JPH10244218A - Coating method for top coat of automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve interlaminar adhesion between a first clear paint film and a second clear paint film by a method wherein a colored base coating material and a first clear coating material are applied to a shell part of a car body, preheated at a specific temperature, and thereafter a second clear coating material is applied, and heated to cure three layers of paint films simultaneously. SOLUTION: A colored base coating material and a first clear coating material are applied to a shell part of a car body, and both paint films are preheated at 70-100 deg.C. After applying a second clear coating material thereto, these three paint films are simultaneously cured by heating. Herein, both paint films composed of the colored base coating material and the first clear coating material are not crosslinked and cured by this preheating, gel fraction is about utmost 5wt.%, and further a solid content of the first clear coating material is preferably about 80wt.% or higher. Thereby, thick film (for example, about 30μm or over in cured paint film) application of the second clear coating material can be executed, and further interlayer adhesion between the first clear paint film and the second clear paint film is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel automotive top coating method for forming a three-layer coating on a vehicle body outer panel by applying a colored base paint, a first clear paint and a second clear paint. .

[0002]

2. Description of the Related Art As a method of forming an overcoat film on the outer panel of an automobile body, a three-coat method of applying a clear paint twice is used from the viewpoint of improving the smoothness and sharpness of the paint film. . For example, a three-coat one-bake (3C1B) system in which a colored base paint, a first clear paint, and a second clear paint are applied by wet-on-wet and then heated to simultaneously cure the three-layer coating film, A three-coat two-bake (3C2B) system is known in which after applying one clear coating, the coating is heated to cure both coatings, then the second clear coating is applied, and then heated and cured again to form a three-layer coating. .
However, in the 3C1B method, the heating of the coating film is one step, which is energy saving. However, the second clear coating material is applied to a thick film (for example, 30 μm or more), and the smoothness of the coating film is improved.
It is difficult to improve sharpness and the like, and there are defects such as easy sagging. On the other hand, the 3B2C method requires two heating steps, and furthermore, the interlayer between the first clear coating film and the second clear coating film. It has defects such as reduced adhesiveness.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned deficiencies of the prior art and to make it possible to apply a second clear coating to a thick film in a three-coat system, to provide a first clear coating film and a second clear coating film. It is an object of the present invention to provide a novel method of coating an automobile with excellent interlayer adhesion to a film and energy saving.

[0004]

Means for Solving the Problems In order to achieve the above object, the present inventor has conducted intensive studies and, as a result, preheats the first clear coating film at 70 to 100 ° C. in the process of the 3C1B method, and then performs the second clear coating. It has been found that the object can be achieved by applying a paint, and the present invention has been completed.

That is, according to the present invention, a colored base paint (A) is applied to the outer panel of an automobile body, a first clear paint (B) is applied without curing, and after preheating at 70 to 100 ° C., The present invention relates to an automotive topcoat coating method wherein a two-layer paint (C) is applied and then heated to simultaneously cure the three-layer coating.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION An outer plate portion of an automobile body, which is an object to be coated by the coating method of the present invention, is a portion located outside the vehicle body with a door closed, and is, for example, a passenger car, a mini car, a bus Hoods for trucks, etc., roofs, trunk lids, fenders, bumpers, outside doors and the like.

[0007] The material of the vehicle body outer plate portion is usually a steel plate, plastic (polyolefin, polyurethane, etc.), but any of these materials may be used.

Prior to carrying out the method of the present invention, an undercoat or an intermediate paint such as a cationic electrodeposition paint may be applied to the outer panel of the body to be coated in advance, and the paint film may be cured. preferable.

The colored base paint (A) is a paint to be applied to the outer panel prior to the first clear paint (B), and is an organic material containing a base resin, a crosslinking agent, a coloring pigment and an organic solvent as essential components. Solvent-based liquid paints, including solid color paints, metallic paints, pearlescent paints, and the like.

Examples of the base resin include acrylic resins, polyester resins, and alkyd resins having a functional group such as a hydroxyl group, a carboxyl group, and an epoxy group. Examples of the crosslinking agent include a melamine resin, a urea resin, a polyisocyanate compound, a block polyisocyanate compound, and a carboxyl group-containing compound that can react with a functional group in the base resin. The ratio of the base resin to the crosslinking agent is 50 to 90% by weight, particularly 60 to 8% by weight, based on the total weight of the two components.
0% by weight, 50 to 10% by weight of crosslinking agent, especially 40 to 20%
% By weight is suitable.

As the coloring pigment, for example, solid color pigments, metallic pigments, pearlescent pigments and the like can be used. As solid color pigments, for example, titanium oxide,
Inorganic pigments such as zinc white, carbon black, cadmium red, molybdenum red, chrome yellow, chromium oxide, Prussian blue, cobalt blue, etc .; Is mentioned. Examples of the metallic pigment include flaky aluminum and mica-like iron oxide. Examples of the pearl pigment include mica, mica whose surface is coated with a metal oxide, and the like.

These coloring pigments can be used alone or in combination of two or more. The compounding amount of these coloring pigments can be arbitrarily selected according to the intended color tone, metallic feeling and pearl tone, and there is no particular limitation.

The organic solvent may be any one which can dissolve or disperse the above-mentioned base resin, cross-linking agent and color pigment by mixing.
For example, hydrocarbon-based, ester-based, ether-based, alcohol-based, ketone-based coating solvents and the like can be used.

The colored base paint (A) can be prepared by mixing and dissolving or dispersing the above-mentioned base resin, crosslinking agent and coloring pigment in an organic solvent by a conventional method.

The clear coatings (B) and (C) contain a base resin, a crosslinking agent and an organic solvent as essential components to form a transparent coating film. As the base resin, the crosslinking agent and the organic solvent, those exemplified for the colored base paint (A) are suitable. The clear paints (B) and (C) can be prepared in the same manner as in the case of the colored base paint (A).
The base resin, crosslinking agent and organic solvent of the clear coatings (B) and (C) may be the same or different in the same coating line.

In the coating method of the present invention, a colored base coating material (A) and a first clear coating material (B) are applied to an outer panel of an automobile body, and both the coating films are heated at 70 to 100 ° C. and preheated. After applying the second clear coating (C), the coating is heated to simultaneously cure the three-layer coating film.

The colored base paint (A) is an electrostatic coating method,
The outer plate can be coated by a spray coating method or the like.
For example, when the solid content of the base paint (A) at the time of coating is 1
0 to 50% by weight, the viscosity was adjusted to 10 to 30 seconds (Ford cup # 4/20 ° C),
It is preferable to apply the first clear coating material (B) after painting so as to have a thickness of 40 μm and leaving it at room temperature for 1 to 20 minutes.

The first clear coating material (B) is adjusted to have a solid content concentration of 10 to 60% by weight and a viscosity of 10 to 40 seconds (Ford cup # 4/20 ° C.) at the time of coating. It is preferable that the uncured coating surface of A) is coated with a cured coating film to have a thickness of 20 to 50 μm by an electrostatic coating method, a spray coating method, or the like.

In the coating method of the present invention, after the first clear coating material (B) is applied and before the second clear coating material (C) is applied, the coloring base coating material (A) and the first clear coating material (B) are used. It is necessary to preheat the uncured two-layer coating at a temperature of 70 to 100C, preferably 80 to 95C. Due to this preheating, the two coating films were not crosslinked and cured, and the gel fraction was 5% by weight or less, and the solid content of the first clear coating material (B) was 80% by weight.
It is preferably at least 90% by weight. It is usually appropriate that the preheating time is about 2 to 30 minutes.

By performing such preheating, it is possible to apply a thick film (for example, a cured film of 30 μm or more) of the second clear coating material (C) as compared with the conventional 3C1B system, and to prevent sagging of the coating film. In addition, since the number of heating steps is reduced as compared with the 3B2C method, energy saving can be realized, and effects such as improved adhesion between layers can be obtained.

Next, after preheating the uncured two-layer coating film composed of the colored base coating material (A) and the first clear coating material (B), the coated surface is coated with a second clear coating material (C).

The second clear coating material (C) is adjusted to have a solid content concentration of 20 to 60% by weight and a viscosity of 10 to 60 seconds (Ford cup # 4/20 ° C.) at the time of coating, and then to preheat the second solid coating material (C). (1) The clear paint (B) is coated on the coated surface by an electrostatic method, a spray method, or the like so that the thickness becomes 10 to 50 μm based on the cured coating film. Then, the coating method of the present invention is achieved by leaving the mixture at room temperature for about 1 to 10 minutes and then heating it at 100 to 160 ° C. for 10 to 40 minutes to simultaneously cure the three-layer coating film.

[0023]

EXAMPLES Hereinafter, Production Examples, Examples and Comparative Examples will be given,
The present invention will be described more specifically.

Production Example 1 Preparation of object to be coated Steel plate for automobile (size 100 × 150 × 0.8 mm)
In addition, cationic electrodeposition paint (“Elecron 9800”, manufactured by Kansai Paint Co., Ltd., trade name, polyamine-modified epoxy resin-block polyisocyanate-based water-based paint) and intermediate paint (“Lugabake TP-37”, Kansai Paint Co., Ltd.) ), Trade name, polyester resin-melamine resin-based organic solvent type paint), and each was heated and cured to obtain an object to be coated.

Production Example 2 Preparation of Colored Base Coating (A-1) Hydroxyl-containing acrylic resin (number-average molecular weight 15,000,
Hydroxyl value 50 mgKOH / g, acid value 4 mgKOH / g) 75 parts by weight,
25 parts by weight (solid content) of "Yuban 20SE" (methyl / butyl mixed etherified melamine resin, manufactured by Mitsui Toatsu Co., Ltd.), 4 parts by weight of aluminum paste (manufactured by Toyo Aluminum, "Aluminum Paste 4919", trade name) And 3 parts by weight of carbon black and a mixed solvent of ethyl acetate / toluene / solvesso 150 (hydrocarbon solvent, manufactured by Cosmo Oil Co., Ltd., trade name) = 50/30/20 (weight ratio). The solid content at the time of coating was adjusted to 40% by weight, and the viscosity was adjusted to 30 seconds (Ford cup # 4/20 ° C).
A colored base paint (A-1) was obtained.

Production Example 3 Preparation of First Clear Coating (B-1) Hydroxyl-containing acrylic resin (number-average molecular weight 10,000,
80 parts (solid content) of hydroxyl value 100 mgKOH / g, acid value 5 mgKOH / g and 20 parts (solid content) of "Uban 20SE" were dissolved in Solvesso 100 (hydrocarbon solvent, manufactured by Cosmo Oil Co., Ltd.).
Mixed in a mixed solvent consisting of (trade name) / solvesso 150 = 50/50 (weight ratio) and dissolved in a solid content at coating 40
The first clear paint (B-1) was obtained by adjusting the weight% and the viscosity to 20 seconds (Ford cup # 4/20 ° C.).

Production Example 4 Preparation of Second Clear Coating (C-1) Hydroxyl-containing acrylic resin (number average molecular weight 12,000,
80 parts (solid content) of hydroxyl value 110 mgKOH / g, acid value 5 mgKOH / g and 20 parts (solid content) of "Uban 20SE" are mixed and dissolved in a mixed solvent consisting of Solvesso 100 / solvesso 150 = 50/50 (weight ratio). And a coating solid content of 40% by weight and a viscosity of 20 seconds (Ford Cup # 4/20
C.) to obtain a second clear coating material (C-1).

Example 1 and Comparative Examples 1-2 The first clear coating composition (A-1) was applied to the object to be coated obtained in Production Example 1 so that the cured coating film had a thickness of 15 μm. B-1) was cured to a thickness of 30 μm, and the second clear coating (C-1) was cured to a thickness of 30 μm.
According to the steps shown in Table 1 below,
Painted, dried, heated and cured.

[0029]

[Table 1]

Next, the performance of the coating film obtained above was examined by the following test method.

Thick film coating: on the surface of the first clear coating,
The second clear paint is applied with a cured coating film so as to have a film thickness of 30 μm, and the coated film surface obtained by heating and curing at 140 ° C. for 30 minutes is observed.
Those with occurrence of sagging etc. were regarded as defective.

The interlayer adhesion: to reach the base material, with a cutter knife, approximately in the middle of the specimen, the parallel lines of each vertical and horizontal eleven orthogonal pulling at 1mm intervals, in 1 cm ² 10
Cut and scratches were made in the shape of a square so as to form 0 squares, an adhesive cellophane tape was adhered to the coated surface, and the coated surface was sharply peeled and then observed. A sample in which no peeling of the coating film was observed was regarded as good, and a sample in which one or more peeling was observed between the first clear coated surface and the second clear coated surface was evaluated as poor.

Image sharpness: IMAGE CLARITY ME
TER: manufactured by Suga Test Instruments Co., Ltd.)
A value within the range of 00% was taken, and the larger the numerical value, the better the sharpness (image clarity) was measured. A sample having an ICM value of 80 or more was evaluated as good, and a sample with an ICM value of less than 80 was evaluated as defective.

Gloss: JIS K-5400 7.6 (1
990), the reflectance was measured when the incident angle and the light receiving angle were each 60 degrees as the degree of gloss of the coating film in accordance with the 20-degree mirror glossiness. The glossiness of the reference surface of the mirror glossiness is 100
When expressed as a percentage, those with a reflectance of 90% or more were evaluated as good, and those with a reflectance of less than 90% were evaluated as defective.

Table 2 shows the test results of the coating film performance.

[0036]

[Table 2]

[0037]

According to the coating method of the present invention, in particular, in the 3C1B method, a two-layer coating film composed of a colored base coating material (A) and a first clear coating material (B) is formed before the coating of the second clear coating material (C). By preheating at 70 to 100 ° C., it becomes possible to apply a thick film of the second clear coating (C) (for example, 30 μm or more in a cured coating) as compared with the conventional 3C1B method, and prevent dripping of the coating. In addition, since the number of heating steps is smaller than that of the 3B2C method, energy saving can be realized, and further, effects such as an improved interlayer adhesion between the first clear coating film and the second clear coating film can be obtained.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shigeru Nakamura 1st floor of Azaji, Miyoshi-cho, Nishikamo-gun, Aichi Prefecture Inside Kansai Paint Co., Ltd. No. 1 Kansai Paint Co., Ltd.

Claims (1)

[Claims] 1. A method of applying a colored base coating material (A) to an outer panel of an automobile body, applying a first clear coating material (B) without curing, and preheating at 70 to 100 ° C.
An automotive topcoat coating method comprising applying a second clear coating (C) and then heating to simultaneously cure the three-layer coating.