Lubricating oil composition

Abstract

Provided is a lubricating oil composition comprising: a base oil (A); zinc dialkyldithiophosphate (B); and a copolymer (C) which includes a structural unit (c1) derived from an alkyl acrylate represented by general formula (c-1) and a structural unit (c2) derived from a hydroxyalkyl acrylate represented by general formula (c-2), in which the content ratio [(c1) / (c2)] of the structural unit (c1) to the structural unit (c2) is 50 / 50 to 90 / 10 in terms of molar ratio, and which has a weight-average molecular weight of not less than 2,000 but less than 40,000. (In formula (c-1), Rc1 is a C10-18 alkyl group. In formula (c-2), Rc2 is a C2-4 alkylene group.)

Description

lubricating oil composition

[0001] The present invention relates to a lubricating oil composition, a method for suppressing wear using the lubricating oil composition, and a method for producing the lubricating oil composition.

[0002] Engines, transmissions, speed reducers, compressors, hydraulic systems, and other various devices have mechanisms such as torque converters, wet clutches, gear bearing mechanisms, oil pumps, and hydraulic control mechanisms. Lubricating oil compositions are used in these mechanisms, and lubricating oil compositions that can meet various requirements have been developed. For example, Patent Document 1 discloses a lubricating oil composition containing predetermined amounts of naphthenic base oil, dioctyl terephthalate, molybdenum dialkyldithiophosphate, silicone oil, overbasic calcium salicylate, and zinc dialkyldithiophosphate, with the aim of providing a lubricating oil composition suitable for lubricating the seal ring of a tire sealing mixer. Lubricating oil additives used in lubricating oil compositions have also been developed. For example, Patent Document 2 discloses a friction and wear additive for lubricating oil that is composed of specific monomers and has a weight-average molecular weight within a predetermined range, which has extreme pressure performance equivalent to existing extreme pressure additives containing metal elements, and further has a friction and wear reduction effect, and is essentially free of metal elements and highly safe.

[0003] Japanese Patent Publication No. 2013-124266, CN107177401A

[0004] For example, seal rings in rubber mixing machines have large contact surfaces, and the surface pressure applied to the components being lubricated tends to be low. In lubrication of components in such low-surface-pressure environments, the effects of extreme-pressure additives such as zinc dialkyldithiophosphate (hereinafter also referred to as "ZnDTP") are less pronounced compared to environments with high surface pressure, and a decrease in wear resistance becomes a problem. In this situation, there is a need for a new lubricating oil composition that can exhibit excellent wear resistance even when used to lubricate components in environments with low surface pressure.

[0005] One aspect of the present invention provides a lubricating oil composition comprising a base oil, zinc dialkyldithiophosphate, and a copolymer having specific constituent units and having a weight-average molecular weight adjusted to a predetermined range. More specifically, the present invention provides a lubricating oil composition according to the following aspect, a method for suppressing wear, and a method for producing a lubricating oil composition. [1] A lubricating oil composition comprising a base oil (A), zinc dialkyldithiophosphate (B), and a copolymer (C) comprising a constituent unit (c1) derived from an alkyl acrylate represented by the following general formula (c-1) and a constituent unit (c2) derived from a hydroxyalkyl acrylate represented by the following general formula (c-2), wherein the content ratio of constituent unit (c1) to constituent unit (c2) [(c1) / (c2)] is 50 / 50 to 90 / 10 in molar ratio, and the weight-average molecular weight is 2000 or more and less than 40000. (In the above formula (c-1), R ｃ１ R is an alkyl group having 10 to 18 carbon atoms. In the above formula (c-2), ｃ２ ( is an alkylene group having 2 to 4 carbon atoms.) [2] The lubricating oil composition described in [1] above, used for lubricating seal rings. [3] The lubricating oil composition described in [1] above, used for lubricating seal rings of rubber compounding machines. [4] The lubricating oil composition described in any one of [1] to [3] above, wherein the content ratio of component (B) to component (C) [(B) / (C)] is 10 / 90 to 90 / 10 by mass ratio. [5] The lubricating oil composition described in any one of [1] to [4] above, wherein component (B) contains a compound (B1) represented by the following general formula (b-1). (In the above formula (b-1), R ｂ１ ~R ｂ４ Each of these is independently a hydrocarbon group, and they may be the same or different from each other.) [6] In the general formula (b-1), R ｂ１ ~R ｂ４The lubricating oil composition according to [5] above, wherein each is independently a primary alkyl group or a secondary alkyl group. [7] The lubricating oil composition according to any one of [1] to [6] above, wherein the content of component (B) is 0.10% by mass or more and 2.00% by mass or less on a total basis of the lubricating oil composition. [8] The lubricating oil composition according to any one of [1] to [7] above, wherein the content of component (C) is 0.10% by mass or more and 2.00% by mass or less on a total basis of the lubricating oil composition. [9] The lubricating oil composition according to any one of [1] to [8] above, which is used for lubricating a member in an environment where the surface pressure applied to the member to be lubricated is 1.2 MPa or less.

[10] The lubricating oil composition according to any one of [1] to [9] above, wherein the content of the organic molybdenum compound is less than 1.0% by mass on a total basis of the lubricating oil composition.

[11] The kinematic viscosity of the lubricating oil composition at 40°C is 80 mm ２

[12] A lubricating oil composition according to any one of the above items [1] to

[10] , wherein the ratio is 1 / s or higher.

[13] A wear suppression method for suppressing wear of a member by using the lubricating oil composition according to any one of the above items [1] to

[11] to lubricate the member in an environment in which the surface pressure applied to the member to be lubricated is 1.2 MPa or less.

[14] A method for producing the lubricating oil composition according to any one of the above items [1] to

[11] , comprising the step of blending a base oil (A) with zinc dialkyldithiophosphate (B) and a copolymer (C).

[0006] A lubricating oil composition according to one preferred embodiment of the present invention can exhibit excellent wear resistance even when used for lubricating a component in an environment where the surface pressure applied to the component is low. Therefore, a lubricating oil composition according to one embodiment of the present invention can be suitably used for lubricating components in environments where the surface pressure applied to the component is low, such as seal rings in rubber compounding machines. Furthermore, a lubricating oil composition according to one preferred embodiment of the present invention can exhibit excellent wear resistance even when lubricating components such as seal rings made of non-ferrous alloy components that do not have iron as the main component, such as Stellite.

[0007] The numerical ranges described herein can be any combination of upper and lower limits. For example, if the numerical range is described as "preferably 30 to 100, more preferably 40 to 80," the ranges of "30 to 80" and "40 to 100" are also included in the numerical range described herein. Similarly, if the numerical range is described as "preferably 30 or more, more preferably 40 or more, and also preferably 100 or less, more preferably 80 or less," the ranges of "30 to 80" and "40 to 100" are also included in the numerical range described herein. In addition, for example, if the numerical range described herein is described as "60 to 100," it means the range is "60 or more (60 or greater than 60), and 100 or less (100 or less than 100)." Furthermore, in the provisions for upper and lower limits described herein, the numerical range from the lower limit to the upper limit can be defined by appropriately selecting and combining the options from each set of choices.

[0008] In this specification, kinematic viscosity and viscosity index mean values ​​measured or calculated in accordance with JIS K2283:2000. Furthermore, in this specification, "substantially absent" of a particular compound excludes the addition of the compound with a specific intention, but does not exclude the unavoidable presence of the compound. When a particular compound is substantially absent, the specific content of the compound may be less than 0.1% by mass, less than 0.01% by mass, less than 0.001% by mass, less than 0.0001% by mass, or less than 0.00001% by mass, based on the total amount (100% by mass) of the lubricating oil composition.

[0009] [Composition of the lubricating oil composition] The lubricating oil composition of the present invention comprises a base oil (A) (hereinafter also referred to as "component (A)"), zinc dialkyldithiophosphate (B) (hereinafter also referred to as "component (B)"), and a specific copolymer (C) (hereinafter also referred to as "component (C)").

[0010] For example, components such as seal rings in rubber compounding machines have large contact surfaces and tend to be in environments where the surface pressure applied to the component being lubricated is low. In lubrication of components in such low-surface-pressure environments, there was a problem that sufficient wear resistance was not achieved even when using a lubricating oil composition containing ZnDTP. Furthermore, it was found that when components such as seal rings are made of non-ferrous alloys that do not have iron as the main component, such as Stellite, a decrease in wear resistance tends to occur. Focusing on these problems, the inventors diligently studied to solve them and found that a lubricating oil composition containing a specific copolymer together with ZnDTP can solve these problems, and thus completed a lubricating oil composition according to one embodiment of the present invention.

[0011] In a lubricating oil composition according to one embodiment of the present invention, from the viewpoint of providing a lubricating oil composition that can exhibit even better wear resistance when used for lubricating members in an environment where the surface pressure applied to the member to be lubricated is low, or for lubricating non-ferrous alloy members, the content ratio of component (B) to component (C) [(B) / (C)] is preferably 10 / 90 or more, 15 / 85 or more, 20 / 80 or more, 25 / 75 or more, 30 / 70 or more, 35 / 65 or more, 40 / 60 or more, 45 / 55 or more, 50 / 50 or more, 52 / 48 or more, 54 / 46 or more, or 56 / 44 or more by mass ratio, and also preferably 90 / 10 or less, 85 / 15 or less, 80 / 20 or less, 75 / 25 or less, 70 / 30 or less, 68 / 32 or less, 66 / 34 or less, or 64 / 36 or less.

[0012] In a lubricating oil composition according to one aspect of the present invention, from the viewpoint of providing a lubricating oil composition that exhibits superior wear resistance even when used for lubricating members in environments where the surface pressure applied to the lubricated member is low, or for lubricating non-ferrous alloy members, the total content of component (B) and component (C) shall be 0.20% by mass or more, 0.25% by mass or more, 0.30% by mass or more, 0.35% by mass or more, and 0.40% by mass or more, based on the total amount (100% by mass) of the lubricating oil composition. Preferably, the amount is 0.45% by mass or more, 0.50% by mass or more, 0.55% by mass or more, or 0.60% by mass or more, and also preferably 4.00% by mass or less, 3.50% by mass or less, 3.00% by mass or less, 2.50% by mass or less, 2.00% by mass or less, 1.80% by mass or less, 1.60% by mass or less, 1.40% by mass or less, 1.20% by mass or less, 1.00% by mass or less, 0.90% by mass or less, or 0.80% by mass or less.

[0013] A lubricating oil composition according to one aspect of the present invention may further contain various lubricating oil additives other than components (B) to (C) as needed, to the extent that it does not impair the effects of the present invention. However, in a lubricating oil composition according to one aspect of the present invention, the total content of components (A), (B), and (C) is preferably 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, 98% by mass or more, or 99% by mass or more, based on the total amount (100% by mass) of the lubricating oil composition, from the viewpoint of providing a lubricating oil composition that can exhibit even better wear resistance when used for lubricating members in an environment where the surface pressure on the member to be lubricated is low or for lubricating non-ferrous alloy members. Furthermore, although it is usually 100% by mass or less, it may be 99.5% by mass or less, 99.0% by mass or less, 98.5% by mass or less, or 98.0% by mass or less. The details of each component contained in a lubricating oil composition according to one embodiment of the present invention will be described below.

[0014] <Component (A): Base Oil> In one aspect of the present invention, the base oil, which is component (A), can be one or more selected from mineral oils and synthetic oils. Examples of mineral oils include atmospheric residue obtained by atmospheric distillation of crude oils such as paraffinic crude oil, intermediate crude oil, and naphthenic crude oil; distillate obtained by vacuum distillation of these atmospheric residues; and refined oil obtained by subjecting the distillate to one or more refining treatments such as solvent delamination, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining (hydrocracking). Alternatively, a bright stock obtained by subjecting the above-mentioned refining treatment to the residue oil accumulated at the bottom of a distillation column obtained by atmospheric or vacuum distillation of crude oils such as paraffinic crude oil, intermediate crude oil, and naphthenic crude oil may be used.

[0015] Examples of synthetic oils include poly-α-olefins such as α-olefin homopolymers or α-olefin copolymers (e.g., 8-14 carbon olefin copolymers such as ethylene-α-olefin copolymers); isoparaffins; polyalkylene glycols; ester oils such as polyol esters, dibasic acid esters, and phosphate esters; ether oils such as polyphenyl ethers; alkylbenzenes; alkylnaphthalenes; GTL base oils obtained by isomerizing GTL wax (Gas To Liquids Wax) produced from natural gas by the Fischer-Tropsch process, etc.; CTL base oils obtained by direct liquefaction methods (such as the Bergius process) in which coal is crushed, mixed with a solvent, and reacted directly with hydrogen under high temperature and pressure; and CTL base oils obtained by indirect liquefaction methods (such as the Fischer-Tropsch process) in which coal is gasified (coal gasification), and the resulting gas is separated and purified and reacted with the raw materials to liquefy it. Component (A) used in one aspect of the present invention may contain one or more selected from these synthetic oils, or it may not contain one or more selected from these synthetic oils.

[0016] In the lubricating oil composition according to one aspect of the present invention, from the viewpoint of obtaining a lubricating oil composition capable of forming an oil film with a sufficient thickness by supplying a required amount to a member in an environment where the surface pressure applied to the member to be lubricated is low, component (A) preferably contains bright stock (A1). In the lubricating oil composition according to one aspect of the present invention, from the above viewpoint, the content ratio of bright stock (A1) in base oil (A) is based on the total amount (100% by mass) of component (A) in the lubricating oil composition, it is preferably 30% by mass or more, 40% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, or 80% by mass or more, and may be 100% by mass or less, 98% by mass or less, 96% by mass or less, 94% by mass or less, 92% by mass or less, 90% by mass or less, or 88% by mass or less.

[0017] Component (A) used in one aspect of the present invention, from the viewpoint of obtaining a lubricating oil composition capable of forming an oil film with a sufficient thickness by supplying a required amount to a member in an environment where the surface pressure applied to the member to be lubricated is low, preferably contains a mineral oil classified into any one of Groups I to III of the API (American Petroleum Institute) base oil category, more preferably contains a mineral oil classified into Group I or II, and even more preferably contains at least a mineral oil classified into Group I. In the lubricating oil composition according to one aspect of the present invention, from the above viewpoint, the content ratio of the mineral oil classified into Group I in base oil (A) is based on the total amount (100% by mass) of component (A) in the lubricating oil composition, it is preferably 30% by mass or more, 40% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, or 95% by mass or more, and may be 100% by mass or less, 99% by mass or less, 98% by mass or less, or 97% by mass or less.

[0018] The kinematic viscosity at 40°C of component (A) used in one aspect of the present invention, from the viewpoints of suppressing evaporation loss, and obtaining a lubricating oil composition capable of forming an oil film with a sufficient thickness by supplying a required amount to a member in an environment where the surface pressure applied to the member to be lubricated is low, is 80 mm ２ / s or more, 100 mm ２ / s or more, 120mm ２ / s or more, 140mm ２ / s or more, 160mm ２ / s or more, 180mm ２ / s or more, 200mm ２ / s or more, 220mm ２ / s or more, 240mm ２ / s or more, 260mm ２ / s or more, 280mm ２ / s or more, 300mm ２ / s or more, 320mm ２ / s or more, 340mm ２ / s or more, or 360 mm ２ It is preferable to have a pressure of 0.5 / s or higher, and from the viewpoint of providing a lubricating oil composition that is easy to supply to components in an environment where the surface pressure on the component to be lubricated is low, 900 mm ２ / s or less, 850mm ２ / s or less, 800mm ２ / s or less, 750mm ２ / s or less, 700mm ２ / s or less, 650mm ２ / s or less, 600mm ２ / s or less, 550mm ２ / s or less, 500mm ２ / s or less, 480mm ２ / s or less, 460mm ２ / s or less, 440mm ２ / s or less, 420mm ２ / s or less, 400mm ２ / s or less, or 390 mm ２ It is preferable to keep it below / s.

[0019] The kinematic viscosity of component (A) used in one aspect of the present invention at 100°C is set to 8.0 mm, from the viewpoint of suppressing evaporation loss and providing a lubricating oil composition that can supply the necessary amount to a component in an environment where the surface pressure on the component to be lubricated is low, thereby forming an oil film of sufficient thickness. ２ / s or more, 10.0mm ２ / s or more, 12.0mm ２ / s or more, 14.0mm ２ / s or more, 16.0mm ２ / s or more, 18.0mm ２ / s or more, 20.0mm ２ / s or more, 22.0mm ２ / s or more, 24.0mm ２ / s or more, 25.0mm ２ / s or more, 26.0mm ２ / s or more, or 27.0 mm ２ It is preferable to have a pressure of 0.2 / s or higher, and from the viewpoint of providing a lubricating oil composition that is easy to supply to components in an environment where the surface pressure on the component to be lubricated is low, 90.0 mm ２ / s or less, 80.0mm ２ / s or less, 70.0mm ２ / s or less, 60.0mm ２ / s or less, 55.0mm ２ / s or less, 50.0mm ２ / s or less, 45.0mm ２ / s or less, 40.0mm ２ / s or less, 38.0mm ２ / s or less, 36.0mm ２ / s or less, 34.0mm ２ / s or less, or 32.0 mm ２ It is preferable to keep it below / s.

[0020] The viscosity index of component (A) used in one aspect of the present invention is preferably 60 or higher, 65 or higher, 70 or higher, 75 or higher, 80 or higher, 85 or higher, 90 or higher, 95 or higher, 100 or higher, 102 or higher, or 104 or higher, from the viewpoint of providing a lubricating oil composition with low temperature dependence. It may also be 300 or lower, 250 or lower, 200 or lower, 180 or lower, 160 or lower, 150 or lower, 140 or lower, or 130 or lower.

[0021] Furthermore, in one embodiment of the present invention, when a mixed oil is used as component (A), it is preferable that the kinematic viscosity and viscosity index of the mixed oil are within the above range. For this reason, a low-viscosity base oil and a high-viscosity base oil may be used in combination to prepare a mixture that has a kinematic viscosity and viscosity index within the above range.

[0022] In a lubricating oil composition according to one aspect of the present invention, from the viewpoint of providing a lubricating oil composition that can exhibit even better wear resistance when used for lubricating members in environments where the surface pressure applied to the member to be lubricated is low, or for lubricating non-ferrous alloy members, the content of component (A) is preferably 50% by mass or more, 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, 92% by mass or more, 94% by mass or more, 95% by mass or more, 96% by mass or more, or 97% by mass or more, based on the total amount (100% by mass) of the lubricating oil composition, and also preferably 99.80% by mass or less, 99.75% by mass or less, 99.70% by mass or less, 99.65% by mass or less, 99.60% by mass or less, 99.55% by mass or less, 99.50% by mass or less, or 99.40% by mass or less.

[0023] <Component (B): Zinc Dialkyldithiophosphate> A lubricating oil composition according to one aspect of the present invention contains zinc dialkyldithiophosphate (ZnDTP), which is component (B), as an anti-wear agent. Component (B) may be used alone or in combination of two or more. From the viewpoint of providing a lubricating oil composition that exhibits even better anti-wear properties, component (B) used in one aspect of the present invention is preferably a compound represented by the following general formula (b-1).

[0024]

[0025] In the above formula (b-1), R ｂ１ ~R ｂ４ Each of these is independently a hydrocarbon group, and these hydrocarbon groups may be the same as or different from each other. ｂ１ ~R ｂ４ The number of carbon atoms in the hydrocarbon group that can be selected may be 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, or 8 or more, and may also be 30 or less, 28 or less, 26 or less, 24 or less, 22 or less, 20 or less, 18 or less, 16 or less, or 14 or less.

[0026] R ｂ１ ~R ｂ４Examples of hydrocarbon groups that can be selected include alkyl groups, alkenyl groups, cycloalkyl groups, aryl groups, alkylaryl groups, and arylalkyl groups. Examples of alkyl groups include linear alkyl groups or branched alkyl groups such as methyl groups, ethyl groups, propyl groups (n-propyl groups, isopropyl groups), butyl groups (n-butyl groups, s-butyl groups, t-butyl groups, isobutyl groups), pentyl groups, hexyl groups, heptyl groups, octyl groups, 2-ethylhexyl groups, nonyl groups, decyl groups, undecyl groups, dodecyl groups, tridecyl groups, tetradecyl groups, pentadecyl groups, hexadecyl groups, heptadecyl groups, and octadecyl groups. Examples of the alkenyl group include linear alkenyl groups or branched alkenyl groups such as ethenyl group (vinyl group), propenyl group, butenyl group, pentenyl group, hexenyl group, heptenyl group, octenyl group, nonenyl group, decenyl group, dodecenyl group, tridecenyl group, tetradecenyl group, pentadecenyl group, hexadecenyl group, and octadecenyl group (oleyl group). Examples of the cycloalkyl group include cycloalkyl groups that may be substituted with alkyl groups such as cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, dimethylcyclohexyl group, ethylcyclohexyl group, methylcyclohexylmethyl group, cyclohexylethyl group, propylcyclohexyl group, butylcyclohexyl group, and heptylcyclohexyl group. Examples of the aryl group include phenyl group, naphthyl group, anthracenyl group, biphenyl group, and terphenyl group. Examples of the alkylaryl group include tolyl group, dimethylphenyl group, butylphenyl group, nonylphenyl group, methylbenzyl group, and dimethylnaphthyl group. Examples of the arylalkyl group include phenylmethyl group, phenylethyl group, and diphenylmethyl group.

[0027] Among these, R ｂ１ ~R ｂ４The hydrocarbon group that can be selected is preferably an alkyl group, more preferably a primary alkyl group or a secondary alkyl group, and even more preferably a primary alkyl group having 1 to 30 carbon atoms or a secondary alkyl group having 1 to 30 carbon atoms. Examples of the primary alkyl group include a group represented by the following general formula (i). Examples of the secondary alkyl group include a group represented by the following general formula (ii).

[0028] In the above equations (i) and (ii), R ｂ５ ~R ｂ７ Each of these is an alkyl group, independently. * indicates the bond position with the oxygen atom in the above formula (b-1). R ｂ５ The number of carbon atoms in the alkyl group that can be selected as, and R ｂ６ and R ｂ７ The total number of carbon atoms in the selectable alkyl groups may be 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, or 8 or more, and may also be 30 or less, 28 or less, 26 or less, 24 or less, 22 or less, 20 or less, 18 or less, 16 or less, or 14 or less. ｂ５ ~R ｂ７ The alkyl group that can be selected is the above-mentioned R ｂ１ ~R ｂ４ Examples of alkyl groups that can be selected are similar to those mentioned above. Furthermore, the alkyl group may be a linear alkyl group or a branched alkyl group.

[0029] In a lubricating oil composition according to one aspect of the present invention, from the viewpoint of providing a lubricating oil composition that can exhibit even better wear resistance, the content of component (B) is, based on the total amount (100% by mass) of the lubricating oil composition, 0.10% by mass or more, 0.12% by mass or more, 0.14% by mass or more, 0.16% by mass or more, 0.18% by mass or more, 0.20% by mass or more, 0.22% by mass or more, 0.24% by mass or more, 0.26% by mass or more, 0.28% by mass or more, and 0. It is preferable that the amount be 30% by mass or more, 0.32% by mass or more, 0.34% by mass or more, or 0.36% by mass or more, and it is also preferable that the amount be 2.00% by mass or less, 1.80% by mass or less, 1.60% by mass or less, 1.40% by mass or less, 1.20% by mass or less, 1.00% by mass or less, 0.90% by mass or less, 0.80% by mass or less, 0.70% by mass or less, 0.60% by mass or less, 0.50% by mass or less, or 0.45% by mass or less.

[0030] Furthermore, in a lubricating oil composition according to one aspect of the present invention, from the same viewpoint as above, the content of component (B) in terms of zinc atoms is, based on the total amount (100% by mass) of the lubricating oil composition, 60 ppm by mass or more, 80 ppm by mass or more, 100 ppm by mass or more, 120 ppm by mass or more, 140 ppm by mass or more, 160 ppm by mass or more, 180 ppm by mass or more, 200 ppm by mass or more, 220 ppm by mass or more, 240 ppm by mass or more, 260 ppm by mass or more, 280 ppm by mass or more, and 30 ppm by mass or more. It is preferable that the zinc atom content be 0 ppm or more, or 320 ppm or more, and also preferable that it be 2000 ppm or less, 1800 ppm or less, 1600 ppm or less, 1400 ppm or less, 1200 ppm or less, 1000 ppm or less, 900 ppm or less, 800 ppm or less, 700 ppm or less, 600 ppm or less, 500 ppm or less, 450 ppm or less, 400 ppm or less, or 350 ppm or less. In this specification, the zinc atom content refers to the value measured in accordance with JPI-5S-38-92.

[0031] <Component (C): Copolymer> The lubricating oil composition according to one aspect of the present invention contains a copolymer having a specific structure, which is component (C). Component (C) may be used alone, or two or more types thereof may be used in combination. By containing component (C) together with component (B), the resulting lubricating oil composition can sufficiently exhibit the wear resistance of component (B) even when used for lubricating a member in an environment where the surface pressure applied to the member to be lubricated is low or for lubricating a member made of a non-ferrous alloy.

[0032] Component (C) used in one aspect of the present invention comprises a structural unit (c1) derived from an alkyl acrylate represented by the following general formula (c-1) and a structural unit (c2) derived from a hydroxyalkyl acrylate represented by the following general formula (c-2).

[0033] In the above formula (c-1), R ｃ１ is an alkyl group having 10 to 18 carbon atoms. As the alkyl group that can be selected as R ｃ１ , examples include linear alkyl groups or branched alkyl groups such as decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, and octadecyl group, with linear alkyl groups being preferred. The number of carbon atoms of the alkyl group that can be selected as R ｃ１ is 10 or more, preferably 11 or more, or 12 or more, and is 18 or less, preferably 16 or less, or 14 or less.

[0034] In the above formula (c-2), R ｃ２ is an alkylene group having 2 to 4 carbon atoms. As the alkylene group that can be selected as R ｃ２ , examples include ethylene group (-CH ２ CH ２ -), ethylidene group (-CH(CH ３ )-), trimethylene group (-CH ２ CH ２ CH ２ -), propylene group (-CH(CH ３ )CH ２ -), propylidene group (-CHCH ２ (CH ３)-), isopropylidene group (-C(CH ３ ) ２ -), tetramethylene group (-CH ２ CH ２ CH ２ CH ２ -), 1-methyltrimethylene group (-CH(CH ３ )CH ２ CH ２ -), 2-methyltrimethylene group (-CH ２ CH(CH ３ )CH ２ -), butylene group (-C(CH ３ ) ２ CH ２ -), etc., and an ethylene group is preferable. R ｃ２ The alkylene group that can be selected as has 2 to 4 carbon atoms, with 2 or 3 being preferable, and 2 being more preferable.

[0035] In component (C) used in one aspect of the present invention, the component may have structural units derived from monomers other than the structural units (c1) and (c2). However, in component (C) used in one aspect of the present invention, even when used for lubricating members in an environment where the surface pressure applied to the member to be lubricated is low or for lubricating non-ferrous alloy members, from the viewpoint of obtaining a lubricating oil composition that can more effectively exhibit excellent wear resistance, the total content of the structural unit (c1) and the structural unit (c2) is 70 to 100 mol%, 75 to 100 mol%, 80 to 100 mol%, 85 to 100 mol%, 90 to 100 mol%, 95 to 100 mol%, 98 to 100 mol%, 99 to 100 mol%, or 100 mol%, based on the total structural units (100 mol%) of component (C), and it is preferably any of the above ranges.

[0036] In one embodiment of the present invention, in component (C) used, from the viewpoint of providing a lubricating oil composition that exhibits even better wear resistance when used for lubricating members in environments where the surface pressure applied to the member to be lubricated is low, or for lubricating non-ferrous alloy members, the content ratio of constituent unit (c1) to constituent unit (c2) [(c1) / (c2)] is preferably 50 / 50 or more, 55 / 45 or more, 60 / 40 or more, 62 / 38 or more, 64 / 36 or more, 66 / 34 or more, 68 / 32 or more, 70 / 30 or more, 72 / 28 or more, 74 / 36 or more, or 76 / 34 or more in molar ratio, and also preferably 90 / 10 or less, 88 / 12 or less, 86 / 14 or less, 84 / 16 or less, 82 / 18 or less, or 80 / 20 or less.

[0037] In one aspect of the present invention, the weight-average molecular weight (Mw) of component (C) used is preferably 2000 or more, 3000 or more, 4000 or more, 5000 or more, 6000 or more, 7000 or more, 8000 or more, 9000 or more, 10000 or more, 11000 or more, or 12000 or more, from the viewpoint of providing a lubricating oil composition that exhibits superior wear resistance even when used for lubricating members in environments where the surface pressure applied to the member to be lubricated is low, or for lubricating non-ferrous alloy members. Furthermore, it is preferable that the weight-average molecular weight (Mw) of component (C) used in one aspect of the present invention be less than 40000, 35000 or less, 30000 or less, 28000 or less, 26000 or less, 24000 or less, 22000 or less, 20000 or less, 18000 or less, 17000 or less, 16000 or less, 15000 or less, or 14000 or less. In this specification, the weight-average molecular weight (Mw) of component (C) refers to the value measured by the method described in the examples below.

[0038] In a lubricating oil composition according to one aspect of the present invention, from the viewpoint of providing a lubricating oil composition that exhibits even better wear resistance when used for lubricating members in environments where the surface pressure applied to the member to be lubricated is low, or for lubricating non-ferrous alloy members, the content of component (C) is, based on the total amount (100% by mass) of the lubricating oil composition, 0.10% by mass or more, 0.12% by mass or more, 0.14% by mass or more, 0.16% by mass or more, 0.18% by mass or more, 0.20% by mass or more, 0.21% by mass or more, 0.22% by mass or more, and 0.2% by mass or more. It is preferable that the amount be 3% by mass or more, 0.24% by mass or more, or 0.25% by mass or more, and it is also preferable that it be 2.00% by mass or less, 1.80% by mass or less, 1.60% by mass or less, 1.40% by mass or less, 1.20% by mass or less, 1.00% by mass or less, 0.90% by mass or less, 0.80% by mass or less, 0.70% by mass or less, 0.60% by mass or less, 0.50% by mass or less, 0.45% by mass or less, 0.40% by mass or less, 0.35% by mass or less, 0.30% by mass or less, or 0.28% by mass or less.

[0039] <Other Lubricant Additives> A lubricant composition according to one embodiment of the present invention may contain other lubricant additives as necessary, as long as they do not impair the effects of the present invention. Examples of such lubricant additives include pour point depressants, viscosity index improvers, antioxidants, metal-based detergents, ashless dispersants, extreme pressure agents (anti-wear agents) other than component (B), friction modifiers, rust inhibitors, metal deactivators, and defoamers. These lubricant additives may be used individually or in combination of two or more.

[0040] In a lubricating oil composition according to one aspect of the present invention, the content of each of these lubricating oil additives can be appropriately adjusted within a range that does not impair the effects of the present invention. Based on the total amount (100% by mass) of the lubricating oil composition, the content of each additive can be independently set to typically 0.001% by mass or more, 0.005% by mass or more, 0.01% by mass or more, 0.05% by mass or more, or 0.10% by mass or more, or 15% by mass or less, 10% by mass or less, 5.0% by mass or less, 2.0% by mass or less, or 1.0% by mass or less.

[0041] Furthermore, in one embodiment of the present invention, the content of the above-mentioned lubricating oil additives may be limited, and the content of each of the above-mentioned lubricating oil additives may be less than 5.0% by mass, less than 2.0% by mass, less than 1.0% by mass, less than 0.1% by mass, less than 0.01% by mass, less than 0.001% by mass, less than 0.0001% by mass, or less than 0.00001% by mass, based on the total amount (100% by mass) of the lubricating oil composition.

[0042] Furthermore, considering handling ease and solubility with base oil (A), lubricating oil additives are often commercially available in the form of a solution dissolved in diluent oil. However, in this specification, the content of lubricating oil additives (including components (B) and (C) mentioned above) in a solution diluted with diluent oil is the content converted to the active ingredients constituting the lubricating oil additive, excluding the mass of the diluent oil.

[0043] <Pour Point Depressant> The lubricating oil composition according to one aspect of the present invention may further contain a pour point depressant, or it may substantially not contain a pour point depressant, or it may not contain a pour point depressant at all. The pour point depressant may be used alone, or two or more may be used in combination. Examples of pour point depressants used in one aspect of the present invention include ethylene-vinyl acetate copolymer, condensate of chlorinated paraffin and naphthalene, condensate of chlorinated paraffin and phenol, polymethacrylate, polyalkylstyrene, and the like. The mass-average molecular weight (Mw) of the pour point depressant used in one aspect of the present invention may be 5,000 or more, 7,000 or more, 10,000 or more, 15,000 or more, 20,000 or more, 25,000 or more, 30,000 or more, 35,000 or more, 40,000 or more, 45,000 or more, 50,000 or more, 55,000 or more, or 60,000 or more, or 150,000 or less, 120,000 or less, 100,000 or less, 90,000 or less, or 80,000 or less.

[0044] <Viscosity Index Improvers> A lubricating oil composition according to one aspect of the present invention may further contain a viscosity index improver, or may substantially not contain a viscosity index improver, or may not contain a viscosity index improver at all. The viscosity index improver may be used alone, or two or more may be used in combination. Examples of viscosity index improvers used in one aspect of the present invention include polymers such as non-dispersible polymethacrylate, dispersed polymethacrylate, olefin copolymers (e.g., ethylene-propylene copolymer, etc.), dispersed olefin copolymers, and styrene copolymers (e.g., styrene-diene copolymer, styrene-isoprene copolymer, etc.). The weight-average molecular weight (Mw) of the viscosity index improver used in one aspect of the present invention may be 5,000 or more, 7,000 or more, 10,000 or more, 15,000 or more, or 20,000 or more, or it may be 1,000,000 or less, 700,000 or less, 500,000 or less, 300,000 or less, 200,000 or less, 100,000 or less, or 50,000 or less.

[0045] [Antioxidants] A lubricating oil composition according to one aspect of the present invention may further contain antioxidants, or may substantially not contain antioxidants, or may not contain antioxidants at all. Antioxidants may be used alone or in combination of two or more. Examples of antioxidants used in one aspect of the present invention include amine-based antioxidants such as alkylated diphenylamine, phenylnaphthylamine, and alkylated phenylnaphthylamine; phenol-based antioxidants such as 2,6-di-t-butylphenol, 4,4'-methylenebis(2,6-di-t-butylphenol), isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; and sulfur-based antioxidants such as phenothiazine, dioctadecyl sulfide, dilauryl-3,3'-thiodipropionate, and 2-mercaptobenzimidazole.

[0046] [Metal-based detergent] The lubricating oil composition according to one aspect of the present invention may further contain a metal-based detergent, or it may substantially not contain a metal-based detergent, or it may not contain a metal-based detergent at all. The metal-based detergent may be used alone, or two or more may be used in combination. Examples of metal-based detergents used in one aspect of the present invention include metal salts such as metal sulfonates, metal salicylates, and metal phenates. Examples of metal atoms constituting the metal salt include metal atoms selected from alkali metals and alkaline earth metals, such as sodium, calcium, and magnesium.

[0047] In addition, in a lubricating oil composition according to one embodiment of the present invention, the content of a metal-based detergent may be limited. Specifically, the content of a metal-based detergent containing metal atoms selected from calcium atoms, magnesium atoms, and sodium atoms, in terms of the amount of such metal atoms, may be less than 500 ppm by mass, less than 400 ppm by mass, less than 300 ppm by mass, less than 200 ppm by mass, less than 150 ppm by mass, less than 100 ppm by mass, less than 50 ppm by mass, less than 20 ppm by mass, less than 10 ppm by mass, or less than 5 ppm by mass, based on the total amount (100% by mass) of the lubricating oil composition. The content of the calcium atom-containing metal-based detergent, in terms of calcium atoms, may be less than 500 ppm by mass, less than 400 ppm by mass, less than 300 ppm by mass, less than 200 ppm by mass, less than 150 ppm by mass, less than 100 ppm by mass, less than 50 ppm by mass, less than 20 ppm by mass, less than 10 ppm by mass, or less than 5 ppm by mass, based on the total amount (100% by mass) of the lubricating oil composition.

[0048] <Ashless Dispersant> The lubricating oil composition according to one aspect of the present invention may further contain an ashless dispersant, or it may substantially not contain an ashless dispersant, or it may not contain an ashless dispersant at all. The ashless dispersant may be used alone, or two or more may be used in combination. Examples of ashless dispersants used in one aspect of the present invention include boron-free succinimides such as boron-free alkenyl succinimides, boron-containing succinimides such as boron-containing alkenyl succinimides, benzylamines, boron-containing benzylamines, succinic acid esters, monovalent or divalent carboxylic acid amides represented by fatty acids or succinic acid, and the like.

[0049] <Extreme Pressure Agents (Anti-Abrasives)> The lubricating oil composition according to one aspect of the present invention may further contain extreme pressure agents (anti-abrasives) other than component (B), or it may not substantially contain extreme pressure agents (anti-abrasives) other than component (B), or it may not contain extreme pressure agents (anti-abrasives) other than component (B). The ashless dispersant may be used alone or two or more may be used in combination. Examples of extreme pressure agents (anti-abrasives) other than component (B) used in one aspect of the present invention include phosphorus atom-containing extreme pressure agents such as phosphite esters, phosphate esters, phosphonic acid esters, and their amine salts or metal salts; sulfur atom and phosphorus atom-containing extreme pressure agents such as thiophosphite esters, thiophosphate esters, thiophosphonic acid esters, and their amine salts or metal salts; sulfur atom-containing extreme pressure agents such as polysulfide compounds, thiocarbamate compounds, and sulfurized oil compounds; and the like.

[0050] Furthermore, when using a lubricating oil composition according to one aspect of the present invention for lubricating a seal ring of a rubber compounding machine, it is preferable to limit the content of active sulfur additives such as sulfurized olefins from the viewpoint of suppressing crosslinking with rubber, and it is more preferable that the active sulfur additive is substantially absent. In a lubricating oil composition according to one aspect of the present invention, the content of active sulfur additives (or sulfurized olefins) is preferably less than 1.0% by mass, less than 0.1% by mass, less than 0.01% by mass, less than 0.001% by mass, less than 0.0001% by mass, or less than 0.00001% by mass, based on the total amount (100% by mass) of the lubricating oil composition. In addition, the content of active sulfur additives (or sulfurized olefins) in terms of sulfur atoms is preferably less than 50 ppm by mass, less than 10 ppm by mass, less than 5.0 ppm by mass, less than 1.0 ppm by mass, less than 0.1 ppm by mass, or less than 0.01 ppm by mass, based on the total amount (100% by mass) of the lubricating oil composition. In this specification, the sulfur atom content refers to the value measured in accordance with JIS K2541-6:2013.

[0051] <Friction Modifiers> A lubricating oil composition according to one aspect of the present invention may further contain a friction modifier, or may substantially not contain a friction modifier, or may not contain a friction modifier at all. The friction modifier may be used alone or in combination of two or more types. Examples of friction modifiers used in one aspect of the present invention include organic molybdenum compounds such as molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDTP), and amine salts of molybdic acid; ashless friction modifiers such as aliphatic amines, fatty acid esters, fatty acid amides, fatty acids, aliphatic alcohols, and aliphatic ethers having at least one alkyl group or alkenyl group with 6 to 30 carbon atoms in the molecule; and oils and fats, amines, amides, sulfur esters, etc.

[0052] In addition, the lubricating oil composition of one embodiment of the present invention may have a limited content of the organic molybdenum compound, may not substantially contain the organic molybdenum compound, or may not contain the organic molybdenum compound at all. In the lubricating oil composition of this embodiment, the content of the organic molybdenum compound is preferably less than 1.0% by mass, less than 0.1% by mass, less than 0.01% by mass, less than 0.001% by mass, less than 0.0001% by mass, or less than 0.00001% by mass, based on the total amount (100% by mass) of the lubricating oil composition. Furthermore, the content of the organic molybdenum compound in terms of molybdenum atoms is preferably less than 50 ppm by mass, less than 30 ppm by mass, less than 10 ppm by mass, less than 5.0 ppm by mass, or less than 2.0 ppm by mass, based on the total amount (100% by mass) of the lubricating oil composition. In this specification, the molybdenum atom content refers to the value measured in accordance with JPI-5S-38-92.

[0053] <Rust Inhibitor> The lubricating oil composition according to one aspect of the present invention may further contain a rust inhibitor, or may substantially not contain a rust inhibitor, or may not contain a rust inhibitor at all. The rust inhibitor may be used alone, or two or more may be used in combination. Examples of rust inhibitors used in one aspect of the present invention include fatty acids, alkenyl succinate half esters, fatty acid soaps, alkyl sulfonates, polyhydric alcohol fatty acid esters, fatty acid amines, oxidized paraffins, alkyl polyoxyethylene ethers, and the like.

[0054] <Metal Deactivators> The lubricating oil composition according to one aspect of the present invention may further contain a metal deactivator, or it may substantially not contain a metal deactivator, or it may not contain a metal deactivator at all. The metal deactivator may be used alone, or two or more may be used in combination. Examples of metal deactivators used in one aspect of the present invention include benzotriazole compounds, tolyltriazole compounds, imidazole compounds, pyrimidine compounds, and the like.

[0055] <Antifoaming agent> The lubricating oil composition according to one aspect of the present invention may further contain an antifoaming agent, or it may substantially not contain an antifoaming agent, or it may not contain an antifoaming agent at all. The antifoaming agent may be used alone, or two or more types may be used in combination. Examples of antifoaming agents used in one aspect of the present invention include alkyl silicone antifoaming agents, fluorosilicone antifoaming agents, fluoroalkyl ether antifoaming agents, and the like.

[0056] [Method for Manufacturing Lubricating Oil Composition] There are no particular limitations on the method for manufacturing the lubricating oil composition according to one embodiment of the present invention, but from the viewpoint of productivity, it is preferable to have a step of blending component (A) with the above-mentioned components (B) and (C). In this step, the above-mentioned lubricating oil additive may be blended together with components (B) and (C) as needed. The types and amounts of components (A), (B), and (C), as well as the lubricating oil additive, are as described above.

[0057] [Properties of the Lubricating Oil Composition] The kinematic viscosity of the lubricating oil composition according to one embodiment of the present invention at 40°C is set to 80 mm, from the viewpoint of suppressing evaporation loss and providing a lubricating oil composition that can supply the necessary amount to a component in an environment where the surface pressure on the component to be lubricated is low, thereby forming an oil film of sufficient thickness. ２ / s or more, 100mm ２ / s or more, 120mm ２ / s or more, 140mm ２ / s or more, 160mm ２ / s or more, 180mm ２ / s or more, 200mm ２ / s or more, 220mm ２ / s or more, 240mm ２ / s or more, 250mm ２ / s or more, 260mm ２ / s or more, 270mm ２ / s or more, 280mm ２ / s or more, 290mm ２ / s or more, 300mm ２ / s or more, 310mm ２ / s or more, or 320 mm ２It is preferable to have a pressure of 0.5 / s or higher, and from the viewpoint of providing a lubricating oil composition that is easy to supply to components in an environment where the surface pressure on the component to be lubricated is low, 900 mm ２ / s or less, 850mm ２ / s or less, 800mm ２ / s or less, 750mm ２ / s or less, 700mm ２ / s or less, 650mm ２ / s or less, 600mm ２ / s or less, 550mm ２ / s or less, 500mm ２ / s or less, 450mm ２ / s or less, 400mm ２ / s or less, 380mm ２ / s or less, 360mm ２ / s or less, 340mm ２ / s or less, or 330 mm ２ It is preferable to keep it below / s.

[0058] The kinematic viscosity of a lubricating oil composition according to one aspect of the present invention at 100°C is 6.0 mm, from the viewpoint of suppressing evaporation loss and providing a lubricating oil composition that can supply the necessary amount to a component in an environment where the surface pressure on the component to be lubricated is low, thereby forming an oil film of sufficient thickness. ２ / s or more, 8.0mm ２ / s or more, 10.0mm ２ / s or more, 12.0mm ２ / s or more, 14.0mm ２ / s or more, 16.0mm ２ / s or more, 18.0mm ２ / s or more, 20.0mm ２ / s or more, 22.0mm ２ / s or more, 24.0mm ２ / s or more, 25.0mm ２ / s or more, or 26.0 mm ２ It is preferable to have a pressure of 0.2 / s or higher, and from the viewpoint of providing a lubricating oil composition that is easy to supply to components in an environment where the surface pressure on the component to be lubricated is low, 90.0 mm ２ / s or less, 80.0mm ２ / s or less, 70.0mm ２ / s or less, 60.0mm ２ / s or less, 55.0mm ２ / s or less, 50.0mm ２ / s or less, 45.0mm ２ / s or less, 40.0mm ２ / s or less, 38.0mm ２ / s or less, 36.0mm ２ / s or less, 34.0mm ２ / s or less, 32.0mm ２ / s or less, 30.0mm ２ / s or less, or 28.0 mm ２ It is preferable to keep it below / s.

[0059] The viscosity index of the lubricating oil composition according to one embodiment of the present invention is preferably 60 or higher, 65 or higher, 70 or higher, 75 or higher, 80 or higher, 85 or higher, 90 or higher, 95 or higher, 100 or higher, 102 or higher, 104 or higher, or 106 or higher, from the viewpoint of providing a lubricating oil composition with low temperature dependence. It may also be 300 or lower, 250 or lower, 200 or lower, 180 or lower, 160 or lower, 150 or lower, 140 or lower, or 130 or lower.

[0060] [Uses of the Lubricating Oil Composition] As described above, the lubricating oil composition according to one embodiment of the present invention can exhibit excellent wear resistance even when used to lubricate a component in an environment where the surface pressure applied to the component to be lubricated is low. The surface pressure in the above-mentioned "environment where the surface pressure applied to the component to be lubricated is low" may be 1.2 MPa or less, 1.1 MPa or less, 1.0 MPa or less, 0.9 MPa or less, 0.8 MPa or less, 0.7 MPa or less, or 0.6 MPa or less.

[0061] Considering these characteristics, a lubricating oil composition according to one embodiment of the present invention can be used, for example, in hydraulic fluid, turbine oil, transmission oil, speed reducer oil, compressor oil, machine tool oil, gear oil, etc., but it is particularly preferable to use it for lubricating seal rings, more preferably for lubricating seal rings in rubber compounding machines, and even more preferably for lubricating seal rings in batch-type rubber compounding machines (e.g., Banbury mixers) or inner mixers.

[0062] Furthermore, a lubricating oil composition according to one embodiment of the present invention can exhibit excellent wear resistance even when used to lubricate non-ferrous alloy components that do not primarily contain iron. Examples of non-ferrous alloy components include stellite material, a non-ferrous alloy primarily composed of cobalt, and the seal rings of the rubber compounding machine, batch-type rubber compounding machine, or inner mixer may also be made of a non-ferrous alloy primarily composed of cobalt.

[0063] Examples of non-ferrous alloy components with cobalt as the main component include Stellite No. 1, Stellite No. 6, Stellite No. 12, Stellite No. 21, etc. The cobalt content in a non-ferrous alloy component with cobalt as the main component may be 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, or 60% by mass or more, based on the total amount of the component (100% by mass), or it may be 80% by mass or less, 75% by mass or less, 70% by mass or less, 65% by mass or less, 60% by mass or less, or 55% by mass or less. In addition to cobalt, the non-ferrous alloy component may also contain chromium, tungsten, carbon, and nickel, and may also contain iron.

[0064] [Wear Suppression Method] One aspect of the present invention is a method for suppressing wear of a component by using the lubricating oil composition of one aspect of the present invention described above for lubrication of the component in an environment in which the surface pressure applied to the component to be lubricated is 1.2 MPa or less. In the wear suppression method of one aspect of the present invention, the surface pressure applied to the component to be lubricated is 1.2 MPa or less, but may be 1.1 MPa or less, 1.0 MPa or less, 0.9 MPa or less, 0.8 MPa or less, 0.7 MPa or less, or 0.6 MPa or less.

[0065] In a wear suppression method according to one aspect of the present invention, the component to be lubricated is preferably a seal ring, more preferably a seal ring of a rubber mixer, and even more preferably a seal ring of a batch-type rubber mixer (e.g., a Banbury mixer) or an inner mixer, from the viewpoint of exhibiting a more effective wear suppression. Furthermore, the component to be lubricated is preferably a non-ferrous alloy component that does not mainly consist of iron, from the viewpoint of exhibiting a more effective wear suppression. Examples of non-ferrous alloy components include stellite material, a non-ferrous alloy mainly composed of cobalt, and the seal rings provided in the above-mentioned rubber mixer, batch-type rubber mixer, or inner mixer may also be made of a non-ferrous alloy mainly composed of cobalt. The cobalt content in the non-ferrous alloy and other metals that may be contained are as described above.

[0066] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited in any way by these examples. The methods for measuring various physical properties are as follows.

[0067] (1) Kinematic viscosity and viscosity index were measured and calculated in accordance with JIS K2283:2000. (2) Zinc and molybdenum atom content was measured in accordance with JPI-5S-38-92. (3) Weight-average molecular weight (Mw) was measured using a gel permeation chromatograph (Agilent, "1260 HPLC") under the following conditions, and the value measured in terms of standard polystyrene was used. (Measurement conditions) ・Column: Two "Shodex LF404" columns linked in sequence. ・Column temperature: 35℃ ・Developing solvent: Chloroform ・Flow rate: 0.3 mL / min

[0068] In Example 1 and Comparative Examples 1-2, lubricating oil compositions were prepared by adding and mixing the types of base oils and various additives shown in Table 1 in the amounts shown in Table 1. The details of each component used in the preparation of the lubricating oil compositions are as follows, and the amounts of components (B) and (C) listed in Table 1 indicate the amount in the solution including the active ingredient and diluent. In all lubricating oil compositions, the molybdenum atom content was less than 2 ppm by mass.

[0069] <Component (A): Base Oil> ・"500N Mineral Oil (A-i)": Mineral oil classified as Group I of the API base oil category, kinematic viscosity at 40°C = 90.58 mm ２ / s, 100℃ kinematic viscosity = 10.87mm ２ / s, viscosity index = 104. • "Brightstock (A-ii)": Mineral oil classified as Group I of the API base oil category (Brightstock), kinematic viscosity at 40°C = 436.6 mm² ２ / s, 100℃ kinematic viscosity = 31.88mm ２ / s, viscosity index=105.

[0070] <Component (B): Zinc dialkyldithiophosphate> ・"ZnDTP(B-i)": R in the general formula (b-1) above ｂ１ ~R ｂ４ A solution with an active ingredient concentration of 75% by mass, obtained by diluting zinc dialkyldithiophosphate, in which is an alkyl group having 1 to 14 carbon atoms (a group represented by the general formula (i) or (ii) above), with mineral oil. The zinc atom content in the zinc dialkyldithiophosphate = 9.0% by mass. <Component (C): Copolymer> ・Copolymer (C-i): R in the general formula (c-1) above ｃ１ The constituent unit (c1) is derived from an alkyl acrylate in which is a dodecyl group (C12 alkyl group), and R in the general formula (c-2) ｃ２ is an ethylene group (-CH ２ CH ２ A 50% by mass solution of active ingredient obtained by diluting a copolymer containing a constituent unit (c2) derived from a hydroxyalkyl acrylate (-) with a content ratio [(c1) / (c2)] of 78 / 22 (molar ratio) and Mw = 12,000 in mineral oil.

[0071] The kinematic viscosity and viscosity index of the prepared lubricating oil composition were measured or calculated, and the following tests were performed. The results are shown in Table 1.

[0072] [Wear test of components under low surface pressure conditions] Using a batch-type rubber mixer (manufactured by Kobe Steel, Ltd.), the amount of wear of seal ring components was measured when the lubricating oil compositions prepared in the examples and comparative examples were used to lubricate the seal ring components under the following conditions. <Measurement conditions> ・Material of seal ring components: Stellite #1 (Co composition: 51.86%) on the wear ring side, Stellite #6 (Co composition: 64.71%) on the gland ring side ・Oil injection amount: 0.21 mL / s ・Peripheral speed: 1.56 m / s ・Surface pressure: 0.65 MPa ・Test time: 8 hours ・Rotor rotation speed: 75 rpm ・Cylinder pressure: 3.05 MPa ・Pump rotation speed: 60 ・Temperature control temperature: 30℃ The amount of wear measured was evaluated based on the following evaluation criteria to assess the wear suppression effect of the components under low surface pressure conditions. The evaluation results are shown in Table 1. <Evaluation criteria for the wear suppression effect of the component in an environment where the surface pressure on the component is low> A: The amount of wear of the seal ring component is 0.001 mm or less. B: The amount of wear of the seal ring component is greater than 0.001 mm.

[0073]

[0074] As shown in Table 1, when used to lubricate a seal ring member under a low surface pressure of 0.6 MPa, the lubricating oil composition of Example 1 showed a higher wear suppression effect compared to the lubricating oil compositions of Comparative Examples 1 and 2.

Claims

1. A lubricating oil composition comprising a base oil (A), zinc dialkyldithiophosphate (B), and a copolymer (C) comprising a constituent unit (c1) derived from an alkyl acrylate represented by the following general formula (c-1) and a constituent unit (c2) derived from a hydroxyalkyl acrylate represented by the following general formula (c-2), wherein the content ratio of constituent unit (c1) to constituent unit (c2) [(c1) / (c2)] is 50 / 50 to 90 / 10 in molar ratio, and the weight-average molecular weight is 2000 or more and less than 40000. (In the above formula (c-1), R ｃ１ R is an alkyl group having 10 to 18 carbon atoms. In the above formula (c-2), ｃ２ (This refers to an alkylene group with 2 to 4 carbon atoms.) 2. The lubricating oil composition according to claim 1, used for lubricating a seal ring.

3. The lubricating oil composition according to claim 1, used for lubricating the seal ring of a rubber compounding machine.

4. The lubricating oil composition according to any one of claims 1 to 3, wherein the content ratio of component (B) to component (C) [(B) / (C)] is 10 / 90 to 90 / 10 by mass ratio.

5. The lubricating oil composition according to any one of claims 1 to 4, wherein component (B) comprises a compound (B1) represented by the following general formula (b-1). (In the above formula (b-1), R ｂ１ ~R ｂ４ These are each a hydrocarbon group, and may be identical or different from one another.

6. In the general formula (b-1), R ｂ１ ~R ｂ４ The lubricating oil composition according to claim 5, wherein each of them is independently a primary alkyl group or a secondary alkyl group.

7. The lubricating oil composition according to any one of claims 1 to 6, wherein the content of component (B) is 0.10% by mass or more and 2.00% by mass or less based on the total amount of the lubricating oil composition.

8. The lubricating oil composition according to any one of claims 1 to 7, wherein the content of component (C) is 0.10% by mass or more and 2.00% by mass or less on a basis of the total amount of the lubricating oil composition.

9. The lubricating oil composition according to any one of claims 1 to 8, which is used for lubricating a component in an environment where the surface pressure applied to the component to be lubricated is 1.2 MPa or less.

10. The lubricating oil composition according to any one of claims 1 to 9, wherein the content of the organic molybdenum compound is less than 1.0% by mass on a total basis of the lubricating oil composition.

11. The kinematic viscosity of the lubricating oil composition at 40°C is 80 mm². ２ A lubricating oil composition according to any one of claims 1 to 10, wherein the ratio is 1 / s or more.

12. A method for suppressing wear of a member, comprising using the lubricating oil composition described in any one of claims 1 to 11 to lubricate the member in an environment in which the surface pressure applied to the member to be lubricated is 1.2 MPa or less.

13. The wear suppression method according to claim 12, wherein the member is a seal ring.

14. A method for producing a lubricating oil composition according to any one of claims 1 to 11, comprising the step of blending a base oil (A) with zinc dialkyldithiophosphate (B) and a copolymer (C).

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