JPH07148458A - Coating method - Google Patents

Abstract

PURPOSE:To provide a coating method excellent in coating efficiency, reducing the recovery amt. of powder coating and useful from the aspect of the conservation of resources and a waste measure in an electrostatic coating method using powder coating. CONSTITUTION:In an electrostatic coating method applying powder coating to the surface of an object to be coated composed of plastics or a film, the temp. of the object to be coated is set to the glass transition temp. of the resin contained in the powder coating or higher before the powder coating is applied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a plastic or
The present invention relates to a coating method in which powder coating is applied to the surface of a coating film obtained by coating the surface of metal or plastic by electrostatic coating.

[0002]

2. Description of the Related Art For plastic products such as automobile parts, building materials, household appliances, and products coated with metal or plastic, there has been a conventional technique for improving the durability by forming a coating film on the surface. It is progressing. In these cases, a method of applying a powder coating material by an electrostatic coating method has been widely used in recent years for reasons such as prevention of environmental pollution and improvement of factory productivity.

In such an electrostatic coating method, as the coating film of the powder coating material is formed on the object to be coated, an electric charge is accumulated and electrostatic repulsion occurs to drop a part of the powder coating material. ,
Due to technical problems such as a part of the powder coating adhered to the object to be coated falling off due to the air flow during electrostatic coating, it was not possible to obtain a sufficiently high coating efficiency.

Further, when the powder coating material is applied by the electrostatic coating method, it is essentially difficult to adhere all of the powder coating material used to the object to be coated, and the powder coating material which has not been attached yet is not adhered. Establishing a method of collecting and reusing was a problem in terms of cost and prevention of environmental pollution.

In Japanese Patent Publication No. 51-43152, when the powder coating material is overcoated on the object to be coated with the thermosetting coating material, the undercoating material is heated to reduce the volatile component content to 6%.
There is disclosed a technique of improving the metallic feel and durability and further improving the coating efficiency by adjusting the content to be less than 10% by weight.

Japanese Unexamined Patent Publication (Kokai) No. 2-194878 discloses a technique for preventing popping by applying a powder coating material after heating to a sufficient temperature for degassing when coating a plastic substrate. .

[0007]

Each of the above techniques relates to an improvement in the coating method of powder paint, but while limiting the volatile content of the undercoat paint to 6% by weight or less,
Since the remaining volatile component improves the coating efficiency, there is no fact that the coating efficiency is substantially improved so much, and the problem has not been essentially solved.

When powder coating is applied to the surface of plastic, the problem of so-called popping caused by the porosity of the plastic surface occurs, but if the heating temperature is too high, the powder coating will partially cure. Then, there is a drawback that it is unavoidable that it causes a deterioration in appearance.

In view of the above problems, the present invention is excellent in coating efficiency in powder coating by electrostatic coating method, reduces the amount of recovered powder coating, and saves resources and waste. The purpose is to provide a useful coating method.

[0010]

Means for Solving the Problems The gist of the present invention is a coating method for applying a powder coating material to the surface of an object to be coated, which is made of plastic or a coating film, by an electrostatic coating method, before applying the powder coating material. In, the temperature of the article to be coated is not less than the glass transition temperature of the resin contained in the powder coating material, or
It is at or above the glass transition temperature of the plastic or the resin contained in the coating film. The present invention is described in detail below.

The coating method of the present invention can be applied to the surface of plastic. Further, the coating method of the present invention,
As a base coat on the surface of metal or plastic,
It is possible to form a coating film such as an electrodeposition coating film, an aqueous coating film, a solvent type coating film, a powder coating film and the like, and then apply it. Examples of the metal include a conductive material such as iron and the like, and among them, iron phosphate treated steel sheet, zinc phosphate treated steel sheet and the like are preferably used. In the present specification, these are referred to as an article to be coated made of plastic or a coating film.

The powder paint used in the present invention is not particularly limited, and examples thereof include paints using a vehicle such as polyester resin, acrylic resin, and epoxy resin, and the like. A pigment, an additive, and the like are appropriately added, and the powder is supplied in the form of powder having a solid content of 100%. The particle diameter of the powder coating is 5 to 50 μm in volume average particle diameter,
It is preferably 8 to 40 μm. Average particle size is 5 ~ 20μ
m, the proportion of particles of 5 μm or less is 25% by weight or less,
When the average particle size is 20 to 50 μm, the standard deviation of the particle size distribution is more preferably 20 μm or less. The particle size distribution standard deviation is [Σ {(D−X) ² F} / ΣF] ^1/2 , D is the particle size of each particle, X is the volume average particle size, and X = Σ ( D
F) / ΣF, and F represents the frequency of particles.

The above-mentioned plastic is not particularly limited, and may be either thermosetting type or thermoplastic type, and may or may not use a reinforcing agent. As such, for example, phenolic resin including phenol-cellulose composite, silicone resin, amino resin, polyurethane, polystyrene, polypropylene,
Examples thereof include thermoplastic acrylic resins, polyvinyl chloride, and various polymers and copolymers of acrylonitrile and butadiene. When fibers are used as the reinforcing agent, fibers other than glass fibers such as boron fibers may be used.

In the coating method of the present invention, before applying the powder coating material, the temperature of the object to be coated is set to be equal to or higher than the glass transition temperature of the resin contained in the powder coating material, or the plastic or the coating film is coated. The temperature is not lower than the glass transition temperature of the contained resin. In order to reach the above temperature or higher, the article to be coated can be preheated before coating. Further, in the case of baking for forming a coating film on the object to be coated before the electrostatic coating of the present invention, in order to reach the temperature above the above, the powder coating is applied as it is before cooling after baking. can do.

In the present invention, it is generally preferable that the above temperature is lower than or equal to the upper limit baking temperature of the powder coating used, and when an object to be coated is used, the upper limit of temperature is above the above coating film. And, it is preferable that the baking temperature is not higher than the upper limit of the powder coating used. When an article to be coated made of plastic is used, the upper limit of the temperature is preferably the plastic deformation temperature or lower.

In a more effective method of the present invention, the temperature is 40 to 140 ° C. If the temperature is lower than 40 ° C, the coating efficiency will be poor, and if the temperature is higher than 140 ° C, the powder coating material will be partially cured and the appearance after coating will be deteriorated.

When the coating method of the present invention is applied to an object to be coated consisting of a coating film, in the effective method of the present invention,
The content of volatile components in the coating film on the surface of the article is 10% by weight
It is the following. If it exceeds 10% by weight, the finished coating film may have blisters, rough skin, yellowing, etc., resulting in a poor appearance. More preferably, it is 5% by weight or less.

In a more effective method of the present invention, when the coating film on the surface of the article to be coated is an electrodeposition coating film or an aqueous coating film, the content of the volatile amine compound is such that the total solid content is It is 2.0% by weight or less. When it exceeds 2.0% by weight, the appearance is deteriorated. It is preferably 1.5% by weight or less,
More preferably, it is 1.2% by weight or less.

In the present invention, after the temperature is set to the above temperature, the powder coating material is applied to the surface of the article to be coated, which is made of plastic or a coating film, by the electrostatic coating method. A usual method can be applied to the electrostatic coating. In the present invention,
It is possible to make the plastic conductive by incorporating conductive particles such as graphite particles into the plastic, or by using a conductive fiber reinforcing agent or the like. If necessary, a conductive primer or a conductive wash solution can be applied to the plastic to impart conductivity.

[0020]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Reference Example 1 Preparation of Aqueous Metallic Paint Cymel 303 was added to 140 parts by weight of an aqueous acrylic resin having a hydroxyl value of 20 and an acid value of 58 (amine neutralization, non-volatile content of 50%).
(Methoxylated methylol melamine, manufactured by Mitsui Toatsu Chemicals, Inc.)
30 parts by weight was added, and further 15 parts by weight of an aluminum pigment paste (AW-666, manufactured by Asahi Kasei Corp.) was added and mixed to prepare an aqueous metallic paint.

Reference Example 2 Preparation of Acrylic Powder Coating A glycidyl group-containing acrylic resin (glass transition temperature (hereinafter referred to as “Tg”): 52 ° C.) 315 parts by weight, decanedicarboxylic acid 80.5 parts by weight, and surface modifier 4 parts by weight. Parts and 2 parts by weight of benzoin were melt-kneaded and then finely pulverized to prepare an acrylic powder coating material.

Reference Example 3 Preparation of Polyester Powder Coating Carboxyl Group-Containing Polyester Resin (Tg: 63 ° C.)
7.5 parts by weight of triglycidyl isocyanurate to 100 parts by weight
By weight, 60 parts by weight of titanium oxide, 0.4 parts by weight of a surface modifier and 1.1 parts by weight of benzoin were melt-kneaded and then finely pulverized to prepare a polyester powder coating material.

Example 1 An iron phosphate-treated steel sheet was electrodeposited (Power Top, U series, made by Nippon Paint Co., Ltd.) at a film thickness of 20 μm, and then an intermediate coating (OTOH series, made by Nippon Paint Co., Ltd.) was made at a film thickness of 35 μm. Was applied. After coating the water-borne metallic paint prepared in Reference Example 1 on the above intermediate coated steel sheet and baking it at 80 ° C. for 10 minutes, 100 ° C. for 10 minutes and 120 ° C. for 10 minutes, and then setting the temperature of the coated plate to each temperature in Table 1. Electrostatically coating the acrylic powder coating material prepared in Reference Example 2 (coating conditions, applied voltage: -80 kV, discharge rate: 120 g / min),
The coating efficiency was measured. The results are shown in Table 1.

[0025]

[Table 1]

From the above, T of acrylic resin in powder coating is
It has been found that the coating efficiency is improved when the article to be coated is heated to a temperature of g or more.

Example 2 A plastic material for an automobile bumper (Tg: 90 ° C., manufactured by Mitsui Petrochemical Co., Ltd.) was treated with trichloroethane, and a conductive primer (RB-1140CD primer, manufactured by Nippon Bee Chemical Co., Ltd.) was applied. This plastic material was brought to each temperature shown in Table 2 and the acrylic powder coating material prepared in Reference Example 2 was electrostatically coated under the same coating conditions as in Example 1,
The coating efficiency was measured. The results are shown in Table 2.

[0028]

[Table 2]

From the above, T of acrylic resin in powder coating is
It has been found that the coating efficiency is improved by setting the temperature to g or more, but the coating efficiency is significantly improved by setting the temperature to Tg or more of the plastic material.

Example 3 In the same manner as in Example 1, the iron phosphate-treated steel sheet was subjected to electrodeposition and intermediate coating, and the aqueous metallic coating material prepared in Reference Example 1 was coated. 5 minutes and 10 minutes at 80 ℃, 5 minutes at 90 ℃,
5 minutes at 100 ℃, 5 minutes at 130 ℃, and 140 ℃
The acrylic powder coating material prepared in Reference Example 2 was preheated for 5 minutes in the same manner without cooling and applied under the same conditions as in Example 1 and baked at 150 ° C. for 25 minutes. The non-volatile content (% by weight) and the content of the volatile amine compound (% by weight relative to the total solid content) of the aqueous metallic coating film after preheating were measured, and the appearance was evaluated. The appearance was measured by measuring the NSIC with a portable image clarity measuring instrument (manufactured by Suga Test Instruments Co., Ltd.) and expressing the numerical value. The results are shown in Table 3.

[0031]

[Table 3]

As is apparent from Table 3, a good appearance can be obtained by adjusting the amount of the volatile substance to 10% by weight or less or the amine content to 2% by weight or less of the solid content. did it.

Example 4 A zinc phosphate-treated steel sheet having a thickness of 0.6 mm was coated with the intermediate coating composition used in Example 1 to obtain a coating film having a thickness of 35 μm. This coated plate was set to each temperature shown in Table 4, the polyester powder coating material prepared in Reference Example 3 was electrostatically coated in the same manner as in Example 1, and the coating efficiency was measured. The results are shown in Table 4.

[0034]

[Table 4]

[0035]

According to the present invention, the T of the resin of the powder coating is
By preheating to g or more, the coating efficiency is improved and the amount of recovered powder coating material is reduced, which is useful as a waste countermeasure.
Further, among the steps of (steel sheet)-(primer)-(baking)-(cooling)-(powder coating), the step of (cooling) can be omitted, and in the coating process of the automobile body, Among the steps of (base coat)-(preheat)-(cooling)-(powder top coat clear), the step of (cooling) can be omitted, which is effective in saving labor and energy.

Claims (5)

[Claims] 1. In a coating method of applying a powder coating material to the surface of a coating material made of plastic or a coating film by an electrostatic coating method, the temperature of the coating material is adjusted before coating the powder coating material. A coating method comprising setting the glass transition temperature of a resin contained in the powder coating material or higher. 2. In a coating method of applying a powder coating material to the surface of a coating material made of plastic or a coating film by an electrostatic coating method, the temperature of the coating material is adjusted before applying the powder coating material. A coating method, wherein the glass transition temperature of the resin contained in the plastic or the coating film is equal to or higher than the glass transition temperature. 3. In a coating method of applying a powder coating material to the surface of an object to be coated, which is made of plastic or a coating film, by electrostatic coating, the temperature of the coating object is set to 40 before applying the powder coating material. The coating method is characterized in that the temperature is set to 140 ° C. 4. The coating method according to claim 1, 2 or 3, wherein the content of the volatile component in the coating film on the surface of the article to be coated is 10% by weight or less. 5. The coating film on the surface of the article to be coated is an electrodeposition coating film or an aqueous coating film, and the content of the volatile amine compound is 2.0% by weight or less of the total solid content. The coating method according to 2, 3 or 4.