JP2025034716A - Powder particles, powder coating composition containing powder particles and fluororesin, and method for producing the same - Google Patents

Abstract

To provide powder particles which improve adhesive force between a base material and a fluororesin layer.SOLUTION: Powder particles are obtained by previously mixing a heat-fusible polymer and a filler in water and forming an aqueous dispersion, and then heating the aqueous dispersion.SELECTED DRAWING: None

Description

The present invention relates to powder particles that improve the adhesion between a substrate and a fluororesin layer, and to a powder coating composition that contains powder particles and a fluororesin and is useful as a primer. The present invention also relates to a method for producing these powder particles and the powder coating composition.

Fluororesin has excellent properties such as chemical resistance, non-adhesiveness, heat resistance, and electrical insulation, and has been widely used as a coating material. Because fluororesin has non-adhesive properties, it is prone to poor adhesion when applied directly to a substrate (especially various metal substrates). For this reason, in many cases, a primer layer that has good adhesion to the substrate is applied as an undercoat layer for the fluororesin.

The applicant has proposed polymer particles that have excellent adhesion between substrates and layers and prevent peeling due to heat, moisture, etc., and a coating composition containing the polymer particles (Patent Document 1). This coating composition has excellent effects, but has problems such as concerns about the burden on the environment because an organic solvent is used to produce the polymer particles, and the resulting coating composition is an aqueous dispersion, so it is necessary to add a surfactant to ensure the dispersibility of the fluororesin.

On the other hand, powder coatings are known to have advantages such as being environmentally friendly because they do not use solvents, being resource-saving because the powder is easily recycled, and being easy to apply. Patent Document 2 discloses a powder primer composition containing a melt-soluble fluororesin powder and a polyethersulfone powder. However, there is still a demand for coating compositions with better adhesion and corrosion resistance.

JP 2013-231098 A JP 2022-137848 A JP 2007-320267 A

The present invention aims to provide powder particles that have excellent adhesion between the substrate and the fluororesin layer, and to provide a powder coating composition that contains the powder particles and, by virtue of the excellent adhesion, can suppress the intrusion of heat, moisture, corrosive substances, etc., thereby preventing peeling of the fluororesin laminate and improving corrosion resistance, steam resistance, and durability. Another object of the present invention is to provide a method for producing these powder particles and powder coating composition.

One embodiment of the present invention is a powder particle obtained by mixing a heat-fusible polymer and a filler in water in advance to form an aqueous dispersion, and then heating the mixture. The powder particle is preferably a mixture of the heat-fusible polymer and the filler. The heat-fusible polymer is preferably at least one selected from polyimide, polyamideimide, polyamide, polyester, polyethylene terephthalate, polyphenylene sulfide, polysulfone, polyetherimide, polyethersulfone, polyetheretherketone, and polyetherketoneketone, and more preferably at least one selected from polyphenylene sulfide, polyetherimide, polyetheretherketone, and polyetherketoneketone. The filler is preferably at least one inorganic particle selected from silicon carbide, silicon oxide, aluminum oxide, zinc oxide, tin oxide, titanium oxide, barium sulfate, and carbon black. The powder particle preferably contains 30 to 300 parts by weight of the filler per 100 parts by weight of the heat-fusible polymer. The particle size is preferably 150 μm or less.

Another embodiment of the present invention is a powder coating composition containing powder particles obtained by premixing a thermofusible polymer and a filler in water to form an aqueous dispersion, and then heating the mixture, and a fluororesin powder. The fluororesin powder is preferably made of a thermofusible fluororesin, and more preferably a perfluororesin. The present invention is also a powder coating composition that contains 80 to 50% by weight of powder particles and 20 to 50% by weight of fluororesin powder, based on the total weight of the powder coating composition.

Further, one embodiment of the present invention includes a process for producing an aqueous dispersion comprising the steps of: (1) mixing a heat-fusible polymer and a filler in water to obtain an aqueous dispersion;
(2) heating the aqueous dispersion to remove water to obtain a solid;
(3) pulverizing the solid to obtain powder particles;
It is preferable that the method for producing powder particles further includes, following the step (2), a step of heating at a temperature equal to or higher than the glass transition point of the heat-fusible polymer.

Further, one embodiment of the present invention includes a process for producing an aqueous dispersion comprising the steps of: (1) mixing a heat-fusible polymer and a filler in water to obtain an aqueous dispersion;
(2) heating the aqueous dispersion to remove water to obtain a solid;
(3) pulverizing the solid to obtain powder particles;
(4) adding and mixing a fluororesin powder with the powder particles to obtain a powder coating composition;
The present invention relates to a method for producing a powder coating composition.

The powder coating composition of the present invention has excellent adhesion between the substrate and the fluororesin layer, and prevents the intrusion of heat, moisture, corrosive substances, etc., preventing peeling of the fluororesin laminate, and can obtain a coating film with improved corrosion resistance, steam resistance, and durability. Therefore, it can be widely used in office automation applications, chemical corrosion protection applications, food heating and processing equipment applications, sliding materials, automotive applications, building materials, and semiconductor manufacturing equipment components.

The powder coating composition of the present invention does not require the addition of a surfactant, and furthermore, since no organic solvent is used in the manufacturing process, it also has the advantage of being less environmentally hazardous. Furthermore, by not adding a surfactant in the coating manufacturing process, the powder coating composition of the present invention can increase the purity of the coating film and obtain better performance.

The powder particles of the present invention are powder particles in which (A) a heat-fusible polymer and (B) a filler are fused together. The powder particles can be obtained by premixing the heat-fusible polymer and the filler in water to form an aqueous dispersion, and then heating the mixture.

A. Heat-melting polymer The heat-melting polymer of the present invention refers to a polymer that melts by heating, and is a polymer that has a glass transition point and/or a melting point. Specific examples of heat-melting polymers include polyimide (PI), polyamideimide (PAI), polyamide, polyester, polyethylene terephthalate, polyphenylene sulfide, polysulfone, polyetherimide, polyethersulfone (PES), polyetheretherketone, polyetherketoneketone, and the like. Among these heat-melting polymers, polyetherimide (PEI), polyphenylsulfone (PPS), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and the like, which have heat resistance and high mechanical strength, are preferred. Since the heat-melting polymer is used by welding with a filler, the heat-melting polymer used in the present invention does not include fluororesins, which generally have excellent non-adhesive properties. The shape of the heat-melting polymer is not particularly limited, and examples thereof include powder, granules, granulated granules, pellets, and the like. The average particle size of the heat-fusible polymer is preferably 0.1 to 300 μm, more preferably 1 to 100 μm, and further preferably 5 to 70 μm.

Commercially available heat-fusible polymers can be used. Examples of commercially available heat-fusible polymers include the ULTEM (registered trademark) series manufactured by SABIC Corporation and PPS manufactured by DIC Corporation.

B. Filler The filler of the present invention can be inorganic particles, and can be selected according to the application of the coating film, taking into consideration its water resistance and chemical resistance. The filler of the present invention is preferably made of a material that does not dissolve in water. Specific examples of the filler include metal powder, metal oxide (aluminum oxide, zinc oxide, tin oxide, titanium oxide, etc.), glass beads, glass flakes, glass particles, ceramics, silicon carbide, silicon oxide, calcium fluoride, carbon black, graphite, mica, barium sulfate, etc. The filler of the present invention is preferably heat-resistant to at least 200°C or more, preferably 300°C or more, and does not promote the decomposition of the fluororesin. Among the above fillers, silicon oxide, aluminum oxide, zinc oxide, tin oxide, and barium sulfate are preferred. The particle size of the filler is not particularly limited, but it is preferably smaller than the average particle size of the heat-fusible polymer in terms of ease of uniform mixing with the heat-fusible polymer. The average particle size of the filler is from 0.1 to 30 μm, more preferably from 0.2 to 20 μm, and further preferably from 0.3 to 10 μm.

(Powder particles of the present invention)
The powder particles of the present invention are powder particles in which (A) a heat-fusible polymer and (B) a filler are fused together. The powder particles can be obtained by premixing the heat-fusible polymer and the filler in water to form an aqueous dispersion, and then heating the mixture. It is preferable that the particle size of the filler is small, but when a grinding step described below is included, the filler is also ground in this step, so the particle size of the filler used is not particularly limited. The amount of the filler added is preferably 30 to 300 parts by weight, more preferably 50 to 200 parts by weight, and even more preferably 80 to 150 parts by weight, relative to 100 parts by weight of the polymer.

The particle size of the powder particles of the present invention is preferably 1 to 200 μm, and more preferably 150 μm or less. For example, if a sieve with a mesh size of 150 μm is used and the particles that pass through this sieve are collected, particles with a particle size of 150 μm or less, usually particles of about 5 to 150 μm, can be obtained. By using a sieve, particles with a uniform particle size can be easily obtained.

Generally, fluororesin has non-adhesive properties and does not adhere well to fillers. Therefore, if the contact interface between the fluororesin and the filler increases, the filler part and the fluororesin laminate tend to peel off, and this causes the corrosion resistance, steam resistance, and durability of the part to be deteriorated. In contrast, the powder particles of the present invention, as described above, are integrated with the heat-fusible polymer by welding, thereby reducing the contact interface between the filler and the fluororesin added later. As a result, the adhesion between the substrate and the fluororesin layer is excellent, and it is possible to obtain a coating film with improved corrosion resistance, steam resistance, and durability by suppressing the intrusion of heat, moisture, corrosive substances, etc., preventing peeling of the fluororesin laminate.

2. Powder Coating Composition The powder coating composition of the present invention is a composition containing (A) powder particles having a heat-fusible polymer and (B) a filler melt-adhered thereto, and (C) a fluororesin powder.

C. Fluorine Resin The fluororesin of the present invention may be, but is not limited to, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-hexafluoropropylene-perfluoro(alkyl vinyl ether) copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, polychlorotrifluoroethylene, chlorotrifluoroethylene-ethylene copolymer, or the like.

The fluororesin of the present invention is preferably a heat-meltable fluororesin that exhibits melt fluidity at or above its melting point. Among these, from the viewpoint of the non-adhesiveness and heat resistance of the coating film, heat-meltable perfluororesins such as low molecular weight PTFE, PFA, FEP, and tetrafluoroethylene-hexafluoropropylene-perfluoro(alkyl vinyl ether) copolymers can be preferably used, with PFA being particularly preferably used.

The alkyl group of the perfluoro(alkyl vinyl ether) in the PFA preferably has 1 to 5 carbon atoms, and among these, perfluoro(propyl vinyl ether) (PPVE), perfluoro(ethyl vinyl ether) (PEVE), and perfluoro(methyl vinyl ether) (PMVE) are particularly suitable. The amount of perfluoro(alkyl vinyl ether) in the PFA is preferably in the range of 1 to 50% by weight.

The fluororesin used in the present invention is preferably one that has a melt flow rate (MFR) of (1-100) g/10 min, preferably (1-70) g/10 min at 372°C±1°C, and is melt moldable. Here, several copolymers with different MFRs can be mixed and used to achieve a melt flow rate (MFR) of (1-100) g/10 min, preferably (1-70) g/10 min at 372°C±1°C.

As the fluororesin of the present invention, for example, fluororesin particles having a so-called core-shell structure made of fluororesins with different melting points, as described in Patent Document 3, may be used. A fluororesin having a multilayer structure made of at least two fluororesins with different melting points preferably has an outermost layer of 90 to 5% by weight of fluororesin and an inner layer of 10 to 95% by weight of high-melting-point fluororesin. The ratio of the outermost layer to the inner layer can be selected taking into consideration the desired chemical resistance and gas permeability, linear expansion coefficient, maximum strength, etc. Such a fluororesin can be obtained as PFA particles containing PTFE, for example, by dispersing PTFE particles in a polymerization medium in a PFA polymerization tank in advance to initiate polymerization of PFA.

The fluororesin powder of the present invention may be any powder of the fluororesin, with an average particle size of 0.05 to 75 μm, preferably 5 to 40 μm, and more preferably 5 to 30 μm. The fluororesin powder of the present invention can be obtained by powdering the fluororesin by a conventionally known method, but a commercially available product may also be used. Examples of commercially available products include Teflon (registered trademark) MJ-102, MJ-103, etc., manufactured by Mitsui-Chemours Fluoroproducts Co., Ltd., and Teflon (registered trademark) 532G-5011, etc., manufactured by Chemours.

(Powder coating composition of the present invention)
The powder coating composition of the present invention is a composition containing the powder particles of the present invention and a fluororesin powder, that is, a composition containing powder particles to which (A) a heat-fusible polymer and (B) a filler are fused, and (C) a fluororesin powder. The powder coating composition of the present invention contains 80 to 50% by weight of powder particles and 20 to 50% by weight of fluororesin powder, preferably 75 to 55% by weight of powder particles and 25 to 45% by weight of fluororesin powder, and more preferably 60 to 70% by weight of powder particles and 40 to 30% by weight of fluororesin powder, based on the total amount of the powder coating composition. If the content of the fluororesin powder is too high, the adhesion to the substrate may decrease, and if the content is too low, the adhesion to layers containing other fluororesins may decrease.

(Optional ingredients)
In the powder coating composition of the present invention, in addition to the powder particles and the fluororesin powder, any additive may be further contained as necessary. The additive is not particularly limited, and may be, for example, one used in a general coating composition. The additive may be, for example, a pigment, a filler, a leveling agent, a solid lubricant, a moisture absorbent, a surface conditioner, an ultraviolet absorber, a light stabilizer, a plasticizer, a color separation inhibitor, a scratch inhibitor, an antifungal agent, an antibacterial agent, an antioxidant, an antistatic agent, a silane coupling agent, etc.

Specific examples of the additives include color pigments such as carbon, titanium oxide, red iron oxide, and mica, anti-rust pigments, calcined pigments, body pigments, lustrous flat pigments, scaly pigments, wood flour, quartz sand, carbon black, clay, talc, diamond, fluorinated diamond, corundum, silica stone, boron nitride, boron carbide, silicon carbide, fused alumina, tourmaline, jade, germanium, zirconium oxide, zirconium carbide, chrysoberyl, topaz, beryl, garnet, glass, glass powder, mica powder, metal powder (gold, silver, copper, platinum, stainless steel, aluminum, etc.), various reinforcing materials, various extenders, conductive fillers, etc.

The content of the additives is preferably 0 to 10.0% by weight, more preferably 0 to 5.0% by weight, based on the powder composition. The powder coating composition of the present invention is usually suitable for use as a primer coating (undercoat) for adhering a fluororesin layer to a substrate, but can also be used as a one-coat coating without using a primer coating.

(Preparation of coating film)
A coating film can be formed by applying the powder coating composition of the present invention to a substrate and heating it. The substrate is not particularly limited, and examples thereof include metal substrates such as iron, aluminum, copper, and stainless steel, glass, ceramic, and heat-resistant plastic substrates. The method of application to the substrate is not particularly limited, and can be appropriately selected depending on the form of the substrate, and a conventionally known method such as electrostatic powder coating can be used. The thickness of the coating depends on the application, and is, for example, 20 to 150 μm, preferably 30 to 100 μm.

A coating film containing the powder coating composition of the present invention has non-adhesive properties, as well as excellent corrosion resistance, steam resistance, and adhesion to substrates. Therefore, it can be widely used in office automation applications, chemical corrosion protection applications, food heating and processing equipment applications, sliding materials, automotive applications, building materials, and semiconductor manufacturing equipment components.

3. Method for producing powder particles and powder coating composition (method for producing powder particles)
The powder particles of the present invention can be obtained by the following steps (1) to (3).
(1) A step of mixing a heat-fusible polymer and a filler in water to obtain an aqueous dispersion;
(2) a step of heating the aqueous dispersion to remove water to obtain a solid, and (3) a step of pulverizing the solid to obtain powder particles.

In step (1), the heat-fusible polymer and filler are added to water and dispersed. The water used here is preferably water that is usually called pure water, from which impurities such as ions have been removed by distillation or ion exchange. Methods for dispersing the heat-fusible polymer and filler include dispersion treatment using a normal stirrer, as well as homogenizers, ultrasonic dispersers, colloid mills, bead mills, etc. Here, a dispersant such as a surfactant may be added, but it is preferable not to add a dispersant because this reduces the burden on the environment.

In step (2), the dispersion obtained in step (1) is heated and dried to remove moisture. The drying temperature can be, for example, 60 to 160°C, preferably 80 to 140°C, and more preferably 100°C to 120°C. The drying time can be 5 minutes to 10 hours, preferably 1 hour to 8 hours, more preferably 2 hours to 6 hours, and even more preferably 3 hours to 5 hours. The drying apparatus can be a method of drying in an oven set at a predetermined temperature, or a method using, for example, an arch dryer, a floating dryer, a drum dryer, or an infrared dryer. Since no organic solvent is used in the manufacturing method of the present invention, the drying process can be carried out without requiring special equipment such as explosion-proof equipment.

Following step (2), it is preferable to include a step of heating at a temperature equal to or higher than the glass transition point of the heat-fusible polymer. By including this step, powder particles in which the heat-fusible polymer and the filler are fused together can be obtained. By forming powder particles in which the heat-fusible polymer and the filler are fused together, the filler is less likely to detach from the powder particles, and as a result, a coating film with superior corrosion resistance and steam resistance can be obtained.

Step (3) is a step of pulverizing the solid obtained in step (2). For example, a pulverizer such as a high-pressure homogenizer, grinder, impact pulverizer, bead mill, jet mill, hammer mill, pin mill, ball mill, tube mill, grinding mill, air sweep mill, disk mill, vibration mill, stone mill, or planetary motion mill can be used for the pulverization method. After pulverization, it is preferable to adjust the particle size using a sieve. The opening of the sieve used can be appropriately selected depending on the size of the particles obtained in step (3), but it is preferable to set the opening to 150 μm or less from the viewpoint of uniformity of the powder coating composition.

(Method of producing powder coating composition)
The powder coating composition of the present invention can be produced by adding a fluororesin powder and mixing it in step (4) in addition to steps (1) to (3) in the above-mentioned method for producing powder particles. In mixing, a conventionally known method for mixing powders can be used. For example, any method can be used, such as a method of putting the powders to be mixed in one container and rotating the container itself, a method of mixing the powders in a container containing the powders to be mixed with a mixing blade, or a method of stirring and mixing with an air current.

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

<Ingredients>
A. Heat-fusible polymers 1. Polyetherimide (PEI)
ULTEM 1010P Powder (made by SABIC INNOVATIVE PLASTICS, glass transition point 217°C)
2. Polyphenylene sulfide (PPS)
Manufactured by DIC Corporation. Average particle size: 12-16 μm, melting point: 278°C
3. Polyetheretherketone (PEEK)
VICOTE (registered trademark) 704 (manufactured by VICTREX, melting point 343°C)
4. Polyetherketoneketone (PEKK)
KSTONE (registered trademark) CC-5601 (manufactured by Shandong Kaisheng New Materials Co., Ltd., melting point 308°C)
B. Filler 1. Barium sulfate ( _BaSO4 )
BLANC FIXE MICRO (manufactured by SACHTLEBEN, average particle size 0.8 μm)
_2. Aluminum oxide ( _Al2O3 )
SGA-16 (manufactured by ALMATIS, average particle size 0.4 μm)
3. Carbon Black (CB)
MPC Channel Black (manufactured by Keystone Aniline)
C. Fluoroplastic PFA (MJ-102, manufactured by Mitsui-Chemours Fluoroproducts, average particle size 20 μm)

[Example 1]
(Preparation of Powder Coating Composition)
(Step (1)) 3.2 L of pure water was placed in a 5 L beaker, and 1 kg of barium sulfate and 1 kg of PEI were added thereto, followed by stirring at 300 rpm for 30 minutes using a stirrer (manufactured by Yamato Scientific Co., Ltd.).
(Step (2)) The dispersion obtained in step (1) was left to stand for 2 hours in an oven set at 120° C. to remove moisture, and then left to stand for another 2 hours in an oven set at 300° C.
(Step (3)) The solid obtained in step (2) was pulverized in a mill grinder (manufactured by Osaka Chemical Co., Ltd.) at 25,000 rpm, and then passed through a sieve with 150 μm openings to obtain powder particles.
(Step (4)) 350 g of PFA was added to 650 g of the powder particles obtained in step (3) to obtain a powder coating composition. The blending ratio of PEI:BaSO ₄ :PFA was 32.5%:32.5%:35.0%.

(Preparation of test specimens)
A 50 mm x 100 mm aluminum (A1050) substrate was used, and about 10 mm of one side was masked and shot blasted with #60 alumina. The powder coating composition was then electrostatically powder coated using a powder coating spray gun (PARKER IONICS, GX355HW) to form a primer layer with a thickness of 50 μm. The masking tape was peeled off, and PFA (MJ-102) was electrostatically powder coated on the primer layer using a powder coating spray gun, and baked at 390°C (substrate temperature) for 30 minutes to form a topcoat layer, and the resulting fluororesin laminate was used as a test piece.

(Measurement of Adhesion Strength)
Using the above test piece, the fluororesin laminate was cut into a width of 10 mm in the short side direction, and the masking portion (the fluororesin laminate portion without the primer layer) was peeled off toward the fluororesin laminate portion with the primer layer. The peeled off masking portion (the fluororesin laminate portion without the primer layer) was protected with masking tape. Using a Tensilon universal testing machine (manufactured by A&D Co., Ltd.), the portion protected with the masking tape was clamped in the chuck of the testing machine and pulled at a speed of 50 mm/min in accordance with the measurement method of adhesive peel strength (90 degree peel test method) specified in JIS K 6854, to measure the adhesion force of the fluororesin laminate portion with the primer layer. The unit is gf/cm. The adhesion force was measured on the test piece before the steam resistance test described later and on the test piece after the steam resistance test.

(Steam resistance test)
Using a pressure cooker tester (PCT VS-277, manufactured by Kyosin Engineering Corporation), the test pieces were left in steam at 170°C and 0.8 MPa for 300 hours, and then allowed to cool to room temperature. The presence or absence of blisters (eczema-like swelling) was observed visually and under a microscope. Those without blisters were rated as ◯, and those with blisters were rated as ×. The adhesion strength was measured using the test pieces after the steam resistance test.

[Examples 2 to 4]
Test pieces were obtained in the same manner as in Example 1, except that the amounts of PEI and barium sulfate added were changed to the blend ratios shown in Table 1, instead of 32.5% PEI and 32.5% barium sulfate used in Example 1.

[Example 5]
Test pieces were obtained in the same manner as in Example 1, except that PEEK was used instead of PEI in Example 1, and step 2 was carried out at the following temperature.
(Step (2) (Example 5))
The dispersion obtained in step (1) was left to stand for 2 hours in an oven set at 120° C. to remove moisture, and then left to stand for another 2 hours in an oven set at 350° C.

[Example 6]
Test pieces were obtained in the same manner as in Example 1, except that PEKK was used instead of PEI in Example 1, and step 2 was performed at the following temperature.
(Step (2) (Example 6))
The dispersion obtained in step (1) was left to stand for 2 hours in an oven set at 120° C. to remove moisture, and then left to stand for another 2 hours in an oven set at 310° C.

[Example 7]
A test piece was obtained in the same manner as in Example 1, except that the step (2) in Example 1 was changed to the following step (2').
(Step (2'))
The dispersion obtained in step (1) was left to stand in an oven set at 120° C. for 2 hours to remove moisture.

[Example 8]
A test piece was obtained in the same manner as in Example 5, except that the step (2) in Example 5 was changed to the following step (2').
(Step (2'))
The dispersion obtained in step (1) was left to stand in an oven set at 120° C. for 2 hours to remove moisture.

[Comparative Example 1]
A composition was obtained by mixing 325 g of PEI, 325 g of barium sulfate, and 350 g of PFA in a weight ratio of 32.5%:32.5%:35.0%. A test piece was obtained using the obtained composition in the same manner as in Example ₁ (preparation of test piece).

[Comparative Examples 2 to 6]
Test pieces were obtained in the same manner as in Comparative Example 1, except that the amounts of PEI and barium sulfate added were changed to the blend ratios shown in Table 1, instead of 32.5% PEI and 32.5% barium sulfate used in Comparative Example 1.

The compounding ratios and test results of the Examples and Comparative Examples are shown in Table 1. Example 1 and Comparative Example 1 have the same composition, but Example 1 uses a powder coating composition produced by the manufacturing method of the present invention, while Comparative Example 1 is an example using a composition obtained by simply mixing materials. It can be seen that Example 1 has clearly greater adhesion. Similar results were obtained in Comparative Examples 2 to 6, which correspond to Examples 2 to 4 and 6 to 8.

The present invention is not limited to the disclosure of the examples described in this specification or the embodiments of the invention disclosed in this specification, but includes the contents of the invention with appropriate modifications based on the matters disclosed in this specification, etc., as long as they do not contradict the spirit of the present invention.

The powder coating composition of the present invention has excellent adhesion between the substrate and the fluororesin layer, and prevents the intrusion of heat, moisture, corrosive substances, etc., preventing peeling of the fluororesin laminate, and can provide a coating film with improved corrosion resistance, steam resistance, and durability.

Claims (14)

Powder particles obtained by premixing a heat-fusible polymer and a filler in water to form an aqueous dispersion, and then heating it. The powder particles according to claim 1, in which the heat-fusible polymer and the filler are fused together. The powder particles according to claim 1, wherein the heat-fusible polymer is at least one selected from polyimide, polyamideimide, polyamide, polyester, polyethylene terephthalate, polyphenylene sulfide, polysulfone, polyetherimide, polyethersulfone, polyetheretherketone, and polyetherketoneketone. The powder particles according to claim 1, wherein the heat-fusible polymer is at least one selected from polyphenylene sulfide, polyetherimide, polyetheretherketone, and polyetherketoneketone. The powder particles according to claim 1, wherein the filler is at least one inorganic particle selected from silicon carbide, silicon oxide, aluminum oxide, zinc oxide, tin oxide, titanium oxide, barium sulfate, and carbon black. The powder particles according to claim 1 contain 30 to 300 parts by weight of a filler per 100 parts by weight of the heat-fusible polymer. The powder particles according to claim 1, having a particle size of 150 μm or less. A powder coating composition containing the powder particles according to any one of claims 1 to 7 and a fluororesin powder. The powder coating composition according to claim 8, wherein the fluororesin powder is a thermofusible fluororesin. The powder coating composition according to claim 8, wherein the fluororesin powder is a perfluororesin. The powder coating composition according to claim 8, which contains 80-50% by weight of powder particles and 20-50% by weight of fluororesin powder, based on the total weight of the powder coating composition. (1) mixing a heat-fusible polymer and a filler in water to obtain an aqueous dispersion;
(2) heating the aqueous dispersion to remove water to obtain a solid;
(3) pulverizing the solid to obtain powder particles;
A method for producing powder particles comprising the steps of: The method for producing powder particles according to claim 12, further comprising, following step (2), a step of heating at a temperature equal to or higher than the glass transition point of the heat-fusible polymer. (1) mixing a heat-fusible polymer and a filler in water to obtain an aqueous dispersion;
(2) heating the aqueous dispersion to remove water to obtain a solid;
(3) pulverizing the solid to obtain powder particles;
(4) adding and mixing a fluororesin powder with the powder particles to obtain a powder coating composition;
A method for producing a powder coating composition comprising the steps of: