Lubricating oil composition

Abstract

Provided is a lubricating oil composition containing a base oil (A), an imide compound (B), a calcium-based cleaning agent (C), a polymer component (D), and zinc dithiophosphate (E), wherein the imide compound (B) contains at least one non-boron modified succinic acid imide compound (Bx) selected from succinic acid monoimides (B1x) represented by general formula (b-1) and succinic acid bisimides (B2x) represented by general formula (b-2), the polymer component (D) has a mass-average molecular weight (Mw) of 10,000-50,000, and contains at least one selected from olefin polymers (D1) and polymethacrylates (D2), and the lubricating oil composition has excellent wear resistance and oil film-holding properties even if the viscosity thereof is reduced.

Description

[Technical Field]

[0001] The present invention relates to a lubricating oil composition. [Background technology]

[0002] BACKGROUND ART In recent years, in order to reduce the environmental load, there has been a demand for improved fuel economy in vehicles such as automobiles. Known methods for improving fuel economy include lowering the viscosity of a lubricating oil composition to reduce the viscous resistance of the lubricating oil composition and suppress energy loss (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-137317 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the viscosity of a lubricating oil composition is reduced, it becomes difficult to properly maintain an oil film on sliding parts inside the engine, and engine parts become more susceptible to damage due to fatigue and wear, so further improvements in fatigue life and wear resistance are desired for lubricating oil compositions. In the following explanation, the ability to maintain an oil film is also referred to as "oil film retention ability."

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a lubricating oil composition that has excellent wear resistance and oil film retention properties even when the viscosity of the lubricating oil composition is reduced. [Means for solving the problem]

[0006] The present inventors have found that a lubricating oil composition containing a base oil (A), a specific imide compound (B), a calcium-based detergent (C), a specific polymer component (D), and a zinc dithiophosphate (E) can solve the above problems, and have completed the present invention. That is, the present invention provides the following [1] to [9]. [1] A lubricating oil composition comprising a base oil (A), an imide compound (B), a calcium-based detergent (C), a polymer component (D), and a zinc dithiophosphate (E), The imide compound (B) includes one or more non-boron-modified succinimide compounds (Bx) selected from succinic acid monoimides (B1x) represented by the following general formula (b-1) and succinic acid bisimides (B2x) represented by the following general formula (b-2), The lubricating oil composition, wherein the polymer component (D) has a mass average molecular weight (Mw) of 10,000 or more and 50,000 or less, and comprises at least one selected from an olefin polymer (D1) and a polymethacrylate (D2). [ka] [In the above general formulas (b-1) and (b-2), R A , R A1 , and R A2 are each independently an alkenyl group having a mass average molecular weight (Mw) of 500 to 4,000. R B , R B1 , and R B2 are each independently an alkylene group having 2 to 5 carbon atoms. R C is an alkyl group having 1 to 10 carbon atoms, or a group represented by -(AO)nH (wherein A is an alkylene group having 2 to 4 carbon atoms, and n is an integer of 1 to 10). x1 is an integer from 1 to 10, and x2 is an integer from 1 to 10. [2] The imide compound (B) further contains one or more boron-modified succinimide compounds (By) selected from the boron-modified succinimide (B1y) of the succinic acid monoimide (B1x) and the boron-modified succinic acid bisimide (B2x), The lubricating oil composition according to [1], wherein the content of boron atoms (By-B) derived from the boron-modified succinimide compound (By) is 0.020 mass% or less based on the total amount of the lubricating oil composition. [3] The lubricating oil composition according to [2], wherein the ratio of the content of boron atoms (By-B) derived from the boron-modified succinimide compound (By) to the content of nitrogen atoms (BN) derived from the imide compound (B) [(By-B) / (BN)] is 1.0 or less in mass ratio. [4] The lubricating oil composition according to any one of [1] to [3] above, wherein the ratio [(EP) / (BN)] of the content of phosphorus atoms (EP) derived from the zinc dithiophosphate (E) to the content of nitrogen atoms (BN) derived from the imide compound (B) is, in mass ratio, 0.5 or more and 5.0 or less. [5] The lubricating oil composition according to any one of [1] to [4] above, wherein the nitrogen atom (N) content is 0.010 mass % or more and 0.10 mass % or less, based on the total amount of the lubricating oil composition. [6] The lubricating oil composition according to any one of the above [1] to [5], wherein the calcium-based detergent (C) is a calcium sulfonate. [7] Kinematic viscosity at 100°C is 4.0mm 2 / s or more 20.0mm 2 The lubricating oil composition according to any one of the above [1] to [6], wherein the viscosity is less than 1 / s. [8] The lubricating oil composition according to any one of the above [1] to [7], which is used in an internal combustion engine of a motorcycle. [9] A method for producing a lubricating oil composition, comprising the step of mixing a base oil (A), an imide compound (B), a calcium-based detergent (C), a polymer component (D), and a zinc dithiophosphate (E), The imide compound (B) includes one or more non-boron-modified succinimide compounds (Bx) selected from succinic acid monoimides (B1x) represented by the following general formula (b-1) and succinic acid bisimides (B2x) represented by the following general formula (b-2), The method for producing a lubricating oil composition, wherein the polymer component (D) has a mass average molecular weight (Mw) of 10,000 or more and 50,000 or less, and comprises one or more selected from an olefin polymer (D1) and a polymethacrylate (D2). [ka] [In the above general formulas (b-1) and (b-2), R A , R A1 and R A2 are each independently an alkenyl group having a mass average molecular weight (Mw) of 500 to 4,000. R B , R B1 and R B2 are each independently an alkylene group having 2 to 5 carbon atoms. R C is an alkyl group having 1 to 10 carbon atoms, or a group represented by -(AO)nH (wherein A is an alkylene group having 2 to 4 carbon atoms, and n is an integer of 1 to 10). x1 is an integer from 1 to 10, and x2 is an integer from 1 to 10. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a lubricating oil composition that is excellent in wear resistance and oil film retention even when the viscosity of the lubricating oil composition is reduced. DETAILED DESCRIPTION OF THE INVENTION

[0008] In this specification, for preferred numerical ranges (e.g., ranges of content, etc.), the lower and upper limits described in stages can be independently combined. For example, the description "preferably 10 to 90, more preferably 30 to 60" can be combined with the "preferable lower limit (10)" and the "more preferable upper limit (60)" to form "10 to 60." Similarly, in this specification, the numerical values ​​of "greater than or equal to," "less than or equal to," "less than," and "more than" in describing numerical ranges can be arbitrarily combined.

[0009] [Lubricating oil composition] The lubricating oil composition of the present embodiment is a lubricating oil composition containing a base oil (A), an imide compound (B), a calcium-based detergent (C), a polymer component (D), and a zinc dithiophosphate (E), The imide compound (B) includes one or more non-boron-modified succinimide compounds (Bx) selected from succinic acid monoimides (B1x) represented by the following general formula (b-1) and succinic acid bisimides (B2x) represented by the following general formula (b-2), The polymer component (D) is a lubricating oil composition having a mass average molecular weight (Mw) of 10,000 or more and 50,000 or less, and containing at least one selected from an olefin polymer (D1) and a polymethacrylate (D2). [ka] [In the above general formulas (b-1) and (b-2), R A , R A1 , and R A2 are each independently an alkenyl group having a mass average molecular weight (Mw) of 500 to 4,000. R B , R B1 , and R B2 are each independently an alkylene group having 2 to 5 carbon atoms. R C is an alkyl group having 1 to 10 carbon atoms, or a group represented by -(AO)nH (wherein A is an alkylene group having 2 to 4 carbon atoms, and n is an integer of 1 to 10). x1 is an integer from 1 to 10, and x2 is an integer from 1 to 10.

[0010] When the viscosity of a lubricating oil composition is reduced to improve fuel economy, the oil film becomes thinner and the oil film retention ability decreases. Therefore, the present inventors have conducted extensive research and found that the oil film retention ability can be improved by including a base oil (A) and a polymer component (D) having a specific mass average molecular weight (Mw) in the lubricating oil composition. In order to ensure high-temperature detergency, the lubricating oil composition also contains an imide compound (B) and a calcium-based detergent. Furthermore, in order to ensure wear resistance, the lubricating oil composition also contains a zinc dithiophosphate (E). However, as a result of extensive investigations by the present inventors, it has been found that the structure of the imide compound (B) is such that R c It was found that when R is a hydrogen atom in the uncapped succinimide compound (B'), the abrasion resistance is poor. This is because, in the case of the uncapped succinimide compound (B'), R c The hydrogen atom at position 1 is a highly reactive active amine hydrogen, and it is presumed that the effect of this active amine hydrogen is to inhibit the function of zinc dithiophosphate (E) as a friction modifier, thereby inhibiting the wear resistance-improving effect of zinc dithiophosphate (E). Therefore, the present inventors have proposed a method for producing an imide compound (B) containing R c It has been found that by using a specific non-boron-modified succinimide compound (Bx) in which the structure (capped type) of the zinc dithiophosphate (E) is substituted with an alkyl group or the like, it is possible to fully exhibit wear resistance without inhibiting the wear resistance-improving effect of the zinc dithiophosphate (E). This effect is presumably due to the fact that the non-boron-modified succinimide compound (Bx) does not have active amine hydrogen, and therefore the zinc dithiophosphate (E) is not affected by the active amine hydrogen, and the wear resistance-improving effect of the zinc dithiophosphate (E) is not inhibited.

[0011] In the lubricating oil composition of this embodiment, the total content of the base oil (A), the imide compound (B), the calcium-based detergent (C), the polymer component (D), and the zinc dithiophosphate (E) is preferably 60 mass % or more, more preferably 70 mass % or more, even more preferably 80 mass % or more, and still more preferably 90 mass % or more, based on the total amount (100 mass %) of the lubricating oil composition. In the lubricating oil composition of this embodiment, the upper limit of the total content of the base oil (A), imide compound (B), calcium-based detergent (C), polymer component (D), and zinc dithiophosphate (E) may be 100% by mass. However, when other lubricating oil additives are contained, this upper limit can be adjusted in relation to the lubricating oil additives other than the imide compound (B), calcium-based detergent (C), polymer component (D), and zinc dithiophosphate (E), and is preferably 99.5% by mass or less, more preferably 99.0% by mass or less, and even more preferably 98.0% by mass or less.

[0012] Each component contained in the lubricating oil composition of this embodiment will be described below.

[0013] <Base oil (A)> The lubricating oil composition of this embodiment contains a base oil (A). As the base oil (A), one or more types selected from mineral oils and synthetic oils conventionally used as base oils for lubricating oils can be used without any particular limitation.

[0014] Examples of mineral oils include atmospheric residues obtained by atmospheric distillation of crude oils such as paraffin-based crude oil, intermediate-based crude oil, and naphthene-based crude oil; vacuum residues obtained by vacuum distillation of the atmospheric residues; and mineral oils obtained by subjecting the vacuum residues to one or more refining processes such as solvent deasphalting, solvent extraction, hydrofinishing, hydrocracking, advanced hydrocracking, solvent dewaxing, catalytic dewaxing, and hydroisomerization dewaxing.

[0015] Examples of synthetic oils include poly-α-olefins such as α-olefin homopolymers and α-olefin copolymers (e.g., α-olefin copolymers having 8 to 14 carbon atoms, such as ethylene-α-olefin copolymers); isoparaffins; various esters such as polyol esters and dibasic acid esters; various ethers such as polyphenyl ethers; polyalkylene glycols; alkylbenzenes; alkylnaphthalenes; and GTL base oils obtained by isomerizing wax produced from natural gas by the Fischer-Tropsch process or the like (GTL wax (Gas To Liquids WAX)).

[0016] The base oil used in this embodiment is preferably a base oil classified into Group II or III of the base oil category of the API (American Petroleum Institute).

[0017] The base oil (A) may be a mineral oil, either alone or in combination, or a synthetic oil, or may be a combination of one or more mineral oils and one or more synthetic oils.

[0018] There are no particular restrictions on the kinematic viscosity and viscosity index of the base oil (A), but in order to improve the oil film retention, fuel economy, and wear resistance of the lubricating oil composition, it is preferable that the kinematic viscosity and viscosity index be in the following ranges. The kinematic viscosity of the base oil (A) at 40°C (hereinafter also referred to as "40°C kinematic viscosity") is 2.0 mm 2 / s~100.0mm 2 / s is preferred, 5.0 mm 2 / s~80.0mm 2 / s is more preferable, 10.0 mm 2 / s~60.0mm 2 / s is more preferable, 15 mm 2 / s~55mm 2 / s is even more preferable, 25mm 2 / s~45mm 2 / s is even more preferred. The kinematic viscosity of the base oil (A) at 100°C (hereinafter also referred to as "100°C kinematic viscosity") is 2.0 mm 2 / s~20.0mm 2 / s is preferred, 3.0 mm 2 / s~9.0mm 2 / s is more preferable, 4.0 mm 2 / s~8.0mm 2 / s is more preferable, and 5.0 mm 2 / s~7.0mm 2 / s is even more preferred. The viscosity index of the base oil (A) is preferably 80 or more, more preferably 90 or more, even more preferably 100 or more, and even more preferably 105 or more. The 40°C kinematic viscosity, the 100°C kinematic viscosity, and the viscosity index can be measured or calculated in accordance with JIS K 2283:2000. When the base oil (A) is a mixed base oil containing two or more types of base oils, the kinematic viscosity and viscosity index of the mixed base oil preferably fall within the above ranges.

[0019] In the lubricating oil composition of this embodiment, the content of base oil (A) is not particularly limited, but from the viewpoint of making it easier to exhibit the effects of the present invention, it is preferably 60% by mass to 99% by mass, more preferably 70% by mass to 98% by mass, and even more preferably 80% by mass to 97% by mass, based on the total amount (100% by mass) of the lubricating oil composition.

[0020] <Imide compound (B)> The imide compound (B) includes one or more non-boron-modified succinimide compounds (Bx) selected from succinic acid monoimides (B1x) represented by the following general formula (b-1) and succinic acid bisimides (B2x) represented by the following general formula (b-2): The imide compound (B) can function as an ashless dispersant in the lubricating oil composition of this embodiment. The imide compound (B) is a compound in which at least a part of the active amine hydrogen atoms contained in a succinic acid monoimide or succinic acid bisimide compound produced using a polyamine compound as a raw material is substituted with a substituent such as an alkyl group (R c ) has a structure substituted with The lubricating oil composition of this embodiment can improve wear resistance by containing the imide compound (B). It should be noted that the lubricating oil composition of this embodiment cannot provide good wear resistance if it does not contain the imide compound (B), or if it does not contain the imide compound (B) but contains an imide compound other than the imide compound (B).

[0021] [ka]

[0022] In the above general formulas (b-1) and (b-2), R A , R A1 , and R A2 are each independently an alkenyl group having a mass average molecular weight (Mw) of 500 to 4,000. Examples of the alkenyl group include a polybutenyl group, a polyisobutenyl group, and an ethylene-propylene copolymer. Among these, a polybutenyl group and a polyisobutenyl group are preferred, and a polyisobutenyl group is more preferred. The mass average molecular weight (Mw) of the alkenyl group is 500 to 4,000, preferably 900 to 3,000, more preferably 1,300 to 2,800, and even more preferably 1,800 to 2,600. In the present invention, the mass average molecular weight (Mw) of the alkenyl group can be evaluated as the mass average molecular weight (Mw) in terms of standard polystyrene by, for example, measuring a polyolefin that is the source of the alkenyl group using a GPC apparatus (apparatus name: Model HLC-8220, manufactured by Tosoh Corporation) equipped with columns (two columns with product name: TSKgel GMH-XL and one column with product name: G2000H-XL, manufactured by Tosoh Corporation) under the following conditions: detector: refractive index detector, measurement temperature: 40°C, mobile phase: tetrahydrofuran, flow rate: 1.0 mL / min, concentration: 0.5 mg / mL. Alternatively, the mass average molecular weight (Mw) of the alkenyl groups can be determined by subtracting the theoretical molecular weight of structures other than the alkenyl groups from the mass average molecular weight of the imide compound (B) measured by the same method as above, and then dividing the result by the number of alkenyl groups contained in one molecule.

[0023] R B , R B1 , and R B2 are each independently an alkylene group having 2 to 5 carbon atoms. Examples of the alkylene group include a methylene group, an ethylene group, a trimethylene group, various butylene groups, various pentylene groups, etc. In this specification, the term "various" in the various butylene groups, etc. refers to linear, branched, and isomers thereof.

[0024] R C is an alkyl group having 1 to 10 carbon atoms, or a group represented by -(AO)nH (wherein A is an alkylene group having 2 to 4 carbon atoms, and n is an integer of 1 to 10). Examples of the alkyl group include linear or branched alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1-dimethylhexyl, 2-ethylhexyl, nonyl, 1,1-dimethylheptyl, and decyl. Examples of the alkylene group having 2 to 4 carbon atoms represented by A include an ethylene group, a trimethylene group, and various butylene groups, with an ethylene group being preferred. n is an integer of 1 to 10, preferably an integer of 1 to 5, and more preferably an integer of 1 to 3.

[0025] x1 is an integer of 1 to 10, preferably an integer of 2 to 5, and more preferably 3 or 4. x2 is an integer of 1 to 10, preferably an integer of 3 to 7, and more preferably 5 or 6.

[0026] The imide compound (B) is a compound represented by the general formula (b-1), AIn addition, in the general formula (b-2), R A1 , and R A2 However, each of them may independently contain succinic acid bisimide (B2x), which is an alkyl group having a mass average molecular weight (Mw) of 500 to 4,000.

[0027] The imide compound (B) may be a single succinic acid monoimide (B1x) or a combination of two or more succinic acid bisimides (B2x). The imide compound (B) may be a single succinic acid monoimide (B1x) or a combination of two or more succinic acid bisimides (B2x). Furthermore, one or more succinic acid monoimides (B1x) may be used in combination with one or more succinic acid bisimides (B2x).

[0028] The non-boron-modified succinimide compound (Bx) can be prepared, for example, by reacting alkenyl succinic anhydride obtained by reacting polyolefin with maleic anhydride with polyamine to obtain an alkenyl succinimide having active amine hydrogen (R in the above general formula (b-1) or (b-2)). c is a hydrogen atom), and at least a portion of the active amine hydrogen is converted to the above R c The compound can be produced by substituting a group represented by the formula: The polyolefin may be, for example, a polymer obtained by polymerizing one or more α-olefins having 2 to 8 carbon atoms, and a copolymer of isobutene and 1-butene is preferred. Examples of the polyamine include single diamines such as ethylenediamine, propylenediamine, butylenediamine, and pentylenediamine; polyalkylenepolyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, di(methylethylene)triamine, dibutylenetriamine, tributylenetetramine, and pentapentylenehexamine; and piperazine derivatives such as aminoethylpiperazine. The substitution reaction of the active amine hydrogen may be carried out by a known method, for example, by reacting an alkenyl succinimide compound having the active amine hydrogen with R c and an alkyl halide to give

[0029] The imide compound (B) may further contain a boron-modified succinimide compound (By). When the imide compound (B) further contains a boron-modified succinimide compound (By), the high-temperature detergency of the lubricating oil composition tends to be improved. The boron-modified succinimide compound (By) is preferably at least one selected from the boron-modified succinic acid monoimide (B1x) (B1y) and the boron-modified succinic acid bisimide (B2x) (B2y). However, from the viewpoint of improving the wear resistance of the lubricating oil composition, the content of boron atoms (By-B) derived from the boron-modified succinimide compound (By) is preferably 0.020 mass% or less, more preferably 0.015 mass% or less, even more preferably 0.010 mass% or less, and even more preferably 0.005 mass% or less, based on the total amount of the lubricating oil composition.

[0030] In the imide compound (B), the total content of the non-boron-modified succinimide compound (Bx) and the boron-modified succinimide compound (By) contained as needed is preferably 70% by mass to 100% by mass, more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, and even more preferably 100% by mass.

[0031] [Ratio〔(By-B) / (BN)〕] The ratio [(By-B) / (BN)] of the content of boron atoms (By-B) derived from the boron-modified succinimide compound (By) to the content of nitrogen atoms (BN) derived from the imide compound (B) is preferably 1.0 or less, more preferably 0.5 or less, and even more preferably 0.3 or less, in mass ratio.

[0032] In the lubricating oil composition of this embodiment, the content of the imide compound (B) calculated as nitrogen atoms is, from the viewpoint of improving wear resistance, preferably 0.010 mass % or more and 0.10 mass % or less, more preferably 0.012 mass % or more and 0.080 mass % or less, even more preferably 0.013 mass % or more and 0.060 mass % or less, still more preferably 0.014 mass % or more and 0.050 mass % or less, and even more preferably 0.020 mass % or more and 0.035 mass % or less, based on the total amount of the lubricating oil composition.

[0033] In the lubricating oil composition of this embodiment, the content of imide compound (B) is preferably adjusted so that the content calculated as nitrogen atoms is within the above range. Specifically, from the viewpoint of improving wear resistance, the content is preferably 1.0 to 10.0 mass%, more preferably 1.2 to 8.0 mass%, even more preferably 1.3 to 6.0 mass%, still more preferably 1.4 to 4.0 mass%, and even more preferably 2.0 to 3.5 mass%, based on the total amount (100 mass%) of the lubricating oil composition.

[0034] The lubricating oil composition of this embodiment may contain an ashless dispersant other than the imide compound (B) within a range that does not impair the effects of the present invention, or may not contain the other ashless dispersant. Examples of ashless dispersants other than the imide compound (B) include benzylamines, boron-containing benzylamines, succinic acid esters, fatty acids, and mono- or di-carboxylic acid amides typified by succinic acid.

[0035] Here, from the viewpoint of improving wear resistance, it is preferable that the lubricating oil composition of this embodiment is substantially free of an uncapped succinimide compound (B') selected from an uncapped succinic acid monoimide (B'1) represented by the following general formula (i) and an uncapped succinic acid bisimide (B'2) represented by the following general formula (ii): [ka] [In the above general formulas (i) and (ii), R A , R A1 , R A2 , R B , R B1 , R B2 , x1, and x2 are the same as in the general formulae (b-1) and (b-2). In this specification, the term "uncapped" refers to a group having R C is a hydrogen atom. C is an alkyl group having 1 to 10 carbon atoms or a group represented by -(AO)nH (wherein A is an alkylene group having 2 to 4 carbon atoms, and n is an integer of 1 to 10), is also called a "capped type." In this specification, "substantially free of uncapped succinimide compound (B')" means that the content of the uncapped succinimide compound (B') is preferably less than 1.0 mass%, more preferably less than 0.1 mass%, even more preferably less than 0.01 mass%, based on the total amount of the lubricating oil composition, and most preferably the lubricating oil composition is free of uncapped imide compound (B').

[0036] <Calcium-based detergent (C)> The lubricating oil composition of this embodiment contains a calcium-based detergent (C). By containing the calcium-based detergent (C), the lubricating oil composition can improve high-temperature detergency.

[0037] Examples of the calcium-based detergent (C) include calcium salts such as calcium sulfonate represented by the following general formula (C1), calcium phenate represented by the following general formula (C2), and calcium salicylate represented by the following general formula (C3). Among these, calcium sulfonate is preferred from the viewpoint of improving high-temperature detergency. The calcium-based detergent (C) may be used alone or in combination of two or more kinds.

[0038] [ka]

[0039] In the above general formula (C2), q is an integer of 0 or more, and preferably an integer of 0 or more and 3 or less. Each R is independently a hydrogen atom or a hydrocarbon group. The hydrocarbon group that can be selected as R may have a linear structure, a branched chain, or a ring. Among these, a branched chain hydrocarbon group is preferred. 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. As R, a branched alkyl group is particularly preferred. The hydrocarbon group preferably has 3 or more and 26 or less carbon atoms, more preferably 7 or more and 24 or less carbon atoms, and even more preferably 10 or more and 20 or less carbon atoms. In the hydrocarbon group having a branched chain, the number of carbon atoms in the branched chain is preferably 1 or more and 8 or less, more preferably 2 or more and 6 or less, and even more preferably 2 or more and 5 or less.

[0040] The calcium-based detergent (C) may be neutral, basic, or overbased, but from the viewpoint of further improving high-temperature detergency, basic or overbased detergents are preferred, and overbased detergents are more preferred. In this specification, a basic or overbased metal-based detergent refers to a detergent obtained by reacting a metal with an acidic organic compound and containing an excess amount of metal relative to the stoichiometric amount required for neutralizing the metal and the acidic organic compound. That is, when the "metal ratio" is defined as the total chemical equivalent of the metal in the metal-based detergent relative to the chemical equivalent of the metal in the metal salt (neutral salt) obtained by reacting the metal with the acidic organic compound in the stoichiometric amount required for neutralization, the metal ratio of the basic or overbased metal-based detergent is greater than 1. The metal ratio of the basic or overbased metal-based detergent used in this embodiment is preferably greater than 1.3, more preferably 5 to 30, and even more preferably 7 to 22. Specific examples of basic or overbased metal-based detergents include those containing one or more selected from the group consisting of the above-mentioned metal salicylates, metal phenates, and metal sulfonates, and containing an excess amount of metal. In this specification, a base number measured by the measurement method described below of less than 50 mgKOH / g is defined as "neutral," a base number of 50 mgKOH / g or more but less than 150 mgKOH / g is defined as "basic," and a base number of 150 mgKOH / g or more is defined as "overbased."

[0041] When the calcium-based detergent (C) is a calcium sulfonate, the base number of the calcium sulfonate is preferably 5 mgKOH / g or more, more preferably 100 mgKOH / g or more, even more preferably 150 mgKOH / g or more, and still more preferably 250 mgKOH / g or more, and is preferably 500 mgKOH / g or less, more preferably 450 mgKOH / g or less, and even more preferably 400 mgKOH / g or less. When the calcium-based detergent (C) is a calcium phenate, the base number of the calcium phenate is preferably 50 mgKOH / g or more, more preferably 100 mgKOH / g or more, even more preferably 150 mgKOH / g or more, still more preferably 200 mgKOH / g or more, and is preferably 500 mgKOH / g or less, more preferably 450 mgKOH / g or less, even more preferably 400 mgKOH / g or less. When the calcium-based detergent (C) is calcium salicylate, the base number of the calcium salicylate is preferably 50 mgKOH / g or more, more preferably 100 mgKOH / g or more, even more preferably 150 mgKOH / g or more, still more preferably 200 mgKOH / g or more, and is preferably 500 mgKOH / g or less, more preferably 450 mgKOH / g or less, even more preferably 400 mgKOH / g or less. In this specification, the "base number" of the calcium-based detergent (C) means the base number measured by the perchloric acid method in accordance with JIS K 2501:2003.

[0042] In the lubricating oil composition of one embodiment of the present invention, the content of calcium atoms derived from the calcium-based detergent (C) is preferably 0.005% by mass to 0.40% by mass, more preferably 0.010% by mass to 0.35% by mass, even more preferably 0.050% by mass to 0.30% by mass, and even more preferably 0.10% by mass to 0.25% by mass, based on the total amount of the lubricating oil composition, from the viewpoint of making it easier to improve high-temperature detergency.

[0043] In the lubricating oil composition of one embodiment of the present invention, the content of the calcium-based detergent (C) may be adjusted so that the content of calcium atoms derived from the calcium-based detergent (C) falls within the above range. Specifically, the content of the calcium-based detergent (C) is preferably 0.5% by mass or more and 5.0% by mass or less, more preferably 1.0% by mass or more and 3.0% by mass or less, and even more preferably 1.5% by mass or more and 2.0% by mass or less, based on the total amount of the lubricating oil composition.

[0044] <Polymer component (D)> The lubricating oil composition of this embodiment contains a polymer component (D). The polymer component (D) has a mass average molecular weight (Mw) of 10,000 or more and 50,000 or less, and includes at least one selected from an olefin polymer (D1) and a polymethacrylate (D2). The polymer component (D) can function as an oil film retention improver in the lubricating oil composition of this embodiment. If the lubricating oil composition does not contain the polymer component (D), it is difficult to ensure oil film retention. Furthermore, if a polymer component having a mass average molecular weight (Mw) of less than 10,000 is used instead of polymer component (D), the oil film retention ability cannot be improved. If a polymer component having a mass average molecular weight (Mw) of more than 50,000 is used instead of polymer component (D), the polymer component cannot penetrate into sliding parts inside the engine, and the effect of improving oil film retention ability cannot be obtained. In addition, when a polymer component other than the olefin polymer (D1) and the polymethacrylate (D2) is contained in place of the polymer component (D), the oil film retention property cannot be improved.

[0045] The polymer component (D) contains at least one selected from an olefin polymer (D1) and a polymethacrylate (D2). Examples of monomers constituting the olefin polymer (D1) include at least one selected from ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene, and may be copolymers of two or more of them. Examples of the olefin polymer (D1) include poly-α-olefins (PAO), ethylene-propylene copolymers, polybutene, etc. Among these, poly-α-olefins and ethylene-propylene copolymers are preferred.

[0046] The polymer component (D) may be any one of an olefin polymer (D1) and a polymethacrylate (D2), or two or more of them may be used in combination.

[0047] In the polymer component (D), the content of one or more selected from the olefin polymer (D1) and the polymethacrylate (D2) is preferably 70% by mass to 100% by mass, more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, and even more preferably 100% by mass.

[0048] The polymer component (D) has a mass average molecular weight (Mw) of 10,000 or more and 50,000 or less, preferably 10,000 or more and 40,000 or less, more preferably 10,000 or more and 30,000 or less, and particularly preferably 10,000 or more and 15,000 or less, in order to improve oil film retention while also improving shear stability and further adjust the flash point and evaporation loss within appropriate ranges. When the polymer component (D) is an olefin polymer (D1), the mass average molecular weight (Mw) is preferably 10,000 or more and 20,000 or less, more preferably 12,000 or more and 18,000 or less, even more preferably 14,000 or more and 16,000 or less, and even more preferably 14,000 or more and 15,000 or less. When the polymer component (D) is a polymethacrylate (D2), the mass average molecular weight (Mw) is preferably 20,000 or more and 50,000 or less, more preferably 30,000 or more and 40,000 or less, and even more preferably 32,000 or more and 35,000 or less. The mass average molecular weight (Mw) of the polymer component (D) is a value measured by gel permeation chromatography and calculated in terms of polystyrene.

[0049] The content of the polymer component (D) is not particularly limited, but from the viewpoint of improving oil film retention, it is preferably from 0.05 to 10.0 mass %, more preferably from 0.1 to 4.0 mass %, even more preferably from 0.3 to 3.0 mass %, and even more preferably from 0.5 to 2.0 mass %, based on the total amount of the lubricating oil composition. In this specification, the polymer component (D) may be blended with other components in the form of a solution obtained by diluting and dissolving it in a portion of the base oil (A), taking into consideration ease of handling, solubility in the base oil (A), etc. In such a case, the content of the polymer component (D) as described above in this specification means the content calculated as the active ingredient (resin content) excluding the diluent oil.

[0050] <Zinc dithiophosphate (E)> The lubricating oil composition of this embodiment contains zinc dithiophosphate (E). The zinc dithiophosphate (E) may be used alone or in combination of two or more kinds.

[0051] Examples of the zinc dithiophosphate (E) include compounds represented by the following general formula (d-1).

[0052] [ka] (In the formula, R 11 ~R 14 each independently represents a hydrocarbon group having 1 to 24 carbon atoms.

[0053] R 11 ~R 14 Examples of the hydrocarbon group represented by the formula (I) include a linear or branched alkyl group having 1 to 24 carbon atoms, a linear or branched alkenyl group having 3 to 24 carbon atoms, a cycloalkyl group or a linear or branched alkylcycloalkyl group having 5 to 13 carbon atoms, an aryl group or a linear or branched alkylaryl group having 6 to 18 carbon atoms, and an arylalkyl group having 7 to 19 carbon atoms. Among these, a linear or branched alkyl group having 1 to 24 carbon atoms is preferred, and a branched alkyl group having 1 to 24 carbon atoms is more preferred. The branched alkyl group preferably has 2 to 12 carbon atoms, and more preferably 3 to 6 carbon atoms. Examples of branched alkyl groups having 1 to 24 carbon atoms include an isopropyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an isopentyl group, a tert-pentyl group, an isohexyl group, a 2-ethylhexyl group, an isononyl group, an isodecyl group, an isotridecyl group, an isostearyl group, and an isoicosyl group. Of these, a sec-butyl group is preferred. Specifically, zinc dialkyldithiophosphates are preferred as the zinc dithiophosphate (E), and among these, secondary zinc dialkyldithiophosphates are more preferred.

[0054] In the lubricating oil composition of this embodiment, the content of phosphorus atoms (EP) derived from the zinc dithiophosphate (E) is preferably 0.10 mass% or less, more preferably 0.080 mass% or less, even more preferably 0.070 mass% or less, and even more preferably 0.065 mass% or less, based on the total amount of the lubricating oil composition, from the viewpoint of reducing phosphorus atom emissions.

[0055] In the lubricating oil composition of this embodiment, the content of zinc dithiophosphate (E) is preferably adjusted so that the content in terms of phosphorus atoms falls within the above range; specifically, based on the total amount (100 mass%) of the lubricating oil composition, it is preferably less than 1.0 mass%, more preferably less than 0.9 mass%, and even more preferably less than 0.8 mass%; and from the viewpoint of improving wear resistance, it is preferably 0.1 mass% or more, more preferably 0.5 mass% or more.

[0056] [ratio [(EP) / (BN)]] The ratio [(EP) / (BN)] of the content of phosphorus atoms (EP) derived from the zinc dithiophosphate (E) to the content of nitrogen atoms (BN) derived from the imide compound (B) is preferably 0.5 or more and 5.0 or less, more preferably 0.5 or more and 4.0 or less, and even more preferably 1.0 or more and 3.5 or less, in mass ratio.

[0057] <Other ingredients> The lubricating oil composition of this embodiment may contain components other than those described above, provided that the effects of the present invention are not impaired. Examples of the additives as other components include antioxidants, metal-based detergents other than the calcium-based detergent (C), and antifoaming agents. These components may be used alone or in combination of two or more.

[0058] Examples of antioxidants include amine-based antioxidants, phenol-based antioxidants, molybdenum-based antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, etc. Among these, one or more selected from amine-based antioxidants and phenol-based antioxidants are preferred.

[0059] Examples of metal-based detergents other than the calcium-based detergent (C) include metal salicylates, metal phenates, and metal sulfonates based on metals other than calcium. Examples of the metal other than calcium include alkali metals and alkaline earth metals, and more specifically, sodium, magnesium, barium, etc. Among these, magnesium is preferred.

[0060] Examples of the antifoaming agent include silicone oil, fluorosilicone oil, and fluoroalkyl ether.

[0061] The contents of the above-mentioned other components can be adjusted as appropriate within a range that does not impair the effects of the present invention, but each of them is typically 0.001 to 15 mass%, preferably 0.005 to 10 mass%, more preferably 0.01 to 7 mass%, and even more preferably 0.03 to 5 mass%, based on the total amount (100 mass%) of the lubricating oil composition. In this specification, the additives as the other components may be blended with other components in the form of a solution diluted and dissolved in a part of the base oil (A), taking into consideration handleability, solubility in the base oil (A), etc. In such cases, the content of the additives as the other components as described above means the content calculated as the active ingredient (resin content) excluding the diluent oil.

[0062] [Physical properties of lubricating oil composition] The lubricating oil composition of this embodiment has a kinematic viscosity at 100°C of 4.0 mm 2 / s or more is preferable, 5.0 mm 2 / s or more is preferable, 6.1 mm 2 / s or more is more preferable, 6.9 mm 2 / s or more is even more preferable, 6.9 mm 2 The kinematic viscosity at 100°C of the lubricating oil composition of this embodiment is more preferably 22.0 mm / s or more. 2 / s or less is preferable, 20.0 mm 2 / s or less is preferable, 16.3 mm 2 / s or less is more preferable, and 12.5 mm 2 / s or less is even more preferable, 9.3 mm 2 / s or less is even more preferable, and 8.2 mm 2 More preferably, the kinematic viscosity at 100°C is less than 4.0 mm / s. 2 When the kinematic viscosity at 100°C is low, it is easy to ensure fuel economy, but it is difficult to maintain an oil film. 2 Even if the viscosity is less than 1 / s, the oil film retention is good, and both fuel economy and oil film retention can be achieved. The 100°C kinematic viscosity can be measured or calculated in accordance with JIS K 2283:2000.

[0063] The lubricating oil composition of this embodiment has a kinematic viscosity at 40°C of 10.0 mm 2 / s or more 150.0mm 2 / s or less is preferable, 20.0 mm 2 / s or more 100.0mm 2 / s or less is more preferable, and 30.0 mm 2 / s or more 60.0mm 2 / s or less is more preferable. 2 / s or more 140.0mm 2 / s or less is preferable, 60.0 mm 2 / s or more 130.0mm 2 / s or less is more preferable, and 80.0 mm 2 / s or more 120.0mm 2 When the kinematic viscosity at 40°C is within the above range, both fuel economy and oil film retention can be achieved. The viscosity index of the lubricating oil composition of this embodiment is preferably at least 80, more preferably at least 85, even more preferably at least 90, and even more preferably at least 95. When the viscosity index is 80 or higher, the viscosity change due to temperature is small. The 40°C kinematic viscosity and viscosity index can be measured or calculated in accordance with JIS K 2283:2000.

[0064] High temperature high shear viscosity (HTHS viscosity) is the viscosity at high temperature (150°C) and a shear rate of 10 6 S -1 The viscosity is measured under the following conditions. The high temperature, high shear viscosity at 150°C (150°C HTHS viscosity) of the lubricating oil composition of this embodiment is, from the viewpoints of fuel economy and oil film retention, preferably from 1.7 mPa·s to 3.7 mPa·s, more preferably from 2.0 mPa·s to 3.5 mPa·s, even more preferably from 2.3 mPa·s to 2.9 mPa·s, and even more preferably from 2.3 mPa·s to 2.6 mPa·s. When the HTHS viscosity at 150°C is within the above range, the lubricating oil composition has low viscous resistance and low energy loss while still ensuring oil film retention, making it easy to improve fuel economy. The 150°C HTHS viscosity can be measured or calculated in accordance with JPI-5S-36-03.

[0065] [Content of boron atoms, calcium atoms, phosphorus atoms, and zinc atoms] The content of boron atoms in the lubricating oil composition of this embodiment is preferably 0.010% by mass or less, more preferably 0.008% by mass or less, and even more preferably 0.006% by mass or less, based on the total amount of the lubricating oil composition. When the lubricating oil composition contains boron atoms, the content of boron atoms is usually 0.001% by mass or more, based on the total amount of the lubricating oil composition. The calcium atom content in the lubricating oil composition of this embodiment is preferably 0.50 mass% or less, more preferably 0.40 mass% or less, and even more preferably 0.30 mass% or less, based on the total amount of the lubricating oil composition, and is preferably 0.05 mass% or more, more preferably 0.10 mass% or more, and even more preferably 0.15 mass% or more, based on the total amount of the lubricating oil composition. The phosphorus atom content in the lubricating oil composition of this embodiment is preferably 0.080 mass% or less, more preferably 0.070 mass% or less, even more preferably 0.065 mass% or less, and even more preferably 0.062 mass% or less, based on the total amount of the lubricating oil composition. The phosphorus atom content is preferably 0.010 mass% or more, more preferably 0.050 mass% or more, based on the total amount of the lubricating oil composition. The zinc atom content in the lubricating oil composition of this embodiment is preferably 0.090 mass% or less, more preferably 0.080 mass% or less, and even more preferably 0.075 mass% or less, based on the total amount of the lubricating oil composition, and is preferably 0.010 mass% or more, more preferably 0.050 mass% or more, based on the total amount of the lubricating oil composition. The contents of boron atoms, calcium atoms, phosphorus atoms, and zinc atoms can be measured in accordance with JPI-5S-38-03.

[0066] [Nitrogen atom content] In the lubricating oil composition of this embodiment, the content (total amount) of nitrogen atoms (N), including nitrogen atoms derived from the imide compound (B) and nitrogen atoms derived from components other than the imide compound (B), is, from the viewpoint of improving wear resistance, preferably from 0.010 mass % to 0.10 mass %, more preferably from 0.012 mass % to 0.080 mass %, even more preferably from 0.013 mass % to 0.060 mass %, and even more preferably from 0.014 mass % to 0.050 mass %, based on the total amount of the lubricating oil composition. The nitrogen atom content can be measured in accordance with JIS K 2609:1998. Examples of the nitrogen atom-containing component other than the imide compound (B) include amine-based antioxidants.

[0067] [Wear resistance] The wear resistance of the lubricating oil composition of this embodiment can be evaluated, for example, using a Falex Block-on-Ring friction and wear tester (LFW-1). Specifically, it can be evaluated by the method described in the Examples below. The wear width of the test piece in the method described in the Examples below is preferably 410 μm or less, more preferably 385 μm or less, and even more preferably 380 μm or less.

[0068] [Oil film retention] The oil film retention of the lubricating oil composition of this embodiment can be evaluated by the oil film thickness (EHL oil film thickness) in elasto-hydrodynamic lubrication (EHL), specifically by the method described in the examples below. As a measuring device for the EHL oil film thickness, for example, EHD2 (manufactured by PCS Instruments) can be used. The EHL oil film thickness in the method described in the examples below is preferably 17.0 nm or more, more preferably 19.0 nm or more, and even more preferably 20.0 nm or more.

[0069] [Uses of lubricating oil composition] The lubricating oil composition of this embodiment is excellent in wear resistance and oil film retention. The lubricating oil composition of this embodiment is preferably used in internal combustion engines, more preferably in internal combustion engines of four-wheeled vehicles and motorcycles, and even more preferably in internal combustion engines of motorcycles.

[0070] An automobile's internal combustion engine uses many rotating shafts and bearings that hold the shafts in place. Known types of bearings include sliding bearings, which reduce friction by using a lubricant oil film between the shaft and bearing, and rolling bearings, which reduce friction by supporting rotating bodies such as balls and rollers in the bearing with an oil film. Widely used rolling bearings include ball bearings, roller bearings, and needle bearings, depending on the shape of the rotating body. Ball bearings and roller bearings generally have an outer ring, an inner ring, a rotating body, and a cage that holds the rotating body in position. On the other hand, needle roller bearings can be composed of only the rotating body and cage, depending on the shape of the cage. Therefore, because needle roller bearings do not require an outer ring and an inner ring, they can be made smaller and lighter than ball bearings and roller bearings.

[0071] Rolling bearings, particularly needle roller bearings, are often used for the bearings in internal combustion engines of motorcycles because of the simplicity and compactness of the engine structure. Needle roller bearings are also sometimes used in roller-type valve trains in automobiles. However, because rolling bearings have a smaller contact area with the shaft than sliding bearings, if the oil film retention ability that holds the lubricating oil composition is insufficient, an appropriate oil film will not be maintained in the sliding parts inside the engine, resulting in increased friction and the risk of engine parts being damaged by fatigue or wear. Therefore, the lubricating oil composition according to this embodiment has excellent oil film retention ability and is therefore suitable for use in rolling bearings and the like.

[0072] [Method of manufacturing lubricating oil composition] This embodiment relates to a method for producing a lubricating oil composition, which includes a step of mixing a base oil (A), an imide compound (B), a calcium-based detergent (C), a polymer component (D), and a zinc dithiophosphate (E), The imide compound (B) includes one or more non-boron-modified succinimide compounds (Bx) selected from succinic acid monoimides (B1x) represented by the following general formula (b-1) and succinic acid bisimides (B2x) represented by the following general formula (b-2), The present invention provides a method for producing a lubricating oil composition, wherein the polymer component (D) has a mass average molecular weight (Mw) of 10,000 or more and 50,000 or less, and comprises one or more selected from an olefin polymer (D1) and a polymethacrylate (D2). [ka] [In the above general formulas (b-1) and (b-2), RA , R A1 and R A2 are each independently an alkenyl group having a mass average molecular weight (Mw) of 500 to 4,000. R B , R B1 and R B2 are each independently an alkylene group having 2 to 5 carbon atoms. R C is an alkyl group having 1 to 10 carbon atoms, or a group represented by -(AO)nH (wherein A is an alkylene group having 2 to 4 carbon atoms, and n is an integer of 1 to 10). x1 is an integer from 1 to 10, and x2 is an integer from 1 to 10.

[0073] The method for mixing the above components is not particularly limited, and examples thereof include a step of adding the imide compound (B), the calcium-based detergent (C), the polymer component (D), and the zinc dithiophosphate (E) to the base oil (A) and then mixing them. The manufacturing method may further include the step of adding the other components described above. Each component may be added in the form of a solution (dispersion) by adding a diluent oil or the like. After each component is added, it is preferable to include a step of stirring the components by a known method to uniformly disperse them. [Example]

[0074] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. The various properties of the components used in the examples and comparative examples and the resulting lubricating oil compositions were measured by the following methods.

[0075] [40℃ kinematic viscosity, 100℃ kinematic viscosity, and viscosity index] The kinematic viscosity at 40°C, the kinematic viscosity at 100°C, and the viscosity index were measured or calculated in accordance with JIS K 2283:2000.

[0076] [150℃HTHS viscosity] The 150°C HTHS viscosity was measured or calculated in accordance with JPI-5S-36-03.

[0077] [Content of boron atoms, calcium atoms, phosphorus atoms, and zinc atoms] The contents of boron atoms, calcium atoms, phosphorus atoms, and zinc atoms were measured in accordance with JPI-5S-38-03.

[0078] [Nitrogen atom content] The nitrogen atom content (total amount, measured value) was measured in accordance with JIS K 2609:1998. The actually measured nitrogen atom content includes the content of nitrogen atoms derived from the antioxidant, and therefore the theoretical value was calculated from the content of the imide compound and the content of nitrogen atoms contained in the imide compound itself.

[0079] [Atomic content ratio] Of the contents of each atom thus determined, the content of boron atoms (By-B) derived from the boron-modified succinimide compound (By) was divided by the content of nitrogen atoms (BN) derived from the imide compound (B) to calculate the ratio [(By-B) / (BN)] of the content of boron atoms (By-B) derived from the boron-modified succinimide compound (By) to the content of nitrogen atoms (BN) derived from the imide compound (B). Furthermore, among the contents of each atom thus determined, the content of phosphorus atoms (EP) derived from the zinc dithiophosphate (E) was divided by the content of nitrogen atoms (BN) derived from the imide compound (B) to calculate the ratio [(EP) / (BN)] of the content of phosphorus atoms (EP) derived from the zinc dithiophosphate (E) to the content of nitrogen atoms (BN) derived from the imide compound (B).

[0080] [Base number] The base number of the calcium-based detergent (C) was measured by the perchloric acid method in accordance with JIS K 2501:2003.

[0081] [Examples 1 to 9 and Comparative Examples 1 to 4] The components shown below were added in the amounts shown in Tables 1 to 3 and mixed thoroughly to obtain lubricating oil compositions. Details of each component used in Examples 1 to 9 and Comparative Examples 1 to 4 are as follows.

[0082] <Base oil (A)> Base oil (A1): Mineral oil (API base oil category classification: Group III, kinematic viscosity at 40°C: 32.7 mm) 2 / s, 100℃ kinematic viscosity: 6.0mm 2 / s, viscosity index: 132) Base oil (A2): Mineral oil (API base oil category classification: Group II, kinematic viscosity at 40°C: 88.7 mm) 2 / s, 100℃ kinematic viscosity: 10.2mm 2 / s, viscosity index: 96)

[0083] <Imide compound (B)> Non-boron-modified succinimide compound (Bx): A non-boron-modified capped alkenyl succinic acid bisimide (a succinic acid bisimide (B2x) represented by the general formula (b-2) above). In the general formula (b-2), R A1 and R A2 is a polybutenyl group with a mass average molecular weight (Mw) of 2300, and R B1 and R B2 is an ethylene group, and R C is a group represented by -CH2CH2OCH2CH2OH, and x2 is 5. Nitrogen atom content: 1.0% by mass Boron-modified succinimide compound (By): boron-modified capped alkenyl succinimide (polybutene skeleton, nitrogen atom content: 2.3% by mass, boron atom content: 1.9% by mass) Uncapped succinimide compound (B'): Unmodified alkenyl succinic acid bisimide (uncapped succinic acid bisimide (B'2) represented by the general formula (ii) above). In the general formula (ii), R A1 and R A2 is a polybutenyl group with a mass average molecular weight (Mw) of 950, and R B1 and R B2is an ethylene group, and x2 is 3. Nitrogen atom content: 1.9% by mass

[0084] <Calcium-based detergent (C)> Calcium-based detergent (C1): Calcium sulfonate (base number: 300 mg KOH / g, calcium atom content: 11.6% by mass) with a branched chain of butyl groups and an alkyl group containing a total of 16 carbon atoms, including the carbon atoms in the branched chain.

[0085] <Polymer component (D)> Polymer component (D1-1): ethylene-propylene copolymer (product name: Lucant HC-2000 (registered trademark), manufactured by Mitsui Chemicals, Inc., mass average molecular weight (Mw): 14,000) Polymer component (D1-2): Poly-α-olefin (PAO, mass average molecular weight (Mw): 16,000) Polymer component (D2): Polymethacrylate (PMA, mass average molecular weight (Mw): 35,000) Polymer component (D3): ethylene-propylene copolymer (product name: Lucant HC-600 (registered trademark), manufactured by Mitsui Chemicals, Inc., mass average molecular weight (Mw): 7,000) The mass average molecular weight (Mw) of the polymer component (D) was measured by gel permeation chromatography and calculated in terms of polystyrene.

[0086] <Zinc dithiophosphate (E)> ZnDTP: secondary zinc dialkyldithiophosphate (phosphorus atom content: 7.1% by mass)

[0087] <Other ingredients> Antioxidant: Alkyl-substituted diphenylamine antioxidant

[0088] The lubricating oil compositions thus prepared were also measured for the following physical properties and elemental amounts. These results are shown in Tables 1 to 3.

[0089] The lubricating oil compositions obtained were also evaluated as follows, and the results are shown in Tables 1 to 3.

[0090] [Wear resistance evaluation] Using a Falex Block-on-Ring friction and wear tester (LFW-1), the wear width of test pieces was measured when the lubricating oil compositions obtained under the following conditions were used. If the wear width of the test pieces was 410 μm or less, the lubricating oil composition was evaluated as having excellent wear resistance. Device name: Falex Block on Ring Test Machine (manufactured by Falex Corporation) Ring: Falex S-10 Test Ring (SAE4620 Steel) Block: Falex H-60 ​​Test Block (SAE01 Steel) ·Oil temperature: 100℃ Load: 294N ·Speed: 250rpm Exam time: 60 minutes ·Sample oil amount: 120mL

[0091] [Evaluation of oil film retention] The oil film thickness of the obtained lubricating oil composition was measured under the following conditions. The oil film thickness was measured three times under the same conditions, and the average of the three measurements was taken as the EHL oil film thickness of the lubricating oil composition. A lubricating oil composition with an EHL oil film thickness of 17.0 nm or more was evaluated as having excellent oil film retention properties. Device name: EHD2 (manufactured by PCS Instruments) ·Test piece: Steel Ball (diameter: 7.5mm) Disc: SiO2 / Cr coated glass disc ·Oil temperature: 80℃ Load: 20N (surface pressure: 0.5GPa) ·Speed: 100mm / s Slip Rate (SRR): 200%

[0092] [Table 1]

[0093] [Table 2]

[0094] [Table 3]

[0095] All of the lubricating oil compositions of Examples 1 to 9, which met all of the requirements of the present invention, were found to be excellent in wear resistance and oil film retention. On the other hand, the lubricating oil composition of Comparative Example 1, which did not contain the non-boron-modified succinimide compound (Bx) but contained only the boron-modified capped imide compound (By) as the imide compound (B), and the lubricating oil composition of Comparative Example 2, which contained only the non-capped imide compound (B') as the imide compound (B), resulted in poor wear resistance. Furthermore, the lubricating oil composition of Comparative Example 3, which did not contain polymer component (D), and the lubricating oil composition of Comparative Example 4, which contained polymer component (D) with a mass average molecular weight (Mw) of less than 10,000, showed poor oil film retention.

Claims

1. A lubricating oil composition comprising a base oil (A), an imide compound (B), a calcium-based detergent (C), a polymer component (D), and a zinc dithiophosphate (E), The imide compound (B) includes one or more non-boron-modified succinimide compounds (Bx) selected from succinic acid bisimides (B2x) represented by the following general formula (b-2): the polymer component (D) has a mass average molecular weight (Mw) of 10,000 or more and 50,000 or less, and includes at least one selected from an olefin polymer (D1) and a polymethacrylate (D2), the zinc dithiophosphate (E) comprises a secondary zinc dialkyldithiophosphate, When the imide compound (B) further contains one or more boron-modified succinimide compounds (By) selected from the boron-modified products (B2y) of the succinic acid bisimides (B2x), the ratio of the content of boron atoms (By-B) derived from the boron-modified succinimide compound (By) to the content of nitrogen atoms (B-N) derived from the imide compound (B), [(By-B) / (B-N)], in mass ratio, is 0.5 or less. 【Chemistry 1】 [In the above general formula (b-2), R Ａ１ , and R Ａ２ are each independently an alkenyl group having a mass average molecular weight (Mw) of 500 to 4,000. R Ｂ１ , and R Ｂ２ are each independently an alkylene group having 2 to 5 carbon atoms. R Ｃ is an alkyl group having 1 to 10 carbon atoms, or a group represented by -(AO)n-H (wherein A is an alkylene group having 2 to 4 carbon atoms, and n is an integer of 1 to 10). x2 is an integer from 1 to 10.

2. The imide compound (B) further contains the boron-modified succinimide compound (By), 2. The lubricating oil composition according to claim 1, wherein the content of boron atoms (By-B) derived from the boron-modified succinimide compound (By) is 0.020 mass% or less, based on the total amount of the lubricating oil composition.

3. 3. The lubricating oil composition according to claim 1, wherein the ratio [(E-P) / (B-N)] of the content of phosphorus atoms (E-P) derived from the zinc dithiophosphate (E) to the content of nitrogen atoms (B-N) derived from the imide compound (B) is 0.5 or more and 5.0 or less in mass ratio.

4. The lubricating oil composition according to any one of claims 1 to 3, wherein the content of nitrogen atoms (N) is 0.010 mass % or more and 0.10 mass % or less, based on the total amount of the lubricating oil composition.

5. The lubricating oil composition according to any one of claims 1 to 4, wherein the calcium-based detergent (C) is a calcium sulfonate.

6. Kinematic viscosity at 100°C: 4.0 mm ２ / s or more 20.0mm ２ The lubricating oil composition according to any one of claims 1 to 5, wherein the viscosity is less than 1000 kJ / s.

7. The lubricating oil composition according to any one of claims 1 to 6, which is used in an internal combustion engine of a motorcycle.

8. A method for producing a lubricating oil composition, comprising the step of mixing a base oil (A), an imide compound (B), a calcium-based detergent (C), a polymer component (D), and a zinc dithiophosphate (E), The imide compound (B) includes one or more non-boron-modified succinimide compounds (Bx) selected from succinic acid bisimides (B2x) represented by the following general formula (b-2): the polymer component (D) has a mass average molecular weight (Mw) of 10,000 or more and 50,000 or less, and includes at least one selected from an olefin polymer (D1) and a polymethacrylate (D2), the zinc dithiophosphate (E) comprises a secondary zinc dialkyldithiophosphate, When the imide compound (B) further contains one or more boron-modified succinimide compounds (By) selected from the boron-modified derivatives (B2y) of the succinic acid bisimide (B2x), the ratio of the content of boron atoms (By-B) derived from the boron-modified succinimide compound (By) to the content of nitrogen atoms (B-N) derived from the imide compound (B), [(By-B) / (B-N)], is 0.5 or less in mass ratio. 【Chemistry 2】 [In the above general formula (b-2), R Ａ１ and R Ａ２ are each independently an alkenyl group having a mass average molecular weight (Mw) of 500 to 4,000. R Ｂ１ and R Ｂ２ are each independently an alkylene group having 2 to 5 carbon atoms. R Ｃ is an alkyl group having 1 to 10 carbon atoms, or a group represented by -(AO)n-H (wherein A is an alkylene group having 2 to 4 carbon atoms, and n is an integer of 1 to 10). x2 is an integer from 1 to 10.

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