Oil composition, use of oil composition, and friction-reducing agent or abrasion-reducing agent

Abstract

The present disclosure pertains to an oil composition comprising a base oil and a modified conjugated diene-based polymer. The modified conjugated diene-based polymer has at least one functional group selected from the group consisting of dicarboxylic acid anhydride groups, dicarboxylic acid monoester groups, dicarboxylic acid monoamide groups, and carboxylic acid imide groups. The number average molecular weight of the modified conjugated diene-based polymer is 4,000-500,000. The kinematic viscosity of the oil composition at 100°C is 10.0 mm2 / s or less.

Description

Oil compositions, uses of oil compositions, and friction or wear reducers

[0001] The present disclosure relates to oil compositions, uses of oil compositions, and friction or wear reducers.

[0002] Lubricating oil compositions used as engine oils and automatic transmission fluids contain additives commonly called viscosity index improvers to improve their viscosity characteristics. Various polymers, such as olefin copolymers, polymethacrylates, and styrene / hydrogenated diene block polymers, have been investigated as such viscosity index improvers.

[0003] For example, Patent Document 1 discloses a lubricating oil composition containing a lubricating base oil and a specific amount of a polydiene having a number average molecular weight of 500 to 3,000 and having a specific terminal functional group. Patent Document 2 describes a lubricating oil additive composition prepared by a process including a step of reacting a hydrocarbon polymer having a specific number average molecular weight and functionality with a hydroxyl-bonded polycyclic fused ring component. Patent Documents 3 to 6 similarly disclose oil compositions containing specific additives.

[0004] International Publication No. 2019 / 073294, JP 2016-512274 A, International Publication No. 2011 / 005740, JP 5-287290 A, U.S. Patent No. 578054, JP 11-506978 A

[0005] In an attempt to improve fuel economy, it is conceivable to reduce the viscosity of oil compositions used as lubricating oils, etc., but when low-viscosity oil compositions are used as lubricating oils, etc., friction properties and wear resistance may be insufficient. For this reason, the present disclosure provides an oil composition having a kinematic viscosity of 10.0 mm at 100°C. ２ The object of the present invention is to provide an oil composition that has high friction properties and wear resistance despite having a low viscosity of 1 / s or less.

[0006] The present inventors have conducted extensive research to solve the above problems and have completed the present invention. That is, the present invention includes the following preferred embodiments: [1] An oil composition comprising a base oil and a modified conjugated diene polymer, wherein the modified conjugated diene polymer has at least one functional group selected from the group consisting of a dicarboxylic anhydride group, a dicarboxylic acid monoester group, a dicarboxylic acid monoamide group, and a carboxylic acid imide group, the number average molecular weight of the modified conjugated diene polymer is 4,000 to 500,000, and the kinematic viscosity of the oil composition at 100°C is 10.0 mm ２ [2] The kinematic viscosity of the oil composition at 100°C is 1.0 mm / s or less. ２The oil composition according to [1], wherein the functional group equivalent of the functional group possessed by the modified conjugated diene polymer is 500 to 35,000 g / eq. [3] The oil composition according to [1] or [2], wherein the functional group equivalent of the functional group possessed by the modified conjugated diene polymer is 500 to 35,000 g / eq. [4] The oil composition according to any of [1] to [3], wherein the modified conjugated diene polymer contains 50 mass% or more of structural units derived from butadiene and / or structural units derived from isoprene, based on the total amount of the modified conjugated diene polymer. [5] The oil composition according to any of [1] to [4], wherein the iodine value of the modified conjugated diene polymer is 200 g / 100 g to 500 g / 100 g. [6] The oil composition according to any of [1] to [5], wherein the vinyl content of the modified conjugated diene polymer is 0 to 50 mol%. [7] The oil composition according to any one of [1] to [6], wherein the ratio of cis-1,4-bond units to the total amount of 1,4-bond units in the structural units derived from the conjugated diene monomer of the modified conjugated diene polymer is 30 mol % or more. [8] The oil composition according to any one of [1] to [7], wherein the dicarboxylic acid monoester group is a group formed by reacting a dicarboxylic acid or its anhydride with at least one alcohol selected from the group consisting of aliphatic alcohols having 1 to 30 carbon atoms. [9] The oil composition according to any one of [1] to [8], wherein the content of the modified conjugated diene polymer is 0.1 to 10 mass % based on the total amount of the oil composition.

[10] The oil composition according to any one of [1] to [9], wherein the base oil is at least one selected from the group consisting of base oils belonging to Groups I, II, III, and IV of the API (American Petroleum Institute) classification.

[11] The oil composition according to any one of [1] to

[10] , further comprising at least one additive selected from the group consisting of rust inhibitors, antioxidants, surfactants, pour point depressants, detergents and dispersants, metal deactivators, antifoaming agents, viscosity modifiers, friction modifiers, extreme pressure agents, wear inhibitors, corrosion inhibitors, colorants, and oiliness agents.

[12] The oil composition according to any one of [1] to

[11] , wherein the oil composition is a lubricating oil.

[13] The oil composition according to

[12] , wherein the lubricating oil is a transmission fluid or an e-axle lubricating oil.

[14] Use of the oil composition according to any one of [1] to

[13] as a lubricating oil.

[15] A friction reducer or wear reducer containing a modified conjugated diene polymer, wherein the modified conjugated diene polymer has at least one functional group selected from the group consisting of a dicarboxylic acid anhydride group, a dicarboxylic acid monoester group, a dicarboxylic acid monoamide group, and a carboxylic acid imide group, and the modified conjugated diene polymer has a number average molecular weight of 4,000 to 500,000 and a kinematic viscosity at 100°C of 10.0 mm. ２ Friction or wear reducers that are agents for reducing friction or wear in low viscosity oil compositions of 0.15g / s or less.

[0007] According to the present disclosure, the kinematic viscosity at 100°C is 10.0 mm ２ This makes it possible to provide an oil composition that has high friction characteristics and wear resistance despite having a low viscosity of 0.15g / s or less.

[0008] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the scope of the present disclosure is not limited to the embodiments described herein, and various modifications can be made without departing from the spirit of the present disclosure. Furthermore, in this specification, the expression "x to y" (x and y each represent a number) representing a numerical range means "not less than x and not more than y." Furthermore, when multiple upper and lower limit values ​​are described for a specific parameter, any upper and lower limit values ​​may be combined to form a suitable numerical range.

[0009] The oil composition of the present disclosure is an oil composition comprising a base oil and a modified conjugated diene polymer, wherein the modified conjugated diene polymer has at least one functional group selected from the group consisting of a dicarboxylic anhydride group, a dicarboxylic acid monoester group, a dicarboxylic acid monoamide group, and a carboxylic acid imide group, the number average molecular weight of the modified conjugated diene polymer is 4,000 to 500,000, and the kinematic viscosity of the oil composition at 100°C is 10.0 mm ２ / s or less.

[0010] (Modified Conjugated Diene Polymer) The modified conjugated diene polymer contained in the oil composition is a modified conjugated diene polymer having at least one functional group selected from the group consisting of a dicarboxylic anhydride group, a dicarboxylic acid monoester group, a dicarboxylic acid monoamide group, and a carboxylic acid imide group. The oil composition may contain one type of modified conjugated diene polymer, or may contain two or more types of modified conjugated diene polymers.

[0011] The conjugated diene polymer constituting the modified conjugated diene polymer is a polymer containing structural units derived from a conjugated diene monomer. For example, at least one selected from the group consisting of butadiene, isoprene, and β-farnesene can be used as the conjugated diene monomer. The conjugated diene polymer may be a homopolymer of these conjugated diene monomers, a copolymer containing two or more of these, or a copolymer of a conjugated diene monomer and another monomer. When the conjugated diene polymer is a copolymer, it may be a random copolymer or a block copolymer.

[0012] From the viewpoints of friction properties, wear resistance, shear stability, and oxidation stability, the amount of structural units derived from conjugated diene monomers in the modified conjugated diene polymer is preferably 50 to 100 mass%, more preferably 70 to 100 mass%, even more preferably 80 to 100 mass%, still more preferably 90 to 100 mass%, and particularly preferably 95 to 100 mass%, based on the total amount of the modified conjugated diene polymer.

[0013] The conjugated diene polymer constituting the modified conjugated diene polymer preferably has at least a structural unit derived from butadiene and / or a structural unit derived from isoprene. The conjugated diene polymer constituting the modified conjugated diene polymer may have a structural unit derived from butadiene and / or a structural unit derived from isoprene and a structural unit derived from one or more other conjugated diene monomers, or may have a structural unit derived from butadiene and / or a structural unit derived from isoprene, optionally with another conjugated diene monomer and another structural unit (for example, a structural unit derived from an aromatic vinyl compound).

[0014] The total amount of the butadiene-derived structural units and / or isoprene-derived structural units in the modified conjugated diene polymer is, from the viewpoints of friction properties, wear resistance, thickening properties, shear stability, oxidation stability, and low-temperature viscosity, preferably 50 to 100 mass%, more preferably 70 to 100 mass%, even more preferably 90 to 100 mass%, still more preferably 95 to 100 mass%, particularly preferably 98 to 100 mass%, and especially more preferably 100 mass%, relative to the total amount of the modified conjugated diene polymer.

[0015] In a preferred embodiment of the present invention, the amount of structural units derived from butadiene in the modified conjugated diene polymer is, from the viewpoints of friction properties, wear resistance, thickening property, shear stability, oxidation stability, and low-temperature viscosity, preferably 50 to 100 mass%, more preferably 70 to 100 mass%, even more preferably 90 to 100 mass%, still more preferably 95 to 100 mass%, particularly preferably 98 to 100 mass%, and especially more preferably 100 mass%, relative to the total amount of the modified conjugated diene polymer.

[0016] In another preferred embodiment of the present invention, the amount of structural units derived from isoprene in the modified conjugated diene polymer is 50 to 100% by mass, preferably 70 to 100% by mass, more preferably 90 to 100% by mass, even more preferably 95 to 100% by mass, particularly preferably 98 to 100% by mass, and especially preferably 100% by mass, based on the total amount of the modified conjugated diene polymer, from the viewpoints of friction properties, wear resistance, thickening property, shear stability, oxidation stability, and low-temperature viscosity.

[0017] The amount of structural units derived from butadiene in the modified conjugated diene polymer, the amount of structural units derived from isoprene in the modified conjugated diene polymer, and the amount of structural units derived from other conjugated diene monomers in the modified conjugated diene polymer are １ H-NMR and １３ It can be calculated from the amount of butadiene monomer or conjugated diene monomer in the monomer mixture used in producing the modified conjugated diene polymer by C-NMR measurement or from the amount of butadiene monomer or conjugated diene monomer in the monomer mixture used in producing the modified conjugated diene polymer.

[0018] The structural unit derived from butadiene is not particularly limited as long as it is a structural unit derived from the monomer 1,3-butadiene. Examples include 1,2-bond units, 1,4-bond units (cis-1,4-bond units and trans-1,4-bond units), and structural units in which a modifying group is bonded to these. The 1,2-bond units have a vinyl group in the structural unit derived from butadiene, and the cis-1,4-bond units and trans-1,4-bond units have a carbon-carbon double bond moiety in the structural unit derived from butadiene. Furthermore, examples of structural units in which a modifying group is bonded to these include structural units obtained by bonding a modifying group to a moiety derived from a vinyl group in a 1,2-bond unit, and such structural units do not have a vinyl group.

[0019] The structural unit derived from isoprene is not particularly limited as long as it is a structural unit derived from isoprene, a monomer. Examples include 1,2-bond units, 3,4-bond units, 1,4-bond units (cis-1,4-bond units and trans-1,4-bond units), and structural units in which a modifying group is bonded to any of these. The 1,2-bond units and 3,4-bond units have a vinyl group in the structural unit derived from isoprene, and the cis-1,4-bond units and trans-1,4-bond units have a carbon-carbon double bond moiety in the structural unit derived from isoprene. Examples of structural units in which a modifying group is bonded to any of these include structural units obtained by bonding a modifying group to a moiety derived from a vinyl group in the 1,2-bond units and 3,4-bond units, and these structural units do not have a vinyl group.

[0020] From the viewpoints of friction properties, wear resistance, thickening ability, viscosity index, shear stability, oxidation stability, low-temperature viscosity, and handleability, the vinyl content of the modified conjugated diene polymer is preferably 0 to 50 mol%, more preferably 0 to 30 mol%, even more preferably 0.5 to 20 mol%, even more preferably 1 to 15 mol%, and particularly preferably 1 to 12 mol%, relative to the total amount of the modified conjugated diene polymer. The vinyl content refers to the total molar ratio of conjugated diene units bonded via 1,2-bonds, 3,4-bonds (in the case of other than farnesene), and 3,13-bonds (in the case of farnesene) relative to 100 moles of the modified conjugated diene polymer units. In other words, the vinyl content refers to the total molar ratio of conjugated diene units bonded via bonds other than 1,4-bonds (in the case of other than farnesene) and 1,13-bonds (in the case of farnesene) relative to 100 moles of the modified conjugated diene polymer units. When the conjugated diene polymer is polybutadiene, the vinyl content may be the ratio of 1,2-bond units to the total amount of the polybutadiene (total amount of 1,4-bond units and 1,2-bond units). When the conjugated diene polymer is polyisoprene, the vinyl content may be the total molar ratio of 1,2-bond units and 3,4-bond units to the total amount of the polyisoprene (total amount of 1,4-bond units, 1,2-bond units and 3,4-bond units). The "vinyl content" can be determined by infrared absorption spectroscopy, １ It can be determined by H-NMR measurement or the like, for example, by the method described in the Examples.

[0021] In a preferred embodiment of the present disclosure, the ratio of the amount of 1,4-bond units to the total amount of structural units derived from conjugated diene monomers in the modified conjugated diene polymer is preferably 30 to 100 mol %, more preferably 50 to 100 mol %, and even more preferably 60 to 100 mol %, from the viewpoints of friction properties, wear resistance, thickening property, viscosity index, shear stability, oxidation stability, low-temperature viscosity, and handleability. The amounts of 1,4-bond units, cis-1,4-bond units, and trans-1,4-bond units to the total amount of structural units derived from conjugated diene monomers in the modified conjugated diene polymer are, respectively, １It can be measured by H-NMR and infrared absorption spectroscopy, specifically by the method described in the examples.

[0022] In a preferred embodiment of the present disclosure, the ratio of the amount of 1,4-bond units to the total amount of structural units derived from butadiene in the conjugated diene polymer is preferably 30 to 100 mol %, more preferably 50 to 100 mol %, and even more preferably 60 to 100 mol %, from the viewpoints of friction properties, wear resistance, thickening property, viscosity index, shear stability, oxidation stability, low-temperature viscosity, and handleability. The amounts of 1,4-bond units, cis-1,4-bond units, and trans-1,4-bond units to the total amount of structural units derived from butadiene in the conjugated diene polymer are, respectively, １ It can be measured by H-NMR and infrared absorption spectroscopy, specifically by the method described in the examples.

[0023] In another preferred embodiment of the present disclosure, the ratio of the amount of 1,4-bond units to the total amount of structural units derived from isoprene in the conjugated diene polymer is preferably 30 to 100 mol %, more preferably 50 to 100 mol %, and even more preferably 60 to 100 mol %, from the viewpoints of friction properties, wear resistance, thickening property, viscosity index, shear stability, oxidation stability, low-temperature viscosity, and handleability. The amounts of 1,4-bond units, 3,4-bond units, cis-1,4-bond units, and trans-1,4-bond units to the total amount of structural units derived from isoprene in the conjugated diene polymer are respectively １ It can be measured by H-NMR and infrared absorption spectroscopy, specifically by the method described in the examples.

[0024] In a preferred embodiment of the present disclosure, in the structural units derived from conjugated diene monomers of the conjugated diene polymer, the amount of cis-1,4-bond units relative to the total amount of 1,4-bond units is preferably 30 to 100 mol %, more preferably 35 to 100 mol %, and even more preferably 40 to 100 mol %, from the viewpoints of friction properties, wear resistance, thickening property, viscosity index, shear stability, oxidation stability, low-temperature viscosity, and handleability. Furthermore, in the structural units derived from conjugated diene monomers of the conjugated diene polymer, the amount of trans-1,4-bond units relative to the total amount of 1,4-bond units is preferably 0 to 70 mol %, more preferably 0 to 65 mol %, and even more preferably 0 to 60 mol %.

[0025] In a preferred embodiment of the present disclosure, the amount of cis-1,4-bond units relative to the total amount of 1,4-bond units in the butadiene-derived structural units of the modified conjugated diene polymer is preferably 70 mol% or less, more preferably 0 to 70 mol%, even more preferably 0.1 to 60 mol%, even more preferably 10 to 50 mol%, and particularly preferably 30 to 45 mol%. Furthermore, the amount of trans-1,4-bond units relative to the total amount of 1,4-bond units in the butadiene-derived structural units of the modified conjugated diene polymer is preferably 30 mol% or more, more preferably 30 to 100 mol%, even more preferably 40 to 99.9 mol%, even more preferably 50 to 95 mol%, and particularly preferably 55 to 70 mol%.

[0026] In a preferred embodiment of the present disclosure, the amount of cis-1,4-bond units relative to the total amount of 1,4-bond units in the structural units derived from isoprene of the modified conjugated diene polymer is preferably 60 mol% or more, more preferably 60 to 100 mol%, even more preferably 70 to 100 mol%, even more preferably 80 to 100 mol%, and particularly preferably 90 to 100 mol%. Furthermore, the amount of trans-1,4-bond units relative to the total amount of 1,4-bond units in the structural units derived from isoprene of the modified conjugated diene polymer is preferably 40 mol% or less, more preferably 0 to 40 mol%, even more preferably 0 to 30 mol%, even more preferably 0 to 20 mol%, and particularly preferably 0 to 10 mol%.

[0027] The modified conjugated diene polymer has a number average molecular weight of 4,000 to 500,000. When the number average molecular weight is 4,000 or more, the friction properties, wear resistance, thickening properties, and low-temperature viscosity are sufficient. When the number average molecular weight is 500,000 or less, the shear stability, oxidation stability, and low-temperature viscosity are sufficient. From the viewpoints of friction properties, wear resistance, thickening properties, shear stability, oxidation stability, and low-temperature viscosity, the number average molecular weight of the modified conjugated diene polymer is preferably 5,000 to 300,000, more preferably 7,000 to 150,000, even more preferably 8,000 to 80,000, and still more preferably 8,000 to 50,000. Note that the number average molecular weight in this specification refers to the number average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC).

[0028] From the viewpoints of friction properties, wear resistance, thickening properties, shear stability, and oxidation stability, the modified conjugated diene polymer preferably has a weight average molecular weight of 5,000 to 300,000, more preferably 7,000 to 150,000, even more preferably 8,000 to 80,000, and still more preferably 8,000 to 50,000. Note that the weight average molecular weight in this specification refers to a weight average molecular weight calculated in terms of polystyrene obtained by measurement using gel permeation chromatography (GPC).

[0029] From the viewpoints of friction properties, wear resistance, thickening properties, shear stability, oxidation stability, and low-temperature viscosity, the modified conjugated diene polymer preferably has a molecular weight distribution of 1.0 to 2.0, more preferably 1.0 to 1.5, even more preferably 1.0 to 1.3, still more preferably 1.0 to 1.2, and particularly preferably 1.0 to 1.1. The molecular weight distribution (Mw / Mn) means the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in terms of standard polystyrene, determined by GPC measurement.

[0030] The modified conjugated diene polymer has at least one functional group selected from the group consisting of a dicarboxylic anhydride group, a dicarboxylic acid monoester group, a dicarboxylic acid monoamide group, and a carboxylic acid imide group. The modified conjugated diene polymer may have one type of dicarboxylic acid anhydride group, or two or more types of dicarboxylic acid anhydride groups, and the same applies to other functional groups. The modified conjugated diene polymer may also have a combination of two or more of these functional groups. From the viewpoints of friction properties, wear resistance, thickening properties, shear stability, oxidation stability, and low-temperature viscosity, these functional groups are preferably incorporated into the side chain portion of the modified conjugated diene polymer.

[0031] A dicarboxylic acid anhydride group is a group in which one water molecule has been eliminated from a dicarboxylic acid group. Examples of the dicarboxylic acid anhydride group include anhydride groups of dicarboxylic acids having 3 to 10 carbon atoms, and specific examples thereof include a maleic anhydride group, a succinic anhydride group, and an itaconic anhydride group.

[0032] In one preferred embodiment, the dicarboxylic acid anhydride group has formula (I): [In the formula, R １ represents a saturated or unsaturated, linear or branched, trivalent hydrocarbon group having 1 to 7 carbon atoms, and * represents a bond to the conjugated diene polymer skeleton. １ R is preferably a trivalent hydrocarbon group having 2 to 3 carbon atoms, more preferably a linear trivalent hydrocarbon group having 2 to 3 carbon atoms, and even more preferably a linear trivalent hydrocarbon group having 2 carbon atoms. １ When R represents a branched hydrocarbon group, it has 3 or more carbon atoms. ２ ~R ３ The same is true for .

[0033] The dicarboxylic acid monoester group is a group in which one carboxylic acid group of dicarboxylic acid groups forms an ester. Examples of the dicarboxylic acid monoester group include a group in which a dicarboxylic acid or an anhydride group thereof reacts with an aliphatic alcohol having 1 to 30 carbon atoms. As the aliphatic alcohol, an aliphatic alcohol having 1 to 20 carbon atoms is preferred, and an aliphatic alcohol having 1 to 10 carbon atoms is more preferred. Specific examples of the dicarboxylic acid monoester group include a maleic acid monomethyl ester group, a succinic acid monomethyl ester group, a fumaric acid monomethyl ester group, and an itaconic acid monomethyl ester group.

[0034] In one preferred embodiment, the dicarboxylic acid monoester group has the formula (II): [In the formula, R ２ represents a saturated or unsaturated, linear or branched, trivalent hydrocarbon group having 1 to 7 carbon atoms; R ３ represents a saturated or unsaturated, linear or branched, monovalent alkyl group having 1 to 30 carbon atoms, and * represents a bond to the conjugated diene polymer skeleton. ２ As for R １ and R １ A preferred embodiment of R ２ The same applies to R ３ R is preferably a monovalent alkyl group having 1 to 20 carbon atoms, more preferably a monovalent alkyl group having 1 to 10 carbon atoms. ３ Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, and an isopropyl group.

[0035] A dicarboxylic acid monoamide group is a group in which one carboxylic acid group of dicarboxylic acid groups forms an amide. A carboxylic acid imide group is a group in which one water molecule is eliminated from a dicarboxylic acid monoamide group. Examples of dicarboxylic acid monoamide groups include groups in which a dicarboxylic acid or its anhydride group reacts with ammonia or an aliphatic amine having 1 to 30 carbon atoms. Ammonia or an aliphatic amine having 1 to 20 carbon atoms is preferred, and ammonia or an aliphatic amine having 1 to 10 carbon atoms is more preferred. Specific examples of dicarboxylic acid monoamide groups include a maleic acid monoamide group, a succinic acid monoamide group, a fumaric acid monoamide group, and an itaconic acid monoamide group. Specific examples of carboxylic acid imide groups include a maleic acid imide group, a succinic acid imide group, and an itaconic acid imide group.

[0036] In a preferred embodiment, the modified conjugated diene polymer has at least one functional group selected from the group consisting of a dicarboxylic acid anhydride group, a dicarboxylic acid monoester group, and a dicarboxylic acid monoamide group, and more preferably has at least one functional group selected from the group consisting of a dicarboxylic acid anhydride group and a dicarboxylic acid monoester group. The modified conjugated diene polymer may have both a dicarboxylic acid anhydride group and a dicarboxylic acid monoester group.

[0037] The functional group equivalent of the functional group contained in the modified conjugated diene polymer is preferably 500 to 35,000 g / eq, more preferably 1,000 to 20,000 g / eq, and even more preferably 1,500 to 10,000 g / eq, from the viewpoints of friction characteristics, wear resistance, thickening ability, oxidation stability, and low-temperature viscosity. The functional group equivalent can be calculated by the method described in the examples.

[0038] From the viewpoints of friction properties, wear resistance, thickening ability, oxidation stability, and low-temperature viscosity, the content of the functional group in the modified conjugated diene polymer is preferably 0.1 to 20 parts by mass, more preferably 0.3 to 15 parts by mass, and even more preferably 0.5 to 10 parts by mass, relative to 100 parts by mass of the total amount of the modified conjugated diene polymer. The content of the functional group can be calculated by the method described in the Examples.

[0039] From the viewpoints of friction characteristics, wear resistance, thickening ability, oxidation stability, and low-temperature viscosity, the average number of functional groups per molecule of the modified conjugated diene polymer is preferably 1.5 to 30, more preferably 2.0 to 30, more preferably 2.5 to 20, and even more preferably 3.0 to 15. The average number of functional groups can be calculated by the method described in the examples.

[0040] From the viewpoints of friction properties, wear resistance, thickening ability, oxidation stability, and low-temperature viscosity, the acid value of the modified conjugated diene polymer is preferably 3 to 150 mgKOH / g, more preferably 5 to 100 mgKOH / g, and even more preferably 10 to 50 mgKOH / g. The acid value can be measured by neutralization titration using a 0.1 N ethanol solution of potassium hydroxide, specifically, by the method described in the Examples.

[0041] The modified conjugated diene polymer may or may not have other functional groups in addition to the functional groups such as the dicarboxylic anhydride. Examples of other functional groups include functional groups selected from the group consisting of hydroxyl groups, sulfonic acid groups, alkoxysilyl groups, amino groups, imide groups, nitrile groups, and mercapto groups. Preferably, the modified conjugated diene polymer does not have other functional groups (functional groups selected from the group consisting of hydroxyl groups, sulfonic acid groups, alkoxysilyl groups, amino groups, imide groups, nitrile groups, and mercapto groups) in addition to the functional groups such as the dicarboxylic anhydride groups. Whether or not the polymer has the above functional groups is determined depending on the functional groups, and can be determined by acid value titration, infrared absorption spectroscopy, １ This can be confirmed by H-NMR measurement or the like.

[0042] From the viewpoints of friction properties, wear resistance, and low-temperature viscosity, the modified conjugated diene polymer is preferably a modified conjugated diene polymer having a low hydrogenation rate or not being hydrogenated. The hydrogenation rate of the modified conjugated diene polymer is preferably 0 to 50 mol%, more preferably 0 to 40 mol%, even more preferably 0 to 20 mol%, still more preferably 0 to 10 mol%, particularly preferably 0 to 5 mol%, and especially preferably 0 mol%. The hydrogenation rate of the modified conjugated diene polymer is determined by the content of carbon-carbon double bonds derived from the conjugated diene compound in the modified conjugated diene polymer, as follows: １ It is a value measured by H-NMR measurement.

[0043] In a preferred embodiment of the present disclosure, the iodine value of the modified conjugated diene polymer is, from the viewpoints of friction properties, wear resistance, and low-temperature viscosity, preferably 200 g / 100 g to 500 g / 100 g, more preferably 250 g / 100 g to 500 g / 100 g, even more preferably 350 g / 100 g to 500 g / 100 g, still more preferably 400 g / 100 g to 500 g / 100 g, particularly preferably 420 g / 100 g to 500 g / 100 g, and especially preferably 450 g / 100 g to 500 g / 100 g. The iodine value is a value that can be determined in accordance with JIS K 0070:1992, and more specifically, is a value measured according to the method described in the Examples.

[0044] The content of the modified conjugated diene polymer in the oil composition may be determined depending on the properties such as viscosity required of the oil composition, and is not particularly limited, but is preferably 0.1 to 10 mass%, more preferably more than 0.1 to 10 mass%, even more preferably 0.3 to 8 mass%, still more preferably 0.5 to 7 mass%, and especially preferably 1.0 to 5 mass%, based on the total amount of the oil composition. A conjugated diene polymer content of not less than the above lower limit is preferred from the viewpoint of the friction properties and wear resistance of the oil composition, and a content of not more than the above upper limit is preferred from the viewpoint of improving the fuel economy and production costs of the oil composition.

[0045] The reason why the inclusion of a modified conjugated diene polymer in an oil composition improves friction properties and wear resistance despite its low viscosity is unclear, but it is thought that when the oil composition is used, the functional groups of the modified conjugated diene polymer are adsorbed to the surface of the metal component. This increases the concentration of the polymer locally on the surface of the metal component, thereby increasing the viscosity. This is thought to prevent oil film breakdown and reduce friction and wear.

[0046] (Method for Producing Modified Conjugated Diene Polymer) The method for producing the modified conjugated diene polymer is not particularly limited. For example, it is preferable to produce the modified conjugated diene polymer by polymerizing a conjugated diene monomer such as butadiene or isoprene and other monomers that are optionally contained, for example, by solution polymerization to produce an unmodified conjugated diene polymer, and then reacting the polymer with a modifying compound.

[0047] As the solution polymerization method, a known method or a method equivalent to a known method can be applied, for example, a conjugated diene monomer such as butadiene or isoprene is polymerized in a solvent using a Ziegler catalyst, a metallocene catalyst, or an anionically polymerizable active metal or active metal compound, optionally in the presence of a polar compound.

[0048] Examples of the solvent include aliphatic hydrocarbons such as n-butane, n-pentane, isopentane, n-hexane, n-heptane, and isooctane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, and methylcyclopentane; and aromatic hydrocarbons such as benzene, toluene, and xylene.

[0049] Examples of the anionically polymerizable active metal include alkali metals such as lithium, sodium, and potassium; alkaline earth metals such as beryllium, magnesium, calcium, strontium, and barium; and lanthanoid rare earth metals such as lanthanum and neodymium. Among the anionically polymerizable active metals, alkali metals and alkaline earth metals are preferred, and alkali metals are more preferred.

[0050] The anionically polymerizable active metal compound is preferably an organic alkali metal compound. Examples of the organic alkali metal compound include organic monolithium compounds such as methyllithium, ethyllithium, n-butyllithium, sec-butyllithium, t-butyllithium, hexyllithium, phenyllithium, and stilbenelithium; polyfunctional organic lithium compounds such as dilithiomethane, dilithionaphthalene, 1,4-dilithiobutane, 1,4-dilithio-2-ethylcyclohexane, and 1,3,5-trilithiobenzene; sodium naphthalene, potassium naphthalene, and the like. Among these organic alkali metal compounds, organic lithium compounds are preferred, and organic monolithium compounds are more preferred.

[0051] The amount of the organic alkali metal compound used can be appropriately determined depending on the target molecular weight of the conjugated diene polymer, but is usually 0.01 to 3 parts by mass per 100 parts by mass of all monomers.

[0052] The above organic alkali metal compounds can also be reacted with a secondary amine such as dibutylamine, dihexylamine, or dibenzylamine to form organic alkali metal amides.

[0053] In anionic polymerization, polar compounds are usually used to adjust the microstructure (e.g., vinyl content) of the unmodified liquid diene polymer without deactivating the reaction. Examples of polar compounds include ether compounds such as dibutyl ether, tetrahydrofuran, and ethylene glycol diethyl ether; tertiary amines such as tetramethylethylenediamine and trimethylamine; alkali metal alkoxides; and phosphine compounds. The polar compound is usually used in an amount of 0.01 to 1,000 moles per mole of the organic alkali metal compound.

[0054] The temperature for solution polymerization is usually in the range of −80 to 150° C., preferably in the range of 0 to 100° C., and more preferably in the range of 10 to 90° C. The polymerization may be carried out in either a batch or continuous manner.

[0055] The polymerization reaction can be terminated by adding a polymerization terminator. Examples of the polymerization terminator include alcohols such as methanol and isopropanol. The conjugated diene polymer can be isolated by pouring the obtained polymerization reaction solution into a poor solvent such as methanol to precipitate the conjugated diene polymer, or by washing the polymerization reaction solution with water, separating it, and then drying it. The unmodified conjugated diene polymer obtained in this manner may be reacted directly with a modifying compound described below, or may be reacted with a modifying compound after hydrogenating at least a portion of the unsaturated bonds (carbon-carbon double bonds) contained in the conjugated diene polymer.

[0056] By reacting the unmodified conjugated diene polymer obtained as described above with a modifying compound, at least one functional group selected from the group consisting of a dicarboxylic acid anhydride group, a dicarboxylic acid monoester group, a dicarboxylic acid monoamide group, and a carboxylic acid imide group can be introduced, thereby producing a modified conjugated diene polymer.

[0057] Examples of modifying compounds for introducing dicarboxylic acid anhydride groups include maleic anhydride and itaconic anhydride. Examples of modifying compounds for introducing dicarboxylic acid monoester groups include maleic acid monoester, fumaric acid monoester, and itaconic acid monoester. Examples of modifying compounds for introducing dicarboxylic acid monoamide groups include maleic acid monoamide, fumaric acid monoamide, and itaconic acid monoamide. Examples of modifying compounds for introducing carboxylic acid imide groups include maleic acid imide and itaconic acid imide.

[0058] A modified conjugated diene polymer having a dicarboxylic acid anhydride group can be obtained by reacting an unmodified conjugated diene polymer with a dicarboxylic acid anhydride. Subsequently, a modified conjugated diene polymer having a dicarboxylic acid monoester group, a dicarboxylic acid monoamide group, or a carboxylic acid imide group can be produced by reacting the conjugated diene polymer having a dicarboxylic acid anhydride group with a modifying compound. When an aliphatic alcohol having 1 to 30 carbon atoms is used as the modifying compound, a modified conjugated diene polymer having a dicarboxylic acid monoester group can be obtained. When ammonia or an aliphatic amine having 1 to 30 carbon atoms is used as the modifying compound, a modified conjugated diene polymer having a dicarboxylic acid monoamide group or a carboxylic acid imide group can be obtained. The modifying compound to be reacted with the modified conjugated diene polymer having a functional group such as a dicarboxylic acid anhydride group may be used alone or in combination of two or more.

[0059] A known method can be used to react the modifying compound with the unmodified conjugated diene polymer, for example, a method can be used in which the unmodified conjugated diene polymer, the modifying compound, and optionally a radical catalyst are added, and then heated in the presence or absence of an organic solvent.

[0060] As the organic solvent, hydrocarbon solvents and halogenated hydrocarbon solvents can be used. Among these organic solvents, hydrocarbon solvents are preferred, and at least one solvent selected from the group consisting of n-butane, n-hexane, n-heptane, cyclohexane, benzene, toluene, and xylene is preferred.

[0061] Examples of the radical catalyst include di-s-butyl peroxydicarbonate, t-amyl peroxypivalate, t-amyl peroxy-2-ethylhexanoate, azobisisobutyronitrile, etc. Among these radical catalysts, azobisisobutyronitrile is preferred.

[0062] The functional group equivalent of the functional group possessed by the modified conjugated diene polymer is controlled by the reaction temperature and reaction time. The reaction temperature is preferably 60 to 200°C, and more preferably 80 to 200°C. The reaction time is preferably 2 to 200 hours, and more preferably 3 to 200 hours. For example, the reaction temperature of the unmodified conjugated diene polymer and maleic anhydride is preferably 100 to 200°C, and more preferably 120 to 180°C. The reaction time is preferably 3 to 200 hours, more preferably 4 to 100 hours, and even more preferably 5 to 50 hours.

[0063] In order to prevent an increase in the molecular weight distribution of the modified conjugated diene polymer during the reaction between the unmodified conjugated diene polymer and the modifying compound, an antioxidant may be used or the unmodified conjugated diene polymer may be purified to thoroughly remove components that inhibit the reaction with the modifying compound. As a purification method, washing with water or hot water, or an organic solvent such as methanol or acetone, or supercritical fluid carbon dioxide is preferred.

[0064] Antioxidants include 2,6-di-t-butyl-4-methylphenol (BHT), 2,2'-methylenebis(4-methyl-6-t-butylphenol), 4,4'-thiobis(3-methyl-6-t-butylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol) (AO-40), 3,9-bis[1,1-dimethyl-2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane (AO-80), 2,4-bis[(octylthio)methyl]-6-methylphenol (Irganox 1520L), and 2,4-bis[(dodecylthio)methyl]-6-methylphenol (Irganox 1726), 2-[1-(2-hydroxy-3,5-di-t-pentylphenyl)ethyl]-4,6-di-t-pentylphenyl acrylate (Sumilizer GS), 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate (Sumilizer GM), 6-t-butyl-4-[3-(2,4,8,10-tetra-t-butyldibenzo[d,f][1,3,2]dioxaphosphepin-6-yloxy)propyl]-2-methylphenol (Sumilizer GP), tris(2,4-di-t-butylphenyl) phosphite (Irgafos 168), dioctadecyl 3,3'-dithiobispropionate, hydroquinone, p-methoxyphenol, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (Nocrac 6C), bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate (LA-77Y), N,N-dioctadecylhydroxylamine (Irgastab FS 042), bis(4-t-octylphenyl)amine (Irganox 5057), etc. The above antioxidants may be used alone or in combination of two or more.

[0065] The amount of the antioxidant used is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 3 parts by mass, per 100 parts by mass of the unmodified conjugated diene polymer or modified conjugated diene polymer.

[0066] (Base Oil) The base oil contained in the oil composition is not particularly limited, and known base oils may be appropriately selected and used depending on the application of the oil composition. Examples of base oils include fuel oils such as middle distillate fuels, synthetic and natural lubricating oils, unrefined oils, and industrial oils. The base oil may be at least one of paraffinic base oils, naphthenic base oils, and aromatic base oils, or at least one of natural oils and synthetically prepared oils. The base oil may be any of Groups I to V of the API (American Petroleum Institute) classification. From the viewpoint of economy, the base oil is preferably at least one selected from the group consisting of base oils belonging to Groups I, II, III, and IV of the API (American Petroleum Institute) classification. From the viewpoint of viscosity characteristics and oxidation stability, the base oil is more preferably at least one selected from the group consisting of base oils belonging to Groups II, III, and IV. From the viewpoint of viscosity characteristics and oxidation stability, the base oil is even more preferably at least one selected from the group consisting of base oils belonging to Groups III and IV. Examples of base oils that can be used in the oil composition of the present invention include the base oils described in Japanese Patent No. 5933263 and JP-A-2005-23320. The oil composition may contain one type of base oil as the base oil, or may contain a combination of two or more types of base oils.

[0067] The content of the base oil in the oil composition may be determined depending on the properties such as viscosity desired for the oil composition, and is not particularly limited, but may be preferably 50 to 99.9 mass%, more preferably 60 to 99 mass%, even more preferably 70 to 99 mass%, and even more preferably 80 to 98 mass%, based on the total amount of the oil composition. A base oil content of not less than the above lower limit is preferred from the viewpoint of the production cost of the oil composition, and a base oil content of not more than the above upper limit is preferred from the viewpoint of the friction properties, wear resistance, viscosity index, and low-temperature viscosity of the oil composition.

[0068] (Other Components) The oil composition may contain other components (additives) in addition to the conjugated diene polymer and base oil, depending on the properties desired for the oil composition. Examples of other components include at least one additive selected from the group consisting of rust inhibitors, antioxidants, surfactants, pour point depressants, detergent-dispersants, metal deactivators, antifoaming agents, viscosity modifiers, friction modifiers, extreme pressure agents, antiwear agents, corrosion inhibitors, colorants, and oiliness agents. The other components may be at least one additive selected from the group consisting of rust inhibitors, antioxidants, surfactants, pour point depressants, detergent-dispersants, metal deactivators, antifoaming agents, viscosity modifiers, friction modifiers, extreme pressure agents, and antiwear agents. The amount of additives that may be included in the oil composition is not particularly limited, but is preferably 0 to 20% by mass, more preferably 0 to 15% by mass, even more preferably 0 to 10% by mass, and even more preferably 0 to 6% by mass, based on the total amount of the oil composition, from the viewpoint of balancing the various required properties and production costs.

[0069] (Rust Inhibitor) Examples of the rust inhibitor include known rust inhibitors such as fatty acids, fatty acid salts, alkenyl succinic acid half esters, fatty acid soaps, alkyl sulfonates, polyhydric alcohol fatty acid esters, fatty acid amines, phosphoric acid, phosphates, oxidized paraffins, alkyl polyoxyethylene ethers, petroleum sulfonates, alkyl benzene sulfonates, and dinonyl naphthalene sulfonates. The above rust inhibitors may be used alone or in combination of two or more. The content of the rust inhibitor in the oil composition may be determined depending on the rust prevention properties required of the oil composition and is not particularly limited, but is preferably 0.01 to 1 mass %, more preferably 0.1 to 1 mass %, and even more preferably 0.1 to 0.5 mass %, based on the total amount of the oil composition. A content of the rust inhibitor of at least the above lower limit is preferred from the viewpoint of the rust prevention properties of the oil composition, while a content of at most the above upper limit is preferred from the viewpoint of the friction properties, wear resistance, electrical insulation properties, and production costs of the oil composition.

[0070] (Antioxidant) Examples of the antioxidant include known antioxidants such as aromatic amine antioxidants, hindered amine antioxidants, phenolic antioxidants, zinc dithiophosphate, organic sulfur compounds, and N,N'-disalisidene-1,2-diaminopropane.

[0071] Examples of the aromatic amine antioxidant include primary aromatic amine compounds such as alkylated α-naphthylamine; and secondary aromatic amine compounds such as alkylated diphenylamine, phenyl-α-naphthylamine, alkylated phenyl-α-naphthylamine, and phenyl-β-naphthylamine.

[0072] Examples of the hindered amine antioxidant include 2,2,6,6-tetraalkylpiperidine derivatives. As the 2,2,6,6-tetraalkylpiperidine derivative, a 2,2,6,6-tetraalkylpiperidine derivative having a substituent at the 4-position is preferred. Two 2,2,6,6-tetraalkylpiperidine skeletons may be bonded via the substituent at the 4-position of each. The N-position of the 2,2,6,6-tetraalkylpiperidine skeleton may be unsubstituted, or may be substituted at the N-position with an alkyl group having 1 to 4 carbon atoms. The 2,2,6,6-tetraalkylpiperidine skeleton is preferably a 2,2,6,6-tetramethylpiperidine skeleton. Examples of the substituent at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton include an acyloxy group (R ４ COO-), alkoxy group (R ４ O-), alkylamino group (R ４ NH-), acylamino group (R ４ CONH-), etc. ４ is preferably a hydrocarbon group having 1 to 30 carbon atoms, more preferably 1 to 24 carbon atoms, and even more preferably 1 to 20 carbon atoms. Examples of the hydrocarbon group include an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an alkylaryl group, and an arylalkyl group. When two 2,2,6,6-tetraalkylpiperidine skeletons are bonded via a substituent at each 4-position, examples of the substituent include a hydrocarbylene bis(carbonyloxy) group (-OOC-R ５-COO-), hydrocarbylenediamino group (-HN-R ５ -NH-), hydrocarbylene bis(carbonylamino) group (-HNCO-R ５ -CONH-), etc. ５ is preferably a hydrocarbylene group having 1 to 30 carbon atoms, and more preferably an alkylene group. The substituent at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton is preferably an acyloxy group. An example of a compound having an acyloxy group at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton is an ester of 2,2,6,6-tetramethyl-4-piperidinol with a carboxylic acid. An example of the carboxylic acid is a linear or branched aliphatic carboxylic acid having 8 to 20 carbon atoms.

[0073] Examples of phenolic antioxidants include 4,4'-methylenebis(2,6-di-tert-butylphenol); 4,4'-bis(2,6-di-tert-butylphenol); 4,4'-bis(2-methyl-6-tert-butylphenol); 2,2'-methylenebis(4-ethyl-6-tert-butylphenol); 2,2'-methylenebis(4-methyl-6-tert-butylphenol); 4,4 4,4'-butylidenebis(3-methyl-6-tert-butylphenol); 4,4'-isopropylidenebis(2,6-di-tert-butylphenol); 2,2'-methylenebis(4-methyl-6-nonylphenol); 2,2'-isobutylidenebis(4,6-dimethylphenol); 2,2'-methylenebis(4-methyl-6-cyclohexylphenol); 2,6-di-tert-butyl-4-methyl ethylphenol; 2,6-di-tert-butyl-4-ethylphenol; 2,4-dimethyl-6-tert-butylphenol; 2,6-di-tert-butyl-4-(N,N'-dimethylaminomethyl)phenol; 4,4'-thiobis(2-methyl-6-tert-butylphenol); 4,4'-thiobis(3-methyl-6-tert-butylphenol); 2,2'-thiobis(4-methyl-6-tert-butylphenol); bis(3-methyl-4-hydroxy-5-tert-butylbenzyl)sulfide; bis(3,5-di-tert-butyl-4-hydroxybenzyl)sulfide; 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid esters; 3-methyl-5-tert-butyl-4-hydroxyphenol fatty acid esters, and the like can be mentioned.Examples of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid esters include octyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; decyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; dodecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; tetradecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; propionate; hexadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; pentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; 2,2'-thio-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the like.

[0074] The antioxidants may be used alone or in combination of two or more. The content of the antioxidant in the oil composition may be determined depending on the oxidation stability properties required of the oil composition and is not particularly limited, but is preferably 0.01 to 1 mass%, more preferably 0.05 to 1 mass%, even more preferably 0.05 to 0.5 mass%, and even more preferably 0.05 to 0.2 mass%, based on the total amount of the oil composition. An antioxidant content of not less than the above lower limit is preferred from the viewpoint of the oxidation stability of the oil composition, and an antioxidant content of not more than the above upper limit is preferred from the viewpoint of the electrical insulation properties and production costs of the oil composition.

[0075] (Surfactants) Surfactants are mainly divided into emulsifiers and demulsifiers based on their role. Examples of emulsifiers include known emulsifiers such as fatty acid soaps and polyoxyethylene fatty acid esters. Examples of demulsifiers include known demulsifiers such as ethylene oxide adducts, block polymers of ethylene oxide and propylene oxide, polyalkylene glycol-based nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, and polyoxyethylene alkyl naphthyl ethers, sulfated oils, and quaternary ammonium salts. The above surfactants may be used alone or in combination of two or more. The content of the surfactant in the oil composition may be determined depending on the emulsion stability and water separation properties required for the oil composition, but is not particularly limited. It is preferably 0.1 to 3 mass %, more preferably 0.5 to 3 mass %, and even more preferably 1 to 3 mass %, based on the total amount of the oil composition. If the surfactant content is equal to or greater than the above lower limit, this is preferred from the viewpoints of emulsion stability and water separability of the oil composition, and if it is equal to or less than the above upper limit, this is preferred from the viewpoints of friction properties, wear resistance, electrical insulation properties, and production costs of the oil composition.

[0076] (Pour Point Depressant) Examples of pour point depressants include known pour point depressants such as polymethacrylates, alkylated aromatic compounds, fumarate-vinyl acetate copolymers, ethylene-vinyl acetate copolymers, condensates of chlorinated paraffins and naphthalene, and condensates of chlorinated paraffins and phenols. The above pour point depressants may be used alone or in combination of two or more. The content of the pour point depressant in the oil composition may be determined depending on the pour point desired for the oil composition and is not particularly limited, but is preferably 0.05 to 2 mass%, more preferably 0.1 to 1 mass%, and even more preferably 0.1 to 0.5 mass%, based on the total amount of the oil composition. A pour point depressant content of at least the above lower limit is preferred from the viewpoint of the pour point of the oil composition, while a pour point content of at most the above upper limit is preferred from the viewpoint of the friction properties, wear resistance, electrical insulation properties, and production costs of the oil composition.

[0077] (Detergent-Dispersant) Detergent-dispersant is divided into detergent and dispersant.

[0078] (Detergent) Examples of detergents include known detergents such as metal salts such as metal sulfonates, metal salicylates, and metal phenates. Furthermore, the metal atoms constituting the metal salts are preferably metal atoms selected from alkali metals and alkaline earth metals, more preferably sodium, calcium, magnesium, or barium, and even more preferably calcium. Among detergents, it is preferable to include one or more selected from calcium sulfonate, calcium salicylate, and calcium phenate, and more preferably calcium salicylate. The detergent may be a neutral metal detergent or an overbased metal detergent. Note that a neutral metal detergent refers to a metal detergent having a base number of 0 to 100 mgKOH / g or more, whereas an overbased metal detergent refers to a metal detergent having a base number of more than 100 mgKOH / g. The above detergents may be used alone or in combination of two or more. The content of the detergent in the oil composition may be determined depending on the detergency and thermal stability required of the oil composition, and is not particularly limited, but is preferably 0.1 to 30 mass %, more preferably 0.5 to 20 mass %, even more preferably 1 to 10 mass %, and even more preferably 1 to 5 mass %, based on the total amount of the oil composition. A detergent content of not less than the above lower limit is preferred from the viewpoint of the detergency and thermal stability of the oil composition, and a detergent content of not more than the above upper limit is preferred from the viewpoint of the friction properties, wear resistance, electrical insulation properties, and production costs of the oil composition.

[0079] (Dispersants) Examples of dispersants include known dispersants such as nitrogen-containing compounds or derivatives thereof having at least one alkyl or alkenyl group having 40 to 400 carbon atoms in the molecule, which has a linear or branched structure, or modified products such as succinimides and boronated succinimides, which have at least one alkyl or alkenyl group having 40 to 400 carbon atoms in the molecule, which has a linear or branched structure. The above dispersants may be used alone or in combination of two or more. The content of the dispersant in the oil composition may be determined depending on the dispersibility required for the oil composition and is not particularly limited, but is preferably 0.1 to 30 mass%, more preferably 0.5 to 20 mass%, even more preferably 1 to 10 mass%, and even more preferably 1 to 5 mass%, based on the total amount of the oil composition. A dispersant content of at least the above lower limit is preferred from the viewpoint of dispersibility of the oil composition, while a dispersant content of at most the above upper limit is preferred from the viewpoint of friction properties, wear resistance, electrical insulation properties, and production costs of the oil composition.

[0080] (Metal Deactivator) Examples of metal deactivators include known metal deactivators such as benzotriazole, triazole derivatives, benzotriazole derivatives, and thiadiazole derivatives. The above metal deactivators may be used alone or in combination of two or more. The content of the metal deactivator in the oil composition may be determined depending on the oxidation stability and corrosion prevention properties required of the oil composition and is not particularly limited. It is preferably 0.001 to 0.5 mass%, more preferably 0.001 to 0.3 mass%, and even more preferably 0.001 to 0.1 mass%, based on the total amount of the oil composition. A content of the metal deactivator equal to or greater than the above lower limit is preferred from the viewpoints of oxidation stability and corrosion prevention properties of the oil composition, while a content of the metal deactivator equal to or less than the above upper limit is preferred from the viewpoints of friction properties, wear resistance, electrical insulation properties, and production costs of the oil composition.

[0081] (Antifoaming Agent) Examples of antifoaming agents include known antifoaming agents such as silicone, fluorosilicone, fluoroalkyl ether, fatty acid ester, polyether, higher alcohol, and polyacrylate. The above antifoaming agents may be used alone or in combination of two or more. The content of the antifoaming agent in the oil composition may be determined depending on the antifoaming properties required of the oil composition and is not particularly limited, but is preferably 0.0001 to 0.5 mass%, more preferably 0.0001 to 0.3 mass%, and even more preferably 0.0001 to 0.1 mass%, based on the total amount of the oil composition. A content of the antifoaming agent equal to or greater than the above lower limit is preferred from the viewpoint of the antifoaming properties of the oil composition, while a content of the antifoaming agent equal to or less than the above upper limit is preferred from the viewpoint of the friction properties, wear resistance, electrical insulation properties, and production costs of the oil composition.

[0082] (Viscosity Modifier) ​​Examples of viscosity modifiers include known viscosity modifiers such as non-dispersant polymethacrylate, dispersant polymethacrylate, ethylene-propylene copolymer, polyisobutylene and its hydrogenated products, styrene-diene hydrogenated copolymer, styrene-maleic anhydride ester copolymer, and polyalkylstyrene. The above viscosity modifiers may be used alone or in combination of two or more. The content of the viscosity modifier in the oil composition may be determined according to the viscosity index required for the oil composition and is not particularly limited, but is preferably 0.1 to 20 mass%, more preferably 0.1 to 10 mass%, even more preferably 1 to 10 mass%, and even more preferably 1 to 5 mass%, based on the total amount of the oil composition. A content of the viscosity modifier equal to or greater than the above lower limit is preferred from the viewpoint of the viscosity index of the oil composition, while a content of the viscosity modifier equal to or less than the above upper limit is preferred from the viewpoint of the production cost of the oil composition.

[0083] (Friction modifier) ​​Examples of friction modifiers include known friction modifiers such as organic molybdenum compounds. Examples of organic molybdenum compounds include sulfur-containing organic molybdenum compounds and organic molybdenum compounds that do not contain sulfur as a constituent element. Examples of sulfur-containing organic molybdenum compounds include molybdenum dithiocarbamate compounds; molybdenum dithiophosphate compounds; molybdenum compounds (e.g., molybdenum oxides such as molybdenum dioxide and molybdenum trioxide, molybdic acids such as orthomolybdic acid, paramolybdic acid, and (poly)molybdic sulfide, metal salts of these molybdic acids, molybdates such as ammonium salts, molybdenum sulfides such as molybdenum disulfide, molybdenum trisulfide, molybdenum pentasulfide, and polymolybdenum sulfide, molybdic acid, metal salts or amine salts of molybdic sulfide, and molybdenum chloride. and complexes of sulfur-containing organic compounds (e.g., molybdenum halides) with sulfur-containing organic compounds (e.g., alkyl(thio)xanthates, thiadiazoles, mercaptothiadiazoles, thiocarbonates, tetrahydrocarbylthiuram disulfides, bis(di(thio)hydrocarbyldithiophosphonate)disulfides, organic (poly)sulfides, sulfurized esters, etc.) or other organic compounds; and sulfur-containing organic molybdenum compounds such as complexes of sulfur-containing molybdenum compounds such as the above-mentioned molybdenum sulfide and molybdic acid with alkenyl succinimides. The organic molybdenum compounds may be mononuclear molybdenum compounds or polynuclear molybdenum compounds such as dinuclear molybdenum compounds and trinuclear molybdenum compounds. Examples of organic molybdenum compounds that do not contain sulfur as a constituent element include molybdenum-amine complexes, molybdenum-succinimide complexes, molybdenum salts of organic acids, and molybdenum salts of alcohols. The friction modifiers may be used alone or in combination of two or more. The content of the friction modifier in the oil composition is not particularly limited and may be determined depending on the friction characteristics required of the oil composition, but is preferably 0.01 to 2 mass %, more preferably 0.1 to 2 mass %, and even more preferably 0.5 to 2 mass %, based on the total amount of the oil composition.A friction modifier content of at least the above lower limit is preferred from the viewpoint of the friction properties of the oil composition, while a friction modifier content of at most the above upper limit is preferred from the viewpoint of the electrical insulating properties and production costs of the oil composition.

[0084] (Extreme Pressure Agents) Examples of extreme pressure agents include known extreme pressure agents such as sulfur-based compounds such as disulfides, sulfurized olefins, sulfurized oils and fats, dialkyl polysulfides, diaryl alkyl polysulfides, and diaryl polysulfides, and phosphorus-based compounds such as phosphate esters, thiophosphate esters, phosphites, alkyl hydrogen phosphites, phosphate ester amine salts, and phosphite ester amine salts. The above extreme pressure agents may be used alone or in combination of two or more. The content of the extreme pressure agent in the oil composition may be determined depending on the load-bearing property and seizure resistance required of the oil composition, and is not particularly limited. It is preferably 0.01 to 10 mass%, more preferably 0.1 to 5 mass%, and even more preferably 1 to 5 mass%, based on the total amount of the oil composition. A content of the extreme pressure agent of at least the above lower limit is preferred from the viewpoint of the load-bearing property and seizure resistance of the oil composition, while a content of at most the above upper limit is preferred from the viewpoint of the electrical insulation property and production costs of the oil composition.

[0085] (Anti-wear Agents) Examples of anti-wear agents include sulfur-based compounds such as disulfides, sulfurized olefins, dialkyl polysulfides, diaryl alkyl polysulfides, and diaryl polysulfides; phosphorus-based compounds such as phosphate esters, thiophosphate esters, phosphites, alkyl hydrogen phosphites, phosphate ester amine salts, and phosphite ester amine salts; ashless friction modifiers such as fatty acid esters, fatty acid amides, fatty acids, aliphatic alcohols, aliphatic ethers, urea compounds, and hydrazide compounds; and known anti-wear agents such as zinc dialkyldithiophosphates. The above anti-wear agents may be used alone or in combination of two or more. The content of the anti-wear agent in the oil composition may be determined depending on the anti-wear properties required for the oil composition and is not particularly limited, but is preferably 0.01 to 10 mass%, more preferably 0.1 to 5 mass%, and even more preferably 1 to 5 mass%, based on the total amount of the oil composition. When the content of the antiwear agent is equal to or greater than the above lower limit, it is preferable from the viewpoint of the antiwear properties of the oil composition, and when it is equal to or less than the above upper limit, it is preferable from the viewpoint of the electrical insulating properties of the oil composition and production costs.

[0086] (Corrosion Inhibitor) Examples of corrosion inhibitors include known corrosion inhibitors such as benzotriazole and its derivatives, imidazole compounds, 1,3,4-thiadiazole compounds, and 1,2,4-thiadiazole compounds. The corrosion inhibitors may be used singly or in combination. The content of the corrosion inhibitor in the oil composition is not particularly limited and may be determined depending on the corrosion inhibition properties required of the oil composition. It is preferably 0.01 to 3 mass%, more preferably 0.1 to 2 mass%, and even more preferably 0.3 to 2 mass%, based on the total amount of the oil composition. A content of the corrosion inhibitor equal to or greater than the above-mentioned lower limit is preferred from the viewpoint of the corrosion inhibition properties of the oil composition, while a content of the corrosion inhibitor equal to or less than the above-mentioned upper limit is preferred from the viewpoint of the friction properties, wear resistance, electrical insulation properties, and production costs of the oil composition.

[0087] (Colorant) Examples of colorants include known colorants such as oil-soluble dyes and azo compounds. The colorants may be used singly or in combination. The content of the colorant in the oil composition is not particularly limited and may be determined depending on the colorability required for the oil composition, but is preferably 1 to 1,000 ppm, more preferably 5 to 500 ppm, and even more preferably 10 to 100 ppm, based on the total amount of the oil composition. A colorant content of at least the above lower limit is preferred from the viewpoint of the colorability of the oil composition, while a colorant content of at most the above upper limit is preferred from the viewpoint of the production cost of the oil composition.

[0088] (Oilability Agents) Examples of oilability agents include known oiliness agents such as saturated and unsaturated aliphatic monocarboxylic acids such as stearic acid and oleic acid, polymerized fatty acids such as dimer acid and hydrogenated dimer acid, hydroxy fatty acids such as ricinoleic acid and 12-hydroxystearic acid, saturated and unsaturated aliphatic monoalcohols such as lauryl alcohol and oleyl alcohol, saturated and unsaturated aliphatic monoamines such as stearylamine and oleylamine, saturated and unsaturated aliphatic monocarboxylic amides such as lauric acid amide and oleic acid amide, aliphatic imide compounds, fatty acid hydrazides, fatty acid metal salts, aliphatic alcohols, aliphatic ethers, and aliphatic urea compounds. The above oiliness agents may be used alone or in combination of two or more. The content of the oiliness agent in the oil composition may be determined depending on the friction characteristics desired for the oil composition and is not particularly limited, but is preferably 0.01 to 3 mass %, more preferably 0.05 to 2 mass %, and even more preferably 0.1 to 1 mass % based on the total amount of the oil composition. When the content of the oily agent is equal to or greater than the above lower limit, this is preferred from the viewpoint of the friction properties of the oil composition, and when it is equal to or less than the above upper limit, this is preferred from the viewpoint of the electrical insulating properties and production costs of the oil composition.

[0089] (Oil composition) The kinematic viscosity of the oil composition at 100°C is 10.0 mm ２ The kinematic viscosity of the oil composition at 100°C is 1.0 mm / s or less. ２ It is preferable that the kinematic viscosity at 100°C is 10.0 mm / s or more. ２When the kinematic viscosity is 1.0 mm / s or less, it is preferable from the viewpoint of fuel economy. ２ In the present disclosure, the kinematic viscosity is a value measured at 100°C in accordance with JIS K2283:2000. The kinematic viscosity of the oil composition at 100°C is preferably 1.0 to 8.0 mm / s or more. ２ / s, more preferably 1.5 to 6.0 mm ２ / s, more preferably 2.0 to 5.0 mm ２ / s.

[0090] The total amount of the base oil and modified conjugated diene polymer contained in the oil composition is preferably 80 to 100 mass %, more preferably 85 to 100 mass %, even more preferably 90 to 100 mass %, and still more preferably 94 to 100 mass %, based on the total amount of the oil composition, from the viewpoints of thickening property, viscosity index, shear stability, oxidation stability, low-temperature viscosity, and handleability.

[0091] From the viewpoint of using the oil composition over a wide temperature range, it is preferable that the low-temperature viscosity of the oil composition of the present disclosure is not too high. Specifically, it is preferable that the Brookfield viscosity at -40°C is not too high. In a preferred embodiment, the Brookfield viscosity of the oil composition at -40°C is 13.5 to 24.0 mmHg, and the kinematic viscosity of the oil composition at 100°C is 13.5 to 24.0 mmHg. ２ When the kinematic viscosity of the oil composition is in the range of 1,000 to 70,000 mPa·s, more preferably 1,500 to 65,000 mPa·s, and even more preferably 2,000 to 60,000 mPa·s, the Brookfield viscosity at −40° C. of the oil composition is 13.5 mm / s. ２ When the viscosity is less than 100 to 2,500 mPa·s, it is preferably 100 to 2,500 mPa·s, more preferably 500 to 2,400 mPa·s, and even more preferably 1,000 to 2,300 mPa·s.

[0092] The method for producing the oil composition of the present disclosure is not particularly limited, and the oil composition can be produced, for example, by mixing the base oil and the conjugated diene polymer together with other additives, etc., as necessary. Mixing can be carried out using, for example, a known mixing device. Mixing is preferably carried out while heating, and the heating temperature is preferably 40 to 180°C.

[0093] The oil composition of the present disclosure is advantageously used, for example, as a lubricating oil. Therefore, the oil composition of the present disclosure may preferably be a lubricating oil composition. Examples of lubricating oils include driveline oils, industrial lubricating oils, and engine oils. Preferably, the lubricating oil is a transmission oil or an e-axle lubricating oil. Examples of transmission oils include manual transmission oils, automatic transmission oils, belt-type continuously variable transmission oils, and dual-clutch transmission oils. Examples of e-axle lubricating oils include lubricating oils for e-axle reducers, coolants for e-axle motors and inverters, and lubricating oils that double as lubricating oils for e-axle reducers and coolants for e-axle motors and inverters. Note that e-axles are installed in fuel cell vehicles, electric vehicles, and hybrid vehicles. Examples of engine oils include engine oils for vehicles having only an internal combustion engine, and lubricating oils for the internal combustion engines of hybrid systems having an internal combustion engine and an electric motor as power sources.

[0094] The oil compositions of the present disclosure may preferably be lubricating oils, and more preferably may be transmission fluids or e-axle lubricants.

[0095] The oil composition of the present disclosure is a composition that, despite being a low-viscosity oil composition, has a low coefficient of friction and exhibits the effects of reducing friction and wear. This is thought to be due to the modified conjugated diene polymer contained in the composition. Therefore, the modified conjugated diene polymer is suitable as a friction reducer or wear reducer for low-viscosity oil compositions. Thus, in a preferred embodiment, the present disclosure provides a friction reducer or wear reducer comprising a modified conjugated diene polymer, wherein the modified conjugated diene polymer has at least one functional group selected from the group consisting of a dicarboxylic acid anhydride group, a dicarboxylic acid monoester group, a dicarboxylic acid monoamide group, and a carboxylic acid imide group, the number-average molecular weight of the modified conjugated diene polymer is 4,000 to 500,000, and the kinematic viscosity at 100°C is 10.0 mm ２ The oil may also be used as a friction or wear reducer, that is, an agent for reducing friction or wear in low viscosity oil compositions of 0.15 to 1.005 g / s or less.

[0096] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In the examples, percentages refer to mass unless otherwise specified. First, the measurement and evaluation methods are described below.

[0097] [Production Example 1: Synthesis of Modified Conjugated Diene Polymer (P-1)] A thoroughly dried 3 L autoclave was purged with nitrogen, and 955 g of hexane and 15 g of n-butyllithium (17 mass % hexane solution) were charged. The temperature was raised to 60°C, and 730 g of isoprene was successively added under stirring conditions to polymerize. Methanol was then added to terminate the polymerization reaction, yielding a polymer solution. Water was added to the obtained polymer solution, and the mixture was stirred. The polymer solution was washed with water. After stirring was stopped, it was confirmed that the polymer solution phase and the aqueous phase had separated, and then the water was separated. The polymer solution after washing was vacuum dried at 140°C for 3 hours to yield an unmodified conjugated diene polymer (P'-1).

[0098] Subsequently, 300 g of the obtained unmodified conjugated diene polymer (P'-1) was charged into a 1-liter autoclave that had been purged with nitrogen, and 4.5 g of maleic anhydride and 0.3 g of BHT (2,6-di-t-butyl-4-methylphenol) were added, followed by reaction at 160°C for 20 hours to obtain a maleic anhydride-modified conjugated diene polymer (P-1).

[0099] [Production Example 2: Synthesis of modified conjugated diene polymer (P-2)] A 1-liter autoclave purged with nitrogen was charged with 300 g of unmodified conjugated diene polymer (P'-1) obtained by the same procedure as in Production Example 1, and 15 g of maleic anhydride and 0.3 g of Nocrac 6C were added, followed by a reaction for 24 hours at 170°C. Thereafter, 5.4 g of methanol was added, and the reaction was continued for 6 hours at 80°C, yielding a maleic acid monomethyl ester-modified conjugated diene polymer (P-2).

[0100] [Production Example 3: Synthesis of Modified Conjugated Diene Polymer (P-3)] A thoroughly dried 3 L autoclave was purged with nitrogen, and 314 g of hexane and 111 g of sec-butyllithium (10.5 mass % cyclohexane solution) were charged. The temperature was raised to 60°C, and then 1,070 g of isoprene was successively added under stirring conditions to polymerize. Methanol was then added to terminate the polymerization reaction, yielding a polymer solution. Water was added to the obtained polymer solution, followed by stirring, and the polymer solution was washed with water. After stirring was stopped, it was confirmed that the polymer solution phase and the aqueous phase had separated, and then the water was separated. The polymer solution after washing was vacuum dried at 140°C for 3 hours to yield an unmodified conjugated diene polymer (P'-2).

[0101] Subsequently, 300 g of the obtained unmodified conjugated diene polymer (P'-2) was charged into a 1-liter autoclave that had been purged with nitrogen, and 15 g of maleic anhydride and 0.3 g of BHT (2,6-di-t-butyl-4-methylphenol) were added, followed by reaction at 160°C for 20 hours to obtain a maleic anhydride-modified conjugated diene polymer (P-3).

[0102] [Production Example 4: Synthesis of Modified Conjugated Diene Polymer (P-4)] A thoroughly dried 3 L autoclave was purged with nitrogen, and 955 g of hexane and 21 g of n-butyllithium (17% by mass hexane solution) were charged. The temperature was raised to 60°C, and 770 g of butadiene was successively added under stirring conditions to polymerize. Methanol was then added to terminate the polymerization reaction, yielding a polymer solution. Water was added to the obtained polymer solution, followed by stirring, and the polymer solution was washed with water. After stirring was stopped, it was confirmed that the polymer solution phase and the aqueous phase had separated, and then the water was separated. The polymer solution after washing was vacuum dried at 140°C for 3 hours to yield an unmodified conjugated diene polymer (P'-3).

[0103] Subsequently, 300 g of the unmodified conjugated diene polymer (P'-3) obtained was charged into a 1-liter autoclave whose interior had been purged with nitrogen, and 15 g of maleic anhydride and 0.3 g of Nocrac 6C were added thereto, followed by reaction at 170°C for 24 hours to obtain a maleic anhydride-modified conjugated diene polymer (P-4).

[0104] [Production Example 5: Synthesis of modified conjugated diene polymer (P-5)] In a 1-liter autoclave that had been purged with nitrogen, 315 g of the maleic anhydride-modified conjugated diene polymer (P-4) obtained by the same procedure as in Production Example 4 was charged, and 5.4 g of methanol was added. The mixture was reacted at 80°C for 6 hours to obtain a maleic acid monomethyl ester-modified conjugated diene polymer (P-5).

[0105] [Production Example 6: Synthesis of modified conjugated diene polymer (P-6)] In a 1-liter autoclave that had been purged with nitrogen, 315 g of the maleic anhydride-modified conjugated diene polymer (P-1) obtained by the same procedure as in Production Example 1 was charged, and 1.6 g of methanol was added. The mixture was reacted at 80°C for 6 hours to obtain a maleic acid monomethyl ester-modified conjugated diene polymer (P-6).

[0106] [Production Example 7: Synthesis of modified conjugated diene polymer (P-7)] In a 1-liter autoclave purged with nitrogen, 300 g of unmodified conjugated diene polymer (P′-1) obtained by the same procedure as in Production Example 1 was charged, and 15 g of maleic anhydride and 0.3 g of Nocrac 6C were added, followed by reaction at 170° C. for 24 hours to obtain a maleic anhydride-modified conjugated diene polymer (P-7).

[0107] [Production Example 8: Synthesis of modified conjugated diene polymer (P-8)] In a 1-liter autoclave purged with nitrogen, 300 g of the unmodified conjugated diene polymer (P′-3) obtained by the same procedure as in Production Example 4 was charged, and 4.5 g of maleic anhydride and 0.3 g of Nocrac 6C were added, followed by reaction at 170° C. for 24 hours to obtain a maleic anhydride-modified conjugated diene polymer (P-8).

[0108] [Production Example 9: Synthesis of modified conjugated diene polymer (P-9)] In a 1-liter autoclave that had been purged with nitrogen, 315 g of the maleic anhydride-modified conjugated diene polymer (P-8) obtained by the same procedure as in Production Example 8 was charged, and 1.6 g of methanol was added. The mixture was reacted at 80°C for 6 hours to obtain a maleic acid monomethyl ester-modified conjugated diene polymer (P-9).

[0109] The weight average molecular weight (Mw), number average molecular weight (Mn), molecular weight distribution (Mw / Mn), proportion of cis-1,4-bond units and proportion of trans-1,4-bonds relative to the total amount of structural units derived from conjugated diene monomers, vinyl content, proportion of cis-1,4-bond units in 1,4-bond units, iodine value, hydrogenation rate, type of functional group (MAh: maleic anhydride-modified, MMM: maleic acid monomethyl ester-modified, -: no functional group), acid value, functional group equivalent, amount of added modifying compound, and average number of functional groups per molecule of the resulting modified conjugated diene polymers (P-1) to (P-9) and unmodified conjugated diene polymers (P'-1) and (P'-3) were measured according to the following methods. The measurement results are shown in Table 1.

[0110] <Weight-average molecular weight, number-average molecular weight, and molecular weight distribution> The weight-average molecular weight (Mw), number-average molecular weight (Mn), and molecular weight distribution (Mw / Mn) of the modified conjugated diene polymer and the unmodified conjugated diene polymer were determined by gel permeation chromatography (GPC) in terms of standard polystyrene equivalent molecular weight. The measurement device and conditions were as follows: Device: GPC device "HLC-8320GPC" manufactured by Tosoh Corporation Separation column: "TSKgel Super HZ4000 x 2" manufactured by Tosoh Corporation Eluent: tetrahydrofuran Eluent flow rate: 0.35 mL / min Sample concentration: 5 mg / 10 mL Column temperature: 40°C

[0111] <Proportion of cis-1,4-bond units and proportion of trans-1,4-bond units relative to the total amount of structural units derived from conjugated diene monomers, as well as vinyl content and proportion of cis-1,4-bond units in 1,4-bond units> [Production Examples 1 to 3] Each proportion relative to the total amount of structural units derived from isoprene as a conjugated diene monomer was determined by the following method. 30 mg of each unmodified conjugated diene polymer (P'-1 to P'-3, 6) was dissolved in 10 mL of carbon disulfide to prepare a measurement sample, and its absorption spectrum was measured using a Fourier transform infrared spectrophotometer (FT-IR). The detected absorption peak absorbance (A ８３６ ), wavelength 889cm －１ The absorption peak absorbance (A ８８９ ), wavelength 906cm －１ The absorption peak absorbance (A ９０６ ), wavelength 1128cm －１ The absorption peak absorbance (A １１２８ ), wavelength 1151cm －１ The absorption peak absorbance (A １１５１ ), and cell thickness b (cm), the concentration C of each component in the sample solution can be calculated by solving the following simultaneous equations: Ｃ (concentration of cis-1,4-bonding units), C Ｔ (concentration of trans-1,4-bond units), C １，２ (concentration of 1,2-bond units), C ３，４ The concentration of 3,4-bond units (mol / L) was calculated. ８３６ / b=19.9CＣ +9.84C Ｔ +0.633C １，２ +1.95C ３，４ A ８８９ / b=1.79C Ｃ +1.92C Ｔ +10.2C １，２ +145C ３，４ A ９０６ / b=1.75C Ｃ +2.52C Ｔ +149C １，２ +7.36C ３，４ A １１２８ / b=6.18C Ｃ +2.01C Ｔ +3.53C １，２ +1.82C ３，４ A １１５１ / b=3.4C Ｃ +6.06C Ｔ +3.53C １，２ +1.54C ３，４ The composition ratio was calculated from the calculated concentration using the calculation formula (ii). In the present examples and comparative examples, the ratio of cis-1,4-bond units and the like to the total amount of structural units derived from isoprene is equal to the ratio of cis-1,4-bond units and the like in the polymer. Calculation formula (ii) Ratio of cis-1,4-bond units in the polymer (mol %) = C Ｃ / (C Ｃ +C Ｔ +C １，２ +C ３，４ ) * 100 Proportion of trans-1,4-bond units in the polymer (mol%) = C Ｔ / (C Ｃ +C Ｔ +C １，２ +C ３，４ ) * 100 Total proportion of 1,2-bond units and 3,4-bond units in the polymer (vinyl content) (mol%) = (C １，２ +C ３，４ ) / (C Ｃ +C Ｔ +C １，２ +C ３，４ ) * 100 Ratio of cis-1,4-bonded units in 1,4-bonded units (mol %) = C Ｃ / (C Ｃ +C Ｔ ) * 100

[0112] [Production Examples 4 and 5] The proportion of each structural unit derived from butadiene as a conjugated diene monomer relative to the total amount was determined by the following method. 30 mg of each unmodified conjugated diene polymer (P'-4, 5, 7) was dissolved in 10 mL of carbon disulfide to prepare a measurement sample, and the absorption spectrum was measured using a Fourier transform infrared spectrophotometer (FT-IR). The detected absorption peak absorbance (A ＢＶ ), the absorption peak absorbance (A ＢＣ ), the absorption peak absorbance (A ＢＴ The composition ratio was calculated using the formula (i) from the absorption coefficient of Morero and the cis-1,4-bond units in the total amount of structural units derived from butadiene. In the present examples and comparative examples, the ratio of cis-1,4-bond units to the total amount of structural units derived from butadiene is equal to the ratio of cis-1,4-bond units in the polymer. Formula (i) cis-1,4-bond (C) ... 1.7455 * A ＢＣ -0.0151*A ＢＶ Trans-1,4-bond (T)...0.4292*A ＢＴ -0.0129*A ＢＶ -0.0454*A ＢＣ 1.2-Bond (V)...0.3746*A ＢＶ -0.007*A ＢＣ Proportion of cis-1,4-bonding units in polymer (mol %) = C / (C+V+T) * 100 Proportion of trans-1,4-bonding units in polymer (mol %) = T / (C+V+T) * 100 Proportion of 1,2-bonding units in polymer (vinyl content) (mol %) = V / (C+V+T) * 100 Proportion of cis-1,4-bonding units in 1,4-bonding units (mol %) = C / (C+T) * 100

[0113] <Iodine Value> According to JIS K 0070:1992, 0.1 g of each unmodified conjugated diene polymer (P') was weighed out and diluted with 100 mL of chloroform. Next, 20.0 mL of Wiess's reagent (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 0.1 mol / L iodine chloride / acetic acid solution) was added, the mixture was shaken well, and the mixture was left for 30 minutes to allow the reaction to proceed. 20 mL of a 10% by mass potassium iodide aqueous solution was added thereto, followed by 100 mL of water and stirring. Then, 0.1 N sodium thiosulfate aqueous solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was gradually added dropwise until the solution became transparent (drop amount <X> mL). Next, the blank drop amount (drop amount <Y> mL) was determined in the same manner except that no sample was added. The iodine value of each unmodified conjugated diene polymer (P') was calculated using the above <X> and <Y> according to the following calculation formula: In the following calculation formula, f is the factor value of a 0.1 N aqueous sodium thiosulfate solution, and specifically, is 1. Iodine value (g / 100 g) = (<Y> - <X>) x f x 1.269 / <weight (g) of conjugated diene polymer (P)>

[0114] <Hydrogenation Rate> Each unmodified conjugated diene polymer (P') was subjected to hydrogenation with CDCl ３ Dissolve in １ H-NMR measurement was carried out [apparatus: "AVANCE 400 Nanobay" (manufactured by Bruker), sample concentration: 50 mg / 1 mL, measurement temperature: 30°C, number of accumulations: 1,024]. The hydrogenation rate was calculated from the ratio of the peak area derived from one or more residual olefins selected from butadiene and isoprene to the peak area derived from one or more olefins selected from ethylene, propylene, and butylene.

[0115] <Acid Value> After the modification reaction, the sample was washed four times with methanol (5 mL per 1 g of sample) to remove impurities such as antioxidants, and then dried under reduced pressure at 80°C for 12 hours. 180 mL of toluene and 20 mL of ethanol were added to 3 g of the dried sample to dissolve it, and then neutralization titration was performed with a 0.1 N potassium hydroxide ethanol solution. The acid value was calculated using the following formula. In the formula, 56.11 represents the molecular weight of potassium hydroxide (g / mol). Acid Value (mg KOH / g) = (A - B) x F x 56.11 / S A: Amount of 0.1 N potassium hydroxide ethanol solution dropped (mL) required for neutralization B: Amount of 0.1 N potassium hydroxide ethanol solution dropped (mL) for a blank containing no sample F: Potency of the 0.1 N potassium hydroxide ethanol solution S: Mass of weighed sample (g)

[0116] <Functional Group Equivalent> From the acid value, the mass of the functional group contained per 1 g of the modified conjugated diene polymer (P) and the mass other than the functional group (polymer main chain mass) contained per 1 g of the modified conjugated diene polymer (P) were calculated. The functional group equivalent (g / eq) was calculated from the following formula. In the formula, 56.11 means the molecular weight (g / mol) of potassium hydroxide, and the functional group molecular weight means the molecular weight of the functional group contained in the modified conjugated diene polymer (P). [Mass of functional group per 1 g] = [acid value] / [56.11] × [molecular weight of functional group] / 1000 [Mass of polymer main chain per 1 g] = 1 - [mass of functional group per 1 g] [Functional Group Equivalent] = [Mass of polymer main chain per 1 g] / ([Mass of functional group per 1 g] / [molecular weight of functional group]

[0117] <Content of Functional Group (Amount of Added Modifying Compound)> The amount of the modified compound (parts by mass) added to 100 parts by mass of each unmodified conjugated diene polymer was calculated based on the following formula: [Amount of Added Modifying Compound] = [Mass of Functional Group per 1 g] / [Mass of Polymer Main Chain per 1 g] × 100

[0118] <Average Number of Functional Groups Per Molecule> Using the equivalent weight (g / eq) of the functional groups of the modified conjugated diene polymer (P) and the polystyrene-equivalent number average molecular weight Mn of the modified conjugated diene polymer (P) obtained by GPC measurement, the average number of functional groups (number) per molecule of the modified conjugated diene polymer (P) was calculated according to the following formula. In the formula, "molecular weight of styrene unit" means the molecular weight of styrene. "Average molecular weight of conjugated diene monomer and other monomer units contained as needed" means the weighted average molecular weight based on the respective content ratios of conjugated diene monomer and other monomers contained as needed in the modified conjugated diene polymer (P). [Average number of functional groups per molecule] (number) = {[number average molecular weight] / [molecular weight of styrene unit] × [average molecular weight of conjugated diene monomer and other monomer units contained as needed]} / [equivalent weight of functional group]

[0119]

[0120] [Example 1] The kinematic viscosity of the oil composition at 100°C is 2.8 to 3.2 mm ２ The modified conjugated diene polymer (P-1) obtained in Production Example 1 was mixed with 1.5% by mass of a base oil (base oil a: SK Lubricants' "YUBASE 2", Group III mineral oil, kinematic viscosity at 100°C: 2.6 mmHg) so that the viscosity was in the range of 1 / sec. ２ The mixture was stirred for 6 hours in a nitrogen-purged pressure vessel at a heating temperature of 60°C and a rotation speed of 350 rpm. This gave an oil composition of Example 1.

[0121] [Examples 2 to 11, Comparative Examples 3 to 4] The oil compositions of Examples 2 to 11 and Comparative Examples 3 to 4 were obtained in the same manner as in Example 1, except that the modified conjugated diene polymer (P) or unmodified conjugated diene polymer (P') shown in Table 1 was used and the raw materials were mixed in the ratios shown in Table 2 or 3.

[0122] [Comparative Example 1] Base oil (base oil b: "YUBASE3" manufactured by SK Lubricants, Group III mineral oil, kinematic viscosity at 100°C: 3.1 mm ２ The oil composition of Comparative Example 1 was obtained by using only 100% by mass of PEG-100 / s.

[0123] [Comparative Example 2] Base oil (base oil a: "YUBASE 2" manufactured by SK Lubricants, Group III mineral oil, kinematic viscosity at 100°C: 2.6 mm ２ The oil composition of Comparative Example 2 was obtained by using only 100% by mass of PEG-100 / s.

[0124] [Comparative Example 5] The kinematic viscosity of the oil composition at 100°C is 12.5 to 13.0 mm ２ The modified conjugated diene polymer (P-1) obtained in Production Example 1 was mixed with 11.5% by mass of a base oil (base oil a: SK Lubricants' "YUBASE 2", Group III mineral oil, kinematic viscosity at 100°C: 2.6 mmHg) so that the viscosity was in the range of 1 / sec. ２ The mixture was stirred for 6 hours in a nitrogen-purged pressure vessel at a heating temperature of 60°C and a rotation speed of 350 rpm. This gave an oil composition of Comparative Example 5.

[0125] The oil compositions obtained in the above Examples and Comparative Examples were measured and evaluated for kinematic viscosity (100°C), fuel economy performance (relative value), and friction coefficient (relative value) according to the following methods. The results are shown in Tables 2 and 3.

[0126] <Kinematic Viscosity> The kinematic viscosity at 100°C of each oil composition was measured in accordance with JIS K2283:2000.

[0127] <Fuel Economy Performance (Relative Value)> Using each oil composition, the kinematic viscosity at 40°C was measured in accordance with JIS K2283: 2000. The kinematic viscosity at 40°C of each example relative to the kinematic viscosity at 40°C of Comparative Example 1 set at 100 is shown in Tables 2 and 3 as an index of fuel economy performance.

[0128] <Friction Coefficient (Relative Value)> Using each oil composition, the absolute value of the friction coefficient was measured under the following conditions using an MTM Mini Traction Tester manufactured by PCS Instruments. Furthermore, the friction coefficient was similarly measured using base oil b described in Comparative Example 1 (Group III base oil "YUBASE3" manufactured by SK Lubricants) as a reference oil that did not contain a conjugated diene graft polymer. The fuel economy performance and the relative value of the friction coefficient of each example are shown in Tables 2 and 3, where the fuel economy performance and the friction coefficient of base oil b described in Comparative Example 1, which does not contain a modified conjugated diene polymer but has a kinematic viscosity at 100°C similar to that of the compositions of the Examples, are set to 100. <Measurement Conditions> Temperature: 100°C Load: 30 N Peripheral Speed: 84 mm / s Slide-to-Slide Ratio: 50% Material: Steel ball, steel disc

[0129]

[0130]

[0131] The oil composition of the present invention has a viscosity of 10.0 mm at 100°C. ２ It was confirmed that the compositions had a low kinematic viscosity of 10.0 mm / s or less and a low coefficient of friction. In contrast, the compositions of Comparative Examples 1 and 2, which did not contain a modified conjugated diene polymer, and Comparative Examples 3 and 4, which contained an unmodified conjugated diene polymer, were able to achieve a low kinematic viscosity, but had a high coefficient of friction. Such compositions are considered to be inferior in wear resistance, metal fatigue properties, and fuel economy under severe friction conditions. In addition, the compositions containing a modified conjugated diene polymer but having a kinematic viscosity of 10.0 mm / s or less at 100°C were ２ In the case of the composition of Comparative Example 5, where the axial length was more than 1 / s, sufficient fuel economy could not be obtained.

Claims

1. An oil composition comprising a base oil and a modified conjugated diene polymer, wherein the modified conjugated diene polymer has at least one functional group selected from the group consisting of a dicarboxylic anhydride group, a dicarboxylic acid monoester group, a dicarboxylic acid monoamide group, and a carboxylic acid imide group, and the modified conjugated diene polymer has a number average molecular weight of 4,000 to 500,000, and the kinematic viscosity of the oil composition at 100°C is 10.0 mm ２ / s or less.

2. The kinematic viscosity of the oil composition at 100°C is 1.0 mm ２ 2. The oil composition of claim 1, wherein the .alpha.-methyl-.beta.-methyl.beta.

3. The oil composition according to claim 1 or 2, wherein the functional group equivalent of the functional group possessed by the modified conjugated diene polymer is 500 to 35,000 g / eq.

4. An oil composition according to claim 1 or 2, wherein the modified conjugated diene polymer contains structural units derived from butadiene and / or structural units derived from isoprene in an amount of 50 mass% or more relative to the total amount of the modified conjugated diene polymer.

5. The oil composition according to claim 1 or 2, wherein the iodine value of the modified conjugated diene polymer is 200 g / 100 g to 500 g / 100 g.

6. The oil composition according to claim 1 or 2, wherein the vinyl content of the modified conjugated diene polymer is 0 to 50 mol %.

7. The oil composition according to claim 1 or 2, wherein the ratio of cis-1,4-bond units to the total amount of 1,4-bond units in the structural units derived from the conjugated diene monomer of the modified conjugated diene polymer is 30 mol % or more.

8. The oil composition according to claim 1 or 2, wherein the dicarboxylic acid monoester group is a group formed by reacting a dicarboxylic acid or its anhydride with at least one alcohol selected from the group consisting of aliphatic alcohols having 1 to 30 carbon atoms.

9. The oil composition according to claim 1 or 2, wherein the content of the modified conjugated diene polymer is 0.1 to 10 mass % based on the total amount of the oil composition.

10. The oil composition according to claim 1 or 2, wherein the base oil is at least one selected from the group consisting of base oils belonging to Groups I, II, III, and IV of the API (American Petroleum Institute) classification.

11. The oil composition of claim 1 or 2, further comprising at least one additive selected from the group consisting of rust inhibitors, antioxidants, surfactants, pour point depressants, detergent-dispersants, metal deactivators, antifoam agents, viscosity modifiers, friction modifiers, extreme pressure agents, antiwear agents, corrosion inhibitors, colorants, and oiliness agents.

12. The oil composition of claim 1 or 2, wherein the oil composition is a lubricating oil.

13. The oil composition of claim 12, wherein the lubricating oil is a transmission fluid or an e-axle lubricating oil.

14. Use of the oil composition according to claim 1 or 2 as a lubricating oil.

15. A friction reducer or wear reducer containing a modified conjugated diene polymer, wherein the modified conjugated diene polymer has at least one functional group selected from the group consisting of a dicarboxylic anhydride group, a dicarboxylic acid monoester group, a dicarboxylic acid monoamide group, and a carboxylic acid imide group, and the number average molecular weight of the modified conjugated diene polymer is 4,000 to 500,000, and the kinematic viscosity at 100°C is 10.0 mm ２ Friction or wear reducers that are agents for reducing friction or wear in low viscosity oil compositions of 0.15g / s or less.

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