JP6718197B2 - Organic solvent-based undercoat coating composition - Google Patents

Description

The present invention relates to an organic solvent-based undercoat coating composition which is particularly useful for repair coating of automobiles and the like, and a repair coating method using the same.

Generally, repair of automobile outer panels is roughly divided into partial repair painting when the damage is minor and replacement of new parts when the damage is large.

In the case of partial repair coating, after peeling or sanding the old coating film at the damaged portion, a sheet metal putty is thickly applied to the portion with a spatula, etc., and the putty surface is polished after drying. It consists of a large number of steps such as applying with a spatula or the like so as to cover the old coating film around the area, polishing the putty surface after drying, and then successively applying primer surfacer coating and top coating.

In addition, the process of putting putty to primer surfacer painting is a process to eliminate the distortion of the damaged part and arrange the car body in its original shape.Applying different types of putty to shallow scratches such as dots and lines In addition, a great deal of labor and time are spent because the coated surface is polished step by step using a plurality of waterproof papers having different coarseness and fineness for each coating.

In the automobile repair painting process, after coating the primer surfacer, it is dried and polished, then the color surface coating to the desired color is applied to the polished surface, and the resulting color base coating film is clear coated and then dried. 2 bake is the mainstream. In this case, since the primer surfacer coating process includes not only the coating process but also the drying process and the polishing process, much work time is spent.

Therefore, if the solvent-based or water-based color base is applied wet-on-wet after the conventional primer surfacer coating, the final finish is not satisfactory, and the primer surfacer adhesion strength also has a problem. .. Therefore, there is a demand for the development of an undercoat coating composition that does not affect the appearance of the topcoat in the next step or the performance as a repair coating film even if the drying and polishing steps are reduced or omitted.

Regarding such requirements, Patent Documents 1 and 2 disclose a three-component undercoat coating composition comprising a main component component containing an acrylic polyol and a pigment, a curing agent component containing a polyisocyanate compound, and a polyol component containing almost no pigment. Proposed. With such an undercoat coating composition, wet-on-wet coating can be realized between the undercoat paint and the topcoat paint, the undercoat coating film formed has an appropriate adhesive strength, and a natural appearance is repaired together with the topcoat paint film. A coating film is obtained.

However, in the compositions described in Patent Documents 1 and 2, when the coating film is a thin film, the surface layer may be rough, and in addition to the undercoat paint and the topcoat paint, a clear paint is wet-on-wet coated, and 3 When the layer was dried, the clear coat, which was the top coat, could be dusty.

By the way, as a repair method when the degree of damage to replaceable parts such as doors and fenders is great, there is a method of replacing a part with severe damage with a new part. The surface of such a new part is usually pre-painted with electrodeposition paint.At the repair painting site, the electrodeposition coating surface of the new part is ground with sandpaper, etc., and then the undercoat paint for repair is applied all over to adjust the groundwork. After that, the colored topcoat paint and the clear paint, which are toned to have the desired paint color, are sequentially applied.

In recent years, even in the coating of such new parts, a repair process of performing undercoating and colored topcoating by wet-on-wet coating has become mainstream. However, when the undercoat paints described in Patent Documents 1 and 2 are used in such a repair coating process, there are cases in which a poor appearance occurs due to poor durability of the undercoat film.

JP, 2014-472272, A JP, 2005-96594, A

The object of the present invention is to obtain a natural and smooth appearance even when wet-on-wet coating or a thin film thickness, and an undercoating coating composition suitable for forming a coating film excellent in durability and the same. It is to provide a repair coating method used.

As a result of diligent studies on the above problems, the present inventors have found that a composition obtained by combining a main component component containing an acrylic polyol and a pigment and a curing agent component containing a polyisocyanate compound has a plurality of specific acrylic polyols and By using a specific organosilane compound, a base layer that enables a repair multilayer coating with a natural appearance that does not feel uncomfortable with the surroundings even with wet-on-wet coating and that has excellent durability is formed. And has reached the present invention.

That is, the present invention is
What is claimed is: 1. A multi-component undercoat coating composition for preparing an undercoat coating composition by mixing two or more components before coating,
A lactone-modified acrylic polyol (A), a lactone-unmodified acrylic polyol (B), and a pigment composition (C), wherein the lactone-unmodified acrylic polyol (B) has an acid group and is more than the lactone-modified acrylic polyol (A). Also has a high acid number,
In the coating composition, the content of the pigment composition (C) is within the range of 50 to 500 parts by mass based on 100 parts by mass of the total solid content of the lactone-modified acrylic polyol (A) and the lactone-unmodified acrylic polyol (B). A combination of a main component (I) and a curing agent component (II) containing a polyisocyanate compound,
The present invention relates to an undercoat coating composition in which either or both of a main agent component (I) and a curing agent component (II) contain an alkoxysilane compound (D) and a repair coating method using the undercoat coating composition for undercoating.

The undercoating coating composition of the present invention is excellent in both adhesion to the base and the topcoating coating film, and since a undercoating coating film in which roughness is suppressed even in a thin film can be obtained, it is formed by coating a topcoating paint thereon. The obtained multilayer coating film has a natural appearance with little influence of the base.

Further, even when the undercoat coating composition and the topcoat coating composition are subjected to wet-on-wet coating, the obtained multilayer coating film has a natural appearance that is not different from the surroundings and is durable. Is also good enough.

The undercoat coating composition of the present invention is a multi-component composition for preparing an undercoat coating composition by mixing two or more components before coating. Hereinafter, they will be described in order.

First, the main ingredient (I) will be described.

<Lactone modified acrylic polyol (A)>
In the present invention, the acrylic polyol component that can be a polyurethane film-forming component together with the polyisocyanate compound described below includes a lactone-modified acrylic polyol (A).

By containing the lactone-modified acrylic polyol (A), the adhesion of the undercoat coating film formed by the undercoat coating composition of the present invention is improved.

The lactone-modified acrylic polyol (A) can be, for example, a copolymer of a polymerizable unsaturated monomer containing a lactone-modified hydroxyalkyl (meth)acrylate and at least one (meth)acryloyl group-containing monomer. ..

The lactone-modified hydroxyalkyl (meth)acrylate can be a reaction product of a lactone and a hydroxyalkyl (meth)acrylate, and examples thereof include compounds represented by the following general formula (1).

[In the formula, R ¹ represents a hydrogen atom or a methyl group, R ² represents an alkylene group having 2 to 6 carbon atoms, and n is 1 to 25. ].

The lactone-modified hydroxyalkyl (meth)acrylate is specifically, "Plaxel FA-1", "Plaxel FA-2", "Plaxel FA-2D", "Plaxel FA-3", "Plaxel FA-4", "Plaxel FA-5", "Plaxel FM-1", "Plaxel FM-2", "Plaxel FM-2D", "Plaxel FM-3", "Plaxel FM-4", "Plaxel FM-5" (any Also, commercially available products such as those manufactured by Daicel Chemical Co., Ltd. can be mentioned.

The copolymerization ratio of the lactone-modified hydroxyalkyl (meth)acrylate is 1 to 50% by mass, preferably 5 to 30% by mass, based on the total polymerizable unsaturated monomer used for producing the lactone-modified acrylic polyol (A). It is suitable for the content to be in the range of from the viewpoint of the adhesion to the top coating film formed from the coating composition of the present invention and the polishing property.

Examples of the (meth)acryloyl group-containing monomer copolymerized with the lactone-modified hydroxyalkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and n-butyl (meth). Acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, etc. Chain or branched alkyl (meth)acrylate; alicyclic alkyl (meth)acrylate such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; aralkyl (meth)acrylate such as benzyl (meth)acrylate; 2-methoxyethyl ( Alkoxyalkyl (meth)acrylates such as (meth)acrylate and 2-ethoxyethyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, hydroxybutyl Hydroxyalkyl (meth)acrylates such as (meth)acrylates, other lactone-modified (meth)acryloyl monomers that are not modified with lactones such as polyoxyethylene chain-containing (meth)acrylates whose molecule ends are hydroxyl groups; perfluoroalkyl (meth ) Acrylate; N,N-dialkylaminoalkyl(meth)acrylates such as N,N-diethylaminoethyl(meth)acrylate; (meth)acrylamide; allyl(meth)acrylate, ethylene glycol di(meth)acrylate, triethylene glycol. Di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl Glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, glycerol di(meth)acrylate, 1,1,1-trishydroxy Methylethanedi(meth)acrylate, 1,1,1-trishydroxymethylethanetri(meth)acrylate, 1 , 1,1-Trishydroxymethylpropane tri(meth)acrylate and other (meth)acryloyl monomers having at least two polymerizable unsaturated groups in one molecule; (meth)acrylic acid; acetoacetoxyethyl (meth) Carbonyl group-containing (meth)acryloyl monomers such as acrylate and diacetone (meth)acrylamide; glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4- Epoxy group-containing (meth)acryloyl monomers such as 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 methacryloyloxypropyltrimethoxysilane and γ-methacryloyloxypropyltriethoxysilane; dicyclopentenyloxyethyl (meth)acrylate, dicyclopentenyloxypropyl (meth)acrylate, dicyclopentenyl Examples thereof include oxidatively curable group-containing (meth)acryloyl monomers such as (meth)acrylate, and these can be used alone or in combination of two or more kinds.

Other polymerizable unsaturated monomers other than the (meth)acryloyl group-containing monomer include, for example, (meth)acrylonitrile; vinyl ester compounds such as vinyl acetate and vinyl propionate; styrene and α-methylstyrene. Polyvinyl compounds having at least two polymerizable unsaturated groups in one molecule such as vinyl aromatic compounds such as triallyl isocyanurate, diallyl terephthalate, and divinylbenzene; maleic acid, crotonic acid, β-carboxyethyl acrylate, etc. A carboxyl group-containing polymerizable unsaturated monomer; a hydroxyl group-containing polymerizable unsaturated monomer such as allyl alcohol; (meth)acrolein, formyl styrene, a vinyl alkyl ketone having 4 to 7 carbon atoms (for example, vinyl methyl ketone, vinyl ethyl ketone, Carbonyl group-containing polymerizable unsaturated monomer such as vinyl butyl ketone) and acetoacetoxyallyl ester; epoxy group-containing polymerizable unsaturated monomer such as allyl glycidyl ether; isocyanato such as m-isopropenyl-α,α-dimethylbenzyl isocyanate Group-containing polymerizable unsaturated monomer; vinyltrimethoxysilane, vinyltriethoxysilane and other alkoxysilyl group-containing polymerizable unsaturated monomer; epoxy group-containing polymerizable unsaturated monomer or hydroxyl group-containing polymerizable unsaturated monomer and unsaturated fatty acid Examples of the reaction product include an oxidatively curable group-containing polymerizable unsaturated monomer and the like, and these can be used alone or in combination of two or more kinds.

The lactone-modified acrylic polyol (A) has a weight average molecular weight of 5,000 to 80,000, preferably 6,000 to 70,000, and a solid hydroxyl value of 200 mgKOH/g or less, preferably 50 to 150 mg. /KOH, the solid content acid value is 1 to 30 mgKOH/g, preferably 5 to 15 mgKOH/g, and the glass transition temperature is 0 to 70)°C, preferably 20 to 50°C. However, it is suitable from the viewpoint of improving the adhesion of the formed coating film.

In the present specification, the weight average molecular weight is a value obtained by converting the weight average molecular weight measured by gel permeation chromatograph (“HLC8120GPC” manufactured by Tosoh Corporation) based on the weight average molecular weight of polystyrene. The columns are “TSKgel G-4000H×L”, “TSKgel G-3000H×L”, “TSKgel G-2500H×L”, and “TSKgel G-2000H×L” (both manufactured by Tosoh Corp., trade names). 4), the mobile phase: tetrahydrofuran, measurement temperature: 40° C., flow rate: 1 ml/min, detector: RI.

The glass transition temperature (Tg) can be calculated using the following formula.

1/Tg(K)=W ₁ /T ₁ +W ₂ /T ₂ +... W _n /T _n
Tg (°C) = Tg (K)-273
In the formula, W ₁ , W ₂ ,... W _n are mass fractions of each monomer, and T ₁ , T _2, ... T _n are glass transition temperatures Tg(K) of homopolymers of each monomer. ..

The glass transition temperature of the homopolymer of each monomer is as described in POLYMER HANDBOOK Fourth Edition, J. Am. Brandrup, E.; h. Immergut, E.; A. It is a value according to Grulke ed. (1999), and the glass transition temperature of a monomer not described in the literature is a static value when a homopolymer of the monomer is synthesized so that the weight average molecular weight is about 50,000. The glass transition temperature.

The static glass transition temperature is measured by, for example, using a differential scanning calorimeter "DSC-50Q type" (manufactured by Shimadzu Corporation, trade name), placing a sample in a measuring cup, vacuum suction to completely remove the solvent, and then 3 It can be measured by measuring the change in the amount of heat in the range of -100°C to 150°C at a rate of temperature increase of ℃/min, and setting the change point from the first baseline on the low temperature side as the static glass transition temperature. ..

In addition, in the present specification, the solid content means a residue excluding volatile components, and the residue may be solid or liquid at room temperature. The mass of the solid content can be calculated by multiplying the mass of the sample before drying with the solid content as the ratio of the amount of the residual substance when dried to the mass before drying.

<Lactone unmodified acrylic polyol (B)>
In the present invention, a lactone-unmodified acrylic polyol (B) is contained as an acrylic polyol component in addition to the lactone-modified acrylic polyol (A).

Such a lactone-unmodified acrylic polyol (B) does not contain a lactone-modified hydroxyalkyl (meth)acrylate, but contains a hydroxyl group-containing (meth)acryloyl monomer, another (meth)acryloyl group-containing monomer, and other polymerization as required. It may be a copolymer of monomers including a polyunsaturated monomer.

As the hydroxyl group-containing (meth)acryloyl monomer and the other copolymerizable polymerizable unsaturated monomer other than the other (meth)acryloyl group-containing monomer, the same compounds as those described above can be used.

The lactone-unmodified acrylic polyol (B) has a weight average molecular weight of 5,000 to 80,000, preferably 6,000 to 70,000 and a solid hydroxyl value of 200 mgKOH/g or less, preferably 50 to 50. Within the range of 150 mg/KOH, the solid acid value is within the range of 1 to 60 mgKOH/g, preferably within the range of 5 to 50 mgKOH/g, and the glass transition temperature is within the range of -20 to 60°C, preferably 0 to 40°C. Is suitable. This is because when the undercoat paint composition of the present invention and the colored topcoat paint are wet-on-wet coated, the finished appearance becomes good.

In particular, the present invention is characterized in that the lactone-unmodified acrylic polyol (B) has a larger solid content acid value than the lactone-modified acrylic polyol (A). When the solid content acid value of the polyol (B) is lower than that of the polyol (A), the skin feel of the undercoat coating composition, the colored topcoat coating composition and the clear coating composition becomes poor when wet-on-wet coating is unfavorable.

The lactone-unmodified acrylic polyol (B) has a lower glass transition temperature and a lower weight average molecular weight and a higher solid content hydroxyl value than the lactone-modified acrylic polyol (A). It is suitable from the standpoint of appearance when a colored top coat is applied wet-on-wet.

The blending ratio of the lactone-modified acrylic polyol (A) and the lactone-unmodified acrylic polyol (B) is 90/10 to 40/60 in terms of solid content mass ratio of lactone-modified acrylic polyol (A)/lactone-unmodified acrylic polyol (B). Suitably, it is preferably in the range of 80/20 to 50/50. If the blending amount of the lactone-unmodified acrylic polyol (B) is too large, the dryness to the touch is deteriorated, and it may be difficult to remove the dust adhering to the coating film.

<Pigment composition (C)>
Examples of the pigment composition (C) used in the present invention include pigments known in the paint field such as extender pigments, coloring pigments and rust preventive pigments, and they are used in an appropriate combination so as to obtain a desired coating color. You can The content of the pigment composition (C) in the undercoat coating composition of the present invention is 100 parts by mass of the total solid content of the lactone-modified acrylic polyol (A) and the lactone-unmodified acrylic polyol (B) contained in the main component (I). From the viewpoint of the adhesion strength of the undercoating film and the finished appearance after the topcoating, it is suitable that the amount is in the range of 50 to 500 parts by mass, preferably 100 to 300 parts by mass.

Examples of the extender pigment include clay such as kaolinite, halloysite, pyroferrite or sericite; calcium carbonate, barium sulfate, barium carbonate, aluminum silicate, gypsum, talc, silica, white carbon, diatomaceous earth, magnesium carbonate, alumina white. , Gloss white, mica powder and the like, and these can be used alone or in combination of two or more kinds.

Examples of coloring 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 iron oxide, titanium yellow, monoazo yellow, and the like. Yellow pigments such as condensed azo yellow, azomethine yellow, bismuth vanadate, benzimidazolone, isoindolinone, isoindoline, quinophthalone, benzidine yellow, permanent yellow; orange pigments such as permanent orange; red iron oxide, naphthol AS-based azo red, Red pigments such as Ansanthuron, anthraquinonyl red, perylene maroon, quinacridone red pigments, diketopyrrolopyrrole, watching red, and permanent red; purple pigments such as cobalt purple, quinacridone violet, dioxazine violet; cobalt blue, phthalocyanine blue. , Blue pigments such as Slen blue; Green pigments such as phthalocyanine green; Metallic pigments such as aluminum powder, bronze powder, copper powder, tin powder, iron phosphide, zinc powder; Metal oxide coated mica powder, mica-like iron oxide, etc. The pearlescent pigments mentioned above can be used, and these pigments can be used alone or in combination of two or more kinds.

As the rust preventive pigment, those known in the coating field can be used, and examples thereof include zinc compounds such as zinc and zinc oxide; magnesium phosphate, magnesium phosphate/ammonium phosphate eutectoid, magnesium monohydrogen phosphate, Magnesium dihydrogen phosphate, magnesium phosphate/calcium eutectoid, magnesium phosphate/cobalt eutectoid, magnesium phosphate/nickel eutectoid, magnesium phosphite, magnesium phosphite/calcium eutectoid, calcium phosphate, Calcium phosphite, calcium ammonium phosphate, calcium monohydrogen phosphate, calcium dihydrogen phosphate, calcium phosphate phosphate, aluminum phosphate, aluminum hydrogen phosphate, aluminum tripolyphosphate, aluminum dihydrogen tripolyphosphate, magnesium tripolyphosphate, tripolyphosphate Phosphorous metal salts such as magnesium oxide treated products of aluminum dihydrogen and magnesium oxide treated trizinc dihydrogen tripolyphosphate; silica, colloidal silica, metal ion exchange silica; vanadium pentoxide, calcium vanadate, magnesium vanadate and metavanazine. Ammonium acid, vanadium compounds such as calcined products of manganese oxide and vanadium oxide, calcined products of calcium phosphate and vanadium oxide: aluminum molybdate, calcium molybdate, aluminum phosphomolybdate, cobalt hydroxide and the like can be mentioned. Can be used alone or in combination of two or more.

From the viewpoint of water resistance of the undercoating film and adhesion to the substrate, a phosphoric acid metal salt and/or a zinc compound, preferably a zinc compound, is suitable as the above-mentioned rust preventive pigment.

In the present invention, the composition of the pigment composition (C) can be variously selected according to the lightness of the target coating film, but generally, the total solid content of the lactone-modified acrylic polyol (A) and the lactone-unmodified acrylic polyol (B) is 100. Based on parts by mass,
The extender pigment is in the range of 10 to 200 parts by mass, preferably 30 to 150 parts by mass,
0.1 to 180 parts by weight of color pigment, preferably 5 to 150 parts by weight,
It is suitable that the amount of the rust preventive pigment is in the range of 5 to 60 parts by mass, preferably 10 to 50 parts by mass, since an undercoating film excellent in hiding property and smoothness in a thin film can be obtained.

Further, when a black pigment is used as a color pigment to form a primer coating film having low brightness, the total solid content of the lactone-modified acrylic polyol (A) and the lactone-unmodified acrylic polyol (B) is 100 parts by mass as a reference. It can be contained within the range of 0.1 to 5 parts by mass.

In the present invention, it is suitable that the pigment composition (C) contains clay as a part of its components.
The content of clay is 0.1 to 100 parts by mass, preferably 20 parts by mass based on 100 parts by mass of the total solid content of the lactone-modified acrylic polyol (A) and the lactone-unmodified acrylic polyol (B) contained in the main component (I). It is preferably in the range of ˜80 parts by mass.

In the present invention, the undercoat coating composition contains clay, and by having the content of clay within this range, the undercoat coating film does not have a rough feeling even in a thin film, has a proper polishing property, and is used for the top coating of the next step. There is an effect that a coating film having a good appearance can be obtained even if it is applied by wet-on-wet coating.

<Alkoxysilane compound (D)>
In the present invention, either or both of the main agent component (I) and the curing agent component (II) contain an alkoxysilane compound (D). By including the alkoxysilane compound (D), there is an effect that an undercoat coating film having excellent durability can be obtained especially when the undercoat coating composition of the present invention is applied to the electrodeposition coated surface of a new part.

The alkoxysilane compound (D) is preferably a silicon compound having a functional group such as a vinyl group, an epoxy group, an amino group, a (meth)acryloyl group, a carboxyl group and a mercapto group in addition to an alkoxy group. Specific examples of the alkoxysilane compound (D) include, for example, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane and N-. (Β-Aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, γ-ureidopropyltriethoxysilane, N-β-(N-vinylbenzylamino) Ethyl)-γ-aminopropyltrimethoxysilane, γ-anilinopropyltrimethoxysilane and other amino group-containing alkoxysilane compounds; γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldimethoxy. Silane, mercapto group-containing alkoxysilane compound such as γ-mercaptopropylmethyldiethoxysilane; γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γglycidoxypropyltriethoxysilane, β- Epoxy group-containing alkoxysilane compounds such as (3,4-epoxycyclohexyl)ethyltrimethoxysilane; β-carboxylethylphenylbis(2-methoxyethoxy)silane, N-β-(N-carboxylmethylaminoethyl)-γ- Carboxy-containing alkoxysilane compounds such as aminopropyltrimethoxysilane; Vinyl group-containing alkoxysilane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane; 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyl Examples thereof include (meth)acryloyl group-containing alkoxysilane compounds such as triethoxysilane, and these may be used alone or in combination of two or more kinds.

Of these, epoxy group-containing alkoxysilane compounds are preferable from the viewpoint of durability of the formed coating film.

In the present invention, the content of the above-mentioned alkoxysilane compound (D) has an appropriate amount, and even if the addition amount is increased, a certain effect or more cannot be obtained. Specifically, the appropriate amount is 0.1 to 15 parts by mass, preferably 1 to 10 parts by mass, based on 100 parts by mass of the total solid content of the lactone-modified acrylic polyol (A) and the lactone-unmodified acrylic polyol (B). Within the range is suitable.

<Main ingredient (I)>
In the present invention, as the main component (I), in addition to the lactone-modified acrylic polyol (A), the lactone-unmodified acrylic polyol (B) and the pigment composition (C), an organic solvent, a viscosity modifier, a curing catalyst, a cellulose acetate. Butyrate and its modified products; modifying resins other than lactone-modified acrylic polyol (A) and lactone-unmodified acrylic polyol (B) such as polyester resin, alkyd resin, and polyurethane resin; pigment dispersant, surface modifier, resin particles Additives for paints such as can be appropriately blended.

Among these, examples of the organic solvent include organic compounds having a molecular weight of 58 to 220, particularly 72 to 200, and those known in the coating field can be used without limitation. It is desirable to contain at least one organic solvent selected from ester organic solvents and ketone organic solvents.

Examples of the ester organic solvent 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. , Diethylene glycol monoethyl ether acetate, and the like, examples of the ketone-based organic solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl isoamyl ketone, diisobuytyl ketone, methylhexyl ketone, isophorone, and the like. They can be used alone or in combination of two or more.

The amount of at least one organic solvent selected from such ester-based organic solvents and ketone-based organic solvents is 5% by mass or more, and particularly 20% by mass, based on all the organic solvents contained in the undercoat coating composition of the present invention. It is desirable to have the above.

In the present invention, as the other organic solvent other than the ester organic solvent and the ketone organic solvent, n-butane, n-hexane, n-heptane, n-pentane, n-octane, n-nonane, n-decane, Linear alkanes such as n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane and n-heptadecane; 2-methylbutane, 2,2-dimethylpropane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 2,4-dimethylpentane, 2,2,3-trimethyl Pentane, 2,2,4-trimethylpentane, 3,4-diethylhexane, 2,6-dimethyloctane, 3,3-dimethyloctane, 3,5-dimethyloctane, 4,4-dimethyloctane, 3-ethyl- Branched alkanes such as 3-methylheptane, 2-methylnonane, 3-methylnonane, 4-methylnonane, 5-methylnonane, 2-methylundecane, 3-methylundecane, 2,2,4,6,6-pentamethylheptane; Cyclopentane, t-decalin, cyclohexane, methylcyclohexane, ethylcyclohexane, 1,2-dimethylcyclohexane, 1,3-dimethylcyclohexane, 1,4-dimethylcyclohexane, propylcyclohexane, isopropylcyclohexane, 1,2-methylethylcyclohexane, Aliphatics such as cyclic alkanes such as 1,3-methylethylcyclohexane, 1,4-methylethylcyclohexane, 1,2,3-trimethylcyclohexane, 1,2,4-trimethylcyclohexane and 1,3,5-trimethylcyclohexane Hydrocarbon-based organic solvent; aromatic hydrocarbon-based organic solvent 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 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 Examples include ether organic solvents such as glycol monoethyl ether, dipropylene glycol mono n-propyl ether, and dipropylene glycol monoisopropyl ether.

The organic solvent can be added as a polymerization solvent or a diluting solvent in the production of the lactone-modified acrylic polyol (A) and/or the lactone-unmodified acrylic polyol (B), or for dilution in the production of the main ingredient (I).

Further, as the viscosity adjusting agent, conventionally known ones can be used, but it is particularly preferable to use an amide type viscosity adjusting agent.

By using an amide-based viscosity modifier, the storage stability of the main component (I) and the coating workability of the undercoat coating composition of the present invention are improved, and the adhesion strength of the undercoat coating composition to the top coating film is improved. Has the effect of improving.

As such an amide-based viscosity modifier, those known in the paint field can be used without limitation, the synthesis method, materials used, etc. are not particularly limited, and commercially available products can also be used.

Specifically, fatty acid monoamide synthesized by dehydration of fatty acid ammonium salt or ammonia decomposition of fats and oils (ester); condensation reaction of fatty acid amide and formaldehyde, heat condensation reaction of monocarboxylic acid and diamine, or dibasic acid and monoamine. Fatty acid diamide (bisamide) synthesized by heat condensation reaction with diamine; obtained by polycondensation of dibasic acid and diamine, polycondensation of diamine derivative and dibasic acid, dimerization of diamine and dibasic acid derivative or unsaturated fatty acid Examples thereof include fatty acid polyamides obtained by polycondensation of dimer acid or ring-opening polymerization of lactam.

The amide-based viscosity modifier may be diluted with a diluent medium such as an organic solvent.

In the present invention, the content of the active ingredient (the ingredient other than the dilution medium) of the amide-based viscosity modifier is 100 parts by mass of the total solid content of the lactone-modified acrylic polyol (A) and the lactone-unmodified acrylic polyol (B). Then, it is desirable to be in the range of 0.1 to 15 parts by mass, preferably 0.5 to 8 parts by mass.

Further, as the curing catalyst, conventionally known urethanization catalysts can be applied without particular limitation, for example, bismuth nitrate, lead oleate, tin octylate, dibutyltin dilaurate, dibutyltin bis(acetylacetonate), dibutyltin diacetate, Examples thereof include metal compounds such as dibutyltin octanoate, dioctyltin dilaurate, dioctyltin dineodecanoate, titanium tetrachloride, dibutyltitanium dichloride, tetrabutyltitanate, iron trichloride, zinc octylate, and tertiary amines.

The curing catalyst may be contained in either the main component (I) or the curing agent component (II), and the content of the curing catalyst may be a lactone-modified acrylic polyol (A) and a lactone-unmodified acrylic polyol (B). Within 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 total solid content, the curability of the composition of the present invention and the main component (I) and the curing agent component ( II) Suitable from the viewpoint of suppressing increase in viscosity after mixing.

<Curing agent component (II)>
In the present invention, the curing agent component (II) contains a polyisocyanate compound and, if necessary, an alkoxysilane compound (D).

Such a polyisocyanate compound is a polyisocyanate compound having two or more isocyanate groups in one molecule. Specific examples thereof include hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, xylylene diisocyanate, meta-tetramethylxylylene diisocyanate, tolylene diisocyanate, 4,4'. A polyisocyanate compound such as diphenylmethane diisocyanate or lysine diisocyanate, or an adduct of these polyisocyanates with a polyhydric alcohol, a low molecular weight polyester resin or water, or a cyclized polymer of the polyisocyanates mentioned above. Further, isocyanate biuret and the like can be mentioned, and these may be used alone or in combination of two or more.

In addition to the polyisocyanate compound, the curing agent component (II) may contain an organic solvent; a paint additive such as a viscosity modifier, a curing catalyst and a surface modifier, if necessary.

<Undercoat composition>
In the present invention, the ratio of the main agent component (I) and the curing agent component (II) used is such that the isocyanate group in the curing agent component (II) is equivalent to 1 equivalent of the hydroxyl group in the resin contained in the main agent component (I). Is suitably 0.8 to 4.0 equivalents, and preferably 1.0 to 3.5 equivalents.

The composition of the present invention thus obtained is a multi-component composition in which each component is stored separately, and generally, each component is mixed immediately before coating, and the viscosity is adjusted using a diluting thinner if necessary for use. Be served.

The present invention further provides a repair coating method using the undercoat coating composition for undercoating.

The member applicable to the method of the present invention is not particularly limited, but examples thereof include a coating film applied to an outer plate portion or an inner plate portion of an automobile, a household electric appliance, or the like, which is, for example, an electrodeposition coating film. In many cases, it is a multi-layer coating film consisting of an intermediate coating film (which may be omitted) and a top coating film. The coating film may be either solid type or metallic type. These coatings may be three-dimensional crosslinked cured coatings or non-crosslinked coatings.

In the method of the present invention, in the case of partial repair coating of a damaged portion and its periphery, first, the damaged portion of the coating film is scraped off, sanding is performed to the periphery of the damaged portion as needed, and then degreasing is performed as necessary. .. In the case of line scratches or spots, the composition of the present invention can be directly applied to the degreased portion, and depending on the damage, the composition of the present invention can be applied after filling the scraped portion with various putties. .. The filling of the putty can be performed by a method known per se, such as using a spatula. As the putty, there are conventionally known sheet metal putty and resin putty, and examples thereof include nitrification cotton type, acrylic resin type, epoxy acrylate resin type, unsaturated polyester resin type and urethane resin type. When the putty is applied, it is preferable to dry the putty and then polish the putty surface.

On the other hand, when the method of the present invention is applied to a new part such as an automobile part, the surface of the present invention can be sanded if necessary, and the composition of the present invention can be directly applied thereon.

For the coating of the composition of the present invention, conventionally known coating methods can be adopted, and spray coating is particularly preferable. It is suitable that the coating film thickness is 10 to 60 μm, preferably 20 to 50 μm as a dry film thickness.

According to the present invention, even when the top coat paint is applied in the next step in the uncured state of the coating film formed by the undercoat paint composition, it has an advantage that the final finish appearance is little affected. However, this does not exclude curing and polishing of the undercoat coating film.

In the case of wet-on-wet coating, the drying conditions of the undercoat coating film include, for example, a condition of standing at room temperature for 5 to 20 minutes. The conditions of 30° C. for 20 to 120 minutes, especially 30 to 90 minutes can be mentioned.

For the coating of the above-mentioned top-coat paint, a one-coat finish using only a colored base paint prepared by mixing a metallic pigment and/or a coloring pigment, or a two-coat finish using the colored base paint and a clear paint, is conventionally known. Painting is included.

As the above-mentioned colored base paint, an organic solvent-based or water-based top-coating paint that is usually used for repair can be used without particular limitation, and it is applied by a known coating means such as spray coating, electrostatic coating, brush coating, roller coating. can do.

When the colored base paint is applied a plurality of times, steps such as flash-off (the coating film is allowed to stand at room temperature after coating), air blowing and preheating may be provided between the respective coatings, if necessary.

Drying after the coating of the colored base paint is completed is not particularly limited, and may be uncured when the top clear is repeatedly applied. Generally, it is preferable to dry at a temperature condition of 20 to 100° C. for 5 to 60 minutes.

As the top clear coating, conventionally known coatings can be used without particular limitation. For example, an acrylic resin or a fluororesin containing a crosslinkable functional group such as a hydroxyl group as a main component, and a block polyisocyanate, a polyisocyanate or a melamine resin as a curing agent. Curable coatings contained as, or lacquer coatings containing a cellulose acetate butyrate-modified acrylic resin as a main component can be preferably used, and further pigments, fibrin derivatives, added resins, ultraviolet absorbers, if necessary. Additives for paints such as a light stabilizer, a surface conditioner and a curing catalyst can be contained.

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

Hereinafter, the present invention will be described more specifically with reference to Examples. However, the present invention is not limited to these examples. In addition, "part" and "%" in the following examples mean "mass part" and "mass %", respectively.

<Production of lactone-modified acrylic polyol>
Production example 1
Into a reaction vessel, 52 parts of butyl acetate was charged and heated to 110° C. with stirring, and 15 parts of styrene, 10 parts of methyl methacrylate, 10 parts of n-butyl methacrylate, 20 parts of t-butyl methacrylate and 2-methacrylate were used. 19 parts of ethylhexyl, 15 parts of 2-hydroxyethyl methacrylate, Praxel FA-2D (trade name, manufactured by Daicel Chemical Industries, a reaction product of caprolactone and hydroxyethyl acrylate): 10 parts, 1 part of acrylic acid and azobisisobutyronitrile A monomer mixture consisting of 2.0 parts of a monomer and a polymerization initiator was added dropwise at a constant rate at 110° C. or lower for 3 hours using a dropping pump. After the dropping was completed, the temperature was maintained at 110° C. for 60 minutes, and stirring was continued. After that, 0.5 parts of azobisisobutyronitrile dissolved in 7 parts of butyl acetate as an additional catalyst was added dropwise at a constant rate over 60 minutes. After completion of the dropping, the temperature was maintained at 110° C. for 60 minutes to complete the reaction. The obtained lactone-modified acrylic resin solution (A-1) is a uniform yellow transparent solution with a nonvolatile content of 55%, the resin has a weight average molecular weight of 14,000, a solid content hydroxyl value of 81 mgKOH/g, and a solid content acid value of 8 mgKOH/g, glass transition temperature was 44°C.

Production example 2
A lactone-modified acrylic resin solution (A-2) was obtained in the same manner as in Production 1 except that the monomer composition was changed to the following. The weight average molecular weight of the resin was 14,000, the hydroxyl value of solid content was 80 mgKOH/g, the acid value of solid content was 8 mgKOH/g, and the glass transition temperature was 35°C.
15 parts of styrene,
Methyl methacrylate 10 parts,
N-butyl methacrylate 10 parts,
T-butyl methacrylate 10 parts,
29 parts of 2-ethylhexyl methacrylate,
16 parts of 2-hydroxyethyl methacrylate,
Praxel FA-2D (trade name, manufactured by Daicel Chemical Co., Ltd., reaction product of caprolactone and hydroxyethyl methacrylate) 9 parts,
Acrylic acid 1 part.

<Production of lactone-unmodified acrylic polyol>
Production Example 3
42 parts of butyl acetate was charged into a reaction vessel, the temperature was raised to 110° C. with stirring, and 29 parts of styrene, 1 part of n-butyl methacrylate, 35 parts of 2-ethylhexyl acrylate, 2.4 parts of acrylic acid, and 2-hydroxyethyl. A monomer mixture of a monomer and a polymerization initiator consisting of 29 parts of methacrylate and 2.3 parts of azobisisobutyronitrile was added dropwise at a constant rate over 3 hours at 110° C. or lower using a dropping pump. After the dropping was completed, the temperature was maintained at 110° C. for 60 minutes, and stirring was continued. After that, 0.5 parts of azobisisobutyronitrile dissolved in 7 parts of butyl acetate as an additional catalyst was added dropwise at a constant rate over 60 minutes. After completion of the dropping, the temperature was maintained at 110° C. for 60 minutes to complete the reaction. The obtained acrylic resin solution (B-1) was a non-volatile content of 65% and was a uniform yellow transparent solution. The weight average molecular weight of the resin was 10,000, the solid content acid value was 20 mgKOH/g, and the solid content hydroxyl value was 130 mgKOH/. The glass transition temperature was 15°C.

Production Example 4
An acrylic resin solution (B-2) having a nonvolatile content of 65% was obtained in the same manner as in Production Example 3 except that the monomer composition was changed to the following. The weight average molecular weight of the resin was 10,000, the hydroxyl value of solid content was 118 mgKOH/g, the acid value of solid content was 37 mgKOH/g, and the glass transition temperature was 10°C.
18 parts of styrene,
N-butyl methacrylate 1 part,
T-butyl methacrylate 10 parts,
43 parts of 2-ethylhexyl acrylate,
29 parts of 2-hydroxyethyl methacrylate,
Acrylic acid 5 parts.

Production Example 5
42 parts of butyl acetate was charged into a reaction vessel, the temperature was raised to 110° C. with stirring, 29 parts of styrene, 1 part of n-butyl methacrylate, 35 parts of 2-ethylhexyl acrylate, 31.4 parts of 2-hydroxyethyl methacrylate and azo. A monomer mixture of 2.3 parts of bisisobutyronitrile and a polymerization initiator was added dropwise at a constant rate over 3 hours at 110° C. or lower using a dropping pump. After the dropping was completed, the temperature was maintained at 110° C. for 60 minutes, and stirring was continued. After that, 0.5 parts of azobisisobutyronitrile dissolved in 7 parts of butyl acetate as an additional catalyst was added dropwise at a constant rate over 60 minutes. After completion of the dropping, the temperature was maintained at 110° C. for 60 minutes to complete the reaction. The resulting acrylic resin solution (B-3) was a transparent solution having a non-volatile content of 65% and a uniform yellow color. The resin had a weight average molecular weight of 10,000, a solid content acid value of 0 mgKOH/g, and a solid content hydroxyl value of 140 mgKOH/. g, glass transition temperature was 14°C.

Production Example 6
An acrylic resin solution (B-4) having a nonvolatile content of 65% was obtained in the same manner as in Production Example 3 except that the monomer composition was changed to the following. The weight average molecular weight of the resin was 10,000, the hydroxyl value of solid content was 55 mgKOH/g, the acid value of solid content was 18 mgKOH/g, and the glass transition temperature was 55°C.
68 parts of styrene,
N-butyl methacrylate 1 part,
17 parts of 2-ethylhexyl acrylate,
13 parts of 2-hydroxyethyl methacrylate,
2.4 parts of acrylic acid.

<Production of two-component undercoat paint composition>
Example 1
30 parts of an acrylic resin solution (A-1) having a solid content of 55%, 15 parts of an acrylic resin solution (B-1) having a solid content of 65%, 6 parts of butyl acetate, 0.4 parts of a pigment dispersant, and 13 parts of titanium white. , 13 parts of clay, 13 parts of barium sulfate, 4 parts of zinc oxide, 1 part of γ-glycidoxypropyltrimethoxysilane, 0.1 part of dibutyltin dilaurate, amide thickener (fatty acid amide, amide viscosity modifier, 0.6 part of the active ingredient (20%) was sequentially mixed, mixed and stirred, and dispersed for 30 minutes to obtain a main ingredient. 20 parts of a polyisocyanate compound (“Sumijour N3390EA”, trade name, manufactured by Sumika Bayer Urethane Co., Ltd.) as a curing agent was mixed with the main component immediately before use to obtain a base coating composition (X-1). It was

Examples 2 to 27 and Comparative Examples 1 to 4
Each of the undercoating coating compositions (X-2) to (X-31) was obtained in the same manner as in Example 1 except that the compounding composition shown in Table 1 was used.

<Performance test>
(*) Drying property test A 300×100×0.8 mm mild steel plate was spray-coated with each of the undercoating coating compositions obtained in the above Examples and Comparative Examples so that the dry film thickness was 30 μm. The coating film dried at 20° C. for 20 minutes was pressed with a finger and evaluated according to the following criteria.
◎: No sticky feeling on fingers, no change in coating film,
◯: A little sticky feeling is observed on the finger, but there is no change in the coating film,
Δ: A sticky feeling was recognized on the finger, and a trace of pressing with the finger remained on the coating film slightly,
X: A sticky feeling is remarkably observed on the finger, and a mark left by the finger is remarkably left.

(*) Adhesion test After spray-coating a 300×100×0.8 mm mild steel plate with each coating composition for undercoating obtained in the above Examples and Comparative Examples so that the dry film thickness becomes 30 μm, room temperature Let PG Hybrid Eco #202 Sun Metallic Base (trade name, 1-pack type automotive topcoat paint manufactured by Kansai Paint Co., Ltd.) be a dry film thickness of 15 μm on the uncured coating film left for 10 minutes at Painted with air spray. After coating, lettane PG Eco HX(Q) clear (trade name, 2-pack top clear paint for car repair made by Kansai Paint Co., Ltd.) on the uncured coating film left at room temperature for 5 minutes as a dry film thickness of 40 μm It was painted by air spray so that After being left at room temperature for 10 minutes, it was heated at 60° C. for 20 minutes using a hot air circulation type drying furnace to obtain a test plate. This test coated plate was subjected to a cross cut test in accordance with JIS K5600. Specifically, 100 cuts reaching the material in a grid pattern are made vertically and horizontally at intervals of 2 mm on the coating film, and an adhesive tape having an adhesive force (120 gf/10 mm) is attached. Then, this adhesive tape was instantly peeled off, and the number of coating film pieces that had been peeled off and adhered to the adhesive tape was examined and evaluated according to the following criteria.
○: No peeling between the undercoat coating and the metallic base coating,
Δ: less than 10% peeling between the undercoat coating and the metallic base coating,
X: 10% or more of the number of peels between the undercoat coating and the metallic base coating.

(*) Finishing property in a thin film Each of the undercoating coating compositions obtained in the above Examples and Comparative Examples was dried on an electrodeposition coated plate coated with an epoxy resin-based electrodeposition coating having a size of 30×45 cm. After spray coating to a film thickness of 30 μm, it was left at room temperature for 10 minutes and then left on an uncured coating film, Retan PG Hybrid Eco #400 Deep Black Base (trade name, 1-pack automotive repair topcoat paint Kansai (Manufactured by Paint Co., Ltd.) was applied by air spray to a dry film thickness of 15 μm. After coating, lettane PG Eco HX(Q) clear (trade name, 2 component type top clear paint for car repair, manufactured by Kansai Paint Co., Ltd.) on the uncured coating film left at room temperature for 5 minutes as a dry film thickness of 40 μm It was painted by air spray so that After being left at room temperature for 10 minutes, it was heated at 60° C. for 20 minutes using a hot air circulation type drying furnace to obtain a test plate. After that, the appearance of each test coated plate was observed from the squash direction (oblique direction) and evaluated according to the following evaluation criteria.
⊚: Good luster, no inhalation observed, no clear skin feeling on clear coating film,
◯: Good glossiness, no inhalation observed, very slight dust skin feel on clear coating film Δ: Good glossiness, but inhalation observed, clear skin film dust on clear coating film Obviously recognized.
X: Poor glossiness, inhalation was observed, and appearance was extremely poor.
(*) Water resistance The coated plate obtained in the finish test was immersed in warm water at 40°C for 10 days, and then the surface of the coating film was observed.
◎; very good,
◯: Swelling of the coating film is extremely slight,
Δ: Swelling of the coating film is generally recognized,
X: The coating film swells and abnormalities such as blisters and whitening are observed.

(*) Durability test at the time of applying new parts 7×15 cm of an electrodeposition coated plate coated with an epoxy resin type electrodeposition coating is sanded and polished, and the above examples and Each of the undercoating coating compositions obtained in Comparative Examples was spray-coated to a dry film thickness of 30 μm, and then left standing at room temperature for 10 minutes to form an uncured coating film, and Retan PG Hybrid Eco # 202 Sun metallic base (trade name, 1-pack top coat paint for automobile repair, manufactured by Kansai Paint Co., Ltd.) was applied by air spray to a dry film thickness of 15 μm. After coating, lettane PG Eco HX(Q) clear (trade name, 2 component type top clear paint for car repair, manufactured by Kansai Paint Co., Ltd.) on the uncured coating film left at room temperature for 5 minutes as a dry film thickness of 40 μm It was painted by air spray so that Furthermore, after cross-cutting scratches were added to the coating film that had been completely dried by drying at 60°C for 3 hours or more, a salt spray test was carried out for 10 days, and then the cut portion was peeled off with an adhesive tape. The condition was evaluated.
◎: The peeling from the cut portion is 3 mm or less,
◯: The peeling from the cut portion is less than 4 to 7 mm,
Δ: peeling from the cut portion is less than 7 to 10 mm,
X: The peeling from the cut portion is 10 mm or more.

Claims (7)

What is claimed is: 1. A multi-component undercoat coating composition for preparing an undercoat coating composition by mixing two or more components before coating,
A lactone-modified acrylic polyol (A), a lactone-unmodified acrylic polyol (B), and a pigment composition (C), wherein the lactone-unmodified acrylic polyol (B) has an acid group and is more than the lactone-modified acrylic polyol (A). Also has a high acid number,
In the coating composition, the content of the pigment composition (C) is within the range of 50 to 500 parts by mass based on 100 parts by mass of the total solid content of the lactone-modified acrylic polyol (A) and the lactone-unmodified acrylic polyol (B). A combination of a main component (I) and a curing agent component (II) containing a polyisocyanate compound,
An undercoat coating composition in which either or both of the main agent component (I) and the curing agent component (II) contain an alkoxysilane compound (D). The undercoat paint composition according to claim 1, wherein the lactone-unmodified acrylic polyol (B) is a resin having both a glass transition temperature and a weight average molecular weight lower than those of the lactone-modified acrylic polyol (A). The compounding ratio of lactone-modified acrylic polyol (A)/lactone-unmodified acrylic polyol (B) is within the range of 90/10 to 40/60 in terms of (A)/(B) solid content mass ratio. Undercoat paint composition. The undercoat coating composition according to any one of claims 1 to 3, wherein the pigment composition (C) contains clay as a part of its components. A repair coating method using the undercoat coating composition according to any one of claims 1 to 4 for base coating. A step of applying the undercoat paint composition according to any one of claims 1 to 4 on a member surface, and applying the topcoat color paint composition in a state where the coating film of the undercoat paint composition is uncured A repair coating method characterized in that The undercoat paint composition according to any one of claims 1 to 4 is applied to the surface of the member, and the topcoat colored paint composition is applied in a state where the coating film of the undercoat paint composition is uncured. A repair coating method comprising a step of coating a top clear coating composition in an uncured state with a colored coating composition and drying the composition.