JP5979758B2 - Water-based coating composition and multilayer coating film forming method - Google Patents

Description

  The present invention relates to an aqueous coating composition and a method for forming a multilayer coating film characterized by containing a specific polyester resin, a film-forming resin and a crosslinking agent.

  In recent years, from the viewpoint of environmental protection, there is an increasing demand for water-based paints that release less volatile organic compounds (VOC) into the atmosphere. As a method for forming a multilayer coating film using water-based base paints, (Painted steel sheet, plastic, etc.), primer coating (intermediate coating) coating → heat curing → water-based base coating → clear coating coating → multi-layer coating by the three-bake method that performs heat curing The method of forming is widely adopted. In general, the 3-coat 2-bake method is used when a so-called metallic-colored coating film is formed using an aqueous base paint containing a bright pigment.

  On the other hand, from the viewpoint of shortening the line process and saving energy, the heat-curing process after primer coating is omitted, and primer coating, water-based coating, clear coating, and heat-curing are performed in order. The system (a preheating (preheating) process may be added after the paint is applied) is being studied, and in the case of white pearl paint, the base paint process is divided into two stages: a white base paint process and an interference color base paint process. A 4-coat 1-bake method divided into these processes has been studied.

  However, when the 3-coat 1-bake method or the 4-coat 1-bake method is used, the smoothness and sharpness of the coating film formed by the mixed layer between the base paint and the primer paint and / or the aqueous base paint and the clear paint are used. There was a case where a decrease in the temperature occurred, which was a problem. In the case of a multi-layer coating film forming method aiming at curing of the base coating film and the primer coating film by using a two-component urethane coating containing a polyisocyanate compound in the clear coating film, and soaking the polyisocyanate compound from the clear coating film, When the base coating film is thick and the clear coating film becomes thin, the polyisocyanate compound will not be sufficiently soaked and the coating film will be insufficiently crosslinked, resulting in a decrease in the adhesion and water resistance of the multilayer coating film. was there.

  Furthermore, in base paints that require a large number of varieties for each paint color, it is possible to reduce costs and improve color consistency by using a common paint for the car body and car parts. From the viewpoint of the heat resistance (and / or energy saving) of plastics, the outer skin of automobiles usually requires a baking temperature higher than 120 ° C, whereas a method for forming a multilayer coating film that cures at a lower temperature is required. It has been. However, in the conventional multilayer coating film forming method and water-based base coating, the coating film becomes insufficiently crosslinked when heated and cured at a low temperature (for example, 70 to 120 ° C.). In some cases, the properties and the like deteriorated.

  For example, Patent Document 1 describes a method for forming a multilayer coating film in which a water-based primer, a water-based metallic base, and a high solid clear coating are sequentially applied to a plastic material to be coated and simultaneously heated and cured. It is described that the forming method has a large amount of migration of the polyisocyanate compound from the clear layer to the base layer, and has high curability even at a low baking temperature of 70 to 100 ° C. Patent Document 2 describes a method for forming a multilayer coating film in which a white conductive primer, an aqueous color base, an aqueous mica base, and a clear paint are sequentially applied to a polypropylene material to be coated, and further heated and cured. An example is described in which a melamine resin is used as the curing agent and an isocyanate compound is blended as the curing agent for the clear coating. In Patent Document 3, an aqueous primer, an aqueous base paint, and a clear paint are applied onto a plastic substrate, and three layers are simultaneously baked at a temperature of 100 ° C. or lower. Aqueous acrylic resin and / or aqueous polyester resin and melamine resin containing a hydroxyl group, and when the clear paint further contains a hydroxyl group-containing resin and an isocyanate crosslinking agent, adhesion, water resistance and durability It is described that an excellent multilayer coating film can be formed. In Patent Document 4, a water-based intermediate coating, a water-based base coating, and a clear coating are sequentially applied onto a substrate having both a steel plate and a plastic substrate, and further heat-cured. When the base paint contains (a) an acrylic resin emulsion, (b) a water-soluble acrylic resin, (c) a melamine resin solid content, and (d) propylene glycol monoalkyl ether, It is described that the appearance is uniform.

JP 2008-200587 A JP 2011-240266 A WO2008 / 050778 pamphlet JP 2011-131135 A

  However, in the coating film forming method described in Patent Document 1, when the film thickness of the base coating film is 20 μm or more and / or when the film thickness of the clear coating film becomes a thin film, the polyisocyanate from the clear coating film There was a case where the penetration (migration) of the compound did not proceed sufficiently and the multilayer coating film was insufficiently cured or had poor finish. The coating film forming method described in Patent Document 2 describes that rapid curing cannot be performed at a baking temperature of less than 110 ° C., and a preferable baking temperature is 120 to 130 ° C. The coating film forming method described in Patent Document 3 has excellent low-temperature curability, but when the base film is thick and the clear film is thin, the polyisocyanate from the clear paint to the base paint and primer paint Infiltration of the compound may be reduced, and water resistance may be deteriorated due to poor finish or insufficient curing. In the coating film forming method described in Patent Document 4, the baking temperature is set to 120 ° C. or less due to the heat resistance of the plastic base material, or the base coating film becomes a thick film and / or the clear coating film becomes a thin film. In some cases, the multilayer coating film was insufficiently cured.

  Accordingly, the present invention provides a multilayer coating film forming method in which three or four coating layers are applied and each layer is heated and cured at the same time when the base coating film becomes thick or a clear coating film containing a polyisocyanate compound. Can form a multilayer coating film excellent in smoothness, sharpness, adhesion and water resistance even when it becomes a thin film or when it is cured by heating at a low temperature (for example, 70 to 120 ° C.). It is an object to provide a coating composition and a method for forming a multilayer coating film.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a primer paint (X), a water-based base paint (Y), and a polyisocyanate compound-containing clear paint (Z) are formed on the article to be coated. Coat 1 bake method, or 4 coats in which the water-based base paint (Y) is divided into two types: water-based base paint (Y) (for example, white base) and water-based second base paint (Y2) (for example, interference color base) When recoating as a one-bake method, as the aqueous base paint (Y), a polyester resin (A) having a hydroxyl value of less than 10 mgKOH / g, an acid value of less than 30 mgKOH / g, and a number average molecular weight of 8,000 or more (A ) And a crosslinker (C) containing an active methylene block polyisocyanate (CB) having at least one specific structure. By using Narubutsu found that can achieve the above object, and have completed the present invention.

That is, the present invention provides the following aqueous coating composition and a method for forming a multilayer coating film using the aqueous coating composition as an aqueous base coating.
Item 1. At least one of a polyester resin (A), a film-forming resin (B), and a crosslinking agent (C) having a hydroxyl value of less than 10 mgKOH / g, an acid value of less than 30 mgKOH / g, and a number average molecular weight of 8,000 or more. As a blocked isocyanate group represented by the following general formula (I)

[In the formula (I), R ¹ , R ² , R ⁴ and R ⁵ independently represent a hydrocarbon group having 1 to 12 carbon atoms, and R ³ is a straight chain having 1 to 12 carbon atoms or Represents a branched alkylene group. ],
Blocked isocyanate group represented by the following general formula (II)

[In formula (II), R ² , R ³ , R ⁴ and R ⁵ are the same as above. ],
And a blocked isocyanate group represented by the following general formula (III)

Wherein ^{(III), R 2, R} 3, R 4 and ^{R 5} are as defined above, ^{R 6} represents a hydrocarbon group having 1 to 12 carbon atoms. ]
An aqueous coating composition comprising an active methylene type blocked polyisocyanate compound (CB) having at least one type of blocked isocyanate group selected from:
Item 2. A straight-chain alkylene group containing an aliphatic polybasic acid in the range of 15 to 100 mol% based on the total acid component constituting the polyester resin (A) and having 4 or more carbon atoms based on the total alcohol component Item 5. The aqueous coating composition according to Item 1, which contains an aliphatic polyhydric alcohol having a content of 50 to 100 mol%.
Item 3. Item 3. The aqueous coating composition according to Item 1 or 2, wherein, in the general formula (I), R ¹ is an isopropyl group.
Item 4. Item 4. The aqueous coating composition according to any one of Items 1 to 3, wherein in General Formula (III), R ⁶ is an isopropyl group.
Item 5. The active methylene type block polyisocyanate compound (CB) is represented by the following general formula (IV)

[In Formula (IV), R < ¹ > is the same as the above, and may be the same as or different from each other. ]
A blocked polyisocyanate compound intermediate (cb3-1) having a blocked isocyanate group represented by the formula (II) and a secondary alcohol (cb4) represented by the following general formula (VI)

[In the formula (VI), R ² , R ³ , R ⁴ and R ⁵ are the same as described above. ]
Item 6. The aqueous coating composition according to any one of Items 1 to 5, which is obtained by reacting
Item 6. The active methylene type block polyisocyanate compound (CB) is represented by the following general formula (V)

[In formula (V), R ⁶ is the same as described above, and R ⁷ represents a hydrocarbon group having 1 to 12 carbon atoms. ]
Item 6. The aqueous coating composition according to item 1, 2, 4, or 5 obtained by reacting the blocked polyisocyanate compound intermediate (cb3-2) having a blocked isocyanate group represented by the above and the secondary alcohol (cb4). .
Item 7. Item 7. The aqueous coating composition according to any one of Items 1 to 6, wherein the active methylene-type block polyisocyanate compound (CB) is a block polyisocyanate compound (CB ′) having a hydrophilic group.
Item 8. The following steps (1-1) to (1-4),
Step (1-1): A step of applying a primer coating (X) on an article to form a primer coating film,
Step (1-2): a step of applying a water-based base coating (Y) on the uncured primer coating formed in the step (1-1) to form a base coating,
Step (1-3): a step of applying a clear coating (Z) containing a polyisocyanate compound on the uncured base coating formed in the step (1-2) to form a clear coating, and a step (1-4): The temperature of 70 to 120 ° C. of the uncured primer coating film, the uncured base coating film, and the uncured clear coating film formed in steps (1-1) to (1-3). A method for forming a multilayer coating film in which the steps of heat curing at the same time are sequentially performed, wherein the aqueous base coating material (Y) is the aqueous coating composition according to any one of Items 1 to 7. A method for forming a multilayer coating film.
Item 9. The following steps (2-1) to (2-5),
Step (2-1): A step of applying a primer paint (X) on an object to form a primer coating film,
Step (2-2): A step of coating the water-based base coating (Y) on the uncured primer coating formed in the step (2-1) to form a base coating,
Step (2-3): On the uncured base coating film formed in the step (2-2), an aqueous second base coating material (Y2) containing a glitter pigment is applied to form a second base coating film. Forming step,
Step (2-4): a step of applying a clear coating (Z) containing a polyisocyanate compound on the uncured second base coating film formed in the step (2-3) to form a clear coating film, And Step (2-5): The uncured primer coating, uncured base coating, and uncured clear coating formed in Steps (2-1) to (2-4) at 70 to 120 ° C. A method for forming a multilayer coating film in which the steps of heat-curing at the same time are sequentially performed, wherein the aqueous base coating material (Y) is the aqueous coating composition according to any one of Items 1 to 8. A method for forming a multilayer coating film characterized by the following.
Item 10. The aqueous base paint (Y) contains 50 to 200 parts by mass of titanium white with respect to 100% by mass of the resin solid content, and the L value of the coating film to which the aqueous base paint (Y) is applied is 60 or more, Furthermore, the aqueous | water-based 2nd base coating material (Y2) contains 1-30 mass parts of luster pigments with respect to 100 mass% of resin solid content, The multilayer coating-film formation method of the said claim | item 9 characterized by the above-mentioned.
Item 11. Item | item containing the multilayer coating film formed by the multilayer coating-film formation method of any one of said claim | item 8-10.

The water-based coating composition and the method for forming a multilayer coating film of the present invention include a specific polyester resin and film formation as a composition of an aqueous base coating material in a multilayer coating film forming method in which three or four layers are applied and cured simultaneously. Multi-layer coating film with excellent smoothness, sharpness, adhesion and water resistance even when heat-cured at low temperatures by using a water-based coating composition containing an active resin and an active methylene block polyisocyanate compound Can be formed.

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

Aqueous coating composition The aqueous coating composition of the present invention contains a polyester resin (A), a film-forming resin (B) other than (A), and a crosslinking agent (C). As content of each component, content of polyester resin (A) is 10-70 mass% on the basis of solid content total amount of polyester resin (A), film-forming resin (B), and crosslinking agent (C). Preferably, 20-60 mass% is more preferable. The content of the film-forming resin (B) is preferably 10 to 90% by mass, and more preferably 20 to 80% by mass. 3-50 mass% is preferable and, as for content of a crosslinking agent (C), 5-40 mass% is more preferable.

Polyester resin (A)
The polyester resin (A) used in the present invention can be usually produced by an esterification reaction or an ester exchange reaction between an acid component and an alcohol component.

  As said acid component, the compound normally used as an acid component can be used at the time of manufacture of a polyester resin. Examples of the acid component include an aliphatic polybasic acid, an alicyclic polybasic acid, an aromatic polybasic acid, and the like.

  The aliphatic polybasic acid 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. Examples of the aliphatic polybasic acid include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassic acid, octadecanedioic acid, citric acid, butane. Aliphatic polycarboxylic acids such as tetracarboxylic acids; anhydrides of the aliphatic polyvalent carboxylic acids; esterified products of lower alkyl having about 1 to 4 carbon atoms of the aliphatic polyvalent carboxylic acids, etc. It is preferable to use an aliphatic polybasic acid having a number of 4 or more, and it is more preferable to use succinic acid, adipic acid, sebacic acid, or dodecanedioic acid. The said aliphatic polybasic acid can be used individually or in combination of 2 or more types.

  The alicyclic polybasic acid is generally a compound having one or more alicyclic structures and two or more carboxyl groups in one molecule, an acid anhydride of the compound, and an esterified product of the compound. The alicyclic structure is mainly a 4- to 6-membered ring structure. Examples of the alicyclic polybasic acid include 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, 3-methyl- Alicyclic polycarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, 1,3,5-cyclohexanetricarboxylic acid; An anhydride of an alicyclic polyvalent carboxylic acid; an esterified product of a lower alkyl having about 1 to 4 carbon atoms of the alicyclic polyvalent carboxylic acid. The said alicyclic polybasic acid can be used individually or in combination of 2 or more types.

  The aromatic polybasic acid 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, phthalic acid , Isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, trimellitic acid, pyromellitic acid and other aromatic polycarboxylic acids; anhydrides of the aromatic polycarboxylic acids; aromatics Examples thereof include esterified products of lower alkyl having about 1 to 4 carbon atoms of polyvalent carboxylic acid. The said aromatic polybasic acid can be used individually or in combination of 2 or more types.

  As the aromatic polybasic acid, it is preferable to use phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic acid, or trimellitic anhydride.

  As the polybasic acid used in the polyester resin (A) of the present invention, 15 to 100 aliphatic polybasic acids are used on the basis of the total acid components from the viewpoint of excellent permeation of the polyisocyanate compound into the obtained base coating film. It is preferable to contain within the range of mol%, and it is more preferable to contain within the range of 30-85 mol%. In addition, from the viewpoint of excellent smoothness, sharpness, and water resistance of the coating film obtained, it is preferable to contain an aromatic polybasic acid within a range of 15 to 85 mol% based on the total polybasic acid component, It is more preferable to contain within the range of 30-85 mol%.

  Moreover, acid components other than the said aliphatic polybasic acid, alicyclic polybasic acid, and aromatic polybasic acid can also be used. Such acid component is not particularly limited, for example, 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, Fatty acids such as castor oil fatty acid, dehydrated castor oil fatty acid, safflower oil fatty acid; lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, p-tert-butylbenzoic acid, cyclohexane Examples thereof include monocarboxylic acids such as acid and 10-phenyloctadecanoic acid; hydroxycarboxylic acids such as lactic acid, 3-hydroxybutanoic acid, and 3-hydroxy-4-ethoxybenzoic acid. These acid components can be used alone or in combination of two or more.

  As said alcohol component, 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, 2-methyl-1,3-propanediol, 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, , 4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, 1,4-cyclohexanedi Dihydric alcohols such as methanol, tricyclodecane dimethanol, hydroxypivalic acid neopentyl glycol ester, hydrogenated bisphenol A, hydrogenated bisphenol F, and dimethylolpropionic acid; lactone compounds such as ε-caprolactone in these dihydric alcohols Added polylactone diol; ester diol compound such as bis (hydroxyethyl) terephthalate; alkylene oxide adduct of bisphenol A, polyether such as polyethylene glycol, polypropylene glycol, polybutylene glycol Terdiol compounds; glycerin, trimethylolethane, trimethylolpropane, diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, tris (2-hydroxyethyl) isocyanuric acid, sorbitol, mannitol, etc. A trilactone or higher alcohol; a polylactone polyol compound obtained by adding a lactone compound such as ε-caprolactone to the trihydric or higher alcohol; a fatty acid esterified product of glycerin, and the like. These polyhydric alcohols can be used alone or in combination of two or more.

  The polyhydric alcohol used in the polyester resin (A) of the present invention has 4 or more carbon atoms, preferably 4 to 12 carbon atoms, more preferably 4 to 10 carbon atoms, from the viewpoint of excellent penetration of the polyisocyanate compound into the resulting coating film. An aliphatic polyhydric alcohol having a straight-chain alkylene group can be preferably used. Examples of the aliphatic polyhydric alcohol having a linear alkylene group having 4 or more carbon atoms include 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol and the like can be mentioned, and these can be used alone or in combination of two or more. In addition, the content of the aliphatic polyhydric alcohol having a linear alkylene group having 4 or more carbon atoms is preferably contained in the range of 50 to 100 mol%, based on the total alcohol components, and is preferably 70 to 100 mol. It is more preferable to contain within the range of%.

  Moreover, alcohol components other than the said polyhydric alcohol can also be used. The alcohol component is not particularly limited, and examples thereof include monoalcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, stearyl alcohol, and 2-phenoxyethanol; propylene oxide, butylene oxide, “Cardura E10” (trade name, HEXION Specialty) Examples include alcohol compounds obtained by reacting monoepoxy compounds such as Chemicals, Inc. (glycidyl esters of synthetic highly branched saturated fatty acids) and acids.

  The polyester resin (A) of the present invention has a hydroxyl value of preferably less than 10 mgKOH / g, more preferably less than 5 mgKOH / g, from the viewpoint of penetration of the polyisocyanate compound from the clear coating film, and more preferably 1 mgKOH. / G is particularly preferred.

  When the polyester resin (A) further has a carboxyl group, the acid value is 30 mgKOH / g or less from the viewpoint of stability in the aqueous coating composition column and / or water resistance of the multilayer coating film. Is more preferable, it is more preferable that it is 3-27 mgKOH / g, and it is still more preferable that it is 5-25 mgKOH / g.

  In addition, the number average molecular weight of the hydroxyl group-containing polyester resin (A) is preferably 8,000 or more, and is 9,001 to 30,000, from the viewpoint of coating film properties and water resistance of the multilayer coating film. More preferably, it is more preferably from 10,001 to 25,000, even more preferably from 10,501 to 20,000.

  In addition, in this specification, an acid value and a hydroxyl value are the values calculated | required based on JIS-K1557 (2007). In addition, the number average molecular weight or the weight average molecular weight is determined based on the retention time (retention capacity) of a standard polystyrene whose molecular weight is known measured under the same conditions as the retention time (retention capacity) measured using a gel permeation chromatograph (GPC). It is the value calculated in terms of the molecular weight of polystyrene. Specifically, “HLC-8120GPC” (trade name, manufactured by Tosoh Corporation) is used as a gel permeation chromatograph, and “TSKgel G4000HXL”, “TSKgel G3000HXL”, “TSKgel G2500HXL” and “TSKgel” are used as columns. G2000HXL "(trade name, all manufactured by Tosoh Corporation), using a differential refractometer as the detector, mobile phase: tetrahydrofuran, measurement temperature: 40 ° C, flow rate: 1 mL / min Can be measured below.

  The manufacturing method of a polyester resin (A) is not specifically limited, It can carry out according to a normal method. For example, by heating the acid component and the alcohol component in a nitrogen stream at 150 to 250 ° C. for 5 to 10 hours, and performing an esterification reaction or a transesterification reaction between the acid component and the alcohol component, a polyester resin is obtained. Can be manufactured.

  When performing the esterification reaction or transesterification reaction of the acid component and alcohol component, these may be added to the reaction vessel at one time, or one or both of them may be added several times or continuously. May be. Moreover, after synthesizing a hydroxyl group-containing polyester resin, the resulting hydroxyl group-containing polyester resin may be half-esterified by reacting with an acid anhydride to obtain a carboxyl group-containing polyester resin. Conversely, after synthesizing a carboxyl group-containing polyester resin, the alcohol component may be added to obtain a hydroxyl group-containing polyester resin.

In addition, a compound having two or more acid anhydride groups in the molecule is subjected to ring-opening addition to a polyester resin having a terminal hydroxyl group synthesized by an ordinary method according to the method described in JP2011-184629A. It is also possible to increase the molecular weight of the polyester resin without causing dimensionalization as much as possible.
Examples of the compound having two or more acid anhydride groups in the molecule include pyromellitic anhydride, 1,2,3,4-butanetetracarboxylic dianhydride, and 1,3,3a, 4,5. , 9b-Hexahydro-5- (tetrahydro-2,5-dioxo-3-furanyl) naphtho [1,2-c] furan-1,3-dione, 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic Acid dianhydride, glycerin bisanhydro trimellitate monoacetate, ethylene glycol bisanhydro trimellitate, 3,3 ′, 4,4′-benzophene tetracarboxylic dianhydride, 3,4,9, 10-perylenetetracarboxylic dianhydride etc. are mentioned, These can be used individually by 1 type or in combination of 2 or more types. If necessary, phthalic anhydride having one anhydride group in the molecule, hexahydrophthalic anhydride or trimellitic anhydride can be used as appropriate for adjusting the acid amount and molecular weight. Among these, pyromellitic anhydride can be suitably used from the viewpoint of availability, purity, cost, and the like.

  Further, the polyester resin can be made to have a high molecular weight by reacting with a hydroxyl group of the polyester resin using a polyfunctional isocyanate compound such as a diisocyanate compound or a triisocyanate compound by the method described in JP-A-4-318012.

  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.

  Further, the polyester resin (A) can be modified with a fatty acid, an oil or fat, a monoepoxy compound, a polyisocyanate compound or the like during or after the preparation of the resin.

  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 An oil fatty acid, safflower oil fatty acid, etc. are mentioned. Examples of the fats and oils include fatty acid oils of these fatty acids. As the monoepoxy compound, for example, “Cardura E10” (trade name, manufactured by HEXION Specialty Chemicals, glycidyl ester of a synthetic highly branched saturated fatty acid) can be suitably used.

  Examples of the polyisocyanate compound include aliphatic diisocyanate compounds such as lysine diisocyanate, hexamethylene diisocyanate, and trimethylhexane diisocyanate; hydrogenated xylylene diisocyanate, isophorone diisocyanate, methylcyclohexane-2,4-diisocyanate, and methylcyclohexane-2. , 6-diisocyanate, 4,4'-methylenebis (cyclohexylisocyanate), 1,3- (isocyanatomethyl) cyclohexane and other alicyclic diisocyanate compounds; tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate and other aromatic diisocyanate compounds ; Organic polyisocyanates such as polyisocyanates having 3 or more valences such as lysine triisocyanate Adduct of each of these organic polyisocyanates with polyhydric alcohol, low molecular weight polyester resin, water, etc .; cyclized polymer (for example, isocyanurate) between these organic polyisocyanates, biuret type addition Thing etc. are mentioned. These polyisocyanate compounds can be used alone or in admixture of two or more.

  The polyester resin (A) of the present invention can contain an organic solvent by a method known per se, if necessary. The content of the organic solvent is preferably 20% by mass or less, and more preferably 10% by mass or less, based on the resin solid content of the polyester resin, in consideration of the environment.

  Moreover, the polyester resin (A) of this invention can be water-soluble or water-dispersed by neutralizing the carboxyl group in a molecule | numerator with a basic compound. Examples of the basic compound include hydroxides of alkali metals or alkaline earth metals such as sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, barium hydroxide; ammonia; ethylamine, propylamine, butylamine , Primary monoamines such as benzylamine, monoethanolamine, 2,2-dimethyl-3-amino-1-propanol, 2-aminopropanol, 2-amino-2-methyl-1-propanol, 3-aminopropanol; Secondary monoamines such as diethylamine, diethanolamine, di-n-propanolamine, di-isopropanolamine, N-methylethanolamine, N-ethylethanolamine; dimethylethanolamine, trimethylamine, triethylamine, triisopropylamine Tertiary monoamines such as methyldiethanolamine and 2- (dimethylamino) ethanol; polyamines such as diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, methylaminopropylamine, etc., and these may be used alone or in combination of two or more. Can be used. The basic compound is preferably water-soluble.

A polyester resin aqueous dispersion or an aqueous polyester resin solution can be obtained by gradually adding water while stirring the polyester resin neutralized with the basic compound.
From the viewpoint of suppressing the viscosity of the aqueous coating composition and increasing the solid content concentration, the polyester resin is preferably a polyester resin aqueous dispersion (A ′). The average particle size of the aqueous polyester resin dispersion (A ′) is preferably 250 nm or less, and more preferably 50 to 200 nm.

  In addition, in this specification, the average particle diameter of the polyester resin aqueous dispersion (A ′) is a value measured at 20 ° C. after diluting with deionized water by a conventional method using a submicron particle size distribution analyzer. is there. As the submicron particle size distribution measuring device, for example, “COULTER N4 type” (trade name, manufactured by Beckman Coulter, Inc.) can be used.

  Moreover, as a phase inversion temperature of the polyester resin aqueous dispersion (A ′) when water is added to cause phase inversion emulsification, 40 to 95 ° C. is preferable, 45 to 95 ° C. is more preferable, and 50 to 95 ° C. is particularly preferable. preferable. If the temperature at the time of phase inversion emulsification is low, the viscosity of the aqueous resin dispersion increases, and uniform dispersion may not be possible.

Film-forming resin (B)
The aqueous coating composition of the present invention is characterized by containing a film-forming resin (B) as a resin component other than the polyester resin (A) and the curing agent (C).
Examples of the film-forming resin (B) include acrylic resins, polyurethane resins, polyester resins other than the polyester resin (A), epoxy resins, alkyd resins, and the like. These can be used alone or in combination of two or more. The polyester resin other than the polyester resin (A) is, for example, a polyester resin having a hydroxyl value of 10 mgKOH / g or more, an acid value of 30 mgKOH / g or more, or a number average molecular weight of less than 8,000.

  The film-forming resin (B) contains a hydroxyl group-containing acrylic resin (B1) and a hydroxyl group-containing polyurethane resin (B2) from the viewpoints of smoothness, sharpness and water resistance of the multilayer coating film to be formed. It is preferable to include a hydroxyl group-containing acrylic resin (B1).

Hydroxyl group-containing acrylic resin (B1)
The hydroxyl group-containing acrylic resin (B1) is obtained by, for example, a hydroxyl group-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer by a method known per se, for example, It can be produced by copolymerization by a method such as a solution polymerization method in an organic solvent, an emulsion polymerization method in water, or a miniemulsion polymerization method in water.

  The hydroxyl group-containing polymerizable unsaturated monomer is a compound having at least one hydroxyl group and one polymerizable unsaturated bond in one molecule. Examples of the hydroxyl group-containing polymerizable unsaturated monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and the like. Monoesterified product of (meth) acrylic acid and dihydric alcohol having 2 to 8 carbon atoms; ε-caprolactone modified product of monoesterified product of (meth) acrylic acid and dihydric alcohol having 2 to 8 carbon atoms; N- Examples thereof include hydroxymethyl (meth) acrylamide; allyl alcohol, and (meth) acrylate having a polyoxyethylene chain whose molecular end is a hydroxyl group. These can be used alone or in combination of two or more.

As the other polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer, for example, the following monomers (i) to (xix) can be used. These polymerizable unsaturated monomers can be used alone or in combination of two or more.
(I) alkyl or cycloalkyl (meth) acrylate: for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl ( (Meth) acrylate, tert-butyl (meth) acrylate, n-hexyl (meth) acrylate, n-octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, tridecyl (meth) acrylate, lauryl ( (Meth) acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, t-butylcyclohexyl (meth) a Relate, cyclododecyl (meth) acrylate, tricyclodecanyl (meth) acrylate.
(Ii) Polymerizable unsaturated monomer having an isobornyl group: isobornyl (meth) acrylate and the like.
(Iii) Polymerizable unsaturated monomer having an adamantyl group: adamantyl (meth) acrylate and the like.
(Iv) Polymerizable unsaturated monomer having a tricyclodecenyl group: tricyclodecenyl (meth) acrylate and the like.
(V) Aromatic ring-containing polymerizable unsaturated monomers: benzyl (meth) acrylate, styrene, α-methylstyrene, vinyltoluene and the like.
(Vi) Polymerizable unsaturated monomer having an alkoxysilyl group: vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane, γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) Acryloyloxypropyltriethoxysilane and the like.
(Vii) Polymerizable unsaturated monomer having a fluorinated alkyl group: perfluoroalkyl (meth) acrylate such as perfluorobutylethyl (meth) acrylate and perfluorooctylethyl (meth) acrylate; fluoroolefin and the like.
(Viii) A polymerizable unsaturated monomer having a photopolymerizable functional group such as a maleimide group.
(Ix) Vinyl compound: N-vinyl pyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, vinyl acetate and the like.
(X) Carboxyl group-containing polymerizable unsaturated monomer: (meth) acrylic acid, maleic acid, crotonic acid, β-carboxyethyl acrylate and the like.
(Xi) Nitrogen-containing polymerizable unsaturated monomer: (meth) acrylonitrile, (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylamino Propyl (meth) acrylamide, methylene bis (meth) acrylamide, ethylene bis (meth) acrylamide, an adduct of glycidyl (meth) acrylate and an amine compound, and the like.
(Xii) Polymerizable unsaturated monomers having two or more polymerizable unsaturated groups in one molecule: allyl (meth) acrylate, 1,6-hexanediol di (meth) acrylate, and the like.
(Xiii) Epoxy group-containing polymerizable unsaturated monomer: glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, 3,4-epoxycyclohexylethyl (meth) acrylate 3,4-epoxycyclohexylpropyl (meth) acrylate, allyl glycidyl ether and the like.
(Xiv) (meth) acrylate having a polyoxyethylene chain whose molecular end is an alkoxy group.
(Xv) polymerizable unsaturated monomer having a sulfonic acid group: 2-acrylamido-2-methylpropanesulfonic acid, 2-sulfoethyl (meth) acrylate, allylsulfonic acid, 4-styrenesulfonic acid, etc .; sodium salt of these sulfonic acids And ammonium salts.
(Xvi) polymerizable unsaturated monomer having a phosphate group: acid phosphooxyethyl (meth) acrylate, acid phosphooxypropyl (meth) acrylate, acid phosphooxypoly (oxyethylene) glycol (meth) acrylate, acid phosphooxypoly (Oxypropylene) glycol (meth) acrylate and the like.
(Xvii) polymerizable unsaturated monomer having an ultraviolet-absorbing functional group: 2-hydroxy-4- (3-methacryloyloxy-2-hydroxypropoxy) benzophenone, 2-hydroxy-4- (3-acryloyloxy-2-hydroxy) Propoxy) benzophenone, 2,2′-dihydroxy-4- (3-methacryloyloxy-2-hydroxypropoxy) benzophenone, 2,2′-dihydroxy-4- (3-acryloyloxy-2-hydroxypropoxy) benzophenone, 2- (2′-hydroxy-5′-methacryloyloxyethylphenyl) -2H-benzotriazole and the like.
(Xviii) UV-stable polymerizable unsaturated monomer: 4- (meth) acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4- (meth) acryloyloxy-2,2,6,6- Tetramethylpiperidine, 4-cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 1- (meth) acryloyl-4- (meth) acryloylamino-2,2,6,6 -Tetramethylpiperidine, 1- (meth) acryloyl-4-cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-2,2,6,6- Tetramethylpiperidine, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2, , 6-tetramethylpiperidine and the like.
(Xix) polymerizable unsaturated monomer having a carbonyl group: acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formylstyrol, vinyl alkyl ketone having 4 to 7 carbon atoms (for example, vinyl methyl ketone) , Vinyl ethyl ketone, vinyl butyl ketone) and the like.

  In the present specification, the polymerizable unsaturated group means an unsaturated group capable of radical polymerization. Examples of the polymerizable unsaturated group include a vinyl group and a (meth) acryloyl group.

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

  The use ratio of the hydroxyl group-containing polymerizable unsaturated monomer in producing the hydroxyl group-containing acrylic resin (B1) is preferably 0.5 to 50% by mass, based on the total amount of the monomer components, and is 1.0 to 40. % By mass is more preferable, and 1.5 to 30% by mass is even more preferable.

  The hydroxyl group-containing acrylic resin (B1) has a hydroxyl value of 1 to 150 mgKOH / from the viewpoint of water resistance of the formed multilayer coating film and / or the penetration of the polyisocyanate compound from the clear coating film. g is preferable, 5 to 100 mgKOH / g is more preferable, and 10 to 50 mgKOH / g is still more preferable. Further, from the viewpoint of the storage stability of the paint and the sharpness and water resistance of the formed multilayer coating film, the acid value is preferably 55 mgKOH / g or less, and preferably 3 to 50 mgKOH / g. More preferably, it is 5-45 mgKOH / g.

  The hydroxyl group-containing acrylic resin (B1) preferably has a glass transition temperature of 30 ° C. or less, and −50 to 20 ° C. from the viewpoint of the penetration property of the polyisocyanate compound from the clear coating film. More preferably, it is -40-10 degreeC.

  The hydroxyl group-containing acrylic resin (B1) is a water-dispersible hydroxyl group-containing acrylic resin (B1 ′) as at least one kind from the viewpoint of improving the smoothness, sharpness and water resistance of the multilayer coating film to be formed. ) Is preferably contained.

  The water-dispersible hydroxyl group-containing acrylic resin (B1 ′) is known per se, for example, the hydroxyl group-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer. It can be produced by copolymerization by the above method, for example, a method such as an emulsion polymerization method in water or a miniemulsion polymerization method in water.

  The water-dispersible hydroxyl group-containing acrylic resin (B1 ′) preferably has a hydroxyl value of 1 to 150 mgKOH / g and 5 to 100 mgKOH / g from the viewpoint of water resistance of the formed multilayer coating film. More preferably, it is more preferably 10 to 50 mgKOH / g.

  The water-dispersible hydroxyl group-containing acrylic resin (B1 ′) has an acid value of 55 mgKOH from the viewpoint of improving the storage stability of the paint, the smoothness of the formed multilayer coating film, the sharpness, and the water resistance. / G or less, more preferably 3 to 50 mgKOH / g, even more preferably 5 to 45 mgKOH / g.

  The water-dispersible hydroxyl group-containing acrylic resin (B1 ′) is a core / shell having a core / shell structure from the viewpoint of smoothness, sharpness, adhesion and water resistance of the formed multilayer coating film. It is preferably a type water dispersible hydroxyl group-containing acrylic resin (B1 ″).

  The core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) includes a polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule and a polymerizable unsaturated group in one molecule. A core part which is a copolymer (I) having one polymerizable unsaturated monomer as a copolymerization component, and a copolymer having a carboxyl group-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers as a copolymerization component A core / shell type water-dispersible hydroxyl group-containing acrylic resin composed of a shell portion which is the combined body (II) can be suitably used. Moreover, it can bridge | crosslink with a crosslinking agent (C) as a hydroxyl-containing acrylic resin by copolymerizing a hydroxyl-containing polymerizable unsaturated monomer in a core part and / or a shell part.

  Examples of the polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule used as the monomer for the core copolymer (I) include allyl (meth) acrylate, ethylene glycol di (meth) acrylate, Triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1,4-butanediol di (meth) acrylate , Neopentyl glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tetra (meth) acrylate, glycerol di (meth) acrylate, 1,1,1 -Birds Hydroxymethylethane di (meth) acrylate, 1,1,1-trishydroxymethylethane tri (meth) acrylate, 1,1,1-trishydroxymethylpropane tri (meth) acrylate, triallyl isocyanurate, diallyl terephthalate, divinyl Examples include benzene, methylene bis (meth) acrylamide, and ethylene bis (meth) acrylamide. These monomers can be used alone or in combination of two or more.

  The polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule has a function of imparting a crosslinked structure to the core copolymer (I). The use ratio of the polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule can be appropriately determined depending on the degree of crosslinking of the core copolymer (I). It is preferably 20% by mass or less, more preferably 0.1 to 10% by mass, and more preferably 0.2 to 7% by mass, based on the total mass of monomers constituting the polymer (I). Further preferred.

  The polymerizable unsaturated monomer having one polymerizable unsaturated group in one molecule used as a monomer for the core copolymer (I) is a polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule. A polymerizable unsaturated monomer copolymerizable with a saturated monomer.

  Specific examples of the polymerizable unsaturated monomer having one polymerizable unsaturated group per molecule include, for example, the hydroxyl group-containing polymerizable unsaturated monomer and the hydroxyl group described in the description of the hydroxyl group-containing acrylic resin (B1). Among the polymerizable unsaturated monomers exemplified as other polymerizable unsaturated monomers copolymerizable with the containing polymerizable unsaturated monomer, other than the polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule And monomers (i) to (xi), (xiii) to (xix), which are polymerizable unsaturated monomers. These monomers can be used alone or in combination of two or more according to the performance required for the core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″).

  Among these, from the viewpoint of smoothness and sharpness of the coating film to be formed, the polymerizable unsaturated monomer having one polymerizable unsaturated group in one molecule is at least one of the hydrophobic polymerizable monomers. It is preferable to contain a saturated monomer.

  In the present specification, the hydrophobic polymerizable unsaturated monomer is a polymerizable unsaturated group having a linear, branched or cyclic saturated or unsaturated hydrocarbon group having 4 or more carbon atoms, preferably 6 to 18 carbon atoms. Monomers having a hydrophilic group such as a hydroxyl group-containing polymerizable unsaturated monomer are excluded. Examples of the monomer include n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, and 2-ethylhexyl. (Meth) acrylate, nonyl (meth) acrylate, tridecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, tert -Alkyl or cycloalkyl (meth) acrylates such as butylcyclohexyl (meth) acrylate, cyclododecyl (meth) acrylate, tricyclodecanyl (meth) acrylate Polymerizable unsaturated compounds having an isobornyl group such as isobornyl (meth) acrylate; polymerizable unsaturated compounds having an adamantyl group such as adamantyl (meth) acrylate; benzyl (meth) acrylate, styrene, α-methylstyrene, An aromatic ring-containing polymerizable unsaturated monomer such as vinyl toluene can be mentioned. These monomers can be used alone or in combination of two or more.

  Among these, from the viewpoints of smoothness, sharpness, water resistance, etc. of the formed multilayer coating film, the hydrophobic polymerizable unsaturated monomer includes n-butyl (meth) acrylate, 2-ethylhexyl (meth). At least one polymerizable unsaturated monomer selected from the group consisting of acrylate and styrene can be suitably used.

  When the above-mentioned hydrophobic polymerizable unsaturated monomer is used as the monomer for the core copolymer (I), the proportion of the hydrophobic polymerizable unsaturated monomer used is a core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 )) In an aqueous medium, and from the viewpoint of excellent smoothness, sharpness, water resistance, and the like of the resulting coating film, it is 5 based on the total mass of monomers constituting the core copolymer (I). It is preferably within the range of -90% by mass, more preferably within the range of 20-85% by mass, and even more preferably within the range of 40-75% by mass.

  Shell part copolymer (II) uses a carboxyl group-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers as a copolymerization component.

  Specific examples of the carboxyl group-containing polymerizable unsaturated monomer used as the monomer for the shell part copolymer (II) are the same as those exemplified as the monomer for the core part copolymer (I). That is, among the polymerizable unsaturated monomers exemplified as other polymerizable unsaturated monomers copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer in the description of the hydroxyl group-containing acrylic resin (B1), carboxyl group-containing polymerizable unsaturated monomers A monomer (x) is mentioned. As the carboxyl group-containing polymerizable unsaturated monomer, it is particularly preferable to use acrylic acid and / or methacrylic acid. By copolymerizing the above-mentioned carboxyl group-containing polymerizable unsaturated monomer in the shell portion, it is possible to ensure the stability of the obtained core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) in an aqueous medium. .

  When the carboxyl group-containing polymerizable unsaturated monomer is used, the use ratio depends on the stability of the core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) in the aqueous medium and the water resistance of the resulting coating film. From the standpoint of superiority, it is preferably 0.1 to 30% by mass, more preferably 2 to 25% by mass, based on the total mass of monomers constituting the shell copolymer (II), and 3 to 19 More preferably, it is mass%.

  The other polymerizable unsaturated monomer used as the monomer for the shell copolymer (II) is a polymerizable unsaturated monomer other than the carboxyl group-containing polymerizable unsaturated monomer, and among them, at least one hydroxyl group-containing polymerization is used. It is preferable to use a polymerizable unsaturated monomer. The hydroxyl group-containing polymerizable unsaturated monomer is a hydroxyl group that undergoes a crosslinking reaction with the polyisocyanate compound and / or the crosslinking agent (C) soaked from the clear into the obtained core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″). In addition to improving the water resistance and the like of the coating film by appropriately introducing the water, the core / shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) has a function of improving the stability in an aqueous medium.

  Examples of the hydroxyl group-containing polymerizable unsaturated monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate. Monoesterified product of (meth) acrylic acid and dihydric alcohol having 2 to 8 carbon atoms; ε-caprolactone modified product of monoesterified product of (meth) acrylic acid and dihydric alcohol having 2 to 8 carbon atoms; N- Examples thereof include hydroxymethyl (meth) acrylamide, allyl alcohol, and (meth) acrylate having a polyoxyethylene chain whose molecular end is a hydroxyl group. These monomers can be used alone or in combination of two or more. As the hydroxyl group-containing polymerizable unsaturated monomer, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate are preferable. -Hydroxyethyl (meth) acrylate is more preferred.

  From the viewpoint of excellent stability of the core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) in an aqueous medium and excellent water resistance of the resulting coating film, The amount is preferably 1 to 40% by mass, more preferably 4 to 25% by mass, based on the total mass of monomers constituting the partial copolymer (II).

  Examples of other polymerizable unsaturated monomers other than the hydroxyl group-containing polymerizable unsaturated monomer include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n- Butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) Acrylate, dodecyl (meth) acrylate, tridecyl (meth) acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate Relates, alkyls such as tert-butylcyclohexyl (meth) acrylate, cyclododecyl (meth) acrylate, tricyclodecanyl (meth) acrylate or cycloalkyl (meth) acrylates; polymerizability having an isobornyl group such as isobornyl (meth) acrylate Unsaturated compounds; polymerizable unsaturated compounds having an adamantyl group such as adamantyl (meth) acrylate; aromatic ring-containing polymerizable unsaturated monomers such as benzyl (meth) acrylate, styrene, α-methylstyrene, vinyltoluene, etc. Can do. These monomers can be used alone or in combination of two or more.

  In addition, the other polymerizable unsaturated monomer used as the monomer for the shell copolymer (II) has two or more polymerizable unsaturated groups in one molecule from the viewpoint of improving the glitter of the resulting coating film. It is preferable not to use a polymerizable unsaturated monomer and to make the copolymer (II) uncrosslinked.

  The ratio of copolymer (I) / copolymer (II) in the core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) improves the vividness and glitter of the formed coating film. From a viewpoint, 5 / 95-95 / 5 are preferable by solid content mass ratio, 50 / 50-85 / 15 are more preferable, and 60 / 40-80 / 20 are further more preferable.

  The core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) preferably has a hydroxyl value of 1 to 150 mgKOH / g from the viewpoint of excellent chipping resistance and water resistance of the resulting coating film. It is more preferably 5 to 100 mgKOH / g, and further preferably 10 to 50 mgKOH / g. In addition, from the viewpoint of improving the storage stability of the paint, the smoothness of the formed multilayer coating film, the sharpness, and the water resistance, the acid value is preferably 55 mgKOH / g or less, and 3 to 50 mgKOH / g. It is more preferable that it is 5-45 mgKOH / g.

  The core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) may have a glass transition temperature of 30 ° C. or less from the viewpoint of the penetration property of the polyisocyanate compound from the clear coating film. Preferably, it is -50-20 degreeC, More preferably, it is -40-10 degreeC.

  The core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) is, for example, 20% by mass or less of a polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule, and a polymerizable unsaturated group After emulsion polymerization of a monomer mixture consisting of 80% by mass or more of a polymerizable unsaturated monomer having 1 per molecule in the molecule to obtain an emulsion of the core copolymer (I), hydroxyl group-containing polymerizability is added to the emulsion. A monomer mixture consisting of 1 to 40% by weight of unsaturated monomer, 0.1 to 30% by weight of carboxyl group-containing polymerizable unsaturated monomer, and 30 to 98.9% by weight of other polymerizable unsaturated monomer is added and further emulsified. It can be obtained by polymerizing to prepare the shell copolymer (II).

  Emulsion polymerization for preparing an emulsion of the core copolymer (I) can be performed by a conventionally known method. For example, it can be carried out by emulsion polymerization of the monomer mixture using a polymerization initiator in the presence of a surfactant.

  As the surfactant, an anionic surfactant and a nonionic surfactant are suitable. Examples of the anionic surfactant include sodium salts and ammonium salts such as alkylsulfonic acid, alkylbenzenesulfonic acid, and alkylphosphoric acid. Examples of nonionic surfactants include polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene phenyl ether, polyoxyethylene nonyl phenyl ether, Polyoxyethylene octyl phenyl ether, polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene monooleate, sorbitan monolaurate, sorbitan monostearate, sorbitan trioleate, polyoxyethylene sorbitan monolaurate, etc. Is mentioned.

  Also, a polyoxyalkylene group-containing anionic surfactant having an anionic group and a polyoxyalkylene group such as a polyoxyethylene group or a polyoxypropylene group in one molecule; an anionic group and radical polymerizability in one molecule A reactive anionic surfactant having an unsaturated group can also be used. Of these, it is preferable to use a reactive anionic surfactant.

  Examples of the reactive anionic surfactant include sodium salts of sulfonic acid compounds having radically polymerizable unsaturated groups such as allyl group, methallyl group, (meth) acryloyl group, propenyl group, butenyl group, An ammonium salt etc. can be mentioned. Among these, an ammonium salt of a sulfonic acid compound having a radically polymerizable unsaturated group is preferable because the resulting coating film is excellent in water resistance. Examples of the commercially available ammonium salt of the sulfonic acid compound include “Latemul S-180A” (trade name, manufactured by Kao Corporation).

  Of the ammonium salts of sulfonic acid compounds having radically polymerizable unsaturated groups, ammonium salts of sulfonic acid compounds having radically polymerizable unsaturated groups and polyoxyalkylene groups are more preferred. Examples of commercially available ammonium salts of sulfonic acid compounds having a radical polymerizable unsaturated group and a polyoxyalkylene group include “AQUALON KH-10” (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), “Latemul PD- 104 ”(trade name, manufactured by Kao Corporation),“ ADEKA rear soap SR-1025 ”(trade name, manufactured by ADEKA), and the like.

  The amount of the surfactant used is preferably 0.1 to 15% by mass, more preferably 0.5 to 10% by mass, and further preferably 1 to 5% by mass based on the total amount of all monomers used. preferable.

  Examples of the polymerization initiator include benzoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, cumene hydroperoxide, tert-butyl peroxide, di-tert-amyl peroxide, and tert-butyl peroxide. Organic peroxides such as 2-ethylhexanoate, tert-butyl peroxylaurate, tert-butyl peroxyisopropyl carbonate, tert-butyl peroxyacetate, diisopropylbenzene hydroperoxide; azobisisobutyronitrile, Azobis (2,4-dimethylvaleronitrile), azobis (2-methylpropiononitrile), azobis (2-methylbutyronitrile), 4,4′-azobis (4-cyanobutyl) Acid), dimethylazobis (2-methylpropionate), azobis [2-methyl-N- (2-hydroxyethyl) -propionamide], azobis {2-methyl-N- [2- (1-hydroxy Butyl)]-propionamide}; persulfates such as potassium persulfate, ammonium persulfate, sodium persulfate, and the like. These polymerization initiators can be used singly or in combination of two or more. Moreover, it is good also as a redox initiator by using together with reducing agents, such as saccharide | sugar, sodium formaldehyde sulfoxylate, and an iron complex, as needed to the said polymerization initiator.

  Generally the usage-amount of the said polymerization initiator is 0.1-5 mass% on the basis of the total mass of all the monomers used, and 0.2-3 mass% is more preferable. The method for adding the polymerization initiator is not particularly limited, and can be appropriately selected according to the type and amount thereof. For example, it may be previously contained in the monomer mixture or the aqueous medium, or may be added all at once during the polymerization, or may be added dropwise.

  The core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) is prepared by adding a carboxyl group-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers to the emulsion of the core copolymer (I) obtained above. It can be obtained by adding a monomer mixture consisting of and further polymerizing to form a shell copolymer (II).

  The monomer mixture forming the shell part copolymer (II) can appropriately contain components such as the polymerization initiator, a chain transfer agent, a reducing agent, and a surfactant as necessary. The monomer mixture can be dropped as it is, but it is desirable to drop the monomer mixture as a monomer emulsion obtained by dispersing the monomer mixture in an aqueous medium. In this case, the particle size of the monomer emulsion is not particularly limited.

  As a polymerization method of the monomer mixture for forming the shell copolymer (II), for example, the monomer mixture or an emulsion thereof is dripped in a batch or gradually, and an emulsion of the core copolymer (I) is obtained. And a method of heating to an appropriate temperature while stirring. The core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) thus obtained has a polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule and a polymerizable unsaturated group in one molecule. A monomer mixture copolymer (I) comprising a polymerizable unsaturated monomer having one in the core, and a monomer mixture copolymer comprising a carboxyl group-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers ( It has a multilayer structure with II) as a shell part.

  In addition, the core / shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) is used between the step of obtaining the core copolymer (I) and the step of obtaining the shell portion copolymer (II). Addition of a polymerizable unsaturated monomer (one or a mixture of two or more) to form a resin layer and an emulsion polymerization step is added to thereby add a water-dispersible hydroxyl group-containing acrylic composed of three or more layers. It is good also as resin.

  In the present invention, the “shell part” of the acrylic resin (B1 ″) having a core / shell type water-dispersible hydroxyl group means a polymer layer present in the outermost layer of the resin particles, and the “core part” means the shell. This means a polymer layer of the resin particle inner layer excluding the part, and “core / shell structure” means a structure having the core part and the shell part.

  The core / shell type structure is generally a layer structure in which the core part is completely covered with the shell part. However, depending on the mass ratio of the core part and the shell part, the monomer amount of the shell part may be a layer structure. It may be insufficient to form In such a case, it is not necessary to have a complete layer structure as described above, and a structure in which a shell part covers a part of the core part may be used. In addition, the concept of the multilayer structure in the core / shell structure is similarly applied to the case where a multilayer structure is formed in the core portion of the core / shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″). .

The core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) thus obtained generally has an average particle size in the range of about 10 to 1,000 nm, particularly about 30 to 500 nm, more particularly about 50 to 200 nm. be able to.
In this specification, the average particle size of the core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) is 20 ° C. after being diluted with deionized water by a conventional method using a submicron particle size distribution analyzer. It is the value measured by. As the submicron particle size distribution measuring device, for example, “COULTER N4 type” (trade name, manufactured by Beckman Coulter, Inc.) can be used.

In order to improve the mechanical stability of the particles of the core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″), neutralize acid groups such as carboxyl groups of the water-dispersible acrylic resin with a neutralizing agent. It is desirable to do. The neutralizing agent is not particularly limited as long as it can neutralize an acid group. For example, sodium hydroxide, potassium hydroxide, trimethylamine, 2- (dimethylamino) ethanol, 2- (diethylamino) ethanol, 2 -(Dibutylamino) ethanol, 2-amino-2-methyl-1-propanol, triethylamine, tributylamine, aqueous ammonia and the like can be mentioned, and these can be used alone or in combination of two or more.
These neutralizing agents are added in such an amount that the pH of the aqueous dispersion of the core-shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) after neutralization becomes 6.5 to 9.0. It is desirable to use it.

Hydroxyl-containing polyurethane resin (B2)
When the aqueous coating composition of the present invention contains a hydroxyl group-containing polyurethane resin (B2) as the film-forming resin (B), examples of the hydroxyl group-containing polyurethane resin include aliphatic diisocyanate compounds and alicyclic diisocyanate compounds. And at least one diisocyanate compound selected from aromatic diisocyanate compounds and at least one polyol compound selected from polyether polyols, polyester polyols and polycarbonate polyols.

  Specifically, for example, at least one diisocyanate selected from aliphatic diisocyanates and alicyclic diisocyanates, at least one diol selected from polyether diols, polyester diols and polycarbonate diols, low molecular weight polyhydroxy compounds and dimethylol. A urethane prepolymer is produced by reacting an alkanoic acid, neutralized with a tertiary amine, emulsified and dispersed in water, and if necessary, contains a chain extender such as polyamine, a crosslinking agent, a terminator, etc. Examples thereof include a mixture obtained by mixing with an aqueous medium and reacting until the isocyanate group is substantially eliminated. By the above method, a self-emulsifying type polyurethane resin having an average particle diameter of 0.001 to 3 μm can be usually obtained.

Cross-linking agent (C)
The crosslinking agent (C) of the present invention is a compound capable of reacting with a hydroxyl group in the polyester resin (A) and / or the film-forming resin (B) to crosslink the aqueous coating composition. The water-based coating composition of the present invention contains at least one active methylene type block polyisocyanate compound (CB) having a specific structure as a crosslinking agent (C). As other crosslinking agents (C), for example, amino resins, block polyisocyanate compounds other than active methylene type block polyisocyanate compounds (CB), polyisocyanate compounds, and the like can be suitably used. These can be used alone or in combination of two or more. Among these, from the viewpoint of water resistance and storage stability of the resulting coating film, the block polyisocyanate compound (CA) and / or amino other than the active methylene type block polyisocyanate compound (CB) having a specific structure which is an essential component. Resin (CM) is preferred.

Active methylene type block polyisocyanate compound (CB)
The crosslinking agent (C) used in the aqueous coating composition of the present invention contains at least one active methylene type block polyisocyanate compound (CB). The active methylene type blocked polyisocyanate compound (CB) is a blocked isocyanate group represented by the following general formula (I):

〔式（Ｉ）中、Ｒ^１、Ｒ^２、Ｒ^４及びＲ^５は、独立して、炭素数１〜１２の炭化水素基を表し、Ｒ^３は、炭素数１〜１２の直鎖状又は分岐状のアルキレン基を表す。〕、
下記一般式（ＩＩ）で示されるブロックイソシアネート基

[In the formula (I), R ¹ , R ² , R ⁴ and R ⁵ independently represent a hydrocarbon group having 1 to 12 carbon atoms, and R ³ is a straight chain having 1 to 12 carbon atoms or Represents a branched alkylene group. ],
Blocked isocyanate group represented by the following general formula (II)

〔式（ＩＩ）中、Ｒ^２、Ｒ^３、Ｒ^４及びＲ^５は前記と同じ。〕
及び下記一般式（ＩＩＩ）で示されるブロックイソシアネート基

[In formula (II), R ² , R ³ , R ⁴ and R ⁵ are the same as above. ]
And a blocked isocyanate group represented by the following general formula (III)

〔式（ＩＩＩ）中、Ｒ^２、Ｒ^３、Ｒ^４及びＲ^５は前記と同じであり、Ｒ^６は、炭素数１〜１２の炭化水素基を表す。〕
から選ばれる少なくとも一種のブロックイソシアネート基を有する活性メチレン型ブロックポリイソシアネート化合物（ＣＢ）である。

Wherein ^{(III), R 2, R} 3, R 4 and ^{R 5} are as defined above, ^{R 6} represents a hydrocarbon group having 1 to 12 carbon atoms. ]
It is an active methylene type block polyisocyanate compound (CB) which has at least 1 type of block isocyanate group chosen from these.

  As a synthesis method of the above active methylene type block polyisocyanate compound (CB), for example, an active methylene compound (cb2) is reacted with an isocyanate group in a polyisocyanate compound (cb1) having two or more isocyanate groups in one molecule. To obtain an active methylene type blocked polyisocyanate compound intermediate (cb3) and then reacting the obtained active methylene type block polyisocyanate compound intermediate (cb3) with a secondary alcohol (cb4), There is a method obtained by reacting a reaction product of the active methylene compound (cb2) and the secondary alcohol (cb4) with an isocyanate group in the polyisocyanate compound (cb1), and the former method is particularly preferable.

Polyisocyanate compound (cb1)
The polyisocyanate compound (cb1) is a compound having at least two isocyanate groups in one molecule, and examples thereof include aliphatic polyisocyanates, alicyclic polyisocyanates, araliphatic polyisocyanates, aromatic polyisocyanates, And polyisocyanate derivatives.

  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, dimer acid diisocyanate, methyl 2,6-diisocyanatohexanoate (common name: lysine diisocyanate); 2 , 6-Diisocyanatohexanoic acid 2-isocyanatoethyl, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,6 1-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyl Examples thereof include aliphatic triisocyanates such as octane.

  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), 4-methyl-1,3-cyclohexylene diisocyanate (common name: hydrogenated TDI), 2-methyl-1,3-cyclohexylene diisocyanate, 1,3- or 1,4-bis (isocyanato) Methyl) cyclohexane (common name: hydrogenated xylylene diisocyanate) or a mixture thereof, methylenebis (4,1-cyclohexanediyl) diisocyanate (common name: hydrogenated MDI), alicyclic diisocyanate such as norbornane diisocyanate 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2- (3-isocyanatopropyl) -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-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) ) Heptane, 6- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 5- (2-isocyanate) Toethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) -heptane, 6- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3 An alicyclic triisocyanate such as -isocyanatopropyl) -bicyclo (2.2.1) heptane can be used.

  Examples of the araliphatic polyisocyanate include methylene bis (4,1-phenylene) diisocyanate (common name: MDI), 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω, ω′-diisocyanato- Aromatic aliphatic diisocyanates such as 1,4-diethylbenzene, 1,3- or 1,4-bis (1-isocyanato-1-methylethyl) benzene (common name: tetramethylxylylene diisocyanate) or mixtures thereof; 1,3 And araliphatic triisocyanates such as 5-triisocyanatomethylbenzene.

  Examples of the aromatic polyisocyanate include m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4-tolylene diisocyanate (common name: 2,4- TDI), 2,6-tolylene diisocyanate (common name: 2,6-TDI) or mixtures thereof, aromatic diisocyanates such as 4,4′-toluidine diisocyanate, 4,4′-diphenyl ether diisocyanate; triphenylmethane-4 , 4 ′, 4 ″ -triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene and the like; 4,4′-diphenylmethane-2,2 ′ , 5,5'-tetraisocyanate and other aromatics Mention may be made of the tiger isocyanate.

  Examples of the polyisocyanate derivatives include, for example, the above-mentioned polyisocyanate dimers, trimers, biurets, allophanates, uretdiones, uretimines, isocyanurates, oxadiazine triones, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI). And Crude TDI.

  The above polyisocyanates and derivatives thereof may be used alone or in combination of two or more. Of these polyisocyanates, as the polyisocyanate compound (cb1), since the resulting active methylene type block polyisocyanate compound (CB) is less likely to yellow when heated, aliphatic diisocyanates and alicyclics are used. Diisocyanates and their derivatives are preferred. Of these, aliphatic diisocyanates and derivatives thereof are more preferable from the viewpoint of improving the flexibility of the formed coating film.

  Moreover, as said polyisocyanate compound (cb1), you may use the prepolymer formed by making the said polyisocyanate and its derivative (s), and the compound which can react with this polyisocyanate react on an isocyanate group excess condition. Examples of the compound capable of reacting with the polyisocyanate include compounds having an active hydrogen group such as a hydroxyl group and an amino group. Specifically, for example, polyhydric alcohol, low molecular weight polyester resin, amine, water, etc. Can be used.

  The polyisocyanate compound (cb1) is a polymer of an isocyanate group-containing polymerizable unsaturated monomer or a polymerizable unsaturated monomer other than the isocyanate group-containing polymerizable unsaturated monomer and the isocyanate group-containing polymerizable unsaturated monomer. A copolymer with a monomer may be used.

  The polyisocyanate compound (cb1) is a number from the viewpoint of the reactivity of the obtained active methylene block polyisocyanate compound (CB) and the compatibility between the active methylene block polyisocyanate compound (CB) and other coating components. The average molecular weight is preferably in the range of 300 to 20,000, more preferably in the range of 400 to 8,000, and still more preferably in the range of 500 to 2,000.

  The polyisocyanate compound (cb1) is used from the viewpoint of the reactivity of the obtained active methylene block polyisocyanate compound (CB) and the compatibility between the active methylene block polyisocyanate compound (CB) and other coating components. The average number of isocyanate functional groups in one molecule is preferably in the range of 2 to 100. As a minimum, 3 is more preferable from a viewpoint of improving the reactivity of the active methylene type block polyisocyanate compound (CB) obtained. The upper limit is more preferably 20 from the viewpoint of preventing gelation during the production of the active methylene type block polyisocyanate compound (CB).

Active methylene compound (cb2)
Examples of the active methylene compound (cb2) that blocks the isocyanate group in the polyisocyanate compound (cb1) include dimethyl malonate, diethyl malonate, di-n-propyl malonate, diisopropyl malonate, di-n-malonate. Butyl, diisobutyl malonate, di-sec-butyl malonate, di-t-butyl malonate, di-n-pentyl malonate, di-n-hexyl malonate, di (2-ethylhexyl) malonate, methyl isopropyl malonate, malonic acid Such as ethyl isopropyl, methyl n-butyl malonate, ethyl n-butyl malonate, methyl isobutyl malonate, ethyl isobutyl malonate, methyl sec-butyl malonate, ethyl sec-butyl malonate, diphenyl malonate and dibenzyl malonate Malonic acid diester, ace Methyl acetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, n-butyl acetoacetate, isobutyl acetoacetate, sec-butyl acetoacetate, t-butyl acetoacetate, n-pentyl acetoacetate, n-hexyl acetoacetate Acetoacetate such as 2-ethylhexyl acetoacetate, phenyl acetoacetate and benzyl acetoacetate, methyl isobutyrylacetate, ethyl isobutyrylacetate, n-propyl isobutyrylacetate, isopropyl isobutyrylacetate, n-butyl isobutyrylacetate, isobutyl isobutylylacetate, isobutyrylacetate sec-butyl, t-butyl isobutyryl acetate, n-pentyl isobutyryl acetate, n-hexyl isobutyryl acetate, 2-ethylhexyl isobutyryl acetate, phenyl isobutyryl acetate and iso Isobutyryl acetates such as styryl benzyl acetate and the like, which may be used alone or in combination.

  Among them, from the viewpoint of smoothness and sharpness of the formed multilayer coating film, the active methylene compound (cb2) is dimethyl malonate, diethyl malonate, diisopropyl malonate, methyl acetoacetate, ethyl acetoacetate, isobutyryl. It is preferably at least one compound selected from the group consisting of methyl acetate and ethyl isobutyryl acetate, and more preferably at least one compound selected from the group consisting of diisopropyl malonate, methyl isobutyryl acetate and ethyl isobutyryl acetate. preferable. Among them, diisopropyl malonate is used from the viewpoint of smoothness and sharpness of the formed multilayer coating film, reactivity of the obtained active methylene type block polyisocyanate compound (CB) and storage stability of the aqueous coating composition. More preferably it is.

  For the blocking reaction of the isocyanate group with the active methylene compound (cb2), a reaction catalyst can be used as necessary. Examples of the reaction catalyst include metal hydroxide, metal alkoxide, metal carboxylate, metal acetyl acetylate, hydroxide of onium salt, onium carboxylate, metal salt of active methylene compound, onium salt of active methylene compound, aminosilanes Basic compounds such as amines and phosphines are preferred. Of these, ammonium salts, phosphonium salts, and sulfonium salts are preferred as onium salts. The amount of the reaction catalyst used is usually preferably in the range of 10 to 10,000 ppm, based on the total solid mass of the polyisocyanate compound (cb1) and the active methylene compound (cb2). More preferably, it is in the range of 000 ppm.

  The blocking reaction of the isocyanate group with the active methylene compound (cb2) can be performed at 0 to 150 ° C., and a solvent may be used. In this case, the solvent is preferably an aprotic solvent, and particularly preferably an ester, ether, N-alkylamide, ketone or the like. If the reaction proceeds as intended, an acid component may be added to neutralize the basic compound as a catalyst and stop the reaction.

  In the blocking reaction of the isocyanate group with the active methylene compound (cb2), the amount of the active methylene compound (cb2) used is not particularly limited, but is 0.1% with respect to 1 mol of the isocyanate group in the polyisocyanate compound (cb1). It is suitable to use -3 mol, preferably 0.2-2 mol. In addition, the active methylene compound that has not reacted with the isocyanate group in the polyisocyanate compound (cb1) can be removed after completion of the blocking reaction.

  In addition to the active methylene compound (cb2), for example, alcohol, phenol, oxime, amine, acid amide, imidazole, pyridine, mercaptan and the like blocking agents may be used in combination.

  Further, some of the isocyanate groups in the polyisocyanate compound (cb1) may be reacted with an active hydrogen-containing compound. By reacting some of the isocyanate groups in the polyisocyanate compound (cb1) with an active hydrogen-containing compound, for example, the storage stability of the resulting active methylene type block polyisocyanate compound (CB) is improved, the active methylene It is possible to adjust the compatibility between the mold block polyisocyanate compound (CB) and other coating components and to improve the flexibility of the formed coating film.

  When some of the isocyanate groups in the polyisocyanate compound (cb1) are reacted with the active hydrogen-containing compound, the reaction of the polyisocyanate compound (cb1), the active methylene compound (cb2) and the active hydrogen-containing compound The order is not particularly limited. Specifically, a method in which a part of the isocyanate group in the polyisocyanate compound (cb1) is blocked with an active methylene compound (cb2) and then the remaining isocyanate group is reacted with an active hydrogen-containing compound, polyisocyanate compound (cb1) A method of reacting an active hydrogen-containing compound with a part of the isocyanate group in the mixture and then blocking the remaining isocyanate group with the active methylene compound (cb2) and an active methylene compound (cb2) on the isocyanate group in the polyisocyanate compound (cb1) ) And an active hydrogen-containing compound are reacted at the same time.

  Examples of the active hydrogen-containing compound include a hydroxyl group-containing compound and an amino group-containing compound.

  Examples of the hydroxyl group-containing compound include propanol, butanol, pentanol, hexanol, heptanol, 2-ethyl-1-hexanol, octanol, nonanol, decanol, tridecanol, stearyl alcohol, ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol. , Polyethylene glycol (propylene glycol), polyethylene glycol monoalkyl ether, polypropylene glycol monoalkyl ether, polyethylene glycol (propylene glycol) monoalkyl ether, trimethylolpropane and the like. These may be used alone or in combination of two or more. be able to. In the present specification, “polyethylene glycol (propylene glycol)” means a copolymer of ethylene glycol and propylene glycol, and includes both a block copolymer and a random copolymer.

  Especially, it is preferable that the said hydroxyl-containing compound is a monohydric alcohol from a viewpoint of suppressing the viscosity increase of the active methylene type block polyisocyanate compound (CB) obtained. Examples of the monohydric alcohol include propanol, butanol, pentanol, hexanol, heptanol, 2-ethyl-1-hexanol, octanol, nonanol, decanol, tridecanol, stearyl alcohol, polyethylene glycol monoalkyl ether, polypropylene glycol monoalkyl. Examples include ether, polyethylene glycol (propylene glycol) monoalkyl ether, and the like. These can be used alone or in combination of two or more.

  Examples of the amino group-containing compound include butylamine, octylamine, stearylamine, dibutylamine, dioctylamine, dicyclohexylamine, dilaurylamine, α- (aminoalkyl) -ω-alkoxypolyoxyethylene (oxypropylene). , Hexamethylenediamine, diethylenetriamine, polyoxypropylene-α, ω-diamine (as commercial products, for example, “Jeffamine D-400” manufactured by Huntsman, etc.) can be used, and these can be used alone or Two or more types can be used in combination.

  Especially, it is preferable that the said amino group containing compound is a monovalent amine from a viewpoint of suppressing the viscosity increase of the active methylene type block polyisocyanate compound (CB) obtained. Examples of the monovalent amine include butylamine, octylamine, stearylamine, dibutylamine, dioctylamine, dicyclohexylamine, dilaurylamine, α- (aminoalkyl) -ω-alkoxypolyoxyethylene (oxypropylene), and the like. These may be used alone or in combination of two or more.

  When some of the isocyanate groups in the polyisocyanate compound (cb1) are reacted with the active hydrogen-containing compound, the storage stability and curability of the aqueous coating composition, and the smoothness, freshness of the formed multilayer coating film, From the viewpoints of film quality and water resistance, the reaction ratio between the polyisocyanate compound (cb1) and the active hydrogen-containing compound is based on 1 mole of isocyanate groups in the polyisocyanate compound (cb1). The number of moles of hydrogen is preferably in the range of 0.03 to 0.6 mole. As an upper limit, 0.4 is more preferable from the viewpoint of curability of the aqueous coating composition and water resistance of the multilayer coating film to be formed, and 0.3 is more preferable. The lower limit is more preferably 0.04, and even more preferably 0.05, from the viewpoint of the storage stability of the aqueous coating composition and the smoothness and sharpness of the formed multilayer coating film.

  The active methylene type block polyisocyanate compound (CB) has an activity having a hydrophilic group from the viewpoints of storage stability and curability of the aqueous coating composition and smoothness and sharpness of the formed multilayer coating film. A methylene type block polyisocyanate compound (CB ′) is preferred.

  The active methylene type block polyisocyanate compound (CB ′) having a hydrophilic group can be obtained, for example, by using an active hydrogen-containing compound having a hydrophilic group as the active hydrogen-containing compound.

  Examples of the active hydrogen-containing compound having a hydrophilic group include an active hydrogen-containing compound having a nonionic hydrophilic group, an active hydrogen-containing compound having an anionic hydrophilic group, and an active hydrogen-containing compound having a cationic hydrophilic group. These can be used alone or in combination of two or more. Especially, since the reaction which blocks the isocyanate group in the said polyisocyanate compound (cb1) by the said active methylene compound (cb2) is hard to be inhibited, it is preferable to use the active hydrogen containing compound which has a nonionic hydrophilic group. .

  As the active hydrogen-containing compound having a nonionic hydrophilic group, for example, an active hydrogen-containing compound having a polyoxyalkylene group can be suitably used. As said polyoxyalkylene group, a polyoxyethylene group, a polyoxypropylene group, a polyoxyethylene (oxypropylene) group etc. are mentioned, for example, These can be used individually or in combination of 2 or more types. Of these, active hydrogen-containing compounds having a polyoxyethylene group are preferred from the viewpoint of storage stability of the aqueous coating composition.

  The active hydrogen-containing compound having a polyoxyethylene group is 3 or more, preferably 5 to 100, more preferably from the viewpoint of the storage stability of the aqueous coating composition and the water resistance of the multilayer coating film to be formed. Preferably has 8 to 45 consecutive oxyethylene groups.

  Moreover, the active hydrogen containing compound which has the said polyoxyethylene group may contain oxyalkylene groups other than an oxyethylene group other than the continuous oxyethylene group. Examples of the oxyalkylene group other than the oxyethylene group include an oxypropylene group, an oxybutylene group, and an oxystyrene group. The molar ratio of the oxyethylene group in the oxyalkylene group in the active hydrogen-containing compound having a polyoxyethylene group is within the range of 20 to 100 mol% from the viewpoint of the storage stability of the aqueous coating composition. Preferably, it is in the range of 50 to 100 mol%. When the molar ratio of the oxyethylene group in the oxyalkylene group is less than 20 mol%, imparting hydrophilicity may be insufficient, and the storage stability of the aqueous coating composition may be lowered.

  Further, the active hydrogen-containing compound having a nonionic hydrophilic group has a number average molecular weight in the range of 200 to 2,000 from the viewpoint of storage stability of the aqueous coating composition and water resistance of the formed multilayer coating film. It is preferable to be within. The lower limit of the number average molecular weight is more preferably 300 and even more preferably 400 from the viewpoint of storage stability of the aqueous coating composition. As an upper limit, 1,500 is more preferable from the viewpoint of water resistance of the multilayer coating film to be formed, and 1,200 is more preferable.

  Examples of the active hydrogen-containing compound having a nonionic hydrophilic group include polyethylene glycol monoalkyl ethers (also known as ω-alkoxypolyoxyethylene) such as polyethylene glycol monomethyl ether and polyethylene glycol monoethyl ether, polypropylene glycol monomethyl ether, and Polypropylene glycol monoalkyl ethers such as polypropylene glycol monoethyl ether (also known as ω-alkoxypolyoxypropylene), ω-alkoxypolyoxyethylene (oxypropylene), ω-alkoxypolyoxyethylene (oxypropylene), etc. Oxyethylene (oxypropylene), polyethylene glycol (propylene glycol) monomethyl ether, polyethylene glycol Poly (ethylene glycol) (propylene glycol) monoalkyl ether such as ru (propylene glycol) monoethyl ether, polyethylene glycol, polypropylene glycol, polyethylene glycol (propylene glycol), α- (aminoalkyl) -ω-alkoxypolyoxyethylene, α- ( Aminoalkyl) -ω-alkoxypolyoxypropylene, α- (aminoalkyl) -ω-alkoxypolyoxyethylene (oxypropylene) and the like can be mentioned, and these can be used alone or in combination of two or more. Of these, polyethylene glycol monomethyl ether, polyethylene glycol monoethyl ether and polyethylene glycol are preferable, and polyethylene glycol monomethyl ether is more preferable.

  Moreover, as a commercial item of the said polyethyleneglycol monomethyl ether, for example, "UNIOX M-400", "UNIOX M-550", "UNIOX M-1000", "UNIOX M-" made by NOF CORPORATION 2000 "and the like. Examples of the commercially available polyethylene glycol include “PEG # 200”, “PEG # 300”, “PEG # 400”, “PEG # 600”, “PEG # 1000”, “ PEG # 1500 "," PEG # 1540 "," PEG # 2000 "and the like.

  Examples of the active hydrogen-containing compound having an anionic hydrophilic group include an active hydrogen-containing compound having a carboxyl group, an active hydrogen-containing compound having a sulfonic acid group, an active hydrogen-containing compound having a phosphate group, and neutralization thereof. A salt etc. are mentioned, These can be used individually or in combination of 2 or more types. Especially, the active hydrogen containing compound which has a carboxyl group can be used suitably from a compatible viewpoint with the active methylene type block polyisocyanate compound (CB) and other coating component obtained.

  A part or all of the acid groups in the active hydrogen-containing compound having an anionic hydrophilic group are inhibited from blocking the isocyanate group in the polyisocyanate compound (cb1) with the active methylene compound (cb2). Since it becomes difficult, it is preferable to be neutralized with a basic compound.

  The neutralization of the acid group in the active hydrogen-containing compound having an anionic group may be performed before the reaction between the active hydrogen-containing compound having the anionic group and the polyisocyanate compound (cb1) or after the reaction. May be.

  Examples of the basic compound include hydroxides of alkali metals or alkaline earth metals such as sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, and barium hydroxide; metal alkoxides; ammonia; ethylamine, propyl First, such as amine, butylamine, benzylamine, monoethanolamine, 2,2-dimethyl-3-amino-1-propanol, 2-aminopropanol, 2-amino-2-methyl-1-propanol, 3-aminopropanol Secondary monoamines such as diethylamine, diethanolamine, di-n-propanolamine, di-isopropanolamine, N-methylethanolamine, N-ethylethanolamine; dimethylethanolamine, trimethylamine, triethylamine, Tertiary monoamines such as isopropylamine, methyldiethanolamine, 2- (dimethylamino) ethanol; polyamines such as diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, methylaminopropylamine, and the like. It can be used in combination of more than one species. The basic compound is used in an amount of usually 0.1 to 1.5 equivalents, preferably 0.2 to 1.2 equivalents, based on the anionic group in the active hydrogen-containing compound having an anionic group. can do.

  Examples of the active hydrogen-containing compound having a carboxyl group include monohydroxycarboxylic acids such as glycolic acid, lactic acid, hydroxypivalic acid, malic acid and citric acid, 2,2-dimethylolacetic acid, 2,2-dimethylollactic acid, , 2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, dimethylolheptanoic acid, dimethylolnonanoic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid and other dihydroxycarboxylic acids, these dihydroxycarboxylic acids Examples include acid lactone ring-opening adducts, glycine, 1-carboxy-1,5-pentylenediamine, dihydroxybenzoic acid, 3,5-diaminobenzoic acid, lysine, and arginine.

  Examples of the active hydrogen-containing compound having a sulfonic acid group include 2-amino-1-ethanesulfonic acid, N, N-bis (2-hydroxyethyl) -2-aminoethanesulfonic acid, and 1,3-phenylenediamine. -4,6-disulfonic acid, diaminobutanesulfonic acid, 3,6-diamino-2-toluenesulfonic acid, 2,4-diamino-5-toluenesulfonic acid, 2- (cyclohexylamino) -ethanesulfonic acid, 3- (Cyclohexylamino) -propanesulfonic acid and the like.

  Examples of the active hydrogen-containing compound having a phosphoric acid group include 2,3-dihydroxypropylphenyl phosphate, hydroxyalkylphosphonic acid, aminoalkylphosphonic acid and the like.

  When some of the isocyanate groups in the polyisocyanate compound (cb1) are reacted with the active hydrogen-containing compound having the hydrophilic group, the storage stability and curability of the aqueous coating composition, and the formed multilayer coating film From the viewpoints of smoothness, sharpness and water resistance, the reaction ratio between the polyisocyanate compound (cb1) and the active hydrogen-containing compound having a hydrophilic group is based on 1 mole of isocyanate groups in the polyisocyanate compound (cb1). The number of moles of active hydrogen in the active hydrogen-containing compound is preferably in the range of 0.03 to 0.6 mole. As an upper limit, 0.4 is more preferable from the viewpoint of curability of the aqueous coating composition and water resistance of the multilayer coating film to be formed, and 0.3 is more preferable. The lower limit is more preferably 0.04, and even more preferably 0.05, from the viewpoint of the storage stability of the aqueous coating composition and the smoothness and sharpness of the formed multilayer coating film.

  The active methylene type block polyisocyanate compound (CB) can be imparted with water dispersibility by mixing with a surfactant in advance. In this case, from the viewpoint of the stability of the coating material, the surfactant is preferably a nonionic surfactant and / or an anionic surfactant.

Active methylene type block polyisocyanate compound intermediate (cb3)
The active methylene type block polyisocyanate compound intermediate (cb3) is obtained by reacting the polyisocyanate compound (cb1) having two or more isocyanate groups in one molecule and the active methylene compound (cb2), A part or all of isocyanate groups in cb1) are compounds blocked with an active methylene compound (cb2).

  Among them, the active methylene type block polyisocyanate compound intermediate (cb3) is represented by the following general formula (IV).

〔式（ＩＶ）中、Ｒ^１は、独立して、炭素数１〜１２の炭化水素基を表し、互いに同一でも異なっていてもよい。〕
で示されるブロックイソシアネート基を有する活性メチレン型ブロックポリイソシアネート化合物中間体（ｃｂ３−１）及び下記一般式（Ｖ）

[In Formula (IV), R ¹ independently represents a hydrocarbon group having 1 to 12 carbon atoms, and may be the same or different from each other. ]
An active methylene-type blocked polyisocyanate compound intermediate (cb3-1) having a blocked isocyanate group represented by the following general formula (V)

〔式（Ｖ）中、Ｒ^６及びＲ^７は、独立して、炭素数１〜１２の炭化水素基を表す。〕
で示されるブロックイソシアネート基を有する活性メチレン型ブロックポリイソシアネート化合物中間体（ｃｂ３−２）の少なくとも一方であることが好ましい。

Wherein (V), ^{R 6} and ^{R 7} independently represent a hydrocarbon group having 1 to 12 carbon atoms. ]
It is preferable that it is at least one of the active methylene type | mold block polyisocyanate compound intermediates (cb3-2) which have the block isocyanate group shown by these.

Active methylene type block polyisocyanate compound intermediate (cb3-1)
The active methylene type block polyisocyanate compound intermediate (cb3-1) is an active methylene type block polyisocyanate compound intermediate having a blocked isocyanate group represented by the general formula (IV).

Among them, the active methylene compound which is one of the raw materials of the active methylene-type blocked polyisocyanate compound as an intermediate (cb2), from viewpoint of using the active methylene compound can be relatively easily manufactured, R ¹ is, the number of carbon atoms It is preferable that it is a 1-3 alkyl group. Among these, from the viewpoint of improving the compatibility between the obtained active methylene block polyisocyanate compound (CB) and other coating components, it is preferably an alkyl group having 2 or 3 carbon atoms, and the storage stability of the aqueous coating composition. From the viewpoint of the properties, smoothness of the formed multi-layer coating film and sharpness, it is more preferable that it is an isopropyl group.

  The active methylene type block polyisocyanate compound intermediate (cb3-1) is obtained, for example, by reacting the polyisocyanate compound (cb1) with a dialkyl malonate having a hydrocarbon group having 1 to 12 carbon atoms. Can do.

  Examples of the dialkyl malonate include dimethyl malonate, diethyl malonate, di-n-propyl malonate, diisopropyl malonate, di-n-butyl malonate, diisobutyl malonate, disec-butyl malonate, and di-t malonate. -Butyl, di-n-pentyl malonate, di-n-hexyl malonate, di (2-ethylhexyl) malonate and the like can be mentioned, and these can be used alone or in combination of two or more. Of these, dimethyl malonate, diethyl malonate, di-n-propyl malonate, diisopropyl malonate, di-n-butyl malonate, diisobutyl malonate, di-sec-butyl malonate, and di-t-butyl malonate are preferred. Diethyl acid, di-n-propyl malonate, and diisopropyl malonate are more preferable, and diisopropyl malonate is more preferable.

Active methylene type block polyisocyanate compound intermediate (cb3-2)
The active methylene type block polyisocyanate compound intermediate (cb3-2) is an active methylene type block polyisocyanate compound intermediate having a blocked isocyanate group represented by the general formula (V).

Among them, as the active methylene compound (cb2), which is one of the raw materials of the active methylene type block polyisocyanate compound, an active methylene compound that can be produced relatively easily can be used, so that R ⁶ and R ⁷ are carbon. It is preferable that it is a C1-C3 alkyl group. Among these, from the viewpoint of improving the compatibility between the obtained active methylene type block polyisocyanate compound (CB) and other coating components, the alkyl group having 2 or 3 carbon atoms is preferable, and the storage stability of the aquatic coating composition is preferred. From the viewpoints of the properties, smoothness of the multilayer coating film, and sharpness, it is more preferable that it is an isopropyl group.

  The active methylene type block polyisocyanate compound intermediate (cb3-2) may be prepared by, for example, reacting the polyisocyanate compound (cb1) with an acetoacetate ester having a hydrocarbon group having 1 to 12 carbon atoms, or a polyisocyanate compound. It can be obtained by reacting (cb1) with an isobutyryl acetate having a hydrocarbon group having 1 to 12 carbon atoms. Especially, it is preferable to obtain by making the said polyisocyanate compound (cb1) react with the isobutyryl acetate ester which has a C1-C12 hydrocarbon group.

  Examples of the isobutyryl acetate include, for example, methyl isobutyryl acetate, ethyl isobutyryl acetate, n-propyl isobutyryl acetate, isopropyl isobutyryl acetate, n-butyl isobutylyl acetate, isobutyl isobutylyl acetate, sec-butyl isobutyryl acetate, t-butyl isobutyryl acetate, isobutyryl Examples include n-pentyl acetate, n-hexyl isobutyryl acetate, 2-ethylhexyl isobutyryl acetate, phenyl isobutyryl acetate, benzyl isobutyryl acetate and the like, and these can be used alone or in combination of two or more. Of these, methyl isobutyryl acetate, ethyl isobutyryl acetate and isopropyl isobutyryl acetate are preferred.

  Examples of the acetoacetate ester include methyl acetoacetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, n-butyl acetoacetate, isobutyl acetoacetate, sec-butyl acetoacetate, and t-butyl acetoacetate. , N-pentyl acetoacetate, n-hexyl acetoacetate, 2-ethylhexyl acetoacetate, phenyl acetoacetate, benzyl acetoacetate and the like, and these can be used alone or in combination of two or more. Of these, methyl acetoacetate, ethyl acetoacetate and isopropyl acetoacetate are preferred.

  The active methylene-type block polyisocyanate compound intermediate (cb3) reacts the polyisocyanate compound (cb1) having two or more isocyanate groups in one molecule, the active methylene compound (cb2), and the active hydrogen-containing compound. The compound obtained by this may be sufficient. Specifically, for example, by using an active hydrogen-containing compound having the polyoxyalkylene group as the active hydrogen-containing compound, a part of the isocyanate group in the polyisocyanate compound (cb1) is converted into an active methylene compound (cb2). ) And an active methylene type blocked polyisocyanate compound in which a part or all of other isocyanate groups are reacted with an active hydrogen-containing compound having a polyoxyalkylene group.

Secondary alcohol (cb4)
In the present invention, the active methylene type block polyisocyanate compound (CB) includes, for example, the above active methylene type block polyisocyanate compound intermediate (cb3) and a secondary alcohol (cb4) represented by the following general formula (VI):

〔式（ＶＩ）中、Ｒ^２、Ｒ^４及びＲ^５は、独立して、炭素数１〜１２の炭化水素基を表し、Ｒ^３は、炭素数１〜１２の直鎖状又は分岐状のアルキレン基を表す。〕
とを反応させることによって、得ることができる。

[In Formula (VI), R ² , R ⁴ and R ⁵ independently represent a hydrocarbon group having 1 to 12 carbon atoms, and R ³ represents a linear or branched group having 1 to 12 carbon atoms. Represents an alkylene group. ]
Can be obtained by reacting.

The secondary alcohol (cb4) is a compound represented by the above general formula (VI). Among them, from the viewpoint of enhancing the reactivity with the active methylene-type blocked polyisocyanate compound intermediate (cb3) and the secondary alcohol (cb4), R ² is preferably a methyl group. Further, when R ³ , R ⁴ and R ⁵ each have a large number of carbon atoms, the polarity of the resulting active methylene type block polyisocyanate compound (CB) may be reduced, and the compatibility with other paint components may be reduced. Therefore, R ³ is preferably an alkylene group having 1 to ³ carbon atoms, and R ⁴ and R ⁵ are preferably methyl groups.

  Examples of the secondary alcohol (cb4) include 4-methyl-2-pentanol, 5-methyl-2-hexanol, 6-methyl-2-heptanol, 7-methyl-2-octanol, and the like. Can be used alone or in combination of two or more. In particular, after the reaction of the block polyisocyanate compound intermediate (cb3) and the secondary alcohol (cb4), the secondary alcohol (cb4) is subjected to distillation to remove a part or all of the secondary alcohol (cb4). Since removal of (cb4) is relatively easy, 4-methyl-2-pentanol having a relatively low boiling point is more preferable.

  Specifically, the active methylene type block polyisocyanate compound (CB) is, for example, the following general formula (IV) described in the description of the active methylene type block polyisocyanate compound intermediate (cb3).

〔式（ＩＶ）中、Ｒ^１は、独立して、炭素数１〜１２の炭化水素基を表し、互いに同一でも、異なっていてもよい。〕
で示されるブロックイソシアネート基を有する活性メチレン型ブロックポリイソシアネート化合物中間体（ｃｂ３−１）及び上記２級アルコール（ｃｂ４）を反応させることによって得ることができる。

[In Formula (IV), R ¹ independently represents a hydrocarbon group having 1 to 12 carbon atoms, and may be the same or different. ]
It can obtain by making the active methylene type block polyisocyanate compound intermediate (cb3-1) which has the block isocyanate group shown by said, and the said secondary alcohol (cb4) react.

In this case, at least one of R ¹ in the blocked isocyanate group in the active methylene type blocked polyisocyanate compound intermediate (cb3-1) is represented by the following general formula (VII)

〔式（ＶＩＩ）中、Ｒ^２、Ｒ^４及びＲ^５は、独立して、炭素数１〜１２の炭化水素基を表し、Ｒ^３は、炭素数１〜１２の直鎖状又は分岐状のアルキレン基を表す。〕
で示される基に置換される。

[In Formula (VII), R ² , R ⁴ and R ⁵ independently represent a hydrocarbon group having 1 to 12 carbon atoms, and R ³ represents a linear or branched group having 1 to 12 carbon atoms. Represents an alkylene group. ]
It is substituted with a group represented by

  In this case, the obtained active methylene type block polyisocyanate compound (CB) is a blocked isocyanate group represented by the following general formula (I).

〔式（Ｉ）中、Ｒ^１、Ｒ^２、Ｒ^４及びＲ^５は、独立して、炭素数１〜１２の炭化水素基を表し、Ｒ^３は、炭素数１〜１２の直鎖状又は分岐状のアルキレン基を表す。〕
ここで、式（Ｉ）中、Ｒ^１は炭素数１〜８の炭化水素基がより好ましく、炭素数１〜４の炭化水素基がさらに好ましく、炭素数２〜３の炭化水素基がさらに特に好ましい。
又は下記一般式（ＩＩ）で示されるブロックイソシアネート基

[In the formula (I), R ¹ , R ² , R ⁴ and R ⁵ independently represent a hydrocarbon group having 1 to 12 carbon atoms, and R ³ is a straight chain having 1 to 12 carbon atoms or Represents a branched alkylene group. ]
Here, in formula (I), R ¹ is more preferably a hydrocarbon group having 1 to 8 carbon atoms, more preferably a hydrocarbon group having 1 to 4 carbon atoms, and particularly preferably a hydrocarbon group having 2 to 3 carbon atoms. preferable.
Or a blocked isocyanate group represented by the following general formula (II)

〔式（ＩＩ）中、Ｒ^２、Ｒ^３、Ｒ^４及びＲ^５は前記と同じ。〕
を有する。

[In formula (II), R ² , R ³ , R ⁴ and R ⁵ are the same as above. ]
Have

The reaction of the active methylene type blocked polyisocyanate compound intermediate (cb3-1) and the secondary alcohol (cb4) is, for example, R ¹ in the blocked isocyanate group in the active methylene type blocked polyisocyanate compound intermediate (cb3-1). There is no particular limitation as long as at least one of the methods can be substituted with the group represented by the general formula (VII). In particular, by heating and reducing pressure, a part or all of the alcohol derived from at least one of R ^{1 in} the active methylene-type block polyisocyanate compound intermediate (cb3-1) is distilled off to accelerate the reaction. And obtaining an active methylene type block polyisocyanate compound (CB) having a blocked isocyanate group represented by the general formula (I) or (II) is preferable.

  Specifically, the production method is 20 to 150 ° C., preferably 45 to 125 ° C., more preferably 75 to 95 ° C., and the pressure is reduced as necessary for 5 minutes to 20 hours, preferably 10 It is appropriate to remove a part or all of the alcohol over a period of 10 minutes to 10 minutes. If the temperature is too low, the exchange reaction of the alkoxy group in the active methylene type blocked polyisocyanate compound intermediate (cb3-1) is slowed down and the production efficiency is reduced. On the other hand, if the temperature is too high, the active methylene type block polyisocyanate is obtained. Degradation and degradation of the compound (CB) become severe and the curability may be lowered, which is not desirable.

  The active methylene type block polyisocyanate compound (CB) is represented by the following general formula (V) described in the description of the active methylene type block polyisocyanate compound intermediate (cb3).

Wherein (V), ^{R 6} and ^{R 7} independently represent a hydrocarbon group having 1 to 12 carbon atoms. ]
It can obtain by making the active methylene type block polyisocyanate compound intermediate (cb3-2) which has the block isocyanate group shown by, and the said secondary alcohol (cb4) react.

In this case, R ⁷ in the blocked isocyanate group in the active methylene type blocked polyisocyanate compound intermediate (cb3-2) is represented by the following general formula (VII)

[In Formula (VII), R ² , R ⁴ and R ⁵ independently represent a hydrocarbon group having 1 to 12 carbon atoms, and R ³ represents a linear or branched group having 1 to 12 carbon atoms. Represents an alkylene group. ]
It is substituted with a group represented by

  In this case, the obtained active methylene type blocked polyisocyanate compound (CB) is a blocked isocyanate group represented by the following general formula (III):

〔式（ＩＩＩ）中、Ｒ^２、Ｒ^３、Ｒ^４及びＲ^５は前記と同じであり、Ｒ^６は、炭素数１〜１２の炭化水素基を表す。〕
を有する。

Wherein ^{(III), R 2, R} 3, R 4 and ^{R 5} are as defined above, ^{R 6} represents a hydrocarbon group having 1 to 12 carbon atoms. ]
Have

The reaction of the active methylene type blocked polyisocyanate compound intermediate (cb3-2) and the secondary alcohol (cb4) is, for example, R ⁷ in the blocked isocyanate group in the active methylene type blocked polyisocyanate compound intermediate (cb3-2). Is not particularly limited as long as it can be substituted with the group represented by the general formula (VII). Among them, part or all of the alcohol derived from R ⁷ in the active methylene type block polyisocyanate compound intermediate (cb3-2) is removed by distillation out of the system by heating, decompression, etc., and the reaction is promoted. A method for obtaining an active methylene type blocked polyisocyanate compound (CB) having a blocked isocyanate group represented by the general formula (III) is preferred.

  As the above production method, specifically, the pressure is reduced as necessary at a temperature of 20 to 150 ° C., preferably 75 to 95 ° C., and 5 minutes to 20 hours, preferably 10 minutes to 10 hours. It is appropriate to remove some or all of the alcohol. If the temperature is too low, the exchange reaction of the alkoxy group in the active methylene type blocked polyisocyanate compound intermediate (cb3-2) is slowed to reduce the production efficiency. On the other hand, if the temperature is too high, the active methylene type block polyisocyanate is obtained. This is not desirable because the degradation of the compound (CB) is severe and the curability may be lowered.

  In addition, in the production of the active methylene type block polyisocyanate compound (CB), the mixing ratio of the active methylene type block polyisocyanate compound intermediate (cb3) and the secondary alcohol (cb4) is obtained as the obtained active methylene type block polyisocyanate compound. From the viewpoint of the reactivity of (CB) and production efficiency, the secondary alcohol (cb4) is in the range of 5 to 500 parts by mass based on 100 parts by mass of the solid content of the active methylene type block polyisocyanate compound intermediate (cb3). It is preferable that it is in the range of 10 to 200 parts by mass. If it is less than 5 mass parts, the reaction rate of an active methylene type block polyisocyanate compound intermediate (cb3) and secondary alcohol (cb4) may be too slow. Moreover, when it exceeds 500 mass parts, the density | concentration of the active methylene type block polyisocyanate compound (CB) produced | generated may become low too much, and manufacturing efficiency may fall.

  In the reaction of the active methylene type block polyisocyanate compound intermediate (cb3) and secondary alcohol (cb4), the active methylene type block is used to adjust the molecular weight of the active methylene type block polyisocyanate compound (CB). The removal operation may be performed after adding the polyfunctional hydroxyl group-containing compound to the polyisocyanate compound intermediate (cb3) and the secondary alcohol (cb4).

  The number average molecular weight of the active methylene type block polyisocyanate compound (CB) is in view of compatibility with other paint components, smoothness of the formed multilayer coating film, sharpness, water resistance and chipping resistance, etc. From the above, it is preferable to be within the range of 600 to 30,000. The upper limit of the number average molecular weight is more preferably 10,000, and even more preferably 5,000, from the viewpoints of compatibility with other coating components and the smoothness and sharpness of the formed multilayer coating film. The lower limit is more preferably 900 and more preferably 1,000 from the viewpoint of water resistance and chipping resistance of the multilayer coating film to be formed.

  The multilayer coating film formed using the water-based coating composition containing the active methylene type block polyisocyanate compound (CB) has good smoothness, sharpness and water resistance, and has a low temperature (70 ° C to 120 ° C). Less than 2). The smoothness and sharpness are good because the active methylene type block polyisocyanate compound (CB) has a hydrocarbon group having a specific branched structure, so that the uncured primer coated with an aqueous primer coating composition is used. It is inferred that when the aqueous coating composition (aqueous base coating composition) is applied on the coating film, a mixed layer between both coating films is suppressed. Moreover, since the active methylene type block polyisocyanate compound (CB ′) having a hydrophilic group has particularly high storage stability in some cases, the curability and water resistance are good even after long-term storage.

  In the aqueous coating composition of the present invention, the blending ratio of the active methylene type block polyisocyanate compound (CB) is determined from the viewpoint of smoothness, sharpness, water resistance, etc. of the formed multilayer coating film. ), Preferably 3 to 50% by mass, more preferably 5 to 40% by mass, based on the total solid content of the film-forming resin (B) and the crosslinking agent (C).

Block polyisocyanate compound (CA)
The block polyisocyanate compound (CA) is a block polyisocyanate compound other than the active methylene type block polyisocyanate compound (CB) having the specific structure described above, and is not particularly limited. Can be synthesized.

The polyisocyanate compound (CA) is obtained using the following diisocyanate as a main raw material.
The diisocyanate is an aliphatic, alicyclic and / or aromatic diisocyanate. Aliphatic diisocyanates include those having 4 to 30 carbon atoms, and alicyclic diisocyanates preferably having 8 to 30 carbon atoms, such as 1,4-tetramethylene diisocyanate and 1,5-pentamethylene. Diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, 1,3-bis (isocyanatomethyl) -cyclohexane, 4,4'-dicyclohexyl Examples of aromatic diisocyanates include xylylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, polyphenylmethane diisocyanate (hereinafter referred to as polymeric MD). I)). Among these, 1,6-hexamethylene diisocyanate or isophorone diisocyanate is preferable from the viewpoint of weather resistance and / or industrial availability, and these may be used alone or in combination.

  The polyisocyanate compound has about 2 to 20 isocyanate groups in one molecule and forms, for example, biuret bond, urea bond, isocyanurate bond, uretdione bond, urethane bond, allophanate bond, oxadiazine trione bond, etc. 1 to 20-mer monomer or oligomer of diisocyanate produced by

  As the blocking agent used for blocking the isocyanate group of the polyisocyanate compound, known ones can be used. For example, active methylene, phenol, alcohol, mercaptan, acid amide, imide, Amine, imidazole, urea, carbamate, imine, oxime, sulfite compounds and the like can be suitably used. The active methylene blocking agent is a blocking agent other than the active methylene blocking agent having a specific structure used in the aforementioned active methylene type blocked polyisocyanate compound (CB).

  The block polyisocyanate compound (CA) is a block polyisocyanate compound having a hydrophilic group from the viewpoints of storage stability and curability of the aqueous coating composition and smoothness and sharpness of the formed multilayer coating film. It is preferable that

  Examples of the block polyisocyanate compound having a hydrophilic group include an active hydrogen-containing compound having a nonionic hydrophilic group, an active hydrogen-containing compound having an anionic hydrophilic group, and an active hydrogen-containing compound having a cationic hydrophilic group. It can be obtained by using an active hydrogen-containing compound having a hydrophilic group. The active hydrogen-containing compound having a hydrophilic group is preferably an active hydrogen-containing compound having a nonionic hydrophilic group, more preferably polyethylene glycol monomethyl ether, polyethylene glycol monoethyl ether and polyethylene glycol, and polyethylene glycol monomethyl ether. Is more preferable.

  The said block polyisocyanate compound (CA) can be used individually by 1 type or in combination of 2 or more types.

Amino resin (CM)
As said amino resin (CM), the partial methylolation amino resin or the complete methylolation amino resin obtained by reaction of an amino component and an aldehyde component can be used. Examples of the amino component include melamine, urea, benzoguanamine, acetoguanamine, steroguanamine, spiroguanamine, dicyandiamide and the like. Examples of the aldehyde component include formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde, and the like.

  Moreover, what methylated the methylol group of the said methylolated amino resin partially or completely with suitable alcohol can also be used. Examples of the alcohol used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-ethylbutanol, and 2-ethylhexanol.

  As the amino resin (CM), a melamine resin (CM ′) is preferable. In particular, methyl ether melamine resins in which methylol groups of partially or fully methylolated melamine resins are partially or completely etherified with methyl alcohol, methylol groups of partially or fully methylolated melamine resins are partially or completely with butyl alcohol. Preference is given to butyl etherified melamine resins which have been etherified, and methyl-butyl mixed etherified melamine resins in which the methylol groups of the partially or fully methylolated melamine resin are partially or completely etherified with methyl alcohol and butyl alcohol.

  The melamine resin preferably has a weight average molecular weight of 400 to 6,000, more preferably 500 to 4,000, and more preferably 600 to 3, from the viewpoint of excellent water resistance of the resulting coating film. More preferably, it is 000.

  A commercially available product can be used as the melamine resin (CM ′). Examples of commercially available product names include “Cymel 202”, “Cymel 203”, “Cymel 238”, “Cymel 251”, “Cymel 303”, “Cymel 323”, “Cymel 324”, “Cymel 325”, “Cymel 327”, “Cymel 350”, “Cymel 385”, “Cymel 1156”, “Cymel 1158”, “Cymel 1116”, “Cymel 1130” (above, made by Nippon Cytec Industries, Inc.), “Uban 120”, “ “Uban 20HS”, “Uban 20SE60”, “Uban 2021”, “Uban 2028”, “Uban 28-60” (manufactured by Mitsui Chemicals, Inc.), and the like.

Composition and preparation method of aqueous coating composition The aqueous coating composition of the present invention preferably further contains a pigment. Examples of the pigment include a color pigment, an extender pigment, a glitter pigment, a functional pigment, and the like, and these can be used alone or in combination of two or more. It is preferable to contain at least one of the pigments.

  Examples of the color pigment 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. , Dioxazine pigments, diketopyrrolopyrrole pigments, and the like.

  When the water-based paint composition of the present invention contains the above-described color pigment, the content of the color pigment is usually 1 to 200 parts by weight, particularly 5 to 5 parts on the basis of 100 parts by weight of the resin solid content in the water-based paint composition. It is preferable to be within the range of 160 parts by weight, more particularly 10 to 130 parts by weight.

  Examples of the bright pigment include aluminum (including vapor-deposited aluminum), copper, zinc, brass, nickel, aluminum oxide, mica, aluminum oxide coated with titanium oxide and iron oxide, and titanium oxide and iron oxide. And mica, glass flakes, and hologram pigments. 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 aluminum pigment includes non-leafing aluminum and leafing aluminum, and any of them can be used. The above luster pigments can be used alone or in combination of two or more.

  When the aqueous paint composition of the present invention contains the glitter pigment, the content of the glitter pigment is usually 1 to 50 parts by mass, preferably 100 parts by mass of resin solid content in the aqueous paint composition, preferably May be in the range of 2-30 parts by weight, more preferably 3-20 parts by weight.

  The aqueous coating composition of the present invention usually uses deionized water as an aqueous medium, but further contains a hydrophobic solvent from the viewpoint of improving the smoothness of the formed coating film, sharpness, and resistance to cracking. Is preferred.

  The hydrophobic solvent is desirably 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. Examples of the organic solvent include hydrocarbon solvents such as rubber volatile oil, mineral spirit, toluene, xylene, and solvent naphtha; 1-hexanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, 1-hexanol, Decanol, benzyl alcohol, ethylene glycol mono-2-ethylhexyl ether, propylene glycol mono-n-butyl ether, dipropylene glycol mono-n-butyl ether, tripropylene glycol mono-n-butyl ether, propylene glycol mono-2-ethylhexyl ether, propylene Alcohol solvents such as glycol monophenyl ether; S such as n-butyl acetate, isobutyl acetate, isoamyl acetate, methyl amyl acetate, ethylene glycol monobutyl ether Le solvents; methyl isobutyl ketone, may be mentioned cyclohexanone, ethyl n- amyl ketone solvents such as diisobutyl ketone. These can be used alone or in combination of two or more.

  When the aqueous coating composition of the present invention contains a hydrophobic solvent, the content thereof is generally 2 to 100 parts by mass, particularly 5 to 80 parts by mass, more particularly 8 to 8 parts by mass, based on 100 parts by mass of the resin solid content. It is preferably within the range of 60 parts by mass.

  In addition, the aqueous coating composition of the present invention includes a thickener, a curing catalyst, an ultraviolet absorber, a light stabilizer, an antifoaming agent, a plasticizer, an organic solvent other than the hydrophobic solvent, and a surface conditioner, if necessary. In addition, paint additives such as anti-settling agents can be contained.

  Examples of the thickener include inorganic thickeners such as silicate, metal silicate, montmorillonite, colloidal alumina; copolymer of (meth) acrylic acid and (meth) acrylic ester, poly Polyacrylic acid thickeners such as sodium acrylate; one molecule has a hydrophilic part and a hydrophobic part. In an aqueous medium, the hydrophobic part is adsorbed on the surface of pigments and emulsion particles in the paint. Or an associative thickener that effectively exhibits a thickening action by associating the hydrophobic parts; a fibrin derivative-based thickener such as carboxymethylcellulose, methylcellulose, hydroxyethylcellulose; casein, sodium caseinate Protein thickeners such as ammonium caseinate; Alginic acid thickeners such as sodium alginate; Polyvinyl alcohol, Polyvinyl pyrrole Polyvinyl thickeners such as styrene, polyvinyl benzyl ether copolymer; polyether thickeners such as pluronic polyether, polyether dialkyl ester, polyether dialkyl ether, polyether epoxy modified product; vinyl methyl ether-anhydrous maleic Examples thereof include maleic anhydride copolymer thickeners such as partial esters of acid copolymers; and polyamide thickeners such as polyamide amine salts. These thickeners can be used alone or in combination of two or more.

  Commercially available products can be used as the polyacrylic acid-based thickener. Examples of commercially available product names include “ACRYSOL ASE-60”, “ACRYSOL TT-615”, and “Products manufactured by Rohm and Haas” ACRYSOL RM-5 "(above, trade name)," SN thickener 613 "," SN thickener 618 "," SN thickener 630 "," SN thickener 634 "," SN thickener 636 "(above, trade name) manufactured by San Nopco ) And the like. Commercially available products can be used as the associative thickener. Examples of commercially available product names include “UH-420”, “UH-450”, “UH-462”, “UH-462”, “ “UH-472”, “UH-540”, “UH-752”, “UH-756VF”, “UH-814N” (above, trade name), “ACRYSOL RM-8W”, “ACRYSOL” manufactured by Rohm and Haas. "RM-825", "ACRYSOL RM-2020NPR", "ACRYSOL RM-12W", "ACRYSOL SCT-275" (trade name), San Nopco's "SN thickener 612", "SN thickener 621N", "SN “Thickener 625N”, “SN thickener 627N”, “SN thickener 660T” (above, trade name), and the like. Examples of the polyamide thickener include “AQ-630” and “AQ-870” (trade name) manufactured by Enomoto Kasei Co., Ltd.

  When the aqueous coating composition of the present invention contains the above thickener, the content of the thickener is usually 0.01 to 15 parts by weight, particularly 0.05, based on 100 parts by weight of the resin solid content. It is preferable that it is in the range of 10 to 10 parts by mass, more preferably 0.1 to 5 parts by mass.

  The aqueous coating composition of the present invention comprises a polyester resin (A), a film-forming resin (B) and a curing agent (C), and, if necessary, a pigment, a hydrophobic solvent, and other coating additives. It can be prepared by mixing and dispersing in an aqueous medium by a method known per se. Moreover, as the aqueous medium, a hydrophilic organic solvent can be used in addition to deionized water. Examples of the hydrophilic organic solvent include ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether and the like.

  The aqueous coating composition of the present invention can generally have a solid content concentration in the range of 10 to 60% by mass, preferably 15 to 50% by mass, and more preferably 20 to 40% by mass.

  In the present specification, “solid content” of paints, resins, and the like means non-volatile components remaining after drying at 110 ° C. for 1 hour. For example, the solid content of the coating means a non-volatile component such as a base resin, a curing agent, or a pigment contained in the coating that remains after drying at 110 ° C. for 1 hour. Therefore, the solid content concentration of the paint is determined by measuring the paint in a heat-resistant container such as an aluminum foil cup, spreading the paint on the bottom of the container, drying at 110 ° C. for 1 hour, and the mass of the paint component remaining after drying. Can be calculated by determining the ratio of the mass of the paint component remaining after drying to the total mass of the paint before drying.

Multilayer coating film forming method of the present invention A multilayer coating film forming method using the aqueous coating composition of the present invention as an aqueous base coating material (Y) is a method I for forming a multilayer coating film by a 3-coat 1-bake method, Or it can use suitably in either of the method II which forms a multilayer coating film by a 4-coat 1-bake system.

Method I
The first multilayer coating film forming method (Method I) of the present invention comprises a multilayer coating film comprising a primer coating film, a base coating film and a clear coating film on an object to be coated such as an automobile body or an automobile part. It can be suitably used when forming by a 3-coat 1-bake method.
In this case, the multilayer coating film can be formed according to the following steps 1-1 to 1-4.

Following steps 1-1 to 1-4:
Step 1-1: A step of applying a primer paint (X) to an article to form a primer coating film,
Step 1-2: A step of applying a water-based base coating (Y) on the uncured primer coating to form a base coating,
Step 1-3: A step of applying a clear coating (Z) containing a polyisocyanate compound on the uncured base coating to form a clear coating, and Step 1-4: the uncured primer In the step of sequentially heating and curing the coating film, the uncured base coating film and the uncured clear coating film at the same time, the above-mentioned aqueous base coating material (Y) is the aqueous coating composition of the present invention. Method.

Step 1-1
In the first multilayer coating film forming method (Method I) of the present invention, first, a primer coating (X) is applied on an object to be coated.

In the method for forming a multi-layer coating film of the present invention, the object to be coated with the primer coating composition (X) is not particularly limited. For example, automobiles such as passenger cars, trucks, motorcycles, buses, etc. Examples of the outer plate portion of the vehicle body; automobile parts such as bumpers; and the outer plate portion of home electric products such as mobile phones and audio devices. Of these, the outer plate portion of the automobile body and the automobile parts are preferable.

  The material of these objects to be coated is not particularly limited. For example, iron, aluminum, brass, copper, tinplate, stainless steel, galvanized steel, zinc alloy (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. Plastic materials such as FRP; inorganic materials such as glass, cement and concrete; wood; fiber materials such as paper and cloth. Of these, metal materials and plastic materials are preferred.

  The object to be coated may be a metal surface of the metal material or a vehicle body formed from the metal material, and may be subjected to surface treatment such as phosphate treatment, chromate treatment, complex oxide treatment, A coating film may be formed thereon.

  As an object to be coated, a surface treatment is applied to the substrate as necessary, and an undercoat film is formed thereon, for example, a vehicle body in which an undercoat film is formed by an electrodeposition paint It may be.

  The article to be coated may be obtained by subjecting the plastic surface of the plastic material or an automobile part or the like molded therefrom to a surface treatment as necessary. Further, a combination of a plastic material and a metal material may be used.

Primer paint (X)
As the primer coating (X) used in the method for forming a multilayer coating film of the present invention, a known intermediate coating or a primer coating for plastics can be used. Specifically, for example, a coating composition containing a film-forming resin, a crosslinking agent, a color pigment, an extender pigment, a bright pigment, a conductive pigment and a solvent can be suitably used, and the primer coating (X) If necessary, paint additives such as UV absorbers, light stabilizers, curing catalysts, plasticizers, adhesion-imparting agents, compatibilizers, antifoaming agents, viscosity modifiers, rust inhibitors, surface modifiers, etc. Can be included.

  Examples of the film-forming resin include acrylic resin, polyester resin, alkyd resin, urethane resin, polyolefin resin, and the like, and preferably contains a hydroxyl group. These can be used alone or in combination of two or more.

The primer paint (X) may be crosslinked by blending a crosslinking agent, or may be substantially uncrosslinked without blending a crosslinking agent. Moreover, when it contains a crosslinking agent, for example, it may be a one-component primer paint containing the block polyisocyanate compound or amino resin, or a two-component primer in which a crosslinking agent such as a polyisocyanate compound is mixed before coating. Although a paint may be used, a one-component primer paint is preferable, and a one-component primer paint containing a block polyisocyanate compound is more preferable.
Further, it is preferable to crosslink the primer coating by soaking in the crosslinking agent contained in the upper base coating or clear coating. As the crosslinking agent, for example, a melamine resin, a polyisocyanate compound, a blocked polyisocyanate compound, and the like can be suitably used, but the base coating film and the polyisocyanate compound are contained in the clear coating film and penetrated into the lower layer. More preferably, the primer coating is cured.

  As the primer paint, either an organic solvent-type paint or an aqueous paint may be used, but an aqueous paint is preferably used.

Further, when the object to be coated is a plastic material and the aqueous base paint (Y) is applied to the upper layer of the primer coating film by an electrostatic application method, it is preferable to use a conductive primer paint as the primer paint. The conductive primer paint is a paint characterized in that the surface electrical resistance value of the primer coating is less than 10 ⁹ Ω / cm ² when applying the water-based base coating (Y), and imparts conductivity to the coating. Therefore, it is preferable to include a conductive filler such as conductive carbon, metal, or conductive metal oxide.

  The primer paint (X) can be applied by a known method such as air spray coating, airless spray coating, rotary atomization coating, or the like, and electrostatic application may be performed during the coating. .

  The surface electric resistance value can be measured using an electric resistance measuring device (trade name “MODEL150”, manufactured by TREK).

Step 1-2
Next, an aqueous base paint (Y), which is the aqueous paint composition of the present invention, is applied onto the primer coating film formed in Step 1-1 described above.

  The primer coating film can be subjected to preheating (preliminary drying), air blowing, and the like under heating conditions in which the coating film is not substantially cured before the aqueous base paint (Y) is applied. In the present invention, the cured coating film is a cured and dried state 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 a dent due to fingerprints. The coating film does not stick, the movement of the coating film is not felt, and the center of the coating surface is rapidly and repeatedly rubbed with a fingertip so that the coating surface is not rubbed. 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 preheating temperature is preferably 40 to 100 ° C, more preferably 50 to 90 ° C, and still more preferably 60 ° C or more and less than 80 ° C. The preheating time is preferably 30 seconds to 15 minutes, more preferably 1 to 10 minutes, and even more preferably 2 to 5 minutes. Moreover, the said air blow can be normally performed by spraying the air heated to the normal temperature or the temperature of 25-80 degreeC on the coating surface of the to-be-coated article for 30 seconds-15 minutes.

  From the viewpoint of improving the smoothness and sharpness of the formed multi-layer coating film and suppressing the armpit, the primer coating film may be preheated or air blown as necessary before applying the aqueous base paint (Y). It is preferable to adjust so that the solid content of the coating film is usually in the range of 60 to 100% by mass, particularly 80 to 100% by mass, and more particularly 90 to 100% by mass.

Here, the solid content of the coating film can be measured by the following method:
First, the primer paint (X) is applied onto the article to be coated, and at the same time, the primer paint (X) is applied onto the aluminum foil whose mass (W1) has been measured in advance. Subsequently, after the coating, the aluminum foil that has been preheated or the like is collected just before the water-based base coating (Y) is coated, and its mass (W2) 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, and then the mass (W3) of the aluminum foil is measured, and the solid content is determined according to the following formula.
Solid content (mass%) = {(W3-W1) / (W2-W1)} × 100
The water-based base paint (Y) can be applied on the substrate by a method known per se, for example, air spray coating, airless spray coating, rotary atomization coating, curtain coat coating, etc. Electricity may be applied. Of these, methods such as air spray coating and rotary atomization coating are preferred.

Step 1-3
In the first multilayer coating film forming method (Method I) of the present invention, the clear paint (Z) is applied on the base coating film formed in the above step 1-2.

  From the viewpoint of preventing the occurrence of coating film defects such as armpits, the base coating film should be preheated (preliminary drying), air blown, etc. under heating conditions that do not substantially cure the coating film before applying the clear coating (Z). Preferably it is done. The preheating temperature is preferably 40 to 100 ° C, more preferably 50 to 90 ° C, and still more preferably 60 ° C to less than 80 ° C. The preheating time is preferably 30 seconds to 15 minutes, more preferably 1 to 10 minutes, and further preferably 2 to 5 minutes. Moreover, the said air blow can be normally performed by spraying the air heated to the normal temperature or the temperature of 25-80 degreeC on the coating surface of the to-be-coated article for 30 seconds-15 minutes.

  The base coating film is usually subjected to the above preheating, air blowing or the like before coating the clear coating (Z), so that the solid content of the coating film is usually 60 to 100% by mass, particularly 80 to 100%. It is preferable to adjust so that it may become in the range of mass%, especially 90-100 mass%.

  As the clear paint (Z), a clear paint containing a hydroxyl group-containing resin and a polyisocyanate compound which are known per se can be used for coating automobile bodies, automobile parts or household electrical appliances.

  The clear paint (Z) may be a one-component paint or a multi-component paint as long as it contains a hydroxyl group-containing resin and a polyisocyanate compound. A two-component clear coating mixed before coating is more preferable.

  The mixing ratio of the hydroxyl group-containing resin to the polyisocyanate compound is such that the ratio of the isocyanate equivalent of the polyisocyanate compound / the hydroxyl equivalent of the hydroxyl group-containing resin is 1 from the viewpoints of penetration of the polyisocyanate compound and curability of the multilayer coating film. It is blended in an amount of 0.0 to 2.0, preferably 1.1 to 1.5. If the ratio of the isocyanate equivalent of the polyisocyanate compound / the hydroxyl equivalent of the hydroxyl group-containing resin is less than 1.0, the crosslinkability becomes insufficient, and if it is more than 2.0, yellowing due to heat tends to occur.

  In addition, the clear paint (Z) can contain coloring pigments, bright pigments, dyes, and the like as long as they do not impair the transparency, as well as extender pigments, ultraviolet absorbers, and light stabilizers. An agent, an antifoaming agent, a viscosity adjusting agent, a rust preventive agent, a surface adjusting agent and the like can be appropriately contained.

The clear paint (Z) can be applied to the coating surface of the aqueous base paint (Y) by a method known per se, for example, a method such as air spray coating, airless spray coating, or rotary atomization coating. Moreover, if the surface electrical resistance value of the multilayer coating film when applying the clear coating is less than 10 ⁹ Ω / cm ^2, it can be applied by an electrostatic application method.

  In addition, after applying the clear paint (Z), if necessary, an interval of about 1 to 60 minutes is provided at room temperature, or heating conditions under which the coating film is not substantially cured (for example, at a temperature of 40 to 80 ° C.). Preheating (preheating) or air blowing can be performed in 1 to 60 minutes.

Step 1-4
In the first multilayer coating film forming method (Method I) of the present invention, the uncured primer coating film, the uncured base coating film and the uncured base coating film formed in Steps 1-1 to 1-3 described above. The cured clear coating is simultaneously cured by heating.

  Curing of the primer coating film, base coating film and clear coating film can be carried out by a normal coating film baking means, for example, hot air heating, infrared heating, high-frequency heating or the like.

  The heating temperature is preferably 70 ° C. to 120 ° C., more preferably 70 to 110 ° C., and still more preferably 80 to 100 ° C. from the viewpoint of energy saving and / or heat resistance of the substrate.

  The heating time is preferably 10 to 60 minutes, and more preferably 15 to 40 minutes. By this heating, a multilayer coating film composed of three layers of a primer coating film, a base coating film, and a clear coating film can be simultaneously cured.

  In Method I, the coating film thickness of the primer coating (X) is preferably a cured film thickness, usually in the range of 3 to 40 μm, particularly 5 to 30 μm, more particularly 7 to 20 μm. The coating thickness of the aqueous base paint (Y) is preferably 3 to 50 μm, particularly preferably 5 to 35 μm, more preferably 10 to 25 μm as a cured film thickness. The coating film thickness of the clear paint (Z) is a cured film thickness and is usually within the range of 10 to 80 μm, particularly 15 to 60 μm, and more particularly 20 to 45 μm.

Method II
In the second multilayer coating film forming method (Method II) of the present invention, four multilayer coating films comprising a primer coating film, a base coating film, a second base coating film, and a clear coating film are coated on an object to be coated. It can be suitably used when forming by the 1-bake method. In addition, the second multilayer coating film forming method (Method II) of the present invention, in particular, is a multilayer coating of white pearl color using a white base as the base coating film and an interference pigment base as the second base coating film. When forming a film | membrane, it can use suitably.
In this case, the multilayer coating film can be formed according to the following steps 2-1 to 2-5.

Following steps 2-1 to 2-5:
Step 2-1: a step of applying a primer paint (X) to an object to form a primer coating film,
Step 2-2: A step of applying a water-based base coating (Y) on the uncured primer coating to form a base coating,
Step 2-3: A step of applying the aqueous second base coating (Y2) on the uncured primer coating and the uncured base coating to form a second base coating,
Step 2-4: A clear coating (Z) containing a polyisocyanate compound is applied on the uncured primer coating, the uncured base coating, and the uncured second base coating to form a clear coating. And the step 2-5: a step of simultaneously heating and curing the uncured primer coating, the uncured base coating, the uncured second base coating, and the uncured clear coating,
In the step of sequentially performing the steps, a method for forming a multilayer coating film, wherein the aqueous base paint (Y) is the aqueous paint composition of the present invention.

Step 2-1
In the second multilayer coating film forming method (Method II) of the present invention, first, on the article to be coated such as an automobile body or automobile part described in the first multilayer coating film forming method (Method I). The primer paint (X) described in Step 1-1 is applied. When the coating color of the multilayer coating film to be formed is a white pearl coating color, from the viewpoint of concealing the base color, the L value of the primer coating film is preferably 60 or more, more preferably 70 or more, More preferably, it is 80 or more.
The L value is a value in the CIE color matching function, and the larger the L value is, the whiter it is.
Moreover, L value is the value which measured L value using Minolta color difference meter CR-200.

Step 2-2
Next, on the primer coating film of the primer coating (X) formed in the above step 2-1, the aqueous base coating (Y) which is the aqueous coating composition of the present invention described in the step 1-2 is applied. Is done.
When the coating color of the multilayer coating film to be formed is a white pearl coating color, the aqueous base paint (Y) is suitable to have a high whiteness, and the white pigment content is It is preferable that it exists in the range of 50-200 mass parts with respect to 100 mass parts of resin solid content of 80-150 mass parts especially. Examples of white pigments that can be used include titanium oxide (rutile titanium oxide, anatase titanium oxide, etc.), lead white, zinc white, zinc sulfide, lithopone, and the like. To titanium oxide. As the average particle diameter, rutile type titanium oxide having about 0.05 to 2.0 μm, particularly about 0.1 to 1.0 μm is most preferable.
Furthermore, a coloring pigment other than a white pigment, an extender pigment, a functional pigment, etc. can be used as needed.

Step 2-3
Next, the aqueous second base paint (Y2) is applied onto the base coating film of the aqueous base paint (Y) formed in the above step 2-2. As the aqueous second base paint (Y2), an aqueous paint composition known per se can be suitably used, but it is more preferred to use the aqueous paint composition of the present invention. As the pigment to be contained in the aqueous second base paint (Y2), the above-mentioned glitter pigment is preferable, and an interference pigment is more preferable. Examples of the interference pigment include mica, mica surface-coated with a metal oxide such as titanium oxide and iron oxide, and graphite surface-coated with titanium oxide.
As content of the said luster pigment (interference pigment), it is preferable that it exists in the range of 1-30 mass parts with respect to 100 mass parts of resin solid content in a coating material, especially 5-20 mass parts.
In addition, other pigments, such as titanium oxide, carbon black, zinc white, cadmium red, molybdenum red, chromium yellow, chromium oxide, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, within a range not greatly reducing whiteness Inorganic or organic coloring pigments such as quinacridone pigments, isoindoline pigments, selenium pigments, perylene pigments, extender pigments and / or functional pigments can be suitably used. These may be used alone or in combination of two or more.

  The water-based second base paint (Y2) can be applied on the substrate by a method known per se, for example, air spray coating, airless spray coating, rotary atomization coating, curtain coat coating, etc. Alternatively, electrostatic application may be performed. Of these, methods such as air spray coating and rotary atomization coating are preferred.

Step 2-4
Next, the polyisocyanate compound-containing clear paint (Z) described in Step 1-3 is applied onto the second base coating film of the aqueous second base paint (Y2) formed in Step 2-3. The

  In addition, after the application of the clear coating composition (Z), if necessary, an interval of about 1 to 60 minutes is provided at room temperature, or a heating condition in which the coating film is not substantially cured (for example, 40 to 80 ° C. Preheating (preheating) or air blowing can be performed at a temperature of 1 to 60 minutes.

Step 2-5
The uncured primer coating, uncured base coating, uncured second base coating, and uncured clear coating formed in steps 2-1 to 2-4 described above are simultaneously heat cured. It is done.
The heat curing of the multilayer coating film can be performed by the method described in Step 1-4 above.

In the above method II, the coating thickness of the primer coating (X) is preferably 3 to 40 μm, particularly 5 to 30 μm, more preferably 7 to 20 μm, as a cured film thickness.
The coating film thickness of the water-based base paint (Y) is preferably 3 to 50 μm, particularly preferably 10 to 40 μm, and more preferably 15 to 35 μm because it is necessary to hide the underlying color as the cured film thickness.
The coating film thickness of the aqueous second base paint (Y2) is preferably in the range of usually 1 to 30 μm, particularly 3 to 20 μm, more particularly 5 to 10 μm, as the cured film thickness.
The coating thickness of the clear paint (Z) is preferably within a range of usually 10 to 80 μm, particularly 15 to 60 μm, and more particularly 20 to 45 μm as a cured film thickness.

The reason why the aqueous coating composition of the present invention can provide good coating performance (adhesion, water resistance, etc.) even at a relatively low curing temperature (70 to 120 ° C.) When the aqueous coating composition of the present invention is used, since the Tg of the base coating film is relatively low and the polyester resin (A) having a low hydroxyl value is contained, the polyisocyanate compound contained in the clear coating film is the lower layer. It is considered that the base coating film and the primer coating film are easily soaked and the curability of each coating film is improved. Although the base coating film may be insufficiently cross-linked by lowering the hydroxyl value of the polyester, the active methylene type blocked polyisocyanate compound (CB) having high molecular weight and good storage properties and low-temperature curability as a coating composition. ) And a film-forming resin (C) can be supplemented. With respect to the film-forming resin (B), the coating film performance is further improved by using the core / shell type water-dispersible hydroxyl group-containing acrylic resin (B1 ″) that is cross-linked inside.
Therefore, if the water-based coating composition of the present invention is used, the base coating (white coating) is coated with a thick film (25 μm or more) in order to ensure concealment, and another layer is coated on top of the white coating in the 4C1B process. Even in the case of the pearl coating color, the polyisocyanate compound can sufficiently permeate from the clear coating film into the lower base coating film and the primer coating film, and a multilayer coating film with good coating performance can be obtained.
Further, it is considered that the polyisocyanate compound contained in the clear coating film soaks uniformly into the underlying coating film, thereby eliminating uneven curing speed and improving the finished skin (smoothness and sharpness).

For the above reasons, the water-based coating composition of the present invention can obtain the greatest effect when it is applied using the second multilayer coating film forming method (Method II), and can be preferably used.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to only these examples. “Part” and “%” are based on mass. Moreover, the film thickness of a coating film is based on a cured coating film.

Production and production example 1 of hydroxyl group-containing acrylic resin (B1-1)
To a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser and water separator, 60 parts of ethylene glycol monobutyl ether and 15 parts of isobutyl alcohol were added and heated to 110 ° C. in a nitrogen stream. When the temperature reached 110 ° C., a mixture of 10 parts of styrene, 48 parts of methyl methacrylate, 26 parts of n-butyl acrylate, 10 parts of 2-hydroxyethyl methacrylate, 6 parts of acrylic acid and 1 part of azobisisobutyronitrile was added dropwise over 3 hours. did. After completion of the addition, the mixture was aged at 110 ° C. for 30 minutes, and a mixture of 1 part of azobisisobutyronitrile and 15 parts of ethylene glycol monobutyl ether was added dropwise over 1 hour. Further, after aging at 110 ° C. for 1 hour, the reaction mixture was cooled, neutralized with dimethylaminoethanol, and deionized water was added to obtain a hydroxyl group-containing acrylic resin (B1-1). The obtained hydroxyl group-containing acrylic resin had a solid content of 50%.

Production and production example 2 of hydroxyl group-containing polyester resin (PE)
In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and water separator, 109 parts of trimethylolpropane, 141 parts of 1,6-hexanediol, 126 parts of 1,2-cyclohexanedicarboxylic acid anhydride and adipine After charging 120 parts of acid and raising the temperature from 160 ° C. to 230 ° C. over 3 hours, the resulting condensed water was distilled off with a water separator and subjected to a condensation reaction at 230 ° C. for 4 hours. Subsequently, in order to add a carboxyl group to the obtained condensation reaction product, 38.3 parts of trimellitic anhydride was further added, reacted at 170 ° C. for 30 minutes, diluted with ethylene glycol monobutyl ether, solid content A hydroxyl group-containing polyester resin (PE) having a concentration of 70% was obtained. The obtained hydroxyl group-containing 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 and production example 3 of pigment dispersion (P-1)
In a stirring and mixing container, 42.9 parts of hydroxyl group-containing polyester resin (PE) obtained in Production Example 2 (30 parts of solid content), 112 parts of “JR-806” (trade name, manufactured by Teika, rutile titanium oxide), Add 8 parts of “Ketjen Black EC600J” (trade name, manufactured by Lion, conductive carbon) and 137.1 parts of deionized water, and add 2- (dimethylamino) ethanol to adjust the pH to 8.0. did. Next, the obtained mixed liquid is put in a wide-mouth glass bottle, glass beads having a diameter of about 1.3 mmφ are added as a dispersion medium and sealed, and dispersed for 4 hours with a paint shaker to obtain a pigment dispersion (P-1). Obtained.

Production Example 4 of Primer Paint Composition (X)
Hydroxyl-containing acrylic resin (B1-1) obtained in Production Example 1 30 parts (solid content 15 parts), “Takelac WS5000” 50 parts (solid content 15 parts) (trade name, manufactured by Mitsui Takeda Chemical Co., polyurethane dispersion, Silanol group-containing self-crosslinking type, solid content 30%), "Supercron E-403" 133.3 parts (solid content 40 parts) (trade name, manufactured by Nippon Paper Industries Co., Ltd., water dispersion of chlorinated polypropylene, resin Chlorine content 15%, solid content 30%) and 300 parts of the pigment dispersion (P-1) obtained in Production Example 3 were mixed uniformly, and “ACRYSOL ASE-60” (trade name, Rohm and Haas) Manufactured by Polyacrylic acid type thickener), 2- (dimethylamino) ethanol and deionized water, pH 8.0, solid concentration 45%, Ford Cup No. 20 at 20 ° C. A primer coating composition (X-1) having a viscosity of 40 according to 4 was obtained.

Production Example 5 of Polyester Resin Aqueous Dispersion (A)
In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and water separator, 173.6 parts 1,4-butanediol, 227.6 parts 1,6-hexanediol, 135.2 parts adipic acid , 346.0 parts of dodecanedioic acid and 224.1 parts of isophthalic acid were added, and the temperature was raised from 160 ° C. to 230 ° C. over 3 hours with stirring, followed by condensation reaction at 230 ° C. while removing condensed water. . After confirming that the acid value was less than 1.0, the mixture was cooled to 170 ° C., and 29.6 parts of trimellitic anhydride was added to add a carboxyl group to the resulting condensation reaction product. For 30 minutes. Subsequently, it cooled to 95 degreeC and added 100 parts of propylene glycol monomethyl ether. Thereafter, 20 parts of dimethylethanolamine was added with stirring, and deionized water was gradually added, and water dispersion was performed while maintaining the temperature so that the temperature did not become 40 ° C. or lower, to a solid content of 30.0% by mass. It was adjusted. Further, dimethylethanolamine was added to adjust pH to obtain a polyester resin aqueous dispersion (A-1) having a pH of 8.0, an acid value of 18 mgKOH / g, a hydroxyl value of 0.9 mgKOH / g, and a number average molecular weight of 10,500. .
In addition, the acid value and the hydroxyl value were measured based on JIS-K1557 (2007).

Production Examples 6-12
The polyester resin aqueous dispersions (A-2) to (A-8) were obtained by synthesizing in the same manner as in Production Example 5 except that the composition shown in Table 1 below was used.

  Table 1 shows the raw material composition (parts), acid value (mgKOH / g), hydroxyl value (mgKOH / g) and number average molecular weight (Mn) of polyester resin aqueous dispersions (A-1) to (A-8). Show.

尚、表１中の略号は、それぞれ下記の意味を有する。
１４ＢＧ：１，４−ブタンジオール、
１６ＨＤ：１，６−ヘキサンジオール、
ＣＨＤＭ：１，４−シクロヘキサンジメタノール、
ＮＰＧ：ネオペンチルグリコール、
ＴＭＰ：トリメチロールプロパン、
ＡＤ：アジピン酸、
ＤＤＡ：ドデカン二酸、
ｔＰＡ：テレフタル酸、
ｉＰＡ：イソフタル酸、
ＨＨＰＡ：１，２−シクロヘキサンジカルボン酸無水物、
ＴＭＡ：無水トリメリット酸。

The abbreviations in Table 1 have the following meanings.
14BG: 1,4-butanediol,
16HD: 1,6-hexanediol,
CHDM: 1,4-cyclohexanedimethanol,
NPG: Neopentyl glycol
TMP: trimethylolpropane
AD: adipic acid,
DDA: dodecanedioic acid,
tPA: terephthalic acid,
iPA: isophthalic acid,
HHPA: 1,2-cyclohexanedicarboxylic anhydride,
TMA: trimellitic anhydride.

Production and production example 13 of hydroxyl group-containing acrylic resin aqueous dispersion (B1)
In a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser, nitrogen inlet tube and dropping device, 120 parts of deionized water and “ADEKA rear soap SR-1025” (trade name, manufactured by ADEKA, emulsifier, effective Ingredient 25%) 0.8 parts was charged, stirred and mixed in a nitrogen stream, and heated to 80 ° C.
Next, 5% of the total amount of the monomer emulsion for core part below and 2.5 parts of a 6% ammonium persulfate aqueous solution were introduced into the reaction vessel and maintained at 80 ° C. for 15 minutes. Then, the remainder of the monomer emulsion for core part was dropped into a reaction vessel maintained at the same temperature over 3 hours, and aging was performed for 1 hour after the completion of the dropping. Next, the following monomer emulsion for shell part was added dropwise over 1 hour and aged for 1 hour, and then cooled to 30 ° C. while gradually adding 3.8 parts of 5% 2- (dimethylamino) ethanol aqueous solution to the reaction vessel. Then, the mixture was discharged while being filtered through a 100 mesh nylon cloth to obtain an acrylic resin particle aqueous dispersion (B1-2) having an average particle diameter of 100 nm and a solid content of 30%. The obtained acrylic resin particles had an acid value of 17 mgKOH / g, a hydroxyl value of 23 mgKOH / g, and a glass transition temperature of −20 ° C.

  Monomer emulsion for core part: 54 parts of deionized water, 3.1 parts of “ADEKA rear soap SR-1025”, 1 part of allyl methacrylate, 5 parts of styrene, 44 parts of n-butyl acrylate, 7 parts of methyl methacrylate and 20 parts of ethyl acrylate The monomer emulsion for core part was obtained by mixing and stirring a part.

  Monomer emulsion for shell part: 50 parts of deionized water, 1.8 parts of “ADEKA rear soap SR-1025”, 0.04 part of 6% aqueous ammonium persulfate solution, 5.3 parts of 2-hydroxyethyl methacrylate, 2. 6 parts, 4 parts of n-butyl acrylate, 3.1 parts of methyl methacrylate and 8 parts of ethyl acrylate were mixed and stirred to obtain a monomer emulsion for shell part.

Production Examples 14-16
The hydroxyl group-containing acrylic resin aqueous dispersions (B1-3) to (B1-5) were obtained in the same manner as in Production Example 13 except that the composition shown in Table 2 below was used.

  Table 2 shows the raw material composition (parts), solid content (%), acid value (mgKOH / g), hydroxyl value (mgKOH / g) of the hydroxyl group-containing acrylic resin aqueous dispersions (B1-2) to (B1-5). And the glass transition temperature (° C.).

The abbreviations in Table 2 have the following meanings.
AMA: Allyl methacrylate,
St: Styrene,
nBA: n-butyl methacrylate,
MMA: methyl methacrylate,
EA: ethyl acrylate,
HEMA: 2-hydroxyethyl methacrylate,
MAAc: methacrylic acid.

Production Production Example 17 of Active Methylene Block Polyisocyanate Compound Solution (CB)
In a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser, nitrogen inlet tube, dropping device and removal solvent simple trap, “Sumidule N-3300” (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., hexamethylene) Diisocyanate-derived isocyanurate structure-containing polyisocyanate, solid content of about 100%, isocyanate group content of 21.8%) 480 parts, ethyl acetate 150 parts and diisopropyl malonate 365 parts, while stirring under a nitrogen stream, sodium 4 parts of 28% methanol solution of methoxide was added and stirred at 65 ° C. for 8 hours. The amount of isocyanate in the obtained resin solution was 0.07 mol / Kg. To this was added 870 parts of 4-methyl-2-pentanol, the solvent was distilled off under reduced pressure for 3 hours while maintaining the temperature of the system at 90 to 95 ° C., and 120 parts of 4-methyl-2-pentanol was further removed. Was added to obtain 1400 parts of an active methylene type block polyisocyanate compound solution (CB-1). The removal solvent simple trap contained 183 parts of isopropanol. The obtained active methylene type block polyisocyanate compound solution (CB-1) had a solid concentration of about 60%.

Production Example 18
In a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser, nitrogen inlet tube, dropping device and removal solvent simple trap, 480 parts of “Sumidule N-3300”, 150 parts of ethyl acetate, 330 parts of diisopropyl malonate And 27 parts of isopropyl acetoacetate were added, and 4 parts of a 28% methanol solution of sodium methoxide was added while stirring under a nitrogen stream, followed by stirring at 65 ° C. for 8 hours. The amount of isocyanate in the obtained resin solution was 0.08 mol / Kg. To this was added 870 parts of 4-methyl-2-pentanol, the solvent was distilled off under reduced pressure for 3 hours while maintaining the temperature of the system at 90 to 95 ° C., and 120 parts of 4-methyl-2-pentanol was further removed. Was added to obtain 1390 parts of an active methylene block polyisocyanate compound solution (CB-2). The removal solvent simple trap contained 173 parts of isopropanol. The obtained active methylene type block polyisocyanate compound solution (CB-2) had a solid content concentration of about 60%.

Production Example 19
In a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser, nitrogen inlet tube, dropping device and removal solvent simple trap, 480 parts of “Sumidule N-3300”, 150 parts of ethyl acetate, 280 parts of diethyl malonate Then, 30 parts of ethyl isobutyryl acetate was added, and 4 parts of a 28% methanol solution of sodium methoxide was added while stirring under a nitrogen stream, followed by stirring at 65 ° C. for 8 hours. The amount of isocyanate in the obtained resin solution was 0.08 mol / Kg. To this was added 870 parts of 4-methyl-2-pentanol, the solvent was distilled off under reduced pressure for 3 hours while maintaining the temperature of the system at 90 to 95 ° C., and 120 parts of 4-methyl-2-pentanol was further removed. Was added to obtain 1350 parts of an active methylene block polyisocyanate compound solution (CB-3). The removal solvent simple trap contained 133 parts of ethanol. The obtained active methylene type block polyisocyanate compound solution (CB-3) had a solid concentration of about 60%.

Production Example 20
In a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser, nitrogen introducing tube, dropping device and removal solvent simple trap, 480 parts of “Sumidule N-3300”, 150 parts of ethyl acetate and 360 parts of diisopropyl malonate Then, 4 parts of a 28% methanol solution of sodium methoxide was added with stirring under a nitrogen stream and stirred at 65 ° C. for 8 hours. The amount of isocyanate in the obtained resin solution was 0.07 mol / Kg. To this was added 990 parts of 5-methyl-2-hexanol, the solvent was distilled off under reduced pressure for 3 hours while maintaining the temperature of the system at 90 to 95 ° C., and 120 parts of 5-methyl-2-hexanol was further removed. Was added to obtain 1400 parts of an active methylene type block polyisocyanate compound solution (CB-4). The removal solvent simple trap contained 180 parts of isopropanol. The obtained active methylene type block polyisocyanate compound solution (CB-4) had a solid concentration of about 60%.

Production Example 21
In a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser, nitrogen inlet tube, dropping device and removal solvent simple trap, 450 parts of “Duranate TPA-100”, 150 parts of ethyl acetate and 360 parts of diisopropyl malonate were added. While stirring under a nitrogen stream, 4 parts of a 28% methanol solution of sodium methoxide was added and stirred at 65 ° C. for 8 hours. The amount of isocyanate in the obtained resin solution was 0.07 mol / Kg. To this was added 1110 parts of 6-methyl-2-heptanol, the solvent was distilled off under reduced pressure for 6 hours while maintaining the temperature of the system at 80 to 85 ° C., and 120 parts of 6-methyl-2-heptanol was further added. In addition, 1430 parts of an active methylene type block polyisocyanate compound solution (CB-5) was obtained. The removal solvent simple trap contained 170 parts of isopropanol. The obtained active methylene type block polyisocyanate compound solution (CB-5) had a solid content concentration of about 60%.

Production Example 22
In a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser, nitrogen inlet tube, dropping device and removal solvent simple trap, 360 parts of “Sumidule N-3300”, “Uniox M-550” (Nippon Oil) 60 parts of polyethylene glycol monomethyl ether, average molecular weight of about 550) and 0.2 part of 2,6-di-tert-butyl-4-methylphenol were mixed and mixed well at 130 ° C. under a nitrogen stream. Heated for hours. Next, 110 parts of ethyl acetate and 252 parts of diisopropyl malonate were charged, and 3 parts of a 28% methanol solution of sodium methoxide was added while stirring under a nitrogen stream, followed by stirring at 65 ° C. for 8 hours. The amount of isocyanate in the obtained resin solution was 0.12 mol / Kg. To this was added 683 parts of 4-methyl-2-pentanol, and the solvent was distilled off under reduced pressure for 3 hours while maintaining the temperature of the system at 80 to 85 ° C. to obtain an active methylene block polyisocyanate compound solution (CB- 6) 1010 parts were obtained. The removal solvent simple trap contained 95 parts of isopropanol. The obtained active methylene type block polyisocyanate compound solution (CB-6) had a solid concentration of about 60%.

Production Example 23
In a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser, nitrogen inlet tube, dropping device and removal solvent simple trap, 480 parts of “Sumidule N-3300”, 150 parts of ethyl acetate and 310 parts of diethyl malonate Then, 4 parts of a 28% methanol solution of sodium methoxide was added with stirring under a nitrogen stream and stirred at 65 ° C. for 8 hours. The amount of isocyanate in the obtained resin solution was 0.06 mol / Kg. To this was added 630 parts of n-butanol, the solvent was distilled off under reduced pressure for 3 hours while maintaining the temperature of the system at 90 to 95 ° C., and 90 parts of n-butanol was further added. 1270 parts of a type block polyisocyanate compound solution (CB-7) were obtained. The removal solvent simple trap contained 100 parts of ethanol. The obtained active methylene type block polyisocyanate compound solution (CB-7) had a solid concentration of about 60%.

Production Example 24
In a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser, nitrogen inlet tube, dropping device and removal solvent simple trap, 480 parts of “Sumidule N-3300”, 150 parts of ethyl acetate and 310 parts of diethyl malonate Then, 4 parts of a 28% methanol solution of sodium methoxide was added with stirring under a nitrogen stream and stirred at 65 ° C. for 8 hours. The amount of isocyanate in the obtained resin solution was 0.06 mol / Kg. To this was added 630 parts of 2-butanol, the solvent was distilled off under reduced pressure for 3 hours while maintaining the temperature of the system at 90 to 95 ° C., and 90 parts of 2-butanol was further added to form active methylene. 1250 parts of a type block polyisocyanate compound solution (CB-8) were obtained. The removal solvent simple trap contained 70 parts of ethanol. The obtained active methylene type block polyisocyanate compound solution (CB-8) had a solid content concentration of about 60%.

Production Example 25
In a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser, nitrogen inlet tube, dropping device and removal solvent simple trap, 480 parts of “Sumidule N-3300”, 150 parts of ethyl acetate and 310 parts of diethyl malonate Then, 4 parts of a 28% methanol solution of sodium methoxide was added with stirring under a nitrogen stream and stirred at 65 ° C. for 8 hours. The amount of isocyanate in the obtained resin solution was 0.06 mol / Kg. To this was added 1110 parts of 2-ethyl-1-hexanol, the solvent was distilled off under reduced pressure for 6 hours while maintaining the temperature of the system at 80 to 85 ° C., and 2-ethyl-1-hexanol was further removed. 120 parts were added to obtain 1410 parts of an active methylene type block polyisocyanate compound solution (CB-9). The removal solvent simple trap contained 130 parts of ethanol. The obtained active methylene type block polyisocyanate compound solution (CB-9) had a solid concentration of about 60%.

Production Example 26
In a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser, nitrogen inlet tube, dropping device and removal solvent simple trap, 480 parts of “Sumidule N-3300”, 150 parts of ethyl acetate and 310 parts of diethyl malonate Then, 4 parts of a 28% methanol solution of sodium methoxide was added with stirring under a nitrogen stream and stirred at 65 ° C. for 8 hours. The amount of isocyanate in the obtained resin solution was 0.06 mol / Kg. To this was added 1000 parts of propylene glycol monopropyl ether, the solvent was distilled off under reduced pressure for 3 hours while maintaining the system temperature at 90 to 95 ° C., and 120 parts of propylene glycol monopropyl ether was further added. As a result, 1380 parts of an active methylene block polyisocyanate compound solution (CB-10) were obtained. The removal solvent simple trap contained 125 parts of ethanol. The obtained active methylene type block polyisocyanate compound solution (CB-10) had a solid concentration of about 60%.

Production and production example 27 of glitter pigment dispersion (M)
In a stirring and mixing container, 19 parts of aluminum pigment paste “GX-180A” (trade name, manufactured by Asahi Kasei Metals Co., Ltd., metal content: 74%), 34.8 parts of 2-ethyl-1-hexanol, resin solution containing a phosphate group (B1-6) (Note 1) 8 parts and 2- (dimethylamino) ethanol 0.2 part were mixed uniformly to obtain a bright pigment dispersion (M-1).

Production Example 28
In a stirring and mixing container, 11 parts of silver white mica “Iriodin 103” (trade name, manufactured by Merck Japan, average particle size 22.2 μm), 34.8 parts of 2-ethyl-1-hexanol, a phosphate group-containing resin solution ( B1-6) (Note 1) 8 parts and 2- (dimethylamino) ethanol 0.2 part were mixed uniformly to obtain a bright pigment dispersion (M-2).
(Note 1) Phosphoric acid group-containing acrylic resin solution (B1-6): 27.5 parts of methoxypropanol, isobutanol in a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube and dropping device 27.5 parts of a mixed solvent is added, heated to 110 ° C., 25 parts of styrene, 27.5 parts of n-butyl methacrylate, “isostearyl acrylate” (trade name, Osaka Organic Chemical Industries, Ltd., branched higher alkyl acrylate) 20 parts, 7.5 parts of 4-hydroxybutyl acrylate, 15 parts of a phosphoric acid group-containing polymerizable unsaturated monomer (Note 2), 12.5 parts of 2-methacryloyloxyethyl acid phosphate, 10 parts of isobutanol, t-butyl per 121.5 parts of a mixture consisting of 4 parts of oxyoctanoate is added to the above mixed solvent over 4 hours, and t-butyl is added. The chromatography oxy octanoate 0.5 parts of a mixture consisting of 20 parts of isopropanol was added dropwise 1 hour. Thereafter, the mixture was aged and stirred for 1 hour to obtain a phosphoric acid group-containing acrylic resin solution (B1-6) 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 2) Phosphoric acid group-containing polymerizable unsaturated monomer: 57.5 parts monobutyl phosphoric acid and 41 parts isobutanol were added to a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, a nitrogen introducing tube and a dropping device. The mixture was heated to 90 ° C., 42.5 parts of glycidyl methacrylate was added dropwise over 2 hours, and the mixture was further aged and stirred for 1 hour. Thereafter, 59 parts of isopropanol was added to obtain a phosphate group-containing polymerizable unsaturated 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 and production example 29 of pigment dispersion (P-2)
In a stirring and mixing container, 40 parts of the hydroxyl group-containing acrylic resin (B1-1) obtained in Production Example 1 (solid content 20 parts), titanium white “CR-93” (trade name, manufactured by Ishihara Sangyo Co., Ltd., rutile titanium oxide) 120 parts and 140 parts of deionized water were added, and 2- (dimethylamino) ethanol was further added to adjust the pH to 8.0. Next, the obtained mixed liquid is put in a wide-mouth glass bottle, sealed with glass beads having a diameter of about 1.3 mmφ as a dispersion medium, dispersed with a paint shaker for 4 hours, and a pigment dispersion (P-2) is obtained. Obtained.

Production Example 1 of Aqueous Base Coating Composition (Y) and Aqueous Second Base Coating Composition (Y2)
116.7 parts of polyester resin aqueous dispersion (A-1) obtained in Production Example 5 (solid content 35 parts), 66.7 parts of hydroxyl group-containing acrylic resin aqueous dispersion (B1-2) obtained in Production Example 13 ( Solid content 20 parts), hydroxyl group-containing polyurethane resin solution “Yukot UX-5210” (trade name, polycarbonate-based aqueous polyurethane resin, Sanyo Chemical Industries, solid content 32%) 15.6 parts (solid content 5 parts) , 16.7 parts (solid content 10 parts) of the block polyisocyanate compound (CB-1) obtained in Production Example 17, melamine resin solution “Cymel 325” (trade name, methylated melamine resin, manufactured by Nippon Cytec Co., Ltd., solid content 80%) 12.5 parts (solid content 10 parts), pigment dispersion (P-2) 300 parts obtained in Production Example 29 (titanium white 120 parts, hydroxyl group-containing acrylic resin solid content 20 parts) and 2-ethyl- 1- 10 parts of hexanol was mixed uniformly, and further, “ACRYSOL ASE-60”, 2- (dimethylamino) ethanol and deionized water were added to adjust pH 8.0, solid content concentration 25%, 20 ° C. An aqueous base coating composition (Y-1) having a viscosity of 40 according to 4 was obtained.

Examples 2-18, Comparative Examples 1-11
Except for the formulation shown in Table 3 below, in the same manner as in Example 1, the aqueous base coating compositions (Y-2) to (Y-27), and the aqueous second base coating composition (Y2-1) and (Y2-2) was obtained.
In addition, all the compounding quantities in following Table 3 are the values in solid content.

Example 19
The primer coating composition (X-1) obtained in Production Example 4 was air spray-coated on a degreased polypropylene plate (PP plate) so as to have a cured film thickness of 10 μm to form a primer coating film. After standing for 3 minutes and preheating at 60 ° C. for 3 minutes, the aqueous base coating composition (Y-1) obtained in Example 1 was applied on the uncured primer coating film to a cured film thickness of 25 μm. The base coating film was formed by coating with an electrostatic rotary atomizer. After leaving for 5 minutes and preheating at 60 ° C. for 5 minutes, the aqueous second base coating composition (Y2-1) obtained in Example 18 was applied to the uncured base coating film with a cured film thickness of 7 μm. Then, coating was performed using an electrostatic rotary atomizing coating machine to form a second base coating film. After standing for 5 minutes and preheating at 60 ° C. for 5 minutes, “Soflex # 520 Clear” (trade name, polyisocyanate, manufactured by Kansai Paint Co., Ltd.) is used as a clear paint on the uncured second base coating film. Compound-containing two-component acrylic urethane organic solvent-type clear coating (hereinafter sometimes referred to as “clear coating (Z-1)”) is applied using an electrostatic rotary atomizing coating machine so that the cured film thickness is 30 μm. A clear coating film was formed. After leaving it for 7 minutes, it heated at 80 degreeC for 30 minutes, the said primer coating film, the base coating film, the 2nd base coating film, and the clear coating film were hardened simultaneously, and the test board was produced.

Examples 20-39 and Comparative Examples 12-19
A test plate was prepared in the same manner as in Example 19 except that the coating composition, the cured film thickness, and / or the baking temperature shown in Table 4 below were changed.

Example 40
The primer coating composition (X-1) obtained in Production Example 4 was air spray-coated on a degreased polypropylene plate (PP plate) so as to have a cured film thickness of 10 μm to form a primer coating film. After standing for 3 minutes and preheating at 60 ° C. for 3 minutes, the aqueous base coating composition (Y-17) obtained in Example 17 was applied on the uncured primer coating film to a cured film thickness of 25 μm. The base coating film was formed by coating with an electrostatic rotary atomizer. After standing for 5 minutes and preheating at 60 ° C. for 5 minutes, “Clear Paint (Z-1)” as a clear paint on the uncured base coating film was statically adjusted to a cured film thickness of 30 μm. It was painted using an electric rotary atomizing coating machine to form a clear coating film. After leaving it for 7 minutes, it heated at 80 degreeC for 30 minutes, the said primer coating film, the base coating film, and the clear coating film were hardened simultaneously, and the test board was produced.

Example 41 and Comparative Examples 20-21
A test plate was prepared in the same manner as in Example 40 except that the coating composition or the cured film thickness shown in Table 4 below was changed.

Evaluation Test Using the test plates obtained in Examples 19 to 41 and Comparative Examples 12 to 21, evaluation was performed by the following test method. The evaluation results are shown in Table 4 below.

(Test method)
Smoothness: The test plate was evaluated using the Wc value measured by “Wave Scan DOI” (trade name, manufactured by BYK Gardner). It shows that the smoothness of a coating surface is so high that Wc value is small.

  Sharpness: The test plate was evaluated using a Wa value measured by “Wave Scan DOI” (trade name, manufactured by BYK Gardner). The smaller the Wa value, the higher the clearness of the paint surface.

Water resistance adhesion: After immersing the test plate in warm water at 40 ° C. for 240 hours, pulling it up and drying at 20 ° C. for 12 hours, the multi-layer coating film of the test plate is cut into a grid shape with a cutter so as to reach the substrate, Make 100 2mm x 2mm gobangs. Then, the adhesive cellophane tape was stuck on the surface, and the remaining state of the goby eye coating after the tape was rapidly peeled off at 20 ° C. was examined.
(Double-circle): 100 galvanic coatings remain | survive and the small edge of a coating film does not arise in the edge of a cutting of a cutter.
◯: 100 gobanged paint films remain, but small edges of the paint film are formed at the edge of the cutter.
(Triangle | delta): 90-99 pieces of gobang eyes coating films remain | survive.
X: The remaining number of gobang eye coats is 89 or less.

Claims (10)

At least one of a polyester resin (A), a film-forming resin (B), and a crosslinking agent (C) having a hydroxyl value of less than 10 mgKOH / g, an acid value of less than 30 mgKOH / g, and a number average molecular weight of 8,000 or more. As a blocked isocyanate group represented by the following general formula (I)

[In the formula (I), R ¹ , R ² , R ⁴ and R ⁵ independently represent a hydrocarbon group having 1 to 12 carbon atoms, and R ³ is a straight chain having 1 to 12 carbon atoms or Represents a branched alkylene group. ],
Blocked isocyanate group represented by the following general formula (II)

[In formula (II), R ² , R ³ , R ⁴ and R ⁵ are the same as above. ],
And a blocked isocyanate group represented by the following general formula (III)

Wherein ^{(III), R 2, R} 3, R 4 and ^{R 5} are as defined above, ^{R 6} represents a hydrocarbon group having 1 to 12 carbon atoms. ]
An aqueous coating composition comprising an active methylene type blocked polyisocyanate compound (CB) having at least one type of blocked isocyanate group selected from:   A straight-chain alkylene group containing an aliphatic polybasic acid in the range of 15 to 100 mol% based on the total acid component constituting the polyester resin (A) and having 4 or more carbon atoms based on the total alcohol component The water-based paint composition according to claim 1, comprising an aliphatic polyhydric alcohol having a content of 50 to 100 mol%. The water-based coating composition according to claim 1 or 2, wherein, in the general formula (I), R ¹ is an isopropyl group. The water-based coating composition according to any one of claims 1 to 3, wherein in the general formula (III), R ⁶ is an isopropyl group. The active methylene type block polyisocyanate compound (CB) is represented by the following general formula (IV)

[In Formula (IV), R < ¹ > is the same as the above, and may be the same as or different from each other. ]
A blocked polyisocyanate compound intermediate (cb3-1) having a blocked isocyanate group represented by the formula (II) and a secondary alcohol (cb4) represented by the following general formula (VI)

[In the formula (VI), R ² , R ³ , R ⁴ and R ⁵ are the same as described above. ]
The water-based coating composition according to any one of claims 1 to 5, which is obtained by reacting The active methylene type block polyisocyanate compound (CB) is represented by the following general formula (V)

[In formula (V), R ⁶ is the same as described above, and R ⁷ represents a hydrocarbon group having 1 to 12 carbon atoms. ]
The water-based coating composition according to claim 1, 2, 4 or 5, which is obtained by reacting a blocked polyisocyanate compound intermediate (cb3-2) having a blocked isocyanate group represented by the above and the secondary alcohol (cb4). .   The water-based coating composition according to any one of claims 1 to 6, wherein the active methylene type block polyisocyanate compound (CB) is a block polyisocyanate compound (CB ') having a hydrophilic group. The following steps (1-1) to (1-4),
Step (1-1): A step of applying a primer coating (X) on an article to form a primer coating film,
Step (1-2): a step of applying a water-based base coating (Y) on the uncured primer coating formed in the step (1-1) to form a base coating,
Step (1-3): a step of applying a clear coating (Z) containing a polyisocyanate compound on the uncured base coating formed in the step (1-2) to form a clear coating, and a step (1-4): The temperature of 70 to 120 ° C. of the uncured primer coating film, the uncured base coating film, and the uncured clear coating film formed in steps (1-1) to (1-3). A method for forming a multilayer coating film in which the steps of heat-curing at the same time are sequentially performed, wherein the aqueous base paint (Y) is the aqueous paint composition according to any one of claims 1 to 7. A method for forming a multilayer coating film. The following steps (2-1) to (2-5),
Step (2-1): A step of applying a primer paint (X) on an object to form a primer coating film,
Step (2-2): A step of coating the water-based base coating (Y) on the uncured primer coating formed in the step (2-1) to form a base coating,
Step (2-3): On the uncured base coating film formed in the step (2-2), an aqueous second base coating material (Y2) containing a glitter pigment is applied to form a second base coating film. Forming step,
Step (2-4): a step of applying a clear coating (Z) containing a polyisocyanate compound on the uncured second base coating film formed in the step (2-3) to form a clear coating film, And Step (2-5): The uncured primer coating, uncured base coating, and uncured clear coating formed in Steps (2-1) to (2-4) at 70 to 120 ° C. a multilayer coating film forming method of sequentially performing the steps allowed to heat curing at the same time at temperature, the aqueous base coating composition (Y) is, it is an aqueous coating composition according to any one of claims 1-7 A method for forming a multilayer coating film characterized by the following.   The aqueous base paint (Y) contains 50 to 200 parts by mass of titanium white with respect to 100% by mass of the resin solid content, and the L value of the coating film to which the aqueous base paint (Y) is applied is 60 or more, The water-based second base paint (Y2) further contains 1 to 30 parts by mass of a luster pigment with respect to 100% by mass of the resin solid content.