Powder particles, powder coating composition containing powder particles and fluororesin, and method for producing same

Abstract

The purpose of the present invention is to provide powder particles for improving the adhesive strength between a substrate and a fluororesin layer. The present invention is a powder particle obtained by premixing a hot melt polymer and a filler in water to obtain an aqueous dispersion and then heating the aqueous dispersion.

Description

Cross-references to related applications

[0001] This application claims priority to Japanese Patent Application No. 2023-141274, filed on August 31, 2023, the entire disclosure of which is incorporated herein by reference. Technical Field

[0002] This invention relates to: powder particles that improve adhesion between a substrate and a fluoropolymer layer; and powder coating compositions containing powder particles and fluoropolymers that are useful as primers. Furthermore, this invention also relates to methods for manufacturing these powder particles and powder coating compositions. Background Technology

[0003] Fluororesin possesses excellent chemical resistance, non-pressure-sensitive adhesion, heat resistance, and electrical insulation properties, and has been widely and routinely used as a coating material. However, the non-pressure-sensitive adhesion of fluororesins tends to cause adhesion defects when directly applied to substrates (especially various metal substrates). Therefore, in many cases, a primer layer with good adhesion to the substrate is provided as the base coat for the fluororesin.

[0004] The applicant has proposed polymer particles that exhibit excellent adhesion between the substrate and the layer and prevent peeling caused by heat, moisture, etc., as well as a coating composition containing the polymer particles (Patent Document 1). This coating composition has excellent effects, but it has some problems, such as the use of organic solvents in the preparation of the polymer particles, which can cause environmental burden, and the resulting coating composition being an aqueous dispersion, which requires the addition of surfactants to ensure the dispersibility of the fluoropolymer, etc.

[0005] On the other hand, powder coatings are known to have the following advantages: they are environmentally friendly because they do not use solvents, they are resource-efficient because the powder can be easily reused, and they have excellent coating processability. Patent Document 2 discloses a powder primer composition containing meltable fluoropolymer powder and polyethersulfone powder. However, there is still a need for coating compositions with excellent adhesion and corrosion resistance.

[0006] Existing technical documents

[0007] Patent documents

[0008] [Patent Document 1] Japanese Unexamined Patent Application 2013-231098

[0009] [Patent Document 2] Japanese Unexamined Patent Application 2022-137848

[0010] [Patent Document 3] Japanese Unexamined Patent Application 2007-320267 Summary of the Invention

[0011] The problem to be solved by the present invention

[0012] The object of this invention is to provide powder particles with excellent adhesive strength between a substrate and a fluoropolymer layer, and to provide a powder coating composition that, by containing the powder particles, prevents the fluoropolymer laminate from peeling off and improves corrosion resistance, steam resistance, and durability by inhibiting the penetration of heat, moisture, corrosive substances, etc., through excellent adhesion. Furthermore, the object of this invention is to provide a method for manufacturing these powder particles and the powder coating composition.

[0013] Problem Solving Methods

[0014] One embodiment of the invention involves obtaining powder particles by premixing a hot-melt polymer and a filler in water to obtain an aqueous dispersion, and then heating the aqueous dispersion. In the powder particles, the hot-melt polymer and the filler are preferably fused together. The hot-melt polymer is preferably selected from at least one of polyimide, polyamide-imide, polyamide, polyester, polyethylene terephthalate, polyphenylene sulfide, polysulfone, polyetherimide, polyethersulfone, polyetheretherketone, and polyetherketoneketone, and more preferably from at least one of polyphenylene sulfide, polyetherimide, polyetheretherketone, and polyetherketoneketone. Furthermore, the filler is preferably at least one inorganic particle selected from inorganic particles selected from silicon carbide, silicon oxide, alumina, zinc oxide, tin oxide, titanium oxide, barium sulfate, and carbon black. The powder particles preferably contain 30 to 300 parts by weight of filler relative to 100 parts by weight of the hot-melt polymer. The particle size is preferably 150 µm or smaller.

[0015] Furthermore, one embodiment of the present invention is a powder coating composition comprising: powder particles obtained by premixing a hot-melt polymer and a filler in water to obtain an aqueous dispersion, followed by heating the aqueous dispersion; and fluoropolymer powder. The fluoropolymer powder preferably contains a hot-melt fluoropolymer, and more preferably a perfluorinated resin. Furthermore, the present invention is a powder coating composition containing, based on the total amount of the powder coating composition, 80% to 50% by weight of powder particles and 20% to 50% by weight of fluoropolymer powder.

[0016] Furthermore, one embodiment of the present invention is a method for manufacturing powder particles, the method comprising: (1) The step of mixing hot melt polymer and filler in water to obtain an aqueous dispersion; (2) The step of heating the aqueous dispersion and removing water to obtain a solid; and (3) The step of pulverizing the solid to obtain powder particles. After step (2), it is preferable to further include a step of heating at or above the glass transition point of the hot melt polymer.

[0017] Furthermore, one embodiment of the present invention is a method for manufacturing a powder coating composition, the method comprising: (1) The step of mixing hot melt polymer and filler in water to obtain an aqueous dispersion; (2) The step of heating the aqueous dispersion and removing water to obtain a solid; (3) The step of pulverizing the solid to obtain powder particles; and (4) The step of adding fluoropolymer powder to the powder particles and mixing them to obtain a powder coating composition.

[0018] Effects of the present invention

[0019] The powder coating composition of this invention exhibits excellent adhesive strength between the substrate and the fluoropolymer layer, and prevents the fluoropolymer laminate from peeling off by inhibiting the penetration of heat, moisture, corrosive substances, etc., thereby obtaining a coating film with improved corrosion resistance, vapor resistance, and durability. Therefore, it can be widely used in OA applications, chemical corrosion prevention applications, food heating and processing equipment applications, sliding material applications, automotive applications, building material applications, and components for semiconductor manufacturing equipment, etc.

[0020] Furthermore, the powder coating composition of the present invention does not require the addition of surfactants or the use of organic solvents during its manufacturing process, which also has the advantage of low environmental impact. In addition, by not adding surfactants during the coating film manufacturing process, the powder coating composition of the present invention can improve the purity of the coating film and obtain more favorable performance. Detailed Implementation

[0021] 1. Powder particles

[0022] The powder particles of the present invention are powder particles in which (A) a hot-melt polymer and (B) a filler are fused together. These powder particles can be obtained by premixing the hot-melt polymer and the filler in water to obtain an aqueous dispersion and then heating the aqueous dispersion.

[0023] A. Hot melt polymer

[0024] The hot-melt polymer of the present invention is a polymer that melts upon heating and has a glass transition point and / or melting point. Specific examples of such hot-melt polymers may include polyimide (PI), polyamide-imide (PAI), polyamide, polyester, polyethylene terephthalate, polyphenylene sulfide, polysulfone, polyetherimide, polyethersulfone (PES), polyetheretherketone, polyetherketoneketone, etc. Among these hot-melt polymers, polyetherimide (PEI), polyphenylene sulfone (PPS), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), etc., are preferred due to their heat resistance and high mechanical strength. The hot-melt polymer is used by fusing with fillers, and therefore, the hot-melt polymers used in the present invention do not include fluoropolymers, which generally have excellent non-pressure-sensitive adhesion. The shape of the hot-melt polymer is not particularly limited, but may be, for example, powder, granules or granulated pellets, granules, etc. The average particle size of the hot melt polymer is preferably from 0.1 μm to 300 μm, more preferably from 1 μm to 100 μm, and even more preferably from 5 μm to 70 μm.

[0025] Commercially available hot melt polymers can be used. Examples of commercially available hot melt polymers include ULTEM, which is available from SABIC. ® Series, PPS available from DIC, etc.

[0026] B. Packing

[0027] Inorganic particles can be used as fillers in this invention, and the selection can be based on the application of the coating film, taking into account factors such as water resistance and chemical resistance. The filler of this invention is preferably prepared from a material insoluble in water. Specific examples of fillers include metal powders, metal oxides (alumina, 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 this invention has a heat resistance of at least 200°C or higher, and preferably 300°C or higher, and preferably does not promote the decomposition of fluoropolymers. Among the above fillers, silicon oxide, alumina, zinc oxide, tin oxide, and barium sulfate are preferred. The particle size of the filler is not particularly limited, but is preferably smaller than the average particle size of the hot-melt polymer from the perspective of promoting uniform mixing with the hot-melt polymer. The average particle size of the filler is preferably from 0.1 μm to 30 μm, more preferably from 0.2 μm to 20 μm, and even more preferably from 0.3 μm to 10 μm.

[0028] The powder particles of the present invention

[0029] The powder particles of the present invention are powder particles in which (A) a hot-melt polymer and (B) a filler are fused together. These powder particles can be obtained by premixing the hot-melt polymer and the filler in water to obtain an aqueous dispersion and then heating the aqueous dispersion. The filler particle size is preferably small. However, if the step includes a pulverizing step described later, the filler is also pulverized in that step. Therefore, there is no particular limitation on the particle size of the filler used. The amount of filler added relative to 100 parts by weight of polymer is from 30 parts by weight to 300 parts by weight, preferably from 50 parts by weight to 200 parts by weight, and more preferably from 80 parts by weight to 150 parts by weight.

[0030] The particle size of the powder particles of the present invention is preferably from 1 μm to 200 μm, and even more preferably from 150 μm or smaller. For example, using a 150 μm mesh sieve to collect particles passing through the sieve can yield particles with a size of 150 μm or smaller, typically from about 5 μm to 150 μm. By using a sieve, particles of uniform size can be easily obtained.

[0031] Generally, fluoropolymers have non-pressure-sensitive adhesion properties and do not adhere well to fillers. Therefore, if the contact interface between the fluoropolymer and the filler increases, the filler portion is prone to peeling off from the fluoropolymer laminate, resulting in poor corrosion resistance, vapor resistance, and durability in that portion. In contrast, the powder particles of the present invention reduce the contact interface between the filler and the subsequently added fluoropolymer by fusing and integrating the hot-melt polymer and filler as described above. Therefore, the adhesion strength between the substrate and the fluoropolymer layer is excellent, and peeling of the fluoropolymer laminate is prevented by inhibiting the penetration of heat, moisture, corrosive substances, etc., thereby obtaining a coating film with improved corrosion resistance, vapor resistance, and durability.

[0032] 2. Powder coating composition

[0033] The powder coating composition of the present invention is a composition containing the following components: (A) hot melt polymer and (B) filler fused together in powder particles; and (C) fluoropolymer powder.

[0034] C. Fluoropolymer

[0035] Examples of fluororesins of the present invention include, but are not limited to, polytetrafluoroethylene (PTFE), perfluoroethylene tetrafluoroethylene (PFA), perfluoroethylene tetrafluoropropylene (FEP), perfluoroethylene tetrafluoropropylene (PFA), perfluoroethylene tetrafluoropropylene (PFA), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene, and chlorotrifluoroethylene copolymer.

[0036] The fluororesin of the present invention is preferably a hot-melt fluororesin that exhibits melt flowability at or above its melting point. From the perspective of non-pressure-sensitive adhesion and heat resistance of the coating film, hot-melt perfluororesins, such as low molecular weight PTFE, PFA, FEP, perfluoropropylene tetrafluoroethylene copolymer, etc., are preferred, and PFA is particularly preferred.

[0037] The alkyl group of the perfluoro(alkyl vinyl ether) in 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 preferred. The amount of perfluoro(alkyl vinyl ether) in PFA is preferably in the range of 1% to 50% by weight.

[0038] The fluoropolymer used in this invention has a melt flow rate (MFR) of (1 to 100) g / 10 min, preferably (1 to 70) g / 10 min, at 372°C ± 1°C, and is preferably melt-molded. In this document, several copolymers with different MFRs may be blended to obtain a melt flow rate (MFR) of (1 to 100) g / 10 min, preferably (1 to 70) g / 10 min, at 372°C ± 1°C.

[0039] Alternatively, fluoropolymer particles with a so-called core-shell structure containing fluoropolymers with different melting points can be used as the fluoropolymer in this invention, as described, for example, in Patent Document 3. The fluoropolymer having a multilayer structure (containing at least two types of fluoropolymers with different melting points) preferably contains 90% to 5% fluoropolymer in the outermost layer and 10% to 95% high-melting-point fluoropolymer in the inner layer. The ratio of the outermost to the inner layer can be selected based on desired chemical resistance and permeability, linear expansion coefficient, maximum strength, etc. Such fluoropolymers can be obtained, for example, as PTFE-containing PFA particles by pre-dispersing PTFE particles in a PFA polymerization tank in a polymerization medium to initiate the polymerization of PFA.

[0040] The fluororesin powder of the present invention can be any of the above-mentioned fluororesin powders, and its average particle size is 0.05 μm to 75 μm, preferably 5 μm to 40 μm, and more preferably 5 μm to 30 μm. The fluororesin powder of the present invention can be obtained by pulverizing the above-mentioned fluororesin using conventionally known methods, or by using commercially available products. Examples of commercially available products include Teflon, which is available from Chemours-Mitsui Fluoroproducts Co., Ltd. ® MJ-102, MJ-103, and other Teflon models available from Chemours.® 532G-5011, etc.

[0041] The powder coating composition of the present invention

[0042] The powder coating composition of the present invention is a composition containing the powder particles of the present invention and fluoropolymer powder; in other words, it is a composition containing: powder particles in which (A) a hot-melt polymer and (B) a filler are fused; and (C) fluoropolymer powder. Based on the total amount of the powder coating composition, the powder coating composition of the present invention contains 80% to 50% by weight of powder particles and 20% to 50% by weight of fluoropolymer powder, preferably 75% to 55% by weight of powder particles and 25% to 45% by weight of fluoropolymer powder, and more preferably 60% to 70% by weight of powder particles and 40% to 30% by weight of fluoropolymer powder. If the amount of fluoropolymer powder is too high, the adhesion to the substrate may be reduced; and if the amount is too low, the adhesion to another fluoropolymer-containing layer may be reduced.

[0043] Optional components

[0044] In addition to powder particles and fluoropolymer powders, the powder coating compositions of the present invention may further contain optional additives as needed. There are no particular limitations on the aforementioned additives, and they include, for example, those additives used in general coating compositions. Examples of the aforementioned additives include pigments, fillers, leveling agents, solid lubricants, hygroscopic agents, surface modifiers, UV absorbers, light stabilizers, plasticizers, anti-staining agents, anti-scratch agents, antifungal agents, antibacterial agents, antioxidants, antistatic agents, silane coupling agents, etc.

[0045] Specific examples of additives include carbon, titanium dioxide, iron oxide red, mica and other colored pigments, anti-corrosion pigments, fired pigments, bulk pigments, photoluminescent polarizing pigments, flake pigments, wood flour, quartz sand, carbon black, clay, talc, diamond, fluorinated diamond, corundum, quartz, 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 powders (gold, silver, copper, platinum, stainless steel, aluminum, etc.), various reinforcing materials, various reinforcing and additive materials, conductive fillers, etc.

[0046] The amount of the additives is preferably from 0% to 10.0% by weight, and more preferably from 0% to 5.0% by weight, relative to the powder composition described above. The powder coating composition of the present invention is generally suitably used as a primer coating (inner coating) for adhering a fluoropolymer layer to a substrate; however, the composition can also be used as a single-coat coating without using a primer coating.

[0047] Preparation of coating film

[0048] The powder coating composition of the present invention can be applied to a substrate and heated to form a coating film. The substrate is not particularly limited and includes iron, aluminum, copper, stainless steel and other metallic substrates, glass, ceramics, and heat-resistant plastic substrates, etc. The method of application to the above-mentioned substrates is not particularly limited and can be selected according to the form of the substrate, etc. For example, conventionally known methods, such as electrostatic powder coating, can be used. The coating thickness depends on the application. For example, it can be applied at a thickness of 20 μm to 150 μm, preferably 30 μm to 100 μm.

[0049] The coating film containing the powder coating composition of the present invention exhibits excellent corrosion resistance, vapor resistance, adhesion to substrates, and non-pressure-sensitive adhesion. Therefore, it can be widely used in OA applications, chemical corrosion prevention applications, food heating and processing equipment applications, sliding material applications, automotive applications, building material applications, and components for semiconductor manufacturing equipment, etc.

[0050] 3. Method for manufacturing powder particles and powder coating compositions

[0051] Methods for manufacturing powder particles

[0052] The powder particles of the present invention can be obtained by the following steps (1) to (3). (1) The step of mixing hot melt polymer and filler in water to obtain an aqueous dispersion; (2) The step of heating the aqueous dispersion and removing water to obtain a solid; and (3) The step of crushing the solid to obtain powder particles.

[0053] In step (1), the hot-melt polymer and filler are added to water and dispersed. The water used herein is preferably water commonly referred to as pure water, from which impurities (such as ions) have been removed by distillation or ion exchange. As a method for dispersing the hot-melt polymer and filler, in addition to common dispersion methods using mixers, homogenizers, ultrasonic dispersers, colloid mills, bead mills, etc., can also be used. Although dispersants (such as surfactants) may be added herein, it is preferable not to add dispersants from the perspective of reducing environmental impact.

[0054] In step (2), the dispersion obtained in step (1) is heated and dried to remove moisture. For example, a drying temperature of 60°C to 160°C, preferably 80°C to 140°C, and more preferably 100°C to 120°C can be used. 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. Regarding the drying apparatus, acceptable drying methods include drying in an oven set to a predetermined temperature, and methods using, for example, arched dryers, floating dryers, drum dryers, infrared dryers, etc. No organic solvents are used in the manufacturing method of the present invention, therefore the drying step is carried out without the need for special facilities (such as explosion-proof equipment).

[0055] Following step (2), a heating step is preferably included at or above the glass transition point of the hot-melt polymer. By including this step, powder particles in which the hot-melt polymer and filler are fused can be obtained. By obtaining powder particles in which the hot-melt polymer and filler are fused, the filler is more difficult to detach from the powder particles, thereby producing a coating film with excellent corrosion resistance and vapor resistance.

[0056] Step (3) is the step of pulverizing the solid obtained in step (2). For example, a high-pressure homogenizer, a grinder, an impact mill, a bead mill, a jet mill, a hammer mill, a pin mill, a ball mill, a tube mill, a pulverizing mill, an air-swept mill, a disc mill, a vibratory mill, a stone mill, a planetary ball mill, or other pulverizers can be used as the pulverizing method. After pulverization, the particle size is preferably adjusted using a sieve. The sieve aperture used can be appropriately selected according to the size of the particles obtained in step (3), but from the perspective of the uniformity of the powder coating composition, it is preferably 150 μm or smaller.

[0057] Method for manufacturing powder coating composition

[0058] In addition to steps (1) to (3) of the above-described method for manufacturing powder particles, the powder coating composition of the present invention can also be manufactured by adding and mixing fluoropolymer powder in step (4). For mixing, any conventionally known method for mixing powders can be used. For example, any of the following methods can be used: placing the powder to be mixed in a single container and rotating the container itself; mixing with mixing blades in a container containing the powder to be mixed; mixing by agitation with airflow; etc. Example

[0059] The present invention will now be described in more detail based on embodiments and comparative examples. However, the present invention is not limited to these embodiments.

[0060] raw material

[0061] A. Hot melt polymer

[0062] 1. Polyetherimide (PEI)

[0063] ULTEM 1010P powder (available from SABIC INNOVATIVE PLASTICS, glass transition point: 217℃)

[0064] 2. Polyphenylene sulfide (PPS)

[0065] Available from DIC Corporation, average particle size: 12μm to 16μm, melting point: 278℃

[0066] 3. Polyetheretherketone (PEEK)

[0067] VICOTE ® 704 (available from VICTREX, melting point: 343°C)

[0068] 4. Polyetherketoneketone (PEKK)

[0069] KSTONE ® CC-5601 (available from Shandong Kaisheng New Materials, melting point 308℃)

[0070] B. Packing

[0071] 1. Barium sulfate (BaSO4)

[0072] BLANC FIXE MICRO (available from SACHTLEBEN, average particle size: 0.8 μm)

[0073] 2. Aluminum oxide (Al2O3)

[0074] SGA-16 (available from ALMATIS, average particle size: 0.4 μm)

[0075] 3. Carbon black (CB)

[0076] MPC channel black (available from Keystone Aniline)

[0077] C. Fluoropolymer

[0078] PFA (MJ-102, available from Chemours-Mitsui Fluoroproducts Co., Ltd., average particle size: 20 μm)

[0079] Example 1

[0080] Preparation of powder coating compositions

[0081] (Step (1)) Place 3.2L of pure water in a 5L beaker, add 1kg of barium sulfate and 1kg of PEI, and use a mixer (available from YAMATO SCIENTIFIC CO.LTD.) to stir the mixture at 300rpm for 30 minutes.

[0082] (Step (2)) Place the dispersion obtained in step (1) in an oven set to 120°C for 2 hours to remove moisture. Then place it in an oven set to 300°C for 2 hours.

[0083] (Step (3)) The solid obtained in step (2) is crushed at 25,000 rpm in a mill pulverizer (available from Osaka Chemical Co., Ltd.). It is then passed through a 150 μm mesh sieve to obtain powder particles.

[0084] (Step (4)) Add 350g of PFA to the 650g of powder particles obtained in step (3) to obtain a powder coating composition. The blending ratio of PEI: BaSO4: PFA is 32.5%: 32.5%: 35.0%.

[0085] Preparation of test pieces

[0086] Using a 50mm × 100mm aluminum (A1050) substrate, approximately 10mm of it was masked on one side and shot-blasted with #60 alumina. Subsequently, the powder coating composition was applied via electrostatic powder coating using a powder coating gun (GX355HW, available from Parker Ionics) to form a primer layer with a film thickness of 50μm. After removing the masking tape, PFA (MJ-102) was applied to the primer layer via electrostatic powder coating using a powder coating gun, and baked at 390°C (substrate temperature) for 30 minutes to form a topcoat. The resulting fluoropolymer laminate was used as a test piece.

[0087] Measurement of adhesive strength

[0088] Using the test pieces described above, the fluoropolymer laminate was cut into 10mm wide pieces along its short side. The masked portion (the portion of the fluoropolymer laminate without a primer layer) was peeled off from the masked portion toward the primer-coated portion of the fluoropolymer laminate. The peeled masked portion (the fluoropolymer laminate without a primer layer) was protected with masking tape. Using a Tensilon universal testing machine (available from A&D), the portion protected by the masking tape was placed between the chucks of the testing machine and pulled at a rate of 50mm / min. The adhesive strength of the fluoropolymer laminate portion with the primer layer was measured according to the method for measuring the peel strength of adhesives using a Tensilon universal testing machine (available from A&D) as specified in JIS K 6854 (90-degree peel test method). The unit is gf / cm. The adhesive strength was measured on each test piece in the test pieces before and after the steam resistance test described later.

[0089] Steam resistance test

[0090] Using a pressure cooker tester (PCT VS-277, available from Kyosin Engineering Corporation), the test pieces were placed in steam at 170°C and 0.8 MPa for 300 hours, then cooled to ambient temperature. The presence or absence of blistering (rash-like swelling) was visually inspected and observed under a microscope. If no blistering was observed, a blistering rating of "0" was given; if blistering was observed, a rating of "X" was given. The adhesive strength was then measured using the test pieces after the steam resistance test.

[0091] Examples 2 to 4

[0092] Test pieces were obtained in the same manner as in Example 1, except that the amounts of PEI: 32.5% and barium sulfate: 32.5% were replaced in Example 1, and the blending ratios were changed to those shown in Table 1.

[0093] Example 5

[0094] The test piece was obtained in the same manner as in Example 1, except that PEEK was used instead of PEI in Example 1 and step 2 was performed at the following temperature.

[0095] (Step (2) (Example 5))

[0096] The dispersion obtained in step (1) was placed in an oven set at 120°C for 2 hours to remove moisture. The dispersion was then further placed in an oven at 350°C for 2 hours.

[0097] Example 6

[0098] The test piece was 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.

[0099] (Step (2) (Example 6))

[0100] The dispersion obtained in step (1) was placed in an oven set at 120°C for 2 hours to remove moisture. It was then placed in an oven at 310°C for 2 hours.

[0101] Example 7

[0102] The test piece was obtained in the same manner as in Example 1, except that step (2) in Example 1 was changed to step (2').

[0103] (Step (2'))

[0104] The dispersion obtained in step (1) was placed in an oven set at 120°C for 2 hours to remove moisture.

[0105] Example 8

[0106] The test piece was obtained in the same manner as in Example 5, except that step (2) in Example 5 was changed to step (2').

[0107] (Step (2'))

[0108] The dispersion obtained in step (1) was placed in an oven set at 120°C for 2 hours to remove moisture.

[0109] Comparative Example 1

[0110] The composition was obtained by mixing 325g PEI, 325g barium sulfate, and 350g PFA (by weight). The blending ratio of PEI:BaSO4:PFA was 32.5%:32.5%:35.0%. The obtained composition was used to prepare test pieces as in Example 1 (Preparation of Test Pieces).

[0111] Comparative Examples 2 to 6

[0112] Test pieces were obtained in the same manner as in Comparative Example 1, except that the amounts of PEI: 32.5% and barium sulfate: 32.5% were replaced in Comparative Example 1, and the blending ratios were changed to those shown in Table 1.

[0113] The blending ratios and test results for each example and comparative example are shown in Table 1. Although the compositions of Example 1 and Comparative Example 1 are the same, Example 1 uses a powder coating composition prepared by the manufacturing method of the present invention, while Comparative Example 1 simply uses a composition obtained by mixing materials. It can be seen that the adhesive strength in Example 1 is significantly greater. Similar results were obtained in Comparative Examples 2 to 6, corresponding to Examples 2 to 4 and Examples 6 to 8.

[0114]

[0115] This invention is not limited to the embodiments described in this specification or the implementation schemes of this invention disclosed in this specification, but also covers the content of this invention with appropriate modifications based on the details disclosed in this specification, as long as such content does not conflict with the spirit of this invention.

[0116] Industrial applicability

[0117] The powder coating composition of the present invention has excellent adhesive strength between the substrate and the fluoropolymer layer, and prevents the fluoropolymer laminate from peeling off by inhibiting the penetration of heat, moisture, corrosive substances, etc., thereby obtaining a coating film with improved corrosion resistance, vapor resistance and durability.

Claims

1. A powder particle obtained by premixing a hot-melt polymer and a filler in water to obtain an aqueous dispersion and then heating the aqueous dispersion.

2. The powder particles according to claim 1, wherein the hot-melt polymer and the filler are fused together.

3. The powder particles according to claim 1, wherein the hot melt polymer is selected from at least one of polyimide, polyamide-imide, polyamide, polyester, polyethylene terephthalate, polyphenylene sulfide, polysulfone, polyetherimide, polyethersulfone, polyetheretherketone, and polyetherketoneketone.

4. The powder particles according to claim 1, wherein the hot melt polymer is selected from at least one of polyphenylene sulfide, polyetherimide, polyetheretherketone, and polyetherketoneketone.

5. The powder particles according to claim 1, wherein the filler is at least one inorganic particle selected from inorganic particles of silicon carbide, silicon oxide, aluminum oxide, zinc oxide, tin oxide, titanium oxide, barium sulfate and carbon black.

6. The powder particles according to claim 1, wherein the powder particles comprise 30 to 300 parts by weight of the filler relative to 100 parts by weight of the hot melt polymer.

7. The powder particles according to claim 1, wherein the particle size is 150 μm or smaller.

8. A powder coating composition comprising: powder particles according to any one of claims 1 to 7; and fluoropolymer powder.

9. The powder coating composition according to claim 8, wherein the fluoropolymer powder comprises a hot-melt fluoropolymer.

10. The powder coating composition according to claim 8, wherein the fluoropolymer powder contains a perfluorinated resin.

11. The powder coating composition according to claim 8, wherein, based on the total amount of the powder coating composition, the powder coating composition comprises 80% to 50% by weight of the powder particles and 20% to 50% by weight of the fluoropolymer powder.

12. A method for manufacturing powder particles, the method comprising: (1) The step of mixing hot melt polymer and filler in water to obtain an aqueous dispersion; (2) The step of heating the aqueous dispersion and removing water to obtain a solid; and (3) The step of crushing the solid to obtain powder particles.

13. The method for manufacturing powder particles according to claim 12, the method further comprising, after step (2), heating at or above the glass transition point of the hot melt polymer.

14. A method for manufacturing a powder coating composition, the method comprising: (1) The step of mixing hot melt polymer and filler in water to obtain an aqueous dispersion; (2) The step of heating the aqueous dispersion and removing water to obtain a solid; (3) The step of pulverizing the solid to obtain powder particles; and (4) The step of adding fluoropolymer powder to the powder particles and mixing them to obtain a powder coating composition.

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