JP2001064546A - Formation of coated film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for forming a coated film showing an excellent finish appearance. SOLUTION: This formation process includes steps wherein a powder slurry intercoat is applied to form a wet coating from which moisture is blown of and subsequently an aqueous base coating is applied onto the surface of the obtained wet coating. In an embodiment, the process includes steps wherein a powder slurry intercoat is applied and moisture is blown of to form a first wet coating, subsequently an aqueous base coating is applied onto the surface of the obtained first wet coating and moisture is blown of to form a second wet coating, a powder slurry clear coating is applied onto the surface of the obtained second wet coating to form a third wet coating, and finally, these wet coatings are simultaneously baked.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a coating film that achieves both suppression of VOC emissions and reduction of baking energy in a coating process of an industrial coating line represented by an automobile.

[0002]

[Prior Art] At present, CO is considered to be the main cause of global warming
₍₂₎ Various painting process improvement plans have been proposed to minimize the energy consumption of the painting process in order to suppress the occurrence of such problems.The painting line has been reduced, the baking process has been reduced, the baking time has been reduced, or the baking temperature has been reduced Is required. The painting process of the automotive line, which is a representative of the industrial coating line, involves applying an electrodeposition coating to the surface-treated automobile body to give a rust-preventive function, then applying an intermediate coating, baking, and applying a top coating. It is common to bake again. If the top coat is a solid paint, the painting and baking process is performed once, but if it is a metallic paint,
A two-coat, one-bake process is used, in which a clear paint is applied after the base paint is applied and then baked at once. In other words, the coating process after electrodeposition coating includes the intermediate coating / overcoating process,
In the case of solid finish, two coats and two bake processes are used, and in the case of metallic finish, three coats and two bake processes are adopted.

[0003] Solvent-based paints are mainly used as intermediate paints and top coats. However, in some painting lines, high-solid paints and water-based paints that use as little organic solvent as possible are used in the intermediate and top coat processes in order to comply with VOC regulations. We are starting to adopt it. Recently, powder coatings and powder slurry coatings that can achieve zero emissions have been adopted as top clear coatings.
There are many cases where VOC regulations have been passed. Recently, in order to achieve both VOC regulation and reduction of the baking process, there has been proposed a process of applying a water-based intermediate coating material, applying a water-based base coating material, a powder slurry clear coating material, and baking at once.

[0004]

However, these have the following disadvantages.

When the intermediate coating and the top coating are solvent-based coatings, it is difficult to meet future VOC regulations even if they can be adapted to current VOC regulations. In particular, it is almost impossible with a combination of solvent-based paints to pass regulations in Europe and the United States, which are advanced countries. It is conceivable to use an intermediate paint as a water-based paint or a base paint with a low coating efficiency (a large amount of VOC generated) as a water-based paint. However, water-based paints are easily affected by ambient temperature and humidity. However, there is a problem that the energy required for air conditioning of a coating booth is larger than that of a solvent-based coating because the range of atmospheric conditions under which a normal finish can be obtained under high humidity is narrow. It is possible to convert the intermediate paint or clear paint into a powder paint without a color change process.However, the coating equipment for powder paint is completely different from the current equipment for liquid paint, so if it is applied to the line, the equipment will be significantly modified. Is required. The use efficiency of paint can be improved because the powder paint can be recovered and reused.However, there are many problems in removing dust from the recovered powder and stability of particle size distribution. I have. The present invention
An object of the present invention is to provide a method for forming a coating film in which a water-based base coating can obtain a normal finish under a wide range of atmospheric conditions and can reduce the number of baking steps in compliance with VOC regulations.

[0006]

Means for Solving the Problems The inventor of the present invention has conducted intensive studies in order to solve the above-mentioned conventional problems, and as a result, an undried coating film obtained by applying a powder slurry intermediate coating and blowing off moisture. Forming a coating film, and then applying a water-based base coating to the surface of the formed wet coating film. Forming a film, then applying an aqueous base paint to the surface of the formed first wet coating film and blowing off moisture to form a second wet coating film, and further forming the second wet coating film After applying a powder slurry clear coating on the surface of the wet coating film to form a third wet coating film, the inventors found that the solution was achieved by a coating film forming method including a step of simultaneously baking these wet coating films. The present invention is provided.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a powder slurry intermediate coating is applied to an object to which electrodeposition coating has been completed, and at the same time as setting, in a blow-off zone, a low-temperature low temperature which does not reach the melting temperature of the powder is applied. Excess moisture in the coating film can be evaporated by warm air. Usually 30-70 ° C, preferably 45
Using hot air of ~ 55 ° C, wind speed is 3 ~ 5m / sec on the surface to be coated
The following is desirable. If the wind speed is too high, the intermediate coating film flows and the smoothness is impaired. If the wind speed is too low, a problem occurs in the line space where the blow-off process becomes longer.

As the powder slurry intermediate coating, a thermosetting intermediate coating obtained by blending a coloring pigment with a conventionally known powder slurry coating can be used. In particular, as the resin used in the coating material, a resin obtained by blending a melamine crosslinking agent with a hydroxyl group-containing polyester base resin which has been conventionally provided with an adhesive function is particularly preferable. Then, when the aqueous base paint is applied to the powder slurry intermediate coating film kept in an appropriate undried state, excess water in the atomized particles of the applied aqueous base paint is applied to the powder slurry intermediate coating. Water is absorbed by the coating film, and the flow of aluminum particles and mica particles, which are metallic pigments, in the base coating film is suppressed. Aqueous base paints are conventionally used for automobiles. Aqueous hydroxyl group-containing acrylic base resin or aqueous hydroxyl group-containing polyester base resin is coated with a melamine crosslinking agent or a blocked polyisocyanate crosslinking agent in a curable resin composition in a metallic or colored mica. It is particularly preferable to use a composition containing a coloring agent such as a pigment or a coloring pigment.

[0009] After the application of the aqueous base paint, excess water is evaporated in a blow-off zone. Usually 30-90
C., preferably 50-70.degree. C., and the air velocity is preferably 3-5 m / sec or less on the surface of the substrate. In about 2 minutes, the NV (solid content, hereinafter the same meaning) of the aqueous base coating film is increased to 80% by weight or more. IR ((far) infrared drying, hereinafter the same meaning) can be used in combination, and it is effective when there is not enough room in the line space. In that case, it is better to provide an IR zone in the first half and a warm air zone in the second half.
Time distribution is preferably about 1 minute for IR and about 1 minute for warm air.

When the pre-drying of the aqueous base coating is completed,
A powder slurry clear coating is applied thereon. As the resin suitable for the clear paint, an acrylic resin which emphasizes weather resistance is preferable. After the application of the powder slurry clear coating, preliminary drying is performed simultaneously with the setting, and the powder slurry intermediate coating film, the aqueous base coating film, and the powder slurry clear coating film are baked at once. Baking temperature is usually 140 ℃
At ~ 160 ° C, the baking time is about 20-30 minutes. In order to suppress paint film defects such as armpits and pinholes, the baking temperature is set in two steps. It is effective in improving the finish.

[0011]

FIG. 1 is a process explanatory view according to an embodiment of the present invention. FIG. 2 is a process explanatory view of a typical conventional automobile coating line. Electrodepositing a cationic electrodeposition coating (coating using epoxy polyamine resin / block polyisocyanate crosslinking agent as a curable resin composition) on the alkali-degreased coated panel to a dry film thickness of about 25 microns Was. Next, a powder slurry intermediate coating (manufactured by Kansai Paint Co., Ltd., trade name, PS100 primer) was applied to the substrate panel. The coating machine uses Corpes μ microbell (Randsburg, product name), applied voltage is -60kv,
Atomization was performed at a rotation speed of 30,000 rpm, a shaping air pressure of 2 kg / cm ² , a discharge rate of 210 cc / min, and a coating distance of 30 cm. The automatic machine was applied at a conveyor speed of 3.0 m / min, a reciprocating width of 1.0 m, and a reciprocating speed of 30 m / min, to form an intermediate coating film of about 45 microns (dry film thickness). Thereafter, blow-off was performed for about 5 minutes with 60 ° C. warm air (approximately 3 m / sec on the coated surface). Next, an aqueous base paint (manufactured by Kansai Paint Co., Ltd., trade name, WT-500 silver metallic) was applied to the coating film after the blow-off. Metabell (manufactured by Randsburg, product name) is used for the coating machine, applied voltage is -60 kv, rotation speed is 15000 rpm, shaping air pressure is 3 kg / cm ² , discharge amount is 160
Atomization was performed at cc / min and a coating distance of 25 cm. The conditions of the automatic machine are the same as those of the powder slurry intermediate coating. The formed film thickness was about 13 microns (dry film thickness), and after the completion of the coating, blow-off was performed for about 3 minutes with warm air at 80 ° C. (wind velocity on the coated surface: average 5 m / sec). Next, a powder slurry clear paint (trade name, PS200 clear, manufactured by Kansai Paint Co., Ltd.) was applied to the coating film after the blow-off. The conditions of the coating machine and the automatic machine are the same as the coating conditions of the powder slurry intermediate coating. After the completion of the coating, a two-step baking was performed on the three-layer film formed of the intermediate coating / base coating / clear coating. First, 9
After baking for about 10 minutes in a baking furnace set at 0 ° C., baking was performed for 20 minutes in a baking furnace set at 160 ° C.

According to the above-mentioned coating process, a three-coat, one-bake coating of silver metallic finish was performed, and the coating film formed by the conventional coating method without blow-off had poor metallic orientation, but the coating film formed by the present invention. Could get a very good metallic finish.

[0013]

According to the present invention, since a powder slurry coating is used as the intermediate coating and an aqueous base coating and the powder slurry clear coating are used as the top coating, VOC is hardly generated. Although a blow-off zone is required, one baking process is reduced, so that energy can be reduced and line space can be reduced.

Since the flow of the metallic paint is suppressed at the initial stage of application by utilizing the water absorption of the intermediate coating film of the blow-off powder slurry, the orientation of the pigment is good even when the booth is in a high humidity condition. In addition, problems such as metallic unevenness and unevenness of the edge of the object to be coated are eliminated, and a good finish can be obtained. As a result, the air conditioning control area of the painting booth is widened, and the energy used for air conditioning of temperature and humidity is greatly reduced.

[Brief description of the drawings]

FIG. 1 is a process explanatory view according to an embodiment of the present invention.

FIG. 2 is a process explanatory view of a conventional typical automobile coating line.

Claims (2)

[Claims] 1. A step of applying a powder slurry intermediate coating to form a wet coating film from which water has been blown off, and then applying an aqueous base coating material to the surface of the formed wet coating film. Coating film forming method. 2. An intermediate coating material for powder slurry is applied to blow off water to form a first wet coating film, and then an aqueous base paint is applied to the surface of the first wet coating film formed. Blow off water to form a second wet coating, and further apply a powder slurry clear coating to the surface of the formed second wet coating to form a third wet coating The method of claim 1, further comprising the step of baking these undried coating films simultaneously after the drying.