Anti-peeling agent and lubricant composition containing same

Abstract

To provide an anti-spalling agent and a lubricant composition containing the anti-spalling agent, which are capable of suppressing white layer spalling in rolling bearings, or the like.SOLUTION: An anti-spalling agent and a lubricant composition containing the anti-spalling agent, the anti-spalling agent comprising at least one kind selected from the group consisting of (A) compounds having a volume resistivity of 1.0×1010 Ω cm or less and (B) compounds in which the number of aromatic ring-forming carbon atoms is at least 40%, based on the total number of carbon atoms that form the compound, and the total amount of compounds (A) and (B) exceeding 0.1 mass%, based on the total mass of the anti-spalling agent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a novel anti-exfoliation agent that can be included in a lubricant that can be applied to metal surfaces such as rolling bearings. The present invention also relates to a lubricant composition containing said anti-exfoliation agent. [Background technology]

[0002] Peculiar early abnormal flaking accompanied by white structural changes that occurs on the rolling surfaces of rolling bearings has been a problem since the mid-1980s because it reduces the fatigue life of rolling bearings. This type of flaking is known as white flaking, white phase flaking, brittle flaking, hydrogen embrittlement flaking, or hydrogen embrittlement flaking. Although the mechanism by which this type of peeling occurs has not yet been elucidated, for example, Patent Document 1 introduces a hydrogen theory. Specifically, when grease is used under high load, the grease decomposes and generates hydrogen. This hydrogen penetrates into the steel material of the rolling bearing and reacts with carbide at the grain boundaries. As a result, the steel material becomes brittle. Patent Document 1 reports that the problem of white layer peeling, i.e., the penetration of hydrogen generated by the decomposition of the lubricant into the metal, can be addressed by adding a specific compound containing at least one sulfur atom, such as a thiazole derivative, sulfurized oil or fat, or sulfurized olefin, to the grease composition.

[0003] The mechanism of delamination has also been explained by the formation of new metal surfaces. Specifically, when wear occurs on the metal's transfer surface, new surfaces are easily formed due to the wear. These new surfaces then act as catalysts, causing the grease to chemically decompose, resulting in the generation of large amounts of hydrogen. This hydrogen then penetrates into the steel, ultimately causing cracks on the metal surface. Patent Document 2 reports an additive that adds a passivating oxidizing agent, such as a nitrite, to grease to oxidize the metal surface, suppressing its catalytic activity and ultimately inhibiting hydrogen generation due to lubricant decomposition. Patent Document 3 reports a technique that combines a passivating oxidizing agent with an organic sulfonate. Patent Document 4 reports a technique that incorporates a specific amount of an azo compound into grease. Patent Document 5 reports a technique that suppresses hydrogen generation from grease by using a phenyl ether-based synthetic oil as the grease's base oil. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2015 / 016376 [Patent Document 2] Japanese Patent Application Publication No. 3-210394 [Patent Document 3] Japanese Patent Application Publication No. 5-263091 [Patent Document 4] Japanese Patent Application Laid-Open No. 2002-130301 [Patent Document 5] Japanese Patent Application Publication No. 3-250094 Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, it is known that plasma is generated in microscopic areas of a few micrometers to a few millimeters on friction surfaces (Nakayama, K., Yagasaki, F., Tribology Letters (2018)). Such plasma is called "triboplasma." It has been reported that discharge light emission and electrolytic corrosion occur even in the elastohydrodynamic lubrication (EHL) thin film of grease formed on rolling bearings, suggesting that discharge plasma is generated in the EHL thin film (Nakayama and Tanaka: Proceedings of the Tribology Conference, Tokyo (2016) A2). The present inventors thought that if the generation of triboplasma could be suppressed, it would be possible to prevent the peeling of white layers in rolling bearings and the like. Therefore, an object of the present invention is to provide an anti-exfoliation agent that can suppress white layer peeling in rolling bearings and the like, and a lubricant composition containing the anti-exfoliation agent. [Means for solving the problem]

[0006] The inventors measured the amount of hydrogen generated using a compound that can be used as a base oil in a lubricant composition or grease composition, and found that the specific volume resistivity was 1.0 × 10 10 We found that compounds with a resistivity of Ω·cm or less can effectively suppress hydrogen generation. Based on this finding, we have completed an invention that can effectively prevent white layer peeling in rolling bearings and other components. That is, the present invention provides the following anti-peeling agent.

[0007] [1] An amount of more than 0.1% by weight based on the total weight of the anti-peeling agent, (A) Volume resistivity is 1.0×10 10 Compounds with a resistivity of Ω·cm or less, and (B) A compound in which the ratio of the number of carbon atoms forming an aromatic ring structure to the total carbon atoms constituting the molecule is 40% or more. An anti-peeling agent containing at least one selected from the group consisting of: [2] The anti-peeling agent according to the above item 1, wherein the compound (A) is at least one selected from the group consisting of compounds having a dielectric constant ε of 3.0 or more at 25°C at 500 MHz and 1 GHz. [3] The anti-peeling agent according to the above item 1, wherein the compound (A) is at least one selected from the group consisting of compounds having a dipole term δp of the Hansen solubility parameter of 3.5 or more. [4] The anti-peeling agent according to any one of items 1 to 3, wherein the compound (A) is at least one selected from the group consisting of polyvalent esters, glycols, sulfur-based compounds, phosphorus-based compounds, nitrogen-based compounds, antistatic agents, ionic liquids, liquid crystals, SP compounds, NS compounds, and fatty acid amine salts.

[0008] [5] The anti-peeling agent according to any one of the above items 1 to 4, wherein the compound (A) is a diester of an aliphatic monoalcohol having 6 or less carbon atoms with a saturated or unsaturated fatty acid having 3 to 10 carbon atoms, an alicyclic fatty acid having 3 to 10 carbon atoms, or an aromatic dibasic acid having 3 to 10 carbon atoms. [6] The anti-peeling agent according to any one of the above items 1 to 5, wherein the compound (A) is a diester selected from the group consisting of dimethyl phthalate, dimethyl maleate, dimethyl malonate, dimethyl succinate, dimethyl glutarate, dimethyl adipate, dimethyl suberate, dimethyl sebacate, diethyl malonate, dibutyl malonate, and dihexyl malonate.

[0009] [7] The peel-resistant agent according to any one of items 1 to 4 above, wherein the compound (A) is an antistatic agent selected from the group consisting of poly(oxyethylene) alkylamines, poly(oxyethylene) alkylamides, poly(oxyethylene) alkyl ethers, poly(oxyethylene) alkylphenyl ethers, glycerin aliphatic esters, sorbitan aliphatic esters, alkyl sulfonates, alkylbenzenesulfonates, alkyl phosphates, quaternary ammonium chlorides, quaternary ammonium sulfates, quaternary ammonium nitrates, alkyl betaines, alkyl imidazolines, alkyl alanines, polyvinyl benzyls, polyacrylics, amine derivatives, succinic acid derivatives, partial esters of poly(oxyalkylene) glycols and polyhydric alcohols, ammonium compounds of alkyl naphthalene sulfonic acids, polyalkyl sulfones, and neutralized salts of alkylaryl sulfonic acids and alkyl amines. [8] The anti-peeling agent according to any one of the above items 1 to 7, wherein the compound (B) is at least one selected from the group consisting of phenyl ether, alkylbenzene, and alkylnaphthalene.

[0010] The present invention also provides the following lubricant composition. [9] A lubricant composition containing the compound according to any one of the above items 1 to 8.

[10] The lubricant composition according to item 9, further comprising at least one conventional base oil selected from the group consisting of mineral oils and synthetic oils. [1] The lubricant composition according to item 10 above, wherein the base oil is at least one selected from the group consisting of mineral oils, synthetic hydrocarbon oils, and ether oils.

[12] The lubricant composition according to any one of claims 9 to 11, wherein the content of the compound is more than 0.1 mass % based on the total mass of the composition.

[13] The lubricant composition according to any one of the above items 9 to 11, wherein the content of the compound exceeds 1 mass % based on the total mass of the composition.

[14] The lubricant composition according to any one of the above items 9 to 11, wherein the content of the compound is 2 mass % or more based on the total mass of the composition.

[15] The lubricant composition according to any one of the above items 9 to 11, wherein the content of the compound is 3 mass % or more based on the total mass of the composition.

[16] The lubricant composition according to any one of the above items 9 to 11, wherein the content of the compound is 40 mass % or less based on the total mass of the composition.

[17] The lubricant composition according to any one of the above items 9 to 16, further comprising a thickener. [Effects of the Invention]

[0011] The anti-peeling agent and lubricant composition of the present invention can effectively prevent white layer peeling (to 20% or less when compared with n-hexadecane). [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of an apparatus for generating hydrogen gas by triboplasma, used in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Definition] In this specification, the specific volume resistivity represents the ratio of the DC electric field (V / m) applied to a sample at 25°C to the current per unit cross-sectional area applied to the sample at that time, and is equal to the resistance between the opposing faces of a cube of the sample with a side length of 1 cm. The specific volume resistivity can be measured based on the test method for electrical insulating oil specified in JIS C2101. In this specification, the dielectric constant ε is a coefficient that indicates the relationship between the charge and the force exerted by the charge in a material. The dielectric constant ε was measured at 25°C using an E4991B Impedance Analyzer (Keysight Technologies, Inc.).

[0014] In this specification, the "Hansen solubility parameter" is an index that indicates the ease with which a certain solute dissolves in a certain solvent, and is composed of three components: a dispersion term (δD), a dipole term (δP), and a hydrogen bonding term (δH). The dispersion term (δD) indicates the effect due to dispersion forces, the dipole term (δP) indicates the effect due to dipole-dipole forces, and the hydrogen bonding term (δH) indicates the effect due to hydrogen bonding forces. The definition of the Hansen solubility parameter and details of its calculation method are described in the following literature: Charles M. Hansen, "Hansen Solubility Parameters: A Users Handbook," CRC Press, 2007.

[0015] As used herein, "white layer peeling" refers to a unique, early, abnormal peeling accompanied by white structural changes. The term "white layer peeling" as used herein is synonymous with terms used in the industry, such as white peeling, white phase peeling, brittle peeling, hydrogen embrittlement peeling, and hydrogen embrittlement peeling. Rolling fatigue life can usually be estimated based on life calculation formulas established in standards (ISO 281, JIS B-1518). However, when white layer peeling occurs, the life is reached in a shorter time than the calculated life. In actual applications, it has been reported that the life is reached approximately 1 / 10 to 1 / 20 of the calculated life. White layer peeling is a type of internally initiated damage, and is a unique phenomenon in which a white layer is observed when the metal structure is etched with nital solution after occurrence.

[0016] [Compounds used as anti-peeling agents] The compound used in the present invention has a specific volume resistivity of 1.0×10 10 The present inventors have found that compounds with such physical properties can suppress hydrogen generation by plasma. The experimental method and results are described in detail in the Examples section, but the present inventors have systematically investigated the effect of the carbon chain length of the ester on the amount of hydrogen generation, and found that the ester with methanol (R 2 OOC-R 1 -COOR 2 ) derived from the carbon chain length (i.e., R 1When the carbon number of the dibasic acid was 6 or less, no hydrogen was generated at all, but when the carbon number was 8 (i.e., the dibasic acid was sebacic acid), hydrogen was generated. However, the amount of hydrogen generated was only 17% of that generated when compared with n-hexadecane, which is used as a standard substance. When dimethyl sebacate was used, it was thought that triboplasma was generated, and the volume resistivity was measured and found to be 9.0 x 10 9 Ω·cm. Furthermore, R 1 When the volume resistivity was measured by changing the number of carbon atoms in R 1 It was found that the specific volume resistivity increases as the number of carbon atoms increases.

[0017] [Table 1] *The amount of hydrogen generated from n-hexadecane is set at 100.

[0018] On the other hand, the carbon chain length derived from the alcohol that constitutes the ester with sebacic acid (i.e., R 2 ) to the amount of hydrogen generated. 2 It was found that the specific volume resistivity increased as the carbon number of the ester increased. This tendency was also observed in the case of monoesters.

[0019] [Table 2] *The amount of hydrogen generated from n-hexadecane is set at 100.

[0020] The inventors also found that the specific volume resistivity was 1.0×10 10 We found that certain aromatic compounds can effectively suppress hydrogen evolution, even when the resistivity exceeds Ω·cm.

[0021] Thus, the compounds of the present invention are (A) The volume resistivity is 1.0 × 10 10 Compounds with a resistivity of Ω·cm or less, and (B) A compound in which the ratio of the number of carbon atoms forming an aromatic ring structure to the total carbon atoms constituting the molecule is 40% or more. At least one selected from the group consisting of:

[0022] (Compound (A)) The compound (A) has a specific volume resistivity of 5.0×10 9 It is preferable that the resistivity is Ω·cm or less. The compound (A) is also preferably liquid at 25°C. The compound (A) preferably has a dielectric constant ε of 3.0 or more at 500 MHz (25° C.) and 1 GHz (25° C.). The compound (A) preferably has a dipole term δp of the Hansen solubility parameter of 3.5 or more.

[0023] δp is expressed by the following formula, and the larger the dielectric constant ε, the larger δp. It is generally said that the dielectric constant ε of oil affects electromagnetic wave absorption, and the larger the dielectric constant ε and the larger the dielectric loss tangent, the more effectively electromagnetic waves can be absorbed, which can be one way to counter electromagnetic wave noise.

[0024]

number

[0025] Volume resistivity is 1.0×10 10 It was found that compounds with a δp of Ω·cm have a δp of 3.5 or more. Therefore, it is believed that a δp of 3.5 or more can prevent hydrogen generation and white layer peeling. δp is preferably 4.0 or more. The dipole term δp of the Hansen solubility parameter is preferably 20 or less. When Δp is 3.5 or more, the material has conductivity sufficient to prevent charging and a high dielectric constant, which is thought to suppress the generation of triboplasma and thereby suppress white layer peeling, which is preferable.

[0026] Specific examples of the compound (A) include polyvalent esters, glycols, sulfur-based compounds, phosphorus-based compounds, nitrogen-based compounds, antistatic agents, ionic liquids, liquid crystals, SP compounds, NS compounds, and fatty acid amine salts.

[0027] The polyhydric ester is selected from a diester, a triester, and a tetraester. A polyhydric ester having 15 or less carbon atoms is preferred. A diester having 15 or less carbon atoms is more preferred. Of these, a diester of a linear or branched aliphatic monoalcohol having 6 or less carbon atoms, preferably 4 or less carbon atoms, with a linear or branched saturated or unsaturated aliphatic dibasic acid having 3 to 10 carbon atoms, a saturated or unsaturated alicyclic dibasic acid having 3 to 10 carbon atoms, or an aromatic dibasic acid having 3 to 10 carbon atoms is preferred. A diester of a linear or branched aliphatic monoalcohol having 6 or less carbon atoms and a saturated or unsaturated dibasic acid having 3 to 10 carbon atoms is particularly preferred. A diester of a linear or branched aliphatic monoalcohol having 4 or less carbon atoms and a saturated or unsaturated dibasic acid having 3 to 10 carbon atoms is most preferred.

[0028] Specific examples of diesters include those in which the alcohol is methanol, ethanol, propanol, butanol, or hexanol and the dibasic acid is malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, fumaric acid, maleic acid, dihydromuconic acid, 1,4-phenylenediacetic acid, or cis-4-cyclohexene-1,2-dicarboxylic acid. Among these, diesters in which the alcohol is methanol, ethanol, n-propanol, or n-butanol and the dibasic acid is malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, phthalic acid, or maleic acid are particularly preferred. Particularly preferred are dimethyl malonate, dimethyl succinate, dimethyl glutarate, dimethyl adipate, dimethyl suberate, dimethyl sebacate, diethyl malonate, dibutyl malonate, and dihexyl malonate. A specific example of a triester is tributyl trimellitate. Specific examples of tetraesters include full esters of pentaerythritol and carboxylic acids, and preferred are tetraesters of pentaerythritol in which the carboxylic acids are mainly composed of 2-ethylhexanoic acid, n-heptanoic acid, and n-octanoic acid.

[0029] Examples of glycols that can be used in the present invention include alkylene glycols, polyalkylene glycols, and alkyl ethers thereof. Examples of alkylene glycols include tetraethylene glycol and tripropylene glycol. Examples of polyalkylene glycols include polyethylene glycol, polypropylene glycol, polybutylene glycol, poly(oxyethylene) glycol, poly(oxypropylene) glycol, poly(oxybutylene) glycol, and poly(oxypropylene, oxybutylene) glycol. Examples of alkyl ethers of alkylene glycols include tetraethylene glycol dimethyl ether. Examples of alkyl ethers of polyalkylene glycols include polyethylene glycol alkyl ethers, polypropylene glycol alkyl ethers (e.g., polypropylene glycol monobutyl ether), polybutylene glycol alkyl ethers, and poly(oxypropylene, oxybutylene) glycol alkyl ethers. The alkyl of the alkyl ether has 1 to 18 carbon atoms, and may be a monoether or a diether.

[0030] The sulfur-based compounds that can be used in the present invention are compounds containing a sulfur atom in one molecule, which are usually used as solvents or building blocks in organic synthesis. Specific examples include dimethyl sulfoxide, 2,2'-thiodiethanol, diethyl sulfoxide, dibutyl sulfoxide, butyl sulfide, butyl disulfide, propyl sulfide, propyl disulfide, phenyl sulfide, and bis(2-hydromethoxy)disulfide. Among these, dimethyl sulfoxide and 2,2'-thiodiethanol are preferred. The phosphorus-based compounds that can be used in the present invention are compounds that contain a phosphorus atom in one molecule and are usually used as extreme pressure agents or antiwear agents in lubricating oils. Specific examples include trimethyl phosphate, triethyl phosphate, tributyl phosphate, trimethylphosphine, triethylphosphine, tributylphosphine, and 2-ethylhexyldiphenyl phosphate. Of these, trimethyl phosphate is preferred. The nitrogen-based compounds that can be used in the present invention are compounds containing a nitrogen atom in one molecule, which are usually used as solvents or building blocks in organic synthesis. Specific examples include formamide, N-methylformamide, N-ethylformamide, N-tert-butylformamide, tetramethylurea, tetraethylurea, and tetrabutylurea. Of these, formamide, N-methylformamide, N-tert-butylformamide, tetramethylurea, and tetraethylurea are preferred.

[0031] Antistatic agents may be anionic, cationic, amphoteric, or nonionic, such as poly(oxyethylene) alkylamines, poly(oxyethylene) alkylamides, poly(oxyethylene) alkyl ethers, poly(oxyethylene) alkylphenyl ethers, glycerin aliphatic esters, sorbitan aliphatic esters, alkyl sulfonates, alkylbenzene sulfonates, alkyl phosphates, quaternary ammonium chlorides, quaternary ammonium sulfates, quaternary ammonium nitrates, alkyl betaines, alkyl imidazolines, alkyl alanines, polyvinyl benzyl, and polyacrylics, as described on page 1238 of Chemical Products, 2018, 16918, published by Chemical Engineering Daily. Other examples include amine derivatives, succinic acid derivatives, partial esters of poly(oxyalkylene) glycols and polyhydric alcohols, ammonium compounds of alkyl naphthalene sulfonic acid, polyalkyl sulfones, and neutralized salts of alkylaryl sulfonic acids and alkyl amines.

[0032] Ionic liquid is also called room temperature molten salt, it is a molten salt that becomes liquid at room temperature.The ionic liquid that can be used in the present invention can be selected from the group consisting of hexafluorophosphate, trifluoromethanesulfonic acid, bis(perfluoroalkylsulfonyl)imide, (trifluoromethylsulfonyl) (heptafluoropropylsulfonyl)imide, bis[fluorosulfonyl]imide, bispentafluoroethanesulfonimide, nitrogen trioxide, p-toluenesulfonic acid, diethylene glycol monomethyl ether sulfonic acid, acetic acid, trifluoromethanecarboxylic acid, biscyanoimide, and tristrifluoromethanesulfonic acid methide, tris(perfluoroalkyl)trifluorophosphate, bis(perfluoroalkyl)(trifluoromethyl)trifluorophosphate.

[0033] For example, ionic liquids in which the anion is represented by either formula 1 or 2 below can also be suitably used. (Rf1-SO2)(Rf2-SO2)N - formula 1 (Rf3)(Rf3)(Rf3)PF3 - formula 2 (In formula 1, Rf1 and Rf2 may be the same or different and represent F, CF3, C2F5, C3F7, or C4F9. In formula 2, Rf3 may be the same or different and represent CF3, C2F5, C3F7, or C4F9.)

[0034] Examples of the anion represented by formula 1 include bis(perfluoroalkylsulfonyl)imide, (trifluoromethylsulfonyl)(heptafluoropropylsulfonyl)imide, bis[fluorosulfonyl]imide, etc. Examples of the anion represented by formula 2 include tris(perfluoroalkyl)trifluorophosphate, bis(perfluoroalkyl)(trifluoromethyl)trifluorophosphate, etc.

[0035] Cations constituting ionic liquids include imidazolium, pyridinium, pyrazolium, piperidinium, pyrrolidium, morpholine, piperazine, pyrrole, phosphonium, quaternary ammonium salts, and isoxazolium, including imidazoliums such as ethylmethylimidazolium, hexylmethylimidazolium, methyloctylimidazolium, and butyldimethylimidazolium; pyridiniums such as butyl-4-methylpyridinium; piperidiums such as methoxyethyl-methylpiperidinium; pyrrolidiniums such as methoxyethyl-methylpyrrolidinium; phosphoniums such as octyltriethylphosphonium and triethyloctylphosphonium; and isoxazoliums such as propyldimethylisoxazolium. Ionic liquids are also classified into aliphatic amines, alicyclic amines, and pyridine (aromatic) systems.

[0036] Preferred ionic liquids that can be used in the present invention include an ionic liquid in which the anion is bis(trifluoromethylsulfonyl)imide and the cation is 1-butyl-2,3-dimethylimidazolium, an ionic liquid in which the anion is bis(trifluoromethylsulfonyl)imide and the cation is 1-(2-methoxyethyl)-1-methylpyrrolidinium, an ionic liquid in which the anion is bis(trifluoromethylsulfonyl)imide and the cation is triethyloctylphosphonium, and an ionic liquid in which the anion is (trifluoromethylsulfonyl)(heptafluoropropylsulfonyl)imide and the cation is 1-ethyl-3-methylimidazolium.

[0037] A liquid crystal compound is a compound that appears liquid in a certain temperature range and exhibits birefringence specific to optically anisotropic crystals. Liquid crystal compounds are classified into smectic liquid crystals, nematic liquid crystals, cholestric liquid crystals, and discotic liquid crystals depending on their molten state, and any of these liquid crystal compounds can be used in the present invention.

[0038] Specific examples of the liquid crystal compound used in the present invention include (1) Schiff base-based compounds, (2) azo-based compounds, azoxy-based compounds, (3) benzoate ester-based compounds, (4) biphenyl-based compounds, terphenyl-based compounds, (5) cyclohexylcarboxylate ester-based compounds, (6) phenylcyclohexane-based compounds, biphenylcyclohexane-based compounds, (7) pyrimidine-based compounds, dioxane-based compounds, (8) cyclohexylcyclohexane ester-based compounds, (9) cyclohexylethane-based compounds, (10) cyclohexane-based compounds, (11) tolan-based compounds, (12) cholesteric compounds, (13) triazine-based compounds, (14) COS-based compounds, (15) CCN-based compounds, and (16) discotic liquid crystal compounds.

[0039] Although the cyanobiphenyl-based liquid crystal compounds of (4) have excellent chemical stability, the temperature range of the liquid crystal phase is somewhat narrow, and it is desirable to use them in combination with other liquid crystal compounds. However, they are nematic liquid crystals with high dielectric anisotropy and are widely used in liquid crystal displays. For example, cyanobiphenyl liquid crystals include 4-cyano-4'-pentylbiphenyl, 4-cyano-4'-butylbiphenyl, 4-cyano-4'-hexylbiphenyl, 4-cyano-4'-heptylbiphenyl, 4-cyano-4'-octylbiphenyl, 4-cyano-4'-nonylbiphenyl, 4-cyano-4'-undecylbiphenyl, 4-cyano-4'-dodecylbiphenyl, 4-butoxy-4'-cyanobiphenyl, 4-ethoxy-4'-cyanobiphenyl, 4-propoxy-4'-cyanobiphenyl, 4-pentoxy-4'-cyanobiphenyl, 4-hexoxy-4'-cyanobiphenyl, 4-heptoxy-4'-cyanobiphenyl, 4-octoxy-4'-cyanobiphenyl, 4-nonoxy-4'-cyano ...nonoxy-4'-cyanobiphenyl, 4-nonoxy-4'-cyanobiphenyl, 4-nonoxy-4'-cyanobiphenyl, 4-nonoxy-4'-cyanobiphenyl, 4-nonoxy-4'-cyanobiphenyl, 4-nonoxy-4'-cyanobiphenyl, 4-nonoxy-4'-cyanobiphenyl, 4-nonoxy-4'-cyanobiphenyl, 4-nonoxy-4'-cyanobiphenyl, trans-4-cyanobiphenyl, 4-decyloxy-4'-cyanobiphenyl, 4-dodecyloxy-4'-cyanobiphenyl, (S)-4-cyano-4'-(2-methylbutyl)biphenyl, 4-(trans-4-propylcyclohexyl)benzonitrile, 4-(trans-4-butylcyclohexyl)benzonitrile, 1-(trans-4-amylcyclohexyl)-4-cyanobenzene, 4-[trans-4-[(E)-1-propenyl]cyclohexyl]benzonitrile, 4-cyano-4''-pentyl-p-terphenyl, 4-cyano-4''-propyl-p-terphenyl, and trans-4'-(4-amylcyclohexyl)biphenyl-4-carbonitrile.

[0040] The SP compounds that can be used in the present invention are compounds containing a sulfur atom and a phosphorus atom in one molecule, which are usually used as extreme pressure agents or antiwear agents in lubricating oils. Specific examples include alkylated triphenyl phosphorothioate and ZnDTP. Of these, alkylated triphenyl phosphorothioate is preferred. The NS compounds that can be used in the present invention are compounds containing a nitrogen atom and a sulfur atom in one molecule, which are usually used as metal corrosion inhibitors in lubricating oils. Specific examples include dimercaptothiadiazole derivatives, molybdenum dithiocarbamate, and ZnDTC. Among these, dimercaptothiadiazole derivatives and molybdenum dithiocarbamate are preferred. The fatty acid amine salts that can be used in the present invention are compounds that are usually used as rust inhibitors for lubricating oils.Specific examples include dicycloamine oleate salt, amine laurate salt, amine myristate salt, amine palmitate salt, amine stearate salt, amine linoleate salt, amine arachidonic acid salt, amine linoleate salt, etc.Among these, dicycloamine oleate salt is preferred.

[0041] (Compound (B)) Compound (B) is a compound in which the proportion of carbon atoms forming an aromatic ring structure among all carbon atoms constituting the molecule is 40% or more, preferably 50% or more, and more preferably 60% or more. Here, the ratio of the number of carbon atoms forming an aromatic ring structure to the total number of carbon atoms constituting the molecule can be calculated. For example, in the case of diphenylamine, the total number of carbon atoms is 13 and the number of carbon atoms forming an aromatic ring structure is 12, so the ratio is calculated by dividing 12 by 13. Compound (B) is preferably an alkyl or alkenyl compound having two or more aromatic rings. Specific examples include diphenylmethane, diphenylpropane, and diphenylethylene. Phenyl ethers having three or more aromatic rings are also preferred, and phenyl ethers such as pentaphenyl ether, tetraphenyl ether, and alkyltetraphenyl ether, alkylbenzenes, and alkylnaphthalenes are preferred.

[0042] The anti-peeling agent of the present invention may contain any substance as long as it does not negatively affect the anti-peeling effect of the compound (A) or (B). Based on the total mass of the anti-peeling agent of the present invention, the content of the compound is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more. When either compound (A) or compound (B) is used as the compound, its content is, like the above compound, more than 0.1% by mass, preferably more than 1% by mass, more preferably 2% by mass or more, and even more preferably 4% by mass or more. When compound (A) and compound (B) are used in combination, their total amount is preferably 2% or more, more preferably 4% or more. There is no particular upper limit on the proportion of the compound in the anti-peeling agent of the present invention. In the case of polyvalent esters and glycols, from the viewpoints of heat resistance and resin resistance, their content is preferably less than 40% by mass, more preferably 10% by mass or less, based on the total mass of the anti-peeling agent. In the case of compounds other than polyvalent esters and glycols, from an economical point of view, the content is preferably 10% by mass or less, and more preferably 3% by mass or less.

[0043] Because there is a risk of ignition due to plasma generated by friction of lubricated parts, the flash point of the compound of the present invention is preferably not more than 70° C. The flash point can be measured in accordance with JIS K2265.

[0044] [Lubricant composition] Since the compound is liquid at room temperature, it can be used alone as a lubricant composition, or can be used as a base oil for a lubricant or grease, or can be mixed with a conventional base oil as a base oil for a lubricant or grease to form a lubricant composition.

[0045] (conventional base oil) The conventional base oil has a specific volume resistivity of 1.0×10 10Those with a viscosity exceeding Ω·cm can be used. Those containing saturated or unsaturated hydrocarbon groups with a total carbon number of 12 or more are preferred, specifically mineral oils or synthetic oils. Examples of mineral oils that can be used include paraffinic mineral oils, naphthenic mineral oils, and mixtures thereof. Highly refined mineral oils (i.e., mineral oils that have been dewaxed to reduce the deposition of wax components at low temperatures, thereby lowering the pour point (approximately −5°C to −20°C, measured according to JIS K 2269) compared to unrefined mineral oils) are preferred. Examples of synthetic oils include synthetic hydrocarbons, ester oils, ether oils, glycol oils, silicone oils, and fluorinated oils. Examples of synthetic hydrocarbon oils include polyalphaolefins (PAOs) and polybutenes. Among these, polyalphaolefins are preferred. Examples of ester oils include diesters, trimellitic esters, and polyol esters. Examples of ether oils include alkyl diphenyl ethers (ADEs), dialkyl diphenyl ethers, and polypropylene glycols. Examples of glycol oils include polypropylene glycols and polypropylene alkyl ethers.

[0046] When used in combination with mineral oil or synthetic hydrocarbons (especially poly-alphaolefins), hydrogen generation can be effectively suppressed even with small amounts of the compound, for example, greater than 0.1 mass%, preferably greater than 1 mass%, more preferably 2 mass% or more, and even more preferably 3 mass% or more, based on the total mass of the lubricant composition. The content of the compound in the lubricant composition of the present invention can be, for example, 40 mass% or less, 20 mass% or less, 10 mass% or less, 5 mass% or less, or 3 mass% or less. In consideration of compatibility with the compound, preferred conventional oils include ester oils such as diesters and polyol esters, ether oils such as alkyl phenyl ether oils, glycol oils such as water-insoluble polyalkylene glycols, silicone oils, and fluorinated oils. In terms of resin resistance and heat resistance, mineral oils, synthetic hydrocarbon oils, phenyl ether oils, and alkyl phenyl ether oils are preferred.

[0047] The kinematic viscosity at 40°C of the base oil in the lubricant composition of the present invention (i.e., the compound (A) and / or (B) alone or a mixture thereof with the conventional oil) is 10 to 500 mm 2 The kinematic viscosity of the base oil at 40°C is preferably 10 mm / s. 2 If it is less than 500mm / s, a sufficient oil film may not be secured at low speeds or high temperatures. 2 If it exceeds / s, torque may increase at high speeds or low temperatures. For the same reason, 2 / s is more preferable, 60 to 130 mm 2 The kinematic viscosity of the base oil can be measured in accordance with JIS K2283. The content of the base oil in the lubricant composition of the present invention is preferably 60 to 99.9 parts by mass, more preferably 90 to 99.9 parts by mass, and even more preferably 97 to 99.9 parts by mass, relative to 100 parts by mass of the total of the base oil and anti-peeling agent. A base oil content within this range is preferred because it provides excellent lubricity and low volatility.

[0048] (Optional additives) The lubricant composition of the present invention may further contain general-purpose additives as needed. For example, rust inhibitors, load-bearing additives, antioxidants, etc. may be contained as needed. The content of these optional additives is usually 0.5 to 5 mass % based on the total mass of the lubricant composition of the present invention.

[0049] Rust inhibitors include inorganic and organic rust inhibitors. Inorganic rust inhibitors include inorganic metal salts such as sodium silicate, lithium carbonate, potassium carbonate, and zinc oxide. Organic rust inhibitors include sodium benzoate, benzoates of lithium benzoate, calcium sulfonates, sulfonate salts of zinc sulfonates, zinc naphthenate, carboxylates of sodium sebacate, succinic acid, succinic anhydride, succinic acid derivatives of succinic acid half esters, sorbitan monooleate, sorbitan esters of sorbitan trioleate, and fatty acid amine salts.

[0050] Examples of load-bearing additives include phosphorus-based additives such as phosphate esters, sulfur-based additives such as polysulfides and sulfurized oils, phosphorus-sulfur-based additives such as phosphorothionates, thiocarbamates, thiophosphates, and organic phosphate esters.

[0051] Antioxidants are known to inhibit oxidation degradation of grease, and examples thereof include phenol-based antioxidants and amine-based antioxidants. Examples of phenolic antioxidants include 2,6-di-tert-butyl-p-cresol (BHT), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), 2,6-di-tert-butyl-phenol, 2,4-dimethyl-6-tert-butylphenol, tert-butylhydroxyanisole (BHA), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), 4,4'-methylenebis(2,3-di-tert-butylphenol), 4,4'-thiobis(3-methyl-6-tert-butylphenol), and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. Of these, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate is preferred. Examples of the amine antioxidant include Nn-butyl-p-aminophenol, 4,4'-tetramethyl-di-aminodiphenylmethane, α-naphthylamine, N-phenyl-α-naphthylamine, phenothiazine, alkyldiphenylamine, etc. Among these, alkyldiphenylamine is preferred.

[0052] The lubricant composition of the present invention can be used as a lubricating oil, a conductive oil, a dynamic pressure oil, etc. The lubricant composition of the present invention is effective in preventing exfoliation wear.

[0053] [Grease composition] The lubricant composition of the present invention may further contain a thickener to form a grease composition. For the same reasons as those described for the lubricant composition, the content of the compounds (A) and / or (B) is preferably more than 0.1% by mass, more preferably more than 1% by mass, even more preferably 2% by mass or more, and particularly preferably 3% by mass or more, based on the total mass of the grease composition of the present invention, and the upper limit may be, for example, 40% by mass or less, 20% by mass or less, 10% by mass or less, 5% by mass or less, or 3% by mass or less. Examples of thickeners that can be used in the grease composition of the present invention include urea-based thickeners such as diurea, Li soap-based thickeners such as Li soap and Li complex soap, and solid thickeners such as bentonite and silica gel. Urea-based thickeners and Li soap-based thickeners are preferred.

[0054] The grease composition of the present invention may further contain general-purpose additives as needed. Usable additives include those described for the lubricant composition. The content of the optional additives is usually 0.1 to 5 mass % based on the total mass of the grease composition of the present invention.

[0055] (Consistency) The worked penetration of the grease composition of the present invention is preferably 200 to 300, more preferably 220 to 280. If the worked penetration exceeds 300, leakage due to high speed rotation increases, and the lubrication life may not be sufficient. On the other hand, if the worked penetration is below 200, the fluidity of the grease deteriorates, and the lubrication life may not be sufficient. In this specification, the term "penetration" refers to the 60-stroke worked penetration. The penetration can be measured according to JIS K2220 7.

[0056] (Thickener content) The content of the thickener is preferably 5 to 25 mass%, more preferably 10 to 20 mass%, based on the total mass of the grease composition of the present invention. If the content is less than 5 mass%, the grease may be soft and leak, and may not be able to provide a sufficient lubrication life. On the other hand, if the content is more than 25 mass%, the fluidity is poor, making it difficult for the grease to penetrate into the lubricated parts, and may not be able to provide a sufficient lubrication life. (Base oil content) The content of the base oil is preferably 60 to 90 mass %, more preferably 70 to 90 mass %, based on the total mass of the grease composition of the present invention, since a content of the base oil within this range is preferred because it provides excellent lubricity and low volatility.

[0057] [Bearings] The grease composition of the present invention is used in various rolling bearings for industrial machinery and automobiles. Examples of rolling bearings for industrial machinery include rolling bearings for various motors for industrial machinery, reduction gears and hydraulic equipment for industrial robots, main shafts and reduction gears for wind power generators, and rolling bearings around elevator hoists. For automobiles, the rolling bearings are preferably for automotive electrical equipment and accessories. Examples of automotive electrical equipment and accessories include alternators, electromagnetic clutches for car air conditioners, intermediate pulleys, idler pulleys, and tension pulleys. [Example]

[0058] [Hydrogen generation test and measurement of hydrogen generation amount] The amount of hydrogen generated was measured according to the method described in Noyama, Nakayama et al., Proceedings of the Tribology Conference, Tokyo (2017) 185. Specifically, a triboplasma generator (Figure 1) capable of generating triboplasma between a needle and a flat electrode was used. The needle served as the cathode, and the flat electrode served as the anode. The needle was made of SCM435 steel with a 120° apex angle. The needle was positioned perpendicular to the anode plate and fixed at a position where the distance between the tip of the needle and the top surface of the anode was 50 μm. The distance between the needle and the flat electrode was controlled with a micrometer. The anode plate was made of SPCC steel. The anode plate formed the bottom of the vessel. The vessel was filled with the anti-peeling agent of the example or comparative example, and the needle was in contact with the anti-peeling agent inside the vessel. The anode plate and the cathode needle were connected by a high-voltage power supply. The voltage and current when a voltage was applied could be measured with an oscilloscope. The vessel and the needle were enclosed in a larger enclosure (hereinafter referred to as the "atmosphere-controlled vessel") that covered both. An opening is provided at the top of the atmospheric-controlled chamber, allowing gas inside the chamber to be sampled via a microsyringe. Another opening is provided at the top of the side of the atmospheric-controlled chamber, allowing dry air to be introduced. The gas inside the atmospheric-controlled chamber can be detected by a semiconductor sensor.

[0059] Dry air was introduced for 30 seconds to replace the gas inside the atmosphere-controlled chamber. After the gas inside the atmosphere-controlled chamber had been replaced with dry air, discharge was performed for 30 seconds while monitoring the current and voltage values ​​with an oscilloscope, and then the chamber was left to stand for 20 seconds, after which the generated gas was sampled with a microsyringe. The sampled gas was introduced into a gas chromatograph to measure the amount of hydrogen gas. Gas chromatography was performed using a gas chromatograph GC-2010 (Shimadzu Corporation), an RT-Msieve φ0.43 mm x 30 m column, and a TCD detector. The amount of hydrogen generated from n-hexadecane was set at 100%, and the amount of hydrogen generated for each compound was calculated. The results are shown in Tables 3 to 10. Examples 1 to 38 are examples of anti-stripping agents, and Examples 39 to 71 are examples of lubricating oil compositions containing anti-stripping agents. Example 42 is a mixture of 3.0 mass% of dimethyl malonate from Example 3 and 97.0 mass% of poly-α-olefin from Comparative Example 8, and the specific volume resistivity of the mixture was 1.0 × 10 10Even if the specific volume resistivity exceeds Ω·cm, 10 This shows that if a predetermined amount of the anti-peeling agent of the present invention, which has a resistivity of Ω·cm or less, is contained, the amount of hydrogen generation can be suppressed to 0%.

[0060] [Table 3]

[0061] [Table 4]

[0062] [Table 5]

[0063] [Table 6]

[0064] [Table 7]

[0065] [Table 8]

[0066] [Table 9]

[0067] [Table 10]

[0068] The suppliers and trade names of the compounds used in the examples and comparative examples are shown below. TIFF0007787214000012.tif208161

Claims

1. An amount greater than 0.1% by weight, based on the total weight of the anti-stripping agent, Volume resistivity is 1.0 x 10 10 An anti-exfoliation agent for a lubricant composition for a rolling bearing, comprising a diester compound having a solubility of Ω cm or less and a dipole term δp of the Hansen solubility parameter of 3.5 or more, the compound being a diester selected from the group consisting of dimethyl phthalate, dimethyl maleate, dimethyl malonate, dimethyl succinate, dimethyl glutarate, dimethyl adipate, dimethyl suberate, diethyl malonate, and dibutyl malonate.

2. A lubricant composition for rolling bearings, comprising the compound according to claim 1 in an amount of more than 0.1 mass % and not more than 40 mass % based on the total mass of the composition.

3. 3. The lubricant composition of claim 2, further comprising at least one conventional base oil selected from the group consisting of mineral oils and synthetic oils.

4. 4. The lubricant composition according to claim 3, wherein the base oil is at least one selected from the group consisting of mineral oils, synthetic hydrocarbon oils, and ether oils.

5. The lubricant composition according to any one of claims 2 to 4, wherein the content of the compound is more than 1 mass % and not more than 40 mass % based on the total mass of the composition.

6. The lubricant composition according to any one of claims 2 to 4, wherein the content of the compound is 2 mass % or more and 40 mass % or less, based on the total mass of the composition.

7. The lubricant composition according to any one of claims 2 to 4, wherein the content of the compound is 3 mass % or more and 40 mass % or less, based on the total mass of the composition.

8. The lubricant composition according to any one of claims 2 to 7, further comprising a thickener.

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