclohexanedicarboxylic acid can be suitably used. The said alicyclic polybasic acid (a1-2-2) can be used individually or in combination of 2 or more types.

  As the alicyclic polybasic acid (a1-2-1) having the carboxyl group at the 1-position and 2-position, 1,2-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic anhydride, 4-cyclohexene-1, An alicyclic ring using at least one alicyclic polybasic acid selected from the group consisting of 2-dicarboxylic acid and 4-cyclohexene-1,2-dicarboxylic anhydride and having carboxyl groups at the 1-position and 4-position When 1,4-cyclohexanedicarboxylic acid is used as the aliphatic polybasic acid (a1-2-2), 1,2-cyclohexanedicarboxylic acid in the alicyclic polybasic acid (a1-2), 1,2- The total content of cyclohexanedicarboxylic acid anhydride, 4-cyclohexene-1,2-dicarboxylic acid and 4-cyclohexene-1,2-dicarboxylic acid anhydride is the total amount of acid component (a1). As a quasi-standard, it is suitable to be in the range of 5 to 50 mol%, preferably 8 to 40 mol%, more preferably 12 to 30 mol%, and the content of 1,4-cyclohexanedicarboxylic acid is the acid component (a1) It is suitable that it is in the range of 5 to 50 mol%, preferably 8 to 40 mol%, more preferably 12 to 30 mol%, based on the total amount.

  The aromatic polybasic acid (a1-3) is generally an aromatic compound having two or more carboxyl groups in one molecule, an acid anhydride of the aromatic compound, and an esterified product of the aromatic compound. For example, aromatic polyvalent carboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, trimellitic acid, pyromellitic acid; anhydrous aromatic polycarboxylic acid A lower alkyl esterified product of the aromatic polyvalent carboxylic acid. The aromatic polybasic acid (a1-3) can be used alone or in combination of two or more.

  As the aromatic polybasic acid (a1-3), it is preferable to use phthalic acid, phthalic anhydride, isophthalic acid, trimellitic acid, trimellitic anhydride from the viewpoint of the clarity of the resulting coating film. is there.

  When the acid component (a1) contains the aromatic polybasic acid (a1-3), the content of the aromatic polybasic acid (a1-3) is based on the total amount of the acid component (a1). It is suitable to be in the range of 10 to 80 mol%, preferably 15 to 60 mol%, more preferably 20 to 50 mol%.

  The acid component other than the aliphatic polybasic acid (a1-1), alicyclic polybasic acid (a1-2), and aromatic polybasic acid (a1-3) is not particularly limited. Palm oil fatty acid, cottonseed oil fatty acid, hemp seed oil fatty acid, rice bran oil fatty acid, fish oil fatty acid, tall oil fatty acid, soybean oil fatty acid, linseed oil fatty acid, tung oil fatty acid, rapeseed oil fatty acid, castor oil fatty acid, dehydrated castor oil fatty acid, safflower oil fatty acid Fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, p-tert-butylbenzoic acid, cyclohexane acid, 10-phenyloctadecanoic acid and the like; Examples thereof include hydroxycarboxylic acids such as lactic acid, 3-hydroxybutanoic acid and 3-hydroxy-4-ethoxybenzoic acid. The above acid components can be used alone or in combination of two or more.

Alcohol component (a2)
As said alcohol component (a2), the polyhydric alcohol which has a 2 or more hydroxyl group in 1 molecule can be used conveniently. Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3 -Butanediol, 1,2-butanediol, 3-methyl-1,2-butanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,2-pentanediol, 1,5-pentanediol 1,4-pentanediol, 2,4-pentanediol, 2,3-dimethyltrimethylene glycol, tetramethylene glycol, 3-methyl-4,3-pentanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentane 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, tricyclodecane dimethanol, water Dihydric alcohols such as hydrogenated bisphenol A and hydrogenated bisphenol F; polylactone diols obtained by adding lactones such as ε-caprolactone to these dihydric alcohols; ester diols such as bis (hydroxyethyl) terephthalate; alkylenes of bisphenol A Oxide adducts, polyether diols such as polyethylene glycol, polypropylene glycol, polybutylene glycol; glycerin, trimethylolethane, trimethylolpropane, diglycerin, triglycerin, 1,2,6- Trivalent or higher alcohols such as hexanetriol, pentaerythritol, dipentaerythritol, tris (2-hydroxyethyl) isocyanuric acid, sorbitol, mannitol; lactones such as ε-caprolactone are added to these trivalent or higher alcohols And polylactone polyols.

  As the alcohol component (a2), in addition to the polyhydric alcohol, for example, monoalcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, stearyl alcohol, 2-phenoxyethanol; propylene oxide, butylene oxide, “Cardura E10” An alcohol compound obtained by reacting a monoepoxy compound such as (trade name, glycidyl ester of a synthetic highly branched saturated fatty acid, manufactured by HEXION Specialty Chemicals) and an acid, and the like can be used.

  The alcohol component (a2) preferably contains a trivalent or higher valent alcohol (a2-1) from the viewpoint of water resistance of the resulting coating film. Among them, trimethylolethane, trimethylolpropane, penta Erythritol, dipentaerythritol, glycerin, diglycerin and sorbitol, preferably trimethylolethane and trimethylolpropane can be suitably used.

  When the alcohol component (a2) contains the above trivalent or higher alcohol (a2-1), the content of the trivalent or higher alcohol (a2-1) is based on the total amount of the alcohol component (a1). It is suitable to be in the range of 5 to 80 mol%, preferably 15 to 60 mol%, more preferably 20 to 40 mol%.

  The production method of the hydroxyl group-containing polyester resin (A) is not particularly limited, and can be performed according to a usual method. For example, the carboxyl group in the acid component (a1) and the alcohol component (a2) It can be produced by setting the equivalent ratio of hydroxyl groups (COOH / OH) to less than 1 and carrying out an esterification reaction or a transesterification reaction in a state where there are more hydroxyl groups than carboxyl groups. Moreover, it can manufacture also by making the said alcohol component (a2) react with a carboxyl group-containing polyester resin.

  The esterification reaction or transesterification reaction of the acid component (a1) and the alcohol component (a2) is carried out by a method known per se, for example, the acid component (a1) and the alcohol component (a2) in a nitrogen stream at 150 to It can be carried out by heating at 250 ° C. for about 5 to 10 hours and performing polycondensation.

  In addition, when the acid component (a1) and the alcohol component (a2) are esterified or transesterified, they may be added at once, or may be added in several times. Moreover, after first synthesizing the hydroxyl group-containing polyester resin, the obtained hydroxyl group-containing polyester resin may be reacted with an acid anhydride to be half-esterified. Moreover, after synthesizing a carboxyl group-containing polyester resin first, the alcohol component (a2) may be added.

  In the esterification or transesterification reaction, as a catalyst for promoting the reaction, dibutyltin oxide, antimony trioxide, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, lead acetate, tetrabutyl titanate, tetraisopropyl A catalyst known per se, such as titanate, can be used.

  The hydroxyl group-containing polyester resin (A) can be modified with a fatty acid, a monoepoxy compound, or the like during the preparation of the resin, or after the esterification reaction or after the transesterification reaction.

  Examples of the fatty acid include coconut oil fatty acid, cottonseed oil fatty acid, hemp seed oil fatty acid, rice bran oil fatty acid, fish oil fatty acid, tall oil fatty acid, soybean oil fatty acid, linseed oil fatty acid, tung oil fatty acid, rapeseed oil fatty acid, castor oil fatty acid, dehydrated castor Oil fatty acid, safflower oil fatty acid and the like can be mentioned, and as the above-mentioned monoepoxy compound, for example, “Cardura E10” (trade name, manufactured by HEXION Specialty Chemicals, glycidyl ester of synthetic highly branched saturated fatty acid) is preferably used. it can.

  The hydroxyl group-containing polyester resin (A) is generally 50 to 250 mgKOH / g, preferably 70 to 180 mgKOH / g, more preferably 100 to 150 mgKOH / g, from the viewpoint of curability of the resulting coating film. It is preferable to have a valence. In addition, from the viewpoint of the smoothness of the resulting multilayer coating film, it has a number average molecular weight in the range of 500 to 10,000, preferably 700 to 5,000, and more preferably 1,000 to 3,000. Is preferred.

  Adjustment of the acid value, hydroxyl value, and number average molecular weight of the hydroxyl group-containing polyester resin (A) is, for example, equivalent ratio of the carboxyl group in the acid component (a1) to the hydroxyl group in the alcohol component (a2) (COOH / OH ) Or by adjusting the reaction time in the esterification reaction or transesterification reaction. The equivalent ratio (COOH / OH) of the carboxyl group in the acid component (a1) to the hydroxyl group in the alcohol component (a2) is generally 0.75 to 0.95, preferably 0.78 to 0.92. More preferably, it is in the range of 0.80 to 0.90.

  In addition, the number average molecular weight and the weight average molecular weight in this specification are based on the number average molecular weight and the weight average molecular weight measured with a gel permeation chromatograph (manufactured by Tosoh Corporation, “HLC8120GPC”) based on the molecular weight of standard polystyrene. It is a converted value. In this measurement, four columns of “TSKgel G-4000HXL”, “TSKgel G-3000HXL”, “TSKgel G-2500HXL”, and “TSKgel G-2000HXL” (both trade names, manufactured by Tosoh Corporation) were used as columns. The measurement conditions of mobile phase tetrahydrofuran, measurement temperature 40 ° C., flow rate 1 mL / min, detector RI were used.

Polyisocyanate compound (B)
The polyisocyanate compound (B) used as a crosslinking agent in the coating composition of the present invention is a compound having at least two isocyanate groups in one molecule, and examples thereof include aliphatic polyisocyanates, alicyclic polyisocyanates, Examples thereof include aromatic aliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of the polyisocyanates.

  Examples of the aliphatic polyisocyanate include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3. Aliphatic diisocyanates such as butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanatomethylcaproate, for example lysine ester triisocyanate, 1,4,8 -Triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane 2,5,7 and aliphatic triisocyanates such as trimethyl-1,8-diisocyanato-5-isocyanatomethyl octane and the like.

  Examples of the alicyclic polyisocyanate include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name) : Isophorone diisocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3- or 1,4-bis (isocyanatomethyl) cyclohexane (common name: hydrogenated xylylene diisocyanate) or The mixture, alicyclic diisocyanates such as norbornane diisocyanate; 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2- (3-iso Anatopropyl) -2,5-di (isocyanatomethyl) -bicyclo (2.2.1) heptane, 2- (3-isocyanatopropyl) -2,6-di (isocyanatomethyl) -bicyclo (2. 2.1) Heptane, 3- (3-isocyanatopropyl) -2,5-di (isocyanatomethyl) -bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2-isocyanate Natomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 6- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) -heptane, 6- (2 -B Shianatoechiru) -2-isocyanatomethyl-2- (3-isocyanatopropyl) - bicyclo (2.2.1) such as alicyclic triisocyanates such as heptane and the like.

  Examples of the araliphatic polyisocyanate include 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω, ω′-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis. Aroaliphatic diisocyanates such as (1-isocyanato-1-methylethyl) benzene (common name: tetramethylxylylene diisocyanate) or mixtures thereof, for example, aromatic aliphatic triisates such as 1,3,5-triisocyanatomethylbenzene An isocyanate etc. can be mentioned.

  Examples of the aromatic polyisocyanate include m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4′- or 4,4′-diphenylmethane diisocyanate or the like. Mixtures, 2,4- or 2,6-tolylene diisocyanate or mixtures thereof, aromatic diisocyanates such as 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, for example triphenylmethane-4,4 ', Aromatic triisocyanates such as 4 ″ -triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, such as 4,4′-diphenylmethane-2,2 ′, 5 , 5 ' Etc. and aromatic tetraisocyanates such as tetra isocyanates.

  Examples of the polyisocyanate derivatives include dimer, trimer, biuret, allophanate, uretdione, uretoimine, isocyanurate, oxadiazine trione, polymethylene polyphenyl polyisocyanate (crude MDI, polymeric MDI) described above. ) And crude TDI.

  The above polyisocyanates and derivatives thereof may be used alone or in combination of two or more. Of these polyisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, and derivatives thereof can be used alone or in combination of two or more.

  The polyisocyanate compound (B) preferably has a number average molecular weight of generally 3,000 or less, particularly 120 to 1,500, from the viewpoint of the smoothness of the resulting multilayer coating film. .

  The ratio of the polyisocyanate compound (B) used with respect to the hydroxyl group-containing polyester resin (A) is not particularly limited, but the isocyanate of the polyisocyanate compound (B) is used from the viewpoints of coating curability and coating stability. The equivalent ratio (NCO / OH) of the hydroxyl group to the hydroxyl group-containing resin (A) is generally within the range of 0.5 to 2.0, particularly 0.8 to 1.5, more particularly 0.9 to 1.2. Preferably there is.

Coating Composition The coating composition of the present invention comprises 30 hydroxyl group-containing resins (A) based on 100 parts by mass of the total solid content of the hydroxyl group-containing polyester resin (A) and polyisocyanate compound (B) in the coating composition. To 95 parts by mass, preferably 50 to 90 parts by mass, more preferably 60 to 80 parts by mass, and polyisocyanate compound (B) 5 to 70 parts by mass, preferably 10 to 50 parts by mass, more preferably It can contain within the range of 20-40 mass parts.

  The coating composition of the present invention can contain a modifying resin such as a polyurethane resin, an acrylic resin, an alkyd resin, a silicon resin, a fluororesin, and an epoxy resin in addition to the hydroxyl group-containing polyester resin (A). It is desirable to include a polyurethane resin and / or an acrylic resin from the viewpoints of finish and chipping resistance.

  Moreover, the coating composition of this invention can use a melamine resin etc. together in addition to a polyisocyanate compound (B) as an auxiliary | assistant crosslinking agent. Examples of melamine resins that can be used include methylolated melamine resins obtained by reaction of melamine and aldehydes. Examples of the aldehyde include formaldehyde and paraformaldehyde. Those obtained by etherifying a part or all of the methylol groups of the methylolated melamine resin with monoalcohol can be used. Examples of the alcohol used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, Examples include i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, 2-ethylbutanol, and 2-ethylhexanol.

Examples of commercially available melamine resins include “Cymel 202”, “Cymel 203”, “Cymel 238”, “Cymel 251”, “Cymel 303”, “Cymel 323”, “Cymel 324”, and “Cymel 325”. “Cymel 327”, “Cymel 350”, “Cymel 385”, “Cymel 1156”, “Cymel 1158”, “Cymel 1116”, “Cymel 1130” (manufactured by Nihon Cytec Industries, Inc.), “Uban 120”, “Uban 20HS”, “Uban 20SE60”, “Uban 2021”, “Uban 2028”, “Uban 28-60” (manufactured by Mitsui Chemicals, Inc.), and the like.
The said melamine resin can be used individually or in combination of 2 or more types.

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

  The said melamine resin is 30 mass parts or less on the basis of the total solid content of 100 mass parts of a hydroxyl-containing polyester resin (A) and a polyisocyanate compound (B), Preferably it is used within the range of 1-20 mass parts. it can.

  Moreover, the coating composition of this invention can contain a polyol compound (C). Especially, the coating composition of this invention is a polyol compound whose number average molecular weight exists in the range of 100-2,000, preferably 300-1,600, more preferably 400-900 as this polyol compound (C). Since it is possible to obtain a multi-layer coating film excellent in smoothness, it is preferable.

  The polyol compound (C) is a compound having at least two hydroxyl groups in one molecule, and examples thereof include polyether polyol, polyester polyol, polycarbonate polyol, polybutadiene polyol, and hydrogenated polybutadiene polyol. These can be used alone or in combination of two or more.

  Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, poly (ethylene / propylene) glycol, polytetramethylene glycol, poly (ethylene / tetramethylene) glycol and the like.

  The polyester polyol preferably has an acid value of less than 3 mgKOH / g and a number average molecular weight of 200 to 900, preferably 300 to 800. The polyester polyol is preferably linear.

  Examples of the polyester polyol include a polyester polyol obtained by esterifying a polyhydric alcohol component and a polybasic acid component, a polyester polyol obtained by a ring-opening reaction of a lactone compound using a polyhydric alcohol component as an initiator, and the like. Is mentioned. Examples of the polyhydric alcohol component and the polybasic acid component include the polyhydric alcohol and polybasic acid exemplified in the description of the hydroxyl group-containing polyester resin (A). It can be used individually or in combination of 2 or more types. In the latter case, examples of the lactone compound include ε-caprolactone and poly β-methyl-δ-valerolactone.

  Examples of the polycarbonate polyol include a reaction product of a polyhydric alcohol and phosgene, a ring-opening polymer of a cyclic carbonate (such as alkylene carbonate), and the like. Examples of the polyhydric alcohol include 3-methyl-1,5-pentanediol and 1,6-hexanediol. Examples of the cyclic carbonate include ethylene carbonate, trimethylene carbonate, and tetramethylene carbonate. . In addition, the polycarbonate polyol may have an ester bond as well as a carbonate bond in the molecule.

  When the coating composition of this invention contains the said polyol compound (C), the compounding quantity of this polyol compound (C) is 100 mass of total solid content of a hydroxyl-containing polyester resin (A) and a polyisocyanate compound (B). 1 to 50 parts by weight, preferably 2 to 30 parts by weight, more preferably 3 to 15 parts by weight, based on parts.

  The coating composition of the present invention can further contain silicon dioxide (D). Among them, the coating composition of the present invention has a carbon content of 1.0% by mass or less, preferably 0.5% by mass or less, more preferably 0.1% by mass or less as the silicon dioxide (D). It is preferable that silicon is contained because a multilayer coating film excellent in sharpness can be obtained.

  In the present specification, the carbon content of silicon dioxide (D) is the mass ratio of carbon contained in silicon dioxide (D) to silicon dioxide (D), and the solid-in-carbon analyzer EMIA-110 (trade name) , Manufactured by Horiba, Ltd.). Specifically, silicon dioxide is charged into a crucible, heated to 1,000 ° C., the generated gas component is analyzed by an infrared absorption method, and the total amount of carbon is determined from the amounts of detected carbon monoxide and carbon dioxide, The mass fraction with respect to the amount of silicon dioxide charged is the carbon amount of silicon dioxide.

  The reason why the coating composition of the present invention has a low carbon content, that is, a small amount of hydrophobic groups and contains silicon dioxide having a relatively high hydrophilicity, is not clear why a coating film having excellent sharpness can be obtained. When the aqueous second colored paint (Y) is reapplied on the paint composition of the present invention, this relatively hydrophilic silicon dioxide gathers in the vicinity of the interface between the two paint films, resulting in a mixed layer between the paint films. It is inferred to suppress.

  When the coating composition of this invention contains silicon dioxide (D), as a compounding quantity of silicon dioxide (D), the total solid content of 100 mass parts of a hydroxyl-containing polyester resin (A) and a polyisocyanate compound (B) is used. As a standard, it is generally suitable that the content is in the range of 0.05 to 10 parts by mass, particularly 0.1 to 5 parts by mass, more particularly 0.3 to 2 parts by mass. In addition, the amount of silicon dioxide having a carbon content of 1.0% by mass or less is generally 0.05 to 0.005 based on 100 parts by mass of the total solid content of the hydroxyl group-containing polyester resin (A) and the polyisocyanate compound (B). It is suitable to be in the range of 10 parts by weight, especially 0.1-5 parts by weight, more particularly 0.3-2 parts by weight.

  Moreover, it is preferable that the coating composition of this invention contains a curing catalyst (E). Examples of the curing catalyst (E) include tin octylate, dibutyltin diacetate, dibutyltin di (2-ethylhexanoate), dibutyltin dilaurate, dioctyltin diacetate, dioctyltin di (2-ethylhexanoate). Ate), dibutyltin oxide, dioctyltin oxide, dibutyltin fatty acid salt, lead 2-ethylhexanoate, zinc octylate, zinc naphthenate, zinc fatty acids, cobalt naphthenate, calcium octylate, copper naphthenate, tetra (2 -An organic metal compound such as ethylhexyl) titanate; a tertiary amine; a phosphoric acid compound, and the like. These may be used alone or in combination of two or more.

  When the coating composition of this invention contains the said curing catalyst (E), the compounding quantity of this curing catalyst (E) is 100 mass of total solid content of a hydroxyl-containing polyester resin (A) and a polyisocyanate compound (B). It is suitable that it is in the range of 0.005 to 5 parts by mass, preferably 0.01 to 0.5 parts by mass, more preferably 0.03 to 0.3 parts by mass, based on parts.

  Moreover, it is preferable that the coating composition of this invention contains a pigment (F) further. Examples of the pigment (F) include a color pigment (F1), an extender pigment (F2), and a glitter pigment (F3). The pigment (F) can be used alone or in combination of two or more.

  When the coating composition of this invention contains the said pigment (F), the compounding quantity of this pigment (F) is 100 mass parts of total solid content of the said hydroxyl-containing polyester resin (A) and a polyisocyanate compound (B). Is based on 1 to 200 parts by mass, preferably 20 to 150 parts by mass, more preferably 50 to 120 parts by mass.

  Examples of the color pigment (F1) include titanium oxide, zinc white, carbon black, molybdenum red, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, isoindoline pigment, selenium pigment, and perylene pigment. Among them, titanium oxide and carbon black can be preferably used.

  When the coating composition of this invention contains the said color pigment (F1), the compounding quantity of this color pigment (F1) is 100 mass of total solid content of a hydroxyl-containing polyester resin (A) and a polyisocyanate compound (B). 1 to 120 parts by weight, preferably 10 to 100 parts by weight, more preferably 15 to 90 parts by weight, based on parts.

  Examples of the extender pigment (F2) include clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, talc, and alumina white. Among these, barium sulfate and / or talc are preferably used.

  Especially, the coating composition of this invention is barium sulfate whose average primary particle diameter is 1 micrometer or less as said extender pigment (F2), More preferably, an average primary particle diameter exists in the range of 0.01-0.8 micrometer. It is preferable to contain barium sulfate because a multilayer coating film excellent in smoothness can be obtained.

  The average primary particle diameter of barium sulfate in the present invention was obtained by observing barium sulfate with a scanning electron microscope and averaging the maximum diameter of 20 barium sulfate particles on a straight line drawn randomly on an electron micrograph. Value.

  When the coating composition of this invention contains the said extender pigment (F2), the compounding quantity of this extender pigment (F2) is 100 mass of total solid content of a hydroxyl-containing polyester resin (A) and a polyisocyanate compound (B). 1 to 100 parts by weight, preferably 11 to 60 parts by weight, more preferably 16 to 40 parts by weight, based on parts. The blending amount of barium sulfate having an average primary particle size of 1 μm or less is 1 to 100 parts by mass, preferably 100 parts by mass of the total solid content of the hydroxyl group-containing polyester resin (A) and the polyisocyanate compound (B). Is preferably in the range of 11-60 parts by weight, more preferably 16-40 parts by weight.

  Further, the glitter pigment (F3) is a pigment that imparts a glittering glitter feeling or a pearl-like light interference pattern to the coating film. Specifically, it is a non-leafing type or leafing type aluminum (evaporated aluminum). In addition, copper, zinc, brass, nickel, aluminum oxide, mica, aluminum oxide coated with titanium oxide or iron oxide, mica coated with titanium oxide or iron oxide, and the like can be used. Among these, examples of the bright pigment (F3) capable of imparting a pearl-like light interference pattern include aluminum oxide coated with titanium oxide or iron oxide, mica coated with titanium oxide or iron oxide, and the like. be able to.

  The glitter pigment (F3) is preferably flake shaped. Further, as the glitter pigment (F3), those having a longitudinal dimension of 1 to 100 μm, particularly 5 to 40 μm, and a thickness of 0.0001 to 5 μm, particularly 0.001 to 2 μm are suitable. .

  In addition, the coating composition of the present invention can be used as usual paints such as thickeners, ultraviolet absorbers, light stabilizers, antifoaming agents, plasticizers, organic solvents, surface conditioners, anti-settling agents, etc. The additive for use can be contained alone or in combination of two or more.

From the viewpoint of the smoothness of the resulting coating film, the coating composition of the present invention is applied so that the cured film thickness is 30 μm and heated at 80 ° C. for 10 minutes (G _80). ) Is preferably 40% by mass or more, particularly 45 to 98% by mass, more preferably 50 to 95% by mass.

In addition, the said gel fraction ( _G80 ) can be measured with the following method.
First, the coating composition of the present invention is applied on a polypropylene plate so as to have a cured film thickness of 30 μm and heated at 80 ° C. for 10 minutes. Next, the coating film on the polypropylene plate is collected, and the mass (W _a ) is measured. Then, put a coating film on a stainless steel mesh container 200 mesh, and extracted with refluxing for 5 hours in acetone was warmed to 64 ° C., after drying for 60 minutes at 110 ° C. coating weight (W _b ) And the insoluble coating film residual ratio (mass%) calculated according to the following formula is defined as the gel fraction.
Gel fraction (mass%) = (W _b / W _a ) × 100
Adjustment of the gel fraction ( _G80 ) of the coating composition of this invention can be performed by adjusting the compounding quantity of the curing catalyst in a coating composition, for example.

  In addition, the coating composition of the present invention has a maximum viscosity of 5 Pa · sec or less measured under the condition of a frequency of 0.1 Hz in the range of 30 to 80 ° C. from the viewpoint of the smoothness of the obtained multilayer coating film. It is preferable that

  In this specification, the viscosity is a value measured using a viscoelasticity measuring device, and for example, “Rheostress RS-150” (trade name, manufactured by HAAKE) is used as the viscoelasticity measuring device. can do. As a specific method for measuring the viscosity, the surface of a tin plate (300 × 450 × 0.3 mm) degreased with isopropanol was used. The coating composition of the present invention, whose viscosity at 20 ° C. according to 4 was adjusted to 20 seconds, was applied by air spraying to a dry film thickness of 30 μm, and the uncured coating film formed on the tinplate was scraped off to obtain a sample. A sample collected in a bottle, immediately capped and sealed is used as a sample, and 1.0 g of the sample is measured with a rheo-stress RS-150 to measure dynamic viscoelasticity (frequency 0.1 Hz, strain 1. 0, temperature rising rate 6 ° C./min, sensor: parallel plate (Φ = 20 mm), gap: 0.5 mm) is performed in the temperature range from 30 ° C. to 80 ° C., and the maximum value of the complex viscosity is measured. be able to.

  The maximum value of the viscosity can be adjusted, for example, by adjusting the monomer composition of the hydroxyl group-containing polyester resin (A).

  The coating composition of the present invention may be in the form of a one-component paint or a multi-component paint. From the viewpoint of storage stability, the hydroxyl group-containing resin (A) is used. A two-component paint comprising a main component contained and a curing agent component containing the polyisocyanate compound (B) is preferred. In general, it is desirable that the main agent further contains a pigment, a curing catalyst and a solvent, and that the curing agent component further contains a solvent.

  The coating composition of the present invention may be in any form of an organic solvent-type paint and a water-based paint, but is an organic solvent-type paint from the viewpoint of storage stability, smoothness, sharpness, etc. Is preferred. In the present specification, the water-based paint is a paint whose main component is water, and the organic solvent-type paint is a paint containing substantially no water as a solvent.

  The coating composition of the present invention described above is applied as the first colored coating (X) onto the article to be coated by a method known per se, for example, air spray, airless spray, rotary atomizer and the like. Electrostatic application may be performed during painting. Among these, electrostatic coating by air spray and electrostatic coating by a rotary atomizing coating machine are preferable, and electrostatic coating by a rotary atomizing coating machine is particularly preferable. The coating film thickness is a cured film thickness, and is usually 10 to 100 μm, preferably 10 to 50 μm, and more preferably 15 to 35 μm.

  In the coating composition of the present invention, a metal member having an undercoat film formed by various electrodeposition paints as needed and a plastic member having an undercoat film formed by various primer paints as necessary are integrated. It is also possible to paint on the object to be coated, whereby the coating colors of the metal member and the plastic member match, and a multilayer coating film having excellent smoothness can be formed on both members. can get.

Process (2)
In this step, the gel fraction of the uncured first colored coating film formed in the step (1) is 5% by mass or more and less than 40% by mass, preferably 10 to 35% by mass, more preferably 15 to 30%. It is adjusted to mass%.

  In this specification, the cured coating is a cured and dried state as defined in JIS K 5600-1-1, that is, the center of the coating surface is strongly sandwiched between the thumb and index finger, and the coating surface has dents due to fingerprints. It is a coating film in which the movement of the coating film is not felt, and the center of the coating surface is rubbed rapidly with a fingertip so that no trace is left on the coating surface. On the other hand, an uncured coating film is a state in which the coating film has not reached the above-mentioned cured and dried state, and includes a finger-touch dried state and a semi-cured dried state defined in JIS K 5600-1-1.

  The gel fraction of the first colored coating film can be adjusted, for example, by performing preheating (preheating), air blowing, or the like. The preheating is usually performed at a temperature of 30 to 110 ° C., preferably 40 to 90 ° C., more preferably 50 to 70 ° C., in a drying furnace for an object coated with the first colored paint (A), 30 Second to 15 minutes, preferably 1 to 10 minutes, more preferably 2 to 5 minutes can be performed by heating directly or indirectly, and the air blow is usually applied to the coated surface of the object at room temperature. Or it can carry out by blowing the air heated to the temperature of about 25 degreeC-about 80 degreeC.

Moreover, the gel fraction of a 1st colored coating film can be measured with the following method.
First, the first colored paint (X) is applied to the object to be coated, and at the same time, the first colored paint (X) is also applied to the polypropylene plate, and preheating is performed as necessary. The polypropylene plate is collected immediately before the aqueous second colored paint (Y) is applied, and then the first colored coating film on the polypropylene plate is collected, and the mass (W _c ) is measured. Then, put a coating film on a stainless steel mesh container 200 mesh, and extracted with refluxing for 5 hours in acetone was warmed to 64 ° C., the dried coating weight after 60 minutes at 110 ° C. (W _d ) And the insoluble coating film residual ratio (mass%) obtained according to the following formula is defined as the gel fraction.
Gel fraction (mass%) = (W _d / W _c ) × 100
In addition, from the viewpoint of the smoothness of the obtained multilayer coating film, in this step, the solid content of the first colored coating film is generally 70 to 100% by mass, particularly 80 to 100% by mass, more particularly 90 to 90%. It is preferable to adjust within the range of 100% by mass.

  The solid content of the first colored coating film can be adjusted, for example, by performing preheating (preheating), air blowing, or the like.

In addition, the solid content rate of a 1st colored coating film can be measured with the following method.
First, the first colored paint (X) is applied to the object, and at the same time, the first colored paint (X) is also applied to the aluminum foil whose mass (W ₁ ) has been measured in advance. After the preliminary heating or the like, the aluminum foil is collected just before the water-based second colored paint (Y) is applied to the article to be coated, and its mass (W ₂ ) is measured. Next, the recovered aluminum foil is dried at 110 ° C. for 60 minutes, and allowed to cool to room temperature in a desiccator. Then, the mass (W ₃ ) of the aluminum foil is measured, and the solid content is determined according to the following formula.
Solid content (mass%) = {(W ₃ −W ₁ ) / (W ₂ −W ₁ )} × 100
In the multilayer coating film forming method of the present invention, by coating the aqueous second colored paint (Y) with the gel fraction of the first colored coating film adjusted to 5% by mass or more and less than 40% by mass, The reason why a multilayer coating film excellent in smoothness and sharpness is formed is not clear, but the fluidity of the first colored coating film is ensured by the low gel fraction of the first colored coating film. Smoothness is improved, and the relatively low acid value hydroxyl group-containing polyester resin (A) in the first colored coating film suppresses water permeation from the upper aqueous second colored paint (Y). It is presumed that the mixed layer between the first colored coating film and the second colored coating film is suppressed, and the sharpness is improved.

Process (3)
In this step, the aqueous second colored paint (Y) is applied on the uncured first colored coating film formed in the above step (2) to form an uncured second colored coating film.

Water-based second colored paint (Y)
As the water-based second colored paint (Y), for example, those known per se that are usually used in the painting of automobile bodies can be used. Specifically, for example, a base resin such as an acrylic resin, a polyester resin, an alkyd resin, a urethane resin, and an epoxy resin having a crosslinkable functional group such as a carboxyl group and a hydroxyl group, and a polyisocyanate compound that may be blocked, A coating material obtained by dissolving or dispersing a crosslinking agent such as a melamine resin or a urea resin in water together with a pigment or other additives can be used. Among these, a thermosetting water-based paint containing a hydroxyl group-containing resin and a melamine resin is preferable.

  Moreover, as said pigment, the said color pigment (F1), extender pigment (F2), luster pigment (F3), etc. can be used. Among these, by using the bright pigment (F3) as at least a part of the pigment component, a metallic or pearly coating film can be formed.

  Examples of the glitter pigment (F3) include non-leafing type or leafing type aluminum (including vapor-deposited aluminum), copper, zinc, brass, nickel, and oxidation exemplified in the description of the water-based first colored paint (X). Examples thereof include aluminum, mica, aluminum oxide coated with titanium oxide and iron oxide, and mica coated with titanium oxide and iron oxide. Among these, aluminum, aluminum oxide, mica, aluminum oxide coated with titanium oxide or iron oxide, mica coated with titanium oxide or iron oxide are preferably used, and aluminum is particularly preferably used. The glitter pigment (F3) can be used alone or in combination of two or more.

  Moreover, it is preferable that the said luster pigment (F3) is flake shaped. Further, as the glitter pigment (F3), those having a longitudinal dimension of 1 to 100 μm, particularly 5 to 40 μm, and a thickness of 0.0001 to 5 μm, particularly 0.001 to 2 μm are suitable. .

  When the aqueous second colored paint (Y) contains the glitter pigment (F3), the blending amount of the glitter pigment (F3) is 100 mass of resin solids in the aqueous second colored paint (Y). Generally, it is suitable to be in the range of 1 to 50 parts by weight, particularly 3 to 30 parts by weight, more particularly 5 to 20 parts by weight, based on parts.

  Moreover, it is preferable that water-based 2nd coloring coating material (Y) contains a hydrophobic solvent further. The hydrophobic solvent is an organic solvent having a mass dissolved in 100 g of water at 20 ° C. of 10 g or less, preferably 5 g or less, more preferably 1 g or less, such as rubber volatile oil, mineral spirit, toluol, xylol. Hydrocarbon solvents such as solvent naphtha; n-hexanol, n-octanol, 2-octanol, 2-ethylhexanol, n-decanol, benzyl alcohol, ethylene glycol mono 2-ethylhexyl ether, propylene glycol mono n-butyl ether, di Alcohol solvents such as propylene glycol mono n-butyl ether, tripropylene glycol mono n-butyl ether, propylene glycol mono 2-ethylhexyl ether, propylene glycol monophenyl ether; Ester solvents such as butyl acetate, isobutyl acetate, isoamyl acetate, methyl amyl acetate, and ethylene glycol monobutyl ether; and ketone solvents such as methyl isobutyl ketone, cyclohexanone, ethyl n-amyl ketone, and diisobutyl ketone, each of which is independent Or in combination of two or more.

  When the aqueous second colored paint (Y) contains the hydrophobic solvent, the amount of the hydrophobic solvent is 2 to 70 based on 100 parts by mass of the solid content in the aqueous second colored paint (Y). It is suitable that it is in the range of 11 parts by weight, preferably 11-50 parts by weight, more preferably 16-40 parts by weight.

  As the hydrophobic solvent, an alcohol-based hydrophobic solvent is preferably used from the viewpoint of smoothness and sharpness of the resulting multilayer coating film. Among them, alcohol-based hydrophobic solvents having 7 to 14 carbon atoms such as n-octanol, 2-octanol, 2-ethyl-1-hexanol, ethylene glycol mono 2-ethylhexyl ether, propylene glycol mono n-butyl ether, dipropylene Glycol mono n-butyl ether is particularly preferred.

  When the aqueous second colored paint (Y) contains the above-mentioned alcohol-based hydrophobic solvent, the blending amount of the alcohol-based hydrophobic solvent is based on 100 parts by mass of the solid content in the aqueous second colored paint (Y). 2 to 70 parts by mass, preferably 11 to 50 parts by mass, more preferably 16 to 40 parts by mass.

  If necessary, the water-based second colored paint (Y) may further include a curing catalyst, a thickener, an ultraviolet absorber, a light stabilizer, an antifoaming agent, a rust inhibitor, a plasticizer, an organic solvent, a surface conditioner, and a sedimentation agent. Ordinary paint additives such as an inhibitor may be contained alone or in combination of two or more.

  The water-based second colored paint (Y) can be applied by a method known per se, for example, air spray, airless spray, rotary atomizing coater, etc. Good. The coating film thickness is usually 5 to 40 μm, preferably 10 to 30 μm, and more preferably 12 to 20 μm as a cured film thickness.

  From the viewpoint of preventing the occurrence of coating film defects such as armpits, the coated film of the water-based second colored paint (Y) is subjected to preheating (preheating), air blowing, etc. under heating conditions in which the coating film is not substantially cured. Preferably it is done. The preheating temperature can be 40 to 100 ° C., preferably 50 to 90 ° C., more preferably 60 to 80 ° C., and the preheating time is 30 seconds to 15 minutes, preferably 1 to 10 minutes, more preferably. Can be 2-5 minutes. Moreover, the said air blow can be normally performed by spraying the air heated to normal temperature or the temperature of 25 to 80 degreeC on the coating surface of the to-be-coated object.

Step (4)
In this step, the clear paint (Z) is further applied onto the uncured second colored coating film formed in the above step (3) to form an uncured clear coating film.

Clear paint (Z)
As the clear paint (Z), for example, those known per se that are usually used in the painting of automobile bodies can be used. Specifically, for example, a base resin such as an acrylic resin, a polyester resin, an alkyd resin, a urethane resin, an epoxy resin, or a fluororesin having a crosslinkable functional group such as a hydroxyl group, a carboxyl group, an epoxy group, or a silanol group, and melamine Resin, urea resin, optionally blocked polyisocyanate compound, carboxyl group-containing compound or resin, epoxy group-containing compound or resin-containing organic solvent-based thermosetting paint, aqueous thermosetting type A paint, a thermosetting powder paint, or the like can be used. Among these, a thermosetting paint comprising a hydroxyl group-containing acrylic resin and a melamine resin, a thermosetting paint comprising a hydroxyl group-containing acrylic resin and an optionally blocked polyisocyanate compound, or a carboxyl group-containing resin and an epoxy group A thermosetting paint comprising a resin is particularly preferred.

  The clear paint (Z) may be any one of two-part paints such as a one-part paint and a two-part urethane resin paint.

  If necessary, the clear paint (Z) can contain the color pigment (F1), the glitter pigment (F3), the dye, and the like to such an extent that the transparency is not hindered. Further, the extender pigment (F2) Ordinary paint additives such as curing catalysts, thickeners, UV absorbers, light stabilizers, antifoaming agents, rust inhibitors, plasticizers, organic solvents, surface conditioners, anti-settling agents, etc. Or it can contain in combination of 2 or more types.

  In addition, the coating of the clear paint (Z) generally has a solid content of 70 to 100% by mass, particularly 80 to 80%, from the viewpoint of suppression of sagging and the sharpness of the resulting coating film. It is preferable to carry out the treatment while it is in the range of 100% by mass, more particularly 90-100% by mass.

  The solid content of the second colored coating film can be adjusted, for example, by performing preheating (preheating), air blowing, etc. before applying the clear paint (Z). The preheating is usually performed at 40 to 100 ° C., preferably 50 to 90 ° C., more preferably in a drying furnace, on an object coated with the first colored paint (X) and the aqueous second colored paint (Y). It can be carried out by heating directly or indirectly at a temperature of 60 to 80 ° C. for 30 seconds to 15 minutes, preferably 1 to 10 minutes, more preferably 2 to 5 minutes. It can be carried out by spraying air heated to a normal temperature or a temperature of about 25 ° C. to about 80 ° C. on the surface to be coated.

In addition, the solid content rate of a 2nd colored coating film can be measured with the following method.
First, the aqueous second colored paint (Y) is applied onto the first colored coating film, and at the same time, the aqueous second colored paint (Y) is applied onto the aluminum foil whose mass (W ₄ ) has been measured in advance. After preheating as necessary, the aluminum foil is recovered just before the clear paint (Z) is applied on the second colored coating film, and its mass (W ₅ ) is measured. Next, the collected aluminum foil is dried at 110 ° C. for 60 minutes, and allowed to cool to room temperature in a desiccator. Then, the mass (W ₆ ) of the aluminum foil is measured, and the solid content is determined according to the following formula.
Solid content (mass%) = {(W ₆ -W ₄ ) / (W ₅ -W ₄ )} × 100
The clear paint (Z) can be applied to the uncured coating surface of the water-based second colored paint (Y) by a method known per se, for example, airless spray, air spray, rotary atomizing coater, etc. Electrostatic application may be performed during coating. The coating film thickness is usually 10 to 60 μm, preferably 25 to 50 μm in terms of cured film thickness.

  After application of the clear paint (Z), an interval of 1 to 60 minutes at room temperature, preferably 3 to 20 minutes, or 40 to 90 ° C. for 1 to 30 minutes, preferably 3 to 10 minutes, as necessary. It can be preheated for about a minute.

Process (5)
A multi-layer coating film composed of three layers of the first colored coating film, the second colored coating film, and the clear coating film formed as described above can be obtained, for example, by a conventional coating film baking means. Heating at 80 to 180 ° C., preferably 120 to 160 ° C., more preferably 130 to 150 ° C. for 10 to 40 minutes, preferably 15 to 30 minutes by hot air heating, infrared heating, high frequency heating, etc. Thereby, a multi-layer coating film having excellent smoothness and sharpness composed of a three-layer cured coating film of a first colored coating film, a second colored coating film, and a clear coating film can be formed. it can.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited only to these Examples. “Parts” and “%” indicate “parts by mass” and “% by mass”.

Production production example 1 of polyester resin solution (A)
In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and water separator, 52.6 parts (0.36 mol) of adipic acid (molecular weight 146), 1,2-cyclohexanedicarboxylic acid anhydride (molecular weight 154) ) 20.8 parts (0.135 mol), 1,4-cyclohexanedicarboxylic acid (molecular weight 172) 23.2 parts (0.135 mol), isophthalic acid (molecular weight 166) 44.8 parts (0.27 mol), trimethylol After 33.5 parts (0.25 mol) of propane (molecular weight 134) and 78 parts (0.0.75 mol) of neopentyl glycol (molecular weight 104) were charged and heated from 160 ° C. to 230 ° C. over 3 hours, The reaction was continued at 230 ° C. until the acid value reached 5 mgKOH / g. The produced condensed water was distilled off with a water separator. Next, it is diluted with a mixed solvent of xylene / swazol 1000 (trade name, manufactured by Cosmo Oil Co., Ltd., petroleum aromatic hydrocarbon solvent) = 50/50 (mass ratio) to a solid content concentration of 60%, and a hydroxyl group-containing polyester A resin solution (A-1) was obtained. The obtained hydroxyl group-containing polyester resin had a hydroxyl value of 118 and a number average molecular weight of 1,870.

Production Examples 2-12
In the same manner as in Production Example 1, the hydroxyl group-containing polyester resin solutions (A-2) to (A-12) were reacted by reacting the monomers having the blending ratios shown in Table 1 below until the acid values shown in Table 1 were reached. Obtained. The blending amount of each monomer and the acid value, hydroxyl value and number average molecular weight of each obtained hydroxyl group-containing polyester resin are shown in Table 1 below together with the hydroxyl group-containing polyester resin solution (A-1) obtained in Production Example 1. .

Production and production examples 13 to 32 of the first colored paint (X)
Polyester resin solutions (A-1) to (A-12) obtained in Production Examples 1 to 8, “JR-806” (trade name, manufactured by Teica, rutile titanium dioxide), “Carbon MA-100” (Product) Name, manufactured by Mitsubishi Chemical Corporation, carbon black), “Variace B-35” (trade name, manufactured by Sakai Chemical Industry Co., Ltd., barium sulfate powder, average primary particle size 0.5 μm), “SPARWITE W-5HB” (trade name, Wilber Ellis, barium sulfate powder, average primary particle size 1.6 μm), “MICRO ACE S-3” (trade name, manufactured by Nihon Talc, talc), “Sumijour N3300” (trade name, Sumika Bayer Urethane) Made by the company, isocyanurate of hexamethylene diisocyanate, solid content 100%, NCO content 21.8%), "Cymel 325" (trade name, Nippon Cytec Indust , Melamine resin, solid content 80%), "TPA-B80X" (trade name, manufactured by Asahi Kasei Chemical Co., Ltd., methylmethylene ketoxime blocked product of hexamethylene diisocyanate, solid content 80%), "Kuraray polyol P-510" (Trade name, manufactured by Kuraray Co., Ltd., polyester polyol, number average molecular weight 500), “AEROSIL 200” (trade name, manufactured by Nippon Aerosil Co., Ltd., carbon mass 0% by mass), “AEROSIL R-972” (trade name, manufactured by Nippon Aerosil Co., Ltd.) Manufactured, carbon content 0.8% by mass), “AEROSIL R-104” (trade name, manufactured by Nippon Aerosil Co., Ltd., carbon content 1.1% by mass) and dibutyltin diacetate in the mixing ratio shown in Table 2 below. Stirring and mixing were performed to form a paint, and first colored paints (X-1) to (X-32) were obtained.
In addition, when blending the pigment component, 15 parts of xylene and glass beads were added to and mixed with 42 parts of the hydroxyl group-containing polyester resin solution (25 parts of resin solid content) in the first colored paint and the amount of pigment shown in Table 2. Then, after dispersing for 30 minutes with a paint shaker, the glass beads were removed to obtain a pigment dispersion paste, which was subjected to stirring and mixing with other components. In addition, in blending silicon dioxide, 5 parts of xylene and glass beads were added to 2 parts of the hydroxyl group-containing polyester resin solution (1.2 parts of resin solid content) in the first colored paint and the amount of silicon dioxide shown in Table 2. In addition, after mixing for 30 minutes with a paint shaker, the glass beads were removed to obtain a pigment dispersion paste, which was then stirred and mixed with other components.
Ford cup No. 1 was added to the first colored paint by adding a mixed solvent of xylene / swazol 1000 (trade name, manufactured by Cosmo Oil Co., Ltd., petroleum aromatic hydrocarbon solvent) = 50/50 (mass ratio). . 4 was used to adjust the viscosity to 20 seconds at 20 ° C.
Moreover, about the obtained 1st colored coating materials (X-1)-(X-20), it applied so that a cured film thickness might be set to 30 micrometers on a polypropylene board, and the coating film after heating for 10 minutes at 80 degreeC. The measurement results of the maximum value of the viscosity measured under the conditions of gel fraction (G ₈₀ ) and frequency of 0.1 Hz at 30 to 80 ° C. are shown in Table 2.

Production Example of Acrylic Resin Emulsion for Aqueous Second Colored Paint (Y) Production Example 33
In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube and dripping device, charge 130 parts of deionized water and 0.52 part of Aqualon KH-10 (Note 1) in a nitrogen stream. The mixture was stirred and heated to 80 ° C. Next, 1% of the total amount of the following monomer emulsion (1) and 5.3 parts of a 6% aqueous ammonium persulfate solution were introduced into the reaction vessel and maintained at 80 ° C. for 15 minutes. Then, the remaining monomer emulsion (1) was dripped in the reaction container hold | maintained at the same temperature over 3 hours, and it age | cure | ripened for 1 hour after completion | finish of dripping. Thereafter, the following monomer emulsion (2) was added dropwise over 1 hour, and after aging for 1 hour, the mixture was cooled to 30 ° C. while gradually adding 40 parts of 5% dimethylethanolamine aqueous solution to the reaction vessel, and 100 mesh nylon Ejected while filtering through cloth, average particle size 100 nm (submicron particle size distribution measuring device “COULTER N4 type” (manufactured by Beckman Coulter), diluted with deionized water and measured at 20 ° C.), solid content An acrylic resin emulsion (AC) having a concentration of 30% was obtained. The obtained acrylic resin had an acid value of 33 mgKOH / g and a hydroxyl value of 25 mgKOH / g.
(Note 1) Aqualon KH-10: Polyoxyethylene alkyl ether sulfate ester ammonium salt: 97% active ingredient manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

  Monomer emulsion (1): 42 parts deionized water, 0.72 parts Aqualon KH-10, 2.1 parts allyl methacrylate, 2.8 parts styrene, 16.1 parts methyl methacrylate, 28 parts ethyl acrylate and n-butyl 21 parts of acrylate was mixed and stirred to obtain a monomer emulsion (1).

  Monomer emulsion (2): 18 parts deionized water, 0.31 part Aqualon KH-10, 0.03 part ammonium persulfate, 5.1 parts methacrylic acid, 5.1 parts 2-hydroxyethyl acrylate, 3 parts styrene, 6 parts of methyl methacrylate, 1.8 parts of ethyl acrylate and 9 parts of n-butyl acrylate were mixed and stirred to obtain a monomer emulsion (2).

Manufacture example 34 of polyester resin for water-based second colored paint (Y)
A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and water separator was charged with 109 parts of trimethylolpropane, 141 parts of 1,6-hexanediol, 126 parts of hexahydrophthalic anhydride and 120 parts of adipic acid. The temperature was raised between 160 ° C. and 230 ° C. over 3 hours, and then a condensation reaction was performed at 230 ° C. for 4 hours. The produced condensed water was distilled off with a water separator. Subsequently, in order to add a carboxyl group to the obtained condensation reaction product, 38.3 parts of trimellitic anhydride was further added and reacted at 170 ° C. for 30 minutes, and then 2-ethyl-1-hexanol (20 The polyester resin solution (PE1) having a solid content concentration of 70% was obtained by diluting with a mass dissolved in 100 g of water at 0.1 ° C. (0.1 g). The obtained polyester resin had an acid value of 46 mgKOH / g, a hydroxyl value of 150 mgKOH / g, and a number average molecular weight of 1,400.

Production Example 35
Polyester resin (PE2) in the same manner as in Production Example 34, except that 2-ethyl-1-hexanol as a dilution solvent is changed to ethylene glycol mono n-butyl ether (mass dissolved in 100 g of water at 20 ° C .: infinite). Got.

Production Example of Bright Pigment Concentrated Liquid Production Example 36
In the stirring and mixing vessel, 19 parts of aluminum pigment paste “GX-180A” (made by Asahi Kasei Metals Co., Ltd., metal content 74%), 35 parts of 2-ethyl-1-hexanol, resin solution containing phosphate group (Note 2) 8 And 0.2 part of 2- (dimethylamino) ethanol were mixed uniformly to obtain a bright pigment concentrate (P1).
(Note 2) Phosphate group-containing resin solution: put a mixed solvent of 27.5 parts of methoxypropanol and 27.5 parts of isobutanol in a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser and a dropping device, 6. Heat to 110 ° C., 25 parts of styrene, 27.5 parts of n-butyl methacrylate, 20 parts of “isostearyl acrylate” (trade name, Osaka Organic Chemical Industries, Ltd., branched higher alkyl acrylate), 4-hydroxybutyl acrylate 51.5 parts, 15 parts of a phosphoric acid group-containing polymerizable monomer (Note 3), 12.5 parts of 2-methacryloyloxyethyl acid phosphate, 10 parts of isobutanol, 4 parts of t-butyl peroxyoctanoate 121.5 Is added to the above mixed solvent over 4 hours, and 0.5 part of t-butylperoxyoctanoate and A mixture of propanol 20 parts was added dropwise for 1 hour. Thereafter, the mixture was aged and stirred for 1 hour to obtain a phosphate group-containing resin solution having a solid concentration of 50%. The acid value due to the phosphoric acid group of this resin was 83 mgKOH / g, the hydroxyl value was 29 mgKOH / g, and the weight average molecular weight was 10,000.
(Note 3) Phosphoric acid group-containing polymerizable monomer: Put 57.5 parts of monobutyl phosphate and 41 parts of isobutanol in a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and dropping device, and raise the temperature to 90 ° C. After warming, 42.5 parts of glycidyl methacrylate was added dropwise over 2 hours, followed by stirring and aging for another hour. Thereafter, 59 parts of isopropanol was added to obtain a phosphate group-containing polymerizable monomer solution having a solid content concentration of 50%. The acid value due to the phosphate group of the obtained monomer was 285 mgKOH / g.

Production Example 37
A bright pigment concentrate (P2) was obtained in the same manner as in Production Example 36 except that 35 parts of 2-ethyl-1-hexanol was changed to 35 parts of ethylene glycol mono n-butyl ether.

Production and production example 38 of water-based second colored paint (Y)
100 parts of the acrylic resin emulsion (AC) obtained in Production Example 33, 57 parts of the polyester resin solution (PE1) obtained in Production Example 34, 62 parts of the bright pigment concentrate (P1) obtained in Production Example 36, and “Cymel 325” "37.5 parts (trade name, manufactured by Nippon Cytec Industries, Inc., melamine resin, solid content 80%) were uniformly mixed, and further" Primal ASE-60 "(trade name, manufactured by Rohm and Haas, polyacrylic acid) System thickener), 2- (dimethylamino) ethanol and deionized water were added, pH 8.0, paint solid content 25%, Ford Cup No. 20 at 20 ° C. An aqueous second colored paint (Y-1) having a viscosity of 4 according to 4 was obtained.

Production Example 39
100 parts of the acrylic resin emulsion (AC) obtained in Production Example 33, 57 parts of the polyester resin solution (PE2) obtained in Production Example 35, 62 parts of the glitter pigment concentrate (P2) obtained in Production Example 37, and “Cymel 325” 37.5 parts of “Nippon Cytec Industries, trade name, melamine resin, solid content 80%” were mixed uniformly, and “Primal ASE-60” (Rohm and Haas, trade name, polyacrylic acid) System thickener), 2- (dimethylamino) ethanol and deionized water were added, pH 8.0, paint solid content 25%, Ford Cup No. 20 at 20 ° C. An aqueous second colored paint (Y-2) having a viscosity of 4 and a viscosity of 40 seconds was obtained.

Coating Film Formation Method The first colored paints (X-1) to (X-20) obtained in Production Examples 13 to 32, and the aqueous second colored paint (Y-1) obtained in Production Examples 38 and 39 and Using (Y-2), test coated plates were respectively prepared as described below, and an evaluation test was performed.

(Preparation of test article)
"Electron GT-10" (trade name, manufactured by Kansai Paint Co., Ltd., cationic electrodeposition paint) is electrodeposited onto a cold-rolled steel sheet that has been subjected to zinc phosphate chemical conversion treatment so that the cured film thickness is 20 μm. It was cured by heating for 30 minutes to obtain a test article.

Example 1
The first colored paint (X-) obtained in Production Example 13 on the above-described test object, the above-described polypropylene plate for measuring the gel fraction of the coated film, and the aluminum foil for measuring the solid content, respectively. 1) was electrostatically coated using a rotary atomizing type electrostatic coating machine so that the cured film thickness was 30 μm. After standing for 5 minutes and preheating at 60 ° C. for 5 minutes, the gel fraction and solid content of the first colored coating film were measured. Table 3 shows the measurement results.
Next, the aqueous second colored paint (Y-1) obtained in Production Example 38 is statically applied on the first colored coating film using a rotary atomizing type electrostatic coating machine so that the cured film thickness becomes 15 μm. After electrocoating and leaving for 3 minutes, preheating was performed at 80 ° C. for 3 minutes.
Next, on the second colored coating film, “Majicron KINO-1210” (trade name, manufactured by Kansai Paint Co., Ltd., acrylic resin solvent-type clear coating, hereinafter referred to as “clear coating (Z-1)”) Is coated electrostatically so that the cured film thickness is 40 μm, and is allowed to stand for 7 minutes, and then heated at 140 ° C. for 30 minutes to simultaneously cure the first colored coating film, the second colored coating film, and the clear coating film. A test coated plate was prepared.

Examples 2-19, Comparative Examples 1-7
In Example 1, the first colored paint (X-1) obtained in Production Example 13 was changed to the first colored paint (X-2) to (X-20) shown in Table 3, and the first colored paint (X The preheating conditions after coating -1) are changed to the preheating conditions shown in Table 3, and the aqueous second colored paint (Y-1) obtained in Production Example 38 is the aqueous second colored paint (Y-) shown in Table 3. A test coated plate was produced in the same manner as in Example 1 except that the aqueous second colored paint (Y-2) obtained in 1) or Production Example 39 was used.

Evaluation Test Each test plate obtained in Examples 1 to 19 and Comparative Examples 1 to 7 was evaluated by the following test method. The evaluation results are shown in Table 3.
(Test method)
Smoothness: Evaluated using a Long Wave (LW) value measured by Wave Scan (trade name, manufactured by BYK Gardner). The Long Wave (LW) value is an index of the amplitude of the surface roughness having a wavelength of about 1.2 to 12 mm, and the smaller the measured value, the higher the smoothness of the coated surface.

  Vividness: Evaluated using the Short Wave (SW) value measured by the above Wave Scan. The Short Wave (SW) value is an index of the amplitude of the surface roughness with a wavelength of about 0.3 to 1.2 mm, and the smaller the measured value, the higher the sharpness of the coating surface.

Claims (6)

The following steps (1) to (5), step (1): a step of forming an uncured first colored coating film by coating the first colored paint (X) on the article to be coated, step (2) : A step of setting the gel fraction of the uncured first colored coating film formed in the step (1) to 5% by mass or more and less than 40% by mass, step (3): an unformed product formed in the step (2) A step of applying an aqueous second colored paint (Y) on the cured first colored coating to form an uncured second colored coating, step (4): not formed in step (3) A step of applying a clear paint (Z) on the cured second colored coating film to form an uncured clear coating film, and a step (5): the first step formed in the steps (1) to (4). In the method of forming a multilayer coating film by sequentially performing a step of baking and curing the first colored coating film, the second colored coating film and the clear coating film simultaneously, the first coloring As the raw material (X), the content of the aliphatic polybasic acid (a1-1) obtained by the reaction of the acid component (a1) and the alcohol component (a2) and the acid component (a1) is the acid component (a1). ) And a coating composition comprising a hydroxyl group-containing polyester resin (A) having an acid value of 15 mgKOH / g or less and a polyisocyanate compound (B) in the range of 20 to 70 mol% based on the total amount of A method for forming a multilayer coating film, comprising: 2. The compound according to claim 1, wherein the content of the alicyclic polybasic acid (a1-2) in the acid component (a1) is in the range of 20 to 70 mol% based on the total amount of the acid component (a1). Layer coating film forming method. The acid component (a1) contains an alicyclic polybasic acid (a1-2), and 1,2-cyclohexanedicarboxylic acid or 1,2-cyclohexanedicarboxylic acid in the alicyclic polybasic acid (a1-2) The total content of the acid anhydride, 4-cyclohexene-1,2-dicarboxylic acid and 4-cyclohexene-1,2-dicarboxylic anhydride is in the range of 5 to 50 mol% based on the total amount of the acid component (a1). The multilayer coating film formation according to claim 1 or 2, wherein the content of 1,4-cyclohexanedicarboxylic acid is in the range of 5 to 50 mol% based on the total amount of the acid component (a1). Method. The multilayer coating composition according to any one of claims 1 to 3, wherein the coating composition has a maximum viscosity value of 5 Pa · sec or less measured at a frequency of 0.1 Hz at 30 to 80 ° C. Film forming method. The coating composition has a gel fraction (G80) of 40% by mass or more after coating the coating composition so that the cured film thickness is 30 μm and heating at 80 ° C. for 10 minutes. The method for forming a multilayer coating film according to any one of claims 1 to 4. The method for forming a multilayer coating film according to any one of claims 1 to 5, wherein the article to be coated is a vehicle body on which an undercoat coating film is formed by an electrodeposition coating.