Acrylic urethane composite resin, aqueous coating composition, and method for forming multilayer coating film

Abstract

To provide an acrylic urethane composite resin in which a coating film formed from an aqueous coating composition is excellent in chipping resistance and flip-flop property when being used as a component of the aqueous coating composition.SOLUTION: An acrylic urethane composite resin contains (A) a urethane resin part obtained from components containing (a1) a polyisocyanate component and (a2) (a2-1) a compound having two or more hydroxyl groups and one or more polymerizable unsaturated groups, and (a2-2) a polyol component containing polycarbonate polyol, and (B) an acrylic resin part obtained from a component containing (b) a compound having a polymerizable unsaturated group and no or one hydroxyl group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an acrylic urethane composite resin, an aqueous coating composition, and a method for forming a multilayer coating film. [Background technology]

[0002] In the field of automotive paints, metallic paint colors are one of the most highly sought-after colors by users. A metallic finish is a texture characterized by a large difference in brightness between the highlight and shade areas; it appears shiny when viewed nearly perpendicular to the painted surface (highlights) and dark when viewed obliquely from above (shades). This large difference in brightness between the highlight and shade areas is said to have a high flip-flop effect.

[0003] Furthermore, one of the performance requirements for multi-layer coatings for automobiles is chipping resistance (chipping: damage to the coating caused by pebbles or other objects flying off the road and hitting the coating), but when attempts are made to improve chipping resistance by using an acrylic urethane composite resin, which has excellent physical properties, the flip-flop properties described above may be reduced.

[0004] Patent Document 1 discloses a method for producing a copolymer (CP) by the steps of: (i) first charging an aqueous dispersion of at least one polyurethane; and (ii) polymerizing a mixture of olefinically unsaturated monomers in the presence of the polyurethane from (i), wherein (a) a water-soluble initiator is used; (b) the olefinically unsaturated monomers are metered in so that their concentration in the reaction solution does not exceed 6.0% by mass relative to the total amount of olefinically unsaturated monomers used in the polymerization during the entire reaction time; and (c) the mixture of olefinically unsaturated monomers includes at least one polyolefinically unsaturated monomer. The present invention discloses an aqueous coating composition that has excellent stone-mark resistance, the composition comprising at least one linear hydroxy-functional reaction product (R) having an acid number of less than KOH / g, the preparation of which involves the use of at least one compound (v) having two functional groups (va) and an aliphatic or araliphatic hydrocarbyl group (vb) having from 12 to 70 carbon atoms disposed between said functional groups. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication 2017-509725 Summary of the Invention [Problem to be solved by the invention]

[0006] In the technique described in Patent Document 1, although the coating film formed from the aqueous coating composition has excellent resistance to scratches caused by stones, the flip-flop properties are sometimes insufficient.

[0007] An object of the present invention is to provide an acrylic-urethane composite resin which, when used as a constituent component of an aqueous coating composition, gives a coating film formed from the aqueous coating composition that is excellent in chipping resistance and flip-flop properties. [Means for solving the problem]

[0008] As a result of extensive research into achieving the above-mentioned object, the present inventors have found that the above-mentioned object can be achieved by an acrylic urethane composite resin (AB) comprising: a urethane resin portion (A) obtained from constituent components including a polyisocyanate component (a1); and a polyol component (a2) containing a compound (a2-1) having two or more hydroxyl groups and one or more polymerizable unsaturated groups, and a polycarbonate polyol (a2-2); and an acrylic resin portion (B) obtained from a constituent component (b) containing a compound having a polymerizable unsaturated group and no hydroxyl groups or having one hydroxyl group.

[0009] That is, the present invention provides the following <1> ~ <9> It is related to. <1> (A) (a1) a polyisocyanate component; (a2) a urethane resin portion obtained from constituent components including (a2-1) a compound having two or more hydroxyl groups and one or more polymerizable unsaturated groups, and (a2-2) a polyol component including a polycarbonate polyol; (B)(b) An acrylic urethane composite resin comprising an acrylic resin portion obtained from a constituent containing a compound having a polymerizable unsaturated group and no hydroxyl group or one hydroxyl group. <2> The polycarbonate polyol (a2-2) includes a polycarbonate polyol (a2-2') made from a linear or branched aliphatic polyol having 3 to 10 carbon atoms. <1> The acrylic urethane composite resin according to claim 1. <3> The polycarbonate polyol (a2-2) includes a polycarbonate polyol having a number average molecular weight in the range of 1,000 to 5,000. <1> or <2> The acrylate composite resin according to claim 1. <4> The polyol component (a2) further contains polytetramethylene ether glycol (a2-3). <1> ~ <3> The acrylic urethane composite resin according to any one of the above. <5> It has a core-shell structure consisting of a shell portion made of the urethane resin portion (A) and a core portion made of the acrylic resin portion (B). <1> ~ <4> The acrylic urethane composite resin according to any one of the above. <6> <1> ~ <5> 1. An aqueous coating composition comprising the acrylic urethane composite resin (AB) according to any one of the above. <7> Further, the composition contains at least one resin selected from an acrylic resin (C) and a polyester resin (D). <6> The aqueous coating composition according to claim 1. <8> Further containing a curing agent (E), <6> or <7> The aqueous coating composition according to claim 1. <9> Step (1): On the object to be coated, <6> ~ <8> a step of applying the aqueous coating composition according to claim 1 to form a base coat film; Step (2): A step of applying a clear coat paint composition onto the base coat film formed in step (1) to form a clear coat film; and Step (3): A method for forming a multilayer coating film, comprising a step of simultaneously heating and curing the base coat coating film formed in step (1) and the clear coat coating film formed in step (2). [Effects of the Invention]

[0010] According to the acrylic urethane composite resin of the present invention, when used as a constituent component of an aqueous coating composition, a coating film having excellent chipping resistance and flip-flop properties can be obtained. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below, but these are examples of preferred embodiments, and the present invention is not limited to these details.

[0012] [Acrylic urethane composite resin (AB)] The acrylic urethane composite resin (AB) of the present invention comprises a urethane resin portion (A) obtained from constituent components including a polyisocyanate component (a1), a polyol component (a2) including a compound (a2-1) having two or more hydroxyl groups and one or more polymerizable unsaturated groups, and a polycarbonate polyol (a2-2); The acrylic urethane composite resin comprises an acrylic resin portion (B) obtained from a component (b) containing a compound having a polymerizable unsaturated group and having no hydroxyl group or one hydroxyl group.

[0013] The acrylic urethane composite resin (AB) can be produced by a conventionally known method for producing an acrylic urethane composite resin. However, from the viewpoint of production stability, it is preferable to produce it by the following method (consisting of the following production steps 1 to 3).

[0014] Manufacturing Process 1. First, the urethane resin portion (A) is synthesized in the presence of compound (b), which is a component of the acrylic resin portion (B), and has a polymerizable unsaturated group and either no hydroxyl group or one hydroxyl group.

[0015] Production step 2: Next, deionized water is added and emulsified to obtain an aqueous dispersion. If necessary, a chain extension reaction and desolvation are further carried out.

[0016] Production step 3: Next, a polymerization initiator is added to the aqueous dispersion to carry out a polymerization reaction, thereby obtaining an acrylic urethane composite resin (AB) containing a urethane resin portion (A) and an acrylic resin portion (B).

[0017] Manufacturing process 1 First, the urethane resin portion (A) is synthesized in the presence of a compound (b) that has a polymerizable unsaturated group and has no hydroxyl group or one hydroxyl group, which is a component of the acrylic resin portion (B).

[0018] The polymerizable unsaturated group is an unsaturated group capable of radical polymerization, and specific examples thereof include an acryloyl group, a methacryloyl group, a vinyl group, an allyl group, a propenyl group, an isopropenyl group, a maleimide group, a vinyl ether group, etc. Among these polymerizable unsaturated groups, from the viewpoint of excellent reactivity, an acryloyl group and a methacryloyl group are preferred, and an acryloyl group is particularly preferred.

[0019] In addition, in this 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."

[0020] Examples of the compound (b) having a polymerizable unsaturated group and no hydroxyl group or one hydroxyl group include a compound (b1) having one polymerizable unsaturated group and no hydroxyl group or one hydroxyl group, and a compound (b2) having two or more polymerizable unsaturated groups and no hydroxyl group or one hydroxyl group.

[0021] Examples of the compound (b1) having one polymerizable unsaturated group and having no hydroxyl group or one hydroxyl group include a compound (b1-1) having one hydroxyl group and one polymerizable unsaturated group, and a compound (b1-2) having no hydroxyl group and one polymerizable unsaturated group.

[0022] Examples of the compound (b1-1) having one hydroxyl group and one polymerizable unsaturated group include monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone-modified products of the monoesters; N-hydroxymethyl (meth)acrylamide; allyl alcohol; and hydroxyl group-containing polymerizable unsaturated monomers, such as (meth)acrylates having a polyoxyethylene chain with a hydroxyl group at the molecular terminal.

[0023] These compounds (b1-1) having one hydroxyl group and one polymerizable unsaturated group can be used singly or in combination of two or more.

[0024] Examples of the compound (b1-2) having no hydroxyl group and one polymerizable unsaturated group include methyl(meth)acrylate, ethyl(meth)acrylate, n-propyl(meth)acrylate, i-propyl(meth)acrylate, n-butyl(meth)acrylate, i-butyl(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, Alkyl or cycloalkyl (meth)acrylates such as acrylate, stearyl (meth)acrylate, "isostearyl acrylate" (trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd.), cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate, and tricyclodecanyl (meth)acrylate; polymerizable unsaturated monomers having an isobornyl group such as isobornyl (meth)acrylate; polymerizable unsaturated monomers having an adamantyl group such as adamantyl (meth)acrylate; polymerizable unsaturated monomers having a tricyclodecenyl group, such as tricyclodecenyl (meth)acrylate; polymerizable unsaturated monomers containing an aromatic ring, such as benzyl (meth)acrylate, styrene, α-methylstyrene, and vinyltoluene; polymerizable unsaturated monomers having an alkoxysilyl group, such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, γ-(meth)acryloyloxypropyltrimethoxysilane, and γ-(meth)acryloyloxypropyltriethoxysilane; Perfluoroalkyl (meth)acrylates such as perfluorobutylethyl (meth)acrylate and perfluorooctylethyl (meth)acrylate; polymerizable unsaturated monomers having a fluorinated alkyl group such as fluoroolefins; polymerizable unsaturated monomers having a photopolymerizable functional group such as a maleimide group; vinyl compounds such as N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, and vinyl acetate; carboxyl group-containing polymerizable unsaturated monomers such as (meth)acrylic acid, maleic acid, crotonic acid, and β-carboxyethyl acrylate;Examples of such polymerizable unsaturated monomers include nitrogen-containing polymerizable unsaturated monomers such as (meth)acrylonitrile, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, and adducts of glycidyl (meth)acrylate and amines; epoxy group-containing polymerizable unsaturated monomers such as glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, 3,4-epoxycyclohexylpropyl (meth)acrylate, and allyl glycidyl ether; and (meth)acrylates having a polyoxyethylene chain with an alkoxy group at the molecular terminal.

[0025] These compounds (b1-2) having no hydroxyl group and one polymerizable unsaturated group can be used singly or in combination of two or more.

[0026] The compound (b1) having one polymerizable unsaturated group and having no hydroxyl group or having one hydroxyl group preferably includes a compound (b1-2) having no hydroxyl group but having one polymerizable unsaturated group, from the viewpoint of production stability, etc.

[0027] When the compound (b1) having one polymerizable unsaturated group and either no hydroxyl group or one hydroxyl group is contained, the content of the compound (b1) having one polymerizable unsaturated group and either no hydroxyl group or one hydroxyl group is preferably in the range of 5 to 99 mass %, more preferably in the range of 40 to 98 mass %, and even more preferably in the range of 50 to 98 mass %, based on the total solid content of the acrylic resin portion (B), from the viewpoint of production stability, etc.

[0028] Examples of the compound (b2) having two or more polymerizable unsaturated groups and having no hydroxyl group or one hydroxyl group include a compound (b2-1) having one hydroxyl group and two or more polymerizable unsaturated groups, and a compound (b2-2) having no hydroxyl group but two or more polymerizable unsaturated groups.

[0029] Examples of the compound (b2-1) having one hydroxyl group and two or more polymerizable unsaturated groups include glycerol di(meth)acrylate and 1,1,1-trishydroxymethylethane di(meth)acrylate.

[0030] These compounds (b2-1) having one hydroxyl group and two or more polymerizable unsaturated groups can be used singly or in combination of two or more.

[0031] Examples of the compound (b2-2) having no hydroxyl group and two or more polymerizable unsaturated groups 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, (meth)acrylate, pentaerythritol tetra(meth)acrylate, 1,1,1-trishydroxymethylethane tri(meth)acrylate, 1,1,1-trishydroxymethylpropane tri(meth)acrylate, methylene bis(meth)acrylamide, ethylene bis(meth)acrylamide, triallyl isocyanurate, diallyl terephthalate, divinylbenzene, polyethylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, and the like.

[0032] These compounds (b2-2) which do not have a hydroxyl group and have two or more polymerizable unsaturated groups can be used alone or in combination of two or more.

[0033] From the viewpoint of production stability and the like, the compound (b2) having two or more polymerizable unsaturated groups and having no hydroxyl group or one hydroxyl group preferably includes a compound (b2-2) having two or more polymerizable unsaturated groups but no hydroxyl group.

[0034] The compound (b2) having two or more polymerizable unsaturated groups and no hydroxyl group or one hydroxyl group has the function of imparting a crosslinked structure to the copolymer.

[0035] When the composition contains the compound (b2) having two or more polymerizable unsaturated groups and either no hydroxyl group or one hydroxyl group, the content of the compound (b2) having two or more polymerizable unsaturated groups and either no hydroxyl group or one hydroxyl group is preferably within a range of 0.5 to 50 mass %, more preferably within a range of 1.0 to 40 mass %, and even more preferably within a range of 2.0 to 20 mass %, based on the total solid content of the acrylic resin portion (B), from the viewpoint of the flip-flop properties of the coating film to be formed, etc.

[0036] Synthesis of urethane resin part (A) The urethane resin portion (A) can be obtained from constituent components including a polyisocyanate component (a1), a polyol component (a2) containing a compound (a2-1) having two or more hydroxyl groups and one or more polymerizable unsaturated groups and a polycarbonate polyol (a2-2), and, if necessary, a compound containing both an active hydrogen group and an ion-forming group as a water-dispersible group-imparting component.

[0037] Polyisocyanate component (a1) Examples of the polyisocyanate component (a1) include alicyclic polyisocyanates, aliphatic polyisocyanates, araliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of the polyisocyanates.

[0038] The polyisocyanate component (a1) preferably contains an alicyclic polyisocyanate from the viewpoint of chipping resistance, flip-flop properties, weather resistance, etc. of the coating film to be formed.

[0039] 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, Alicyclic diisocyanates such as 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated xylylene diisocyanate) or a mixture thereof, methylenebis(4,1-cyclohexanediyl)diisocyanate (common name: hydrogenated MDI), and 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)-bicyclo(2.2.1)heptane Examples include alicyclic triisocyanates such as (2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, and 6-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane.

[0040] 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-butylene diisocyanate, 2,4,4 or 2,2,4-trimethylhexamethylene diisocyanate, dimer acid diisocyanate, methyl 2,6-diisocyanatohexanoate (trivial name: lysine diisocyanate), aliphatic diisocyanates such as 2-isocyanatoethyl 2,6-diisocyanatohexanoate, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, and 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane.

[0041] Examples of the aromatic aliphatic polyisocyanate include aromatic aliphatic diisocyanates such as methylenebis(4,1-phenylene)diisocyanate (common name: MDI), 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene (common name: tetramethylxylylene diisocyanate) or a mixture thereof; and aromatic aliphatic triisocyanates such as 1,3,5-triisocyanatomethylbenzene.

[0042] Examples of the aromatic polyisocyanate include aromatic diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4-tolylene diisocyanate (common name: 2,4-TDI) or 2,6-tolylene diisocyanate (common name: 2,6-TDI) or a mixture thereof, 4,4'-toluidine diisocyanate, and 4,4'-diphenyl ether diisocyanate; aromatic triisocyanates such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, and 2,4,6-triisocyanatotoluene; and aromatic tetraisocyanates such as 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate.

[0043] Furthermore, examples of the derivatives of the polyisocyanates include dimers, trimers, biurets, allophanates, uretdione, uretoimine, isocyanurates, oxadiazinetrione, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI), crude TDI, and the like of the polyisocyanates.

[0044] The above polyisocyanates and derivatives thereof may be used alone or in combination of two or more kinds.

[0045] The above polyisocyanates may be used in the form of blocked isocyanates blocked with a blocking agent.

[0046] Examples of the blocking agent include phenol-based agents such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; lactam-based agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; aliphatic alcohol-based agents such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, and lauryl alcohol; ether-based agents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and methoxymethanol; benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, butyl lactate, methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate ... Alcohol-based compounds such as hydroxyethyl methacrylate; oxime-based compounds such as formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, and cyclohexane oxime; active methylene-based compounds such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone; butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, and methylthiophene mercaptans such as acetanilide, acetanisidide, acetotoluide, acrylamide, methacrylamide, acetic amide, stearic acid amide, benzamide, and other acid amides; imides such as succinimide, phthalic acid imide, and maleic acid imide; amines such as diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, and butylphenylamine; imidazoles such as imidazole and 2-ethylimidazole;Examples of suitable azole compounds include urea-based compounds such as urea, thiourea, ethyleneurea, ethylenethiourea, and diphenylurea; carbamate ester-based compounds such as N-phenylphenylcarbamate; imine-based compounds such as ethyleneimine and propyleneimine; sulfite-based compounds such as sodium bisulfite and potassium bisulfite; and azole-based compounds. Examples of suitable azole-based compounds include pyrazole or pyrazole derivatives such as pyrazole, 3,5-dimethylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 4-bromo-3,5-dimethylpyrazole, and 3-methyl-5-phenylpyrazole; imidazole or imidazole derivatives such as imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole, and 2-phenylimidazole; and imidazoline derivatives such as 2-methylimidazoline and 2-phenylimidazoline.

[0047] When the blocking reaction is carried out (reaction of the blocking agent), a solvent may be added as necessary. The solvent used in the blocking reaction is preferably one that is not reactive with the isocyanate group, and examples thereof include ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, and N-methyl-2-pyrrolidone (NMP).

[0048] Polyol component (a2) The polyol component (a2) is a compound having at least two hydroxyl groups in one molecule.

[0049] The polyol component (a2) includes a compound (a2-1) having two or more hydroxyl groups and one or more polymerizable unsaturated groups and a polycarbonate polyol (a2-2).

[0050] The compound (a2-1) having two or more hydroxyl groups and one or more polymerizable unsaturated groups provides a polymerizable unsaturated group to the side chain of the urethane resin portion (A).

[0051] Examples of the compound (a2-1) having two or more hydroxyl groups and one or more polymerizable unsaturated groups include a reaction product of a glycidyl group-containing compound with (meth)acrylic acid, and a reaction product of a tri- or higher functional polyol with (meth)acrylic acid.

[0052] The compound (a2-1) having two or more hydroxyl groups and one or more polymerizable unsaturated groups can be commercially available. Examples of commercially available products under the trade names include "Epoxy Ester 40EM," "Epoxy Ester 70PA," "Epoxy Ester 200PA," "Epoxy Ester 80MFA," "Epoxy Ester 3002M," "Epoxy Ester 3002A," "Epoxy Ester 3000MK," and "Epoxy Ester 3000A" (all manufactured by Kyoeisha Chemical Co., Ltd.), "Denacol Acrylate DA-212," "Denacol Acrylate DA-314," "Denacol Acrylate DA-911M," "Denacol Acrylate DA-920," and "Denacol Acrylate DA-931" (all manufactured by Nagase ChemteX Corporation), "Blenmer GLM," "Blenmer GLM-EX," and "Blenmer GLM-R" (all manufactured by NOF Corporation).

[0053] The compound (a2-1) having two or more hydroxyl groups and one or more polymerizable unsaturated groups preferably includes a compound having two or more hydroxyl groups and one polymerizable unsaturated group, from the viewpoint of the flip-flop properties of the coating film to be formed.

[0054] The compound having two or more hydroxyl groups and one polymerizable unsaturated group can be commercially available, for example, under the trade names "BLEMMER GLM," "BLEMMER GLM-EX," and "BLEMMER GLM-R" (all manufactured by NOF Corporation).

[0055] From the viewpoint of the chipping resistance and flip-flop properties of the coating film to be formed, the content of the compound (a2-1) having two or more hydroxyl groups and one or more polymerizable unsaturated groups is preferably within a range of 1.0 to 15 mass %, more preferably within a range of 2.0 to 10 mass %, and even more preferably within a range of 3.0 to 8.0 mass %, based on the total solid content of the polyol component (a2).

[0056] The polycarbonate polyol (a2-2) is a compound obtained by a conventional polycondensation reaction of a known polyol component with a carbonylating agent. Examples of the polyol component include a diol component and a polyhydric alcohol component such as a trihydric or higher alcohol.

[0057] Examples of the diol component include linear diols such as 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol; 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 2-ethyl-1,6-hexanediol, 2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3- Examples of suitable diol components include branched diols such as propanediol, 2-methyl-1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, and 2-ethyl-1,3-hexanediol; alicyclic diols such as 1,3-cyclohexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol; aromatic diols such as p-xylenediol and p-tetrachloroxylenediol; and ether diols such as diethylene glycol and dipropylene glycol. These diol components can be used alone or in combination of two or more.

[0058] Examples of the trihydric or higher alcohol include glycerin, trimethylolethane, trimethylolpropane, a dimer of trimethylolpropane, pentaerythritol, etc. These trihydric or higher alcohols can be used alone or in combination of two or more.

[0059] From the viewpoint of chipping resistance of the coating film to be formed, the polycarbonate polyol (a2-2) preferably contains a polycarbonate polyol (a2-2') made from a linear or branched aliphatic polyol having 3 to 10 carbon atoms.

[0060] Examples of the linear or branched aliphatic polyol having 3 to 10 carbon atoms include linear diols such as 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol; branched diols such as 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 2-ethyl-1,6-hexanediol, 2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, and 2-ethyl-1,3-hexanediol; and ether diols such as diethylene glycol and dipropylene glycol. These may be used alone or in combination of two or more.

[0061] As the carbonylating agent, known agents can be used. Specific examples include alkylene carbonate, dialkyl carbonate, diallyl carbonate, phosgene, etc., and these can be used alone or in combination of two or more. Among these, preferred examples include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, diphenyl carbonate, etc.

[0062] The number average molecular weight of the polycarbonate polyol (a2-2) is preferably within a range of 1,000 to 5,000, more preferably within a range of 1,300 to 4,500, and even more preferably within a range of 1,500 to 3,500, from the viewpoints of chipping resistance and flip-flop properties of the coating film to be formed.

[0063] From the viewpoint of chipping resistance and flip-flop properties of the coating film to be formed, the content of the polycarbonate polyol (a2-2) is preferably within a range of 20 to 95 mass %, more preferably within a range of 40 to 95 mass %, and even more preferably within a range of 70 to 90 mass %, based on the total solid content of the polyol component (a2).

[0064] When the polycarbonate polyol (a2-2) contains a polycarbonate polyol (a2-2') made from a linear or branched aliphatic polyol having 3 to 10 carbon atoms, the content of the polycarbonate polyol (a2-2') made from a linear or branched aliphatic polyol having 3 to 10 carbon atoms is, from the viewpoint of chipping resistance of the coating film to be formed, preferably 1 to 100 mass %, more preferably 50 to 100 mass %, and even more preferably 70 to 100 mass %, based on the total solids content of the polycarbonate polyol (a2-2).

[0065] From the viewpoint of chipping resistance of the coating film to be formed, it is preferable that the polyol component (a2) further contains polytetramethylene ether glycol (a2-3).

[0066] The number average molecular weight of the polytetramethylene ether glycol (a2-3) is preferably within a range of 500 to 10,000, more preferably within a range of 1,000 to 5,000, and even more preferably within a range of 1,600 to 4,000, from the viewpoint of the chipping resistance of the coating film to be formed.

[0067] When the polyol component (a2) contains polytetramethylene ether glycol (a2-3), the content of the polytetramethylene ether glycol (a2-3) is preferably within a range from 1 to 85 mass %, more preferably from 1 to 70 mass %, and even more preferably from 5 to 50 mass %, based on the total solid content of the polyol component (a2), from the viewpoints of chipping resistance and flip-flop properties of the coating film to be formed.

[0068] The polyol component (a2) can include a compound (a2-1) having two or more hydroxyl groups and one or more polymerizable unsaturated groups, a polycarbonate polyol (a2-2), and a polytetramethylene ether glycol (a2-3) other than a polyol component (a2-4).

[0069] Examples of the polyol component (a2-4) other than the compound (a2-1) having two or more hydroxyl groups and one or more polymerizable unsaturated groups, the polycarbonate polyol (a2-2), and the polytetramethylene ether glycol (a2-3) include low-molecular-weight polyols such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 1,4-butylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexane glycol, 2,5-hexanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, tricyclodecane dimethanol, and 1,4-cyclohexane dimethanol. These low-molecular-weight polyols can be used alone or in combination of two or more.

[0070] Furthermore, as the polyol component (a2-4) other than the compound (a2-1) having two or more hydroxyl groups and one or more polymerizable unsaturated groups, the polycarbonate polyol (a2-2), and the polytetramethylene ether glycol (a2-3), high molecular weight polyols such as polyether polyols other than polytetramethylene ether glycol (a2-3), polyester polyols, polyether ester polyols, etc. These high molecular weight polyols can be used alone or in combination of two or more.

[0071] Examples of polyether polyols other than the polytetramethylene ether glycol (a2-3) include alkylene oxide adducts of the low molecular weight polyols, ring-opening (co)polymers of alkylene oxides or cyclic ethers (tetrahydrofuran, etc.), etc. Specific examples include polyethylene glycol, polypropylene glycol, ethylene glycol-propylene glycol (block or random) copolymers, polyhexamethylene glycol, polyoctamethylene glycol, etc.

[0072] The polyether polyols other than the polytetramethylene ether glycol (a2-3) can be used singly or in combination of two or more.

[0073] Examples of the polyester polyols include those obtained by polycondensing dicarboxylic acids (anhydrides) such as adipic acid, succinic acid, sebacic acid, glutaric acid, maleic acid, fumaric acid, and phthalic acid with low-molecular-weight polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,8-octamethylenediol, and neopentyl glycol under conditions of excess hydroxyl groups. Specific examples include ethylene glycol-adipic acid condensates, butanediol-adipic acid condensates, hexamethylene glycol-adipic acid condensates, and ethylene glycol-propylene glycol-adipic acid condensates, as well as polylactone polyols obtained by ring-opening polymerization of lactones using glycols as initiators. These polyester polyols can be used alone or in combination of two or more.

[0074] Examples of the polyetherester polyol include those obtained by adding an ether group-containing polyol (such as the polytetramethylene ether glycol (a2-3), a polyether polyol other than the polytetramethylene ether glycol (a2-3), or diethylene glycol) or a mixture of this with other glycols to a dicarboxylic acid (anhydride) such as those exemplified for the polyester polyols, and reacting it with an alkylene oxide, such as polytetramethylene glycol-adipic acid condensate. These polyetherester polyols can be used alone or in combination of two or more.

[0075] Compounds having both active hydrogen groups and ion-forming groups Examples of compounds having both an active hydrogen group and an ion-forming group include compounds having two or more hydroxyl groups and one or more carboxyl groups in one molecule, compounds having two or more hydroxyl groups and one or more sulfonic acid groups in one molecule, and compounds having two or more amino groups and one or more carboxyl groups in one molecule, and these can be used alone or in combination of two or more.

[0076] Among these, compounds having both the active hydrogen group and the ion-forming group are preferably compounds having two or more hydroxyl groups and one or more carboxyl groups in one molecule, and compounds having two or more hydroxyl groups and one or more sulfonic acid groups in one molecule.

[0077] In the present invention, compounds having both two or more hydroxyl groups and an ion-forming group, such as the above-mentioned compounds having two or more hydroxyl groups and one or more carboxyl groups in one molecule, and compounds having two or more hydroxyl groups and one or more sulfonic acid groups in one molecule, are considered to be included in the polyol component (a2).

[0078] Examples of the compound having two or more hydroxyl groups and one or more carboxyl groups in one molecule include alkanolcarboxylic acid compounds such as dimethylolpropionic acid, dimethylolacetic acid, dimethylolbutanoic acid, dimethylolheptanoic acid, dimethylolnonanoic acid, 1-carboxy-1,5-pentylenediamine, dihydroxybenzoic acid, and 3,5-diaminobenzoic acid, and half ester compounds of polyoxypropylenetriol with maleic anhydride and / or phthalic anhydride.

[0079] Examples of the compound having two or more hydroxyl groups and one or more sulfonic acid groups in one molecule include 2-sulfonic acid-1,4-butanediol, 5-sulfonic acid-di-β-hydroxyethyl isophthalate, and N,N-bis(2-hydroxyethyl)aminoethylsulfonic acid.

[0080] As the compound having both the above-mentioned active hydrogen group and the ion-forming group, it is preferable to use a compound having two or more hydroxyl groups and one or more carboxyl groups in one molecule, from the viewpoint of flexibility of the coating film to be formed.

[0081] From the viewpoint of water dispersion stability and the like, the urethane resin portion (A) preferably contains the compound having both the active hydrogen group and the ion-forming group.

[0082] When the compound having two or more hydroxyl groups and one or more carboxyl groups is used, the amount used is preferably within a range of 1 to 30% by mass, more preferably within a range of 1 to 25% by mass, and even more preferably within a range of 1 to 20% by mass, relative to the total amount of compounds constituting the polyol component (a2), from the viewpoint of the flip-flop properties of the coating film to be formed.

[0083] The method for producing the urethane resin portion (A) is not particularly limited, and conventionally known methods can be used. For example, a prepolymer can be synthesized by urethane-forming a polyisocyanate component (a1) and a polyol component (a2) in an organic solvent, or by adding a compound having both an active hydrogen group and an ion-forming group, if necessary. If necessary, the prepolymer can be further reacted with a compound (b1-1) having one hydroxyl group and one polymerizable unsaturated group and / or a compound (b2-1) having one hydroxyl group and two or more polymerizable unsaturated groups to form a compound having a terminal polymerizable unsaturated group. A polymerization inhibitor can also be added if necessary.

[0084] In the urethane-forming reaction of the polyisocyanate component (a1) and the polyol component (a2), a catalyst can be used as needed.

[0085] Examples of the catalyst include bismuth carboxylate compounds such as tris(2-ethylhexanoate)bismuth(III); organotin compounds such as dibutyltin dilaurate, dibutyltin dioctoate, and stannous octoate; and tertiary amine compounds such as triethylamine and triethylenediamine.

[0086] The urethane reaction is preferably carried out at a temperature of 50 to 120°C.

[0087] In the synthesis of the urethane resin portion (A), an organic solvent that is inactive to isocyanates and does not interfere with the urethane reaction can be used. Examples of such organic solvents include aromatic hydrocarbon solvents such as toluene and xylene, ester solvents such as ethyl acetate and butyl acetate, and ketone solvents such as acetone and methyl ethyl ketone. Among these, ketone solvents and ester solvents are preferred from the viewpoint of aqueous dispersion stability.

[0088] These organic solvents can be used alone or in combination of two or more.

[0089] The compound (b) having a polymerizable unsaturated group and no or one hydroxyl group can be used instead of a solvent. When using these compounds as a solvent, it is preferable to use a compound (b1-2) having one polymerizable unsaturated group but no hydroxyl group and / or a compound (b2-2) having two or more polymerizable unsaturated groups but no hydroxyl group.

[0090] As the polymerization inhibitor, for example, polymerization inhibitors known per se can be used, such as phenolic hydroxyl group-containing compounds such as di-t-butylhydroxytoluene and methoxyphenol; carbonyl group-containing aromatic compounds such as benzoquinone; nitroso skeleton-containing compounds; and N-oxyl skeleton-containing compounds.

[0091] From the viewpoint of manufacturability, the content ratio of the polyisocyanate component (a1) and the polyol component (a2) in the urethane resin portion (A) is preferably in the range of 1 / 1.01 to 1 / 3.0, more preferably 1 / 1.05 to 1 / 2.0, in terms of the molar ratio of the active hydrogen groups in the polyol component (a2) to the isocyanate groups in the polyisocyanate component (a1).

[0092] The number average molecular weight of the urethane resin portion (A) is preferably within the range of 2,000 to 20,000, more preferably within the range of 2,500 to 15,000, and even more preferably within the range of 3,000 to 10,000, from the viewpoint of chipping resistance and flip-flop properties of the coating film to be formed.

[0093] In this specification, the average molecular weight is a value calculated from a chromatogram measured by gel permeation chromatography using the molecular weight of standard polystyrene as a reference. The gel permeation chromatograph used was an "HLC8120GPC" (manufactured by Tosoh Corporation). Four columns were used: "TSKgel G-4000HXL," "TSKgel G-3000HXL," "TSKgel G-2500HXL," and "TSKgel G-2000HXL" (all manufactured by Tosoh Corporation, trade names). The analysis was performed under the following conditions: mobile phase: tetrahydrofuran, measurement temperature: 40°C, flow rate: 1 mL / min, and detector: RI.

[0094] Manufacturing process 2 Next, deionized water is added and emulsified to obtain an aqueous dispersion, which is then subjected to a chain extension reaction and solvent removal, if necessary.

[0095] When deionized water is added, a neutralizer for the ion-forming groups may be added, if necessary.

[0096] The neutralizing agent is not particularly limited as long as it can neutralize the ion-forming group, and examples of basic compounds for neutralization include organic amines such as ammonia, diethylamine, ethylethanolamine, diethanolamine, triethanolamine, monoethanolamine, monopropanolamine, isopropanolamine, ethylaminoethylamine, hydroxyethylamine, triethylamine, tributylamine, dimethylethanolamine, diethylenetriamine, N-methylmorpholine, and N-ethylmorpholine; and alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. These neutralizing agents can be used alone or in combination of two or more.

[0097] The neutralizing agent is preferably used in an amount such that the final pH of the aqueous dispersion of the acrylic urethane composite resin (AB) is about 6.0 to 9.0.

[0098] When the neutralizing agent is added, the amount of the neutralizing agent added is preferably 0.1 to 1.5 equivalents, more preferably 0.3 to 1.2 equivalents, relative to the acid group such as a carboxyl group.

[0099] In order to improve the water dispersion stability of the acrylic urethane composite resin (AB), an emulsifier such as a surfactant may be used.

[0100] The emulsifier may be any of the well-known anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, polymeric surfactants, reactive surfactants, etc. When using these, anionic surfactants, nonionic surfactants, or cationic surfactants are preferred because they are inexpensive and can provide good emulsification.

[0101] Examples of the anionic surfactant include alkyl sulfates such as sodium dodecyl sulfate, potassium dodecyl sulfate, and ammonium dodecyl sulfate; sodium dodecyl polyglycol ether sulfate; sodium sulforicinoleate; alkyl sulfonates such as alkali metal salts of sulfonated paraffin and ammonium salts of sulfonated paraffin; fatty acid salts such as sodium laurate, triethanolamine oleate, and triethanolamine abietate; alkylaryl sulfonates such as sodium benzenesulfonate and alkali metal sulfates of alkali phenol hydroxyethylene; high alkyl naphthalene sulfonates; naphthalene sulfonate-formalin condensates; dialkyl sulfosuccinates; polyoxyethylene alkyl sulfate salts; and polyoxyethylene alkylaryl sulfate salts.

[0102] Examples of the nonionic surfactant include ethylene oxide and / or propylene oxide adducts of alcohols having 1 to 18 carbon atoms, ethylene oxide and / or propylene oxide adducts of alkylphenols, and ethylene oxide and / or propylene oxide adducts of alkylene glycols and / or alkylenediamines.

[0103] Examples of the alcohol having 1 to 18 carbon atoms constituting the nonionic surfactant include methanol, ethanol, propanol, 2-propanol, butanol, 2-butanol, tertiary butanol, amyl alcohol, isoamyl alcohol, tertiary amyl alcohol, hexanol, octanol, decane alcohol, lauryl alcohol, myristyl alcohol, palmityl alcohol, and stearyl alcohol. Examples of the alkylphenol include phenol, methylphenol, 2,4-di-tert-butylphenol, 2,5-di-tert-butylphenol, 3,5-di-tert-butylphenol, 4-(1,3-tetramethylbutyl)phenol, 4-isooctylphenol, 4-nonylphenol, 4-tert-octylphenol, and 4-dodecanol. Examples of alkylene glycols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, and 1,6-hexanediol. Examples of alkylene diamines include alkylene glycols in which the alcoholic hydroxyl groups are substituted with amino groups. The ethylene oxide and propylene oxide adducts may be random adducts or block adducts.

[0104] Examples of the cationic surfactant include primary to tertiary amine salts, pyridinium salts, alkylpyridinium salts, and quaternary ammonium salts such as alkyl halide quaternary ammonium salts.

[0105] These surfactants can be used alone or in combination of two or more.

[0106] The emulsification can be carried out by dispersing with a conventional stirrer, but a homomixer, homogenizer, disperser, line mixer, etc. can also be used to obtain a uniform aqueous dispersion with finer particle sizes.

[0107] When carrying out the chain extension reaction (polymerization), a chain extender other than water may be added as necessary to react the urethane resin portion (A) with the chain extender. Known chain extenders having active hydrogen may be used as the chain extender. Specific examples include diamine compounds such as ethylenediamine, hexamethylenediamine, cyclohexanediamine, cyclohexylmethanediamine, and isophoronediamine; triamine compounds such as diethylenetriamine; tetraamine compounds such as triethylenetetraamine; aminoalcohol compounds such as hydroxyethylhydrazine, hydroxyethyldiethylenetriamine, N-(2-aminoethyl)ethanol, 1,3-diamino-2-propanol, and 3-aminopropanediol; and hydrazine.

[0108] As the chain extender, from the viewpoint of the flip-flop properties of the coating film to be formed, it is possible to suitably use tri- or higher functional amine compounds, such as triamine compounds such as diethylenetriamine, and from the viewpoint of the chipping resistance of the coating film to be formed, it is possible to suitably use diamine compounds such as ethylenediamine.

[0109] As the chain extender, an amino alcohol compound such as N-(2-aminoethyl)ethanol can be suitably used for the purpose of introducing a reactive functional group into the acrylic urethane composite resin (AB).

[0110] Manufacturing process 3 Next, a polymerization initiator is added to the aqueous dispersion to carry out a polymerization reaction, thereby obtaining an acrylic urethane composite resin (AB) containing a urethane resin portion (A) and an acrylic resin portion (B).

[0111] Examples of the polymerization initiator include organic peroxides such as benzoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, cumene hydroperoxide, tert-butyl peroxide, tert-butyl peroxylaurate, tert-butylperoxyisopropyl carbonate, tert-butyl peroxyacetate, and diisopropylbenzene hydroperoxide; azobisisobutyronitrile, azobis(2,4-dimethylvaleronitrile), azobis(2-methyl Examples of suitable polymerization initiators include azo compounds such as azobis(N-(2-methylpropionate), azobis(2-methylbutyronitrile), 4,4'-azobis(4-cyanobutanoic acid), dimethylazobis(2-methylpropionate), azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], azobis{2-methyl-N-[2-(1-hydroxybutyl)]-propionamide}, and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamide]; and persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate. These polymerization initiators can be used alone or in combination. Furthermore, the polymerization initiators can also be used in combination with reducing agents such as sugars, sodium formaldehyde sulfoxylate, and iron complexes, as needed, to form redox initiators.

[0112] The amount of the polymerization initiator used is generally preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and preferably 5% by mass or less, more preferably 3% by mass or less, based on the total amount of all monomers used. The method of adding the polymerization initiator is not particularly limited and can be appropriately selected depending on the type and amount. For example, the polymerization initiator can be previously added to the monomer mixture or aqueous medium, or can be added all at once or dropwise during polymerization.

[0113] The polymerization reaction can be carried out by a conventionally known method, for example, an emulsion polymerization method in water, a self-emulsification method, or the like.

[0114] The acrylic urethane composite resin (AB) synthesized in the above production steps 1 to 3 is synthesized as a dispersion in an aqueous solvent, and is thought to have a particulate form.

[0115] Here, the aqueous solvent refers to a solvent containing water as the main component (for example, a solvent in which water accounts for 70 to 100% by mass).

[0116] From the viewpoints of aqueous dispersion stability and the flip-flop properties of the coating film formed, the average particle size of the acrylic urethane composite resin (AB) is preferably within the range of 10 to 5,000 nm, more preferably within the range of 10 to 1,000 nm, particularly preferably within the range of 20 to 500 nm, and even more particularly preferably within the range of 50 to 140 nm.

[0117] The average particle diameter of the acrylic urethane composite resin (AB) can be adjusted to a desired average particle diameter by adjusting particle diameter control factors such as the composition of raw materials (polyisocyanate component, polyol component, amine component, etc.), the type and amount of emulsifier, the emulsifier charging ratio, the type and amount of neutralizer, etc.

[0118] In this specification, the average particle size of the acrylic urethane composite resin (AB) is a value measured at 20° C. using a particle size distribution analyzer based on the dynamic light scattering method after dilution with deionized water in a conventional manner. As a particle size distribution analyzer based on the dynamic light scattering method, for example, "ELSZ-2000" (trade name, manufactured by Otsuka Electronics Co., Ltd.) can be used.

[0119] From the viewpoint of chipping resistance of the coating film to be formed, the hydroxyl value of the urethane resin portion (A) is preferably within the range of 0 to 45 mgKOH / g, more preferably within the range of 0 to 30 mgKOH / g, and even more preferably within the range of 0 to 25 mgKOH / g.

[0120] The acid value of the urethane resin portion (A) is preferably within the range of 3.0 to 75 mgKOH / g, more preferably within the range of 10 to 60 mgKOH / g, and even more preferably within the range of 20 to 40 mgKOH / g, from the viewpoint of the flip-flop properties of the coating film to be formed.

[0121] From the viewpoint of chipping resistance of the coating film to be formed, the hydroxyl value of the acrylic resin portion (B) is preferably within the range of 0.5 to 90 mgKOH / g, more preferably within the range of 2.0 to 65 mgKOH / g, and even more preferably within the range of 10 to 45 mgKOH / g.

[0122] The acid value of the acrylic resin portion (B) is preferably within the range of 0.7 to 80 mgKOH / g, more preferably within the range of 3.5 to 40 mgKOH / g, and even more preferably within the range of 7.5 to 25 mgKOH / g, from the viewpoint of the flip-flop properties of the coating film to be formed.

[0123] From the viewpoint of chipping resistance of the coating film to be formed, the hydroxyl value of the acrylic urethane composite resin (AB) is preferably in the range of 0 to 100 mgKOH / g, more preferably in the range of 0 to 50 mgKOH / g, and even more preferably in the range of 0 to 10 mgKOH / g.

[0124] From the viewpoint of the flip-flop properties of the coating film to be formed, the acid value of the acrylic urethane composite resin (AB) is preferably within the range of 5 to 40 mgKOH / g, more preferably within the range of 5 to 30 mgKOH / g, and even more preferably within the range of 7 to 30 mgKOH / g.

[0125] The mass ratio (B) / (A) of the acrylic resin portion (B) to the urethane resin portion (A) of the acrylic urethane composite resin (AB) is preferably within a range of 20 / 80 to 80 / 20, more preferably within a range of 30 / 70 to 70 / 30, and particularly preferably within a range of 40 / 60 to 60 / 40, from the viewpoint of chipping resistance and flip-flop properties of the coating film formed.

[0126] The solid content concentration of the acrylic urethane composite resin (AB) in the aqueous dispersion is preferably in the range of 20 to 50% by mass, more preferably in the range of 30 to 50% by mass. When the solid content concentration is 50% by mass or less, emulsification is facilitated, and the aqueous dispersion can be easily obtained. When the solid content concentration is 20% by mass or more, the solvent component is reduced, and the solid content concentration of the aqueous coating composition can be increased.

[0127] In this specification, the term "solid content" refers to non-volatile components such as resins, curing agents, and pigments that remain after drying for 1 hour at 110° C. The solid content can be determined, for example, by weighing a sample into a heat-resistant container such as an aluminum foil cup, spreading the sample on the bottom of the container, drying it for 1 hour at 110° C., and weighing the mass of the components remaining after drying.

[0128] In this specification, the term "solid content concentration" refers to the mass ratio of the solid content in the composition. Therefore, the solid content concentration of the composition can be calculated by, for example, weighing 1.0 g of the composition into a heat-resistant container such as an aluminum foil cup, spreading the composition on the bottom of the container, drying at 110°C for 1 hour, weighing the mass of the components remaining in the composition after drying, and determining the ratio of the mass of the components remaining after drying to the total mass of the composition before drying.

[0129] The content of the acrylic urethane composite resin (AB) in the aqueous coating composition of the present invention is preferably within the range of 2 to 70 mass %, more preferably within the range of 5 to 50 mass %, and even more preferably within the range of 10 to 40 mass %, based on the resin solid content in the aqueous coating composition.

[0130] In the acrylic urethane composite resin (AB), by adjusting the composition of the urethane resin portion (A), the composition of the acrylic resin portion (B), the reaction conditions, etc., it is possible to obtain an aqueous dispersion of the acrylic urethane composite resin (AB) having a desired form, such as a core-shell structure including at least two layers: a core layer including either the urethane resin portion (A) or the acrylic resin portion (B), and a shell layer including either the urethane resin portion (A) or the acrylic resin portion (B), or a form in which the urethane resin portion (A) and the acrylic resin portion (B) are partially or entirely mixed.

[0131] The core-shell structure specifically refers to a structure in which components of different resin compositions exist within the same particle, with the central portion (core) and outer shell portion (shell) having different resin compositions.

[0132] From the viewpoint of the flip-flop property and chipping resistance of the coating film to be formed, the acrylic urethane composite resin (AB) is preferably an acrylic urethane composite resin (AB') having a core-shell structure consisting of a shell portion made of the urethane resin portion (A) and a core portion made of the acrylic resin portion (B).

[0133] Acrylic urethane composite resin (AB') with a core-shell structure The acrylic urethane composite resin (AB') having a core-shell structure is usually synthesized as a dispersion in an aqueous solvent.

[0134] The acrylic urethane composite resin (AB') having a core-shell structure is preferably dispersed in water as particles having a structure in which the urethane resin portion (A) constituting the shell portion is positioned around the acrylic resin portion (B) constituting the core portion like a dispersion stabilizer. In other words, it is preferably dispersed in an aqueous solvent in a form having a core-shell structure in which the urethane resin portion (A) constituting the shell portion is on the outside and the acrylic resin portion (B) constituting the core portion is on the inside. It is thought that the particle morphology actually is approximately like this.

[0135] The core-shell structure is generally a layer structure in which the core part is completely covered with the shell part, but there may be cases in which the shell part is insufficient to form a layer structure depending on the mass ratio of the core part to the shell part, other conditions, etc. In such cases, the above-mentioned complete layer structure is not necessary, and a structure in which the core part is partially covered with the shell part may also be used.

[0136] As a method for producing the acrylic urethane composite resin (AB') having a core-shell structure, any conventionally known method for producing an acrylic urethane composite resin can be used as long as it can be made into a form having a core-shell structure. For example, in production step 1 of the acrylic urethane composite resin (AB), the acrylic urethane composite resin (AB') having a core-shell structure can be produced by using a compound having both an active hydrogen group and an ion-forming group as a constituent component of the urethane resin portion (A).

[0137] As the compound having both an active hydrogen group and an ion-forming group, the compounds having both an active hydrogen group and an ion-forming group exemplified for the acrylic urethane composite resin (AB) can be used, and these can be used alone or in combination of two or more.

[0138] Among these, compounds having both the active hydrogen group and the ion-forming group are preferably compounds having two or more hydroxyl groups and one or more carboxyl groups in one molecule, and compounds having two or more hydroxyl groups and one or more sulfonic acid groups in one molecule.

[0139] As the compound having two or more hydroxyl groups and one or more carboxyl groups in one molecule, compounds having two or more hydroxyl groups and one or more carboxyl groups in one molecule, such as those exemplified in the acrylic urethane composite resin (AB), can be used, and these can be used alone or in combination of two or more.

[0140] As the compound having two or more hydroxyl groups and one or more sulfonic acid groups in one molecule, compounds having two or more hydroxyl groups and one or more sulfonic acid groups in one molecule, such as those exemplified in the acrylic urethane composite resin (AB), can be used, and these can be used alone or in combination of two or more.

[0141] As the compound having both the active hydrogen group and the ion-forming group, it is preferable to use a compound having two or more hydroxyl groups and one or more carboxyl groups in the molecule, from the viewpoint of the flip-flop properties of the coating film to be formed.

[0142] When the urethane resin portion (A) constituting the shell uses the compound having two or more hydroxyl groups and one or more carboxyl groups, the amount used is preferably within the range of 1 to 30% by mass, more preferably within the range of 1 to 25% by mass, and even more preferably within the range of 1 to 20% by mass, relative to the total amount of compounds constituting the polyol component (a2), from the viewpoint of the flip-flop properties of the coating film to be formed.

[0143] From the viewpoints of aqueous dispersion stability and the flip-flop properties of the coating film formed, the average particle size of the acrylic urethane composite resin (AB') having a core-shell structure is preferably within the range of 10 to 5000 nm, more preferably within the range of 10 to 1000 nm, particularly preferably within the range of 20 to 500 nm, and even more particularly preferably within the range of 50 to 140 nm.

[0144] The average particle size of the acrylic urethane composite resin (AB') having a core-shell structure can be adjusted to a desired average particle size by adjusting particle size control factors such as the composition of raw materials (polyisocyanate component, polyol component, amine component, etc.), the type and amount of emulsifier, the emulsifier charging ratio, the type and amount of neutralizer, etc.

[0145] The hydroxyl value of the urethane resin portion (A) constituting the shell is preferably within the range of 0 to 45 mgKOH / g, more preferably within the range of 0 to 30 mgKOH / g, and even more preferably within the range of 0 to 25 mgKOH / g, from the viewpoint of chipping resistance of the coating film to be formed.

[0146] The acid value of the urethane resin portion (A) constituting the shell is preferably within the range of 3.0 to 75 mgKOH / g, more preferably within the range of 10 to 60 mgKOH / g, and even more preferably within the range of 20 to 40 mgKOH / g, from the viewpoint of the flip-flop properties of the coating film to be formed.

[0147] The hydroxyl value of the acrylic resin portion (B) constituting the core part is preferably within a range of 0.5 to 90 mgKOH / g, more preferably within a range of 2.0 to 65 mgKOH / g, and even more preferably within a range of 10 to 45 mgKOH / g, from the viewpoint of chipping resistance of the coating film to be formed.

[0148] The acid value of the acrylic resin portion (B) constituting the core part is preferably within the range of 0.7 to 80 mgKOH / g, more preferably within the range of 3.5 to 40 mgKOH / g, and even more preferably within the range of 7.5 to 25 mgKOH / g, from the viewpoint of the flip-flop properties of the coating film to be formed.

[0149] The hydroxyl value of the acrylic urethane composite resin (AB') having the core-shell structure is preferably in the range of 0 to 100 mgKOH / g, more preferably in the range of 0 to 50 mgKOH / g, and even more preferably in the range of 0 to 10 mgKOH / g, from the viewpoint of the chipping resistance of the coating film to be formed.

[0150] The acid value of the acrylic urethane composite resin (AB') having the core-shell structure is preferably within the range of 5 to 40 mgKOH / g, more preferably within the range of 5 to 30 mgKOH / g, and even more preferably within the range of 7 to 30 mgKOH / g, from the viewpoint of the flip-flop properties of the coating film formed.

[0151] In the acrylic urethane composite resin (AB') having the core-shell structure, the mass ratio (B) / (A) of the acrylic resin portion (B) constituting the core to the urethane resin portion (A) constituting the shell is preferably within the range of 20 / 80 to 80 / 20, more preferably within the range of 30 / 70 to 70 / 30, and particularly preferably within the range of 40 / 60 to 60 / 40, from the viewpoint of the chipping resistance and flip-flop properties of the coating film formed.

[0152] The solid content concentration in the aqueous dispersion of the acrylic urethane composite resin (AB') having the core-shell structure is preferably in the range of 20 to 50% by mass, more preferably in the range of 30 to 50% by mass. When the solid content concentration is 50% by mass or less, emulsification is facilitated, and the aqueous dispersion can be easily obtained. When the solid content concentration is 20% by mass or more, the solvent component is reduced, and the solid content concentration of the aqueous coating composition can be increased.

[0153] The content of the acrylic urethane composite resin (AB') having a core-shell structure in the aqueous coating composition of the present invention is preferably within the range of 2 to 70 mass%, more preferably within the range of 5 to 50 mass%, and even more preferably within the range of 10 to 40 mass%, based on the resin solid content in the aqueous coating composition.

[0154] [Water-based paint composition] The aqueous coating composition of the present invention contains the acrylic urethane composite resin (AB) and, if necessary, further contains at least one resin selected from an acrylic resin (C) and a polyester resin (D), and a curing agent (E).

[0155] Acrylic resin (C) As the acrylic resin (C), any known water-soluble or water-dispersible acrylic resin that has been conventionally used in water-based paints can be used.

[0156] The acrylic resin (C) preferably has a crosslinkable functional group capable of reacting with the curing agent (E) described below. Examples of the crosslinkable functional group include a hydroxyl group, a carboxyl group, and an epoxy group. Of these, it is preferable that at least one of the crosslinkable functional groups is a hydroxyl group. Therefore, it is preferable to use a hydroxyl-containing acrylic resin (C') as the acrylic resin (C).

[0157] Hydroxyl group-containing acrylic resin (C') The hydroxyl group-containing acrylic resin (C') can be produced, for example, by copolymerizing 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, such as a solution polymerization method in an organic solvent or an emulsion polymerization method in water.

[0158] The hydroxyl group-containing polymerizable unsaturated monomer is a compound having one or more hydroxyl groups and one or more polymerizable unsaturated bonds per molecule. Examples of the hydroxyl group-containing polymerizable unsaturated monomer include monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone-modified monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 8 carbon atoms; N-hydroxymethyl (meth)acrylamide; allyl alcohol; and (meth)acrylates having a polyoxyethylene chain with a hydroxyl group at the molecular terminal. However, even if a monomer that falls under the category of "(xvii) polymerizable unsaturated monomer having an ultraviolet-absorbing functional group" described below is a monomer having a hydroxyl group, in the present invention it should be defined as the above-mentioned "other polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer," and is excluded from the above-mentioned "hydroxyl group-containing polymerizable unsaturated monomer." These can be used alone or in combination of two or more kinds.

[0159] As other polymerizable unsaturated monomers copolymerizable with the above-mentioned hydroxyl group-containing polymerizable unsaturated monomers, for example, the following monomers (i) to (xx) can be used. These polymerizable unsaturated monomers can be used alone or in combination of two or more. (i) Alkyl or cycloalkyl (meth)acrylates: 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)acrylate, cyclododecyl (meth)acrylate, tricyclodecanyl (meth)acrylate, and the like. (ii) Polymerizable unsaturated monomers having an isobornyl group: isobornyl (meth)acrylate, etc. (iii) Polymerizable unsaturated monomers having an adamantyl group: adamantyl (meth)acrylate, etc. (iv) Polymerizable unsaturated monomers having a tricyclodecenyl group: tricyclodecenyl (meth)acrylate, etc. (v) Aromatic ring-containing polymerizable unsaturated monomers: benzyl (meth)acrylate, styrene, α-methylstyrene, vinyltoluene, and the like. (vi) Polymerizable unsaturated monomers having an alkoxysilyl group: vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyloxypropyltriethoxysilane, etc. (vii) Polymerizable unsaturated monomers having a fluorinated alkyl group: perfluoroalkyl (meth)acrylates such as perfluorobutylethyl (meth)acrylate and perfluorooctylethyl (meth)acrylate; fluoroolefins, and the like. (viii) Polymerizable unsaturated monomers having a photopolymerizable functional group such as a maleimide group. (ix) Vinyl compounds: N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, vinyl acetate, etc. (x) Carboxyl group-containing polymerizable unsaturated monomers: (meth)acrylic acid, maleic acid, crotonic acid, β-carboxyethyl (meth)acrylate, etc. (xi) Nitrogen-containing polymerizable unsaturated monomers: (meth)acrylonitrile, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, methylenebis(meth)acrylamide, ethylenebis(meth)acrylamide, adducts of glycidyl (meth)acrylate with amine compounds, and the like. (xii) Polymerizable unsaturated monomers having two or more polymerizable unsaturated groups in one molecule: allyl (meth)acrylate, ethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, etc. (xiii) Epoxy group-containing polymerizable unsaturated monomers: 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, etc. (xiv) (meth)acrylates having a polyoxyethylene chain with an alkoxy group at the molecular terminal. (xv) Polymerizable unsaturated monomers having a sulfonic acid group: 2-acrylamido-2-methylpropanesulfonic acid, 2-sulfoethyl (meth)acrylate, allylsulfonic acid, 4-styrenesulfonic acid, etc.; sodium salts and ammonium salts of these sulfonic acids, etc. (xvi) Polymerizable unsaturated monomers having a phosphoric acid group: acid phosphooxyethyl (meth)acrylate, acid phosphooxypropyl (meth)acrylate, acid phosphooxypoly(oxyethylene)glycol (meth)acrylate, acid phosphooxypoly(oxypropylene)glycol (meth)acrylate, etc. (xvii) Polymerizable unsaturated monomers having an ultraviolet-absorbing functional group: 2-hydroxy-4(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, 2-hydroxy-4-(3-acryloyloxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4-(3-acryloyloxy-2-hydroxypropoxy)benzophenone, 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole, and the like. (xviii) Light-stable polymerizable unsaturated monomers: 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-2,2,6,6-tetramethylpiperidine, etc. (xix) Polymerizable unsaturated monomers having a carbonyl group: acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formyl styrene, vinyl alkyl ketones having 4 to 7 carbon atoms (for example, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone), etc. (xx) Polymerizable unsaturated monomers having an acid anhydride group: maleic anhydride, itaconic anhydride, citraconic anhydride, etc.

[0160] The proportion of the hydroxyl-containing polymerizable unsaturated monomer used in producing the hydroxyl-containing acrylic resin (C') is preferably 1 to 50 mass%, more preferably 2 to 40 mass%, and even more preferably 3 to 30 mass%, based on the total amount of the monomer components.

[0161] From the viewpoints of the curability, chipping resistance, adhesion and finished appearance of the coating film to be formed, the hydroxyl group-containing acrylic resin (C') preferably has a hydroxyl value of 1 to 200 mgKOH / g, more preferably 2 to 180 mgKOH / g, and even more preferably 5 to 150 mgKOH / g.

[0162] Furthermore, from the viewpoint of the flip-flop property and chipping resistance of the coating film to be formed, the hydroxyl group-containing acrylic resin (C') preferably has an acid value of 1 to 150 mgKOH / g, more preferably 5 to 100 mgKOH / g, and even more preferably 5 to 80 mgKOH / g.

[0163] When the aqueous coating composition contains the hydroxyl group-containing acrylic resin (C'), the content of the hydroxyl group-containing acrylic resin (C') is preferably 2 to 70 mass%, more preferably 5 to 50 mass%, and even more preferably 10 to 40 mass%, based on the resin solid content in the aqueous coating composition.

[0164] Polyester resin (D) As the polyester resin (D), any known water-soluble or water-dispersible polyester resin that has been conventionally used in water-based paints can be used.

[0165] The polyester resin (D) preferably has a crosslinkable functional group capable of reacting with the curing agent (E) described below. Examples of the crosslinkable functional group include a hydroxyl group, a carboxyl group, and an epoxy group. Of these, it is preferable that at least one of the crosslinkable functional groups is a hydroxyl group. Therefore, it is preferable to use a hydroxyl group-containing polyester resin (D') as the polyester resin (D).

[0166] Hydroxyl group-containing polyester resin (D') The hydroxyl group-containing polyester resin (D') can usually be produced by an esterification reaction or transesterification reaction between an acid component and an alcohol component.

[0167] The acid component may be any compound that is commonly used as an acid component in the production of polyester resins, such as an aliphatic polybasic acid, an alicyclic polybasic acid, or an aromatic polybasic acid.

[0168] The aliphatic polybasic acids are generally aliphatic compounds having two or more carboxyl groups per molecule, acid anhydrides of the aliphatic compounds, and esters of the aliphatic compounds. Examples of the aliphatic polybasic acids include aliphatic polycarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, octadecanedioic acid, citric acid, and butanetetracarboxylic acid; anhydrides of the aliphatic polycarboxylic acids; and esters of the aliphatic polycarboxylic acids with lower alkyls having about 1 to 4 carbon atoms. The aliphatic polybasic acids can be used alone or in combination of two or more.

[0169] As the aliphatic polybasic acid, it is preferable to use adipic acid and / or adipic anhydride from the viewpoint of the flip-flop properties of the coating film to be formed.

[0170] The alicyclic polybasic acids are generally compounds having one or more alicyclic structures and two or more carboxyl groups per molecule, acid anhydrides of the compounds, and esters of the compounds. The alicyclic structures are mainly 4- to 6-membered ring structures. Examples of the alicyclic polybasic acids include alicyclic polycarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, 3-methyl-1,2-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, and 1,3,5-cyclohexanetricarboxylic acid; anhydrides of the alicyclic polycarboxylic acids; and esters of the alicyclic polycarboxylic acids with lower alkyls having about 1 to 4 carbon atoms. The alicyclic polybasic acids can be used alone or in combination of two or more.

[0171] As the alicyclic polybasic acid, from the viewpoint of the flip-flop properties of the coating film to be formed, it is preferable to use 1,2-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic anhydride, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, or 4-cyclohexene-1,2-dicarboxylic anhydride, and among these, it is more preferable to use 1,2-cyclohexanedicarboxylic acid and / or 1,2-cyclohexanedicarboxylic anhydride.

[0172] The aromatic polybasic acids are generally aromatic compounds having two or more carboxyl groups per molecule, acid anhydrides of the aromatic compounds, and esters of the aromatic compounds, and examples thereof include aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, trimellitic acid, and pyromellitic acid; anhydrides of the aromatic polycarboxylic acids; and esters of the aromatic polycarboxylic acids with lower alkyls having about 1 to 4 carbon atoms. The aromatic polybasic acids can be used alone or in combination of two or more.

[0173] As the aromatic polybasic acid, it is preferable to use phthalic acid, phthalic anhydride, isophthalic acid, trimellitic acid, or trimellitic anhydride.

[0174] Acid components other than the aliphatic polybasic acids, alicyclic polybasic acids, and aromatic polybasic acids may also be used. Examples of such acid components include, but are not limited to, fatty acids such as coconut oil fatty acids, cottonseed oil fatty acids, hempseed oil fatty acids, rice bran oil fatty acids, fish oil fatty acids, tall oil fatty acids, soybean oil fatty acids, linseed oil fatty acids, tung oil fatty acids, rapeseed oil fatty acids, castor oil fatty acids, dehydrated castor oil fatty acids, and safflower oil fatty acids; monocarboxylic acids such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, p-tert-butylbenzoic acid, cyclohexanoic acid, and 10-phenyloctadecanoic acid; and hydroxycarboxylic acids such as lactic acid, 3-hydroxybutanoic acid, and 3-hydroxy-4-ethoxybenzoic acid. These acid components may be used alone or in combination.

[0175] As the alcohol component, a polyhydric alcohol having two or more hydroxyl groups in one molecule can be suitably used. 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, 1,6-pentanediol, 1,7-pentanediol, 1,8-pentanediol, 1,9-pentanediol, 2,10-pentanediol, 2,11-pentanediol, 2,12-pentanediol, 2,13-pentanediol, 2,14-pentanediol, 2,15-pentanediol, 2,16-pentanediol, 2,17-pentanediol, 2,18-pentanediol, 2,19-pentanediol, 2,20-pentanediol, 2,21-pentanediol, 2,22-pentanediol, 2,23-pentanediol, 2,24-pentanediol, 2,25-pentanediol, 2,26-pentanediol, 2,27-pentanediol, 2,28-pentanediol, 2,29 ... hexanediol, 1,4-pentanediol, 2,4-pentanediol, 2,3-dimethyltrimethylene glycol, tetramethylene glycol, 3-methyl-4,3-pentanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, tricyclodecanedimethanol dihydric alcohols such as hydroxypivalic acid neopentyl glycol ester, hydrogenated bisphenol A, hydrogenated bisphenol F, and dimethylolpropionic acid; polylactone diols obtained by adding a lactone compound such as ε-caprolactone to these dihydric alcohols; ester diol compounds such as bis(hydroxyethyl) terephthalate; polyether diol compounds such as alkylene oxide adducts of bisphenol A, polyethylene glycol, polypropylene glycol, polybutylene glycol, and polytetramethylene ether glycol; trihydric or higher alcohols such as glycerin, trimethylolethane, trimethylolpropane, diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, tris(2-hydroxyethyl)isocyanuric acid, sorbitol, and mannite; polylactone polyol compounds obtained by adding a lactone compound such as ε-caprolactone to these trihydric or higher alcohols; and fatty acid esters of glycerin.

[0176] Furthermore, alcohol components other than the above polyhydric alcohols can also be used. Examples of such alcohol components include, but are not limited to, monoalcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, stearyl alcohol, and 2-phenoxyethanol; and alcohol compounds obtained by reacting a monoepoxy compound such as propylene oxide, butylene oxide, or "Cardura E10P" (trade name, manufactured by HEXION, a glycidyl ester of synthetic highly branched saturated fatty acid) with an acid.

[0177] The method for producing the hydroxyl group-containing polyester resin is not particularly limited and can be carried out according to a conventional method. For example, the hydroxyl group-containing polyester resin can be produced by heating the acid component and the alcohol component in a nitrogen stream at about 150 to 250°C for about 5 to 10 hours to cause an esterification reaction or transesterification reaction between the acid component and the alcohol component.

[0178] When the acid component and the alcohol component are subjected to an esterification reaction or an ester exchange reaction, they may be added to a reaction vessel all at once, or one or both may be added in several divided portions. Alternatively, a hydroxyl-containing polyester resin may be first synthesized, and then the resulting hydroxyl-containing polyester resin may be reacted with an acid anhydride to carry out half-esterification, thereby producing a carboxyl- and hydroxyl-containing polyester resin. Alternatively, a carboxyl-containing polyester resin may be first synthesized, and then the alcohol component may be added to produce a hydroxyl-containing polyester resin.

[0179] In the esterification or transesterification reaction, a catalyst known per se, such as dibutyltin oxide, antimony trioxide, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, lead acetate, tetrabutyl titanate, or tetraisopropyl titanate, can be used as a catalyst for promoting the reaction.

[0180] The hydroxyl group-containing polyester resin can be modified with a fatty acid, a monoepoxy compound, a polyisocyanate compound, an acrylic resin, or the like during or after the preparation of the resin.

[0181] Examples of the fatty acids include coconut oil fatty acids, cottonseed oil fatty acids, hempseed oil fatty acids, rice bran oil fatty acids, fish oil fatty acids, tall oil fatty acids, soybean oil fatty acids, linseed oil fatty acids, tung oil fatty acids, rapeseed oil fatty acids, castor oil fatty acids, dehydrated castor oil fatty acids, and safflower oil fatty acids. An example of the monoepoxy compound that can be suitably used is "Cardura E10P" (trade name, manufactured by HEXION, glycidyl ester of synthetic highly branched saturated fatty acid).

[0182] Examples of the polyisocyanate compound include aliphatic diisocyanate compounds such as lysine diisocyanate, hexamethylene diisocyanate, and trimethylhexane diisocyanate; and aliphatic diisocyanate compounds such as hydrogenated xylylene diisocyanate, isophorone diisocyanate, methylcyclohexane-2,4-diisocyanate, methylcyclohexane-2,6-diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 1,3-(isocyanatomethyl)cyclohexane. Examples of suitable polyisocyanates include cyclic diisocyanate compounds, aromatic diisocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate, and diphenylmethane diisocyanate, organic polyisocyanates themselves such as trivalent or higher polyisocyanates such as lysine triisocyanate, adducts of these organic polyisocyanates with polyhydric alcohols, low-molecular-weight polyester resins, water, and the like, and cyclized polymers (for example, isocyanurates) and biuret-type adducts of these organic polyisocyanates. These polyisocyanate compounds can be used alone or in combination of two or more.

[0183] Furthermore, the method for modifying the hydroxyl group-containing polyester resin with an acrylic resin can be a known method, such as a method of polymerizing a mixture of a polymerizable unsaturated group-containing polyester resin and a polymerizable unsaturated monomer, or a method of reacting a hydroxyl group-containing polyester resin with an acrylic resin.

[0184] The hydroxyl group-containing polyester resin (D') preferably has a hydroxyl group value of 1 to 250 mgKOH / g, more preferably 2 to 200 mgKOH / g, and even more preferably 5 to 180 mgKOH / g.

[0185] When the hydroxyl group-containing polyester resin (D') further contains a carboxyl group, the acid value thereof is preferably 1 to 150 mgKOH / g, more preferably 2 to 100 mgKOH / g, and even more preferably 2 to 80 mgKOH / g.

[0186] The number average molecular weight of the hydroxyl group-containing polyester resin (D') is preferably 500 to 50,000, more preferably 800 to 30,000, and even more preferably 1,000 to 10,000.

[0187] When the aqueous coating composition contains the above-mentioned hydroxyl group-containing polyester resin (D'), the content of the hydroxyl group-containing polyester resin (D') is preferably 2 to 70 mass%, more preferably 5 to 50 mass%, and even more preferably 10 to 40 mass%, based on the resin solid content in the aqueous coating composition.

[0188] Hardener (E) The curing agent (E) is a compound capable of curing the aqueous coating composition by reacting with the crosslinkable functional groups in the acrylic resin (C) and the polyester resin (D). The curing agent (E) can be used alone or in combination of two or more kinds.

[0189] Examples of the curing agent (E) include amino resins, polyisocyanate compounds, blocked polyisocyanate compounds, epoxy group-containing compounds, carboxyl group-containing compounds, carbodiimide group-containing compounds, hydrazide group-containing compounds, and semicarbazide group-containing compounds.

[0190] Among these, from the viewpoint of the water resistance, chipping resistance, adhesion, etc. of the coating film to be formed, the amino resin (E1), polyisocyanate compound (E2), and blocked polyisocyanate compound (E3) capable of reacting with a hydroxyl group, and a carbodiimide group-containing compound capable of reacting with a carboxyl group are preferred, the amino resin (E1), polyisocyanate compound (E2), and blocked polyisocyanate compound (E3) are more preferred, and the amino resin (E1) and blocked polyisocyanate compound (E3) are particularly preferred.

[0191] The amino resin (E1) may be a partially methylolated amino resin or a fully methylolated amino resin obtained by reacting an amino component with an aldehyde component. Examples of the amino component include melamine, urea, benzoguanamine, acetoguanamine, steroguanamine, spiroguanamine, and dicyandiamide. Examples of the aldehyde component include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde.

[0192] Alternatively, the methylolated amino resins may be partially or completely etherified with an appropriate alcohol, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-ethyl-1-butanol, or 2-ethyl-1-hexanol.

[0193] The amino resin is preferably a melamine resin. In particular, a methyl-etherified melamine resin obtained by partially or completely etherifying the methylol groups of a partially or completely methylolated melamine resin with methyl alcohol, a butyl-etherified melamine resin obtained by partially or completely etherifying the methylol groups of a partially or completely methylolated melamine resin with butyl alcohol, or a methyl-butyl mixed etherified melamine resin obtained by partially or completely etherifying the methylol groups of a partially or completely methylolated melamine resin with methyl alcohol and butyl alcohol are preferred, with a methyl-butyl mixed etherified melamine resin being more preferred.

[0194] The melamine resin preferably has a weight average molecular weight of 400 to 6,000, more preferably 500 to 4,000, and even more preferably 600 to 3,000.

[0195] As the melamine resin, commercially available products can be used. Examples of commercially available product names include "Cymel 202," "Cymel 203," "Cymel 238," "Cymel 250," "Cymel 251," "Cymel 303," "Cymel 323," "Cymel 324," "Cymel 325," "Cymel 327," "Cymel 350," "Cymel 385," "Cymel 1156," "Cymel 1158," "Cymel 1116," and "Cymel 1130" (all manufactured by Allnex Japan Co., Ltd.), "U-Van 120," "U-Van 20HS," "U-Van 20SE60," "U-Van 2021," "U-Van 2028," and "U-Van 28-60" (all manufactured by Mitsui Chemicals, Inc.).

[0196] When the aqueous coating composition contains the above-mentioned melamine resin, the aqueous coating composition may contain, as a curing catalyst, a sulfonic acid such as paratoluenesulfonic acid, dodecylbenzenesulfonic acid, or dinonylnaphthalenesulfonic acid; a neutralized salt of such a sulfonic acid with an amine; or a neutralized salt of a phosphoric acid ester compound with an amine.

[0197] The polyisocyanate compound (E2) 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 derivatives of the polyisocyanates.

[0198] 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-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, dimer acid diisocyanate, methyl 2,6-diisocyanatohexanoate (trivial name: lysine diisocyanate), aliphatic diisocyanates such as 2-isocyanatoethyl 2,6-diisocyanatohexanoate, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, and 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane.

[0199] 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, Alicyclic diisocyanates such as 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated xylylene diisocyanate) or a mixture thereof, methylenebis(4,1-cyclohexanediyl)diisocyanate (common name: hydrogenated MDI), and 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)-bicyclo(2.2.1)heptane Examples include alicyclic triisocyanates such as (2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, and 6-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane.

[0200] Examples of the aromatic aliphatic polyisocyanate include aromatic aliphatic diisocyanates such as methylenebis(4,1-phenylene)diisocyanate (common name: MDI), 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene (common name: tetramethylxylylene diisocyanate) or a mixture thereof; and aromatic aliphatic triisocyanates such as 1,3,5-triisocyanatomethylbenzene.

[0201] Examples of the aromatic polyisocyanate include aromatic diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4-tolylene diisocyanate (common name: 2,4-TDI) or 2,6-tolylene diisocyanate (common name: 2,6-TDI) or a mixture thereof, 4,4'-toluidine diisocyanate, and 4,4'-diphenyl ether diisocyanate; aromatic triisocyanates such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, and 2,4,6-triisocyanatotoluene; and aromatic tetraisocyanates such as 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate.

[0202] Furthermore, examples of the derivatives of the polyisocyanates include dimers, trimers, biurets, allophanates, uretdione, uretoimine, isocyanurates, oxadiazinetrione, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI), crude TDI, and the like of the above polyisocyanates.

[0203] The polyisocyanates and derivatives thereof may be used alone or in combination of two or more thereof. Among these polyisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, and derivatives thereof are preferred.

[0204] The polyisocyanate compound may be a prepolymer obtained by reacting the polyisocyanate or a derivative thereof with a compound reactive with the polyisocyanate under conditions of excess isocyanate groups. Examples of the compound reactive with the polyisocyanate include compounds having an active hydrogen group such as a hydroxyl group or an amino group. Specific examples of the compound that can be used include polyhydric alcohols, low-molecular-weight polyester resins, amines, and water.

[0205] Furthermore, as the polyisocyanate compound, a polymer of an isocyanate group-containing polymerizable unsaturated monomer, or a copolymer of the isocyanate group-containing polymerizable unsaturated monomer and a polymerizable unsaturated monomer other than the isocyanate group-containing polymerizable unsaturated monomer may be used.

[0206] The blocked polyisocyanate compound (E3) is a compound in which the isocyanate group of the polyisocyanate compound (E2) is blocked with a blocking agent.

[0207] Examples of the blocking agent include phenol-based agents such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; lactam-based agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; aliphatic alcohol-based agents such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, and lauryl alcohol; ether-based agents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and methoxymethanol; benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, butyl lactate, methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate ... Alcohol-based compounds such as hydroxyethyl methacrylate; oxime-based compounds such as formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, and cyclohexane oxime; active methylene-based compounds such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone; butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, and methylthiophene mercaptans such as acetanilide, acetanisidide, acetotoluide, acrylamide, methacrylamide, acetic amide, stearic acid amide, benzamide, and other acid amides; imides such as succinimide, phthalic acid imide, and maleic acid imide; amines such as diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, and butylphenylamine; imidazoles such as imidazole and 2-ethylimidazole;Examples of suitable azole compounds include urea-based compounds such as urea, thiourea, ethyleneurea, ethylenethiourea, and diphenylurea; carbamate ester-based compounds such as N-phenylphenylcarbamate; imine-based compounds such as ethyleneimine and propyleneimine; sulfite-based compounds such as sodium bisulfite and potassium bisulfite; and azole-based compounds. Examples of suitable azole-based compounds include pyrazole or pyrazole derivatives such as pyrazole, 3,5-dimethylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 4-bromo-3,5-dimethylpyrazole, and 3-methyl-5-phenylpyrazole; imidazole or imidazole derivatives such as imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole, and 2-phenylimidazole; and imidazoline derivatives such as 2-methylimidazoline and 2-phenylimidazoline.

[0208] Among these, preferred blocking agents include active methylene-based blocking agents, pyrazole, and pyrazole derivatives.

[0209] When blocking (reacting with a blocking agent), a solvent can be added as needed. The solvent used in the blocking reaction is preferably one that is not reactive with isocyanate groups, and examples thereof include ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, and N-methyl-2-pyrrolidone (NMP).

[0210] The blocking agent may also be a hydroxycarboxylic acid having one or more hydroxyl groups and one or more carboxyl groups, such as hydroxypivalic acid, dimethylolpropionic acid, etc. In particular, a blocked polyisocyanate compound obtained by blocking an isocyanate group with the hydroxycarboxylic acid and then neutralizing the carboxyl group of the hydroxycarboxylic acid to impart water dispersibility can be preferably used.

[0211] The curing agents (E) can be used either alone or in combination of two or more.

[0212] When the aqueous coating composition contains the curing agent (E), the content of the curing agent (E) is preferably 1 to 50 mass%, more preferably 5 to 45 mass%, and even more preferably 10 to 40 mass%, based on the resin solid content in the aqueous coating composition.

[0213] Other ingredients The aqueous coating composition of the present invention may further contain, as necessary, resins other than the acrylic urethane composite resin (AB), the acrylic resin (C), the polyester resin (D) and the curing agent (E), pigments, organic solvents, curing catalysts, dispersants, anti-settling agents, antifoaming agents, thickeners, ultraviolet absorbers, light stabilizers, surface conditioners, etc.

[0214] Examples of resins other than the acrylic urethane composite resin (AB), the acrylic resin (C), the polyester resin (D), and the curing agent (E) include acrylic urethane composite resins other than the acrylic urethane composite resin (AB), polyurethane resins, polyolefin resins, and epoxy resins.

[0215] Examples of the pigment include color pigments, extender pigments, luster pigments, etc. The pigments can be used alone or in combination of two or more.

[0216] When the aqueous coating composition of the present invention contains the above-mentioned pigment, the amount of the pigment is preferably in the range of 0.1 to 200 parts by mass, more preferably in the range of 1 to 150 parts by mass, and even more preferably in the range of 3 to 120 parts by mass, based on 100 parts by mass of the resin solids in the aqueous coating composition.

[0217] Examples of the color pigment include titanium oxide, zinc oxide, carbon black, molybdenum red, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, threne pigments, perylene pigments, dioxazine pigments, diketopyrrolopyrrole pigments, etc. Among these, titanium oxide and carbon black are preferably used.

[0218] When the aqueous coating composition contains the above-mentioned coloring pigment, the amount of the coloring pigment is preferably in the range of 1 to 180 parts by mass, more preferably in the range of 5 to 150 parts by mass, and even more preferably in the range of 15 to 120 parts by mass, based on 100 parts by mass of the resin solids in the aqueous coating composition.

[0219] Examples of the extender pigment include barium sulfate, talc, clay, kaolin, barium carbonate, calcium carbonate, silica, alumina white, etc. From the viewpoints of paint stability and finish quality, barium sulfate and talc are preferably used as the extender pigment.

[0220] When the aqueous coating composition contains the above-mentioned extender pigment, the amount of the extender pigment is preferably in the range of 1 to 180 parts by mass, more preferably in the range of 5 to 140 parts by mass, and even more preferably in the range of 10 to 120 parts by mass, based on 100 parts by mass of the resin solids in the aqueous coating composition.

[0221] Examples of the bright pigment include aluminum (including vapor-deposited aluminum), copper, zinc, brass, nickel, glass flakes, aluminum oxide, mica, aluminum oxide coated with titanium oxide and / or iron oxide, and mica coated with titanium oxide and / or iron oxide. Of these, it is preferable to use an aluminum pigment. Aluminum pigments include non-leafing aluminum pigments and leafing aluminum pigments, and either can be used.

[0222] The above-mentioned bright pigment is preferably in the form of a scale, and the bright pigment suitably has a longitudinal dimension in the range of 1 to 100 μm, particularly 5 to 40 μm, and a thickness in the range of 0.001 to 5 μm, particularly 0.01 to 2 μm.

[0223] When the aqueous coating composition contains the above-mentioned luster pigment, the amount of the luster pigment is preferably within the range of 0.1 to 100 parts by mass, more preferably within the range of 1 to 50 parts by mass, and even more preferably within the range of 3 to 25 parts by mass, based on 100 parts by mass of the resin solids in the aqueous coating composition.

[0224] Examples of the organic solvent include ketone-based solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ester-based solvents such as ethyl acetate, butyl acetate, methyl benzoate, ethyl ethoxypropionate, ethyl propionate, and methyl propionate; alcohol-based solvents such as isopropanol, n-butanol, isobutanol, and 2-ethylhexanol; ether-based solvents such as tetrahydrofuran, dioxane, and dimethoxyethane; glycol ether-based solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, and 3-methoxybutyl acetate; aromatic hydrocarbon-based solvents; and aliphatic hydrocarbon-based solvents.

[0225] When using the aqueous coating composition, it can be diluted by adding water and / or an organic solvent, etc., as necessary, and adjusted to an appropriate viscosity before coating.

[0226] The optimum viscosity varies depending on the coating composition, but for example, the viscosity after 1 minute at 60 rpm measured with a Brookfield viscometer at 20°C (sometimes referred to herein as the "B60 value") is preferably in the range of 100 to 3000 mPa·s, more preferably 300 to 2000 mPa·s, and even more preferably 500 to 1500 mPa·s, from the viewpoint of the flip-flop properties of the coating film formed. The viscometer used here is the "LVDV-I" (trade name, Brookfield, Brookfield B-type viscometer).

[0227] In the above, the coating solids concentration of the aqueous coating composition is generally about 5 to 70 mass %, preferably about 10 to 55 mass %.

[0228] The aqueous coating composition may be either a one-component coating or a multi-component coating, but a one-component coating is preferred from the viewpoints of excellent productivity due to the absence of a coating mixing step and simplification of maintenance of coating machines.

[0229] [Multi-layer coating film formation method] The aqueous coating composition of the present invention is prepared by the following steps (1) to (3): Step (1): A step of applying an aqueous coating composition to a substrate to form a base coat film; Step (2): A step of applying a clear coat paint composition onto the base coat film formed in step (1) to form a clear coat film; and Step (3): A step of simultaneously heating and curing the base coat film formed in step (1) and the clear coat film formed in step (2); The composition can be suitably used as an aqueous coating composition in a method for forming a multilayer coating film comprising the steps of:

[0230] Examples of substrates include outer and inner panels of automobile bodies such as passenger cars, trucks, motorcycles, and buses; automobile parts; and outer panels of household electrical appliances such as mobile phones and audio equipment. Of these, outer and inner panels of automobile bodies and automobile parts are preferred.

[0231] The material of these substrates is not particularly limited. Examples include metal materials such as iron, aluminum, brass, copper, tinplate, stainless steel, zinc-plated steel, and zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.)-plated steel; resins such as polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, and epoxy resin; plastic materials such as various FRPs; inorganic materials such as glass, cement, and concrete; wood; and fibrous materials such as paper and cloth. Among these, metal materials and plastic materials are preferred.

[0232] The surfaces of the objects to which the coating film is applied may be metal surfaces such as outer and inner panels of automobile bodies, automobile parts, household electrical appliances, and metal substrates such as the steel plates that make up these products, which have been subjected to surface treatments such as phosphate treatment, chromate treatment, and composite oxide treatment.

[0233] A coating film may be further formed on an object that may or may not have been surface-treated. For example, a substrate to be coated may be subjected to a surface treatment as necessary, and a primer coating film may be formed thereon. For example, when the substrate to be coated is an automobile body, the primer coating film may be formed using a known primer paint that is commonly used in painting automobile bodies.

[0234] In particular, the substrate is preferably a metal substrate, which may or may not have been subjected to a surface treatment, on which an undercoat coating film is formed using an electrodeposition paint, preferably a cationic electrodeposition paint, and it is even more preferable that the undercoat coating film formed using the electrodeposition paint, preferably a cationic electrodeposition paint, has been heat-cured.

[0235] When the substrate is coated with a primer paint, an intermediate coating film may be further formed thereon. For example, when the substrate is an automobile body, the intermediate coating film may be formed using a known intermediate coating material that is commonly used in painting automobile bodies. The intermediate coating film may or may not be heat-cured.

[0236] The aqueous coating composition can be applied to a substrate by a known method, such as air spray coating, airless spray coating, rotary atomization coating, or curtain coating, and electrostatic application may be performed during application. Of these, air spray coating and rotary atomization coating are preferred. Furthermore, such coating methods can be performed once or several times until the desired film thickness is obtained.

[0237] The amount of the aqueous coating composition to be applied is preferably an amount that results in a cured base coat film having a thickness of 5 to 40 μm, more preferably 7 to 35 μm, and even more preferably 10 to 30 μm.

[0238] As the clear coat paint composition, any known thermosetting clear paint composition for painting automobile bodies, etc. can be used. Examples of the thermosetting clear paint composition include organic solvent-based thermosetting paint compositions containing a base resin having a crosslinkable functional group and a curing agent, aqueous thermosetting paint compositions, and powder thermosetting paint compositions. Among these, from the viewpoint of the finished appearance of the multilayer paint film to be formed, organic solvent-based thermosetting paint compositions containing a base resin having a crosslinkable functional group and a crosslinking agent are preferred.

[0239] Examples of crosslinkable functional groups possessed by the base resin include carboxyl groups, hydroxyl groups, epoxy groups, silanol groups, etc. Types of base resins include acrylic resins, polyester resins, alkyd resins, urethane resins, epoxy resins, fluororesins, etc. Examples of curing agents include polyisocyanate compounds, blocked polyisocyanate compounds, melamine resins, urea resins, carboxyl group-containing compounds, carboxyl group-containing resins, epoxy group-containing resins, and epoxy group-containing compounds.

[0240] Preferred combinations of base resin / curing agent for the above clear coat paint composition include hydroxyl group-containing resin / polyisocyanate compound, carboxyl group-containing resin / epoxy group-containing resin, hydroxyl group-containing resin / blocked polyisocyanate compound, and hydroxyl group-containing resin / melamine resin, with hydroxyl group-containing resin / polyisocyanate compound being more preferred.

[0241] The clear coat paint composition may be a one-component paint or a multi-component paint such as a two-component urethane resin paint.

[0242] Furthermore, the above-mentioned clear coat paint composition may contain coloring pigments, luster pigments, dyes, etc., as needed, to the extent that transparency is not impaired, and may further contain extender pigments, ultraviolet absorbers, light stabilizers, antifoaming agents, thickeners, rust inhibitors, surface conditioners, etc., as appropriate.

[0243] The application method of the clear coat paint composition is not particularly limited, but a wet coating film can be formed by, for example, air spray coating, airless spray coating, rotary atomization coating, curtain coating, or other coating methods. In these coating methods, electrostatic application may be performed as necessary. Of these, air spray coating or rotary atomization coating is particularly preferred. The amount of application of the clear coat paint composition is usually preferably an amount that results in a cured film thickness of 10 to 70 μm, more preferably an amount that results in a cured film thickness of 20 to 50 μm.

[0244] Furthermore, when air spray coating, airless spray coating, or rotary atomization coating is performed, it is preferable to adjust the viscosity of the clear coating composition appropriately using a solvent such as an organic solvent so that it falls within a viscosity range suitable for the coating, typically a viscosity range of about 15 to 60 seconds, particularly about 20 to 50 seconds, at 20°C using a Ford Cup No. 4 viscometer.

[0245] The heating can be carried out by known means, for example, a drying oven such as a hot air oven, an electric oven, or an infrared induction heating oven. The heating temperature is preferably within the range of 60 to 180°C, more preferably within the range of 70 to 170°C, and even more preferably within the range of 80 to 160°C. The heating time is not particularly limited, but is preferably within the range of 10 to 90 minutes, and more preferably within the range of 20 to 60 minutes. [Example]

[0246] The present invention will be explained in more detail below with reference to Production Examples, Examples, and Comparative Examples. However, the present invention is not limited thereto. In each example, "parts" and "%" are by mass unless otherwise specified. Furthermore, the film thickness of the coating film is based on the cured coating film.

[0247] Manufacture of acrylic urethane composite resin (AB') Example 1 A reaction vessel equipped with a thermometer, a thermostat, a stirrer, and a reflux condenser was charged with 42.7 parts of n-butyl acrylate, 2.0 parts of allyl methacrylate, 10.5 parts of "ETERNACOLL UH-200" (trade name, manufactured by Ube Industries, Ltd., polycarbonate diol having 1,6-hexanediol as the main skeleton, molecular weight 2000), 19.8 parts of "Kuraray Polyol C-3090" (trade name, manufactured by Kuraray Co., Ltd., polycarbonate diol, molecular weight 3000), 0.27 parts of 1,4-cyclohexanedimethanol, 1.5 parts of "Blenmer GLM" (trade name, manufactured by NOF Corporation, glycerin monomethacrylate), 3.6 parts of dimethylolpropionic acid, 0.025 parts of p-methoxyphenol (polymerization inhibitor for unsaturated groups), and "Neostanol 0.004 parts of "U-600" (trade name, manufactured by Nitto Kasei Co., Ltd., bismuth-based catalyst) was charged and the mixture was heated to 80°C while stirring and mixing in an air stream, after which 6.1 parts of isophorone diisocyanate and 8.0 parts of dicyclohexylmethane-4,4'-diisocyanate were added dropwise over 30 minutes. The mixture was then heated to 100°C and allowed to react until the retained free isocyanate group content was 13.4% or less. The mixture was then cooled to room temperature, and 5.0 parts of 2-hydroxyethyl methacrylate was added to obtain a diluted acrylic monomer solution of a polyurethane prepolymer having acid groups and isocyanate groups.

[0248] Next, 1.6 parts of dimethylethanolamine and 123.7 parts of deionized water were added dropwise to the diluted acrylic monomer solution of polyurethane prepolymer obtained above over 60 minutes. After emulsification, 11.8 parts of a 5% aqueous solution of diethylenetriamine was added dropwise over 15 minutes to carry out a chain extension reaction.

[0249] Next, the temperature was raised to 70°C while stirring in a nitrogen stream, and a polymerization initiator solution prepared by dissolving 0.15 parts of "VA-057" (trade name, manufactured by Wako Pure Chemical Industries, Ltd., polymerization initiator, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamide]) in 4.6 parts of deionized water was added dropwise over 30 minutes, followed by stirring for 3 hours to carry out the polymerization reaction of the acrylic resin component (polymerizable unsaturated groups). During this time, the temperature was appropriately controlled as necessary.

[0250] The mixture was then cooled to room temperature, and the concentration was adjusted with deionized water to obtain an aqueous dispersion of acrylic urethane composite resin (AB'-1) with a core-shell structure consisting of a shell made of urethane resin and a core made of acrylic resin, with a solids concentration of 40%, an acid value of 15 g KOH / g, and an average particle diameter of 140 nm (measured at 20°C using a particle size distribution analyzer "ELSZ-2000" (trade name, manufactured by Otsuka Electronics Co., Ltd.) using dynamic light scattering).

[0251] Examples 2 to 17, Comparative Examples 1 to 4 Acrylic urethane composite resins (AB'-2) to (AB'-17) and (AB'-19) to (AB'-22) were obtained in the same manner as in Production Example 1, except that the blending compositions in Production Example 1 were as shown in Table 1 below.

[0252] Example 18 A reaction vessel equipped with a thermometer, a thermostat, a stirrer, and a reflux condenser was charged with 43.0 parts of n-butyl acrylate, 2.0 parts of allyl methacrylate, 10.5 parts of "ETERNACOLL UH-200" (trade name, manufactured by Ube Industries, Ltd., polycarbonate diol having 1,6-hexanediol as the main skeleton, molecular weight 2000), 19.9 parts of "Kuraray Polyol C-3090" (trade name, manufactured by Kuraray Co., Ltd., polycarbonate diol, molecular weight 3000), 0.28 parts of 1,4-cyclohexanedimethanol, 1.5 parts of "Blenmer GLM" (trade name, manufactured by NOF Corporation, glycerin monomethacrylate), 3.6 parts of dimethylolpropionic acid, 0.025 parts of p-methoxyphenol (polymerization inhibitor for unsaturated groups), and "Neostanol 0.004 parts of "U-600" (trade name, manufactured by Nitto Kasei Co., Ltd., bismuth-based catalyst) was charged and heated to 80°C while stirring and mixing in an air stream, after which 6.1 parts of isophorone diisocyanate and 8.0 parts of dicyclohexylmethane-4,4'-diisocyanate were added dropwise over 30 minutes. The temperature was then raised to 100°C, and the reaction was continued until the retained free isocyanate group content was 13.4% or less. Next, 5.0 parts of 2-hydroxyethyl methacrylate was added, and the reaction was continued until the free isocyanate group content was 2.0% or less. The mixture was then cooled to room temperature, yielding a diluted acrylic monomer solution of a polyurethane prepolymer having acid groups and terminal unsaturated groups.

[0253] Next, 1.6 parts of dimethylethanolamine and 124.5 parts of deionized water were added dropwise over 60 minutes to the acrylic monomer diluted solution of polyurethane prepolymer obtained above.

[0254] Next, the temperature was raised to 70°C while stirring in a nitrogen stream, and a polymerization initiator solution prepared by dissolving 0.15 parts of "VA-057" (trade name, manufactured by Wako Pure Chemical Industries, Ltd., polymerization initiator, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamide]) in 4.6 parts of deionized water was added dropwise over 30 minutes, followed by stirring for 3 hours to carry out the polymerization reaction of the acrylic resin component (polymerizable unsaturated groups). During this time, the temperature was appropriately controlled as necessary.

[0255] The mixture was then cooled to room temperature, and the concentration was adjusted with deionized water to obtain an aqueous dispersion of acrylic urethane composite resin (AB'-18) with a core-shell structure consisting of a shell made of urethane resin and a core made of acrylic resin, with a solids concentration of 40%, an acid value of 14 mgKOH / g, and an average particle diameter of 120 nm (measured at 20°C using a particle size distribution analyzer "ELSZ-2000" (trade name, manufactured by Otsuka Electronics Co., Ltd.) using dynamic light scattering).

[0256] [Table 1]

[0257] [Table 2]

[0258] [Table 3]

[0259] [Table 4]

[0260] The components listed in the table are as follows: (Note 1) "Epoxy Ester 70PA": Product name, manufactured by Kyoeisha, acrylic acid adduct of propylene glycol diglycidyl ether. (Note 2) "Epoxy Ester 200PA": Product name, manufactured by Kyoeisha, acrylic acid adduct of tripropylene glycol diglycidyl ether. (Note 3) "ETERNACOLL UH-100": Product name, manufactured by Ube Industries, Ltd., polycarbonate diol with 1,6-hexanediol as the main skeleton, molecular weight 1,000, (Note 4) "ETERNACOLL UM-90 (3 / 1)": Trade name, manufactured by Ube Industries, Ltd., polycarbonate diol with a main skeleton of 1,6-hexanediol and 1,4-cyclohexanedimethanol, molecular weight 900, (Note 5) "ETERNACOLL UM-90 (1 / 3)": Trade name, manufactured by Ube Industries, Ltd., polycarbonate diol with a main skeleton of 1,6-hexanediol and 1,4-cyclohexanedimethanol, molecular weight 900, (Note 6) "ETERNACOLL UC-100": Product name, manufactured by Ube Industries, Ltd., polycarbonate diol with a main skeleton of 1,4-cyclohexanedimethanol, molecular weight 1,000, (Note 7) "PTMG3000": Product name, manufactured by Mitsubishi Chemical Corporation, polytetramethylene ether glycol, molecular weight 3000 (Note 8) "PTMG2000": Trade name, manufactured by Mitsubishi Chemical Corporation, polytetramethylene ether glycol, molecular weight 2000, (Note 9) "PTMG1000": Trade name, manufactured by Mitsubishi Chemical Corporation, polytetramethylene ether glycol, molecular weight 1000, (Note 10) "Sannyx PP-2000": Trade name, manufactured by Sanyo Chemical Industries, Ltd., polypropylene glycol, molecular weight 2000) (Note 11) "PEG#600": Trade name, manufactured by NOF Corporation, polyethylene glycol, molecular weight 600.

[0261] Preparation of hydroxyl group-containing acrylic resin (C') Manufacturing Example 1 A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, a nitrogen inlet pipe, and a dropping device was charged with 120 parts of deionized water and 0.8 parts of "ADEKA REASOAP SR-1025" (trade name, manufactured by ADEKA Corporation, emulsifier, active ingredient 25%), and the mixture was stirred and mixed under a nitrogen stream and heated to 80°C.

[0262] Next, 5% of the total amount of the core monomer emulsion described below and 2.5 parts of a 6% aqueous solution of ammonium persulfate were introduced into a reaction vessel and maintained at 80°C for 15 minutes. The remaining core monomer emulsion was then added dropwise over 3 hours to the reaction vessel, which was maintained at the same temperature. After the addition, the mixture was aged for 1 hour. Next, the shell monomer emulsion described below was added dropwise over 1 hour. After aging for 1 hour, the reaction vessel was cooled to 30°C while 3.8 parts of a 5% aqueous solution of 2-(dimethylamino)ethanol was gradually added. The mixture was then filtered through a 100-mesh nylon cloth and discharged to obtain a hydroxyl-containing acrylic resin (C'-1) particle dispersion with an average particle size of 100 nm and a solids content of 30%. The resulting hydroxyl-containing acrylic resin particles had an acid value of 17.2 mgKOH / g and a hydroxyl value of 27.2 mgKOH / g.

[0263] Core monomer emulsion: A core monomer emulsion was obtained by mixing and stirring 54 parts of deionized water, 3.1 parts of "ADEKA REASOAP SR-1025", 1 part of allyl methacrylate, 10 parts of styrene, 35 parts of n-butyl acrylate, 10 parts of methyl methacrylate, 20 parts of ethyl acrylate, and 1 part of 2-hydroxyethyl methacrylate.

[0264] Shell portion monomer emulsion: A shell portion monomer emulsion was obtained by mixing and stirring 50 parts of deionized water, 1.8 parts of "ADEKA REASOAP SR-1025," 0.04 parts of ammonium persulfate, 5.3 parts of 2-hydroxyethyl acrylate, 2.6 parts of methacrylic acid, 8 parts of ethyl acrylate, and 7.1 parts of methyl methacrylate.

[0265] Preparation of hydroxyl group-containing polyester resin (D') Manufacturing Example 2 A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and water separator was charged with 126 parts of trimesic acid, 1365 parts of "PTMG650" (trade name, manufactured by Mitsubishi Chemical Corporation, polytetramethylene ether glycol, molecular weight 650), and 37 parts of glycerin. The temperature was raised from 160 to 230 ° C over 3 hours, and then the condensation reaction was carried out at 230 ° C until the end-point acid value reached 3 mg KOH / g. Next, 77 parts of trimellitic anhydride was added to add carboxyl groups to the resulting condensation reaction product, and the reaction was carried out at 170 ° C for 30 minutes. After that, 0.5 equivalents of 2-(dimethylamino)ethanol relative to the acid groups were added, and the mixture was diluted with 2-ethyl-1-hexanol to obtain a hydroxyl group-containing polyester resin (D'-1) solution with a solids concentration of 70%. The resulting hydroxyl group-containing polyester resin had an acid value of 32 mgKOH / g, a hydroxyl value of 117 mgKOH / g, a solid content of 70%, and a number average molecular weight of 1,200.

[0266] Production of blocked polyisocyanate compound (E3) Manufacturing Example 3 A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, dropping device, and simple solvent removal trap was charged with 360 parts of "Sumidur N-3300" and 60 parts of "Uniox M-550" (NOF Corporation, polyethylene glycol monomethyl ether, average molecular weight approximately 550), and 0.2 parts of 2,6-di-tert-butyl-4-methylphenol. The mixture was mixed thoroughly and heated at 130 °C for 3 hours under a nitrogen stream. 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. The mixture was then stirred at 65 °C for 8 hours. The isocyanate content in the resulting 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 over 3 hours while maintaining the system temperature at 80-85°C, yielding 1010 parts of an active methylene-blocked polyisocyanate compound (E3-1) solution. The simple solvent removal trap contained 95 parts of isopropanol. The solids concentration of the resulting active methylene-blocked polyisocyanate compound (E3-1) solution was approximately 60%.

[0267] Manufacturing of phosphoric acid group-containing dispersion resin (R) Production Example 4 A mixed solvent of 27.5 parts methoxypropanol and 27.5 parts isobutanol was placed in a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropping device, and heated to 110 ° C. 25 parts styrene, 27.5 parts n-butyl methacrylate, 20 parts "isostearyl acrylate" (trade name, Osaka Organic Chemical Industry, Ltd., branched higher alkyl acrylate), 7.5 parts 4-hydroxybutyl acrylate, 15 parts phosphate group-containing polymerizable unsaturated monomer (Note 1), 12.5 parts 2-methacryloyloxyethyl acid phosphate, 10 parts isobutanol, and 4 parts t-butyl peroxyoctanoate (121.5 parts of a mixture) was added to the mixed solvent over 4 hours, and a mixture of 0.5 parts t-butyl peroxyoctanoate and 20 parts isopropanol was added dropwise over 1 hour. The mixture was then stirred and aged for 1 hour to obtain a phosphate group-containing dispersion resin (R-1) solution with a solids concentration of 50%. The acid value of this resin due to the phosphate group was 83 mg KOH / g, the hydroxyl value was 29 mg KOH / g, and the weight average molecular weight was 10,000. (Note 1) Phosphate group-containing polymerizable unsaturated monomer: 57.5 parts of monobutyl phosphate and 41 parts of isobutanol were placed in a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropping device, and the temperature was raised to 90°C. 42.5 parts of glycidyl methacrylate was added dropwise over 2 hours, and the mixture was then stirred and aged for an additional hour. 59 parts of isopropanol was then added to obtain a phosphate group-containing polymerizable unsaturated monomer solution with a solids concentration of 50%. The acid value of the resulting monomer due to the phosphate group was 285 mgKOH / g.

[0268] Manufacture of brilliant pigment dispersion (P) Manufacturing Example 5 In a stirring and mixing vessel, 19 parts (solids content: 14 parts) of aluminum pigment paste "GX-180A" (trade name, manufactured by Asahi Kasei Metals Corporation, metal content: 74%), 34.8 parts of 2-ethyl-1-hexanol, 10 parts (solids content: 5 parts) of the phosphate group-containing dispersion resin (R-1) solution obtained in Production Example 4, and 0.2 parts of 2-(dimethylamino)ethanol were uniformly mixed to obtain a brilliant pigment dispersion liquid (P-1).

[0269] Preparation of aqueous coating composition Example 19 50 parts (solid content 20 parts) of the acrylic urethane composite resin (AB'-1) obtained in Example 1, 100 parts (solid content 30 parts) of the hydroxyl group-containing acrylic resin (C'-1) particle dispersion obtained in Production Example 1, 21.4 parts (solid content 15 parts) of the hydroxyl group-containing polyester resin (D'-1) solution obtained in Production Example 2, 20 parts (solid content 20 parts) of "Cymel 350" (trade name, manufactured by Mitsui Cytec Co., Ltd., methyl etherified melamine resin, weight average molecular weight 550, solid content 100%), and the active methylene-blocked acrylic resin (AB'-1) obtained in Production Example 3. 16.67 parts (solids content: 10 parts) of the polyisocyanate compound (E3-1) solution and 64 parts (resin solids content: 5 parts) of the brilliant pigment dispersion (P-1) obtained in Production Example 5 were mixed uniformly, and then "UH-752" (trade name, manufactured by ADEKA Corporation, thickener, solids content: 28%), 2-(dimethylamino)ethanol, and deionized water were added to obtain aqueous coating composition No. 1 having a pH of 8.0, a solids content of 20%, and a viscosity of 800 mPa s after 1 minute at 60 rpm as measured with a Brookfield viscometer at 20°C.

[0270] Examples 20 to 36 and Comparative Examples 5 to 8 Water-based coating compositions Nos. 2 to 22 were obtained in the same manner as water-based coating composition No. 1 in Example 19, except that the coating compositions were as shown in Table 2 below.

[0271] [Table 5]

[0272] [Table 6]

[0273] [Table 7]

[0274] [Table 8]

[0275] Preparation of test specimens Preparation of test specimen (O-1) A test substrate (O-1) was prepared by electrocoating a cold-rolled steel sheet that had been subjected to zinc phosphate conversion treatment with "Elecron GT-10" (product name, cationic electrocoating paint manufactured by Kansai Paint Co., Ltd.) to a dry film thickness of 20 μm, and then heating at 170°C for 30 minutes to cure the electrocoated coating.

[0276] Preparation of test specimen (O-2) A zinc phosphate-treated cold-rolled steel sheet was electrocoated with "Elecron GT-10" (product name, Kansai Paint Co., Ltd., cationic electrodeposition paint) to a dry film thickness of 20 μm, and then heated and cured at 170°C for 30 minutes to obtain an electrodeposition coating. Next, this electrodeposition coating was electrostatically coated with water-based primer paint "WP-522H" (product name, Kansai Paint Co., Ltd., polyester resin / amino resin-based water-based primer paint) using a rotary atomizer electrostatic coater to a cured film thickness of 30 μm. After leaving the coating for 5 minutes, the coating was preheated at 80°C for 5 minutes to prepare a test substrate (O-2).

[0277] Preparation of test coated panels Example 37 Preparation of test coated plate (S1) The aqueous coating composition No. 1 obtained in Example 19 was electrostatically applied to the test substrate (O-1) using a rotary atomizer electrostatic sprayer to a cured film thickness of 15 μm, forming an uncured basecoat film. After leaving it for 3 minutes and preheating at 80°C for 3 minutes, "KINO6510" (trade name, Kansai Paint Co., Ltd., a hydroxyl / isocyanate-curing acrylic resin / urethane resin-based two-component organic solvent-based clearcoat paint) was electrostatically applied to a cured film thickness of 35 μm, forming an uncured clearcoat film. After leaving it for 7 minutes, the coating was heated at 140°C for 30 minutes to simultaneously bake the basecoat and clearcoat films, producing a test coated panel (S1-1).

[0278] Preparation of test coated plate (S2) The aqueous coating composition No. 1 obtained in Example 19 was electrostatically applied to the test substrate (O-2) using a rotary atomizer electrostatic sprayer to a cured film thickness of 15 μm, forming an uncured basecoat film. After leaving it for 3 minutes and preheating at 80°C for 3 minutes, "KINO6510" (trade name, Kansai Paint Co., Ltd., a hydroxyl / isocyanate-curing acrylic resin / urethane resin-based two-component organic solvent-based clearcoat paint) was electrostatically applied to a cured film thickness of 35 μm, forming an uncured clearcoat film. After leaving it for 7 minutes, it was heated at 140°C for 30 minutes to simultaneously bake the primer, basecoat, and clearcoat films, producing a test coated panel (S2-1).

[0279] Examples 38 to 54, Comparative Examples 9 to 12 In Example 37, test coated plates (S1-2) to (S1-22), (S2-2) to (S2-22) were prepared in the same manner as in Example 37, except that the combinations of aqueous coating compositions and film thicknesses were as shown in Table 3.

[0280] Flip-flop test Using a multi-angle spectrophotometer (product name "MA-68II", manufactured by X-Rite), the L* value at a light-receiving angle of 15 degrees (L*15 value) and the L* value at a light-receiving angle of 110 degrees (L*110 value) were measured for each of the coated test panels obtained in Examples 37 to 54 and Comparative Examples 9 to 12 above, and the FF value of the coating film on each coated test panel was calculated using the following formula and evaluated according to the following criteria. ◎ and ◯ are pass levels. The evaluation results are shown in Table 3.

[0281] FF value = L*15 value / L*110 value ◎: FF value was 3.5 or more, ○: FF value was 3.0 or more and less than 3.5, △: FF value was 2.5 or more and less than 3.0, ×: FF value was less than 2.5.

[0282] Chipping resistance test Chipping resistance: Each of the coated test panels obtained in Examples 37-54 and Comparative Examples 9-12 was placed on the specimen holder of a stone chipping tester "JA-400" (product name, manufactured by Suga Test Instruments, chipping resistance tester). At -20°C, 50 g of crushed stone (S-5) for road use as specified in JIS A 5001 was impacted at a 90-degree angle onto the test panel from a distance of 35 cm using compressed air at 0.39 MPa (4 kgf / cm²). The test panels were then rinsed with water, dried, and a cloth adhesive tape (manufactured by Nichiban Co., Ltd.) was applied to the coated surface. After peeling, the coating was visually inspected for scratches and evaluated according to the following criteria: Excellent and Good indicate passing. The evaluation results are shown in Table 3. ⊚: The size of the scratches is extremely small, and the electrodeposited surface or the base steel sheet is not exposed. ◯: The size of the scratches is small and the electrodeposited surface or the base steel sheet is not exposed. △: The size of the scratches is small, but the electrodeposited surface and the base steel sheet are exposed. ×: The size of the scratch is quite large, and a large part of the base steel sheet is exposed.

[0283] [Table 9]

[0284] Table 10

[0285] Table 11

[0286] Table 12

Claims

1. An aqueous coating composition containing an acrylic urethane composite resin and a luster pigment, The acrylic urethane composite resin is (A) a urethane resin portion obtained from constituent components including a polyisocyanate component (a1), a polyol component (a2) including a compound (a2-1) having two or more hydroxyl groups and one or more polymerizable unsaturated groups, and a polycarbonate polyol (a2-2); (B) an acrylic resin portion (b) obtained from a component containing a compound having a polymerizable unsaturated group and no hydroxyl group or one hydroxyl group, the compound (a2-1) having two or more hydroxyl groups and one or more polymerizable unsaturated groups includes a reaction product of a glycidyl group-containing compound with (meth)acrylic acid, or a reaction product of a tri- or higher functional polyol with (meth)acrylic acid, The acrylic urethane composite resin has a core-shell structure consisting of a shell portion made of the urethane resin portion (A) and a core portion made of the acrylic resin portion (B).

2. 2. The aqueous coating composition according to claim 1, wherein the polycarbonate polyol (a2-2) comprises a polycarbonate polyol (a2-2') made from a linear or branched aliphatic polyol having 3 to 10 carbon atoms.

3. 3. The aqueous coating composition according to claim 1, wherein the polycarbonate polyol (a2-2) comprises a polycarbonate polyol having a number average molecular weight in the range of 1,000 to 5,000.

4. 4. The aqueous coating composition according to claim 1, wherein the polyol component (a2) further comprises a polytetramethylene ether glycol (a2-3).

5. 5. The aqueous coating composition according to claim 1, further comprising at least one resin selected from the group consisting of an acrylic resin (C) and a polyester resin (D).

6. The aqueous coating composition according to any one of claims 1 to 5, further comprising a curing agent (E).

7. Step (1): A step of applying the aqueous coating composition according to any one of claims 1 to 6 onto a substrate to form a base coat film; Step (2): A step of applying a clear coat paint composition onto the base coat film formed in step (1) to form a clear coat film; and Step (3): A method for forming a multilayer coating film, comprising a step of simultaneously heating and curing the base coat coating film formed in step (1) and the clear coat coating film formed in step (2).

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