Lubricating oil composition

Abstract

The present invention pertains to a lubricating oil composition comprising a mineral base oil (A), a polymer (B) having a weight-average molecular weight (Mw) of 100-15,000, and a molybdenum-based friction regulator (M), and having a kinematic viscosity of at most 35.0 mm2 / s at 40ºC. The present invention thus provides a lubricating oil composition having an excellent friction coefficient-reducing effect even when a member having a small surface roughness is lubricated in a low oil temperature range.

Description

[Technical Field]

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

[0002] In recent years, there has been a strong demand for improved fuel efficiency in vehicles such as automobiles, from the perspective of efficient use of petroleum resources and reduction of CO2 emissions. Therefore, there is a growing demand for improved fuel efficiency in lubricating oil compositions used in the engines of automobiles and other vehicles. One method for improving fuel efficiency is to reduce viscous resistance by lowering the viscosity of the lubricating oil composition. However, simply lowering the viscosity can negatively affect the friction characteristics.

[0003] Furthermore, in vehicles equipped with hybrid or idle stop mechanisms, the engine operating rate is low and the oil temperature does not rise easily, making it even more important to reduce viscosity in the low oil temperature range, and low viscosity mineral oil or synthetic oil is sometimes used as the base oil. In such cases, molybdenum-based friction modifiers may be used to reduce the coefficient of friction (see, for example, Patent Document 1). On the other hand, in recent years, progress has been made in developing technologies to reduce the surface roughness of engine components such as pistons and cylinder liners. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-189668 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, the inventors' investigations revealed that when lubricating components with low surface roughness in a low oil temperature range, the coefficient of friction deteriorates. The present invention has been made in view of the above-mentioned problems, and aims to provide a lubricating oil composition that exhibits excellent friction coefficient reduction effect even when lubricating components with small surface roughness in a low oil temperature range. [Means for solving the problem]

[0006] As a result of diligent research by the inventors, we have found that the above problems can be solved by a low-viscosity lubricating oil composition containing a polymer of a specific weight-average molecular weight and a molybdenum-based friction modifier, and have completed the present invention.

[0007] In other words, the present invention provides the following [1]. [1] A mineral oil base oil (A), a polymer (B) with a weight-average molecular weight (Mw) of 100 to 15,000, and a molybdenum-based friction modifier (M), with a kinematic viscosity of 35.0 mm at 40°C. 2 Lubricating oil composition with a viscosity of / s or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a lubricating oil composition that exhibits excellent friction coefficient reduction effects even when lubricating components with low surface roughness in a low oil temperature range. [Modes for carrying out the invention]

[0009] The upper and lower limits of the numerical ranges described herein can be combined in any way. For example, if the numerical ranges "A to B" and "C to D" are described, the numerical ranges "A to D" and "C to B" are also included within the scope of the present invention. Furthermore, unless otherwise specified, the numerical range "lower limit to upper limit" described herein means that the value is greater than or equal to the lower limit and less than or equal to the upper limit. Furthermore, in this specification, the numerical values ​​in the examples are values ​​that can be used as upper or lower limits. In this specification, for example, "(meth)acrylate" is used to refer to both "acrylate" and "methacrylate," and the same applies to other similar terms and similar notations.

[0010] [Lubricating oil composition] The lubricating oil composition of this embodiment contains a mineral oil base oil (A), a polymer (B) with a weight-average molecular weight (Mw) of 100 to 15,000, and a molybdenum-based friction modifier (M), and has a kinematic viscosity of 35.0 mm at 40°C. 2 This is anything below / s.

[0011] As a result of diligent research by the inventors to solve the above problems, it was found that when lubricating a component with a small surface roughness in a low oil temperature range, a film of molybdenum-based friction modifier is less likely to form in the boundary lubrication region, and the coefficient of friction deteriorates. Therefore, after diligent research by the inventors, we discovered that by incorporating a polymer with a small molecular weight, the coefficient of friction between metal components in the low oil temperature range can be reduced, and thus completed the present invention.

[0012] The following describes each component included in the lubricating oil composition of this embodiment.

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

[0014] Examples of the mineral oil mentioned above include atmospheric residue obtained by atmospheric distillation of crude oil such as paraffinic crude oil, intermediate crude oil, and naphthenic crude oil; lubricating oil fraction obtained by vacuum distillation of the atmospheric residue; and mineral oil obtained by subjecting the lubricating oil fraction to one or more refining treatments such as solvent dewaxing, solvent extraction, hydrofinishing, hydrocracking, advanced hydrocracking, solvent dewaxing, catalytic dewaxing, and hydroisomerization dewaxing.

[0015] In this embodiment, the mineral oil base oil (A) used is preferably a base oil classified as Group II or III of the API (American Petroleum Institute) base oil categories, and more preferably a base oil classified as Group III.

[0016] As the mineral oil base oil (A), one kind selected from mineral oils may be used alone, or two or more kinds may be used in combination.

[0017] From the viewpoint of making the fuel efficiency good, the upper limit value of the kinematic viscosity and viscosity index of the mineral oil base oil (A) is set, and from the viewpoint of reducing the loss of the lubricating oil composition due to evaporation and ensuring the oil film holding property, the lower limit value is set. It is preferably in the following range. The kinematic viscosity of the mineral oil base oil (A) at 40°C is preferably 4.0 mm 2 / s or more, more preferably 8.0 mm 2 / s or more, still more preferably 12.0 mm 2 / s or more, and preferably 50.0 mm 2 / s or less, more preferably 35.0 mm 2 / s or less, still more preferably 24.0 mm 2 / s or less. The upper limit value and the lower limit value of these numerical ranges can be arbitrarily combined. Specifically, 4.0 mm 2 / s to 50.0 mm 2 / s is preferable, 8.0 mm 2 / s to 35.0 mm 2 / s is more preferable, 12.0 mm 2 / s to 24.0 mm 2 / s is still more preferable. The kinematic viscosity of the mineral oil base oil (A) at 100°C is preferably 2.0 mm 2 / s or more, and preferably 20.0 mm 2 / s or less, more preferably 10.0 mm 2 / s or less, still more preferably 8.0 mm 2 / s or less, still more preferably 7.0 mm 2 / s is even more preferable. The upper limit value and the lower limit value of these numerical ranges can be arbitrarily combined. Specifically, 2.0 mm 2 / s to 20.0 mm 2 / s is preferable, 2.0 mm 2 / s to 10.0 mm 2 / s is more preferable, 2.0 mm 2 / s to 8.0 mm 2 / s is still more preferable, 2.0 mm 2 / s to 7.0 mm2 / s is even more preferable. The viscosity index of the base oil (A) is preferably 80 or higher, more preferably 90 or higher, even more preferably 100 or higher, even more preferably 105 or higher, and still more preferably 120 or higher. The kinematic viscosity at 40°C, the kinematic viscosity at 100°C, and the viscosity index can be measured or calculated in accordance with JIS K 2283:2000. Furthermore, if the mineral oil base oil (A) is a mixed base oil containing two or more types of mineral oil base oils, it is preferable that the kinematic viscosity and viscosity index of the mixed base oil are within the above range.

[0018] In the lubricating oil composition of this embodiment, the content of the mineral oil 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% to 99% by mass, more preferably 70% to 95% by mass, and even more preferably 80% to 93% by mass, based on the total amount (100% by mass) of the lubricating oil composition.

[0019] <Polymer (B)> The polymer (B) used in the lubricating oil composition of this embodiment must have a weight-average molecular weight (Mw) of 100 to 15,000. If the weight-average molecular weight (Mw) of the polymer is less than 100, the oil film enhancing effect will not be exhibited, and if it is greater than 15,000, the polymer will not be able to penetrate the sliding surface, so in either case, the friction coefficient reduction effect will not be exhibited. The weight-average molecular weight (Mw) of polymer (B) is preferably 500 or more, more preferably 800 or more, even more preferably 1,000 or more, and also preferably 13,000 or less, more preferably 12,000 or less, even more preferably 11,000 or less, and particularly preferably 3,500 or less. The upper and lower limits of these numerical ranges can be arbitrarily combined, specifically preferably 500 to 13,000, more preferably 800 to 12,000, even more preferably 1,000 to 11,000, and particularly preferably 1,000 to 3,500. Furthermore, the number-average molecular weight (Mn) of polymer (B) is preferably 100 or more, more preferably 500 or more, even more preferably 700 or more, and particularly preferably 800 or more, and also preferably 10,000 or less, more preferably 5,000 or less, even more preferably 3,000 or less, and particularly preferably 1,700 or less. The upper and lower limits of these numerical ranges can be arbitrarily combined, specifically preferably 100 to 10,000, more preferably 500 to 5,000, even more preferably 700 to 3,000, and particularly preferably 800 to 1,700.

[0020] The molecular weight distribution (Mw / Mn) of the polymer (B) is preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. In this specification, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of each component are values ​​calculated on a standard polystyrene basis using gel permeation chromatography (GPC).

[0021] Examples of the polymer (B) mentioned above include polyolefins, ethylene-vinyl acetate copolymers, condensates of chlorinated paraffin and naphthalene, condensates of chlorinated paraffin and phenol, poly(meth)acrylates, and polyalkylstyrenes. It is preferable to use polyolefin (B-1) or poly(meth)acrylate (B-2) as the polymer (B) mentioned above.

[0022] The polyolefin (B-1) is preferably an olefin polymer having 2 or more carbon atoms, more specifically an ethylene-propylene copolymer or an olefin polymer having 4 or more carbon atoms, and also preferably an olefin polymer having 20 or fewer carbon atoms, and more preferably an olefin polymer having 12 or fewer carbon atoms. The upper and lower limits of these numerical ranges can be arbitrarily combined, and as for the olefin polymer having 4 or more carbon atoms, specifically, an olefin polymer having 4 to 20 carbon atoms is preferred, and an olefin polymer having 4 to 12 carbon atoms is more preferred. Specific examples of the above olefins include ethylene, propylene, 1-butene, 2-butene, isobutene, 3-methyl-1-butene, 4-phenyl-1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3,3-dimethyl-1-pentene, 3,4-dimethyl-1-pentene, 4,4-dimethyl-1-pentene, 1-hexene, 4-methyl-1-hexene, 5-methyl-1-hexene, 6-phenyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, and 1-eicosene. Among these, 1-butene and 1-decene are preferred.

[0023] Furthermore, the above-mentioned polyolefin (B-1) may be a hydrogenated product.

[0024] The content of polymer (B) is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and also preferably 5.0% by mass or less, more preferably 4.0% by mass or less, and even more preferably 3.0% by mass or less, based on the solid content of the total composition. The upper and lower limits of these numerical ranges can be arbitrarily combined, specifically preferably 0.1 to 5.0% by mass, more preferably 0.2 to 4.0% by mass, and even more preferably 0.3 to 3.0% by mass.

[0025] [Molybdenum-based friction modifier (M)] The lubricating oil composition of this embodiment further contains a molybdenum-based friction modifier (M). If the lubricating oil composition does not contain a molybdenum-based friction modifier (M), the friction reduction effect will be insufficient.

[0026] Any compound containing molybdenum atoms can be used as the molybdenum-based friction modifier (M). Examples of molybdenum-based friction modifiers (M) include molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDTP), and molybdenum amine complexes. These may be used individually or in combination of two or more. Among these, from the viewpoint of reducing the intermetallic friction coefficient and obtaining excellent fuel efficiency, one or more selected from the group consisting of molybdenum dithiocarbamate (MoDTC) and molybdenum amine complexes are preferred. Examples of molybdenum dithiocarbamate (MoDTC) include dinuclear molybdenum dithiocarbamate containing two molybdenum atoms in one molecule, and trinuclear molybdenum dithiocarbamate containing three molybdenum atoms in one molecule.

[0027] In other words, in this embodiment, the molybdenum-based friction modifier (M) preferably contains one or more selected from the group consisting of dinuclear molybdenum dithiocarbamate, trinuclear molybdenum dithiocarbamate, and molybdenamine complexes, and more preferably contains two or more. The following provides a detailed explanation of these molybdenum-based friction modifiers.

[0028] <Binuclear molybdenum dithiocarbamate> Examples of dinuclear molybdenum dithiocarbamate include the compound represented by the following general formula (1) and the compound represented by the following general formula (2).

[0029] [ka]

[0030] In the above general formulas (1) and (2), R 11 ~R 14 Each of these independently represents a hydrocarbon group, which may be the same as or different from one another. X 11 ~X 18Each of these independently represents either an oxygen atom or a sulfur atom, and they may be the same or different from each other. However, X in formula (1) 11 ~X 18 At least two of them are sulfur atoms. R 11 ~R 14 The number of carbon atoms in the hydrocarbon group that can be selected is preferably 6 to 22.

[0031] In the above general formulas (1) and (2), R 11 ~R 14 Examples of hydrocarbon groups that can be selected include alkyl groups, alkenyl groups, cycloalkyl groups, aryl groups, alkylaryl groups, and arylalkyl groups. Examples of the alkyl group include hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl groups. Examples of such alkenyl groups include hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl, and pentadecenyl groups. Examples of the cycloalkyl group include cyclohexyl group, dimethylcyclohexyl group, ethylcyclohexyl group, methylcyclohexylmethyl group, cyclohexylethyl group, propylcyclohexyl group, butylcyclohexyl group, and heptylcyclohexyl group. Examples of the aryl group include phenyl, naphthyl, anthracenyl, biphenyl, and terphenyl groups. Examples of the alkylaryl group include tolyl group, dimethylphenyl group, butylphenyl group, nonylphenyl group, and dimethylnaphthyl group. Examples of the arylalkyl group include methylbenzyl group, phenylmethyl group, phenylethyl group, and diphenylmethyl group.

[0032] Among these, molybdenum dialkyldithiocarbamate (M1), represented by the following general formula (m1) (hereinafter also referred to as "compound (M1)") is preferred. [ka]

[0033] In the above general formula (m1), R 1 , R 2 , R 3 , and R 4 Each independently represents either a short-chain substituent group (α) which is an aliphatic hydrocarbon group having 4 to 12 carbon atoms, or a long-chain substituent group (β) which is an aliphatic hydrocarbon group having 13 to 22 carbon atoms. However, the molar ratio [(α) / (β)] of the short-chain substituent group (α) to the long-chain substituent group (β) in the total molecule of compound (M1) is 0.10 to 2.0. Also, in the general formula (m1), X 1 , X 2 , X 3 , and X 4 Each of these independently represents either an oxygen atom or a sulfur atom.

[0034] Examples of aliphatic hydrocarbon groups having 4 to 12 carbon atoms that can be selected as the short-chain substituent group (α) include alkyl groups having 4 to 12 carbon atoms and alkenyl groups having 4 to 12 carbon atoms. Specifically, examples include butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, butenyl group, pentenyl group, hexenyl group, heptenyl group, octenyl group, nonenyl group, decenyl group, undecenyl group, and dodecenyl group. These may be linear or branched. Furthermore, the number of carbon atoms in the aliphatic hydrocarbon group that can be selected as the short-chain substituent group (α) is preferably 5 to 11, more preferably 6 to 10, and even more preferably 7 to 9, from the viewpoint of making it easier to exhibit the effects of the present invention.

[0035] Examples of aliphatic hydrocarbon groups having 13 to 22 carbon atoms that can be selected as the long-chain substituent group (β) include alkyl groups having 13 to 22 carbon atoms and alkenyl groups having 13 to 22 carbon atoms. Specifically, examples include tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, icosyl group, henicosyl group, docosyl group, tridecenyl group, tetradecenyl group, pentadecenyl group, hexadecenyl group, heptadecenyl group, octadecenyl group, oleyl group, nonadecenyl group, icocenyl group, henicosenyl group, and dococenyl group. These may be linear or branched. Furthermore, the number of carbon atoms in the aliphatic hydrocarbon group that can be selected as the long-chain substituent group (β) is preferably 13 to 20, more preferably 13 to 16, and even more preferably 13 to 14, from the viewpoint of making it easier to exhibit the effects of the present invention.

[0036] Here, the compound (M1) represented by the general formula (m1) has a molar ratio [(α) / (β)] of 0.10 to 2.0 between the short-chain substituent group (α) and the long-chain substituent group (β) in its entire molecule. When the molar ratio [(α) / (β)] is 0.10 or higher, the influence of compound (M1) on copper corrosion resistance is reduced, and the friction reduction effect is also easily improved. Furthermore, when the molar ratio [(α) / (β)] is 2.0 or lower, it is easier to ensure low-temperature storage stability. Here, from the viewpoint of minimizing the impact on copper corrosion resistance and making it easier to improve the friction reduction effect, the molar ratio [(α) / (β)] is preferably 0.15 or higher, more preferably 0.20 or higher. Furthermore, from the viewpoint of making it easier to ensure low-temperature storage stability, the molar ratio [(α) / (β)] is preferably 1.2 or less, more preferably 1.0 or less, even more preferably 0.80 or less, and even more preferably 0.60 or less. The upper and lower limits of these numerical ranges can be combined in any way. Specifically, they are preferably 0.15 to 1.2, more preferably 0.20 to 1.0, even more preferably 0.20 to 0.80, and even more preferably 0.20 to 0.60.

[0037] Here, the short-chain substituent group (α) and the long-chain substituent group (β) may or may not coexist within the same molecule. That is, the average value of the molar ratio [(α) / (β)] of the short-chain substituent group (α) to the long-chain substituent group (β) in the entire molecule of the compound (M1) represented by the general formula (m1) is within the range of 0.10 to 2.0. Therefore, compound (M1) contains R in the general formula (m1) above. 1 , R 2 , R 3 and R 4 It is also possible that a group of molecules (m1-1) in which all are short-chain substituents (α) may be mixed, 1 , R 2 , R 3 and R 4 It is also possible that a group of molecules (m1-2) in which all of the substituents are long chain substituents (β) may be mixed, 1 , R 2 , R 3 and R 4 A group of molecules (m1-3) may be mixed in which some of the molecules are short-chain substituents (α) and the remainder are long-chain substituents (β).

[0038] <Trinuclear molybdenum dithiocarbamate> Examples of trinuclear molybdenum dithiocarbamate include compounds represented by the following general formula (3). Mo3S k E m L n A p Q z (3)

[0039] In the general formula (3) above, k is an integer greater than or equal to 1, m is an integer greater than or equal to 0, and k+m is an integer between 4 and 10, preferably between 4 and 7. n is an integer between 1 and 4, and p is an integer greater than or equal to 0. z is an integer between 0 and 5, including non-stoichiometric values. Each of E is independently either an oxygen atom or a selenium atom, and can, for example, be substituted with sulfur in the core described later. Each L is an anionic ligand having an organic group containing carbon atoms, where the total number of carbon atoms in the organic group of each ligand is 14 or more, and the ligands may be the same or different. Each A is an anion other than L, independently of the others. Each Q is an independently electron-donating neutral compound that exists to satisfy the vacant coordination on the trinuclear molybdenum compound.

[0040] The total number of carbon atoms in the organic group of the anionic ligand represented by L is preferably 14 to 50, more preferably 16 to 30, and even more preferably 18 to 24. L is preferably a monoanionic ligand, which is a monovalent anionic ligand, and more preferably a ligand represented by the following general formulas (i) to (iv). Furthermore, the anionic ligand selected as L in the above general formula (3) is preferably a ligand represented by the following general formula (iv). Furthermore, it is preferable that all the anionic ligands selected as L in the above general formula (3) are the same, and more preferably that they are all ligands represented by the following general formula (iv).

[0041] [ka]

[0042] In the above general formulas (i) to (iv), X 31 ~X 37 , and Y are each independently an oxygen atom or a sulfur atom, and may be the same as or different from each other. In the above general formulas (i) to (iv), R 31 ~R 35 Each of these is an organic group, and they may be identical or different from one another.

[0043] Note, R 31 , R 32 , and R33 The number of carbon atoms in each of the organic groups that can be selected is preferably 14 to 50, more preferably 16 to 30, and even more preferably 18 to 24.

[0044] R in equation (iv) 34 and R 35 The total number of carbon atoms in the two organic groups that can be selected is preferably 14 to 50, more preferably 16 to 30, and even more preferably 18 to 24. R 34 and R 35 The number of carbon atoms in each of the organic groups that can be selected is preferably 7 to 30, more preferably 7 to 20, and even more preferably 8 to 13. Note, R 34 The organic group and R 35 The organic groups may be the same as or different from each other, but it is preferable that they be different from each other. Also, R 34 The number of carbon atoms in the organic group and R 35 The number of carbon atoms in the organic groups may be the same or different, but it is preferable that they be different.

[0045] R 31 ~R 35 Examples of organic groups that can be selected include alkyl groups, aryl groups, substituted aryl groups, and hydrocarbyl groups such as ether groups. The term "hydrocarbyl" refers to a substituent having a carbon atom directly bonded to the remainder of the ligand, and within the scope of this embodiment, its properties are primarily hydrocarbyl. Examples of such substituents are listed below. 1. Hydrocarbon substituents Examples of hydrocarbon substituents include aliphatic substituents such as alkyl and alkenyl substituents, alicyclic substituents such as cycloalkyl and cycloalkenyl substituents, aromatic groups, aromatic nuclei substituted with aliphatic and alicyclic groups, and cyclic groups in which the ring is completed via another site in the ligand (i.e., any two indicated substituents may together form an alicyclic group). 2. Substituted hydrocarbon substituents Examples of substituted hydrocarbon substituents include those obtained by substituting the above-mentioned hydrocarbon substituents with non-hydrocarbon groups that do not alter the properties of hydrocarbil. Examples of non-hydrocarbon groups include halogen groups such as chloro and fluoro, amino groups, alkoxy groups, mercapto groups, alkylmercapto groups, nitro groups, nitroso groups, and sulfoxy groups.

[0046] In the general formula (3) above, the anionic ligand selected as L is preferably derived from alkylxanthogenic salts, carboxylates, dialkyldithiocarbamates, and mixtures thereof, and more preferably derived from dialkyldithiocarbamates.

[0047] In the general formula (3) above, the anion that can be selected as A may be a monovalent anion or a divalent anion. Examples of anions that can be selected as A include disulfides, hydroxides, alkoxides, amides and thiocyanates or their derivatives.

[0048] In the general formula (3) above, Q can be water, amine, alcohol, ether, phosphine, etc. Q may be the same or different, but it is preferable that it be the same.

[0049] As the trinuclear molybdenum dithiocarbamate, a compound is preferred in which, in the general formula (3), k is an integer from 4 to 7, n is 1 or 2, L is a monoanionic ligand, p is an integer that imparts electrical neutrality to a compound based on the anionic charge at A, and m and z are each 0. A compound is more preferred in which k is an integer from 4 to 7, L is a monoanionic ligand, n is 4, and p, m, and z are each 0.

[0050] Furthermore, the trinuclear molybdenum dithiocarbamate is preferably a compound having a core represented by the following formula (IV-A) or (IV-B). Each core has an effective charge (net electrical charge) of +4. These cores are surrounded by an anionic ligand and, if necessary, anions other than the anionic ligand.

[0051] [ka]

[0052] The formation of trinuclear molybdenum-sulfur compounds requires, for example, the selection of appropriate anionic ligands (L) and other anions (A) depending on the number of sulfur and E atoms present in the core; that is, the total anionic charge composed of the sulfur atom, E atom (if present), L, and A (if present) must be -4. The trinuclear molybdenum-sulfur compound may also contain cations other than molybdenum, such as (alkyl)ammonium, amine, or sodium, if the anionic charge is greater than -4. A preferred embodiment of the anionic ligand (L) and other anions (A) is a configuration having four monoanionic ligands. The molybdenum-sulfur cores, for example, the structures represented by (IV-A) and (IV-B) above, can be interconnected by one or more polydentate ligands, i.e., ligands having one or more functional groups capable of bonding to molybdenum atoms to form oligomers.

[0053] <Molybdenamine complex> Examples of molybdenamine complexes include molybdenamine complexes obtained by reacting a hexavalent molybdenum compound, such as molybdenum trioxide and / or molybdic acid, with an amine compound. Preferred amine compounds include alkylamines, dialkylamines, and the like. The alkylamines and dialkylamines reacted with the hexavalent molybdenum compound are not particularly limited, and examples include alkylamines and dialkylamines having an alkyl group with 1 to 30 carbon atoms.

[0054] <Content of molybdenum-based friction modifier (M)> In the lubricating oil composition of this embodiment, the content of the molybdenum-based friction modifier (M) is preferably 0.30% by mass or more, more preferably 0.40% by mass or more, even more preferably 0.50% by mass or more, based on the total amount of the lubricating oil composition, and also preferably 3.0% by mass or less, more preferably 2.0% by mass or less, and even more preferably 1.0% by mass or less, from the viewpoint of lowering the intermetallic friction coefficient and obtaining excellent fuel efficiency. The upper and lower limits of these numerical ranges can be combined in any way. Specifically, they are preferably 0.30% to 3.0% by mass, more preferably 0.40% to 2.0% by mass, and even more preferably 0.50% to 1.0% by mass.

[0055] In the lubricating oil composition of this embodiment, the content of molybdenum atoms derived from the molybdenum-based friction modifier (M) is preferably 50 ppm by mass or more, more preferably 80 ppm by mass or more, and even more preferably 100 ppm by mass or more, based on the total amount (100% by mass) of the lubricating oil composition, from the viewpoint of improving the friction reduction effect. Furthermore, it is preferably 2,000 ppm by mass or less, more preferably 1,500 ppm by mass or less, and even more preferably 1,000 ppm by mass or less. The upper and lower limits of these numerical ranges can be arbitrarily combined, and specifically, preferably 50 to 2,000 ppm by mass, more preferably 80 to 1,500 ppm by mass, and even more preferably 100 to 1,000 ppm by mass.

[0056] <Content ratio of dinuclear molybdenum dithiocarbamate and molybdenamine complex> In this embodiment, the ratio of dinuclear molybdenum dithiocarbamate to molybdenamine complex [(dinuclear MoDTC) / (MoAmn)] is preferably 0.1 to 10, more preferably 1.5 to 8.0, and even more preferably 3.0 to 7.0 by mass, from the viewpoint of improving the friction reduction effect.

[0057] <Other ingredients> The lubricating oil composition of this embodiment may contain other components besides those mentioned above, as necessary, as long as they do not impair the effects of the present invention. Examples of additives as other components include metal-based detergents, pour point depressants, antioxidants, wear inhibitors, friction modifiers other than molybdenum-based friction modifiers (M), extreme pressure agents, viscosity index improvers, rust inhibitors, defoamers, oiliness improvers, metal deactivators, and anti-emulsifiers. These may be used individually or in combination of two or more types.

[0058] -Metal-based cleaner- Examples of metal-based cleaning agents include organic acid metal salt compounds containing metal atoms selected from alkali metals and alkaline earth metals. Specifically, examples include metal salicylates, metal phenates, and metal sulfonates containing metal atoms selected from alkali metals and alkaline earth metals. In this specification, "alkali metals" refers to lithium, sodium, potassium, rubidium, and cesium. Furthermore, "alkaline earth metals" refer to beryllium, magnesium, calcium, strontium, and barium. From the viewpoint of improving cleaning performance at high temperatures, sodium, calcium, magnesium, or barium are preferred as metal atoms in the metal-based cleaning agent, with calcium and magnesium being more preferred.

[0059] As the metal salicylate, a compound represented by the following general formula (4) is preferred; as the metal phenate, a compound represented by the following general formula (5) is preferred; and as the metal sulfonate, a compound represented by the following general formula (6) is preferred.

[0060] [ka]

[0061] In the above general formulas (4) to (6), M is a metal atom selected from alkali metals and alkaline earth metals, and sodium, calcium, magnesium, or barium are preferred, with calcium and magnesium being more preferred. E is an alkaline earth metal, preferably calcium, magnesium, or barium, with calcium and magnesium being more preferred. q is the valence of M, which is 1 or 2. R 31 and R 32 Each of these is independently a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms. S represents a sulfur atom. r is an integer of 0 or more, preferably an integer from 0 to 3. R 31 and R 32 Examples of hydrocarbon groups that can be selected include C1-C18 alkyl groups, C1-C18 alkenyl groups, C3-C18 cycloalkyl groups, C6-C18 aryl groups, C7-C18 alkylaryl groups, C7-C18 arylalkyl groups, and C7-C18 arylalkyl groups. These may be used individually or in combination of two or more. Among these, it is preferable to use one or more selected from calcium salicylate, calcium phenate, calcium sulfonate, magnesium salicylate, magnesium phenate, and magnesium sulfonate, from the viewpoint of improving high-temperature cleaning and dispersibility, and from the viewpoint of solubility in base oil.

[0062] These metal-based cleaning agents may be neutral salts, basic salts, superbasic salts, or mixtures thereof. The base number of the aforementioned metal-based detergent is preferably 0 to 600 mg KOH / g. If the metal-based detergent is a basic salt or an overbasic salt, the base number of the metal-based detergent is preferably 10 to 600 mg KOH / g, more preferably 20 to 500 mg KOH / g. In this specification, "base number" refers to the base number measured by the perchloric acid method in accordance with JIS K 2501:2003 "Petroleum products and lubricating oils - Neutralization number test method" 7.

[0063] In the lubricating oil composition of this embodiment, the content of the metal-based detergent is preferably 0.01% to 10% by mass, more preferably 0.1% to 5.0% by mass, even more preferably 0.2% to 3.0% by mass, and even more preferably 0.3% to 2.0% by mass, based on the total amount (100% by mass) of the lubricating oil composition, from the viewpoint of making it easier to exhibit the effects of the present invention. Furthermore, metal-based cleaning agents may be used alone or in combination of two or more types. The optimal total content when using two or more types is the same as the content mentioned above.

[0064] In the lubricating oil composition of this embodiment, when the metal atoms contained in the metal-based detergent are calcium, the content of calcium atoms derived from the metal-based detergent is preferably 0.05% by mass or more, more preferably 0.10% by mass or more, and even more preferably 0.11% by mass or more, based on the total amount (100% by mass) of the lubricating oil composition, from the viewpoint of high-temperature cleaning and dispersibility. Furthermore, from the viewpoint of reducing sulfated ash and preventing LSPI (abnormal combustion), the calcium atom content derived from the metal-based detergent is preferably 0.50% by mass or less, more preferably 0.40% by mass or less, even more preferably 0.30% by mass or less, even more preferably 0.20% by mass or less, even more preferably 0.15% by mass or less, and even more preferably 0.13% by mass or less, based on the total amount (100% by mass) of the lubricating oil composition.

[0065] In the lubricating oil composition of this embodiment, when the metal atoms contained in the metal-based detergent are magnesium, the content of magnesium atoms derived from the metal-based detergent is preferably 0.02% by mass or more, more preferably 0.03% by mass or more, and even more preferably 0.04% by mass or more, based on the total amount (100% by mass) of the lubricating oil composition, from the viewpoint of high-temperature cleaning and dispersibility. Furthermore, from the viewpoint of reducing sulfated ash and preventing LSPI (abnormal combustion), the magnesium atom content derived from the metal-based detergent is preferably 0.07% by mass or less, more preferably 0.06% by mass or less, and even more preferably 0.05% by mass or less, based on the total amount (100% by mass) of the lubricating oil composition.

[0066] -Pour point depressant- Examples of pour point depressants include ethylene-vinyl acetate copolymers, condensates of chlorinated paraffin and naphthalene, condensates of chlorinated paraffin and phenol, polymethacrylates (PMA-based; polyalkyl(meth)acrylate, etc.), polyvinyl acetate, polybutene, and polyalkylstyrene, with polymethacrylates being preferred. The weight-average molecular weight (Mw) of these polymers used as pour point depressants is preferably 50,000 to 150,000. These may be used individually or in combination of two or more types.

[0067] -Antioxidant- Examples of antioxidants include amine-based antioxidants and phenol-based antioxidants. Examples of amine-based antioxidants include diphenylamine antioxidants such as diphenylamine and alkylated diphenylamines having an alkyl group with 3 to 20 carbon atoms; naphthylamine antioxidants such as phenyl-α-naphthylamine, phenyl-β-naphthylamine, substituted phenyl-α-naphthylamine having an alkyl group with 3 to 20 carbon atoms, and substituted phenyl-β-naphthylamine having an alkyl group with 3 to 20 carbon atoms; and the like. Examples of phenolic antioxidants include monophenolic antioxidants such as 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, isooctyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; diphenolic antioxidants such as 4,4'-methylenebis(2,6-di-tert-butylphenol) and 2,2'-methylenebis(4-ethyl-6-tert-butylphenol); and hindered phenolic antioxidants. These may be used individually or in combination of two or more types.

[0068] -Abrasion-resistant agent- Examples of wear-resistant agents include zinc-containing compounds such as zinc dialkyldithiophosphate (ZnDTP) and zinc phosphate; sulfur-containing compounds such as disulfides, sulfurized olefins, sulfurized oils and fats, sulfurized esters, thiocarbonates, thiocarbamates, and polysulfides; phosphorus-containing compounds such as phosphite esters, phosphate esters, phosphonic acid esters, and their amine salts or metal salts; and sulfur and phosphorus-containing wear-resistant agents such as thiophosphite esters, thiophosphate esters, thiophosphonic acid esters, and their amine salts or metal salts. Among these, zinc dialkyldithiophosphate (ZnDTP) is preferred. These may be used individually or in combination of two or more types. The zinc dithiophosphate content is preferably 200 to 5,000 ppm by mass, more preferably 300 to 2,000 ppm by mass, based on phosphorus atoms in the total composition.

[0069] - Friction modifiers other than component (M) - The lubricating oil composition of this embodiment may also contain friction modifiers other than component (M). The aforementioned component (M) is excellent at effectively exhibiting a friction-reducing effect in environments where the temperature of the lubricating oil composition is high. However, by including friction modifiers other than component (M) in the lubricating oil composition, the friction-reducing effect can also be effectively exhibited in environments where the temperature of the lubricating oil composition is low. Other friction modifiers besides molybdenum-based friction modifiers (M) include, for example, ashless friction modifiers such as aliphatic amines, fatty acid esters, fatty acid amides, fatty acids, aliphatic alcohols, and aliphatic ethers; and oils and fats, amines, amides, sulfur esters, phosphate esters, phosphite esters, and phosphate ester amine salts. These may be used individually or in combination of two or more types. Here, as a friction modifier other than component (M), an aliphatic amine is preferred, and among aliphatic amines, an aliphatic amine having at least one alkyl group or alkenyl group with 2 to 30 carbon atoms in the molecule is preferred.

[0070] Furthermore, among aliphatic amines having at least one alkyl or alkenyl group with 2 to 30 carbon atoms in the molecule, diethanolamine compounds represented by the following general formula (7) are preferred.

[0071] [ka]

[0072] In the above general formula (7), R 1 It is a monovalent aliphatic hydrocarbon group having 12 to 30 carbon atoms. R 1 Examples of aliphatic hydrocarbon groups having 12 to 30 carbon atoms include linear or branched alkyl groups or linear or branched alkenyl groups having 12 to 30 carbon atoms. The number of carbon atoms in these groups is more preferably 12 to 24, and even more preferably 16 to 20.

[0073] For example, linear or branched alkyl groups having 12 to 30 carbon atoms include various dodecyl groups such as n-dodecyl, isododecyl, sec-dodecyl, tert-dodecyl, and neododecyl groups (hereinafter, functional groups having a predetermined number of carbon atoms, including linear, branched, and their isomers, may be abbreviated as "various functional groups"), various tridecyl groups, various tetradecyl groups, various pentadecyl groups, various hexadecyl groups, various heptadecyl groups, various octadecyl groups, various nonadecyl groups, various icosyl groups, various henicosyl groups, various docosyl groups, various tricosyl groups, various tetracosyl groups, various pentacosyl groups, various hexacosyl groups, various heptacosyl groups, various octacosyl groups, various nonacosyl groups, and various triacontyl groups. Furthermore, examples of linear or branched alkenyl groups having 12 to 30 carbon atoms include various dodecenyl groups, various tridecenyl groups, various tetradecenyl groups, various pentadecenyl groups, various hexadecenyl groups, various heptadecenyl groups, various octadecenyl groups, various nonadecenyl groups, various icocenyl groups, various henicocenyl groups, various dococenyl groups, various tricocenyl groups, various tetracocenyl groups, various pentacocenyl groups, various hexacocenyl groups, various heptacocenyl groups, various octacocenyl groups, various nonacocenyl groups, and various triacontinyl groups. In particular, considering the effect of improving long drainability, various hexadecyl groups, various heptadecyl groups, and various octadecyl groups which are alkyl groups having 16 to 18 carbon atoms, and various hexadecenyl groups, various heptadecenyl groups, and various octadecenyl groups which are alkenyl groups having 16 to 18 carbon atoms are preferred, various hexadecyl groups, various octadecyl groups, and various octadecenyl groups are more preferred, and n-hexadecyl groups (palmityl group), n-octadecyl groups (stearyl group), and n-octadecenyl groups (oleyl group) are even more preferred.

[0074] A preferred specific compound of the diethanolamine compound represented by the above general formula (7) is stearyldiethanolamine (in general formula (7), R 1 The n-octadecyl group (stearyl group) is present. ), oleyldiethanolamine (in general formula (7), R1 R is an n-octadecenyl group (oleyl group). ), and palmityldiethanolamine (in general formula (7), R 1 The group is an n-hexadecyl group (palmityl group). One or more of these can be selected from the following. Among these, oleyldiethanolamine is preferred. These may be used individually or in combination of two or more types.

[0075] -Extreme pressure agent- Examples of extreme pressure agents include sulfur-based extreme pressure agents such as sulfides, sulfoxides, sulfones, and thiophosphinates, halogen-based extreme pressure agents such as chlorinated hydrocarbons, and organometallic extreme pressure agents. Furthermore, compounds that function as extreme pressure agents among the aforementioned wear-resistant agents can also be used. These may be used individually or in combination of two or more types.

[0076] -Rust Inhibitor- Examples of rust inhibitors include fatty acids, alkenyl succinate half esters, fatty acid soaps, alkyl sulfonates, polyhydric alcohol fatty acid esters, fatty acid amines, oxidized paraffins, and alkyl polyoxyethylene ethers. These may be used individually or in combination of two or more types.

[0077] -Antifoaming agent- Examples of defoaming agents include silicone oils such as dimethylpolysiloxane, fluorosilicone oils, and fluoroalkyl ethers. These may be used individually or in combination of two or more types.

[0078] -Oil-enhancing agent- Examples of oiliness improvers include aliphatic saturated or unsaturated monocarboxylic acids such as stearic acid and oleic acid; polymerized fatty acids such as dimer acid and hydrogenated dimer acid; hydroxy fatty acids such as ricinoleic acid and 12-hydroxystearic acid; aliphatic saturated or unsaturated monoalcohols such as lauryl alcohol and oleyl alcohol; aliphatic saturated or unsaturated monoamines such as stearylamine and oleylamine; aliphatic saturated or unsaturated monocarboxylic acid amides such as lauric acid amide and oleic acid amide; and partial esters of polyhydric alcohols such as glycerin and sorbitol with aliphatic saturated or unsaturated monocarboxylic acids.

[0079] -Metal deactivator- Examples of metal deactivators include benzotriazole compounds, toltriazole compounds, thiadiazole compounds, imidazole compounds, and pyrimidine compounds. These may be used individually or in combination of two or more types.

[0080] -Anti-emulsifier- Examples of antiemulsifiers include anionic surfactants such as castor oil sulfates and petroleum sulfonates; cationic surfactants such as quaternary ammonium salts and imidazolines; polyalkylene glycol-based nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, and polyoxyethylene alkylnaphthyl ethers; esters of polyoxyalkylene polyglycols and their dicarboxylic acids; alkylene oxide adducts of alkylphenol-formaldehyde polycondensates; and the like. These may be used individually or in combination of two or more types.

[0081] The content of the above-mentioned other components can be appropriately adjusted within the range that does not impair the effects of the present invention. For each of them, based on the total amount (100% by mass) of the lubricating oil composition, it is usually 0.001% to 15% by mass, preferably 0.005% to 10% by mass, more preferably 0.01% to 7% by mass, and still more preferably 0.03% to 5% by mass. In addition, in this specification, the additive as the other component may be blended with other components in the form of a solution diluted and dissolved in a part of the above-mentioned mineral oil base oil (A) in consideration of handling properties, solubility in the mineral oil base oil (A), etc. In such a case, in this specification, the above-mentioned content of the additive as the other component means the content in terms of the active ingredient (resin content) excluding the diluent oil.

[0082] [Physical property values of the lubricating oil composition] <Kinematic viscosity at 40°C, kinematic viscosity at 100°C, and viscosity index> The kinematic viscosity at 40°C of the lubricating oil composition of this embodiment, from the viewpoint of making the fuel economy good for the upper limit value, and from the viewpoint of reducing the loss of the lubricating oil composition due to evaporation and ensuring the oil film retention property for the lower limit value, is preferably 5.0 mm 2 / s or more, more preferably 10.0 mm 2 / s or more, still more preferably 15.0 mm 2 / s or more, and preferably 65.0 mm 2 / s or less, more preferably 45.0 mm 2 / s or less, still more preferably 30.0 mm 2 / s or less. The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 5.0 to 65.0 mm 2 / s, more preferably 10.0 to 45.0 mm 2 / s, and even more preferably 15.0 to 30.0 mm 2 / s. The kinematic viscosity at 100°C of the lubricating oil composition of this embodiment, from the viewpoint of making the fuel economy good for the upper limit value, and from the viewpoint of reducing the loss of the lubricating oil composition due to evaporation and ensuring the oil film retention property for the lower limit value, is preferably 3.0 mm 2 / s or more, more preferably 3.5 mm2 / s or more, more preferably 4.0 mm 2 The value is 1 / s or more, and preferably 9.3 mm 2 / s or less, more preferably 8.2 mm 2 / s or less, more preferably 7.1 mm 2 The values ​​are less than or equal to / s. The upper and lower limits of these numerical ranges can be combined arbitrarily, and specifically, preferably 3.0 to 9.3 mm. 2 / s, more preferably 3.5~8.2mm 2 The value is / s, and more preferably 4.0 to 7.1 mm 2 It is / s. The viscosity index of the lubricating oil composition of this embodiment is preferably 100 or higher, more preferably 110 or higher, even more preferably 120 or higher, and even more preferably 130 or higher. When the viscosity index is within the above range, the change in viscosity due to temperature is small. The kinematic viscosity at 40°C, the kinematic viscosity at 100°C, and the viscosity index can be measured or calculated in accordance with JIS K 2283:2000.

[0083] [150℃HTHS viscosity (HTHS 150 )] The viscosity of the lubricating oil composition of this embodiment at 150°C (HTHS) 150 The pressure is preferably 1.5 mPa·s or higher, more preferably 1.7 mPa·s or higher, and also preferably less than 3.7 mPa·s, and more preferably less than 3.0 mPa·s. The viscosity of the lubricating oil composition of this embodiment at 150°C (HTHS) 150 ) conforms to ASTM D4683 and uses a TBS (Tapered Bearing Simulator Viscometer) to measure the shear rate at 10 6 Measurement can be performed using / s.

[0084] [Coefficient of friction] The coefficient of friction when using the lubricating oil composition of this embodiment can be evaluated, for example, using an SRV tester (manufactured by Optimol). Specifically, it can be evaluated by the method described in the examples below. The lubricating oil composition of this embodiment preferably has a coefficient of friction of 0.097 or less, and more preferably 0.095 or less, under conditions where the oil temperature is 30°C and the maximum height roughness (Rz) of the disk surface is less than 0.20 μm.

[0085] [Uses of lubricating oil compositions] The lubricating oil composition of this embodiment exhibits excellent friction coefficient reduction effects. Therefore, the lubricating oil composition of this embodiment is preferably used in internal combustion engines, and more preferably in internal combustion engines of four-wheeled vehicles and motorcycles. The lubricating oil composition of this embodiment is preferably used as engine oil, but is more preferably used as engine oil for automobile engines equipped with a hybrid mechanism or an idle stop mechanism, due to its excellent effect in reducing the coefficient of friction in low-temperature ranges. The lubricating oil composition of this embodiment is preferably used as a lubricating oil composition (engine oil for internal combustion engines) for use in automobiles and the like, but it can also be applied to other uses.

[0086] Furthermore, the lubricating oil composition of this embodiment has the effect of particularly reducing the coefficient of friction between components with low surface roughness, and is therefore also suitable as engine oil for engines in which the inside of the cylinder bore of the engine block has been mirror-finished. More specifically, in an engine using the lubricating oil composition of this embodiment, the maximum height roughness (Rz) inside the cylinder bore is preferably less than 0.45 μm, more preferably less than 0.30 μm, and even more preferably less than 0.20 μm. The above maximum height roughness (Rz) can be measured specifically according to JIS B 0601-2001.

[0087] [Method for producing a lubricating oil composition] The method for producing the lubricating oil composition according to this embodiment is not particularly limited. For example, the method for producing the lubricating oil composition according to this embodiment includes the step of mixing the mineral oil base oil (A), polymer (B), and molybdenum-based friction modifier (M). If necessary, one or more other components selected from the above may be further mixed in.

[0088] There are no particular restrictions on the method of mixing the above components, but for example, one method may involve blending each component (component (B), component (M), and one or more selected from the other components) into a mineral oil base oil (A). Alternatively, each component may be blended in the form of a solution (dispersion) by adding a diluent oil or the like. After blending each component, it is preferable to stir and disperse it uniformly using a known method.

[0089] [engine] This embodiment also provides an engine containing the lubricating oil composition of the present invention described above. As mentioned above, examples of such engines include vehicle engines such as those for automobiles, but automobile engines are preferred, and automobile engines equipped with a hybrid mechanism or an idle stop mechanism that easily lowers oil temperature are more preferred. Furthermore, for the reasons described above, the engine of this embodiment preferably has a maximum height roughness (Rz) of less than 0.45 μm on the inner surface of the cylinder bore of the engine block, more preferably less than 0.30 μm, and even more preferably less than 0.20 μm.

[0090] [Engine lubrication methods] The present invention also provides an engine lubrication method using the lubricating oil composition of the above-described embodiment. The engine to be lubricated by the lubrication method of this embodiment is the same as the engine provided by the present invention as described above. In other words, a preferred embodiment of the engine lubrication method of this embodiment is an engine lubrication method that uses the above-described lubricating oil composition of the present invention to lubricate an engine of an automobile equipped with a hybrid mechanism or an idle stop mechanism, wherein the maximum height roughness (Rz) of the inner surface of the cylinder bore of the engine block is preferably less than 0.45 μm, more preferably less than 0.30 μm, and less than 0.20 μm.

[0091] [One aspect of the present invention provided] According to one aspect of the present invention, the following [1] to [9] are provided. [1] A mineral oil base oil (A), a polymer (B) with a weight-average molecular weight (Mw) of 100 to 15,000, and a molybdenum-based friction modifier (M), with a kinematic viscosity of 35.0 mm at 40°C. 2 Lubricating oil composition with a viscosity of / s or less. [2] The lubricating oil composition according to [1], wherein the content of polymer (B) is 0.1 to 5.0% by mass on a solid content basis for the total amount of lubricating oil. [3] The lubricating oil composition according to [1] or [2], wherein the polymer (B) is polyolefin (B-1). [4] The lubricating oil composition according to any one of [1] to [3], wherein the weight-average molecular weight (Mw) of the polymer (B) is 1,000 to 11,000. [5] The lubricating oil composition according to any one of [1] to [4], wherein the molybdenum-based friction modifier (M) comprises two or more selected from dinuclear molybdenum dithiocarbamate, trinuclear molybdenum dithiocarbamate, and molybdenamine complexes. [6] The lubricating oil composition according to any one of [1] to [5], wherein the content of the molybdenum-based friction modifier (M) is 50 to 2,000 ppm by mass in terms of molybdenum atoms on a basis of the total composition. [7] A lubricating oil composition according to any one of [1] to [6], used in an engine having components with a maximum surface height roughness (Rz) of less than 0.45 μm. [8] A lubricating oil composition according to any one of [1] to [7], used in an automobile engine equipped with a hybrid mechanism or an idle stop mechanism. A method for lubricating an engine, comprising a component having a maximum surface height roughness (Rz) of less than 0.45 μm, using a lubricating oil composition described in any of [1] to [7]. [Examples]

[0092] The present invention will be specifically described by the following examples, but the present invention is not limited to these examples. The various properties of each component used in the examples and comparative examples and the resulting lubricating oil compositions were measured by the following methods.

[0093] [Kinematic viscosity at 40°C, kinematic viscosity at 100°C, and viscosity index] The kinematic viscosity at 40°C, kinematic viscosity at 100°C, and viscosity index of the lubricating oil composition were measured or calculated in accordance with JIS K 2283:2000.

[0094] [150℃HTHS viscosity] The viscosity at 150°C HTHS was measured or calculated in accordance with JPI-5S-36-03.

[0095] [Content of molybdenum and phosphorus atoms] The molybdenum and phosphorus atom content was measured in accordance with JPI-5S-38-03.

[0096] [Weight average molecular weight (Mw), number average molecular weight (Mn), molecular weight distribution (Mw / Mn)] A Waters 1515 isocratic HPLC pump and a 2414 differential refractive index (RI) detector were used, with one TSKguardcolumn SuperHZ-L and two TSKSuperMultipore HZ-M columns from Tosoh Corporation installed in that order from upstream. Measurements were taken at a temperature of 40°C, with tetrahydrofuran as the mobile phase, a flow rate of 0.35 mL / min, and a sample concentration of 1.0 mg / mL. The results were then calculated in terms of standard polystyrene equivalents.

[0097] [Examples 1-11 and Comparative Examples 1-4] The following components were added in the amounts shown in Table 1 and thoroughly mixed to obtain a lubricating oil composition. Details of each component used in Examples 1-11 and Comparative Examples 1-4 are as follows. Note that the content figures in Table 1 are calculated based on resin content.

[0098] <Base oil (A)> • Mineral oil 1 (Classification in API base oil category: Group III, kinematic viscosity at 40°C: 19.8 mm) 2 / s, 100℃ kinematic viscosity: 4.0mm 2 / s, viscosity index: 125) • Mineral oil 2 (Classification in API base oil category: Group II, kinematic viscosity at 40°C: 406.6 mm) 2 / s, 100℃ kinematic viscosity: 30.6mm 2 / s, viscosity index: 106)

[0099] <polymer> [(B) Polymer equivalent to component] • Polymer 1 (olefin oligomer, weight-average molecular weight (Mw): 2,500, number-average molecular weight (Mn): 1,600, molecular weight distribution (Mw / Mn): 1.6) • Polymer 2 (olefin oligomer, weight-average molecular weight (Mw): 4,800, number-average molecular weight (Mn): 3,000, molecular weight distribution (Mw / Mn): 1.6) • Polymer 3 (olefin oligomer, weight-average molecular weight (Mw): 10,000, number-average molecular weight (Mn): 5,900, molecular weight distribution (Mw / Mn): 1.7) • Polymer 4 (Poly-α-olefin, weight-average molecular weight (Mw): 6,600, number-average molecular weight (Mn): 3,300, molecular weight distribution (Mw / Mn): 2.0) • Polymer 5 (Poly-α-olefin, weight-average molecular weight (Mw): 1,100, number-average molecular weight (Mn): 900, molecular weight distribution (Mw / Mn): 1.2) • Polymer 6 (polybutene, weight-average molecular weight (Mw): 5,300, number-average molecular weight (Mn): 4,500, molecular weight distribution (Mw / Mn): 1.2) Polymer 7 (Polybutene, weight-average molecular weight (Mw): 8,100, number-average molecular weight (Mn): 6,600, molecular weight distribution (Mw / Mn): 1.2) Polymer 8 (polybutene, weight-average molecular weight (Mw): 14,000, number-average molecular weight (Mn): 10,000, molecular weight distribution (Mw / Mn): 1.4) [Other polymers] Polymer 9 (olefin oligomer, weight-average molecular weight (Mw): 17,000, number-average molecular weight (Mn): 11,000, molecular weight distribution (Mw / Mn): 1.5) Polymer 10 (polymethacrylate, weight-average molecular weight (Mw): 26,000, number-average molecular weight (Mn): 19,000, molecular weight distribution (Mw / Mn): 1.4)

[0100] <Molybdenum-based friction modifier (M)> • Molybdenum DTC: Molybdenum dialkyldithiocarbamate (MoDTC, molybdenum atom content: 10.0% by mass), represented by the following structural formula. [ka] [In the above structural formula, R 1 , R 2 , R 3 , and R 4 Each of these groups is independently selected from the isooctyl group (8 carbon atoms: short-chain substituent group) and the isotridecyl group (13 carbon atoms: long-chain substituent group), and the molar ratio of isooctyl groups to isotridecyl groups in the entire molecule of molybdenum dialkyldithiocarbamate is 50:50. 1 and X 2 X is a sulfur atom, 3 and X 4 This is an oxygen atom. • Molybdenamine complex: (Molybdenum atom content: 7.9% by mass) • Trinuclear dithiocarbamate molybdenum (MoDTC, molybdenum atom content: 10% by mass)

[0101] <Other ingredients> Pour point depressant, antioxidant, zinc dialkyldithiophosphate (ZnDTP)

[0102] [Atomic content] In Table 1, the molybdenum atom content in the lubricating oil composition reflects the molybdenum atom content derived from the molybdenum-based friction modifier (M). In Tables 1 and 2, the phosphorus atom content in the lubricating oil composition reflects the phosphorus atom content derived from other additives, such as ZnDTP.

[0103] The lubricating oil compositions obtained in Examples 1-11 and Comparative Examples 1-4 were evaluated as follows. The results are shown in Table 1.

[0104] [Evaluation of friction coefficient] The coefficient of friction was measured using the prepared lubricating oil composition under the following conditions, using an SRV testing machine (manufactured by Optimol). First, the test was conducted by sliding the parts for 5 minutes at each temperature while increasing the temperature from 30°C to 140°C in 10°C increments, under the following conditions. During the final minute of the 140°C test described above, the coefficient of friction was measured every second, and the average value of the coefficient of friction during that final minute was calculated. Cylinder: AISI52100 • Standard disk: AISI52100 (Maximum height roughness (Rz): 0.45~0.65μm) • Mirror-finish disc: AISI52100 (Maximum height roughness (Rz): Less than 0.20 μm) • Frequency: 50Hz ·Amplitude: 1.5mm • Load: 400N Temperature: 30-140℃, increasing in 10-degree increments. • Test time: 5 minutes for each temperature

[0105] [Table 1]

[0106] As can be seen from Table 1, the lubricating oil compositions of Examples 1 to 11, which satisfy all the requirements of the present invention, have a friction coefficient of 0.098 or less with respect to a mirror-finished disc at an oil temperature of 30°C, demonstrating excellent friction coefficient reduction effects. On the other hand, it can be seen that the lubricating oil compositions of Comparative Examples 1 to 4 have a higher coefficient of friction than the lubricating oil compositions of Examples 1 to 11.

Claims

1. It contains mineral oil base oil (A), a polymer (B) with a weight-average molecular weight (Mw) of 100 to 15,000, and a molybdenum-based friction modifier (M). The molybdenum-based friction modifier (M) comprises molybdenum dialkyldithiocarbamate (M1) represented by the following general formula (m1), 【Chemistry 1】 [In the general formula (m1), R1, R2, R3, and R4 each independently represent either a short-chain substituent group (α) having 4 to 12 carbon atoms and an aliphatic hydrocarbon group having 13 to 22 carbon atoms and a long-chain substituent group (β). However, the molar ratio [(α) / (β)] of the short-chain substituent group (α) to the long-chain substituent group (β) in the total molecule of the dialkyldithiocarbamate molybdenum (M1) is 0.20 to 1.

0. Also, in the general formula (m1), X1, X2, X3, and X4 each independently represent either an oxygen atom or a sulfur atom.] The kinematic viscosity at 40°C is 35.0 mmHg. ２ A lubricating oil composition with a coefficient of s or less.

2. The lubricating oil composition according to claim 1, wherein the content of the polymer (B) is 0.1 to 5.0% by mass on a solid content basis for the total amount of lubricating oil.

3. The lubricating oil composition according to claim 1 or 2, wherein the polymer (B) is polyolefin (B-1).

4. The lubricating oil composition according to any one of claims 1 to 3, wherein the weight-average molecular weight (Mw) of the polymer (B) is 1,000 to 11,000.

5. The lubricating oil composition according to any one of claims 1 to 4, wherein the molybdenum-based friction modifier (M) further comprises one or more selected from trinuclear molybdenum dithiocarbamate and molybdenamine complexes.

6. The lubricating oil composition according to any one of claims 1 to 5, wherein the content of the molybdenum-based friction modifier (M) is 50 to 2,000 ppm by mass in terms of molybdenum atoms based on the total amount of the composition.

7. A lubricating oil composition according to any one of claims 1 to 6, for use in an engine having a component with a maximum surface height roughness (Rz) of less than 0.45 μm.

8. A lubricating oil composition according to any one of claims 1 to 7, for use in an automobile engine equipped with a hybrid mechanism or an idle stop mechanism.

9. A method for lubricating an engine, comprising a component having a maximum surface height roughness (Rz) of less than 0.45 μm, using the lubricating oil composition described in any one of claims 1 to 7.

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