GB2479075A - Coating composition and method for forming coating film - Google Patents

Abstract

A coating composition which is capable of forming a cured coating film having excellent abrasion resistance, acid resistance, contamination resistance and finish appearance. The coating composition is characterized by containing (A) a hydroxyl group-containing resin having a hydroxyl number of 80-200 mgKOH/g and a weight average molecular weight of 2,500-40,000, (B) a polyisocyanate compound and (C) an alkoxysilyl group-containing reaction product which is obtained by a reaction of a polycarbonate diol and an alkoxysilane compound, and has a hydroxyl number of 0-50 mgKOH/g and a number average molecular weight of 500-5,000.

Description

DESCRIPTION

Title of Invention: COATING COMPOSITION AND METHOD FOR

FORMING COATING FILM

Technical Field

[0001] The present invention relates to a coating composition that is excellent in scratch resistance, acid resistance and stain resistance.

Background Art

[0002] Coating compositions that are applied to automobile bodies or like objects to be coated are required to provide excellent coating film performance in terms of scratch resistance, acid resistance, stain resistance, finishing quality, and the like.

[0003] Hitherto, melamine crosslinking coating compositions have been widely used as compositions for coating the objects described above. A melamine crosslinking coating composition contains a hydroxy-containing resin and a melamine resin that acts as a crosslinking agent. Since the melamine crosslinking coating composition has a high crosslinking density during heat curing, the coating film formed therefrom has excellent coating film performance such as scratch resistance, finishing quality, and the like. However, the melamine crosslinkage in this coating composition easily undergoes hydrolysis from acid rain; therefore, this coating composition exhibits unsatisfactory acid resistance.

[C004] Japanese Unexamined Patent Publication No. H6- 220397 discloses a two-package type urethane crosslinking coating composition comprising a hydroxy-containing acrylic resin, a hydroxy-containing oligoester, and an isocyanate prepolymer. Because the urethane crosslinkage in this coating composition resists hydrolysis, a coating film formed from this coating composition has excellent acid resistance. However, the scratch resistance of this coating film is not satisfactory.

Citation List Patent Literature [0005] PTL 1: Japanese Unexamined Patent Publication No. H6-22 03 97

Summary of Invention

Technical Problem [0006] An object of the present invention is to provide a coating composition that can form a cured coating film that is excellent in scratch resistance, acid resistance, stain resistance, and finishing quality.

Solution to Problem [0007] The present inventors conducted extensive research to achieve the above object, and found that the above object can be achieved by a coating composition comprising a hydroxy-containing resin that has a specific hydroxy value and number average molecular weight; a polyisocyanate compound; and a reaction product that is obtainable by a reaction of polycarbonatediol and an alkoxysilane compound.

The reaction product contains an alkoxysilyl group and has a hydroxy value and a number average molecular weight within specific ranges.

[C008] Specifically, the present invention provides a coating composition comprising a hydroxy-containing resin (A) that has a hydroxy value of 80 to 200 mgKOH/g and a weight average molecular weight of 2,500 to 40,000, a polyisocyanate compound (B), and a reaction product (C) obtainable by a reaction of polycarbonatediol and an alkoxysilane compound. The reaction product (C) contains an alkoxysilyl group and has a hydroxy value of 0 to 50 mgKOH/g and a number average molecular weight of 500 to 5,000.

[0009] The present invention also provides a method for forming a multilayer coating film, comprising sequentially forming on an object to be coated at least one layer of a colored base coating composition and at least one layer of a clear coating composition, wherein the method comprises the step of applying the coating composition described above as the clear coating composition for forming the uppermost layer.

[0010] The present invention further provides a coated article obtained by the method for forming the multilayer coating film described above.

Advantageous Effects of Invention [0011] The coating composition of the present invention that comprises a specific hydroxy-containing resin, a polyisocyanate compound, and a specific alkoxysilyl group-containing reaction product that is obtainable by a reaction of a specific polycarbonatediol and an alkoxysilane compound enables the formation of a coating film that is excellent in finishing quality because the specific alkoxysilyl group-containing reaction product obtainable by the reaction of polycarbonatediol and an alkoxysilane compound has excellent compatibility with the hydroxy-containing resin and the polyisocyanate compound.

[0012] The alkoxysilyl group-containing reaction product is able to improve mechanical strength and other coating properties. Furthermore, because of the excellent resistance against hydrolysis due to acid that is made possible by the urethane crosslinking bond between a hydroxy-containing resin and a polyisocyanate compound, the crosslinking between the alkoxysilyl group in the alkoxysilyl group-containing reaction product and a hydroxy group, the condensation binding between alkoxysilyl groups, and the carbonate binding in the alkoxysilyl group-containing reaction product, the present invention achieves the effect of enabling the formation of a cured coating film having excellent scratch resistance, acid resistance, stain resistance and the like.

Description of Embodiments

[0013] The coating composition of the present invention (hereunder, this may be referred to as "the coating composition") and the method for forming the multilayer coating film of the present invention are explained in detail below.

[0014] The coating composition of the present invention is characterized in that it comprises a hydroxy-containing resin (A) having a hydroxy value of 80 to 200 mgKOH/g and a weight average molecular weight of 2,500 to 40,000, a polyisocyanate compound (B), and an alkoxysilyl group-containing reaction product (C) having a hydroxy value of 0 to 50 mgKOH/g and a number average molecular weight of 500 to 5,000 that is obtainable by a reaction between polycarbonatediol and an alkoxysilane compound.

[0015] Hydroxy-cDntaining resin (A) The hydroxy-containing resin (A) contained in the coating composition of the present invention has a hydroxy value of 80 to 200 mgKOH/g and a weight average molecular weight of 2,500 to 40,000.

[0016] The hydroxy-containing resin (A) is not particularly limited as long as it has a hydroxy value ranging from 80 to 200 mgKOH/g and a weight average molecular weight ranging from 2,500 to 40,000.

Specifically, acrylic resins, polyester resins, polyether resins,, polyurethane resins, and the like are usable.

Preferable examples include hydroxy-containing acrylic resins, hydroxy-containing polyester resins, and hydroxy- containing polyurethane resins. Among these, hydroxy-containing acrylic resins are particularly preferable.

[0017] In the preferred embodiments of the present invention, the hydroxy-containing acrylic resin can be prepared by copolymerizing a hydroxy-containing unsaturated monomer (M-1) and other copolymerizable unsaturated monomers (M-2) by a conventional method.

[0018] The hydroxy-containing unsaturated monomer (M-1) is a compound having one hydroxy group and one unsaturated bond per molecule. The hydroxy group mainly acts as a functional group that reacts with a crosslinking agent.

Specifically, monoesterified products of acrylic acid or methacrylic acid with a dihydric alcohol containing 2 to 10 carbon atoms are preferable as the monomers. Examples of preferable monoesterified products include 2-hydroxyethyl (meth) acrylate, hydroxypropyl acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxypentyl (meth) acrylate, hydroxyhexyl (meth) acrylate, hydroxyheptyl (meth) acrylate, hydroxyoctyl (meth) acrylate, hydroxynonyl (meth)acrylate, hydroxydecyl (meth)acrylate, and the like.

More preferable examples thereof include 2-hydroxyethyl (meth) acrylate, hydroxypropyl acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, and the like.

Examples of monoesterified products of a polyhydric alcohol with an acrylic acid or methacrylic acid, other than those mentioned above, include compounds obtained by subjecting -caprolactone to ring-opening condensation, such as "Placcel FA-1", "Placcel FA-2", "Placcel FA-3", "Placcel FA-4", "Placcel FA-5", "Placcel FM-i", "Placcel FM-2", "Placcel FM-3", "Placcel FN-4", "Placcel FM-5" (trade names, produced by Daicel Chemical Industries Co., Ltd.), and the like.

[0019] The proportion of the hydroxy-containing unsaturated monomer (N-i) preferably ranges from 20 to 50 mass%, and more preferably ranges from 25 to 45 mass%, based on the total amount of the monomer mixture.

[0020] By setting the proportion of the hydroxy-containing unsaturated monomer (N-i) within the above range, a sufficiently crosslinked cured coating film is obtained, providing the desired scratch resistance. This also provides sufficiently high compatibility with other copolymerizable unsaturated monomers (M-2) and excellent compatibility of the resulting hydroxy-containing acrylic resin with other components (polyisocyanate compound (B) and reaction product (C)); thereby obtaining a coating film having an excellent finished appearance.

[0021]

In this specification, "(meth)acrylate" means

acrylate or methacrylate.

[0022] The other copolymerizable unsaturated monomers (N- 2) are compounds that contain one unsaturated bond per molecule other than the hydroxy-containing unsaturated monomer (N-i) . Specific examples thereof are listed as (1) to (8) below.

[0023] (1) Acid group-containing unsaturated monomers: The acid group-containing unsaturated monomer is a compound having one or more acid groups and one unsaturated bond per molecule. Specific examples thereof include carboxy-containing monomers such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, and maleic anhydride; sulfonic acid group-containing monomers such as vinylsulfonic acid and sulfoethyl (meth)acrylate; acid phosphate unsaturated monomers such as 2- (meth)acryloyloxyethyl acid phosphate, 2- (meth)acryloyloxypropyl acid phosphate, 2- (meth)acryloyloxy-3-chloropropyl acid phosphate, and 2-methacryloyloxyethylphenyl phosphoric acid; and the like.

These monomers may be used singly or in a combination of two or more. The acid group-containing unsaturated monomer also acts as an internal catalyst for the cross-linking reaction of component (A) and the cross linking agent. The amount of the acid group-containing unsaturated monomer is preferably 0 to 5 mass%, and more preferably 0.1 to 3 mass% per total amount of the monomer mixture that constitutes the hydroxy-containing acrylic resin.

[0024] (2) Monoesterified. products of acrylic acid or methacrylic acid with a monohydric alcohol having 1 to 20 carbon atoms; for example, methyl (meth)acrylate, ethyl acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, isornyristyl (meth) acrylate, "Isostearyl Acrylate" (trade name, produced by Osaka Organic Chemica] Industry, Ltd.), cyclohexyl (meth)acrylate, lauryl (meth) acrylate, isobornyl (meth) acrylate, tricyclodecanyl (meth) acrylate, adamantyl (meth) acrylate, 3, 5-dimethyl adamantyl (meth)acrylate, 3-tetracyclo dodecyl methacrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, 4- methylcyclohexylmethyl (meth) acrylate, 4-ethylcyclohexylmethyl (meth) acrylate, 4-methoxy cyclohexylmethyl (meth) acrylate, tert-butylcyclohexyl (meth) acrylate, cyclooctyl (meth) acrylate, cyclododecyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, and the like.

[0025] When monomer (2) is included as a constituent component, the proportion of the monomer preferably ranges from 3 to 50 mass%, and more preferably 10 to 40 mass%, based on the total amount of the monomer mixture.

[0026] (3) Alkoxysilane group-containing unsaturated monomers: for example, vinyltrimethoxysilane, vinyltriethoxysilane, acryloxyethyl trimethoxysilane, methacryloxyethyl trimethoxysilane, acryloxypropyl trimethoxysilane, methacryloxypropyl trimethoxysilane, acryloxypropyl triethoxysilane, methacryloxypropyl triethoxysilane, vinyltris (f3-methoxyethoxy)silane, and the like. Preferable examples of the alkoxysilane group-containing unsaturated monomers include vinyltrimethoxysilane, y-acryloxyprophyl trimethoxysilane, -y-methacryloxpropyl trimethoxysilane, and the like.

[0027] When an alkoxysilane group-containing unsaturated monomer is used as the constituent component, crosslinkages may be formed, in addition to the crosslinkages of hydroxy groups and isocyanate groups, by a condensation reaction of alkoxysilane groups and a reaction of alkoxysilane groups and hydroxy groups. Thereby, the crosslinking density of the obtained coating film is raised, resulting in improved acid resistance and stain resistance effects.

When the alkoxysilane group-containing unsaturated monomer is included as a constituent component, the proportion of the monomer preferably ranges from 3 to 50 mass%, and more preferably 5 to 35 mass%, based on the total amount of the monomer mixture.

[0028] (4) Aromatic-based unsaturated monomers: for example, styrene, a-methylstyrene, vinyltoluene, and the like.

When an aromatic-based unsaturated monomer is included as a constituent component, the Tg of the resulting resin is raised and a hydrophobic coating film with a high refractive index can be obtained. This results in improved water resistance and acid resistance effects, and an enhanced finishing quality achieved by improving the gloss of the coating film.

[0029] When the aromatic-based unsaturated monomer is included as a constituent component, the proportion of the aromatic unsaturated monomer preferably ranges from 3 to 50 mass%, and more preferably 5 to 40 mass%, based on the total amount of the monomer mixture.

[0030] (5) Glycidyl group-containing unsaturated monomers: compounds having one glycidyl group and one unsaturated bond per molecule, such as glycidyl acrylate, glycidyl methacrylate, and the like.

[0031] (6) Nitrogen-containing unsaturated monomers: for example, methacrylamide, dimethylacrylamide, N,N- dimethyipropylacrylamide, N-butoxymethylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, diacetone acrylamide, N,N-dimethylaminoethyl (meth) acrylate, vinylpyridine, vinylimidazol, and the like.

[0032] (7) Other vinyl compounds: for example, vinyl acetate, vinyl propionate, vinyl chloride, vinyl versatates ("VEOVA 9" and "VEOVA 10"; produced by Japan Epoxy Resin Co., Ltd.), and the like.

[0033] (8) Unsaturated bond-containing nitrile compounds: for example, acrylonitrile, methacryloriitrile, and the like.

[0034] These other vinyl monomers (M-2) may be used singly -10 -or in a combination of two or more.

[0035] The hydroxy-containing acrylic resin can be produced by copolymerizing the mixture of monomers (M-1) and (M-2).

[0036] Hydroxy-containing acrylic resins obtainable by copolymerizing the mixture of monomers (M-1) and (M-2) having components as described below are preferably used to obtain a coating composition that can form a cured coating film that is excellent in coating film performance, such as scratch resistance, acid resistance and stain resistance, and finishing quality.

[0037] A hydroxy-containing acrylic resin obtained by copolymerizing the monomer mixture of (i) 20 to 50 mass% of a hydroxy-containing unsaturated monomer, (ii) 0 to 60 mass% of a monoesterified product of acrylic acid or methacrylic acid with a monohydric alcohol having 1 to 20 carbon atoms, and (iii) 0 to 40 mass% of an aromatic-based unsaturated monomer.

[0038] The method for copolymerizing the monomer mixture to obtain the hydroxy-containing acrylic resin is not particularly limited and known copolymerization methods can be employed. Among those, a solution polymerization method, in which polymerization is conducted in an organic solvent in the presence of a polymerization initiator, is preferably employed.

[0039] Examples of organic solvents used in the solution polymerization method include toluene, xylene, Swasol 1000 (tradename, produced by Cosmo Oil Co., Ltd., an oil-based high-boiling-point solvent), and like aromatic-based solvents; ethyl acetate, 3-methoxybutyl acetate, ethylene glycol ethyl ether acetate, propylene glycol methyl ether -11 -acetate, and like ester-based solvents; methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone, and like ketone-based solvents; propyl propionate, butyl propionate, ethoxyethyl propionate; and the like.

[0040] These organic solvents may be used singly, or in a combination of two or more. However, because the hydroxy-containing acrylic resin used in the coating composition has a high hydroxy value, considering the solubility of the resin, high-boiling-point ester solvents or high-boiling- point ketone solvents are preferably used. A high-boiling-point aromatic-based solvent may be suitably used in combination.

[0041] Examples of polymerization initiators used for copolymerizing the hydroxy-containing acrylic resin include known radical polymerization initiators, such as 2,2'-azobisisobutyronitrile, benzoyl peroxide, di-t-butyl peroxide, di-t-amyl peroxide, t-butyl peroctoate, 2,2'-azobis (2-methylbutyronitrile), and the like.

[0042] The hydroxy-containing acrylic resin preferably has a hydroxy value ranging from 80 to 200 mgKOH/g, and more preferably 90 to 190 mgKOH/g. When the hydroxy value is less than 80 mgKOH/g, the scratch resistance may be insufficient due to a low crosslinking density. When the hydroxy value exceeds 200 mgKOH/g, the coating film may show insufficient water resistance.

[0043] The hydroxy-containing acrylic resin preferably has a weight average molecular weight ranging from 2,500 to 40,000, and more preferably 5,000 to 30,000. The use of a hydroxy-containing acrylic resin having a weight average molecular weight within the above-mentioned range is preferable because it provides a coating film having high acid resistance and like coating film performance, and an -12 -excellent finishing quality with high surface smoothness.

[0044] In this specification, the weight average molecular weight is a value calculated using a weight average molecular weight measured by a gel permeation chromatograph (produced by Tosoh Corporation, "HLC812OGPC"), based on the weight average molecular weight of polystyrene. The measurements were conducted using the four columns "TSKge1 G-4000 HxL", "TSKgel G-3000 HxL", "TSKgel G-2500 HxL" and "TSKge1 G-2000 HxL" (tradenames, all produced by Tosoh Corporation), under the following conditions: mobile phase: tetrahydrofuran; measurement temperature: 40°C; flow rate: 1 cc/mm; and detector: RI. The number average molecular weight is a value obtained by the measurement conducted under the same conditions as above.

[0045] The hydroxy-containing acrylic resin preferably has a glass transition temperature ranging from -40°C to 85°C, and more preferably -30°C to 80°C. When the glass transition temperature is less than -40°C, the resulting coating film may have insufficient hardness. When it exceeds 85°C,. the resulting coating film may have insufficient surface smoothness.

[0046] The hydroxy-containing polyester resin that is used as hydroxy-containing resin (A) may be produced by a known method, for example, by an esterification reaction of a polybasic acid and polyhydric alcohol. The polybasic acid is a compound having at least two carboxyl groups per molecule, and examples thereof include phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, hexahydrophthal±c acid, maleic acid, fumaric acid, itaconic acid, triinellitic acid, pyromellitic acid, and anhydrides thereof. The polyhydric alcohol is a compound having at least two hydroxy groups per molecule, and examples thereof -13 -include diols, such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-diethyl-1,3-propanediol, neopentyl glycol, 1, 9-nonanediol, 1, 4-cyclohexanediol, hydroxypivalic acid neopentyl glycol ester, 2-butyl-2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl pentanediol, hydrogenation bisphenol A, and the like; trihydric or higher polyol components, such as trimethylolpropane, trimethylolethane, glycerin, pentaerythritol, and the like; and hydroxycarboxylic acids, such as 2,2- dimethyloipropionic acid, 2,2-dimethylolbutanoic acid, 2,2- dimethylolpentanoic acid, 2,2-dimethylolhexanoic acid, 2,2-dimethyloloctanoic acid, and the like.

[0047] Alternatively, a monoepoxy compound, such as propylene oxide, butylene oxide or like a-olefin epoxide, "Cardura ElO" (tradename, produced by Japan Epoxy Resin Co., Ltd.; a synthetic highly branched saturated fatty acid glycidyl ester) or the like may be reacted with an acid, and the resulting compound may be introduced into the polyester resin.

[0048] Carboxyl groups can be introduced into the polyester resin by, for example, adding an acid anhydride to a hydroxy-containing polyester for haif-esterification.

[0049] The hydroxy-containing polyester resin preferably has a hydroxy value ranging from 80 to 200 mgKOH/g, and more preferably 100 to 170 mgKOH/g. It is preferable that the hydroxy-containing polyester resin has a hydroxy value within the above-mentioned range in order to provide sufficiently high scratch resistance and to impart high water resistance to the resulting coating film.

[0050] The hydroxy-containing polyester resin preferably has a we-ight average molecular weight ranging from 2,500 to -14 - 40,000 and more preferably 5,000 to 30,000.

[0051] It is preferable to use a hydroxy-containing polyester resin having a weight average molecular weight within the above range, because a coating composition that can form a coating film exhibiting excellent coating film performance, such as acid resistance, and having a high surface smoothness can thereby be obtained.

[0052] The hydroxy-containing polyester resin preferably has a glass transition temperature ranging from -40°C to 85°C, and more preferably -30°C to 80°C. It is preferable to use a hydroxy-containing polyester resin having a glass transition temperature within the above-mentioned range, because this renders sufficient hardness and excellent surface smoothness to the resulting coating film.

[0053] Hydroxy-containing resins (A) include so-called urethane-modified acrylic resins and urethane-modified polyester resins.

[0054] Examples of hydroxy-containing polyurethane resins include hydroxy-containing polyurethane resins that are obtainable by a reaction of a polyol and a polyisocyanate.

[0055] Examples of polyols include low molecular weight polyols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, hexamethylene glycol and like dihydric alcohols; trimethyloipropane, glycerol, pentaerythritol, sorbitol and like trihydric of higher alcohols; and higher molecular weight polyols such as polyether poiyols, polyester polyols, acrylic polyols, epoxy polyols and the like. Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polytetrarnethylene glycol and the like. Examples of polyester polyols include polycondensates of the dihydric -15 - alcohols described above, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol or like alcohols with a dibasic acid such as adipic acid, azelaic acid, sebacic acid or the like; polyols obtained by ring-opening polymerization of a lactone such as polycaprolactone; polycarbonate diols; and the like.

Further, for example, carboxy-containing polyois such as 2, 2-dimethyloipropionic acid, 2, 2-dimethiolbutanoic acid and the like may also be utilized.

[0056] Examples of polyisocyanates to be reacted with such polyols include aliphatic polyisocyanate compounds such as hexamethylene diisocyanate, trimethylhexamethylene dilsocyanate, dimer acid diisocyanate, lysine diisocyanate and the like; biuret adducts and isocyanurate ring adducts of such polyisocyanates; alicyclic diisocyanate compounds such as isophorone diisocyanate, 4,4'- methylenebis (cyclohexylisocyanate), methylcyclohexane-2, 4- (or -2,6-)diisocyanate, l,3-(or 1,4-) di (isocyanatomethyl) cyclohexane, 1, 4-cyclohexane diisocyanate, 1,3-cyclopentane diisocyanate, 1,2-cyclohexane diisocyanate and the like; biuret adducts and isocyanurate ring adducts of such polyisocyanates; aromatic diisocyanate compounds such as xylylene diisocyanate, metaxylylene diisocyanate, tetramethylxylylene diisocyanate, tolylene diisocyanate, 4,4' -diphenylmethane dilsocyanate, l,5-naphthalene diisocyanate, 1,4-naphthalene dilsocyanate, 4, 4'-toluidine diisocyanate, 4,4'-diphenylether diisocyanate, m-(or p-)phenylene diisocyanate, 4,4'-biphenylene diisocyanate, 3,3' -dimethyl-4, 4' -biphenylene diisocyanate, bis (4-isocyanatophenyl) sulfone, isopropylidene bis(4-phenylisocyanate) and the like; biuret adducts and isocyanuric ring adducts of such polyisocyanates; polyisocyanate compounds having at least three isocyanate groups per molecule, such as triphenylmethane-4,4' ,4"-triisocyanate, 1,3,5- -16 - triisocyanatobenzene, 2,4, 6-triisocyanatotoluene, 4,4'-dimethyldiphenylmethane-2, 2', 5,5' -tetraisocyanate and the like; biuret adducts and isocyanurate ring adducts of such polyisocyanates; and the like.

[0057] The hydroxy-containing polyurethane resin preferably has a hydroxy value ranging from 80 to 200 mgKOH/g, and more preferably 100 to 170 mgKOH/g. When the hydroxy value is less than 80 mgKOH/g, the scratch resistance may be insufficient. When the hydroxy value exceeds 200 mgKOH/g, the resulting coating film may have insufficient water resistance.

[0058] The hydroxy-containing polyurethane resin preferably has a weight average molecular weight ranging from 2,500 to 40,000 and more preferably from 5,000 to 30,000. When the weight average molecular weight is less than 2,500, acid resistance and like coating film performance may be undesirably low. When the weight average molecular weight exceeds 40,000, the resulting coating film may have insufficient surface smoothness.

[0059] The hydroxy-containing polyurethane resin preferably has a glass transition temperature ranging from -40°C to 85°C and more preferably from -30°C to 80°C. When the glass transition temperature is less than -40°C, the coating film may have insufficient hardness, and when it exceeds 85°C, the resulting coating film may have insufficient surface smoothness. Hydroxy-containing resins (A) may be used singly or in a combination of two or more.

Preferable examples of hydroxy-containing resins (A) include hydroxy-containing acrylic resins or hydroxy-containing polyester resins.

[0060] Polyisocyanate compound (B) The polyisocyanate compound (B) contained in the -17 -coating composition of the present invention has at least two free isocyanate groups per molecule, and polyisocyanate compounds that have been generally employed in the production of polyurethane can be utilized. Examples of polyisocyanate compound (B) include aliphatic polyisocyanates, alicyclic polyisocyanates, aliphatic-aromatic polyisocyanates, aromatic polyisocyantates, derivatives of these polyisocyanates, and the like.

[0061] Examples of aliphatic polyisocyanates include compounds containing a C38 linear or branched, saturated or unsaturated aliphatic hydrocarbon or fatty acid as the skeleton, and 2 to 3 isocyanate groups. Specific examples of aliphatic polyisocyanates 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, 2,6-diisocyanatomethylcaproate and like aliphatic diisocyanates, for example, lysine ester triisocyanates, 1,4,8- triisocyanato octane, l,6,1l-triisocyanato undecane, 1,8-diisocyanato-4--isocyanato methyloctane, 1,3, 6-triisocyanato hexane, 2,5, 7-trimethyl-1, 8-diisocyanate-5-isocyanato methyloctane and like aliphatic triisocyanates; and the like.

[0062] Examples of alicyclic polyisocyanates include 1,3-cyclopentene diisocyanate, 1, 4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), 4,4' -methylenebis (cyclohexylisocyanate), methyl-2, 4-cyclohexane diisocyanate, methyl-2, 6-cyclohexane diisocyanate, 1,3-or 1, 4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated xylylene diisocyanate) or a mixture thereof, norbornane diisocyanate and like alicyclic -18 -diisocyanates, for example, l,3,5-triisocyanato cyclohexane, 1,3,5-trimethylisocyanato cyclohexane, 2-(3- isocyanatopropyl) -2,5-di (isocyanatomethyl) - bicyclo[2.2.l]heptane, 2-(3-isocyanatopropyl)-2, 6- di(isocyanatomethyl)-bicyclo[2.2.1]heptane, 3-(3-- isocyanatopropyl) -2, 5-di (isocyanatomethyl) - bicyclo[2.2.l]heptane, 5-(2-isocyanatoethyl)-2- isocyantemethyl-3-(3-isocyanatopropyl) - bicyclo[2.2.l]heptane, 6-(2-isocyanatoethyl)-2- ±socyanatomethyl-3-(3-isocyanatopropyl) - bicyclo[2.2.l]heptane, 5-(2-isocyanatoethyl)-2- isocyanatomethyl-2-(3-isocyanatopropyl) - bicyclo[2.2.1]heptane, 6-(2-isocyanatoethyl)-2- isocyanatomethyl-2-(3-isocyanatopropyl) -bicyclo[2.2.l]heptane and like alicyclic triisocyanates; and the like.

[0063] Examples of aliphatic-aromatic polyisocyanates include 1,3-or l,4-xylylene diisocyanate or a mixture thereof, o, w' -diisocyanato-l, 4-diethylbenzene, 1, 3-or 1,4-bis(1-isocyanato-l-methylethyl)benzene (common name: tetramethyixylylene diisocyanate) or a mixture thereof, and like aliphatic-aromatic diisocyanates; and 1,3,5-triisocyanate methylbenzene and like aliphatic-aromatic triisocyanates; and the like.

[0064] Examples of aromatic polyisocyanates include m- phenylene diisocyanate, p-phenylene diisocyanate, 4,4'- diphenyl diisocyanate, 1, 5-naphthalene diisocyanate, 2,4' -or 4,4'-diphenylmethane diisocyanate, or a mixture thereof, 2,4-or 2,6-tolylene diisocyanate, or a mixture thereof, 4,4' -toluidine diisocyanate, 4,4' -diphenylether diisocyanate and like aromatic diisocyanates, for example, tr±phenylmethane-4,4' ,4' -triisocyanate, 1,3,5-triisocyanato benzene, 2,4,6-triisocyanato toluene and like aromatic triisocyanates, for example, 4,4'-diphenylmethane- -19 - 2,2' ,5,5'-tetraisocyanate and like aromatic tetraisocyanates; and the like.

[0065] Examples of polyisocyanate derivatives include dimers, trimers, biurets, allophanates, carbodiimides, urethodiones, urethoimines, isocyanurates, oxadiazine triones, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI), crude TDI, and the like of the aforementioned polyisocyanate compounds.

[0066] These polyisocyanate compounds may be used singly, or in a combination of two or more. Among these polyisocyanate compounds, aliphatic diisocyanates and derivatives thereof can suitably be used, from the viewpoint of scratch resistance, weather resistance and the like.

[0067] Blocked polyisocyanate compounds obtained by blocking with a blocking agent the isocyanate groups of polyisocyanate compounds having at least two free isocyanate groups per molecule, may be used as the polyisocyanate compound.

[0068] A blocking agent blocks free isocyanate groups.

When the blocked polyisocyanate compounds are heated at, for example, 100°C or more, preferably 130°C or more, the isocyanate groups are regenerated to easily react with hydroxy groups. Examples of such blocking agents include phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, non1phenol, octyiphenol, methyl hydroxybenzoate and like phenol compounds; c-caprolactam, 8-valerolactam, y-butyrolactam, 3-propiolactam and like lactam compounds; methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, lauryl alcohol and like aliphatic alcohols; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol -20 -monobutyl ether, diethylene glycol monomethyJ. ether, diethylene glycol monoethyl ether, propylene giycol monomethyl ether, methoxymethanol and like ether compounds; benzyl alcohol; glycolic acid; methyl glycolate, ethyl glycolate, butyl glycolate and like glycolates; lactic acid, methyl lactate, ethyl lactate, butyl lactate and like lactates; methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate and like alcohol compounds; formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monoxime, benzophenone oxime, cyclohexane oxime and like oxime compounds; dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, acetylacetone and like active methylene compounds; butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, ethylthiophenol and like mercaptan compounds; acetanilide, acetanisidide, acetotoluide, acrylamide, methacrylamide, acetamide, stearamide, benzamide and like acid amide compounds; succinimide, phthalimide, maleimide and like imide compounds; diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, butylphenylamine and like amine compounds; imidazole, 2-ethylimidazole and like imidazole compounds; 3,5-dimethylpyrazole and like pyrazole compounds; urea, thiourea, ethylene urea, ethylenethiourea, diphenylurea and like urea-based compounds; phenyl N-phenylcarbamate and like carbamate ester compounds; ethyleneimine, propyleneimine and like imine compounds; sodium bisulfite, potassium bisulfite and like sulfites; and the like.

[0069] A solvent may be added for blocking (reacting with a blocking agent), if necessary. The solvents usable for the blocking reaction are preferably those that do not undergo reaction with isocyanate groups. Examples of such -21 -solvents include ketone-based solvents such as acetone and methyl ethyl ketone, ester-based solvents such as ethyl acetate, and other solvents, such as N-methylpyrrolidone (NMP), and the like.

[0070] Polyisocyanate compound (B) may be used singly, or in a combination of two or more.

[0071] Reaction product (C) The reaction product (C) used in the coating composition is obtainable by a reaction of polycarbonatediol and an alkoxysilane compound. The reaction product (C) comprises an alkoxysilyl group and has a hydroxy value ranging from 0 to 50 mgKOH/g and a number average molecular weight ranging from 500 to 5,000.

[0072] Reaction product (C) preferably has a hydroxy value ranging from 0 to 50 mgKOH/g and more preferably from 0 to mgKOH/g from the viewpoint of compatibility with hydroxy-containing resin (A) and polyisocyanate compound (B), the curability of the obtainable coating composition, and the acid resistance and scratch resistance of the resulting coating film.

[0073] Reaction product (C) can be synthesized by a reaction of polycarbonatediol and an alkoxysilane compound.

[0074] Pclycarbonatediol is a compound obtainable by subjecting diol and a carbonylating agent to a polycondensation reaction.

[0075] Examples of diol components contained in the polycarbonatediol used for synthesizing reaction product (C) include dihydric alcohols preferably having 2 to 10, and more preferably 4 to 8 carbon atoms. Specific examples thereof include 1,2-propanediol, 1,3-propanediol, 1,3- -22 -butanediol, 1,4-butanedial, 1,5-pentanediol, 1, 6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 2-ethyl--i, 6-hexanediol, 2-methyl-i, 3-propanediol, 3-methyl-i, 5-pentanediol, neopentyl glycol and like aliphatic dials; 1,3-cyclahexanediol, 1,4-cyclahexanedial, 1, 4-cyclahexanedimethanal and like alicyclic dials; p-xylenedial, p-tetrachlaraxylenedial and like aramatic dials; diethylene glycal, diprapylene glycol and like dials. These dials may be used singly ar in a cambinatian af twa ar mare.

[0076] Preferable examples af the palycarbanatedials used far synthesizing reactian praduct (C) are thase abtained by subjecting a dial campanent camprising i,6-hexanedial and a carbonylating agent ta a palycandensatian reactian fram the viewpoint af durability and hardness.

[0077] Examples af particularly preferable palycarbanatedials include those abtainable by subjecting a carbonylating agent and twa ar mare dial campanents, which include 1,6-hexanedial as the essential dial camponent, such as the combination of 1,6-hexanediol with 1,5- pentanedial, 1,6-hexanedial with 1,4-butanediol, or 1,6-hexanedioi with 1, 4-cyclohexanedimethanal.

[0078] Examples of carbanylating agents include commonly used alkyiene carbonates, dialkyl carbanates, diallyl carbonate, and phosgene; they may be used singly or in a cambination at twa or mare. Preferable examples thereof include ethylene carbonate, propylene carbonate, dimethyi carbonate, diethyl carbonate, dibutyl carbonate, diphenyi carbonate, and the like.

[0079] It is preferable to use a polycarbonatediol having a viscosity at 50°C of 10,000 mPas far synthesizing reaction product (C). Viscosity exceeding 10,000 mPas may cause handling difficulties and insufficient compatibility -23 - of the resulting reaction product (C) with hydroxy-containing resin (A) and polyisocyanate compound (B) . This may lower the gloss or cause the formation of cloudiness and the like in the coating film, resulting in an undesirable finishing quality in the coating film.

[0080] The polycarbonatediol used for synthesizing reaction product (C) preferably has a viscosity at 50°C of 10,000 mPas or less, more preferably 8,000 mPas or less, and still more preferably 5,000 mPas or less. Viscosity is measured at 50°C and 6 rpm using a B-type viscometer.

[0081] The polycarbonatediol used for synthesizing reaction product (C) preferably has a number average molecular weight ranging from 300 to 2,000, more preferably ranging from 500 to 1,800, and still more preferably ranging from 700 to 1,500 from the viewpoint of the acid resistance and scratch resistance of the coating film.

[0082] The weight average molecular weight herein is a value calculated using the chromatogram measured by a gel permeation chromatograph, based on the weight average molecular weight of standard polystyrene. The HLC812OGPC gel permeation chromatograph (produced by Tosoh Corporation) was used. The measurements were conducted using the four columns "TSKge1 G-4000 HxL", "TSKge1 G-3000 HxL", "TSKgel G-2500 HxL" and "TSKgel G-2000 HxL" (tradenames, all produced by Tosoh Corporation), under the following conditions: mobile phase: tetrahydrofuran; measurement temperature: 40°C; flow rate: 1 cc/mm; and detector: RI.

[0083] The polycarbonatediol used for synthesizing reaction product (C) may be a commercial product.

Commercially available polycarbonatediols include, for example, "T-5650J" (tradename, produced Asahi Kasei -24 - Chemicals Corp.; diol components: 1,6-hexanediol and 1,5-pentanediol); \\T_4671H (tradename, produced by Asahi Kasei Chemicals Corp.; diol components: 1,6-hexanediol and 1,4-butanediol); "UM-CARB9O" (tradename, produced by Ube Industries, Ltd.; diol components: 1,6-hexanediol and 1,4-cyclohexanedimethanol); and the like.

[0084] Examples of the alkoxysilane compounds used for synthesizing reaction product (C) include dialkoxysilane, trialkoxysilane, tetraalkoxysilane, isocyanate group-containing trialkoxysilane, alkoxysilane oligomer, and the like.

Examples of dialkoxysilanes include dimethyldiethoxysilane, dimethyldipropoxysilane, dimethyldibutoxysilane, and diethyldiethoxysilane.

Examples of trialkoxysilanes include methyltrimetoxysilane, hexyltrimethoxysilane, decyltrimetoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, hexyltriethoxysilane, decyltriethoxysilane, phenyltriethoxysilane, and the like.

Examples of isocyanate group-containing trialkoxysilanes include y-isocyanatepropyl triethoxysilane, y-isocyanate propyltriethoxysilan, and 7-isocyanate propyltributoxysilane. Examples of tetraalkoxysilanes include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, and the like.

[0085] -Among these, y-isocyanatepropyl triethoxysilane is preferably used from the viewpoint of the finishing quality, scratch resistance and the like of the coating film.

[0086] These alkoxysilane compounds may be suitably used singly or in a combination of two or more, if necessary.

[0087] Reaction product (C) is usually synthesized under conditions that allow a polycarbonatediol compound whose -25 -terminal groups are modified with an alkoxysilane compound to be obtained.

[0088] The optimum reaction temperature varies depending on the main alkoxysilane compound used. When methyltrimethoxysilane is used as the alkoxysilane compound, the reaction temperature is approximately 100 to 150°C.

[0089] The polycarbonatediol and the alkoxysilane compound can be synthesized by a condensation reaction conducted at an equivalent ratio (alkoxy in alkoxysilane compound/hydroxy group in polycarbonatediol) of 5.0 or less.

The equivalent ratio preferably ranges from 2.0 to 4.0, more preferably 2.3 to 3.5, and still more preferably 2.5 to 3.0 from the viewpoint of the curability of the obtained coating composition and the acid resistance and stain resistance of the obtained coating film, and the like.

[0090] In reaction product (C), the lower the equivalent ratio, the greater the proportion of the compound in which only one end of the polycarbonatediol has been converted to an alkoxysilane compound; and the higher the equivalent ratio, the greater the proportion of the compound in which both ends of the polycarbonatediol have been converted to an alkoxysilane compound.

[0091] The lower the equivalent ratio, the larger the amount of unreacted polycarbonatediol remaining in reaction product (C); however, in the present invention, reaction product (C) containing unreacted polycarbonatediol can generally be used without isolating the polycarbonatediol that remains unreacted.

[0092] Among the alkoxysilane compounds described above, in particular, when an isocyanate group-containing trialkoxysilane is used, reaction product (C) can be -26 -synthesized by preferentially reacting the hydroxy group in polycarbonatediol and the isocyanate group in isocyanate group-containing trialkoxysilane.

[0093] The reaction temperature is, for example, when y-isocyanatepropyl triethoxysilane is used as the isocyanate group-containing trialkoxysilane, approximately from 60 to 10000.

[0094] The polycarbonatediol and the isocyanate group-containing trialkoxysilane can be synthesized by a urethanization reaction conducted at an equivalent ratio (isocyanate group in isocyanate group-containing trialkoxysilane /hydroxy group in polycarbonatediol) of 1.05 or less. The equivalent ratio is preferably ranging from 0.85 to 1.03, more preferably 0.9 to 1.02, and further more preferably 0.95 to 1.00 from the viewpoint of the curability of the coating composition obtained and the acid resistance, stain resistance, and the like of the resulting coating film.

[0095] In reaction product (C), the lower the equivalent ratio, the greater the proportion of the compound in which only one end of the polycarbonatediol has been converted to an alkoxysilane compound; and the higher the equivalent ratio, the greater the proportion of the compound in which both ends of the polycarbonatediol have been converted to an alkoxysilane compound.

[0096] The lower the equivalent ratio, the larger the amount of unreacted polycarbonatediol remaining in reaction product (C); however, in the present invention, reaction product (C) containing unreacted polycarbonatediol can generally be used without isolating the polycarbonatediolL that remains unreacted.

[0097] -27 -Reaction product (C) preferably has a hydroxy value ranging from 0 to 50 mgKOH/g, more preferably 0 to 40 mgKOH/g, and still more preferably 0 to 30 mgKOH/g from the viewpoint of the curability of the coating composition obtained and the stain resistance and the like of the resulting coating film.

[0098] Reaction product (C) preferably has a number average molecular weight ranging from 500 to 5,000, more preferably 600 to 3,000, and still more preferably 700 to 1,500 to achieve excellent compatibility with hydroxy-containing resin (A) and polyisocyanate compound (B), and to provide satisfactory scratch resistance, hardness, weather resistance and the like to the resulting coating film.

[0099] In the present invention, the hydroxy value and number average molecular weight mean those of the reaction product (C) including polycarbonatediol that remains unreacted [0100] In the coating composition of the present invention, to achieve excellent curability, scratch resistance, and the like of the coating film, the equivalent ratio (NCO/OH) of the hydroxy group in hydroxy-containing resin (A) and reaction product (C) and the isocyanate group in polyisocyanate compound (B) is preferably in the range of 0.5 to 2.0 and more preferably 0.8 to 1.5.

[0101] The amount of hydroxy-containing resin (A), polyisocyanate compound (B), and reaction product (C) in the coating composition of the present invention is, based on 100 parts by mass of the total solids content of components (A), (B), and (C), as nonvolatile content, within the range of 30 to 75 rnass% and preferably 40 to 65 mass% of hydroxy-containing resin (A); 20 to 65 mass% and -28 -preferably 30 to 55 mass% of polyisocyanate compound (B); and 3 to 30 mass%, preferably 5 to 25 mass%, and more preferably 10 to 20 mass% of reaction product (C) [0102] Other Components The present coating composition comprises, as essential components, the hydroxy-containing resin (A), polyisocyanate compound (B), and reaction product (C) described above. The present coating composition also generally contains an organic solvent, and may further contain, as necessary, additives for coating compositions, such as curing catalysts, pigments, pigment dispersants, leveling agents, UV absorbers, light stabilizers, plasticizers, surface control agents, and the like that are generally utilized in the field of coating compositions.

[0103] Examples of curing catalysts include tin octylate, dibutyltin di(2-ethylhexanoate), dioctyltin di(2-ethylhexanoate), dioctyltin diacetate, dibutyltin dilaurate, dibutyltin oxide, dioctyltin oxide, 2-ethyihexanoic acid lead, and like organic metal catalysts, tertiary amines, and the like.

[0104] The compounds exemplified above as the curing catalysts may be used singly, or in a combination of two or more. The amount of curing catalyst used varies depending on the type, but the curing catalyst is preferably used in a proportion of 5 parts by mass or less, and preferably approximately ranging from 0.1 to 4 parts by mass, based on the total 100 parts by mass of the solids content of components (A), (B), and (C) [0105] Examples of pigments include titanium oxide, zinc white, carbon black, cadmium red, molybdenum red, chrome yellow, chromium oxide, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, -29 -isoindoline pigments, threne pigments, perylene pigments, and like coloring pigments (D); talc, clay, kaolin, baryta, barium sulfate, barium carbonate, calcium carbonate, silica, alumina white, and like extender pigments; and aluminum powder, mica powder, titanium oxide-coated mica powder, and like metallic pigments.

[0106] These pigments may be used singly, or in a combination of two or more. The amount of pigment used varies depending on the type, but the pigment is preferably used in a proportion of 200 parts by mass or less, and more preferably approximately 1 to 100 parts by mass, based on the total solids content of components (A), (B), and (C) [0107] The amount of coloring pigment used varies depending on the type, but the coloring pigment is preferably used in a proportion of 150 parts by mass or less, and more preferably approximately 1 to 100 parts by mass, based on the total solids content of components (A), (B), and (C).

[0108] Usable examples of UV absorbers include known UV absorbers, such as benzotriazole UV absorbers, triazine tJV absorbers, salicylic acid derivative UV absorbers, benzophenone UV absorbers, and the like.

[0109] From the viewpoint of weather resistance and yellowing resistance, the proportion of UV absorber in the coating composition is preferably 10 parts by mass or less, more preferably ranging from 0.2 to 5 parts by mass, and still more preferably ranging from 0.3 to 2 parts by mass, based on the total solids content of components (A), (B), and (C).

[0110] Examples of usable light stabilizers include known light stabilizers, such as hindered amine light stabilizers.

-30 -[0111] From the viewpoint of weather resistance and yellowing resistance, the proportion of light stabilizer in the coating composition is preferably within a range of from 0 to 10 parts by mass, more preferably 0.2 to 5 parts by mass, and still more preferably 0.3 to 2 parts by mass, based on the total solids content of components (A), (B), and (C).

[0112] When the coating composition of the present invention contains a polyisocyanate compound (component (B)) with unblocked isocyanate groups, it is preferable, from the viewpoint of storage stability, that the coating composition is a two-package-type coating composition comprising a package of hydroxy-containing resin (A) and reaction product (C), and a package of polyisocyanate compound (B); these packages are packed separately, and are mixed immediately before use.

[0113] Application Method for Coating Composition Preferable examples of objects onto which the present coating composition is applied include, but are not particularly limited to, the bodies of various vehicles, such as automobiles, motorcycles, containers and the like.

Examples of objects to be coated also include those that constitute such vehicle bodies, such as cold rolled steel sheets, galvanized steel sheets, zinc alloy-plated steel sheets, stainless steel sheets, tinned steel sheets, and like steel sheets; aluminum sheets, aluminum alloy sheets, and like metal substrates; plastic substrates; and the like.

[0114] Ccatable objects also include such vehicle bodies, metal substrates, etc., whose metal surfaces have undergone a surface treatment such as phosphate treatment, chromate treatmentr composite oxide treatment, or the like.

Coatable objects further include such vehicle bodies, metal -31 -substrates, etc., onto which an undercoat, such as an electrodeposition undercoat, and/or an intermediate coat, has been formed.

[0115] The method of applying the present coating composition is not limited. For example, air spray coating, airless spray coating, rotary atomization coating, curtain coating, or other coating methods may be employed to forra a wet coat. In these coating methods, an electrostatic charge may be applied, if necessary. Of the above, air spray coating is particularly preferable. It is usually preferable to apply the coating composition to a film thickness of approximately 10 to 50 pin (when cured).

[0116] When carrying out air spray coating, airless spray coating or rotary atomization coating, it is preferable that the viscosity of the coating composition be suitably adjusted using a solvent such as an organic solvent or the like, to a viscosity range that is suitable for use in the coating method, the range of which is generally from approximately 15 to 60 seconds at 20°C (viscometer: Ford cup No. 4).

[0117] The wet coat, which is formed by applying the present coating composition to an object to be coated, is cured by heating. Heating can be performed by known heating means. For example, drying furnaces, such as hot air furnaces, electric furnaces, infrared induction heating furnaces, and the like can be used. The heating temperature is generally 60°C to 180°C, and preferably 90°C to 150°C. The heating time is not particularly limited, but is preferably approximately 15 to 30 minutes.

[0118] The present coating composition can form a cured coating film that is excellent in scratch resistance, acid resistance, stain resistance and finishing quality; -32 -therefore, the present coating composition can be suitably used as a top coat clear coating composition. The present coating composition can be suitably used as a coating composition for, in particular, automobiles.

[0119] Method for Forming a Multilayer Coating Film The method for forming a multilayer coating film, in which the present coating composition is applied as a top coat clear coating composition, may comprise successively forming on an object to be coated at least one layer of a colored base coating composition and at least one layer of a clear coating composition, wherein the present coating composition is applied as the clear coating composition for forming the uppermost layer.

[0120] Specific examples of such a method include a method for forming a multilayer coating film by a 2-coat 1-bake method, in which a solvent-or aqueous-based base coating composition is applied to an object to be coated onto which an electrodeposition coating film and/or intermediate coating film has been applied. The resulting uncured coating film is, as necessary, preheated at, for example, 40 to 90°C for 3 to 30 minutes to accelerate the vaporization of the solvent in the base coating composition, and the present coating composition is then applied as a clear coating composition to the uncured base coating film, followed by simultaneous curing of the base coating film and the clear coating film.

[0121] The present coating composition is also suitably used as a top coat clear coating composition for a top clear coating in a 3-coat 2-bake method or a 3-coat 1-bake method.

[01221! The base coating composition used in the above manner may be a corranonly known thermosetting base coating -33 -composition, and specific examples thereof include coating compositions obtained by combining a curing agent such as amino resins, polyisocyanate compounds, blocked polyisocyanate compounds, or the like with reactive functional groups of a base resin such as acrylic resin, polyester resin, alkyd resin, urethane resin, or the like.

[0123] From an environmental and resource-saving point of view, the base coating composition is preferably a high-solids type that uses a small amount of organic solvent; further, an aqueous coating composition or a powder coating composition may also be used.

[0124] In the method for forming a multilayer coating film, comprising forming two or more clear coating films, a commonly known thermosetting clear coating composition may be used as the clear coating composition, in addition to the present coating composition.

[0125]

Examples

Hereunder, the present invention is explained in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following Examples. In the following examples, parts and percentages are by mass, and the film thickness is the thickness of a cured coating film.

[0126] Production of Hydroxy-Containing Resin (A) Production Examples 1-9 In each example, 31 parts of ethoxyethyl propionate was introduced into a four-necked flask equipped with a stirrer, a thermometer, a condenser tube, and a nitrogen gas inlet; and the resulting mixture was heated to 155°C under a nitrogen gas atmosphere. When the temperature reached 155°C, the supply of nitrogen gas was stopped, after which each of monomer mixtures comprising the -34 -monomers and the polymerization initiator at the proportions shown in Table 1 below was added thereto dropwise over 4 hours. Subsequently, aging was performed for 2 hours under a nitrogen gas atmosphere at 155°C, and each of the resulting products was then cooled to 10000, followed by dilution with 32.5 parts of butyl acetate. In such a manner, each example produced a coating resin having a solids content of 60%. Table 1 below shows the solids mass concentrations (%) and resin properties of the obtained coating resins.

[0127] The hydroxy group value measurement shown in Table 1 was carried out according to JISK-0070 (1992). More specifically, 5 ml of acetylating reagent (anhydrous acetic acid pyridine solution obtained by adding pyridine to 25 g of anhydrous acetic acid, adjusted to 100 ml in total) was added to the sample, and the sample was heated in a glycerin bath. Thereafter, the sample was titrated in a potassium hydroxide solution using phenolphthalein as an indicator. Then, the hydroxy group value was found according to the following equation.

Hydroxy group value (mg KOH/g) = [Vx56.lxC/m]+D wherein V represents titration amount (ml), C represents concentration (mol/l) of titrate liquid, m represents solids content by weight (g) of the sample, and D represents acid value (mgKOH/g) of the sample.

[C128] The acid value measurement was carried out according to JISK-5601-2-1 (1999) . More specifically, each sample was dissolved by a mixture solution of toluene/ethanol (2:1 in volume), and the sample was titrated with a potassium hydroxide solution using phenolphthalein as an indicator. Then, the acid value was found according to the following equation.

Acid value (mg KOH/g) 56.lxVxC/m wherein V represents titration amount (ml), C represents -35 -concentration (mol/l) of titrate liquid, and m represents solids content by weight (g) of the sample.

[0129] The glass transition temperature (Tg (°C)) shown in Table 1 was calculated using the following formulae.

l/Tg (K) = (Wi/Ti) + (W2/T2) + . Tg (°C) = Tg(K)-273 In each formula, Wi, W2, ... represent the mass fractions of the monomers used for copoiymerization, and Ti, T2, ... represent the Tg (K) of homopoiymers of each of the monomers. Ti, T2, ... are the values disclosed in the Polymer Handbook (2nd Edition, J. Brandup, E. H. Immergut ed.).

[01301

Table 1

Production Example No. 1 2 3 4 5 6 7 8 9 Hyciroxy-Containing Resin (A) No. 1 2 3 4 5 6 7 8 9 Styrene (parts) 20 20 20 20 20 20 20 20 20 a n-Butyl Acrylate (parts) 20 20 20 20 20 20 20 20 20 Isobutyl Methacrylate (parts) 22 39.1 16 22 22 44 11.3 22 22 a 2-Hydroxyethyl Methacrylate 38 20.9 44 38 38 16 48.7 38 38 4 0 (parts) ______ ______ ______ ______ ______ ______ ______ d di-t-myl Peroxide (*1) (parts) 5 5 10 0.6 5 5 11 0.5 Solids Mass Concentrations 60 60 60 60 60 60 60 60 60 a ____ ____ ____ ____ ____ ____ ____ U) Weight Average Molecular Weight 10000 10000 10000 2600 38000 10000 10000 2300 42000 Hydroxy Value (mg KOfi/g) 164 90 190 164 164 69 210 164 164 o Glass Transition Temperature 31.6 31.3 31.3 31.6 31.6 31.2 31.8 31.6 31.6 ______ (°C) ______ ______ ______ -______ ______ ______ -______ *1 Polymerization Initiator [0131] Production Examples of Reaction Product (C) Containing Alkoxysilyl Group Production Examples 10-23 A polycarbonate diol and "Swasol 1000" (product of COSNO OIL CO., LTD.; hydrocarbon solvent) shown in Table 2 below were added to a four-necked flask equipped with a stirrer, a thermometer, a condenser tube, and a nitrogen gas inlet; and heated to the temperature (reaction temperature) shown in Table 2 under a nitrogen atmosphere.

After reaching the predetermined temperature, an alkoxysilane compound shown in Table 2 was added, and a reaction was carried out for 5 hours. Solutions of reaction products (c) 1 to 14 were obtained in the above manner. Table 2 shows solids mass concentrations (%) and properties of the obtained reaction products. In Table 2, with respect to hydroxy values, 1> means a hydroxy value of less than 1.

[0132] In Table 2, (*1) to (*6) indicate the following.

The viscosity of the polycarbonate diol was measured using a B-type viscometer (Rotor No. 4) at 50°C and 6 rpm.

(*1) T-5650J: tradename of Asahi Kasei Chemicals Corp.; polycarbonate diol comprising 1,6-hexanediol and 1,5-pentanediol as diol components; number average molecular weight: 800; viscosity: 860 mPas; hydroxy value: mg KOH/g; solids content: 100% (*2) T-467l: tradename of Asahi Kasei Chemicals Corp.; polycarbonate diol comprising 1,6-hexanediol and 1,4-butanediol as diol components; number average molecular weight: 1,000; viscosity: 2,400 mPas; hydroxy value: 112 mg KOH/g; solids content: 100% (*3) UM-90: tradename of Ube Industries, Ltd.; polycarbonate diol comprising 1,6-hexanediol and 1,4-cyclohexanedimethanol as diol components; number average molecular weight: 900; viscosity: 7,000 mPas; hydroxy value: 124 mg KOH/g; solids content: 100% (*4) PC-N: polycarbonate diol synthesized using 1,6-hexanediol and 3-methylpentanediol as diol components and diphenyl carbonate as a carbonylating agent; number average molecular weight: 2,000; viscosity: 7,000 mPas; hydroxy value: 56 mg KOH/g; solids content: 100% (*5) PC-N: polycarbonate diol synthesized using 1,6-hexanediol and 3-methylpentanediol as diol components and diphenyl carbonate as a carbonylating agent; number average molecular weight: 380; viscosity: 120 mPas; hydroxy value: 260 mg KOH/g; solids content: 100% (*6) RR51O: tradename of Shin-Etsu Chemical Co., Ltd.; methyl/phenyl-type alkoxysilane oligomer [0133]

Table 2

Production Example No. 10 11 12 13 14 15 [ 16 f 17 1 18 19 r 20 21 22 r 23 Reaction Product No. 1 2 3 [ 4 [ 5 [ 6 [ 7 { 8 j 9 [ 10 [ 11 12 13[ 14 Polycarbonate Diol T5650J (*1) 500 500 500 500 500 500 500 500 T4671 (*2) 500 UM-90 (*3) 500 500 PC-N (*4) 500 PC-N (*5) 500 500 Solvent Swasol 1000 346.4 326.6 280.3 295.6 275.3 432.5 300.0 428.6 320.0 331.3 407.5 267.1 459.6 422.8 Alkoxysilane Compound y-Isocyanate propyltriethoxy-308.2 262.0 154.1 246.6 273.0 123.3 572.4 486.5 silane Li.) Tetramethoxy-189.7 142.3 silane _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ Methyltrimethoxy-silane 509.1 450.9 KR51O (*6) 200.0 500.0 Ratio of Alkoxysilyl Group --4/1 3/1 3/1 ----3/1 --- /Hydroxy Group _______ _______ _______ _______ _______ _______ _______ ______ _______ _______ _______ ______ _______ ______ Ratio of NCO Group 1/1 0.85/1 0.5/1 -----1/1 1/1 -1/1 1/1 0.85/1 /Hyclroxy Group _______ _______ _______ _______ _______ _______ _______ ______ _______ _______ _______ ______ ______ Reaction Temperature (°C) 100 100 100 120 120 120 120 120 100 100 120 100 100 100 Properties I Solids Mass Concentrations 70 70 70 70 70 70 70 70 70 70 70 70 70 I (%) _______ _______ _______ _______ _______ _______ _______ ______ _______ _______ _______ ______ _______ Number Average Molecular 1000 950 850 1100 1100 2400 5100 1200 1100 1100 1200 2200 550 450 Weight ______ ______ ______ ______ ______ ______ ______ _____ ______ ______ ______ _____ ______ Hydroxy Value 14 53.5 9 3 10 3 1> 1> 1> 8 1> 1> 18 (mg KOH/g) _______ _______ _______ _______ _______ _______ _______ ______ _______ _______ _______ ______ _______ _______ [0134] In Table 2, the numerical values showing proportions of polycarbonate diol and alkoxysilane compound are based on parts by mass.

[0135] Production of Coating Composition Examples 1-15 and Comparative Examples 1-9 Each compound and resin obtained in the above Production Examples, and raw materials shown in the after-mentioned Table 3 were mixed at the proportions shown in Table 3 by being stirred with a disperser so as to produce coating compositions. Coating Compositions 1 to 24 were thus obtained. In Table 3, the proportions of respective components of coating compositions are based on solids mass ratio. Further, (*7) to (*10) indicate the following.

(*7) N-3300: tradename of Sumika Bayer Urethane Co., Ltd.; hexamethylene diisocyanate, solids content: 100%, NCO content: 21.8% (*8) UV1164: Chiba-Geigy K.K.; UV absorber (*9) HALS292: Chiba-Geigy K.K.; Light stabilizer (*10) BYK-300: tradename of BYK-Chemie; Surface conditioner -[0136] Butyl acetate was added to each coating composition (No. 1-24) obtained in the above-mentioned Examples 1-15 and Comparative Examples 1-9, and the viscosity of each mixture was adjusted to 25 seconds at 20°C using Ford Cup No. 4.

[0137] Preparation of Test Plates Coating compositions 1 to 24 obtained in the above-mentioned Examples 1-15 and Comparative Examples 1-9 with a viscosity adjusted as above were used in the following manner to prepare test plates.

[0138] Elecron GT-10 (produced by Kansai Paint Co., Ltd., a thermosetting epoxy resin cationic electrodeposition coating composition) was applied by electrodeposition to a cold rolled steel plate having a thickness of 0.8 mm treated with zinc phosphate to a film thickness of 20 Tim, and cured by heating at 170°C for 30 minutes. Subsequently, Amilac TP-65-2 (produced by Kansai Paint Co., Ltd.; a polyester/melamine resin intermediate coating composition for automobiles) was applied to the coating film by air-spraying to a film thickness of 35 pm, and cured by heating at 140°C for 30 minutes. Aqueous metallic base coat WBC 713T #202 (produced by Kansai Paint Co., Ltd.; an acryl/melamine resin base coating composition for automobile basecoats; black paint) was applied to the coating film to a film thickness of 15 pm, allowed to stand at room temperature for 5 minutes and pre-heated at 80°C for 10 minutes. Thereafter, each of the viscosity-adjusted coating compositions obtained in the above Examples and Comparative Examples was applied on the above uncured base coating layer to a film thickness of about 35 pm. The coated substrate was allowed to stand at room temperature for 10 minutes, and then heated at 140°C for 20 minutes to cure the two coating layers simultaneously. Thus, test plates were prepared. The obtained test plates were allowed to stand at room temperature for seven days, and were subjected to the following coating performance test.

[0139] Performance Test Results Scratch Resistance: Each test plate was attached to an automobile roof using a water-resistant adhesive tape (produced by Nichiban Co., Ltd.), and the automobile having the test plate on its roof was washed 15 times in a car wash under the condition of 20°C±5°C. Thereafter, the 20° specular reflection (200 gloss value) of the test plate was measured, and the gloss retention (%) relative to the 20° gloss value before the test was calculated to evaluate the scratch resistance.

The higher the gloss retention, the better the scratch resistance. A required gloss retention (%) for a coating composition for automobiles etc. is generally 85% or greater. The car wash used was "P020 FWRC" (produced by Yasui Sangyo K.K.).

[0140] Acid Resistance: 0.4 cc of 40% sulfuric acid was added dropwise onto each test plate. The test plate was then heated for 15 minutes on a hot plate having a temperature of 60°C, and washed with water. The etching depth (pm) of the portion at which the sulfuric acid had been added was measured using a surface roughness tester ("Surfcom 570A"; a surface roughness measuring device; produced by Tokyo Seimitsu Co., Ltd.), with a cutoff of 0.8 mm (scanning rate of 0.3 rnm/sec, magnification of 5,000 times), to evaluate the acid resistance. The smaller the etching depth, the better the acid resistance. A required etching depth for a coating composition for automobiles etc. is generally 0.6 pm or lower.

[0141] Finishing quality (gloss) The 20° specular reflection (20° gloss value) of the test plate was measured to evaluate finishing quality. The greater the specular reflection, the better the finishing quality. A required specular reflection for a coating composition for automobiles etc. is generally 83 or greater.

[0142] Stain Resistance: The coated test plate was subjected to accelerated weathering in an accelerated weathering tester ("Sunshine Weather-C-Meter"; produced by Suga Test Instruments Co., Ltd.) for 600 hours. Thereafter, a staining material made of a mixture of mud, carbon black, mineral oil, and clay was applied to a piece of flannel, and lightly rubbed onto the coating surface of the coated test plate. The coated test plate was then allowed to stand in a constant temperature, constant humidity room at 20°C with a relative humidity of 75% for 24 hours, after which the coating surface was washed with running water. The degree of staining of the coating film was evaluated according to the difference in lightness (AL value) of the coated plate based on the following criteria. The smaller the AL value, the better the stain resistance. AL was calculated according to the following formula.

AL= (L value before the stain resistance test) -(L value after the stain resistance test) The L value was measured using "CR-200" (a colorimeter; produced by Konica Minolta Co., Ltd.).

a: AL < 0.2 b: 0.2 «= AL < 1 c: 1 «= AL < 2 d: 2 «= AL [0143] The stain resistance test was performed using test plates, each of which was prepared by applying Elecron GT- (produced by Kansai Paint Co., Ltd.; a thermosetting epoxy resin cationic electrodeposition coating composition) by electrodeposition to a cold rolled steel plate having a thickness of 0.8 mm treated with zinc phosphate to a film thickness of 20 pm, and curing the plate by heating at 170°C for 30 minutes; then, applying Amilac TP-65-2 (produced by Kansai Paint Co., Ltd.; a polyester/melamine resin intermediate coating composition for automobiles; white paint) to the coating film by air-spraying to a film thickness of 35 tim, and curing the film by heating at 140°C for 30 minutes; thereafter, each coating composition obtained in the above-mentioned Examples and Comparative Examples adjusted in viscosity was applied to the resulting coating substrate to a film thickness of 35 tim; afterward, each film was allowed to stand for 10 minutes at room temperature and then heated at 140°C for 20 minutes to cure the film. The obtained test plates were allowed to stand for seven days before subjected to the stain resistance test.

Table 3 summarizes the performance test results.

[0144]

Table 3

______ Examples _______ _______ _______ ________ _______ _______ ________ _______ _______ ________ _______ ________ 1 2 1 1 5 6 1 8 9 1 10 11 12 1 13 14 1 15 Coating Composition No. 1 2 3 4 5 6 7 8 9 j 10 11 12 13 14 15 A Hydroxy-No. 1 2 3 4 5 1 1 1 1 1 1 1 1 1 i Containing Resin Amount 58 69 55 58 58 58 1 58 58 58 58 58 58 58 58 58 Solution (part) ______ _______ _______ _______ _______ _______ I _______ _______ _______ _______ _______ _______ _______ _______ _______ B Polyisocyanate Compound 32 21 36 32 32 32 32 32 32 32 32 32 32 32 32 ______ N3300(*7) _________ ______ _______ _______ _______ _______ _______ I _______ _______ _______ _______ _______ _______ _______ _______ _______ C Reaction Product No. 1 1 1 1 1 2 4 5 6 7 9 10 11 12 13 Solution Amount Containing (Part) 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 Alkoxysilyl ______ Group _________ ______ _______ ________ _______ _______ _______ _______ _______ _______ ________ _______ _______ ________ _______ ________ 0v1l64(*8) 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 HALS292(*9) 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 BYK-300 (*10) 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Scratch Resistance 90 88 92 88 90 90 88 90 90 90 90 92 90 90 90 Acid Resistance (pm) 0.4 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.5 StainResistance b b a b a b b b b a b b b b b -Finishing Quality (Gloss) 90 92 88 95 86 90 88 89 88 87 90 91 90 88 93 [0145]

Table 3 (continued)

______ Comparative Examples ________ ________ ________ ________ _______ 1 2 3 4 5 6 7 8 9 Coating Composition 16 17 18 19 20 21 22 23 24 No. ______ ______ ______ ______ ______ ______ ______ A Hydroxy-No. 1 1 6 7 8 9 1 1 1 Containing Pmount 64 55 72.8 52.3 57.6 57.6 57.6 57.6 57.6 Resin (Part) -Solution ________ ______ ______ _______ _______ _______ _______ _______ _______ _______ B Polyisocyanate 36 35 17.2 37.7 32.4 32.4 32.4 32.4 32.4 -Compound N3300(*7) _____ _____ ______ ______ ______ ______ ______ ______ ______ C Reaction No. 1 1 1 1 3 8 14 Product I-\mount 10 10 10 10 10 10 10 Solution (Part) Containing Alkoxysilyl Group _______ ______ ______ _______ _______ _______ _______ _______ _______ _______ UV1164(*8) 2 2 2 2 2 2 2 2 2 HALS292(*9) 2 2 2 2 2 2 2 2 2 BYK-300 (*10) 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 T5650 (*1 10 -Polycarbonate Diol) ______ ______ _______ _______ ______ ______ _______ _______ ______ Scratch Resistance 70 90 83 90 90 90 90 90 88 Acid Resistance (pm) 0.4 0.5 0.7 0.4 0.8 0.4 0.6 0.4 0.7 Stain Resistance b c b b c a c a c Finishing Quality 90 90 90 80 96 75 91 73 92 (Gloss) ______ ______ _______ _______ _______ _______ _______ _______ _______ [0146] As shown in Table 3, Coating Compositions No. 1-15 (Examples 1-15) satisfy all of the required properties, i.e., scratch resistance, acid resistance, stain resistance, and finishing quality. In contrast, Coating Compositions No. 16-24 are remarkably inferior in at least one of those characteristics.