Grease composition for rolling bearing

Abstract

This grease composition for a rolling bearing contains a diurea thickener represented by formula (2): R5-NHCONH-R6-NHCONH-R7 (in the formula, R6 represents a divalent aromatic hydrocarbon group having 6-15 carbon atoms; and R5 and R7 may be the same or different, and each represent a cyclohexyl group or a linear or branched alkyl group having 8-22 carbon atoms), an ester-based synthetic base oil having a kinematic viscosity of 60 mm2 / s or more at 40°C, 0.2-2.5 mass% of an amine phosphate based on the total mass of the composition, and 0.5-4 parts by mass of a carboxylic acid-based rust inhibitor with respect to 1 part by mass of the amine phosphate. However, said composition contains neither a carboxylate-based rust inhibitor nor a fatty acid amine salt.

Description

Grease composition for rolling bearings

[0001] The present invention relates to a grease composition for rolling bearings, particularly to a grease composition suitable for use in rolling bearings that are lubricated at high temperatures, such as those used in automotive electrical components that are directly connected to or located near engines, which are heat-generating elements, household electrical appliances that rotate at high speeds and high temperatures, such as cleaner motors, and continuous casting equipment.

[0002] Rolling bearings used in various industrial machines are operated in a variety of environments, from cold regions to high-temperature environments such as the inside of an automobile engine compartment. Therefore, rolling bearings are required to be able to operate over a wide temperature range and for long periods without maintenance, and the demands for durability are constantly increasing. Ester oils are known as base oils with excellent heat resistance. Patent Document 1 discloses that a grease base oil having a condensed ester of a specific alcohol and a carboxylic acid and a grease composition containing the grease base oil have excellent heat resistance.

[0003] (Prior Art Related to Fretting Resistance) Furthermore, automobiles, electrical appliances, and various machine parts and products are often transported by rail or truck. During this transportation, vibrations caused by rail joints and rough roads can cause fretting in greased bearings. Fretting is surface damage that occurs under very small amplitudes. In the atmosphere, it is said that oxidized wear particles are generated, and the abrasive action of these particles often leads to severe wear (Non-Patent Document 1). Measures proposed to prevent fretting include (1) reducing the relative amount of sliding, (2) separating the two surfaces to prevent direct contact, and (3) preventing adhesion between surfaces by coating the contact surfaces with a phosphate coating or by applying a lubricating oil or grease (Non-Patent Document 1). Furthermore, a grease composition containing an alicyclic aliphatic diurea thickener and an amine phosphate has been disclosed as a grease composition that is excellent at suppressing fretting wear under more severe conditions (below −30°C, very small amplitude) (Patent Document 2).

[0004] (Prior Art Related to Rust Prevention) On the other hand, for example, rolling bearings used in automotive electrical accessories are often mounted in the lower part of the engine compartment, and are therefore susceptible to rainwater while the automobile is running. Furthermore, rolling bearings for steel rolling mills are used in environments where they are exposed to large amounts of water. For this reason, grease for rolling bearings is also required to have rust prevention properties. A grease composition containing a carboxylic acid-based rust inhibitor, a carboxylate-based rust inhibitor, and an amine-based rust inhibitor is known as a grease composition with excellent rust prevention properties (Patent Document 3).

[0005] Patent No. 7216563 Patent No. 6040750 Patent No. 5714922

[0006] Yuji Yamamoto et al.: Tribology, Rikogakusha, February 28, 1998, pp. 201-203

[0007] Patent Document 1 discloses a grease base oil having a condensed ester of a specific alcohol and a carboxylic acid, and a grease composition containing the grease base oil, as a grease composition with excellent heat resistance. However, ester oils are generally said to have poor fretting resistance. Meanwhile, Patent Document 2 discloses a grease composition containing an amine phosphate as a grease composition with excellent fretting resistance. However, due to its high reactivity with metal surfaces, amine phosphate may deteriorate rust prevention properties. Patent Document 3 also discloses a grease composition containing a carboxylic acid-based rust inhibitor, a carboxylate-based rust inhibitor, and an amine-based rust inhibitor as a grease composition with excellent rust prevention properties. However, the presence of these rust inhibitors in excessive amounts may inhibit the function of the amine phosphate and deteriorate fretting resistance. While the above-mentioned conventional technologies are excellent in individual performances of high-temperature durability, fretting resistance, and rust prevention, they do not fully satisfy all of these performances, and there are problems, particularly in achieving both fretting resistance and rust prevention. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a grease composition for rolling bearings which is excellent in all of high-temperature durability, fretting resistance, and rust prevention properties.

[0008] We have overcome the above-mentioned problems by selecting the appropriate base oil, thickener, and additives. That is, the present invention provides the following grease composition for rolling bearings: 1. A grease composition for rolling bearings comprising a thickener, a base oil, and an additive, wherein the thickener is a diurea compound represented by formula (2): R5-NHCONH-R6-NHCONH-R7 ... (2) (wherein R6 represents a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R5 and R7, which may be the same or different, represent a cyclohexyl group, or a linear or branched alkyl group having 8 to 22 carbon atoms). The base oil has a kinematic viscosity of 60 mm at 40°C. 2 1. The grease composition for rolling bearings, wherein the base oil contains a condensed ester of an alcohol (A) and a carboxylic acid (B), and has a kinematic viscosity at 40°C of 80 to 110 mm / s or more, and the additives include an amine phosphate, a carboxylic acid-based rust inhibitor, and an antioxidant, the content of the amine phosphate is 0.2 to 2.5 mass% based on the total mass of the composition, the content of the carboxylic acid-based rust inhibitor is 0.5 to 4 mass parts per 1 mass part of the amine phosphate, and the content of other rust inhibitors is 3.5 mass parts or less per 1 mass part of the amine phosphate, and the grease composition for rolling bearings, wherein the grease composition does not contain any carboxylate-based rust inhibitor or an amine salt of a fatty acid. 2 / s, and the alcohol (A) is represented by the formula (1):

[0009]

[0010] 2. The grease composition for a rolling bearing according to 1 above, wherein the grease composition contains a polyhydric alcohol represented by formula (1): (in formula (1), R1 to R4 independently represent a hydrogen atom, a methyl group, or a hydroxyl group, and at least two of R1 to R4 represent a hydroxyl group), and the carboxylic acid (B) contains a fatty acid (B-1) having from 5 to 9 carbon atoms, a branched fatty acid (B-2) having from 15 to 20 carbon atoms, a cycloalkane monocarboxylic acid (B-3) having from 4 to 8 carbon atoms, and an aromatic carboxylic acid (B-4), and in the carboxylic acid (B), a proportion of the fatty acid (B-1) is 30 to 50 mol %, a proportion of the branched fatty acid (B-2) is 30 to 50 mol %, a proportion of the cycloalkane monocarboxylic acid (B-3) is 10 to 30 mol %, and a proportion of the aromatic carboxylic acid (B-4) is 1 to 15 mol %. 3. The grease composition for rolling bearings according to any one of 1 to 2 above, wherein the amine phosphate is tertiary alkylamine dimethyl phosphate or phenylamine phosphate. 4. The grease composition for rolling bearings according to any one of 1 to 3 above, wherein the thickener is an alicyclic aliphatic diurea compound in which, in formula (2), the ratio 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 any one of 1 to 4 above, wherein the antioxidants contain 0.5 to 5 mass % of an amine-based antioxidant and 0.5 to 5 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 1 to 5 above, further containing an anti-flaking additive. 7. 7. The grease composition for a rolling bearing according to 6 above, comprising, as the anti-exfoliation additive, 0.2 to 5 mass% of an organic sulfonic acid metal salt, and 0.2 to 5 mass% of a dialkyldithiophosphate metal salt, based on the total mass of the composition.

[0011] According to the present invention, it is possible to provide a grease composition for rolling bearings with sufficient high-temperature durability, fretting resistance, and rust prevention properties. The grease composition of the present invention also has excellent flaking resistance.

[0012] Schematic diagram of the four-ball rolling test

[0013] Thickeners The fluidity of grease in bearings in high-temperature environments varies depending on the type of thickener, which significantly affects the bearing's lubrication life. For a grease to have a long lubrication life, it must remain in the 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) (wherein R6 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R5 and R7, which may be the same or different, represent a cyclohexyl group or a linear or branched alkyl group having 8 to 22 carbon atoms.) Representative examples of R6 include those represented by the following structural formula. Of these, a diphenylmethane group is most preferred.

[0014]

[0015] As the linear or branched alkyl group having 8 to 22 carbon atoms, a linear alkyl group having 8 to 18 carbon atoms is preferred. A linear alkyl group having 18 carbon atoms is most preferred. A diurea compound in which one of R5 and R7 in formula (2) is a cyclohexyl group and the other is a linear or branched alkyl group having 8 to 22 carbon atoms is preferred. This diurea compound is a reaction product of a mixture of cyclohexylamine and a monoamine having a linear or branched alkyl group having 8 to 22 carbon atoms with a diisocyanate, and is called an alicyclic aliphatic diurea compound. The reaction product includes, in addition to the alicyclic aliphatic diurea compound, an alicyclic diurea compound having cyclohexyl groups at both ends and an aliphatic diurea compound having linear or branched alkyl groups having 8 to 22 carbon atoms at both ends.

[0016] In formula (2), the ratio 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 [{(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%, more preferably 80 to 90 mol%. A ratio of 70 mol% or more can particularly adequately prevent softening and leakage of the grease composition in high-temperature environments, while a ratio of 90 mol% or less can ensure particularly sufficient flowability and excellent high-temperature durability. A particularly preferred thickener of the present invention is an alicyclic aliphatic diurea compound containing a diurea compound in which one of R5 and R7 in formula (2) is a cyclohexyl group and the other is a linear alkyl group having 18 carbon atoms, and the ratio of the number of moles of cyclohexyl groups is 83.3 mol%. The content of the thickener in the grease composition of the present invention varies depending on the 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 the amount necessary to achieve this consistency. The content of the thickener in the grease composition of the present invention is usually 9 to 19 mass%, preferably 12 to 16 mass%. If the content is less than 9 mass%, the grease may be soft and leak, and the lubrication life may not be satisfied. On the other hand, if the content is more than 19 mass%, the fluidity may be poor, making it difficult for the grease to penetrate into the lubricated parts, and the lubrication life may not be satisfied.

[0017] Base oil The base oil used in the present invention has a kinematic viscosity of 60 mm at 40°C. 2 The ester-based synthetic oil has a kinematic viscosity of 80 mm / s or more at 40°C. The ester-based synthetic oil has excellent high-temperature durability. 2 / s or more, and 2 / s or more is more preferable, and 110 mm 2 / s or less, and 2 From the viewpoint of improving lubrication at high temperatures, the ester-based synthetic oil preferably has a kinematic viscosity at 100°C of 11 mm / s or less. 2 / s or more, and 11.5 mm2 / s or more is more preferable, and 14 mm 2 / s or less, and 13 mm 2 The ester-based synthetic oil of the present invention preferably contains a condensation ester of an alcohol (A) and a carboxylic acid (B). The alcohol (A) is represented by the formula (1):

[0018]

[0019] (In formula (1), R 1 From R 4 each independently represents a hydrogen atom, a methyl group, or a hydroxyl group, and R 1 From R 4 wherein at least two of the groups represent a hydroxyl group.) The carboxylic acid (B) contains a fatty acid (B-1) having 5 to 9 carbon atoms, a branched fatty acid (B-2) having 15 to 20 carbon atoms, a cycloalkane monocarboxylic acid (B-3) having 4 to 8 carbon atoms, and an aromatic carboxylic acid (B-4).

[0020] <Alcohol (A)> The alcohol (A) contains a polyhydric alcohol represented by the formula (1). 1 From R 4 is R 1 From R 4 Among these, at least two are hydroxyl groups, and three or more hydroxyl groups are preferred. Examples of polyhydric alcohols include pentaerythritol, trimethylolpropane, trimethylolethane, and neopentyl glycol. From the viewpoint of improving the heat resistance and lubricity of the condensed ester, pentaerythritol, trimethylolpropane, and neopentyl glycol are preferred as polyhydric alcohols, and pentaerythritol is more preferred. As the alcohol (A), various monohydric alcohols or polyols can be appropriately used as alcohol components other than the polyhydric alcohol. The number of carbon atoms in the monohydric alcohol is typically 1 to 24, and the carbon chain may be either linear or branched, and may be either saturated or unsaturated. A dihydric to decahydric polyol is typically used.

[0021] 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; 1,2,4-butanetriol, 1,3,5-pentanetriol, and 1 , 2,6-hexanetriol, and other triol compounds; trimethylolalkane polymers such as dipentaerythritol and tripentaerythritol; polyglycerols such as glycerin, diglycerin, triglycerin, and tetraglycerin; and sugars such as sorbitol, sorbitan, sorbitol-glycerin condensates, adonitol, arabitol, xylitol, mannitol, xylose, arabinose, ribose, rhamnose, glucose, fructose, galactose, mannose, sorbose, cellobiose, maltose, isomaltose, trehalose, and sucrose.

[0022] <Carboxylic Acid (B)> The carboxylic acid (B) contains a fatty acid (B-1) having 5 to 9 carbon atoms, a branched fatty acid (B-2) having 15 to 20 carbon atoms, a cycloalkane monocarboxylic acid (B-3) having 4 to 8 carbon atoms, and an aromatic carboxylic acid (B-4). The carbon chain of the fatty acid (B-1) having 5 to 9 carbon atoms may be unsaturated or saturated, but is preferably saturated from the viewpoint of improving the heat resistance of the condensed ester. Furthermore, the fatty acid (B-1) preferably has 6 to 8 carbon atoms, more preferably 7, from the viewpoint of improving the heat resistance and lubricity of the condensed ester. 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-nonanoic acid, etc. From the viewpoint of 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.

[0023] 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, and phytanic acid. From the viewpoint of improving the heat resistance and 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. The cycloalkane monocarboxylic acid (B-3) having 4 to 8 carbon atoms may be substituted with an alkyl chain, and the alkyl chain may be linear or branched. From the viewpoint of improving the heat resistance of the condensed ester, the cycloring of the cycloalkane monocarboxylic acid (B-3) is preferably a 5- to 7-membered ring, and more preferably a 6-membered ring. Examples of the cycloalkane monocarboxylic acid (B-3) include cyclopropanecarboxylic acid, cyclobutanecarboxylic acid, cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cycloheptanecarboxylic acid, methylcyclohexanecarboxylic acid, etc. 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 acid, or methylcyclohexanecarboxylic acid, more preferably cyclohexanecarboxylic acid, cycloheptanecarboxylic acid, or methylcyclohexanecarboxylic acid, and even more preferably cyclohexanecarboxylic acid.

[0024] The aromatic carboxylic acid (B-4) may be substituted with an alkyl chain, and the alkyl chain may be linear or branched. 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. Examples of the aromatic carboxylic acid (B-4) include benzoic acid, toluic acid, dimethylbenzoic acid, trimethylbenzoic acid, and naphthoic acid. Benzoic acid is preferred from the viewpoint of improving the heat resistance of the condensed ester. Regarding the carboxylic acid (B), various carboxylic acids (hereinafter also referred to as "other carboxylic acid compounds") can be appropriately used as carboxylic acid components other than the components (B-1) to (B-4). Examples of other carboxylic acid compounds include capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid. The amounts of each component of the condensed ester in the grease composition of the present invention are described below. In the alcohol (A), the proportion of the polyhydric alcohol represented by the formula (1) is preferably 80 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, even more preferably 98 mol% or more, and even more preferably 100 mol%.

[0025] The proportion of the fatty acid (B-1) in the carboxylic acid (B) is 30 to 50 mol %. The proportion of the fatty acid (B-1) in the carboxylic acid (B) is preferably 35 mol % or more from the viewpoint of improving the heat resistance and lowering 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. The proportion of the branched fatty acid (B-2) in the carboxylic acid (B) is 30 mol % or more and 50 mol % or less. The proportion of the branched fatty acid (B-2) in the carboxylic acid (B) is preferably 35 mol % or more from the viewpoint 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 decreasing the kinematic viscosity of the condensed ester. The proportion of the cycloalkane monocarboxylic acid (B-3) in the carboxylic acid (B) is 10 mol % or more and 30 mol % or less. The proportion of the cycloalkane monocarboxylic acid (B-3) in the carboxylic acid (B) is preferably 12 mol% or more from the viewpoint of improving the heat resistance of the condensed ester, and is preferably 25 mol% or less from the viewpoint of improving the lubricity of the condensed ester.

[0026] The proportion of the aromatic carboxylic acid (B-4) in the carboxylic acid (B) is 1 to 15 mol %. From the viewpoints of improving the heat resistance and increasing the kinematic viscosity of the condensed ester, the proportion of the aromatic carboxylic acid (B-4) in the carboxylic acid (B) is preferably 2 mol % or more, and from the viewpoint of decreasing the kinematic viscosity of the condensed ester, the proportion is preferably 13 mol % or less. From the viewpoint of improving the low-temperature storage stability of the condensed ester, the molar ratio ((B-3) / (B-4)) of the cycloalkane monocarboxylic acid (B-3) to the aromatic carboxylic acid (B-4) in the carboxylic acid (B) is preferably 0.5 to 20. From the viewpoint of improving the low-temperature storage stability of the condensed ester, the molar ratio ((B-3) / (B-4)) of the cycloalkane monocarboxylic acid (B-3) to the aromatic carboxylic acid (B-4) in the carboxylic acid (B) is preferably 0.8 or more, and preferably 15 or less, more preferably 12 or less. The total proportion 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) in the carboxylic acid (B) is preferably 80 mol % or more, more preferably 90 mol % or more, even more preferably 95 mol % or more, even more preferably 98 mol % or more, and even more preferably 100 mol % from the viewpoint of improving the heat resistance and lubricity of the condensed ester. 2 / s or more, and 2 / s or more is more preferable, and 110 mm 2 / s or less, and 2 From the viewpoint of improving lubrication properties at high temperatures, the condensed ester in the grease composition of the present invention preferably has a 100°C kinematic viscosity of 11 mm / s or less. 2 / s or more, and 11.5 mm 2 / s or more is more preferable, and 14 mm 2 / s or less, and 13 mm 2 It is more preferable that the ratio is 1 / s or less.

[0027] <Method for Preparing Condensed Ester> The condensed ester can be prepared by subjecting the alcohol (A) and the carboxylic acid (B) to an esterification reaction according to a known method. In the reaction between the alcohol (A) and the carboxylic acid (B), the equivalent ratio between the two is typically adjusted so that, from the viewpoint of accelerating the esterification reaction, the carboxyl groups of the carboxylic acid component of the carboxylic acid (B) are preferably 1.05 to 1.5 equivalents, more preferably 1.1 to 1.3 equivalents, per equivalent of the hydroxyl groups of the alcohol component of the alcohol (A). While increasing the ratio of carboxyl groups of the carboxylic acid component of the carboxylic acid (B) improves the reactivity between the alcohol component and the carboxylic acid component, it is necessary to remove excess carboxylic acid (B) after the reaction is complete. Examples of such removal methods include vacuum distillation, steaming, adsorption using an adsorbent, and removal. The ester-based synthetic oil of the present invention may be a so-called biomass oil produced from biological resources derived from animals and plants. For example, biomass ester oils synthesized from various fatty acids and alcohols using vegetable oil as a raw material can also be used. The base oil may be used alone or in combination of two or more.

[0028] The ester-based base oil of the present invention preferably consists solely of a condensation ester of a polyhydric alcohol represented by formula (1) and the carboxylic acid (B). Among these, an ester oil in which the molar 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 more preferred. In particular, an ester compound of pentaerythritol and a carboxylic acid (B) that is a mixture of 37.5 mol% n-heptane (B-1), 37.5 mol% isostearic acid (B-2), 22.5 mol% cyclohexanecarboxylic acid (B-3), and 2.5 mol% benzoic acid (B-4) in the carboxylic acid (B) is preferred. The content of the ester-based synthetic oil of the present invention is preferably 84 to 74 mass%, more preferably 81 to 77 mass%, and even more preferably 80 to 77 mass%, based on the total mass of the composition. By including the base oil in such a ratio, high-temperature durability is improved. The content of the ester oil represented by the formula (1) is preferably 60 to 100 mass%, more preferably 80 to 100 mass%, and even more preferably 100 mass%, based on the total mass of the base oil. By including the base oil in such a proportion, particularly good high-temperature durability is achieved.

[0029] <Amine Phosphate> The amine phosphate in the grease composition of the present invention is not particularly limited. Suitable examples include tertiary alkylamine dimethyl phosphate and phenylamine phosphate. Tertiary alkylamine dimethyl phosphate is more preferred. Commercially available amine phosphates include Vanlube 672 (tertiary alkylamine dimethyl phosphate) manufactured by RT Vanderbilt and Vanlube 692 (phenylamine phosphate) manufactured by RT Vanderbilt. The number of carbon atoms in the tertiary alkylamine dimethyl phosphate is not particularly limited and can be, for example, 1 to 24. The content of the amine phosphate is 0.2 to 2.5 mass%, preferably 0.3 to 1.0 mass%, and more preferably 0.4 to 0.7 mass%, based on the total mass of the grease composition. At 0.2 mass % or more, sufficient fretting resistance is exhibited, and on the other hand, even if it exceeds 2.5 mass %, the fretting suppression effect is exerted, but the effect saturates, so from an economical viewpoint, 2.5 mass % or less is preferable.

[0030] <Carboxylic Acid-Based Rust Inhibitor> Examples of the carboxylic acid-based rust inhibitor in the grease composition of the present invention include monocarboxylic acids such as straight-chain fatty acids such as lauric acid and stearic acid, and saturated carboxylic acids having a naphthenic nucleus; dicarboxylic acids such as succinic acid, alkylsuccinic acids, alkylsuccinic acid half esters, alkenylsuccinic acids, alkenylsuccinic acid half esters, succinic acid derivatives such as succinimides, tetrapropenylbutanedioic acid, hydroxy fatty acids, mercapto fatty acids, and sarcosine derivatives. Of these, 2-tetrapropenylsuccinic acid half esters and tetrapropenylbutanedioic acid are preferred, and combinations of these are particularly preferred.

[0031] The content of the carboxylic acid-based rust inhibitor in the grease composition of the present invention is determined by the ratio to the content of the amine phosphate. It 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, per 1 part by mass of amine phosphate. At 0.5 parts by mass or more, sufficient rust prevention can be ensured to compensate for the decrease in rust prevention performance due to the high reactivity of the amine phosphate with metal surfaces. On the other hand, if the content exceeds 4 parts by mass, the adsorption of the rust inhibitor to the metal surface may outweigh the reactivity of the amine phosphate, resulting in sufficient rust prevention but poor fretting resistance. The grease composition of the present invention may also contain a rust inhibitor other than the carboxylic acid-based rust inhibitor, such as an ester-based rust inhibitor, but the amount thereof is at most 3.5 parts by mass per 1 part by mass of amine phosphate. If the content exceeds 3.5 parts by mass, the adsorption of the rust inhibitor to the metal surface may outweigh the reactivity of the amine phosphate, resulting in sufficient rust prevention but poor fretting resistance. The grease composition of the present invention does not contain either a carboxylate-based rust inhibitor or an amine salt of a fatty acid. If a carboxylate-based rust inhibitor or an amine salt of a fatty acid is contained, the reactivity of the amine phosphate may be greater than the adsorption of the rust inhibitor to the metal surface, resulting in poor rust prevention although sufficient fretting resistance.

[0032] Antioxidant: The grease composition of the present invention contains an antioxidant. The antioxidant contributes to high-temperature durability. The antioxidant used in the present invention may be an amine-based antioxidant, a phenol-based antioxidant, or a mixture thereof. A mixture of these is preferred. <Amine-Based Antioxidant> The amine-based antioxidant that can be used in the grease composition of the present invention is preferably selected from the group consisting of alkyldiphenylamine, N-phenyl-α-naphthylamine, alkylated phenyl-α-naphthylamine, and a mixture thereof. Of these, alkyldiphenylamine is more preferred, and alkyldiphenylamine, which is a reaction product of N-phenylbenzenamine and 2,2,4-trimethylpentene, is particularly preferred. The content of the amine-based antioxidant in the grease composition of the present invention is preferably 0.5 to 5 mass%, more preferably 1 to 3 mass%, and even more preferably 1.5 to 2.5 mass%. A content of 0.5 mass% or more exhibits sufficient antioxidant effect against oxidative degradation. On the other hand, although antioxidant effect is exhibited at more than 5 mass%, the effect saturates. Therefore, from an economical viewpoint, 5 mass% or less is preferred.

[0033] <Phenol-Based Antioxidant> The phenol-based antioxidant that can be used 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 thereof. Of these, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate is particularly preferred. The content of the phenol-based antioxidant in the grease composition of the present invention is preferably 0.5 to 5 mass%, more preferably 0.5 to 3 mass%, and even more preferably 0.8 to 2 mass%. A content of 0.5 mass% or more exhibits a sufficient effect of preventing oxidative degradation. On the other hand, although the antioxidant effect is still exhibited at levels exceeding 5 mass %, the effect saturates, and therefore from an economical point of view, a level of 5 mass % or less is preferable.A particularly preferred antioxidant for use in the grease composition of the present invention is a combination of an alkyldiphenylamine, which is a reaction product of N-phenylbenzeneamine and 2,2,4-trimethylpentene, and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate.

[0034] When the grease composition of the present invention contains a mixture of an amine-based antioxidant and a phenol-based antioxidant as the antioxidant, the total amount thereof is preferably 1 to 10 mass%, more preferably 1.5 to 6 mass%, and even more preferably 2.3 to 4.5 mass%, based on the total mass of the composition. By containing a mixture of an amine-based antioxidant and a phenol-based antioxidant in such a ratio, a particularly effective antioxidant effect can be achieved. When the grease composition of the present invention contains a mixture of an alkyldiphenylamine, which is a reaction product of N-phenylbenzenamine and 2,2,4-trimethylpentene, and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate as the antioxidant, the total amount thereof is preferably 1 to 10 mass%, more preferably 1.5 to 6 mass%, and even more preferably 2.3 to 4.5 mass%, based on the total mass of the composition. By containing a mixture of an alkyldiphenylamine, which is a reaction product of N-phenylbenzenamine and 2,2,4-trimethylpentene, and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate in such a ratio, a particular antioxidant effect can be exhibited.

[0035] Optional Additives General-purpose additives may be added to the grease composition of the present invention as needed. Examples of such additives include the following: Anti-Strip Additives <Organic Sulfonate Metal Salts> Examples of organic sulfonate metal salts in the grease composition of the present invention include those represented by the following formula (4). Zinc salts are preferred. [R10-SO3]M2 Formula (4) In 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 or alkenyl group is linear or branched and has 2 to 22 carbon atoms. M2 represents an alkaline earth metal or zinc, preferably zinc or calcium. Zinc dinonylnaphthalene sulfonate is particularly preferred. The content of the organic sulfonate metal salt in the grease composition of the present invention is typically 0.5 to 5 mass%, preferably 1 to 3 mass%, and more preferably 1.5 to 2.5 mass%.

[0036] <Metal Dialkyldithiophosphate> The metal dialkyldithiophosphate in the grease composition of the present invention may be one represented by the following formula (3): [(RO)(RO)P(=S)-S]-M1 x O m S n ...Formula (3) In formula (3), R8 and R9 are alkyl groups having 1 to 24 carbon atoms or aryl groups having 6 to 30 carbon atoms, and the alkyl groups may be linear or branched and may be primary, secondary, or tertiary. M1 is zinc or molybdenum, preferably zinc. x is 1 or 2, and n and m are each 0 to 4. The content of the dialkyldithiophosphate metal salt in the grease composition of the present invention is usually 0.5 to 3 mass%, preferably 0.5 to 3 mass%, and more preferably 0.8 to 2 mass%.

[0037] Extreme pressure agents Phosphorus compounds: tricresyl phosphate, tri-2-ethylhexyl phosphate, etc. Sulfur compounds: dibenzyl disulfide, various polysulfides, etc. Sulfur-phosphorus compounds: triphenyl phosphorothioate Organometallic extreme pressure agents: dialkyldithiocarbamic acid salts of Zn, Mo, Sb, Ni, Cu, Bi, etc., ashless dithiocarbamate, ashless dithiophosphate carbamate, etc. Solid lubricants: molybdenum disulfide, graphite, PTFE, MCA, etc. Metal corrosion inhibitors: benzotriazole or its derivatives, zinc oxide, etc. Oily agents: sorbitan trioleate, sorbitan monooleate, etc.

[0038] It is preferable that the additive of the present invention contains: an amine phosphate which is at least one selected from the group consisting of tertiary alkylamine dimethyl phosphate and phenylamine phosphate; a carboxylic acid-based rust inhibitor which is at least one selected from the group consisting of 2-tetrapropenyl succinic acid half ester and tetrapropenyl butanedioic acid; and an antioxidant which is at least one selected from the group consisting of an alkyldiphenylamine which is a reaction product of N-phenylbenzenamine and 2,2,4-trimethylpentene and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and does not contain any of a carboxylate-based rust inhibitor and an amine salt of a fatty acid.

[0039] In this embodiment, it is more preferable that the content of the amine phosphate in the composition is 0.3 to 1.0 mass % and the content of the carboxylic acid-based rust inhibitor is 0.8 to 3 mass parts per 1 mass part of the amine phosphate.

[0040] In this embodiment, it is preferable to further include an anti-peeling additive, and the anti-peeling additive is more preferably at least one selected from the group consisting of organic metal sulfonates and metal dialkyldithiophosphates, and even more preferably at least one selected from the group consisting of zinc dinonylnaphthalenesulfonate and zinc dialkyldithiophosphate.

[0041] It is more preferred that the additive of the present invention comprises or consists of: an amine phosphate which is tertiary alkylamine dimethyl phosphate; a carboxylic acid-based rust inhibitor which is a mixture of 2-tetrapropenyl succinic acid half ester and tetrapropenyl butanedioic acid; an antioxidant which is a mixture of an alkyldiphenylamine which is a reaction product of N-phenylbenzenamine and 2,2,4-trimethylpentene and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; and an anti-exfoliation additive which is a mixture of zinc dinonylnarethenesulfonate and zinc dialkyldithiophosphate, and that the additive does not contain any of a carboxylate-based rust inhibitor and an amine salt of a fatty acid.

[0042] In this embodiment, it is more preferable that the content of the amine phosphate in the composition is 0.4 to 0.7 mass % and the content of the carboxylic acid-based rust inhibitor is 1 to 2 mass parts per 1 mass part of the amine phosphate.

[0043] In any of the above-mentioned preferred aspects of the additive, it is particularly preferred that the thickener is an alicyclic aliphatic diurea compound containing a diurea compound represented by formula (2) in which one of R5 and R7 is a cyclohexyl group and the other is a linear alkyl group having 18 carbon atoms, the proportion of the number of moles of cyclohexyl groups being 83.3 mol%, and the base oil is an ester compound of pentaerythritol and a 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 monocarboxylic acid (B-3), and 2.5 mol% of benzoic acid (B-4) in the carboxylic acid (B).

[0044] The grease composition of the present invention has excellent high-temperature durability, fretting resistance, and rust prevention properties, and is therefore suitable for use in rolling bearings of automobile electrical components, household electrical appliances used at high speeds and high temperatures, such as cleaner motors, and rolling bearings of continuous casting equipment that is lubricated at high temperatures, etc. Among these, the grease composition is particularly suitable as a grease for use in rolling bearings for automobile electrical accessory parts, which require both high high-temperature durability and fretting resistance and rust prevention properties.

[0045] <Preparation of Grease Composition> A predetermined amount of amine (a mixture of cyclohexylamine and stearylamine in the molar ratio shown in the table below) was reacted in the base oil shown in the table below at a ratio of 2 moles per mole of 4,4'-diphenylmethane diisocyanate (MDI), the mixture was heated, cooled, and then further diluted with the base oil. The additives shown in the table below were added, and the mixture was adjusted so that the worked penetration after 60 strokes on a triple roll mill was 280 (measured according to JIS K2220 7). The kinematic viscosities of the base oils at 40°C and 100°C (measured according to JIS K2220 23) were as follows. Unless otherwise specified, the numbers in the table indicate mass % based on the total mass of the composition. The remainder is base oil.

[0046] Ester: 93mm 2 / s (an ester compound of pentaerythritol and a 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 monocarboxylic 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: 393mm 2 / s Mineral oil A: 101mm 2 / s Mineral oil B: 39.5mm 2 / s

[0047] <Test method and judgment> [Heat resistance (bearing lubrication life test)] Evaluation method The test was conducted using a bearing lubrication life tester conforming to ASTM D3336. The test conditions are shown below. The seizure life was defined as the shorter of the time until the motor generated an overcurrent (4 amperes) or until the bearing temperature rose by +15°C. Bearing type: 6204 metal seal Test temperature: 180°C Rotation speed: 10,000 rpm Amount of grease: 1.8 g Test load: Axial load 66.7 N Radial load 66.7 N Judgment Bearing lubrication life 1,000 hours or more...○ (pass) Less than 1,000 hours...× (fail)

[0048] [Rust prevention (bearing rust prevention test)] Evaluation method: This was performed in accordance with ASTM D1743-73. The test grease was filled into a bearing (32304J) and rotated at 1750 rpm for 10 seconds while applying an axial load of 26.5 N. The grease weight was then adjusted to 3.5 g and the bearing was rotated for an additional 60 seconds under the same conditions. The bearing was then immersed in 1% salt water for 10 seconds, and then left to stand at 52°C and 100% humidity for 48 hours. After cleaning, the state of rust on the outer ring raceway of the bearing was visually inspected. Evaluation: #1 (no rust)...○ (pass); #2 (three or fewer visually visible rust spots)...× (fail); #3 (larger rust than #2 or four or more visually visible rust spots)...× (fail).

[0049] [Fretting resistance (fretting test)] Evaluation method The test grease was applied to two pairs of thrust bearings listed below, and the specified oscillation operation was performed to determine the amount of wear (weight loss due to fretting wear). Bearing: 51204 thrust bearing Load: 4000 N (surface pressure: 1.9 GPa) Oscillation angle: ±6° Oscillation cycle: 25 Hz Time: 2 h Temperature: 25°C Amount of grease packed: 1.0 g per bearing pair Wear amount: Race mass loss per bearing pair (total mass loss of test bearing races / 2) Evaluation Wear amount Less than 7 mg...○ (pass) 7 mg or more...× (fail)

[0050]

[0051]

[0052] Examples 1 to 4 pass the high-temperature durability, rust prevention, fretting resistance, and peeling resistance tests. Comparative Examples 1 and 2, which use PAO or mineral oil as the base oil instead of ester oil, fail to provide satisfactory high-temperature durability. Comparative Examples 3 and 5, which contain more than 4 parts by mass of rust inhibitor per 1 part by mass of amine phosphate, pass the rust prevention test but fail to provide satisfactory fretting resistance. Comparative Examples 4 and 6, which contain less than 0.5 parts by mass of rust inhibitor per 1 part by mass of amine phosphate, pass the fretting resistance test but fail to provide satisfactory rust prevention. Comparative Examples 7 to 11, which contain carboxylic acid salts, fatty acid amine salts, esters, oxidized wax, or organic sulfonic acid barium salts, fail to provide satisfactory rust prevention. Comparative Example 12, which does not contain an antioxidant, fails to provide satisfactory high-temperature durability. Therefore, it can be said that the grease composition of the present invention is capable of providing satisfactory high-temperature durability, rust prevention, and fretting resistance.

Claims

1. A grease composition for rolling bearings comprising a thickener, a base oil and an additive, wherein the thickener is a diurea compound represented by the formula (2): R5-NHCONH-R6-NHCONH-R7 ... (2) (wherein R6 represents a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R5 and R7 may be the same or different and represent a cyclohexyl group, or a linear or branched alkyl group having 8 to 22 carbon atoms). The base oil has a kinetic viscosity of 60 mm at 40°C. 2 / s or more, the additives include an amine phosphate, a carboxylic acid-based rust inhibitor, and an antioxidant, the content of the amine phosphate is 0.2 to 2.5 mass% based on the total mass of the composition, the content of the carboxylic acid-based rust inhibitor is 0.5 to 4 parts by mass per 1 part by mass of the amine phosphate, and the content of the other rust inhibitor is 3.5 parts by mass or less per 1 part by mass of the amine phosphate, and the grease composition for rolling bearings contains neither a carboxylate-based rust inhibitor nor an amine salt of a fatty acid.

2. The base oil contains a condensation ester of an alcohol (A) and a carboxylic acid (B) and has a kinetic viscosity of 80 to 110 mm at 40°C. 2 / s, and the alcohol (A) is represented by the formula (1):

2. The grease composition for a rolling bearing according to claim 1, wherein the grease composition contains a polyhydric alcohol represented by formula (1): (in formula (1), R1 to R4 independently represent a hydrogen atom, a methyl group, or a hydroxyl group, and at least two of R1 to R4 represent a hydroxyl group), the carboxylic acid (B) contains a fatty acid (B-1) having from 5 to 9 carbon atoms, a branched fatty acid (B-2) having from 15 to 20 carbon atoms, a cycloalkane monocarboxylic acid (B-3) having from 4 to 8 carbon atoms, and an aromatic carboxylic acid (B-4), and in the carboxylic acid (B), a proportion of the fatty acid (B-1) is 30 to 50 mol %, a proportion of the branched fatty acid (B-2) is 30 to 50 mol %, a proportion of the cycloalkane monocarboxylic acid (B-3) is 10 to 30 mol %, and a proportion of the aromatic carboxylic acid (B-4) is 1 to 15 mol %.

3. A grease composition for rolling bearings according to claim 1, wherein the amine phosphate is tertiary alkylamine dimethyl phosphate or phenylamine phosphate.

4. A grease composition for rolling bearings as recited in claim 1, wherein the thickener is an alicyclic aliphatic diurea compound in which, in formula (2), the ratio 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. A grease composition for rolling bearings according to claim 1, comprising, as the antioxidants, 0.5 to 5 mass % of an amine-based antioxidant and 0.5 to 5 mass % of a phenol-based antioxidant, based on the total mass of the composition.

6. The rolling bearing grease composition according to claim 1, further comprising an anti-flaking additive.

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

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