Grease composition and axle bearing

Abstract

The present invention provides a grease composition and an axle bearing packed therewith. This grease composition comprises a base oil, a thickener, and an additive, wherein: the additive comprises an organic metal salt of a divalent metal and an inorganic metal salt of a divalent metal; the total mass of the metal content of the organic metal salt and the metal content of the inorganic metal salt is 1.00 mass% or more based on the grease composition; and the ratio of the metal content of the organic metal salt to the total mass of the metal content of the organic metal salt and the metal content of the inorganic metal salt is 0.20 or more by mass.

Description

Grease composition and axle bearing

[0001] The present invention relates to a grease composition and an axle bearing containing the same.

[0002] In recent years, in order to reduce power consumption, there has been a demand for higher efficiency in electrical equipment and mechanical parts used in various industries, including automobiles. Various studies have been conducted, including weight reduction and structural improvements of parts. One method for improving the efficiency of automobiles is to reduce the torque of automobile axle bearings. Furthermore, automobiles are often transported by train or truck. During transportation, minute vibrations are generated due to rail joints and rough roads, which can cause fretting wear in greased lubricated parts. Particularly in low-temperature environments, the base oil of the grease becomes less fluid, which leads to insufficient flow of grease into the lubricated parts, making fretting wear more likely to occur. Various studies have been conducted to address this problem. Patent Document 1 discloses a grease composition containing a base oil, a thickener, and a specific combination of additives, with the aim of providing a grease composition that can reduce the occurrence of fretting in low-temperature environments. Patent Document 2 discloses a grease composition for tapered roller bearings that aims to provide a grease composition having excellent wear resistance, flaking resistance, low torque, and low-temperature properties for tapered roller bearings, and contains at least one compound selected from the group consisting of metal salts whose metal group has a valence of two, a base oil containing 40% or more of a synthetic oil having a viscosity index of 110 or more and a pour point of -35°C or less, a thickener, and an antioxidant. Patent Document 3 also discloses a grease composition that aims to provide a grease composition that can reduce fretting wear, and contains a urea-based thickener, a base oil, a phosphorothioate-based compound, and an amine-based compound. However, these conventional grease compositions are not sufficiently effective in terms of low torque and low-temperature fretting resistance, and further improvements are needed.

[0003] International Publication No. 2018 / 061134 Japanese Patent Application Laid-Open No. 2020-083994 Japanese Patent Application Laid-Open No. 2008-239687

[0004] An object of the present invention is to provide a grease composition that has low torque properties and can suppress fretting wear under small vibrations at low temperatures, and to provide an axle bearing containing the grease composition.

[0005] After extensive research, the present inventors have found that the above-mentioned problems can be solved by using a specific combination of an organic metal salt of a divalent metal and an inorganic metal salt of a divalent metal in a grease composition containing a base oil, a thickener, and an additive. That is, the present invention has the following configurations. [1] A grease composition containing a base oil, a thickener, and an additive, wherein the additive contains an organic metal salt of a divalent metal and an inorganic metal salt of a divalent metal, the total mass of the metal content of the organic metal salt and the metal content of the inorganic metal salt is 1.00 mass% or more based on the grease composition, and the ratio of the metal content of the organic metal salt to the total mass of the metal content of the organic metal salt and the metal content of the inorganic metal salt is 0.20 or more by mass. [2] The grease composition according to [1], wherein the thickener is a diurea compound represented by formula (1). R 2 -NHCONH-R 1 -NHCONH-R 3 (1) (wherein, R 1 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R 2 and R 3 may be the same or different and are an alkyl group having 6 to 30 carbon atoms, an aryl group having 6 to 7 carbon atoms, or a cyclohexyl group; R 2 and R 3 [3] The base oil contains a synthetic hydrocarbon oil and has a kinematic viscosity at 40°C of 10 to 100 mm. 2 / s and a base oil having a kinematic viscosity of 150 to 1000 mm at 40°C 2 and a base oil having a kinematic viscosity of 20 to 100 mm / s at 40°C. 2[4] The grease composition according to any one of [1] to [3], wherein the additive further comprises a phenolic antioxidant. [5] An axle bearing packed with the grease composition according to any one of [1] to [4].

[0006] According to the present invention, it is possible to provide a grease composition that has low torque properties and can suppress fretting wear under small vibrations at low temperatures, and an axle bearing containing the grease composition.

[0007] [Grease Composition] <Base Oil> In the present invention, the type of base oil is not particularly limited. It may be a mineral oil, a synthetic oil, or a mixture thereof. Examples of mineral oils include paraffinic mineral oil, naphthenic mineral oil, a mixture of paraffinic mineral oil and naphthenic mineral oil, refined paraffinic mineral oil, and refined naphthenic mineral oil. Examples of synthetic oils include synthetic hydrocarbon oils such as poly-α-olefin (PAO) and polybutene; ether-based synthetic oils such as alkyl diphenyl ether and polypropylene glycol; ester-based synthetic oils such as diesters and polyol esters; silicone oil, and fluorinated oil. The synthetic oil may be a so-called biomass oil produced using biological resources derived from animals and plants as raw materials. For example, biomass ester oils synthesized from various fatty acids and alcohols using vegetable oils as raw materials, or biomass hydrocarbon oils using vegetable oils such as palm oil, corn oil, and soybean oil, can also be used. The base oil preferably contains a synthetic hydrocarbon oil, and more preferably contains a poly-α-olefin. When the base oil contains a poly-α-olefin, the low-temperature fluidity is excellent. When the base oil contains a poly-α-olefin, the content of the poly-α-olefin is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, based on the total mass of the base oil. When the proportion of the poly-α-olefin in the base oil is within the above range, the low-temperature fluidity is improved and the low-temperature fretting resistance is excellent. In the present invention, from the viewpoint of low-temperature fretting resistance, it is preferable that the base oil does not contain an ester-based synthetic oil. One type of base oil may be used alone, or two or more types may be used in combination. The base oil may also be a mixed base oil of base oils having different kinematic viscosities, and the mixed base oil may be a mixed base oil of base oils having a kinematic viscosity at 40°C of 10 to 100 mm 2 / s and a base oil having a viscosity of 150 to 1000 mm 2 and a base oil having a kinematic viscosity of 10 to 50 mm / s at 40°C. 2 / s and a base oil of 150 to 500 mm 2 It is more preferable that the kinematic viscosity at 40°C is 20 to 50 mm / s.2 / s and a base oil of 300 to 500 mm 2 It is more preferable that the base oil is a mixed base oil containing a base oil having a kinematic viscosity of 10 to 100 mm / s. By using a mixed base oil of base oils having different kinematic viscosities in this way, low-temperature fretting resistance is excellent. The reason for this is presumed to be that in the mixed base oil described above, the base oil having a low kinematic viscosity contributes to fluidity, and the base oil having a high kinematic viscosity contributes to oil film formation. When the base oil is a mixed base oil, the kinematic viscosity at 40°C is 10 to 100 mm / s. 2 The content of the base oil having a kinematic viscosity of 10 to 100 mm / s is preferably 50 to 95 mass %, more preferably 60 to 95 mass %, and even more preferably 70 to 95 mass %, based on the total mass of the base oil. 2 When the content of the base oil having a kinematic viscosity of 1 / 2 s is within this range, the low torque performance is excellent. The type of base oil constituting the mixed base oil is not particularly limited, and each may be a mineral oil or a synthetic oil. In particular, from the viewpoint of low-temperature fretting resistance, it is preferable that the mixed base oil contains two or more synthetic hydrocarbon oils having different kinematic viscosities, and in particular, two or more poly-α-olefins (PAO) having different kinematic viscosities. In the present invention, the kinematic viscosity of the entire base oil at 40°C is 20 to 100 mm 2 / s, and 20 to 60 mm 2 / s is more preferable, and 30 to 60 mm 2 / s. Whether the base oil is a single type or a mixed base oil of two or more types, it is preferable that the kinematic viscosity of the entire base oil at 40°C is in the above range. When the kinematic viscosity of the entire base oil at 40°C is in this range, the low torque performance is excellent. When the base oil is a mixed base oil, the kinematic viscosity at 40°C is 10 to 100 mm 2 / s and a base oil having a viscosity of 150 to 1000 mm 2 and a base oil having a kinematic viscosity of 20 to 100 mm / s at 40°C. 2 / s, and the kinematic viscosity at 40°C is preferably 10 to 50 mm 2 / s and a base oil of 150 to 500 mm 2and a base oil having a kinematic viscosity of 20 to 60 mm / s at 40°C. 2 / s, and the kinematic viscosity at 40°C is preferably 20 to 50 mm 2 / s and a base oil of 300 to 500 mm 2 and a base oil having a kinematic viscosity of 30 to 60 mm / s at 40°C. 2 / s. In this specification, the kinematic viscosity of the base oil is a value measured by a method in accordance with JIS K2283. From the viewpoint of improving fluidity at low temperatures, the viscosity index of the base oil is preferably 100 or more, and more preferably 120 or more. The content of the base oil in the grease composition of the present invention is preferably 60 to 90 mass%, more preferably 70 to 90 mass%, and even more preferably 70 to 85 mass%, based on the total mass of the composition. When the content of the base oil is within this range, excellent low torque properties are achieved.

[0008] <Thickener> The thickener that can be used in the present invention is not particularly limited. Specific examples include soap-based thickeners such as Li soap and complex Li soap, urea-based thickeners such as diurea, inorganic thickeners such as organic clay and silica, and organic thickeners such as PTFE. In the present invention, from the viewpoint of low torque, it is preferable to use a diurea compound represented by formula (1). R 2 -NHCONH-R 1 -NHCONH-R 3 (1) In formula (1), R 1 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and is preferably a group derived from tolylene diisocyanate or diphenylmethane-4,4'-diisocyanate, and more preferably a group derived from diphenylmethane-4,4'-diisocyanate. 2 and R 3 may be the same or different and are an alkyl group having 6 to 30 carbon atoms, an aryl group having 6 to 7 carbon atoms, or a cyclohexyl group, and are preferably an alkyl group having 6 to 30 carbon atoms or a cyclohexyl group; R 2and R 3 are both alkyl groups having 6 to 30 carbon atoms (aliphatic diurea), or R 2 and R 3 It is more preferable that one of the groups is an alkyl group having 6 to 30 carbon atoms and the other is a cyclohexyl group (alicyclic aliphatic diurea). As the alkyl group having 6 to 30 carbon atoms, a linear alkyl group having 8 to 20 carbon atoms is more preferable, a linear alkyl group having 8 to 18 carbon atoms is more preferable, and a linear alkyl group having 8 carbon atoms or a linear alkyl group having 18 carbon atoms is particularly preferable. As the aryl group having 6 to 7 carbon atoms, a phenyl group and a tolyl group can be mentioned, with a phenyl group being preferred. R 2 and R 3 Among them, the molar ratio of the alkyl group having 6 to 30 carbon atoms to the total molar ratio of the alkyl group having 6 to 30 carbon atoms, the aryl group having 6 to 7 carbon atoms, and the cyclohexyl group is preferably 10 to 100 mol %, more preferably 10 to 50 mol %, and even more preferably 10 to 20 mol %. 2 and R 3 When the alkyl group having 6 to 30 carbon atoms is in this range, the low torque property is excellent. Here, the diurea compound of formula (1) may be a mixture of compounds represented by the following formulas (1-1), (1-2), and (1-3). 2 -NHCONH-R 1 -NHCONH-R 2 (1-1) R 2 -NHCONH-R 1 -NHCONH-R 3 (1-2) R 3 -NHCONH-R 1 -NHCONH-R 3 (1-3) For example, in formula (1), R 2 is an alkyl group having 6 to 30 carbon atoms, and R 3 is a cyclohexyl group, R 1 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R 2 is an alkyl group having 6 to 30 carbon atoms, and R3 is a cyclohexyl group. In this case, in the mixture of compounds represented by formula (1-1), formula (1-2), and formula (1-3), the number of moles of the alkyl group having 6 to 30 carbon atoms is preferably 10 to 100 mol %, more preferably 10 to 50 mol %, and even more preferably 10 to 20 mol %, relative to the total number of moles of the alkyl group having 6 to 30 carbon atoms and the cyclohexyl group. Among these, in formula (1-1), formula (1-2), and formula (1-3), R 1 is a group derived from diphenylmethane-4,4'-diisocyanate, and R 2 is a linear alkyl group having 18 carbon atoms, and R 3 is preferably a cyclohexyl group, and in the mixture of compounds represented by Formula (1-1), Formula (1-2), and Formula (1-3), the number of moles of the linear alkyl group having 18 carbon atoms is preferably 10 to 100 mol%, more preferably 10 to 50 mol%, and even more preferably 10 to 20 mol%, relative to the total number of moles of the linear alkyl group having 18 carbon atoms and cyclohexyl groups. Having the number of moles of the linear alkyl group having 18 carbon atoms in this range relative to the total number of moles of the linear alkyl group having 18 carbon atoms and cyclohexyl groups provides particularly excellent low torque properties. From the viewpoint of low torque properties, the grease composition of the present invention preferably has a consistency of 220 to 350, more preferably 235 to 330, and even more preferably 250 to 300. In this specification, consistency refers to the 60-stroke worked consistency measured in accordance with JIS K 2220 7. The content of the thickener in the grease composition of the present invention may be any amount suitable for adjusting the consistency to within the above range, and is preferably 5 to 20 mass %, more preferably 8 to 16 mass %, and even more preferably 9 to 13 mass %, based on the total mass of the composition.

[0009] <Additives> The grease composition of the present invention contains additives that include an organic metal salt of a divalent metal and an inorganic metal salt of a divalent metal. (Organic metal salt of a divalent metal) The organic metal salt of a divalent metal may be a salt of a divalent metal and an organic acid. The organic metal salt of a divalent metal is not particularly limited, but is preferably an organic sulfonic acid metal salt, and is preferably a compound represented by the following formula (2): [R 4 -SO3]M 1 (2) In the formula, R 4 represents an alkyl group, an alkenyl group, an alkylnaphthyl group, a dialkylnaphthyl group, an alkylphenyl group, or a residue of a high-boiling petroleum fraction. The alkyl group or alkenyl group is preferably linear or branched and has 2 to 22 carbon atoms. 4 As M, a dialkyldialkylnaphthyl group or an alkylphenyl group, in which the number of carbon atoms in the alkyl group is preferably 6 to 18, more preferably 8 to 18, is more preferred. 1represents an alkaline earth metal or zinc, preferably calcium or zinc, and more preferably calcium. That is, the organic sulfonate metal salt is preferably a calcium salt of an organic sulfonic acid or a zinc salt of an organic sulfonic acid. By using a calcium salt of an organic sulfonic acid or a zinc salt of an organic sulfonic acid as the organic sulfonate metal salt, excellent low torque properties are achieved. Examples of organic sulfonate metal salts include calcium salts or zinc salts of alkylbenzenesulfonic acid, calcium salts or zinc salts of dinonylnaphthalenesulfonic acid, or highly basic salts thereof, with highly basic salts of calcium salts of alkylbenzenesulfonic acid or neutral salts of zinc salts of dinonylnaphthalenesulfonic acid being preferred. From the viewpoint of wear resistance and low torque properties, the total base number (TBN) of the organic sulfonate calcium salt is preferably 0.1 to 500 mgKOH / g, more preferably 50 to 500 mgKOH / g (highly basic), and even more preferably 300 to 500 mgKOH / g. In this specification, the base number is a value measured in accordance with JIS K 2501. The divalent metal organometallic salt may be used singly or in combination of two or more. The content of the divalent metal organometallic salt is preferably 1 to 15 mass %, more preferably 2 to 10 mass % or more, and even more preferably 3 to 8 mass % or more, based on the total mass of the composition. By including the divalent metal organometallic salt in such an amount, good low torque properties are achieved.

[0010] (Inorganic metal salt of divalent metal) The inorganic metal salt of a divalent metal may be a salt of a divalent metal and an inorganic acid. The inorganic metal salt of a divalent metal is not particularly limited, but is preferably a carbonate, and is preferably a compound represented by the following formula (3): M 2 CO3 (3) where M 2represents an alkaline earth metal or zinc, preferably calcium or zinc, and more preferably calcium. It is also preferable that the divalent metal contained in the divalent inorganic metal salt is the same as the divalent metal contained in the divalent organic metal salt. Furthermore, when two or more organic metal salts of divalent metals are used in combination, it is preferable that the divalent metal contained in the divalent inorganic metal salt is the same as the divalent metal contained in one of the organic metal salts. The divalent metal carbonate is preferably calcium carbonate or zinc carbonate, and more preferably calcium carbonate. The use of calcium carbonate as the divalent metal carbonate provides excellent low-temperature fretting resistance. In the present invention, the divalent inorganic metal salt can be used as a solid lubricant. The average particle size of the divalent inorganic metal salt is preferably 1.0 to 4.0 μm, more preferably 1.0 to 2.5 μm. By having the average particle size of the divalent inorganic metal salt within this range, it acts on the lubricated part and provides excellent low-temperature fretting resistance. In this specification, the term "average particle size" refers to the 50% diameter of the mass cumulative particle size distribution, and is a value measured, for example, using a laser diffraction particle size distribution analyzer. The inorganic metal salt of a divalent metal may be used alone or in combination of two or more. The content of the inorganic metal salt of a divalent metal is preferably 1 to 15% by mass, more preferably 2 to 10% by mass or more, and even more preferably 3 to 8% by mass or more, based on the total mass of the composition. By including the inorganic metal salt of a divalent metal in such an amount, excellent low-temperature fretting resistance is achieved. The combination of the organic metal salt of a divalent metal and the inorganic metal salt of a divalent metal preferably includes a combination of a calcium salt of an organic sulfonic acid or a zinc salt of an organic sulfonic acid with calcium carbonate or zinc carbonate, more preferably a combination of a calcium salt of an organic sulfonic acid or a zinc salt of an organic sulfonic acid with calcium carbonate, and even more preferably a combination of a calcium salt of an organic sulfonic acid with calcium carbonate.

[0011] (Metal Content of Organic Metal Salt of Divalent Metal and Metal Content of Inorganic Metal Salt of Divalent Metal) In the present invention, the total mass of the metal content of the organic metal salt of a divalent metal and the metal content of the inorganic metal salt of a divalent metal is 1.00 mass% or more, preferably 1.50 mass% or more, and more preferably 2.00 mass% or more, based on the total mass of the grease composition. The upper limit is preferably 5.00 mass% or less, more preferably 4.00 mass% or less, and even more preferably 3.50 mass% or less. In particular, it is particularly preferable to use a combination of a calcium salt of an organic sulfonic acid or a zinc salt of an organic sulfonic acid with calcium carbonate or zinc carbonate so that the metal content falls within the above-mentioned range. By using an organic metal salt of a divalent metal and an inorganic metal salt of a divalent metal so that the total metal content falls within this range, low torque properties and low-temperature fretting resistance are improved. In this specification, the metal content of an organic metal salt of a divalent metal and the metal content of an inorganic metal salt of a divalent metal refer to values ​​measured by ICP (Inductively Coupled Plasma) atomic emission spectrometry in accordance with ASTM D-4951. Furthermore, the metal content of an organic metal salt of a divalent metal relative to the total mass of the metal content of an organic metal salt of a divalent metal and the metal content of an inorganic metal salt of a divalent metal (metal content of organic metal salt / (metal content of organic metal salt + metal content of inorganic metal salt)) is 0.20 or more, preferably 0.20 to 0.65, more preferably 0.20 to 0.50, and even more preferably 0.20 to 0.40, on a mass basis. In particular, it is particularly preferable to use a calcium salt of an organic sulfonic acid or a zinc salt of an organic sulfonic acid in combination with calcium carbonate or zinc carbonate so that the ratio of the metal contents of the organic sulfonic acid metal salts falls within the above-mentioned range. By using the organic metal salt and the inorganic metal salt so that the ratio of the metal contents of the organic metal salts falls within this range, low torque properties and low-temperature fretting resistance are improved.The reason for this is thought to be that in a specific combination containing an organic metal salt of a divalent metal and an inorganic metal salt of a divalent metal, the organic metal salt of the divalent metal contributes to reducing stirring resistance by inhibiting grease adhesion, and the inorganic metal salt of the divalent metal is present in the lubricated part and inhibits metal-to-metal contact, thereby contributing to the inhibition of fretting wear.

[0012] (Other Additives) The grease composition of the present invention may further contain other additives in addition to the divalent metal organic metal salt and the divalent metal inorganic metal salt. Any additives commonly used in greases can be used as needed, including rust inhibitors, antioxidants, metal corrosion inhibitors, oiliness agents, and anti-wear agents. Examples of the rust inhibitor include amine-based rust inhibitors; carboxylic acids and derivatives thereof, such as alkenylsuccinic anhydrides, alkenylsuccinic acid esters, and alkenylsuccinic acid half esters; carboxylic acid salts, such as amine salts of fatty acids, dibasic acids, naphthenic acids, lanolin fatty acids, and alkenylsuccinic acids; sulfonates; passivators, such as sodium nitrite and sodium molybdate; and esters, such as sorbitan trioleate and sorbitan monooleate. Examples of antioxidants include amine-based antioxidants such as phenyl α-naphthylamine, alkylated phenyl α-naphthylamine, and alkylated diphenylamine; phenol-based antioxidants such as hindered phenols such as 2,6-di-tert-butyl-p-cresol, pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; and quinoline-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer. Phenol-based or amine-based antioxidants are preferred, with phenol-based antioxidants being more preferred from the viewpoint of having excellent antioxidant performance even at relatively low temperatures. Examples of metal corrosion inhibitors include benzotriazole or derivatives thereof, zinc oxide, and the like. Examples of oily agents include fatty acids, fatty acid esters, and phosphate esters. Examples of anti-wear agents include phosphorus-based compounds such as amine phosphate and tricresyl phosphate; sulfur-based compounds such as dibenzyl disulfide and various polysulfides; sulfur-phosphorus-based compounds such as triphenyl phosphorothioate and derivatives thereof; organometallic compounds such as dialkyldithiophosphate salts of Zn, Mo, Sb, Bi, etc., and dialkyldithiocarbamate salts of Zn, Mo, Sb, Bi, etc.; and other anti-wear agents such as ashless dithiocarbamates and ashless dithiophosphates.Preferred anti-wear agents include amine phosphate, triphenyl phosphorothioate and its derivatives, Zn or Mo salts of dialkyldithiophosphate, and Zn or Mo salts of dialkyldithiocarbamate. From the perspective of further improving various performance properties, the grease composition of the present invention preferably contains other additives, such as a rust inhibitor, antioxidant, or anti-wear agent. The antioxidant content is preferably 0.1 to 7.0 mass%, more preferably 0.5 to 5.0 mass%, and even more preferably 0.5 to 3.0 mass%, based on the total mass of the composition. Including the antioxidant in such an amount improves heat resistance. The total content of the other additives is, for example, preferably 0.1 to 10 mass%, more preferably 0.5 to 8 mass%, and even more preferably 0.5 to 7 mass%, based on the total mass of the composition.

[0013] Among the grease compositions of the present invention, the following embodiment is particularly preferred: A grease composition containing a base oil, a thickener, and an additive, wherein the additive comprises an organic metal salt of a divalent metal and an inorganic metal salt of a divalent metal, the total mass of the metal content of the organic metal salt and the metal content of the inorganic metal salt is 1.00 mass% or more based on the grease composition, the ratio of the metal content of the organic metal salt to the total mass of the metal content of the organic metal salt and the metal content of the inorganic metal salt is 0.20 or more by mass, and the organic metal salt of a divalent metal is a calcium salt of an organic sulfonic acid, and the inorganic metal salt of a divalent metal is calcium carbonate. In this embodiment, the base oil has a kinematic viscosity at 40°C of 10 to 100 mm 2 / s and a poly-α-olefin having a kinematic viscosity at 40°C of 150 to 1000 mm 2 and a poly-α-olefin having a kinematic viscosity of 20 to 100 mm / s at 40°C. 2 It is also preferable that the base oil does not contain an ester-based synthetic oil.

[0014] In another aspect, the grease composition of the present invention preferably has the following configuration: A grease composition containing a base oil, a thickener, and an additive, wherein the additive comprises two organic metal salts of a divalent metal and one or more inorganic metal salts of a divalent metal, the divalent metals contained in the two organic metal salts are different from each other and the divalent metal contained in the one or more inorganic metal salts is the same as the divalent metal contained in any of the two organic metal salts, and the total mass of the metal contents of the two organic metal salts and the one or more inorganic metal salts is 1.04 mass% or more based on the grease composition. In this aspect, it is also preferable that the ratio of the metal content of the organic metal salt to the total mass of the metal content of the organic metal salt and the inorganic metal salt is 0.20 or more by mass. In this embodiment, it is also preferable that the two organic metal salts of the divalent metal are a calcium salt of an organic sulfonic acid and a zinc salt of an organic sulfonic acid, and the inorganic metal salt of the divalent metal is calcium carbonate. 2 / s and a poly-α-olefin having a kinematic viscosity at 40°C of 150 to 1000 mm 2 and a poly-α-olefin having a kinematic viscosity of 20 to 100 mm / s at 40°C. 2 It is also preferable that the base oil does not contain an ester-based synthetic oil.

[0015] In yet another aspect, the grease composition of the present invention preferably has the following configuration: A grease composition containing a base oil, a thickener, and an additive, wherein the additive comprises three types of organic metal salts and one or more inorganic metal salts, wherein the metals contained in the three organic metal salts are different from one another and the metal contained in the one or more inorganic metal salts is the same as the metal contained in any one of the three organic metal salts, and wherein the total mass of the metal contents of the three organic metal salts and the one or more inorganic metal salts is 1.14 mass% or more based on the grease composition. In this aspect, it is also preferable that the ratio of the metal content of the organic metal salt to the total mass of the metal content of the organic metal salt and the inorganic metal salt is 0.20 or more by mass. In this aspect, it is also preferable that the three organic metal salts are a calcium salt of an organic sulfonic acid, a zinc salt of an organic sulfonic acid, and molybdenum dialkyldithiocarbamate, and the inorganic metal salt of a divalent metal is calcium carbonate. Further, in this embodiment, the base oil has a kinematic viscosity at 40°C of 10 to 100 mm 2 / s and a poly-α-olefin having a kinematic viscosity at 40°C of 150 to 1000 mm 2 and a poly-α-olefin having a kinematic viscosity of 20 to 100 mm / s at 40°C. 2 It is also preferable that the base oil does not contain an ester-based synthetic oil.

[0016] [Axle bearing] The axle bearing of the present invention is an axle bearing filled with the grease composition of the present invention. The axle bearing is preferably a hub unit bearing, and is preferably a hub unit bearing using an angular contact ball bearing. The axle bearing filled with the grease composition of the present invention can more effectively exhibit the effects of the present invention, that is, it has low torque properties and is excellent in suppressing fretting wear under small vibrations at low temperatures.

[0017] [Preparation of Test Greases] Grease compositions of Examples and Comparative Examples were prepared using the components shown in the table below. Specifically, 1 mole of diphenylmethane diisocyanate was reacted with 2 moles of a specified amine in the base oil shown in the table below, heated, cooled, and then kneaded using a three-roll mill to obtain a base grease. Additives were blended thereto in the amounts shown in the table below, and further base oil was added to obtain the thickener amount shown in the table below, thereby obtaining the grease compositions of Examples and Comparative Examples. The kinematic viscosity of the base oil at 40°C was measured in accordance with JIS K2283, the base number was measured in accordance with JIS K2501, and the consistency was measured in accordance with JIS K2220. The base oil, thickener, and additives in the table are as follows. Unless otherwise specified, the component numbers in the table represent mass % based on the total mass of the composition. <Thickener> Thickener: Alicyclic aliphatic diurea obtained using cyclohexylamine and stearylamine (cyclohexylamine:stearylamine=7:1 (molar ratio)) as amines <Base oil> Synthetic hydrocarbon oil A: PAO8, kinematic viscosity at 40°C 48 mm 2 / s Synthetic hydrocarbon oil B: PAO40, kinematic viscosity at 40 ° C. 400 mm 2 / s Mineral oil A: Product name: Super Oil K-100, manufactured by ENEOS Corporation, viscosity at 40°C: 102 mm 2 / s Refined mineral oil B: Product name: YUBASE 6+, manufactured by SK Enmove Japan Co., Ltd., kinematic viscosity at 40°C: 33.8 mm 2 / s <Additives> Organic metal salt A1: Ca sulfonate (calcium dodecylbenzenesulfonate, trade name: Bryton C-400C, manufactured by LANXESS Solutions Ltd., base number 405 mg KOH / g, calcium content 15.2% by mass) Organic metal salt A2: Zn sulfonate (zinc dinonylnaphthalenesulfonate, trade name: NA-SUL ZS-HT, manufactured by KING INDUSTRIES, INC., base number 0.50 mg KOH / g, zinc content 3.63% by mass) Inorganic metal salt: calcium carbonate (average particle size 2 μm, calcium content 40% by mass) Antioxidant : Phenolic antioxidant (octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, trade name: ADEKA ECO ROYAL AIN-100, manufactured by ADEKA Corporation)

[0018] [Test method and evaluation] (1) Low torque (bearing torque test) The grease composition was packed into a rolling bearing, the inner ring was rotated under the following conditions, and the torque value applied to the outer ring of the bearing 20 minutes after rotation was measured. Bearing type: Angular contact spherical bearing 7204B Test temperature: Room temperature Rotation speed: 1560 rpm Test load: Axial load 500 N Radial load 0 N Amount of grease packed: 2.67 g (Evaluation criteria) Bearing torque of 0.070 Nm or less ◎ (Pass) Bearing torque of more than 0.070 Nm and less than 0.075 Nm ○ (Pass) Bearing torque of more than 0.075 Nm × (Fail) (2) Low-temperature fretting resistance (Fafnir test) A Fafnir test was conducted in accordance with ASTM D4170. That is, the test grease was applied to two sets of test thrust bearings described below, and an oscillating operation was carried out under the following conditions to determine the amount of wear (mass loss due to fretting wear). Bearing type: 51204 thrust bearing Test load: 4000 N (surface pressure: 1.9 GPa) Oscillation angle: ±3° Oscillation cycle: 2 Hz Test time: 22 hours Test temperature: -30°C Amount of grease filled: 1.0 g per bearing set Amount of wear: Race mass loss per bearing set (total loss of bearing race mass / 2) (Evaluation criteria) After the test, the bearing wear mass was 2.0 mg or less ◎ (Pass) After the test, the bearing wear mass was more than 2.0 mg and less than 3.0 mg ○ (Pass) After the test, the bearing wear mass was more than 3.0 mg × (Fail) (Overall evaluation) All tests passed ○ (Pass) Either test failed × (Fail)

[0019]

[0020]

[0021] The grease compositions of Examples 1 to 6 exhibited good results in both low torque and low-temperature fretting resistance. In contrast, the grease composition of Comparative Example 1, in which the total mass of the metal content of the organic metal salt of a divalent metal and the metal content of the inorganic metal salt of a divalent metal was less than 1.00 mass% based on the grease composition, exhibited high torque and a large amount of low-temperature fretting wear. The grease composition of Comparative Example 2, which did not contain an inorganic metal salt of a divalent metal, exhibited a large amount of low-temperature fretting wear. The grease composition of Comparative Example 3, which did not contain an organic metal salt of a divalent metal, and the grease composition of Comparative Example 4, in which the metal content of the organic metal salt relative to the total mass of the metal content of the organic metal salt and the metal content of the inorganic metal salt was less than 0.20 by mass, exhibited high torque.

Claims

1. A grease composition containing a base oil, a thickener, and an additive, wherein the additive comprises an organic metal salt of a divalent metal and an inorganic metal salt of a divalent metal, the total mass of the metal content of the organic metal salt and the metal content of the inorganic metal salt is 1.00 mass% or more based on the grease composition, and the ratio of the metal content of the organic metal salt to the total mass of the metal content of the organic metal salt and the metal content of the inorganic metal salt is 0.20 or more based on mass.

2. The grease composition according to claim 1, wherein the thickener is a diurea compound represented by formula (I). 2 -NHCONH-R 1 -NHCONH-R 3 (1) (wherein, R 1 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R 2 and R 3 may be the same or different and are an alkyl group having 6 to 30 carbon atoms, an aryl group having 6 to 7 carbon atoms, or a cyclohexyl group; R 2 and R 3 Among these, the number of moles of alkyl groups having 6 to 30 carbon atoms is 10 to 100 mol % relative to the total number of moles of alkyl groups having 6 to 30 carbon atoms, aryl groups having 6 to 7 carbon atoms, and cyclohexyl groups.

3. The base oil contains a synthetic hydrocarbon oil and has a kinematic viscosity at 40°C of 10 to 100 mm 2 / s and a base oil having a kinematic viscosity of 150 to 1000 mm at 40°C 2 and a base oil having a kinematic viscosity of 20 to 100 mm / s at 40°C. 2 2. The grease composition according to claim 1, wherein the grease composition is:

4. The grease composition of claim 1, wherein the additive further comprises a phenolic antioxidant.

5. An axle bearing packed with the grease composition according to any one of claims 1 to 4.

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