JP2884199B2 - Painting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A so-called wet-on-wet (W / W) system in which an intermediate coating is applied, a top coating is applied to the coated surface without curing, and both the coatings are simultaneously heated and cured. As a specific example of the coating method using the method, there is a method of coating a sash portion of an automobile outer panel.

That is, a method of coating a vehicle body outer panel including a sash section (a frame of a door window glass) is as follows. First, an intermediate coating is applied to the entire outer panel, and then only the sash section is cured without curing the coating film. After applying a top coat paint (in general, matte type black paint is often used), the car body is guided to a heating furnace, and both the coats are heated and cured, and then the other parts except the sash portion of the outer panel are applied. To another top coat. The present invention relates to a coating method having a particularly remarkable technical effect for coating a sash portion in the coating system.

Heretofore, when the intermediate coating and the sash topcoat are applied by the W / W method, there is a limitation 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,
If the latter is significantly lower than the former, spray particles (dust) of the latter (overcoat) adhering to portions other than the sash remain in a convex shape and the smoothness and the like are reduced. Conversely, if the latter is higher,
Both coating films are reversed, and the finished appearance of the sash portion is significantly reduced. Therefore, since the relative allowable range of the surface tension of both paints is extremely narrow, there is a defect that the adjustment requires a great deal of labor and time. 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 sealant prior to the intermediate coating, and the filled portion may be filled with the above-mentioned two paints. Is coated in a W / W method, plasticizers and the like contained in the sol paint and the like are transferred to the intermediate coating surface, and the surface tension that has been adjusted in advance is fluctuated, which causes a decrease in finished appearance.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned various defects. That is, no or little delicate adjustment of the surface tension between the intermediate coating and the top coating is required, and even if the sol paint or the like is previously filled in the welding portion of the sash base material or the like, the finished appearance can be improved. The aim is to develop a coating method that does not lower the paint quality. As a result of intensive studies, the present inventor has found that the object can be achieved by blending a silica-based fine powder with an overcoat to make it thixotropic, thereby completing the present invention.

Namely, the present invention is to paint the colored top coating composition on the intermediate coating film surface of the uncured, and then in the coating method of curing the both said coating film by heating, its colored top coat
0.1 to 5 per 100 parts by weight of the total of the base resin and the curing agent
The present invention relates to a coating method characterized in that thixotropic properties are imparted by adding a silica fine powder in parts by weight .

In the present invention, the intermediate coating is preferably a thermosetting liquid coating known per se using an organic solvent to be applied to the surface to be coated prior to the top coating as a solvent or a dispersion medium. And a pigment and an organic solvent as main components, and if necessary, additives such as an antifoaming agent and a coating surface adjusting agent. Examples of the base resin include an alkyd resin and a polyester resin, and examples of the curing agent include an amino resin such as a melamine resin and a urea resin, and a blocked polyisocyanate compound. Examples of the pigment include a color pigment and an extender pigment. The composition ratio is not particularly limited, but the base resin and the curing agent are preferably about 60 to 80% by weight and the curing agent about 40 to 20% by weight based on the total weight of the two components. It is preferable that the amount of the pigment is about 30 to 100 parts by weight per 100 parts by weight of both components.

The intermediate coating is obtained by dissolving or dispersing the above components in an organic solvent. Although the method of applying the intermediate coating is not limited, for example, air spray, airless spray, air static, airless static, and the like are particularly preferable. For intermediate coatings, the coating viscosity is 25-6
0 seconds (Ford Cup # 4/20 ° C.), solid content at the time of coating is 30-70% by weight, surface tension 20-4
About 0 dyn / cm is suitable.

The top coating used in the present invention is a coating applied to the surface of the uncured intermediate coating film and contains silica-based fine powder. Specifically, the coating material 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 an antifoaming agent and a coating surface adjusting agent as necessary. Thus, a thermosetting liquid paint using an organic solvent as a solvent or a dispersion medium is preferable.

The silica-based fine powder is a powder having SiO ₂ , for example, clay (Al ₂ O ₃ .2SiO ₂ .2H ₂₎
O), diatomaceous earth (SiO ₂ .nH ₂ O), white carbon (SiO ₂ .nH ₂ O), hydrous magnesium silicate (3
_{MgO · 4SiO 2 · nH 2 O} ), bentonite (Monmo containing <br/> Li b Knight about 80%), organic bentonite, and the like, among these, organic bentonite is most preferred.

Organic bentonite is a reaction product (inclusion compound) of the above bentonite and an organic compound, and examples of the organic compound include aliphatic primary amines and aliphatic quaternary amines (both of which have 20 or less carbon atoms). Are preferred). As a commercial product, "Orben" manufactured by Shiraishi Industry
And Benton (B
entone) 34 "(dimethyloctadecyl 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 resins, alkyd resins, and acrylic resins. As the curing agent, those exemplified for the above-mentioned intermediate coating are used. The ratio of the two components is suitably in the range of 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 two components. As the pigment, an organic or inorganic coloring pigment is used, and the blending amount thereof can be arbitrarily selected according to the intended color tone.

The amount of the silica-based fine powder is 0.1 to 5 parts by weight per 100 parts by weight of the total of the base resin and the curing agent.
Parts by weight . The amount is particularly preferably in the range of 0.5 to 2 parts by weight.

The top coat is obtained by dissolving or dispersing the above components in an organic solvent. In the method of the present invention, it is not particularly necessary to adjust the surface tension between the intermediate paint and the top coat, but it is preferable that the surface tension is equal for both paints or that the top coat is lower than the intermediate paint. is there. However, the tolerance is much wider than in the prior art.

The colored top coat used in the present invention has a thixotropic property because it contains silica fine powder. The degree of thixotropy is 2 to 5 based on the Ti value.
Is preferably within the range. This Ti value was measured using a B-type rotational viscometer (BM type) at 20 ° C. with a viscosity of 30 to
The topcoat paint adjusted to 70 seconds (Ford Cup # 4) was heated at the same temperature and the number of rotations of the rotor was 6 rpm and 60 rpm.
The viscosity at 60 rpm was measured and the viscosity measured at 6 rpm / 60.
It is shown as the ratio of the viscosities measured in rpm. The rotor used is arbitrarily selected according to the viscosity of the paint and the number of rotations.
o. 1 to 3 were used.

Further, the surface tension of the top coat (adjusted to the above-mentioned viscosity and measured by a dinometer (trade name of BYK Labofron)) at 20 to 22 ° C. and a paint drop rate of 1.5
mm / min) is 10 to 35 dyn / cm.
² is preferred. Further, the viscosity of the top coat at the time of application is suitably 30 to 70 seconds (for a cup # 4/120 ° C.).

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

On such an object to be coated, an intermediate coating is applied so as to have a thickness of about 15 to 40 μm based on the cured coating film. After painting to about 60μ,
Heat to about 200 ° C. to cure both.

[0019]

According to the present invention, since the silica-based fine powder is added to the top coat, the top coat coating liquid exhibits an appropriate thixotropic property. Even without such adjustment, the finished appearance did not deteriorate. In addition, no deterioration in the finished appearance was observed even if it had been previously treated with a sol-based paint or a sealing agent.

[0020]

The present invention will be described below with reference to examples and comparative examples of the present invention. All parts and percentages are in principle based on weight.

I sample (1) Sealant (A) Putty containing plasticizer (trade name "SAMICS" manufactured by Sunstar Giken Co., Ltd.) (2) Intermediate coating polyester resin / butanol-modified melamine resin / titanium white pigment / Carbon black / Bengara = 65/35 /
40 / trace / trace (solid weight ratio), and this was converted to an organic solvent [xylene / butyl cellosolve = 1/1 (weight ratio)] with a non-volatile content of 65% and a viscosity of 40 seconds (Ford Cup # 4/20 ° C). It was adjusted. The surface tension of this intermediate coating was 29 to 30 dyn / cm ² .

(3) Top coat (A) polyester resin / butanol-modified melamine resin / carbon black / matte / “Benton 34” = 65 /
35/3/6/1 (solid content weight ratio), which was treated with 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 (Ford Cup # 4/20 ° C). The surface tension of this top coat (A) is 29.5 to 30.
dyn / cm ² , and the thixotropy was 2.0 to 3.0.

(4) Topcoat (B) The same procedure was carried out as for the topcoat (A) except that the organic bentonite was not used. Non-volatile content 55
%, Viscosity 35 seconds (Ford Cup # 4/20 ° C.). The surface tension of the top coating material (B) is 30 to 30.5.
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 an electrocoating primer, cured by heating (film thickness 15 μm), and then coated with a sealing agent (A) and cured (film thickness 20 μm). .

Next, an intermediate coating is applied to the surface coated with the sealing agent with a hand-blown spray gun so that the film thickness based on the cured coating film becomes 25 μm, and left at room temperature for 3 minutes. The top coat (A) or (B) is applied with a hand spray gun so that the film thickness based on the cured coating is inclined to 0 to 40 μm, and then heated at 140 ° C. for 30 minutes to cure both the coatings. Was.

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

[0027]

[Table 1]

Test method (1) Limiting film thickness of opacity: The minimum film thickness of the overcoat film that conceals the intermediate coating film and does not show any bleed from the coating film. If the top coat is thicker than 30μ, it will be easy to sag.

(2) Appearance: As a result of observing the surface of the overcoated film having a film thickness of 20 μ, 〇 indicates that no bleeding was observed and the smoothness was excellent, and × indicates that bleeding was clearly observed. Is inferior.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-57676 (JP, A) JP-A-1-139177 (JP, A) JP-A-1-210082 (JP, A) JP-A-63-1987 111971 (JP, A) JP-A-63-252579 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B05D 1/00-7/24 303

Claims (1)

(57) [Claims] 1. A coating a colored top coating composition on the intermediate coating film surface of the uncured, and then in the coating method of curing the both said coating film by heating, the base resin and the curing agent in the colored top coating
A coating method characterized by adding thixotropic property by adding 0.1 to 5 parts by weight of silica-based fine powder per 100 parts by weight in total .