JP7069555B2 - Powder coating and electrostatic powder coating method - Google Patents

Description

The present invention relates to a powder coating method and an electrostatic powder coating method.

In recent years, powder coating technology using powder coatings has been used to produce powder coatings that emit less volatile organic compounds (VOCs) in the coating process and do not adhere to the object to be coated after coating. Since it can be collected and reused, it is attracting attention in terms of protecting the global environment. Therefore, various powder coating materials have been studied.

Patent Document 1 describes a powder coating composition for electrostatic coating, characterized in that the carbon black content is 0.1 to 5% by mass and the lubricant content for synthetic resin is 0.1 to 5% by mass. The thing is listed.

Patent Document 2 describes that the surface of powder particles composed of at least a binder resin and a curing agent and having a volume average particle diameter of 5 to 20 μm has a volume specific resistance of 1 × 10 ⁴ Ω · cm or less. A powder coating material to which powder or conductive titanium oxide fine powder is adhered or fixed. Is described.

Patent Document 3 describes a powder coating material in which at least one additive selected from a curing agent, a curing catalyst, and a colorant is embedded or fixed on the surface of powder resin particles, and has a volume average particle diameter of 10 to 10 to. A powder coating material having a particle shape of 30 μm, a standard deviation of 15 μm or less, and a spherical shape. Is described.

Patent Document 4 describes a powder coating material obtained by mixing conductive metal oxide fine powder having a volume specific resistance value of 1 to 100Ω · cm into powder coating particles by a melt-kneading method. A powder coating material for electrostatic coating is described, wherein the metal oxide fine powder is 0.1 to 10.0% by weight in the powder coating material.

Patent Document 5 has a core portion containing a thermosetting resin and a thermosetting agent, and a resin coating portion that covers the surface of the core portion, and has a volume particle size distribution index GSDv of 1.50 or less, which is an average. A thermosetting powder coating material having powder particles having a circularity of 0.96 or more is described.

Patent Document 6 includes a core portion containing a thermosetting resin and a thermosetting agent having a blocked isocyanate group, and a thermosetting resin having a glass transition temperature of 45 ° C. or higher, and covers the surface of the core portion. Described is a thermosetting powder coating material comprising a resin-coated portion and powder particles having the following (1) to (4).
(1) The volume particle size distribution index GSDv is 1.50 or less.
(2) The average circularity is 0.96 or more.
(3) The melting temperature measured by the flow tester by the 1/2 method is 90 ° C. or higher and 115 ° C. or lower.
(4) The exothermic peak is in the range of 80 ° C. or higher and 150 ° C. or lower in the differential scanning calorimetry.

Patent Document 7 describes a coating method for obtaining a coating film having a uniform hue by mixing two or more powder coating materials having different hues, wherein the volume average particle diameter of one or more of the powder coating materials used is 100 nm or less. A coating method that uses a combination of powder paints containing hydrophilic inorganic fine particles.

Japanese Patent Application Laid-Open No. 2003-064316 Japanese Unexamined Patent Publication No. 8-253711 Japanese Unexamined Patent Publication No. 2007-084709 Japanese Unexamined Patent Publication No. 11-100534 Japanese Unexamined Patent Publication No. 2015-232063 Japanese Unexamined Patent Publication No. 2016-183300 Japanese Unexamined Patent Publication No. 2001-062385

INDUSTRIAL APPLICABILITY The present invention is excellent in suppressing the generation of electrostatic repulsion and is obtained as compared with the case where the dielectric loss ratio of the powder particles is less than 40 × 10 ^-3 or exceeds 150 × 10 ^-3 . It is an object of the present invention to provide a powder coating material having excellent film smoothness.

The above problem is solved by the following means. That is,
< 1 >
Containing powder particles having a dielectric loss ratio of 40 × 10 ^-3 or more and 150 × 10 ^-3 or less,
Powder paint.
< 2 >
The powder coating according to < 1 > , wherein the powder particles contain colloidal silica having a volume average particle size of 1 nm to 100 nm in an amount of 3% by mass or more and 20% by mass or less based on the total mass of the powder particles.
< 3 >
The powder coating material according to < 2 > , wherein the content of the colloidal silica is 5% by mass or more and 20% by mass or less with respect to the total mass of the powder particles.
< 4 >
The powder coating material according to < 1 > or < 2 > , wherein the water content of the powder particles is 0.1% by mass or more and 5% by mass or less with respect to the total mass of the powder particles.
< 5 >
The powder coating material according to < 4 > , wherein the water content of the powder particles is 0.2% by mass or more and 3% by mass or less with respect to the total mass of the powder particles.
< 6 >
The powder coating material according to < 1 > , wherein the powder particles contain titanium oxide in an amount of less than 25% by mass based on the total mass of the powder particles.
< 7 >
The powder coating material according to any one of < 1 > to < 3 > , wherein the powder particles contain titanium oxide in an amount of 25% by mass or more and 50% by mass or less with respect to the total mass of the powder particles.
< 8 >
The step of discharging the charged powder coating material according to any one of < 1 > to < 7 > , and electrostatically adhering the powder coating material to the coated material .
An electrostatic powder coating method comprising a step of heating a powder coating electrostatically adhered to an object to be coated to form a coating film.

According to the invention according to < 1 > , the occurrence of electrostatic repulsion is excellently suppressed as compared with the case where the dielectric loss ratio of the powder particles is less than 40 × 10 ^-3 or exceeds 150 × 10 ^-3 . Moreover, a powder coating material having excellent smoothness of the obtained coating film is provided.

According to the invention according to < 2 > , when the content of colloidal silica having a volume average particle diameter of 1 nm to 100 nm is less than 3% by mass or more than 20% by mass with respect to the total mass of the powder particles. In comparison, a powder coating material which is excellent in suppressing the generation of electrostatic repulsion and has excellent smoothness of the obtained coating film is provided.

According to the invention according to < 3 > , when the content of colloidal silica having a volume average particle diameter of 1 nm to 100 nm is less than 5% by mass or more than 20% by mass with respect to the total mass of the powder particles. In comparison, a powder coating material which is excellent in suppressing the generation of electrostatic repulsion and has excellent smoothness of the obtained coating film is provided.

According to the invention according to < 4 > , the water content of the powder particles is less than 0.1% by mass or more than 5% by mass with respect to the total mass of the powder particles. Provided is a powder coating material which is excellent in suppressing the generation of electrostatic repulsion and has excellent smoothness of the obtained coating film.

According to the invention according to < 5 > , the water content of the powder particles is less than 0.2% by mass or more than 4% by mass with respect to the total mass of the powder particles. Provided is a powder coating material which is excellent in suppressing the generation of electrostatic repulsion and has excellent smoothness of the obtained coating film.

According to the invention according to < 6 > , there is provided a clear powder coating material which is excellent in suppressing the generation of electrostatic repulsion and is excellent in the smoothness of the obtained coating film.

According to the invention according to < 7 > , there is provided a colored powder coating material which is excellent in suppressing the generation of electrostatic repulsion and is excellent in the smoothness of the obtained coating film.

According to the invention according to < 8 > , the occurrence of electrostatic repulsion is excellently suppressed as compared with the case where the dielectric loss rate of the powder particles is less than 40 × 10 ^-3 or exceeds 150 × 10 ^-3 . Moreover, an electrostatic powder coating method having excellent smoothness of the obtained coating film is provided.

Hereinafter, preferred embodiments of the present invention will be described in detail.

(Powder paint)
The powder coating material of the present embodiment contains powder particles having a dielectric loss ratio of 40 × 10 ^-3 or more and 150 × 10 ^-3 or less.
According to the powder coating material of the present embodiment, the generation of electrostatic repulsion is suppressed and the smoothness of the obtained coating film is excellent. The reason is not clear, but it can be inferred as follows.

Conventionally, powder paints (powder particles) used for powder coating include a binder resin, a curing agent for curing the binder resin used as needed, a pigment for coloring, a flame retardant, a leveling agent, and the like. It is produced by mixing the components of the above, melting the mixture, and then pulverizing to a desired particle size. The powder coating material thus produced is applied to the object to be coated by a method such as an electrostatic coating method. The electrostatic coating method is a method of electrostatically adhering powder particles to a grounded object by discharging powder particles charged by contact electrification or corona discharge using a spray gun.

However, when coating with a conventional powder coating method by an electrostatic coating method or the like, particularly when powder particles having a small particle size are used, the amount of adhesion is increased, for example, a film of powder coating. When a thick coating film having a thickness of 100 μm or more was produced, electrostatic repulsion may occur in the obtained coating film. Electrostatic repulsion means that when the layer of powder particles becomes too thick, a charge opposite to that of the object to be coated is induced, and the powder particles repel each other to generate a circular (crater-like) dent. It means to let you.
Here, by using a powder coating material containing powder particles and having a dielectric loss ratio of 40 × 10 ^-3 or more and 15 × 10 ^-3 or less, the generation of the electrostatic repulsion is suppressed.
The detailed mechanism by which the above effect is obtained is unknown, but it is speculated as follows.
When the dielectric loss ratio of the powder particles is 40 × 10 ^-3 or more, the electrostatic repulsion between the powder particles at the time of coating is suppressed, and the generation of the electrostatic repulsion is suppressed when the coating film is formed. ..
In addition, since the dielectric loss ratio of the powder coating is 150 × 10 ^-3 or less, the powder coating has a charge during coating, so that the powder particles are excellent in electrostatic adhesion. For example, it is possible to prevent the powder particles from being blown off by the air flow during coating, and a coating film having excellent smoothness is formed.
Hereinafter, the details of the powder coating material of this embodiment will be described.

<Powder particles>
The powder coating material according to the present embodiment contains powder particles having a dielectric loss ratio of 40 × 10 ^-3 or more and 150 × 10 ^-3 or less.
The dielectric loss ratio of the powder particles is 40 × 10 ^-3 or more and 150 × 10 ^-3 or less, preferably 50 × 10 ^-3 or more and 120 × 10 ^-3 or less, and 60 × 10 ^-3 or more and 100. More preferably, it is × 10 ^-3 or less.
The dielectric loss rate of powder particles in a powder coating material is measured by the following method.

[Removal of external additives]
First, in order to remove the external additive, 5.0 g of anionic surfactant (Neogen RK), 995 g of ion-exchanged water, and 5.0 g of powder paint were placed in a 500 ml beaker, and the mixture was shaken with an ultrasonic shaker for 30 minutes. After dispersion, centrifugation was performed at 2,000 rpm for 20 minutes, the supernatant was discarded, and the precipitate was collected. This precipitate is put into a mixed solution of 995 g of ion-exchanged water and 5.0 g of anionic surfactant (Neogen RK), stirred at a rate that does not foam for 60 minutes, and dispersed again with an ultrasonic shaker for 30 minutes. After that, centrifugation was performed at 2,000 rpm for 20 minutes, the supernatant was discarded, and the precipitate was collected.
The recovered precipitate was put into 1,000 g of ion-exchanged water and dispersed at 5,000 rpm for 5 minutes using Ultratarax, and then stirred and dispersed at 150 rpm for 30 minutes with a 4-blade stirrer. , This was filtered with an aspirator. The obtained solid content was put into 1000 g of ion-exchanged water again and dispersed at 5,000 rpm for 5 minutes using Ultratarax, and then stirred and dispersed at 150 rpm for 30 minutes with a 4-blade stirrer. Then, this was filtered with an aspirator. This operation was repeated until the conductivity of the ejector filtrate became 10 μS / cm or less. When the conductivity of the filtrate became 10 uS / cm or less, the solid content was dried by a freeze-dryer (freezing temperature −40 ° C., drying temperature 30 ° C.).
The obtained dry powder was used as powder particles, and the dielectric loss rate was measured by the following method.

[Measurement method of dielectric loss rate of powder particles]
First, 5 g of powder particles are molded into pellets, set between electrodes [SE-71 type solid electrode, manufactured by Ando Electric Co., Ltd.] at 20 ° C. and 60% relative humidity, and LCR meter (4274A type). , Yokogawa Hewlett-Packard), 5V, frequency 100kHz.
The dielectric loss rate is calculated by the following formula (1).
(14.39 / (W × D ² )) × Gx × Tx × 10 ¹² ... Equation (1)
Here, W = 2πf (f: measurement frequency 100 kHz), D: electrode diameter (cm), Gx: conductivity (S), Tx: sample thickness (cm).
The dielectric loss rate of the powder particles is determined, for example, by the amount of water contained in the powder particles, the type of colorant such as titanium oxide contained in the powder particles, the particle size, the presence or absence of hydrophobicity, and the content thereof. Will be done.

Further, the powder particles preferably contain a thermosetting resin and a thermosetting agent. The powder particles may contain colloidal silica, a colorant, and other additives, if necessary.

[Thermosetting resin]
The thermosetting resin is a resin having a thermosetting reactive group. Examples of the thermosetting resin include various types of resins conventionally used as powder particles of powder coating materials.
The thermosetting resin is preferably a water-insoluble (hydrophobic) resin. When a water-insoluble (hydrophobic) resin is applied as the thermosetting resin, the environmental dependence of the charging characteristics of the powder coating material (powder particles) is reduced. Further, when the powder particles are produced by the aggregation and coalescence method, the thermosetting resin is preferably a water-insoluble (hydrophobic) resin from the viewpoint of realizing emulsification and dispersion in an aqueous medium. The water-insoluble (hydrophobic) means that the amount of the target substance dissolved in 100 parts by mass of water at 25 ° C. is less than 5 parts by mass.

Examples of the thermosetting resin include at least one selected from the group consisting of a thermosetting (meth) acrylic resin and a thermosetting polyester resin. Among the thermosetting resins, the thermosetting polyester resin is preferable from the viewpoints that the charge train is easily controlled at the time of painting, the strength of the coating film, the beauty of the finish, and the like.
Examples of the thermosetting reactive group contained in the thermosetting polyester resin include an epoxy group, a carboxyl group, a hydroxyl group, an amide group, an amino group, an acid anhydride group, a blocked isocyanate group and the like, but the synthesis is easy. From the point of view, carboxyl groups and hydroxyl groups are preferable.

-Thermosetting polyester resin-
The thermosetting polyester resin is a polyester resin having a curing reactive group. Examples of the thermosetting reactive group contained in the thermosetting polyester resin include an epoxy group, a carboxyl group, a hydroxyl group, an amide group, an amino group, an acid anhydride group, a blocked isocyanate group and the like, but from the viewpoint of easy synthesis. , Carboxyl groups, and hydroxyl groups are preferred.

The thermosetting polyester resin is, for example, a polycondensate obtained by at least polycondensing a polybasic acid and a polyhydric alcohol.
The thermosetting reactive group of the thermosetting polyester resin is introduced by adjusting the amount of the polybasic acid and the polyhydric alcohol used in synthesizing the polyester resin. By this adjustment, a thermosetting polyester resin having at least one of a carboxyl group and a hydroxyl group can be obtained as a thermosetting reactive group.
Further, after synthesizing the polyester resin, a thermosetting reactive group may be introduced to obtain a thermosetting polyester resin.

Examples of the polybasic acid include terephthalic acid, isophthalic acid, phthalic acid, methylterephthalic acid, trimellitic acid, pyromellitic acid, and anhydrides of these acids; Anhydrous; maleic acid, itaconic acid, anhydrides of these acids; fumaric acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid hexahydrophthalic acid, methylhexahydrophthalic acid, anhydrides of these acids; cyclohexanedicarboxylic acid, 2,6 -Naphthalenedicarboxylic acid and the like can be mentioned.

Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and neopentyl. Glycer, triethylene glycol, bis (hydroxyethyl) terephthalate, cyclohexanedimethanol, octanediol, diethylpropanediol, butylethylpropanediol, 2-methyl-1,3-propanediol, 2,2,4-trimethylpentanediol, Hydrogenated bisphenol A, ethylene oxide adduct of hydrogenated bisphenol A, propylene oxide adduct of hydrogenated bisphenol A, trimethylolethane, trimethylolpropane, glycerin, pentaerythritol, trishydroxyethylisocyanurate, hydroxypivalylhydroxypivalate And so on.

The thermosetting polyester resin may be polycondensed with a monomer other than the polybasic acid and the polyhydric alcohol.
Examples of other monomers include compounds having a carboxyl group and a fatty acid in one molecule (for example, dimethanol propionic acid, hydroxypivalate, etc.) and monoepoxy compounds (for example, "Cadura E10 (manufactured by Shell)". (Glysidyl ester of branched aliphatic carboxylic acid, etc.), various monohydric alcohols (eg, methanol, propanol, butanol, benzyl alcohol, etc.), various monovalent basic acids (eg, benzoic acid, p-tert-butyl benzoic acid, etc.) Acids, etc.), various fatty acids (eg, castor oil fatty acid, palm oil fatty acid, soybean oil fatty acid, etc.) and the like.

The structure of the thermosetting polyester resin may be a branched structure or a linear structure.

The thermosetting polyester resin preferably has a total acid value and hydroxyl value of 10 mgKOH / g or more and 250 mgKOH / g or less, and a number average molecular weight of 1000 or more and 100,000 or less.
When the total of the acid value and the hydroxyl value is within the above range, the smoothness and mechanical properties of the coating film are likely to be improved. When the number average molecular weight is within the above range, the smoothness and mechanical properties of the coating film are improved, and the storage stability of the powder coating material is also likely to be improved.

The measurement of the acid value and the hydroxyl value of the thermosetting polyester resin conforms to JIS K-0070-1992. Further, the measurement of the number average molecular weight of the thermosetting polyester resin is the same as the measurement of the number average molecular weight of the thermosetting (meth) acrylic resin described later.

-Thermosetting (meth) acrylic resin-
The thermosetting (meth) acrylic resin is a (meth) acrylic resin having a thermosetting reactive group. For the introduction of the thermosetting reactive group into the thermosetting (meth) acrylic resin, it is preferable to use a vinyl monomer having a thermosetting reactive group. The vinyl monomer having a thermosetting reactive group may be a (meth) acrylic monomer (a monomer having a (meth) acryloyl group) or a vinyl monomer other than the (meth) acrylic monomer. It may be a monomer.

Here, examples of the thermosetting reactive group of the thermosetting (meth) acrylic resin include an epoxy group, a carboxyl group, a hydroxyl group, an amide group, an amino group, an acid anhydride group, and a (blocking) isocyanate group. .. Among these, the thermosetting reactive group of the (meth) acrylic resin is at least one selected from the group consisting of an epoxy group, a carboxyl group, and a hydroxyl group from the viewpoint of easy production of the (meth) acrylic resin. Is preferable. In particular, from the viewpoint of excellent storage stability of the powder coating material and the appearance of the coating film, it is more preferable that at least one thermosetting reactive group is an epoxy group.

Examples of the vinyl monomer having an epoxy group as a curable reactive group include various chain-type epoxy group-containing monomers (for example, glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, glycidyl vinyl ether, and allyl). (Glysidyl ether, etc.), various (2-oxo-1,3-oxolan) group-containing vinyl monomers (for example, (2-oxo-1,3-oxolan) methyl (meth) acrylate, etc.), various alicyclic formulas Examples thereof include epoxy group-containing vinyl monomers (for example, 3,4-epoxide cyclohexyl (meth) acrylate, 3,4-epoxide cyclohexylmethyl (meth) acrylate, 3,4-epoxide cyclohexylethyl (meth) acrylate, etc.).

Examples of the vinyl monomer having a carboxyl group as a curable reactive group include various carboxyl group-containing monomers (for example, (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, etc.) and various types. Monoesters of α, β-unsaturated dicarboxylic acid and a monohydric alcohol having 1 or more and 18 or less carbon atoms (for example, monomethyl fumarate, monoethyl fumarate, monobutyl fumarate, monoisobutyl fumarate, monotert-butyl fumarate). , Monohexyl fumarate, monooctyl fumarate, mono2-ethylhexyl fumarate, monomethyl maleate, monoethyl maleate, monobutyl maleate, monoisobutyl maleate, monotert-butyl maleate, monooctyl maleate, monooctyl maleate, Mono2-ethylhexyl maleate, etc.), monoalkyl ester of itaconic acid (eg, monomethyl itaconic acid, monoethyl itaconic acid, monobutyl itaconate, monoisobutyl itaconate, monohexyl itaconate, monooctyl itaconate, mono2-ethylhexyl itaconate, etc.) And so on.

Examples of the vinyl monomer having a hydroxyl group as a curable reactive group include various hydroxyl group-containing (meth) acrylates (for example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 3-hydroxy. Propyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, etc.) , Addition reaction products of the above various hydroxyl group-containing (meth) acrylates and ε-caprolactone, various hydroxyl group-containing vinyl ethers (eg 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl). Vinyl ether, 3-hydroxybutyl vinyl ether, 2-hydroxy-2-methylpropyl vinyl ether, 5-hydroxypentyl vinyl ether, 6-hydroxyhexyl vinyl ether, etc.), addition reaction products of the above various hydroxyl group-containing vinyl ethers and ε-caprolactone, various Hydroxyl-containing allyl ethers (eg, 2-hydroxyethyl (meth) allyl ether, 3-hydroxypropyl (meth) allyl ether, 2-hydroxypropyl (meth) allyl ether, 4-hydroxybutyl (meth) allyl ether, 3- Hydroxybutyl (meth) allyl ether, 2-hydroxy-2-methylpropyl (meth) allyl ether, 5-hydroxypentyl (meth) allyl ether, 6-hydroxyhexyl (meth) allyl ether, etc.), various hydroxyl group-containing allyls described above. Examples thereof include addition reaction products of ether and ε-caprolactone.

In addition to the (meth) acrylic monomer, the thermosetting (meth) acrylic resin may be copolymerized with another vinyl monomer having no thermosetting reactive group.
Other vinyl monomers include various α-olefins (eg ethylene, propylene, butene-1, etc.), various halogenated olefins excluding fluoroolefins (eg vinyl chloride, vinylidene chloride, etc.), and various aromatic vinyls. Diesters of monomers (eg, styrene, α-methylstyrene, vinyltoluene, etc.), various unsaturated dicarboxylic acids and monovalent alcohols with 1 to 18 carbon atoms (eg, dimethyl fumarate, diethyl fumarate, dibutyl fumarate). , Dioctyl fumarate, dimethyl maleate, diethyl maleate, dibutyl maleate, dioctyl maleate, dimethyl itaconate, diethyl itaconate, dibutyl itaconate, dioctyl itaconate, etc.), various acid anhydride group-containing monomers ( For example, maleic anhydride, itaconic anhydride, citraconic anhydride, (meth) acrylic acid, tetrahydrophthalic anhydride, etc.), various steric acid phosphate group-containing monomers (eg, diethyl-2- (meth) acryloyloxyethyl phosphate). , Dibutyl-2- (meth) acryloyloxybutyl phosphate, dioctyl-2- (maecryloyloxyethyl phosphate, diphenyl-2- (meth) acryloyloxyethyl phosphate, etc.), various hydrolyzable silyl group-containing singles Metrics (eg, γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropyltriethoxysilane, γ- (meth) acryloyloxypropylmethyldimethoxysilane, etc.), various aliphatic carboxylic acid vinyls (for example, For example, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, branched aliphatic carboxylate vinyl having 9 or more and 11 or less carbon atoms, vinyl stearate. Etc.), various vinyl esters of carboxylic acid having a cyclic structure (for example, vinyl cyclohexanecarboxylate, vinyl methylcyclohexanecarboxylate, vinyl benzoate, p-tert-vinyl benzoate, etc.) and the like.

In the thermosetting (meth) acrylic resin, when a vinyl monomer other than the (meth) acrylic monomer is used as the vinyl monomer having a thermosetting reactive group, the thermosetting (meth) acrylic resin has a curable reactive group. Do not use acrylic monomers.
Examples of the acrylic monomer having no curable reactive group include (meth) acrylic acid alkyl ester (for example, (meth) methyl acrylate, (meth) ethyl acrylate, (meth) acrylic acid n-propyl, and (meth) acrylic acid. ) Isopropyl acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, (meth) acrylic 2-Ethylhexyl acid, n-octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethyloctyl (meth) acrylate, dodecyl (meth) acrylate, isodecyl (meth) acrylate, (meth) acrylic acid Lauryl, stearyl (meth) acrylate, etc.), various (meth) acrylic acid aryl esters (eg, benzyl (meth) acrylate, phenyl (meth) acrylate, phenoxyethyl (meth) acrylate, etc.), various alkylcarbi Thor (meth) acrylate (eg ethylcarbitol (meth) acrylate, etc.), various other (meth) acrylic acid esters (eg, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyl (meth)) Acrylate, dicyclopentenyloxyethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, etc.), various amino group-containing amide-based unsaturated monomers (eg, N-dimethylaminoethyl (meth) acrylamide, N- Diethylaminoethyl (meth) acrylamide, N-dimethylaminopropyl (meth) acrylamide, N-diethylaminopropyl (meth) acrylamide, etc.), various dialkylaminoalkyl (meth) acrylates (eg, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (eg, dimethylaminoethyl (meth) acrylate) (Meta) acrylate, etc.), various amino group-containing monomers (eg, tert-butylaminoethyl (meth) acrylate, tert-butylaminopropyl (meth) acrylate, aziridinylethyl (meth) acrylate, pyrrolidinyl ethyl (eg Meta) acrylate, piperidinyl ethyl (meth) acrylate, etc.).

The thermosetting (meth) acrylic resin is preferably an acrylic resin having a number average molecular weight of 1,000 or more and 20,000 or less (preferably 1,500 or more and 15,000 or less).
When the number average molecular weight is within the above range, the smoothness and mechanical properties of the coating film are likely to be improved.

The weight average molecular weight and the number average molecular weight of the thermosetting (meth) acrylic resin are measured by gel permeation chromatography (GPC). The molecular weight measurement by GPC is carried out by using GPC / HLC-8120GPC manufactured by Tosoh Corporation as a measuring device and column / TSKgel SuperHM-M (15 cm) manufactured by Tosoh Corporation in a THF solvent. The weight average molecular weight and the number average molecular weight are calculated from this measurement result using a molecular weight calibration curve prepared from a monodisperse polystyrene standard sample.

The thermosetting resin may be used alone or in combination of two or more.

The content of the thermosetting resin is preferably 20% by mass or more and 99% by mass or less, and preferably 30% by mass or more and 95% by mass or less with respect to the entire powder particles.
As will be described later, when the powder particles are core-shell type particles and a thermosetting resin is applied as the resin of the resin coating portion, the content of the thermosetting resin is the core portion. And the content of the total thermosetting resin in the resin coating portion.

[Thermosetting agent]
The thermosetting agent is selected according to the type of thermosetting reactive group of the thermosetting resin.
Here, the thermosetting agent means a compound having a functional group capable of reacting with a thermosetting reactive group which is a terminal group of a thermosetting resin.

When the thermosetting reactive group of the thermosetting resin is a carboxyl group, examples of the thermosetting agent include various epoxy resins (for example, polyglycidyl ether of bisphenol A) and epoxy group-containing acrylic resins (for example, glycidyl group-containing acrylic). Resins, etc.), polyglycidyl ethers of various polyvalent alcohols (eg, 1,6-hexanediol, trimethylolpropane, trimethylolethane, etc.), various polyvalent carboxylic acids (eg, phthalic acid, terephthalic acid, isophthalic acid, hexa). Polyglycidyl esters of hydrophthalic acid, methylhexahydrophthalic acid, trimellitic acid, pyromellitic acid, etc., various alicyclic epoxy group-containing compounds (eg, bis (3,4-epoxycyclohexyl) methyladipate, etc.), hydroxy Examples thereof include amides (eg, triglycidyl isocyanurate, β-hydroxyalkylamide, etc.).

When the thermosetting reactive group of the thermosetting resin is a hydroxyl group, examples of the thermosetting agent include polyblock isocyanate and aminoplast. Examples of the polyblock polyisocyanate include various aliphatic diisocyanates (for example, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, etc.), various cyclic aliphatic diisocyanates (for example, xylylene diisocyanate, isophorone diisocyanate, etc.), and various aromatic diisocyanates (for example, xylylene diisocyanate, isophorone diisocyanate, etc.). Organic diisocyanates such as tolylene diisocyanates, 4,4'-diphenylmethane diisocyanates, etc .; adducts of these organic diisocyanates with polyhydric alcohols, low molecular weight polyester resins (eg, polyester polyols), water, etc .; Polymer (polymer containing isocyanurate-type polyisocyanate compound); various polyisocyanate compounds such as isocyanate / biuret are blocked with a known and commonly used blocking agent; self-blocking having a uretdione bond as a structural unit. Examples thereof include polyisocyanate compounds.

When the thermosetting reactive group of the thermosetting resin is an epoxy group, the thermosetting agents include, for example, succinic acid, glutaric acid, adipic acid, pimelli acid, suberic acid, azelaic acid, sebatic acid, dodecanedioic acid and aicosan. Diacid, maleic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, trimellitic acid, pyromellitic acid, tetrahydrophthalic acid, hexahydrophthalic acid, cyclohexene-1,2-dicarboxylic acid, trimellitic acid, pyromerit Acids such as acids; anhydrides of these acids; urethane modified products of these acids and the like can be mentioned. Among these, as the thermosetting agent, aliphatic dibasic acid is preferable from the viewpoint of coating film physical characteristics and storage stability, and dodecane diic acid is particularly preferable from the viewpoint of coating film physical properties.

The thermosetting agent may be used alone or in combination of two or more.

The content of the thermosetting agent is preferably 1% by mass or more and 30% by mass or less, and preferably 3% by mass or more and 20% by mass or less with respect to the thermosetting resin.
As will be described later, when the powder particles are core-shell type particles and a thermosetting resin is applied as the resin of the resin coating portion, the content of the thermosetting agent is the core portion and the content of the thermosetting agent. It means the content of the resin coating portion with respect to the total thermosetting resin.

[Coloidal silica]
The powder particles according to the present embodiment preferably contain colloidal silica from the viewpoint of suppressing electrostatic repulsion. In the present embodiment, colloidal silica refers to silica particles having the property of becoming colloidal in a liquid medium.
Colloidal silica is preferably contained in the powder particles in a state of having water of crystallization.
For example, the dielectric loss rate of the powder particles is adjusted by adding colloidal silica having a water content of 2% by mass or more to the powder particles.
The water content of colloidal silica is preferably 2% by mass or more, more preferably 3% by mass or more, and further preferably 4% by mass or more.
The volume average particle size of colloidal silica is preferably 1 nm or more and 100 nm or less, more preferably 8 nm or more and 80 nm or less, and further preferably 15 nm or more and 50 nm or less.
The volume average particle size is measured using Nanotrack UPA-ST (dynamic light scattering type particle size measuring device manufactured by Microtrac Bell). The measurement conditions are that the sample concentration is 20% and the measurement time is 300 seconds. This device measures the particle size by utilizing the Brownian motion of the dispersoid, and measures the particle size by irradiating the solution with laser light and detecting the scattered light. Based on the measured particle size distribution, draw a cumulative distribution of the volume of each particle from the small diameter side for each divided particle size range (channel), and the particle size that makes the cumulative 50% is the volume average particle size. demand.

The powder particles according to the present embodiment may contain colloidal silica alone or in combination of two or more.
The content of colloidal silica is preferably 3% by mass or more and 20% by mass or less, more preferably 4% by mass or more and 20% by mass or less, and 5% by mass or more and 20% by mass, based on the total mass of the powder particles. It is more preferably mass% or less.

[Colorant]
Examples of the colorant include pigments. As the colorant, a dye may be used in combination with the pigment.
Pigments include, for example, iron oxide (eg, red iron oxide, etc.), titanium oxide, titanium yellow, zinc flower, lead white, zinc sulfide, lithopon, antimony oxide, cobalt blue, carbon black and other inorganic pigments; quinacridone red, phthalocyanine blue, etc. Examples thereof include organic pigments such as phthalocyanine green, permanent red, Hansa yellow, indanslen blue, brilliant first scarlet, and benzimidazolone yellow.
Other examples of the pigment include a bright pigment. Examples of the brilliant pigment include metal powders such as pearl pigments, aluminum powders and stainless steel powders; metal flakes; glass beads; glass flakes; mica; phosphotric iron oxide (MIO) and the like.

The colorant may be used alone or in combination of two or more.

The content of the colorant is selected according to the type of pigment and the color, lightness, depth and the like required for the coating film.
For example, the content of the colorant is preferably 1% by mass or more and 70% by mass or less, and more preferably 2% by mass or more and 60% by mass or less, based on the total resin constituting the powder particles.

Here, the powder particles may contain a coloring pigment other than the white pigment as a coloring agent together with the white pigment. When the powder particles contain the white pigment together with the coloring pigment, the color of the surface of the object to be coated is concealed by the coating film, and the color developing property of the coloring pigment is improved. Examples of the white pigment include well-known white pigments such as titanium oxide, barium sulfate, zinc oxide, and calcium carbonate, but titanium oxide is preferable in terms of high whiteness (that is, high hiding power).

In the present embodiment, when the powder paint is a clear paint, the content of titanium oxide is preferably less than 25% by mass and less than 20% by mass with respect to the total mass of the powder particles. Is more preferably less than 10% by mass, particularly preferably less than 5% by mass, and most preferably less than 1% by mass. The lower limit is not particularly limited and may be 0% by mass.
When the powder paint is a clear paint, it is presumed that electrostatic repulsion is likely to occur because the colorant contained in the powder particles is little or no. Therefore, when the dielectric loss rate of the powder particles is 40 × 10 ^-3 or more in the clear paint, it is more electrostatic than when the dielectric loss rate of the powder particles is 40 × 10 ^-3 or more in the colored paint. It is considered that the occurrence of repulsion is greatly suppressed.
Further, in the present embodiment, when the powder coating material is a colored coating material, the content of titanium oxide is preferably 25% by mass or more and 50% by mass or less, and is 30% by mass or more and 50% by mass or less. Is more preferable.
In the present embodiment, when the powder particles contain titanium oxide, the titanium oxide is preferably titanium oxide produced by the sulfuric acid method.
Examples of the method for producing titanium oxide include a chlorine method and a sulfuric acid method. However, from the viewpoint that the dielectric loss rate of titanium oxide itself is high and electrostatic repulsion is further suppressed, titanium oxide by the sulfuric acid method is used in this embodiment. Is preferable.

[Metal ion of divalent or higher]
The powder particles may contain divalent or higher metal ions (hereinafter, also simply referred to as “metal ions”). As will be described later, this metal ion is a component contained in both the core portion and the resin coating portion of the powder particles when the powder particles are core-shell type particles.
When the powder particles contain metal ions having a valence of 2 or more, the powder particles form an ion cross-linking by the metal ions. For example, the functional group of the thermosetting resin (for example, when the thermosetting polyester resin is used as the thermosetting resin, the carboxyl group or the hydroxyl group of the thermosetting polyester resin) and the metal ion interact with each other and ion-crosslinked. To form. Due to this ion cross-linking, inclusions of powder particles (heat curing agent, colorant added as needed other than heat curing agent, other additives, etc.) are deposited on the surface of the powder particles (so-called). , Bleed) is suppressed, and the storability is likely to be improved. Further, in this ion cross-linking, the bond of the ion cross-linking is broken by heating during thermal curing after coating the powder coating material, so that the melt viscosity of the powder particles is lowered and a highly smooth coating film is formed. It will be easier to do.

Examples of the metal ion include a metal ion having a valence of 2 or more and a valence of 4 or less. Specifically, examples of the metal ion include at least one metal ion selected from the group consisting of aluminum ion, magnesium ion, iron ion, zinc ion, and calcium ion.

Examples of the source of the metal ion (compound contained in the powder particles as an additive) include a metal salt, an inorganic metal salt polymer, a metal complex and the like. This metal salt and the inorganic metal salt polymer are added to the powder particles as a coagulant, for example, when the powder particles are produced by the coagulation-union method.
Examples of the metal salt include aluminum sulfate, aluminum chloride, magnesium chloride, magnesium sulfate, iron (II) chloride, zinc chloride, calcium chloride, calcium sulfate and the like.
Examples of the inorganic metal salt polymer include polyaluminum chloride, polyaluminum hydroxide, polyiron (II) sulfate, and calcium polysulfide.
Examples of the metal complex include a metal salt of an aminocarboxylic acid. Specific examples of the metal complex include known chelate-based metal salts such as ethylenediamine 4acetic acid, propanediamine 4acetic acid, nitrile 3 acetic acid, triethylenetetramine 6 acetic acid, and diethylenetriamine 5 acetic acid (eg, calcium salt, etc.). Magnesium salt, iron salt, aluminum salt, etc.) and the like.

The source of these metal ions may be added as a mere additive, not as a flocculant.

The higher the valence of the metal ion, the easier it is to form a mesh-like ion crosslink, which is suitable in terms of the smoothness of the coating film and the storage property of the powder coating material. Therefore, Al ion is preferable as the metal ion. That is, as a source of metal ions, aluminum salts (for example, aluminum sulfate, aluminum chloride, etc.) and aluminum salt polymers (for example, polyaluminum chloride, polyaluminum hydroxide, etc.) are preferable. Further, in terms of the smoothness of the coating film and the storage property of the powder coating material, even if the valences of the metal ions are the same among the sources of the metal ions, the inorganic metal salt polymer is compared with the metal salt. preferable. Therefore, as a source of metal ions, an aluminum salt polymer (for example, polyaluminum chloride, polyaluminum hydroxide, etc.) is particularly preferable.

The content of the metal ion is preferably 0.002% by mass or more and 0.2% by mass or less, preferably 0.005% by mass, based on the entire powder particles in terms of the smoothness of the coating film and the storage property of the powder coating material. % Or more and 0.15% by mass or less are more preferable.
When the content of the metal ion is 0.002% by mass or more, appropriate ion cross-linking by the metal ion is formed, bleeding of the powder particles is suppressed, and the storability of the coating paint is easily improved. On the other hand, when the content of the metal ion is 0.2% by mass or less, the formation of excessive ion crosslinks due to the metal ion is suppressed, and the smoothness of the coating film tends to be improved.

Here, when the powder particles are produced by the aggregation and coalescence method, the source of the metal ion (metal salt, metal salt polymer) added as the aggregating agent contributes to the control of the particle size distribution and shape of the powder particles. do.

Specifically, the higher the valence of the metal ion, the more suitable it is to obtain a narrower particle size distribution. Further, in terms of obtaining a narrow particle size distribution, a metal salt polymer is more suitable than a metal salt even if the valences of the metal ions are the same. Therefore, from these points as well, aluminum salts (for example, aluminum sulfate, aluminum chloride, etc.) and aluminum salt polymers (for example, polyaluminum chloride, polyaluminum hydroxide, etc.) are preferable as the source of metal ions, and the aluminum salt weight is preferable. A coalescence (eg, polyaluminum chloride, polyaluminum hydroxide, etc.) is particularly preferred.

Further, when the flocculant is added so that the content of the metal ion is 0.002% by mass or more, the aggregation of the resin particles in the aqueous medium proceeds, which contributes to the realization of a narrow particle size distribution. Further, the aggregation of the resin particles to be the resin coating progresses with respect to the aggregated particles to be the core portion, which contributes to the realization of the formation of the resin coating portion on the entire surface of the core portion. On the other hand, when an aggregating agent is added so that the content of metal ions is 0.2% by mass or less, excessive formation of ion cross-linking in the agglomerated particles is suppressed, and the powder produced at the time of fusion and coalescence. It becomes easier for the shape of the particles to approach a spherical shape. Therefore, from these points as well, the content of the metal ion is preferably 0.002% by mass or more and 0.2% by mass or less, and more preferably 0.005% by mass or more and 0.15% by mass or less.

The content of metal ions is measured by quantitative analysis of the fluorescent X-ray intensity of the powder particles. Specifically, for example, first, a resin and a source of metal ions are mixed to obtain a resin mixture having a known concentration of metal ions. A pellet sample of 200 mg of this resin mixture is obtained using a tablet molding machine having a diameter of 13 mm. The mass of this pellet sample is precisely weighed, and the fluorescent X-ray intensity of the pellet sample is measured to obtain the peak intensity. Similarly, the pellet sample in which the amount of the metal ion source added is changed is also measured, and a calibration curve is prepared from these results. Then, using this calibration curve, the content of metal ions in the powder particles to be measured is quantitatively analyzed.

As a method for adjusting the content of the metal ion, for example, 1) a method for adjusting the addition amount of the metal ion source, and 2) when the powder particles are produced by the aggregation and coalescence method, the metal ion is used in the aggregation step. After adding a flocculant (eg, a metal salt or metal salt polymer) as a source, chelating agents (eg, EDTA (ethylenediaminetetraacetic acid), DTPA (diethylenetriaminepentaacetic acid), NTA (nitrilotriacetic acid)) are added at the end of the flocculation step. Etc.), a method of forming a complex with the metal ion with a chelating agent, and removing the complex salt formed in the subsequent washing step or the like to adjust the content of the metal ion and the like can be mentioned.

[Other additives]
Examples of other additives include various additives used in powder coating materials.
Specifically, as other additives, for example, an anti-foaming (armpit) agent (for example, benzoin, benzoin derivative, etc.), a curing accelerator (amine compound, imidazole compound, cationic polymerization catalyst, etc.), a surface conditioner (for example). Leveling agents), plasticizers, charge control agents, antioxidants, pigment dispersants, flame retardants, flow-imparting agents and the like.

[Core-shell type particles]
In the present embodiment, the powder particles may be core-shell type particles having a core portion containing a thermosetting resin and a thermosetting agent, and a resin coating portion covering the surface of the core portion. ..
At this time, in addition to the thermosetting resin and the thermosetting agent, the core portion may contain the above-mentioned colloidal silica, a colorant, other additives and the like, if necessary.

Further, the resin-coated portion of the core-shell type particles will be described below.
The resin coating portion may be composed of only the resin, or may contain other components (thermosetting agent described as a component constituting the core portion, other additives, etc.).
However, from the viewpoint of reducing bleeding, the resin coating portion is preferably made of only resin. Even when the resin-coated portion contains components other than the resin, the resin may occupy 90% by mass or more (preferably 95% by mass or more) of the entire resin-coated portion.

The resin constituting the resin coating portion may be a non-curable resin or a thermosetting resin, but is a thermosetting resin from the viewpoint of improving the curing density (crosslinking density) of the coating film. That's good.
When a thermosetting resin is applied as the resin of the resin coating portion, examples of the thermosetting resin include those similar to those of the thermosetting resin of the core portion, and preferred examples thereof are also the same. However, the thermosetting resin of the resin coating portion may be the same type of resin as the thermosetting resin of the core portion, or may be a different resin.
When a non-curable resin is applied as the resin of the resin coating portion, at least one selected from the group consisting of an acrylic resin and a polyester resin is preferably mentioned as the non-curable resin.

The coverage of the resin-coated portion is preferably 30% or more and 100% or less, and more preferably 50% or more and 100% or less, from the viewpoint of suppressing bleeding.

The coverage of the resin coating is a value obtained by XPS (X-ray photoelectron spectroscopy) measurement for the coverage of the resin coating on the surface of the powder particles.
Specifically, XPS measurement is carried out by using JPS-9000MX manufactured by JEOL Ltd. as a measuring device, using MgKα ray as an X-ray source, setting an acceleration voltage of 10 kV and an emission current of 30 mA. ..
By peak-separating the component caused by the material of the core portion of the powder particle surface and the component caused by the material of the coated resin portion from the spectrum obtained under the above conditions, the coverage of the resin coated portion on the surface of the powder particle is increased. Is quantified. Peak separation separates the measured spectrum into components using curve fitting by the least squares method.
As the component spectrum that is the basis of separation, the spectrum obtained by independently measuring the thermosetting resin, the curing agent, the pigment, the additive, and the coating resin used for producing the powder particles is used. Then, the coverage is obtained from the ratio of the spectral intensities resulting from the coating resin to the total of the total spectral intensities obtained from the powder particles.

The thickness of the resin coating portion is preferably 0.2 μm or more and 4 μm or less, and more preferably 0.3 μm or more and 3 μm or less, from the viewpoint of suppressing bleeding.
The thickness of the resin coating portion is a value measured by the following method. Thin sections are prepared by embedding powder particles in epoxy resin or the like and cutting them with a diamond knife or the like. This thin section is observed with a transmission electron microscope (TEM) or the like, and cross-sectional images of a plurality of powder particles are taken. The thickness of the resin coating portion is measured at 20 points from the cross-sectional image of the powder particles, and the average value is adopted. When it is difficult to observe the resin coating portion in the cross-sectional image with clear powder paint or the like, it is possible to facilitate the measurement by observing the resin coating portion by dyeing.

[Preferable characteristics of powder particles]
-Volume particle size distribution index GSDv-
The volume particle size distribution index GSDv of the powder particles is preferably 1.50 or less, more preferably 1.40 or less, and more preferably 1.30 or less in terms of the smoothness of the coating film and the storage property of the powder coating. Is more preferable. When the volume particle size distribution index GSDv is 1.40 or less, deterioration of the smoothness of the coating film is suppressed.

-Volume average particle size D50v-
The volume average particle size D50v of the powder particles is preferably 1 μm or more and 25 μm or less, more preferably 2 μm or more and 20 μm or less, and further preferably 3 μm or more and 15 μm or less, from the viewpoint of forming a coating film having high smoothness with a small amount.

-Average circularity-
Further, the average circularity of the powder particles is preferably 0.97 or more, more preferably 0.98 or more, still more preferably 0.99 or more.
When the average circularity of the powder particles is 0.97 or more, it is excellent in suppressing electrostatic repulsion.
The details of the reason why the suppression of electrostatic repulsion is superior are unknown, but if the average circularity of the powder particles is 0.97 or more, the density of the powder particles in the coating film becomes high when the coating film is formed. Since the surface area per unit mass of the powder particles is small, the charge retention amount of the powder particles in the coating film is also small, and it is presumed that the electrostatic repulsion between the powder particles is suppressed.

Here, the volume average particle size D50v of the powder particles and the volume particle size distribution index GSDv use Coulter Multisizer II (manufactured by Beckman Coulter), and the electrolytic solution uses ISOTON-II (manufactured by Beckman Coulter). Is measured.
At the time of measurement, 0.5 mg or more and 50 mg or less of the measurement sample is added to 2 ml of a 5% aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant. This is added to 100 ml or more and 150 ml or less of the electrolytic solution.
The electrolytic solution in which the sample is suspended is dispersed for 1 minute with an ultrasonic disperser, and the particle size distribution of particles having a particle size in the range of 2 μm or more and 60 μm or less is obtained by using an aperture with an aperture diameter of 100 μm by Coulter Multisizer II. taking measurement. The number of particles to be sampled is 50,000.
Draw a cumulative distribution of the volume from the small diameter side for each particle size range (channel) divided based on the measured particle size distribution, and the particle size with a cumulative total of 16% is the volume particle size D16v and the cumulative 50%. The particle size is defined as the volume average particle size D50v, and the particle size having a cumulative total of 84% is defined as the volume particle size D84v.
Then, the volume particle size distribution index (GSDv) is calculated as (D84v / D16v) ^1/2 .

Further, the average circularity of the powder particles is measured by using a flow type particle image analyzer "FPIA-3000 (manufactured by Sysmex Corporation)". Specifically, a surfactant (alkylbenzene sulfonate) as a dispersant is added in an amount of 100 ml or more and 150 ml or less of water from which impurities have been removed in advance, and 0.1 ml or more and 0.5 ml or less are added as a dispersant. Add 1 g or more and 0.5 g or less. The suspension in which the measurement sample is dispersed is subjected to a dispersion treatment with an ultrasonic disperser for 1 minute or more and 3 minutes or less, and the concentration of the dispersion liquid is 3,000 pieces / μl or more and 10,000 pieces / μl or less. The average circularity of the powder particles is measured for this dispersion using a flow-type particle image analyzer.

Here, the average circularity of the powder particles is a value obtained by obtaining the circularity (Ci) of each of the n particles measured for the powder particles, and then calculated by the following formula. However, in the following formula, Ci indicates circularity (= circumference of a circle equal to the projected area of particles / circumference of a projected particle image), and fi indicates the frequency of powder particles.

-Moisture content-
From the viewpoint of suppressing electrostatic repulsion, the water content of the powder particles is preferably 0.1% by mass or more and 5% by mass or less, and 0.2% by mass or more and 4% by mass with respect to the total mass of the powder particles. % Or less is more preferable.
The water content of the powder particles is measured by igniting to 100 ° C. by TGA.

<Inorganic particles>
The powder particles of the present embodiment preferably contain inorganic particles.
The inorganic particles are externally attached to the surface of the powder particles.
The external addition method is not particularly limited, and an external addition method known in the field of powder coating material can be used.
Examples of the inorganic particles include SiO ₂ , TiO ₂ , Al ₂ O ₃ , CuO, ZnO, SnO ₂ , CeO ₂ , Fe ₂ O ₃ , MgO, BaO, CaO, K ₂ O, Na ₂ O, ZrO ₂ , CaO. Particles containing SiO ₂ , K ₂ O · ₍ TIO ₂ ) _n , Al ₂ O 3.2 SiO ₂ , CaCO ₃ , MgCO ₃ , BaSO ₄ , and Л ₄ are preferably mentioned.
As the inorganic particles used in the present embodiment, titania particles or zinc oxide particles are preferable, and titania particles are more preferable, from the viewpoint of being superior in suppressing electrostatic repulsion.
As the crystal morphology of the titania particles, rutile type and anatase type are mainly known, and any of them can be used in the present embodiment, but from the viewpoint of light resistance of the coating film, rutile type can be used. Mold is preferred.
In the present embodiment, one kind of inorganic particles may be used alone, or two or more kinds may be used in combination.

〔Particle size〕
The volume average particle size of the inorganic particles is preferably 10 nm or more and 100 nm or less, more preferably 15 nm or more and 90 nm or less, and further preferably 20 nm or more and 80 nm or less.
When the volume average particle size of the inorganic particles is within the above range, the adhesion to the powder particles is excellent, and the smoothness of the coating film obtained by the powder coating material is further improved.
The volume average particle size of the inorganic particles is measured by the following method.
First, the powder coating material to be measured is observed with a scanning electron microscope (SEM). Then, the equivalent circle diameter of each of the 100 inorganic particles to be measured is obtained by image analysis, and the cumulative 50% circle equivalent diameter on the volume basis from the small diameter side in the volume-based distribution is defined as the volume average particle diameter.
For image analysis to obtain the equivalent circle diameter of 100 inorganic particles to be measured, a two-dimensional image with a magnification of 10,000 times is taken using an analysis device (ERA-8900: manufactured by Elionix), and the image analysis software WinROOF. Using (manufactured by Mitani Shoji Co., Ltd.), the projected area is calculated under the condition of 0.010000 μm / pixel, and the equivalent circle diameter is calculated by the formula: circle equivalent diameter = 2 × (projected area / π) ^1/2 .
In order to measure the volume average particle diameter of a plurality of types of external additives from the powder coating material, it is necessary to distinguish each external additive. Specifically, each type of external additive is elementally mapped by SEM-EDX (scanning electron microscope equipped with an energy dispersive X-ray analyzer), and the element derived from each type of external additive is applicable. Distinguish by associating with an external additive.

〔aspect ratio〕
The aspect ratio of the inorganic particles used in this embodiment is preferably 1 or more and 10 or less.
When the aspect ratio is in the above range, the inorganic particles are less likely to be released from the powder particles, and the smoothness of the coating film obtained by the powder coating material is further improved, which is preferable.
The aspect ratio is preferably 1 or more and less than 2, and more preferably 1 or more and 1.5 or less, from the viewpoint of further improving the smoothness of the obtained coating film.
Further, the aspect ratio is preferably 2 or more and 5 or less, and more preferably 2.5 or more and 4.5 or less, from the viewpoint of preventing the release of the inorganic particles from the powder particles.
The above aspect ratio is the image analysis software (Mitani Shoji Co., Ltd., product, manufactured by Mitani Shoji Co., Ltd.) that attaches the image of the scanning electron microscope (SEM, manufactured by Hitachi High-Technologies Co., Ltd., product name: SU8010) to the inorganic particles on the powder particles. By performing particle shape analysis by name: WinROOF), it is measured as the ratio (L / S) of the major axis (L) and the minor axis (S).

[Hydrophobic treatment]
The surface of the inorganic particles used in the present embodiment may be hydrophobized in advance, but from the viewpoint of further improving the smoothness of the coating film obtained by the powder coating material, the inorganic particles are not excessively hydrophobized. Is preferable.
The hydrophobizing treatment can be performed by immersing the inorganic oxide particles in the hydrophobizing agent. The hydrophobizing agent is not particularly limited, and examples thereof include a silane coupling agent, a silicone oil, a titanate-based coupling agent, and an aluminum-based coupling agent. These may be used alone or in combination of two or more.

[Volume resistivity]
The inorganic particles used in the present embodiment preferably have a volume resistivity of 1 × 10 ⁵ Ω · cm or more and 1 × 10 ¹³ Ω · cm or less, and 1 × 10 ⁶ Ω · cm or more and 1 × 10 ¹² Ω ·. It is more preferably cm or less, and further preferably 1 × 10 ⁷ Ω · cm or more and 1 × 10 ¹¹ Ω · cm or less.
When the volume resistivity is within the above range, the smoothness of the coating film obtained by the powder coating material is further improved, which is preferable.
The volume resistivity of the inorganic particles is measured by the following method.
First, the inorganic particles are separated from the powder particles. Then, the separated inorganic particles to be measured are placed on the surface of a circular jig on which a 20 cm ² electrode plate is arranged so as to have a thickness of about 1 mm or more and 3 mm or less to form an inorganic particle layer. The same 20 cm ² electrode plate as described above is placed on this, and the inorganic layer is sandwiched. In order to eliminate voids between the inorganic particles, a load of 4 kg is applied on the electrode plate installed on the inorganic particle layer, and then the thickness (cm) of the inorganic particle layer is measured. Both electrodes above and below the inorganic layer are connected to an electrometer and a high-voltage power generator. A high voltage is applied to both electrodes, and the volume resistivity (Ω · cm) of the inorganic particles is calculated by reading the current value (A) flowing at this time. The above measurement is performed under the conditions of a temperature of 20 ° C. and a relative humidity of 50%. The formula for calculating the volume resistivity (Ω · cm) of inorganic particles is as shown in the formula below.
In the formula, ρ is the volume resistivity (Ω · cm) of the inorganic particles, E is the applied voltage (V), I is the current value (A), I ₀ is the current value (A) at the applied voltage 0V, and L is. Represents the thickness (cm) of the inorganic particle layer. In this embodiment, the volume resistivity when the applied voltage is 1000 V is used.
-Formula: ρ = E × 20 / (I-I ₀ ) / L

〔Content〕
The content of the inorganic particles is preferably 0.1% by mass or more and 3% by mass or less, preferably 0.3% by mass, based on the total mass of the powder particles from the viewpoint of improving the smoothness of the coating film obtained by the powder coating. % Or more and 1.5% by mass or less are more preferable.

(Manufacturing method of powder paint)
Next, a method for producing the powder coating material according to the present embodiment will be described.
The powder coating material according to the present embodiment is obtained by externally adding an external additive to the powder particles after producing the powder particles.

The powder particles may be produced by any of a dry production method (for example, a kneading and pulverizing method, etc.) and a wet production method (for example, an agglomeration coalescence method, a suspension polymerization method, a dissolution suspension method, etc.). The manufacturing method of the powder particles is not particularly limited to these manufacturing methods, and a well-known manufacturing method is adopted.

For example, in the dry manufacturing method, 1) a kneading crushing method in which a thermosetting resin and other raw materials are kneaded, crushed, and classified, and particles obtained by the kneading crushing method are changed in shape by mechanical impact force or thermal energy. There is a dry manufacturing method to make it.
On the other hand, in the wet production method, for example, 1) a dispersion obtained by emulsifying and polymerizing a polymerizable monomer for obtaining a thermosetting resin and a dispersion of other raw materials are mixed, aggregated and heat-fused. , Aggregation and coalescence method to obtain powder particles, 2) Suspension polymerization method in which a polymerizable monomer for obtaining a thermosetting resin and a solution of another raw material are suspended in an aqueous solvent to polymerize, 3. ) There is a dissolution suspension method in which a thermosetting resin and a solution of another raw material are suspended in an aqueous solvent for granulation. The wet method can be preferably used because it has a smaller thermal effect.
Further, by incorporating the above-mentioned colloidal silica in the powder particles in an aqueous solvent, the colloidal silica having a high water content can be contained in the powder particles. As a result, the water content of the powder particles becomes higher, and the dielectric loss rate of the powder particles becomes higher, so that electrostatic repulsion is further suppressed.
Further, the powder particles obtained by the above-mentioned production method may be used as a core portion, and resin particles may be further adhered and heat-fused to obtain powder particles which are core-shell type particles.

Among these, it is preferable to obtain powder particles by the aggregation coalescence method from the viewpoint that the volume particle size distribution index GSDv, the volume average particle size D50v, and the average circularity can be easily controlled within the above preferable ranges.

Hereinafter, a coagulation-union method for producing powder particles, which are core-shell type particles, will be described as an example.
specifically,
In the dispersion liquid in which the first resin particles containing the thermosetting resin and the thermosetting agent are dispersed, the first resin particles and the thermosetting agent are aggregated, or the thermosetting resin and the thermosetting agent are heat-cured. A step of aggregating the composite particles to form a first agglomerated particle (first agglomerated particle forming step) in a dispersion liquid in which the composite particles containing an agent are dispersed.
The first agglomerated particle dispersion liquid in which the first agglomerated particles are dispersed and the second resin particle dispersion liquid in which the second resin particles containing the resin are dispersed are mixed, and the second agglomerated particles are surfaced on the surface of the first agglomerated particles. A step of aggregating the resin particles and forming the second agglomerated particles in which the second resin particles adhere to the surface of the first agglomerated particles (second agglomerated particle forming step).
A step of heating the second agglomerated particle dispersion liquid in which the second agglomerated particles are dispersed to fuse and coalesce the second agglomerated particles (fusion union step).
It is preferable to produce powder particles through the above.
In the powder particles produced by this aggregation and coalescence method, the portion where the first aggregated particles are fused and coalesced becomes the core portion, and the portion where the second resin particles adhering to the surface of the first aggregated particles are fused and coalesced. Is the resin coating part.
Therefore, if the first agglomerated particles formed in the first agglomerated particle forming step are subjected to the fusion union step without going through the second agglomerated particle forming step, and are fused and united in place of the second agglomerated particles, Powder particles having a single layer structure can be obtained.
By further adding colloidal silica in the first aggregation particle aggregation step, powder particles containing colloidal silica can be obtained. Colloidal silica may be added as a dry matter or as a dispersion, but it is preferably added as a dispersion, and more preferably as an aqueous dispersion.

Hereinafter, details of each step will be described.
In the following description, a method for producing powder particles containing a colorant will be described, but the colorant is contained as needed.

<Preparation process for each dispersion>
First, each dispersion used in the aggregation and coalescence method is prepared.
Specifically, the first resin particle dispersion liquid in which the first resin particles containing the thermosetting resin in the core are dispersed, the thermosetting agent dispersion liquid in which the thermosetting agent is dispersed, and the colorant in which the colorant is dispersed. Prepare a second resin particle dispersion liquid in which the second resin particles containing the dispersion liquid and the resin of the resin coating portion are dispersed.
Further, instead of the first resin particle dispersion liquid and the thermosetting agent dispersion liquid, a thermosetting resin for the core portion and a composite particle dispersion liquid in which the composite particles containing the thermosetting agent are dispersed are prepared.
In each step of the powder coating manufacturing method, the first resin particles, the second resin particles, and the composite particles are generally referred to as "resin particles", and the dispersion liquid of these resin particles is referred to as "resin particle dispersion liquid". It will be explained as.

Here, the resin particle dispersion liquid is prepared, for example, by dispersing the resin particles in a dispersion medium with a surfactant.

Examples of the dispersion medium used for the resin particle dispersion liquid include an aqueous medium.
Examples of the aqueous medium include water such as distilled water and ion-exchanged water; alcohols and the like. These may be used alone or in combination of two or more.

Examples of the surfactant include anionic surfactants such as sulfate ester salt type, sulfonate type, phosphoric acid ester type and soap type; cationic surfactants such as amine salt type and quaternary ammonium salt type; Examples thereof include nonionic surfactants such as polyethylene glycol-based, alkylphenol ethylene oxide adduct-based, and polyhydric alcohol-based. Among these, anionic surfactants and cationic surfactants are particularly mentioned. The nonionic surfactant may be used in combination with an anionic surfactant or a cationic surfactant.
The surfactant may be used alone or in combination of two or more.

Examples of the method for dispersing the resin particles in the dispersion medium in the resin particle dispersion liquid include general dispersion methods such as a rotary shear homogenizer, a ball mill having a medium, a sand mill, and a dyno mill. Further, depending on the type of the resin particles, the resin particles may be dispersed in the resin particle dispersion liquid by using, for example, a phase inversion emulsification method.
In the phase inversion emulsification method, the resin to be dispersed is dissolved in a hydrophobic organic solvent in which the resin is soluble, and a base is added to the organic continuous phase (O phase) to neutralize the resin, and then the aqueous medium is used. By adding (W phase), the resin is converted from W / O to O / W (so-called phase inversion) to form a discontinuous phase, and the resin is dispersed in an aqueous medium in the form of particles. be.

Specifically, there are the following methods as a method for preparing the resin particle dispersion liquid.
For example, when the resin particle dispersion is a polyester resin particle dispersion in which polyester resin particles are dispersed, the polyester resin particle dispersion is obtained after heating and melting the raw material monomer and polycondensing the raw material monomer under reduced pressure. The condensate is dissolved by adding a solvent (for example, ethyl acetate, etc.), and further, stirring and phase inversion emulsification are performed while adding a weakly alkaline aqueous solution to the obtained solution.

When the resin particle dispersion liquid is a composite particle dispersion liquid, the thermosetting resin and the thermosetting agent are mixed and dispersed in a dispersion medium (for example, emulsification such as phase inversion emulsification) to disperse the composite particles. Get the liquid

The volume average particle size of the resin particles dispersed in the resin particle dispersion is, for example, preferably 1 μm or less, preferably 0.01 μm or more and 1 μm or less, more preferably 0.08 μm or more and 0.8 μm or less, and 0.1 μm or more. 0.6 μm is more preferable.
The volume average particle size of the resin particles is determined by using the particle size distribution obtained by the measurement of a laser diffraction type particle size distribution measuring device (for example, manufactured by Horiba Seisakusho, LA-700) with respect to the divided particle size range (channel). , The cumulative distribution is subtracted from the small particle size side for the volume, and the particle size that is 50% cumulative with respect to all the particles is measured as the volume average particle size D50v. The volume average particle size of the particles in the other dispersion is also measured in the same manner.

Here, a known emulsification method can be used to prepare the resin particle dispersion, but the obtained particle size distribution is narrow and the volume average particle size is 1 μm or less (particularly 0.08 μm or more and 0.40 μm or less). ) Is effective in the phase inversion emulsification method.

In the phase inversion emulsification method, the resin is dissolved in an organic solvent that dissolves the resin, or an amphipathic organic solvent alone or in a mixed solvent to obtain an oil phase. A small amount of the basic compound is dropped while stirring the oil phase, and water is gradually dropped while further stirring, and water droplets are incorporated into the oil phase. Next, when the amount of water dropped exceeds a certain amount, the oil phase and the water phase are reversed and the oil phase becomes oil droplets. After that, the aqueous dispersion is obtained through the desolvation step of reducing the pressure.

The amphipathic organic solvent means a solvent having a solubility in water at 20 ° C. of at least 5 g / L or more, preferably 10 g / L or more. If the solubility is less than 5 g / L, the effect of accelerating the aqueous treatment rate is poor, and the obtained aqueous dispersion is also inferior in storage stability. Examples of the amphoteric organic solvent include ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-amyl alcohol, isoamyl alcohol, sec-amyl alcohol and tert-amyl. Alcohols, alcohols such as 1-ethyl-1-propanol, 2-methyl-1-butanol, n-hexanol, cyclohexanol, ketones such as methyl ethyl ketone, methyl isobutyl ketone, ethyl butyl ketone, cyclohexanone, isophorone, tetrahydrofuran, dioxane Ethers such as ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, -sec-butyl acetate, -3-methoxybutyl acetate, methyl propionate, ethyl propionate, diethyl carbonate, etc. Esters such as dimethyl carbonate, ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol ethyl ether acetate, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol Glycol derivatives such as monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol ethyl ether acetate, propylene glycol, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol methyl ether acetate, dipropylene glycol monobutyl ether, and further. , 3-methoxy-3-methylbutanol, 3-methoxybutanol, acetonitrile, dimethylformamide, dimethylacetamide, diacetone alcohol, ethyl acetoacetate and the like. These solvents can be used alone or in admixture of two or more.

The thermosetting polyester resin as the thermosetting resin is neutralized with a basic compound when dispersed in an aqueous medium. The neutralization reaction of the thermosetting polyester resin with the carboxyl group is the starting force for making it water-based, and the electric repulsive force between the generated carboxyl anions makes it easier to suppress the aggregation between the particles.
Examples of the basic compound include ammonia and an organic amine compound having a boiling point of 250 ° C. or lower. Examples of preferred organic amine compounds are triethylamine, N, N-diethylethanolamine, N, N-dimethylethanolamine, aminoethanolamine, N-methyl-N, N-diethanolamine, isopropylamine, iminobispropylamine, ethylamine. , Diethylamine, 3-ethoxypropylamine, 3-diethylaminopropylamine, sec-butylamine, propylamine, methylaminopropylamine, dimethylaminopropylamine, methyliminobispropylamine, 3-methoxypropylamine, monoethanolamine, diethanolamine, Examples thereof include triethanolamine, morpholin, N-methylmorpholin, N-ethylmorpholin and the like.
The basic compound is added in an amount that can be at least partially neutralized depending on the carboxyl group contained in the thermosetting polyester resin, that is, 0.2 times or more and 9.0 times or less the equivalent with respect to the carboxyl group. It is preferable, and it is more preferable to add 0.6 times equivalent or more and 2.0 times equivalent or less. If the equivalent is 0.2 times or more, the effect of adding the basic compound is likely to be recognized. If the equivalent is 9.0 times or less, it is considered that the hydrophilicity of the oil phase is suppressed from being excessively increased, but the particle size distribution is difficult to be widened and a good dispersion can be easily obtained.

The content of the resin particles contained in the resin particle dispersion is, for example, preferably 5% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 40% by mass or less.

Similar to the resin particle dispersion, for example, a thermosetting agent dispersion and a colorant dispersion are also prepared. That is, regarding the volume average particle size, dispersion medium, dispersion method, and particle content of the resin particles in the resin particle dispersion liquid, the particles are dispersed in the colorant particles and the curing agent dispersion liquid dispersed in the colorant dispersion liquid. The same applies to the particles of the curing agent.

<First aggregate particle forming step>
Next, the first resin particle dispersion liquid, the thermosetting agent dispersion liquid, and the colorant dispersion liquid are mixed.
Then, in the mixed dispersion, the first resin particles, the heat-curing agent, and the coloring agent are heteroaggregated, and the first resin particles, the heat-curing agent, and the coloring agent have a diameter close to the diameter of the target powder particles. The first aggregated particles containing and are formed.
By further adding colloidal silica to the above-mentioned mixed dispersion liquid, colloidal silica can be contained in the first aggregated particles.

Specifically, for example, a coagulant is added to the mixed dispersion, the pH of the mixed dispersion is adjusted to be acidic (for example, the pH is 2 or more and 5 or less), and a dispersion stabilizer is added as necessary. Particles dispersed in a mixed dispersion liquid heated to a temperature of the glass transition temperature of the first resin particles (specifically, for example, the glass transition temperature of the first resin particles is -30 ° C or higher and the glass transition temperature is -10 ° C or lower). To agglomerate to form first agglomerated particles.

In the first aggregate particle forming step, the composite particle dispersion containing the thermosetting resin and the thermosetting agent and the colorant dispersion are mixed, and the composite particles and the colorant are mixed in the mixed dispersion. May be heteroaggregated to form first aggregated particles.

In the first aggregate particle forming step, for example, the mixed dispersion is stirred with a rotary shear homogenizer, the above-mentioned flocculant is added at room temperature (for example, 25 ° C.), and the pH of the mixed dispersion is acidic (for example, pH is 2 or more). 5 or less), and if necessary, a dispersion stabilizer may be added, and then the above heating may be performed.

Examples of the flocculant include a surfactant used as a dispersant added to the mixed dispersion and a surfactant having the opposite polarity, a metal salt, a metal salt polymer, and a metal complex. When a metal complex is used as the flocculant, the amount of the surfactant used is reduced and the charging characteristics are improved.
After the completion of aggregation, an additive that forms a complex or a similar bond with the metal ion of the flocculant may be used, if necessary. As this additive, a chelating agent is preferably used. By adding this chelating agent, the content of metal ions in the powder particles can be adjusted when the flocculant is excessively added.

Here, the metal salt as the flocculant, the metal salt polymer, and the metal complex are used as a source of metal ions. These examples are as described above.

Examples of the chelating agent include a water-soluble chelating agent. Specific examples of the chelating agent include oxycarboxylic acids such as tartaric acid, citric acid and gluconic acid, iminodic acid (IDA), nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA).
The amount of the chelating agent added is, for example, preferably 0.01 part by mass or more and 5.0 parts by mass or less, and preferably 0.1 part by mass or more and less than 3.0 parts by mass with respect to 100 parts by mass of the resin particles.

<Second aggregate particle forming step>
Next, the first aggregated particle dispersion liquid in which the obtained first aggregated particles are dispersed and the second resin particle particle dispersion liquid are mixed.
The second resin particles may be of the same type as the first resin particles or may be of different types.

Then, in the mixed dispersion liquid in which the first aggregated particles and the second resin particles are dispersed, the second resin particles are aggregated so as to adhere to the surface of the first aggregated particles, and the second is aggregated on the surface of the first aggregated particles. 2 Form second aggregated particles to which resin particles are attached.

Specifically, for example, in the first agglomerated particle forming step, when the first agglomerated particles reach the target particle size, the second agglomerated particle dispersion liquid is mixed with the second resin particle dispersion liquid. The mixed dispersion is heated below the glass transition temperature of the second resin particles.
Then, by setting the pH of the mixed dispersion in the range of, for example, 6.5 or more and 8.5 or less, the progress of aggregation is stopped.

As a result, the second aggregated particles aggregated so that the second resin particles adhere to the surface of the first aggregated particles can be obtained.

<Fusion union process>
Next, with respect to the second agglomerated particle dispersion liquid in which the second agglomerated particles are dispersed, for example, 10 from the glass transition temperature of the first and second resin particles (for example, 10 from the glass transition temperature of the first and second resin particles). By heating to a temperature higher than 30 ° C.), the second aggregated particles are fused and united to form powder particles.

Through the above steps, powder particles can be obtained.

Here, after the fusion union step is completed, the powder particles formed in the dispersion liquid are subjected to a known washing step, solid-liquid separation step, and drying step to obtain powder particles in a dried state.
In the cleaning step, it is preferable to sufficiently perform replacement cleaning with ion-exchanged water from the viewpoint of chargeability. The solid-liquid separation step is not particularly limited, but suction filtration, pressure filtration and the like may be performed from the viewpoint of productivity. The drying step is also not particularly limited, but from the viewpoint of productivity, freeze-drying, air-flow drying, fluid drying, vibration-type fluid drying and the like may be performed.

The powder coating material according to the present embodiment is produced by adding inorganic particles to the obtained dry powder particles as needed and mixing them.
The above mixing may be performed by, for example, a V blender, a Henschel mixer, a Ladyge mixer, or the like.
Further, if necessary, coarse particles of powder particles may be removed by using a vibration sieving machine, a wind sieving machine, or the like.

(Electrostatic powder coating method)
The electrostatic powder coating method according to the present embodiment is the powder coating according to the present embodiment, and is a step of discharging a charged powder coating to electrostatically adhere the powder coating to an object to be coated (hereinafter referred to as a step). It has a step of forming a coating film by heating the powder coating material electrostatically adhered to the object to be coated (hereinafter referred to as “adhesion step”) (hereinafter referred to as “adhesion step”).

The powder coating material may be either a transparent powder coating material (clear coating material) containing no coloring agent in the powder particles or a colored powder coating material containing a coloring agent in the powder particles.

<Adhesion process>
The adhesion step is the powder coating according to the present embodiment, and the charged powder coating is discharged to electrostatically adhere the powder coating to the object to be coated.
Specifically, in the adhesion step, for example, an electrostatic powder is formed in a state where an electrostatic field is formed between the discharge port of the electrostatic powder coating machine and the coated surface (the surface having conductivity) of the object to be coated. The charged powder coating material is discharged from the discharge port of the coating machine, and the powder coating material is electrostatically adhered to the surface to be coated to form a film of the powder coating material. That is, for example, a voltage is applied by using the surface to be coated of the grounded object as an anode and an electrostatic powder coating machine as a cathode to form an electrostatic field (electrostatic field) at both poles and cause the charged powder coating material to fly. Then, it electrostatically adheres to the coated surface of the object to be coated to form a film of powder coating material.
The bonding step may be performed while relatively moving between the discharge port of the electrostatic powder coating machine and the coated surface of the object to be coated.

Here, as the electrostatic powder coating machine, for example, a corona gun (a coating machine that discharges powder paint charged by corona discharge), a tribo gun (a coating machine that discharges powder paint by friction charging), and a bergan (a coating machine that discharges powder paint by frictional charging). Alternatively, a well-known electrostatic powder coating machine such as a coating machine) that centrifugally discharges powder coating material charged by frictional charging can be used. The ejection conditions for good coating may be within the setting range of each gun.

The amount of powder coating adhered to the coated surface of the object to be coated is 40 g / m ² or more and 200 g / m ² or less (preferably 50 g / m ² or more and 100 g / g /) from the viewpoint of suppressing fluctuations in the smoothness of the coating film. m ² or less) is good.

<Baking process>
In the baking step, the powder coating material electrostatically adhered to the object to be coated is heated to form a coating film. Specifically, the coating film is formed by melting and curing the powder particles of the film of the powder coating film by heating.
The heating temperature (baking temperature) is selected according to the type of powder coating material. As an example, the heating temperature (baking temperature) is, for example, preferably 90 ° C. or higher and 250 ° C. or lower, more preferably 100 ° C. or higher and 220 ° C. or lower, and further preferably 120 ° C. or higher and 200 ° C. or lower. The heating time (baking time) is adjusted according to the heating temperature (baking temperature).

Through the above steps, the coating film is formed, that is, the object to be coated is coated. The powder coating material may be adhered and heated (baked) all at once.
By using the powder coating material according to the present embodiment, a coating film having suppressed electrostatic repulsion and excellent smoothness can be obtained. Therefore, when the powder coating material according to the present embodiment is adhered to the object to be coated, the powder coating material according to the present embodiment or another powder coating material is further adhered, and the powder coating material is baked all at once. A coating film having excellent smoothness at the interface between powder coating materials and the outermost layer can be obtained.

Here, the object to be coated, which is the object to be coated with the powder coating material, is not particularly limited, and examples thereof include various metal parts, ceramic parts, resin parts, and the like. These target articles may be unmolded products such as plate-shaped products and linear products before being molded into each article, or may be molded for electronic parts, road vehicles, building interior / exterior materials, and the like. It may be a product. Further, the target article may be an article in which the surface to be coated is previously subjected to surface treatment such as primer treatment, plating treatment, and electrodeposition coating.

Hereinafter, the present embodiment will be described in detail with reference to Examples, but the present embodiment is not limited to these Examples. In the following description, unless otherwise specified, "parts" and "%" are all based on mass.

(Making powder paint)
<Preparation of colorant dispersion (C1)>
・ Cyan pigment (manufactured by Dainichi Seika Co., Ltd., CI Pigment Blue 15: 3, (copper phthalocyanine)): 100 parts by mass ・ Anionic surfactant (manufactured by Daiichi Kogyo Seiyaku Co., Ltd .: Neogen RK): 15% by mass Part ・ Ion-exchanged water: Mix and dissolve 450 parts by mass or more, and disperse for 1 hour using a high-pressure impact disperser Ultimateizer (HJP30006 manufactured by Sugino Machine Co., Ltd.) to disperse the colorant (cyan pigment). A colorant dispersion was prepared. The average particle size of the colorant (cyan pigment) in the colorant dispersion was 0.13 μm, and the solid content ratio of the colorant dispersion (C1) was 25% by mass.

<Preparation of colorant dispersion (M1)>
Colorant dispersion (Kinacridon) except that magenta pigment (CI Pigment Red 122, (quinacridone) manufactured by Dainichiseika Co., Ltd.) was used instead of the cyan pigment used in the preparation of the colorant dispersion (C1). A colorant dispersion (M1) having a solid content ratio of 25% by mass was obtained by the same method as in the preparation of C1).

<Preparation of colorant dispersion (Y1)>
Colorant dispersion except that yellow pigment (CI Pigment Yellow 74, (monoazo pigment) manufactured by Dainichiseika Co., Ltd.) was used instead of the cyan pigment used in the preparation of the colorant dispersion (C1). A colorant dispersion (Y1) having a solid content ratio of 25% by mass was obtained by the same method as in the preparation of (C1).

<Preparation of white pigment dispersion liquid (W1)>
・ Titanium oxide (A-220 manufactured by Ishihara Sangyo): 100 parts by mass ・ Anionic surfactant (manufactured by Daiichi Kogyo Seiyaku Co., Ltd .: Neogen RK): 15 parts by mass ・ Ion exchanged water: 400 parts by mass ・ 0.3 mol / l Nitrate: A white pigment dispersion prepared by mixing and dissolving 4 parts by mass or more and dispersing it for 3 hours using a high-pressure impact disperser Ultimateizer (manufactured by Sugino Machine Co., Ltd., HJP30006) to disperse titanium oxide. Prepared. When measured using a laser diffraction particle size measuring device, the volume average particle size of titanium oxide in the pigment dispersion was 0.25 μm, and the solid content ratio of the white pigment dispersion was 25%.

<Preparation of polyester resin / curing agent composite dispersion (E1)>
A 3-liter reaction tank with a jacket (manufactured by Tokyo Rika Kikai Co., Ltd .: BJ-30N) equipped with a condenser, a thermometer, a water dripping device, and an anchor wing is maintained at 40 ° C in a water circulation type constant temperature bath. A mixed solvent of 180 parts by mass of ethyl acetate and 80 parts by mass of isopropyl alcohol was added thereto, and the following composition was added thereto.
Polyester resin (PES1) [terephthalic acid / ethylene glycol / neopentyl glycol / trimethylolpropane polycondensate (molecular ratio = 100/60/38/2 (mol%), glass transition temperature = 62 ° C., acid value ( Av) = 12 mgKOH / g, hydroxyl value (OHv) = 55 mgKOH / g, weight average molecular weight (Mw) = 12,000, number average molecular weight (Mn) = 4,000]: 240 parts by mass ・ Block isocyanate curing agent VESTAGON B1530 ( EVONIK): 60 parts by mass ・ Benzoin: 1.5 parts by mass ・ Acrylic oligomer (Acronal 4F BASF): 3 parts by mass

After charging, the mixture was stirred at 150 rpm using a three-one motor and dissolved to obtain an oil phase. A mixed solution of 1 part by mass of a 10% by mass aqueous ammonia solution and 47 parts by mass of a 5% by mass sodium hydroxide aqueous solution was added dropwise to this stirred oil phase in 5 minutes, mixed for 10 minutes, and then further ion exchanged. 900 parts by mass of water was added dropwise at a rate of 5 parts by mass per minute to invert the phase, and an emulsion was obtained.
Immediately, 800 parts by mass of the obtained emulsion and 700 parts by mass of ion-exchanged water were placed in a 2 liter eggplant flask and placed in an evaporator (manufactured by Tokyo Rika Kikai Co., Ltd.) equipped with a vacuum control unit via a trap ball. I set it. While rotating the eggplant flask, it was heated in a hot water bath at 60 ° C., and the pressure was reduced to 7 kPa while paying attention to bumping to remove the solvent. When the amount of solvent recovered reached 1100 parts by mass, the pressure was returned to normal pressure, and the eggplant flask was water-cooled to obtain a dispersion liquid. The obtained dispersion had no solvent odor. The volume average particle size of the resin particles in this dispersion was 145 nm. Then, an anionic surfactant (Dowfax2A1, manufactured by Dow Chemical Co., Ltd., active ingredient amount 45% by mass) was added and mixed as an active ingredient with respect to the resin content in the dispersion liquid, and ion-exchanged water was added to add the solid content. The concentration was adjusted to 25% by mass. This was used as a polyester resin / curing agent composite dispersion (E1).

<Preparation of white powder particles (1)>
-Agglomeration process-
-Polyester resin / curing agent composite dispersion (E1): 180 parts by mass (solid content 45 parts by mass)
-White pigment dispersion liquid (W1): 160 parts by mass (solid content 40 parts by mass)
-Ion-exchanged water: 200 parts by mass or more was mixed and dispersed in a round stainless steel flask using a homogenizer (Ultratarax T50 manufactured by IKA). Then, the pH was adjusted to 3.5 using a 1.0 mass% nitric acid aqueous solution. To this, 0.50 parts by mass of a 10 mass% polyaluminum chloride aqueous solution was added, and the dispersion operation was continued with Ultratalax.
A stirrer and a mantle heater are installed, the temperature is raised to 50 ° C. while adjusting the stirring speed so that the slurry is sufficiently agitated, and the mixture is held at 50 ° C. for 15 minutes, and then the Coulter counter [TA-II] type. The particle size of the aggregated particles was measured with (aperture diameter: 50 μm, manufactured by Beckman-Coulter), and when the volume average particle size became 5.5 μm, the polyester resin / curing agent composite dispersion (E1) 60 was used as the shell. The mass part was slowly added.

-Fusion union process-
After holding for 30 minutes after charging, the pH was adjusted to 7.0 using a 5% aqueous sodium hydroxide solution. Then, the temperature was raised to 90 ° C. and maintained for 5 hours.

-Filtration, cleaning and drying processes-
After completion of the reaction, the solution in the flask was cooled and filtered to obtain a solid content. Next, this solid content was washed with ion-exchanged water and then solid-liquid separated by Nucci-type suction filtration to obtain a solid content again.
Next, this solid content was redistributed in 3 liters of ion-exchanged water at 40 ° C., and the mixture was stirred and washed at 300 rpm for 15 minutes. This washing operation was repeated 5 times, and the solid content obtained by solid-liquid separation by Nucci-type suction filtration was vacuum-dried for 12 hours to obtain white powder particles (1).
When the particle size of the white powder particles (1) was measured, the volume average particle size D50v was 6.1 μm, the volume average particle size distribution index GSDv was 1.24, and the average circularity was 0.99.

To 100 parts of the obtained powder coating material, 1.5 parts of hydrophobic silica (manufactured by Nippon Aerosil Co., Ltd., R972) was added, mixed with a Henshell mixer at a peripheral speed of 30 m / s for 3 minutes, and sieved. , Obtained powder paint.

<Preparation of white powder particles (2)>
-Agglomeration process-
The mixed dispersion system was configured as follows for the white powder particles (1).
・ Polyester resin ・ Hardener composite dispersion (E1): 180 parts by mass ・ White pigment dispersion (W1): 160 parts by mass ・ Ion exchanged water: 200 parts by mass ・ Colloidal silica (model number, manufactured by Nissan Chemical Co., Ltd.): Snowtex OS 2.1 parts by mass ・ Ion-exchanged water: 200 parts by mass or more were mixed and dispersed, 0.60 parts by mass of a 10% by mass polyaluminum chloride aqueous solution was added, and white powder was used except for the dispersion operation with Ultratalax. White powder particles (2) were obtained in the same manner as the particles (1).
The volume average particle size D50v of the white powder particles (2) was 6.2 μm, the volume average particle size distribution index GSDv was 1.25, and the average circularity was 0.99.

<Preparation of white powder particles (3)>
-Agglomeration process-
White powder particles (2) in the same manner as the white powder particles (2) except that the colloidal silica was 2.2 parts by mass and the polyaluminum chloride aqueous solution was 0.60 parts by mass with respect to the white powder particles (1). 3) was obtained.
The volume average particle size D50v of the white powder particles (3) was 6.0 μm, the volume average particle size distribution index GSDv was 1.25, and the average circularity was 0.99.

<Preparation of white powder particles (4)>
-Agglomeration process-
White powder particles (2) in the same manner as the white powder particles (2) except that colloidal silica is 2.3 parts by mass and the polyaluminum chloride aqueous solution is 0.72 parts by mass with respect to the white powder particles (1). 4) was obtained.
The volume average particle size D50v of the white powder particles (4) was 6.1 μm, the volume average particle size distribution index GSDv was 1.24, and the average circularity was 0.99.

<Preparation of white powder particles (5)>
-Agglomeration process-
White powder particles (2) in the same manner as the white powder particles (2) except that the colloidal silica was made up to 2.4 parts by mass and the polyaluminum chloride aqueous solution was made up to 0.74 parts by mass with respect to the white powder particles (1). 5) was obtained.
The volume average particle size D50v of the white powder particles (5) was 6.0 μm, the volume average particle size distribution index GSDv was 1.24, and the average circularity was 0.99. <Preparation of white powder particles (5)>

<Preparation of white powder particles (6)>
-Agglomeration process-
White powder particles (2) in the same manner as the white powder particles (2) except that the colloidal silica is 2.5 parts by mass and the polyaluminum chloride aqueous solution is 0.77 parts by mass with respect to the white powder particles (1). 6) was obtained.
The volume average particle size D50v of the white powder particles (6) was 6.1 μm, the volume average particle size distribution index GSDv was 1.25, and the average circularity was 0.99.

<Preparation of white powder particles (7)>
-Agglomeration process-
White powder particles (2) in the same manner as the white powder particles (2) except that the colloidal silica was 2.7 parts by mass and the polyaluminum chloride aqueous solution was 0.8 parts by mass with respect to the white powder particles (1). 7) was obtained.
The volume average particle size D50v of the white powder particles (7) was 6.1 μm, the volume average particle size distribution index GSDv was 1.25, and the average circularity was 0.99.

<Preparation of blue powder particles (1)>
-Agglomeration process-
Blue powder particles (1) were obtained in the same manner as the white powder particles (7) except that 50 parts by mass of the colorant dispersion liquid (C1) was added to the white powder particles (7).
The volume average particle size D50v of the blue powder particles (1) was 6.3 μm, the volume average particle size distribution index GSDv was 1.25, and the average circularity was 0.99.

<Preparation of red powder particles (1)>
-Agglomeration process-
Red powder particles (1) were obtained in the same manner as the white powder particles (7) except that 50 parts by mass of the colorant dispersion liquid (M1) was added to the white powder particles (7).
The volume average particle size D50v of the red powder particles (1) was 6.1 μm, the volume average particle size distribution index GSDv was 1.24, and the average circularity was 0.99.

<Preparation of yellow powder particles (1)>
-Agglomeration process-
Yellow powder particles (1) were obtained in the same manner as the white powder particles (7) except that 70 parts by mass of the colorant dispersion liquid (Y1) was added to the white powder particles (7).
The volume average particle size D50v of the red powder particles (1) was 6.3 μm, the volume average particle size distribution index GSDv was 1.24, and the average circularity was 0.99.

<Preparation of white powder particles (8)>
-Agglomeration process-
With respect to the white powder particles (1), the amount of colloidal silica was 2.7 parts by mass, the amount of the polyaluminum chloride aqueous solution was 1.1 parts by mass, and the fusion union condition was 80 ° C. for 5 hours. White powder particles (8) were obtained in the same manner as in (2).
The volume average particle size D50v of the white powder particles (8) was 6.3 μm, the volume average particle size distribution index GSDv was 1.24, and the average circularity was 0.98.

<Preparation of white powder particles (9)>
-Agglomeration process-
With respect to the white powder particles (1), the colloidal silica was 2.8 parts by mass, the polyaluminum chloride aqueous solution was 1.6 parts by mass, and the fusion union condition was 80 ° C. for 3 hours. White powder particles (9) were obtained in the same manner as in (2).
The volume average particle size D50v of the white powder particles (9) was 6.2 μm, the volume average particle size distribution index GSDv was 1.24, and the average circularity was 0.97.

<Preparation of white powder particles (10)>
-Agglomeration process-
With respect to the white powder particles (1), the colloidal silica was 2.8 parts by mass, the polyaluminum chloride aqueous solution was 1.9 parts by mass, and the fusion coalescence condition was 75 ° C. for 3 hours. White powder particles (10) were obtained in the same manner as in (2).
The volume average particle size D50v of the white powder particles (9) was 6.1 μm, the volume average particle size distribution index GSDv was 1.25, and the average circularity was 0.96.

<Preparation of white powder particles (11)>
-Agglomeration process-
White powder particles (2) in the same manner as the white powder particles (2) except that the colloidal silica was 2.9 parts by mass and the polyaluminum chloride aqueous solution was 0.8 parts by mass with respect to the white powder particles (1). 11) was obtained.
The volume average particle size D50v of the white powder particles (11) was 6.1 μm, the volume average particle size distribution index GSDv was 1.25, and the average circularity was 0.99.

<Preparation of white powder particles (12)>
-Agglomeration process-
White powder particles (1) in the same manner as the white powder particles (2) except that colloidal silica was made 3.1 parts by mass and the polyaluminum chloride aqueous solution was made 1.0 part by mass with respect to the white powder particles (1). 12) was obtained.
The volume average particle size D50v of the white powder particles (12) was 6.1 μm, the volume average particle size distribution index GSDv was 1.25, and the average circularity was 0.99.

<Preparation of white powder particles (13)>
-Agglomeration process-
White powder particles (1) in the same manner as the white powder particles (2) except that colloidal silica is 3.3 parts by mass and the polyaluminum chloride aqueous solution is 1.0 part by mass with respect to the white powder particles (1). 13) was obtained.
The volume average particle size D50v of the white powder particles (13) was 6.1 μm, the volume average particle size distribution index GSDv was 1.24, and the average circularity was 0.99.

<Preparation of white powder particles (14)>
-Agglomeration process-
With respect to the white powder particles (1), the amount of colloidal silica was 3.5 parts by mass, the amount of the polyaluminum chloride aqueous solution was 1.6 parts by mass, and the fusion and coalescence conditions were 90 ° C. for 6 hours. White powder particles (14) were obtained in the same manner as in (2).
The volume average particle size D50v of the white powder particles (14) was 6.1 μm, the volume average particle size distribution index GSDv was 1.25, and the average circularity was 0.99.

<Preparation of white powder particles (15)>
-Agglomeration process-
With respect to the white powder particles (1), the colloidal silica was made up to 3.8 parts by mass, the polyaluminum chloride aqueous solution was made up to 1.8 parts by mass, and the fusion union condition was set to 92 ° C. for 6 hours. White powder particles (15) were obtained in the same manner as in (2).
The volume average particle size D50v of the white powder particles (15) was 6.1 μm, the volume average particle size distribution index GSDv was 1.25, and the average circularity was 0.99.

<Preparation of white powder particles (16)>
-Agglomeration process-
White powder particles (2) except that colloidal silica was made up to 6 parts by mass, polyaluminum chloride aqueous solution was made up to 1.8 parts by mass, and fusion coalescence conditions were set to 94 ° C. for 6 hours with respect to the white powder particles (1). ), White powder particles (16) were obtained.
The volume average particle size D50v of the white powder particles (16) was 6.1 μm, the volume average particle size distribution index GSDv was 1.25, and the average circularity was 0.99.

<Preparation of white powder particles (17)>
-Agglomeration process-
White powder particles (2) except that colloidal silica was changed to 2.7 parts by mass, polyaluminum chloride aqueous solution was changed to 0.1 parts by mass, and 10% sodium chloride aqueous solution was changed to 30 parts by mass with respect to the white powder particles (1). ), White powder particles (17) were obtained.
The volume average particle size D50v of the white powder particles (17) was 6.1 μm, the volume average particle size distribution index GSDv was 1.36, and the average circularity was 0.99.

<Preparation of white powder particles (18)>
-Agglomeration process-
White powder particles (2) except that colloidal silica was changed to 2.7 parts by mass, polyaluminum chloride aqueous solution was changed to 0.04 parts by mass, and 10% sodium chloride aqueous solution was changed to 50 parts by mass with respect to the white powder particles (1). ), White powder particles (18) were obtained.
The volume average particle size D50v of the white powder particles (18) was 6.1 μm, the volume average particle size distribution index GSDv was 1.45, and the average circularity was 0.99.

<Preparation of white powder particles (19)>
-Agglomeration process-
White powder particles (2) except that colloidal silica was changed to 2.8 parts by mass, polyaluminum chloride aqueous solution was changed to 0.01 parts by mass, and 10% sodium chloride aqueous solution was changed to 70 parts by mass with respect to the white powder particles (1). ), White powder particles (19) were obtained.
The volume average particle size D50v of the white powder particles (18) was 6.1 μm, the volume average particle size distribution index GSDv was 1.53, and the average circularity was 0.99.

The powder particles contained in the powder coating material used in each Example and Comparative Example are as follows.

(Examples 1 to 20, Comparative Examples 1 and 2)
In each Example and Comparative Example, the powder coating material containing the powder particles shown in Table 1 was used, and electrostatic powder coating was carried out as follows.

<Electrostatic powder coating>
The powder paint was loaded with Asahi Sanac Corona Gun XR4-110C.
Then, with respect to a 30 cm x 30 cm square test panel (painted object) of a mirror-finished aluminum plate, at a distance of 30 cm from the front of the panel (distance between the panel and the discharge port of the corona gun), Asahi Sanac Corona Gun XR4-110C Was slid up, down, left and right to eject the powder paint and electrostatically adhere to the panel. The applied voltage of the corona gun is 80 kV, the input air pressure is 0.55 MPa, the discharge rate is 200 g / min, and the amount of powder paint adhered to the panel is 50 g / m ² , 90 g / m ² , 180 g / m ² , 220 g / min. Four painted surfaces with m ² were prepared. It should be noted that each adhesion amount may be in the range of ± 5 g / m ² .
Then, it was placed in a high temperature chamber set at 180 ° C. and heated (baked) for 30 minutes. In this way, electrostatic powder coating was applied to the panel.

<Evaluation of electrostatic repulsion>
The surface of the film due to the discharged powder particles before baking by the above method was observed at each adhesion amount, and the evaluation was made by the following five-step evaluation. The evaluation results are shown in Table 2.
A: No dent on the surface is confirmed even on the painted surface with an adhesion amount of 220 g / m ² .
B: The number of dents on the surface is 1 or more and less than 10 for an area of 1 cm ² on a painted surface having an adhesion amount of 220 g / m ² . However, it is not confirmed at 50 g / m ² , 90 g / m ² , and 180 g / m ² .
C: The number of dents on the surface is 11 or more and less than 20 for an area of 1 cm ² on a painted surface with an adhesion amount of 220 g / m ² . At 180 g / m ² , 1 or more and less than 10, but 50 g / m ² and 90 g / m ² are not confirmed.
D: The number of dents on the surface is 21 or more and less than 30 for an area of 1 cm ² on a painted surface having an adhesion amount of 220 g / m ² . 11 or more and less than 20 at 180 g / m ² , 1 or more and less than 10 at 90 g / m ² , but not confirmed at 50 g / m ² .
E: Confirmed at 50 g / m ² .
Only D is allowed, and when there are multiple evaluation results, the one with the lower grade is given priority. For example, when 3 pieces were confirmed on the coated surface with an adhesion amount of 220 g / m ² and 4 pieces were confirmed at 180 g / m ² , the C was given as a low grade C. The results are shown in Table 2.

<Evaluation of smoothness>
The surface of the coating film after baking by the above method for each adhesion amount was observed and evaluated by the following five-step evaluation. The evaluation results are shown in Table 2.
A: No coating film roughness is observed on the surface of any of the coating films.
B: At 220 g / m ² , although it cannot be confirmed at 50 g / m ² , 90 g / m ² , and 180 g / m ² , slight roughness of the coating film is observed.
C: At 180 g / m ² , the coating film is rough.
Roughness of the coating film is observed at D: 90 g / m ² .
At E: 50 g / m ² , rough coating film is observed.
It should be noted that only D is allowed. The results are shown in Table 2.

From the above, the following points are clear. That is, according to the embodiment described in the present application, a highly smooth coated surface is produced in which the generation of dents on the coated surface due to electrostatic repulsion during coating is suppressed and the separation of powder from the coated surface is also suppressed. A powder coating that can be obtained is obtained.

Claims (8)

Contains powder particles having a dielectric loss ratio of 40 × 10 ^-3 or more and 150 × 10 ^-3 or less.
The powder particles contain a thermosetting polyester resin.
Powder paint.
However, the method for measuring the dielectric loss rate is as follows.
5 g of powder particles are molded into pellets, set between electrodes at 20 ° C. and a relative humidity of 60%, and measured with an LCR meter at 5 V and a frequency of 100 kHz.
The dielectric loss rate is calculated by the following formula (1).
(14.39 / (W × D ² )) × Gx × Tx × 10 ¹² ... Equation (1)
In the formula (1), W = 2πf (f: measurement frequency 100 kHz), D: electrode diameter (cm), Gx: conductivity (S), Tx: sample thickness (cm). The powder coating according to claim 1, wherein the powder particles contain 3% by mass or more and 20% by mass or less of colloidal silica having a volume average particle size of 1 nm to 100 nm with respect to the total mass of the powder particles. The powder coating material according to claim 2, wherein the content of the colloidal silica is 5% by mass or more and 20% by mass or less with respect to the total mass of the powder particles. The powder coating material according to claim 1 or 2, wherein the water content of the powder particles is 0.1% by mass or more and 5% by mass or less with respect to the total mass of the powder particles. The powder coating material according to claim 4, wherein the water content of the powder particles is 0.2% by mass or more and 3% by mass or less with respect to the total mass of the powder particles. The powder coating material according to claim 1, wherein the powder particles contain titanium oxide in an amount of less than 25% by mass based on the total mass of the powder particles. The powder coating material according to any one of claims 1 to 3, wherein the powder particles contain titanium oxide in an amount of 25% by mass or more and 50% by mass or less with respect to the total mass of the powder particles. The step of discharging the charged powder coating material according to any one of claims 1 to 7 and electrostatically adhering the powder coating material to the object to be coated.
An electrostatic powder coating method comprising a step of heating a powder coating electrostatically adhered to an object to be coated to form a coating film.