Grease composition

Abstract

To provide a novel grease composition having excellent wear resistance.SOLUTION: A grease composition comprises a perfluoropolyether oil, a resin powder, and melamine cyanurate, the resin powder having a softening point or melting point higher than 250°C and being powder of resin that does not contain fluorine atoms.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a grease composition. [Background technology]

[0002] Grease compositions are used as lubricants in a variety of fields, including industrial machinery, transportation machinery, and general machinery. Fluorine-based grease compositions, obtained by using perfluoropolyether oil as a base oil and adding a tetrafluoroethylene homopolymer or copolymer as a thickener, have excellent properties over a wide temperature range, from low to high, as well as excellent oxidation stability and chemical resistance, making them primarily used under harsh conditions. However, under certain conditions, such fluorine-based grease compositions can be removed from the vicinity of sliding parts. In such cases, additives intended to reduce friction and wear cannot be fully effective, resulting in seizure of the sliding parts. Furthermore, in recent years, concerns have arisen about the environmental impact of small amounts of PFOA remaining in tetrafluoroethylene during its production process, leading to calls for the elimination of PFOA and the use of alternative materials.

[0003] Patent Document 1 proposes a grease composition in which a powder of a specific high-melting point polymer is added to a perfluoropolyether oil. However, when such a grease composition is used in rolling bearings, etc., an increase in torque can become a problem. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2009-523850 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides, for example, a novel grease composition that has excellent anti-wear properties. [Means for solving the problem]

[0006] In one embodiment of the present invention, the grease composition comprises perfluoropolyether oil, resin powder, and melamine cyanurate, wherein the resin powder is a powder of a resin having a softening or melting point higher than 250°C and containing no fluorine atoms. [Effects of the Invention]

[0007] According to the present invention, for example, a novel grease composition having excellent anti-wear properties is provided. DETAILED DESCRIPTION OF THE INVENTION

[0008] Examples of embodiments of the grease composition of the present invention are listed below. [1] A grease composition comprising a perfluoropolyether oil, a resin powder, and melamine cyanurate, wherein the resin powder has a softening point or melting point higher than 250°C and is a powder of a resin that does not contain fluorine atoms. [2] The grease composition according to [1], wherein the total content of the resin powder and melamine cyanurate is 3% by mass to 50% by mass based on the total mass of the grease composition. [3] The grease composition according to [1] or [2], wherein the content of the resin powder is 10% by mass to 95% by mass based on the total content of the resin powder and melamine cyanurate. [4] The grease composition according to any one of [1] to [3], wherein the resin contains at least one aromatic ring in the repeating unit. [5] The grease composition according to any one of [1] to [4], wherein the resin contains polyether ether ketone or polyphenylene sulfide. [6] The grease composition according to any one of [1] to [5], wherein the particle diameter of the resin powder is 0.5 μm to 30 μm.

[0009] In one embodiment, the grease composition comprises a perfluoropolyether oil, a resin powder, and melamine cyanurate. Each component that the grease composition may contain will be described in detail below.

[0010] [Perfluoropolyether oil] The perfluoropolyether oil is a base oil containing perfluoropolyether. The perfluoropolyether oil may contain a linear or branched perfluoropolyether. As the perfluoropolyether, for example, a compound represented by the following general formula may be used:

[0011] [ka]

[0012] In the formula, the repeating units -(CF2O)-, -(C2F4O)-, and -(C3F6O)- may be arranged randomly in the main chain. Rf represents a perfluoro lower alkyl group. Examples of the perfluoro lower alkyl group include groups having 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms, such as a perfluoromethyl group, a perfluoroethyl group, and a perfluoropropyl group. p, q, and r are 0 or a positive integer. Preferably, p+q+r=3 to 200.

[0013] The perfluoropolyether may be, for example, a compound represented by the following general formula: Such a compound can be obtained, for example, by completely fluorinating a precursor produced by photo-oxidative polymerization of tetrafluoroethylene.

[0014] [ka]

[0015] In the formula, the repeating units -(CF2CF2O)- and -(CF2O)- may be arranged randomly in the main chain. Rf is as defined above. a and b are 0 or positive integers. Preferably, a+b=3 to 200, and a:b=10:90 to 90:10.

[0016] The perfluoropolyether may be, for example, a compound represented by the following general formula: Such a compound can be obtained, for example, by completely fluorinating a precursor produced by photooxidative polymerization of hexafluoropropene.

[0017] [ka]

[0018] In the formula, the repeating units -[CF(CF)CFO]- and -(CFO)- may be randomly arranged in the main chain. Rf is as defined above. c and d are 0 or positive integers. Preferably, c+d=3 to 200, and c:d=10:90 to 90:10.

[0019] The perfluoropolyether may be, for example, a compound represented by the following general formula: Such compounds can be obtained, for example, by fully fluorinating a precursor produced by photooxidative polymerization of tetrafluoroethylene and hexafluoropropene.

[0020] [ka]

[0021] In the formula, the repeating units -[CF(CF3)CF2O]-, -(CF2CF2O)-, and -(CF2O)- may be randomly arranged in the main chain. Rf is as defined above. e, f, and g are 0 or positive integers. Preferably, e+f+g=3 to 200, e:f=1:199 to 199:1, and (e+f):g=10:90 to 90:10.

[0022] The perfluoropolyether may be, for example, a compound represented by the following general formula: Such a compound can be obtained, for example, by anionic polymerization of hexafluoropropene oxide or tetrafluoroethylene oxide in the presence of a cesium fluoride catalyst, and then treating the resulting acid fluoride compound having terminal CFXCOF groups with fluorine gas.

[0023] [ka]

[0024] In the formula, Rf is as defined above, h is an integer of 3 to 50, and X and Y are each independently an F atom or a CF3 group.

[0025] The perfluoropolyether may be, for example, a compound represented by the following general formula: Such a compound can be, for example, a fluorine-containing polyether (CHCFCFO) obtained by anionic polymerization of 2,2,3,3-tetrafluorooxetane in the presence of a cesium fluoride catalyst. n It can be obtained by treating with fluorine gas at about 160 to 300°C under ultraviolet irradiation.

[0026] [ka]

[0027] In the formula, i is an integer of 2 to 100.

[0028] The perfluoropolyether oil may contain one of these perfluoropolyethers alone or two or more of them. The kinematic viscosity of the perfluoropolyether oil is not particularly limited, but it is preferably 5 mm at 40°C. 2 / s~1500mm 2 / s, and 15 mm at 40°C. 2 / s~500mm 2 / s, and 30 mm at 40°C. 2 / s~200mm 2 / s, and 50 mm at 40°C. 2 / s~180mm 2 When the kinematic viscosity of the base oil is within an appropriate range, it is possible to suppress the amount of evaporation and ensure lubricity at low temperatures.

[0029] Commercially available perfluoropolyether oils include, for example, "FOMBLIN (registered trademark) M03" (kinematic viscosity at 40°C: 17 mmHg) manufactured by Solvay Specialty Polymers. 2 / s), "FOMBLIN (registered trademark) M07" (40°C kinematic viscosity: 38 mm 2 / s), "FOMBLIN (registered trademark) M15" (40°C kinematic viscosity: 85 mm 2 / s), "FOMBLIN (registered trademark) M30" (40°C kinematic viscosity: 159 mm 2 / s), "FOMBLIN (registered trademark) M60" (40°C kinematic viscosity: 310 mm 2 / s), "FOMBLIN (registered trademark) M100" (40°C kinematic viscosity: 700mm 2 / s), NOK Kluber "BARRIERTA J60 FLUID" (40℃ kinematic viscosity: 60mm 2 / s) etc.

[0030] The content of the perfluoropolyether oil in the grease composition is not particularly limited, and may be, for example, 50% by mass to 95% by mass, 55% by mass to 90% by mass, 60% by mass to 85% by mass, or 65% by mass to 80% by mass, based on the total mass of the grease composition.

[0031] [Resin powder] The resin powder is a powder of a resin that has a softening or melting point higher than 250°C and does not contain fluorine atoms. The resin powder can act as a thickener in a grease composition. It has now been newly confirmed that in a grease composition in which polytetrafluoroethylene powder is added as a thickener to perfluoropolyether oil, the affinity between polytetrafluoroethylene and perfluoropolyether oil is excessively high, resulting in churning characteristics over a wide shear range, and therefore, depending on the sliding conditions, the grease composition is expelled from the sliding parts, resulting in starvation of lubrication near the sliding parts. In the grease composition according to the present disclosure, the use of a fluorine-free resin powder improves the rheological behavior and reduces the possibility of starvation of lubrication.

[0032] Examples of the resin include, but are not limited to, polyaryletherketone (PAEK), polyphenylene sulfide (PPS), polyamides with a melting point of 250°C or higher, and polyesters with a melting point of 250°C or higher. Examples of polyaryletherketone (PAEK) include, but are not limited to, polyetheretherketone (PEEK), polyetherketone (PEK), and polyetherketoneketone (PEKK). Examples of polyamides with a melting point of 250°C or higher include, but are not limited to, polyamide 66, polyamide 46, polyamide 4T, polyamide 6T, and polyamide 9T. Examples of polyesters with a melting point of 250°C or higher include, but are not limited to, polyethylene terephthalate (PET). The resin powder may contain one or more of these resins.

[0033] The resin preferably contains at least one aromatic ring in the repeating unit. Examples of such resins include polyetheretherketone (PEEK), polyetherketone (PEK), polyetherketoneketone (PEKK), polyphenylene sulfide (PPS), polyamide 4T, polyamide 6T, polyamide 9T, and polyethylene terephthalate. Among these, polyetheretherketone (PEEK) and polyphenylene sulfide (PPS) are preferred.

[0034] The particle size of the resin powder is not particularly limited and may be, for example, within a range of 0.5 μm to 30 μm, or within a range of 1 μm to 25 μm.

[0035] The content of the resin powder in the grease composition is not particularly limited, and may be, for example, 3% by mass to 49% by mass, 5% by mass to 45% by mass, 7% by mass to 40% by mass, 9% by mass to 35% by mass, 10% by mass to 30% by mass, 12% by mass to 25% by mass, or 17% by mass to 23% by mass, based on the total mass of the grease composition.

[0036] The total content of the resin powder and the melamine cyanurate (described later) is preferably 3% by mass to 50% by mass of the entire grease composition. The total content of the resin powder and the melamine cyanurate may be 5% by mass to 47% by mass of the entire grease composition, 10% by mass to 45% by mass of the entire grease composition, 15% by mass to 42% by mass of the entire grease composition, 20% by mass to 40% by mass of the entire grease composition, 25% by mass to 35% by mass of the entire grease composition, or 27% by mass to 33% by mass of the entire grease composition.

[0037] The content of the resin powder is preferably 10% by mass to 95% by mass relative to the total content of the resin powder and melamine cyanurate. When the grease composition contains other thickeners, as described below, the content of the resin powder is preferably within the above range relative to the total content of the resin powder, melamine cyanurate, and other thickeners. The content of the resin powder may be 15% by mass to 90% by mass, 20% by mass to 85% by mass, 25% by mass to 80% by mass, 35% by mass to 75% by mass, 40% by mass to 70% by mass, 45% by mass to 65% by mass, or 55% by mass to 65% by mass relative to the total content of the resin powder and melamine cyanurate, or the total content of the resin powder, melamine cyanurate, and other thickeners.

[0038] [Melamine cyanurate] When a resin powder is added to a grease composition, an increase in torque can become a problem when the grease composition is used in a rolling bearing or the like. The reason for this is not entirely clear, but it is thought that, for example, the resin powder gets caught between the rolling element and the rolling surface, hindering the rolling of the rolling element. When melamine cyanurate is used in combination, this increase in torque is suppressed. The reason for this is also not entirely clear, but it is thought that because melamine cyanurate is a scaly particle, its coexistence with the resin powder makes it difficult for the resin powder to get caught between the rolling element and the rolling surface, or that even if the resin powder does get caught, the melamine cyanurate acts physically to easily eliminate the situation.

[0039] Melamine cyanurate having an average particle size of, for example, 0.1 μm to 30 μm, 0.5 μm to 20 μm, or 1.0 μm to 10 μm can be used. In particular, the use of melamine cyanurate having an average particle size of 10 μm or less can improve static friction. Known melamine cyanurates can be used. Specifically, melamine cyanurates described in JP-B-45-5595, JP-B-61-34430, JP-A-05-310716, JP-A-07-224049, etc., can be suitably used. Commercially available products include, for example, "MCA-1" manufactured by Mitsubishi Chemical Corporation, "MC-860," "MC-4000," "MC-4500," and "MC-6000" manufactured by Nissan Chemical Industries, Ltd., and "Melapur (registered trademark) MC 15" manufactured by BASF. However, the melamine cyanurate that can be used is not limited to these.

[0040] The content of melamine cyanurate in the grease composition is not particularly limited, and may be, for example, 1 to 45% by mass, 2 to 40% by mass, 3 to 35% by mass, 4 to 30% by mass, 5 to 25% by mass, 8 to 20% by mass, or 9 to 15% by mass, based on the total mass of the grease composition.

[0041] The content of melamine cyanurate may be, for example, 2% by mass to 50% by mass, 3% by mass to 40% by mass, 5% by mass to 35% by mass, 7% by mass to 30% by mass, 9% by mass to 25% by mass, 11% by mass to 20% by mass, 12% by mass to 17% by mass, or 13% by mass to 16% by mass, relative to the total content of the perfluoropolyether oil and the melamine cyanurate.

[0042] The content of melamine cyanurate is preferably 5% by mass to 95% by mass relative to the total content of the resin powder and melamine cyanurate. When the grease composition contains other thickeners, as described below, the content of melamine cyanurate is preferably within the above range relative to the total content of the resin powder, melamine cyanurate, and other thickeners. The content of melamine cyanurate may be 10% by mass to 90% by mass, 15% by mass to 85% by mass, 20% by mass to 80% by mass, 25% by mass to 70% by mass, 30% by mass to 60% by mass, 32% by mass to 55% by mass, or 33% by mass to 50% by mass relative to the total content of the resin powder and melamine cyanurate, or the total content of the resin powder, melamine cyanurate, and other thickeners. When the content of melamine cyanurate relative to the total content of resin powder and melamine cyanurate, or the content of melamine cyanurate relative to the total content of resin powder, melamine cyanurate, and other thickeners, is within an appropriate range, it becomes easier to suppress an increase in torque, particularly when used in a small-diameter bearing, leading to a longer life.

[0043] [Other ingredients] The grease composition may further contain components other than those described above. For example, the grease composition may contain other thickeners, antioxidants, rust inhibitors, corrosion inhibitors, extreme pressure agents, oiliness agents, solid lubricants, viscosity index improvers, etc. The grease composition may contain components other than the perfluoropolyether oil, resin powder, and melamine cyanurate in an amount of, for example, 20% by mass or less, 15% by mass or less, 10% by mass or less, 7% by mass or less, 5% by mass or less, or 4% by mass or less, based on the total amount of the grease composition. In one embodiment, the grease composition may contain a conductivity imparting agent such as carbon nanotubes. In another embodiment, the grease composition does not contain a conductivity imparting agent.

[0044] (Other thickeners) Other thickeners include, for example, fluororesins. Examples of fluororesins include polytetrafluoroethylene (PTFE) and tetrafluoroethylene / hexafluoropropylene copolymer (FEP). PTFE may be synthesized by emulsion polymerization, suspension polymerization, or solution polymerization of tetrafluoroethylene, and typically decomposed by thermal decomposition, electron beam irradiation decomposition, physical pulverization, or other techniques to reduce the molecular weight to approximately 1,000 to 1,000,000. FEP may be synthesized by copolymerization of tetrafluoroethylene and hexafluoropropylene, and decomposed by the same techniques as PTFE to reduce the molecular weight to approximately 1,000 to 600,000. The molecular weight can also be suppressed by using a chain transfer agent during the copolymerization reaction. The resulting powdered resin preferably has an average primary particle size of approximately 0.1 to 20 μm to maintain the homogeneity of the grease. Because fluororesin may contain impurities such as low-molecular-weight PFAS that remain during the manufacturing process, it is desirable to use fluororesin from which impurities such as PFAS have been removed by reviewing the manufacturing process or by post-processing after manufacturing. The content of fluororesin as an additional thickener may be, for example, 20% by mass or less, 15% by mass or less, 10% by mass or less, 5% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, or 0% by mass, based on the total content of the resin powder, melamine cyanurate, and additional thickener. A moderately low fluororesin content makes it easier to obtain the desired rheological behavior and also makes it less likely that the grease composition will be expelled from sliding parts.

[0045] In one embodiment, the grease composition may contain calcium carbonate as an additional thickener. The content of calcium carbonate as an additional thickener may be, for example, less than 5% by mass, 4% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less, based on the total content of the resin powder, melamine cyanurate, and the additional thickener. In another embodiment, the grease composition does not contain calcium carbonate as a thickener.

[0046] (antioxidant) Examples of antioxidants include, but are not limited to, phenolic antioxidants such as 2,6-di-t-butyl-4-methylphenol and 4,4'-methylenebis(2,6-di-t-butylphenol), and amine antioxidants such as alkyldiphenylamines, phenothiazine, alkylated phenyl-α-naphthylamines, phenithiazine, and alkylated phenothiazine.

[0047] (rust inhibitor) Examples of rust inhibitors include, but are not limited to, fatty acids, fatty acid soaps, alkyl sulfonates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, fatty acid amines, oxidized paraffins, and polyoxyethylene alkyl ethers. In certain embodiments, the grease composition may contain alkyl benzene sulfonates and / or alkyl naphthalene sulfonates. In other embodiments, the grease composition does not contain either alkyl benzene sulfonates or alkyl naphthalene sulfonates.

[0048] (corrosion inhibitor) Examples of corrosion inhibitors include, but are not limited to, benzotriazoles, benzimidazoles, thiadiazoles, and the like.

[0049] (extreme pressure agent) Examples of extreme pressure agents include, but are not limited to, phosphorus-based compounds such as phosphate esters, phosphites, and phosphate amine salts; sulfur-based compounds such as sulfides and disulfides; chlorine-based compounds such as chlorinated paraffins and chlorinated diphenyls; and metal organic compounds such as zinc dialkyldithiophosphate (ZnDTP) and molybdenum dialkyldithiocarbamate (MoDTP).

[0050] (oil-based agent) Examples of oily agents include, but are not limited to, fatty acids, higher alcohols, polyhydric alcohols, polyhydric alcohol esters, aliphatic esters, aliphatic amines, and fatty acid monoglycerides.

[0051] (solid lubricant) Examples of solid lubricants include, but are not limited to, molybdenum disulfide, graphite, boron nitride, silane nitride, lithium salts, sodium salts, potassium salts, calcium salts, aluminum salts, and barium salts of fatty acids, aromatic diureas, aliphatic diureas, aromatic polyureas, aliphatic polyureas, and bentonite. In certain embodiments, the grease composition may include calcium carbonate as a solid lubricant. In other certain embodiments, the grease composition does not include calcium carbonate as a solid lubricant.

[0052] The grease composition can be produced by mixing the above components by a known method. The order in which the components are mixed is not particularly limited. The same components may be added and mixed at once, or may be added in portions and then mixed.

[0053] The use of the grease composition according to the present disclosure is not particularly limited. The grease composition according to the present disclosure can be suitably used for the purpose of lubricating and protecting sliding parts and solid-state contact parts, such as rolling bearings, plain bearings, sintered bearings, gears, valves, cocks, oil seals, and electrical contacts. In one embodiment, the grease composition may be for resin-resin or resin-metal sliding contact. In another embodiment, the grease composition is not for resin-resin or resin-metal sliding contact.

[0054] The grease composition according to the present disclosure is suitable for use in, for example, rolling bearings or plain bearings that require heat resistance, load resistance, water resistance, etc., such as automotive electric radiators, fan motors, fan couplings, electronically controlled EGR, electronically controlled throttle valves, alternators, idler pulleys, electric brakes, hub units, water pumps, etc.; rolling bearings, plain bearings, or gear parts that require wear resistance, a low coefficient of friction, and high torque efficiency, such as automotive power transmission devices, power windows, wipers, and electric power steering; electrical contact parts that require heat resistance, wear resistance, and corrosion resistance, such as automotive automatic transmission control switches, lever control switches, and push switches; and automotive screws. It can also be used for sliding parts that require heat resistance, such as the X-ring part of a cast coupling, exhaust brake cylinders, O-rings, etc.; rolling bearings, plain bearings, sliding parts of resin films, or gear parts that require heat resistance and abrasion resistance, such as fixing rolls and fixing belts in copiers and laser beam printers; rolling bearings, plain bearings, pins, oil seals, gears, etc. that require heat resistance and load resistance, such as in film tenters, film laminators, or Banbury mixers, which are resin manufacturing equipment, corrugating machines, which are papermaking equipment, or contipresses, which are wood processing equipment; linear guides or rolling bearings, etc., in bread bakers and ovens; and sliding parts of mobile phone hinges, etc.

[0055] The grease composition according to the present disclosure can also be used for rolling bearings or gears in vacuum pumps in semiconductor manufacturing equipment, liquid crystal manufacturing equipment, electron microscopes, and the like; rolling bearings in circuit breakers in power control devices; rolling bearings, plain bearings, gears, or sliding parts in automobile headlights, seats, ABS, door locks and door hinges, clutch boosters, split flywheels, window regulators, ball joint clutch boosters, and the like; rolling bearings or plain bearings for computer cooling fans; rolling bearings, plain bearings, or oil seals in vacuum cleaners, washing machines, and the like; and rolling bearings and plain bearings that require high torque transmission efficiency, such as spindles and sabot motors for machine tools. [Example]

[0056] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0057] [Preparation of grease composition] (1) Base oil (1a) Perfluoropolyether oil 1 (PFPE1): FOMBLIN (registered trademark) M15 (manufactured by Solvay Specialty Polymers), kinematic viscosity at 40 ° C: 85 mm 2 / s (1b) Perfluoropolyether oil 2 (PFPE2): FOMBLIN (registered trademark) M30 (manufactured by Solvay Specialty Polymers), kinematic viscosity at 40 ° C: 159 mm 2 / s

[0058] (2) Thickeners, etc. (2a) Resin powder 1 (PEEK1): KetaSpire (registered trademark) KT820UFP (Solvay Specialty Polymers), particle size 10 μm to 20 μm, melting point 340° C. (2b) Resin powder 2 (PEEK2): KetaSpire (registered trademark) KT880UFP (Solvay Specialty Polymers), particle size 10 μm to 20 μm, melting point 343 ° C. (2c) Resin powder 3 (PPS): Ryton (registered trademark) PXM-20010 (Solvay Specialty Polymers), particle size 2 μm to 10 μm, melting point 282° C. (2d) Resin powder 4 (PA6): ORGASOL (registered trademark) 1002D NAT1 (Arkema France), particle size 17 μm to 23 μm, melting point 217° C. (2A) Melamine cyanurate (MCA): MC-6000 (Nissan Chemical Co., Ltd.), average particle size less than 2 μm (2Z) Polytetrafluoroethylene (PTFE): TLP 10F-1 (Mitsui Chemours Fluoroproducts Co., Ltd.), particle size 0.1 μm to 0.3 μm

[0059] (3) Additives (3a) Rust inhibitor (disodium sebacate): IRGACOR DSS G (BASF)

[0060] Additives were added to the above mixture of base oil and thickener to obtain the blending ratios shown in Tables 1 and 2, and then mixed to obtain uniform grease compositions (Examples 1-1 to 1-8, Examples 2-1 to 2-5). The blending amounts in each table are in mass %. A blank space in each table indicates that the component was not blended.

[0061] [Evaluation of grease composition] The obtained grease compositions were subjected to the SRV test and bearing torque test as described below.

[0062] (SRV test) Using an SRV tester, the obtained lubricating grease compositions (sample oils) were applied to test specimens, and a sliding test was carried out under the following test conditions to measure the specific wear rate. For each grease composition, the test was carried out at room temperature and 180°C.

[0063] Testing machine: SRV testing machine (friction and wear testing machine manufactured by OPTIMOL) Upper test piece: 10mm diameter sphere (material: 100Cr6) Lower test piece: 24mm diameter, 7.9mm height disc (material: 100Cr6) Load: 50N Amount of sample oil applied: 0.1 mm thick Frequency: 50Hz Amplitude: 1mm Test temperature: Room temperature (25°C) or 180°C Duration: 30 minutes

[0064] (bearing torque test) Using a bearing torque tester, the rotational torque was measured under the following conditions: The torque at the time of starting was defined as the starting torque, and the torque when the torque stabilized was defined as the steady-state torque.

[0065] Testing machine: Bearing torque tester Bearing: Small diameter ball bearing, radial deep groove ball bearing 608 (inner diameter 8mm, outer diameter 22mm) Rotation speed: 300 rpm Radial load: 20N Grease composition content: 0.3g Test temperature: Room temperature (25°C) Duration: 30 minutes

[0066] The results are shown in Tables 1 and 2. Table 1 shows an example when melamine cyanurate was not used, and Table 2 shows an example when melamine cyanurate was used. In each table, "PTFE ratio" indicates the percentage by mass of polytetrafluoroethylene relative to the total content of each resin powder, melamine cyanurate, and polytetrafluoroethylene. "MCA ratio" indicates the percentage by mass of melamine cyanurate relative to the total content of each resin powder, melamine cyanurate, and polytetrafluoroethylene. "Resin powder ratio" indicates the percentage by mass of the total resin powder relative to the total content of each resin powder, melamine cyanurate, and polytetrafluoroethylene. In the bearing torque test, "E" indicates that the torque exceeded the measurement limit (14 mN m).

[0067] [Table 1]

[0068] [Table 2]

[0069] The results shown in Table 1 show that by replacing polytetrafluoroethylene powder with fluorine-free resin powder, the specific wear rate is significantly reduced at both room temperature and 180°C. The reason for this is not entirely clear, but the following hypotheses can be suggested: (i) in a grease composition in which polytetrafluoroethylene powder is added as a thickener to perfluoropolyether oil, the affinity between polytetrafluoroethylene and perfluoropolyether oil is excessively high, resulting in churning characteristics over a wide shear range, which causes the grease composition to be expelled from the sliding parts and makes it prone to starvation of lubrication in the vicinity of the sliding parts; and (ii) the use of fluorine-free resin powder improves the rheological behavior and reduces the possibility of starvation of lubrication occurring.

[0070] Furthermore, the results shown in Table 1 indicate that when polytetrafluoroethylene powder was replaced with polyamide 6 powder, the wear rate at room temperature was small, but the wear rate at 180°C was large. This is thought to be due to the low melting point of polyamide 6, at 217°C. However, considering the results when polyetheretherketone and polyphenylene sulfide were used, it is important to note that even polyamides with high melting points, such as polyamide 66, polyamide 46, polyamide 4T, polyamide 6T, and polyamide 9T, are likely to produce good results in terms of wear rate. Furthermore, similarly good results in terms of wear rate are likely to be obtained when using resin powder with a melting point of 250°C or higher, such as polyethylene terephthalate, in addition to polyamide.

[0071] The results shown in Table 2 show that the specific wear rate can be reduced by using a fluorine-free resin powder in combination with melamine cyanurate. In particular, when the blending amount of melamine cyanurate is within a certain range, the specific wear rate can be significantly reduced.

[0072] As shown in Table 1, when a fluorine-free resin powder is used, the bearing torque tends to be higher than when a polytetrafluoroethylene powder is used, which may be undesirable in some applications. The results shown in Table 2 indicate that the combined use of a fluorine-free resin powder and melamine cyanurate can reduce bearing torque. While the reasons for this are not entirely clear, the following hypotheses can be suggested: (i) melamine cyanurate is a scaly particle, and its coexistence with the resin powder makes it less likely for the resin powder to become trapped between the rolling element and the rolling surface; and (ii) even if the resin powder does become trapped between the rolling element and the rolling surface, the melamine cyanurate acts physically to easily eliminate this state. In Example 2-1, the bearing torque at startup exceeded the measurement limit, but the steady-state bearing torque was very small, and the properties of the grease composition of this example may be desirable in some applications. [Industrial Applicability]

[0073] The grease composition of the present invention can be suitably used for the purpose of lubricating and protecting sliding parts and parts in contact with each other.

Claims

1. The composition comprises perfluoropolyether oil, resin powder, and melamine cyanurate, The grease composition, wherein the resin powder is a powder of a resin having a softening point or melting point higher than 250°C and containing no fluorine atoms.

2. 2. The grease composition according to claim 1, wherein the total content of the resin powder and the melamine cyanurate is 3% by mass to 50% by mass based on the total amount of the grease composition.

3. 3. The grease composition according to claim 1, wherein the content of the resin powder is 10% by mass to 95% by mass based on the total content of the resin powder and melamine cyanurate.

4. 3. The grease composition according to claim 1, wherein the resin contains at least one aromatic ring in a repeating unit.

5. 3. The grease composition according to claim 1, wherein the resin comprises polyether ether ketone or polyphenylene sulfide.

6. 3. The grease composition according to claim 1, wherein the particle size of the resin powder is 0.5 μm to 30 μm.

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