JP2002179982A - Base coat coating composition, method for forming multilayered coating film and multilayered coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a base coat coating composition which excels in adhesion, particularly improved recoating adhesion and the external appearance of coating films and, in addition, has good storage stability of the coating, a method for forming a multilayered coating film, and a multilayered coating film. SOLUTION: The base coat coating composition comprises an acrylic resin, a polyester resin, a crosslinking agent, and at least one of a luster pigment and a color pigment at a ratio (AV2/AV1) of the acid value (AV2) of the polyester resin to that (AV1) of the acrylic resin of 5-15. The crosslinking agent is a melamine resin. By the wet-on-wet method or the wet-on-dry method, a first clear coat is formed on a first base coat and cured, and then a second base coat is formed on the first clear coat, and without curing the second coat a second clear coat is formed on the second base coat, and then the second base coat and the second clear coat are both cured by baking.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a base coat coating composition, a method for forming a multilayer coating film, and a multilayer coating film.

[0002]

2. Description of the Related Art A multi-layer coating film is formed on a metal-coated substrate for the purpose of having a protection effect against corrosion and an aesthetic appearance. In this case, in order to obtain good adhesion between the undercoating film and the topcoating film, a sanding operation for roughening the surface of the undercoating film with polishing paper or the like is performed.

[0003] For example, in the coating of an automobile as a metal substrate (object to be coated), a thermosetting base coat paint is applied, and the thermosetting base coat paint is wet-on-wet without baking. A method of applying a curable clear coat paint and baking and curing the base coat and the clear coat simultaneously (this method is particularly called a two-coat one-bake method) is used.

In an automobile coating line for coating an automobile, when a defect occurs in a coating film formed by a two-coat one-bake method, an object is to eliminate the increase in the number of steps and to secure high productivity. A base coat paint and a clear coat paint are applied again by the two-coat one-bake method on the defective paint film without sanding the defective paint film.

[0005]

However, in the above-mentioned conventional coating method for automobiles, since different raw materials are used for the base coat paint and the clear coat paint, the above-mentioned clear coat (first clear coat) is used. When a base coat (second base coat) is formed on the base coat, adhesion between the lower clear coat and the upper base coat (such adhesion is referred to as "recoat adhesion") is poor, and peeling of the coating film is poor. What happened.

When a melamine resin is used as the base coat paint, the acid catalyst contained in the base coat paint diffuses and transfers to the upper clear coat in order to accelerate the curing of the melamine resin. As a result, the reaction rate of the clear coat is increased. When the base coat paint is repeatedly applied to the cured clear coat, sufficient recoat adhesion cannot be obtained unless sanding is performed. In addition, the presence of the acid catalyst matched the disadvantage that the appearance of the coating film on the vertical surface was impaired when the substrate to be coated had a three-dimensional shape.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has improved adhesion to upper and lower coating layers, in particular, improved recoat adhesion and excellent appearance of the coating film, and also has a good storage stability of the coating. It is an object to provide a composition, a method for forming a multilayer coating film, and a multilayer coating film.

[0008]

Means for Solving the Problems The present inventor has conducted intensive studies in view of the above-mentioned problems, and as a result, has reached the following present invention. 1. In a base coat paint composition containing an acrylic resin, a polyester resin, a crosslinking agent, and / or at least one of a glitter pigment and a coloring pigment, the acid value (AV ₂ ) of the polyester resin relative to the acid value (AV ₁ ) of the acrylic resin Wherein the ratio of (AV ₂ / AV ₁ ) is 5 to 15. 2. The base coat coating composition as described above, wherein the crosslinking agent is a melamine resin and does not contain an acid catalyst that promotes the reaction with the melamine resin, the acrylic resin, and the polyester resin. 3. The acrylic resin has a number average molecular weight of 3,000 to 2
The base coat coating composition as described above, which has a 5,000, hydroxyl value of 30 to 150 and an acid value of 5 to 40. 4. The polyester resin has a number average molecular weight of 1,000
5,000, hydroxyl value 10-40, acid value 100-20
The base coat coating composition as described above, which is 0. 5. The mass ratio (P / A) of the polyester resin (P) and the acrylic resin (A) is from 1/100 to 20 /
100, wherein the base coat composition is 100. 6. After forming and curing a first clear coat on the first base coat by wet-on-wet or wet-on-dry, a second base coat is formed on the first clear coat, and the second base coat is not cured. Forming a second clear coat on the second base coat, and then baking and curing both the second base coat and the second clear coat. A method for forming a multilayer coating film, which is the base coating composition. 7. A multilayer coating film formed by the above multilayer coating film forming method.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail. In addition, the compounding amount, compounding ratio, and adding amount in the present specification indicate amounts in terms of solid content unless otherwise specified.

[0010]Base coat paint composition  The base coat coating composition of the present invention comprises an acrylic resin,
Reester resin, crosslinker and glitter pigment and coloring
Base coat containing at least one of pigments
In the paint composition, the acid value of the acrylic resin (AV₁)
Of acid value of polyester resin (AV₂) Ratio (A
V₂/ AV₁) Is 5 to 15, especially recoat adhesion
Good paintability and appearance, and the storage stability of paint
It is a good basecoat paint composition.

The specific constitution of the above-mentioned base coat paint composition and its function and effect will be described below.

As the acrylic resin, one containing one or more alkyl esters of acrylic acid or methacrylic acid is used, or these alkyl esters and other ethylenically unsaturated monomers or functional monomers are used. A copolymer with at least one monomer is used.

The alkyl esters of acrylic acid or methacrylic acid include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate and 2- (meth) acrylate.
Ethylhexyl and the like can be suitably used.

As the other ethylenically unsaturated monomers, vinyl acetate, vinyl propionate, acrylonitrile, styrene, vinyl toluene and the like can be suitably used.

The other functional monomers include acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, N-
(Alkoxymethyl) acrylamide, N- (alkoxymethyl) methacrylate, glycidyl acrylate, glycidyl methacrylate and the like can be suitably used.

These acrylic resins have a hydroxyl group or a carboxyl group as a crosslinkable functional group.

The number average molecular weight of the acrylic resin is preferably from 3,000 to 25,000, and more preferably from 5,000 to 20,000. When the number average molecular weight is less than 3,000, it may be difficult to perform wet-on-wet coating with a clear coat to be applied repeatedly, and when it exceeds 25,000, the appearance of a coating film may be deteriorated.

The acrylic resin preferably has a hydroxyl value of 30 to 150, more preferably 40 to 7.
0. If the hydroxyl value is less than 30, curing of the coating film may be impaired, while if it exceeds 150,
The storage stability of the paint may decrease. .

The acid value of the acrylic resin is preferably from 5 to 40, more preferably from 10 to 20. If the acid value is less than 5, the curing of the coating film may be impaired, while if it exceeds 40, the storage stability of the paint may be reduced.

As the polyester resin, a resin which is a condensation product of a polyhydric alcohol and a polycarboxylic acid is used.
In addition, as the polyester resin, an alkyd resin obtained by adding a component that provides a fatty acid residue derived from a natural drying oil or a semidrying oil to a polyhydric alcohol and a polycarboxylic acid can also be used. These resins contain a proportion of either one or both free hydroxyl or carboxyl groups available for reaction with conventional crosslinking agents.

The polyhydric alcohols used for producing the polyester resin include ethylene glycol, propylene glycol, butylene glycol, 1,6-hexylene glycol, neopentyl glycol, glycerol, trimethylolpropane, trimethylolethane, pentaerythritol, Preferred are dipentaerythritol, tripentaerythritol, hexanetriol, and condensation products of trimethylolpropane with ethylene oxide or propylene oxide.

The polycarboxylic acid used for producing the polyester resin may be succinic acid (or an anhydride thereof),
Adipic acid, azelaic acid, sebacic acid, maleic acid,
(Or its anhydride), fumaric acid, muconic acid, itaconic acid, phthalic acid (or its anhydride), isophthalic acid, terephthalic acid, trimellitic acid (or its anhydride) and pyromellitic acid (or its anhydride) It is suitable.

In addition, the components providing fatty acid residues derived from natural or semi-dry oils include fatty acid safflower oil derived from linseed oil, soybean oil, tall oil, dehydrated castor oil, fish oil and tung oil, Fatty acids and the like derived from sunflower oil and cottonseed oil can be suitably used.

The alkyd resin obtained by using the above-mentioned components for providing polyhydric alcohol, polycarboxylic acid and fatty acid residue preferably has an oil length not exceeding 50%.

The polyester resin may further contain a monofunctional saturated carboxylic acid for the purpose of imparting plasticity to the resin. Examples of such monofunctional saturated carboxylic acid, and C ₄ saturated aliphatic acids -C _20, benzoic acid, p- tert-butyl benzoic acid and abietic acid.

The number average molecular weight of the polyester resin is preferably from 1,000 to 5,000, more preferably from 1,500 to 3,000. If the number average molecular weight is less than 1,000, it may be difficult to apply wet-on-wet with a clear coat to be overcoated, while if it exceeds 5,000, the appearance of the coating film may be reduced. .

The polyester resin preferably has a hydroxyl value of 10 to 40, more preferably 20 to 40.
~ 40. If the hydroxyl value is less than 10, curing of the coating film may be impaired, while if it exceeds 40,
The storage stability of the paint may decrease.

The acid value of the above polyester resin is preferably 100 to 200, more preferably 150 to 200.
~ 180. If the acid value is less than 100, the recoat adhesion and the appearance may not be improved. On the other hand, if it exceeds 200, the storage stability of the coating material may be reduced.

The ratio (AV ₂ ) of the acid value (AV ₂ ) of the polyester resin to the acid value (AV ₁ ) of the acrylic resin
₂ / AV ₁ ) is preferably 5 to 15, more preferably 5 to 10. If the ratio is less than 5, the recoat adhesion and the appearance cannot be improved, while if it exceeds 15, the storage stability of the paint may be reduced.

A preferable mass ratio (P / A) of the acrylic resin (A) and the polyester resin (P)
Is preferably 1/100 to 20/100, more preferably 2/100 to 5/100. If this ratio is less than 1/100, the recoat adhesion and the appearance may not be improved, while if it exceeds 20/100, the storage stability of the paint may be reduced.

As a crosslinking agent used in the base coat paint, an amino resin, particularly a melamine resin, is preferable. Examples of the melamine resin include a butylated melamine resin etherified by an n-butyl group or an i-butyl group alone, and a mixed methyl-butyl etherified melamine etherified by an n-butyl group or an i-butyl group and a methyl group. Resins are more preferred. In addition, other amino resins, such as benzoguanamine resin, can be used.

When a melamine resin is preferably used as the crosslinking agent, the weather resistance of the coating film is good.

Here, the melamine resin is usually used in combination with an acid catalyst such as paratoluenesulfonic acid or benzenesulfonic acid, which crosslinks with the acrylic resin and the polyester resin, but the melamine resin of the present invention is preferably Such an acid catalyst is not used in combination. The reactivity of the melamine resin with the acrylic resin and the polyester resin is ensured by the above-mentioned properties of the acrylic resin and the polyester resin of the present invention.

Therefore, according to the present invention, the acid catalyst diffuses and transfers to the upper clear coat while exhibiting the above-mentioned effects by using the melamine resin, and as a result, the reaction speed of the clear coat increases, When applying the base coat paint over the cured clear coat, there is no problem that sufficient recoat adhesion cannot be obtained unless sanding is performed. Further, when the substrate to be coated has a three-dimensional shape, there is no problem that the appearance of the coating film on the vertical surface is impaired. Here, the vertical surface means a surface other than a horizontal surface in the posture of the substrate to be coated in the coating process, and includes an inclined surface.

The ratio of the acrylic resin and the polyester resin to the crosslinking agent is preferably 90 to 50% by mass of the acrylic resin and the polyester resin, and 1% of the crosslinking agent.
0 to 50% by mass, more preferably 85 to 60% by mass of the acrylic resin and the polyester resin, and 15 to 40% by mass of the crosslinking agent. If the amount of the crosslinking agent is less than 10% by mass, in other words, if the amount of the acrylic resin or the polyester resin exceeds 90% by mass, the crosslinking in the coating film may not be sufficient. On the other hand, when the crosslinking agent exceeds 50% by mass,
In other words, when the content of the acrylic resin and the polyester resin is less than 50% by mass, the storage stability of the coating material is reduced, and the curing speed is increased, so that the appearance of the coating film may be deteriorated.

The base coat coating composition containing each component described above further contains at least one of various glittering pigments and coloring pigments.

Examples of the bright pigment include aluminum flake pigment, colored aluminum flake pigment, metal oxide coated alumina flake pigment, interference mica pigment, colored mica pigment, metal oxide coated glass flake, metal plated glass flake, metal Oxide-coated glass flakes,
Metal oxide coated silica flake pigment, metal titanium flake, graphite, stainless flake, plate-like iron oxide,
Examples include phthalocyanine flakes and hologram pigments.

Examples of the above color pigments include azo lake pigments, phthalocyanine pigments, indigo pigments,
Perylene pigments, quinophthalone pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments,
Examples thereof include organic pigments such as metal complex pigments, and inorganic pigments such as graphite, yellow iron oxide, red iron oxide, titanium dioxide, and carbon black.

The amount of the above-mentioned brilliant pigments and coloring pigments can be set to any amount necessary for developing a desired hue. In addition, various extender pigments and the like can be used in combination with these glittering pigments and coloring pigments.

The PWC of the bright pigment or the colored pigment as a whole pigment is preferably less than 50%.
% Is more preferable. If the PWC exceeds 50%, the appearance of the coating film is reduced.

In addition to the above components, the basecoat coating composition further comprises a sedimentation inhibitor which is a polyamide wax which is a lubricating dispersion of an aliphatic amide or a polyethylene wax which is a colloidal dispersion mainly composed of polyethylene oxide.
Curing catalyst, ultraviolet absorber, antioxidant, leveling agent,
Surface conditioning agents such as silicone and organic polymers, anti-sagging agents,
Thickeners, defoamers, lubricants, crosslinkable polymer particles (microgels) and the like can be appropriately added as additives and contained. The performance of paints and coatings can be improved by blending these additives at a ratio of 15 parts by mass or less with respect to 100 parts by mass of the total of the resin and the crosslinking agent.

The above-mentioned base coat coating composition is usually provided in a form in which the above-mentioned components are dissolved or dispersed in a solvent.

The solvent may be any one that dissolves or disperses the above-mentioned components, and an organic solvent or water can be used. Examples of the organic solvent include those commonly used in the field of coatings. For example, toluene,
Hydrocarbons such as xylene, ketones such as acetone and methyl ethyl ketone, ethyl acetate, cellosolve acetate,
Esters such as butyl cellosolve, alcohols and the like can be exemplified. When the use of an organic solvent is regulated from the viewpoint of the environment, it is preferable to use water. In this case, it may contain a suitable amount of hydrophilic organic solvent.

[0044]Method for forming multilayer coating film and multilayer coating film  The method for forming a multilayer coating film of the present invention can be directly applied to a substrate to be coated, or
Is the base coat (first base coat)
A clear coat (the first clear coat)
-Coat is formed and cured, resulting in coating defects
In the case of bleeding, the clear coat of the defective coating (first clear coat)
Sanding the coat) or sanding
Without clear coat (1st clear coat)
G) using the base coat coating composition of the present invention.
Form a second base coat and cure the second base coat
After forming a second clear coat without performing
Bake both base coat and second clear coat
It is a method of hardening by hardening.

In this case, the base coat (first base coat) and the clear coat (first clear coat)
After forming a base coat by wet-on-dry and baking and hardening, it may be sequentially and separately baked and hardened by forming a clear coat and baking and hardening, or after forming a base coat by wet-on-wet, May be formed by successively forming a clear coat without baking and curing, and baking and curing both coating films simultaneously.

In the case where a conventionally known base coat paint is applied and then the clear coat paint is applied and then baked and dried, sufficient recoat adhesion between the first clear coat and the second applied second base coat is obtained. Cannot be secured. However, in the case of a multilayer coating film using the base coat coating composition of the present invention as the second base coat coating,
Sufficient recoat adhesion can be ensured. In particular, when a coating defect occurs in the clear coat (first clear coat), recoating can be performed without sanding the clear coat (first clear coat) of the defective coating.

Further, the base coat paint composition of the present invention can be used for the first base coat paint.

In the case where the object to be coated is an automobile body and parts, the object to be coated is subjected to a chemical conversion treatment in advance, and then a base coat formed by an undercoating such as an electrodeposition coating or an intermediate coating is formed. It is preferable to keep it. The intermediate coating is performed for hiding the base, imparting chipping resistance, and ensuring adhesion with the top coat. The intermediate coating can be performed using a common organic solvent type, aqueous or powder coating type intermediate coating.

The multilayer coating film of the present invention can be applied to various substrates to be coated. Specific substrates to be coated include, for example, metals such as iron, aluminum, copper or alloys thereof, glass,
Inorganic materials such as cement and concrete, resins such as polyethylene resin, polypropylene resin, ethylene-vinyl acetate copolymer resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy resin, and various FRPs And natural or synthetic materials such as wood and fiber materials (paper, cloth, etc.). In the present specification, a substrate on which a base coating film formed by chemical conversion treatment, undercoating, intermediate coating, or the like is formed on the substrate to be coated may be referred to as a substrate to be coated.

The base material to be coated is coated with the base coat coating composition of the present invention or a conventional base paint to form a first base coat. For forming the first base coat, a metallic base coat paint containing a glitter pigment or a solid base coat paint containing a coloring pigment can be used.

In the case where the base material to be coated is an undercoat with an undercoat, an intermediate coat or the like, the first base coat paint is wet-on-wet or It can be painted by wet-on-dry.

The method for forming the first base coat film on the substrate to be coated is not particularly limited, but a spray method, a roll coater method and the like are preferable.

Further, the first base coat film can be applied in a plurality of layers on the substrate to be coated.

The dry film thickness of the first base coat is preferably 5 to 50 μm per coat, and 10 to 3 μm.
0 μm is more preferred.

As the first clear coat paint (the same applies to the second clear coat paint) used in the coating film forming method of the present invention, those commonly used for overcoating can be used. It is possible to use a mixture of at least one thermosetting resin selected from an acrylic resin, a polyester resin, a fluororesin, an epoxy resin, a polyurethane resin, a polyether resin, and a modified resin thereof, and the above-described crosslinking agent. it can. In particular, when a clear coat paint containing a carboxyl group-containing polymer and an epoxy group-containing polymer described in Japanese Patent Publication No. Hei 8-19315 is applied to a base coat in a measure against acid rain and wet-on-wet, a brightener in the base coat is used. Is preferably used from the viewpoint of not disturbing the orientation.

These clear coat paints may be used, if necessary, within a range that does not impair the transparency of the clear coat paint, a coloring pigment, an extender pigment, a modifier, an ultraviolet absorber, a leveling agent,
Additives such as dispersants and defoamers can be blended.

The application of the first clear coat paint in the coating film forming method of the present invention can be performed after the first base coat is cured, but the uncoated or semi-cured base coat layer can be applied. It is preferable to perform the wet-on-wet coating. When the first clear coat paint is applied a plurality of times, it may be baked at the same time after the final clear coat paint is applied. Good. The first clear coat thus formed by wet-on-wet using the clear coat paint is baked at 120 to 160 ° C. for a predetermined time together with the base coat and, if necessary, the base coat to obtain a coat. it can. The dry film thickness of the clear coat is preferably from 10 to 80 μm per coat, more preferably from 20 to 50 μm.

When a coating defect occurs on the multilayer coating film thus formed, repair coating is performed, but without sanding the already formed defective coating film, or After sanding, apply the base coat coating composition of the present invention as a second base coat,
Next, a second clear coat paint is applied in a wet-on-wet manner in the same manner as described above, and then baked and dried. Since the base coat paint composition of the present invention is used for the second base coat paint, sufficient recoat adhesion can be ensured.

In the case of this repair, the first base coat may not be the base coat paint of the present invention.
Further, the first clear coat paint and the second clear coat may be the same or different. The method for forming the clear coating film is not particularly limited, but a spray method,
A roll coater method or the like is preferred. The dry film thickness of the clear coating film is preferably 20 to 50 μm per coat, more preferably 25 to 40 μm.

[0060]

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.

[0061]Preparation of base coat paint composition  Acid value, hydroxyl value and number average molecular weight (Mn) shown in Table 1
Acrylic resin and polyester resin, crosslinking agent, face
The additives and additives were adjusted at the ratios shown in Table 1, and then the organic solvent was added.
Agent (toluene / xylene / ethyl acetate / butyl acetate quality)
Amount ratio = 70/15/10/5) with a stirrer.
Stir and mix to achieve proper viscosity
Compositions (base coat paints) 1 to 8 were prepared.

The acrylic resin used herein is a copolymer of styrene / methyl methacrylate / ethyl acrylate / hydroxyethyl methacrylate / methacrylic acid.
As the polyester resin, a condensation product of a polyhydric alcohol and a polycarboxylic acid prepared to have an acid value, a hydroxyl value and a number average molecular weight (Mn) shown in Table 1 was used. As the crosslinking agent, a butylamine melamine resin (trade name “Uban 20N60” manufactured by Mitsui Chemicals, Inc.) was used as the melamine resin.

[0063]

[Table 1] Preparation of substrate to be coated  Dull steel plate (0.8mm thick) with vertical and horizontal surfaces
After degreasing, a zinc phosphate treating agent (“Surdyne SD200
0 ", manufactured by Nippon Paint Co., Ltd.)
Cationic electrodeposition paint ("Power Top U-50",
(Int Co., Ltd.) so that the dry film thickness is 25 μm.
Dressed. Next, after baking at 160 ° C. for 30 minutes,
Intercoat containing polyester resin and melamine resin
Air spray the paint so that the dry film thickness is 40 μm
Paint and bake at 140 ° C for 30 minutes
It was formed and used as a substrate to be coated.

[0064]Formation of multilayer coating film  Basecoat paint compositions 1 to 7
Is spray-coated so that the dry film thickness becomes 15 μm.
After setting the base coat, set for 3 min.
The first clear coat shown in Table 2 was dried to a thickness of 35 μm.
And set at room temperature for 10 minutes.
Was. Then, the first base coat and the first clear coat
Baking at 180 ° C for 60 min.
A layer coating was formed.

Further, after the spots on the multi-layer coating film where dust is adhered are adjusted, the base coat coating compositions 1 to 7 can be prepared without sanding the repaired areas around the defective coating film.
The second base coat was formed by spray coating to a dry film thickness of 15 μm using the above method and then set for 3 minutes. The second clear coat shown in Table 2 was dried to a dry film thickness of 3 μm.
It was formed so as to have a thickness of 5 μm and set at room temperature for 10 minutes. Thereafter, the second base coat and the second clear coat were simultaneously baked at a temperature of 120 ° C. for 30 minutes.

[0066]

[Table 2] The clear coat paint shown in Table 2 is a clear paint (No. 1) containing an acrylic resin and a melamine resin (“Super Lac O-130 Clear”, manufactured by Nippon Paint Co., Ltd.). Paint No. 2 is a clear paint containing a carboxyl group-containing polymer and an epoxy group-containing polymer ("Macflow O-520 Clear", manufactured by Nippon Paint Co., Ltd.).

[0067]Evaluation method  The obtained first clear coat and second base coat
Recoat adhesion, vertical coating appearance and paint storage
The qualities were evaluated by the following evaluation methods, and the results are shown in Table 2.
Was.

The recoat adhesion was measured according to JIS K 5400.
After forming 100 square grids of 1 mm reaching the coating film base on the test piece after forming the multilayer coating according to the above, after adhering the cellophane adhesive tape to the grid, when peeling the cellophane adhesive tape Using the method of measuring the number of cross-cut squares, the following three levels were evaluated.

3: No peeled grids 2: 1 to 10 peeled grids 1: 11 or more peeled grids Appearance of the coating film on the vertical surface of the coated substrate (substrate) after coating The unevenness of the cured coating film was visually evaluated in the following three stages.

3: The state where no unevenness of the coating film was recognized. 2 ... The state where slight unevenness of the coating film was recognized. 1 .: The state where unevenness of the coating film was recognized. The degree of increase in viscosity when the prepared second base coat coating composition was stored at 60 ° C. for one month at room temperature was evaluated in the following three grades.

3: almost no increase in viscosity 2: small increase in viscosity, small amount of viscosity adjusting solvent required 1: large increase in viscosity, large amount of viscosity adjusting solvent required As can be seen from the results in Table 2, the multilayer of the present invention In Examples 1 to 9 in which a coating film was formed by the coating film forming method, non-sanding recoat adhesion without polishing the overcoated coating film and the appearance of the coating film on the vertical surface were good. Also, the second
The base coat coating composition used for the base coat of Example 1 had good storage stability. On the other hand, in Comparative Examples 1 to 6, any of the recoat adhesion, the appearance of the coating film on the vertical surface, and the storage stability of the base coat coating composition could not be obtained in a favorable state.

[0072]

According to the base coat coating composition of the present invention, the ratio (AV ₂ / AV ₁ ) of the acid value (AV ₂ ) of the polyester resin to the acid value (AV ₁ ) of the acrylic resin is from 5 to _1.
By increasing the value of 5, the reactivity of the base coat is increased, and the diffusion and migration of the acid catalyst to the top coat are suppressed, so that the recoat adhesion and non-sanding without polishing the repainted coating film and the appearance of the coating film on the vertical surface are obtained. Can be kept satisfactorily. Further, the base coat coating composition of the present invention can maintain good storage stability. The multilayer coating film obtained by the present invention has the above-mentioned good recoat adhesion and coating film appearance, and is preferably used in the fields of automobile, motorcycle and other vehicle outer plates, container outer surfaces, coil coating, home appliance industry and the like. You.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) B05D 7/24 302 B05D 7/24 302V C09D 5/00 C09D 5/00 D 161/28 161/28 167 / 00 167/00 F-term (reference) 4D075 AE06 CA33 CB13 DB02 DC12 EA05 EB22 EB35 EB45 EB52 EB55 EB56 EC11 4J038 CG141 CH031 CH041 CJ021 CJ101 CJ131 DA162 DD042 DD052 DD062 DD082 DD122 GA03 GA06 HA04KA03 HA0336 NA01 NA03 PA19 PB07 PC02

Claims (7)

[Claims] 1. A base coat paint composition comprising an acrylic resin, a polyester resin, a crosslinking agent, and at least one of a glitter pigment and a coloring pigment, wherein the polyester resin is based on the acid value (AV ₁ ) of the acrylic resin. Acid value (AV ₂ ) ratio (AV ₂ / AV ₁ )
Is a base coat coating composition characterized by the following. 2. The base coat paint composition according to claim 1, wherein the crosslinking agent is a melamine resin, and does not contain an acid catalyst that promotes a reaction between the melamine resin and the acrylic resin and the polyester resin. 3. The method according to claim 1, wherein the acrylic resin has a number average molecular weight of 3,
000-25,000, hydroxyl value 30-150, acid value 5
The base coat coating composition according to claim 1 or 2, wherein 4. The polyester resin has a number average molecular weight of 1,000 to 5,000, a hydroxyl value of 10 to 40, and an acid value of 1
The base coat coating composition according to any one of claims 1 to 3, wherein the number is from 00 to 200. 5. The mass ratio (P / A) of the polyester resin (P) to the acrylic resin (A) is 1/100.
The base coat paint composition according to any one of claims 1 to 4, wherein the ratio is from 20 to 100/100. 6. After forming and curing a first clear coat on the first base coat by wet-on-wet or wet-on-dry, forming a second base coat on the first clear coat, Forming a second clear coat on the second base coat without curing the second base coat, and then baking and hardening the second base coat and the second clear coat together; A method for forming a multi-layer coating film, wherein the coating material used for forming the second base coat is the base coating composition according to any one of claims 1 to 5. 7. A multilayer coating film formed by the multilayer coating film forming method according to claim 6.