Lubricating oil composition

Abstract

There has been a need for development of a lubricating oil composition that has less oil evaporation at lower temperatures and can improve both fuel economy and oil film retention. The present invention is a lubricating oil composition containing a base oil (A) and a viscosity index improver (B), wherein: the base oil (A) contains a fraction (a1) including a hydrocarbon group with a carbon number less than 28 in an amount of 60.0 to 80.0 mass% based on the total amount of the base oil (A); and the viscosity index improver (B) contains a comb polymer (B1) having a weight average molecular weight of 450,000 or more.

Description

lubricating oil composition

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

[0002] The NOACK test at 250°C, as specified in ASTM D5800, is widely used as an indicator of oil evaporation. However, with the increasing sophistication of engines, a correlation between the NOACK value and the amount of oil evaporated (consumed) under actual operating conditions may not be obtained. In this context, it has been reported that oil evaporation values ​​at lower temperatures correlate with actual oil consumption (Non-Patent Literature 1).

[0003] Proceedings of the Society of Automotive Engineers of Japan, Vol.52, No.6, November 2021

[0004] Under these circumstances, there was a need for the development of a lubricating oil composition that reduces oil evaporation at lower temperatures while also improving fuel efficiency and oil film retention.

[0005] As a result of diligent research, the present inventors have found that the above problems can be solved by including a predetermined amount of a specific fraction of base oil and a comb-shaped polymer having a specific mass-average molecular weight, and have completed the present invention. That is, the present invention provides, for example, the following embodiments: [1] A lubricating oil composition comprising a base oil (A) and a viscosity index improver (B), wherein the base oil (A) contains a fraction (a1) having hydrocarbon groups with fewer than 28 carbon atoms in an amount of 60.0 to 80.0% by mass on a basis of the total amount of base oil (A), and the viscosity index improver (B) contains a comb-shaped polymer (B1) having a mass-average molecular weight of 450,000 or more. [2] The lubricating oil composition according to [1], wherein the base oil (A) contains a fraction (a2) having hydrocarbon groups with 28 or more carbon atoms and less than 32 carbon atoms in an amount of 15.0 to 25.0% by mass on a basis of the total amount of base oil (A). [3] The lubricating oil composition according to [1] or [2], wherein the molecular weight distribution (Mw / Mn) of the comb-shaped polymer (B1) is 3.0 or less. [4] The lubricating oil composition according to any one of [1] to [3], wherein the base oil (A) contains mineral oil. [5] The lubricating oil composition according to any one of [1] to [4], wherein the viscosity index of the base oil (A) is 200 or less. [6] The lubricating oil composition according to any one of [1] to [5], wherein the viscosity index of the lubricating oil composition is 250 or more. [7] The kinematic viscosity of the lubricating oil composition at 100°C is 5.0 mm ２ A lubricating oil composition according to any one of [1] to [6], wherein the ratio is 1 / s or more.

[0006] A preferred embodiment of the present invention provides a lubricating oil composition that exhibits low oil evaporation at temperatures below 250°C. Another preferred embodiment of the present invention provides a lubricating oil composition that has low kinematic viscosity at 40°C, a high viscosity index, and appropriate high-temperature shear viscosity (HTHS viscosity), thereby improving fuel efficiency and oil film retention.

[0007] The numerical ranges described herein can be any combination of upper and lower limits. For example, if the numerical range is described as "preferably 30 to 100, more preferably 40 to 80," the ranges of "30 to 80" and "40 to 100" are also included in the numerical range described herein. Similarly, if the numerical range is described as "preferably 30 or more, more preferably 40 or more, and also preferably 100 or less, more preferably 80 or less," the ranges of "30 to 80" and "40 to 100" are also included in the numerical range described herein. In addition, for example, if the numerical range described herein is described as "60 to 100," it means the range is "60 or more (60 or greater than 60), and 100 or less (100 or less than 100)." Furthermore, in the provisions for upper and lower limits described herein, the numerical range from the lower limit to the upper limit can be defined by appropriately selecting and combining the options from each set of choices. In addition, multiple combinations of the various requirements described as preferred embodiments described herein are possible.

[0008] [Composition of Lubricating Oil Composition] One embodiment of the present invention is a lubricating oil composition comprising a base oil (A) (hereinafter also referred to as "component (A)") and a viscosity index improver (B) (hereinafter also referred to as "component (B)"), wherein the base oil (A) contains a fraction (a1) containing hydrocarbon groups with fewer than 28 carbon atoms in an amount of 60.0 to 80.0% by mass on a basis of the total amount of base oil (A), and the viscosity index improver (B) contains a comb-shaped polymer (B1) with a mass average molecular weight of 450,000 or more. With this configuration, the NOACK value at 150°C can be set to less than the specified value, so a lubricating oil composition with low oil consumption can be obtained even in actual use environments. Furthermore, with this configuration, a lubricating oil composition with low kinematic viscosity at 40°C, a high viscosity index, and excellent fuel efficiency can be obtained. Furthermore, this configuration allows for a lubricating oil composition with excellent fuel efficiency and oil film retention, as the ratio of the HTHS viscosity at 80°C to the HTHS viscosity at 150°C (hereinafter also referred to as HTHS80 / 150) is within an appropriate range. In this specification, the NOACK value at 150°C refers to the value measured at 150°C for 12 hours in accordance with ASTM D5800 (hereinafter also referred to as NOACK 150°C). The details of each component contained in the lubricating oil composition of one embodiment of the present invention will be described below.

[0009] <Component (A): Base Oil> In one embodiment of the present invention, a lubricating oil composition is used in which a fraction (a1) containing hydrocarbon groups with fewer than 28 carbon atoms is present in an amount of 60.0 to 80.0% by mass on a total basis of the base oil (A) as the base oil (A). By setting the fraction (a1) of the base oil (A) to be below the upper limit of the above numerical range, the NOACK 150°C value can be adjusted to 5.00% by mass or less, and the oil consumption performance under actual engine operating conditions can be improved. Furthermore, by setting the fraction (a1) of the base oil (A) to be above the lower limit of the above numerical range, the kinematic viscosity at 40°C can be set to 25.0 mm. ２A lubricating oil composition with excellent fuel efficiency of 0 / s or less can be obtained. Furthermore, by setting the fraction (a1) of the base oil (A) within the above numerical range, a lubricating oil composition with excellent oil film retention, where HTHS80 / 150 is 2.00 or higher, can be obtained. From the viewpoint of obtaining a lubricating oil composition that can improve fuel efficiency and oil film retention, the fraction (a1) containing hydrocarbon groups with fewer than 28 carbon atoms is preferably 61.0% by mass or more, 61.5% by mass or more, 62.0% by mass or more, 62.5% by mass or more, or 63.0% by mass or more, and may also be 64.0% by mass or more, 65.0% by mass or more, 66.0% by mass or more, 67.0% by mass or more, 68.0% by mass or more, 69.0% by mass or more, or 70.0% by mass or more. Furthermore, the fraction (a1) containing hydrocarbon groups with fewer than 28 carbon atoms is preferably 79.5% by mass or less, 79.0% by mass or less, 78.5% by mass or less, 78.0% by mass or less, or 77.5% by mass or less, from the viewpoint of providing a lubricating oil composition that has a low oil evaporation rate and can improve oil film retention, and may also be 77.0% by mass or less, 76.0% by mass or less, 75.0% by mass or less, 74.0% by mass or less, 73.0% by mass or less, 72.0% by mass or less, 71.0% by mass or less, or 70.0% by mass or less.

[0010] In one embodiment of the present invention, a lubricating oil composition may be used in which, as the base oil (A), a fraction (a2) containing hydrocarbon groups with 28 or more and less than 32 carbon atoms is present in an amount of 15.0 to 25.0% by mass based on the total amount of base oil (A), together with the above fraction (a1). By setting the fraction (a2) of base oil (A) to be below the upper limit of the above numerical range, the oil consumption performance under actual engine operating conditions can be improved. Furthermore, by setting the fraction (a2) of base oil (A) to be above the lower limit of the above numerical range, a lubricating oil composition with better fuel efficiency can be obtained. Moreover, by setting the fraction (a2) of base oil (A) to be within the above numerical range, a lubricating oil composition with better oil film retention can be obtained. The fraction (a2) containing hydrocarbon groups with 28 or more carbon atoms and less than 32 carbon atoms is preferably 15.5% by mass or more, 16.0% by mass or more, or 16.5% by mass or more, from the viewpoint of providing a lubricating oil composition that can further improve fuel efficiency and oil film retention, and may also be 17.0% by mass or more, 17.5% by mass or more, 18.0% by mass or more, 18.5% by mass or more, 19.0% by mass or more, 19.5% by mass or more, or 20.0% by mass or more. Furthermore, the fraction (a2) containing hydrocarbon groups with 28 or more carbon atoms but less than 32 carbon atoms is preferably 24.9% by mass or less, 24.8% by mass or less, 24.7% by mass or less, or 24.6% by mass or less, from the viewpoint of providing a lubricating oil composition that has less oil evaporation and can further improve oil film retention, and may also be 24.5% by mass or less, 24.0% by mass or less, 23.5% by mass or less, 23.0% by mass or less, 22.5% by mass or less, 22.0% by mass or less, 21.5% by mass or less, or 21.0% by mass or less.

[0011] The base oil (A) described above can be adjusted to the range of each fraction containing the above number of carbon atoms, based on the measurement results of each fraction measured by the method described in the examples below. Alternatively, base oil (A) can be obtained, for example, by combining mineral oils, synthetic oils, or a combination of mineral oil and synthetic oil as described below, and adjusting to the range of each fraction containing the above number of carbon atoms, while taking into account the measurement results of each fraction measured by the method described in the examples below.

[0012] Examples of mineral oils that constitute the fraction (a1) containing hydrocarbon groups having less than 28 carbon atoms and the fraction (a2) containing hydrocarbon groups having 28 or more carbon atoms but less than 32 carbon atoms in a lubricating oil composition according to one aspect of the present invention include atmospheric residue obtained by atmospheric distillation of crude oil such as paraffinic crude oil, intermediate base crude oil, and naphthenic crude oil; distillate obtained by vacuum distillation of these atmospheric residues; and refined oil obtained by subjecting the distillate to one or more refining treatments such as solvent delamination, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining. The base oil (A) used in the lubricating oil composition according to one aspect of the present invention may be one of these mineral oils used alone, or it may be a mixed oil using multiple mineral oils in combination.

[0013] The synthetic oils constituting the fraction (a1) containing a hydrocarbon group having less than 28 carbon atoms and the fraction (a2) containing a hydrocarbon group having 28 or more and less than 32 carbon atoms included in the lubricating oil composition of one embodiment of the present invention include, for example, α-olefins and their homopolymers, or polyα-olefins such as α-olefin copolymers (for example, α-olefin copolymers having 8 to 14 carbon atoms such as ethylene-α-olefin copolymers); isoparaffins; polyalkylene glycols; ether-based oils such as polyphenyl ethers; ester-based oils such as polyol esters, dibasic acid esters, and mono esters; alkylbenzenes; alkylnaphthalenes; synthetic oils (GTL waxes (Gas ToLiquids WAX)) obtained by isomerizing waxes produced from natural gas by the Fischer-Tropsch method or the like; synthetic oils (Ethylene To Liquid (ETL)) obtained by oligomerizing olefins produced from gas as a raw material; CTL base oils obtained by the direct liquefaction method (such as the Bergius method) in which coal is pulverized, mixed with a solvent, and directly reacted with hydrogen under high temperature and high pressure, and CTL base oils obtained by the indirect liquefaction method (such as the Fischer-Tropsch method) in which coal is gasified once (coal gasification), the resulting gas is separated and purified, and then subjected to a synthesis reaction with a raw material and liquefied; and the like. These synthetic oils may be produced from renewable resources. The base oil (A) used in the lubricating oil composition of one embodiment of the present invention may be a single synthetic oil or a mixed oil in which a plurality of synthetic oils are used in combination. Further, as described above, the base oil (A) used in the lubricating oil composition of one embodiment of the present invention may be a mixed oil in which mineral oil and synthetic oil are used in combination.

[0014] Among these, the base oil (A) used in one embodiment of the present invention preferably contains at least one selected from mineral oils classified into API (American Petroleum Institute) base oil categories Group 2 and Group 3, and synthetic oils.

[0015] The kinematic viscosity at 100 °C of the base oil (A) used in one embodiment of the present invention is 2.0 mm ２ / s or more, 2.1 mm ２ / s or more, 2.2 mm ２ / s or more, 2.3 mm２ / s or more, 2.4 mm ２ / s or more, 2.5 mm ２ / s or more, 2.6 mm ２ / s or more, or 2.8 mm ２ / s or more is preferable, and also 3.0 mm ２ / s or more, 3.2 mm ２ / s or more, 3.4 mm ２ / s or more, 3.6 mm ２ / s or more, 3.8 mm ２ / s or more, or 4.0 mm ２ / s or more may be used. Further, from the viewpoint of obtaining a lubricating oil composition having better fuel economy, the kinematic viscosity at 100 °C of the base oil (A) used in one aspect of the present invention is 5.0 mm ２ / s or less, 4.9 mm ２ / s or less, 4.8 mm ２ / s or less, 4.7 mm ２ / s or less, 4.6 mm ２ / s or less, or 4.5 mm ２ / s or less is preferable, and also 4.3 mm ２ / s or less, 4.1 mm ２ / s or less, 4.0 mm ２ / s or less, 3.8 mm ２ / s or less, 3.6 mm ２ / s or less, 3.4 mm ２ / s or less, 3.2 mm ２ / s or less, or 3.0 mm ２ / s or less may be used. In one aspect of the present invention, when a mixed oil is used as the base oil (A), it is preferable that the kinematic viscosity at 100 °C of the mixed oil is within the above range.

[0016] Further, the viscosity index of the base oil (A) used in one aspect of the present invention preferably is 80 or more, more preferably 90 or more, still more preferably 100 or more, and even more preferably 110 or more from the viewpoint of suppressing viscosity change due to temperature change and further improving fuel efficiency and oil film retention. Also, it may be 200 or less, 190 or less, 180 or less, 170 or less, 160 or less, 150 or less, 140 or less, or 130 or less. The base oil (A) used in one aspect of the present invention adjusts the above-described fractions (a1) and (a2), and there is a limitation that the viscosity index becomes low as the base oil composition. However, by combining with the viscosity index improver (B) described later, the viscosity index is improved, and the ratio of the HTMS viscosity at 80°C to the HTMS viscosity at 150°C (HTHS80 / 150) is adjusted to a predetermined range, thereby improving fuel efficiency and oil film retention. In the present specification, the kinematic viscosity and the viscosity index mean values measured or calculated in accordance with ASTM D455.

[0017] In the lubricating oil composition of one aspect of the present invention, the content of the base oil (A) is 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, or 85% by mass or more based on the total amount (100% by mass) of the lubricating oil composition, and also 99% by mass or less, 98% by mass or less, 95% by mass or less, or 90% by mass or less.

[0018] <Component (B): Viscosity Index Improver> A lubricating oil composition according to one aspect of the present invention contains a viscosity index improver (B) comprising a comb-shaped polymer (B1) with a mass-average molecular weight of 450,000 or more. By including the above-mentioned comb-shaped polymer (B1) as the viscosity index improver (B), the viscosity index of the lubricating oil composition is significantly increased, improving the fuel efficiency and oil film retention of the lubricating oil composition. The comb-shaped polymer (B1) is preferably a polymer having a structure in which there are many three-way branching points on the main chain from which high molecular weight side chains protrude. The comb-shaped polymer (B1) used in one aspect of the present invention is more preferably a polymer having at least one constituent unit (X1) derived from a macromonomer (x1). This constituent unit (X1) corresponds to the "high molecular weight side chain" mentioned above. In the present invention, the above-mentioned "macromonomer (x1)" means a high molecular weight monomer having a polymerizable functional group, and it is preferable that it is a high molecular weight monomer having a polymerizable functional group at its terminal.

[0019] The comb-shaped polymer (B1) used in one aspect of the present invention may be a homopolymer consisting only of constituent units (X1) derived from one type of macromonomer (x1), or it may be a copolymer containing constituent units (X1) derived from two or more types of macromonomers (x1). Furthermore, the comb-shaped polymer (B1) used in one aspect of the present invention may be a copolymer containing constituent units (X2) derived from other monomers other than macromonomers (x1) along with constituent units derived from macromonomers (x1). As a specific structure of such a comb-shaped polymer, a copolymer having a main chain containing constituent units (X2) derived from monomers (x2) and side chains containing constituent units (X1) derived from macromonomers (x1) is preferred.

[0020] Examples of monomers (x2) include (meth)acrylates, nitrogen atom-containing vinyl monomers, hydroxyl group-containing vinyl monomers, phosphorus atom-containing monomers, aliphatic hydrocarbon vinyl monomers, alicyclic hydrocarbon vinyl monomers, vinyl esters, vinyl ethers, vinyl ketones, epoxy group-containing vinyl monomers, halogen element-containing vinyl monomers, esters of unsaturated polycarboxylic acids, (di)alkyl fumarates, (di)alkyl maleates, aromatic hydrocarbon vinyl monomers, and the like. Among these, the comb-shaped polymer (B1) used in one aspect of the present invention is preferably a comb-shaped poly(meth)acrylate (b1) having poly(meth)acrylate as the main chain.

[0021] The mass-average molecular weight of the comb-shaped polymer (B1) used in one aspect of the present invention is preferably 460,000 or more, 470,000 or more, 480,000 or more, 490,000 or more, or 500,000 or more, from the viewpoint of further improving the fuel efficiency and oil film retention of the lubricating oil composition, and may also be 520,000 or more, 540,000 or more, 560,000 or more, 580,000 or more, or 600,000 or more. Furthermore, the mass-average molecular weight of the comb-shaped polymer (B1) used in one aspect of the present invention is preferably 2,000,000 or less, 1,500,000 or less, 1,000,000 or less, 800,000 or less, 750,000 or less, or 700,000 or less, from the viewpoint of providing a lubricating oil composition with good shear stability, and may also be 680,000 or less, 660,000 or less, 640,000 or less, 620,000 or less, or 600,000 or less.

[0022] In one aspect of the present invention, the molecular weight distribution (Mw / Mn) of the comb-shaped polymer (B1) used is preferably 3.0 or less, 2.9 or less, or 2.8 or less, and also preferably 2.0 or more, greater than 2.0, 2.1 or more, 2.2 or more, 2.3 or more, or 2.4 or more, from the viewpoint of further improving the fuel efficiency and oil film retention of the lubricating oil composition. In this specification, the mass average molecular weight (Mw) and the number average molecular weight (Mn) are values ​​on a standard polystyrene basis measured by gel permeation chromatography (GPC).

[0023] In a lubricating oil composition according to one embodiment of the present invention, the content of the comb-shaped polymer (B1) in terms of resin content is preferably 2.0% by mass or more, 2.2% by mass or more, 2.4% by mass or more, or 2.5% by mass or more, based on the total amount (100% by mass) of the lubricating oil composition, from the viewpoint of further improving the fuel efficiency and oil film retention of the lubricating oil composition, and is preferably 5.0% by mass or less, 4.5% by mass or less, 4.0% by mass or less, or 3.5% by mass or less, from the viewpoint of maintaining good lubrication performance.

[0024] Furthermore, the viscosity index improver (B) used in one aspect of the present invention may or may not contain a viscosity index improver made of a polymer other than the comb-shaped polymer (B1) described above, as long as it does not impair the effects of the present invention. Examples of such other polymers include polymers that do not fall under the category of comb-shaped polymers, such as dispersed poly(meth)acrylates, olefin copolymers (e.g., ethylene-propylene copolymers), dispersed olefin copolymers, and styrene copolymers (e.g., styrene-diene copolymers, styrene-isoprene copolymers).

[0025] In one aspect of the present invention, the content ratio of component (B1) in component (B) used is preferably 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 98% by mass or more, 99% by mass or more, or 100% by mass, based on the total amount (100% by mass) of component (B).

[0026] <Various Additives> A lubricating oil composition according to one embodiment of the present invention may contain various additives as needed, as long as they do not impair the effects of the present invention. Examples of such additives include pour point depressants, antioxidants, metal-based detergents, ashless dispersants, friction modifiers, wear inhibitors, rust inhibitors, defoamers, metal deactivators, and extreme pressure additives. These lubricating oil additives may be used individually or in combination of two or more. Furthermore, compounds having multiple functions as the above-mentioned additives (for example, compounds having the functions of a wear inhibitor and an extreme pressure additive) may be used.

[0027] The content of each of these additives can be adjusted as appropriate within a range that does not impair the effects of the present invention, but on a basis of the total amount (100% by mass) of the lubricating oil composition, the content of each additive is usually 0.001 to 15% by mass, preferably 0.005 to 10% by mass, and more preferably 0.01 to 5% by mass for each additive independently.

[0028] [Pour point depressant] A lubricating oil composition according to one aspect of the present invention may further contain a pour point depressant. The pour point depressant may be used alone or in combination of two or more types. Examples of pour point depressants used in one aspect of the present invention include ethylene-vinyl acetate copolymer, condensate of chlorinated paraffin and naphthalene, condensate of chlorinated paraffin and phenol, polyalkylstyrene, and the like.

[0029] [Antioxidants] A lubricating oil composition according to one embodiment of the present invention may further contain antioxidants. Antioxidants may be used alone or in combination of two or more. Examples of antioxidants used in one embodiment of the present invention include amine-based antioxidants such as alkylated diphenylamine, phenylnaphthylamine, and alkylated phenylnaphthylamine; phenol-based antioxidants such as 2,6-di-t-butylphenol, 4,4'-methylenebis(2,6-di-t-butylphenol), isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; and sulfur-based antioxidants such as phenothiazine, dioctadecyl sulfide, dilauryl-3,3'-thiodipropionate, and 2-mercaptobenzimidazole.

[0030] [Metal-based detergent] A lubricating oil composition according to one aspect of the present invention may further contain a metal-based detergent. The metal-based detergent may be used alone or in combination of two or more types. Examples of metal-based detergents used in one aspect of the present invention include metal salts such as metal sulfonates, metal salicylates, and metal phenates. The metal atoms constituting the metal salt are preferably selected from alkali metals and alkaline earth metals, more preferably sodium, calcium, magnesium, or barium, and even more preferably calcium and magnesium. In one aspect of the present invention, metal salicylates are preferred as the metal-based detergent, and most preferably one or more selected from calcium salicylate and magnesium salicylate.

[0031] [Ashless Dispersant] The lubricating oil composition according to one aspect of the present invention may further contain an ashless dispersant. The ashless dispersant may be used alone or in combination of two or more. The ashless dispersant used in one aspect of the present invention is preferably alkenyl succinimide, and may also be a modified alkenyl succinimide obtained by reacting with one or more selected from boron compounds, alcohols, aldehydes, ketones, alkylphenols, cyclic carbonates, epoxy compounds, and organic acids.

[0032] [Friction Modifier] A lubricating oil composition according to one aspect of the present invention may further contain a friction modifier. The friction modifier may be used alone or in combination of two or more types. Examples of friction modifiers used in one aspect of the present invention include molybdenum-based friction modifiers such as molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDTP), and amine salts of molybdenum acid; and ashless friction modifiers such as aliphatic amines, fatty acid esters, fatty acid amides, fatty acids, aliphatic alcohols, and aliphatic ethers having at least one alkyl group or alkenyl group with 6 to 30 carbon atoms in the molecule.

[0033] [Anti-wear agents] A lubricating oil composition according to one aspect of the present invention may further contain an anti-wear agent. The anti-wear agent may be used alone or in combination of two or more types. Examples of anti-wear agents used in one aspect of the present invention include sulfur-containing compounds such as zinc dialkyldithiophosphate (ZnDTP), zinc phosphate, zinc dithiocarbamate, disulfides, sulfurized olefins, sulfurized oils and fats, sulfurized esters, thiocarbonates, thiocarbamates, and polysulfides; phosphorus-containing compounds such as phosphite esters, phosphate esters, phosphonic acid esters, and their amine salts or metal salts; and sulfur and phosphorus-containing anti-wear agents such as thiophosphite esters, thiophosphate esters, thiophosphonic acid esters, and their amine salts or metal salts.

[0034] [Rust Inhibitor] A lubricating oil composition according to one aspect of the present invention may further contain a rust inhibitor. The rust inhibitor may be used alone or in combination of two or more types. Examples of rust inhibitors used in one aspect of the present invention include fatty acids, alkenyl succinate half esters, fatty acid soaps, alkyl sulfonates, polyhydric alcohol fatty acid esters, fatty acid amines, oxidized paraffins, alkyl polyoxyethylene ethers, and the like.

[0035] [Antifoaming agent] The lubricating oil composition according to one embodiment of the present invention may further contain an antifoaming agent. The antifoaming agent may be used alone or in combination of two or more types. Examples of antifoaming agents used in one embodiment of the present invention include alkyl silicone antifoaming agents, fluorosilicone antifoaming agents, and fluoroalkyl ether antifoaming agents.

[0036] [Metal deactivators] A lubricating oil composition according to one aspect of the present invention may further contain a metal deactivator. The metal deactivator may be used alone or in combination of two or more. Examples of metal deactivators used in one aspect of the present invention include benzotriazole, imidazoline, pyrimidine derivatives, and thiadiazole.

[0037] [Extreme Pressure Additives] A lubricating oil composition according to one aspect of the present invention may further contain extreme pressure additives. Extreme pressure additives may be used alone or in combination of two or more. Examples of extreme pressure additives used in one aspect of the present invention include sulfur-containing compounds such as zinc dialkyldithiophosphate (ZnDTP), zinc phosphate, zinc dithiocarbamate, disulfides, sulfurized olefins, sulfurized oils and fats, sulfurized esters, thiocarbonates, thiocarbamates, and polysulfides; phosphorus-containing compounds such as phosphite esters, phosphate esters, phosphonic acid esters, and their amine salts or metal salts; and sulfur and phosphorus-containing anti-wear agents such as thiophosphite esters, thiophosphate esters, thiophosphonic acid esters, and their amine salts or metal salts.

[0038] [Method for Manufacturing Lubricating Oil Composition] The method for manufacturing a lubricating oil composition according to one aspect of the present invention is not particularly limited, but it is preferable to have a step of blending a base oil (A) and a viscosity index improver (B) with various other additives as needed. The order in which each component is blended can be set as appropriate.

[0039] [Properties of the Lubricating Oil Composition] The kinematic viscosity of the lubricating oil composition according to one embodiment of the present invention at 100°C is 5.0 mm, from the viewpoint of providing a lubricating oil composition that balances fuel efficiency and lubricity. ２ / s or more, 5.2mm ２ / s or more, 5.4mm ２ / s or more, 5.6mm ２ / s or more, 5.8mm ２ / s or more, 6.0mm ２ / s or more, 6.2mm ２ / s or more, or 6.4 mm ２ A value of 10.0 mm or more is preferred. ２ / s or less, 9.5mm ２ / s or less, 9.0mm ２ / s or less, 8.8mm ２ / s or less, 8.6mm ２ / s or less or 8.4mm ２ A value of / s or less is preferable.

[0040] The kinematic viscosity of a lubricating oil composition according to one embodiment of the present invention at 40°C is 25.0 mm, from the viewpoint of providing a lubricating oil composition with excellent fuel efficiency. ２ / s or less, 24.8mm ２ / s or less, or 24.6 mm ２ A value of / s or less is preferable, and the lower limit is not particularly limited, but for example, 10.0 mm. ２ / s or more, 12.0mm ２ / s or more, or 14.0 mm ２ It may be / s or more.

[0041] The viscosity index of the lubricating oil composition according to one embodiment of the present invention is preferably 280 or higher, from the viewpoint of providing a lubricating oil composition with excellent fuel efficiency and oil film retention properties, and may also be 290 or higher, 300 or higher, 310 or higher, 320 or higher, 330 or higher, 340 or higher, or 350 or higher. The upper limit of the viscosity index of the lubricating oil composition is not particularly limited, but may be, for example, 500 or less, 400 or less, 390 or less, or 380 or less.

[0042] The HTHS viscosity at 150°C of a lubricating oil composition according to one embodiment of the present invention is preferably 2.00 mPa·s or higher, 2.10 mPa·s or higher, or 2.20 mPa·s or higher, from the viewpoint of providing a lubricating oil composition with excellent oil film retention properties. The lower limit is not particularly limited, but may be, for example, 3.00 mPa·s or lower, 2.90 mPa·s or lower, or 2.80 mPa·s or lower.

[0043] In a lubricating oil composition according to one embodiment of the present invention, the ratio of the HTHS viscosity at 80°C to the HTHS viscosity at 150°C (HTHS80 / 150) is preferably 2.00 or higher, 2.05 or higher, or 2.10 or higher, and also preferably 2.50 or lower, 2.45 or lower, or 2.40 or lower, from the viewpoint of providing a lubricating oil composition with excellent oil film retention properties.

[0044] In one embodiment of the present invention, from the viewpoint of providing a lubricating oil composition with improved oil evaporation, the NOACK value measured at 150°C for 12 hours in accordance with ASTM D5800 is preferably 5.00% by mass or less, or 4.50% by mass or less, and the lower limit is not particularly limited, but for example, it is 3.00% by mass or more.

[0045] [Uses of the Lubricating Oil Composition] The lubricating oil composition of the present invention has a low oil evaporation rate, indicated by the NOACK value at 150°C, and also exhibits excellent fuel efficiency and oil film retention, making it suitable for use in lubricating internal combustion engines. Therefore, the present invention also provides the following internal combustion engine [I] and the method of using the lubricating oil composition [II]. [I] An internal combustion engine filled with the lubricating oil composition of one aspect of the present invention described above. [II] A method of using the lubricating oil composition for lubricating an internal combustion engine, wherein the lubricating oil composition of one aspect of the present invention described above is applied.

[0046] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited in any way by these examples. The various physical properties of each component used in the examples and comparative examples and the obtained lubricating oil compositions were measured in accordance with the following methods.

[0047] (1) Kinematic viscosity and viscosity index were measured and calculated in accordance with ASTM D455. The kinematic viscosity at 40°C was 25.0 mm². ２Samples with a viscosity index of 280 or less were judged to be acceptable. (2) Mass-average molecular weight (Mw), number-average molecular weight (Mn) One TSKguardcolumn SuperHZ-L and two TSKSuperMultipore HZ-M columns from Tosoh Corporation were attached to a Waters 1515 isocratic HPLC pump and a 2414 differential refractive index (RI) detector, in that order from upstream. Measurements were taken under the following conditions: measurement temperature: 40°C, mobile phase: tetrahydrofuran, flow rate: 0.35 mL / min, sample concentration: 1.0 mg / mL, and the values ​​were calculated on a standard polystyrene basis. (3) Using measuring devices with amounts equal to or less than fraction (a1) and fraction (a2), the peak area of ​​fractions containing hydrocarbon groups for each number of carbon atoms was calculated under the following measurement conditions, starting from 8 to less than 10 carbon atoms, then 10 to less than 12 carbon atoms, and thereafter increasing by 2 carbon atoms up to 36 to less than 38 carbon atoms. Fractions containing hydrocarbon groups with 36 or more carbon atoms were calculated as the residue of fractions containing hydrocarbon groups with fewer than 36 carbon atoms. In addition, the proportion of fractions containing hydrocarbon groups to all peak areas was calculated for each range of carbon atoms. Furthermore, the cumulative amount up to 28 carbon atoms was calculated from the proportion of the fractions. (Measurement device) Device: Shimadzu Corporation GC-2014 Detector type: FID Column: Packed column Packing material: Silicone OV-1 1.5% Shinwasorb-S 60 / 80 (Measurement conditions) Injector temperature: 360°C Detector temperature: 360°C Heating conditions: Initial temperature 60°C Heating rate: 10°C / min Final heating temperature: 350°C Holding time at final heating temperature: 5 min Gas flow rate: N ２ 45 mL / min (4) NOACK 150°C Measured at 150°C for 12 hours in accordance with ASTM D5800. Samples with a NOACK 150°C value of 5.00 mass% or less were judged to be acceptable. (5) HTHS viscosity In accordance with ASTM D4683, using a TBS (Tapered Bearing Simulator Viscometer), under temperature conditions of 80°C and 150°C, with a shear rate of 10 ６ Measurements were taken in seconds. A score of 2.00 or higher and 2.50 or lower for HTHS 80 / 150 was considered acceptable.

[0048] Examples 1-8, Comparative Examples 1-18 Lubricating oil compositions were prepared by adding and mixing the various components and other additives shown in Tables 1-4 in the amounts shown in Tables 1-4. Note that the amounts of viscosity index improvers in Tables 1-4 are listed as amounts equivalent to resin content. In addition, the viscosity index improver content differs for each sample in order to standardize the viscosity grade. Details of each component used in the preparation of the lubricating oil compositions are as follows. <Component (A): Base oil> Using the following mineral oils A1-A7, the fraction containing hydrocarbon groups with fewer than 28 carbon atoms (a1) and the fraction containing hydrocarbon groups with 28 or more carbon atoms but less than 32 carbon atoms (a2) were adjusted to the values ​​shown in Tables 1-4. ・Mineral oil A1: Kinematic viscosity at 100°C is 4.5 mm ２ Mineral oil with viscosity index of 127 (API base oil category group 3). • Mineral oil A2: kinematic viscosity at 100°C is 4.3 mm². ２ Mineral oil with viscosity index of 122 (API base oil category group 3). • Mineral oil A3: kinematic viscosity at 100°C is 4.1 mm². ２ Mineral oil with viscosity index of 121 (API base oil category group 3). • Mineral oil A4: kinematic viscosity at 100°C is 2.7 mm². ２ Mineral oil with viscosity index of 112 (API base oil category group 2). • Mineral oil A5: kinematic viscosity at 100°C is 2.7 mm². ２ Mineral oil with viscosity index of 113 (API base oil category group 2). • Mineral oil A6: kinematic viscosity at 100°C is 2.9 mm². ２ Mineral oil with viscosity index of 119 (API base oil category group 2). • Mineral oil A7: kinematic viscosity at 100°C is 2.8 mm ２ / s, mineral oil with a viscosity index of 123 (API base oil category group 3).

[0049] <Component (B): Viscosity Index Improver> ・Comb-shaped polymer b1: A non-dispersible comb-shaped poly(meth)acrylate (Mw = 520,000, Mw / Mn = 2.8) with a structure having many tridental branching points on the main chain from which high molecular weight side chains protrude. ・Comb-shaped polymer b2: A non-dispersible comb-shaped poly(meth)acrylate (Mw = 600,000, Mw / Mn = 2.4) with a structure having many tridental branching points on the main chain from which high molecular weight side chains protrude.

[0050] <Viscosity Index Improvers (Not applicable to component (B))> - Comb-shaped polymer (1): Non-dispersible poly(meth)acrylate (Mw = 400,000, Mw / Mn = 1.7) - Comb-shaped polymer (2): Non-dispersible comb-shaped poly(meth)acrylate with a structure having many tridental branching points in the main chain from which high molecular weight side chains protrude (Mw = 310,000, Mw / Mn = 2.0)

[0051] <Other Additives> - An additive mixture consisting of a pour point depressant, detergent, ashless dispersant, ZnDTP, antioxidant, metal deactivator, defoamer, and friction modifier. Note that in the following tables, the amount of diluent oil for the viscosity index improver is included in "Other Additives". The amount of diluent oil differs depending on the type of viscosity index improver, so the content of "Other Additives" differs for each sample oil.

[0052]

[0053] From the results in Table 1, the lubricating oil compositions of Examples 1 to 8, which contained a fraction (a1) with fewer than 28 carbon atoms as the base oil (A) in an amount of 60.0 to 80.0% by mass on a total basis of the base oil (A), and a comb-shaped polymer (B1) with a mass-average molecular weight of 450,000 or more, had a NOACK value of 5.00% by mass or less at 150°C and exhibited low oil evaporation. Furthermore, the lubricating oil compositions of Examples 1 to 8 had a kinematic viscosity of 25.0 mm at 40°C. ２ The viscosity index was 280 or higher, and the HTHS80 / 150 was between 2.00 and 2.50, resulting in excellent fuel efficiency and oil film retention.

[0054] On the other hand, as shown in Table 2, the lubricating oil compositions of Comparative Examples 1 to 6, in which the proportion of fraction (a1) in the base oil (A) was 60.0% by mass or less, did not meet the acceptance criteria for kinematic viscosity and viscosity index at 40°C. Furthermore, as shown in Table 3, the lubricating oil compositions of Comparative Examples 7 to 14, in which the proportion of fraction (a1) in the base oil (A) was 80.0% by mass or more, did not meet the acceptance criteria for NOACK value and / or HTHS 80 / 150 at 150°C. Furthermore, as shown in Table 4, the lubricating oil compositions of Comparative Examples 15 to 18, which used viscosity index improvers that did not meet the requirements for comb-type polymer (B1), did not meet the acceptance criteria for viscosity index.

Claims

1. A lubricating oil composition comprising a base oil (A) and a viscosity index improver (B), wherein the base oil (A) contains a fraction (a1) having fewer than 28 carbon atoms in an amount of 60.0 to 80.0% by mass on a basis of the total amount of the base oil (A), and the viscosity index improver (B) contains a comb-shaped polymer (B1) with a mass average molecular weight of 450,000 or more.

2. The lubricating oil composition according to claim 1, wherein the base oil (A) contains a fraction (a2) having hydrocarbon groups with 28 or more and less than 32 carbon atoms in an amount of 15.0 to 25.0% by mass on a basis of the total amount of the base oil (A).

3. The lubricating oil composition according to claim 1 or 2, wherein the molecular weight distribution (Mw / Mn) of the comb-shaped polymer (B1) is 3.0 or less.

4. The lubricating oil composition according to any one of claims 1 to 3, wherein the base oil (A) contains mineral oil.

5. The lubricating oil composition according to any one of claims 1 to 4, wherein the viscosity index of the base oil (A) is 200 or less.

6. The lubricating oil composition according to any one of claims 1 to 5, wherein the viscosity index of the lubricating oil composition is 250 or higher.

7. The kinematic viscosity of the lubricating oil composition at 100°C is 5.0 mm. ２ A lubricating oil composition according to any one of claims 1 to 6, wherein the ratio is 1 / s or more.

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