JPH06277614A - Method for finishing of coating - Google Patents

Abstract

PURPOSE:To avoid drying of the surface of a base coat film and generation of foaming by compounding a specified amt. of a hydrophobic high b.p. solvent in an aqueous base coat coating. CONSTITUTION:5-30 pts.wt., pref. 10-20 pts.wt. hydrophobic high b.p. solvent based on 100 pts.wt. resin solid content are incorporated into an aqueous base coat coating. In this case, the hydrophobic high b.p. solvent means a solvent being insoluble in water and with a b.p. of at least about 140 deg.C and the surface tension is pref. at most about 28dyn/cm. Concretely, aliph. hydrocarbon solvents such as paraffinic and isoparaffinic hydrocarbons and mineral spirits are cited and especially, 9-12C isoparaffinic solvents such as isononane, and isodecane and isododecane are pref. It is possible thereby prevent blister of a cured coating film from being generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating finishing method capable of obtaining a good coating film appearance without causing cracking during baking.

[0002]

2. Description of the Related Art For coating outer panels of automobiles, motorcycles, electric appliances, etc., a base coat paint containing an organic solvent-diluted thermosetting paint and a pigment component is conventionally used.
Then, a two-coat system such as a so-called two-coat / one-bake system in which clear top coat paints are repeatedly applied to cure both coating films at the same time is often adopted. On the other hand, in recent years, reduction of organic solvent has been required from the viewpoint of air pollution and resource saving, and coating finish using the above two-coat type base coat paint as an aqueous paint is being performed. For water,
Unlike organic solvent systems, moisture does not evaporate simply by leaving it alone, and since the surface tension is large, it is easy to leave moisture on the surface of the coating film, so it is possible to apply it twice or three times without thick coating at one time. By the way, it has been devised such that it is usually preheated before coating or applying clear topcoat paint to vaporize water.

However, when performing such preheating,
Often, the surface of the base coat coating will dry first,
Moisture and air bubbles are trapped inside the coating film, and in that state a clear top coat coating film is formed and both coating films are baked and cured. There has been a problem that the appearance is significantly impaired. As measures against this, the temperature at the time of preheating is lowered, and the temperature rising curve at the time of baking is made gradual. However, it is difficult to adjust the evaporation of water per se, so it is desired to study other measures.

[0004]

Means for Solving the Problems As a result of diligent study of the above-mentioned measures, the present inventors have found that by mixing a specific amount of a hydrophobic high-boiling solvent in an aqueous basecoat paint, surface drying of the basecoat paint film surface is prevented. The inventors have found that it is possible to prevent the occurrence, and have completed the present invention.

That is, the present invention provides a two-coat, one-bake coating finishing method in which a water-based base coat paint is applied to the surface to be coated, then a clear top coat paint is applied, and then both coatings are cured by heating. The present invention relates to a coating finishing method, characterized in that 5 to 30 parts by weight of a hydrophobic high boiling point solvent is mixed with 100 parts by weight of a resin solid content in the above water-based base coat paint.

As the water-based base coat paint which can be used in the present invention, conventionally known water-dispersible resins and / or water-soluble paints containing a coloring pigment and / or a metallic pigment mainly containing a water-soluble resin can be used. Examples of the water-soluble resin include acrylic resin emulsion and urethane resin emulsion, and examples of the water-soluble resin include acrylic resin system, alkyd resin system and epoxy resin system. Further, a melamine resin or a phenol formaldehyde resin can be blended in the coating material as a cross-linking agent.
As the pigment, metallic pigments such as aluminum flakes and mica flakes, which are commonly used in the field of paints, inorganic or organic coloring pigments such as titanium white and phthalocyanine blue, and extender pigments can be used. In addition, a hydrophilic organic solvent may be used in the coating material for dispersing the pigment, and a thickener may be used for preventing unevenness and sagging.

In the present invention, a hydrophobic high boiling point solvent is added to the above water-based base coat paint in an amount of 5 parts by weight per 100 parts by weight of resin solids.
-30 parts by weight, preferably 10 to 20 parts by weight is essential. The hydrophobic high-boiling point solvent here is a solvent which is insoluble in water and has a boiling point of about 140 ° C. or higher, and preferably has a surface tension of about 28 dyn / cm or less. Specific examples thereof include paraffin-based and isoparaffin-based aliphatic hydrocarbon solvents, mineral spirits, and the like. Particularly, isononane, isodecane, isododecane, and other isoparaffinic solvents having 9 to 12 carbon atoms are preferable. If the amount is less than 5 parts by weight, the effect of preventing armpits is not observed, while if it exceeds 30 parts by weight, the pigment components such as aluminum flakes in the base coat paint are aggregated, or the base coat coating and the clear top coat coating are applied. This is not preferable because the films may mix with each other and the orientation of the aluminum may be disturbed to darken the coating film.

In the present invention, the clear top coat paint to be applied to the surface of the above water-based base coat paint is as follows:
Conventionally known ones can be used, and specifically, for example, organic solvent diluting type paints such as amino alkyd resins, acrylic resins, amino acrylic resins, amino oil-free alkyd resins, silicone polyester resins, fluororesins, urethane resins, etc. Can be mentioned. Especially as clear paint,
From the viewpoint of environmental problems and resource saving, high solid type (high solid content type) with less organic solvent usage is desirable.
Further, a powder coating material can be used.

Next, the coating process of the method of the present invention will be described. The above-mentioned water-based base coat paint is appropriately adjusted in concentration and viscosity by adding deionized water according to a usual method, and coated on the surface to be coated with an air spray, an airless spray rotary atomizer or the like so that the dry film thickness becomes about 10 to 50 μ. To be done. At this time, the coating may be repeated several times until the required film thickness is obtained. The obtained coating film is dried by preheating such as warm air drying or air drying until the volatile component of the coating film becomes about 25% by weight, preferably about 15% by weight or less. Next, the clear top coat paint is applied repeatedly so that the dry film thickness is about 15 to 70 μm. Next, after performing the usual settings, at 120-160 ° C for 15-
After baking for about 30 minutes, a cured coating film is obtained by the 2-coat 1-bake method.

The surface to be coated according to the present invention may be a metallic material, a plastic material, or the like. Such a metallic material is surface-treated, or electrodeposition coating, primer coating, or intermediate coating is applied. One can also be used as the coated surface.

[0011]

In the method of the present invention, the reason why it is possible to prevent the occurrence of cracking in the baked coating film by adding a specific amount of the hydrophobic high-boiling point solvent to the aqueous base coat paint is presumed as follows. That is, since the solvent has a low surface tension and is insoluble in water, it surrounds the bubbles in the applied coating film, and the bubbles surrounded by the solvent become particles and easily migrate to the coating surface. The surface of the film is easy to break. Further, since the solvent has a high boiling point, it delays the drying of the coating film surface at the time of preheating the coated coating film and lowers the viscosity of the surface, so that air bubbles and water inside the coating film can easily escape. Therefore, a cured coating film obtained by forming a clear topcoat coating film on a basecoat coating film formed by such a basecoat paint and then baking it can have a good finished appearance without any cracking.

[0012]

EXAMPLES The present invention will be specifically described below with reference to examples. In addition, "part" and "%" are "part by weight",
It means "% by weight". "Electron No. 9200" (Kansai Paint Co., Ltd., epoxy resin-based cationic electrodeposition paint) is electrodeposited on a steel plate surface-treated with "Palbond # 3030" (Nihon Parker Rising Co., Ltd., zinc phosphate treatment agent), "Amilak N-2 Sealer" (Kansai Paint Co., Ltd., aminopolyester resin-based intermediate coating material) was applied thereon to prepare a test plate.

Next, using the water-based base coat paint having the composition shown in Table 1, the test plate was coated with a bell-type coating gun, which is a rotary atomizer, and then with an air spray gun, each having a film thickness of about 10 μ (dry film thickness). I did so. The setting was for 1 minute between the two applications.
After forming the base coat applied coating film, preheating was carried out at a temperature of 60 ° C. for 10 minutes, then cooled to room temperature, and the clear top coat paint shown in Table 1 was formed into a film having a thickness of 40 μ (dry film thickness) by an air spray gun. After coating for 7 minutes, it was baked for 7 minutes at 140 ° C. for 20 minutes. Thus, coated plates of Examples and Comparative Examples by the 2-coat 1-bake system were obtained. The coated surface state of the obtained coated plate and the whiteness of the metallic finish were visually evaluated. (◯: good) The evaluation results are shown in Table 1.

[0014]

[Table 1] (Note 1) Shellsol 71L ... Shell Chemical Co., trade name, isoparaffin solvent (mixed product of C9 to C12), boiling point 180 to 220 ° C. (Note 2) Diethylene glycol monoethyl ether acetate ... Osaka Organic Chemistry , Miscible with water, boiling point 213
~ 221 ℃ (Note 3) Clear topcoat paint T-1 ... 60%
A xylene solution of an acrylic resin and a 60% hydrophobic melamine resin were mixed at a solid content weight ratio of 75:25,
"Swazol # 1500" (organic solvent, manufactured by Cosmo Oil Co., Ltd.) has a viscosity of 25 seconds (Ford cup No. 4/20 ° C).
The clear topcoat paint T-1 was prepared.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Nakamura No. 1 flat land in Sakai, Miyoshi-cho, Nishikamo-gun, Aichi Kansai Paint Co., Ltd.

Claims (2)

[Claims] 1. A two-coat, one-bake coating finishing method comprising coating a water-based base coat paint on a surface to be coated, then applying a clear top coat paint, and then curing both the paint films by applying the water-base base coat. Hydrophobic high-boiling point solvent for paint 5 to 3 per 100 parts by weight of resin solids
A coating finishing method characterized by containing 0 part by weight. 2. The coating finishing method according to claim 1, wherein the hydrophobic high boiling point solvent is an isoparaffinic solvent.