Grease composition

Abstract

Provided is a grease composition containing a base oil (A), an antioxidant (B), and a urea-based thickener (C), wherein the base oil (A) contains a poly-alpha-olefin (A1) having a ratio of methyl groups on tertiary carbons having bonds with secondary carbons and tertiary carbons determined by formula (1) from the 13C-NMR spectrum of 10.0% or more and an ester oil (A2), the total content of the poly-alpha-olefin (A1) and the ester oil (A2) in terms of the total amount of the base oil (A) is 70 mass% or more, the bearing life is long, and the bearing torque is low.　Formula (1): ratio of methyl groups on tertiary carbons having bonds with secondary carbons and tertiary carbons = alpha / (alpha + beta + gamma + delta) × 100, where alpha is the integral value of 15.1-16.1 ppm, beta is the integral value of 13.7-14.7 ppm, gamma is the integral value of 19.6-20.6 ppm, and delta is the integral value of 26.3-27.3 ppm.

Description

Grease composition

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

[0002] Grease compositions are easier to seal than lubricating oils, allowing for the miniaturization and weight reduction of machines to which they are applied. Therefore, they have been widely used for lubricating various sliding parts of automobiles, electrical equipment, industrial machinery, and other machinery. Furthermore, for example, since fluid lubricating oil compositions cannot be used on automobile wheels, semi-solid grease compositions are used as lubricants. Furthermore, rubber components are also used in hub bearings and the like attached to automobile wheels from the viewpoint of sealing properties (sealing properties, leak prevention). In other words, in such parts, metal components and rubber components come into contact with each other, and therefore lubrication for metal-rubber sliding is required.

[0003] As such grease compositions, for example, Patent Documents 1 and 2 disclose grease compositions containing poly-α-olefin and an ester.

[0004] JP 2014-088527 A JP 2017-002306 A

[0005] Grease compositions used in automobiles often use low-volatility base oils to ensure a long seizure life. However, low-volatility base oils also have relatively high viscosities, which means that bearings using these oils have high torque. In other words, in grease compositions, extending the seizure life and reducing bearing torque are in a trade-off relationship.

[0006] An object of the present invention is to provide a grease composition that has a long seizure life and low bearing torque.

[0007] According to the present invention, the following [1] to

[13] are provided: [1] A grease composition containing a base oil (A), an antioxidant (B), and a urea-based thickener (C), wherein the base oil (A) is １３A grease composition comprising a poly-α-olefin (A1) having a ratio of methyl groups on tertiary carbons having bonds to secondary and tertiary carbons of 10.0% or more, as determined from a C-NMR spectrum using the following formula (1), and an ester oil (A2), wherein the total content of the poly-α-olefin (A1) and the ester oil (A2) is 70% by mass or more based on the total amount of the base oil (A). Ratio of methyl groups on tertiary carbons having bonds to secondary carbons and tertiary carbons = α / (α + β + γ + δ) × 100 (1) α: integral value from 15.1 to 16.1 ppm β: integral value from 13.7 to 14.7 ppm γ: integral value from 19.6 to 20.6 ppm δ: integral value from 26.3 to 27.3 ppm [2] The grease composition according to [1] above, wherein the content of the poly-α-olefin (A1) is 50.0 mass% or more based on the total amount of the base oil (A). [3] The grease composition according to [1] above, wherein the ester-based oil (A2) is one or more selected from the group consisting of diester-based oils, aromatic ester-based oils, polyol ester-based oils, and complex ester-based oils. [4] The grease composition according to any one of [1] to [3], wherein the content of the ester oil (A2) is 2.0 to 15.0 mass% based on the total amount of the base oil (A). [5] The grease composition according to any one of [1] to [4], further comprising a polymer (D). [6] The grease composition according to [5], wherein the content of the polymer (D) is 1.0 to 10.0 mass% based on the total amount of the grease composition. [7] The grease composition according to any one of [1] to [6], wherein the antioxidant (B) contains an amine-based antioxidant (B1). [8] The grease composition according to [7], wherein the amine-based antioxidant (B1) is at least one selected from the group consisting of a diphenylamine-based compound represented by the following general formula (b1-1) and a naphthylamine-based compound represented by the following general formula (b1-2) or (b1-3): [In the above general formulae (b1-1), (b1-2), and (b1-3), R １１ ~R １８are each independently an alkyl group having 1 to 20 carbon atoms, n1, n2, n3, and n6 are each independently an integer of 0 to 5, m4 and m7 are each independently an integer of 0 to 3, and p5 and p8 are each independently an integer of 0 to 4.] [9] The grease composition according to any one of [1] to [8] above, wherein the content of the antioxidant (B) is 0.1 to 5.0 mass% based on the total amount of the grease composition.

[10] The grease composition according to any one of [1] to [8] above, wherein the kinematic viscosity of the base oil (A) at 40°C is 14.0 to 45.0 mm ２

[11] The grease composition according to any one of [1] to

[10] above, wherein the urea-based thickener (C) is one or more diurea compounds represented by the following general formula (c1): １ -NHCONH-R ３ -NHCONH-R ２ (c1) [In the above general formula (c1), R １ and R ２ R each independently represents a monovalent chain hydrocarbon group or alicyclic hydrocarbon group having 6 to 24 carbon atoms. １ and R ２ may be the same or different from each other. ３ represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms.]

[12] The grease composition according to any one of [1] to

[11] above, wherein the content of the urea-based thickener (C) is 1.0 mass % to 20.0 mass % based on the total amount of the grease composition.

[13] The grease composition according to any one of [1] to

[12] above, wherein the worked penetration at 25°C is 265 to 340.

[0008] According to the present invention, it is possible to provide a grease composition that has a long seizure life and low bearing torque.

[0009] In this specification, for preferred numerical ranges (e.g., ranges of content, etc.), the lower and upper limits described in stages can be independently combined. For example, from a description of a lower limit such as "preferably 10 or more, more preferably 30 or more, and even more preferably 40 or more" and a description of an upper limit such as "preferably 90 or less, more preferably 80 or less, and even more preferably 70 or less," it is possible to select ranges that combine independently selected lower and upper limits, such as "10 to 70," "30 to 70," or "40 to 80." Furthermore, from similar descriptions, it is also possible to select ranges that simply specify either the lower or upper limit, such as "40 or more" or "70 or less." The same applies to suitable ranges that can be selected from descriptions such as "preferably 10 to 90, more preferably 30 to 80, and even more preferably 40 to 70," or "preferably 10 to 90, more preferably 30 to 80, and even more preferably 40 to 70." In the description of a numerical range in this specification, for example, "10 to 90" is synonymous with "10 or more and 90 or less." The terms "greater than," "less than," "less than," and "more than" used in describing a numerical range can also be combined arbitrarily. In this specification, for example, "(meth)acrylate" is used to refer to both "acrylate" and "methacrylate," and the same applies to other similar terms and similar notations. In addition, in this specification, additives such as polymer (D) may be blended with other components in the form of a solution dissolved in diluent oil, taking into account solubility in the base oil, etc. In such cases, the content of additives such as polymer (D) in this specification is the content in terms of active ingredients (resin content) excluding diluent oil.

[0010] [Grease Composition] The grease composition of the present embodiment is a grease composition containing a base oil (A), an antioxidant (B), and a urea-based thickener (C), wherein the base oil (A) is １３The grease composition comprises a poly-α-olefin (A1) having a ratio of methyl groups on tertiary carbons having bonds to secondary and tertiary carbons of 10.0% or more, as determined from a C-NMR spectrum using the following formula (1), and an ester oil (A2), wherein the total content of the poly-α-olefin (A1) and the ester oil (A2) is 70% by mass or more based on the total amount of the base oil (A): Ratio of methyl groups on tertiary carbons having bonds to secondary and tertiary carbons = α / (α + β + γ + δ) × 100 (1), where α is the integral from 15.1 to 16.1 ppm, β is the integral from 13.7 to 14.7 ppm, γ is the integral from 19.6 to 20.6 ppm, and δ is the integral from 26.3 to 27.3 ppm.

[0011] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by using a base oil (A), an antioxidant (B), and a urea-based thickener (C), in which the base oil (A) contains a poly-α-olefin (A1) having a certain ratio or more of methyl groups on tertiary carbons having bonds to secondary carbons and tertiary carbons, and an ester-based oil (A2), in a predetermined total content or more, thereby completing the present invention.

[0012] In the following description, the “base oil (A),” the “antioxidant (B),” and the “urea-based thickener (C)” will also be referred to as “component (A),” “component (B),” and “component (C),” respectively.

[0013] In the grease composition of this embodiment, the total content of components (A), (B), and (C) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on the total amount (100% by mass) of the grease composition. It is also typically 100% by mass or less, preferably less than 100% by mass, more preferably 99% by mass or less, and even more preferably 98% by mass or less. The grease composition of this embodiment may contain components other than components (A), (B), and (C) as long as the effects of the present invention are not impaired.

[0014] Each component contained in the grease composition of this embodiment will be described in detail below.

[0015] <Base Oil (A)> The grease composition of this embodiment contains a base oil (A). The base oil (A) further contains the above-mentioned poly-α-olefin (A1) (hereinafter also referred to as "PAO" or "component (A1)") and an ester oil (A2) (hereinafter also referred to as "component (A2)"). By including component (A1) in the base oil (A), the resulting grease composition can be adjusted to be soft, which makes it easier to achieve good lubricity.

[0016] The poly-α-olefin (A1) must have a ratio of methyl groups on tertiary carbons having bonds to secondary and tertiary carbons, as calculated by the formula (1), of 10.0% or more. A ratio of methyl groups of 10.0% or more can achieve both an extended seizure life and reduced bearing torque. The ratio of methyl groups is preferably 10.0 to 50.0%, more preferably 11.0 to 30.0%, even more preferably 12.0 to 25.0%, and even more preferably 12.0 to 20.0%.

[0017] The reason why a methyl group ratio within the above range can achieve both an extended seizure life and reduced bearing torque will be explained below. First, poly-α-olefins are usually obtained as a mixture of multiple structural isomers resulting from the polymerization process. For example, in the case of a trimer, it is a mixture of structural isomers represented by the following formulas (a), (b), and (c):

[0018] (In the formula, L represents a divalent saturated aliphatic hydrocarbon group.)

[0019] The poly-α-olefin used in this embodiment contains a large amount of the structural isomer represented by the above formula (a). In this embodiment, the ratio of the structural isomer represented by the formula (a) is １３In order to identify the compound by C-NMR, the above formula (1) is used to define the integral values. Here, the integral values ​​of α, β, γ, and δ defined by the above formula (1) are each derived from a specific methyl group, and their correspondence is shown in the above formulas (a), (b), and (c). More specifically, the integral value (α) from 15.1 to 16.1 ppm is derived from the methyl group represented by α in the above formula (a), the integral value (β) from 13.7 to 14.7 ppm is derived from the methyl group represented by β in the above formulas (a), (b), and (c) or other isomers or tetramers or higher, the integral value (β) from 19.6 to 20.6 ppm is derived from the methyl group represented by γ in the above formula (b), and the integral value (δ) from 26.3 to 27.3 ppm is derived from the methyl group represented by δ in the above formula (c). Thus, a poly-α-olefin having a methyl group ratio specified by the above formula (1) of 10.0% or more contains a relatively large amount of the structural isomer represented by the above formula (a). A grease composition obtained by using a poly-α-olefin containing a relatively large amount of the structural isomer represented by the above formula (a) as a base oil has low kinetic viscosity of the base oil but can have a large molecular weight, so that it has low volatility, long seizure life, and low bearing torque.

[0020] The method for producing poly-α-olefins having a methyl group ratio of 10.0% or more as specified by the above formula (1) is not particularly limited, but for example, they can be obtained by synthesizing an α-olefin as a raw material using a metallocene catalyst and an acid catalyst in that order. More specifically, when a dimer is synthesized using a poly-α-olefin as a raw material using a metallocene catalyst and then a trimer is synthesized using an acid catalyst, the transfer of methyl groups can be selectively induced only in the reaction using the acid catalyst, and therefore poly-α-olefins having a high methyl group ratio as specified by the above formula (1) can be efficiently synthesized. Furthermore, the methyl group ratio as specified by the above formula (1) can also be adjusted by mixing multiple poly-α-olefins.

[0021] Examples of the poly-α-olefin (A1) include polybutene, polyisobutylene, 1-decene oligomer, ethylene-propylene copolymer, and hydrogenated products thereof. One PAO may be used alone, or two or more PAOs may be used in combination. The poly-α-olefin (A1) is preferably a 1-decene oligomer, and particularly preferably a 1-decene trimer.

[0022] In the grease composition of this embodiment, the kinematic viscosity at 40°C of component (A1) (when multiple types of PAOs are used, the kinematic viscosity at 40°C of the entire component (A1) after mixing) is preferably 5 mm ２ / s or more 50mm ２ / s or less, more preferably 10 mm ２ / s or more 40mm ２ / s or less, more preferably 13 mm ２ / s or more 35mm ２ / s or less, and even more preferably 15 mm ２ / s or more 35mm ２ / s or less. When the 40°C kinematic viscosity of component (A1) is within the above range, the effects of the present invention are more likely to be improved. In the grease composition of this embodiment, the viscosity index of component (A1) (when multiple types of PAOs are used, the viscosity index of component (A1) as a whole after mixing) is preferably 90 or more, more preferably 100 or more, and even more preferably 110 or more. When the viscosity index of component (A1) is 90 or more, the effects of the present invention are more likely to be improved.

[0023] In the grease composition of this embodiment, the content of poly-α-olefin (A1) in the base oil (A) is preferably 50.0 mass % or more, more preferably 70 mass % or more, even more preferably 80 mass % or more, and still more preferably 85 mass % or more, based on the total amount of the base oil (A), from the viewpoint of achieving both an extension of the seizure life and a reduction in bearing torque.

[0024] Examples of the ester oil (A2) include one or more selected from diester oils, aromatic ester oils, polyol ester oils, and complex ester oils. Examples of the diester oils include dibutyl sebacate, dioctyl sebacate, di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate, ditridecyl glutarate, and methyl acetyl ricinoleate. Examples of the aromatic ester oils include trioctyl trimellitate, tridecyl trimellitate, and tetraoctyl pyromellitate. Examples of the polyol ester oils include trimethylolpropane caprylate, trimethylolpropane bellargonate, pentaerythritol-2-ethylhexanoate, and pentaerythritol bellargonate. Examples of the complex ester oil include oligoesters of polyhydric alcohols and mixed fatty acids of dibasic and monobasic acids.

[0025] The kinematic viscosity of the ester oil (A2) at 40°C is preferably 5 mm ２ / s or more 40mm ２ / s or less, more preferably 10 mm ２ / s or more 40mm ２ / s or less, more preferably 10 mm ２ / s or more 25mm ２ / s or less, and even more preferably 10 mm ２ / s or more 20mm ２ / s or less, and even more preferably 10 mm ２ / s or more 15mm ２ The ester oil (A2) has a kinematic viscosity of 5 mm / s or less at 40°C. ２ / s or more 40mm ２ When the base oil (A) contains an ester oil (A2), the viscosity index of the ester oil (A2) is preferably 90 or more, more preferably 100 or more, and even more preferably 110 or more. When the viscosity index of the ester oil (A2) is 90 or more, the effects of the present invention are more likely to be improved.

[0026] From the viewpoint of compatibility with the hub bearing seal material, the content of the ester oil (A2) in the base oil (A) is preferably 1 mass% or more, more preferably 2 mass% or more, even more preferably 3 mass% or more, and even more preferably 5 mass% or more, based on the total amount of the base oil (A), and is preferably 20 mass% or less, more preferably 18 mass% or less, and even more preferably 15 mass% or less. The content ratio of the poly-α-olefin (A1) to the ester oil (A2) [(A2) / (A1)] is preferably 0.01 to 0.5, more preferably 0.02 to 0.3, and even more preferably 0.03 to 0.2, by mass.

[0027] Furthermore, from the viewpoint of achieving both an extension of the seizure life and a reduction in bearing torque, the total content of the poly-α-olefin (A1) and the ester-based oil (A2) in the base oil (A) must be 70% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more, based on the total amount of the base oil (A).

[0028] In the grease composition of this embodiment, the base oil (A) may contain a base oil other than the poly-α-olefin (A1) and the ester-based oil (A2). The other base oil may be one or more selected from synthetic oils other than the component (A1) or the component (A2) and mineral oils.

[0029] Examples of mineral oils include atmospheric residues obtained by atmospheric distillation of crude oils such as paraffin-based crude oil, intermediate-based crude oil, and naphthene-based crude oil; distillates obtained by vacuum distillation of the atmospheric residues; and mineral oils obtained by subjecting the distillates to one or more refining treatments such as solvent deasphalting, solvent extraction, hydrofinishing, hydrocracking, advanced hydrocracking, solvent dewaxing, catalytic dewaxing, and hydroisomerization dewaxing.

[0030] Examples of synthetic oils other than component (A1) or component (A2) include normal paraffins, isoparaffins, aromatic oils, ether oils, and synthetic oils obtained by isomerizing wax (GTL wax) produced by the Fischer-Tropsch process, etc. These may be used alone or in combination of two or more.

[0031] Examples of aromatic oils include alkylbenzenes such as monoalkylbenzenes and dialkylbenzenes; and alkylnaphthalenes such as monoalkylnaphthalenes, dialkylnaphthalenes, and polyalkylnaphthalenes.

[0032] Examples of ether-based oils include polyglycols such as polyethylene glycol, polypropylene glycol, polyethylene glycol monoether, and polypropylene glycol monoether; and phenyl ether-based oils such as monoalkyl triphenyl ether, alkyl diphenyl ether, dialkyl diphenyl ether, pentaphenyl ether, tetraphenyl ether, monoalkyl tetraphenyl ether, and dialkyl tetraphenyl ether.

[0033] In the grease composition of this embodiment, the kinematic viscosity of the base oil (A) at 40°C is preferably 5 mm ２ / s or more, more preferably 10 mm ２ / s or more, more preferably 14 mm ２ / s or more, and even more preferably 15 mm ２ The kinematic viscosity of the base oil (A) at 40°C is 5 mm ２ In the grease composition of this embodiment, the kinematic viscosity at 40°C of the base oil (A) is preferably 50 mm / s or more. ２ / s or less, more preferably 45 mm ２ / s or less, more preferably 40 mm ２ / s or less, and even more preferably 35 mm ２ The kinematic viscosity of the base oil (A) at 40°C is 50 mm / s or less. ２ When the value is equal to or less than 5 mm / s, the bearing torque can be more easily reduced. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 5 mm ２ / s or more 50mm ２ / s or less, more preferably 10 mm ２ / s or more 45mm ２ / s or less, more preferably 14 mm ２ / s or more 40mm ２ / s or less, and even more preferably 15 mm ２ / s or more 35mm ２ / s or less. The Brookfield viscosity (BF viscosity) of the base oil (A) at -20°C is preferably 10,000 mPa·s or less, more preferably 5,000 mPa·s or less, even more preferably 2,000 mPa·s or less, and even more preferably 1,500 mPa·s or less. Thus, in the grease composition of this embodiment, when the Brookfield viscosity (BF viscosity) of the base oil (A) at -20°C is low, the anti-seizure performance at low temperatures is improved. In this specification, the Brookfield viscosity (BF viscosity) at -20°C is measured in accordance with ASTM D2983-09.

[0034] In the grease composition of this embodiment, the viscosity index of the base oil (A) is preferably 90 or more, more preferably 100 or more, and even more preferably 110 or more. The effects of the present invention are more likely to be improved when the viscosity index is 90 or more. In this specification, the 40°C kinematic viscosity and viscosity index refer to values ​​measured or calculated in accordance with JIS K2283:2000.

[0035] In the grease composition of this embodiment, the content of the base oil (A) is, based on the total amount (100 mass%) of the grease composition, preferably 60 mass% or more, more preferably 70 mass% or more, even more preferably 75 mass% or more, still more preferably 80 mass% or more, and is preferably 97 mass% or less, more preferably 95 mass% or less, even more preferably 93 mass% or less, and still more preferably 90 mass% or less.

[0036] <Antioxidant (B)> The grease composition of this embodiment contains an antioxidant (B). The antioxidant (B) may be any compound capable of imparting antioxidant properties, but preferably contains one or more selected from the group consisting of amine-based antioxidants (B1) and phenol-based antioxidants (B2). The antioxidant (B) may be used alone or in combination of two or more.

[0037] The amine antioxidant (B1) may be any compound having an amino group, but diphenylamine compounds and naphthylamine compounds are preferred. Examples of diphenylamine compounds include monoalkyldiphenylamine compounds having one alkyl group having 1 to 30 carbon atoms (preferably 4 to 30, more preferably 8 to 30), such as monooctyldiphenylamine and monononyldiphenylamine; 4,4'-dibutyldiphenylamine, 4,4'-dipentyldiphenylamine, 4,4'-dihexyldiphenylamine, 4,4'-diheptyldiphenylamine, 4,4'-dioctyldiphenylamine, and 4,4'-dinonyldiphenylamine. dialkyldiphenylamine compounds having two alkyl groups each having 1 to 30 carbon atoms (preferably 4 to 30, more preferably 8 to 30), such as tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, and tetranonyldiphenylamine; polyalkyldiphenylamine compounds having three or more alkyl groups each having 1 to 30 carbon atoms (preferably 4 to 30, more preferably 8 to 30), such as tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, and tetranonyldiphenylamine; and 4,4'-bis(α,α-dimethylbenzyl)diphenylamine.

[0038] Examples of naphthylamine compounds include 1-naphthylamine, N-phenyl-1-naphthylamine, butylphenyl-1-naphthylamine, pentylphenyl-1-naphthylamine, hexylphenyl-1-naphthylamine, heptylphenyl-1-naphthylamine, octylphenyl-1-naphthylamine, nonylphenyl-1-naphthylamine, decylphenyl-1-naphthylamine, and dodecylphenyl-1-naphthylamine.

[0039] Among diphenylamine compounds, compounds represented by the following general formula (b1-1) are preferred. Furthermore, among naphthylamine compounds, compounds represented by the following general formula (b1-2) or (b1-3) are preferred.

[0040]

[0041] In the above general formulae (b1-1), (b1-2), and (b1-3), R １１~R １８ are each independently an alkyl group having 1 to 20 carbon atoms (preferably 4 to 18, more preferably 6 to 16, and even more preferably 8 to 14). Examples of the alkyl group include the same alkyl groups having 1 to 20 carbon atoms as those that may be contained in the alkylbenzene (B) described above. n1, n2, n3, and n6 are each independently an integer of 0 to 5, preferably an integer of 0 to 3, more preferably an integer of 0 to 1, and even more preferably 1. m4 and m7 are each independently an integer of 0 to 3, preferably an integer of 0 to 1, and even more preferably 0. p5 and p8 are each independently an integer of 0 to 4, preferably an integer of 0 to 2, more preferably an integer of 0 to 1, and even more preferably 0.

[0042] Examples of the phenolic antioxidant (B2) include 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, 2,4,6-tri-t-butylphenol, 2,6-di-t-butyl-4-hydroxymethylphenol, 2,6-di-t-butylphenol, 2,4-dimethyl-6-t-butylphenol, 2,6-di-t-butyl-4-(N,N-dimethylaminomethyl)phenol, 2,6-di-t-amyl-4-methylphenol, and n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propanol. Examples of the phenolic antioxidant (B2) include monocyclic phenolic compounds such as phenate, and polycyclic phenolic compounds such as 4,4'-methylenebis(2,6-di-t-butylphenol), 4,4'-isopropylidenebis(2,6-di-t-butylphenol), 2,2'-methylenebis(4-methyl-6-t-butylphenol), 4,4'-bis(2,6-di-t-butylphenol), 4,4'-bis(2-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), and 4,4'-butylidenebis(3-methyl-6-t-butylphenol). These phenolic antioxidants (B2) may be used alone or in combination of two or more.

[0043] In the grease composition of the present embodiment, the content of component (B) is preferably 0.01 to 15 mass %, more preferably 0.05 to 10 mass %, even more preferably 0.10 to 7 mass %, still more preferably 0.10 to 5 mass %, and even more preferably 0.50 to 4 mass %, based on the total amount (100 mass %) of the grease composition.

[0044] <Urea-based thickener (C)> The grease composition of this embodiment contains a urea-based thickener (C). The urea-based thickener (C) may be any compound having a urea bond, but is preferably a diurea compound having two urea bonds, and more preferably one or more diurea compounds represented by the following general formula (c1): R １ -NHCONH-R ３ -NHCONH-R ２ (c1) [In the above general formula (c1), R １ and R ２ R each independently represents a monovalent chain hydrocarbon group or alicyclic hydrocarbon group having 6 to 24 carbon atoms. １ and R ２ may be the same or different from each other. ３ represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms.]

[0045] R in the general formula (c1) １ and R ２ The number of carbon atoms in the monovalent chain hydrocarbon group or alicyclic hydrocarbon group that can be selected as R is 6 to 24, preferably 6 to 20, and more preferably 6 to 18. １ and R ２ Examples of the monovalent chain hydrocarbon group that can be selected as R include saturated or unsaturated chain hydrocarbon groups, with saturated chain hydrocarbon groups being preferred. １ and R ２ Examples of the monovalent alicyclic hydrocarbon group that can be selected as R include saturated or unsaturated monovalent alicyclic hydrocarbon groups, with saturated alicyclic hydrocarbon groups being preferred. １ and R ２The monovalent hydrocarbon group that can be selected as the diurea compound may include a monovalent aromatic hydrocarbon group.

[0046] Examples of the monovalent saturated chain hydrocarbon group include linear or branched alkyl groups having 6 to 24 carbon atoms, and specific examples include hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl (stearyl), octadecenyl, nonadecyl, and icosyl groups. The monovalent saturated chain hydrocarbon group may be linear or branched. Among these, the octadecyl (stearyl) group is preferred.

[0047] Examples of the monovalent unsaturated chain hydrocarbon group include straight-chain or branched-chain alkenyl groups having 6 to 24 carbon atoms, and specific examples include a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, an undecenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group, a pentadecenyl group, a hexadecenyl group, a heptadecenyl group, an octadecenyl group, a nonadecenyl group, an icosenyl group, an oleyl group, a geranyl group, a farnesyl group, a linoleyl group, etc. The monovalent unsaturated chain hydrocarbon group may be straight-chain or branched.

[0048] Examples of the monovalent saturated alicyclic hydrocarbon group include cycloalkyl groups such as cyclohexyl, cycloheptyl, cyclooctyl, and cyclononyl; and cycloalkyl groups substituted with an alkyl group having 1 to 6 carbon atoms, such as methylcyclohexyl, dimethylcyclohexyl, ethylcyclohexyl, diethylcyclohexyl, propylcyclohexyl, isopropylcyclohexyl, 1-methyl-propylcyclohexyl, butylcyclohexyl, pentylcyclohexyl, pentyl-methylcyclohexyl, and hexylcyclohexyl (preferably, a cyclohexyl group substituted with an alkyl group having 1 to 6 carbon atoms). Of these, cyclohexyl is preferred.

[0049] Examples of the monovalent unsaturated alicyclic hydrocarbon group include cycloalkenyl groups such as a cyclohexenyl group, a cycloheptenyl group, and a cyclooctenyl group; and cycloalkenyl groups substituted with an alkyl group having 1 to 6 carbon atoms such as a methylcyclohexenyl group, a dimethylcyclohexenyl group, an ethylcyclohexenyl group, a diethylcyclohexenyl group, and a propylcyclohexenyl group (preferably a cyclohexenyl group substituted with an alkyl group having 1 to 6 carbon atoms).

[0050] Examples of the monovalent aromatic hydrocarbon group include a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a diphenylmethyl group, a diphenylethyl group, a diphenylpropyl group, a methylphenyl group, a dimethylphenyl group, an ethylphenyl group, and a propylphenyl group.

[0051] R in the general formula (c1) ３ The carbon number of the divalent aromatic hydrocarbon group that can be selected as R is 6 to 18, preferably 6 to 15, and more preferably 6 to 13. ３ Examples of the divalent aromatic hydrocarbon group that can be selected as aryl include a phenylene group, a diphenylmethylene group, a diphenylethylene group, a diphenylpropylene group, a methylphenylene group, a dimethylphenylene group, an ethylphenylene group, etc. Among these, a phenylene group, a diphenylmethylene group, a diphenylethylene group, or a diphenylpropylene group is preferred, and a diphenylmethylene group is more preferred.

[0052] In the grease composition of this embodiment, the content of the urea-based thickener (C) is preferably 1.0 to 20.0 mass%, more preferably 3.0 to 19.0 mass%, even more preferably 5.0 to 18.0 mass%, even more preferably 7.0 to 17.0 mass%, and even more preferably 10.0 to 16.0 mass%, based on the total amount (100 mass%) of the grease composition. If the content of component (C) is 1.0 mass% or more, the worked penetration of the resulting grease composition can be easily adjusted to an appropriate range. On the other hand, if the content of component (C) is 20.0 mass% or less, the resulting grease composition can be adjusted to a softer consistency, making it easier to achieve good lubricity.

[0053] <Polymer (D)> The grease composition of this embodiment may further contain a polymer (D) (hereinafter also referred to as "component (D)"). Examples of the polymer (D) include non-dispersant poly(meth)acrylates, dispersant poly(meth)acrylates, star polymers, olefin copolymers (e.g., ethylene-propylene copolymers), dispersant olefin copolymers, and styrene copolymers (e.g., styrene-diene copolymers, styrene-isoprene copolymers). Of these, ethylene-propylene copolymers are preferred. These may be used alone or in combination of two or more.

[0054] In the grease composition of this embodiment, the content of polymer (D) (equivalent to the resin content) is preferably 1.0 to 20.0 mass%, more preferably 2.0 to 17.0 mass%, even more preferably 3.0 to 15.0 mass%, still more preferably 3.0 to 13.0 mass%, even more preferably 3.0 to 10.0 mass%, even more preferably 5.0 to 10.0 mass%, and even more preferably 7.0 to 10.0 mass%, based on the total amount (100 mass%) of the grease composition. When the content of component (D) is 1.0 mass% or more, the bearing life of the resulting grease composition is further improved. On the other hand, when the content of component (D) is 20.0 mass% or less, the shear stability of the resulting grease composition is improved.

[0055] In order to improve oil film retention and shear stability, the polymer (D) preferably has a mass average molecular weight (Mw) of 5,000 to 50,000, more preferably 8,000 to 50,000, even more preferably 8,000 to 40,000, still more preferably 9,000 to 30,000, and even more preferably 10,000 to 30,000. The mass average molecular weight (Mw) of the polymer (D) is a value measured by gel permeation chromatography and calculated in terms of polystyrene.

[0056] <Other Additives (E)> The grease composition of this embodiment may contain other additives (E) (hereinafter also referred to as "component (E)") other than component (B), component (C), and component (D) that are blended in general greases, within a range that does not impair the effects of the present invention. Examples of other additives include extreme pressure agents, oiliness agents, rust inhibitors, solid lubricants, detergents and dispersants, corrosion inhibitors, and metal deactivators. One type of each of the other additives (E) may be used alone, or two or more types may be used in combination.

[0057] Examples of extreme pressure agents include one or more selected from phosphorus-based extreme pressure agents and sulfur-phosphorus-based extreme pressure agents. Examples of phosphorus-based extreme pressure agents include one or more phosphates selected from orthophosphates, hydrogen phosphates, polyphosphates, phosphites, and metaphosphates. Examples of polyphosphates include pyrophosphates (diphosphates), tripolyphosphates, and tetrapolyphosphates. The phosphates are preferably alkali metal salts. Examples of alkali metal salts include sodium salts, potassium salts, and lithium salts, with sodium salts being particularly preferred. Examples of sulfur-phosphorus-based extreme pressure agents include one or more selected from thiophosphates and amine salts of thiophosphates. Examples of thiophosphates include monothiophosphates, dithiophosphates, trithiophosphates, monothiophosphites, dithiophosphites, and trithiophosphites, with trithiophosphates being preferred. Examples of trithiophosphate esters include trialkyl phosphorothioates such as tributyl phosphorothioate, tripentyl phosphorothioate, trihexyl phosphorothioate, triheptyl phosphorothioate, trioctyl phosphorothioate, trinonyl phosphorothioate, tridecyl phosphorothioate, triundecyl phosphorothioate, tripentadecyl phosphorothioate, and trihexadecyl phosphorothioate; triaryl phosphorothioates such as triphenyl phosphorothioate, tricresyl phosphorothioate, and trixylenyl phosphorothioate; tris(n-propylphenyl) phosphorothioate, tris(isopropylphenyl) phosphorothioate, tris(n-butylphenyl) phosphorothioate, tris(isobutylphenyl) phosphorothioate, tris(s-butylphenyl) phosphorothioate, tris(t-butylphenyl) phosphorothioate, and tris(2,4-C ９ , C １０Examples of the amine salt of a thiophosphate include the amine salts of the thiophosphate esters exemplified above. The content of the extreme pressure agent contained in the grease composition of this embodiment is preferably 0.01 to 5.0 mass%, more preferably 0.1 to 3.0 mass%, and even more preferably 0.5 to 2.0 mass%, based on the total amount (100 mass%) of the grease composition.

[0058] Polyamide is preferably used as the oiliness agent. Examples of rust inhibitors include carboxylic acid-based rust inhibitors such as alkenyl succinic acid polyhydric alcohol esters, zinc stearate, thiadiazole and its derivatives, and benzotriazole and its derivatives. Examples of solid lubricants include polyimide, PTFE, graphite, metal oxides, boron nitride, and molybdenum disulfide. Examples of detergent dispersants include ashless dispersants such as succinimide and boron-based succinimide. Examples of corrosion inhibitors include benzotriazole-based compounds and thiazole-based compounds. Examples of metal deactivators include benzotriazole-based compounds. These may be used alone or in combination of two or more.

[0059] [Physical Properties of Grease Composition] <Worked Penetration at 25°C> The lower limit of the worked penetration at 25°C of the grease composition of this embodiment is preferably 210 or more, more preferably 240 or more, even more preferably 250 or more, and still more preferably 265 or more, from the viewpoints of reducing the torque of the grease composition, maintaining the sealing properties of the grease composition, and maintaining an appropriate softness at 25°C. Furthermore, the upper limit of the worked penetration at 25°C of the grease composition of this embodiment is preferably 450 or less, more preferably 400 or less, even more preferably 370 or less, and still more preferably 340 or less, from the viewpoints of reducing the torque of the grease composition, maintaining the sealing properties of the grease composition, and maintaining an appropriate softness at 25°C. The upper and lower limits can be combined as appropriate and are preferably 210 to 450, more preferably 240 to 400, even more preferably 250 to 370, and still more preferably 265 to 340. In this specification, the worked penetration at 25°C means a value measured at 25°C in accordance with JIS K2220:2013 (Clause 7).

[0060] <Requirement (I)> In the grease composition of this embodiment, it is preferable that the particles containing the urea-based thickener (C) in the grease composition satisfy the following requirement (I): Requirement (I): The particles have an area-based arithmetic mean particle diameter of 2.0 μm or less when measured by a laser diffraction / scattering method. By satisfying the above requirement (I), the grease composition has excellent wear resistance.

[0061] The above requirement (I) can also be considered a parameter indicating the state of aggregation of the urea-based thickener (C) in the grease composition. Here, the "particles containing the urea-based thickener (C)" to be measured by the laser diffraction / scattering method refer to particles formed by aggregation of the urea-based thickener (C) contained in the grease composition. When the grease composition contains an additive other than the urea-based thickener (C), the particle size specified by the above requirement (I) can be obtained by measuring a grease composition prepared under the same conditions but without the additive by the laser diffraction / scattering method. However, when the additive is liquid at room temperature (25°C) or when the additive is soluble in the base oil (A), the grease composition containing the additive may also be used as the measurement target.

[0062] The urea-based thickener (C) is usually obtained by reacting an isocyanate compound with a monoamine, but because the reaction rate is very fast, the urea-based thickener (C) tends to aggregate, resulting in the formation of excessive large particles (micelle particles, so-called "lumps"). In the grease composition of this embodiment, the particle size specified by the above requirement (I) is more preferably 1.5 μm or less, even more preferably 1.0 μm or less, and particularly preferably 0.7 μm or less. Furthermore, the particle size specified by the above requirement (I) is usually 0.01 μm or more.

[0063] <Requirement (II)> Here, it is preferable that the grease composition of this embodiment further satisfies the following requirement (II): Requirement (II): The specific surface area of ​​the particles measured by a laser diffraction / scattering method is 0.5 × 10 ５ cm ２ / cm ３ That's all. The specific surface area specified in the above requirement (II) is a secondary index that indicates the state of fineness of particles containing the urea-based thickener (C) in the grease composition and the presence of large particles (lumps). In other words, by satisfying the above requirement (I) and also the above requirement (II), the state of fineness of particles containing the urea-based thickener (B) in the grease composition is better, and the presence of large particles (lumps) is further suppressed. From the above viewpoint, the specific surface area specified in the above requirement (II) is more preferably 0.8 × 10 ５ cm２ / cm ３ More preferably, 1.5×10 ５ cm ２ / cm ３ More preferably, 2.0 × 10 ５ cm ２ / cm ３ The specific surface area specified in the above requirement (II) is usually 1.0 × 10 ６ cm ２ / cm ３ The following is the result.

[0064] In this specification, the values ​​specified in the above requirement (I) and further requirement (II) are values ​​measured by the method described in the Examples below. The values ​​specified in the above requirement (I) and further requirement (II) can be adjusted mainly by the production conditions of the urea-based thickener (C).

[0065] [Uses of Grease Composition] The grease composition of this embodiment can be suitably used in various fields, including bicycles, automobiles, office equipment, machine tools, wind turbines, construction machinery, agricultural machinery, and industrial robots. Examples of lubricating parts in automobiles where the grease composition of this embodiment can be suitably used include bearing parts in devices such as radiator fan motors, fan couplings, alternators, idler pulleys, hub units, hub bearings, water pumps, power windows, wipers, electric power steering, electric drive motor flywheels, ball joints, wheel bearings, spline parts, and constant velocity joints; bearing parts, gear parts, and sliding parts in devices such as door locks, door hinges, and clutch boosters. More specifically, examples include bearing parts of hub units, hub bearings, electric power steering, electric drive motor flywheels, ball joints, wheel bearings, spline parts, constant velocity joints, clutch boosters, servo motors, blade bearings, and generators. The grease composition of this embodiment has a long seizure life and low bearing torque. Therefore, from the viewpoint of improving fuel economy, it can be particularly suitably used in bearings used in hubs attached to automobile wheels.

[0066] Examples of lubricated parts in devices in the field of office equipment for which the grease composition of this embodiment can be suitably used include fuser rolls in devices such as printers, and bearings and gear parts in devices such as polygon motors. Examples of lubricated parts in devices in the field of machine tools for which the grease composition of this embodiment can be suitably used include bearing parts in reducers of spindles, servo motors, machine tool robots, etc. Examples of lubricated parts in devices in the field of wind turbines for which the grease composition of this embodiment can be suitably used include bearing parts of blade bearings and generators, etc. Examples of lubricated parts in devices in the field of construction or agricultural machinery for which the grease composition of this embodiment can be suitably used include bearing parts such as ball joints, spline parts, gear parts, and sliding parts.

[0067] [Method for Lubricating a Sliding Mechanism] The method for lubricating a sliding mechanism according to the present embodiment is a method for lubricating a sliding mechanism on which metal members slide by applying the grease composition according to the present embodiment described above. The sliding mechanism may be one in which metal members slide against each other, or one in which a metal member slides against a rubber member.

[0068] The present invention will be specifically described with reference to the following examples, although the present invention is not limited to the following examples.

[0069] [Examples 1 to 3, Comparative Examples 1 to 3, and Reference Example] Grease compositions of Examples 1 to 3, Comparative Examples 1 to 3, and Reference Example were prepared by the methods described below, and the grease compositions were evaluated as described below. Details of each component listed in Table 1 are shown below. Base oil (A) PAO1: kinematic viscosity at 40°C of 14 mm ２ Metallocene catalyst-based poly-α-olefin PAO2: kinematic viscosity at 40°C of 30 mm ２ Nonmetallocene catalyst-based poly-α-olefin PAO3: kinematic viscosity at 40°C of 17 mm ２ Nonmetallocene catalyst-based poly-α-olefin PAO4: kinematic viscosity at 40°C of 396 mm ２ / s nonmetallocene catalyst poly-α-olefin Ester oil 1: dioctyl sebacate Ester oil 2: fatty acid ester Antioxidant (B) Amine antioxidant 1: bis(nonylphenyl)amine and 1-(N-phenylamino)naphthalene Amine antioxidant 2: phenyl-α-naphthylamine Amine antioxidant 3: reaction product of N-phenyl-benzylamine and 2,4,4-trimethylpentene Phosphate ester antioxidant: diethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate Polymer (D): ethylene-propylene copolymer (product name: LUCANT HC-600 (registered trademark), manufactured by Mitsui Chemicals, Inc., number average molecular weight: 5,463, mass average molecular weight (Mw): 9,575) In Table 1 described later, polymer (D) is the content without diluent oil (resin equivalent value). Other Additives (E) Extreme pressure agent 1: HITEC 317, manufactured by Afton Chemical Co. Extreme pressure agent 2: ADEKA ECO ROYAL AWP3000, manufactured by Adeka Corporation Antiwear agent: VANLUBE AZ, manufactured by Vanderbilt Inc. Rust inhibitor 1: K-CORR G-1340, manufactured by King Industries Rust inhibitor 2: Lunac 8-98, manufactured by Kao Corporation Corrosion inhibitor 1: HITEC 4313, manufactured by Afton Chemical Co. Corrosion inhibitor 2: IRGAMET 39, manufactured by BASF Dispersant: OLOA 340DT, manufactured by Chevron

[0070] (Preparation of base oil) Poly-α-olefins were prepared in the proportions shown in Table 1. Multiple poly-α-olefins (PAO1, PAO2, PAO3) were mixed as needed. The poly-α-olefins were measured under the following measurement conditions. １３ C-NMR measurement was performed, and the ratio of methyl groups on tertiary carbons having bonds to secondary and tertiary carbons was calculated using the following formula: Ratio of methyl groups on tertiary carbons having bonds to secondary and tertiary carbons = α / (α + β + γ + δ) × 100 (1) α: integral value from 15.1 to 16.1 ppm β: integral value from 13.7 to 14.7 ppm γ: integral value from 19.6 to 20.6 ppm δ: integral value from 26.3 to 27.3 ppm

[0071] [Measurement conditions] １３C-NMR spectra were measured under the following conditions: NMR apparatus magnet: NM-04840SCMJJY manufactured by JEOL RESONANCE; Spectrometer: JNM-ECZ400RS3 manufactured by JEOL RESONANCE; Probe: 5 mmφ cryoprobe NM-05560SCCC manufactured by JEOL RESONANCE; Number of points: 32,760; Number of dummy scans: 4; Number of integrations: 4,000; Observation center: 100 ppm; Observation width: 250 ppm; Acquisition time: 1.30 seconds; Relaxation delay: 25 seconds; NMR sample tube: 5 mmφ; Sample amount: 5 to 15 mg; Measurement solvent: deuterated chloroform; Measurement temperature: room temperature.

[0072] Thereafter, an ester oil was added to the poly-α-olefin to prepare the base oil (A) shown in Table 1. The kinematic viscosity of the base oil (A) (mixed base oil) at 40°C was measured in accordance with JIS K2283:2000. In addition, the Brookfield viscosity (BF viscosity) of the base oil (A) (mixed base oil) at -20°C was measured in accordance with ASTM D2983-09.

[0073] (Preparation of Base Grease) Next, diphenylmethane-4,4'-diisocyanate (MDI) was added to a portion of the base oil (A) to prepare solution α. ​​Meanwhile, the remainder of the base oil (A) was heated to 70°C, and stearylamine and cyclohexylamine were added to prepare solution β. Then, while stirring solution β heated to 75°C, solution α heated to 75°C was added, and the stirring blade was rotated. While continuing stirring, the temperature was raised to 150°C and maintained at that temperature for 1 hour to prepare a base grease containing 10.2 mass% of a urea-based thickener (C).

[0074] (Preparation of Grease Composition) Next, the antioxidant (B), polymer (D) and other additives (E) shown in Table 1 were added to and mixed with the base grease that had been naturally cooled to 80°C in the amounts shown in Table 1. The mixture was then homogenized using a triple roll mill to obtain a grease composition.

[0075] <Measurement of Worked Penetration> The worked penetration of each of the grease compositions of Examples 1 to 3 and Comparative Examples 1 to 3 was measured at 25°C in accordance with JIS K2220:2013 (Clause 7).

[0076] <Bearing life measurement> Using a testing machine specified in the old ASTM D1741, the test bearing was continuously operated at an outer ring temperature of 140°C and the time until the bearing seized and stopped was evaluated. Seizure was judged when the motor current value exceeded 7 A. The test bearing was a deep groove ball bearing 6306 (double-sided seal type) filled with 2 g of test grease, with rubber seals (heat-resistant seals) attached to both sides of the bearing, and the test was conducted under sealed conditions.

[0077] <Measurement of bearing torque> An acoustic testing machine manufactured by Sugawara Laboratories Inc. was modified, and 5.0 g of grease was evenly filled in the vicinity of the rolling surfaces of the inner and outer rings of a deep groove ball bearing 6306. The inner ring of the bearing was rotated under an axial load of 200 N at a rotational speed of 1,000 rpm, and the average rotational static force of the outer ring retainer to which the axial load was applied was measured for 20 to 30 minutes from the start of rotation and evaluated as the bearing torque.

[0078]

[0079] As shown in Table 1, when the grease compositions obtained in Comparative Examples 1 to 3 were compared, the grease compositions of Comparative Examples 1 and 3 had long bearing life but high bearing torque, while the grease composition of Comparative Example 2 had low bearing torque but short bearing life. In contrast, it was confirmed that the grease compositions obtained in Examples 1 to 3 all achieved both a long bearing life and a reduced bearing torque at the same time.

Claims

1. A grease composition containing a base oil (A), an antioxidant (B), and a urea thickener (C), wherein the base oil (A) is １３ a poly-α-olefin (A1) having a ratio of a methyl group on a tertiary carbon having a bond with a secondary carbon and a tertiary carbon of 10.0% or more as determined by the following formula (1) from a C-NMR spectrum, and an ester oil (A2), and a grease composition in which the total content of the poly-α-olefin (A1) and the ester oil (A2) is 70% by mass or more based on the total amount of the base oil (A). Ratio of methyl group on tertiary carbon having a bond with secondary carbon and tertiary carbon = α / (α + β + γ + δ) × 100... (1) α: Integration value of 15.1 to 16.1 ppm β: Integration value of 13.7 to 14.7 ppm γ: Integration value of 19.6 to 20.6 ppm δ: Integration value of 26.3 to 27.3 ppm 2. The grease composition according to claim 1, wherein the content of the poly-α-olefin (A1) is 50.0% by mass or more based on the total amount of the base oil (A).

3. The grease composition according to claim 1 or 2, wherein the ester oil (A2) is at least one selected from diester oils, aromatic ester oils, polyol ester oils, and complex ester oils.

4. The grease composition according to any one of claims 1 to 3, wherein the content of the ester oil (A2) is 2.0 to 15.0% by mass based on the total amount of the base oil (A).

5. The grease composition according to any one of claims 1 to 4, further containing a polymer (D).

6. The grease composition according to claim 5, wherein the content of the polymer (D) is 1.0 to 10.0% by mass based on the total amount of the grease composition.

7. The grease composition according to any one of claims 1 to 6, wherein the antioxidant (B) contains an amine-based antioxidant (B1).

8. The grease composition according to claim 7, wherein the amine-based antioxidant (B1) is at least one selected from diphenylamine-based compounds represented by the following general formula (b1-1) and naphthylamine-based compounds represented by the following general formula (b1-2) or (b1-3). [In the above general formulas (b1-1), (b1-2), and (b1-3), R １１ to R １８ are each independently an alkyl group having 1 to 20 carbon atoms, n1, n2, n3, and n6 are each independently an integer of 0 to 5, m4 and m7 are each independently an integer of 0 to 3, and p5 and p8 are each independently an integer of 0 to 4.] 9. The grease composition according to any one of claims 1 to 8, wherein the content of the antioxidant (B) is 0.1 to 5.0% by mass based on the total amount of the grease composition.

10. The kinematic viscosity at 40 °C of the base oil (A) is 14.0 to 45.0 mm ２ / s, and the grease composition according to any one of claims 1 to 9.

11. The grease composition according to any one of claims 1 to 10, wherein the urea-based thickener (C) is at least one selected from diurea compounds represented by the following general formula (c1). R １ -NHCONH-R ３ -NHCONH-R ２ (c1) [In the above general formula (c1), R １ and R ２ each independently represents a monovalent chain hydrocarbon group or alicyclic hydrocarbon group having 6 to 24 carbon atoms. R １ and R ２ may be the same or different from each other. R ３ represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms.] 12. The grease composition according to any one of claims 1 to 11, wherein the content of the urea thickener (C) is 1.0% by mass to 20.0% by mass based on the total amount of the grease composition.

13. The grease composition according to any one of claims 1 to 12, wherein the consistency at 25°C is 265 to 340.

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