JP2003003122A - Thermally curable powder coating and method of forming thermally curable coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder coating that gives the coating film of high surface smoothness. SOLUTION: The thermally curable powder coating is applied to the substrates by using an electrostatic powder coating applicator in which the electrostatic charge remaining on the powder coating is characteristically >=80% based on the initial static charge on the substrate to be coated, 1 minute elapse after the initial charging. In the method of forming thermally curable powder coating layer, an electrostatic powder coating applicator is used to apply the powder coating to the substrate, then the applied coating is cured by heating the applied coating at >=100 deg.C, while the electrostatic charge of the powder coating remains >=80% based on the initial static charge on the substrate, 1 minute elapse after the initial charge on the powder coating applied on the substrate.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel powder coating composition and a thermosetting powder coating film forming method.

[0002]

2. Description of the Related Art In recent years, powder paints have been attracting attention as paints containing mainly solvents and containing almost no volatile substances from the viewpoints of preventing pollution and protecting the global environment. Further, conventionally, powder coatings have been widely used as outdoor or indoor applications in the field of industrial products such as home electric appliances, automobiles, vehicles, office supplies, steel furniture, and building materials.

As such powder coatings, thermosetting acrylic resin powder coatings, thermosetting polyester resin powder coatings and thermosetting epoxy resin powder coatings are mainly used. .

In recent years, powder coatings having an excellent finished appearance have been demanded, but in order to obtain the same level of smoothness of the coating surface as that of the conventional solvent-type coating film of about 40 microns, it is necessary to set the coating powder to about 60 microns or more. The coating thickness is required, and improvement of smoothness in a thin film of powder coating is required. As a method of improving the smoothness of the powder coating, it is conceivable to make the particle diameter of the powder coating as small as possible. However, reducing the particle diameter of the powder coating reduces the fluidity of the powder coating. In addition, the workability of powder coating becomes poor, and when the powder coating is electrostatically charged by a spray gun, the chargeability of the powder coating becomes non-uniform, resulting in poor filling of the coating powder. Therefore, there is a problem that the smoothness of the powder coating film deteriorates, and the smoothness of the powder coating film has not been improved yet.

[0005]

[Means for Solving the Problems] The inventors of the present invention have conducted extensive studies in order to solve such problems. As a result, it is a powder coating applied using an electrostatic powder coating machine, and the powder after 1 minute has elapsed from the amount of charge of the initial powder coating applied to the object to be coated. It has been found that a thermosetting powder coating material having a charge amount of 80% or more provides a powder coating film excellent in coating workability, coating efficiency and smoothness, The present invention has been completed.

[0006] That is, the present invention is a powder coating material applied by using an electrostatic powder coating machine, wherein the charge amount of the initial powder coating material applied to the object is 1 The present invention relates to a thermosetting powder coating material characterized in that the charge amount of the powder coating material after 80 minutes is 80% or more, and a coating film forming method thereof.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the present specification, the charge amount of the powder coating material coated on the object is measured by measuring the surface potential using a surface potential measuring device MODEL-169-3 manufactured by Monro Electronics Co., Ltd. It can be the amount of charge. In the present invention, the charge amount of the powder coating material 1 minute after coating is 80% of the charge amount of the initial powder coating material applied to the object to be coated.
Above all, especially preferably 85% or more. If it is less than 80%, the coating workability, coating efficiency and smoothness are poor.

The powder coating material of the present invention has an average particle size of 5
μm to 30 μm, preferably 10 μm to 25 μm. When the average particle size is less than 5 μm, the coating workability is poor and the electrostatic coating property of the powder coating is poor, so that the finish appearance of the baked coating film is poor, while when it exceeds 30 μm, the smoothness of the baked coating film is poor. It is not preferable.

The powder coating material of the present invention has a heat softening temperature of 30 ° C.
The temperature is 100 ° C, preferably 40 ° C to 90 ° C. If the heat softening temperature is lower than 30 ° C, the blocking property of the powder coating material is deteriorated, and lumps are easily formed during storage.
If the temperature exceeds ℃, the minimum melt viscosity of the melted powder coating material becomes high and the smoothness of the baked coating film becomes poor, which is not preferable. Further, as the powder coating material used in the present invention, a conventionally known thermosetting powder coating material can be used. Specifically, it is possible to use a thermosetting powder coating which is preferably a thermosetting powder-based resin that melts and flows by heating and which is mixed with a curing agent.

As the thermosetting powder base resin, a resin having a functional group which reacts with a curing agent by heat can be used.
Specifically, for example, acrylic resins, polyester resins, epoxy resins and hybrid resins thereof are suitable. Examples of the functional group include a hydroxyl group, a carboxyl group, an epoxy group, and a blocked isocyanate group. As the curing agent, a functional group contained in the curing agent reacts with a functional group in the base resin to form a cured coating film. For example, a base resin containing a hydroxyl group contains an amino group. Amino resins (hexamethoxymelamine resin, etc.), hardeners such as blocked polyisocyanate group-containing blocked isocyanate compounds (caprolactam block diisocyanate, etc.), carboxyl group-containing base resins, epoxy group-containing polyepoxides (triglycidyl isocyanate, etc.) and Curing agents such as β-hydroxyethylalkylamides, polycarboxylic acids containing carboxyl groups in epoxy group-containing base resins (dodecanedioic acid, eicosanedioic acid, sebacic acid, adipic acid, trimellitic acid, etc.), and these polycarboxylic acids Of anhydrides of those polycarboxylic acids Hardeners such as hydrazides, polymerization initiators such as imidazoles, hardeners for polyols (trimethylolpropane, etc.) containing hydroxyl groups in blocked isocyanate group-containing base resins, and benzyl-4-hydroxyphenylmethylsulfonium hexafluoroantimonate. A polymerization initiator etc. are mentioned.

In the present invention, a pigment (eg, an organic pigment (eg, quinacridone-based quinacridone,
Pigment Red, azo series, phthalocyanine blue,
Phthalocyanine such as phthalocyanine blue), inorganic pigments (eg, titanium oxide, calcium carbonate, barita,
Clay, talc, silica, etc.), carbon-based pigments (eg, carbon black, graphite, etc.), metallic powders (eg, mica-like iron oxide, aluminum, etc.) and rust preventive pigments (eg, red iron oxide, strontium chromate, zinc phosphate, etc.) Etc)), curing catalyst (dibutyltin diacetate, dibutyltin dilaurate, triethylamine,
Or diethanolamine), UV absorbers (benzophenone compounds, benzotriazole compounds, salicylate compounds, anilide oxalate compounds, etc.), UV stabilizers (hindered amine compounds, etc.), antioxidants (phenolic compounds, organic compounds) Additives such as sulfur compounds, phosphite compounds, etc.), surface conditioners, anti-armpitting agents and the like can be added.

The powder coating composition of the present invention is prepared by a conventional method, for example, by blending a base resin, a curing agent and, if necessary, other components and dry blending with a mixer, followed by heat-melt kneading, cooling and coarse pulverization. It can be produced by a melt-kneading method of pulverizing, filtering, a freeze-drying method, or the like.

The powder paint of the present invention is preferably applied by corona type electrostatic powder spray or triboelectric powder spray.

The powder coating composition of the present invention comprises the above-mentioned powder coating on the surface of a conductive base material (for example, metal, surface-treated metal, and coated material obtained by electrodeposition coating or intermediate coating of these metals). Painted by painting (usually film thickness 30μm ~ 150μm)
Then, the coating film can be usually formed by baking at 140 ° C. to 300 ° C. for 1 minute to 60 minutes.

According to the method of the present invention, powder coating is electrostatically coated on an object to be coated by using an electrostatic powder coating machine, and then the charge amount of the initial powder coating applied to the object is compared with While the charge of the powder coating is 80% or more 1 minute after coating, 100 ℃
It can be cured by the above heating.

[0016]

EXAMPLES The present invention will be described in more detail below with reference to examples. In the following, "parts" and "%" mean "parts by weight" and "% by weight", respectively.

Production Example 1 (Production of polyester resin powder coating (block polyisocyanate crosslinked)) As a material, Finedec M8032 (manufactured by Dainippon Ink and Chemicals, Inc., trade name, softening temperature 70 ° C., hydroxyl value 30 m)
gKOH / g) 770 parts, ε-caprolactam blocked isophorone diisocyanate (blocked polyisocyanate crosslinking agent) 230 parts, Disparlon PL540
(Kusumoto Kasei Co., Ltd., powdered vinyl-based polymer, trade name) 30 parts, 300 parts of titanium white are dry blended at room temperature using Henschel Mixer-FM10C manufactured by Mitsui Mining Co., Ltd., and extruder-APV. It was melted and kneaded with a product of MP-30. After cooling and coarsely pulverizing it, it was finely pulverized with a fine pulverizer (Hosokawa Micron Co., Ltd., ACM5) and then classified with an air stream classifier (DSX-2, Japan Pneumatic Industry Co., Ltd.) to obtain fine particles. Coarse particles were removed to obtain a polyester powder coating material A having an average particle diameter of 24 μm. The average particle size is a particle size distribution meter (manufactured by Nikkiso Co., Ltd.,
It is a value measured using a trade name Microtrac HRA).

Production Example 2 0.1% of aluminum oxide C (trade name, manufactured by Nippon Aerosil Co., Ltd.) was added to the coating material obtained in Production Example 1 and mixed with a Henschel mixer to obtain a polyester powder coating material B.

Production Example 3 0.1% of R-972 (manufactured by Nippon Aerosil Co., Ltd.) was added to the coating material obtained in Production Example 1 and mixed with a Henschel mixer to obtain a polyester powder coating material C.

Coating test SPC obtained by degreasing the powder coating materials of the above-mentioned Examples and Comparative Examples.
A C-SB steel plate (0.8 × 70 × 150 mm) was coated with various electrostatic powder coating machines, and the charge amount (surface potential) of the powder coating material coated on the object was determined. Further, various tests were carried out on each baked coated plate obtained by heating.

Table 1 shows the test results of Examples and Comparative Examples.

Test method Charge rate: The surface potential of the initial powder coating applied to the article to be coated and the surface potential of the powder coating one minute after coating were measured,
It was calculated by the following calculation formula. (Surface potential of the powder coating after 1 minute from coating) / (Surface potential of the initial powder coating applied on the object to be coated) x 100 Visual appearance: The visual appearance of the coating is glossy and smooth. From the feeling, it was evaluated according to the following criteria. ○: good, △: somewhat bad,
X: Poor appearance (L value): WaveScanP manufactured by BYK
L value was measured in lus. The smaller the value, the better the smoothness. Specular reflectance: The 60 degree specular gloss of JIS K-5400 was measured.

[0023]

[Table 1] Table 1

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4D075 AA09 AA87 BB26Z BB93Z                       CA48 EA02 EA19                 4J038 CG001 DA162 DB001 DD001                       DG102 DG302 GA03 GA06                       GA07 GA11 JA21 JA35 JB12                       JB17 JB36 MA02 MA13 MA14                       NA01 NA23 NA27 PA19 PB02                       PB05 PB07 PB09 PC02

Claims (5)

[Claims] 1. A powder coating applied by using an electrostatic powder coating machine, wherein the amount of charge of the initial powder coating electrostatically coated on an object is 1 after coating. A thermosetting powder coating material, wherein the charge amount of the powder coating material after the passage of minutes is 80% or more. 2. The powder coating material has an average particle diameter of 5 μm to 30 μm.
The thermosetting powder coating composition according to claim 1, wherein the thermosetting powder coating composition is m. 3. The powder coating material has a heat softening temperature of 30 ° C. to 100 ° C.
3. The thermosetting powder coating material according to claim 1, wherein the thermosetting powder coating material has a temperature of ° C. 4. The electrostatic powder coating machine is a corona charging type electrostatic powder coating machine or a friction charging type electrostatic powder coating machine, according to any one of claims 1 to 3. The thermosetting powder coating material described. 5. An electrostatic powder coating machine is used to electrostatically coat powder coating on an object to be coated, and then after the amount of charge of the initial powder coating applied to the object is coated. A method for forming a thermosetting powder coating film, which comprises curing the powder coating material by heating at 100 ° C. or higher while the charge amount of the powder coating material after 1 minute is 80% or higher.