Grease composition for rolling bearing

Abstract

To provide a grease composition for a rolling bearing, which is excellent in high temperature durability, fretting resistance, and rust prevention.SOLUTION: A grease composition for a rolling bearing comprises: a diurea thickener of formula (2): R5-NHCONH-R6-NHCONH-R7 (in the formula, R6 is a 6-15C divalent aromatic hydrocarbon group, and R5 and R7 may be the same or different, and indicate a cyclohexyl group or a 8-22C linear or branched alkyl group); an ester-based synthetic base oil having a kinematic viscosity of 60 mm2 / s or more at 40°C; 0.2 to 2.5 wt.% of amine phosphate based on a total mass of the composition; and a carboxylic acid-based rust inhibitor in a range of 0.5 to 4 mass% per mass% of the amine phosphate, wherein the grease composition does not contain either a carboxylate-based rust inhibitor or an amine salt of fatty acid.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a grease composition for rolling bearings, particularly to a grease composition suitable for filling rolling bearings lubricated at high temperatures, such as those in automotive electrical components that are directly connected to or located in the vicinity of an engine, which is a heat generating body, household electrical appliances that rotate at high speeds and high temperatures, such as cleaner motors, and continuous casting equipment. [Background technology]

[0002] The rolling bearings used in various industrial machines are operated in a variety of environments, from cold climates to high-temperature environments such as the inside of an automobile engine compartment. As such, rolling bearings are required to be able to operate over a wide temperature range and for long periods of time without maintenance, and the demands regarding durability are constantly increasing. Ester oils are known as base oils with excellent heat resistance. It has been disclosed 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 (Patent Document 1).

[0003] (Prior art regarding fretting resistance) In addition, 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 grease-filled bearings. Fretting is surface damage that occurs under very small amplitudes. In the atmosphere, it generates oxidized wear particles, whose abrasive action often results in severe wear (Non-Patent Document 1). Proposed measures to prevent fretting include (1) reducing the amount of relative sliding, (2) separating the two surfaces and preventing direct contact, and (3) preventing adhesion between surfaces by coating the contact surfaces with a phosphate coating or by supplying lubricating oil or grease (Non-Patent Document 1). In addition, a grease composition that contains an alicyclic aliphatic diurea thickener and an amine phosphate has been disclosed as a grease composition that is excellent in suppressing fretting wear under more severe conditions (-30°C or lower, very small amplitude) (Patent Document 2).

[0004] (Conventional technology regarding rust prevention) On the other hand, for example, rolling bearings used in automotive electrical accessories are often installed under the engine compartment, so they are easily exposed to rainwater while the car is running. Also, 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 anti-rust properties. As a grease composition having excellent rust-preventing properties, a grease composition containing a carboxylic acid-based rust inhibitor, a carboxylate-based rust inhibitor, and an amine-based rust inhibitor is known (Patent Document 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7216563 [Patent Document 2] Patent No. 6040750 [Patent Document 3] Patent No. 5714922 [Non-patent literature]

[0006] [Non-Patent Document 1] Yuji Yamamoto et al.: Tribology, Rikogakusha, February 28, 1998, pp. 201-203 Summary of the Invention [Problem to be solved by the invention]

[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 having excellent heat resistance. However, ester oils are generally said to have poor fretting resistance. On the other hand, Patent Document 2 discloses a grease composition containing an amine phosphate as a grease composition having excellent fretting resistance. However, due to its high reactivity with metal surfaces, the amine phosphate may deteriorate the rust prevention properties. Furthermore, Patent Document 3 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, if these rust inhibitors are present in excessive amounts, they may inhibit the function of the amine phosphate and deteriorate the fretting resistance. The above-mentioned conventional technologies are excellent in terms of high-temperature durability, fretting resistance, and rust resistance, but do not fully satisfy all of these performances, and there is a problem in particular in achieving both fretting resistance and rust resistance. 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. [Means for solving the problem]

[0008] We have overcome the above-mentioned problems by selecting the 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, The thickener is a diurea compound represented by formula (2), R5-NHCONH-R6-NHCONH-R7 (2) (In the formula, 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% by 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 relative to 1 part by mass of the amine phosphate, and the content of the other rust inhibitor is 3.5 parts by mass or less relative to 1 part by mass of the amine phosphate; However, the grease composition for rolling bearings does not contain any of a carboxylate-based rust inhibitor and 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):

[0009] TIFF2025025759000001.tif52127

[0010] (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 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); 2. The grease composition for rolling bearings according to 1 above, wherein, 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 1 or 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 comprise 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 comprising an anti-flaking additive. 7. The grease composition for rolling bearings 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. Effect of the Invention

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

[0012] [Figure 1] Schematic diagram of the four-ball rolling test DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Thickener The fluidity of grease in a bearing in a high-temperature environment varies depending on the type of thickener, and this has a large influence on the lubrication life of the bearing. In order for the grease to have a long lubrication life, it is necessary for the grease to remain in the lubricated parts at all times 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) (In the formula, R6 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R5 and R7 may be the same or different and are 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 formulas: Of these, a diphenylmethane group is most preferred.

[0014] TIFF2025025759000002.tif32170

[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 preferable. A linear alkyl group having 18 carbon atoms is most preferable. In formula (2), a diurea compound is preferred in which 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 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%, and more preferably 80 to 90 mol%. At 70 mol% or more, softening and leakage of the grease composition in high temperature environments can be particularly sufficiently prevented, and at 90 mol% or less, particularly sufficient flowability can be ensured and excellent high temperature durability can be ensured. As the thickener of the present invention, 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 the proportion of the number of moles of the cyclohexyl group is particularly preferred. 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 obtain 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 it 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 it is more than 19 mass%, the fluidity is poor, so the grease is difficult to penetrate into the lubricated parts, and the lubrication life may not be satisfied.

[0017] 〇Base oil The base oil used in the present invention has a kinematic viscosity of 60 mm at 40°C. 2 / s or higher. Ester-based synthetic oils have excellent high-temperature durability. From the viewpoint of high temperature durability, ester-based synthetic oils have a kinetic viscosity of 80mm at 40°C. 2 / s or more is preferable, and 90 mm 2 / s or more is preferable, and 110 mm 2 / s or less is preferable, and 100 mm 2 It is more preferable that the ratio is equal to or less than 1 / s. In order to improve lubrication at high temperatures, ester-based synthetic oils are also recommended with a kinetic viscosity of 11mm at 100°C. 2 / s or more is preferable, and 11.5 mm 2 / s or more is preferable, and 14 mm 2 / s or less is preferable, and 13 mm 2 It is more preferable that the ratio is equal to or less than 1 / s. 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] TIFF2025025759000003.tif52127

[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 At least two of the groups represent hydroxyl groups.) Contains a polyhydric alcohol represented by 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). R in the above formula (1) 1 From R 4 is R 1 From R 4Among them, at least two are hydroxyl groups, and three or more 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, the polyhydric alcohol is preferably pentaerythritol, trimethylolpropane, or neopentyl glycol, and more preferably pentaerythritol. In addition, various monohydric alcohols or polyols can be appropriately used as the alcohol component other than the polyhydric alcohol for the alcohol (A). The number of carbon atoms of the monohydric alcohol is usually 1 to 24, and the carbon chain may be either linear or branched, and may be either saturated or unsaturated. As the polyol, one having a hydricity of 2 to 10 is usually 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) includes 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 fatty acid (B-1) having 5 to 9 carbon atoms may have an unsaturated or saturated carbon chain, but is preferably saturated from the viewpoint of improving the heat resistance of the condensed ester. 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-methyl valeric acid, 4-methyl valeric acid, n-hexanoic acid, 2-methyl hexanoic acid, 5-methyl hexanoic acid, 4,4-dimethyl pentanoic acid, n-heptanoic acid, 2-methyl heptanoic acid, 2-ethyl hexanoic acid, 2,2-dimethyl hexanoic acid, n-octanoic acid, 3,5,5-trimethyl hexanoic 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, isoarachic acid, phytanic acid, etc. 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, isoarachic acid, and more preferably isostearic acid, 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. The cycloring of the cycloalkane monocarboxylic acid (B-3) is preferably a 5- to 7-membered ring, more preferably a 6-membered ring, from the viewpoint of improving the heat resistance of the condensed ester. Examples of the cycloalkane monocarboxylic acid (B-3) include cyclopropane carboxylic acid, cyclobutane carboxylic acid, cyclopentane carboxylic acid, cyclohexane carboxylic acid, cycloheptane carboxylic acid, methylcyclohexane carboxylic acid, etc. From the viewpoint of improving the heat resistance of the condensed ester, the cycloalkane monocarboxylic acid (B-3) is preferably cyclopentane carboxylic acid, cyclohexane carboxylic acid, cycloheptane carboxylic acid, or methylcyclohexane carboxylic acid, more preferably cyclohexane carboxylic acid, cycloheptane carboxylic acid, or methylcyclohexane carboxylic acid, and further preferably cyclohexane carboxylic acid.

[0024] The aromatic carboxylic acid (B-4) may be substituted with an alkyl chain, and the alkyl chain may be a straight chain or a branched chain. 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, and from the viewpoint of improving the heat resistance of the condensed ester, benzoic acid is preferred. The carboxylic acid (B) may be any of various carboxylic acids (hereinafter also referred to as other carboxylic acid compounds) 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 of the condensed ester components contained in the grease composition of the present invention will now be described. 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 ratio of the fatty acid (B-1) in the carboxylic acid (B) is 30 to 50 mol %. The ratio 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 decreasing the kinetic viscosity of the condensed ester, and is preferably 40 mol % or less from the viewpoint of increasing the kinetic 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 kinetic viscosity of the condensed ester, and is preferably 40 mol % or less from the viewpoint of decreasing the kinetic viscosity of the condensed ester. The ratio of the cycloalkane monocarboxylic acid (B-3) in the carboxylic acid (B) is 10 mol% or more and 30 mol% or less. The ratio 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 %. The proportion of the aromatic carboxylic acid (B-4) in the carboxylic acid (B) is preferably 2 mol % or more from the viewpoint of improving the heat resistance and increasing the kinetic viscosity of the condensed ester, and is preferably 13 mol % or less from the viewpoint of decreasing the kinetic viscosity of the condensed ester. In the carboxylic acid (B), the molar ratio ((B-3) / (B-4)) of the cycloalkane monocarboxylic acid (B-3) and the aromatic carboxylic acid (B-4) is preferably 0.5 to 20, from the viewpoint of improving the low-temperature storage property of the condensed ester. In the carboxylic acid (B), the molar ratio ((B-3) / (B-4)) of the cycloalkane monocarboxylic acid (B-3) and 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 property of the condensed ester. In the carboxylic acid (B), 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) 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. From the viewpoint of high temperature durability, the condensed ester in the grease composition of the present invention has a kinetic viscosity of 40°C and a kinematic viscosity of 80mm 2 / s or more is preferable, and 90 mm 2 / s or more is more preferable, and 110 mm 2 / s or less is preferable, and 100 mm 2 From the viewpoint of improving lubrication properties at high temperatures, the condensed ester in the grease composition of the present invention has a 100°C kinetic viscosity of 11 mm / s or less, which will be described later. 2 / s or more is preferable, and 11.5 mm 2 / s or more is more preferable, and 14 mm 2 / s or less is preferable, and 13 mm 2 It is more preferable that the ratio is equal to or less than 1 / s.

[0027] <Method for preparing condensed ester> The condensed ester can be prepared by carrying out an esterification reaction between the alcohol (A) and the carboxylic acid (B) according to a known method. In the reaction of the alcohol (A) with the carboxylic acid (B), the equivalent ratio between them is usually adjusted so that the carboxyl group of the carboxylic acid component of the carboxylic acid (B) is preferably 1.05 to 1.5 equivalents, more preferably 1.1 to 1.3 equivalents, per equivalent of the hydroxyl group of the alcohol component of the alcohol (A), from the viewpoint of promoting the esterification reaction. If the ratio of the carboxyl group of the carboxylic acid component of the carboxylic acid (B) is increased, the reactivity between the alcohol component and the carboxylic acid component becomes good, but it is necessary to remove the excess carboxylic acid (B) after the reaction is completed. Examples of the removal method include vacuum distillation, steaming, adsorption using an adsorbent, removal, etc. 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, a biomass ester oil synthesized from various fatty acids and alcohols using vegetable oil as a raw material may be used. The base oil may be used alone or in combination of two or more.

[0028] The ester 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, ester oils in which the molar ratio of the cycloalkane monocarboxylic acid (B-3) to the aromatic carboxylic acid (B-4) ((B-3) / (B-4)) is 0.5 to 20 are more preferred. In particular, 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 cyclohexanecarboxylic acid (B-3), and 2.5 mol % of 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 further 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 ratio, high temperature durability is particularly good.

[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. As the amine phosphate, commercially available products such as Vanlube 672 (tertiary alkylamine-dimethyl phosphate) manufactured by RT Vanderbilt and Vanlube 692 (phenylamine phosphate) manufactured by RT Vanderbilt can be used. The number of carbon atoms in the tertiary alkyl portion of the tertiary alkylamine-dimethylphosphate is not particularly limited and may be, for example, 1-24. The content of the amine phosphate is 0.2 to 2.5 mass% based on the total mass of the grease composition, preferably 0.3 to 1.0 mass%, and more preferably 0.4 to 0.7 mass%. At 0.2 mass% or more, sufficient fretting resistance is exhibited, while at more than 2.5 mass%, the fretting suppression effect is exhibited, but the effect becomes saturated, so from an economical point of view, 2.5 mass% or less is preferable.

[0030] <Carboxylic acid-based rust inhibitor> The carboxylic acid-based rust inhibitor in the grease composition of the present invention may include, as monocarboxylic acids, for example, straight-chain fatty acids such as lauric acid and stearic acid, and saturated carboxylic acids having naphthenic nuclei; as dicarboxylic acids, for example, succinic acid, alkyl succinic acid, alkyl succinic acid half ester, alkenyl succinic acid, alkenyl succinic acid half ester, succinic acid imide and other succinic acid derivatives, tetrapropenyl butanedioic acid, hydroxy fatty acid, mercapto fatty acid, and sarcosine derivatives. Among these, 2-tetrapropenyl succinic acid half ester and tetrapropenyl butanedioic acid are preferred, and combinations thereof 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 the amine phosphate. When it is 0.5 parts by mass or more, sufficient rust prevention that can cover the decrease in rust prevention caused by the high reactivity of the amine phosphate to the metal surface can be ensured, while when it exceeds 4 parts by mass, the adsorption of the rust inhibitor to the metal surface is superior to the reactivity of the amine phosphate, and although the rust prevention is sufficient, the fretting resistance may be inferior. The grease composition of the present invention may contain a rust inhibitor other than the carboxylic acid-based rust inhibitor, for example, an ester-based rust inhibitor, but the amount is at most 3.5 parts by mass per part by mass of amine phosphate. If the amount exceeds 3.5 parts by mass, the adsorption of the rust inhibitor to the metal surface will be greater than the reactivity of the amine phosphate, and although the rust prevention properties are sufficient, the fretting resistance may be poor. 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 will be greater than the adsorption of the rust inhibitor to the metal surface, and although the fretting resistance is sufficient, the rust prevention properties may be poor.

[0032] Antioxidants The grease composition of the present invention contains an antioxidant, which 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. It is preferred to use a mixture thereof. <Amine-based antioxidants> The amine-based antioxidant that can be used 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 thereof, of which alkyldiphenylamines are more preferred, and alkyldiphenylamines which are reaction products of N-phenylbenzenamine and 2,2,4-trimethylpentene are 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%. At 0.5 mass% or more, a sufficient effect of preventing oxidative deterioration is exhibited. On the other hand, even if it exceeds 5 mass%, the effect of preventing oxidative deterioration is exhibited, but the effect becomes saturated, so from an economical point of view, 5 mass% or less is preferable.

[0033] <Phenol-based antioxidant> The phenolic 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 phenolic 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%. At 0.5 mass% or more, a sufficient effect of preventing oxidative deterioration is exhibited. On the other hand, even if it exceeds 5 mass%, the effect of preventing oxidative deterioration is exhibited, but the effect becomes saturated, so from an economical viewpoint, 5 mass% or less is preferable. As the antioxidant used in the grease composition of the present invention, 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 is particularly preferred.

[0034] When the grease composition of the present invention contains a mixture of an amine-based antioxidant and a phenol-based antioxidant as an antioxidant, the total amount 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 the mixture of the amine-based antioxidant and the phenol-based antioxidant in such a ratio, a particular antioxidant effect can be exhibited. 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 an antioxidant, the total amount 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 required, for example, the additives shown below. Anti-peeling additives <Organic sulfonic acid metal salt> The organic sulfonic acid metal salt in the grease composition of the present invention may be one represented by the following formula (4): Zinc salt is 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. In particular, zinc dinonylnaphthalene sulfonate is preferred. The content of the organic sulfonic acid metal salt in the grease composition of the present invention is usually 0.5 to 5 mass %, preferably 1 to 3 mass %, and more preferably 1.5 to 2.5 mass %.

[0036] <Dialkyldithiophosphate metal salt> The dialkyldithiophosphate metal salt in the grease composition of the present invention may be one represented by the following formula (3). [(RO)(RO)P(=S)-S]2-M1 x O m S n ...Equation (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, and is preferably zinc. x is 1 or 2, and n and m are 0 to 4. The content of the metal dialkyldithiophosphate 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; Triphenylphosphorothionate Organometallic extreme pressure agents: Dialkyldithiocarbamic acid salts of Zn, Mo, Sb, Ni, Cu, Bi, etc., ashless dithiocarbamates, ashless dithiophosphate carbamates, 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] The additive of the present invention 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; an antioxidant which is at least one selected from the group consisting of alkyldiphenylamines, which are reaction products of N-phenylbenzenamine and 2,2,4-trimethylpentene, and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; and preferably contains neither a carboxylate-based rust inhibitor nor 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-exfoliation additive, and the anti-exfoliation additive is more preferably at least one selected from the group consisting of metal salts of organic sulfonates and metal salts of dialkyldithiophosphates, and even more preferably at least one selected from the group consisting of zinc dinonylnaphthalenesulfonate and zinc dialkyldithiophosphate.

[0041] The additive of the present invention an amine phosphate which is a 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 the reaction product of N-phenylbenzenamine and 2,2,4-trimethylpentene, and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; A mixture of zinc dinonyl naltarene sulfonate and zinc dialkyl dithiophosphate as an anti-stripping additive. and more preferably contains neither a carboxylate-based rust inhibitor nor 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 parts by mass per 1 part by mass of the amine phosphate.

[0043] In any of the above preferred embodiments of the additive, 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 ratio of the number of moles of the cyclohexyl group being 83.3 mol %, It is particularly preferred that the base oil is an ester compound of pentaerythritol with 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 is excellent in high-temperature durability, fretting resistance, and rust prevention, and is therefore used for rolling bearings in automobile electrical components, household electrical appliances used at high speeds and high temperatures such as cleaner motors, and rolling bearings in continuous casting equipment lubricated at high temperatures, etc. Among these, the grease is particularly suitable as a grease for use in rolling bearings for automobile electrical accessory parts, which require both high high-temperature durability, fretting resistance, and rust prevention. EXAMPLES

[0045] <Preparation of grease composition> In the base oil shown in the table below, a predetermined amount of amine (a mixture of cyclohexylamine and stearylamine in the molar ratio shown in the table below) was reacted at a ratio of 2 moles per mole of 4,4'-diphenylmethane diisocyanate (MDI), heated, cooled, further diluted with base oil, and the additives shown in the table below were added to adjust the mixture to a worked penetration of 280 (measured according to JIS K2220 7.) when run 60 times on a three-roll mill. The kinetic viscosities of the base oil at 40°C and 100°C (measured according to JIS K2220 23.) are 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% n-heptane (B-1), 37.5 mol% isostearic acid (B-2), 22.5 mol% cyclohexane monocarboxylic acid (B-3), and 2.5 mol% benzoic acid (B-4) in the carboxylic acid (B). The kinetic 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: 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 carried out using a bearing lubrication life test machine conforming to ASTM D3336. The test conditions are as follows. The seizure life was defined as the time until the motor generated an overcurrent (4 amperes) or until the bearing temperature rose by +15°C, whichever was shorter. Bearing type: 6204 metal seal Test temperature: 180℃ Rotational speed: 10,000 rpm Grease quantity: 1.8g Test load: Axial load 66.7N Radial load 66.7N ·judgement Bearing lubrication life: 1000h or more...○(Pass) Less than 1000 hours: × (Fail)

[0048] [Rust prevention (bearing rust prevention test)] Evaluation method This was carried out 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, after which the weight of the grease was adjusted to 3.5 g and rotated under the same conditions for an additional 60 seconds.The bearing was then immersed in 1% salt water for 10 seconds, and left to stand at 52°C with 100% humidity for 48 hours, after which the condition of rust on the outer ring raceway of the bearing was visually inspected after cleaning. ·judgement #1 (No rust) ···○ (Pass) #2 (Less than 3 visible rust spots) × (Failed) #3 (Rust larger than #2 or 4 or more visible rust spots) ···× (Fail)

[0049] [Fretting resistance (fretting test)] Evaluation method The test grease was applied to two pairs of thrust bearings described below, and the specified oscillating operation was carried out to determine the amount of wear (weight loss due to fretting wear). Bearing: 51204 Thrust bearing Load: 4000N (surface pressure: 1.9GPa) Swing angle: ±6° Oscillation cycle: 25Hz Time: 2h Temperature: 25℃ Grease quantity: 1.0g per bearing Amount of wear: Loss in race mass per bearing set (total loss in test bearing race mass / 2) ·judgement Abrasion amount: Less than 7 mg: ○ (Pass) 7mg or more...×(fail)

[0050] [Table 1]

[0051] [Table 2]

[0052] In Examples 1 to 4, the high temperature durability, rust prevention, fretting resistance, and peeling resistance all pass the test. Comparative Examples 1 and 2, in which the base oil is not an ester oil but a PAO or a mineral oil, are not satisfactory in terms of high temperature durability. In Comparative Examples 3 and 5, in which the amount of the rust inhibitor was more than 4 parts by mass per part by mass of the amine phosphate, the rust prevention property was acceptable but the fretting resistance was unsatisfactory. In Comparative Examples 4 and 6, in which the amount of the rust inhibitor was less than 0.5 parts by mass per part by mass of the amine phosphate, the fretting resistance was acceptable but the rust prevention was unsatisfactory. Comparative Examples 7 to 11, which contain carboxylates, fatty acid amine salts, esters, oxidized wax, or organic barium sulfonates, are not satisfactory in terms of rust prevention properties. Comparative Example 12, which does not contain an antioxidant, is not satisfactory in terms of high temperature durability. Therefore, it can be said that the grease composition of the present invention is satisfactory in all respects of 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, The thickener is a diurea compound represented by formula (2), R5-NHCONH-R6-NHCONH-R7...(2) (In the formula, 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% by weight based on the total weight 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; However, the grease composition for rolling bearings does not contain any of a carboxylate-based rust inhibitor and 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 kinematic viscosity at 40° C. of 80 to 110 mm 2 / s, and the alcohol (A) is represented by the formula (1): (in formula (1), R1 to R4 each 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 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); 2. The grease composition for rolling bearings according to claim 1, wherein, 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. 2. The rolling bearing grease composition according to claim 1, wherein the amine phosphate is tertiary alkylamine dimethyl phosphate or phenylamine phosphate.

4. 2. The grease composition for rolling bearings according to 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 the linear or branched alkyl group having 8 to 22 carbon atoms is 70 to 90 mol %.

5. 2. The rolling bearing grease composition according to claim 1, wherein the antioxidants comprise 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. 7. The rolling bearing grease composition 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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