Grease composition for rolling bearing

Abstract

A grease composition for rolling bearings comprises a diurea thickener represented by formula (2): R5-NHCONH-R6-NHCONH-R7 (where R6 represents a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms and R5 and R7, which may be the same or different, each represent a cyclohexyl group or a linear or branched alkyl group having 8 to 22 carbon atoms), an ester-based base oil having a kinematic viscosity of 60 mm2 / s or more at 40°C, 0.2 to 2.5% by mass of an amine phosphate based on a total mass of the composition, and 0.5 to 4 parts by mass of a carboxylic acid-based corrosion inhibitor per part by mass of the amine phosphate, but does not comprise any carboxylate-based corrosion inhibitor or fatty acid amine salt.

Description

Technical Field

[0001] The present invention relates to a grease composition for rolling bearings. In particular, the present invention relates to a grease composition suitable to be filled in rolling bearings lubricated at high temperatures in automotive electrical components each having a lubricated portion directly connected to or located near an engine which is a heat-generating element, household electrical appliances for use under high-speed rotations at high temperatures, such as cleaner motors, continuous casting facilities, and so on.Background Art

[0002] Rolling bearings used in various industrial machines are operated in a variety of environments, from cold regions to high-temperature atmospheres such as the inside of an automobile engine compartment. Therefore, the rolling bearings are required to be usable in a wide range of temperatures for long periods without needing maintenance, and a demand for durability of rolling bearings has been increasing more and more.

[0003] Ester oil is known as a base oil with excellent heat resistance. It has been disclosed that a grease base oil containing a condensed ester of a specific alcohol and a specific carboxylic acid and a grease composition containing the grease base oil have excellent heat resistance (Patent Literature 1).(Background Art related to Fretting Resistance)

[0004] In the meantime, automobiles, electrical products, and various machine components and products are often transported by rail or truck. During transportation, fretting may occur on grease-filled bearings due to vibrations caused by rail joints and rough roads.

[0005] The fretting is a surface damage that occurs under small amplitudes, and is said to often generate oxidized wear particles in the atmosphere and cause severe wear due to an abrasive action of the oxidized wear particles (Non Patent Literature 1).

[0006] Fretting prevention measures have been proposed such as: (1) reducing the amount of relative sliding; (2) separating two surfaces and preventing them from coming into direct contact; and (3) coating contact surfaces with phosphate coatings or the like or preventing adhesion between surfaces by supplying a lubricating oil or grease (Non Patent Literature 1).

[0007] In addition, as a grease composition excellent at suppressing fretting wear under more severe conditions (at -30°C or less under very small amplitude), there has been disclosed a grease composition which contains an alicyclic aliphatic diurea as a thickener and contains an amine phosphate (Patent Literature 2).(Background Art related to Corrosion Inhibitory Effectiveness)

[0008] On the other hand, for example, rolling bearings used in automotive electrical accessories are often attached to the lower sides of the engine compartments, and therefore are often wetted by rainwater while vehicles are in motion. Meanwhile, rolling bearings for steel rolling mills are used in environments where they are exposed to large amounts of water. For this reason, rolling bearings are also required to have corrosion inhibitory effectiveness.

[0009] As grease compositions with excellent corrosion inhibitory effectiveness, there have been known grease compositions containing carboxylic acid-based corrosion inhibitors, carboxylate-based corrosion inhibitors, and amine-based corrosion inhibitors (Patent Literature 3).Citation ListPatent Literatures

[0010] Patent Literature 1: Japanese Patent No. 7216563 Patent Literature 2: Japanese Patent No. 6040750 Patent Literature 3: Japanese Patent No. 5714922 Non Patent Literature

[0011] Non Patent Literature 1: Yuji Yamamoto et al., Tribology, published on February 28, 1998 by Rikogakusha Publishing Co., Ltd., pp. 201-203)Summary of InventionProblems to be solved by the invention

[0012] As the grease compositions having excellent heat resistance, Patent Literature 1 has disclosed the grease base oil containing a condensed ester of a specific alcohol and a specific carboxylic acid and a grease composition containing the grease base oil. However, ester oils are generally said to have poor fretting resistance.

[0013] Meanwhile, as the grease compositions having excellent fretting resistance, Patent Literature 2 has disclosed the grease compositions containing an amine phosphate. However, the amine phosphate may deteriorate the corrosion inhibitory effectiveness due to its high reactivity with metal surfaces.

[0014] Then, as the grease compositions with excellent corrosion inhibitory effectiveness, the grease compositions containing carboxylic acid-based corrosion inhibitors, carboxylate-based corrosion inhibitors, and amine-based corrosion inhibitors have been known from Patent Literature 3. However, if these corrosion inhibitors are present in excessive amounts, the corrosion inhibitors may inhibit the function of the amine phosphate and deteriorate the fretting resistance.

[0015] Although the grease compositions in the above-mentioned background art are each excellent at any of high-temperature durability, fretting resistance, and corrosion inhibitory effectiveness, none of them fully satisfies all these performance requirements, and they still have a problem in particularly achieving both the fretting resistance and the corrosion inhibitory effectiveness.

[0016] The present invention has been made in view of the above circumstances and has an object to provide a grease composition for rolling bearings excellent at all of high-temperature durability, fretting resistance, and corrosion inhibitory effectiveness. Means for solution of the problem

[0017] In order to achieve the above object, we have improved grease compositions by selecting a base oil, a thickener, and additives. Specifically, the present invention provides the following grease compositions for rolling bearings: 1. A grease composition for rolling bearings comprising a thickener, a base oil, and additives, wherein the thickener is a diurea compound represented by formula (2):         R5-NHCONH-R6-NHCONH-R7 ...     (2), where R6 represents a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R5 and R7, which may be the same or different, each represent a cyclohexyl group or a linear or branched alkyl group having 8 to 22 carbon atoms, the base oil is an ester-based synthetic oil having a kinematic viscosity of 60 mm 2< / s or more at 40°C, the additives include an amine phosphate, a carboxylic acid-based corrosion inhibitor, and an antioxidant, a content of the amine phosphate is 0.2 to 2.5% by mass based on a total mass of the composition, a content of the carboxylic acid-based corrosion inhibitor is 0.5 to 4 parts by mass per part by mass of the amine phosphate, and a content of another corrosion inhibitor is 3.5 parts by mass or less per part by mass of the amine phosphate, but the grease composition does not comprise any carboxylate-based corrosion inhibitor or fatty acid amine salt. 2. The grease composition for rolling bearings according to the above 1, wherein the base oil contains a condensed ester of an alcohol (A) and a carboxylic acid (B) and having a kinematic viscosity of 80 to 110 mm 2< / s at 40°C, the alcohol (A) contains a polyhydric alcohol represented by formula (1): where R1 to R4 each independently represent a hydrogen atom, a methyl group, or a hydroxy group, and at least two of R1 to R4 each represent a hydroxy group, the carboxylic acid (B) contains a fatty acid having 5 to 9 carbon atoms (B-1), a branched fatty acid having 15 to 20 carbon atoms (B-2), a cycloalkane monocarboxylic acid having 4 to 8 carbon atoms (B-3), and an aromatic carboxylic acid (B-4), and in the carboxylic acid (B), the fatty acid (B-1) accounts for 30 to 50 mol%, the branched fatty acid (B-2) accounts for 30 to 50 mol%, the cycloalkane monocarboxylic acid (B-3) accounts for 10 to 30 mol%, and the aromatic carboxylic acid (B-4) accounts for 1 to 15 mol%. 3. The grease composition for rolling bearings according to the above 1 or 2, wherein the amine phosphate is a tertiary alkylamine-dimethylphosphate or a phenyl amine phosphate. 4. The grease composition for rolling bearings according to any one of the above 1 to 3, wherein the thickener is an alicyclic aliphatic diurea compound in which, in formula (2), a proportion of the number of moles of the cyclohexyl groups to the total number of moles of the cyclohexyl groups and the linear or branched alkyl groups having 8 to 22 carbon atoms is 70 to 90 mol%. 5. The grease composition for rolling bearings according to any one of the above 1 to 4, comprising, as the antioxidant, 0.5 to 5% by mass of an amine-based antioxidant and 0.5 to 5% by mass of a phenol-based antioxidant based on the total mass of the composition. 6. The grease composition for rolling bearings according to any one of the above 1 to 5, further comprising an anti-spalling additive. 7. The grease composition for rolling bearings according to the above 6, comprising, as the anti-spalling additive, 0.2 to 5% by mass of an organic sulfonic acid metal salt based on the total mass of the composition and 0.2 to 5% by mass of a dialkyldithiophosphate metal salt based on the total mass of the composition. Advantageous Effects of Invention

[0018] According to the present invention, it is possible to provide a grease composition for rolling bearings having sufficient high-temperature durability, fretting resistance, and corrosion inhibitory effectiveness. The grease composition of the present invention has excellent anti-spalling properties.Brief Description of Drawing

[0019] Fig. 1 is a schematic diagram of a four-ball rolling test.Description of Embodimentso Thickener

[0020] Greases in bearings in high-temperature environments vary in fluidity depending on types of thickeners used, which greatly affects bearing lubrication life. In order for a grease to exhibit a long lubrication life, the grease must remain in a lubricated area without softening or leaking. The thickener used in the present invention is a diurea compound represented by the following formula (2):         R5-NHCONH-R6-NHCONH-R7 ...     (2), where R6 represents a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R5 and R7, which may be the same or different, each represent a cyclohexyl group or a linear or branched alkyl group having 8 to 22 carbon atoms.

[0021] Typical examples of R6 are represented by the following structural formulas. Among them, a diphenylmethane group is the most preferable.

[0022] The linear or branched alkyl group having 8 to 22 carbon atoms is preferably a linear alkyl group having 8 to 18 carbon atoms. A linear alkyl group having 18 carbon atoms is the most preferable.

[0023] A diurea compound is preferred in which in formula (2), one of R5 and R7 is a cyclohexyl group and the other is a linear or branched alkyl group having 8 to 22 carbon atoms. This diurea compound is a reaction product of a mixture of cyclohexylamine and monoamine containing a linear or branched alkyl group having 8 to 22 carbon atoms with diisocyanate, and is called an alicyclic aliphatic diurea compound. The reaction product contains the alicyclic aliphatic diurea compound and additionally an alicyclic diurea compound having cyclohexyl groups at both of its ends, and an aliphatic diurea compound having linear or branched alkyl groups having 8 to 22 carbon atoms at both of its ends.

[0024] In formula (2), the proportion of the number of moles of the cyclohexyl groups to the total number of moles of the cyclohexyl groups and the linear or branched alkyl groups having 8 to 22 carbon atoms [{(number of cyclohexyl groups) / (number of cyclohexyl groups+number of linear or branched alkyl groups having 8 to 22 carbon atoms)} × 100] is preferably 70 to 90 mol% and more preferably 80 to 90 mol%. When the above proportion is 70 mol % or more, the grease composition can be particularly sufficiently prevented from softening and leaking in a high-temperature environment. When the above proportion is 90 mol % or less, the grease composition can obtain particularly sufficient inflow properties and obtain excellent high-temperature durability.

[0025] As the thickener in the present invention, particularly preferred is an alicyclic aliphatic diurea compound containing a diurea compound in which, in formula (2), one of R5 and R7 is a cyclohexyl group and the other is a linear alkyl group having 18 carbon atoms, with the proportion of the number of moles of the cyclohexyl groups being 83.3 mol%.

[0026] The content of the thickener in the grease composition of the present invention varies depending on a type of thickener. The consistency of the grease composition of the present invention is preferably 200 to 350, and the content of the thickener is an amount necessary to obtain this consistency. The content of the thickener in the grease composition of the present invention is usually 9 to 19% by mass, and preferably 12 to 16% by mass. When the content is less than 9% by mass, the grease may be soft and leak and may fail to fulfill the lubrication life. On the other hand, when the content is more than 19% by mass, the grease may have poor fluidity and have difficulty in flowing into a lubricated area, thereby failing to fulfill the lubrication life.o Base Oil

[0027] The base oil used in the present invention is an ester-based synthetic oil having a kinematic viscosity of 60 mm 2< / s or more at 40°C. The ester-based synthetic oil has excellent high-temperature durability.

[0028] From the viewpoint of the high-temperature durability, the kinematic viscosity at 40°C of the ester-based synthetic oil is preferably 80 mm 2< / s or more and more preferably 90 mm 2< / s or more, and preferably 110 mm 2< / s or less and more preferably 100 mm 2< / s or less.

[0029] From the viewpoint of improving the lubricity under high temperature, the kinematic viscosity at 100°C of the ester-based synthetic oil is preferably 11 mm 2< / s or more and more preferably 11.5 mm 2< / s or more and preferably 14 mm 2< / s or less, and more preferably 13 mm 2< / s or less.

[0030] The ester-based synthetic oil of the present invention preferably contains a condensed ester of an alcohol (A) and a carboxylic acid (B).

[0031] The alcohol (A) contains a polyhydric alcohol represented by formula (1): where R 1< to R 4< each represent independently a hydrogen atom, a methyl group, or a hydroxy group and at least two of R 1< to R 4< each represent a hydroxy group, and the carboxylic acid (B) contains a fatty acid having 5 to 9 carbon atoms (B-1), a branched fatty acid having 15 to 20 carbon atoms (B-2), a cycloalkane monocarboxylic acid having 4 to 8 carbon atoms (B-3), and an aromatic carboxylic acid (B-4).<Alcohol (A)>

[0032] The alcohol (A) contains a polyhydric alcohol represented by the formula (1).

[0033] In the formula (1), at least two of R 1< to R 4< are hydroxy groups and it is preferable that three of R 1< to R 4< be hydroxy groups. Examples of the polyhydric alcohol include pentaerythritol, trimethylolpropane, trimethylolethane, neopentyl glycol, and so on. From the viewpoint of improving the heat resistance and the lubricity of the condensed ester, the polyhydric alcohol is preferably pentaerythritol, trimethylolpropane, or neopentyl glycol and more preferably pentaerythritol.

[0034] For the alcohol (A), any of various monohydric alcohols or polyols may be used as needed as an alcohol component other than the polyhydric alcohol. The monohydric alcohol usually has 1 to 24 carbon atoms, and its carbon chain may be either linear or branched and either saturated or unsaturated. Dihydric to decahydric polyols are usually used as the polyol.

[0035] Examples of the polyol include: diol compounds such as ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, 1,2-propanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,2-propanediol, 2-methyl-1,3-propanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, and 1,5-pentanediol; triol compounds such as 1,2,4-butanetriol, 1,3,5-pentanetriol, and 1,2,6-hexanetriol; trimethylolalkane polymers such as dipentaerythritol and tripentaerythritol; polyglycerols such as glycerol, diglycerol, triglycerol, and tetraglycerol; sugars such as sorbitol, sorbitan, sorbitol glycerol condensate, adonitol, arabitol, xylitol, mannitol, xylose, arabinose, ribose, rhamnose, glucose, fructose, galactose, mannose, sorbose, cellobiose, maltose, isomaltose, trehalose, and sucrose; and so on.<Carboxylic Acid (B)>

[0036] The carboxylic acid (B) contains a fatty acid having 5 to 9 carbon atoms (B-1), a branched fatty acid having 15 to 20 carbon atoms (B-2), a cycloalkane monocarboxylic acid having 4 to 8 carbon atoms (B-3), and an aromatic carboxylic acid (B-4).

[0037] In the fatty acid having 5 to 9 carbon atoms (B-1), the carbon chain may be either saturated or unsaturated but is preferably saturated from the viewpoint of improving the heat resistance of the condensed ester. In addition, the fatty acid (B-1) has preferably 6 to 8 carbon atoms and more preferably 7 carbon atoms from the viewpoint of improving the heat resistance and the lubricity of the condensed ester.

[0038] Examples of the fatty acid (B-1) include valeric acid, 2-methylvaleric acid, 4-methylvaleric acid, n-hexanoic acid, 2-methylhexanoic acid, 5-methylhexanoic acid, 4,4-dimethylpentanoic acid, n-heptanoic acid, 2-methylheptanoic acid, 2-ethylhexanoic acid, 2,2-dimethylhexanoic acid, n-octanoic acid, 3,5,5-trimethylhexanoic acid, n-nonane, and so on. From the viewpoint of the heat resistance, the fatty acid (B-1) is preferably linear valeric acid, n-hexanoic acid, n-heptanoic acid, n-octanoic acid, or n-nonanoic acid, and more preferably n-heptanoic acid.

[0039] Examples of the branched fatty acid (B-2) include 13-methyltetradecanoic acid, 12-methyltetradecanoic acid, 15-methylhexadecanoic acid, 14-methylhexadecanoic acid, 10-methylhexadecanoic acid, 2-hexyldecanoic acid, isopalmitic acid, isostearic acid, isoarachidic acid, phytanic acid, and so on. From the viewpoint of improving the heat resistance and the lubricity of the condensed ester, the branched fatty acid (B-2) is preferably 2-hexyldecanoic acid, isopalmitic acid, isostearic acid, or isoarachidic acid, and more preferably isostearic acid or isopalmitic acid.

[0040] The cycloalkane monocarboxylic acid having 4 to 8 carbon atoms (B-3) may be substituted with an alkyl chain, and the alkyl chain may be linear or branched.

[0041] The cyclo ring of the cycloalkane monocarboxylic acid (B-3) is preferably a 5-to 7-membered ring and more preferably a 6-membered ring from the viewpoint of improving the heat resistance of the condensed ester.

[0042] Examples of the cycloalkane monocarboxylic acid (B-3) include cyclopropanecarboxylic acid, cyclobutanecarboxylic acid, cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cycloheptanecarboxylic acid, methylcyclohexanecarboxylic acid, and so on. From the viewpoint of improving the heat resistance of the condensed ester, the cycloalkane monocarboxylic acid (B-3) is preferably cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cycloheptanecarboxylic, or methylcyclohexanecarboxylic acid, more preferably cyclohexanecarboxylic acid, cycloheptanecarboxylic, or methylcyclohexanecarboxylic acid, and even more preferably cyclohexanecarboxylic acid.

[0043] The aromatic carboxylic acid (B-4) may be substituted by an alkyl chain, and the alkyl chain may be linear or branched.

[0044] From the viewpoint of improving the heat resistance of the condensed ester, the aromatic ring of the aromatic carboxylic acid (B-4) is preferably a benzene ring or a naphthalene ring, and more preferably a benzene ring.

[0045] Examples of the aromatic carboxylic acid (B-4) include benzoic acid, toluic acid, dimethylbenzoic acid, trimethylbenzoic acid, and naphthoic acid, among which the benzoic acid is preferred from the viewpoint of improving the heat resistance of the condensed ester.

[0046] Here, the carboxylic acid (B) may use, as a carboxylic acid component other than the components (B-1) to (B-4), any of various carboxylic acids (hereinafter referred to as the other carboxylic acid compound) as needed. Examples of the other carboxylic acid compound include capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and so on.

[0047] Hereinafter, the amounts of the components blended in the condensed ester in the grease composition of the present invention will be explained.

[0048] In the alcohol (A), the polyhydric alcohol represented by the formula (1) accounts for preferably 80 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, much more preferably, 98 mol% or more, and even much more preferably 100 mol%.

[0049] In the carboxylic acid (B), the fatty acid (B-1) accounts for 30 to 50 mol%. In the carboxylic acid (B), the fatty acid (B-1) accounts for preferably 35 mol% or more from the viewpoints of improving the heat resistance and reducing the kinematic viscosity of the condensed ester, and is preferably 40 mol% or less from the viewpoint of increasing the kinematic viscosity of the condensed ester.

[0050] In the carboxylic acid (B), the branched fatty acid (B-2) accounts for 30 mol% or more and 50 mol% or less. In the carboxylic acid (B), the branched fatty acid (B-2) accounts for preferably 35 mol% or more from the viewpoints of improving the heat resistance and increasing the kinematic viscosity of the condensed ester, and is preferably 40 mol% or less from the viewpoint of reducing the kinematic viscosity of the condensed ester.

[0051] In the carboxylic acid (B), the cycloalkane monocarboxylic acid (B-3) accounts for 10 mol% or more and 30 mol% or less. In the carboxylic acid (B), the cycloalkane monocarboxylic acid (B-3) preferably accounts for 12 mol% or more from the viewpoint of improving the heat resistance of the condensed ester, and preferably accounts for 25 mol% or less from the viewpoint of improving the lubricity of the condensed ester.

[0052] In the carboxylic acid (B), the aromatic carboxylic acid (B-4) accounts for 1 to 15 mol%. In the carboxylic acid (B), the aromatic carboxylic acid (B-4) preferably accounts for 2 mol% or more from the viewpoints of improving the heat resistance and increasing the kinematic viscosity of the condensed ester, and preferably accounts for 13 mol% or less from the viewpoint of reducing the kinematic viscosity of the condensed ester.

[0053] In the carboxylic acid (B), a mole ratio ((B-3) / (B-4)) of the cycloalkane monocarboxylic acid (B-3) to the aromatic carboxylic acid (B-4) is preferably 0.5 to 20 from the viewpoint of improving low temperature storage properties of the condensed ester. In the carboxylic acid (B), the mole ratio ((B-3) / (B-4)) of the cycloalkane monocarboxylic acid (B-3) to the aromatic carboxylic acid (B-4) is preferably 0.8 or more and is preferably 15 or less and more preferably 12 or less from the viewpoint of improving the low temperature storage properties of the condensed ester.

[0054] In the carboxylic acid (B), the total of the fatty acid (B-1), the branched fatty acid (B-2), the cycloalkane monocarboxylic acid (B-3), and the aromatic carboxylic acid (B-4) accounts for preferably 80 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, much more preferably, 98 mol% or more, and even much more preferably 100 mol% from the viewpoint of improving the heat resistance and the lubricity of the condensed ester.

[0055] From the viewpoint of the high temperature durability, the kinematic viscosity at 40 °C of the condensed ester in the grease composition of the present invention is preferably 80 mm 2< / s or more, and more preferably 90 mm 2< / s or more, and is preferably 110 mm 2< / s or less, and more preferably 100 mm 2< / s or less. From the viewpoint of improving the lubricity at high temperature, the kinematic viscosity at 100°C, to be described later, of the condensed ester in the grease composition of the present invention is preferably 11 mm 2< / s or more, and more preferably 11.5 mm 2< / s or more, and preferably 14 mm 2< / s or less, and more preferably 13 mm 2< / s or less.<Condensed Ester Preparation Method>

[0056] The condensed ester can be prepared by an esterification reaction of the alcohol (A) and the carboxylic acid (B) in accordance with a known method.

[0057] For the reaction of the alcohol (A) with the carboxylic acid (B), from the viewpoint of promoting the esterification reaction, the equivalent ratio of the two is usually adjusted so that an amount of carboxyl groups in the carboxylic acid component of the carboxylic acid (B) is preferably 1.05 to 1.5 equivalents and more preferably 1.1 to 1.3 equivalents per equivalent of hydroxyl groups in the alcohol component of the alcohol (A). Here, increasing the ratio of carboxy groups in the carboxylic acid component of the carboxylic acid (B) improves the reactivity between the alcohol component and the carboxylic acid component, but makes it necessary to remove excess carboxylic acid (B) after the reaction is completed. Examples of this removal method include adsorption and removal using vacuum distillation, steaming, and an adsorbent, and so on.

[0058] The ester-based synthetic oil in the present invention may be a so-called biomass oil, which is produced from any of biological resources derived from animals and plants. For example, biomass ester oils synthesized from various fatty acids derived from vegetable oils and alcohols can be also used. One type of base oil may be used alone or two or more types of base oils may be mixed.

[0059] The ester-based base oil in the present invention preferably consists of only a condensed ester of a polyhydric alcohol represented by the formula (1) and the carboxylic acid (B).

[0060] Among such oils, an ester oil in which the mole ratio ((B-3) / (B-4)) of the cycloalkane monocarboxylic acid (B-3) to the aromatic carboxylic acid (B-4) is 0.5 to 20 is preferred.

[0061] In particular, preferred is an ester compound of pentaerythritol with the carboxylic acid (B) which is a mixture of 37.5 mol% of n-heptane (B-1), 37.5 mol% of isostearic acid (B-2), 22.5 mol% of cyclohexane carboxylic acid (B-3), and 2.5 mol% of benzoic acid (B-4) in the carboxylic acid (B).

[0062] The content of the ester-based synthetic oil of the present invention based on the total mass of the composition is preferably 84 to 74% by mass, more preferably 81 to 77% by mass, and even more preferably 80 to 77% by mass. When the composition contains the base oil in this proportion, the high-temperature durability is improved.

[0063] The content of the ester oil represented by the formula (1) based on the total mass of the base oil is preferably 60 to 100% by mass, more preferably 80 to 100% by mass, even more preferably 100% by mass. When the composition contains the base oil with this proportion, the high-temperature durability is particularly improved.<Amine Phosphate>

[0064] The amine phosphate in the grease composition of the present invention is not particularly limited. Preferred examples thereof include tertiary alkylamine-dimethylphosphate, phenylamine-phosphate, and the like. Tertiary alkylamine-dimethylphosphate is the most preferable. As the amine phosphate, a commercially available product can be used such as Vanlube 672 (tertiary alkylamine-dimethylphosphate) manufactured by R.T. Vanderbilt Holding Company, Inc. or Vanlube 692 (phenylamine-phosphate) manufactured by R.T. Vanderbilt Holding Company, Inc.

[0065] The number of carbon atoms in the tertiary-alkyl moiety in the tertiary alkylamine-dimethylphosphate is not particularly limited and may be, for example, 1 to 24.

[0066] The content of the amine phosphate based on the total mass of the grease composition is 0.2 to 2.5% by mass, preferably 0.3 to 1.0% by mass, and more preferably 0.4 to 0.7% by mass. When the content is 0.2% by mass or more, the composition exhibits the sufficient fretting resistance. On the other hand, when the content exceeds 2.5% by mass, the composition even exhibits the fretting resistant effect, but the effect is saturated. For this reason, the content is preferably 2.5% by mass or less from the economic viewpoint.<Carboxylic Acid-based Corrosion Inhibitor>

[0067] As the carboxylic acid-based corrosion inhibitor in the grease composition of the present invention, there are: monocarboxylic acids including, for example, linear fatty acids such as lauric acid and stearic acid and saturated carboxylic acids having a naphthenic nucleus; and dicarboxylic acids including, for example, succinic acid, alkyl succinic acids, alkyl succinic acid half esters, alkenyl succinic acids, alkenyl succinic acid half esters, succinic acid derivatives such as succinimides, tetrapropenyl butanedioic acids, hydroxy fatty acids, mercapto fatty acids, and sarcosine derivatives. Among them, 2-tetrapropenyl succinic acid half ester and tetrapropenyl butanedioic acid are preferred, and a combination of the two is particularly preferred.

[0068] The content of the carboxylic acid-based corrosion inhibitor in the grease composition of the present invention is determined by a ratio thereof to the content of the amine phosphate. The content per part by mass of the amine phosphate is 0.5 to 4 parts by mass, preferably 0.8 to 3 parts by mass, and more preferably 1 to 2 parts by mass. When the content is 0.5 parts by mass or more, the composition ensures corrosion inhibitory effectiveness sufficient to cover a decrease in the corrosion inhibitory effectiveness due to a high reactivity of the amine phosphate with a metal surface. On the other hand, when the content exceeds 4 parts by mass, the adsorption of the corrosion inhibitor to the metal surface predominates over the reactivity of the amine phosphate, resulting in sufficient corrosion inhibitory effectiveness but poor fretting resistance.

[0069] The grease composition of the present invention may contain a corrosion inhibitor other than the carboxylic acid-based corrosion inhibitor, for example, an ester-based corrosion inhibitor, but the content thereof is at most 3.5 parts by mass per part by mass of the amine phosphate. When the content exceeds 3.5 parts by mass, the adsorption of the corrosion inhibitor to the metal surface predominates over the reactivity of the amine phosphate, which may result in sufficient corrosion inhibitory effectiveness but poor fretting resistance.

[0070] The grease composition of the present invention does not contain any of carboxylate-based corrosion inhibitors or fatty acid amine salts. When the grease composition contains a carboxylate-based corrosion inhibitor or fatty acid amine salt, the reactivity of the amine phosphate predominates over the adsorption of the corrosion inhibitor to the metal surface, which may result in sufficient fretting resistance but poor corrosion inhibitory effectiveness.o Antioxidant

[0071] The grease composition of the present invention contains an antioxidant. The antioxidant contributes to the high-temperature durability.

[0072] As the antioxidant in the present invention, an amine-based antioxidant, a phenol-based antioxidant, or a mixture of them may be used. It is preferable to use a mixture of them.<Amine-based Antioxidant >

[0073] The amine-based antioxidant usable in the grease composition of the present invention is preferably selected from the group consisting of alkyldiphenylamines, N-phenyl-α-naphthylamines, alkylated phenyl-α-naphthylamines, and mixtures of them. Among these, the alkyldiphenylamines are more preferable, and alkyldiphenylamine, which is a reaction product of N-phenylbenzeneamine and 2,2,4-trimethyl pentene, is particularly preferable.

[0074] In the grease composition of the present invention, the content of the amine-based antioxidant is preferably 0.5 to 5% by mass, more preferably 1 to 3% by mass, and even more preferably 1.5 to 2.5% by mass. When the content is 0.5% by mass or more, the grease composition exerts a sufficient antioxidant effect. On the other hand, even when the content exceeds 5% by mass, the grease composition even exerts the antioxidant effect, but the effect is saturated. For this reason, from the economic viewpoint, the content is preferably 5% by mass or less.<Phenol-based Antioxidant>

[0075] The phenol-based antioxidant usable in the grease composition of the present invention is preferably selected from the group consisting of octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,6-di-tert-butyl-4-methylphenol, pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), benzenepropanoic acid, 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy C7-C9 side chain alkyl ester, and mixtures of them. Among these, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate is particularly preferable.

[0076] In the grease composition of the present invention, the content of the phenol-based antioxidant is preferably 0.5 to 5% by mass, more preferably 0.5 to 3% by mass, and even more preferably 0.8 to 2% by mass. When the content is 0.5% by mass or more, the grease composition exerts a sufficient antioxidant effect. On the other hand, even when the content exceeds 5% by mass, the grease composition even exerts the antioxidant effect, but the effect is saturated. For this reason, from the economic viewpoint, the content is preferably 5% by mass or less.

[0077] As the antioxidant used in the grease composition of the present invention, particularly preferred is a combination of alkyldiphenylamine, which is the reaction product of N-phenylbenzeneamine and 2,2,4-trimethyl pentene, and octadecyl-3-(3,5-dit-butyl-4-hydroxyphenyl)propionate.

[0078] When the grease composition of the present invention contains, as the antioxidant, a mixture of an amine-based antioxidant and a phenol-based antioxidant, the total mass of the mixture based on the total mass of the composition is preferably 1 to 10% by mass, more preferably 1.5 to 6% by mass, and even more preferably 2.3 to 4.5% by mass. When the grease composition contains a mixture of a amine-based antioxidant and a phenol-based antioxidant in such proportion, the grease composition can exert particularly the antioxidant effect.

[0079] When the grease composition of the present invention contains, as the antioxidant, a mixture of alkyldiphenylamine, which is a reaction product of N-phenylbenzeneamine and 2,2,4-trimethyl pentene, and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, the total mass of the mixture based on the total mass of the composition is preferably 1 to 10% by mass, more preferably 1.5 to 6% by mass, and even more preferably 2.3 to 4.5% by mass. When the grease composition contains the mixture of alkyldiphenylamine, which is the reaction product of N-phenylbenzeneamine and 2,2,4-trimethyl pentene, and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate in such proportion, the grease composition can exert particularly the antioxidant effect.o Optional Additives

[0080] To the grease composition of the present invention, generally-used additives may be added as needed. For example, the following additives may be added.o Anti-Spalling Additive<Organic Sulfonic Acid Metal Salt>

[0081] As an organic sulfonic acid metal salt in the grease composition of the present invention, there is a salt represented by the following formula (4). Zinc salts are preferred.         [R10-SO 3 ]M2 ...     formula (4)

[0082] In the formula (4), R10 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 linear or branched and has 2 to 22 carbon atoms. M2 represents an alkaline earth metal or zinc, and is preferably zinc or calcium. In particular, zinc dinonylnaphthalene sulfonate is preferred.

[0083] In the grease composition of the present invention, the content of the organic sulfonic acid metal salt is usually 0.5 to 5% by mass, preferably 1 to 3% by mass, and more preferably 1.5 to 2.5% by mass.<Dialkyldithiophosphate Metal Salt>

[0084] As a dialkyldithiophosphate metal salt in the grease composition of the present invention, there is a salt represented by the following formula (3).         [(R8O)(R9O)P(=S)-S] 2 -M1 x O m S n ...     formula (3)

[0085] In formula (3), R8 and R9 each represent an alkyl group having 1 to 24 carbon atoms or an aryl group having 6 to 30 carbon atoms, and the alkyl group may be linear or branched and may be primary, secondary, or tertiary. M1 represents zinc or molybdenum, and is preferably zinc. In addition, x is 1 or 2 and n and m are 0 to 4.

[0086] In the grease composition of the present invention, the content of the dialkyldithiophosphate metal salt is usually 0.5 to 3% by mass, preferably 0.5 to 3% by mass, and more preferably 0.8 to 2% by mass.o Extreme Pressure Agent

[0087] Phosphorus-based compounds: tricresyl phosphate, tri-2-ethylhexyl phosphate, and so on. Sulfur-based compounds: dibenzyl disulfide, various polysulfides, and so on. Sulfur-phosphorus-based compounds: triphenyl phosphorothioate Organometallic extreme pressure agents: dialkyldithiocarbamic acid salts of Zn, Mo, Sb, Ni, Cu, Bi, and so on, ashless dithiocarbamates, ashless dithiophosphate carbamates, and so on. Solid lubricants: molybdenum disulfide, graphite, PTFE, MCA, and so on. Metal corrosion inhibitors: benzotriazole or its derivatives, zinc oxide, and so on. Oiliness agents: sorbitan trioleate, sorbitan monooleate, and so on.

[0088] The additives of the present invention preferably include: an amine phosphate that is at least one selected from the group consisting of tertiary alkylamine dimethyl phosphates and phenylamine phosphates; a carboxylic acid-based corrosion inhibitor that is at least one selected from the group consisting of 2-tetrapropenyl succinic acid half esters and tetrapropenyl butanedioic acid; and an antioxidant that is at least one selected from the group consisting of alkyldiphenylamine, which is the reaction product of N-phenylbenzenamine and 2,2,4-trimethylpentene, and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, but does not contain any of carboxylate-based corrosion inhibitors or fatty acid amine salts.

[0089] In this embodiment, it is more preferable that the content of the amine phosphate in the composition be 0.3 to 1.0% by mass and the content of the carboxylic acid-based corrosion inhibitor be 0.8 to 3 parts by mass per part by mass of the amine phosphate.

[0090] In this embodiment, the grease composition preferably further contains an anti-spalling additive, and the anti-spalling additive is more preferably at least one selected from the group consisting of organic sulfonic acid metal salts and dialkyldithiophosphate metal salts, and even more preferably at least one selected from the group consisting of zinc dinonylnaphthalene sulfonate and zinc dialkyldithiophosphate.

[0091] More preferably, the additives of the present invention include or consist of: an amine phosphate that is tertiary alkylamine dimethyl phosphate, a carboxylic acid-based corrosion inhibitor that is a mixture of 2-tetrapropenyl succinic acid half ester and tetrapropenyl butanedioic acid, an antioxidant that is a mixture of alkyldiphenylamine, which is the reaction product of N-phenylbenzenamine and 2,2,4-trimethylpentene, and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and an anti-spalling additive that is a mixture of zinc dinonylnaphthalene sulfonate and zinc dialkyldithiophosphate, but does not contain any of carboxylate-based corrosion inhibitors or fatty acid amine salts.

[0092] In this embodiment, it is more preferable that the content of the amine phosphate in the composition be 0.4 to 0.7% by mass, and the content of the carboxylic acid-based corrosion inhibitor be 1 to 2 parts by mass per part by mass of the amine phosphate.

[0093] In any of the foregoing preferred embodiments regarding the additives, it is particularly preferable that: the thickener be an alicyclic aliphatic diurea compound containing a diurea compound in which, in formula (2), one of R5 and R7 is a cyclohexyl group and the other is a linear alkyl group having 18 carbon atoms, and in which the proportion of the number of moles of the cyclohexyl groups is 83.3 mol%; and the base oil be an ester compound of pentaerythritol with the carboxylic acid (B) which is a mixture of 37.5 mol% of n-heptane (B-1), 37.5 mol% of isostearic acid (B-2), 22.5 mol% of cyclohexane carboxylic acid (B-3), and 2.5 mol% of benzoic acid (B-4) in the carboxylic acid (B).

[0094] The grease composition of the present invention is excellent in the high-temperature durability, the fretting resistance, and the corrosion inhibitory effectiveness, and therefore is for use in rolling bearings of automotive electrical components, household electrical appliances for use under high-speed rotations at high temperatures, such as cleaner motors, continuous casting facilities to be lubricated at high temperatures, and so on. Among these, the grease composition of the present invention is particularly suitable as a grease for use in rolling bearings of automotive electrical accessory components, for which all of the high high-temperature durability, fretting resistance, and corrosion inhibitory effectiveness are required.[Examples]<Preparation for Grease Composition>

[0095] Each grease composition was prepared by: reacting, in a base oil specified in a table below, a specified amount of amine (a mixture of cyclohexylamine and stearylamine in the mole ratio specified in the table below) with a specified amount of a 4,4'-diphenylmethane diisocyanate (MDI) at a ratio of 2 moles of the amine per mole of the MDI, followed by heating and cooling; then further diluting the resultant with the base oil; adding additives specified in the table below; and adjusting the resultant mixture by a three-roll mill so that the worked penetration after 60 strokes was 280 (measured according to JIS K2220 7.). The kinematic viscosities at 40°C and 100°C of the base oil (measured according to JIS K2220 23.) were as follows. Unless otherwise specified, the numbers in the table indicate % by mass based on the total mass of the composition. The balance is the base oil.

[0096] Ester: 93 mm 2< / s (an ester compound of pentaerythritol with the carboxylic acid (B) which is a mixture of 37.5 mol% of n-heptane (B-1), 37.5 mol% of isostearic acid (B-2), 22.5 mol% of cyclohexane carboxylic acid (B-3), and 2.5 mol% of benzoic acid (B-4) in the carboxylic acid (B). The kinematic viscosity at 100°C is 12.1 mm 2< / s.) PAO A: 65.3 mm 2< / s PAO B: 393 mm 2< / s Mineral oil A: 101 mm 2< / s Mineral oil B: 39.5 mm 2< / s <Test Methods and Judgment>[Heat Resistance (Bearing Lubrication Life Test)]· Evaluation Method

[0097] The test was conducted using a bearing lubrication life tester conforming to ASTM D3336.

[0098] The test conditions are specified below. A seizure life was defined as a shorter one of a time period until a motor generated an overcurrent (4 amperes) and a time period until a bearing temperature rose by +15°C. Bearing Type: 6204 Metal Seal Test Temperature: 180°C Rotation Speed: 10,000 rpm Grease Amount: 1.8 g Test Load: Axial Load 66.7 N, Radial Load 66.7 N · Judgment

[0099] Bearing Lubrication Life: 1000 hours or more ... ∘ (Pass) Less than 1000 hours ... × (Fail) [Corrosion Inhibitory Effectiveness (Bearing Corrosion Inhibition Test)]· Evaluation Method

[0100] The test was conducted in accordance with ASTM D1743-73.

[0101] A test grease was filled into a bearing (32304J), and the bearing was rotated at 1,750 rpm for 10 seconds under application of an axial load of 26.5 N. Then, the grease weight was adjusted to 3.5 g and the bearing was further rotated for 60 seconds under the same conditions. The bearing was immersed in 1% salt water for 10 seconds, then left to stand at 52°C and 100% humidity for 48 hours, and the condition of corrosion generation on a raceway surface of the outer ring of the bearing after cleaning was visually inspected.· Judgment

[0102] #1 (No Corrosion) ... ∘ (Pass) #2 (3 or less visible corrosion spots) ... × (Fail) #3 (larger corrosion than in #2 or four or more visible corrosion spots) ... × (Fail) [Fretting Resistance (Fretting Test)]· Evaluation Method

[0103] The test grease was applied to two sets of thrust bearing sets specified below, and the bearings were subjected to a specified oscillating operation. The amount of wear (weight loss due to fretting wear) was measured. Bearing: 51204 Thrust Bearing Load: 4000 N (Contact Pressure: 1.9 GPa) Oscillating Angle: ±6° Oscillating Cycle: 25 Hz Time: 2 hours Temperature: 25°C Grease Amount: 1.0 g per bearing set Wear Amount: Race mass loss per bearing set (Total mass loss of test bearing races / 2) · Judgment

[0104] Amount of Wear Less than 7 mg ... ∘ (Pass) 7 mg or more ... × (Fail)

[0105] [Table 1]Ex 1Ex 2Ex 3Ex 4Comp. Ex 1Comp. Ex 2Comp Ex 3Comp Ex 4Comp Ex 5ThickenerIsocianaleMDIMDIMDIMDIMDIMDIMDIMDIMDIAmine (Numeric values specify mole ratio of amine)Cyclohexylamine557755555Octadecylamine113111111Amount of Thickener, % by mass13.513.51313.513.513.513.513.513.5Base OilType (% by mass based on total mass of base oil)Ester Oil100100100100--100100100PAO A----80----PAO B----20----Mineral Oil A-----91---Mineral Oil B-----9---Kinematic Viscosity (40°C), mm 2< / s939393939393939393Amine PhosphateTertiary Alkylamine Dimethyl Phosphate0.510.50.50.50.50.10.50.5Corrosion InhibitorCarboxylic Acid Base2-Tetrapropenylsuccinic Acid Half Ester0.280.560.280.280.280.280.280.070.92Tetrapropenylbutanedioic Acid0.480.960.480.480.480.480.480.121.58Carboxylate BaseZinc Naphthenate---------Fatty Acid Amine SaltNeutralized Salt of Oleic Acid and Dicyclohexylamine (1:1)---------Ester BaseSorbitan Trioleate---------Oxidized Wax---------Organic Sulfonic Acid Metal SaltBarium Dinonylnaphthalene Sulfonate---------AntioxidantAmine-based AntioxidantAlkyldiphenylamine*1222222222Phenol-based AntioxidantOctadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate111111111Other AdditivesOrganic Sulfonic Acid Metal SaltZinc Dinonylnaphthalenesulfonale222222222Dialkyldithiophosphate Metal SaltZinc Dialkyldithiophosphate111111111parts by mass of carboxylic acid-based corrosion inhibitor per part by mass of amine phosphate1.51.51.51.51.51.57.60.45.0parts by mass of other corrosion inhibitor per part by mass of amine phosphate000000000Worked Penetration280280280280280280280280280Performance EvaluationHigh-Temperature DurabilityBearing Lubrication Life Test○○○○××○○○Corrosion Inhibitory EffectivenessBearing Corrosion Inhibition Test○○○○○○○×○Fretting ResistanceFretting Test○○○○○○×○×*1: Reaction product of N-phenylbenzeneamine and 2,4,4-trimethylpentene

[0106] [Table 2]Comp. Ex 6Comp Ex 7Comp Ex 8Comp Ex 9Comp. Ex 10Comp. Ex 11Comp Ex 12ThickenerIsocianaleMDIMDIMDIMDIMDIMDIMDIAmine (Numeric values specify mole ratio of amine)Cyclohexylamine5555555Octadecylamine1111111Amount of Thickener, % by mass13.513.513.513.513.513.513.5Base OilType (% by mass based on total mass of base oil)Ester Oil100100100100100100100PAO A-------PAO B-------Mineral Oil A-------Mineral Oil B-------Kinematic Viscosity (40°C), mm 2< / s93939393939393Amine PhosphateTertiary Alkylamine Dimethyl Phosphate20.50.50.50.50.50.5Corrosion InhibitorCarboxylic Acid Base2-Tetrapropenylsuccinic Acid Half Ester0.28-----0.28Tetrapropenylbuianedioic Acid0.48-----0.48Carboxylate BaseZinc Naphthenate-0.76-----Fatty Acid Amine SaltNeutralized Salt of Oleic Acid and Dicyclohexylamine (1:1)--0.76----Ester BaseSorbitan Trioleate---0.76---Oxidized Wax----0.76--Organic Sulfonic Acid Metal SaltBarium Dinonylnaphthalene Sulfonale-----0.76-AntioxidantAmine-based AntioxidantAlkyldiphenylamine*1222222-Phenol-based AntioxidantOctadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate111111-Other AdditivesOrganic Sulfonic Acid Metal SaltZinc Dinonylnaphthalenesulfonate2222222Dialkyldithiophosphate Metal SaltZinc Dialkyldithiophosphate1111111paris by mass of carboxylic acid-based corrosion inhibitor per part by mass of amine phosphate0.4000001.5paris by mass of other corrosion inhibitor per part by mass of amine phosphate01.51.51.51.51.50Worked Penetration280280280280280280280Performance EvaluationHigh-Temperature DurabilityBearing Lubrication Life Test○○○○○○×Corrosion Inhibitory EffectivenessBearing Corrosion Inhibition Test××××××○Fretting ResistanceFretting Test○○○○○○○*1: Reaction product of N-phenylbenzeneamine and 2,4,4-trimethylpentene

[0107] Examples 1 to 4 passed in all of the high-temperature durability, the corrosion inhibitory effectiveness, the fretting resistance, and the anti-spalling properties.

[0108] Comparative Examples 1 and 2 in each of which PAO or a mineral oil was used as the base oil instead of the ester oil did not satisfy the high-temperature durability.

[0109] Comparative Examples 3 and 5 in which more than 4 parts by mass of the corrosion inhibitor per part by mass of the amine phosphate was contained passed in the corrosion inhibitory effectiveness but did not satisfy the fretting resistance.

[0110] Comparative Examples 4 and 6 in which less than 5 parts by mass of the corrosion inhibitor per part by mass of the amine phosphate was contained passed in the fretting resistance but did not satisfy the corrosion inhibitory effectiveness.

[0111] Comparative Examples 7 to 11 in each of which a carboxylate, a fatty acid amine salt, an ester, an oxidized wax, or an organic sulfonic acid barium salt was contained did not satisfy the corrosion inhibitory effectiveness.

[0112] Comparative Example 12 in which an antioxidant was not contained did not satisfy the high-temperature durability.

[0113] Therefore, the grease composition of the present invention can be said to satisfy all of the high-temperature durability, the corrosion inhibitory effectiveness, and the fretting resistance.

Claims

1. A grease composition for rolling bearings, comprising a thickener, a base oil, and additives, wherein the thickener is a diurea compound represented by formula (2):         R5-NHCONH-R6-NHCONH-R7 ...     (2) where R6 represents a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R5 and R7, which may be the same or different, each represent a cyclohexyl group or a linear or branched alkyl group having 8 to 22 carbon atoms, the base oil is an ester-based synthetic oil having a kinematic viscosity of 60 mm2 / s or more at 40°C, the additives include an amine phosphate, a carboxylic acid-based corrosion inhibitor, and an antioxidant, a content of the amine phosphate is 0.2 to 2.5% by mass based on a total mass of the composition, a content of the carboxylic acid-based corrosion inhibitor is 0.5 to 4 parts by mass per part by mass of the amine phosphate, and a content of another corrosion inhibitor is 3.5 parts by mass or less per part by mass of the amine phosphate, but the grease composition does not comprise any carboxylate-based corrosion inhibitor or fatty acid amine salt.

2. The grease composition for rolling bearings according to claim 1, wherein the base oil contains a condensed ester of an alcohol (A) and a carboxylic acid (B) and has a kinematic viscosity of 80 to 110 mm2 / s at 40°C, the alcohol (A) contains a polyhydric alcohol represented by formula (1): where R1 to R4 each independently represents a hydrogen atom, a methyl group, or a hydroxy group and at least two of R1 to R4 each represent a hydroxy group, the carboxylic acid (B) contains a fatty acid having 5 to 9 carbon atoms (B-1), a branched fatty acid having 15 to 20 carbon atoms (B-2), a cycloalkane monocarboxylic acid having 4 to 8 carbon atoms (B-3), and an aromatic carboxylic acid (B-4), and in the carboxylic acid (B), the fatty acid (B-1) accounts for 30 to 50 mol%, the branched fatty acid (B-2) accounts for 30 to 50 mol%, the cycloalkane monocarboxylic acid (B-3) accounts for 10 to 30 mol%, and the aromatic carboxylic acid (B-4) accounts for 1 to 15 mol%.

3. The grease composition for rolling bearings according to claim 1, wherein the amine phosphate is a tertiary alkylamine-dimethylphosphate or a phenyl amine phosphate.

4. The grease composition for rolling bearings according to claim 1, wherein the thickener is an alicyclic aliphatic diurea compound in which, in formula (2), a proportion of the number of moles of cyclohexyl groups to the total number of moles of cyclohexyl groups and linear or branched alkyl groups having 8 to 22 carbon atoms is 70 to 90 mol%.

5. The grease composition for rolling bearings according to claim 1, comprising, as the antioxidant, 0.5 to 5% by mass of an amine-based antioxidant and 0.5 to 5% by mass of a phenol-based antioxidant based on the total mass of the composition.

6. The grease composition for rolling bearings according to claim 1, further comprising an anti-spalling additive.

7. The grease composition for rolling bearings according to claim 6, comprising, as the anti-spalling additive, 0.2 to 5% by mass of an organic sulfonic acid metal salt based on the total mass of the composition and 0.2 to 5% by mass of a dialkyldithiophosphate metal salt based on the total mass of the composition.

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