Lubricating oil composition

Abstract

To provide a lubricating oil composition that is biodegradable and exhibits excellent oxidation stability.SOLUTION: A lubricating oil composition contains per 100 pts.mass of a specific ester compound (A), 0.05 to 1.5 pts.mass of a molybdenum compound (B) and 0.05 to 1.5 pts.mass of an epoxy compound (C) having a specific structure.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In recent years, new initiatives for environmental protection have been progressing worldwide, and lubricating oils that can reduce environmental impact have become more important than ever before. As lubricating oils that can reduce environmental impact, biodegradable lubricating oils that are easily decomposed in nature and have little impact on the ecosystem even in the event of a leak have attracted attention. For example, Patent Document 1 discloses a biodegradable lubricating oil composition that contains a base oil made of a plant-derived oil and a polyol ester, and a polymethacrylate blended therewith.

[0003] Meanwhile, as part of other efforts to protect the environment, countries are promoting the use of clean energy that does not emit CO2. Wind power generation is one type of clean energy. In wind power generation, wind strikes blades, causing them to rotate, and the rotation is transmitted to a gearbox via a power transmission shaft. The gearbox increases the rotational speed, and the rotation is converted into electricity by a generator. Gear oil is used in this gearbox to lubricate the gears and prevent wear. Gear oils for wind power generation equipment typically use lubricating oils based on mineral oil or hydrocarbon-based high-viscosity base oils such as poly-alpha-olefins. However, because wind power generation equipment is often used in natural environments, gear oils for wind power generation equipment must also be highly biodegradable. However, conventional lubricating oils based on mineral oil or hydrocarbon-based base oils such as poly-alpha-olefins are virtually non-biodegradable, and the search for alternatives is ongoing. For example, Patent Document 2 discloses a biodegradable lubricating oil composition useful as a gear oil, which is prepared by blending various additives into an ester base oil.

[0004] Furthermore, because the gearbox is installed at a high altitude, maintenance is not easy, and it is desirable to reduce the frequency of gearbox maintenance. Therefore, gear oil is required to have high oxidation stability to reduce the frequency of change. In recent years, due to the shortage of land area, floating offshore wind power generation has been attracting attention among wind power generation systems, and since maintenance is more advanced, even higher oxidation stability is required for gear oil. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-213920 [Patent Document 2] Special Publication No. 2005-520038 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a lubricating oil composition that is biodegradable and has excellent oxidation stability. [Means for solving the problem]

[0007] As a result of intensive research conducted by the present inventors to solve the above problems, they discovered that a biodegradable lubricating oil with excellent oxidation stability can be obtained by blending an ester compound of trimethylolpropane with a specific monovalent fatty acid and adipic acid with a molybdenum compound and a specific epoxy compound in a specific ratio, thereby completing the present invention.

[0008] That is, the present invention is as follows. A lubricating oil composition comprising 0.05 to 1.5 parts by mass of (B) a molybdenum compound and 0.05 to 1.5 parts by mass of (C) an epoxy compound represented by general formula (1) described below, relative to 100 parts by mass of the following (A) ester compound: (A): An ester compound of (a) trimethylolpropane, (b) a monovalent fatty acid having 8 to 12 carbon atoms, and (c) adipic acid, wherein the molar percentage of the component derived from the (a) trimethylolpropane is 25 to 42 mol%, the molar percentage of the component derived from the (b) monovalent fatty acid having 8 to 12 carbon atoms is 36 to 58 mol%, and the molar percentage of the component derived from the (c) adipic acid is 9 to 29 mol%, and the molar ratio of the component derived from the (c) adipic acid to the component derived from the (b) monovalent fatty acid having 8 to 12 carbon atoms is 0.1 to 0.5. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a lubricating oil composition that is biodegradable and has excellent oxidation stability. DETAILED DESCRIPTION OF THE INVENTION

[0010] The lubricating oil composition of the present invention will now be described. In the present invention, a numerical range defined using the symbol "to" includes both the upper and lower limits of the symbol "to." For example, "2 to 5" represents a range of 2 or more and 5 or less. In the present invention, the number of carbon atoms is sometimes simply expressed as Cx.

[0011] The lubricating oil composition of the present invention contains (A) an ester compound as a lubricating base oil, and (B) a molybdenum compound and (C) an epoxy compound represented by general formula (1) described below as additives, and may further contain other additives within the scope of the present disclosure. Each component contained in the lubricating oil composition of the present invention will now be described in detail.

[0012] <(A) Ester Compound> (A) The ester compound is a complex ester synthesized by an esterification reaction between (a) trimethylolpropane, (b) a monovalent fatty acid having 8 to 12 carbon atoms, and (c) adipic acid.

[0013] The (A) ester compound has excellent oxidation stability and heat resistance because (a) trimethylolpropane is used as the raw material alcohol.

[0014] In the (A) ester compound, (b) a monovalent fatty acid having 8 to 12 carbon atoms and (c) adipic acid are used as raw carboxylic acids. By using (b) a monovalent fatty acid having 8 to 12 carbon atoms (sometimes simply referred to as "(b) fatty acid" in the present invention), the lubricating oil composition of the present invention has good fluidity at low temperatures and is prevented from deteriorating in lubricity (extreme pressure properties) and increasing in viscosity. If the viscosity of the lubricating oil increases, the internal resistance of the lubricating oil itself will cause energy loss in the equipment using the lubricating oil, which may result in a decrease in power generation efficiency and fuel economy. Therefore, it is desirable to prevent the viscosity of the lubricating oil from increasing. When a monovalent fatty acid having less than 8 carbon atoms is used instead of (b) a monovalent fatty acid having 8 to 12 carbon atoms, the resulting ester compound does not have sufficient extreme-pressure properties, and even when an extreme-pressure agent is used in combination, the extreme-pressure properties of the lubricating oil composition may be insufficient.On the other hand, when a monovalent fatty acid having more than 12 carbon atoms is used instead of (b) a monovalent fatty acid having 8 to 12 carbon atoms, the resulting ester compound is likely to have a high viscosity and poor flowability at low temperatures. Furthermore, as the (b) fatty acid, from the viewpoint of the oxidation stability, low-temperature fluidity, lubricity (extreme pressure properties), and suppression of high viscosity of the lubricating oil composition of the present invention, a monovalent straight-chain saturated fatty acid having 8 to 12 carbon atoms is preferably used, that is, a monocarboxylic acid having a straight-chain hydrocarbon chain and no unsaturated bond in the molecule having 8 to 12 carbon atoms is preferably used. Examples of monovalent linear saturated fatty acids having 8 to 12 carbon atoms that can be preferably used in the present invention include caprylic acid, pelargonic acid, capric acid, undecylic acid, and lauric acid. Among these, at least one selected from the group consisting of caprylic acid, capric acid, and lauric acid is particularly preferably used. Furthermore, the smaller the carbon number of the (b) fatty acid, the lower the pour point of the resulting (A) ester compound and lubricating oil composition. Therefore, from the viewpoint of lowering the pour point of the (A) ester compound and lubricating oil composition, it is particularly preferable that the (b) fatty acid have 8 to 10 carbon atoms. These (b) fatty acids can be used alone or in combination of two or more. It is preferable to use a combination of two or more monovalent fatty acids with different carbon numbers as the (b) fatty acids in order to improve the fluidity of the lubricating oil composition at low temperatures, and it is particularly preferable to use a combination of caprylic acid and capric acid. To improve the fluidity of the lubricating oil composition at low temperatures, the total content of caprylic acid and capric acid is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more, relative to 100 mol% of the total amount of constituents derived from the (b) fatty acids.

[0015] The (A) ester compound further uses the dibasic acid (c) adipic acid as a raw carboxylic acid. By using adipic acid among dibasic acids, the lubricating oil composition of the present invention is more likely to exhibit the effects of various additives, and the oxidation stability and heat resistance of the (A) ester compound are improved. If succinic acid, which has a smaller carbon number, is used instead of adipic acid, the effects of various additives are less likely to be exhibited, and the resulting ester compound may not be suitable as a lubricating base oil. On the other hand, if a dimer acid with a larger carbon number or maleic acid containing a double bond is used instead of adipic acid, the oxidation stability of the resulting lubricating oil composition may be impaired.

[0016] The (A) ester compound contains the (a) trimethylolpropane-derived component in a molar percentage (referred to as "a" in the present invention). mol% ") is 25 to 42 mol %, and the molar percentage of the constituent component derived from the (b) monovalent fatty acid having 8 to 12 carbon atoms (in the present invention, "b mol% ") is 36 to 58 mol %, and the molar percentage of the constituent component derived from (c) adipic acid (in the present invention, "cmol% ") is 9 to 29 mol %, and the molar ratio of the (c) adipic acid-derived component to the (b) monovalent fatty acid-derived component having 8 to 12 carbon atoms [c mol% / b mol% ] is 0.1 to 0.5, where a mol% , b mol% and c mol% The sum of (a mol% +b mol% +c mol% ) is 100 mol%. In the (A) ester compound used in the present invention, the (a) trimethylolpropane-derived component is a residue of (a) trimethylolpropane, the (b) C8-12 monovalent fatty acid-derived component is a residue of (b) C8-12 monovalent fatty acid, and the (c) adipic acid-derived component is a residue of (c) adipic acid. In the ester compound (A) contained as the lubricating base oil, mol% , b mol% and c mol% When the content of the lubricating oil composition of the present invention is within the above range, the composition has excellent biodegradability, low-temperature fluidity, lubricity (extreme pressure properties) and wear resistance, and is prevented from becoming highly viscous. From this perspective, a mol% is preferably 27 to 40 mol %, more preferably 28 to 35 mol %, and even more preferably 28 to 32 mol %. mol% is preferably 43 to 56 mol%, more preferably 47 to 55 mol%, and even more preferably 48 to 52 mol%. mol% is preferably 12 to 27 mol %, more preferably 14 to 23 mol %, and even more preferably 18 to 22 mol %.

[0017] In the ester compound (A) used in the present invention, mol% , b mol% and c mol% (A) Ester compound 1 The values ​​were calculated from the amounts (mol) of constituent components derived from each raw material, which were analyzed by H NMR. Below1 The measurement conditions for H NMR are as follows: <Measurement conditions> ·Analytical equipment: 1 H NMR Solvent: deuterated chloroform

[0018] The ester compound (A) obtained under the above measurement conditions 1 By analyzing the H NMR chart, the amount of substance (mol) of each component of the (A) ester compound can be determined. Specifically, the following four peaks are used: Peak (I): 3.40-3.60 ppm = (a) Hydrogen at the α-position of the unreacted hydroxyl group of trimethylolpropane Peak (II): 4.00-4.20 ppm = (a) Hydrogen at the α-position of the reacted hydroxyl group of trimethylolpropane The total number of hydrogen atoms in peak (I) and peak (II) is six. Peak (III): 0.85-0.90 ppm = (b) the three hydrogen atoms bonded to the terminal carbon of monovalent fatty acids with 8-12 carbon atoms and (a) the three hydrogen atoms bonded to the carbon of trimethylolpropane. Peak (IV): 2.25-2.35 ppm = (c) four hydrogen atoms at the α-position of the carbonyl group of adipic acid and (b) two hydrogen atoms at the α-position of the carbonyl group of monovalent fatty acids with 8 to 12 carbon atoms

[0019] From the integral values ​​of the above four peaks, (a) the amount of substance of the constituent components derived from trimethylolpropane (a mol ), (b) the amount of constituents derived from monovalent fatty acids with 8 to 12 carbon atoms (b mol ), and (c) the amount of substance of the constituents derived from adipic acid (c mol ) can be calculated using the following formula: a mol = {Integral value of peak (I) + Integral value of peak (II)} / 6 b mol = {Integral value of peak (III) - (a mol ×3)} / 3 c mol = {Integral value of peak (IV) - (b mol ×2)} / 4

[0020] The a calculated above mol , b mol and c mol From the mole percentages of each, a mol% , b mol% and c mol% can be calculated using the following formula: a mol% =100×a mol / (a mol +b mol +c mol ) b mol% =100×b mol / (a mol +b mol +c mol ) c mol% =100×C mol / (a mol +b mol +c mol )

[0021] Also, the above amol% , b mol% and c mol% From this, the molar ratio of each constituent component can be calculated using the following formula. (b) Molar ratio of the component derived from monovalent fatty acids having 8 to 12 carbon atoms to the component derived from adipic acid (c) = c mol% / b mol% Molar ratio of (a) trimethylolpropane-derived component to (c) adipic acid-derived component = c mol% / a mol% (a) Molar ratio of the component derived from trimethylolpropane to (b) the component derived from monovalent fatty acids having 8 to 12 carbon atoms = b mol% / a mol%

[0022] In the (A) ester compound, the molar ratio of (c) adipic acid-derived component to (b) a monovalent fatty acid-derived component having 8 to 12 carbon atoms (c mol% / b mol% ) is 0.1 to 0.5. mol% / b mol% is 0.1 or more, it has excellent rust prevention properties, mol% / b mol% By keeping c at 0.5 or less, the viscosity is prevented from increasing and the biodegradability is excellent. mol% / b mol% is preferably from 0.15 to 0.5, more preferably from 0.2 to 0.5, further preferably from 0.25 to 0.45, and particularly preferably from 0.4 to 0.45.

[0023] In the (A) ester compound, the molar ratio of the (c) adipic acid-derived component to the (a) trimethylolpropane-derived component (c mol% / a mol% ) is preferably 0.3 to 1.0. mol% / a mol% When c is 0.3 or more, the rust prevention property is improved, and when it is 1.0 or less, the viscosity is prevented from increasing. mol% / a mol% is more preferably 0.4 to 0.7.

[0024] In the (A) ester compound, the molar ratio of (b) a monovalent fatty acid-derived component having 8 to 12 carbon atoms to (a) a trimethylolpropane-derived component (b mol% / a mol% ) is preferably 1.0 to 2.2. mol% / a mol% When b is 1.0 or more, the viscosity is prevented from increasing, and when b is 2.2 or less, the rust prevention property is improved. mol% / a mol% is more preferably 1.5 to 2.0.

[0025] The (A) ester compound preferably has an acid value of 10.0 mgKOH / g or less. When the (A) ester compound has an acid value of 10.0 mgKOH / g or less, the oxidation stability of the lubricating oil composition is improved. From this perspective, the acid value of the (A) ester compound is more preferably 5.0 mgKOH / g or less, even more preferably 3.0 mgKOH / g or less, even more preferably 2.5 mgKOH / g or less, and particularly preferably 1.5 mgKOH / g or less. The lower limit of the acid value of the (A) ester compound is not particularly limited, but may be 0.01 mgKOH / g or more from the viewpoint of ease of production. The acid value of the (A) ester compound can be adjusted, for example, by the reaction time during synthesis of the ester compound. In the present invention, the acid value is measured in accordance with JIS K 0070.

[0026] (A) The ester compound has a kinematic viscosity of 100 to 500 mm at 40°C. 2 (A) The ester compound preferably has a kinematic viscosity of 100 mm / s at 40°C. 2 When the kinematic viscosity of the ester compound (A) at 40°C is 500 mm / s or more, the lubricating oil composition of the present invention exhibits good lubricity (extreme pressure properties). 2 From this viewpoint, the kinematic viscosity of the ester compound (A) at 40°C is more preferably 150 to 450 mm / s. 2 / s, and more preferably 200 to 400 mm 2 / s, and particularly preferably 300 to 370 mm 2 / s. In the present invention, the kinematic viscosity at 40°C is measured in accordance with JIS K 2283.

[0027] The pour point of the (A) ester compound is preferably −15.0° C. or lower. When the (A) ester compound has a pour point of −15.0° C. or lower, the lubricating oil composition of the present invention has good fluidity at low temperatures, making it more suitable for use in cold climates. From this perspective, the pour point of the (A) ester compound is more preferably −25.0° C. or lower, even more preferably −35.0° C. or lower, and particularly preferably −40.0° C. or lower. The pour point of the (A) ester compound can be adjusted by, for example, changing the type of the (b) fatty acid used in the (A) ester compound or mol% , b mol% and c mol% can be adjusted to a desired value. In the present invention, the pour point is measured in accordance with JIS K 2269.

[0028] The (A) ester compound preferably has a biodegradability of 60% or more as determined in accordance with OECD 301F. The excellent biodegradability of the (A) ester compound, which is the lubricating base oil, also makes the biodegradability of the lubricating oil composition of the present invention even more excellent.

[0029] <(B) Molybdenum Compounds> The lubricating oil composition of the present invention contains (B) a molybdenum compound as an oiliness agent. As the (B) molybdenum compound, for example, a sulfur-containing organic molybdenum compound is preferred, and among these, at least one selected from molybdenum dithiocarbamate and molybdenum dithiophosphate is preferred, and at least one selected from molybdenum dialkyldithiocarbamate and molybdenum dialkyldithiophosphate is particularly preferred.

[0030] Examples of molybdenum dithiocarbamates include compounds represented by the following general formula (B1), and examples of molybdenum dithiophosphates include compounds represented by the following general formula (B2).

[0031] [ka]

[0032] In the above general formulas (B1) and (B2), R1 to R8 are monovalent hydrocarbon groups, X1 and X2 are oxygen atoms or sulfur atoms, and Y1 and Y2 are oxygen atoms or sulfur atoms. R1 to R8 may be the same or different, X1 and X2 may be the same or different, and Y1 and Y2 may be the same or different.

[0033] The monovalent hydrocarbon groups represented by R1 to R8 in general formulas (B1) and (B2) preferably have 1 to 30 carbon atoms. Examples of monovalent hydrocarbon groups having 1 to 30 carbon atoms include linear or branched alkyl groups having 1 to 30 carbon atoms; cycloalkyl groups having 4 to 30 carbon atoms; alkenyl groups having 2 to 30 carbon atoms; and aryl, alkylaryl, or arylalkyl groups having 6 to 30 carbon atoms. In the arylalkyl group, the alkyl group may be bonded to any position. Among these, the monovalent hydrocarbon groups represented by R1 to R8 are preferably alkyl groups, from the viewpoints of easily exerting a synergistic effect with the epoxy compound (C) and easily improving the oxidation stability of the lubricating oil composition. More preferably, the monovalent hydrocarbon groups are at least one selected from linear or branched alkyl groups having 1 to 30 carbon atoms and cycloalkyl groups having 4 to 30 carbon atoms, and even more preferably linear or branched alkyl groups having 1 to 30 carbon atoms. Examples of the linear or branched alkyl group having 1 to 30 carbon atoms include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, and branched alkyl groups thereof. Of these, linear or branched alkyl groups having 3 to 8 carbon atoms are particularly preferred.

[0034] In the general formulas (B1) and (B2), X1 and X2 are preferably oxygen atoms, and Y1 and Y2 are preferably sulfur atoms, which facilitates the exertion of a synergistic effect with the epoxy compound (C), thereby further improving the oxidation stability of the lubricating oil composition.

[0035] Furthermore, in terms of ease in improving the oxidation stability of the lubricating oil composition, it is particularly preferred to use, as the (B) molybdenum compound, at least one selected from molybdenum dialkyldithiocarbamates represented by the above general formula (B1) in which R1 to R4 are alkyl groups, X1 and X2 are oxygen atoms, and Y1 and Y2 are sulfur atoms, and molybdenum dialkyldithiophosphates represented by the above general formula (B2) in which R5 to R8 are alkyl groups, X1 and X2 are oxygen atoms, and Y1 and Y2 are sulfur atoms.

[0036] Commercially available products may be used as the (B) molybdenum compound. Commercially available molybdenum dithiocarbamate represented by the general formula (B1) in which X1 and X2 are oxygen atoms and Y1 and Y2 are sulfur atoms includes, for example, ADEKA SAKURA-LUBE 200, 165, 525, and 600 manufactured by ADEKA CORPORATION. Commercially available molybdenum dithiophosphate represented by the general formula (B2) in which X1 and X2 are oxygen atoms and Y1 and Y2 are sulfur atoms includes, for example, ADEKA SAKURA-LUBE 300 and 310G manufactured by ADEKA CORPORATION.

[0037] <(C) Epoxy Compound> The lubricating oil composition of the present invention contains (C) an epoxy compound represented by the following general formula (1) (sometimes referred to as "(C) epoxy compound" in the present invention).

[0038] [ka] (In general formula (1), R 1 is a hydrogen atom or an alkyl group having 3 to 18 carbon atoms.

[0039] In the above general formula (1), R 1 is a hydrogen atom or an alkyl group having 3 to 18 carbon atoms. In order to improve the oxidation stability of the lubricating oil composition of the present invention, the above R 1 is preferably an alkyl group having 3 to 18 carbon atoms. 1 The alkyl group in the above R is preferably a linear or branched alkyl group, and more preferably a branched alkyl group. 1 The number of carbon atoms in the alkyl group in the above R is preferably 6 to 12, and more preferably 6 to 10. 1 If the number of carbon atoms is 2 or less or 19 or more, the oxidation stability of the lubricating oil composition of the present invention may be insufficient.

[0040] <Composition of Lubricating Oil Composition> The lubricating oil composition of the present invention contains 0.05 to 1.5 parts by mass of the (B) molybdenum compound and 0.05 to 1.5 parts by mass of the (C) epoxy compound relative to 100 parts by mass of the (A) ester compound. By containing the (B) molybdenum compound and the (C) epoxy compound as additives in the above-mentioned specific ratios in the (A) ester compound as a base oil, the lubricating oil composition of the present invention can exhibit excellent oxidation stability due to the synergistic effect of the (B) molybdenum compound and the (C) epoxy compound.

[0041] If the content of the (B) molybdenum compound is less than 0.05 parts by mass per 100 parts by mass of the (A) ester compound, the resulting lubricating oil composition will not exhibit excellent oxidation stability. If the content of the (B) molybdenum compound is more than 1.5 parts by mass per 100 parts by mass of the (A) ester compound, the biodegradability of the lubricating oil composition may be impaired. From this perspective, the content of the (B) molybdenum compound is preferably 0.06 to 1.0 parts by mass, more preferably 0.08 to 0.5 parts by mass, and even more preferably 0.1 to 0.2 parts by mass per 100 parts by mass of the (A) ester compound.

[0042] If the content of the (C) epoxy compound is less than 0.05 parts by mass per 100 parts by mass of the (A) ester compound, the resulting lubricating oil composition will not exhibit excellent oxidation stability. Furthermore, if the content of the (C) epoxy compound is more than 1.5 parts by mass per 100 parts by mass of the (A) ester compound, the biodegradability of the lubricating oil composition may be impaired. From these perspectives, the content of the (C) epoxy compound is preferably 0.06 to 1.25 parts by mass, more preferably 0.08 to 1.0 parts by mass, even more preferably 0.1 to 0.5 parts by mass, and even more preferably 0.2 to 0.4 parts by mass per 100 parts by mass of the (A) ester compound.

[0043] In order to further improve the oxidation stability of the lubricating oil composition of the present invention, it is preferable that the content of at least one of the molybdenum compound (B) and the epoxy compound (C) is 0.1 parts by mass or more, and it is more preferable that the content of both the molybdenum compound (B) and the epoxy compound (C) are 0.1 parts by mass or more, per 100 parts by mass of the ester compound (A).

[0044] In addition to the (A) ester compound, (B) molybdenum compound, and (C) epoxy compound described above, the lubricating oil composition of the present invention may contain known lubricating oil additives as needed to further enhance its performance. Examples of such additives include antioxidants, antiwear agents, metal deactivators, rust inhibitors, antifoaming agents, extreme pressure agents, and viscosity index improvers. These additives may be appropriately mixed with the (A) ester, as desired, within the range that does not impair the objectives of the present invention. These additives may be used alone or in combination of two or more.

[0045] Examples of the antioxidant include phenol-based antioxidants, amine-based antioxidants, and sulfur-based antioxidants. Examples of phenolic antioxidants include 2,6-di-t-butyl-paracresol (dibutylhydroxytoluene), 4,4'-methylenebis(2,6-di-t-butylphenol), 4,4'-thiobis(2-methyl-6-t-butylphenol), and 4,4'-bis(2,6-di-t-butylphenol). Examples of amine antioxidants include phenyl-α-naphthylamine, phenyl-β-naphthylamine, alkylphenyl-α-naphthylamine, alkylphenyl-β-naphthylamine, bis(alkylphenyl)amine, phenothiazine, and monooctydiphenylamine. Some of the amine antioxidants can be classified as quinoline antioxidants. Examples of quinoline antioxidants include 2,2,4-trimethyl-1,2-dihydroquinoline or polymers thereof, 6-methoxy-2,2,4-trimethyl-1,2-dihydroquinoline or polymers thereof, and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline or polymers thereof. Examples of sulfur-based antioxidants include alkyl disulfides and benzodiazoles. These antioxidants can be used either alone or in combination of two or more.

[0046] On the other hand, the lubricating oil composition of the present invention, which contains the above-mentioned (B) molybdenum compound and (C) epoxy compound in combination, can exhibit excellent oxidation stability even with a small amount of antioxidant or no antioxidant at all. Therefore, the content of the antioxidant in the lubricating oil composition of the present invention may be 0.1 parts by mass or less, 0.01 parts by mass or less, or even 0 parts by mass per 100 parts by mass of the (A) ester compound.

[0047] Examples of anti-wear agents include sulfurized olefins, sulfurized fats and oils, sulfides, phosphates, phosphites, thiophosphates, phosphate amine salts, zinc dialkyldithiophosphates, dialkyl polysulfides, etc. These anti-wear agents can be used either alone or in combination of two or more.

[0048] Examples of the metal deactivator include benzotriazole or a derivative thereof, alkenyl succinate, etc. These metal deactivators can be used either alone or in combination of two or more. The content of the metal deactivator is preferably 0.001 to 0.1 parts by mass, more preferably 0.002 to 0.08 parts by mass, and even more preferably 0.003 to 0.06 parts by mass, relative to 100 parts by mass of the (A) ester compound.

[0049] Examples of rust inhibitors include alkenyl succinic acid or its derivatives, imidazoline derivatives such as carboxyimidazoline, oleoyl sarcosine, and alkylphenoxyacetic acid. These rust inhibitors can be used alone or in combination of two or more. In the present invention, alkenyl succinic acid or its derivatives are more preferred because they can impart high rust prevention properties to the (A) ester compound.

[0050] Examples of the antifoaming agent include silicone compounds.

[0051] The extreme pressure agent is not particularly limited, and may be any known extreme pressure agent used for lubricating oils, such as a sulfur-based or phosphorus-based agent. Examples of sulfur-based extreme pressure agents include sulfurized fats and oils, sulfurized fatty acids, sulfurized esters, mono- or disulfides, sulfoxide compounds, sulfurized olefins, dihydrocarbyl polysulfides, thiocarbamates, dialkylthiodipropionates, and thioterpenes. As the phosphorus-based extreme pressure agent, for example, a compound containing phosphorus and zinc in the molecule can be used, and a specific example thereof is zinc dialkyldithiophosphate. In addition, sulfur-phosphorus (SP) additives and heat-resistant SP additives that have improved heat resistance than SP additives are commercially available as extreme pressure agents. These can impart even higher extreme pressure properties and are therefore suitable for use as extreme pressure agents. These extreme pressure agents can be used alone or in combination of two or more. Of the extreme pressure agents, sulfur-containing extreme pressure agents such as sulfur-based and SP-based extreme pressure agents are preferably used because they can impart excellent extreme pressure properties and wear resistance.

[0052] As the viscosity index improver, known ones can be used, and although not particularly limited, examples thereof include polymethacrylate, disperse polymethacrylate, olefin copolymers (e.g., ethylene-propylene copolymers, etc.), disperse olefin copolymers, styrene copolymers (e.g., styrene-diene copolymers, styrene-isoprene copolymers, etc.), and the like.

[0053] In the lubricating oil composition of the present invention, the content of these additives is appropriately adjusted within a range that does not impair the object of the present invention, and is not particularly limited, but the total content of additives other than the (B) molybdenum compound or the (C) epoxy compound is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the (A) ester compound, which allows the oxidation stability improving effect of the combination of the (B) molybdenum compound and the (C) epoxy compound to be fully exerted.

[0054] <Characteristics of lubricating oil composition> From the viewpoint of oxidation stability, the lubricating oil composition of the present invention preferably has an acid value of 10.0 mgKOH / g or less, more preferably 5.0 mgKOH / g or less, even more preferably 3.0 mgKOH / g or less, still more preferably 1.5 mgKOH / g or less, and particularly preferably 1.0 mgKOH / g or less. The acid value of the lubricating oil composition of the present invention is adjusted by the acid value of the ester compound (A) contained as the base oil.

[0055] From the viewpoint of lubricity (extreme pressure property), the lubricating oil composition of the present invention has a kinematic viscosity of 100mm at 40°C. 2 / s or more is preferable, and from the viewpoint of suppressing deterioration of the power generation efficiency and fuel efficiency of the equipment, 400 mm 2 From this perspective, the kinematic viscosity at 40°C of the lubricating oil composition of the present invention is more preferably 150 to 450 mm 2 / s, and more preferably 200 to 400 mm 2 / s, and particularly preferably 300 to 370 mm 2 / s.

[0056] From the viewpoint of use in cold climates, the lubricating oil composition of the present invention preferably has a pour point of −15.0° C. or lower, more preferably −25.0° C. or lower, even more preferably −35.0° C. or lower, and particularly preferably −40.0° C. or lower. The pour point of the lubricating oil composition of the present invention is adjusted by the pour point of the ester compound (A) contained as the base oil.

[0057] The lubricating oil composition of the present invention has excellent biodegradability, and therefore preferably has a biodegradability of 60% or more as determined according to OECD301F.

[0058] The lubricating oil composition of the present invention has excellent oxidation stability, and therefore, in a rotating pressure vessel oxidation stability test (RPVOT) in accordance with JIS K2514-3 (2013), the time required from the start of the test until a sudden drop in pressure is observed is preferably 550 minutes or more, more preferably 600 minutes or more, even more preferably 630 minutes or more, even more preferably 680 minutes or more, and particularly preferably 700 minutes or more.

[0059] <Method of manufacturing lubricating oil composition> The method for producing the lubricating oil composition of the present invention is not particularly limited. For example, the lubricating oil composition can be produced by adding a predetermined amount of the (B) molybdenum compound and the (C) epoxy compound to the (A) ester compound, and, if necessary, further adding the various other additives described above. The method for adding and mixing each material is not particularly limited, and various methods can be used. The order of addition is also not particularly limited. For example, a method can be used in which the (B) molybdenum compound, the (C) epoxy compound, and other additives are directly added to the (A) ester compound, followed by heating and mixing. Alternatively, a method can be used in which high-concentration solutions of the (B) molybdenum compound, the (C) epoxy compound, and other additives are each prepared in advance, and these high-concentration solutions are mixed with the (A) ester compound.

[0060] <Uses of lubricating oil composition> The uses of the lubricating oil composition of the present invention are not particularly limited, but it can be suitably used as a bearing oil, hydraulic oil, gear oil, etc., and in particular as a gear oil for wind power generators, more specifically as a gear oil for speed-up gears used in wind power generators. [Example]

[0061] The present invention will be described in more detail below with reference to examples and comparative examples, in which % is by mass unless otherwise specified. In the following, the acid value was measured in accordance with JIS K 0070. The kinematic viscosity at 40°C was measured in accordance with JIS K 2283. The pour point was measured in accordance with JIS K 2269.

[0062] [(A) Synthesis of Ester Compounds] (Synthesis Example 1: Synthesis of ester compound A1) In a 5 L four-neck flask equipped with a thermometer, nitrogen inlet tube, stirrer, and air cooling tube, (a) 980.0 g of trimethylolpropane (TMP, manufactured by Perstorp), (b) 983.6 g of NAA-82 (manufactured by NOF Corporation, industrial caprylic acid, caprylic acid content 99%) and 804.7 g of NAA-102 (manufactured by NOF Corporation, industrial capric acid content 99%) as monovalent fatty acids having 8 to 12 carbon atoms, and (c) 714.0 g of adipic acid (manufactured by Asahi Kasei Corporation) were mixed to obtain a reaction solution. The reaction solution was heated to 240 °C under a nitrogen stream, and the acid value of the reaction solution was measured every hour. The reaction was continued at normal pressure until the decrease in acid value per hour reached 0.5 mg KOH / g or less. Thereafter, the reaction solution was heated to 240° C. and the pressure was reduced to 30 Torr to distill off the unreacted raw materials from the reaction system, thereby obtaining a crude ester. Finally, activated clay was added in an amount equivalent to 2% by mass based on the crude ester, and the mixture was stirred at 80° C. and 30 Torr for 1 hour, and then filtered to remove the adsorbent, thereby obtaining ester compound A1.

[0063] (Synthesis Example 2: Synthesis of ester compound A2) In a 5 L four-neck flask equipped with a thermometer, a nitrogen inlet tube, a stirrer, and an air cooling tube, (a) 946.8 g of trimethylolpropane (TMP, manufactured by Perstorp), (b) 750.8 g of NAA-82 (manufactured by NOF Corporation, industrial-grade caprylic acid, caprylic acid content 99%), 563.0 g of NAA-102 (manufactured by NOF Corporation, industrial-grade capric acid, capric acid content 99%), and 563.0 g of NAA-122 (manufactured by NOF Corporation, industrial-grade lauric acid, lauric acid content 99%), and (c) 676.3 g of adipic acid (manufactured by Asahi Kasei Corporation) were mixed to obtain a reaction solution. The reaction solution was heated to 240°C under a nitrogen stream, and the acid value of the reaction solution was measured every hour. The reaction was carried out at normal pressure until the rate of decrease in the acid value per hour reached 0.5 mgKOH / g or less, thereby obtaining a crude ester. Finally, activated clay was added in an amount equivalent to 2% by mass based on the crude ester, and the mixture was stirred at 80°C and 30 Torr for 1 hour, and then filtered to remove the adsorbent, yielding ester compound A2.

[0064] For each of the obtained ester compound A1 and ester compound A2, (a) the molar percentage of the constituent component derived from trimethylolpropane (a mol% ), (b) the molar percentage of components derived from monovalent fatty acids having 8 to 12 carbon atoms (b mol% ), (c) the mole percentage of components derived from adipic acid (c mol% ), and the molar ratio of (c) adipic acid-derived components to (b) monovalent fatty acids having 8 to 12 carbon atoms (c mol% / b mol% ) are shown in Table 1 below. In Table 1, the component derived from (b) monovalent fatty acids having 8 to 12 carbon atoms contained in ester compound A1 is denoted as b1, and the component derived from (b) monovalent fatty acids having 8 to 12 carbon atoms contained in ester compound A2 is denoted as b2. For each of b1 contained in ester compound A1 and b2 contained in ester compound A2, the molar percentages of the component derived from lauric acid, the molar percentages of the component derived from capric acid, and the molar percentages of the component derived from caprylic acid, when the total amount of the component derived from (b) monovalent fatty acids having 8 to 12 carbon atoms is taken as 100 mol%, are shown in Table 1 below. Furthermore, the acid value, kinematic viscosity at 40° C. and pour point of each of the obtained ester compounds A1 and A2 were measured. The measurement results are shown in Table 1 below.

[0065] [Table 1]

[0066] Examples 1 to 7 and Comparative Examples 1 to 6: Preparation of Lubricating Oil Compositions Lubricating oil compositions were prepared by blending the ester compound A1 or ester compound A2 synthesized above with the additives shown in Table 2 or Table 3. The specific procedure was as follows. Ester compound A1 or Ester compound A2 synthesized above was placed in a 5 L four-neck flask equipped with a thermometer, a nitrogen inlet tube, a stirrer, and a Dimroth condenser, and additives were added thereto according to Table 2 or Table 3. The resulting mixture was stirred and mixed at 80°C for 1 hour, and then the pressure was reduced at 150°C and 50 mmHg for 2 hours to prepare a lubricating oil composition. The blending compositions of the lubricating oil compositions prepared in each Example or Comparative Example are shown in Tables 2 and 3. The details of the additives shown in Tables 2 and 3 are as follows. Molybdenum compound B1: Molybdenum dialkyldithiocarbamate, trade name "ADEKA SAKURA-LUBE 525", manufactured by ADEKA Corporation Molybdenum compound B2: molybdenum dialkyldithiophosphate, product name "ADEKA SAKURA-LUBE 300", manufactured by ADEKA Corporation Epoxy compound C: 2-ethylhexyl glycidyl ether, trade name "Epiol (registered trademark) EH-N", manufactured by NOF Corporation Antioxidant D: Dibutylhydroxytoluene, trade name "K-NOX BHT", manufactured by Kyodo Pharmaceutical Co., Ltd. Common additives: Anti-wear agents, metal deactivators, anti-foaming agents, extreme pressure agents and viscosity index improvers were added as common additives.

[0067] [Physical Properties of Lubricating Oil Composition] The lubricating oil compositions of each Example or Comparative Example were measured for acid value, kinematic viscosity at 40° C., and pour point. The measurement results are shown in Table 2 or Table 3.

[0068] [Performance Evaluation of Lubricating Oil Compositions] The lubricating oil compositions of each Example and Comparative Example were evaluated as follows. The evaluation results are shown in Table 2 or Table 3.

[0069] (Biodegradability test) Biodegradability tests were conducted in accordance with OECD 301F using a measurement method that uses biochemical oxygen consumption (BOD) as an indicator, and the biodegradability (%) was calculated. The Japan Environment Association Ecomark Office, a public interest incorporated foundation, considers a biodegradability of 60% or more in this test to meet the criteria for a biodegradable lubricant. Therefore, products with a biodegradability of 60% or more in this test were deemed to have passed, and those with a biodegradability of less than 60% were deemed to have failed.

[0070] (RPVOT test) A rotating pressure vessel oxidation stability test (RPVOT) was conducted in accordance with Japanese Industrial Standard JIS K2514-3 (2013), and the time (minutes) required from the start of the test until a sudden drop in pressure was observed was determined. The longer this time, the higher the oxidation stability. In this test, the oxidation stability of a lubricating oil composition was evaluated by rating it as "◎" if the time (minutes) required from the start of the test until a sudden drop in pressure was observed was 700 minutes or more, "◯" if it was 550 minutes or more but less than 700 minutes, and "×" if it was less than 550 minutes. The evaluation results and the corresponding times are shown in Table 2 or Table 3.

[0071] [Table 2]

[0072] [Table 3]

[0073] The lubricating oil compositions of Examples 1 to 7 shown in Table 2 contain, as a base oil, (A) an ester compound in which (a) the molar percentage of a component derived from trimethylolpropane is 25 to 42 mol %, (b) the molar percentage of a component derived from a monovalent fatty acid having 8 to 12 carbon atoms is 36 to 58 mol %, and (c) the molar percentage of a component derived from adipic acid is 9 to 29 mol %, mol% / b mol%The lubricating oil compositions of Examples 1 to 7 were lubricating oil compositions of the present invention, in which the molybdenum compound (B) was present in an amount of 0.05 to 1.5 parts by mass and the epoxy compound (C) represented by the general formula (1) was present in an amount of 0.05 to 1.5 parts by mass per 100 parts by mass of the ester compound (A). The lubricating oil compositions of Examples 1 to 7 were excellent in biodegradability and oxidation stability.

[0074] On the other hand, the lubricating oil compositions of Comparative Examples 1 to 6 shown in Table 3 did not contain at least one of (B) the molybdenum compound and (C) the epoxy compound represented by the general formula (1) above, and therefore had excellent biodegradability but insufficient oxidation stability.

[0075] In addition, the lubricating oil composition of Comparative Example 3, in which (A) ester compound A1 was blended with (B) molybdenum compound B2, and the lubricating oil composition of Comparative Example 4, in which (A) ester compound A1 was blended with (C) epoxy compound C, showed slightly improved oxidation stability compared to the lubricating oil composition of Comparative Example 1, which contained only (A) ester compound A1 among the (A) ester compound, (B) molybdenum compound, and (C) epoxy compound. On the other hand, the lubricating oil composition of Example 3, in which (A) ester compound A1 was blended with both (B) molybdenum compound B2 and (C) epoxy compound C, showed significantly improved oxidation stability compared to the lubricating oil compositions of Comparative Examples 3 and 4. The lubricating oil compositions of Examples 1 to 7 all showed significantly improved oxidation stability due to the blending of both the (B) molybdenum compound and the (C) epoxy compound with the (A) ester compound. This significant improvement in oxidation stability is presumed to be due to the synergistic effect of the (B) molybdenum compound and the (C) epoxy compound. [Industrial Applicability]

[0076] The lubricating oil composition of the present invention has excellent biodegradability and oxidation stability, and is therefore a biodegradable lubricating oil composition with an extended life, and can be suitably used, for example, as a bearing oil, hydraulic oil, gear oil, etc., and is particularly suitable for use as a gear oil for wind power generators, more specifically, as a gear oil for the speed increaser used in wind power generators.

Claims

1. A lubricating oil composition comprising, per 100 parts by mass of the following (A) ester compound, 0.05 to 1.5 parts by mass of (B) a molybdenum compound and 0.05 to 1.5 parts by mass of (C) an epoxy compound represented by the following general formula (1): (A): An ester compound of (a) trimethylolpropane, (b) a monovalent fatty acid having 8 to 12 carbon atoms, and (c) adipic acid, wherein the molar percentage of the component derived from the (a) trimethylolpropane is 25 to 42 mol%, the molar percentage of the component derived from the (b) monovalent fatty acid having 8 to 12 carbon atoms is 36 to 58 mol%, and the molar percentage of the component derived from the (c) adipic acid is 9 to 29 mol%, and the molar ratio of the component derived from the (c) adipic acid to the component derived from the (b) monovalent fatty acid having 8 to 12 carbon atoms is 0.1 to 0.

5. 【Chemistry 1】 (In general formula (1), R １ is a hydrogen atom or an alkyl group having 3 to 18 carbon atoms.

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