Primer coating composition and coating method

Abstract

To provide an undercoating composition which does not cause skinning, etc., of a coating film even in thick film coating and is excellent in coating workability, etc.SOLUTION: The main component contains a polyisocyanate compound having a viscosity of 100 to 1500mPa·s, the acrylic polymer contains an acrylic polymer having a weight-average molecular weight of 1,000 to 10,000, a glass-transition temperature of - 20 to 60 °C., an acid number of 1 to 25mgKOH / g, and a hydroxyl number of 100 to 200mgKOH / g, and the content of the colorant composition is 100 to 500 parts by mass based on 100 parts by mass of the solids of the resin components contained in the main component and the curing agent component. A solid content concentration after mixing the main agent component and the curing agent component is 70 to 100% by mass.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a multi-component organic solvent-based primer coating composition and a coating method using the multi-component organic solvent-based primer coating composition. [Background technology]

[0002] Painting the exterior panels or parts of large vehicles such as railway cars, buses, and construction machinery generally involves applying a primer coat, putty coat, primer surfacer coat, and top coat coat in that order to the object being painted.

[0003] Among these, putty painting is a process that smooths out unevenness on the surface of the object being painted, but because the painting area is larger than that of automobile bodies such as passenger cars, the skill of the applicator has a significant impact when applying the paint using a regular putty spatula, making it difficult to obtain a consistently smooth painted surface.

[0004] Patent Document 1 discloses a method for forming a putty coating on the surface of a railway vehicle exterior panel by spraying a putty composition consisting of a base component essential for unsaturated polyester resin, a vinyl monomer, and a filler, and a curing agent component essential for organic peroxide onto the surface of the exterior panel of the railway vehicle. The method comprises: introducing the base component, which is pressurized at a pressure suitable for spray coating, the curing agent component, which is pressurized by compressed air, and separately compressed air, into a spray gun separately; premixing the curing agent component pressurized by the compressed air and a portion of the separately compressed air through a nozzle provided at the rear inside the spray gun; merging the premix with the remaining portion of the separately compressed air at the front inside the spray gun and colliding with an impact member; and spraying the mixture of the curing agent component and the separately compressed air, which has been homogeneously mixed, at the tip of the spray gun while being merged and mixed with the base component. Although applying putty with a spray gun significantly improves paint workability, it is necessary to apply the putty three to five times to fill in any unevenness, which still poses a time and labor-intensive challenge. Furthermore, because the putty must be heated and dried after each application, the number of times it is heated and dried increases with the number of coats applied, resulting in high energy consumption. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-80666 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention was made in consideration of the above circumstances, and aims to eliminate the putty application process itself by applying a thick film of primer surfacer by spraying it one to three times, thereby improving paint workability and reducing the energy required for heat drying. However, simply applying a thick film of conventional primer surfacer has problems such as the coating surface becoming skinned, residual solvent preventing the interior of the coating from curing and causing a bubbling condition, and the coating film cracking after drying. The present invention provides an undercoat paint composition that does not cause skinning, bubbling, or cracking of the coating film, even when applied to a thick film of 200 μm or more in a single coat, and that has excellent paint workability, drying properties, and finish. [Means for solving the problem]

[0007] As a result of intensive research by the inventors to solve the above problems, they have discovered a multi-component organic solvent-based primer coating composition obtainable by mixing a main component (I) and a curing agent component (II), wherein the main component (I) comprises an acrylic polyol (A), a pigment composition (B), and an organic solvent (C), the curing agent component (II) comprises a polyisocyanate compound (D1) having a viscosity of 100 to 1500 mPa·s as measured with an E-type viscometer at 25°C, the acrylic polyol (A) having a weight-average molecular weight of 1,000 or more and 10,000 or less, and a glass transition temperature of -20°C or more and 60°C or less, The present inventors have found that the above-mentioned problems can be solved by an undercoat paint composition comprising an acrylic polyol (A1) having an acid value of from 1 mgKOH / g to 25 mgKOH / g and a hydroxyl value of from 100 mgKOH / g to 200 mgKOH / g, wherein the content of the pigment composition (B) is within the range of from 100 parts by mass to 500 parts by mass based on 100 parts by mass of the solid content of the resin components contained in the main component (I) and the curing agent component (II), and wherein the solid content concentration after mixing the main component (I) and the curing agent component (II) is 70 to 99.9 mass%, and have completed the present invention.

[0008] That is, the present invention provides the following multi-component organic solvent-based primer coating composition and coating method using the same. Section 1. A multi-component organic solvent-based primer coating composition obtained by mixing a main component (I) and a curing agent component (II), The main component (I) contains an acrylic polyol (A), a pigment composition (B), and an organic solvent (C), the curing agent component (II) contains a polyisocyanate compound (D1) having a viscosity of 100 to 1500 mPa s as measured with an E-type viscometer at 25°C; the acrylic polyol (A) comprises an acrylic polyol (A1) having a weight average molecular weight of 1,000 or more and 10,000 or less, a glass transition temperature of -20°C or more and 60°C or less, an acid value of 1 mgKOH / g or more and 25 mgKOH / g or less, and a hydroxyl value of 100 mgKOH / g or more and 200 mgKOH / g or less, the content of the pigment composition (B) is in the range of 100 parts by mass or more and 500 parts by mass or less based on 100 parts by mass of the solid content of the resin components contained in the main component (I) and the curing agent component (II), An undercoat paint composition having a solids concentration of 70 to 99.9 mass % after mixing a main component (I) and a curing agent component (II). Section 2. Item 2. The primer coating composition according to Item 1, wherein the pigment composition (B) contains calcium carbonate. Section 3. Item 3. The undercoat coating composition according to Item 1 or 2, wherein the curing agent component (II) further contains an alicyclic polyisocyanate compound (D2). Section 4. 4. The undercoat coating composition according to any one of Items 1 to 3, wherein the main component (I) and / or the curing agent component (II) contain an amide-based rheology control agent (E), and the amount of the active ingredient of the amide-based rheology control agent (E) is 0.5 to 10 parts by mass based on 100 parts by mass of the solid content of the resin components contained in the main component (I) and the curing agent component (II). Section 5. 5. The undercoat coating composition according to any one of Items 1 to 4, wherein the main component (I) and / or the curing agent component (II) contain an antifoaming agent (F), and the amount of the active ingredient of the antifoaming agent (F) is 0.05 to 3 parts by mass based on 100 parts by mass of the solid content of the resin components contained in the main component (I) and the curing agent component (II). Section 6. A coating method comprising coating an article with the undercoat paint composition according to any one of items 1 to 5. Section 7. Item 7. The coating method according to item 6, wherein the substrate is a railway vehicle, industrial machinery, construction machinery, large vehicle, ship, building, or structure. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a multi-component organic solvent-based primer paint composition which does not cause skinning, oozing, cracking, etc. in the paint film even when applied in a thick film, and which has good paint workability, drying properties, and finish, and a painting method using the same. DETAILED DESCRIPTION OF THE INVENTION

[0010] The primer coating composition of the present invention is a multi-component composition obtained by mixing a main component (I) and a curing agent component (II). If necessary, the primer coating composition of the present invention can also be a multi-component composition obtained by mixing three or more components including components other than the main component (I) and the curing agent component (II). Each component used in the present invention will be described below.

[0011] <Main ingredient (I)> In the present invention, the main component (I) contains an acrylic polyol (A), a pigment composition (B), and an organic solvent (C).

[0012] In the present invention, the non-volatile content of the main component (I) is suitably within the range of 70 to 99.9 mass %, particularly 75 to 90 mass %, from the viewpoints of coating workability and the finish of the formed coating film.

[0013] The main agent component (I) can have a low viscosity relative to its solid content, and can exhibit excellent coating workability. Specifically, the viscosity measured with a Brookfield viscometer in the storage state (sealed can) can be in the range of 2,000 to 15,000 mPa s.

[0014] <Acrylic polyol (A)> In the present invention, the main component (I) contains an acrylic polyol (A).

[0015] The acrylic polyol (A) in the present invention is a component that can serve as a polyurethane film-forming component together with the polyisocyanate compound described below. Any conventionally known acrylic polyol can be used without limitation as long as it has organic solvent dilutability and film-forming ability, and can be, for example, a copolymer of polymerizable unsaturated monomers containing a hydroxyl group-containing polymerizable unsaturated monomer as an essential component and at least one (meth)acryloyl group-containing monomer.

[0016] Examples of hydroxyl group-containing polymerizable unsaturated monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate; ε-caprolactone-modified products of the above hydroxyalkyl (meth)acrylates; hydroxyl group-containing (meth)acryloyl monomers such as polyoxyethylene chain-containing (meth)acrylates whose molecular terminals are hydroxyl groups; and allyl alcohol, and these can be used alone or in combination of two or more.

[0017] Examples of the polymerizable unsaturated monomer to be copolymerized with the hydroxyl group-containing polymerizable unsaturated monomer include linear or branched alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate; cyclohexyl (meth)acrylate; acrylate, alicyclic alkyl (meth)acrylate such as isobornyl (meth)acrylate; aralkyl (meth)acrylate such as benzyl (meth)acrylate; alkoxyalkyl (meth)acrylate such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate; perfluoroalkyl (meth)acrylate; N,N-dialkylaminoalkyl (meth)acrylate such as N,N-diethylaminoethyl (meth)acrylate; (meth)acrylamide; allyl (meth)acrylate acrylate, ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tetra(meth)acrylate (Meth)acryloyl monomers having at least two polymerizable unsaturated groups in one molecule, such as glycerol di(meth)acrylate, 1,1,1-trishydroxymethylethane di(meth)acrylate, 1,1,1-trishydroxymethylethane tri(meth)acrylate, and 1,1,1-trishydroxymethylpropane tri(meth)acrylate; (meth)acrylic acid; carbonyl group-containing (meth)acryloyl monomers, such as acetoacetoxyethyl (meth)acrylate and diacetone (meth)acrylamide;Examples of the epoxy group-containing (meth)acryloyl monomers include glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, and 3,4-epoxycyclohexylpropyl (meth)acrylate; isocyanato group-containing (meth)acryloyl monomers such as isocyanatoethyl (meth)acrylate; alkoxysilyl group-containing (meth)acryloyl monomers such as γ-methacryloyloxypropyltrimethoxysilane and γ-methacryloyloxypropyltriethoxysilane; and oxidatively curable group-containing (meth)acryloyl monomers such as dicyclopentenyloxyethyl (meth)acrylate, dicyclopentenyloxypropyl (meth)acrylate, and dicyclopentenyl (meth)acrylate. These may be used alone or in combination of two or more.

[0018] Examples of copolymerizable polymerizable unsaturated monomers other than (meth)acryloyl monomers include (meth)acrylonitrile; vinyl ester compounds such as vinyl acetate and vinyl propionate; vinyl aromatic compounds such as styrene and α-methylstyrene; polyvinyl compounds having at least two polymerizable unsaturated groups in one molecule such as triallyl isocyanurate, diallyl terephthalate and divinylbenzene; carboxyl group-containing polymerizable unsaturated monomers such as maleic acid, crotonic acid and β-carboxyethyl acrylate; (meth)acrolein, formyl styrene, vinyl alkyl ketones having 4 to 7 carbon atoms (for example, vinyl methyl ketone and vinyl ethyl ketone), vinyl butyl ketone, etc.), acetoacetoxy allyl ester, and other carbonyl group-containing polymerizable unsaturated monomers; allyl glycidyl ether, and other epoxy group-containing polymerizable unsaturated monomers; m-isopropenyl-α,α-dimethylbenzyl isocyanate, and other isocyanato group-containing polymerizable unsaturated monomers; vinyltrimethoxysilane, vinyltriethoxysilane, and other alkoxysilyl group-containing polymerizable unsaturated monomers; and oxidatively curable group-containing polymerizable unsaturated monomers, such as reaction products of epoxy group-containing polymerizable unsaturated monomers or hydroxyl group-containing polymerizable unsaturated monomers with unsaturated fatty acids. These may be used alone or in combination of two or more.

[0019] In the present invention, the acrylic polyol (A) contains an acrylic polyol (A1) having a glass transition temperature of -20°C to 60°C, an acid value of 1 mgKOH / g to 25 mgKOH / g, and a hydroxyl value of 100 mgKOH / g to 200 mgKOH / g. The acrylic polyol (A1) is suitably contained in the acrylic polyol (A) in an amount of 75% by mass or more, preferably 85% by mass or more.

[0020] From the viewpoint of suppressing skinning, the acrylic polyol (A1) has a glass transition temperature of not higher than 60° C., and preferably not higher than 50° C. From the viewpoint of coating film hardness and polishability, the glass transition temperature is not lower than −20° C., preferably not lower than −10° C., and more preferably not lower than 0° C.

[0021] In this specification, the glass transition temperature (Tg) is a value calculated by the following formula. 1 / Tg(K)=W1 / T1+W2 / T2+...Wn / Tn Tg(℃)=Tg(K)-273 where W1, W2, ... Wn are the mass fractions of each monomer, and T1, T2, ... Tn are the glass transition temperatures Tg (K) of the homopolymers of each monomer. The glass transition temperatures of the homopolymers of each monomer are values ​​taken from POLYMER HANDBOOK Fourth Edition, edited by J. Brandrup, Eh Immergut, and E.A. Grulke (1999). The glass transition temperatures of monomers not listed in this document are taken as the static glass transition temperatures when the homopolymers of the monomers are synthesized so as to have a weight-average molecular weight of about 50,000.

[0022] In this specification, the static glass transition temperature of a resin can be measured, for example, by placing a sample in a measuring cup, vacuum suctioning the sample to completely remove the solvent, and then measuring the change in heat quantity in the range of −100° C. to 150° C. at a temperature rise rate of 3° C. / min using a differential scanning calorimeter "DSC-50Q" (trade name, manufactured by Shimadzu Corporation), and defining the first change point in the baseline on the low temperature side as the static glass transition temperature.

[0023] The acrylic polyol (A1) has an acid value of 1 mgKOH / g or more, preferably 2 mgKOH / g or more, and more preferably 3 mgKOH / g or more from the viewpoint of pot life, and an acid value of 25 mgKOH / g or less, preferably 20 mgKOH / g or less, and more preferably 15 mgKOH / g or less from the viewpoint of suppressing scumming.

[0024] The acrylic polyol (A1) has a hydroxyl value of 100 mgKOH / g or more, preferably 110 mgKOH / g or more, and more preferably 120 mgKOH / g or more from the viewpoint of curability, and 200 mgKOH / g or less, preferably 190 mgKOH / g or less, and more preferably 180 mgKOH / g or less from the viewpoint of water resistance and pot life.

[0025] From the viewpoint of suppressing skinning, the acrylic polyol (A1) preferably has a weight average molecular weight of 1,000 or more and 10,000 or less, more preferably 1,500 or more and 8,000 or less, and particularly preferably 2,000 or more and 5,000 or less.

[0026] In this specification, the weight-average molecular weight is a value obtained by converting the weight-average molecular weight measured using a gel permeation chromatograph ("HLC8120GPC" manufactured by Tosoh Corporation) to the weight-average molecular weight of polystyrene as a standard. Four columns, "TSKgel G-4000HxL," "TSKgel G-3000HxL," "TSKgel G-2500HxL," and "TSKgel G-2000HxL" (all manufactured by Tosoh Corporation), were used, and the measurement was performed under the following conditions: mobile phase: tetrahydrofuran, measurement temperature: 40°C, flow rate: 1 ml / min, and detector: RI.

[0027] The acrylic polyol (A) is suitably contained in an amount of 75% by mass or more, preferably 85% by mass or more, of the resin solid content contained in the main component (I).

[0028] In this specification, the term "solid content" or "non-volatile content" refers to the residue remaining after removing the volatile components, and the residue may be solid or liquid at room temperature. For example, the term refers to the residue remaining after treating a sample at 105°C for 3 hours to remove the volatile components.

[0029] The content of the acrylic polyol (A) in the main component (I) is typically within the range of 10 to 50 parts by mass, preferably 15 to 45 parts by mass, and more preferably 20 to 40 parts by mass, in terms of non-volatile content, per 100 parts by mass of the total mass of the main component (I).

[0030] <Pigment composition (B)> In the present invention, the main component (I) contains a pigment composition (B).

[0031] It is preferable that the pigment composition (B) contains a body pigment as part of its components. Specific examples of the body pigment include calcium carbonate, talc, clay, barium sulfate, barium carbonate, aluminum silicate, gypsum, silica, white carbon, diatomaceous earth, magnesium carbonate, alumina white, gloss white, and mica powder. These can be used alone or in combination of two or more. Among these, it is preferable to contain at least one of calcium carbonate, talc, clay, and barium sulfate, and calcium carbonate is particularly preferable. As the body pigment, any of those known as body pigments in the paint industry can be used. They may be synthetic or natural products, and may be surface-treated as necessary. There are also no limitations on their shape or size.

[0032] From the viewpoint of thick coating properties and polishing properties, the content of the extender pigment is preferably in the range of 100 to 500 parts by mass, and more preferably in the range of 120 to 300 parts by mass, based on 100 parts by mass of the solid content of the resin components contained in the main component (I) and the curing agent component (II).

[0033] From the viewpoint of coating workability, the pigment composition (B) preferably contains at least one of bentonite, montmorillonite, beidellite, nottronite, saponite, hectorite, and stevensite. The content is preferably in the range of 0.5 to 10 parts by mass, and more preferably in the range of 1 to 8 parts by mass, based on 100 parts by mass of the solid content of the resin components contained in the main component (I) and the curing agent component (II).

[0034] Furthermore, the pigment composition (B) may contain known pigments such as color pigments and anti-rust pigments, if necessary.

[0035] Examples of color pigments include white pigments such as titanium dioxide; black pigments such as carbon black, acetylene black, lamp black, bone black, graphite, iron black, and aniline black; yellow pigments such as yellow iron oxide, titanium yellow, monoazo yellow, condensed azo yellow, azomethine yellow, bismuth vanadate, benzimidazolone, isoindolinone, isoindoline, quinophthalone, benzidine yellow, and permanent yellow; orange pigments such as permanent orange; red iron oxide, naphthol AS-based azo red, anthanthrone, anthraquinonyl red, and perilemma. Examples of pigments that can be used include red pigments such as rune, quinacridone red pigments, diketopyrrolopyrrole, watching red, and permanent red; purple pigments such as cobalt purple, quinacridone violet, and dioxazine violet; blue pigments such as cobalt blue, phthalocyanine blue, and threne blue; green pigments such as phthalocyanine green; metallic pigments such as aluminum powder, bronze powder, copper powder, tin powder, iron phosphide, and zinc powder; and pearlescent pigments such as metal oxide-coated mica powder and mica-like iron oxide. These pigments can be used alone or in combination of two or more.

[0036] When the undercoat paint composition of the present invention contains a coloring pigment, it is preferable that the mass of the coloring pigment is 1 or more and less than 100 parts by mass, preferably 2 to 80 parts by mass, and more preferably 3 to 60 parts by mass, based on 100 parts by mass of the total of the extender pigments, from the viewpoint of thick coating properties and the finished appearance of the topcoat.

[0037] In the present invention, the content of the pigment composition (B) is suitably within the range of 100 parts by mass or more and 500 parts by mass or less, and preferably 120 parts by mass or more and 400 parts by mass or less, based on 100 parts by mass of the solid content of the resin components contained in the main component (I) and the curing component (II), from the viewpoint of the adhesion strength of the primer coating film and the finished appearance after the topcoat coating.

[0038] <Organic solvent (C)> In the present invention, the organic solvent (C) may be, for example, an organic compound having a molecular weight in the range of 58 to 220, particularly 72 to 200, and any organic solvent known in the field of coatings may be used without limitation. However, it is desirable that the organic solvent (C) contains at least one organic solvent selected from, for example, ester-based organic solvents and ketone-based organic solvents.

[0039] Examples of such ester-based organic solvents include ethyl acetate, butyl acetate, isobutyl acetate, 2-ethylhexyl acetate, cyclohexyl acetate, 3-methoxybutyl acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, and diethylene glycol monoethyl ether acetate. Examples of ketone-based organic solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl amyl ketone, ethyl isoamyl ketone, diisobutyl ketone, methyl hexyl ketone, and isophorone. These can be used alone or in combination of two or more.

[0040] The amount of at least one organic solvent selected from such ester-based organic solvents and ketone-based organic solvents used is desirably 5% by mass or more, and particularly 20% by mass or more, of the total organic solvents contained in the undercoat paint composition of the present invention.

[0041] In the present invention, examples of organic solvents other than the above-mentioned ester-based organic solvents and ketone-based organic solvents include linear alkanes such as n-butane, n-hexane, n-heptane, n-pentane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane, and n-heptadecane; 2-methylbutane, 2,2-dimethylpropane, 2-methylpentane; hexane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 2,4-dimethylpentane, 2,2,3-trimethylpentane, 2,2,4-trimethylpentane, 3,4-diethylhexane, 2,6-dimethyloctane, 3,3-dimethyloctane, 3,5-dimethyloctane, 4,4-dimethyloctane, 3-ethyl-3- branched alkanes such as methylheptane, 2-methylnonane, 3-methylnonane, 4-methylnonane, 5-methylnonane, 2-methylundecane, 3-methylundecane, and 2,2,4,6,6-pentamethylheptane; aliphatic hydrocarbon organic solvents such as cyclic alkanes such as cyclopentane, t-decalin, cyclohexane, methylcyclohexane, ethylcyclohexane, 1,2-dimethylcyclohexane, 1,3-dimethylcyclohexane, 1,4-dimethylcyclohexane, propylcyclohexane, isopropylcyclohexane, 1,2-methylethylcyclohexane, 1,3-methylethylcyclohexane, 1,4-methylethylcyclohexane, 1,2,3-trimethylcyclohexane, 1,2,4-trimethylcyclohexane, and 1,3,5-trimethylcyclohexane; and aromatic hydrocarbon organic solvents such as toluene and xylene.Dioxane, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-propyl ether, ethylene glycol monoisopropyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol monoisobutyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, diethylene glycol monoisopropyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol monoisobutyl ether, diethylene glycol mono Examples of the organic solvent include ether-based organic solvents such as tert-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-propyl ether, propylene glycol monoisopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, and dipropylene glycol monoisopropyl ether; and alcohol-based organic solvents such as methanol, isopropanol, tert-butanol, secondary butanol, isobutanol, n-butanol, 2-ethylhexanol, n-octanol, and benzyl alcohol.

[0042] The organic solvent (C) can be blended as a polymerization solvent or dilution solvent in the production of the acrylic polyol (A), or as a dilution solvent in the production of the main component (I).

[0043] <Hardening agent component (II)> In the present invention, the curing agent component (II) contains a polyisocyanate compound (D1).

[0044] From the viewpoints of workability and miscibility with the main component (I), it is preferable that the curing agent component (II) contains an organic solvent. The organic solvent can be appropriately selected from the compounds exemplified in the description of the organic solvent (C) above. From the viewpoints of coating workability and the finish of the formed coating film, the non-volatile content of the curing agent component (II) is suitably in the range of 70 to 100 mass%, particularly 75 to 100 mass%.

[0045] <Polyisocyanate compounds> The polyisocyanate compound is a polyisocyanate compound having two or more isocyanate groups in one molecule. Specific examples thereof include diisocyanate compounds such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, xylylene diisocyanate, meta-tetramethylxylylene diisocyanate, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, lysine diisocyanate, butane diisocyanate, and pentyl diisocyanate; 1,8-diisocyanato-4-isocyanatomethyloctane, (2S)-2,6-diisocyanatohexanoic acid 2-isocyanatoethyl (trivial name: lysine triisocyanate), 2,6-diisocyanato-4-isocyanatomethyloctane, 2-isocyanatoethyl (2S)-2,6-diisocyanatohexanoate (trivial name: lysine triisocyanate), and 2,6-diisocyanato-4-isocyanatomethyloctane. Examples of the polyisocyanate include triisocyanate compounds such as 2-isocyanatoethyl isocyanatohexanoate, 1,6,11-triisocyanatoundecane, 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 1,3,5-triisocyanatobenzene, and 2,4,6-triisocyanatotoluene; and polyisocyanate compounds, or adducts of these polyisocyanates with polyhydric alcohols, low-molecular-weight polyester resins, or water, or cyclized polymers of the above-mentioned polyisocyanates, and further isocyanate-biuret compounds, and these may be used alone or in combination of two or more.

[0046] In the present invention, the curing agent component (II) contains a polyisocyanate compound (D1) having a viscosity of 100 to 1500 mPa·s as measured at 25°C with an E-type viscometer. By using a polyisocyanate with a viscosity within this range, the viscosity of the coating composition is reduced, enabling the coating composition to have a high solids content. From the viewpoint of coating workability, a viscosity of 100 to 1000 mPa·s is particularly preferred.

[0047] In this specification, when measuring viscosity with an E-type viscometer, the RE215 model manufactured by Toki Sangyo Co., Ltd. is used, and the measurement is carried out at 25°C.

[0048] In this specification, unless otherwise specified, the viscosity is measured on a sample adjusted to 25°C.

[0049] From the viewpoint of curability and coating film hardness, it is preferable to further contain an alicyclic polyisocyanate compound (D2) in addition to the polyisocyanate compound (D1). Specific examples of the alicyclic polyisocyanate compound (D2) include alicyclic diisocyanates such as 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (trivial name: isophorone diisocyanate), 4,4'-methylenebis(cyclohexyl isocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (trivial name: hydrogenated xylylene diisocyanate) or a mixture thereof, and norbornane diisocyanate; 2-(3-isocyanatopropyl)-2,6-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 3-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 6-(2-isocyanatoethyl)-2-isocyanato Examples include alicyclic triisocyanates such as methyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)-heptane, and 6-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane.

[0050] <Other additives> The undercoat paint composition of the present invention may further contain, as appropriate, paint additives such as viscosity modifiers, curing catalysts, modifying resins other than the acrylic polyol (A), such as cellulose acetate butyrate and its modified products, polyester resins, alkyd resins, polyurethane resins, etc., pigment dispersants, antifoaming agents, surface conditioners, resin particles, etc. These additives may be contained in either the main component (I) or the curing agent component (II), but from the viewpoint of storage stability, it is preferable that additives capable of directly reacting with the polyisocyanate compound be contained in the main component (I).

[0051] The primer coating composition of the present invention preferably contains an amide-based rheology control agent (D). The use of the amide-based rheology control agent (D) improves the storage stability of the main component (I) and the application workability of the primer coating composition of the present invention, while also improving the adhesion strength of the primer coating composition to the topcoat coating film. The amide-based rheology control agent (D) may be contained in either the main component (I) or the curing agent component (II), but is preferably contained in the main component (I) because of its effect on the storage stability of the main component (I).

[0052] As such an amide-based rheology control agent (D), any known amide-based rheology control agent in the field of coatings can be used without any restrictions, and the synthesis method, materials used, etc. are not particularly limited, and commercially available products can also be used.

[0053] Specific examples include fatty acid monoamides synthesized by dehydration of fatty acid ammonium salts or ammonolysis of fats and oils (esters); fatty acid diamides (bisamides) synthesized by the condensation reaction of fatty acid amides and formaldehyde, the thermal condensation reaction of monocarboxylic acids and diamines, or the thermal condensation reaction of dibasic acids and monoamines; fatty acid polyamides obtained by polycondensation of dibasic acids and diamines, polycondensation of diamine derivatives and dibasic acids, polycondensation of diamines and dibasic acid derivatives or dimer acids obtained by dimerization of unsaturated fatty acids, or ring-opening polymerization of lactams.

[0054] Such an amide-based rheology control agent may be diluted with a diluting medium such as an organic solvent. In the present invention, the content of the active ingredients (components other than the diluting medium) of the amide-based rheology control agent is desirably within a range of 0.5 to 10 parts by mass, preferably 1 to 8 parts by mass, based on 100 parts by mass of the solid content of the resin components contained in the main component (I) and the curing agent component (II).

[0055] From the viewpoint of suppressing popping, the undercoat coating composition of the present invention preferably contains an antifoaming agent (E). The antifoaming agent (E) may be contained in either the main component (I) or the curing agent component (II), but is preferably contained in the main component (I).

[0056] As the antifoaming agent (E), any known antifoaming agent in the field of paints can be used without any limitation, and the synthesis method, materials used, etc. are not particularly limited, and commercially available products can also be used.Commercially available products include Dappo SN-348, Dappo SN-352, Dappo SN-359, Dappo SN-368 (manufactured by San Nopco), Floren AC-202, Floren AC-262H, Floren AC-300, Floren AC-300HF, Floren AC-326F, Floren AC-901, Floren AC-901HF, Floren AC-902, Floren AC-903, and Floren AC-903. HF, Floren AC-950, Floren AC-1160, Floren AC-1160HF, Floren AC-1190, Floren AC-1190HF, Floren AC-2000, Floren AC-2000HF, Floren AC-2200HF, Floren AO-82, Floren AO-98, Floren AO-108, Aqualen 8020, Aqualen 8021N, Aqualen SB-520, Aqualen SB-630, Aqualene HS-01, Florene AO-5 (Kyoeisha, Kagakusha), BYK-051N, BYK-02N, BYK-055, BYK-065, BYK-077, BYK-081, BYK-088, BYK-354, BYK-1752, BYK-011, BYK-012, BYK-014, BYK-017, BYK-021, BYK-022, BYK-024, BYK-025, BYK-044, BY K-093, BYK-1610, BYK-1640, BYK-1650, BYK-1785 (manufactured by BYK), Disparlon OX-880EF, Disparlon OX-70, Disparlon OX-77EF, Disparlon OX-710, Disparlon OX-66, Disparlon OX-66EF, Disparlon 1952, Disparlon 1958, Disparlon 1930N, Disparlon 1934 (manufactured by Kusumoto Chemicals), TEGO Examples of such foams include Airex 910, TEGO Airex 920, TEGO Airex 931, TEGO Airex 940, TEGO Airex 950, TEGO Airex 901W, TEGO Airex 902W, TEGO Airex 904W, TEGO Foamex 800, TEGO Foamex 815N, TEGO Foamex 840, TEGO Foamex 1488, TEGO Foamex 1495, and TEGO Foamex 8030 (manufactured by Evonik).

[0057] The content of the antifoaming agent (E) is preferably within a range of 0.05 to 3 parts by mass, and more preferably within a range of 0.1 to 2 parts by mass, of the active ingredient based on 100 parts by mass of the solid content of the resin components contained in the main component (I) and the curing agent component (II).

[0058] From the viewpoint of improving adhesion, the undercoat paint composition of the present invention preferably contains a silane coupling agent. The type of silane coupling agent is not particularly limited, but examples thereof include epoxy group-containing silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)methyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)methyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and 2-(3,4-epoxycyclohexyl)methyldimethoxysilane; 3-(2-aminoethyl)aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2 Examples of suitable silane coupling agents include amino group-containing silane coupling agents such as (aminoethyl) 3-aminopropyltrimethoxysilane and N-2(aminoethyl) 3-aminopropylmethyldimethoxysilane; mercapto group-containing silane coupling agents such as 3-mercaptopropyltrimethoxysilane; vinyl group-containing silane coupling agents such as vinyltriethoxysilane, vinyltrimethoxysilane, and vinyltris(methoxyethoxy)silane; and (meth)acryloyl group-containing silane coupling agents such as 3-(meth)acryloyloxypropyltrimethoxysilane, 3-(meth)acryloyloxypropyltriethoxysilane, and 3-(meth)acryloyloxypropyldimethoxymethylsilane. Two or more of these can also be used in combination. Among these, it is preferable to use an epoxy group-containing silane coupling agent.

[0059] The content of the silane coupling agent is preferably 0.5 to 20 parts by mass, more preferably 1 to 10 parts by mass, based on 100 parts by mass of the solid content of the resin components contained in the main component (I) and the curing agent component (II).

[0060] When the silane coupling agent does not have a hydroxyl group, it is preferable that the curing agent component (II) contains the silane coupling agent.

[0061] The undercoat paint composition of the present invention preferably contains a curing catalyst, and as the curing catalyst, any conventionally known urethane catalyst can be used without particular limitation, and examples thereof include metal compounds such as bismuth nitrate, lead oleate, tin octoate, dibutyltin dilaurate, dibutyltin bis(acetylacetonate), dibutyltin diacetate, dibutyltin octanoate, dioctyltin dilaurate, dioctyltin dineodecanoate, titanium tetrachloride, dibutyltitanium dichloride, tetrabutyl titanate, iron trichloride, and zinc octoate, as well as tertiary amines.

[0062] The curing catalyst may be contained in either the main component (I) or the curing agent component (II). When the curing catalyst is contained in the main component (I), the content of the curing catalyst is suitably in the range of 0.01 to 10 parts by mass, preferably 0.1 to 5 parts by mass, based on 100 parts by mass of the solid content of the acrylic polyol (A), from the viewpoints of curability of the composition of the present invention and suppression of viscosity increase after mixing the main component (I) and the curing agent component (II).

[0063] <Undercoat paint composition> In the present invention, it is suitable to mix the main component (I) and the curing component (II) so that the ratio of isocyanate groups in the curing component (II) is 0.8 to 4.0 equivalents, preferably 0.9 to 3.0 equivalents, per equivalent of hydroxyl groups in the main component (I).

[0064] From the viewpoints of ease of application and the finish of the coating film formed, the primer coating composition of the present invention preferably has a solids concentration after mixing the main component (I) and the curing agent component (II) of 70 mass % or more, and more preferably 75 mass % or more, based on 100 parts by mass of the total mass of the primer coating composition.

[0065] The primer paint composition of the present invention is a two-component composition in which each component is stored separately, and is generally prepared by mixing the components together immediately before application, and adjusting the viscosity using a diluting thinner as necessary.

[0066] <Painting method> The primer coating composition of the present invention can be applied to an article to be coated and then dried to obtain a coated article.

[0067] Examples of substrates include metal substrates, plastic substrates, composite substrates thereof, as well as wood, glass, cloth, concrete, and ceramic materials. Metal substrates include metals such as iron, steel, copper, aluminum, tin, and zinc, and alloys containing these metals. Metal substrates may be plated with zinc, copper, chromium, or the like, or may be surface-treated using a surface treatment agent such as chromate, zinc phosphate, or zirconium salt. Examples of plastic substrates include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, and polyamide resin. The surfaces of these metal or various plastic substrates may be surface-treated, such as by degreasing with a detergent or solvent, phosphate treatment, chromate treatment, complex oxide treatment, cleaning, or polishing, and may further be coated with a primer coating.

[0068] The substrate may be a molded article containing the above-mentioned substrate. Examples of molded articles include automobile bodies, various vehicle bodies, and various molded articles such as parts for home appliances. The primer coating composition of the present invention is particularly suitable for use when the substrate is a metal substrate or the like that has a large heat capacity or is large and does not sufficiently transfer heat to the substrate in a heating furnace. Specific examples of such substrates include construction machinery (sometimes abbreviated as construction machinery, for example, bulldozers, scrapers, hydraulic excavators, excavators, transport machinery (railroad cars such as Shinkansen, and large vehicles such as buses, trucks, and trailers), cranes and loading / unloading machinery, foundation construction machinery (diesel hammers, hydraulic hammers, etc.), tunnel construction machinery (boring machines, etc.), road rollers, etc.); industrial machinery such as light and heavy electrical equipment for general industrial use, agricultural machinery, steel furniture, and machine tools; ship hulls, buildings, and structures; and the like. Industrial machinery, construction machinery, railroad cars, large vehicles, ship hulls, buildings, and structures are particularly preferred.

[0069] The primer coating composition of the present invention may also be applied to a coating film (old coating film) already formed on the surface of the substrate or to damaged areas of the coated body. That is, the primer coating composition of the present invention can be applied to the old coating film or the damaged area of ​​the coated body to form a coating film. In this case, for example, the area around the damaged area of ​​the old coating film or the coated body to be coated can be cleaned or sanded with sandpaper in advance, and the surface can be pretreated with a putty composition or the like if necessary.

[0070] The primer composition of the present invention can be applied by any conventional coating method, with airless spray coating being particularly suitable. The primer composition of the present invention allows for thick film application, with the dry film thickness being in the range of 30 to 1000 μm, preferably 50 to 800 μm. The primer composition of the present invention provides excellent coating workability, as it can be applied by airless spray coating to obtain a coating film with a thickness of 50 to 300 μm in a single application.

[0071] Drying conditions include, for example, a temperature of 5 to 80° C., preferably 10 to 60° C., for 10 to 120 minutes, particularly 20 to 90 minutes.

[0072] On the primer coating film obtained by applying the primer coating composition of the present invention, an intermediate coating and a top coating can be applied in this order, if necessary.

[0073] As the intermediate coating, it is preferable to use a polyurethane-based coating made from a combination of polyol / polyisocyanate or a polyurea-based coating made from a combination of polyamine / polyisocyanate, from the viewpoint of drying properties and workability.

[0074] The primer coating can be applied by a conventionally known coating method, with air spray coating or airless spray coating being particularly preferred.

[0075] There are no particular restrictions on the drying method after application of the primer paint. Generally, it is preferable to dry the primer paint for 20 minutes to 24 hours at room temperature (20 to 30°C), or for 5 to 60 minutes at a baking temperature of 40 to 100°C. The film thickness can be adjusted appropriately depending on the condition of the surface to be coated, but a dry film thickness of 5 to 100 μm, and particularly 10 to 60 μm, is generally suitable.

[0076] The undercoat coating may be omitted depending on the intended use of the object to be coated.

[0077] Examples of topcoat coating include conventionally known coatings such as a one-coat finish using only a colored base paint containing a metallic pigment and / or a colored pigment, or a two-coat finish using the colored base paint and a clear paint.

[0078] As the colored base paint, any topcoat paint such as an organic solvent-based or water-based paint normally used for repairs can be used without any particular restrictions, and it can be applied by known painting methods such as spray painting, electrostatic painting, brush painting, and roller painting.

[0079] When applying multiple coats of colored base paint, steps such as flash-off (leaving the paint film at room temperature after application), air blowing, or preheating may be carried out between coats as needed.

[0080] There are no particular restrictions on the drying time after application of the colored base paint, and if a top clear coat is to be applied, the paint may be left uncured. Generally, drying is preferably performed at a temperature of 20 to 100°C for 5 to 60 minutes. The film thickness can be adjusted as appropriate depending on the condition of the surface to be coated, but a dry film thickness of 5 to 100 μm, and particularly 10 to 60 μm, is generally suitable.

[0081] As the top clear coating material, any conventionally known coating material can be used without any particular limitation. For example, curing type coating materials containing an acrylic resin or fluororesin containing a crosslinkable functional group such as a hydroxyl group as the main component and containing a blocked polyisocyanate, polyisocyanate, melamine resin, or the like as a curing agent, or lacquer coating materials containing a cellulose acetate butyrate-modified acrylic resin as the main component can be suitably used, and further coating additives such as pigments, cellulose derivatives, added resins, ultraviolet absorbers, light stabilizers, surface conditioners, and curing catalysts can be contained as necessary.

[0082] The top clear coating is preferably dried for 5 to 60 minutes at a temperature of, for example, 20 to 100° C., preferably 40 to 100° C. The film thickness can be adjusted appropriately depending on the condition of the surface to be coated, but a dry film thickness of 5 to 100 μm, and particularly 10 to 60 μm, is generally suitable. [Example]

[0083] The present invention will be further described below with reference to examples, in which "parts" and "%" mean "parts by mass" and "% by mass", respectively.

[0084] Production Example 1 Production of acrylic polyol (A-1) A reaction vessel was charged with 52 parts of butyl acetate and heated to 110°C with stirring. A monomer mixture consisting of 30 parts of styrene, 14.5 parts of i-butyl methacrylate, 22 parts of 2-ethylhexyl acrylate, 1 part of acrylic acid, 32.5 parts of 2-hydroxyethyl methacrylate, and 1.0 part of azobisisobutyronitrile and a polymerization initiator was added dropwise at a constant rate over 3 hours using a dropping pump at temperatures below 110°C. After the dropwise addition, the mixture was maintained at 110°C for 60 minutes and stirring was continued. Subsequently, an additional catalyst, a solution of 0.5 parts of azobisisobutyronitrile in 7 parts of butyl acetate, was added dropwise at a constant rate over 60 minutes. After the dropwise addition, the mixture was maintained at 110°C for 60 minutes to terminate the reaction. The resulting acrylic polyol (A-1) was a homogeneous, yellow, transparent solution with a non-volatile content of 65%, and the resin had a weight-average molecular weight of 8,000, a glass transition temperature (Tg) of 33°C, an acid value (AV) of 7.8 mgKOH / g, and a hydroxyl value (OHV) of 140 mgKOH / g.

[0085] Production Examples 2 to 14 Production of acrylic polyols (A-2) to (A-14) Acrylic polyol solutions (A-2) to (A-14) were obtained in the same manner as in Production Example 1 above, except that the blending compositions shown in Tables 1 and 2 were used.

[0086] [Table 1]

[0087] [Table 2]

[0088] Example 1 Preparation of primer coating composition (X-1) To 100 parts of the acrylic polyol solution (A-1) (65 parts solids), 100 parts of calcium carbonate, 30 parts of titanium white, 0.3 parts of carbon, 5 parts of methyl amyl ketone, 1 part (solids) of a pigment dispersant (manufactured by BYK under the trade name "BYK-161"), 1 part (solids) of an antifoaming agent (manufactured by BYK under the trade name "BYK-052N"), 1 part (solids) of a surface conditioner (manufactured by BYK under the trade name "BYK-320"), 2 parts of montmorillonite (manufactured by ELEMENTIS under the trade name "BENTONE27"), 3 parts (solids) of an amide-based thickener (fatty acid amide, amide-based rheology control agent), and 0.1 parts (solids) of dioctyltin dilaurate were sequentially blended, mixed, stirred, and dispersed for 30 minutes to obtain a main component.

[0089] A curing agent component was obtained by mixing and stirring 35 parts (solid content) of a polyisocyanate compound ("Desmodur ULTRA N3900", product name, manufactured by Sumika Covestro Urethane Co., Ltd.) and 1.5 parts (solid content) of γ-glycidoxypropyltrimethoxysilane (silane coupling agent).

[0090] The main component and the curing agent component were mixed immediately before use so that the solid content of the acrylic polyol contained in the main component and the solid content of the polyisocyanate compound contained in the curing agent component were in a ratio of 65:35 by mass, and the paint viscosity was adjusted with dilution thinner so that the viscosity measured at 60 rpm with a Brookfield viscometer was 0.3 Pa·s, thereby obtaining an undercoat paint composition (X-1).

[0091] Examples 2 to 18, Comparative Examples 1 to 9 Primer coating compositions (X-2) to (X-27) were obtained in the same manner as in Example 1 above, except for using the formulations shown in Tables 3 to 5. The viscosity of the coating was adjusted with thinner to the values ​​shown in Tables 3 to 5 below. The numerical values ​​for the blending amounts in the tables are the values ​​for the solid content or active ingredients.

[0092] [Table 3]

[0093] [Table 4]

[0094] [Table 5]

[0095] (Note 1) Desmodur ULTRA N3900: Product name, manufactured by Sumika Covestro Urethane Co., Ltd., aliphatic polyisocyanate compound, viscosity measured with an E-type viscometer at 25°C: 730 mPa·s (Note 2) Desmodur ULTRA Z4470BA: Product name, manufactured by Sumika Covestro Urethane Co., Ltd., alicyclic polyisocyanate compound, viscosity measured with an E-type viscometer at 25°C: 600 mPa·s (Note 3) Sumidur N3300: Product name, manufactured by Sumika Covestro Urethane Co., Ltd., aliphatic polyisocyanate compound, viscosity measured at 25°C with an E-type viscometer of 2500 mPa·s.

[0096] <Performance test> The primer coating compositions obtained in the examples and comparative examples were subjected to various performance tests. If any of the following performance tests resulted in a rating of "B" or "C," the coating composition failed.

[0097] Finishability test An aluminum plate measuring 300 × 150 × 2.0 mm was airless spray-coated with "Epomarine GX" (an epoxy resin-based primer paint manufactured by Kansai Paint Co., Ltd.) to a dry film thickness of approximately 60 μm and allowed to dry at 20°C for 16 hours. Each primer coating composition obtained in the Examples and Comparative Examples was airless spray-coated onto the coated surface to a dry film thickness of approximately 500 μm, followed by drying at 60°C for 30 minutes. Next, "Retan PG Ecofleet #535 High Solid White" (a two-component urethane resin-based topcoat paint manufactured by Kansai Paint Co., Ltd.) was airless spray-coated to a dry film thickness of 50 μm. The plate was then left to stand for 4 hours at room temperature (23°C, 50% RH), after which it was sanded with #400 sandpaper, dried at room temperature, and degreased and cleaned using KAR Silicon Off. Then, "Retan PG Ecofleet #531 White" (Kansai Paint Co., Ltd., two-component urethane resin topcoat paint) was air spray painted to a dry film thickness of 40 μm, and the plate was dried by heating at 60°C for 40 minutes to obtain a test panel. The finish of each test coated panel was evaluated according to the following criteria. S: Excellent gloss and surface smoothness. A: Good gloss and smoothness of the coating surface. B: Gloss and surface smoothness are slightly poor. C: Poor gloss and surface smoothness.

[0098] Potlife The coating compositions obtained in the examples and comparative examples were allowed to stand at 25°C, and the time until the viscosity measured at 60 rpm using a Brookfield viscometer reached 0.6 Pa·s was defined as the pot life. S: Pot life is 30 minutes or more. A: The pot life is more than 15 minutes but less than 30 minutes. B: The pot life is 5 minutes or more and less than 15 minutes. C: Pot life is less than 5 minutes.

[0099] Mesopelous Each primer paint composition obtained in the above Examples and Comparative Examples was applied to a mild steel plate of 300 x 100 x 0.8 mm so that the dry film thickness was 500 μm, and after leaving it at 60°C for 30 minutes, a finger was pressed against the surface of each test coated plate to check the film's ability to seep through. S: No marks even when pressed hard. A: If you press hard, it will leave a mark, but it will return to normal within a minute. B: If you press it lightly, no marks will be left, but if you press it hard, marks will be left and will not return to their original state. C: Even if you press it lightly, a mark remains and it does not return to its original shape.

[0100] Abrasion test Each primer coating composition obtained in the above Examples and Comparative Examples was spray-coated onto a 300 x 100 x 0.8 mm mild steel plate to a dry film thickness of 500 μm, and then dried for 30 minutes at 60° C. The dried coating was sanded with P320 paper at a fixed load a fixed number of times, and the condition of the coated surface was evaluated according to the following criteria. A: The surface irregularities that occurred during painting have been completely smoothed out. B: Some of the surface irregularities that occurred during painting remain. C: Most of the surface irregularities created during painting remain.

[0101] hardenability Each primer coating composition obtained in the above Examples and Comparative Examples was spray-coated onto a 300 x 100 x 0.8 mm mild steel plate to a dry film thickness of 500 μm, and then dried at 60°C for 30 minutes. The plate was then cooled to 20°C. Absorbent cotton soaked in xylene solvent was pressed firmly against the coating surface, and the surface was rubbed 10 times at a constant speed, after which the rubbed area was visually evaluated. S: No change on the coating surface, A: The gloss of the coating surface has slightly decreased, but the coating has not softened. B: The surface gloss of the coating film has decreased and the coating film has softened slightly. C: The coating film has softened and peeled off.

[0102] Water resistance test The coated panels obtained in the above finish test were immersed in warm water at 40°C for 10 days, and then the coating surface was observed. S: Very good, A: Very slight swelling of the coating film is observed. B: Swelling of the coating film is observed throughout the entire surface. C: The coating film swells and abnormalities such as blisters and whitening are observed.

[0103] Breakability The coated panels obtained in the above finish test were subjected to a 240-hour salt spray test according to JIS Z 2371, and the coating surface was observed after the test. A: No change in the coating B: There is slight swelling and loss of gloss on the coating, but no cracks are observed. C: Cracks are observed in the coating.

Claims

1. A multi-component organic solvent-based primer coating composition obtained by mixing a main component (I) and a curing agent component (II), The main component (I) contains an acrylic polyol (A), a pigment composition (B), and an organic solvent (C), the curing agent component (II) contains a polyisocyanate compound (D1) having a viscosity of 100 to 1500 mPa s as measured with an E-type viscometer at 25°C, the acrylic polyol (A) comprises an acrylic polyol (A1) having a weight average molecular weight of 1,000 or more and 10,000 or less, a glass transition temperature of −20° C. or more and 60° C. or less, an acid value of 1 mg KOH / g or more and 25 mg KOH / g or less, and a hydroxyl value of 100 mg KOH / g or more and 200 mg KOH / g or less, the content of the pigment composition (B) is in the range of 100 parts by mass or more and 500 parts by mass or less based on 100 parts by mass of the solid content of the resin components contained in the main component (I) and the curing agent component (II), A primer coating composition having a solids concentration of 70 to 99.9 mass % after mixing a main component (I) and a curing agent component (II).

2. The primer coating composition of claim 1 , wherein the pigment composition (B) comprises calcium carbonate.

3. The undercoat coating composition according to claim 1, wherein the curing agent component (II) further contains an alicyclic polyisocyanate compound (D2).

4. 2. The undercoat paint composition according to claim 1, wherein the main component (I) and / or the curing agent component (II) contains an amide rheology control agent (E), and the amount of the active ingredient of the amide rheology control agent (E) is 0.5 to 10 parts by mass based on 100 parts by mass of the solid content of the resin components contained in the main component (I) and the curing agent component (II).

5. 2. The undercoat paint composition according to claim 1, wherein the main component (I) and / or the curing agent component (II) contain an antifoaming agent (F), and the amount of the active ingredient of the antifoaming agent (F) is 0.05 to 3 parts by mass based on 100 parts by mass of the solid content of the resin components contained in the main component (I) and the curing agent component (II).

6. A coating method comprising coating an object with the primer coating composition according to any one of claims 1 to 5.

7. 7. The coating method according to claim 6, wherein the object to be coated is a railway vehicle, industrial machinery, construction machinery, a large vehicle, a ship, a building, or a structure.

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