Grease composition for rolling bearing

Abstract

A grease composition for rolling bearings, which contains a diurea thickener represented by formula (2), an ester-based synthetic base oil having a kinematic viscosity at 40 DEG C of 60 mm2 / s or more, 0.2-2.5 mass% of an amine phosphate ester based on the total mass of the composition, and 0.5-4 parts by mass of a carboxylic acid-based rust inhibitor per 1 part by mass of the amine phosphate ester, and does not contain any one of a carboxylate-based rust inhibitor and an amine salt of a fatty acid. (1) 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. )

Description

Technical Field

[0001] This invention relates to grease compositions for rolling bearings. In particular, it relates to grease compositions suitable for use in rolling bearings that are lubricated at high temperatures, such as automotive electrical components, household appliances used in high-speed, high-temperature rotation, and continuous casting equipment, where the lubrication points are directly connected to or located near an engine that is a heat source. Background Technology

[0002] Rolling bearings used in various industrial machinery operate in a wide range of environments, from cold climates to high-temperature atmospheres such as the engine compartments of automobiles. Therefore, rolling bearings are required to be used over a wide temperature range and for extended periods without maintenance, and have high requirements related to durability.

[0003] Ester oils are known as base oils with excellent heat resistance. Grease base oils having specific alcohol-carboxylic acid condensation esters and grease compositions containing such grease base oils have been disclosed, exhibiting excellent heat resistance (Patent Document 1).

[0004] (Previous technologies regarding resistance to fretting wear)

[0005] In addition, automobiles, electrical products, and various mechanical parts are mostly transported by rail and truck. During this transportation, vibrations caused by the joints of the rails or poor road conditions can cause fretting wear in the grease-sealed bearings.

[0006] Micro-vibration wear is surface damage caused by small amplitude vibrations, which generates oxidized wear powder in the atmosphere. It can be said that severe wear often occurs due to its abrasive action (Non-Patent Literature 1).

[0007] As countermeasures to prevent fretting wear, (1) reducing relative sliding amount, (2) preventing separation and direct contact between the two surfaces, and (3) covering the contact surfaces with phosphate coating or preventing adhesion between surfaces caused by the supply of lubricating oil or grease are proposed (Non-Patent Document 1).

[0008] In addition, as a grease composition that effectively suppresses micro-vibration wear under more stringent conditions (below -30°C, with extremely small amplitude), a grease composition containing an alicyclic aliphatic diurea as a thickener and containing an aminophosphate ester has been disclosed (Patent Document 2).

[0009] (Existing technology regarding rust prevention)

[0010] On the other hand, rolling bearings used in automotive electrical auxiliary equipment are mostly installed in the lower part of the engine compartment, making them susceptible to rainwater accumulation during vehicle operation. Additionally, rolling bearings used in steel rolling mills operate in environments exposed to large amounts of water. Therefore, the grease used in rolling bearings also requires rust prevention.

[0011] As a grease composition with excellent rust prevention properties, grease compositions containing carboxylic acid-based rust inhibitors, carboxylate-based rust inhibitors, and amine-based rust inhibitors are known (Patent Document 3).

[0012] Existing technical documents

[0013] Patent documents

[0014] Patent Document 1: Japanese Patent No. 7216563

[0015] Patent Document 2: Japanese Patent No. 6040750

[0016] Patent Document 3: Japanese Patent No. 5714922

[0017] Non-patent literature

[0018] Non-patent literature 1: Yuji Yamamoto et al., Tribology, Rikogakusha, February 28, 1998, pp. 201-203. Summary of the Invention

[0019] The problem that the invention aims to solve

[0020] Patent Document 1 discloses a grease base oil having a specific alcohol and carboxylic acid condensation ester and a grease composition containing the grease base oil as a grease composition with excellent heat resistance, but it is generally believed that ester oils have poor resistance to fretting wear.

[0021] On the other hand, Patent Document 2 discloses a grease composition containing ammonium phosphate as a grease composition with excellent resistance to fretting wear, but due to the high reactivity of ammonium phosphate with metal surfaces, it sometimes deteriorates the rust prevention properties.

[0022] In addition, in Patent Document 3, as a grease composition with excellent rust prevention properties, there are known grease compositions containing carboxylic acid-based rust inhibitors, carboxylate-based rust inhibitors and amine-based rust inhibitors. However, if these rust inhibitors are present in excess, they may sometimes hinder the effect of amine phosphate esters, thus deteriorating the resistance to fretting wear.

[0023] In the aforementioned existing technologies, although each of them has excellent performance in terms of high temperature durability, resistance to fretting wear, and rust prevention, they cannot fully meet all these performance requirements, especially in terms of balancing resistance to fretting wear and rust prevention.

[0024] The present invention was made in view of the above-mentioned actual situation, and its purpose is to provide a grease composition for rolling bearings with excellent high-temperature durability, resistance to fretting wear and rust prevention.

[0025] Methods for solving problems

[0026] To address the aforementioned issues, we improved these properties by selecting appropriate base oils, thickeners, and additives. Specifically, according to the present invention, we provide the following grease composition for rolling bearings:

[0027] 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).

[0028] R5-NHCONH-R6-NHCONH-R7···(2)

[0029] In the formula, R6 represents a divalent aromatic hydrocarbon group with 6 to 15 carbon atoms, and R5 and R7 can be the same or different, representing a cyclohexyl group or a straight-chain or branched alkyl group with 8 to 22 carbon atoms.

[0030] The base oil mentioned above has a kinematic viscosity of 60 mm at 40°C. 2 The ester-based synthetic oil with a volume of / s or more contains amine phosphate, carboxylic acid rust inhibitor, and 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 rust inhibitor is 0.5 to 4 parts by mass relative to 1 part by mass of the amine phosphate. The content of other rust inhibitors is 3.5 parts by mass or less relative to 1 part by mass of the amine phosphate. The oil does not contain any of the carboxylic acid rust inhibitors or fatty acid amine salts.

[0031] 2. The grease composition for rolling bearings according to claim 1 above, wherein the base oil contains a condensation ester of alcohol (A) and carboxylic acid (B), and has a kinematic viscosity of 80-110 mm at 40°C. 2 / s, the above alcohol (A) contains a polyol represented by formula (1),

[0032]

[0033] (In formula (1), R1 to R4 independently represent hydrogen atoms, methyl groups or hydroxyl groups, and at least two of R1 to R4 represent hydroxyl groups.)

[0034] The aforementioned carboxylic acid (B) contains fatty acids with 5 or more but less than 9 carbon atoms (B-1), branched fatty acids with 15 or more but less than 20 carbon atoms (B-2), cycloalkane monocarboxylic acids with 4 or more but less than 8 carbon atoms (B-3), and aromatic carboxylic acids (B-4). In the aforementioned carboxylic acid (B), the proportion of the aforementioned fatty acid (B-1) is 30 to 50 mol%, the proportion of the aforementioned branched fatty acid (B-2) is 30 to 50 mol%, the proportion of the aforementioned cycloalkane monocarboxylic acid (B-3) is 10 to 30 mol%, and the proportion of the aforementioned aromatic carboxylic acid (B-4) is 1 to 15 mol.

[0035] 3. The grease composition for rolling bearings according to 1 or 2 above, wherein the above-mentioned ammonium phosphate is a tert-alkylamine-dimethyl phosphate or a phenylamine phosphate.

[0036] 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 the molar number of cyclohexyl in formula (2) is 70 to 90 mol% relative to the total molar number of cyclohexyl and straight-chain or branched alkyl groups having 8 to 22 carbon atoms.

[0037] 5. The grease composition for rolling bearings according to any one of 1 to 4 above, wherein, as the antioxidant, it comprises, based on the total mass of the composition, 0.5 to 5% by mass of an amine antioxidant and 0.5 to 5% by mass of a phenolic antioxidant.

[0038] 6. The grease composition for rolling bearings according to any one of claims 1 to 5 above further contains a peel-resistant additive.

[0039] 7. The grease composition for rolling bearings according to claim 6 above, wherein the peel-resistant additive comprises 0.2 to 5% by mass of an organic sulfonate metal salt and 0.2 to 5% by mass of a dialkyl dithiophosphate metal salt based on the total mass of the composition.

[0040] Invention Effects

[0041] According to the present invention, the grease composition for rolling bearings exhibits sufficient high-temperature durability, resistance to fretting wear, and rust prevention. The grease composition of the present invention also demonstrates excellent peel resistance. Attached Figure Description

[0042] [ Figure 1 [This is a schematic diagram of the rolling 4-ball test.] Detailed Implementation

[0043] Thickener

[0044] The fluidity of grease in bearings under high-temperature conditions varies depending on the type of thickener, and is closely related to the bearing's lubrication life. For a long lubrication life, the grease needs to remain in the lubricated area without softening or leaking. The thickener used in this invention is a diurea compound as shown in formula (2).

[0045] R5-NHCONH-R6-NHCONH-R7···(2)

[0046] (In the formula, R6 is a divalent aromatic hydrocarbon group with 6 to 15 carbon atoms, and R5 and R7 can be the same or different, representing a cyclohexyl group or a straight-chain or branched alkyl group with 8 to 22 carbon atoms.)

[0047] As a representative example of R6, groups represented by the following structural formulas can be cited. Among them, diphenylmethane is the most preferred.

[0048]

[0049] As a straight-chain or branched alkyl group with 8 to 22 carbon atoms, a straight-chain alkyl group with 8 to 18 carbon atoms is preferred. A straight-chain alkyl group with 18 carbon atoms is most preferred.

[0050] In formula (2), preferably, one of R5 and R7 is a cyclohexyl group, and the other is a straight-chain or branched alkyl group with 8 to 22 carbon atoms, forming a diurea compound. This diurea compound is a reaction product of a mixture of cyclohexylamine and a monoamine having a straight-chain or branched alkyl group with 8 to 22 carbon atoms, and a diisocyanate; it is called an alicyclic aliphatic diurea compound. In addition to alicyclic aliphatic diurea compounds, the above-mentioned reactants also include alicyclic diurea compounds with cyclohexyl groups at both ends and aliphatic diurea compounds with straight-chain or branched alkyl groups at both ends (8 to 22 carbon atoms).

[0051] In formula (2), the ratio of the molar number of cyclohexyl groups to the total molar number of straight-chain or branched alkyl groups with 8 to 22 carbon atoms ([(number of cyclohexyl groups) / (number of cyclohexyl groups + number of straight-chain or branched alkyl groups with 8 to 22 carbon atoms)]×100) is preferably 70 to 90 mol%, more preferably 80 to 90 mol%. When it is 70 mol% or more, it can particularly adequately prevent the softening and leakage of the grease composition under high temperature conditions, and when it is 90 mol% or less, it can ensure particularly adequate flowability and excellent high temperature durability.

[0052] As a thickener of the present invention, an alicyclic aliphatic diurea compound is particularly preferred, which comprises a diurea compound in which one of R5 and R7 in formula (2) is a cyclohexyl group and the other is a straight-chain alkyl group with 18 carbon atoms, wherein the molar ratio of the cyclohexyl group is 83.3 mol.

[0053] The content of 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 200-350, and the content of the thickener is the amount required to obtain this consistency. The content of the thickener in the grease composition of the present invention is typically 9-19% by mass, preferably 12-16% by mass. Below 9% by mass, the grease may soften and leak, failing to meet lubrication life requirements. On the other hand, above 19% by mass, the fluidity is poor, making it difficult for the grease to enter the lubrication zone, sometimes failing to meet lubrication life requirements.

[0054] 0 base oil

[0055] The base oil used in this invention has a kinematic viscosity of 60 mmHg at 40°C. 2 Ester-based synthetic oils with a viscosity of over 1000 liters per second. Ester-based synthetic oils exhibit excellent high-temperature durability.

[0056] From the perspective of high-temperature durability, the kinematic viscosity of ester-based synthetic oils at 40°C is preferably 80 mmHg. 2 / s or higher, preferably 90mm 2 / s or higher, preferably 110mm 2 / s or less, preferably 100mm 2 / s or less.

[0057] Furthermore, from the viewpoint of improving lubricity at high temperatures, the kinematic viscosity of ester-based synthetic oils at 100°C is preferably 11 mm. 2 / s or higher, preferably 11.5mm 2 / s or higher, preferably 14mm 2 / s or less, preferably 13mm 2 / s or less.

[0058] As the ester-based synthetic oil of the present invention, a condensed ester containing an alcohol (A) and a carboxylic acid (B) is preferred.

[0059] The above alcohol (A) contains a polyol represented by formula (1).

[0060]

[0061] (In equation (1), R) 1 ~R 4 Independently representing a hydrogen atom, methyl group, or hydroxyl group, and R 1 ~R 4 At least two of them represent hydroxyl groups.

[0062] The above-mentioned carboxylic acids (B) contain fatty acids with 5 to 9 carbon atoms (B-1), branched fatty acids with 15 to 20 carbon atoms (B-2), cycloalkane monocarboxylic acids with 4 to 8 carbon atoms (B-3), and aromatic carboxylic acids (B-4).

[0063] <Alcohol(A)>

[0064] The alcohol (A) mentioned above contains the polyol shown in formula (1) above.

[0065] R in the above formula (1) 1 ~R 4 In the middle, R 1 ~R 4At least two of the hydroxyl groups are hydroxyl groups, preferably three or more. Examples of polyols 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, and pentaerythritol is more preferred.

[0066] It should be noted that the alcohol (A) mentioned above can appropriately use various monohydric alcohols or polyols as alcohol components other than the polyols mentioned above. Monohydric alcohols typically have 1 to 24 carbon atoms, and the carbon chain can be either straight or branched; furthermore, it can be either saturated or unsaturated. As for polyols, polyols with a valence of 2 to 10 are typically used.

[0067] Examples of the aforementioned polyols include: 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, 1,5-pentanediol, and other diol compounds; 1,2,4-butanetriol, 1,3,5-pentanetriol, 1,2... Triols such as 6-hexanetriol; polymers of trimethylolamine such as pentaerythritol and tripentaerythritol; polyglycerols such as glycerol, diglycerol, triglycerol, and tetraglycerol; sugars such as sorbitol, sorbitol anhydride, sorbitol glycerol condensate, ribitol, arabinitol, xylitol, mannitol, xylose, arabinose, ribose, rhamnose, glucose, fructose, galactose, mannose, sorbitol, cellobiose, maltose, isomaltose, trehalose, and sucrose.

[0068] <Carboxylic acid (B)>

[0069] The above-mentioned carboxylic acids (B) contain fatty acids with 5 to 9 carbon atoms (B-1), branched fatty acids with 15 to 20 carbon atoms (B-2), cycloalkane monocarboxylic acids with 4 to 8 carbon atoms (B-3), and aromatic carboxylic acids (B-4).

[0070] The carbon chain of the fatty acid (B-1) with 5 to 9 carbon atoms can be unsaturated or saturated, but from the viewpoint of improving the heat resistance of the condensed ester, saturation is preferred. Furthermore, from the viewpoint of improving the heat resistance and lubricity of the condensed ester, the fatty acid (B-1) preferably has 6 to 8 carbon atoms, more preferably 7.

[0071] Examples of the aforementioned fatty acid (B-1) include valeric acid, 2-methylvaleric acid, 4-methylvaleric acid, n-hexanoic acid, 2-methylhexanoic acid, 5-methylhexanoic acid, 4,4-dimethylvaleric acid, n-heptanoic acid, 2-methylheptanoic acid, 2-ethylhexanoic acid, 2,2-dimethylhexanoic acid, n-octanoic acid, 3,5,5-trimethylhexanoic acid, and n-nonanoic acid. From the viewpoint of heat resistance, the aforementioned fatty acid (B-1) is preferably a straight-chain valeric acid, n-hexanoic acid, n-heptanoic acid, n-octanoic acid, or n-nonanoic acid, and more preferably n-heptanoic acid.

[0072] Examples of branched-chain fatty acids (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 phytic acid. From the viewpoint of improving the heat resistance and lubricity of the condensed ester, the aforementioned branched-chain fatty acids (B-2) are preferably 2-hexyldecanoic acid, isopalmitic acid, isostearic acid, and isoarachidic acid, and more preferably isostearic acid and isopalmitic acid.

[0073] The aforementioned cycloalkane monocarboxylic acids (B-3) with 4 to 8 carbon atoms can be replaced by alkyl chains, which can be straight or branched.

[0074] From the viewpoint of improving the heat resistance of condensed esters, the ring of the above-mentioned cycloalkane monocarboxylic acid (B-3) is preferably a 5- or 7-membered ring, more preferably a 6-membered ring.

[0075] Examples of the aforementioned cycloalkane monocarboxylic acid (B-3) include cyclopropane carboxylic acid, cyclobutane carboxylic acid, cyclopentane carboxylic acid, cyclohexane carboxylic acid, cycloheptane carboxylic acid, and methylcyclohexane carboxylic acid. From the viewpoint of improving the heat resistance of the condensed ester, the aforementioned 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 even more preferably cyclohexane carboxylic acid.

[0076] The above-mentioned aromatic carboxylic acid (B-4) can be replaced by an alkyl chain, which can be either straight or branched.

[0077] From the viewpoint of improving the heat resistance of condensed esters, the aromatic rings of the above-mentioned aromatic carboxylic acid (B-4) are preferably benzene rings and naphthalene rings, and more preferably benzene rings.

[0078] Examples of the aforementioned aromatic carboxylic acids (B-4) include benzoic acid, toluene, dimethylbenzoic acid, trimethylbenzoic acid, and naphthoic acid. From the viewpoint of improving the heat resistance of the condensed ester, benzoic acid is preferred.

[0079] It should be noted that the above-mentioned carboxylic acid (B) can appropriately use various carboxylic acids (hereinafter also referred to as other carboxylic acid compounds) as carboxylic acid components other than those in (B-1) to (B-4). Examples of other carboxylic acid compounds include decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, etc.

[0080] The following describes the proportions of each component of the condensed ester in the grease composition of the present invention.

[0081] In the above alcohol (A), the proportion of the polyol shown in the above 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%.

[0082] In the aforementioned carboxylic acid (B), the proportion of the aforementioned fatty acid (B-1) is 30 to 50 mol%. In the aforementioned carboxylic acid (B), from the viewpoint of improving the heat resistance of the condensed ester and reducing the kinematic viscosity, the proportion of the aforementioned fatty acid (B-1) is preferably 35 mol% or more, and from the viewpoint of improving the kinematic viscosity of the condensed ester, it is preferably 40 mol% or less.

[0083] In the aforementioned carboxylic acid (B), the proportion of the aforementioned branched-chain fatty acid (B-2) is 30 mol% or more and 50 mol% or less. From the viewpoint of improving the heat resistance and kinematic viscosity of the condensed ester, the proportion of the aforementioned branched-chain fatty acid (B-2) in the aforementioned carboxylic acid (B) is preferably 35 mol% or more, and from the viewpoint of reducing the kinematic viscosity of the condensed ester, it is preferably 40 mol% or less.

[0084] In the aforementioned carboxylic acid (B), the proportion of the aforementioned cycloalkane monocarboxylic acid (B-3) is 10 mol% or more and 30 mol% or less. From the viewpoint of improving the heat resistance of the condensed ester, the proportion of the aforementioned cycloalkane monocarboxylic acid (B-3) in the aforementioned carboxylic acid (B) is preferably 12 mol% or more, and from the viewpoint of improving the lubricity of the condensed ester, it is preferably 25 mol% or less.

[0085] In the above-mentioned carboxylic acid (B), the proportion of the above-mentioned aromatic carboxylic acid (B-4) is 1 to 15 mol%. In the above-mentioned carboxylic acid (B), from the viewpoint of improving the heat resistance and kinematic viscosity of the condensed ester, the proportion of the above-mentioned aromatic carboxylic acid (B-4) is preferably 2 mol% or more, and from the viewpoint of reducing the kinematic viscosity of the condensed ester, it is preferably 13 mol% or less.

[0086] Of the aforementioned carboxylic acids (B), from the viewpoint of improving the low-temperature storage properties of the condensed ester, the molar ratio ((B-3) / (B-4)) of the aforementioned cycloalkane monocarboxylic acid (B-3) and the aforementioned aromatic carboxylic acid (B-4) is preferably 0.5 to 20. Of the aforementioned carboxylic acids (B), from the viewpoint of improving the low-temperature storage properties of the condensed ester, the molar ratio ((B-3) / (B-4)) of the aforementioned cycloalkane monocarboxylic acid (B-3) and the aforementioned aromatic carboxylic acid (B-4) is preferably 0.8 or more, and preferably 15 or less, more preferably 12 or less.

[0087] From the viewpoint of improving the heat resistance and lubricity of the condensed ester, the total proportion of the above-mentioned carboxylic acid (B) (B-1), the above-mentioned branched fatty acid (B-2), the above-mentioned cycloalkane monocarboxylic acid (B-3), and the above-mentioned 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%.

[0088] From the viewpoint of high-temperature durability, the kinematic viscosity of the condensed ester in the grease composition of the present invention at 40°C is preferably 80 mmHg. 2 / s or higher, preferably 90mm 2 / s or more, and preferably 110mm 2 / s or less, preferably 100mm 2 / s or less. Furthermore, from the viewpoint of improving lubricity at high temperatures, the kinematic viscosity of the condensed ester in the grease composition of the present invention at 100°C (described later) is preferably 11 mm². 2 / s or higher, preferably 11.5mm 2 / s or more, and preferably 14mm 2 / s or less, preferably 13mm 2 / s or less.

[0089] <Preparation method of condensed ester>

[0090] The condensed esters described above can be prepared by esterification of the alcohol (A) and the carboxylic acid (B) using a known method.

[0091] When reacting the alcohol (A) with the carboxylic acid (B), from the viewpoint of promoting esterification, the equivalent ratio of the two is generally adjusted relative to the hydroxyl group of the alcohol component of alcohol (A) by a ratio of preferably 1.05 to 1.5 equivalents, more preferably 1.1 to 1.3 equivalents, of the carboxyl group of the carboxylic acid component of carboxylic acid (B). It should be noted that increasing the ratio of carboxyl groups in the carboxylic acid component of carboxylic acid (B) improves the reactivity between the alcohol and carboxylic acid components; however, after the reaction, excess carboxylic acid (B) needs to be removed. Examples of methods for this removal include vacuum distillation, vaporization, adsorption using an adsorbent, and other similar methods.

[0092] The ester-based synthetic oil of the present invention can be a so-called biomass oil manufactured from biological resources produced by animals and plants. For example, biomass ester oils synthesized from various fatty acids and alcohols derived from vegetable oils can also be used. The base oil can be used alone or in combination of two or more.

[0093] As the ester-based base oil of the present invention, it is preferably composed only of a condensation ester of the polyol shown in formula (1) and the above-mentioned carboxylic acid (B).

[0094] More preferably, the ester oil has a molar ratio ((B-3) / (B-4)) of 0.5 to 20 between the above-mentioned cycloalkane monocarboxylic acid (B-3) and the above-mentioned aromatic carboxylic acid (B-4).

[0095] The preferred ester compound is a pentaerythritol and carboxylic acid (B), wherein the carboxylic acid (B) 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).

[0096] Based on the total mass of the composition, the content of the ester-based synthetic oil in this invention is preferably 84-74% by mass, more preferably 81-77% by mass, and even more preferably 80-77% by mass. By including the base oil in such a proportion, high-temperature durability becomes good.

[0097] Based on the total mass of the base oil, the content of the ester oil shown in formula (1) above is preferably 60 to 100% by mass, more preferably 80 to 100% by mass, and even more preferably 100% by mass. By containing the base oil in such a proportion, the high-temperature durability is particularly good.

[0098] Aminophosphates

[0099] The ammonium phosphate ester in the lubricating grease composition of the present invention is not particularly limited. Preferred examples include tertiary alkylamine-dimethyl phosphate and phenylamine-phosphate. Tertiary alkylamine-dimethyl phosphate is more preferred. As an ammonium phosphate ester, commercially available products such as Vanlube 672 (tertiary alkylamine-dimethyl phosphate) and Vanlube 692 (phenylamine-phosphate) manufactured by RTVanderbilt can be used.

[0100] The number of carbon atoms in the tertiary alkyl group of tertiary alkylamine-dimethyl phosphate is not particularly limited, and can be, for example, 1 to 24.

[0101] The content of ammonium phosphate relative to the total mass of the grease composition is 0.2 to 2.5% by mass, preferably 0.3 to 1.0% by mass, and more preferably 0.4 to 0.7% by mass. When it is 0.2% by mass or more, it exhibits sufficient resistance to fretting wear. On the other hand, even when it exceeds 2.5% by mass, it still has a fretting wear suppression effect, but the effect saturates. Therefore, from an economic point of view, it is preferable to be 2.5% by mass or less.

[0102] <Carboxylic acid-based rust inhibitors>

[0103] As a carboxylic acid-based rust inhibitor in the lubricating grease composition of the present invention, examples of monocarboxylic acids include straight-chain fatty acids such as lauric acid and stearic acid, and saturated carboxylic acids having a cycloalkane core; examples of dicarboxylic acids include 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, tetrapropylene succinic acid, hydroxy fatty acids, mercapto fatty acids, and sarcosine derivatives. Among these, 2-tetrapropylene succinic acid half-ester and tetrapropylene succinic acid are preferred, and combinations thereof are particularly preferred.

[0104] 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 ammonium phosphate. Relative to 1 part by weight of ammonium phosphate, it is 0.5 to 4 parts by weight, preferably 0.8 to 3 parts by weight, and more preferably 1 to 2 parts by weight. If it is 0.5 parts by weight or more, it can compensate for the reduction in rust prevention caused by the high reactivity of ammonium phosphate to the metal surface, ensuring sufficient rust prevention. On the other hand, if it exceeds 4 parts by weight, conversely, the rust inhibitor has a stronger adsorption to the metal surface than the ammonium phosphate, and although the rust prevention is sufficient, the resistance to fretting wear sometimes deteriorates.

[0105] The grease composition of the present invention may contain rust inhibitors other than carboxylic acid-based rust inhibitors, such as ester-based rust inhibitors, in an amount of up to 3.5 parts by weight relative to 1 part by weight of ammonium phosphate. If the amount exceeds 3.5 parts by weight, the rust inhibitor has a stronger adsorption to the metal surface than ammonium phosphate, and although the rust prevention is sufficient, the resistance to fretting wear may sometimes be worse.

[0106] The grease composition of the present invention does not contain either a carboxylate-based rust inhibitor or an amine salt of fatty acids. If it contains a carboxylate-based rust inhibitor or an amine salt of fatty acids, the amine phosphate is more reactive than the rust inhibitor adsorbed onto the metal surface. Although it provides adequate resistance to fretting wear, its rust prevention is sometimes compromised.

[0107] Antioxidants

[0108] The grease composition of the present invention contains an antioxidant. Antioxidants contribute to high-temperature durability.

[0109] As antioxidants of the present invention, amine antioxidants, phenolic antioxidants, and mixtures thereof can be used. Mixtures thereof are preferred.

[0110] <Amine antioxidants>

[0111] The amine antioxidants that can be used in the grease compositions of the present invention are preferably selected from the group consisting of alkyl diphenylamines, N-phenyl-α-naphthylamines, alkylated phenyl-α-naphthylamines, and mixtures thereof. Among these, alkyl diphenylamines are more preferred, and alkyl diphenylamines that are the reaction product of N-phenylaniline and 2,2,4-trimethylpentene are particularly preferred.

[0112] The content of the amine-based antioxidant in the grease composition of the present invention is preferably 0.5 to 5% by mass, more preferably 1 to 3% by mass, and even more preferably 1.5 to 2.5% by mass. A content of 0.5% by mass or more indicates a sufficient antioxidant effect. On the other hand, even if the content exceeds 5% by mass, the antioxidant effect is still present, but the effect becomes saturated. Therefore, from an economic point of view, 5% by mass or less is preferred.

[0113] <Phenolic antioxidants>

[0114] The phenolic antioxidants that can be used in the grease compositions of the present invention are preferably selected from the group consisting of octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 2,6-di-tert-butyl-4-methylphenol, pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), phenylpropionic acid, 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy C7-C9 side-chain alkyl esters and mixtures thereof. Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate is particularly preferred.

[0115] The content of phenolic antioxidant in the grease composition of the present invention is preferably 0.5 to 5% by mass, more preferably 0.5 to 3% by mass, and even more preferably 0.8 to 2% by mass. A content of 0.5% by mass or more indicates a sufficient anti-oxidative degradation effect. On the other hand, even if the content exceeds 5% by mass, the anti-oxidative degradation effect is achieved, but the effect saturates. Therefore, from an economic point of view, 5% by mass or less is preferred.

[0116] As an antioxidant used in the grease composition of the present invention, a combination of alkyl diphenylamine and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, the reaction product of N-phenylaniline and 2,2,4-trimethylpentene, is particularly preferred.

[0117] When the grease composition of the present invention contains a mixture of amine antioxidants and phenolic antioxidants as antioxidants, the total amount of the mixture is preferably 1 to 10% by mass, more preferably 1.5 to 6% by mass, and even more preferably 2.3 to 4.5% by mass, based on the total mass of the composition. By containing a mixture of amine antioxidants and phenolic antioxidants in such a proportion, the antioxidant effect is particularly effective.

[0118] When the grease composition of the present invention contains a mixture of alkyl diphenylamine and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, the reaction product of N-phenylaniline and 2,2,4-trimethylpentene, as an antioxidant, the total amount is preferably 1 to 10% by mass, more preferably 1.5 to 6% by mass, and even more preferably 2.3 to 4.5% by mass, based on the total mass of the composition. The antioxidant effect is particularly effective when the mixture of alkyl diphenylamine and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, the reaction product of N-phenylaniline and 2,2,4-trimethylpentene, is contained in such a proportion.

[0119] Optional additives

[0120] The lubricating grease composition of the present invention may contain general additives as needed. For example, the following additives are examples.

[0121] Peel-resistant additives

[0122] <Organosulfonate metal salts>

[0123] Examples of organic sulfonate metal salts in the grease compositions of the present invention include substances represented by the following formula (4). Zinc salts are preferred.

[0124] [R10-SO3]M2···Equation (4)

[0125] In formula (4), R10 represents alkyl, alkenyl, alkylnaphthyl, dialkylnaphthyl, alkylphenyl, or petroleum high-boiling fraction residues. The alkyl or alkenyl groups are straight-chain or branched, with 2 to 22 carbon atoms. M2 represents an alkaline earth metal or zinc, preferably zinc or calcium. Zinc dinonylnaphthalenesulfonate is particularly preferred.

[0126] The content of the organic sulfonic acid metal salt in the grease composition of the present invention is generally 0.5 to 5% by mass, preferably 1 to 3% by mass, and more preferably 1.5 to 2.5% by mass.

[0127] <Dialkyl dithiophosphate metal salts>

[0128] As a dialkyl dithiophosphate metal salt in the grease composition of the present invention, the salt shown in the following formula (3) can be cited.

[0129] [(R8O)(R9O)P(=S)-S]2-M1 x O m S n ···(3)

[0130] In formula (3), R8 and R9 are alkyl groups with 1 to 24 carbon atoms or aryl groups with 6 to 30 carbon atoms. The alkyl group can be linear or branched, and can be any one of primary, secondary, and tertiary alkyl groups. M1 is zinc or molybdenum, preferably zinc. x is 1 or 2, and n and m are 0 to 4.

[0131] The content of dialkyl dithiophosphate metal salt in the grease composition of the present invention is generally 0.5 to 3% by mass, preferably 0.5 to 3% by mass, and more preferably 0.8 to 2% by mass.

[0132] ○ Extreme pressure agent

[0133] Phosphorus compounds: tricresyl phosphate, tri(2-ethylhexyl) phosphate, etc.

[0134] Chalcogenide compounds: dibenzyl disulfide, various polysulfides, etc.

[0135] Sulfur-phosphorus compounds: Triphenylthiophosphate

[0136] Organometallic extreme pressure agents: Zn, Mo, Sb, Ni, Cu, Bi salts of dialkyl dithiocarbamate, ashless dithiocarbamate, ashless dithiophosphate carbamate, etc.

[0137] Solid lubricants: molybdenum disulfide, graphite, PTFE, MCA, etc.

[0138] Metal corrosion inhibitors: benzotriazole or its derivatives, zinc oxide, etc.

[0139] Oil-reducing agents: sorbitan trioleate, sorbitan monooleate, etc.

[0140] The additives of the present invention preferably comprise at least one of the following: an aminophosphate ester selected from the group consisting of tert-alkylamine-dimethyl phosphate and phenylamine-phosphate; a carboxylic acid-based rust inhibitor selected from the group consisting of 2-tetrapropylene succinate half ester and tetrapropylene succinic acid; and an antioxidant selected from the group consisting of alkyl diphenylamine and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, which are the reaction products of N-phenylaniline and 2,2,4-trimethylpentene; but do not contain any of the following: carboxylic acid-based rust inhibitors and amine salts of fatty acids.

[0141] In this embodiment, it is more preferable that the content of ammonium phosphate in the composition is 0.3 to 1.0% by mass, and the content of carboxylic acid rust inhibitor is 0.8 to 3 parts by mass relative to 1 part by mass of ammonium phosphate.

[0142] In this method, it is further preferred to include a peel-resistant additive, more preferably a peel-resistant additive selected from at least one of the group consisting of an organic sulfonate metal salt and a dialkyl dithiophosphate metal salt, and even more preferably at least one of the group consisting of zinc nonylnaphthalene sulfonate and zinc dialkyl dithiophosphate.

[0143] The additives of the present invention more preferably contain any one of the following: amine phosphates as tert-alkylamine-dimethyl phosphates; carboxylic acid-based rust inhibitors as a mixture of 2-tetrapropylene succinate half-ester and tetrapropylene butyric acid; antioxidants as a mixture of alkyl diphenylamine and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, which is the reaction product of N-phenylaniline and 2,2,4-trimethylpentene; and peel-resistant additives as a mixture of zinc dinonylnaphthalene sulfonate and zinc dialkyl dithiophosphate; or any one of these, but without carboxylic acid-based rust inhibitors and fatty acid amine salts.

[0144] In this embodiment, it is more preferable that the content of ammonium phosphate in the composition is 0.4 to 0.7% by mass, and the content of carboxylic acid-based rust inhibitor is 1 to 2 parts by mass relative to 1 part by mass of ammonium phosphate.

[0145] In any of the above preferred embodiments regarding the additive, the thickener is particularly preferred to be an alicyclic aliphatic diurea compound containing a diurea compound in which one of R5 and R7 of formula (2) is cyclohexyl and the other is a straight-chain alkyl group having 18 carbon atoms, wherein the molar percentage of the cyclohexyl group is 83.3 mol%, and the base oil is an ester compound of pentaerythritol and carboxylic acid (B), wherein the carboxylic acid (B) 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).

[0146] The grease composition of the present invention exhibits excellent high-temperature durability, resistance to fretting wear, and rust prevention, making it suitable for use in rolling bearings of automotive electrical components, household appliances that operate at high speeds and temperatures, such as cleaner motors, and continuous casting equipment that requires lubrication at high temperatures. It is particularly suitable as a grease for use in rolling bearings of automotive electrical auxiliary equipment components that require high high-temperature durability while also offering resistance to fretting wear and rust prevention.

[0147] Example

[0148] <Preparation of Lubricating Grease Compositions>

[0149] In the base oils shown in the table below, an amine (a mixture of cyclohexylamine and stearylamine in the molar ratio described in the table below) is reacted in a specified amount at a ratio of 2 moles relative to 1 mole of 4,4'-diphenylmethane diisocyanate (MDI). After heating and cooling, the mixture is further diluted with the base oil, and the additives described in the table below are added. The mixture is then prepared by using a 3-roll mill to achieve a cone penetration of 280 (measured according to JIS K2220 7) after 60 working passes. It should be noted that the kinematic viscosity of the base oil at 40°C and 100°C (measured according to JIS K 2220 23) is as described below. Furthermore, unless otherwise specified, the figures in the table represent a percentage of mass based on the total mass of the composition. The balance is the base oil.

[0150] Ester: 93mm 2 / s (An ester compound of pentaerythritol and carboxylic acid (B), wherein carboxylic acid (B) 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). The kinematic viscosity at 100°C is 12.1 mm. 2 / s。)

[0151] PAO A: 65.3mm 2 / s

[0152] PAO B: 393mm 2 / s

[0153] Mineral oil A: 101mm 2 / s

[0154] Mineral oil B: 39.5mm 2 / s

[0155] <Experimental Methods and Judgments>

[0156] [Heat resistance (bearing lubrication life test)]

[0157] • Evaluation Methods

[0158] The test was conducted using a bearing lubrication life tester based on ASTM D3336.

[0159] The test conditions are as follows. Furthermore, the shorter of the time intervals—either until the motor generates an overcurrent (4 amps) or until the bearing temperature rises to +15°C—is defined as the seizure life.

[0160] Bearing type: 6204 metal seal

[0161] Test temperature: 180℃

[0162] Speed: 10000rpm

[0163] Grease amount: 1.8g

[0164] Test loads: Axial load 66.7 N, Radial load 66.7 N

[0165] • Judgment

[0166] Bearing lubrication life of over 1000 hours…○ (Qualified)

[0167] Less than 1000h…× (Unqualified)

[0168] [Rust resistance (bearing rust prevention test)]

[0169] • Evaluation Methods

[0170] Performed in accordance with ASTM D1743-73.

[0171] Test grease was sealed into the bearing (32304J). While applying an axial load of 26.5 N, the bearing was rotated at 1750 rpm for 10 seconds. The grease weight was then adjusted to 3.5 g, and the bearing was rotated for another 60 seconds under the same conditions. The bearing was then immersed in 1% saline solution for 10 seconds and left to stand at 52°C for 48 hours at 100% humidity. The rust condition of the outer raceway surface of the bearing after cleaning was then visually observed.

[0172] • Judgment

[0173] #1 (Rust-free)...○ (Pass)

[0174] #2 (No more than 3 spots of rust that can be visually confirmed)...× (Unacceptable)

[0175] #3 (rust larger than #2, with more than 4 visible rust spots)...× (unacceptable)

[0176] [Dermal Wear Resistance (Dermal Wear Test)]

[0177] • Evaluation Methods

[0178] Apply test grease to two sets of thrust bearings and perform specified oscillating operation to determine the wear amount (weight reduction caused by fretting wear).

[0179] Bearing: 51204 Thrust Bearing

[0180] Load: 4000N (Surface pressure: 1.9 GPa)

[0181] Swing angle: ±6°

[0182] Oscillation period: 25Hz

[0183] Time: 2 hours

[0184] Temperature: 25℃

[0185] Grease application rate: 1.0g per bearing group

[0186] Wear amount: The reduction in the mass of the bearing races in each group (the total mass of the bearing races in the test is reduced by 2).

[0187] • Judgment

[0188] Wear amount less than 7mg…○ (Pass)

[0189] 7mg or more... × (Unqualified)

[0190] [Table 1]

[0191]

[0192] [Table 2]

[0193]

[0194] In Examples 1-4, the high-temperature durability, rust prevention, resistance to fretting wear, and peel resistance all passed the test.

[0195] Comparative Examples 1 and 2, where the base oil is not an ester oil but PAO and mineral oil, cannot meet the requirements for high-temperature durability.

[0196] In Comparative Examples 3 and 5, which contain more than 4 parts by mass of rust inhibitor relative to 1 part by mass of ammonium phosphate, the rust prevention performance is satisfactory, but the resistance to fretting wear is not satisfactory.

[0197] In Comparative Examples 4 and 6, which contain less than 0.5 parts by weight of rust inhibitor relative to 1 part by weight of ammonium phosphate, the resistance to fretting abrasion is satisfactory, but the rust prevention performance is not satisfactory.

[0198] Comparative Examples 7-11, which contain carboxylates, fatty acid amines, esters, oxidized waxes, or barium sulfonates, fail to meet the requirements for rust prevention.

[0199] Comparative Example 12, which does not contain antioxidants, fails to meet high-temperature durability requirements.

[0200] Therefore, it can be said that the grease composition of the present invention can meet the requirements of high temperature durability, rust prevention and resistance to fretting wear.

Claims

1. A grease composition for rolling bearings, comprising a thickener, a base oil, and additives; The thickener is a diurea compound as shown in formula (2). R5-NHCONH-R6-NHCONH-R7···(2) In the formula, R6 represents a divalent aromatic hydrocarbon group with 6 to 15 carbon atoms, and R5 and R7 can be the same or different, representing a cyclohexyl group or a straight-chain or branched alkyl group with 8 to 22 carbon atoms. The base oil has a kinematic viscosity of 60 mmHg at 40°C. 2 Ester-based synthetic oils with a density of 1 / s or higher The additives include ammonium phosphate, carboxylic acid-based rust inhibitors, and antioxidants. The content of the ammonium phosphate is 0.2-2.5% 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 weight relative to 1 part by weight of the ammonium phosphate ester, and the content of other rust inhibitors is less than 3.5 parts by weight relative to 1 part by weight of the ammonium phosphate ester. in, It does not contain any of the carboxylate-based rust inhibitors or fatty acid amine salts.

2. The grease composition for rolling bearings according to claim 1, wherein, The base oil contains a condensed ester of alcohol (A) and carboxylic acid (B), and has a kinematic viscosity of 80~110 mm at 40°C. 2 / s; The alcohol (A) contains a polyol represented by formula (1). In formula (1), R1 to R4 independently represent hydrogen atoms, methyl groups or hydroxyl groups, and at least two of R1 to R4 represent hydroxyl groups; The carboxylic acid (B) contains fatty acids with 5 or more but less than 9 carbon atoms (B-1), branched fatty acids with 15 or more but less than 20 carbon atoms (B-2), cycloalkane monocarboxylic acids with 4 or more but less than 8 carbon atoms (B-3), and aromatic carboxylic acids (B-4). In the carboxylic acid (B), the proportion of fatty acid (B-1) is 30-50 mol%, the proportion of branched fatty acid (B-2) is 30-50 mol%, the proportion of cycloalkane monocarboxylic acid (B-3) is 10-30 mol%, and the proportion of aromatic carboxylic acid (B-4) is 1-15 mol.

3. The grease composition for rolling bearings according to claim 1, wherein, The ammonium phosphate is a tert-alkylamine-dimethyl phosphate or a phenylamine phosphate.

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

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

6. The grease composition for rolling bearings according to claim 1, further comprising a peel-resistant additive.

7. The grease composition for rolling bearings according to claim 6, wherein, As the peel-resistant additive, it comprises 0.2 to 5% by mass of an organic sulfonate metal salt and 0.2 to 5% by mass of a dialkyl dithiophosphate metal salt based on the total mass of the composition.

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