JPS5845302B2 - 2 Kotosia Getosohouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves applying a thermosetting electrodeposition paint as an undercoat to a metal substrate, and then finishing it by overcoating a thermosetting water-dispersed powder paint.
Concerning a coat finish painting method.

Water-dispersed powder coating refers to a dispersion of powder coating using water as a dispersion medium, and is also called powder slurry coating.
(b) Since the coating is applied using water as a medium, there is no need to use new powder coating equipment compared to ordinary powder coatings that are applied using air as a medium, and conventional coating equipment can be used as is. ) There is no risk of air pollution or fire, and (c) The coating workability is better than that of conventional water-soluble resin paints or water emulsion paints in terms of paint film sagging, etc.) If unused paint remains in the paint booth, it has various advantages, such as being easily recovered by draining the upper layer of water after the solid content has settled.

However, when water-dispersed powder coatings (hereinafter referred to as slurry coatings) are applied directly to metal substrates, the finished appearance of the paint film is different from when ordinary powder coatings are applied directly to metal substrates. What was inferior was the defect.

That is, (a) the gloss is poor. Phenomena such as (b) skin irritation resulting in the paint film not being flat or smooth, and (c) paint film being colored brown or yellow were often observed.

The reason why these phenomena occur is that when slurry paint is applied and baked onto a metal substrate, metal corrosion products are formed at the interface between the metal substrate and the wet coating film of the slurry paint (for example, It is presumed that the baking of slurry paint applied to a steel plate sometimes produces iron oxide, which oozes into the paint film and causes the above-mentioned defects.

These defects are noticeable when the slurry paint is white or lightly colored, and there has been a demand for the establishment of countermeasures.

As a result of repeated research to improve the above-mentioned defects in the finished appearance of slurry paints, the present inventor applied electrodeposition coating to the metal substrate in advance, (a) wet-on-wet as it is, and (O) the electrodeposition coating film. The above-mentioned problems can be solved by preheating below the curing temperature or (c) baking and curing it, then painting and baking a thermosetting slurry paint to form a cured comprehensive coating. We have discovered that this is possible and have completed the present invention.

That is, the present invention provides a coating process in which a metal substrate is undercoated with a thermosetting electrodeposition paint and then finished with a thermosetting slurry paint. , then burn it, (2)
After undercoating, heating is carried out at a temperature lower than the baking temperature required to cure the electrodeposited coating, and then a topcoat is applied and baked. The present invention relates to a two-coat finish coating method characterized in that a hardened overall coating film is formed by repeatedly applying and baking.

In the following description, (1) will be abbreviated as the wet-on-wet method, (2) as the preheat method, and (3) as the two-coat, two-bague method.

The thermosetting electrodeposition paint used in the present invention may be any of those used as a heat-curable cathodic electrodeposition or anodic electrodeposition undercoating paint, and water-soluble or water-dispersible thermosetting paints. Selected from among paints that contain polyurethane resin as a film-forming component.

Some examples of thermosetting resins that can be used in this type of paint include amine resin-cured epoxy ester resins, amine resin-cured acrylic resins, and phenol-cured resins.
Examples include alkyd resins, amino alkyd resins, and polybutadiene resins.

In addition, the pigments blended into the above-mentioned electrodeposition paints include inorganic pigments (including anti-rust pigments), extender pigments, organic pigments, etc. Also, it is of course possible to add various additives as necessary. do not have.

The thermosetting slurry paint used as a top coat in the present invention is an aqueous dispersion of a water-insoluble thermosetting powder paint, and an appropriate surfactant may be used when dispersing it in water. can.

As the surfactant, anionic or nonionic surfactants can be used. Examples of the anionic surfactant include higher fatty acid alkali salts, alkyl sulfates, alkyl sulfonates, alkylaryl sulfonates, and sulfone succinates. Examples of nonionic surfactants include polyethylene glycol alkyl ether, polyethylene glycol fatty acid ester, and fatty acid monoglyceride, and one or more of these may be used.

The surfactant may be added in advance to the water in which the powder coating is to be dispersed, or may be added after the powder coating is dispersed.

The resin that can be used as a film-forming component of the powder coating is composed of a resin powder containing a crosslinkable functional group and a crosslinking agent, and any type can be used as long as it is practically usable for thermosetting powder coatings.

Some examples of such resins include amino resin-curable polyester resins, amino resin-curable or dibasic acid-curable acrylic resins, and acid anhydride-curable epoxy resins.

The slurry paint may contain pigments, dyes, etc., and such pigments or dyes include inorganic pigments, organic pigments, metallic pigments, oil-soluble dyes, etc. used in various conventional baking paints. It is also possible to use a mixture of two or more of these.

Moreover, it is of course possible to add various additives as necessary.

In the wet-on-wet method of the coating method of the present invention, a thermosetting electrodeposition paint as an undercoat is first prepared in a bath, the bath concentration, bath temperature, voltage, energization time, etc. Electrodeposition coating is applied so that the film has a thickness of 5 to 40 μm.

Next, remove the electrodeposited item from the bath and wash it thoroughly with water.
If necessary, leave it at room temperature inside and outside for 10 minutes.

Note that if relatively large water droplets remain on the electrodeposited coating after washing with water, it is desirable to remove them by air blowing or the like.

A thermosetting slurry paint is usually applied onto this so that the thickness of the dry film is 30 to 100 μm, and after being left at room temperature inside and outside for 10 minutes, it is baked to complete a cured overall paint film.

In addition to air spraying, a roller coating method, a flow coating method, a brush coating method, a dipping coating method, etc. can also be applied to the top coat.

Baking conditions generally include the baking temperature and temperature required to harden the electrodeposition coating.
The temperature is selected in consideration of the time required for curing the coating film of the slurry paint, but it is preferable to carry out baking at a higher baking temperature level to cure both coating films at the same time.

An example of baking conditions is 6 at 160-220℃.
A range of 0 to 15 minutes may be mentioned.

In the preheating method, a thermosetting electrodeposited paint is primed on a metal base using a method similar to the wet-on-wet method, then thoroughly washed with water, and then heated at a temperature lower than the baking temperature required to harden the electrodeposited film. Let's do it.

This is left to cool, and a thermosetting slurry paint is overcoated using a method similar to the wet-on-wet method, and after being left at room temperature inside and outside for 10 minutes, it is baked to complete a cured overall paint film.

The heating temperature for the electrodeposited coating film is normally selected within a range of 10 to 100°C lower than the baking temperature required for curing the coating film, and is set to a temperature that is sufficient to drive out the volatile components contained in the coating film or to a temperature that is at the extreme of curing. Heating time to reach the initial stage (for example, 5 to 50 minutes)
20 minutes).

Furthermore, the baking conditions after topcoating may be selected in accordance with the setting method of baking conditions in the wet-on-wet method.

This is to sufficiently cure and crosslink both the electrodeposition coating film and the slurry coating film.

In the case of the 2-coat 2-bague method, the thermosetting electrodeposition paint is primed on the metal substrate using a method similar to the wet-on-wet method, and then thoroughly washed with water, and the baking conditions necessary for curing the electrodeposition coating are set. Burn it with

This was left to cool, then top coated with a thermosetting slurry paint using a method similar to the wet-on-wet method, left at room temperature inside and outside for 10 minutes, and then baked under the baking conditions necessary to harden the slurry paint film. , a cured overall coating is completed.

Before applying the slurry paint, the surface of the cured electrodeposition coating is polished with abrasive paper, etc., and then wiped with gauze soaked in petroleum benzene to improve the finished appearance after topcoating and between the electrodeposition coating and the slurry paint. The adhesion between coatings is further improved.

By applying the three types of coating methods according to the present invention to industrial coating lines, slurry coatings that are highly safe in coating operations and useful for preventing pollution, but which cause various finish defects when applied alone, can be removed. It has the advantage that it can not only be used effectively and efficiently, but also that it can be adapted to the specifications of various two-coat painting lines to form a comprehensive cured coating film with a good finish.

The present invention will be specifically explained below with reference to Examples and Comparative Examples.

Note that "part" means part by weight, and "%" means percent by weight.

Example 1 A thermosetting electrodeposition paint containing water-soluble jetanolamine neutralized epoxy ester resin and melamine/formaldehyde resin as film-forming components, and containing rutile-type titanium white, carbon black, red iron and talc was applied to an electrodeposition tank. A cold-rolled steel plate (J
ISG3310 (approximately 300 x 90 x 0.8 mm) as a substrate and conduct electricity for 10 seconds to conduct electrodeposition.

After finishing, take it out and wash it thoroughly with water, then leave it for 5 minutes.
When left for a minute, a wet undercoat film without large water droplets is obtained.

On top of this, a thermosetting acrylic resin slurry paint white with a solid content of 45% was applied using an air spray gun (Meiji Kikai Seisakusho, trade name F-5), and after being left for 5 minutes, it was placed in an electric hot air drying tester. Baking was carried out at about 180° C. for 30 minutes to heat and cure the electrodeposited coating and the slurry coating at the same time.

The overall coating film obtained had good flatness and smoothness, and no defects such as poor coloring or gloss were observed, and the 60 degree specular gloss was 9.
It was 0.

The film thickness after baking was 10 μm for the electrodeposited film and 60 μm for the slurry paint film.

The baking temperature required for curing the coating film obtained from the above-mentioned thermosetting electrodeposition paint is approximately 170° C., and the baking time is 30 minutes.

Further, the thermosetting acrylic resin slurry paint white used here was prepared as follows.

That is, a mixture of styrene, methyl methacrylate, butyl methacrylate, glycidyl methacrylate, and hydroxyethyl methacrylate is added dropwise to triol to which a small amount of a polymerization initiator (azobisisobutyronitrile) has been added, while heating and coagulating at the reflux temperature of the triol. Superimposed.

The solvent was removed by distillation under reduced pressure, and after cooling, the mixture was coarsely pulverized using a pulverizer to obtain a powdered acrylic resin.

9 parts of sebacic acid and 40 parts of rutile titanium white were added to 100 parts of this acrylic resin, and the mixture was kneaded at about 90° C. for 10 minutes using a heating roll.

After cooling, the mixture was pulverized to a particle size of 20 to 150 μm to obtain a powder coating material, which is a raw material for a slurry coating material.

To 50 parts of this powder coating, 50 parts of clean water and 0.1 part of polyoxyethylene lauryl ether as a surfactant were added, dispersed in a pebble mill for 16 hours, then discharged, and further diluted with clean water to adjust the solid content to 45%. did.

Comparative Example 1 The same thermosetting acrylic resin slurry paint white as in Example 1 was applied to a degreased cold-rolled steel plate (same as in Example 1) using the same method as the top coating in Example 1 to give a dry film thickness of 60%.
Paint to a thickness of ~70μ.

The coating film obtained by baking this at approximately 180°C for 30 minutes is
Compared to the overall coating film of Example 1, it was inferior in terms of flatness, smoothness, gloss, etc., and was also colored yellow.

The 60 degree specular gloss was 70. Example 2 The thermosetting electrodeposition paint shown in Example 1 was applied to a cold-rolled steel plate by the same method as in Example 1, and after thoroughly rinsing with water, it was heated in an electric hot air dryer at about 100°C for 10 minutes. Heat.

After cooling, the same thermosetting acrylic resin slurry paint white as in Example 1 was applied according to the method shown in Example 1, and after being left at room temperature for 5 minutes, it was baked at about 180°C for 30 minutes and then electrodeposited. The film and the slurry coating were simultaneously heated and cured.

The flatness and smoothness of the resulting overall coating film was slightly better than that of Example 1, and the 60 degree specular gloss was 92.

Example 3 The thermosetting electrodeposition paint shown in Example 1 was applied to a cold-rolled steel plate by the same method as in Example 1, and after thoroughly washing with water, it was heated at about 170°C for 30 minutes using an electric hot air dryer. Baked for a minute to harden.

After cooling, half of the coated surface was lightly polished with 1400 waterproof abrasive paper, and the polishing residue was wiped off with petroleum benzene to clean it.

Next, the same thermosetting acrylic resin slurry paint white as in Example 1 was applied according to the method shown in Example 1, and after being left at room temperature for 5 minutes, it was baked at about 180° C. for 30 minutes to harden it.

The resulting overall coating film had good flatness and smoothness, and was especially superior to that of Example 1 in the area where the undercoat was polished.

The 60 degree specular gloss was 94 in the area where the undercoat was polished and 92 in the other areas.

Claims (1)

[Scope of Claims] 1. In a coating process in which a metal substrate is undercoated with a thermosetting electrodeposition paint and finished by being overcoated with a dispersion of a powder coating using thermosetting water as a dispersion medium, heating or A two-coat finish painting method characterized by repeatedly applying a top coat without baking and then baking to form a hardened comprehensive coating film. 2. In the painting process where a metal substrate is undercoated with a thermosetting electrodeposition paint and finished with a topcoat of a dispersion of a powder paint using thermosetting water as a dispersion medium, the baking required for curing of the electrodeposition coating after the undercoat is performed. A two-coat finish painting method characterized by heating at a temperature lower than the above temperature, then applying a top coat and then baking to form a hardened overall paint film. 3. In the painting process where a metal substrate is undercoated with a thermosetting electrodeposition paint and finished with a top coat of a dispersion of a powder paint using thermosetting water as a dispersion medium, the electrodeposition coating film is cured by baking after the undercoat. A two-coat finish painting method characterized in that a top coat is then applied and baked to form a hardened overall paint film.