Coating composition, film, article, and bearing

Abstract

Provided is a coating composition capable of forming a coating film excellent in electrolytic corrosion prevention and low friction. This coating composition contains a fluororesin (A) partially or exclusively containing a high molecular weight polytetrafluoroethylene (A-1), a polyamideimide resin and / or an epoxy resin (B), and an organic solvent (C).

Description

Coating compositions, coatings, articles and bearings

[0001] The present disclosure relates to coating compositions, coatings, articles and bearings.

[0002] Patent Documents 1 to 4 describe painting bearings. Electric vehicles have become increasingly popular in recent years. The bearings described in these documents do not address the problems that may arise when used in such electric vehicles. Patent Document 5 discloses a paint that can maintain the wear resistance and sliding properties of car air conditioner compressor pistons.

[0003] JP 2000-15720 A JP 2022-42162 A JP 2008-280485 A JP 2013-85441 A JP 2005-198372 A JP 2022-15680 A

[0004] An object of the present disclosure is to provide a coating composition that is capable of forming a coating film that is galvanic corrosion-resistant and has low friction properties, and therefore excellent abrasion resistance.

[0005] The present disclosure relates to a coating composition comprising a fluororesin (A) containing, in whole or in part, a high-molecular-weight polytetrafluoroethylene (A-1), a polyamide-imide resin and / or an epoxy resin (B), and an organic solvent (C).

[0006] The fluororesin (A) preferably further contains one or more copolymers (A-2) made of tetrafluoroethylene and hexafluoropropylene and / or perfluoroalkyl vinyl ether.

[0007] The copolymer (A-2) preferably has a melt flow rate of 1 to 30 (g / 10 min). The coating composition preferably has a mass ratio of the high-molecular-weight polytetrafluoroethylene (A-1) to the copolymer (A-2) of (A-1) / (A-2) = 10 / 90 to 90 / 10. The coating composition preferably has a mass ratio of the fluororesin (A) to the polyamideimide resin of fluororesin (A) / polyamideimide resin = 40 / 60 to 70 / 30. The polyamideimide resin preferably has a number average molecular weight of 10,000 to 40,000.

[0008] In the coating composition, the mass ratio of the fluororesin (A) to the epoxy resin is preferably fluororesin (A) / epoxy resin = 30 / 70 to 70 / 30. In the coating composition, the number average molecular weight of the epoxy resin is preferably 200 to 2,500.

[0009] In the coating composition, the polyamideimide resin and / or epoxy resin (B) is a polyamideimide resin, and the fluororesin (A) further contains one or more copolymers (A-2) consisting of tetrafluoroethylene and hexafluoropropylene and / or perfluoroalkyl vinyl ether, the copolymers (A-2) having a melt flow rate of 1 to 30 (g / 10 min), the mass ratio of the high-molecular-weight polytetrafluoroethylene (A-1) to the copolymer (A-2) being (A-1) / (A-2) = 5 / 95 to 55 / 45, the mass ratio of the fluororesin (A) to the polyamideimide resin being fluororesin (A) / polyamideimide resin being 40 / 60 to 70 / 30, and the number average molecular weight of the polyamideimide resin being 10,000 to 40,000.

[0010] In the coating composition, it is preferable that the polyamideimide resin and / or epoxy resin (B) is an epoxy resin, the fluororesin (A) further contains one or more copolymers (A-2) consisting of tetrafluoroethylene and hexafluoropropylene and / or perfluoroalkyl vinyl ether, the copolymers (A-2) having a melt flow rate of 1 to 30 (g / 10 min), the mass ratio of the high-molecular-weight polytetrafluoroethylene (A-1) to the copolymer (A-2) being (A-1) / (A-2) = 5 / 95 to 55 / 45, the mass ratio of the fluororesin (A) to the epoxy resin being fluororesin (A) / epoxy resin = 30 / 70 to 70 / 30, and the number average molecular weight of the epoxy resin being 200 to 2000.

[0011] The present disclosure also relates to a coating formed from the above-described coating composition. The present disclosure also relates to an article having the coating. The present disclosure also relates to a bearing having the coating. The present disclosure also relates to an article having the bearing.

[0012] The coating composition of the present disclosure has anti-galvanic corrosion properties and low friction properties, and therefore can form a coating film with excellent abrasion resistance.

[0013] The present disclosure will be described in detail below. Bearings have been widely used in the automotive field. Meanwhile, electric vehicles have been expanding into the market in recent years, and bearings are also widely used in electric vehicles.

[0014] Electricity may flow through bearings used in electric vehicles. When electricity flows through a bearing, a phenomenon known as galvanic corrosion occurs. This is a phenomenon in which the passage of current through the bearing causes sparks, melting the metal surface and causing a loss of surface smoothness. Note that the galvanic corrosion referred to in this disclosure is completely different from the phenomenon in which corrosion of one metal is accelerated when different types of metals come into contact and conduct electricity in a corrosive environment (galvanic corrosion).

[0015] To prevent such electrolytic corrosion, it is preferable to improve the insulation of the bearing. For this reason, it is conceivable to form an insulating coating film using paint. To prevent electrolytic corrosion, it is necessary to form a film with excellent insulation and abrasion resistance. This is because if the abrasion resistance is low, the substrate is easily exposed due to wear of the coating film, which causes electricity to flow to the bearing and leads to electrolytic corrosion. In addition, wear of the coating film generates wear powder, and the wear powder itself becomes foreign matter and can hinder the rotation of the bearing. In order to achieve wear resistance, low friction is required.

[0016] The coating composition of the present disclosure exhibits particularly excellent performance when coating such bearings.

[0017] (Fluororesin (A)) The coating composition of the present disclosure contains a fluororesin (A). A fluororesin is a resin that partially contains fluorine atoms. Fluororesins are resins that have excellent low friction properties and are therefore particularly suitable for the purposes of the present disclosure. The fluororesin (A) used in the coating composition of the present disclosure contains, at least in part, high-molecular-weight polytetrafluoroethylene (A-1). The use of such a fluororesin has a particularly favorable effect in that a coating film that combines insulating properties and abrasion resistance can be formed.

[0018] (High-Molecular-Weight Polytetrafluoroethylene (A-1)) In the resin composition of the present disclosure, part or all of the fluororesin (A) is high-molecular-weight polytetrafluoroethylene (hereinafter, this may be referred to as high-molecular-weight PTFE) (A-1). High-molecular-weight PTFE means PTFE that is non-melt-processable and fibrillating.

[0019] The term "non-melt processable" means that the melt flow rate cannot be measured at a temperature higher than the crystallization melting point in accordance with ASTM D-1238 and D-2116.

[0020] The presence or absence of fibrillation properties can be determined by "paste extrusion," a typical method for molding "high molecular weight PTFE powder," which is a powder made from a TFE polymer. Paste extrusion is usually possible because high molecular weight PTFE has fibrillation properties. If the unsintered molded product obtained by paste extrusion has no substantial strength or elongation, for example, if it breaks when pulled at 0% elongation, it can be considered to have no fibrillation properties.

[0021] The high molecular weight PTFE preferably has a standard specific gravity (SSG) of 2.130 to 2.280. The lower limit of the standard specific gravity is more preferably 2.135, and even more preferably 2.140. The upper limit of the standard specific gravity is more preferably 2.275, and even more preferably 2.270. The standard specific gravity is measured by the water displacement method in accordance with ASTM D-792 using a sample molded in accordance with ASTM D4895-89. Since the standard specific gravity of a resin corresponds to the molecular weight, PTFE within the above range can be said to be high molecular weight PTFE.

[0022] Such high molecular weight PTFE is known and can be obtained by known methods. Alternatively, commercially available products can be used.

[0023] (Copolymer (A-2)) The coating composition of the present disclosure preferably further contains one or more copolymers (A-2) composed of tetrafluoroethylene and hexafluoropropylene and / or perfluoroalkyl vinyl ether as part of the fluororesin (A). By including this copolymer, a favorable effect can be obtained in terms of being able to form a coating film with fewer defects such as pinholes.

[0024] In the present disclosure, "perfluoro(alkyl vinyl ether)" (PAVE) is an alkyl vinyl ether that does not contain a C-H bond. Examples of PAVE constituting the PAVE unit include those represented by the general formula (1): CF ２ = CFO (CF ２ CFY １ O) ｐ -(CF ２ CF ２ CF２ O) ｑ -Rf (1) (wherein, Y １ is F or CF ３ where Rf represents a perfluoroalkyl group having 1 to 5 carbon atoms, p represents an integer of 0 to 5, and q represents an integer of 0 to 5.) and a monomer represented by the general formula (2): CFX=CXOCF ２ OR １ (2) (Wherein, X may be the same or different and is H, F or CF ３ wherein R1 represents a linear or branched fluoroalkyl group having 1 to 6 carbon atoms which may contain 1 to 2 atoms of at least one type selected from the group consisting of H, Cl, Br and I, or a cyclic fluoroalkyl group having 5 or 6 carbon atoms which may contain 1 to 2 atoms of at least one type selected from the group consisting of H, Cl, Br and I.

[0025] Among these, the PAVE is preferably a monomer represented by general formula (1), more preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), and perfluoro(propyl vinyl ether) (PPVE), and even more preferably PPVE.

[0026] The content of PAVE units in the TFE / PAVE copolymer is preferably 1.0 to 10% by mass, more preferably 2.0% by mass or more, even more preferably 3.5% by mass or more, more preferably 8.0% by mass or less, even more preferably 7.0% by mass or less, particularly preferably 6.5% by mass or less, and most preferably 6.0% by mass or less, based on the total monomer units. The amount of PAVE units is measured by 19F-NMR. The TFE / PAVE copolymer may be a copolymer consisting only of TFE units and PAVE units.

[0027] When the copolymer (A-2) is a TFE / PAVE copolymer, the melting point is preferably 280 to 322°C, more preferably 290°C or higher, and more preferably 320°C or lower.

[0028] When the copolymer (A-2) is a TFE / PAVE copolymer, the glass transition temperature (Tg) is preferably 70 to 110° C., more preferably 80° C. or higher, and more preferably 100° C. or lower. The glass transition temperature is a value obtained by measuring dynamic viscoelasticity.

[0029] The content of HFP units in the TFE / HFP copolymer is preferably 5 to 30% by mass, more preferably 10% by mass or more, even more preferably 15% by mass or more, and more preferably 25% by mass or less, based on the total monomer units. The amount of HFP units can be measured by F-NMR.

[0030] The TFE / HFP copolymer can further contain (per)fluoro(alkyl vinyl ether) (PAVE) units.The PAVE units contained in the TFE / HFP copolymer can be the same as the PAVE units described above.The TFE / PAVE copolymer does not contain HFP units, so in this respect it is different from the TFE / HFP / PAVE copolymer.

[0031] When the TFE / HFP copolymer is a copolymer containing TFE units, HFP units, and PAVE units (hereinafter also referred to as "TFE / HFP / PAVE copolymer"), the mass ratio (TFE / HFP / PAVE) is preferably 70-99.8 / 0.1-25 / 0.1-25 (mass%). The mass ratio (TFE / HFP / PAVE) is more preferably 75-98 / 1.0-25 / 1.0-10 (mass%). The TFE / HFP / PAVE copolymer preferably contains 1 mass% or more of HFP units and PAVE units in total relative to all monomer units.

[0032] In the TFE / HFP / PAVE copolymer, the HFP unit preferably accounts for 25% by mass or less of all monomer units. The content of HFP units is more preferably 20% by mass or less. The content of HFP units is preferably 0.1% by mass or more, more preferably 1% by mass or more, and particularly preferably 2% by mass or more. The content of HFP units can be measured by 19F-NMR.

[0033] The content of PAVE units is more preferably 20% by mass or less, even more preferably 10% by mass or less, and particularly preferably 3% by mass or less. The content of PAVE units is preferably 0.1% by mass or more, more preferably 1% by mass or more. The content of PAVE units can be measured by 19F-NMR.

[0034] The TFE / PAVE copolymer and the TFE / HFP copolymer may further contain other ethylenic monomer (α) units. The other ethylenic monomer (α) units are not particularly limited as long as they are monomer units copolymerizable with TFE, HFP, and PAVE, and examples thereof include fluorine-containing ethylenic monomers such as vinyl fluoride (VF), vinylidene fluoride (VdF), trifluoroethylene (TrFE), and chlorotrifluoroethylene (CTFE), as well as non-fluorinated ethylenic monomers such as ethylene, propylene, and alkyl vinyl ethers. The content of the other ethylenic monomer (α) units is preferably 0 to 25% by mass, more preferably 0.1 to 25% by mass.

[0035] When the copolymer (A-2) is a TFE / HFP / PAVE / other ethylenic monomer (α) copolymer, the mass ratio (TFE / HFP / PAVE / other ethylenic monomer (α)) is preferably 70 to 98 / 0.1 to 25 / 0.1 to 25 / 0.1 to 25 (mass %). The TFE / HFP / PAVE / other ethylenic monomer (α) copolymer preferably contains 1 mass % or more of monomer units other than TFE units in total.

[0036] The melting point of the TFE / HFP copolymer is preferably 200 to 322°C, more preferably above 200°C, even more preferably 210°C or higher, more preferably 300°C or lower, and even more preferably 280°C or lower.

[0037] The glass transition temperature (Tg) of the TFE / HFP copolymer is preferably 60 to 110° C., more preferably 65° C. or higher, and more preferably 100° C. or lower. The glass transition temperature is a value obtained by measuring dynamic viscoelasticity.

[0038] The polymer (A-2) can be produced by a conventionally known method, for example, by appropriately mixing monomers that form the constituent units thereof and additives such as a polymerization initiator, followed by emulsion polymerization or suspension polymerization. Among these, the polymer (A-2) is more preferably produced by emulsion polymerization.

[0039] The polymer (A-2) preferably has an MFR value measured at 372°C under a load of 5 kg in the range of 1 to 30 (g / 10 min). This range is preferred because it makes it easier to obtain the amount of functional groups described above by the terminal functional groups. The lower limit of the MFR is more preferably 3 (g / 10 min), and even more preferably 10 (g / 10 min). The upper limit of the MFR is more preferably 28 (g / 10 min), and even more preferably 25 (g / 10 min).

[0040] In the coating composition of the present disclosure, the mass ratio of the high molecular weight polytetrafluoroethylene (A-1) to the copolymer (A-2) is preferably (A-1) / (A-2) = 10 / 90 to 90 / 10. The lower limit of the mass ratio is more preferably 10.5 / 89.5, and even more preferably 11 / 89. The upper limit of the mass ratio is more preferably 89.5 / 10.5, and even more preferably 89 / 11. By achieving a ratio within this range, it is possible to form a coating film with few defects such as pinholes and excellent insulation and abrasion resistance, which is preferable.

[0041] (Polyamideimide resin and / or epoxy resin (B)) The coating composition of the present disclosure contains a polyamideimide resin and / or an epoxy resin. This is preferable in that it allows the formation of a coating film that has excellent adhesion to the substrate. The polyamideimide resin and / or epoxy resin that can be used in the present disclosure will be described in detail below.

[0042] (Polyamide-imide Resin) A polyamide-imide resin is typically a resin obtained by reacting an acid component with a diisocyanate component, and has a structural moiety derived from the acid component and a structural moiety derived from the diisocyanate component.

[0043] (Acid Component) The acid component is not particularly limited and includes at least an aromatic tribasic acid anhydride and / or an aromatic tribasic acid halide. In one embodiment, the acid component preferably includes at least an aromatic tribasic acid anhydride, and more preferably includes trimellitic anhydride. Therefore, in one embodiment, the polyamide-imide resin preferably has a structure represented by the following general formula (I):

[0044]

[0045] In the structure represented by general formula (1), R is an organic group (structural moiety) derived from a diisocyanate component, and n is an integer of 1 or more.

[0046] The content of trimellitic anhydride is preferably 50 mol % or more based on the total amount of acid components constituting the polyamide-imide resin (100 mol %). In one embodiment, the content of trimellitic anhydride may be 100 mol %.

[0047] In another embodiment, the content of trimellitic anhydride may be 50 mol% to 95 mol%, and other acid components may be contained in an amount of 5 mol% to 50 mol%, based on the total amount of acid components constituting the polyamide-imide resin (100 mol%). Examples of other acid components that can be used include dicarboxylic acids. Examples of dicarboxylic acids that can be used include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, and terephthalic acid. These compounds may be used alone or in combination of two or more.

[0048] (Diisocyanate Component) The diisocyanate component preferably contains at least an aromatic diisocyanate. Therefore, in one embodiment, in the above general formula (I), R is preferably an organic group derived from an aromatic diisocyanate. Based on the total amount (100 mol%) of the diisocyanate components constituting the polyamide-imide resin, the content of the aromatic diisocyanate is preferably 30 mol% or more, and more preferably 40 mol% or more. In one embodiment, the content of the aromatic diisocyanate may be 100 mol%.

[0049] The aromatic diisocyanate includes one or more selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-diisocyanatobiphenyl, 2,4-toluene diisocyanate, and 2,6-toluene diisocyanate. Among the above aromatic diisocyanates, 4,4'-diphenylmethane diisocyanate is preferred. Therefore, based on the total amount of diisocyanate components constituting the polyamide-imide resin, the content of aromatic diisocyanates including 4,4'-diphenylmethane diisocyanate is preferably 30 mol% or more, more preferably 40 mol% or more, and may even be 100 mol%.

[0050] In one embodiment, the content of 4,4'-diphenylmethane diisocyanate may be 100 mol% based on the total amount of diisocyanate components constituting the polyamideimide resin. In another embodiment, the content of 4,4'-diphenylmethane diisocyanate may be 30 mol% to 95 mol% and the content of other aromatic diisocyanates may be 5 mol% to 70 mol% based on the total amount of diisocyanate components constituting the polyamideimide resin.

[0051] In the coating composition of the present disclosure, the polyamide-imide resin preferably has a number average molecular weight of 10,000 to 40,000. Use of a resin within this range is preferred in that it allows for the formation of a coating film that has excellent adhesion to the substrate.

[0052] The lower limit of the number average molecular weight is preferably 12,000, and more preferably 14,000 or more. The upper limit of the number average molecular weight is preferably 37,000, and more preferably 33,000.

[0053] In this specification, the number average molecular weight of the polyamideimide resin is a value measured by gel permeation chromatography (GPC).

[0054] (Epoxy Resin) In the present disclosure, an epoxy resin is a compound having two or more oxirane rings (epoxy groups) in the molecule.

[0055] The epoxy resin is not particularly limited, and known epoxy resins can be used. Specific examples include bisphenol A epoxy resins, bisphenol F epoxy resins, brominated epoxy resins, bisphenol S epoxy resins, diphenyl ether epoxy resins, hydroquinone epoxy resins, naphthalene epoxy resins, biphenyl epoxy resins, fluorene epoxy resins, bisphenol A novolac epoxy resins, phenol novolac epoxy resins, orthocresol novolac epoxy resins, dicyclopentadienephenol epoxy resins, trishydroxyphenylmethane epoxy resins, trifunctional epoxy resins, tetraphenylolethane epoxy resins, tetrafunctional epoxy resins, hydrogenated bisphenol A epoxy resins, bisphenol A nucleus-containing polyol epoxy resins, polypropylene glycol epoxy resins, glycidyl ester epoxy resins, glycidylamine epoxy resins, glyoxal epoxy resins, alicyclic epoxy resins, alicyclic polyfunctional epoxy compounds, and heterocyclic epoxy resins such as triglycidyl isocyanate (TGIC).

[0056] The epoxy resin preferably has a number average molecular weight of 200 to 2000. The lower limit of the number average molecular weight is preferably 250, and more preferably 300 or more. The upper limit of the number average molecular weight is preferably 2400, and more preferably 2200.

[0057] In this specification, the number average molecular weight of the epoxy resin is a value measured by gel permeation chromatography (GPC).

[0058] (Blending ratio) In the coating composition of the present disclosure, the mass ratio of the fluororesin (A) to the polyamideimide resin is preferably fluororesin (A) / polyamideimide resin = 40 / 60 to 70 / 30. The lower limit of this mass ratio is more preferably 41 / 59, and even more preferably 42 / 58. The upper limit of the mass ratio is more preferably 69 / 31, and even more preferably 68 / 32. A ratio within this range is preferable in that it allows the formation of a coating film that is excellent in insulation properties, abrasion resistance, and adhesion to the substrate.

[0059] In the coating composition of the present disclosure, the mass ratio of the fluororesin (A) to the epoxy resin is preferably fluororesin (A) / epoxy resin = 30 / 70 to 70 / 30. The lower limit of this mass ratio is more preferably 31 / 69, and even more preferably 32 / 68. The upper limit of this mass ratio is more preferably 69 / 31, and even more preferably 68 / 32. A ratio within this range is preferable in that it allows the formation of a coating film that has excellent insulation properties, abrasion resistance, and adhesion to the substrate.

[0060] When the coating composition of the present invention contains both a polyamideimide resin and an epoxy resin, the mass ratio of the fluororesin (A) to the polyamideimide resin and epoxy resin (B) is preferably fluororesin (A) / (B) = 40 / 60 to 70 / 30.

[0061] (Organic solvent (C)) The coating composition of the present disclosure contains an organic solvent (C). In the present disclosure, the fluororesin (A), polyamideimide resin and / or epoxy resin (B) are preferably dissolved and / or dispersed in an organic solvent. More specifically, the coating composition is preferably in a state where the polyamideimide resin and / or epoxy resin (B) is dissolved in the organic solvent (C) and the fluororesin (A) that is difficult to dissolve in the solvent is dispersed therein.

[0062] Forming a coating film using such a composition is preferable in that it allows the formation of a uniform coating film and also allows the properties of the fluororesin, such as low friction, to be fully exhibited.

[0063] The organic solvent (C) that can be used in the present disclosure is preferably one that can dissolve polyamide-imide resins and epoxy resins and easily disperse fluororesins, such as N-methylpyrrolidone, N-ethyl-2-pyrrolidone (NEP), 3-methoxy-N,N-dimethylpropanamide, N-butyl-2-pyrrolidone (NBP), methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone.

[0064] The organic solvent (C) may be a mixed solvent of two or more of the above organic solvents, or may contain other organic solvents or water as long as the above-mentioned object is not impaired. In the organic solvent (C), the above-mentioned components (A) and (B) are present in a dispersed or dissolved state.

[0065] The coating composition of the present disclosure preferably contains the organic solvent (C) in a proportion of 50 to 90% by mass relative to the total amount of the composition. The lower limit is more preferably 55% by mass, and even more preferably 60% by mass. The upper limit is more preferably 85% by mass, and even more preferably 80% by mass.

[0066] (Other Components) The coating composition of the present disclosure may be a composition consisting only of the fluororesin (A), the polyamideimide resin and / or the epoxy resin (B), and the organic solvent (C), or may further contain other components as necessary.

[0067] Other ingredients that may be added include water, fillers, colorants, and the like.

[0068] (Viscosity) The coating composition of the present disclosure preferably has a viscosity of 100 to 40,000 cps. By setting the viscosity within this range, workability in the coating process can be improved. Furthermore, it is also preferable in terms of obtaining a predetermined film thickness.

[0069] The viscosity is a value measured at 25°C using a Brookfield viscometer according to JIS Z8803. For paints used in spray coating or the like, the lower limit is more preferably 110 cps, and even more preferably 120 cps. The upper limit is preferably 3,000 cps, and even more preferably 2,500 cps. For paints used in dispensers or roll coaters, the lower limit is more preferably 4,000 cps, and even more preferably 5,000 cps. The upper limit is more preferably 38,000 cps, and even more preferably 35,000 cps.

[0070] The viscosity can be adjusted to fall within the above range by appropriately adjusting the composition of the coating composition, the amount of solvent, and the molecular weight of the component of the resin used that dissolves in the solvent.

[0071] (Method for producing a coating material) The coating material composition of the present disclosure can be produced by mixing the above-mentioned components. Appropriate crushing can be achieved by using various known mills such as a bead mill, a ball mill, or a three-roll mill, appropriately combining these as needed, and adjusting the crushing conditions, the crushing time, and the blending of the resin components used in combination.

[0072] (Coating Film) The present disclosure also covers a coating film formed using the coating composition of the present disclosure. The coating film can be formed by a general method.

[0073] The coating film of the present disclosure preferably has a friction coefficient of 0.4 or less, measured by the method described in the Examples of this specification. By having such abrasion resistance, the coating film can be made to have excellent strength and durability, and can be made applicable to applications requiring sliding properties. The friction coefficient refers to the value measured by the method described in the Examples. The friction coefficient is more preferably less than 0.3, and even more preferably less than 0.2.

[0074] The coating film of the present disclosure preferably has an abrasion resistance index of 500 or more, measured by the method described in the Examples of this specification. The coating film of the present disclosure can be a coating film that can maintain sliding properties for a long period of time, and can be a coating film that can be used in applications where sliding properties are required. Note that the sliding properties mean the value measured by the method described in the Examples. The abrasion resistance index is more preferably 600 or more, and even more preferably 700 or more.

[0075] The coating film of the present disclosure preferably has a film thickness of 5 to 120 μm, as measured by the method described in the Examples of this specification. The lower limit of the film thickness is more preferably 10 μm, and even more preferably 15 μm. The upper limit of the film thickness is more preferably 110 μm, and even more preferably 105 μm. A film thickness within such a range is preferable in that it has few defects such as pinholes and coating film bubbles, and can form a coating film that is excellent in insulation and abrasion resistance.

[0076] (Applications of Coating Composition) The applications to which the coating composition of the present disclosure can be applied are not particularly limited, and include, in addition to painting bearings for electric vehicles, industrial products such as office automation (OA) rolls, OA belts, OA separation claws, papermaking rolls, and film production calendar rolls; injection molds, molds and dies for polystyrene foam molding, etc.; mold release tools for plywood and decorative panel manufacturing, such as release plates; industrial containers (especially for the semiconductor industry); tools such as saws and files; household items such as irons, scissors, and knives; metal foil; electric wires; plain bearings for food processing machines, packaging machines, spinning and weaving machines, etc.; sliding parts for cameras and watches; automotive parts such as pipes, valves, and bearings; snow shovels; plows; chutes, etc. The coating composition of the present disclosure can be particularly suitably used for painting bearings for electric vehicles.

[0077] The present disclosure also relates to a coating film obtained using the above-described coating composition, and to an article and a bearing having the coating. Furthermore, the present disclosure also relates to an article having the above-described bearing. Examples of such articles include transportation equipment such as automobiles, industrial equipment such as machine tools and semiconductor manufacturing facilities, and power generation equipment such as wind power generators. In particular, the present disclosure is suitable for use in equipment in which a large current flows through the bearing.

[0078] The present disclosure will be specifically described below based on examples. In the tables, "%" and "parts" represent "% by mass" and "parts by mass," respectively.

[0079] [Examples 1 to 9 and Comparative Examples 1 to 7] The components shown in Table 1 were mixed in predetermined amounts, and various resin raw materials were dispersed in a mixed solvent of N-methylpyrrolidone and methyl isobutyl ketone (mixing ratio: 7 / 3) using a stirring mill to obtain a coating composition. The proportion of the mixed solvent in the total amount of the coating composition was 75% (mass ratio). The properties of the film formed from this coating composition are shown in Table 1. The components in the table are as follows:

[0080] High molecular weight PTFE: PTFE that is non-melt-processible and fibrillating. Standard specific gravity: 2.170. Low molecular weight PTFE: PTFE that is non-melt-processible and not fibrillating. It was not possible to mold a sample for measuring the standard specific gravity. TFE / HFP copolymer: TFE / HFP = 78 / 22 (mass%). Melting point: 218°C. MFR: 17 (g / 10 min). TFE / PPVE copolymer: TFE / PPVE = 96 / 4 (mass%). Melting point: 314°C. MFR: 24 (g / 10 min). TFE / HFP / PPVE copolymer: TFE / HFP / PPVE = 79 / 19 / 2 (mass%). Melting point: 256°C. MFR: 21 (g / 10 min). Polyamide-imide resin, molecular weight 15,000: Polycondensation product of trimellitic anhydride and 4,4'-diphenylmethane diisocyanate. Polyamide-imide resin, molecular weight 25,000: Polycondensation product of trimellitic anhydride and 4,4'-diphenylmethane diisocyanate. Polyamide-imide resin, molecular weight 30,000: Polycondensation product of trimellitic anhydride and 4,4'-diphenylmethane diisocyanate. Epoxy resin, molecular weight 340: Bisphenol A type epoxy resin. Epoxy resin, molecular weight 800: Bisphenol A type epoxy resin. Epoxy resin, molecular weight 2000: Bisphenol A type epoxy resin.

[0081] (Molecular weight of polyamide-imide resin) This is a value measured by gel permeation chromatography (GPC), using a GEL PERMEATION CHROMATograph HLC-8020 manufactured by Tosoh Corporation, a Shodex GPC KD-806M column manufactured by Showa Denko K.K., and dimethylformamide (DMF) tetrahydrofuran as the solvent.

[0082] (Molecular Weight of Epoxy Resin) This is a value measured by gel permeation chromatography (GPC) using a GEL PERMEATION CHROMATograph HLC-8020 manufactured by Tosoh Corporation, a Shodex GPC KF-803L column manufactured by Showa Denko K.K., and tetrahydrofuran (THF) as the solvent.

[0083] (Coating method) The above paints were applied to SUS304 substrates that had been subjected to degreasing and blasting treatment. In Tables 1 and 2, the coatings were dried at 100°C for 30 minutes, and then heated at 280°C for 30 minutes to form films. In Tables 3 and 4, the coatings were dried at 100°C for 30 minutes, and then heated at 180°C for 30 minutes to form coating films.

[0084] The resulting coating film was evaluated according to the following methods: (Film Thickness) The film thickness of the coating film was measured using an eddy current film thickness meter (manufactured by Kett Electric Laboratory Co., Ltd.).

[0085] (Breakdown voltage (kV)) Using a breakdown tester YST-243-100RHO (manufactured by Yamayo Test Instruments Co., Ltd.), the breakdown voltage of the coating film was measured in accordance with JIS C2110-1 under the conditions of an AC voltage increase method (short-time method, 50 Hz), a measurement temperature of 23°C, an ambient medium of insulating oil, and test electrodes of Φ20 sphere / Φ25 cylinder.

[0086] (Coefficient of Friction) Using a friction and wear tester Tribogear 38 (manufactured by Shinto Scientific Co., Ltd.), the coefficient of friction of the coating film was measured under the conditions of Baudenleben type, steel ball 8 mm in diameter, linear velocity: 0.27 cm / sec, and load: 1 kgf.

[0087] (Adhesion to Substrate SAICAS (kN / m)) The adhesive strength to the substrate was measured using a surface and interface property analyzer SAICAS (manufactured by Daipla Wintes).

[0088] (Wear Resistance Index) Using a friction and wear tester Friction Player FPR2200 (manufactured by Rhesca Co., Ltd.), the period until the coating film was worn down by 10 μm was measured by reciprocating sliding with a zirconia ball of Φ5 mm as the counter material, a load of 2 kgf, a linear velocity of 20 mm / sec, and a travel distance of 10 mm. In Tables 1 and 2, the wear resistance index was obtained as an index when Comparative Example 2 was set to 100, and in Tables 3 and 4, the wear resistance index was obtained as an index when Comparative Example 5 was set to 100.

[0089]

[0090]

[0091]

[0092] In the above tables, the blending amounts are in mass %.

[0093] From the results in Tables 1 to 5 above, it is clear that the coating composition of the present disclosure has excellent insulating properties and abrasion resistance, and is particularly suitable for coating bearings for electric vehicles.

[0094] The coating composition of the present disclosure can be suitably used for coating bearings for electric vehicles and the like.

Claims

1. A coating composition comprising a fluororesin (A) containing, in whole or in part, high molecular weight polytetrafluoroethylene (A-1), a polyamideimide resin and / or an epoxy resin (B), and an organic solvent (C).

2. The coating composition according to claim 1, wherein the fluororesin (A) further contains one or more copolymers (A-2) consisting of tetrafluoroethylene and hexafluoropropylene and / or perfluoroalkyl vinyl ether.

3. The coating composition according to claim 2, wherein the copolymer (A-2) has a melt flow rate of 1 to 30 (g / 10 min).

4. The coating composition according to claim 2 or 3, wherein the mass ratio of the high molecular weight polytetrafluoroethylene (A-1) to the copolymer (A-2) is (A-1) / (A-2)=10 / 90 to 90 / 10.

5. A coating composition according to any one of claims 1 to 4, wherein the mass ratio of the fluororesin (A) to the polyamideimide resin is fluororesin (A) / polyamideimide resin = 40 / 60 to 70 / 30.

6. A coating composition according to any one of claims 1 to 5, wherein the polyamideimide resin has a number average molecular weight of 10,000 to 40,000.

7. A coating composition according to any one of claims 1 to 6, wherein the mass ratio of the fluororesin (A) to the epoxy resin is fluororesin (A) / epoxy resin = 30 / 70 to 70 / 30.

8. The coating composition according to any one of claims 1 to 7, wherein the epoxy resin has a number average molecular weight of 200 to 2,500.

9. A coating composition according to claim 1, wherein the polyamideimide resin and / or epoxy resin (B) is a polyamideimide resin, the fluororesin (A) further contains one or more copolymers (A-2) consisting of tetrafluoroethylene and hexafluoropropylene and / or perfluoroalkyl vinyl ether, the copolymer (A-2) having a melt flow rate of 1 to 30 (g / 10 min), the mass ratio of the high molecular weight polytetrafluoroethylene (A-1) to the copolymer (A-2) being (A-1) / (A-2) = 5 / 95 to 55 / 45, the mass ratio of the fluororesin (A) to the polyamideimide resin being fluororesin (A) / polyamideimide resin being 40 / 60 to 70 / 30, and the polyamideimide resin having a number average molecular weight of 10,000 to 40,000.

10. A coating composition according to claim 1, wherein the polyamide-imide resin and / or epoxy resin (B) is an epoxy resin, the fluororesin (A) further contains one or more copolymers (A-2) consisting of tetrafluoroethylene and hexafluoropropylene and / or perfluoroalkyl vinyl ether, the copolymer (A-2) having a melt flow rate of 1 to 30 (g / 10 min), the mass ratio of the high molecular weight polytetrafluoroethylene (A-1) to the copolymer (A-2) being (A-1) / (A-2) = 5 / 95 to 55 / 45, the mass ratio of the fluororesin (A) to the epoxy resin being fluororesin (A) / epoxy resin = 30 / 70 to 70 / 30, and the number average molecular weight of the epoxy resin being 200 to 2,000.

11. A coating formed from the coating composition according to any one of claims 1 to 10.

12. An article having the coating of claim 11.

13. A bearing having the coating of claim 11.

14. An article having a bearing according to claim 11.

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