Grease composition and axle bearing

Abstract

The present invention provides a grease composition and an axle bearing in which the grease composition is sealed.SOLUTION: The grease composition of the present invention contains a base oil, a thickener, and an additive, 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% by mass or more based on the grease composition, and the metal content of the organic metal salt with respect 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 on a mass basis.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In recent years, from the perspective of reducing power consumption, there has been a demand for higher efficiency in electrical equipment and mechanical parts used in various industries, including automobiles, and various studies are being conducted to reduce the weight of parts, improve their structure, etc. One method of improving the efficiency of automobiles is to reduce the torque of automobile axle bearings. Furthermore, automobiles are often transported by train or truck, and during this transportation, minute vibrations caused by rail joints and rough roads can cause fretting wear in lubricated parts coated with grease. In particular, in low-temperature environments, the base oil in the grease becomes less fluid, which can lead to insufficient grease flowing into the lubricated parts, making fretting wear more likely to occur. Various studies have been conducted to address these problems. 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 is intended to provide a grease composition that has excellent wear resistance, flaking resistance, low torque, and low-temperature properties for tapered roller bearings, and the grease composition contains a base oil containing at least one compound selected from the group consisting of metal salts whose metal group has a valence of two, 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 contains a urea-based thickener, a base oil, a phosphorothioate-based compound, and an amine-based compound, with the aim of providing a grease composition that can reduce fretting wear. However, these conventional grease compositions are not said to be sufficient in terms of low torque properties and low-temperature fretting resistance, and further improvements are desired. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 061134 [Patent Document 2] Japanese Patent Publication No. 2020-083994 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-239687 Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[0005] As a result of 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 as additives in a grease composition containing a base oil, a thickener, and additives. [1] A grease composition containing a base oil, a thickener, and an additive, 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 grease composition, wherein 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-R1 -NHCONH-R 3 (1) (In the formula, 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, and R 2 and R 3 Among these, the molar number of alkyl groups having 6 to 30 carbon atoms is 10 to 100 mol % relative to the total molar number 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 with a kinematic viscosity of 150 to 1000 mm at 40°C 2 and a base oil mixture containing a base oil of The kinematic viscosity of the mixed base oil at 40°C is 20 to 100 mm 2 The grease composition according to [1] or [2], wherein the grease composition is / s. [4] The grease composition according to any one of [1] to [3], wherein the additives further contain a phenolic antioxidant. [5] An axle bearing containing the grease composition according to any one of [1] to [4]. [Effects of the Invention]

[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. DETAILED DESCRIPTION OF THE INVENTION

[0007] [Grease composition] <Base oil> In the present invention, the type of base oil is not particularly limited, and may be a mineral oil, a synthetic oil, or a mixture thereof. Examples of mineral oils include paraffinic mineral oils, naphthenic mineral oils, mixed oils of paraffinic mineral oils and naphthenic mineral oils, refined paraffinic mineral oils, and refined naphthenic mineral oils. Examples of synthetic oils include synthetic hydrocarbon oils such as poly-α-olefins (PAOs) and polybutenes; ether-based synthetic oils such as alkyl diphenyl ethers and polypropylene glycols; ester-based synthetic oils such as diesters and polyol esters; silicone oils, and fluorinated oils. The synthetic oil may be a so-called biomass oil produced from biological resources derived from animals and plants. For example, biomass ester oils synthesized from various fatty acids and alcohols derived from vegetable oils, or biomass hydrocarbon oils derived from vegetable oils such as palm oil, corn oil, and soybean oil, can also be used. The base oil preferably contains a synthetic hydrocarbon oil, more preferably a poly-α-olefin, which provides excellent low-temperature fluidity. When the base oil contains a poly-α-olefin, the content of the poly-α-olefin is preferably 40 mass% or more, more preferably 50 mass% or more, and even more preferably 60 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, low-temperature fluidity is improved and low-temperature fretting resistance is excellent. In the present invention, it is preferable that the base oil does not contain an ester-based synthetic oil from the viewpoint of low-temperature fretting resistance. The base oil may be used alone or in combination of two or more kinds. The base oil may be a mixed base oil of base oils having different kinematic viscosities, and the kinematic viscosity at 40°C is 10 to 100 mm 2 / s and base oil with a viscosity of 150 to 1000 mm 2 It is preferable that the kinematic viscosity at 40°C is 10 to 50 mm / s. 2 / s and 150 to 500mm 2 It is more preferable that the kinematic viscosity at 40°C is 20 to 50 mm / s. 2 / s and 300-500mm 2 It is more preferable that the mixed base oil contains a base oil having a kinematic viscosity of 0.01 / 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. If the base oil is a mixed base oil, the kinematic viscosity at 40°C is 10 to 100 mm 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, which is 0.15 wt. / s, is in this range, the low torque property is excellent. The types of base oils constituting the mixed base oil are not particularly limited, and may be mineral oils or synthetic oils. 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, in particular, two or more poly-α-olefins (PAOs) 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 is preferable, 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, the kinematic viscosity at 40°C of the entire base oil is preferably in the above range. When the kinematic viscosity at 40°C of the entire base oil is in this range, excellent low torque properties are achieved. If the base oil is a mixed base oil, the kinematic viscosity at 40°C is 10 to 100 mm 2 / s and base oil with a viscosity of 150 to 1000 mm 2 The mixed base oil has 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 150 to 500mm 2 The mixed base oil has a kinematic viscosity of 20 to 60 mm / s at 40°C. 2 / s, and the kinematic viscosity at 40°C is more preferably 20 to 50 mm 2 / s and 300-500mm 2 The mixed base oil has a kinematic viscosity of 30 to 60 mm / s at 40°C. 2 It is more preferable that the ratio is / s. In this specification, the kinematic viscosity of the base oil is a value measured by a method in accordance with JIS K2283. The viscosity index of the base oil is preferably 100 or more, and more preferably 120 or more, from the viewpoint of improving fluidity at low temperatures. 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. By having the content of the base oil in 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. R 2 and R 3may 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 2 and 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 them is an alkyl group having 6 to 30 carbon atoms and the other is a cyclohexyl group (alicyclic aliphatic diurea). The alkyl group having 6 to 30 carbon atoms is more preferably a linear alkyl group having 8 to 20 carbon atoms, more preferably a linear alkyl group having 8 to 18 carbon atoms, and particularly preferably a linear alkyl group having 8 carbon atoms or a linear alkyl group having 18 carbon atoms. Examples of the aryl group having 6 to 7 carbon atoms include a phenyl group and a tolyl group, with a phenyl group being preferred. R 2 and R 3 Among them, the number of moles of alkyl groups having 6 to 30 carbon atoms 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 is preferably 10 to 100 mol %, more preferably 10 to 50 mol %, and even more preferably 10 to 20 mol %. In the diurea compound of formula (1), R 2 and R 3 When the alkyl group having 6 to 30 carbon atoms is in this range, low torque properties are 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). R 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 R 3 is a cyclohexyl group. In this case, in the mixture of the 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 %, based on the total number of moles of the alkyl group having 6 to 30 carbon atoms and the cyclohexyl group. Among them, in the formula (1-1), the formula (1-2), and the 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. When the number of moles of the linear alkyl group having 18 carbon atoms is within this range relative to the total number of moles of the linear alkyl group having 18 carbon atoms and cyclohexyl groups, the low torque property is particularly excellent. From the viewpoint of low torque properties, the grease composition of the present invention preferably has a penetration of 220 to 350, more preferably 235 to 330, and even more preferably 250 to 300. In this specification, the penetration refers to the 60-stroke worked penetration 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 additives in the grease composition of the present invention include an organic metal salt of a divalent metal and an inorganic metal salt of a divalent metal. (organometallic salts of divalent metals) 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. R 4 As the alkyl group, a dialkyldialkylnaphthyl group or an alkylphenyl group, in which the alkyl group preferably has 6 to 18 carbon atoms, more preferably 8 to 18 carbon atoms, is more preferred. M 1 represents an alkaline earth metal or zinc, preferably calcium or zinc, and more preferably calcium. That is, the metal organic sulfonate 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 metal organic sulfonate, excellent low torque properties can be achieved. Examples of the organic sulfonic acid metal salt include calcium salts or zinc salts of alkylbenzenesulfonic acid, calcium salts or zinc salts of dinonylnaphthalenesulfonic acid, and highly basic salts thereof, and highly basic salts of calcium salts of alkylbenzenesulfonic acid or neutral salts of zinc salts of dinonylnaphthalenesulfonic acid are preferred. From the viewpoints of wear resistance and low torque, the total base number (TBN) of the organic calcium sulfonate is preferably 0.1 to 500 mgKOH / g, more preferably 50 to 500 mgKOH / g (high basicity), 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 organic metal salts of divalent metals may be used singly or in combination of two or more. The content of the organic metal salt of a divalent metal is preferably 1 to 15 mass % based on the total mass of the composition, more preferably 2 to 10 mass % or more, and even more preferably 3 to 8 mass % or more. By including the organic metal salt of a divalent metal in such an amount, good low torque properties are achieved.

[0010] (Inorganic metal salts of divalent metals) 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) In the formula, M 2 represents an alkaline earth metal or zinc, preferably calcium or zinc, 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. By using calcium carbonate as the divalent metal carbonate, excellent low-temperature fretting resistance is achieved. In the present invention, a 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. When the average particle size of the divalent inorganic metal salt is within this range, it acts on the lubricated part and provides excellent low-temperature fretting resistance. In this specification, the average particle size refers to the 50% diameter of the mass cumulative particle size distribution, and is a value measured using, for example, a laser diffraction particle size distribution analyzer. The inorganic metal salts of divalent metals may be used singly or in combination of two or more. The content of the inorganic metal salt of a divalent metal is preferably 1 to 15 mass % based on the total mass of the composition, more preferably 2 to 10 mass % or more, and even more preferably 3 to 8 mass % or more. 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 salts of divalent metals and metal content of inorganic metal salts of divalent metals) 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 range. By using an organic metal salt of a divalent metal and an inorganic metal salt of a divalent metal so that the total mass of the metal contents is 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 the organic metal salt of the divalent metal relative to the total mass of the metal content of the organic metal salt of the divalent metal and the metal content of the inorganic metal salt of the 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 by mass, preferably 0.20 to 0.65, more preferably 0.20 to 0.50, and even more preferably 0.20 to 0.40. 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 such that the ratio of the metal content of the organic sulfonic acid metal salt falls within the above-mentioned range. By using an organic metal salt and an inorganic metal salt so that the metal content ratio of the organic metal salt is as described above, low torque and low-temperature fretting resistance are improved. The reason for this is presumably 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 suppressing grease adhesion, and the inorganic metal salt of the divalent metal is present in the lubricated parts and suppresses metal-to-metal contact, thereby contributing to suppressing fretting wear.

[0012] (Other additives) The grease composition of the present invention may further contain other additives in addition to the organic metal salt of a divalent metal and the inorganic metal salt of a divalent metal. Any additives typically 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 that can be used include amine-based rust inhibitors; carboxylic acids and derivatives thereof, such as alkenylsuccinic anhydrides, alkenylsuccinic acid esters, and alkenylsuccinic acid half esters; carboxylates, such as amine salts of fatty acids, dibasic acids, naphthenic acid, lanolin fatty acids, and alkenylsuccinic acids; sulfonates; passivating agents, 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 polymers. Phenol-based or amine-based antioxidants are preferred, with phenol-based antioxidants being more preferred due to their excellent antioxidant properties even at relatively low temperatures. Examples of the metal corrosion inhibitor include benzotriazole or a derivative 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 compounds such as amine phosphate and tricresyl phosphate; sulfur compounds such as dibenzyl disulfide and various polysulfides; sulfur-phosphorus compounds such as triphenyl phosphorothioate and its derivatives; organometallic compounds such as dialkyl dithiophosphate salts with Zn, Mo, Sb, Bi, or the like, and dialkyl dithiocarbamic acid salts with Zn, Mo, Sb, Bi, or the like; and other anti-wear agents such as ashless dithiocarbamates and ashless dithiophosphates. Preferred anti-wear agents are amine phosphate, triphenyl phosphorothioate and its derivatives, dialkyl dithiophosphate salts with Zn or Mo, and dialkyl dithiocarbamic acid salts with Zn or Mo. From the viewpoint of further improving various performances, the grease composition of the present invention preferably contains other additives such as a rust inhibitor, an antioxidant, or an anti-wear agent. The content of the antioxidant 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. By including the antioxidant in such an amount, good heat resistance is achieved. The total content of 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] Of the grease compositions of the present invention, those having the following features are particularly preferred. A grease composition containing a base oil, a thickener, and an additive, 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, The grease composition as described above, wherein the organic metal salt of the divalent metal is a calcium salt of an organic sulfonic acid, and the inorganic metal salt of the divalent metal is calcium carbonate. In this embodiment, the base oil has a kinematic viscosity of 10 to 100 mm at 40°C. 2 / s and a poly-α-olefin having a kinematic viscosity of 150 to 1000 mm at 40°C. 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 aspect. A grease composition containing a base oil, a thickener, and an additive, 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 types of organic metal salts are different from each other, and the divalent metal contained in the one or more types of inorganic metal salts is the same as the divalent metal contained in any one of the two types of organic metal salts; The grease composition, wherein the total mass of the metal content of the two types of organic metal salts and the metal content of the one or more types of inorganic metal salts is 1.04 mass% or more based on the grease composition. In this embodiment, 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 metal content of the inorganic metal salt is 0.20 or more on a mass basis. 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. Furthermore, 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 of 150 to 1000 mm at 40°C. 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 still another embodiment, the grease composition of the present invention preferably has the following embodiment. A grease composition containing a base oil, a thickener, and an additive, the additive comprises three kinds of organic metal salts and one or more kinds of inorganic metal salts; the metals contained in the three kinds of 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 kinds of organic metal salts; The grease composition, wherein the total mass of the metal content of the three organic metal salts and the metal content of the one or more inorganic metal salts is 1.14 mass% or more based on the grease composition. In this embodiment, 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 metal content of the inorganic metal salt is 0.20 or more on a mass basis. In this embodiment, 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 a molybdenum dialkyldithiocarbamate, and that the inorganic metal salt of a divalent metal is calcium carbonate. Furthermore, 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 of 150 to 1000 mm at 40°C. 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 bearings] 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, i.e., it has low torque properties and is excellent in suppressing fretting wear under small vibrations at low temperatures. [Example]

[0017] [Preparation of test grease] The grease compositions of the 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 specific amine in the base oil shown in the table below, and the mixture was heated and cooled, then kneaded using a three-roll mill to obtain a base grease. The additives were blended in the amounts shown in the table below, and further base oil was added to obtain the thickener amount shown in the table, thereby obtaining the grease compositions of the 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 oils, thickeners, and additives in the table are as follows: Unless otherwise specified, the numbers for the components 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 48mm 2 / s Synthetic hydrocarbon oil B: PAO40, kinematic viscosity 400mm at 40℃ 2 / s Mineral oil A: Product name: Super Oil K-100, manufactured by ENEOS, viscosity 102mm at 40°C 2 / s Refined mineral oil B: Product name: YUBASE6+, manufactured by SK Enmove Japan Co., Ltd., kinematic viscosity at 40°C: 33.8 mm 2 / s <Additives> Organic metal salt A1: Calcium 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 KINGINDUSTRIES.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 judgment] (1) Low torque (bearing torque test) The grease composition was filled into a rolling bearing, the inner ring was rotated under the conditions below, and the torque value applied to the outer ring of the bearing was measured 20 minutes after rotation. Bearing type: Angular contact ball bearing 7204B Test temperature: Room temperature Rotation speed: 1560 rpm Test load: Axial load 500N Radial load 0N Grease amount: 2.67g (Judgment criteria) Bearing torque is 0.070Nm or less ◎ (pass) Bearing torque is over 0.070Nm and less than 0.075Nm 〇 (pass) Bearing torque over 0.075Nm × (fail) (2) Low-temperature fretting resistance (Fafnir test) A Fafnir test was conducted in accordance with ASTM D4170. Specifically, the test grease was applied to two pairs of test thrust bearings described below, and oscillating operation was carried out under the conditions described below to determine the amount of wear (mass loss due to fretting wear). Bearing type: 51204 thrust bearing Test load: 4000N (surface pressure: 1.9GPa) Oscillation angle: ±3° Oscillation cycle: 2Hz Exam time: 22 hours Test temperature: -30℃ Grease quantity: 1.0g per bearing set Wear amount: Weight loss of race per bearing (total weight loss of bearing race / 2) (Judgment criteria) After the test, the amount of bearing wear is 2.0 mg or less. ◎ (Pass) After the test, the amount of bearing wear is over 2.0 mg and 3.0 mg or less. 〇 (Pass) After the test, the amount of wear on the bearing exceeds 3.0 mg. × (fail) (comprehensive evaluation) Passed all exams. 〇 (Pass) Fail any of the tests × (failed)

[0019] [Table 1]

[0020] [Table 2]

[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, 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 grease composition, wherein 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. 2. The grease composition according to claim 1, wherein the thickener is a diurea compound represented by formula (I). R 2 -NHGNH-R 1 -NHGNH-R 3 (1) (In the formula, 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 them, 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 mixture containing a base oil selected from the group consisting of hydroxybenzoates, ... The kinematic viscosity of the mixed base oil at 40°C is 20 to 100 mm 2 2. The grease composition according to claim 1, wherein the grease composition is:

4. 10. 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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