Lubricating oil composition

Abstract

The present invention provides a lubricating oil composition having high solubility of molybdenum dithiocarbamate, excellent friction reduction, and excellent oxidation stability and low evaporation properties.　Provided is a lubricating oil composition containing a base oil (A), a polyol ester (B), and molybdenum dithiocarbamate (C), wherein: the base oil (A) is one or more selected from among group III base oils and group IV base oils in a base oil classification of the American Petroleum Institute; the polyol ester (B) contains an ester of a saturated fatty acid having 10 or more carbon atoms and neopentyl glycol; and the molybdenum atom content is 150-1800 mass ppm based on the total amount of the lubricating oil composition.

Description

lubricating oil composition

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

[0002] With the recent strengthening of environmental regulations, high fuel economy is required for lubricating oil compositions (internal combustion oils) used in internal combustion engines of vehicles such as automobiles. As one method for meeting such requirements, various methods for reducing the friction coefficient by blending a friction modifier into a lubricating oil composition have been studied. For example, a method for reducing the friction coefficient by blending a specific ether compound as a friction modifier into a lubricating oil composition is known (see, for example, Patent Document 1).

[0003] Japanese Patent Application Publication No. 9-176668

[0004] Organic molybdenum compounds are also known as the friction modifiers. In recent years, environmental concerns have led to a growing need for extending the life of internal combustion engine oils. For example, methods for extending the life of internal combustion engine oils have been studied, using as the main component a base oil classified as Group III or IV in the base oil classification of the American Petroleum Institute (API), which has excellent oxidation stability and low evaporation properties. However, among the organic molybdenum compounds, molybdenum dithiocarbamate in particular has excellent friction-reducing properties, but its solubility in the base oils classified as Group III or IV is extremely low. Therefore, when molybdenum dithiocarbamate is added to a base oil classified as Group III or IV in order to achieve both improved friction-reducing properties and a longer life of the lubricating oil composition, the molybdenum dithiocarbamate is prone to precipitate during long-term storage, resulting in poor storage stability. Patent Document 1 discloses a (poly)glycerin ether having a specific structure as a friction modifier that is highly soluble in synthetic base oils, but does not consider the solubility of molybdenum dithiocarbamate in base oils. To improve various performances of internal combustion engine oils, it is necessary to combine molybdenum dithiocarbamate with a base oil classified as Group III or IV. However, the solubility of molybdenum dithiocarbamate in base oils classified as Group III or IV has not yet been fully considered.

[0005] An object of the present invention is to provide a lubricating oil composition that has high solubility of molybdenum dithiocarbamate, excellent friction-reducing properties, oxidation stability, and low evaporation properties.

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have found that the above-mentioned problems can be solved by a lubricating oil composition in which the base oil (A) is one or more selected from Group III base oils and Group IV base oils in the base oil classification of the American Petroleum Institute, the composition contains a polyol ester, the polyol ester containing an ester of a saturated fatty acid having 10 or more carbon atoms and neopentyl glycol, and the content of molybdenum dithiocarbamate is adjusted to a specific range. Based on the above findings, the present inventors have conducted further research and have completed the present invention.

[0007] According to the present invention, there is provided the following [1]: [1] A lubricating oil composition containing a base oil (A), a polyol ester (B), and a molybdenum dithiocarbamate (C), wherein the base oil (A) is one or more selected from Group III base oils and Group IV base oils in the base oil classification of the American Petroleum Institute, the polyol ester (B) comprises an ester of a saturated fatty acid having 10 or more carbon atoms and neopentyl glycol, and the molybdenum atom content is 150 to 1800 ppm by mass based on the total amount of the lubricating oil composition.

[0008] According to the present invention, it is possible to provide a lubricating oil composition which has high solubility of molybdenum dithiocarbamate, excellent friction reducing properties, oxidation stability and low evaporation properties.

[0009] The upper and lower limit values ​​of the numerical ranges described in this specification can be combined in any way. For example, when "A to B" and "C to D" are described as numerical ranges, the numerical ranges "A to D" and "C to B" are also included in the scope of the present invention. Furthermore, the numerical range "lower limit to upper limit" described in this specification means that the range is equal to or greater than the lower limit and equal to or less than the upper limit, unless otherwise specified. Furthermore, in this specification, the numerical values ​​in the examples are numerical values ​​that can be used as upper or lower limit values.

[0010] [Embodiments of Lubricating Oil Composition] The lubricating oil composition of this embodiment contains a base oil (A), a polyol ester (B), and a molybdenum dithiocarbamate (C), wherein the base oil (A) is one or more selected from Group III base oils and Group IV base oils in the base oil classification of the American Petroleum Institute, the polyol ester (B) comprises an ester of a saturated fatty acid having 10 or more carbon atoms and neopentyl glycol, and the molybdenum atom content is 150 to 1800 ppm by mass based on the total amount of the lubricating oil composition.

[0011] In the following description, the "base oil (A)," the "polyol ester (B)," and the "molybdenum dithiocarbamate (C)" will also be referred to as "component (A)," "component (B)," and "component (C)," respectively.

[0012] The lubricating oil composition of this embodiment may be composed only of component (A), component (B), and component (C), or may further contain components other than component (A), component (B), and component (C). In the lubricating oil composition of this embodiment, the total content of component (A), component (B), and component (C) is preferably 50 mass% or more, more preferably 60 mass% or more, even more preferably 65 mass% or more, still more preferably 70 mass% or more, even more preferably 75 mass% or more, and even more preferably 78 mass% or more, based on the total amount of the lubricating oil composition.

[0013] Each component contained in the lubricating oil composition of this embodiment will be described in detail below.

[0014] <Base Oil (A)> The lubricating oil composition of this embodiment contains, as base oil (A), one or more base oils selected from base oils classified into Groups III and IV of the American Petroleum Institute base oil classification. As base oil (A), one or more selected from the group consisting of mineral oils and synthetic oils classified into Groups III and IV of the American Petroleum Institute base oil classification, which have conventionally been used as base oils for lubricating oil compositions, can be used without particular limitation.

[0015] As the base oil classified as Group III of the American Petroleum Institute's base oil classification, any base oil classified as Group III of the American Petroleum Institute's base oil classification that has conventionally been used as a base oil for lubricating oil compositions can be used without any particular limitation. Examples of such base oils include mineral oils obtained by vacuum distilling atmospheric residue obtained by atmospheric distillation of crude oils such as paraffinic crude oil, intermediate crude oil, or naphthenic crude oil, and then subjecting the distillate obtained to one or more refining processes such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining; 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); and plant-derived hydrocarbon lubricating base oils (for example, SynNova (registered trademark) 4 Base Oil and SynNova (registered trademark) 9 Base Oil, manufactured by Novvi, which are hydrogenated reaction products of octadecene and hexadecene).

[0016] As the base oil classified as Group IV of the base oil classification of the American Petroleum Institute, any base oil classified as Group IV of the base oil classification of the American Petroleum Institute that has conventionally been used as a base oil for lubricating oil compositions can be used without particular limitation.

[0017] The mineral oils may be used alone or in combination of two or more. The synthetic oils may be used alone or in combination of two or more. Furthermore, one or more mineral oils may be used in combination with one or more synthetic oils.

[0018] The kinematic viscosity of the base oil (A) is not particularly limited, but is preferably in the following range: The base oil (A) preferably has a kinematic viscosity at 100°C (hereinafter also referred to as "100°C kinematic viscosity") of 1.0 mm ２ / s or more 21.9 mm ２ / s or less, more preferably 2.0 mm ２ / s or more 16.3mm ２ / s or less, more preferably 3.8 mm ２ / s or more 12.5mm ２ / s or less.

[0019] The viscosity index of the base oil (A) is not particularly limited, but is preferably within the following ranges. The viscosity index of the base oil (A) is preferably 120 or more, more preferably 124 or more, and even more preferably 130 or more. In this specification, the 100°C kinematic viscosity and viscosity index of the base oil (A) refer to values ​​measured in accordance with JIS K2283:2000. When the base oil (A) is a mixed base oil containing two or more base oils, the 100°C kinematic viscosity and viscosity index of the mixed base oil preferably fall within the above-mentioned ranges.

[0020] In this embodiment, the content of base oil (A) in the lubricating oil composition is preferably 45.0 mass% or more, more preferably 50.0 mass% or more, and even more preferably 60.0 mass% or more, based on the total amount of the lubricating oil composition. It is also preferably 95.0 mass% or less, more preferably 90.0 mass% or less, and even more preferably 85.0 mass% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 45.0 mass% to 95.0 mass%, more preferably 50.0 mass% to 90.0 mass%, and even more preferably 60.0 mass% to 85.0 mass%.

[0021] <Polyol Ester (B)> The lubricating oil composition of this embodiment contains a polyol ester (B), which includes an ester of a saturated fatty acid having 10 or more carbon atoms and neopentyl glycol. The inclusion of an ester of a saturated fatty acid having 10 or more carbon atoms and neopentyl glycol in the lubricating oil composition can improve the solubility of the molybdenum dithiocarbamate (C) in the lubricating oil composition. While the reason for this is unclear, it is presumed that a high level of balance is achieved between the effect of improving the solubility of the molybdenum dithiocarbamate by the polyol ester (B) having a specific structure and the effect of improving the oil solubility of the polyol ester (B) by the hydrocarbon groups of the fatty acid and the hydrocarbon groups of neopentyl glycol. Furthermore, the absence of unsaturated bonds in the fatty acid constituting the polyol ester (B) can improve the oxidation stability of the lubricating oil composition. Furthermore, the low volatility of the lubricating oil composition can be improved by the fatty acid constituting the polyol ester (B) having 10 or more carbon atoms.

[0022] In this embodiment, the polyol ester (B) contains an ester of a saturated fatty acid having 10 or more carbon atoms and neopentyl glycol, as described above. Neopentyl glycol is a compound represented by the following structural formula (b1).

[0023]

[0024] As the saturated fatty acid used as the raw material for polyol ester (B), from the viewpoint of improving the low volatility of the lubricating oil composition, saturated fatty acids having 10 or more carbon atoms are preferred, saturated fatty acids having 10 to 30 carbon atoms are more preferred, saturated fatty acids having 10 to 27 carbon atoms are even more preferred, saturated fatty acids having 10 to 24 carbon atoms are even more preferred, and saturated fatty acids having 10 to 20 carbon atoms are even more preferred. The saturated fatty acids constituting polyol ester (B) may be linear or branched. Furthermore, polyol ester (B) may be a partial ester or a complete ester of neopentyl glycol, but it is preferred that it contains a complete ester of neopentyl glycol from the viewpoint of making it easier to exert the effects of the present invention.

[0025] The saturated fatty acid used as the raw material for polyol ester (B) is not particularly limited as long as it has 10 or more carbon atoms, and specific examples include various decanoic acids, various undecanoic acids, various dodecanoic acids, various tridecanoic acids, various tetradecanoic acids, various pentadecanoic acids, various hexadecanoic acids, various heptadecanoic acids, various octadecanoic acids, various nonadecanoic acids, various icosanoic acids, various docosanoic acids, various tetracosanoic acids, various hexacosanoic acids, various octacosanoic acids, various triacontanoic acids, etc. In this specification, the term "various" in "various decanoic acids" includes linear and branched structural isomers thereof.

[0026] In this embodiment, the content of the polyol ester (B) is preferably 0.1 mass% or more, more preferably 0.2 mass% or more, even more preferably 0.4 mass% or more, and even more preferably 0.8 mass% or more, based on the total amount of the lubricating oil composition. It is also preferably 35 mass% or less, more preferably 30 mass% or less, even more preferably 27 mass% or less, and even more preferably 25 mass% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 0.1 mass% to 35 mass%, more preferably 0.2 mass% to 30 mass%, even more preferably 0.4 mass% to 27 mass%, and even more preferably 0.8 mass% to 25 mass%.

[0027] In the present embodiment, the polyol ester (B) may contain an ester other than an ester of a saturated fatty acid having 10 or more carbon atoms and neopentyl glycol, but from the viewpoint of making it easier to exert the effects of the present invention, it preferably does not contain an ester other than an ester of a saturated fatty acid having 10 or more carbon atoms and neopentyl glycol. The content of the ester other than an ester of a saturated fatty acid having 10 or more carbon atoms and neopentyl glycol in the polyol ester (B) is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, still more preferably 0.01% by mass, and even more preferably 0% by mass, based on the total amount of the polyol ester (B).

[0028] In the lubricating oil composition of this embodiment, these polyol esters (B) may be used alone or in combination of two or more.

[0029] <Ratio of Base Oil (A) to Polyol Ester (B)> In order to more easily exhibit the effects of the present invention, the lubricating oil composition of this embodiment preferably has a ratio of the base oil (A) to the polyol ester (B) [(A) / (B)] in mass ratio of 1.0 to 800, more preferably 2.0 to 400, and even more preferably 2.5 to 200.

[0030] <Molybdenum dithiocarbamate (C)> The lubricating oil composition of this embodiment contains molybdenum dithiocarbamate (C) and contains 150 to 1800 ppm by mass of molybdenum atoms derived from the molybdenum dithiocarbamate (C) based on the total amount of the lubricating oil composition. When the molybdenum atom content is 150 ppm by mass or more based on the total amount of the lubricating oil composition, sufficient friction reduction properties can be exhibited. Furthermore, when the molybdenum atom content is 1800 ppm by mass or less based on the total amount of the lubricating oil composition, sufficient storage stability can be exhibited. Examples of molybdenum dithiocarbamate (C) include binuclear molybdenum dithiocarbamates containing two molybdenum atoms per molecule and trinuclear molybdenum dithiocarbamates containing three molybdenum atoms per molecule.

[0031] Examples of the dinuclear molybdenum dithiocarbamate include a compound represented by the following general formula (c1) and a compound represented by the following general formula (c2).

[0032]

[0033] In the above general formulas (c1) and (c2), R １１ ~R １４ Each of X independently represents a hydrocarbon group, and these may be the same or different. １１ ~X １８ each independently represents an oxygen atom or a sulfur atom, and may be the same as or different from each other. １１ ~X １８At least two of R are sulfur atoms. １１ ~R １４ The hydrocarbon group that can be selected as the alkyl group preferably has 6 to 22 carbon atoms.

[0034] R in the above general formulas (c1) and (c2) １１ ~R １４ Examples of the hydrocarbon group that can be selected as include alkyl groups, alkenyl groups, cycloalkyl groups, aryl groups, alkylaryl groups, and arylalkyl groups. Examples of the alkyl group include hexyl groups, heptyl groups, octyl groups, nonyl groups, decyl groups, undecyl groups, dodecyl groups, tridecyl groups, tetradecyl groups, pentadecyl groups, hexadecyl groups, heptadecyl groups, and octadecyl groups. Examples of the alkenyl group include hexenyl groups, heptenyl groups, octenyl groups, nonenyl groups, decenyl groups, undecenyl groups, dodecenyl groups, tridecenyl groups, tetradecenyl groups, and pentadecenyl groups. Examples of the cycloalkyl group include a cyclohexyl group, a dimethylcyclohexyl group, an ethylcyclohexyl group, a methylcyclohexylmethyl group, a cyclohexylethyl group, a propylcyclohexyl group, a butylcyclohexyl group, and a heptylcyclohexyl group. Examples of the aryl group include a phenyl group, a naphthyl group, an anthracenyl group, a biphenyl group, and a terphenyl group. Examples of the alkylaryl group include a tolyl group, a dimethylphenyl group, a butylphenyl group, a nonylphenyl group, and a dimethylnaphthyl group. Examples of the arylalkyl group include a methylbenzyl group, a phenylmethyl group, a phenylethyl group, and a diphenylmethyl group.

[0035] Among these, dialkylmolybdenum dithiocarbamate (C3) represented by the following structural formula (c3) is preferred.

[0036] In the general formula (c3), R １ , R ２ , R ３ , and R ４each independently represents a group of short-chain substituents (α) that are aliphatic hydrocarbon groups having 4 to 12 carbon atoms or a group of long-chain substituents (β) that are aliphatic hydrocarbon groups having 13 to 22 carbon atoms. １ , X ２ , X ３ , and X ４ each independently represents an oxygen atom or a sulfur atom.

[0037] 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. Specific examples include butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, and dodecenyl groups. These may be linear or branched. The number of carbon atoms in the aliphatic hydrocarbon groups 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 more easily achieving the effects of the present invention.

[0038] 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. Specific examples include tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosyl, henicosyl, docosyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl, octadecenyl, oleyl, nonadecenyl, icosenyl, henicosyl, and docosenyl groups. These may be linear or branched. 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.

[0039] Here, the compound (C3) represented by the general formula (c3) may contain only the short-chain substituent group (α) or the long-chain substituent group (β), or may contain both the short-chain substituent group (α) and the long-chain substituent group (β). Preferably, the molar ratio of the short-chain substituent group (α) to the long-chain substituent group (β) in the entire molecule [(α) / (β)] is 0 to 2.0. More preferably, the molar ratio of the short-chain substituent group (α) to the long-chain substituent group (β) in the entire molecule [(α) / (β)] is 0.050 to 2.0. When the molar ratio [(α) / (β)] is 0.050 or more, the friction-reducing effect is easily improved. Furthermore, when the molar ratio [(α) / (β)] is 2.0 or less, low-temperature storage stability is easily ensured. Here, from the viewpoint of more easily improving the friction-reducing effect, the molar ratio [(α) / (β)] is preferably 0.060 or more, more preferably 0.070 or more. Furthermore, from the viewpoint of more easily ensuring low-temperature storage stability, the molar ratio [(α) / (β)] is preferably 1.8 or less, more preferably 1.5 or less, even more preferably 1.2 or less, and even more preferably 1.1 or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, the molar ratio is preferably 0.060 to 1.8, more preferably 0.070 to 1.5, even more preferably 0.070 to 1.2, and even more preferably 0.070 to 1.1.

[0040] Here, when compound (C3) contains both the short-chain substituent group (α) and the long-chain substituent group (β), the short-chain substituent group (α) and the long-chain substituent group (β) may or may not coexist in the same molecule. That is, it is sufficient that the average molar ratio [(α) / (β)] of the short-chain substituent group (α) to the long-chain substituent group (β) in all molecules of compound (C3) represented by general formula (c3) is in the range of 0.050 to 2.0. Therefore, when compound (C3) contains both the short-chain substituent group (α) and the long-chain substituent group (β), compound (C3) contains R １ , R ２ , R ３ and R ４ may be present in the molecule group (c3-1) in which all of R are short-chain substituent groups (α), １ , R２ , R ３ and R ４ may be present in the molecule group (c3-2) in which all of R １ , R ２ , R ３ and R ４ A molecular group (c3-3) in which a part of the group is a short-chain substituent group (α) and the rest is a long-chain substituent group (β) may be mixed.

[0041] Examples of trinuclear molybdenum dithiocarbamates include compounds represented by the following general formula (c4): ３ S ｋ E ｍ L ｎ A ｐ Q ｚ (c4)

[0042] In the general formula (c4), k is an integer of 1 or more, m is an integer of 0 or more, and k+m is an integer of 4 to 10, preferably an integer of 4 to 7. n is an integer of 1 to 4, and p is an integer of 0 or more. z is an integer of 0 to 5, including non-stoichiometric values. Each E is independently an oxygen atom or a selenium atom, and is capable of substituting, for example, sulfur in the core described below. Each L is independently an anionic ligand having an organic group containing a carbon atom, and the total number of carbon atoms in the organic group in each ligand is 14 or more, and the ligands may be the same or different. Each A is independently an anion other than L. Each Q is independently an electron-donating neutral compound, and is present to fill a vacant coordination position on the trinuclear molybdenum compound.

[0043] In the lubricating oil composition of this embodiment, the content of molybdenum atoms derived from molybdenum dithiocarbamate (C) is, from the viewpoint of improving the friction reducing properties of the lubricating oil composition, preferably 150 mass ppm or more, more preferably 180 mass ppm or more, even more preferably 210 mass ppm or more, still more preferably 240 mass ppm or more, and even more preferably 270 mass ppm or more, based on the total amount of the lubricating oil composition. Also, from the viewpoint of improving the storage stability of the lubricating oil composition, it is preferably 1800 mass ppm or less, more preferably 1750 mass ppm or less, even more preferably 1700 mass ppm or less, still more preferably 1650 mass ppm or less, and even more preferably 1600 mass ppm or less. The upper and lower limits of these numerical ranges can be combined arbitrarily. Specifically, the molybdenum atom content is preferably 150 ppm by mass to 1800 ppm by mass, more preferably 180 ppm by mass to 1750 ppm by mass, even more preferably 210 ppm by mass to 1700 ppm by mass, still more preferably 240 ppm by mass to 1650 ppm by mass, and even more preferably 270 ppm by mass to 1600 ppm by mass. In this specification, the molybdenum atom content of the lubricating oil composition is a value measured in accordance with JPI-5S-38-03.

[0044] In the lubricating oil composition of this embodiment, the molybdenum dithiocarbamate (C) may be used alone or in combination of two or more types.

[0045] <Viscosity Index Improver (D)> The lubricating oil composition of this embodiment preferably contains a viscosity index improver (D) in addition to components (A) to (C). Examples of viscosity index improvers include comb polymers, non-dispersant polymethacrylate (PMA), dispersant polymethacrylate, olefin copolymers (olefin copolymers (OCPs); for example, ethylene-propylene copolymers), dispersant olefin copolymers, and styrene copolymers (for example, hydrogenated styrene-diene copolymers). One type of viscosity index improver may be used alone, or two or more types may be used in combination.

[0046] Here, it is preferable to use a comb polymer as the viscosity index improver (D). The mass average molecular weight (Mw) of the viscosity index improver (D) is preferably within the range of 50,000 to 1,000,000, more preferably within the range of 100,000 to 700,000, and even more preferably within the range of 150,000 to 500,000. The molecular weight distribution (Mw / Mn) of the viscosity index improver is preferably 9.0 or less, more preferably 7.0 or less, even more preferably 5.0 or less, and even more preferably 3.5 or less, and is usually 1.01 or more. The mass average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the viscosity index improver (D) are values ​​measured by gel permeation chromatography and calculated in terms of polystyrene.

[0047] The content of the viscosity index improver (D) is preferably 2 to 20 mass %, more preferably 4 to 15 mass %, and even more preferably 5 to 13 mass %, based on the total amount of the lubricating oil composition.

[0048] <Other Additives (E)> The lubricating oil composition of this embodiment may or may not contain other components (hereinafter also referred to as "other additives") other than component (A), component (B), component (C), and component (D) to the extent that the effects of the present invention are not significantly impaired. Examples of other additives (E) include metal-based detergents, dispersants, pour point depressants, antioxidants, antiwear agents, friction modifiers other than molybdenum dithiocarbamate (C), extreme pressure agents, rust inhibitors, antifoaming agents, oiliness improvers, metal deactivators, and demulsifiers. These may be used alone or in combination of two or more. In the lubricating oil composition of this embodiment, the total content of other additives (E) is preferably 4.0 to 14.0% by mass, more preferably 6.0 to 12.0% by mass, and even more preferably 8.5 to 10.0% by mass, based on the total amount of the lubricating oil composition.

[0049] [Physical Properties of Lubricating Oil Composition] <100°C Kinematic Viscosity and Viscosity Index> The lubricating oil composition of this embodiment preferably has a kinematic viscosity at 100°C of 4.0 mmHg or less. ２ / s or more 21.9 mm ２ / s, more preferably less than 5.0 mm ２ / s or more 16.3mm ２ / s, more preferably less than 6.1 mm ２ / s or more 12.5mm ２ The lubricating oil composition of this embodiment preferably has a viscosity index of 150 or more, more preferably 155 or more, and even more preferably 160 or more. In this specification, the 100°C kinematic viscosity and viscosity index of the lubricating oil composition refer to values ​​measured in accordance with JIS K2283:2000.

[0050] <HTHS (High Temperature High Shear) Viscosity at 150°C> The HTHS viscosity at 150°C of the lubricating oil composition of this embodiment is preferably 1.4 mPa·s or more, more preferably 1.7 mPa·s or more, even more preferably 2.0 mPa·s or more, and even more preferably 2.3 mPa·s or more. Also, it is preferably 4.0 mPa·s or less, more preferably less than 3.7 mPa·s, even more preferably less than 3.0 mPa·s, and even more preferably less than 2.9 mPa·s. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 1.4 mPa·s or more and 4.0 mPa·s or less, more preferably 1.7 mPa·s or more and less than 3.7 mPa·s, even more preferably 2.0 mPa·s or more and less than 3.0 mPa·s, and even more preferably 2.3 mPa·s or more and less than 2.9 mPa·s. The HTHS viscosity of the lubricating oil composition of this embodiment at 150°C is measured in accordance with ASTM D4683 using a TBS high temperature viscometer (Tapered Bearing Simulator Viscometer) at a shear rate of 10 ６ It can be measured in / s.

[0051] <Noack Evaporation Amount> The evaporation loss of the lubricating oil composition of this embodiment measured by the Noack method is preferably 13% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less, based on the total amount of the lubricating oil composition. The Noack evaporation amount can be measured in accordance with JPI-5S-41-2004 Method B.

[0052] <Oxidation Stability> After carrying out an ISOT test using the method described in the Examples below, the lubricating oil composition of this embodiment has a ratio of 100°C kinematic viscosity of the lubricating oil composition before and after the test of preferably 1.20 or less, more preferably 1.15 or less, even more preferably 1.10 or less, and still more preferably 1.05 or less.

[0053] <Friction Coefficient> The lubricating oil composition of this embodiment preferably has a friction coefficient of 0.08 or less, more preferably 0.07 or less, and even more preferably 0.06 or less, measured in accordance with the SRV test described in the Examples below.

[0054] [Method for Producing Lubricating Oil Composition] The method for producing the lubricating oil composition of this embodiment is not particularly limited. For example, the method for producing the lubricating oil composition of this embodiment includes a step of mixing a base oil (A), a polyol ester (B), and a molybdenum dithiocarbamate (C), wherein the base oil (A) is one or more selected from Group III base oils and Group IV base oils in the base oil classification of the American Petroleum Institute, and the polyol ester (B) comprises an ester of a saturated fatty acid having 10 or more carbon atoms and neopentyl glycol, and the molybdenum atom content is adjusted to 150 to 1800 ppm by mass based on the total amount of the lubricating oil composition. In the above step, when additives other than components (A) to (C) are blended, the additives may be blended simultaneously with components (A) to (C) or separately. Furthermore, each component may be blended after being formed into a solution (dispersion) by adding a diluent oil or the like. After blending the components, it is preferable to uniformly disperse them by stirring using a known method. The preferred embodiments of each of the above components are as described above.

[0055] [Uses of Lubricating Oil Composition] The lubricating oil composition of this embodiment has high solubility of molybdenum dithiocarbamate, excellent friction-reducing properties, and excellent oxidation stability and low evaporation properties. Therefore, the lubricating oil composition of this embodiment is preferably used in internal combustion engines, i.e., used as an internal combustion oil, more preferably used in automobile engines, and even more preferably used in gasoline engines. It is also suitable for use in automobile engines equipped with hybrid mechanisms. Therefore, the lubricating oil composition of this embodiment provides the following (1) to (4): (1) A method of using the lubricating oil composition of this embodiment in an internal combustion engine. (2) A method of using the lubricating oil composition of this embodiment in an automobile engine. (3) A method of using the lubricating oil composition of this embodiment in a gasoline engine. (4) A method of using the lubricating oil composition of this embodiment in an automobile engine equipped with a hybrid mechanism.

[0056] [Lubrication Method Using Lubricating Oil Composition] As explained regarding the uses of the lubricating oil composition, the lubricating oil composition of this embodiment is preferably used in internal combustion engines, more preferably in automobile engines, and even more preferably in gasoline engines. It is also suitably used in automobile engines equipped with a hybrid mechanism. Therefore, the lubricating oil composition of this embodiment provides the following (5) to (8). (5) A method for lubricating an internal combustion engine using the lubricating oil composition of this embodiment. (6) A method for lubricating an automobile engine using the lubricating oil composition of this embodiment. (7) A method for lubricating a gasoline engine using the lubricating oil composition of this embodiment. (8) A method for lubricating an automobile engine equipped with a hybrid mechanism using the lubricating oil composition of this embodiment.

[0057] [One Aspect of the Present Invention Provided] In one aspect of the present invention, the following [1] to [6] are provided. [1] A lubricating oil composition containing a base oil (A), a polyol ester (B), and a molybdenum dithiocarbamate (C), wherein the base oil (A) is one or more selected from Group III base oils and Group IV base oils in the base oil classification of the American Petroleum Institute, and the polyol ester (B) comprises an ester of a saturated fatty acid having 10 or more carbon atoms and neopentyl glycol, and the molybdenum atom content is 150 to 1,800 ppm by mass based on the total amount of the lubricating oil composition. [2] The lubricating oil composition according to [1], wherein the saturated fatty acid has 10 to 30 carbon atoms. [3] The lubricating oil composition according to [1] or [2], wherein the content of esters other than the ester of a saturated fatty acid having 10 or more carbon atoms and neopentyl glycol is 5% by mass or less based on the total amount of the polyol ester (B). [4] The lubricating oil composition according to any one of [1] to [3], wherein the content of the polyol ester (B) is 30 mass% or less based on the total amount of the lubricating oil composition. [5] The lubricating oil composition according to any one of [1] to [4], further comprising a viscosity index improver. [6] The lubricating oil composition according to any one of [1] to [5], which is used as an internal combustion engine oil.

[0058] The present invention will be specifically described with reference to the following examples, although the present invention is not limited to the following examples.

[0059] [Methods for Measuring Various Physical Properties] Measurements of the various properties of the raw materials used in each Example and Comparative Example and the lubricating oil compositions of each Example and Comparative Example were carried out according to the procedures shown below.

[0060] (1) 100°C kinematic viscosity and viscosity index The 100°C kinematic viscosity and viscosity index of the base oil and lubricating oil composition were measured or calculated in accordance with JIS K2283: 2000. (2) HTHS viscosity at 150°C The HTHS viscosity was measured or calculated in accordance with ASTM D4683 using a TBS high temperature viscometer (Tapered Bearing Simulator Viscometer) at a temperature of 150°C and a shear rate of 10 ６(3) Molybdenum Atom Content: Measured in accordance with JPI-5S-38-03.

[0061] [Examples 1 to 9, Comparative Examples 1 to 6] The components listed below were mixed to prepare lubricating oil compositions having the compositions shown in Tables 1 and 2, and the evaluations described below were carried out. Details of each component used in preparing the lubricating oil compositions having the compositions shown in Tables 1 and 2 are described below.

[0062] <Base oil (A)> Base oil 1: a base oil classified as Group III in the base oil classification of the American Petroleum Institute (kinematic viscosity at 100°C = 4.3 mm ２ / s, viscosity index 137) Base oil 2: Synthetic oil classified as Group IV in the base oil classification of the American Petroleum Institute (kinematic viscosity at 100°C = 3.9 mm ２ / s, viscosity index 124) Base oil 3: Synthetic oil classified as Group IV in the base oil classification of the American Petroleum Institute (kinematic viscosity at 100°C = 5.9 mm ２ / s, viscosity index 132)

[0063] <Polyol ester (B)> Ester 1: a diester obtained by reacting a branched, saturated fatty acid having 18 carbon atoms with neopentyl glycol (kinematic viscosity at 100°C = 8.2 mm ２ / s, viscosity index 151) Ester 2: a diester obtained by reacting a saturated fatty acid having 8 carbon atoms with neopentyl glycol (kinematic viscosity at 100°C = 2.0 mm ２ / s, viscosity index 47) Ester 3: a diester obtained by reacting a branched unsaturated fatty acid having 18 carbon atoms with neopentyl glycol (kinematic viscosity at 100°C = 7.2 mm ２ / s, viscosity index 196) Ester 4: a diester obtained by reacting a linear saturated fatty acid having 10 carbon atoms with neopentyl glycol (kinematic viscosity at 100°C = 2.9 mm ２ / s, viscosity index 141)

[0064] <Molybdenum dithiocarbamate (C)> A binuclear molybdenum dithiocarbamate represented by the following general formula (c3) (molybdenum atom content: 10.0 mass%, sulfur atom content: 11.5 mass%) In the above general formula (c3), R １ , R ２ , R ３ , and R４ are each independently selected from an isooctyl group (having 8 carbon atoms: a short-chain substituent group) and an isotridecyl group (having 13 carbon atoms: a long-chain substituent group), and the molar ratio of the isooctyl groups to the isotridecyl groups in all molecules of the molybdenum dialkyldithiocarbamate is 50:50. １ and X ２ is a sulfur atom, and X ３ and X ４ is an oxygen atom. In the table, it is expressed as "MoDTC."

[0065] <Viscosity index improver (D)> Comb polymer (mass average molecular weight (Mw): 260,000, molecular weight distribution (Mw / Mn): 3.1)

[0066] <Other additives (E)> Zinc dialkyldithiophosphate, metallic detergent, dispersant, antioxidant, pour point depressant, antifoaming agent

[0067] [Evaluation Method] The tests described below were carried out and various evaluations were carried out.

[0068] [Evaporation loss by Noack method] Measured in accordance with JPI-5S-41-2004 Method B. A lubricating oil composition was evaluated as having excellent low volatility when the evaporation loss by Noack method was 13 mass % or less based on the total amount of the lubricating oil composition.

[0069] [Storage Stability] (1) Test Method 100 mL of each of the lubricating oil compositions of Examples 1 to 9 and Comparative Examples 1 to 6 was placed in a 100 mL glass bottle and allowed to stand at -5°C for 5 days. After that, the presence or absence of precipitation was determined when the bottle was returned to room temperature. The presence or absence of precipitation was determined visually. (2) Evaluation Criteria A lubricating oil composition in which no precipitation occurred was rated as passing, and a lubricating oil composition in which precipitation occurred was rated as failing. In the evaluation results shown in Tables 1 and 2, "Rating A" means passing, and "Rating B" means failing.

[0070] [Oxidation Stability] Copper pieces and iron pieces were added to the test oil (lubricating oil composition) as catalysts, and the ISOT test was conducted in accordance with JIS K 2514-1:2013 to forcibly degrade the test oil. The test temperature (oil temperature) was 165.5°C. Then, for the test oil 96 hours after the start of the ISOT test, the ratio of the 100°C kinematic viscosity to that of the lubricating oil composition (new oil) before the ISOT test was measured. The smaller the 100°C kinematic viscosity ratio, the more excellent the oxidation stability. Note that when the 100°C kinematic viscosity ratio was 1.05 or less, the lubricating oil composition was evaluated as having excellent oxidation stability.

[0071] [Friction Coefficient] Using an SRV tester (manufactured by Optimol), the friction coefficient was measured when the prepared lubricating oil composition was used under the following conditions. The smaller the friction coefficient, the better the friction reduction ability. The average value of the friction coefficients over the 10 minutes from 20 minutes after the start of the test to the end of the test was taken as the friction coefficient. A lubricating oil composition with a friction coefficient of 0.08 or less was evaluated as having excellent friction reduction ability. Cylinder: SUJ-2 Standard disc: AISI52100 (maximum height roughness (Rz): 0.45 to 0.65 μm) Mirror disc: AISI52100 (maximum height roughness (Rz): less than 0.20 μm) Vibration frequency: 50 Hz Amplitude: 1.5 mm Load: 400 N Temperature: 80°C Test time: 30 minutes

[0072] The properties of each lubricating oil composition and the results of each test are shown in Tables 1 and 2.

[0073]

[0074]

[0075] <Evaluation Results> Tables 1 and 2 reveal the following. The lubricating oil compositions of Examples 1 to 9 have good storage stability and excellent solubility of molybdenum dithiocarbamate (C). Furthermore, they are excellent in all of friction-reducing properties, low volatility, and oxidation stability. In contrast, lubricating oil compositions that do not contain polyol ester (B), such as the lubricating oil composition of Comparative Example 2, have poorer storage stability and poorer solubility of molybdenum dithiocarbamate (C) than Examples 1 to 9. Furthermore, lubricating oil compositions having a molybdenum atom content of less than 150 ppm by mass, based on the total amount of the lubricating oil composition, such as the lubricating oil compositions of Comparative Examples 1 and 3, have poor friction-reducing properties, while lubricating oil compositions having a molybdenum atom content of more than 1,800 ppm by mass, based on the total amount of the lubricating oil composition, such as the lubricating oil composition of Comparative Example 4, have poor storage stability and poor solubility of molybdenum dithiocarbamate (C). It is also found that lubricating oil compositions in which the fatty acid constituting the polyol ester (B) has less than 10 carbon atoms, such as the lubricating oil composition of Comparative Example 5, are inferior in low volatility, and lubricating oil compositions in which the fatty acid constituting the polyol ester (B) is an unsaturated fatty acid, such as the lubricating oil composition of Comparative Example 6, are inferior in oxidation stability.

Claims

1. A lubricating oil composition containing a base oil (A), a polyol ester (B), and a molybdenum dithiocarbamate (C), wherein the base oil (A) is one or more selected from Group III base oils and Group IV base oils in the base oil classification of the American Petroleum Institute, the polyol ester (B) comprises an ester of a saturated fatty acid having 10 or more carbon atoms and neopentyl glycol, and the molybdenum atom content is 150 to 1,800 ppm by mass based on the total amount of the lubricating oil composition.

2. The lubricating oil composition according to claim 1, wherein the saturated fatty acid has 10 to 30 carbon atoms.

3. The lubricating oil composition according to claim 1 or 2, wherein the content of esters other than the ester of a saturated fatty acid having 10 or more carbon atoms and neopentyl glycol is 5 mass% or less based on the total amount of the polyol ester (B).

4. The lubricating oil composition according to any one of claims 1 to 3, wherein the content of the polyol ester (B) is 30 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, further comprising a viscosity index improver.

6. The lubricating oil composition according to any one of claims 1 to 5, which is used as an internal combustion engine oil.

Images