Powder coating composition

Abstract

To provide a hot-melt fluororesin powder coating composition containing fillers that can produce a coating film with excellent corrosion resistance and surface properties.SOLUTION: The present invention is a powder coating composition, which is a powder mixture, containing: first hot-melt fluororesin particles in which a filler is dispersed in the particles; and second hot-melt fluororesin particles having an average particle diameter of 10 to 200 μm; and charge adjusting agent particles, wherein the amount of filler is 7 wt.% to 15 wt.%, based on the total amount of the powder mixture.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a filler-containing hot melt processable fluororesin powder coating composition that can be applied thickly by electrostatic powder coating. [Background technology]

[0002] Fluoropolymers have excellent heat resistance, chemical resistance, electrical properties, and mechanical properties, as well as an extremely low coefficient of friction and non-stickiness, and are therefore widely used in all industrial fields, including chemicals, machinery, and electrical machinery. In particular, melt processable fluoropolymers exhibit fluidity at temperatures above their melting point, and are therefore commonly used as paint materials for fluoropolymer coatings, as they can suppress the occurrence of pinholes when formed into coating films.

[0003] Patent Document 1 discloses water-based liquid paints made of fluororesin. These liquid paints are used as so-called slurry paints, which have high concentrations and high viscosities, and can be applied thickly. However, slurry paints have problems such as requiring a drying process and concern about the environmental impact of solvent evaporation.

[0004] On the other hand, melt-processable fluororesin powder coatings have the advantages of being able to be applied thickly without a volatile liquid medium, allowing for the reuse of the coating, and not generating volatile organic compounds (VOCs). Electrostatic coating, in which the substrate and powder coating are electrically charged, is commonly used as a powder coating method using melt-processable fluororesin powder coatings. Furthermore, when a filler is used to impart various properties to the melt-processable fluororesin powder coating, such as electrical conductivity, abrasion resistance, and friction resistance, or to adjust the appearance, such as coloring or brilliance, the melt-processable fluororesin powder coating can be mixed with filler particles. However, dispersing filler particles within the melt-processable fluororesin powder particles is preferable in terms of thick application, coating durability, preventing filler detachment from the coating, and preventing variation within the coating (e.g., Patent Document 2).

[0005] Furthermore, in order to improve the durability and corrosion resistance of coating films, improve productivity, and reduce process costs, coatings must be able to be applied thickly. The present inventors have proposed a heat-meltable fluororesin powder coating composition that allows for a large thickness of coating in a single application and a large limit on the thickness of recoating (Patent Document 3). Patent Document 3 discloses a powder coating composition that uses heat-meltable fluororesin particles containing a relatively small amount of conductive filler, ultimately containing approximately 1% of the conductive filler relative to the total amount of the composition. However, demands for improved corrosion resistance and conductivity of coating films have been increasing year by year, and coatings with further improvements in these properties have been desired. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-041126 [Patent Document 2] Special Publication No. 5-73147 [Patent Document 3] Japanese Patent Publication No. 2022-127831 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a filler-containing melt processable fluororesin powder coating composition which can be applied thickly and which can produce a coating film having excellent corrosion resistance and surface properties. [Means for solving the problem]

[0008] The present invention relates to a powder coating composition comprising a powder mixture containing first melt processable fluororesin particles having a filler dispersed therein, second melt processable fluororesin particles having an average particle size of 10 to 200 μm, and charge control agent particles, wherein the powder mixture contains 7% by weight to 15% by weight of the filler. In the powder coating composition of the present invention, the ratio of the first melt processable fluororesin particles to the second melt processable fluororesin particles is preferably 40-70:30-60 wt %, and the charge control agent particles are preferably contained in an amount of 0.01 wt % to 5 wt % of the total amount of the powder coating composition. The average particle size of the second melt processable fluororesin particles is preferably larger than that of the first melt processable fluororesin particles. The filler is preferably a conductive filler, and more preferably a carbon material having a graphene structure. The charge control agent particles are preferably graphite. The melt processable fluororesin is preferably a perfluororesin. Another aspect of the present invention is a coating film produced from the powder coating composition, the coating film preferably having a thickness of 100 μm or more. [Effects of the Invention]

[0009] The present invention provides a filler-containing melt processable fluororesin powder coating composition which can be applied thickly and which can produce a coating film having excellent corrosion resistance and surface properties. DETAILED DESCRIPTION OF THE INVENTION

[0010] The powder coating composition of the present invention is a powder mixture comprising (1) first melt processable fluororesin particles, (2) second melt processable fluororesin particles, and (3) charge control agent particles.

[0011] (1) First melt processable fluororesin particles The first melt processible fluororesin particles of the present invention are particles in which a filler is dispersed in a melt processible fluororesin, and are produced from a melt processible fluororesin and a filler.

[0012] The melt processible fluororesin used in the present invention can be appropriately selected from resins known as melt processible fluororesins. Examples include polymers or copolymers of monomers selected from tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, perfluoro(alkyl vinyl ether), vinylidene fluoride, and vinyl fluoride, as well as copolymers of these monomers with monomers having double bonds such as ethylene, propylene, butylene, pentene, and hexene, or monomers having triple bonds such as acetylene and propyne. Specific examples of melt processible fluororesins include low-molecular-weight melt processible polytetrafluoroethylene (melt processible PTFE), tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymers (PFA), tetrafluoroethylene-hexafluoropropylene copolymers (FEP), tetrafluoroethylene-hexafluoropropylene-perfluoro(alkyl vinyl ether) copolymers, tetrafluoroethylene-ethylene copolymers, polyvinylidene fluoride, polychlorotrifluoroethylene, and chlorotrifluoroethylene-ethylene copolymers.

[0013] Among these melt processable fluororesins, perfluororesins such as melt processable PTFE, PFA, FEP, and tetrafluoroethylene-hexafluoropropylene-perfluoro(alkyl vinyl ether) copolymers are particularly preferred from the viewpoint of the non-stickiness and heat resistance of the coating film. Among these, PFA is preferred from the viewpoint of heat resistance. When PFA is used, the alkyl group of the perfluoro(alkyl vinyl ether) in the PFA preferably has 1 to 5 carbon atoms, more preferably 1 to 3. Furthermore, the content of the perfluoro(alkyl vinyl ether) in the PFA is preferably in the range of 1 to 50% by weight.

[0014] Furthermore, from the viewpoint of good moldability during high-temperature melting, the melt processable fluororesin used in the present invention is preferably a melt processable fluororesin that exhibits fluidity at temperatures above its melting point. Specifically, the melt flow rate (MFR) of the melt processable fluororesin is preferably 0.1 g / 10 min or more, more preferably 0.5 g / 10 min or more. Examples of such resins include PFA, FEP, and tetrafluoroethylene-hexafluoropropylene-perfluoro(alkyl vinyl ether) copolymer. PFA, which has a high melting point and excellent thermal fluidity, is particularly preferred. On the other hand, if the MFR is too high (the melt viscosity is too low), poor appearance due to sagging or shrinkage is likely to occur during repeated coating and baking, making it difficult to form thick films, which is undesirable. Specifically, the MFR of the melt processable fluororesin is preferably 30 g / 10 min or less, more preferably 25 g / 10 min or less, and particularly preferably 20 g / 10 min or less.

[0015] The melt processible fluororesin used in the present invention may be a blend of two or more types of melt processible fluororesins depending on the desired properties, or may contain non-melt processible polytetrafluoroethylene.

[0016] In the first melt processible fluororesin particle of the present invention, the filler is dispersed inside the particle. Here, it is preferable that the filler is uniformly dispersed inside the particle. Whether the filler is uniformly dispersed inside the particle can be confirmed by observing the surface of the particle with an electron microscope or the like and seeing whether the filler is uniformly dispersed. In order to uniformly disperse the filler in the melt processible fluororesin and produce resin particles, for example, the method described in Patent Document 2 can be used.

[0017] Various fillers can be used as the filler dispersed inside the particles. Examples include metal powder, metal oxides (aluminum oxide, zinc oxide, tin oxide, titanium oxide, etc.), glass, ceramics, silicon carbide (SiC), silicon oxide, boron nitride, calcium fluoride, carbon black, graphite, mica, barium sulfate, and various resin particles. Fillers can be in various shapes, such as particulate, fibrous, and flake form.

[0018] The present invention is particularly effective when using a conductive filler, and examples of conductive fillers include metals, metal oxides (zinc oxide, tin oxide, titanium oxide, indium oxide, etc.), titanium carbide, titanium nitride, carbon materials with graphene structures such as carbon fiber, carbon black, graphite, and carbon nanotubes (CNTs), as well as particles coated with or composite particles of these. To achieve high conductivity, it is preferable to use carbon black and carbon fiber in combination. Furthermore, in the present invention, materials with relatively low insulating properties, such as silicon carbide (SiC), specifically those with a volume resistivity of 10 8 Conductive fillers with a resistivity of Ω·cm or less can also be used. Silicon carbide (SiC) is preferably used to improve the abrasion resistance of the coating film.

[0019] Furthermore, when polar particles with hydrophilic surfaces such as mica, aluminum oxide, boron nitride, and silicon oxide are used, thick coating is difficult (it is thought that the difference in electrical properties between the fluororesin and the filler causes variations in charging during electrostatic coating), but such fillers can also be used. Mica is preferably used because it can impart a lustrous finish to the coating film.

[0020] Fillers of various shapes can be used, such as particles, fibers, flakes, etc. The preferred blending amount varies depending on the desired properties, the type of filler, and the particle size, but is preferably 5 to 30% by weight, more preferably 10 to 25% by weight, and particularly preferably 15 to 20% by weight.

[0021] The first melt processible fluororesin particles have an average particle size of 2 to 100 μm, preferably 3 to 75 μm, more preferably 5 to 50 μm, and particularly preferably 8 to 35 μm. If the average particle size is too small, not only will electrostatic powder coating be difficult due to the effects of wind, but production will also be difficult and the particles will be prone to aggregation during storage, causing defects. If the average particle size is too large, it will be difficult to apply a charge and detachment will be more likely to occur, making electrostatic coating difficult and resulting in an uneven coating surface.

[0022] In this specification, the term "average particle size" refers to the particle size at an integrated value of 50% (volume basis) in the particle size distribution obtained by a laser diffraction / scattering method (d50).

[0023] (2) Second melt-type fluororesin particles The second melt processible fluororesin particles of the present invention are particles made of a melt processible fluororesin and have an average particle size of 10 to 200 μm.

[0024] The second melt processable fluororesin particles can be produced from the resin used in the first melt processable fluororesin particles. Unlike the first melt processable fluororesin particles, the second melt processable fluororesin particles do not contain a filler. Among melt processable fluororesins, perfluororesins such as PFA, FEP, and tetrafluoroethylene-hexafluoropropylene-perfluoro(alkyl vinyl ether) copolymer are particularly preferred from the viewpoint of the non-stickiness and heat resistance of the coating film. Among these, PFA is preferred from the viewpoint of heat resistance.

[0025] The second melt processible fluororesin particles preferably have an average particle size of 15 to 150 μm, more preferably 20 to 100 μm, and particularly preferably 25 to 70 μm. The second melt processible fluororesin particles preferably have an average particle size larger than that of the first melt processible fluororesin particles. As the second melt processible fluororesin particles, commercially available melt processible fluororesin powder coatings can be used. The particles do not contain a filler, but may contain a small amount of additives such as an antifoaming agent outside the particles (in the powder mixture).

[0026] (3) Charge control agent particles Various conductive particles can be used as the charge control agent particles of the present invention. Examples include metal powder, carbon fiber, carbon black, graphite, carbon materials with a graphene structure such as carbon nanotubes (CNTs), metal oxides (zinc oxide, tin oxide, titanium oxide, indium oxide, etc.), titanium carbide, and titanium nitride. Among these, carbon materials with a graphene structure are preferred, with graphite being particularly preferred. The function of the charge control agent particles is believed to be to homogenize the surface charge characteristics of the first melt processable fluororesin particles containing a filler and the second melt processable fluororesin particles without a filler, by adhering to and coating each particle. This homogenizes the surface charge characteristics and allows for uniform mixing without aggregation or separation. The reason graphite is preferred here is that, during high-speed dry mixing, the brittle graphite is pulverized into fine sheets that can adhere to and coat each particle.

[0027] (4) Optional ingredients The powder coating composition of the present invention may optionally contain organic or inorganic additives, provided that the additives do not affect the physical properties of the powder coating composition. Examples of such additives include engineering plastics such as polyarylene sulfide, polyether ether ketone, polyamide, and polyimide; metal powders; metal oxides (aluminum oxide, zinc oxide, tin oxide, titanium oxide, etc.); glass; ceramics; silicon carbide; silicon oxide; calcium fluoride; carbon black; graphite; mica; and barium sulfate. Additives may be in various forms, including particulate, fibrous, and flake forms. The content of such additives is preferably 10% by weight or less, and more preferably 5% by weight or less, based on the total weight of the powder coating composition.

[0028] (5) Powder coating composition of the present invention The powder coating composition of the present invention is characterized by containing 7% to 15% by weight of a filler relative to the total weight of the composition. The filler content in the powder coating composition of the present invention is preferably 9% to 14% by weight, more preferably 11% to 13% by weight, relative to the total weight of the composition. A filler content within the above range makes it possible to achieve both high conductivity and surface smoothness. In conventional techniques, a high filler content makes it difficult to mix uniformly, resulting in failure to obtain a smooth, uniform coating film. In contrast, the powder coating composition of the present invention uses first melt processable fluororesin particles in which the filler is dispersed, and mixes these with two types of particles, the second melt processable fluororesin particles, thereby obtaining a coating film with excellent uniformity despite the large filler content in the total composition. Furthermore, by using first melt processable fluororesin particles in which a filler is dispersed within the particles, the shear force can be reduced when mixing the first melt processable fluororesin particles, the second melt processable fluororesin particles, and the charge control agent particles, making it possible to produce the composition simply and efficiently. The first and second melt processable fluororesin particles are blended so that the filler content is within the above range. The ratio of the first and second melt processable fluororesin particles is preferably 40-70:30-60 wt%, more preferably 45-60:40-55 wt%, and even more preferably 60:40 wt%. The content of the charge control agent particles is preferably 0.01-5 wt%, more preferably 0.1-3.0 wt%, and even more preferably 0.2-2.0 wt%, based on the total powder coating composition.

[0029] (6) Manufacturing method The method for producing the powder coating composition of the present invention is described below. The powder coating composition of the present invention is obtained by mixing first melt processable fluororesin particles, second melt processable fluororesin particles, and charge control agent particles. Mixing methods include mixing dry particles (dry blending) or fluidized bed mixing using a turbular mixer or similar device that stirs the mixing vessel by rolling it. Devices for dry blending include, but are not limited to, cutter mixers, Henschel mixers, V-type blenders with choppers, double cone mixers with choppers, and rocking mixers. Because the powder coating composition of the present invention contains a higher filler content than conventional techniques, the filler's effects can be fully achieved without the application of strong shear forces.

[0030] (7) Coating film prepared from the powder coating composition of the present invention The "coating film" of the present invention is a coating film obtained by applying the powder coating composition of the present invention. To adhere the coating to a substrate, a primer layer containing a fluororesin and capable of adhering to the substrate is preferably provided. While known powder coating methods can be used to apply the powder coating composition of the present invention, electrostatic powder coating is preferred. After application, heating the coating above the melting point of the thermofusible fluororesin results in a coating film free of defects such as pinholes. The powder coating composition of the present invention is suitable for use in coating articles requiring non-stick, water-repellent, and oil-repellent properties, such as cooking utensils such as frying pans and rice cookers, heat-resistant release trays for factory lines (e.g., for bread-baking processes), office automation equipment-related articles such as fixing rolls, belts, and inkjet nozzles, and industrial equipment-related articles for chemical plants (e.g., piping). [Example]

[0031] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0032] <Creating aluminum test pieces> (A) Substrate surface treatment (shot blasting) The surface of the aluminum substrate (JIS A1050 compliant, 95mm x 150mm, 1mm thick) was degreased with isopropyl alcohol, and then roughened by shot blasting with #60 alumina (Resonac Corporation, Showa Blaster) using a sandblaster (Fuji Manufacturing Co., Ltd., Pneuma Blaster SGF-4(A)S-E566).

[0033] (B) Undercoat (primer application) The substrates treated in (A) above were sprayed with a liquid primer paint (Mitsui-Chemours Fluoroproducts Fluoropolymer Teflon® Paint Water-Based Primer PJ-BN910) using an air spray gun (ANEST IWATA Corporation W-88-10E2 φ1mm nozzle (manual gun)) at an air pressure of 3-4 kgf / cm^2. The applied liquid weight was 0.9-1.4 g per substrate, and the substrate was dried at 120°C for 15 minutes in a forced air circulation oven to form a coating film with a thickness of 8-12 μm. The coating environment was a temperature of 25°C and a humidity of 60% RH.

[0034] <Evaluation method> (1) Thick coating ability Using an electrostatic powder coater (Nihon Parkerizing Co., Ltd., Handgun System GX7500CS), the aluminum substrates treated in steps (A) and (B) above were placed vertically and grounded. Powder was electrostatically sprayed at a voltage of 20–40 kV (negative) at a rate of approximately 50 g / min from a distance of approximately 25 cm until no powder adhered. The coating environment was a temperature of 25°C and a humidity of 60% RH. The coated aluminum substrates were baked at 380°C for 30 minutes in a forced-air circulation oven to form a coating film. The resulting coating film was inspected for coating weight, presence or absence of powder shedding, electrostatic repulsion, and appearance. Coatings with a coating weight of 2.8 g (equivalent to a 100 μm film thickness) or more, no powder shedding or electrostatic repulsion, and no defects such as bubbling were evaluated as passing (◯).

[0035] (2) Surface smoothness Using an electrostatic powder coater (Handgun System GX7500CS manufactured by Nihon Parkerizing Co., Ltd.), the aluminum substrate treated in (A) and (B) above was placed horizontally and grounded, and the powder was electrostatically coated from a distance of approximately 25 cm at a coating voltage of 20 to 40 kV (negative) and a discharge rate of approximately 50 g / min to a coating amount of approximately 2.8 g (corresponding to a film thickness of 100 μm). The coating was then baked at a specified temperature for 30 minutes. This process was repeated five times (first at 380°C, and then at 360°C from the second time onwards) to obtain a coated object with a film thickness of 500 μm or more. The surface roughness (Ra) of the resulting coated object was measured. Surface roughness was measured using a HANDYSURF E-45A manufactured by Tokyo Seimitsu Co., Ltd. in accordance with JIS B0601 using a stylus with an evaluation length of 4 mm and a cutoff value of 0.8 mm. Surface roughness of less than 2.0 μm was considered to be acceptable (◯).

[0036] (3) Conductivity (300μm) Using an electrostatic powder coating machine (Handgun System GX7500CS manufactured by Nihon Parkerizing Co., Ltd.), electrostatic coating was applied to a horizontally placed glass substrate (float glass, 95mm x 150mm, thickness 2mm) to a film thickness of 100-120μm per coating, and the substrate was baked at a specified temperature for 30 minutes. This process was repeated three times (380℃ for the first time, 360℃ for the second time and thereafter). After baking, the coating film was peeled off in boiling water to obtain a film. The surface resistance was measured using a UA probe with an applied voltage of 100V on a Hiresta UX manufactured by Nitto Seiko Analytech Co., Ltd. 7 If it was below Ω, it was considered a pass (〇).

[0037] (4) Conductivity (500μm) For the powder coating compositions that were evaluated as passing (◯) in (3), the surface resistance was also measured in the same manner for a coating film with a thickness of 500 μm. 9 If it was below Ω, it was considered a pass (〇).

[0038] (5) Corrosion resistance Corrosion resistance refers to the ability to withstand certain conditions. For the coating compositions of the present invention, the evaluation index was the resistance when the coating composition was electrostatically applied and then treated with a hydrochloric acid solution. It is believed that corrosion resistance is improved when the coating adheres well to the substrate and a uniform, consistent thickness can be achieved. Specifically, an aluminum substrate treated with the above-mentioned (A) and (B) procedures (except that in (B), a 65:35 mixture of EJ-CL107 and SG-CL600 (both manufactured by Mitsui-Chemours Fluoro Products) was used instead of PJ-BN910) was placed horizontally and grounded using an electrostatic powder coating machine (Handgun System GX7500CS, manufactured by Nihon Parkerizing Co., Ltd.). The powder was electrostatically coated from a distance of approximately 25 cm at a coating voltage of 20 to 40 kV (negative) with a discharge rate of approximately 50 g / min to a coating weight of approximately 2.8 g (corresponding to a film thickness of 100 μm), and then baked at a specified temperature for 30 minutes. This was repeated three times (first time at 380°C, second time onwards at 360°C) to obtain a coated object with a coating film thickness of 300 μm or more. Using a Yamazaki lining tester (Yamazaki Seiki Kenkyusho "LA-15"), a 5% aqueous solution of hydrochloric acid (95°C) was applied to the coating surface of the resulting coating. The coating surface was visually observed every 24 hours, and the time until blisters appeared was compared.

[0039] <Raw materials> Graphite A: SGP-5 manufactured by SEC Carbon Co., Ltd. Graphite B: UF-G5 manufactured by Resonac Co., Ltd. (PFA aqueous dispersion) A dispersion of tetrafluoroethylene-perfluoropropyl vinyl ether (TFE-PPVE) copolymer was prepared by a method similar to Examples 1 to 3 described in Japanese Patent No. 5588679. (MFR of solid resin: 16.6 [g / 10 min], average particle size: 0.186 μm, comonomer (PPVE) ratio: 3.3 wt%, PFA content in dispersion: 30.6 wt%) PFA powder coating: Fluoropolymer Teflon® coating powder top coat MJ-508 manufactured by Mitsui Chemours Fluoro Products Co., Ltd., average particle size d50: approximately 50 μm Perfluoroheptene (Opteon (registered trademark) SF10 manufactured by Mitsui-Chemours Fluoroproducts Co., Ltd.) 60% nitric acid aqueous solution (Fujifilm Wako Pure Chemical Industries, Ltd.)

[0040] (Preparation example) (Preparation of First Melt Processible Fluororesin Particles 1) 246.5 g of pure water was placed in a 2 L stainless steel beaker, and 41.2 g of graphite A was added. This was subjected to ultrasonic dispersion for 5 minutes using an ultrasonic generator (UE-100Z28S-8A Ultrasonic Generator, manufactured by Ultrasonic Industries Co., Ltd.). The resulting dispersion was then added to a stainless steel container containing 522 g of PFA aqueous dispersion and stirred at 600 rpm for 5 minutes using a downflow-type propeller-type four-blade mixer. 11.6 g of 60% aqueous nitric acid solution was added thereto. After a rapid increase in viscosity was confirmed, 132.1 g of perfluoroheptene was added to generate coarse aggregate particles in the liquid. The coarse aggregate particles were filtered and washed three times with pure water. The washed sample was placed on a tray and dried at 120 °C for 1 hour and then at 290 °C for 3 hours to obtain first melt processable fluororesin particles 1. The average particle size (d50) of the resulting particles was 31.0 μm. The graphite content of the obtained melt processible fluororesin particles 1 was calculated to be 20% by weight from the weight change when heated at 600°C for 30 minutes in a nitrogen environment using a tubular electric furnace TMF-300N (manufactured by AS ONE Corporation).

[0041] Example 1 1200 g of the first melt processable fluororesin particles 1 produced in the above Preparation Example, 782 g of PFA powder coating (Mitsui-Chemours Fluoroproducts MJ-508, average particle size d50: 51.2 μm) as the second melt processable fluororesin, and 18 g of graphite B as a charge control agent were added to a small Henschel mixer (FM10B, manufactured by Nippon Coke and Engineering Co., Ltd.), and mixed and stirred at 1000 rpm for 10 minutes to obtain a powder coating composition. The proportion of filler to the total powder coating composition was adjusted to 12.0 wt%.

[0042] Example 2 A powder coating composition was prepared in the same manner as in Example 1, except that the amounts of the first melt processible fluororesin particles 1 and the PFA powder coating were changed to 1100 g and 882 g, respectively. The proportion of the filler relative to the total amount of the powder coating composition was adjusted to 11.0 wt %.

[0043] Example 3 A powder coating composition was prepared in the same manner as in Example 1, except that the amounts of the first melt processible fluororesin particles 1 and the PFA powder coating were 1,000 g and 982 g, respectively. The proportion of the filler relative to the total amount of the powder coating composition was adjusted to 10.0 wt %.

[0044] Example 4 A powder coating composition was prepared in the same manner as in Example 1, except that the amounts of the first melt processible fluororesin particles 1 and the PFA powder coating were 900 g and 1,082 g, respectively. The proportion of the filler relative to the total amount of the powder coating composition was adjusted to 9.0 wt %.

[0045] Example 5 A powder coating composition was prepared in the same manner as in Example 1, except that the amounts of the first melt processible fluororesin particles 1 and the PFA powder coating were 800 g and 1,182 g, respectively. The proportion of the filler relative to the total amount of the powder coating composition was adjusted to 8.0 wt %.

[0046] (Preparation of First Melt Processible Fluororesin Particles 2) In the above preparation example, 171.0 g of pure water, 22.5 g of graphite A, 597.4 g of PFA aqueous dispersion, 12.8 g of 60% aqueous nitric acid solution, and 146.2 g of perfluoroheptene were used to obtain first melt processable fluororesin particles 2. The graphite content of the melt processable fluororesin particles 2 was adjusted to 11 wt %.

[0047] (Comparative Example 1) A powder coating composition was obtained in the same manner as in Example 1, except that 950 g of the first melt processible fluororesin particles 2 was used instead of the first melt processible fluororesin particles 1, 1000 g of PFA powder coating, and 50 g of graphite B. The proportion of the filler relative to the total amount of the powder coating composition was adjusted to 5.2 wt %.

[0048] (Comparative Example 2) A powder coating composition was prepared in the same manner as in Example 1, except that the amounts of the first melt processible fluororesin particles 1 and the PFA powder coating were 400 g and 1,582 g, respectively. The proportion of the filler relative to the total amount of the powder coating composition was adjusted to 4.0 wt %.

[0049] (Comparative Example 3) A powder coating consisting only of the first heat-meltable fluororesin particles 1 was used as Comparative Example 3. The proportion of the filler to the total amount of the powder coating was adjusted to 20.0 wt %.

[0050] Comparative Example 4 1880 g of PFA powder coating and 120 g of graphite A were added to a small Henschel mixer (FM10B manufactured by Nippon Coke & Engineering Co., Ltd.) and mixed and stirred at 1000 rpm for 10 minutes to obtain a powder coating composition. The ratio of the filler to the total amount of the powder coating composition was adjusted to 6.0 wt%.

[0051] The compositions of the examples and comparative examples are summarized in Table 1. Table 2 summarizes the results of evaluation methods (1) to (5).

[0052] [Table 1]

[0053] [Table 2]

[0054] In Examples 1 to 5, when the filler was added in an amount of 8 to 12 wt % relative to the final composition, not only did the compositions exhibit good thick coating properties, surface smoothness, and conductivity (300 μm and 500 μm), but they also exhibited significantly improved corrosion resistance compared to Comparative Example 1, which contained 5.2 wt % of the filler relative to the final composition. This improvement in corrosion resistance is thought to be due to the fact that the compositions of the examples were compositions in which a relatively large amount of filler was uniformly dispersed, allowing a good coating film to be formed by electrostatic coating. In addition, in Comparative Examples 1, 2, and 4, which have a low filler content, the surface resistance value was 10 7 The electrical conductivity (500 μm) was not evaluated because the resistance was greater than Ω and the electrical conductivity was insufficient. On the other hand, Comparative Example 3, which contained 20 wt % of filler, had excellent electrical conductivity but was insufficient in terms of thick coating property and surface smoothness.

[0055] The present invention is not limited to the disclosed contents of the examples described in this specification or the embodiments of the invention disclosed in this specification, but includes the contents of the invention that have been appropriately modified based on the matters disclosed in this specification, etc., as long as they do not contradict the spirit of the present invention. [Industrial Applicability]

[0056] The melt processable fluororesin powder coating composition of the present invention can be applied thickly by electrostatic powder coating, and can give a coating film that has excellent surface smoothness, high corrosion resistance, and excellent conductivity.

Claims

1. first melt processible fluororesin particles having a filler dispersed therein; second melt processible fluororesin particles having an average particle size of 10 to 200 μm; and charge control agent particles, A powder coating composition comprising the filler in an amount of 7% by weight to 15% by weight based on the total amount of the powder mixture.

2. 2. The powder coating composition according to claim 1, wherein the ratio of the first melt processible fluororesin particles to the second melt processible fluororesin particles is 40-70:30-60% by weight, and the charge control agent particles are contained in an amount of 0.01-5% by weight based on the total amount of the powder coating composition.

3. 3. The powder coating composition according to claim 1, wherein the filler is a carbon material having a graphene structure.

4. 3. The powder coating composition of claim 1, wherein the charge control agent particles are graphite.

5. 3. The powder coating composition according to claim 1, wherein the melt processible fluororesin is a perfluororesin.

6. A coating film comprising the powder coating composition according to claim 1 or 2 and having a thickness of 100 μm or more.

7. An article having the coating of claim 6.

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