WO2007046533A2

WO2007046533A2 - Multi-package water-borne coating compositions and their coating method

Info

Publication number: WO2007046533A2
Application number: PCT/JP2006/321192
Authority: WO
Inventors: Yasuhiro Tomizaki; Junichi Kajima; Akira Kasari
Original assignee: Kansai Paint Co Ltd
Current assignee: Kansai Paint Co Ltd
Priority date: 2005-10-19
Filing date: 2006-10-18
Publication date: 2007-04-26
Anticipated expiration: 2008-04-19
Also published as: JP2009512736A; WO2007046533A3; JP5103390B2; JP2012158771A

Abstract

This invention provides a multi-package water-borne coating composition which comprises a water-soluble or water-dispersible, acid group-containing resin, pigment, neutralizer, thickener and water, characterized in that it is a multi-package water-borne coating composition in which the water-soluble or water- dispersible, acid group -containing resin is separated from the thickener and at least a part of the neutralizer before the use; and at a time of use a first liquid comprising the water-soluble or water- dispersible, acid group -containing resin is mixed with a second liquid comprising the thickener and at least a part of the neutralizer; the first liquid having a pH within a range of 6 - 9 and a solid content within a range of 20 - 50 mass%; and the second liquid having a solid content within a range of 0.5 - 10 mass%, water content of at least 70 mass% and pH higher than that of the first liquid by at least 0.5.

Description

DESCRIPTION

Multi-package Water-borne Coating Compositions and' Their Coating Method

Technical Field

This invention relates to basic compound-neutralized type multi-package water-borne coating compositions comprising water-soluble or water-dispersible, acid group-containing resin.

Background Art

Recently the guidelines concerning volatile organic compound have become severer, and for the purpose of environmental preservation, organic solvent-borne paint is being substituted with water-borne paint or powder paint. For water-borne paint, generally equivalent or higher coating film performance to or than that of conventional organic solvent-borne paint is required in many cases.

With the view to obtain water-borne paint having excellent coating film performance, use of higher molecular weight base resin, investigations in composition of paint formulations or the like have been practiced, however often encountering such problems as lowering in coating workability or in storage stability, while achieving high coating film performance. As a means for improving these drawbacks, attempts are made to prepare water-borne paint in multi-package form such as two-package form instead of single-package form, and use the contents of the multi-packages by mixing them immediately before application.

For example, JP Hei 9 (1997)-328654A (= EP-A-0835889) discloses a water-borne coating composition which is used by mixing at the time of use an aqueous emulsion of high molecular weight polyol and a hydrophilic polyisocyanate containing ethylene oxide recurring units which is mixed with an ionic surfactant. This water-borne coating composition excels in pot life and can form coating film excelling in water resistance. JP Hei 11 (1999)-140380A discloses an ambient temperature-drying two-package type water-borne coating composition of which pot life is made visible, which is used by mixing a base paint comprising water-dispersible copolymer which contains isocyanateτeactive functional groups, and water-soluble polymer molecule which contains isocyanate-reactive functional groups, with a crosslinking agent comprising a compound having at least two isocyanate groups per molecule, immediately before use. This two-package water-borne coating composition is capable of forming coating film excelling in weatherability, durability, adherability and soiling resistance.

JP 2000-290536A (= WO00/61691) discloses a resin composition for water-borne paint, which comprises the first liquid formed of an aqueous dispersion of organic polymer, colloidal silica and polyether-modified silane coupling agent, and the second liquid formed of organic reactive group -containing silane coupling agent. In this resin composition for water-borne paint, the functional groups of the polymer in the aqueous dispersion of organic polymer in the first liquid react with the organic reactive groups of the organic reactive group -containing silane coupling agent in the second liquid to effect curing.

JP2003-190868A (= EP1323754) discloses a water-borne two-component coating composition comprising an aqueous hydroxy functional component and non-aqueous polyisocyanate component, and a spray-coating method in which the water-borne two-component coating composition is mixed and spray-coated with high speed rotary sprayer. This water-borne two-component coating composition cures upon reaction of the aqueous hydroxy functional component and non-aqueous polyisocyanate component.

All of these water-borne paints as disclosed in the above-cited Official Gazettes are such that a water-borne base paint component and a crosslinking agent or curing agent component which exhibits reactivity with the resin in the water-borne base paint are separated as two components which are to be mixed at the time of actual use, i.e., two-component coating compositions. Whereas, water-borne coating compositions comprising acid group -containing resin emulsion, pigment, neutralizer and thickener and excelling in fluidability controlling ability occasionally show reduction in storage stability even when they do not contain - crosslinking agent or curing agent component, e.g., show viscosity increase with time. Again, water-borne paints comprising acid group-containing resin emulsion, pigment, neutralizer, thickener and crosslinking agent also frequently show storage stability reduction, even when they take the form of two-package system separately storing the crosslinking agent. This problem with storage stability is particularly conspicuous in summer time, and with the view to deal with this problem, low temperature-storage of paint is currently practiced.

Water-borne paint also contains a large quantity of water and there is a demand for saving transportation costs of water-borne paint, by reducing the water content of water-borne paint in the occasion of its transportation and adding water at the coating site.

Disclosure of the Invention

An object of the invention is to provide multi-package water-borne coating compositions comprising acid group -containing resin emulsion, pigment, neutralizer, thickener and, furthermore, crosslinking agent where necessary, which form coating film of excellent performance and finished appearance and show excellent storage stability. Another object of the present invention is to provide a coating method using the multi-package water-borne coating compositions. Still other object of the present invention is to contribute to reduction in transportation costs of water-borne coating compositions.

Objects other than the foregoing of the present invention will become clear from the following descriptions.

We have engaged in concentrative studies and now discovered that the above objects can be accomplished by multi-package coating compositions provided by mixing a specific water-borne coating base comprising acid group -containing resin emulsion and pigment, and a specific diluent containing a neutralize!¹, thickener and water, at a specific ratio at the time of application, and have completed the present invention.

Thus, the present invention provides a multi-package water-borne coating composition which comprises a water-soluble or water-dispersible, acid group -containing resin, pigment, neutralizer, thickener and water, characterized in that it is a multi-package water-borne coating composition in which the water-soluble or water-dispersible, acid group -containing resin is separated from the thickener and at least a part of the neutralizer before the use,^' and at a time of use a first liquid comprising the water-soluble or water-dispersible, acid group -containing resin is mixed with a second liquid comprising the thickener and at least a part of the neutralizer; the first liquid having a pH within a range of 6 - 9 and a solid content within a range of 20 - 50 mass%; and the second liquid having a solid content within a range of 0.5 - 10 mass%, water content of at least 70 mass% and pH higher than that of the first liquid by at least 0.5.

This invention also provides a coating method characterized by formulating a water-borne coating composition at its coating site by mixing a first liquid which comprises a water-soluble or water-dispersible, acid group-containing resin with a second liquid which comprises a thickener and at least a part of a neutralizer, and the remaining components of the multi-package water-borne coating composition,' and carrying out the coating using the same water-borne coating composition.

Conventional single-package water-borne coating compositions have a problem in storage stability such that acid group -containing resin therein is swollen and associated with neutralizer and thickener and the compositions show viscosity increase with time. In the present invention, multi-package water-borne coating composition is provided in which the acid group -containing resin is separated from the thickener and at least a part of the neutralizer, whereby avoiding swelling and association of the acid group -containing resin caused by the neutralizer and thickener during storage and solving the problem of poor storage stability.

Again, when water-borne coating compositions contain aluminum powder as pigment, the problem in storage stability is serious with conventional single-package water-borne coating compositions. By contrast, with the multi-package water-borne coating compositions of the present invention, no storage stability problem arises even when they contain aluminum powder.

According to the invention, where the first liquid is a water-borne coating base (A) comprising a water-soluble or water-dispersible acid group -containing resin, pigment and water! the second liquid is a diluent (B) having a pH within a range of 7 - 10 and comprising a neutralizer, thickener and water! and the two are used as mixed at a mass ratio, water-borne coating base (A)/diluent (B), within a range of 9/1 - 2/3, blendability of water-borne coating base (A) with the diluent (B) becomes very good and coating film formed from the coating composition exhibits particularly favorable performance and finished appearance. Furthermore, the water-borne coating base (A) can have a high concentration. Moreover, the diluent (B) can be prepared at the coating site by addition of water, which enables reduction in transportation cost of the coating composition.

According to the coating method of the present invention using the multi-package water-borne coating composition of the invention, coating film excelling in performance and appearance can be formed.

Hereinafter the multi-package water-borne coating composition of the invention is explained in further details.

The multi-package water-borne coating composition of the invention is a water-borne coating composition comprising a water-soluble or water-dispersible, acid group -containing resin, pigment, neutralizer, thickener and water, in which the water-soluble or water-dispersible, acid group -containing resin is separated from the thickener and at least a part of the neutralizer before the use! and at the time of use, the first liquid comprising the water-soluble or water-dispersible, acid group-containing resin and the second liquid comprising the thickener and at least a part of the neutralizer are mixed.

The first liquid containing a water-soluble or water-dispersible, acid group -containing resin is adjusted to have a pH value within a range of 6 - 9, preferably 7 - 8.6 J and a solid content within a range of 20 - 50 mass%, preferably 25 - 45 mass%; for favorable storage stability. The second liquid containing a thickener and at least a part of neutralizer is prepared to have a solid content of 0.5 - 10 mass%, preferably 0.8 - 5 mass%; a water content of no less than 70 mass%, preferably 80 - 99.5 mass%; and a pH value higher than that of the first liquid by at least 0.5, in particular, by at least 0.8, whereby the coating composition formed by mixing the first and second liquids can exhibit the intended paint and coating film performance. A representative embodiment of the multi-package water-borne coating composition of the invention is two-package water-borne coating composition in which the first liquid is a water-borne coating base (A) comprising a water-soluble or water-dispersible, acid group-containing resin, pigment and water; and the second liquid is a diluent (B) comprising a neutralizer, thickener and water.

Hereafter the multi-package water-borne coating composition of the invention is explained referring to this representative embodiment, it being understood that the water-borne coating compositions are in no way limited to this representative embodiment.

Water-soluble or water-dispersible, acid group -containing resin^

The water-soluble or water-dispersible, acid group -containing resin which is used as the base resin in the water-borne coating base (A) includes those resins having acid group(s) such as carboxyl, sulfo, phospho and the like in their molecules, and can be made water-soluble or water-dispersible by emulsion stabilization with surfactant or neutralization of the acid groups. Among the named acid groups, carboxyl group is preferred. Kind of the acid group -containing resin is subject to no particular limitation and, by way of example, various resins such as acrylic resin, polyester resin, polyurethane resin, epoxy resin; vinyl resin, fluorinated resin, silicone resin, cellulose-derived resin and modified products of these resins can be named. Of these, acrylic resin, polyester resin, polyurethane resin and the like can be conveniently used.

As typical examples of the water-soluble or water-dispersible, acid group -containing resin, hereafter water-soluble or water-dispersible acrylic resin, water-soluble or water-dispersible polyester resin and urethane resin emulsion are explained in further details.

Water-soluble or water-dispersible acrylic resin^ Water-soluble or water-dispersible acrylic resin can be prepared by such methods as, for example, polymerizing a monomeric mixture of acid group -containing polymerizable unsaturated monomer, hydroxyl group -containing polymerizable unsaturated monomer, (meth)acrylic acid ester and optionally still other polymerizable unsaturated monomer(s) by a polymerization method known per se, such as solution polymerization, bulk polymerization or the like, and neutralizing the resulting acrylic copolymer having acid groups such as carboxyl group, with a neutralizer (Method l); or emulsion polymerizing the monomeric mixture as above-described, in an aqueous medium, in the presence of a dispersion stabilizer such as a surfactant, in single stage or plural stages, whereby producing fine particulate acrylic resin emulsion (Method 2).

As the polymerizable unsaturated monomers useful in the above Methods 1 and 2, for example, (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl

(meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, lauryl (meth)acrylate, 2-ethylhexyl (meth)acrylate and the like! hydroxyl group -containing polymerizable unsaturated monomers such as 2-hydroxyethyl (meth) aery late, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate and the like; carboxylic acid group -containing polymerizable unsaturated monomers such as unsaturated monocarboxylic acid, e.g., acrylic acid, methacrylic acid and the like, polymerizable unsaturated polybasic acid, e.g., maleic acid, itaconic acid, fumaric acid, mesaconic acid and the like, modifications thereof, e.g., anhydrides or half-esterification products of these unsaturated polybasic acids; sulfo group -containing polymerizable unsaturated monomers such as

2-acrylamido-2-methylpropanesulfonic acid, allylsulfonic acid, sodium styrenesulfonate, sulfoethyl methacrylate and the like! phospho group-containing polymerizable unsaturated monomers such as (2-acryloyloxyethyl) acid phosphate, (2-methacryloyloxyethyl) acid phosphate, (2-acryloyloxypropyl) acid phosphate, (2-methacryloyloxypropyl) acid phosphate and the like! C2 18 alkoxyalkyl esters of (meth)acrylic acid such as methoxybutyl (meth)acrylate, methqxyethyl (meth) aery late and the like! aminoacrylic monomers such as N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N-t'butylaminoethyl (meth) aery late, N,N-dimethylaminopropyl (meth) aery late and the like; amido group -containing polymerizable unsaturated monomers such as (meth)acrylamide, N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-butyl (meth)acrylamide, N-dimethyl (meth) aery lamide and the like; glycidyl group -containing monomers such as glycidyl (meth) aery late and the like; aromatic vinyl compounds such as styrene, ormethylstyrene, vinyltoluene and the like! acrylonitrile, vinyl acetate, vinyl chloride and the like can be named.

Solution polymerization of those polymerizable unsaturated monomers can be conducted, for example, in a water-compatible organic solvent such as ethylene glycol monobutyl ether or the like, using a radical polymerization catalyst such as

2,2'-azobisisobutyronitrile, benzoyl peroxide, ammonium persulfate and the like. Thus obtained acrylic resin can generally have a hydroxyl value within a range of 20 - 200 mgKOH/g, in particular, 50 - 150 mgKOH/g; an acid value generally within a range of 20 - 150 mgKOH/g, in particular, 30 - 80 mgKOH/g; and a number- average molecular weight generally within a range of about 3,000 - 100,000, in particular, 5,000 - 30,000.

In the present specification, number- average molecular weight is the value measured with gel permeation chromatograph ("HLC 8120GPC", tradename, Tosoh Corporation) and converted based on the number- average molecular weight of standard polystyrene. Each test specimen's number-average molecular weight is measured using four columns of "TSKgel G-4000 HXL", "TSKgel G-3000 HXL", "TSKgel G-2500 HXL" and "TSKgel G-2000 HXL" (tradenames, Tosoh Corporation), under the conditions of mobile phase = tetrahydrofuran, measuring temperature = 40 ⁰C, flow rate = 1 cc/min. and the detecter = RI.

Thus obtained acrylic resins can be made water-soluble or water-dispersible upon neutralization of acid groups present therein. As the neutralizer, for example, ammonia; primary monoamines such as ethylamine, propylamine, butylamine, benzylamine, monoethanolamine, neopentanolamine, 2-aminopropanol, 3-aminopropanol and the like! secondary monoamines such as diethylamine, diethanolamine, di-n or driso-propanolamine, N-methylethanolamine, N-ethylethanolamine and the like! tertiary monoamines such as dimethylethanolamine, trimethylamine, triethylamine, triisopropylamine, methyldiethanolamine, N,N-dimethylaminoethanol and the like! polyamines such as diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, methylaminopropylamine and the like can be named.

In the acrylic resin emulsion obtained by above -described emulsion polymerization method, acrylic resin particles are uniformly dispersed in the aqueous medium. For example, the acrylic resin emulsion prepared by emulsion polymerization of polymerizable unsaturated monomers in single stage or plural stages in the presence of a suitable dispersion stabilizer can contain fine particles of the acrylic resin having an average particle size ranging from 0.05 - 1.0 μm. As the polymerizable unsaturated monomers to be emulsion-polymerized, those above-named by way of examples can be used. Furthermore, where necessary, a minor amount of a polyvinyl compound having at least two polymerizable unsaturated bonds per molecule can be concurrently used to provide an emulsion containing intrap articulately crosslinked acrylic resin particles. As the polyvinyl compound, for example, ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, divinylbenzene, trimethylolpropane tri(meth)acrylate and the like can be named. As the dispersion stabilizer, for example, nonionic surfactant such as polyoxyethylene nonyl phenyl ether and the like! anionic surfactant such as polyoxyethylene alkyl aryl ether sulfate and the like! or water-soluble resin such as acrylic resins having an acid value of 20 - 150 mgKOH/g and a number-average molecular weight ranging about 5,000 - 30,000 can be used.

So obtained acrylic resin emulsion can generally have an acid value within a range of 5 - 200 mgKOH/g, in particular, 5 - 80 mgKOH/g; a hydroxyl value generally within a range of 5 - 150 mgKOH/g, in particular, 20 - 120 mgKOH/g,' a weight-average molecular weight generally within a range of 1,000 - 400,000, in particular, 10,000 - 300,000; and a glass transition temperature within a range of 10 - 80⁰C, in particular, 15 - 70°C.

In the present specification, weight- average molecular weight is the weight-average molecular weight measured with gel permeation chromatograph ("HLC 8120 GPC", tradename, Tosoh Corporation) and converted based on the weight- average molecular weight of standard polystyrene. The measuring conditions of weight-average molecular weight of each test specimen are same to those as described for the case of number-average molecular weight. The acrylic resin emulsion as prepared in the above manner may be neutralized with a neutralizer, where necessary. As the neutralizer, those named earlier by way of examples can be used.

Water-soluble or water-dispersible polyester resin^: As the polyester resin, those obtained by esterification reaction of polybasic acid with polyhydric alcohol and which have hydroxyl groups and also acid groups such as carboxyl group for improving water-dispersibility in their molecules can be used.

Polybasic acid is a compound having at least two carboxyl groups per molecule, examples of which include phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, hexahydrophthalic acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid and anhydrides thereof. Polyhydric alcohol is a compound having at least two hydroxyl groups per molecule, examples of which include ethylene glycol, propylene glycol, butylene glycol, hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, triethylene glycol, glycerine, trimethylolethane, trimethylolpropane and pentaerythritol. Such a polyester resin can be prepared by a means known per se, for example, by esterification reacting polybasic acid with polyhydric alcohol and adding to the product polybasic acid such as trimellitic acid to introduce carboxyl groups. After termination of the reaction, the resulting polyester resin can be fluidized by addition of a minor amount of organic solvent, where necessary, to facilitate its dispersing operation in water and then carboxyl groups in the polyester resin are neutralized to make the resin water-dispersible. As the organic solvent, for example, ethers such as isopropyl ether, ethylene glycol monomethyl ether, diethylene glycol monobutyl ether and the like! alcohols such as ethyl alcohol, butyl alcohol, hexyl alcohol and the like; and ketones such as methyl isobutyl ketone, methyl ethyl ketone and the like can be conveniently used. Preferred use rate of such an organic solvent is within a range of 1 - 20 mass%, in particular, 2 - 8 mass%, based on the reaction product (polyester resin). Also as the neutralizer, those previously exemplified in respect of the water-soluble and/or water-dispersible acrylic resin can be similarly used.

Furthermore, it is also possible to use such polyester resins which are modified with fatty acid such as soybean oil fatty acid, coconut oil fatty acid, dehydrated castor oil fatty acid, tall oil fatty acid, safflower oil fatty acid, linseed oil fatty acid and the like. Preferred content of such a fatty acid is generally not more than 30% by weight in terms of the oil length.

The polyester resin can generally have a hydroxyl value within a range of 50 - 220 mgKOH/g, in particular, 65 - 200 mgKOH/g; acid value generally within a range of 5 - 70 mgKOH/g, in particular, 5 - 50 mgKOH/g; and a number-average molecular weight generally within a range of about 800 - 20,000, in particular, 1,200 - 13,000.

Urethane resin emulsion:

The urethane resin emulsion can be normally obtained by reacting an isocyanate group -containing prepolymer formed of polyisocyanate, polyol and hydroxy acid, in the presence of water. As the urethane resin emulsion, for example, carboxyl-containing polyurethane resin emulsion formed by single-stage or plural-stage polymerization of polyisocyanate (a), high molecular weight polyol (b), dimethylolalkanoic acid (c) and, where necessary, chain-extender (d), adding to the resulting isocyanate-containing prepolymer (i) monoamine and water by any optional order and emulsion-dispersing the prepolymer in the water; carboxyl-containing polyurethane resin emulsion formed by adding, to the prepolymer (i), a chain extender (e), and where necessary, emulsifying agent and water by any optional order and emulsion-dispersing the prepolymer in the water! and the like can be used. As the polyisocyanate (a), for example, C2 12 aliphatic diisocyanate such as hexamethylene diisocyanate, 2,2,4-trimethylhexane diisocyanate, lysine diisocyanate and the like! C4-18 alicyclic diisocyanate such as 1,4-cyclohexane diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, methylcyclohexylene diisocyanate, isopropylidenecyclohexyl-4,4'-diisocyanate and the like! aromatic diisocyate such as xylylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, polyphenylmethane diisocyanate (hereafter referred to as polymeric MDI) and the like; and modification products of these diisocyanates (carbodiimide, urethodione, urethoimine-containing modification products, isocyanurate compound, biuret compound and the like) can be named. They can be each used singly or in combination of two or more. Of these, alicyclic diisocyanates such as 1,4-cyclohexane diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate and the like are particularly preferred.

The high molecular weight polyol (b) includes polyether diols and polyester diols having a number-average molecular weight within a range of 500 - 5,000, in particular, 1,000 - 3,000. More specifically, for example, those obtained by polymerizing or copolymerizing (block or random) alkylene oxide (ethylene oxide, propylene oxide, butylene oxide and the like) and/or heterocyclic ether (tetrahydrofuran and the like), e.g., polyethylene glycol, polypropylene glycol, polyethylene-propylene (block or random) glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol, polyoctamethylene ether glycol and the like; those obtained by polycondensation reaction of dicarboxylic acid (adipic acid, succinic acid, sebacic acid, glutaric acid, maleic acid, fumaric acid, phthalic acid and the like ) with glycol (ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 3-methyM,5-pentanediol, neopentyl glycol, bishydroxymethylcyclohexane and the like), e.g., polyethylene adipate, polybutylene adipate, polyhexamethylene adipate, polyneopentyl adipate, poly-3-methylpentyl adipate, polyethylene/butylene adipate, polyneopentyl/hexyl adipate and the like! polylactonediol, for example, polycaprolactonediol, poly-3-methylvalerolactonediol and the like! polycarbonatediol; and mixtures of at least two of the foregoing can be named.

As the dimethylolalkanoic acid (c), for example, dimethylolacetic acid, dimethylolpropionic acid, dimethylolbutyric acid and the like can be named, dimethylolpropionic acid being particularly preferred. An adequate use rate of such dimethylolalkanoic acid (c) is normally within a range of 0.5 - 20 mass%, preferably 1 - 10 mass%, based on the total constituent components of the prepolymer (i). With the use of such dimethylolkanonic acid (c), carboxyl groups can be introduced into the prepolymer (i).

As the chain-extender (d), low molecular weight (in terms of number-average molecular weight, less than 500) polyol, polyamine and the like are preferred. As the low molecular weight polyol, for example, glycols which are named as the starting material of above polyester diol and their alkylene oxide low molar adducts, trihydric alcohols such as glycerine, trimethylolethane, trimethylolpropane and the like and their alkylene oxide low molar adducts, and the like can be named. As the polyamine, for example, ethylenediamine, tetramethylenediamine, monohydroxyethyldiethylenediamine, ' isophoronediamine and the like can be named. The chain- extender (d) can be adequately used within a range of generally 0 - 20 mass%, preferably 0.5 - 10 mass%, based on the above-described high molecular weight polyol (b). The prepolymer (i) can be obtained by single-stage or plural-stage synthesis using above (a) - (c) components and optionally (d) component, by a means known per se. The (a) - (c) components can be reacted at such ratios that isocyanate groups and carboxyl groups should remain in the formed prepolymer (i). It is normally desirable to react them at such ratios that the equivalent ratio of isocyanate group /hydroxy 1 group lies within a range of 1.1 - 1.9.

Thus a carboxyl-containing polyurethane resin emulsion can be prepared by adding monoamine and water to so obtained prepolymer (i) by optional order to self-emulsify and disperse the prepolymer in the water. As the monoamine, per se known amine, for example, those primary monoamines, secondary monoamines and tertiary monoamines named by way of examples of neutralizer of the acrylic resin can be used.

Again, a carboxyl-containing polyurethane resin emulsion can be also prepared by adding a chain-extender (e), optionally an emulsifier and water, by any optional order, to the resulting prepolymer (i) to emulsify and disperse the latter in the water. As the chain-extender (e), those polyamines named in respect of the chain-extender (d) can be used. As the emulsifier, for example, nonionic surfactant such as higher alcohol, alkylene oxide adduct and the like; anionic surfactant such as alkylbenzene sulfonate and the like can be named.

As the water-soluble or water-dispersible, acid group -containing resin, those comprising as the resin component at least one of the acrylic resins and polyester resins are preferred from the standpoint of coating film performance and storage stability. Furthermore, by concurrent use of these resins with the urethane resin emulsion, coating film performance and appearance can be still improved.

Water-borne coating base (A):

Water-borne coating base (A) in the multi-package water-borne coating compositions of the present invention comprises above described water-soluble or water-dispersible acid group -containing resin, pigment and water.

The water-borne coating base (A) can contain the water-soluble or water-dispersible, acid group -containing resin at a solid concentration generally within a range of 5 - 45 mass%, preferably 8 - 40 mass%, inter alia, 10 - 30 mass%.

Pigment:

Pigment to be contained in the water-borne coating base (A) can be at least one selected from coloring pigments and effect pigments, and where necessary, extender, rust-preventive pigment and the like can also be used. As coloring pigment, for example, titanium dioxide, zinc flower, carbon black, molybdenum red, chrome yellow, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, isoindoline pigment, threne pigment, perilene pigment and the like can be named. As effect pigment, for example, aluminum powder, mica, mica surface-coated with metal oxide, micaceous iron oxide, colored aluminum oxide and the like can be named! and as the extender, for example silica, calcium carbonate, barium sulfate, clay, mica, talc and the like can be named. Again as rust-preventive pigment, for example, aluminum dihydrogentripolyphosphate, calcium ion-exchange silica, zinc -phosphate and the like can be named. These pigments can be used each singly or in combination of two or more.

These pigments can be directly mixed with the water-soluble or water-dispersible, acid group -containing resin, but it is particularly preferred for pigments other than effect pigment to be dispersed in advance with water-soluble or water-dispersible pigment-dispersing resin or the like, and blended as pigment paste.

Blend ratio of such pigment(s) in the water-borne coating base (A) is not subject to any particular limitation, but normally it is preferred to be within a range of 1 - 100 mass parts, in particular, 3 - 80 mass parts, inter alia, 5 - 75 mass parts, per 100 mass parts of solid content of the water-soluble or water-dispersible, acid group -containing resin, from the viewpoint of favorable appearance and physical properties of formed coating film.

Crosslinking agent:

The water-borne coating base (A) can contain crosslinking agent where necessary. As the crosslinking agent, those which can form crosslinkage upon reacting with reactive functional groups in the water-soluble or water-dispersible, acid group -containing resin such as, for example, amino resin crosslinking agent, blocked polyisocyanate compound and the like can be named. The crosslinking agent is not necessarily contained in the water-borne coating base (A), but can be contained in later described diluent (B). As the amino resin crosslinking agent, for example, partially etherified or fully etherified melamine resin formed by etherifying a part or all of methylol groups in methylolated melamine with C₁-S monohydric alcohol, which has 1 to 5 triazine nuclei and a molecular weight within a range of 300 - 3,000 is preferred. Such a melamine resin may further contain imino groups.

The blocked polyisocyanate compound includes those polyisocyanates which are earlier named as polyisocyanate (a) useful for preparation of the urethane resin emulsion, with their isocyanate groups blocked with a blocking agent. As the blocking agent, those known per se can be used. For example, phenols such as phenol, cresol, xylenol and the like," lactams such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, β-propiolactam and the like! alcohols such as methanol, ethanol, n- or i-propyl alcohol, n-, r, or t-butyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, benzyl alcohol and the like! oximes such as formamidoxime, acetaldoxime, acetoxime, methyl ethyl ketoxime, diacetyl monoxime, benzophenone oxime, cyclohexanone oxime and the like; and active methylene-derived blocking agents such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, acetylacetone and the like can be conveniently used. Blocked polyisocyanate compounds can be prepared by any means known per se. For example, free isocyanate groups in those polyisocyanate compounds can be readily blocked by mixing the polyisocyanate compounds with those blocking agents.

The water-borne coating base (A) can be prepared by mixing the water-soluble or water- dispersible, acid group -containing resin, pigment and water and, where necessary, crosslinking agent.

Water-borne coating base (A) excelling in storage stability can be obtained when its pH is adjusted to be within a range of 6 -9, preferably 6.2 - 8.8, inter alia, 7 - 8.6; and the solid content, within a range of 20 - 50 mass%, preferably 25 - 45 mass%, inter alia, 28 - 35 mass%. Adjustment of pH value of the water-borne coating base (A) can be effected, for example, by adjusting pH of the water-soluble or waterdispersible, acid group-containing resin used, or by adding a neutralizer.

When a crosslinking agent is blended in the water-borne coating base (A), its blend ratio is conveniently no more than 50 mass parts, preferably 15 - 40 mass parts, inter alia, 20 - 35 mass parts, per 100 mass parts of combined solid contents of the water-soluble or water-dispersible, acid group -containing resin and the crosslinking agent. Water is the main volatile component in the water-borne coating base (A), and it is convenient that water occupies at least 60 mass%, preferably at least 80 mass%, inter alia, at least 90 mass%, of the total volatile component. Components other than water, which can be present in the volatile component, include neutralizer, organic solvent and the like. A neutralizer is blended for improving stability of the acid group- containing resin in an aqueous medium, by increasing the resin's affinity to water by neutralizing the same. Also an organic solvent is blended, where necessary, for improving stability of the water-borne coating base (A) and finished appearance of the coating film formed. Normally hydrophilic organic solvent is used.

Diluent (B): Diluent (B), which is used in combination with above water-borne coating base (A) in the multi-package water-borne coating composition of the present invention, contains a neutralizer, thickener and water as the essential components.

The neutralizer is used for neutralizing the acid groups of the water-soluble or water-dispersible, acid group-containing resin in the water-borne coating base (A), which normally is basic. As the neutralizer, for example, ammonia; primary monoamines such as ethylamine, propylamine, butylamine, benzylamine, monoethanolamine, neopentanolamine, 2-aminopropanol, 2-amino-2-methyl-l-propanol, 3-aminopropanol and the like; secondary monoamines such as diethylamine, diethanolamine, di-n- or di-iso-propanolamine, N-methylethanolamine, N-ethylethanolamine and the like; tertiary monoamines such as 2-(dimethylamino)ethanol, trimethylamine, triethylamine, triisopropylamine, methyldiethanolamine, dimethylaminoethanol and the like; and polyamines such as diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, methylaminopropylamine and the like can be named. Of these, 2-(dimethylamino)ethanol, 2-amino-2-methyl-l-propanol, N-methylethanolamine and diisopropanolamine are preferred. A thickener is blended aiming at prevention of sagging of coating composition when a water-borne coating composition of the present invention is applied, which includes, for example, cellulose derivatives such as carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose and the like; petroleum waxes such as paraffin wax, microcrystalline wax and the like! vegetable waxes such as carnauba wax, candelilla wax, rice wax, Japan wax and the like! animal waxes such as bees wax; spermaceti and the like! mineral waxes such as montan wax, ozokerite, ceresine and the like! ^v synthesized waxes such as polyethylene wax, Fischer- Tropsch wax, fatty acid amide wax, hardened castor oil (castor wax) and the like! inorganic substances such as silicate, montmorillonite, colloidal alumina, lithium magnesium sodium silicate and the like.' polyvinyl alcohol, polyvinylpyrrolidone, sodium polyacrylate, polyacrylic acid ester copolymer, polyether dialkyl ester, partial ester of vinyl methyl ether-maleic anhydride copolymer, sodium alginate and the like. Of these, fatty acid amide wax, lithium magnesium sodium silicate and polyacrylic acid ester copolymer are preferred. The diluent (B) is adjusted to have a solid content normally within a range of 0.5 - 10 mass%, preferably 0.8 - 5 mass %, inter alia, 1.0 - 4 mass%; a water content of normally at least 70 mass%, preferably within a range of 80 - 99.5 mass%, inter alia, 90 - 99 mass%; and a pH generally within a range of 7 - 10, preferably 7.5 - 9.8, inter alia, 8.0 - 9.5, which is higher than the pH of the water-borne coating base (A) by at least 0.5 , preferably at least 0.8, inter alia, by at least 0.9. Therefore, the neutralizer is blended at such a ratio as will let fall the pH of the diluent (B) within the above-specified range. Convenient amounts of such neutralizer and thickener in the diluent (B) are generally within the following ranges, per 100 mass parts of the diluent (B): neutralizer^ 0.1 - 15 mass parts, preferably 0.2 - 10 mass parts, inter alia, 0.3 - 7.5 mass parts thickener^ 0.1 - 10 mass parts, preferably 0.15 - 7.5 mass parts, inter alia, 0.2 - 5 mass parts.

Multi-package water-borne coating compositions^'

The multi-package water-borne coating composition of the present invention can be formulated at the time of use, for example, at their coating site, by mixing the water-borne coating base (A) with the diluent (B) as described in the above.

In the multi-package water-borne coating composition, no thickener is blended in the water-borne coating base (A) and the neutralizer is blended in the minimum possible amount, whereby swelling or association of the acid group -containing resin in the water-borne coating base (A) can be suppressed, and also in the occasion of formulating the water-borne coating composition by mixing the components, the neutralizer present in the diluent (B) contributes to neutralization of the acid group -containing resin and flowability of the water-borne coating composition can be controlled by this neutralizer and the thickener.

The water-borne coating base (A) and the diluent (B) are conveniently blended to form the water-borne coating composition of the present invention, at the water-borne coating base (A)/diluent (B) mass ratio generally within a range of 9/1 - 2/3, preferably 7/1 - 5/6, inter alia, 5/1 - 1/1, for favorable mixing property of the coating composition.

The diluent (B) can be normally offered in one package, while it is also possible to divide it into, for example, two and mix the two at the time of formulating a coating composition immediately before coating operation, to make a single package diluent (B).

The coating composition of the present invention can further contain, where necessary, paint additives known per se, such as hardening catalyst, defoamer, coated surface treating agent, ultraviolet absorber, ultraviolet stabilizer, flowability controlling agent, surface slipping agent and the like. These paint additives may be added and blended in the occasion of mixing the water-borne coating base (A) with diluent (B), but it is normally convenient to mix them in advance, with either one, or both, of the water-borne coating base (A) and the diluent (B).

Coating method:

According to the present invention, also a method comprising mixing a first liquid comprising a water-soluble or water-dispersible, acid group -containing resin with a second liquid comprising a thickener and at least a part of a neutralizer, and the remaining component(s) of the multi-package water-borne coating composition at a coating site to formulate a water-borne coating composition; and thereafter carrying out the coating using the same coating ^v composition.

Mixing means of those constituent components of the multi-package water-borne coating composition is subject to no particular limitation, and any mixing apparatus known per se can be used. As the mixing apparatus, for example, dynamic agitation devices such as paddle blade-type stirrer, high-speed dissolver (which is also called "disperser"), homo-mixer (rotor/stator type homogenizer) and the like! and static agitation devices such as Kenics static mixer, static mixers by Fujikin Co., such as "KONGOH-KUN", "BUNSAN-KUN" (tradenames), and paint preparation means disclosed in JP Patent Application No. 2004-334448 (see: WO2006/054478) (*) can be named.

(*): Paint preparation means disclosed in JP Patent Application No. 2004-334448: Mixing means comprising throwing into a preparation tank starting materials of a coating composition to be mixed and dispersed, sucking with pump the starting materials in the preparation tank, passing the starting materials sucked with the pump through flow path contraction portion and discharging the flow trough an exit sunk in the starting materials in the preparation tank, whereby carrying out stirring and mixing dispersion. The flow path-contraction portion is preferably formed of plural orifices.

Thus formulated water-borne coating composition is applied onto a substrate. The application can be conducted by per se known means, for example, air spray coating, rotary atomizing coating, dip coating, roll coating or the like. Air spray coating or rotary atomizing coating can be conducted with application of static , electricity. The substrate which can be coated with the water-borne coating composition of the present invention is not particularly limited, which may be, for example, metals such as iron, zinc-plated sheet steel, zinc alloy-plated sheet steel, tin plate and the like! these metals on which primer coating film is formed! plastics, paper, concrete, mortar and the like. The coating film thickness may be within a range of normally 5 - 50 μm, preferably 10 - 40 μm, as dry or cured film thickness. Baking of the coating film can be effected normally at 80 - 200°C, preferably 120 - 18O⁰C, for about 5 - 40 minutes.

Where necessary, clear coating composition may be applied onto the coating film formed by the method of the present invention.

Examples

Hereinafter the present invention is explained more specifically, referring to working examples and comparative examples. The invention, however, is in no way limited to these working examples only. In the following examples, parts and percentages are by mass.

Production Example 1- Preparation of aqueous acrylic resin solution (a-l)

A reactor was charged with 75 parts of ethylene glycol mono-n-butyl ether whose temperature was then raised to 115⁰C in gaseous nitrogen current. When 115°C was reached, a mixture of 20 parts of methyl methacrylate, 20 parts of n-butyl methacrylate, 30 parts of isobornyl acrylate, 11 parts of styrene, 5 parts of 2-hydroxyethyl acrylate, 4 parts of acrylic acid, 10 parts of RMA-450^{(note 1}} and 1 part of 2,2'-azobisisobutyronitrile was added over 3 hours, followed by 2 hours' aging. Then 25 parts of ethylene glycol mono-n-butyl ether was added, to provide an acrylic resin solution having an acid value of 31 mgKOH/g, viscosity Z4 (Gardner bubble viscometer) and a solid content of 50%. Thus obtained 50%-solid acrylic resin solution was neutralized with 2-(dimethylamino)ethanol and mixed with deionized water to provide a water-soluble acrylic resin solution (a-l) having a solid content of 35% and pH 7.5.

(note l) RMA-450M: tradename, Nippon Nyukazai Co., Ltd., methoxypolyetylene glycol monomethacrylate (pentatetracontamer) .

Production Example 2'- Preparation of acrylic resin emulsion (a-2)

A reactor was charged with 140 parts of deionized water, 2.5 parts of Newcol-707SF (tradename, Nippon Nyukazai Co., Ltd., a surfactant, solid content^ 30%) and 1 part of a monomeric mixture (mixture of 55 parts of methyl methacrylate, 8 parts of styrene, 9 parts of n-butyl acrylate, 5 parts of 2 -hydroxy ethyl acrylate, 2 parts of 1,6-hexanediol diacrylate and 1 part of methacrylic acid), which were stirred and mixed in nitrogen gaseous current. After addition of 3 parts of 3% aqueous ammonium persulfate solution at 60°C, the temperature was raised to 80°C, and a pre-emulsion formed of the remaining 79 parts of the monomeric mixture, 2.5 parts of

Newcol-707SF, 4 parts of 3% aqueous ammonium persulfate solution and 42 parts of deionized water was added to the reactor with a quantitative pump over 4 hours, followed by an hour's aging.

Furthermore, to the reactor 20.5 parts of another monomeric mixture (mixture of 5 parts of methyl methacrylate, 7 parts of n-butyl acrylate, 5 parts of 2-ethylhexyl acrylate, 3 parts of methacrylic acid and 0.5 part of Newcol-707SF) and 4 parts of 3% aqueous ammonium persulfate solution were simultaneously dropped at 80°C over 1.5 hours, followed by an hour's aging. The reaction mixture was then diluted with 30 parts of deionized water and filtered through

200-mesh nylon cloth at 30°C. Further adding deionized water to the filtrate and adjusting the pH to 7.5 with 2-(dimethylamino)ethanol, an acrylic resin emulsion (a-2) having an average particle diameter of 0.1 μm and solid content of 20% was obtained. Production Example 3: Preparation of aqueous polyester resin dispersion (b-l)

A reactor was charged with 273 parts of trimethylolpropane, 200 parts of succinic anhydride and 490 part of Cardura ElOP (tradename, Japan Epoxy Resin Co., of which chief ingredient is neodecanoic acid monoglycidyl ester) which were reacted at 100 - 230⁰C for 3 hours (a sample taken at that time had a hydroxyl value of 350 mgKOH/g and a number- average molecular weight of 580). Further 192 parts of trimellitic anhydride was added and condensation reacted at 180⁰C, to provide a polyester resin having an¹- acid value of 49 mgKOH/g, hydroxyl value of 195 mgKOH/g and number- average molecular weight of 1,500.

Adding to this polyester resin 2-(dimethylamino)ethanol and deionized water, an aqueous polyester resin dispersion (b-l) of pH 7.5 having a solid content of 40% was obtained.

Production Example 4: Preparation of urethane resin emulsion (c-l)

A polymerization vessel was charged with 115.5 parts of polybutylene adipate having a number- average molecular weight of 2,000, 115.5 parts of polycaprolactonediol having a number- average molecular weight of 2,000, 23.2 parts of dimethylolpropionic acid, 6.5 parts of 1,4-butanediol and 120.1 parts of l-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane, which were reacted at 85°C for 7 hours in nitrogen gaseous current under stirring to provide a NCO-terminal prepolymer having a NCO content of 4.0%. The prepolymer then was cooled to 50⁰C and uniformly dissolved in 165 parts of acetone added. To the solution 15.7 parts of 2-(dimethylamino)ethanol was added with stirring, and while the system was maintained at no higher than 5O⁰C, 600 parts of deionized water was added. The resulting aqueous dispersion was kept at

50⁰C for 2 hours to complete the chain extending reaction with water. Distilling the acetone off under reduced pressure at a temperature not higher than 7O⁰C, a urethane resin emulsion (c-l) of pH 7.5 having a solid content of 39% was obtained. Preparation of water-borne coating base (A) liquid Production Example 5

Mixing 57 parts of the water-soluble acrylic resin solution (a-l) having a solid content of 35% as obtained in Production Example 1, 150 parts of the acrylic resin emulsion (a-2) having a solid content of 20% as obtained in Production Example 2, 50 parts of the aqueous polyester resin dispersion Gr l) having a solid content of 40% as obtained in Production Example 3, 38 parts of Cymel 325^{(note 2)}, 25 parts of ethylene glycol monobutyl ether, 20 parts of fine particulate barium sulfate, 1 part of ultraviolet absorber, 5 parts of defoaming agent, 2 parts of phospho group -containing acrylic dispersing resin, 5 parts of 2-(dimethylamino)ethanol, 27 parts of ALPASTE 7679NS^(note ³⁾ and tap water, a water-borne coating base (A-l) liquid of pH 7.9 having a solid content of 35% was prepared. (note 2) Cymel 325: trandename, Nihon Cytec Industries Co., a methylated melamine resin, solid content = 80% (note 3) ALPASTE 7679NS: tradename, Toyo Aluminum Co., aluminum flake paste, aluminum content = 65%.

Production Examples 6 - 15

Production Example 5 was repeated except that the components as identified in the following Table 1 were blended at the ratios as indicated in Table 1, to provide each of the water-borne coating base (A) liquid. The solid content, pH, and the result of storage stability test conducted by the following test method of each of the water-borne coating base (A) liquid were as shown in the same Table 1.

Storage stability: Each water-borne coating base (A) liquid immediately after preparation was hermetically sealed and stored at 40°C for 30 days. The condition of the coating base (A) liquid after the storage and its viscosity change were evaluated according to the following standard:

® : nearly no occurrence of seeding and nearly no viscosity change compared with the initial product! excellent O: a little seeding or a little viscosity change occurred compared with the initial product! good Δ^: considerable seeding or large viscosity change occurred compared with the initial product x • water-borne coating base (A) liquid gelled or showed heavy viscosity increase.

The (note 4) in Table 1 signifies the following: (note 4) SUMIDUR BL-3175: tradename Sumika Bayer Urethane Co., Ltd.; HDIisocyanurate-type polyisocyanate compound which is blocked with methyl ethyl ketoxime, solid content = 75%

-Preparation of diluent (B) liquid Production Example 16

Diluent (B-l) liquid of pH 9.5 having a solid content of ,1.2% was prepared by mixing and stirring 1 part of PRIMAL ASE-60^{(note 5)}, 3 parts of 2-(dimethylamino)ethanol, 0.2 part of Laponite RD^{(note 6)}, 1.5 parts of DISPARLON AQ600<^{note η}\ 5 parts of ethylene glycol monobutyl ether and 55 parts of tap water.

(note 5) PRIMAL ASE-60: tradename, Rohm & Haas Co.; an acrylic emulsion type alkali-thickening thickener, solid content = 28%

(note 6) Laponite RD^ tradename, Raport Absorbents Co.; lithium magnesium sodium silicate, a thickener (note 7) DISPARLONAQ 600: tradename, Kusumoto Chemicals, Ltd.! a fatty acid polyamideamine salt, a thickener, solid content = 20%

Production Examples 17 - 20

Production Example 16 was repeated except that the components as identified in the following Table 2 were blended at the ratios as indicated in Table 2, to provide each of the diluent (B) liquid.

Example 1

In a drum can, 409 parts of the water-borne coating base (A"l) liquid as obtained in above Production Example 5 and 65.7 parts of the diluent (B- 1) liquid as obtained in Production Example 16 were blended to make the total amount 180 kg, which were mixed and stirred with a high-speed dissolver having a circular agitation blade of 20 cm in diameter, under the conditions of 25⁰C and 800 rpm, to provide a water-borne coating composition.

Examples 2 - 9 and Comparative Example 1

Example 1 was repeated except that the components as identified in the following Table 3 were blended at the ratios as indicated in Table 3, to provide each of the water-borne coating composition.

Comparative Example 2 In a drum can, 409 parts of the water-borne coating base (A-l) liquid as obtained in above Production Example 5 and 65.7 parts of the diluent (B- 1) liquid as obtained in Production Example 16 were blended to make the total amount 180 kg, which were mixed and stirred with a high-speed dissolver having a circular agitation blade of 20 cm in diameter, under the conditions of 25°C and 800 rpm. So obtained water-borne coating composition was hermetically sealed and stored at 40⁰C for 30 days, to provide the product of Comparative Example 2.

Comparative Example 3

In a drum can, 409 parts of the water-borne coating base (A-5) liquid as obtained in above Production Example 9 and 65.7 parts of the diluent (B- 1) liquid as obtained in Production Example 16 were blended to make the total amount 180 kg, which were mixed and stirred with a high-speed dissolver having a circular agitation blade of 20 cm in diameter, under the conditions of 25°C and 800 rpm. So obtained water-borne coating composition was hermetically sealed and stored at 4O⁰C for 30 days, to provide the product of Comparative Example 3.

The coating compositions as obtained in Examples 1 - 9 and Comparative Examples 1 - 3 were given the following tests. The results were as shown in Table 3 appearing later.

The mixing stability of those water-borne coating compositions after the storage was evaluated as to the coating compositions of

Examples 1 - 9 and Comparative Example 1, which were prepared by separately storing the water-borne coating base (A) liquid and diluent (B) liquid as hermetically sealed at 40⁰C for 30 days and thereafter mixing the two. In Comparative Examples 2 and 3, the coating compositions prepared by mixing the respective water-borne coating base (A) liquid with the diluent (B) liquid were stored as hermetically sealed at 40⁰C for 30 days, and their condition after the storage was evaluated.

Finished appearance and metallic effect were tested as to the multi-layer-coated panels which were prepared by the following method.

Preparation of substrate

A zinc phosphate-treated, 0.8 mπrthick dull sheet steel was electrocoated with a heat-curable epoxy resin type cationic electrodeposition paint (ELECRON 9600, tradename, Kansai Paint Co., Ltd.) to the cured film thickness of about 20 μm, which was cured by heating at 17O⁰C for 30 minutes. Then LUGA BAKE AM (tradename, Kansai Paint Co., Ltd.: a polyester resin/melamine resin type intermediate paint for automobiles) was coated thereon to a dry film thickness of about 20 μm, followed by baking at 14O⁰C for 30 minutes to provide a substrate.

Preparation of multi-layer coated panels Each of water-borne coating compositions as prepared in the above were spray coated onto the above substrate to a cured film thickness of 12 μm, set at room temperature for 5 minutes, and onto which TC-71 Clear (tradename, Kansai Paint Co., Ltd.: an aminoacrylic resin clear coating composition) was spray coated to a cured film thickness of 40 μm. The two coating films were simultaneously cured by heating at 140°C for 30 minutes to provide multi-layer coated panels.

Test method Mixing stability of initial water-borne coating composition:

Each water-borne coating base (A) liquid and diluent (B) liquid were mixed immediately after their preparation. The condition of the mixture after being mixed and stirred in a high-speed dissolver having a circular stirring blade of 20 cm in diameter under the conditions of 800 rpm at 25°C was evaluated. ®: seeding almost nil; excellent O: a little seeding; good

Δ: water-borne coating base (A) liquid and diluent (B) liquid could be mixed but considerable seeding occurred x : mixing of water-borne coating base (A) liquid with diluent (B) liquid was difficult.

Mixing stability of water-borne coating composition after storage: Each water-borne coating base (A) liquid immediately after preparation was hermetically sealed and stored at 40⁰C for 30 days, and then mixed with a diluent (B) liquid. The condition of the mixture after being mixed and stirred in a high-speed dissolver having a circular stirring blade of 20 cm in diameter under the conditions of 800 rpm at 25⁰C was evaluated according to the following standard. The viscosity change was evaluated based on the initial mixture of the water-borne coating base (A) liquid and diluent (B) liquid immediately after their preparation. In Comparative Examples 2 and 3, each of the water-borne coating base (A) liquid and diluent (B) liquid immediately after preparation were mixed and stored as hermetically sealed at 40⁰C for 30 days, and the condition of the coating composition after the storage was evaluated according to the following standard:

®: nearly no seeding and nearly no viscosity change occurred compared with the initial product! excellent O^: a little seeding or a little viscosity change occurred compared with the initial product; good

Δ: water-borne coating base (A) liquid and diluent (B) liquid could be mixed but considerable seeding or substantial viscosity change occurred compared with the initial product X ^: water-borne coating base (A) liquid gelled or showed heavy viscosity increase, and its mixing with diluent (B) liquid was difficult, or the coating composition, which was a mixture of a water-borne base coating (A) liquid and diluent (B), gelled or showed heavy viscosity increase. Finished appearance: Surface smoothness and glossy appearance of the coating film on each of the multi-layer coated panel were evaluated according to the following standard:

O^: both surface smoothness and glossy appearance were good Δ: either of surface smoothness or glossy appearance was inferior x : both surface smoothness and glossy appearance were inferior.

Metallic effect: Uniform dispersibility of the metallic pigment in each coating film of the multilayer coated panel was visually observed and evaluated according to the following standard: O: metallic pigment was uniformly dispersed and no occurrence of unevenness was observed

A- dispersibility of metallic pigment was rather unsatisfactory and minor occurrence of unevenness was observed X : dispersibility of metallic pigment was poor and occurrence of many uneven spots was observed.

ςo

Claims

1. A multi-package water-borne coating composition which comprises a water-soluble or water-dispersible, acid group -containing resin, pigment, neutralizer, thickener and water, characterized in that it is a multi-package water-borne coating composition in which the water-soluble or water-dispersible, acid group -containing resin is separated from the thickener and at least a part of the neutralizer before the use>^" and at a time of use a first liquid comprising the water-soluble or water-dispersible, acid group -containing resin is mixed with a second liquid comprising the thickener and at least a part of the neutralizer; the first liquid having a pfϊ within a range of 6 - 9 and a solid content within a range of 20 - 50 mass%>^' and the second liquid having a solid content within a range of 0.5 - 10 mass%, water content of at least 70 mass% and pH higher than that of the first liquid by at least 0.5.

2. A multi-package water-borne coating composition as set forth in Claim 1, in which the first liquid has a pH within a range of 7 - 8.6.

3. A multi-package water-borne coating composition as set forth in Claim 1, in which the first liquid has a solid content within a range of 25 - 45 mass%.

4. A multi-package water-borne coating composition as set forth in Claim 1, in which the second liquid has a solid content within a range of 0.8 - 5 mass%.

5. A multi-package water-borne coating composition as set forth in Claim 1, in which the second liquid has a water content within a range of 80 - 99.5 mass%.

6. A multi-package water-borne coating composition as set forth in Claim 1, in which the second liquid has a pH higher than that of the first liquid by at least 0.8.

7. A multi-package water-borne coating composition as set forth in Claim 1, which further contains a crosslinking agent.

8. A multi-package water-borne coating composition as set forth in Claim 1, in which the water-soluble or water- dispersible, acid-containing resin is selected from the group consisting of water-soluble or water- dispersible acrylic resin and water-soluble or water- dispersible polyester resin.

9. A multi-package water-borne coating composition as set forth in Claim 8, in which the water-soluble or water-dispersible, acid group -containing resin further contains urethane resin emulsion.

10. A multi-package water-borne coating composition as set forth in Claim 1, which is a two-package water-borne coating composition in which the first liquid is a water-borne coating base (A) comprising water-soluble or water-dispersible, acid group-containing resin, pigment and water, and the second liquid is a diluent (B) comprising a neutralizer, thickener and water.

11. A multi-package water-borne coating composition as set forth in Claim 10, in which the water-borne coating base (A) further contains a crosslinking agent.

12. A multi-package water-borne coating composition as set forth in Claim 10, in which the crosslinking agent is selected from the group consisting of amino resin crosslinking agent and blocked polyisocyanate compound.

13. A multi-package water-borne coating composition as set forth in Claim 10, in which the diluent (B) has a pH within a range of 7 - 10.

14. A multi-package water-borne coating composition as set forth in Claim 10, characterized in that the water-borne coating base (A) and the diluent (B) are mixed at the time of use such that the mass ratio of (A)/(B) becomes within a range of 9/1 - 2/3.

15. A coating method characterized by formulating a water-borne coating composition at its coating site by mixing a first liquid which comprises a water-soluble or water-dispersible, acid group -containing resin with a second liquid which comprises a thickener and at least a part of a neutralizer, and the remaining components of the ^ multi-package water-borne coating composition; and carrying out the coating using the same water-borne coating composition.