JPH057827A - Coating method - Google Patents

Abstract

PURPOSE:To improve finish appearance by compounding fine silica powder with a finish coating material. CONSTITUTION:The coating method consists of applying a colored finish coating material on an uncured surface of intermediate coated film and then heating these two coated films to cure the films. The colored finish coating material contains the fine silica powder and, therefore, has a thixotropic property. More specifically, the finish coating material consists essentially of a base resin, hardener, pigments, the fine silica powder, and an org. solvent. Since the colored finish coating material exhibits the adequate thixotropic property, there is no need for adjusting the surface tension with the intermediate coated film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet-on-wet method for coating an intermediate coating and a top coating.

[0002]

2. Description of the Related Art So-called wet-on-wet (W / W) system in which an intermediate coating material is applied and an upper coating material is applied on the coated surface without curing, and then both coating materials are heated and cured at the same time. As a specific example of the coating method using, the coating of the sash portion of the outer panel of an automobile can be mentioned.

That is, a method of coating a vehicle body outer panel including a sash portion (a window glass frame of a door) is as follows. First, an intermediate coating material is applied to the entire outer panel, and then only the sash portion is not cured. After applying a top coat paint (generally a matte type black paint is commonly used) to the car body, guide the car body to a heating furnace to heat and cure both of the paint films, and then except the sash part of the outer plate. Another top coat paint is applied to. The present invention relates to a coating method having a particularly remarkable technical effect for coating the sash portion of the coating system.

Conventionally, when the intermediate coating composition and the sash top coating composition are applied by the W / W method, there is a restriction that the surface tension of the latter must be slightly lower than that of the former in order to obtain an excellent appearance. For example, regarding surface tension,
When the latter becomes significantly lower than the former, the spray particles (dust) of the latter (top coating material) adhered to areas other than the sash portion remain in a convex shape and the smoothness and the like deteriorate. Conversely, if the latter becomes higher,
Both coatings are reversed and the finished appearance of the sash portion is significantly deteriorated. Therefore, since the relative allowable range of the surface tension of both paints is extremely narrow, there is a defect that a large amount of labor and time are required for the adjustment. Further, the welded portion of the sash base material may be filled with a vinyl chloride resin-based sol paint or a vinyl resin-based sealing agent before the intermediate coating. Is applied by the W / W method, the plasticizer or the like contained in the sol paint migrates to the intermediate coating surface, fluctuating the surface tension that has been adjusted in advance, and causing the finish appearance to deteriorate.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned various defects. That is, no or almost no delicate adjustment of the surface tension between the intermediate coating and the top coating is required, and the finished appearance is obtained even if the sol coating is pre-filled in the welded portion of the sash base material. The purpose is to develop a coating method that does not reduce the As a result of earnest research, the present inventor has found that the object can be achieved by compounding a silica-based fine powder into a topcoat paint to make it thixotropic, and completed the present invention.

That is, according to the present invention, in a coating method in which a colored topcoat paint is applied to the surface of an uncured intermediate coating film, and then both coatings are cured by heating, a fine silica powder is added to the colored topcoat paint. The present invention relates to a coating method characterized by being added to impart thixotropic properties.

In the present invention, the intermediate coating material is preferably a thermosetting liquid coating material known per se which uses an organic solvent for coating the surface to be coated prior to the top coating material as a solvent or a dispersion medium. , A pigment and an organic solvent as main components, and if necessary, additives such as a defoaming agent and a coating surface adjusting agent are added. Examples of the base resin include alkyd resin and polyester resin, examples of the curing agent include amino resin such as melamine resin and urea resin, and blocked polyisocyanate compound. Examples of the pigment include colored pigments and extender pigments. The composition ratio of these is not particularly limited, but the base resin and the curing agent are about 60 to 80% by weight of the base resin and about 40 to 20% by weight of the curing agent based on the total weight of the both components. Each of them is preferable, and about 30 to 100 parts by weight of the pigment is suitable for 100 parts by weight of both components.

The intermediate coating composition is obtained by dissolving or dispersing the above components in an organic solvent. The method of applying the intermediate coating material is not limited, but for example, air spray, airless spray, air electrostatic, airless electrostatic and the like are particularly preferable. Regarding intermediate coating, the coating viscosity is 25-6
About 0 seconds (Ford cup # 4/20 ° C), content of solid content during coating is about 30 to 70% by weight, surface tension is 20 to 4
About 0 dyn / cm is suitable.

The topcoat paint used in the present invention is a paint to be applied to the surface of an uncured intermediate coating film, and contains fine silica powder. Specifically, the coating composition contains a base resin, a curing agent, a pigment, a silica-based fine powder and an organic solvent as main components, and further contains additives such as a defoaming agent and a coating surface adjusting agent if necessary. Therefore, a thermosetting liquid coating material using an organic solvent as a solvent or a dispersion medium is preferable.

The silica-based fine powder is a powder containing SiO _2, and is, for example, clay (Al ₂ O ₃ .2SiO ₂ .2).
H ₂ O), diatomite (SiO ₂ · nH ₂ O), white carbon (SiO ₂ · nH ₂ O), hydrous magnesium silicate (3MgO · 4SiO ₂ · nH ₂ O), bentonite (montmorillonite is approximately 80% or more), organic bentonite, and the like. Of these, organic bentonite is most preferable.

Organic bentonite is a reaction product (inclusion compound) of the above bentonite and an organic compound, and as the organic compound, an aliphatic primary amine and an aliphatic quaternary amine (each of which has 20 or less carbon atoms) Are preferred) and the like are used. As a commercial item, "Olven" manufactured by Shiraishi Kogyo
And Benton (B
Entone) 34 "(dimethyl octadecyl ammonium bentonite). Here, the particle size of the silica-based fine powder is 0.01 to 5 μm.

Examples of the base resin include polyester resin, alkyd resin, acrylic resin, and the like, and as the curing agent, those exemplified in the above intermediate coating composition are used. Based on the total weight of both components, a ratio of the base resin of about 60 to 80 wt% and a curing agent of about 40 to 20 wt% are suitable. As the pigment, an organic or inorganic color pigment is used, and the blending amount thereof can be arbitrarily selected according to the intended color tone.

The amount of silica fine powder blended is 0.1 to 5 per 100 parts by weight of the total amount of the base resin and the curing agent.
It is preferably about part by weight, particularly preferably 0.5 to 2 parts by weight.

The top coating composition is obtained by dissolving or dispersing each of the above components in an organic solvent. In the method of the present invention, it is not particularly necessary to adjust the surface tension of the intermediate coating composition and the top coating composition, but preferably the surface tension is equal in both coating compositions or the top coating composition is lower than the intermediate coating composition. is there. However, the allowable range is significantly wider than the conventional one.

The colored top coating composition used in the present invention contains thixotropic fine powder and thus has thixotropic properties. The degree of thixotropy is 2 to 5 based on the Ti value.
It is preferably within the range. This Ti value was measured by using a B-type rotational viscometer (BM type) at a viscosity of 30 to 30 at 20 ° C.
The topcoat paint adjusted to 70 seconds (Food Cup # 4) was kept at the same temperature and the rotation speed of the rotor was 6 rpm and 60 r.
Viscosity in pm, viscosity at 60 rpm / 60
It is shown as the ratio of the viscosity measured at rpm. The rotor used is arbitrarily selected according to the viscosity of the paint and its rotation speed, and N
o. 1-3 were used.

The surface tension of the top coating composition (adjusted to the above viscosity, and a dynometer (trade name of BYK Labofron Co.) at 20 to 22 ° C. is used for coating descent rate of 1.5).
(measured under the condition of mm / min) is 10 to 35 dyn / cm
² is preferred. Further, the viscosity of the top coating composition during coating is preferably 30 to 70 seconds (Food cup # 4/120 ° C.).

In the coating method of the present invention, the object to be coated can be arbitrarily selected, and the sash portion of the automobile outer plate, the rocker portion at the lower portion of the door, the vertical portion at the front and the like are particularly preferable. These objects to be coated can be coated with an electrodeposition paint as a primer, if necessary, prior to the intermediate coating, or (further) the welded portion or the like can be treated with the sol paint or the sealing agent.

An intermediate coating composition is applied to such an object so as to have a thickness of about 15 to 40 μm based on the cured coating film, and the top coating composition is applied to the coated surface without curing, based on the cured coating film. ~ 100μ after coating to about 60μ
Both are cured by heating to about 200 ° C.

[0019]

In the present invention, since the silica-based fine powder is added to the top coating composition, the top coating solution exhibits appropriate thixotropic properties. Even without such adjustment, the finished appearance was never deteriorated. Moreover, no deterioration in the finished appearance was observed even if it was previously treated with a sol-based paint or a sealing agent.

[0020]

EXAMPLES Examples of the present invention and comparative examples will be described below. All parts and percentages are in principle based on weight.

I Sample (1) Sealing agent (A) Plasticizer-containing putty (manufactured by Sunstar Giken Co., Ltd., trade name "Samix") (2) Intermediate coating polyester resin / butanol-modified melamine resin / titanium white pigment / Carbon black / Bengala = 65/35 /
It consists of 40 / trace amount / trace amount (solid content weight ratio), and it is made into an organic solvent [xylene / butyl cellosolve = 1/1 (weight ratio)] to a nonvolatile content of 65% and a viscosity of 40 seconds (Food Cup # 4/20 ° C). It was adjusted. The surface tension of this intermediate coating material was 29 to 30 dyn / cm ² .

(3) Topcoat paint (A) polyester resin / butanol-modified melamine resin / carbon black / matting agent / “Benton 34” = 65 /
It is composed of 35/3/6/1 (solid content weight ratio), and is made of an organic solvent [xylene / butyl cellosolve / carbitol acetate = 2/1/1 (weight ratio)] to have a nonvolatile content of 53%.
The viscosity was adjusted to 35 seconds (Food cup # 4/20 ° C). The surface tension of this topcoat paint (A) is 29.5-30.
It was dyn / cm ² and the thixotropy was 2.0 to 3.0.

(4) Topcoat paint (B) The same process was carried out as in the above topcoat paint (A) except that the organic bentonite was not added. Nonvolatile matter 55
%, The viscosity was 35 seconds (Food cup # 4/20 ° C.). The surface tension of this topcoat paint (B) is 30 to 30.5.
It was dyn / cm ² and the thixotropy was 1.0 to 1.5.

II Example (1) and Comparative Example 1 A surface-treated copper plate was coated with a KAOTIN electrodeposition primer, and after heating and curing (film thickness 15 μ), a sealing agent (A) was coated and cured (film thickness 20 μ). ..

Next, an intermediate coating material was applied to the surface of the sealing agent coated with a hand spray gun so that the thickness based on the cured coating film would be 25 μ, and allowed to stand at room temperature for 3 minutes, and then the surface was coated. After coating the top coating composition (A) or (B) with a hand spray gun so that the film thickness based on the cured coating film may be inclined from 0 to 40μ, then heat the coating film at 140 ° C for 30 minutes to cure both coating films. It was

The performance test results of the coated plate thus obtained are shown in Table 1.

[0027]

[Table 1]

Test method (1) Hiding limit film thickness: It is the minimum film thickness of the topcoat film which hides the intermediate coating film and shows no bleeding from the coating film. If the top coating film is thicker than 30 μ, it easily sags.

(2) Appearance: As a result of observing the surface of the top coating film having a film thickness of 20 μ, ◯ shows no bleeding at all and excellent smoothness, and × shows clear occurrence of bleeding. Is inferior.

Claims (1)

Claim: What is claimed is: 1. In a coating method in which a colored topcoat paint is applied to the surface of an uncured intermediate coating film, and then both coatings are cured by heating, the colored topcoat paint is coated with a silica-based fine coating. A coating method characterized by adding powder to impart thixotropic properties.