JP2002155240A - Bright coating composition, method for forming film and multilayered film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a bright coating composition having an interference color in a highlight part of a formed film, providing a bright feeling without causing shadow unevenness and yellow cloudiness even when formed on a light chromatic color base film layer and useful for forming the bright film having a good film appearance without causing filter clogging by the glass flake itself during circulation, to provided a method for forming the film and to obtain a multilayered film. SOLUTION: This bright coating composition comprises a titanium dioxide- coated glass flake having 20-40 μm D50 and <=60 μm D90 and a vehicle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glitter coating composition containing a glitter pigment in which glass flakes having a specific particle size is coated with titanium dioxide and a vehicle, a method for forming a coating film, and a multilayer obtained by this method. Related to the coating film.

[0002]

2. Description of the Related Art Metallic paints using metallic pigments in which glass flakes are coated with silver or nickel are described in JP-A-3-23969 and JP-A-5-1248. These metallic pigments can form a coating film exhibiting a brilliant sensation that is more brilliant than aluminum flake pigments.

A coating film formed by using a metallic pigment obtained by coating the above glass flakes with silver or nickel exhibits the above-mentioned strong brilliancy, but when the viewing angle of the coating film is changed, the front highlight No coloring effect due to interference in the part is obtained. In addition, when a coating layer containing the metallic pigment is formed on the light-colored color intermediate coating layer,
There is a problem that the shadow unevenness phenomenon, in which the shadow of the coated metal occurs, and the yellow tinge phenomenon, in which the formed coating layer takes on a yellowish tinge, reduces the glitter, and a new design that solves these problems is desired. It is rare. Also, with such glitter paint containing glass flakes, when circulating at the time of coating, the glass flakes themselves are clogged in the filter installed to remove dust and grit in the circulation pipe. It has the problem of being easy.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a coating film having an interference color in a highlight portion of the formed coating film and to be formed on a light-colored color intermediate coating film layer. An object of the present invention is to provide a brilliant coating composition, a coating film forming method, and a multi-layer coating film, which can provide a brilliant feeling in which shadow unevenness and yellow tinge do not occur, and in which glass flakes themselves do not cause filter clogging during circulation. .

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies in view of the above-mentioned problems, and as a result, have reached the present invention. 1. D ₅₀ is 20~40μm and,, D ₉₀ is, bright coating composition containing the titanium dioxide-coated glass flakes and a vehicle is 60μm or less. 2. D ₅₀ of the glass flakes is 20～35Myuemu, and, above bright coating composition D ₉₀ of a 30 to 50 [mu] m. 3. The glittering paint composition, wherein the glass flake is contained in an amount of 0.01 to 30% by mass of the solid content with respect to the solid content of the paint. 4. A method for forming a coating film, wherein at least one of the layers constituting the multi-layer coating film is formed using the above glittering paint composition. 5. A method for forming a multi-layer coating film on a substrate, which sequentially forms an undercoating film layer, an intermediate coating film layer, a glittering coating layer, and a clear topcoating film layer, wherein the glittering coating layer Is a method for forming a coating film formed from the above glittering coating composition. 6. The above-mentioned method for forming a coating film, wherein the clear top coating film layer is formed from a coating material containing a carboxyl group-containing polymer and an epoxy group-containing polymer. 7. A multilayer coating film obtained by the above coating film forming method.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail.

Glitter coating composition The glass flakes used in the glitter coating composition of the present invention are:
D ₅₀ is 20~40μm and a pigment coated with titanium dioxide on the glass flakes D ₉₀ of at 60μm or less.

[0008] the coating of the titanium dioxide, to be done sufficiently thin compared to the size of the glass flakes, D ₅₀ of the bright pigment in a state in which the titanium dioxide is coated,
It is 20 to 40 μm, preferably 20 to 35 μm. In the present invention, D ₅₀ means the particle diameter when the cumulative amount in the relative cumulative particle diameter distribution curve is 50% in the particle diameter distribution of the long diameter. The D ₅₀ is less than 20 [mu] m, hard can exhibit brilliance expressing interference color effect, resulting in a coating film poor appearance exceeds 40 [mu] m. Also the glass flakes, D ₉₀ is, at 60μm or less, preferably 30 to 50
μm. Note that D ₉₀ in the present invention is such that the cumulative amount in the relative cumulative particle size distribution curve is 9 in the long particle size distribution.
It means the particle size at 0%. When the D ₉₀ is more than 60μm, cause filter plugging at the time of circulation. Here, the filter is a Knoe filter having a filter size of about 200 μm. Further, the thickness of the glass flake is preferably from 0.1 to 10 μm, more preferably from 0.1 to 5 μm. 0.1μ thickness
If it is less than m, an excessive share will be applied during the circulation of the paint, and the glass flakes will be deformed or broken, causing the paint to discolor over time. If it exceeds 10 μm, the appearance of the paint film may be deteriorated. The method for coating the above-mentioned glass flakes with the titanium dioxide is carried out by a usual method of coating the flake pigment such as mica with the titanium dioxide. By adjusting the coating mass of the titanium dioxide coated on the glass flake, a titanium dioxide coated glass flake pigment exhibiting a desired interference color can be obtained.

The content of the above glass flakes (mass ratio of solid content of pigment to 100 parts by mass of solid content of paint: PWC) in the glitter coating composition of the present invention is 0.01 to 30.
% Is preferable, and 1 to 15% is more preferable. 0.01%
If it is less than 30%, it is difficult to exhibit a brilliant effect exhibiting the interference color effect, and if it exceeds 30%, the appearance of the coating film may be deteriorated.

On the other hand, the vehicle contained in the glitter coating composition of the present invention disperses the glitter pigment and comprises a resin for forming a coating film and, if necessary, a crosslinking agent.

The resin for forming a coating film constituting the vehicle includes, for example, (a) an acrylic resin, (b) a polyester resin, (c) an alkyd resin, (d) a fluororesin,
(E) epoxy resin, (f) polyurethane resin, (g)
Examples thereof include polyether resins, and these can be used alone or in combination of two or more. In particular,
Acrylic resins and polyester resins are preferably used.

As the acrylic resin (a), a copolymer of an acrylic monomer and another ethylenically unsaturated monomer can be exemplified. Acrylic monomers that can be used in the above copolymerization include acrylic acid or methacrylic acid methyl, ethyl, propyl, n-butyl, i-butyl, t-butyl, 2-ethylhexyl, lauryl, phenyl, benzyl, 2-hydroxy Esterified products such as ethyl and 2-hydroxypropyl, ring-opened adducts of caprolactone of acrylic acid or 2-hydroxyethyl methacrylate, glycidyl acrylate or methacrylate, acrylamide, methacrylamide and N-methylolacrylamide, polyhydric alcohol (Meth) acrylate. The other ethylenically unsaturated monomers copolymerizable therewith include styrene, α
-Methylstyrene, itaconic acid, maleic acid, vinyl acetate and the like.

Examples of the polyester resin (b) include saturated polyester resins and unsaturated polyester resins. Examples thereof include condensates obtained by heating and condensing a polybasic acid and a polyhydric alcohol. Examples of the polybasic acid include saturated polybasic acids and unsaturated polybasic acids.Examples of the saturated polybasic acids include phthalic anhydride, terephthalic acid, and succinic acid. For example,
Maleic acid, maleic anhydride, fumaric acid and the like can be mentioned. Examples of the polyhydric alcohol include dihydric alcohols and trihydric alcohols, and examples of the dihydric alcohol include ethylene glycol and diethylene glycol. Examples of the trihydric alcohol include:
Glycerin, trimethylolpropane and the like can be mentioned.

The resin for forming a coating film includes a curable type and a lacquer type. Usually, a type having a curable type is used. In the case of a type having curability, it is used as a mixture with a crosslinking agent such as an amino resin, a (block) polyisocyanate compound, an amine-based, a polyamide-based, or a polyvalent carboxylic acid, and the curing reaction proceeds at heating or at room temperature. be able to. It is also possible to use a lacquer type coating film forming resin having no curability and a curable type in combination.

When the vehicle contains a cross-linking agent, the ratio of the resin for forming a film to the cross-linking agent is 90 to 50% by mass and the content of the cross-linking agent is 10 to 50% by mass in terms of solid content. Preferably, the coating film forming resin is 85 to 60% by mass, and the crosslinking agent is 15 to 40% by mass. If the amount of the crosslinking agent is less than 10% by mass (the amount of the resin for forming a coating film exceeds 90% by mass), the crosslinking in the coating film is not sufficient. On the other hand, when the cross-linking agent exceeds 50% by mass (the resin for forming a coating film is 50% by mass
), The storage stability of the coating composition is reduced and the curing speed is increased, so that the appearance of the coating film is deteriorated.

The glitter coating composition of the present invention may contain other glitter pigments and coloring pigments in addition to the above-mentioned glass flakes coated with titanium dioxide.

Other glitter pigments include, for example, aluminum flake pigment, colored aluminum flake pigment, mica pigment, metal titanium flake pigment, alumina flake pigment, silica flake pigment, graphite pigment,
Stainless steel flake pigments, hologram pigments, plate-like iron oxide pigments or phthalocyanine flake pigments, and as coloring pigments, for example, azo lake pigments, phthalocyanine pigments, indigo pigments, perylene pigments, quinophthalone pigments, dioxazine pigments, Examples include quinacridone pigments, isoindolinone pigments, metal complex pigments, graphite, yellow iron oxide, red iron oxide, titanium dioxide, carbon black, and the like. The amount of addition of other brilliant pigments and coloring pigments can be arbitrarily set as long as the effects of the glass flakes and the composite color effect with the underlayer described later are not hindered. Also, various extender pigments and the like can be used in combination.

The glitter coating composition of the present invention may further comprise, in addition to the above components, a polyamide wax which is a lubricating dispersion of an aliphatic amide, a polyethylene wax which is a colloidal dispersion mainly composed of polyethylene oxide, an antisettling agent, Curing catalyst,
UV absorbers, antioxidants, leveling agents, surface conditioners such as silicone and organic polymers, anti-sagging agents, thickeners, defoamers, cross-linkable polymer particles (microgels), etc. are appropriately added and contained. be able to. These additives can improve the performance of paints and coatings by blending, for example, at a ratio of 15 parts by mass or less, respectively, to 100 parts by mass of the vehicle (based on solid content).

The glitter coating composition of the present invention is provided in a form in which the above-mentioned components are usually dissolved or dispersed in a solvent. Any solvent may be used as long as it dissolves or disperses the vehicle, and an organic solvent and / or water may be used. Examples of the organic solvent include those commonly used in the field of coatings. Examples thereof include hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ether ketone, esters such as ethyl acetate, cellosolve acetate, and butyl cellosolve, and alcohols. When the use of an organic solvent is regulated from the viewpoint of the environment, it is preferable to use water. In this case, an appropriate amount of a hydrophilic organic solvent may be contained.

The film forming method of a coating film forming method of the present invention is a method for forming a multilayer coating film on a substrate, among the layers constituting the multilayer coating film, the at least one layer of formation, the This is a method for forming a coating film using a glitter coating composition. Examples of the multilayer coating film include, for example, a coating film layer formed using the glitter coating composition on the undercoat coating layer and a coating layer formed using the glitter coating composition. One having a clear coating layer formed thereon can be exemplified. Here, the multilayer coating film includes an undercoating film layer, an intermediate coating film layer, a glittering pigment-containing glittering coating layer, and a clear top coating film layer, and the glittering coating layer is The method for forming a coating film formed from the conductive coating composition is preferred from the viewpoint of design.

The above-mentioned substrate is not limited, and metals such as iron, aluminum, copper and alloys thereof; inorganic materials such as glass, cement and concrete; polyethylene resin, polypropylene resin, ethylene-vinyl acetate Copolymer resin, polyamide resin, acrylic resin,
Resins such as vinylidene chloride resin, polycarbonate resin, polyurethane resin and epoxy resin, and plastic materials such as various FRPs; natural and synthetic materials such as wood and fiber materials (paper, cloth, etc.); and processed products thereof. .

In the method for forming a coating film of the present invention, the above-mentioned glitter coating composition is applied to the above-mentioned substrate directly or via an undercoating layer. It is preferable to previously apply an undercoat to the base material by chemical conversion treatment, electrodeposition coating, spray coating, powder coating, or the like. If the glitter coating layer is formed directly on the undercoat layer without undercoating,
It can be formed by wet-on-wet (W / W) or wet-on-dry (W / D).

The above-mentioned W / W is a method of forming a lower coating film, drying the film by air drying or the like, and forming an upper coating film on an uncured or semi-cured lower coating film. On the other hand, the W / D is a method of forming an upper coating film on a lower coating film obtained by baking and curing a lower coating film.

It is also possible to apply each coating layer a plurality of times. In the case of baking the coating layer, 80 to 160
Perform baking at a temperature of ° C for a predetermined time. The dry thickness of the glittering coating layer is preferably 5 to 30 μm, more preferably 10 to 2 μm.
0 μm.

In the present invention, an intermediate coating layer can be formed before forming a glittering coating layer on the substrate. When an undercoat layer is formed below the intermediate coat layer, the undercoat layer is preferably formed by W / D with the undercoat layer. The intermediate coating film layer may be formed of a solvent-type paint, an aqueous paint, or a powder-type paint.
As the vehicle, pigment and optional additives to be used for forming the intermediate coating film layer, those exemplified for the glittering coating composition can be used.

Usually, a gray-colored intermediate coating is used for forming the intermediate coating layer. However, when a transparent brilliant top coating layer is provided on the intermediate coating layer, For example, a gray-based intermediate paint or a color intermediate paint is used. This is performed in order to develop a composite color of the intermediate coating film layer and the top coating film layer and to enhance the design. The dry thickness of the intermediate coating film layer is preferably from 20 to 100 μm, and if it is outside this range, the appearance of the coating film may be deteriorated. More preferably, it is 30 to 50 μm.

Next, a glitter coating layer is formed on the intermediate coating layer using the glitter coating composition. This glittering coating layer is preferably formed by the above-mentioned intermediate coating layer and the W / D. The dry film thickness of the glittering coating layer is
5 to 30 μm is preferable, and more preferably 10 to 20 μm
m. Here, a glitter coating film having transparency can be obtained by adjusting the content and type of the glitter pigment or the coloring pigment in the glitter coating composition. By using a material having transparency, it is possible to exhibit a composite color with the undercoating film layer and the intermediate coating film layer.

Further, at least one of the clear top coat layers is formed as a top coat layer on the bright coat layer. When a large amount of glittering pigment is contained in the glittering coating layer, the smoothness of the surface can be improved by applying two or more clear paints. It is preferable to use the above-mentioned W / W for formation of the clear top coat layer. Also, when applying the clear paint multiple times,
What is necessary is just to bake after applying the final clear paint, and it is not necessary to completely cure at the stage of applying the clear paint in the early stage. The dry film thickness of the clear top coat layer is preferably from 20 to 100 μm, and if it is out of this range, the appearance of the coat may deteriorate. More preferably 30 to
50 μm.

As the clear top coat layer, a general clear paint can be used, and a so-called turbid clear coat layer having a semi-transparent feeling may be used. Further, the clear top coat layer may be formed from a solvent type paint, an aqueous paint or a powder type paint. As the solvent-based paint or the water-based paint, a one-pack paint may be used, or a two-pack resin such as a two-pack urethane resin paint may be used. By forming the clear top coat layer on the glitter coating layer, it is possible to improve gloss and prevent the glitter pigment from being damaged. As the clear paint, those generally used for overcoating can be used, and a mixture of the above thermosetting resin and a crosslinking agent can be used. In particular, Tokuhei 8-1931
When a clear paint containing a carboxyl group-containing polymer and an epoxy group-containing polymer described in Japanese Patent No. 5 is applied to a glittering coating layer by acid rain resistance and W / W, It is preferably used from the viewpoint of not disturbing the orientation of the glitter. In addition, these clear coatings may include additives such as coloring pigments, extenders, modifiers, ultraviolet absorbers, leveling agents, dispersants, and defoaming agents as long as the transparency is not impaired. Can be included.

The multilayer coating film of the present invention is obtained by the above-mentioned coating film forming method, is formed on a substrate, and is formed of a layer constituting the multilayer coating film. At least one layer is a glitter coating layer formed using the glitter coating composition. Preferably, the multilayer coating film is formed of an undercoating film layer, an intermediate coating film layer, a glitter coating film layer, and a clear top coating film layer.

In particular, when the glittering coating film has transparency, even if the brightness of the layer located under the glittering coating film in the Munsell display system is N6 to N10, shadow unevenness and yellow tingling may occur. And a complex color without color. Here, when the layer located under the glittering coating film is a substrate, it means the brightness of the substrate. On the other hand, when the layer located below the glittering coating film is the clear intermediate coating film layer, it means the brightness of the lower coating film layer or the substrate.

[0032]

EXAMPLES Next, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. In addition, the compounding amount represents a mass part unless there is particular notice.

Examples 1 to 9 and Comparative Examples 1 to 2 Preparation of Substrates Dull steel sheet (length 300 mm, width 100 mm and thickness 0.8 mm) was treated with a zinc phosphate treating agent (trade name: "Surfdine SD2000", Japan). After the chemical conversion treatment using a paint (manufactured by Nippon Paint Co., Ltd.), the cationic electrodeposition paint (trade name: "Power Top U-50", manufactured by Nippon Paint Co., Ltd.) has a dry thickness of 25 μm.
m was electrodeposited. Then at 160 ° C. for 30
After baking for 30 minutes, apply the following intermediate coating paint to dry film thickness of 40
Air spray coating to a thickness of μm, 3 at 140 ° C
Baking was performed for 0 minutes to form an intermediate coating film layer. The substrates were 1A, 1B, and 1C, respectively. 1A ... Product name: "Olga S-90 Sealer" (N9),
Nippon Paint Co., Ltd., 1B ... Product name: "Olga S-90 Sealer" (N6),
Nippon Paint Co., Ltd., 1C ... Product name: "Olga S-90 Sealer" (N4),
Nippon Paint Co., Ltd., 1D ... 4 types of Nippon Paint Co., Ltd. brand name "Olga S-90 Sealer" (N2). N9, N6, N4, and N2 shown in parentheses to the right of the product name indicate the brightness of the Munsell display system, respectively.

Preparation of glittering paint composition Acrylic resin (styrene / methyl methacrylate / ethyl methacrylate / hydroxyethyl methacrylate /
Methacrylic acid copolymer, number average molecular weight about 20,000
0, hydroxyl value 45, acid value 15, solid content 50% by mass);
A melamine resin (trade name: "U-VAN 20SE", manufactured by Mitsui Chemicals, Inc., solid content 60 mass%) with respect to vehicle obtained by mixing the solid content mass ratio of the 80:20, D ₅₀ and D ₉₀ of Table 1 The brilliant pigment in which glass flakes coated with titanium dioxide were coated with titanium dioxide and the other pigments were blended in proportions as shown in Table 1 if necessary. As comparative examples, those not included in the glitter pigment obtained by coating the glass flakes with titanium dioxide defined in the present invention (Comparative Example 1) and the glitter pigment obtained by coating silver on the glass flakes of silver color (Comparative Example) Example 2) was blended in the ratio shown in Table 1.
Next, an organic solvent (toluene / xylene / ethyl acetate /
With a mass ratio of butyl acetate = 70/15/10/5), the mixture was stirred and mixed by a stirrer so as to obtain an appropriate coating viscosity, thereby preparing a glittering paint.

The clear coating clear paint was used the following paint. 2A: Acrylic resin solvent-based clear paint (trade name:
"Super Lac O-130 Clear", manufactured by Nippon Paint Co., Ltd .; 2B ... Solvent-type clear coating composed of a blend of a carboxyl group-containing polymer and an epoxy group-containing polymer (trade name: "Macflow O-520 Clear", Nippon Paint Co., Ltd.) Manufactured).

On the surface to be coated of the base material for forming the multilayer coating film , the above-mentioned intermediate coating film layer was dried to a thickness of 40 μm
m, and then the glitter coating layer was coated with a glitter paint shown in Table 1 so as to have a dry film thickness of 15 μm. Next, the clear top coat layer was applied by W / W to a dry film thickness of 40 μm to form a multilayer coat. The baking condition was 140 ° C. for 20 minutes. The glitter and filter clogging of the obtained coating film were evaluated by the following evaluation methods. Table 1 shows the results.

Evaluation method Glitter: Glitter when the test plate was viewed almost directly in front (highlight part) was visually evaluated. 3: Remarkable brilliantness 2: Slightly luminous feeling 1: No brilliantness Color tone: The color development when the test plate was viewed almost directly in front (highlight portion) was visually evaluated. 3: remarkable color developing property 2: slight color developing property 1: no color developing property Shadow unevenness: Yellow nigori when viewed at about 15 degrees (shade portion) was visually evaluated. 3: No yellow lingering observed 2: Yellow tingling was slightly observed 1: Yellow tingling was noticeably observed Filter clogging: The degree of clogging of the filter after a continuous circulation test for 7 days using a 200 μm mesh knau filter was evaluated. It was evaluated visually. 3: No clogging is observed 2: Clogging is slightly observed 1: Clogging is noticeably observed

[0038]

[Table 1]

As is clear from the results shown in Table 1, Examples 1 to 9 were obtained by forming a multi-layer coating film by the coating film forming method using the brilliant coating composition of the present invention. While exhibiting the brilliant having, even when applied on the intermediate coating layer of brightness N6-10, there is no shadow unevenness as the entire coating,
A multilayer coating film free of yellowing was obtained. Further, these glittering coating compositions did not cause filter clogging.

On the other hand, in the comparative example, when titanium dioxide coated glass flakes having a large particle size were used, the filter was clogged, and when a metal-plated glass flake pigment was used, only glitter was emphasized. This resulted in a bright feeling and no interference color.

[0041]

Since the glitter coating composition of the present invention contains a glitter pigment obtained by coating glass flakes with titanium dioxide, the multi-layer coating film formed by this paint gives a glitter having an interference color. It is possible to express a feeling. Also,
Since this brilliant pigment has a specific average particle size,
Does not cause filter clogging during circulation.

The multi-layer coating film obtained by applying the coating film formed by the glittering coating composition of the present invention to the intermediate coating film layer having a lightness of N6 to 10 has a color tone of the intermediate coating film layer. The brilliancy of the brilliant pigment is synthesized, and an interference color free of shadow unevenness and free of yellowing can be exhibited as the whole coating layer.

The multi-layer coating film of the present invention exhibits the above brilliant feeling and the above-mentioned color tone, so that the outer skin of vehicles such as automobiles and motorcycles, these parts, outer surfaces of various containers, coil coating, furniture, home appliance industry, communication industry, etc. Is preferably used in the field where brilliancy is required.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) C09D 7/12 C09D 7/12 F term (reference) 4D075 AE03 CB04 CB13 EA43 EC03 EC23 4J038 CD091 CG141 CG171 CH031 CH041 CH081 CH121 CJ251 CR061 DA122 DB001 DD121 DD181 DF001 DG001 DG111 DG301 DH002 GA03 HA486 KA04 KA08 KA15 KA20 MA14 NA01 NA23 PA07

Claims (7)

[Claims] 1. A D ₅₀ of 20 to 40 [mu] m, and, D ₉₀ is 60
A glittering coating composition comprising a titanium dioxide-coated glass flake having a size of not more than μm and a vehicle. 2. The glass flake having a D ₅₀ of 20 to 35 μm.
m, and, glitter paint composition of claim 1, wherein D ₉₀ of a 30 to 50 [mu] m. 3. The glittering coating composition according to claim 1, wherein the glass flakes are contained in an amount of 0.01 to 30% by mass of the solid content with respect to the solid content of the coating material. 4. A method for forming a coating film using the glitter coating composition according to claim 1 for forming at least one of the layers constituting the multilayer coating film. 5. An undercoat film layer, an intermediate coat film layer,
Glitter coating layer, a method of forming a multilayer coating film sequentially forming a clear top coating layer, wherein the glitter coating layer,
A method for forming a coating film formed from the glittering coating composition according to claim 1. 6. The method according to claim 5, wherein said clear top coat layer is formed from a paint containing a carboxyl group-containing polymer and an epoxy group-containing polymer. 7. A multi-layer coating film obtained by the method for forming a coating film according to claim 4.