JPH09302273A - Powder coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a powder coating capable of forming a flat film having a sufficient mechanical strength by attaching fine hydrophobic silica powder having a high degree of hydrophobictiy on the surfaces of powder particles containing a specified binding resin. SOLUTION: This powder coating comprises a fine hydrophobic silica powder having a hydrophobicity of at least 60% and attached to the surfaces of powder particles of a binding resin containing at least one of a polyester resin and an epoxy resin as the main component. The amt. of the fine hydrophobic silica powder attached is preferably 0.5 to 2.0wt.% based on the powder particles. The degree of hydrophobicity of the fine hydrophobic silica powder is controlled by treating silanol groups on the surface of the fine silica powder with a silane coupling agent or the like. This coating is obtained by dry-mixing the powder particles with the fine hydrophobic silica powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder coating which has a matte coating surface.

[0002]

2. Description of the Related Art Powder coatings have less volatile components and odors than solvent coatings, and are very useful in terms of pollution control and environmental regulations. In addition, since it does not use organic solvents, it does not fall under the category of hazardous materials under the Fire Service Law, and it is also excellent in safety.

As a method for delustering the surface of a coating film in powder coating, a powder coating is prepared by melt-kneading and pulverizing inorganic fine particles such as silica and alumina together with the materials constituting the powder coating. There is known a method of matting by scattering the light on the surface of a coating film applied by using it. However, in order to remove the matte by the above matte method, it is necessary to add a large amount of inorganic fine particles, so that the mechanical strength of the coating film is lowered.
Further, since the inorganic fine particles and the material constituting the powder are melt-kneaded in the process of producing the powder coating material by the above-mentioned matte method, there is a problem that productivity is lowered due to defective biting of the kneading machine.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a powder coating having a coating film having sufficient mechanical strength and having no gloss on the surface of the coating film.

[0005]

Means for Solving the Problems The present invention has been made as a result of intensive studies in view of the above-mentioned problems, and a hydrophobic silica fine powder having a high degree of hydrophobicity is attached to the surface of powder particles to form a coating film. It was found that even when baking was carried out, fine particles of hydrophobic silica remained on the surface of the molten coating film, and light was scattered to lose the gloss of the coating film.

The present invention provides a fine powder of hydrophobic silica having a hydrophobicity of 60% or more on the surface of powder particles containing a binder resin containing at least one of a polyester resin and an epoxy resin as a main component. It is a powder coating characterized by being adhered. Hereinafter, the present invention will be described in detail.

As the binder resin constituting the powder coating material of the present invention, a polyester resin, an epoxy resin, or a combination of both is used as a main component. Examples of the acid component of the polyester resin include terephthalic acid, isophthalic acid, phthalic acid, methylterephthalic acid, trimellitic acid,
Pyromellitic acid, adipic acid, sebacic acid, succinic acid,
Maleic acid, fumaric acid, tetrahydrophthalic acid, methyl-tetrahydrophthalic acid, hexahydrophthalic acid, methyl-hexahydrophthalic acid, and their anhydrides are used. On the other hand, as the alcohol component, ethylene glycol, propylene glycol, 1.3-butanediol, 1.4-butanediol, 1.6-hexanediol, neopentyl glycol, bis Use of hydroxyethyl phthalate, hydrogenated bisphenol A, ethylene oxide adduct of hydrogenated bisphenol A or propylene oxide adduct, trimethylolethane, trimethylolpropane, glycerin, pentaerythritol, etc. You can

The epoxy resin is a compound having two or more epoxy groups in the molecule, and is a glycidyl ester type resin, a glycidyl ether type resin, a glycidyl amine type resin, an alicyclic epoxy resin, a linear aliphatic resin. Epoxy resin or the like can be used.

Further, isocyanate, amine, polyamide, acid anhydride and the like can be used as a curing agent in the powder particles constituting the present invention. Further, the powder constituting the present invention,
Acrylic oligomers, leveling agents such as silicone, antifoaming agents such as benzoin, fillers such as barium sulfate, calcium carbonate, aluminum oxide, calcium silicate, slip agents such as polyolefin wax, titanium oxide, chromium oxide, iron oxide, calcium -A pigment such as Bonblack may be added as appropriate.

The hydrophobic silica fine powder used in the present invention must have a hydrophobicity of 60% or more. Silica fine powder is originally hydrophilic, and can be made hydrophobic by performing the following surface treatment. The degree of hydrophobicity is obtained by treating silanol groups present on the surface of silica fine powder with a silane coupling agent or the like. By doing so, it can be adjusted arbitrarily. Specifically, for example, it can be hydrophobized by dissolving hexamethyldisilazane in ethanol, spraying an appropriate amount on untreated silica fine powder in a fluidized state, and heating to volatilize ethanol.
In the powder coating material, when the coating film is baked, the binder resin melts and the viscosity decreases. Since the silica fine powder having a hydrophobicity of less than 60% has a high affinity with the molten binder resin, it is easily incorporated into the coating film. However, the hydrophobic silica fine powder having a hydrophobicity of 60% or more has a low affinity for the molten binder resin when the coating film is baked, and thus is difficult to be incorporated into the coating film. Therefore, since the silica fine powder scatters the remaining light on the surface of the coating film, even if added in a small amount, a sufficient matting effect can be obtained. The powder particles of the present invention contain a binder resin containing at least one of the polyester resin and the epoxy resin as a main component. In this case, when the hydrophobic silica fine powder of the present invention is applied to a binder resin whose main component is an acrylic resin having a low melt viscosity, the hydrophobic silica fine powder has too high an affinity with the binder resin and is baked. At that time, it is easily incorporated into the coating film. As a result, a sufficient matting effect cannot be obtained. Specific examples of the hydrophobic fine powder silica having a hydrophobicity of 60% or more include Cabot Corporation product names TS-720 and TS-530.
Wacker Chemical Co. product name H-2000, H2000
/ 4 etc.

To measure the degree of hydrophobicity, 0.05 g of silica fine powder was floated in 50 ml of pure water, methanol was added dropwise from a buret while stirring with a stirrer, and the silica fine powder floating on the water surface was measured. Allow to settle completely. At this time, the amount of methanol (ml) dropped was measured, and the degree of hydrophobicity was calculated by the following calculation formula.

[0012]

The amount of the fine particles of hydrophobic silica deposited is preferably 0.5% by weight or more and 2.0% by weight or less based on 100% by weight of the powder particles. If it is less than 0.5% by weight, a sufficient matting effect cannot be obtained. On the other hand, if the amount exceeds 2.0% by weight, the strength of the coating film may be deteriorated and the surface condition of the coating film may be poor, which is not preferable.

The powder particles used in the present invention are obtained by dry-mixing the above-mentioned compositions, hot-melt kneading, pulverizing and classifying, or by subjecting each composition to a suspension polymerization method, an emulsion polymerization method and the like. It may be obtained by the polymerization method of. To produce the matte powder coating material of the present invention using the powder particles obtained by the above method,
The powder particles and the hydrophobic silica fine powder may be dry mixed by the following method. Examples of the dry mixer include a V-type blender, a cone-type blender, a Nauta mixer manufactured by Hosokawa Micron, a Henschel mixer manufactured by Mitsui Miike, and a super mixer manufactured by Kawada Seisakusho. The hydrophobic silica fine particles having a hydrophobicity of 60% or more may be simply attached to the surface of the powder particles by using the dry mixer, or a part of the silica fine particles may be powder particles. It may be buried and fixed on the surface of the. In order to embed and fix a part of the silica fine particles on the surface of the powder particles, an impact force and a compressive force are applied to the mixture of the powder particles and the fine silica powder, so that the fine silica particles are thermally softened on the surface of the fine powder particles. A surface modifier that fixes the powder can be used.

The present invention will be described below based on Examples and Comparative Examples.

【Example】

Example 1 The raw materials with the above blending ratios are mixed in a super mixer, hot melt kneaded in a pressure kneader at 120 ° C., pulverized in a jet mill, and then classified in a dry airflow classifier to have a volume 50% diameter of 20 μm. To obtain powder particles. A hydrophobic silica fine powder having a hydrophobicity of 62% with respect to 100% by weight of the powder particles (manufactured by Wacker Chemical Co., trade name:
H-2000) 0.5% by weight was mixed by stirring with a Henschel mixer to obtain the powder coating material of Example 1. Corona spray gun manufactured by Chichibu Onoda Co., Ltd. (product name: GX)
-108) was applied to a SPCC plate (trade name: PB-137M) manufactured by Nippon Test Panel Co., Ltd., and then baked at 180 ° C. for 20 minutes to obtain a coated product of Example 1.

Example 2 An example similar to Example 1 except that the powder particles and the hydrophobic silica fine powder of Example 1 were used and the addition amount of the hydrophobic silica fine powder was changed to 1.0% by weight. A powder coating of 2 was obtained.
The coated material of Example 2 was obtained by using the above powder coating material in the same manner as in Example 1.

Example 3 An example similar to Example 1 except that the powder particles of Example 1 and the hydrophobic silica fine powder were used and the addition amount of the hydrophobic silica fine powder was changed to 2.0% by weight. A powder coating of 3 was obtained.
The powder coating material was processed in the same manner as in Example 1 to obtain a coated article of Example 3.

Example 4 The raw materials with the above blending ratios are mixed in a super mixer, hot melt kneaded in a pressure kneader at 120 ° C., pulverized in a jet mill, and then classified in a dry airflow classifier to have a volume 50% diameter of 20 μm. To obtain powder particles. A hydrophobic silica fine powder having a hydrophobicity of 62% with respect to 100% by weight of the powder particles (manufactured by Wacker Chemical Co., trade name:
H-2000) 1.0% by weight was mixed by stirring with a Henschel mixer to obtain a powder coating material of Example 4. The powder coating material was processed in the same manner as in Example 1 to obtain a coated article of Example 4.

Example 5 The raw materials with the above blending ratios are mixed in a super mixer, hot melt kneaded in a pressure kneader at 120 ° C., pulverized in a jet mill, and then classified in a dry airflow classifier to have a volume 50% diameter of 20 μm. Then, powder particles were obtained. 100% by weight of the powder particles, a hydrophobic silica fine powder having a hydrophobicity of 62% (manufactured by Wacker Chemical Co., trade name: H
-2000) 1.0 wt% was mixed by stirring with a Henschel mixer to obtain a powder coating material of Example 5. The powder coating material was processed in the same manner as in Example 1 to obtain a coated article of Example 4.

[0020]

[Comparative example]

Comparative Example 1 A powder coating material of Comparative Example 1 was obtained in the same manner as in Example 1 except that the hydrophobic silica fine powder was not added to the powder particles of Example 1. The powder coating material was treated in the same manner as in Example 1 to obtain a coated article of Comparative Example 1.

Comparative Example 2 The powder particles of Example 1 were added to the fine particles of hydrophobic silica having a hydrophobicity of 40% (manufactured by Nippon Aerosil Co., Ltd., trade name: R-97).
A powder coating material of Comparative Example 2 was obtained in the same manner as in Example 1 except that 1.0% by weight of 2) was added. Example 1 of the above powder coating material
A coated article of Comparative Example 2 was obtained in the same manner as in.

Comparative Example 3 An example except that 1.0% by weight of silica fine powder having a hydrophobicity of 0% (trade name: Fineseal A, manufactured by Tokuyama Corporation) was added to the powder particles of Example 1. A powder coating material of Comparative Example 3 was obtained in the same manner as in 1. A coated article of Comparative Example 3 was obtained by using the above powder coating material in the same manner as in Example 1.

COMPARATIVE EXAMPLE 4 The procedure of Example 1 was repeated except that 1.0% by weight of alumina fine powder (manufactured by Nippon Aerosil Co., Ltd., trade name: RFY-C) having a hydrophobicity of 0% was added to the powder particles of Example 1. A powder coating material of Comparative Example 4 was obtained in the same manner as in Example 1. A coated article of Comparative Example 4 was obtained using the above powder coating material in the same manner as in Example 1.

Comparative Example 5 The raw materials with the above blending ratios are mixed in a super mixer, hot melt kneaded in a pressure kneader at 120 ° C., pulverized in a jet mill, and then classified in a dry airflow classifier to have a volume 50% diameter of 20 μm. To obtain powder particles. Silica fine powder having a hydrophobicity of 62% (trade name: H-2000, manufactured by Wacker Chemical Co., Ltd.) is added to the powder particles in an amount of 1.0.
A powder coating material of Comparative Example 5 was obtained in the same manner as in Example 1 except that the addition was made by weight. A coated article of Comparative Example 5 was obtained by using the above powder coating material in the same manner as in Example 1.

The glossiness of the coated article and the mechanical strength of the coated article were measured by the following measuring methods as indexes of gloss in the above Examples and Comparative Examples. (1) Gloss: Nippon Denshoku Mirror spectrophotometer (Product name: VG
S-SENSOR), JIS K-5400
According to (7.6), the incident angle and the reflection angle were measured at 60 degrees. (2) Flex resistance: Flexibility with a diameter of 3 mm was measured according to JIS-K5400 (8, 1). (3) Erichsen value: measured according to JIS-K5400 (8, 2). (4) Impact resistance: Measured according to JIS-K5400 (8, 3, 2) DuPont method. Table 1 shows the measurement results of the glossiness and mechanical strength.

[0026]

[Table 1]

As can be seen from the results shown in Table 1, Examples 1 to 5 had a sufficient mechanical strength, a low glossiness, and a sufficient matting effect was confirmed. In Comparative Examples 1 to 5, the glossiness was high and no matting effect was observed.

[0028]

INDUSTRIAL APPLICABILITY According to the present invention, a hydrophobic silica fine powder having a hydrophobicity of 60% or more is formed on the surface of powder particles containing at least one of a polyester resin and an epoxy resin as a main component of a binder resin. By adhering it, it was possible to obtain a powder coating having sufficient mechanical strength and having a matte coating surface. Further, according to the present invention, in the manufacturing method, productivity is reduced due to defective biting during melt-kneading,
The problem of poor dispersion does not occur.

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Claims (2)

[Claims] 1. A hydrophobic silica fine powder having a hydrophobicity of 60% or more adheres to the surface of powder particles containing a binder resin containing at least one of a polyester resin and an epoxy resin as a main component. Powder coating characterized in that 2. The powder coating material according to claim 1, wherein the amount of the fine hydrophobic silica powder adhered is 0.5% by weight or more and 2.0% by weight or less based on the powder particles.