Lubricant composition for internal combustion engines

Abstract

The present invention provides a lubricating oil composition that exhibits excellent soot dispersibility, suppresses the precipitation of zinc dithiophosphate during oxidative degradation, and has excellent wear resistance. [Solution] A lubricating oil composition according to one aspect of the present disclosure contains a base oil, a dispersant, zinc dithiophosphate, and glycerin monooleate, wherein the content of the dispersant is 350 ppm by mass or more and 600 ppm by mass or less in terms of N content, and the zinc dithiophosphate includes primary dialkyldithiophosphate zinc and secondary dialkyldithiophosphate zinc, with the content ratio of primary dialkyldithiophosphate zinc to secondary dialkyldithiophosphate zinc being 4:6 to 2:8 by mass ratio.

Description

[Technical Field]

[0001] This disclosure relates to lubricating oil compositions. [Background technology]

[0002] Patent Document 1 describes a lubricating oil composition aimed at reducing friction while ensuring wear prevention even when viscosity is reduced, and describes adding a metal detergent, zinc dialkyldithiophosphate, an ashless dispersant, an alkyl (meth)acrylate copolymer having a specific molecular structure, and a friction modifier containing molybdenum to a lubricating oil base oil.

[0003] Patent Document 2 describes a nanoparticle-containing lubricant composition that exhibits a low coefficient of friction and aims to improve fuel efficiency. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-25007 [Patent Document 2] Japanese Patent Publication No. 2006-241443 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Incidentally, in the field of lubricating oil compositions, the present inventors believe that the challenge is to provide a lubricating oil that exhibits excellent soot dispersibility, can suppress the precipitation of zinc dithiophosphate (hereinafter sometimes referred to as "ZnDTP") during oxidative degradation, and has excellent wear resistance. However, the technologies described in Patent Documents 1 and 2 do not contain any information that contributes to solving these problems.

[0006] Therefore, one aspect of this disclosure aims to provide a lubricating oil composition that exhibits excellent soot dispersibility, can suppress the precipitation of zinc dithiophosphate during oxidative degradation, and has excellent wear resistance. [Means for solving the problem]

[0007] As a result of diligent research, the present inventors have discovered for the first time that the above problems can be solved by incorporating a dispersant, zinc dithiophosphate, and glycerin monooleate into the base oil of a lubricating oil, and by setting the zinc dithiophosphate to a predetermined proportion, thereby completing the present invention. That is, in order to solve the above problems, a lubricating oil composition according to one aspect of the present disclosure contains a base oil, a dispersant, zinc dithiophosphate, and glycerin monooleate, wherein the content of the dispersant is 350 ppm by mass or more and 600 ppm by mass or less in terms of N content, and the zinc dithiophosphate includes primary dialkyldithiophosphate zinc and secondary dialkyldithiophosphate zinc, and the content ratio of primary dialkyldithiophosphate zinc to secondary dialkyldithiophosphate zinc is 4:6 to 2:8 by mass ratio. [Effects of the Invention]

[0008] According to one aspect of this disclosure, it is possible to provide a lubricating oil composition that exhibits excellent soot dispersibility, suppresses the precipitation of zinc dithiophosphate during oxidative degradation, and has excellent wear resistance. [Modes for carrying out the invention]

[0009] One aspect of this disclosure will be described in detail below. Unless otherwise specified in this specification, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B".

[0010] [Lubricating oil composition] A lubricating oil composition according to one aspect of this disclosure contains a base oil, a dispersant, zinc dithiophosphate, and glycerin monooleate, wherein the zinc dithiophosphate includes primary dialkyldithiophosphate and secondary dialkyldithiophosphate, and the content ratio of primary dialkyldithiophosphate to secondary dialkyldithiophosphate is 4:6 to 2:8 by mass ratio. The lubricating oil composition according to one aspect of this disclosure achieves excellent soot dispersibility by containing a dispersant. Furthermore, the lubricating oil composition according to one aspect of this disclosure achieves excellent wear resistance by containing primary and secondary zinc dithiophosphate in the aforementioned mass ratio. In addition, the lubricating oil composition according to one aspect of this disclosure can suppress the precipitation of zinc dithiophosphate even when it undergoes oxidative degradation by containing glycerin monooleate. In other words, the problem of zinc dithiophosphate precipitation that occurs when zinc dithiophosphate is included to achieve excellent wear resistance can be solved by including glycerin monooleate. The resolution of these issues has not been considered at all in prior art literature.

[0011] Furthermore, suppressing the precipitation of zinc dithiophosphate in this way reduces the frequency of lubricant oil composition changes, leading to a reduction in waste oil volume. Additionally, extending the lifespan of the lubricant oil composition contributes to a reduction in manufacturing energy, thus contributing to the achievement of goals such as Goal 7 of the United Nations' Sustainable Development Goals (SDGs), "Affordable and Clean Energy."

[0012] <Base oil> The type of base oil contained in the lubricating oil composition according to one aspect of this disclosure is not particularly limited, and any base oil classified into Groups I, II, III, IV, and V of the American Petroleum Institute (API) base oil categories can be used, such as mineral oil-based base oils and synthetic base oils. These may be used individually or in combination of two or more types.

[0013] Examples of mineral oil-based base oils include atmospheric residues obtained by atmospheric distillation of crude oils such as paraffinic crude oil, intermediate base oil, or naphthenic crude oil; distillates obtained by vacuum distillation of these atmospheric residues; and mineral oils obtained by subjecting the distillates to one or more refining treatments such as solvent delamination, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining.

[0014] Examples of synthetic base oils include polyalphaolefin (PAO) base oils, other aliphatic hydrocarbon base oils, alphaolefin base oils, glyceride base oils (e.g., vegetable oils and their refined oils), ester base oils, phosphate ester base oils, thioether base oils, polyphenyl ether base oils, alkyldiphenyl ether base oils, polyalkylene glycol base oils (PAG), polyvinyl ether base oils, aromatic synthetic base oils (e.g., alkylbenzene base oils, alkylnaphthalenes, etc.), cycloalkane base oils (e.g., alkylcyclopentanes, etc.), GTL (Gas To Liquids) base oils obtained by hydrogenation, isomerization, and dewaxing wax produced from natural gas by the Fischer-Tropsch process (FT process), etc., and GTL (Gas To Liquids) base oils obtained by hydrogenation, isomerization, and dewaxing wax produced by synthesizing CO and H2 obtained by the aforementioned FT process from CO2. Liquids include base oils, isoparaffins, organosilane compounds, silicone oils, ionic liquids, deep eutectic solvents, fluorinated base oils (e.g., fluorocarbons, perfluoropolyethers, etc.), phosphazene compounds, and liquid metals mainly composed of low-melting-point metals such as mercury and gallium.

[0015] The base oil content of the lubricating oil composition according to one aspect of this disclosure can be the same as the general base oil content found in ordinary lubricating oils. For example, when the total amount of lubricating oil is 100% by mass, the base oil content is 0.01 to 99.999% by mass, preferably 30 to 99.999% by mass, more preferably 50 to 99.999% by mass, and even more preferably 70 to 99.999% by mass.

[0016] <Dispersant> The lubricating oil composition according to one aspect of the present disclosure contains a dispersant. Examples of the dispersant include boron-containing imides, boron-free imides, benzylamines, boron-containing benzylamines, succinic esters, monovalent or divalent carboxylic acid amides represented by fatty acids or succinic acids, and the like. Examples of the boron-containing imides include boron-containing succinic imides. Examples of the boron-containing succinic imides include boron-containing alkenyl succinic imides. Examples of the boron-free succinic imides include boron-free alkenyl succinic imides. Further, examples of the boron-free succinic imides include succinic monimides such as alkenyl succinic monimide and alkyl succinic monimide; succinic bisimides such as alkenyl succinic bisimide and alkyl succinic bisimide; and one or more compounds selected therefrom. Among the dispersants, bisimide ones are more preferable. The bisimide is preferably any of the bisimides of boron-containing succinic imide and boron-free succinic imide, and since it has excellent dispersibility, boron-free succinic bisimide is more preferable. These may be used alone or in combination of two or more.

[0017] The content of the dispersant in the lubricating oil composition may be appropriately set according to the desired dispersibility and the like. From the viewpoint of further improving the dispersibility of soot, for example, it is preferably 350 ppm by mass or more and 600 ppm by mass or less in terms of N, more preferably 370 ppm by mass or more and 550 ppm or less, still more preferably 390 ppm by mass or more and 500 ppm or less, still more preferably 410 ppm by mass or more and 450 ppm or less, and still more preferably 420 ppm by mass or more and 450 ppm or less, based on the total amount of the lubricating oil composition.

[0018] <Zinc dithiophosphate> As the zinc dithiophosphate contained in the lubricating oil composition according to one aspect of the present disclosure, compounds represented by the following general formula (1) are preferably mentioned.

Chemical formula

[0019] Also, the monovalent hydrocarbon group that can be selected as R 1 ~R 4 may have a substituent containing an oxygen atom and / or a nitrogen atom such as a hydroxyl group, a carboxy group, an amino group, an amide group, a nitro group, or a cyano group, or may be partially substituted by a nitrogen atom, an oxygen atom, a halogen atom, etc. When the monovalent hydrocarbon group is a cycloalkyl group or an aryl group, it may further have a substituent such as an alkyl group or an alkenyl group.

[0020] R 1 ~R 4 The alkyl group and alkenyl group that can be selected as may be either linear or branched. From the viewpoint of obtaining better anti-wear property, primary and secondary ones are preferable, and among them, a primary alkyl group and a secondary alkyl group are preferable, and a primary alkyl group is more preferable. That is, the alkyl group that can be selected as R 1 ~R 4 is a primary alkyl group or a secondary alkyl group, and the zinc dialkyldithiophosphate contained in the lubricating oil composition according to one aspect of the present disclosure includes a primary zinc dialkyldithiophosphate and a secondary zinc dialkyldithiophosphate. Further, the content ratio of the primary zinc dialkyldithiophosphate to the secondary zinc dialkyldithiophosphate is 4:6 to 2:8 by mass ratio.

[0021] From the viewpoint of improving the anti-wear property of the lubricating oil composition, R1 ~R 4 The carbon number of the hydrocarbon group is preferably 1 or more, more preferably 2 or more, even more preferably 3 or more, with an upper limit of preferably 24 or less, more preferably 18 or less, even more preferably 12 or less, and even more preferably 10 or less, when the monovalent hydrocarbon group is an alkyl group. When the monovalent hydrocarbon group is an alkenyl group, it is preferably 2 or more, more preferably 3 or more, with an upper limit of preferably 24 or less, more preferably 18 or less, even more preferably 12 or less, and even more preferably 10 or less. Furthermore, when the monovalent hydrocarbon group is a cycloalkyl group, the carbon number is preferably 5 or more, with an upper limit of preferably 20 or less, and when the monovalent hydrocarbon group is an aryl group, the carbon number is preferably 6 or more, with an upper limit of preferably 20 or less.

[0022] From the viewpoint of achieving excellent wear resistance, the zinc dithiophosphate content is preferably 0.1% to 2% by mass, more preferably 0.5% to 2% by mass, even more preferably 0.5% to 1.5% by mass, and even more preferably 0.5% to 1% by mass, based on the total amount of the lubricating oil composition.

[0023] <Glycerin Monooleate> A lubricating oil composition according to one aspect of this disclosure contains glycerin monooleate. The polar portion of the glycerin monooleate captures and disperses the decomposition products and oxidative degradation products of ZnDTP, thus providing excellent suppression of ZnDTP precipitation. The glycerin monooleate may be glyceryl 1-monoleate, glyceryl 2-monoleate, or a mixture thereof. The content of glycerin monooleate can be appropriately set according to the content of zinc dithiophosphate, etc., but from the viewpoint of achieving excellent precipitation suppression performance, it is preferably 0.01% to 1.0% by mass, more preferably 0.03% to 0.5% by mass, even more preferably 0.05% to 0.3% by mass, even more preferably 0.07% to 0.2% by mass, and even more preferably 0.09% to 0.15% by mass on a basis of the total amount of the lubricating oil composition.

[0024] <Additives> A lubricating oil composition according to one aspect of this disclosure may contain additives other than glycerin monooleate, zinc dithiophosphate, and dispersants. Examples of additives include friction modifiers, oiliness agents, extreme pressure agents, detergents, antioxidants, viscosity index improvers, pour point depressants, anti-wear agents, dispersants, rust inhibitors, corrosion inhibitors, anti-emulsifiers, defoaming agents, antibacterial agents / preservatives, and the like.

[0025] (Friction modifier) As friction modifiers, those containing, for example, metallic friction modifiers and ashless friction modifiers are preferred. For metallic friction modifiers, those that form a cleavable layered film on the friction surface, such as organic molybdenum compounds and organic tungsten compounds, are preferred. For ashless friction modifiers, those that exhibit low friction characteristics through physical and chemical adsorption are preferred. Examples of organotungsten compounds include tungsten dithiocarbamate and tungsten dithiophosphate. Furthermore, the aforementioned glycerin monooleate can also be included in lubricating oil compositions as a friction modifier.

[0026] Examples of ashless friction modifiers include aliphatic amines, fatty acid esters, fatty acid amides, fatty acids, aliphatic alcohols, aliphatic ethers, alkylsarcosines, etc., which have at least one alkyl or alkenyl group with 6 to 30 carbon atoms in their molecules.

[0027] In applications where the lubricant is used to lubricate a component having a hydrogen-containing diamond-like carbon coating on its sliding surface, it is preferable that the lubricant is substantially free of molybdenum dithiocarbamate. This is because wear of the hydrogen-containing diamond-like carbon coating occurs. In other words, a lubricant composition that substantially does not contain molybdenum dithiocarbamate according to one aspect of this disclosure is a lubricant composition for use in lubricating a component having a hydrogen-containing diamond-like carbon coating on its sliding surface. Here, "substantially free" means that it is not contained to such an extent that wear of the hydrogen-containing diamond-like carbon coating due to molybdenum dithiocarbamate does not occur.

[0028] (Oily-based agent) Preferred oily agents include, for example, alcohols, fatty acids, fatty acid metal salts, dibasic acids, esters, organic amines, glycerides, partial esters of polyhydric alcohols, ashless dispersants, multi-point adsorption polymers modified with hydroxyl or amine groups, acid amides, alkylimides, aliphatic mercaptans, aliphatic sulfonates, alkylphenyl sulfonates, fatty acid amine salts, and the like. Examples of alcohols include lauryl alcohol, stearyl alcohol, and oleyl alcohol. Examples of fatty acids include lauric acid, stearic acid, oleic acid, and N-oleyl sarcosine. Examples of fatty acid metal salts include sodium fatty acid salts, calcium fatty acid salts, and aluminum fatty acid salts. Examples of dibasic acids include adipic acid, sebacic acid, alkenyl succinic acid, adipic acid, and eicoate diacitate. Examples of esters include monoesters of fatty acids and aliphatic alcohols, and diesters of dibasic acids and aliphatic alcohols. Examples of monoesters of fatty acids and aliphatic alcohols include sorbitan monooleate, sorbitan dioleate, sorbitan trioleate, and sorbitan monostearate. Examples of diesters of dibasic acids and aliphatic alcohols include dioctyl adipate, di-2-ethylhexyl adipate, dioctyl sebacate, and di-2-ethylhexyl sebacate. Examples of organic amines include oleylamine and stearylamine. Examples of glycerides include glycerol monoesters, glycerol diesters, and glycerol triesters. Examples of partial esters of polyhydric alcohols include partial esters of trimethylolpropane and partial esters of pentaerythritol. Examples of ashless dispersants include the reaction product of triethylpentamine and isostearic acid. Examples of multi-point adsorption polymers modified with hydroxyl groups or amine groups include hydroxyl group-containing polymethacrylates. Examples of acid amides include octylic acid amide, dodecyl acid amide, oleic acid amide, stearic acid amide, alkylacetanilide, dioctyl adipate adipate amide, di-2-ethylhexyl adipate amide, dioctyl sebacinate amide, and di-2-ethylhexyl sebacinate amide. Examples of alkylimides include polyalkenyl succinimide and polybutenyl succinimide. Examples of aliphatic mercaptans include octyl mercaptan, oleyl mercaptan, and stearyl mercaptan. Examples of aliphatic sulfonates include octyl sulfonate, oleyl sulfonate, and stearyl sulfonate. Examples of alkylphenyl sulfonates include nonylphenol sulfonic acid and dodecylbenzenesulfonic acid. Examples of fatty acid amine salts include fatty acid amine salts formed by combining organic acids such as fatty acids and dibasic acids with organic amines.

[0029] (Extreme pressure agent) As extreme pressure agents, those containing, for example, phosphite esters, orthophosphate esters, acidic phosphite esters, acidic phosphate esters, acidic phosphate amine salts, sulfur-based extreme pressure agents, high-base-value metal salts, and naphthenate metal salts are preferred. Examples of phosphite esters include triphenylphosphite, tricresylphosphite, triisopropylphosphite, and trioctylphosphite. Examples of orthophosphate esters include triphenylphosphate, tricresylphosphate, triisopropylphenylphosphate, and trioctyl phosphite. Examples of acidic phosphites include dicresyl hydrate phosphite, dilauryl hydrate phosphite, dioleyl hydrate phosphite, and distearyl hydrate phosphite. Examples of acidic phosphate esters include dilauryl acid phosphate and dioleyl acid phosphate. Examples of acidic phosphate amine salts include acidic phosphate amine salts composed of the aforementioned acidic phosphate ester and a primary to tertiary alkylamine or alkylphenylamine. Examples of sulfur-based extreme pressure agents include alkyl monothioethers, alkyl dithioethers, dibenzyl disulfide, sulfurized olefins, sulfurized oils and fats, didodecyl trisulfide, didodecyl polysulfide, dibutyl dithioglycolate, alkyl dithiocarbamate, alkyl dithiathiazole, alkyl polysulfide, and sulfurized esters. Examples of high-base-number metal salts include the over-basic components of the aforementioned cleaning agents, such as overbasic calcium sulfonates, overbasic calcium salicylates, overbasic magnesium sulfonates, and overbasic salicylates. Examples of metal naphthenate salts include zinc naphthenate and copper naphthenate.

[0030] (cleaning agent) Examples of cleaning agents include metal-based cleaning agents obtained by reacting organic acids, such as alkylbenzene sulfonic acid, alkyl salicylic acid, and alkylphenol sulfide, with metals, such as Na, Ca, and Mg. Among these, calcium-based and magnesium-based cleaning agents are preferred, and it is more preferable to use both calcium-based and magnesium-based cleaning agents together. Further preferred specific examples of cleaning agents include calcium sulfonate and magnesium sulfonate, and it is more preferable to use both calcium sulfonate and magnesium sulfonate together. Furthermore, for these compounds, compounds with a base number ranging from neutral (0 TBN) to overbasic (700 TBN or less) can be used as appropriate.

[0031] (Antioxidant) Examples of antioxidants include hindered phosphate antioxidants, amine antioxidants, phosphorus-based peroxide decomposers, sulfur-based peroxide decomposers, complex antioxidants, and plant-derived antioxidants. Examples of hindered phosphate antioxidants include dibutylhydroxytoluene (BHT), octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamic acid, n-octadecyl (3-4'-hydroxy-3',5'-di-tert-butylphenyl)propionic acid, and diethyl 3,5-di-tert-butyl-4-hydroxybenzylsulfonate. Examples of amine-based antioxidants include diphenylamine, alkyldiphenylamine, phenylnaphthylamine, alkylphenylnaphthylamine, and hindered amines (HALS). Examples of phosphorus-based peroxide decomposing agents include alkyl phosphites and alkylphenyl phosphites. Examples of sulfur-based peroxide decomposing agents include alkyl thioethers, phenyl sulfides, and diphenyl sulfides. Examples of complex antioxidants include 4-[[4,6-bis(octylthio)-1,3,5-triazine-2-yl]amino]-2,6-di-tert-butylphenol and zinc dialkyldithiophosphate (ZDDP). Examples of vitamin-based antioxidants include tocopherol. Examples of plant-derived antioxidants include polyphenols. Among the antioxidants exemplified here, amine-based antioxidants are more preferred.

[0032] (Viscosity index improver) Examples of viscosity index improvers include organic polymer-based viscosity index improvers. Examples of organic polymer-based viscosity index improvers include polyalkyl methacrylate (PMA) and its side-chain length modified mixed type, comb-type polymethacrylate, olefin copolymer (OCP), polybutene, polyisobutylene, styrene polymer, etc. Among these, olefin copolymer (OCP) is more preferred.

[0033] (Pour point depressant) Examples of pour point depressants include organic polymer-based pour point depressants and alkylated aromatic compound pour point depressants. Examples of organic polymer-based pour point depressants include polyalkyl methacrylate (PMA), polyacrylate (PA), and ethylene-vinyl acetate copolymer. Examples of alkylated aromatic compound pour point depressants include alkylnaphthalenes.

[0034] (Anti-wear agent) Examples of wear inhibitors include metal dithiophosphate salts, metal phosphate salts, and orthophosphate esters. Examples of metal dithiophosphate salts include zinc dialkyldithiophosphate and copper dialkyldithiophosphate. Examples of metal phosphate salts include zinc dialkylphosphate. Examples of orthophosphate esters include triphenylphosphate, tricresylphosphate, and triisopropylphenylphosphate.

[0035] (Rust inhibitor) Examples of rust inhibitors include sodium and potassium salts of inorganic acids such as boric acid, tungstic acid, molybdic acid, phosphoric acid, carbonic acid, sulfuric acid, silicic acid, nitric acid, and nitrite; metal-based detergents formed by the reaction of organic acids such as fatty acids, dibasic acids, sorbitan esters, succinic acid esters, alkylbenzene sulfonic acid, alkyl salicylic acid, and alkylphenol sulfide with metals such as Na, Ca, and Mg; and tetraalkoxysilanes such as tetraethoxysilane and their salts.

[0036] (Corrosion inhibitor) Examples of corrosion inhibitors include benzotriazole and its derivatives, thiadiazole and its derivatives, dithiadiazole and its derivatives, tetrasodium N,N-bis(carboxymethyl)glutamate (GLDA), tetrasodium N,N-bis(carboxymethyl)aspartate (ASDA), disodium N-2-hydroxyethyliminodiacetate (HIDA), trisodium methylglycinediacetate (MGDA), ethylenediaminesuccinate, diethylenetrinosine pentaacetic acid, ethyl hydroxide ethylenediaminetriacetic acid, succinic acid, iminodisuccinate (IDS), nitrilotriacetic acid, aminocarboxylate (APCA), sodium ethylenediaminesuccinate (EDDS), polyepoxysuccinate, sodium α-peptogluconate, ethylene glycol diacetate, and other chelating agents.

[0037] (Antiemulsifier) Examples of antiemulsifiers include metal-based antiemulsifiers formed by the reaction of organic acids such as alkylbenzene sulfonic acid, alkyl salicylic acid, and alkylphenol sulfide with metals such as Na, Ca, and Mg; ester-based antiemulsifiers such as sorbitan esters; polyalkylene glycol-based antiemulsifiers; and pluronic-based antiemulsifiers such as ethylene oxide-propylene oxide block copolymers.

[0038] (Antifoaming agent) Examples of defoaming agents include silicone oil-based defoamers, such as dimethyl silicone oil, and modified silicone oils in which functional groups such as long-chain alkyl groups, phenyl groups, phenol groups, hydroxyl groups, carboxyl groups, fluorine groups, alkyl fluoride groups, polyether groups, mercapto groups, amino groups, and methacrylic groups are added to the silicone skeleton of these silicone oils. Other examples include ester-based defoamers and polyacrylate-based defoamers.

[0039] (Antibacterial agent / preservative) Examples of antibacterial and preservative agents include thiazole preservatives such as 2-methylisothiazolin-3-one and 1,2-benzoisothiazolin-3-one; iodine preservatives such as 3-iodo-2-propagylbutylcarbamic acid; phenolic preservatives such as O-phenylphenol and 3-methyl-4-chlorophenol; pyridine preservatives such as 2-pyridinethiol-1-oxidosodium; triazine preservatives such as hexahydro-1,3,5,tris(2-hydroxyethyl)-S-triazine and hexahydro-1,3,5,-triethyl-S-triazine; bromine preservatives such as 2-bromo-2-nitropropane; inorganic preservatives such as water-soluble glass-silver, zeolite-copper, and boric acid; and poly{oxyethylene(dimethylimino)ethylene(dimethylimino)ethylene}dichloride.

[0040] (Content of additives) The additives other than glycerin monooleate, zinc dithiophosphate, and dispersant described above may be used individually or in combination of two or more. The content of each additive is 0.001 to 30% by mass, preferably 0.005 to 20% by mass, more preferably 0.01 to 10% by mass, and even more preferably 0.05 to 5% by mass, when the total amount of the lubricating oil composition is 100% by mass.

[0041] <Uses of lubricating oil compositions> A lubricating oil composition according to one aspect of this disclosure can be suitably used in applications of conventionally known lubricating oil compositions, such as sliding guide surfaces, linear motion devices (e.g., linear guides, ball screws, etc.), sliding bearings, rolling bearings, power engines (e.g., external combustion engines, internal combustion engines, electric motors, hydraulic motors, etc.), power transmission devices (e.g., pumps, compressors, hydraulic systems, couplings, gears, clutches, transmissions, chains, actuators, etc.), seals, gaskets, screws, valves, etc. It is particularly preferred for use in internal combustion engines, and more preferably for use in hybrid internal combustion engines and internal combustion engines using hydrogen-containing diamond-like carbon members as sliding surfaces.

[0042] The lubricating oil compositions of this disclosure are not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining each of the disclosed technical means are also included within the technical scope of the present invention.

[0043] <Summary> The lubricating oil composition according to Embodiment 1 of the present disclosure contains a base oil, a dispersant, zinc dithiophosphate, and glycerin monooleate, wherein the zinc dithiophosphate includes primary dialkyldithiophosphate and secondary dialkyldithiophosphate, the content of the dispersant is 350 ppm by mass or more and 600 ppm by mass or less in terms of N content, and the content ratio of primary dialkyldithiophosphate to secondary dialkyldithiophosphate is 4:6 to 2:8 by mass ratio. The lubricating oil composition according to Embodiment 2 of this disclosure is a lubricating oil composition for use in lubricating a member having a hydrogen-containing diamond-like carbon coating on its sliding surface, as described in Embodiment 1 above, and is more preferably substantially free of molybdenum dithiocarbamate. In the lubricating oil composition according to embodiment 3 of this disclosure, in embodiment 1 or 2 above, the dispersant is more preferably boron-free succinimide. [Examples]

[0044] The lubricating oil compositions of this disclosure will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0045] 1. Lubricating oil composition The following raw materials were used for the lubricating oil composition. The lubricating oil compositions for each example and comparative example were obtained by compounding them as shown in Table 1. Base oil: Mineral-based base oil (API classification group III) 40°C kinematic viscosity 20.29 mm 2 / s 100℃ kinematic viscosity 4.34mm 2 / s Viscosity index 167 Viscosity index improver: Ethylene-propylene copolymer (olefin copolymer: OCP) (Mw=185000, Mw / Mn=2.63) Primary dialkyldithiophosphate zinc: P = 7.60 wt%, Zn = 9.10 wt% Zinc secondary dialkyldithiophosphate A: P = 7.40 wt%, Zn = 8.10 wt% Zinc secondary dialkyldithiophosphate B:P=8.10wt%, Zn=9.00wt% Dispersant (boron-free succinic bisimide): B=0.00 wt%, N=1.14 wt% Dispersant (boron-containing succinimide): B=0.45 wt%, N=1.29 wt% Cleaning agent (calcium sulfonate): Ca = 15.4 wt% Cleaning agent (magnesium sulfonate): Mg = 9.3 wt% Other additives: defoaming agents, amine-based antioxidants, and pour point depressants.

[0046] 2. Physical properties The physical properties described in the examples were determined by the following method. <40℃ kinematic viscosity> Measurements were taken in accordance with JIS K 2283:2000. <Kinematic viscosity at 100℃> Measurements were taken in accordance with JIS K 2283:2000. <Each content> The content of Ca, Mg, P, Zn, and B (derived from the dispersant) was measured in accordance with JPI-5S-38-02. The N (derived from the dispersant) was measured in accordance with JIS K2609:1998. <Measurement conditions for molecular weight of viscosity index improvers> (GPC measurement) The weight-average molecular weight (Mw) was determined by gel permeation chromatography (GPC). The following equipment and conditions were used to obtain the weight-average molecular weight in polystyrene terms. (GPC measurement device) Test equipment: GPC / FTIR (Senshu Kagaku) GPC column: Shodex UT-806L (Showa Denko) (2 tubes) Solvent: 1,3,5-trichlorobenzene Temperature: 145℃ Flow rate: 1.0mL / min Molecular weight conversion: Universal Calibration method Detector: JASCO VIR-200 Injection concentration: 0.3w / v% Injection volume: 750μl

[0047] 3. Evaluation The evaluations described in the examples were performed using the following method. <Dispersibility> A sample without carbon black was subjected to ultrasonic treatment (time: 7 minutes, output: 20kHz / 200W). Next, a sample with a carbon black concentration of 6% by mass was subjected to the same ultrasonic treatment (time: 7 minutes, output: 20kHz / 200W). The viscosity increase (rate of change) at 40°C was calculated by comparing the sample without carbon black after ultrasonic treatment with the sample containing carbon black after ultrasonic treatment. The reason for ultrasonic treatment of the sample without carbon black was to consider the shear effect caused by ultrasound.

[0048] <Presence or absence of sediment> The presence or absence of precipitate was evaluated using the ISOT (Indiana Stirring Oxidation Test) in accordance with JIS K 2514-1. Specifically, the presence or absence of precipitate was visually confirmed after a test at 165.5°C for 72 hours.

[0049] <Abrasion Resistance> A FALEX LFW-1 apparatus was used as the test apparatus. FALEX S10 steel was used as the steel block, and FALEX H60 steel was used as the steel ring. A lubricating oil composition was supplied to the contact surface between the steel block and the steel ring. The test conditions were as follows: Rotation speed: 160 rpm Load: 100N Temperature: 55℃ Exam time: 20 minutes After the test, the wear mark width (μm) of the steel block was measured, and a value of 380 μm or less was considered acceptable. A value of 370 μm or less is more preferable.

[0050] 4.Results The results are shown in Table 1. [Table 1]

[0051] As shown in Table 1, the inclusion of a dispersant, with a mass ratio of 4:6 to 2:8 between primary and secondary dialkyldithiophosphates, demonstrated excellent soot dispersibility, suppression of zinc dithiophosphate precipitation during oxidative degradation, and superior abrasion resistance.

Claims

1. It contains a base oil, a dispersant, zinc dithiophosphate, and glycerin monooleate. The content of the dispersant is 350 ppm by mass or more and 600 ppm by mass or less, in terms of N-to-minute ratio. The zinc dithiophosphate comprises primary dialkyldithiophosphate zinc and secondary dialkyldithiophosphate zinc, wherein the content ratio of primary dialkyldithiophosphate zinc to secondary dialkyldithiophosphate zinc is 4:6 to 2:8 by mass ratio. Lubricating oil composition for internal combustion engines.

2. This is a lubricating oil composition for internal combustion engines, intended for use in lubricating components having a hydrogen-containing diamond-like carbon coating on their sliding surfaces. Substantially free of molybdenum dithiocarbamate, The lubricating oil composition for internal combustion engines according to claim 1.

3. The internal combustion engine lubricant composition according to claim 1 or 2, wherein the dispersant is boron-free succinimide.

4. The lubricating oil composition for internal combustion engines according to claim 1 or 2, wherein the content of glycerin monooleate is 0.01% by mass to 0.2% by mass.

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