Lubricating oil composition

Abstract

A lubricating oil composition for shock absorbers having excellent hydraulic responsiveness and component protectiveness is required. A lubricating oil composition for use in the lubrication of a shock absorber, the lubricating oil composition containing (A) a base oil having a kinematic viscosity at 100 DEG C of 5.8 mm2 / s or less, (B) a poly (meth) alkyl acrylate having a weight-average molecular weight of 100,000 or more, (C) a phosphorus-containing compound having an acid value of 1.0 mgKOH / g or more, and (D) a fatty acid ester.

Description

Technical Field

[0001] The present invention relates to a lubricating oil composition and a method for using the lubricating oil composition. Background Art

[0002] A buffer (shock absorber) is a mechanism mounted on a vehicle body for the purpose of generating a damping force that attenuates vehicle body vibrations by filling it with a lubricating oil composition for a buffer, and at the same time, it is required to optimize the friction characteristics of the sliding part to control the ride comfort of the vehicle body, and to suppress friction wear of the sliding part to ensure durability, etc.

[0003] Various lubricating oil compositions for buffers that are suitable for such buffers have been developed.

[0004] For example, Patent Document 1 discloses a lubricating oil composition containing a base oil, a specified zinc dialkylphosphate, calcium sulfonate, and a seal sweller.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: JP-A-2022-022721 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] However, for a lubricating oil composition for a buffer, good hydraulic responsiveness and high component protectiveness are required. For example, bubbles generated in the oil (oil bubbles) reduce the bulk modulus of elasticity of the lubricating oil composition, and thus, there is a concern that the responsiveness of the damping force in the hydraulic mechanism may decrease. In addition, if the friction coefficient of the sliding part (e.g., rubber and metal) (rubber friction coefficient) is high, there is a concern that a high resistance may be generated in the sliding part and the responsiveness may decrease. Furthermore, from the viewpoint of improving the durability of the buffer, it is important to reduce the wear width of the sliding part and improve component protectiveness by providing appropriate lubrication. Thus, in a lubricating oil composition for a buffer, the oil bubble characteristics and the rubber friction coefficient are related to the hydraulic responsiveness, and the wear width is related to the component protectiveness.

[0010] Under such circumstances, a lubricating oil composition for a buffer having excellent hydraulic responsiveness and component protectiveness is required.

[0011] Means for Solving the Problems

[0012] The present invention provides a lubricating oil composition for lubricating a buffer, the lubricating oil composition containing a base oil having a specified kinematic viscosity, a poly(alkyl)acrylate (B) having a specified weight average molecular weight, a phosphorus-containing compound (C) having an acid value of 1.0 mgKOH / g or more, and a fatty acid ester (D).

[0013] Specifically, the present invention provides the following methods [1] to

[10] .

[0014] [1] A lubricating oil composition for lubricating a buffer, the lubricating oil composition containing a base oil (A) having a kinematic viscosity at 100 °C of 5.8 mm 2 / s or less, a poly(alkyl methacrylate) (B) having a weight average molecular weight of 100,000 or more, a phosphorus-containing compound (C) having an acid value of 1.0 mgKOH / g or more, and a fatty acid ester (D).

[0015] [2] The lubricating oil composition according to [1], wherein the content of the poly(alkyl methacrylate) (B) is 0.1% by mass or more based on the total amount of the lubricating oil composition.

[0016] [3] The lubricating oil composition according to [1] or [2], wherein the content of an olefin copolymer having a weight average molecular weight of less than 100,000 is less than 0.05% by mass based on the total amount of the lubricating oil composition.

[0017] [4] The lubricating oil composition according to any one of [1] to [3], wherein the phosphorus-containing compound (C) contains one or more selected from acidic phosphates (C1) and acidic phosphites (C2).

[0018] [5] The lubricating oil composition according to any one of [1] to [4], wherein the fatty acid ester (D) contains an unsaturated fatty acid ester (D1).

[0019] [6] The lubricating oil composition according to any one of [1] to [5], wherein the content ratio [(C) / (D)] of the phosphorus-containing compound (C) to the fatty acid ester (D) is 0.3 to 10 by mass ratio.

[0020] [7] The lubricating oil composition according to any one of [1] to [6], wherein the content of an antifoaming agent is less than 0.05% by mass based on the total amount of the lubricating oil composition.

[0021] [8] The lubricating oil composition according to any one of [1] to [7], having a kinematic viscosity at 100 °C of 6.0 mm 2 / s or less.

[0022] [9] Use of the lubricating oil composition according to any one of [1] to [8] for lubricating a buffer.

[0023] Advantages of the Invention

[0024] A suitable lubricating oil composition according to the present invention has excellent hydraulic responsiveness and component protection. Therefore, a lubricating oil composition according to one embodiment of the present invention is suitable for lubricating buffers. Detailed Embodiments

[0025] Regarding the numerical ranges described in this specification, the upper limit value and the lower limit value can be arbitrarily combined. For example, when described as a numerical range of "preferably 30 to 100, more preferably 40 to 80", ranges of "30 to 80" and "40 to 100" are also included in the numerical ranges described in this specification. Additionally, for example, when described as a numerical range of "preferably 30 or more, more preferably 40 or more, and preferably 100 or less, more preferably 80 or less", ranges of "30 to 80" and "40 to 100" are also included in the numerical ranges described in this specification.

[0026] Furthermore, as the numerical ranges described in this specification, for example, the description of "60 to 100" means a range of "60 or more (60 or greater than 60), 100 or less (100 or less than 100)".

[0027] In addition, in the definition of the upper limit value and the lower limit value described in this specification, the numerical range of the lower limit value to the upper limit value can be appropriately selected and arbitrarily combined from each option.

[0028] In addition, a plurality of various technical features described as preferred embodiments in this specification can be combined.

[0029] 〔Constitution of Lubricating Oil Composition〕

[0030] A lubricating oil composition according to one embodiment of the present invention is used for lubricating buffers, and the lubricating oil composition contains a base oil (A) having a kinematic viscosity at 100 °C of 5.8 mm 2 / s or less (hereinafter, also referred to as "component (A)"), a poly(alkyl methacrylate) (B) having a weight average molecular weight of 100,000 or more (hereinafter, also referred to as "component (B)"), a phosphorus-containing compound (C) having an acid value of 1.0 mgKOH / g or more (hereinafter, also referred to as "component (C)"), and a fatty acid ester (D) (hereinafter, also referred to as "component (D)").

[0031] As described above, for the lubricating oil composition used in the buffer, good hydraulic responsiveness and component protectiveness are required. In order to obtain good hydraulic responsiveness, it is necessary to appropriately set the viscosity and additives of the lubricating oil composition. The present inventors have found that by using a base oil (A) having a specific viscosity and combining components (B) to (D) as additives, a lubricating oil composition having good hydraulic responsiveness can be provided. In addition, the present inventors have also found that by combining these components (A) to (D), a lubricating oil composition having good hydraulic responsiveness and high component protectiveness can be provided.

[0032] The lubricating oil composition according to one embodiment of the present invention has such properties, and thus can be suitably used for lubricating the buffer.

[0033] It should be noted that the lubricating oil composition according to one embodiment of the present invention may further contain other lubricating oil additives other than components (B) to (D) as needed within a range not impairing the effects of the present invention.

[0034] In the lubricating oil composition according to one embodiment of the present invention, based on the total amount (100% by mass) of the lubricating oil composition, the total content of components (A) and (B) is preferably 60% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0035] In the lubricating oil composition according to one embodiment of the present invention, based on the total amount (100% by mass) of the lubricating oil composition, the total content of components (B) to (D) is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, further preferably 1.5% by mass or more, and particularly preferably 1.8% by mass or more.

[0036] In addition, in the lubricating oil composition according to one embodiment of the present invention, from the viewpoint of making a lubricating oil composition having good friction characteristics and abrasion resistance, the content ratio [(C) / (D)] of component (C) and component (D) is preferably 0.1 or more, more preferably 0.2 or more, and further preferably 0.5 or more in terms of mass ratio.

[0037] On the other hand, from the viewpoint of improving the blending balance of each component and maintaining the properties of the lubricating oil composition, this mass ratio is preferably 10 or less, more preferably 7 or less, and further preferably 5 or less.

[0038] Hereinafter, the details of each component contained in the lubricating oil composition according to one embodiment of the present invention will be described.

[0039] <Component (A): Base Oil>

[0040] The base oil contained in the lubricating oil composition as one embodiment of the present invention may be a mineral oil, a synthetic oil, or a mixed oil of a mineral oil and a synthetic oil.

[0041] Examples of the mineral oil include atmospheric residue obtained by subjecting crude oils such as paraffinic crude oil, intermediate-base crude oil, and naphthenic crude oil to atmospheric distillation; distillate oil obtained by subjecting these atmospheric residues to vacuum distillation; and refined oil obtained by subjecting the distillate oil to one or more of refining treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining.

[0042] Examples of the synthetic oil include polyalphaolefins such as α-olefins, their homopolymers, or α-olefin copolymers (e.g., α-olefin copolymers having 8 to 14 carbon atoms such as ethylene-α-olefin copolymers); isoparaffins; polyalkylene glycols; ester oils such as polyol esters, dibasic acid esters, and phosphate esters; ether oils such as polyphenylene ethers; alkylbenzenes; alkylnaphthalenes; synthetic oils (GTL) obtained by isomerizing waxes produced from natural gas by the Fischer-Tropsch method or the like (GTL wax (Gas To Liquids WAX)); synthetic oils (CTL) obtained by isomerizing waxes produced from coal by the Fischer-Tropsch method or the like (CTL wax (Coal To Liquids WAX)); synthetic oils (BTL) obtained by isomerizing waxes produced from biomass by the Fischer-Tropsch method or the like (BTL wax (Biomass To Liquids WAX)), and the like.

[0043] Among them, the base oil used in one embodiment of the present invention preferably contains at least one selected from mineral oils classified as Group 2 and Group 3 in the API (American Petroleum Institute) base oil category and synthetic oils. In one embodiment of the present invention, these base oils may be used alone or in combination of two or more.

[0044] From the viewpoint of producing a lubricating oil composition that suppresses the generation of bubbles caused by vibration and improves hydraulic responsiveness, the kinematic viscosity of the base oil (A) used in one embodiment of the present invention at 100 °C is 5.8 mm 2 / s or less, preferably 5.5 mm 2 / s or less, more preferably 5.0 mm 2 / s or less, further preferably 4.5 mm 2 / s or less, still further preferably 4.0 mm 2 / s or less, still further preferably 3.5 mm 2 / s or less, particularly preferably 3.0 mm 2 / s or less.

[0045] On the other hand, from the viewpoint of producing a lubricating oil composition having good oil film retention and improving component protection by enhancing lubricating performance, the kinematic viscosity of the base oil (A) at 100 °C is preferably 1.0 mm 2 / s or more, more preferably 1.2 mm 2 / s or more, and still more preferably 1.4 mm 2 / s or more.

[0046] In addition, the viscosity index of the base oil (A) used in one embodiment of the present invention is appropriately set according to the use of the lubricating oil composition, and is preferably 70 or more, more preferably 80 or more, still more preferably 90 or more, and particularly preferably 100 or more.

[0047] It should be noted that in one embodiment of the present invention, when a mixed oil composed of two or more base oils is used as the component (A), the kinematic viscosity and viscosity index of the mixed oil are preferably in the above ranges.

[0048] In addition, in this specification, the kinematic viscosity and viscosity index refer to the values measured or calculated in accordance with JIS K2283:2000.

[0049] In the lubricating oil composition of one embodiment of the present invention, the content of the base oil (A) is usually 55% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, particularly preferably 90% by mass or more, based on the total amount (100% by mass) of the lubricating oil composition. In addition, it is preferably 99.9% by mass or less, more preferably 99.0% by mass or less, and still more preferably 98.5% by mass or less.

[0050] <Component (B): Poly(alkyl)acrylate>

[0051] The lubricating oil composition of the present invention contains a poly(alkyl)acrylate having a weight average molecular weight (Mw) of 100,000 or more as the component (B). If the Mw is less than 100,000, oil foaming occurs more frequently. The air bubbles generated in the oil cause a decrease in the bulk modulus of elasticity of the lubricating oil composition, which can lead to a decrease in the responsiveness of the damping force. Therefore, as the component (B), a poly(alkyl)acrylate having an Mw of 100,000 or more is preferably used.

[0052] From the viewpoint of producing a lubricating oil composition that suppresses the generation of bubbles caused by vibration and improves hydraulic responsiveness, the weight-average molecular weight (Mw) of the poly(alkyl methacrylate) used in one embodiment of the present invention is 100,000 or more, preferably 120,000 or more, more preferably 140,000 or more, further preferably 160,000 or more, still further preferably 180,000 or more, particularly preferably 190,000 or more. Additionally, it can be 200,000 or more, 250,000 or more, 300,000 or more, 350,000 or more, 400,000 or more, 450,000 or more, 500,000 or more, 540,000 or more, or 600,000 or more.

[0053] On the other hand, from the viewpoint of producing a lubricating oil composition that improves solubility in base oil and has good storage stability, the weight-average molecular weight (Mw) of the poly(alkyl methacrylate) is preferably 900,000 or less, 800,000 or less, or 700,000 or less.

[0054] It should be noted that in this specification, the weight-average molecular weight (Mw) is a value converted to standard polystyrene measured by gel permeation chromatography (GPC) method, specifically, it refers to the value measured by the method described in the examples.

[0055] In the lubricating oil composition of one embodiment of the present invention, from the viewpoint of producing a lubricating oil composition that suppresses the generation of bubbles caused by vibration and improves hydraulic responsiveness, based on the total amount (100% by mass) of the lubricating oil composition, the content of component (B) is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, further preferably 0.8% by mass or more, still further preferably 1.2% by mass or more, particularly preferably 1.5% by mass or more. Additionally, from the viewpoint of producing a lubricating oil composition that improves solubility in base oil and has good storage stability, it is preferably 10.0% by mass or less, more preferably 8.0% by mass or less, further preferably 5.0% by mass or less, still further preferably 3.0% by mass or less, particularly preferably 2.0% by mass or less.

[0056] Component (B) used in one embodiment of the present invention may be a polymer having a structural unit derived from an alkyl acrylate or alkyl methacrylate (hereinafter, also collectively referred to as “(meth)acrylate”), or may be a copolymer having a structural unit derived from a monomer other than (meth)acrylate.

[0057] The number of carbon atoms of the alkyl group in the (meth)acrylate may be 1 or more, 3 or more, 5 or more, or 10 or more. Additionally, it may be 60 or less, 40 or less, 30 or less, or 20 or less.

[0058] In addition, in component (B) used in one embodiment of the present invention, based on the total amount (100 mol%) of the structural units of component (B), the content of the structural units derived from an alkyl (meth)acrylate may be 10 mol% or more, 30 mol% or more, 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, 90 mol% or more, 95 mol% or more, or 99 mol% or more.

[0059] The lubricating oil composition of one embodiment of the present invention may contain an olefin copolymer having a weight average molecular weight (Mw) of less than 100,000, or may not contain it. From the viewpoint of producing a lubricating oil composition that suppresses the generation of bubbles caused by vibration and improves hydraulic responsiveness, it is preferably substantially free of an olefin copolymer having an Mw of less than 100,000. This is because, in the present invention, if such an olefin copolymer is contained, oil bubbles are generated in a large amount, and the hydraulic responsiveness can be reduced.

[0060] Here, "substantially free of an olefin copolymer having an Mw of less than 100,000" means excluding a lubricating oil composition intentionally blended with the olefin copolymer, and does not exclude a mode in which the olefin copolymer is inevitably blended, but the content of such an olefin copolymer is also preferably as small as possible.

[0061] Based on the total amount (100% by mass) of the lubricating oil composition, the content of the olefin copolymer having an Mw of less than 100,000 contained in the lubricating oil composition of one embodiment of the present invention is preferably less than 0.05% by mass, more preferably less than 0.03% by mass, still more preferably less than 0.01% by mass, and particularly preferably less than 0.001% by mass.

[0062] Specific examples of the olefin copolymer having an Mw of less than 100,000 are copolymers having structural units derived from monomers having an alkenyl group, and examples thereof include copolymers of α-olefins having 2 to 20 carbon atoms. More specifically, ethylene-α-olefin copolymers can be cited.

[0063] It should be noted that the lubricating oil composition of one embodiment of the present invention may contain an olefin copolymer in addition to the poly(alkyl meth)acrylate having an Mw of 100,000 or more, provided that the Mw is 100,000 or more.

[0064] <Component (C): Phosphorus-containing compound>

[0065] The lubricating oil composition of the present invention contains a phosphorus-containing compound (C) having an acid value of 1.0 mgKOH / g or more as component (C). By containing component (C), the lubricating oil composition of the present invention can be made into a lubricating oil composition with improved abrasion resistance and high component protection with a small wear width of the sliding part. The phosphorus-containing compound (C) is not particularly limited as long as it has an acid value of 1.0 mgKOH / g or more and contains a phosphorus atom. The lubricating oil composition of one embodiment of the present invention preferably contains one or more selected from acidic phosphates (C1) and acidic phosphites (C2) as component (C).

[0066] The acidic phosphate (C1) may be an acidic phosphoric acid monoester or an acidic phosphoric acid diester. Examples of the acidic phosphoric acid monoester include ethyl acidic phosphate, propyl acidic phosphate, butyl acidic phosphate, and 2-ethylhexyl acidic phosphate, etc.

[0067] Examples of the acidic phosphoric acid diester include diethyl acidic phosphate, dipropyl acidic phosphate, dibutyl acidic phosphate, and bis(2-ethylhexyl) acidic phosphate, etc.

[0068] These acidic phosphates (C1) can be used alone or in combination of two or more.

[0069] The acidic phosphite (C2) may be an acidic phosphorous acid monoester or an acidic phosphorous acid diester. Examples of the acidic phosphorous acid monoester include ethyl hydrogen phosphite, propyl hydrogen phosphite, butyl hydrogen phosphite, lauryl hydrogen phosphite, oleyl hydrogen phosphite, and 2-ethylhexyl hydrogen phosphite, etc.

[0070] Examples of the acidic phosphorous acid diester include dihexyl hydrogen phosphite, diheptyl hydrogen phosphite, dioctyl hydrogen phosphite, dilauryl hydrogen phosphite, dioleyl hydrogen phosphite, and bis(2-ethylhexyl) hydrogen phosphite, etc.

[0071] These acidic phosphites (C2) can be used alone or in combination of two or more.

[0072] It should be noted that the acidic phosphate (C1) and acidic phosphite (C2) can be in the form of amine salts. Examples of the amines that form amine salts with these phosphates include mono-substituted amines such as butylamine, pentylamine, hexylamine, cyclohexylamine, octylamine, laurylamine, stearylamine, oleylamine, benzylamine; di-substituted amines such as dibutylamine, dipentylamine, dihexylamine, dicyclohexylamine, dioctylamine, dilaurylamine, distearylamine, dioleylamine, dibenzylamine, stearyl monoethanolamine, decyl monoethanolamine, hexyl monopropanolamine, benzyl monoethanolamine, phenyl monoethanolamine, tolyl monopropanolamine; tri-substituted amines such as tributylamine, tripentylamine, trihexylamine, tricyclohexylamine, trioctylamine, trilaurylamine, tristearylamine, trioleylamine, tribenzylamine, dioleyl monoethanolamine, dilauryl monopropanolamine, dioctyl monoethanolamine, dihexyl monopropanolamine, dibutyl monopropanolamine, oleyl diethanolamine, stearyl dipropanolamine, lauryl diethanolamine, octyl dipropanolamine, butyl diethanolamine, benzyl diethanolamine, phenyl diethanolamine, tolyl dipropanolamine, xylyl diethanolamine, triethanolamine, tripropanolamine, etc.

[0073] In addition, the lubricating oil composition according to one embodiment of the present invention preferably contains a phosphorus-containing compound (C) other than the acidic phosphate (C1) and acidic phosphite (C2) as the component (C). Specifically, for example, zinc dialkyldithiophosphate (ZnDTP), zinc phosphate, zinc dithiocarbamate, molybdenum dithiocarbamate, molybdenum dithiophosphate, disulfide compounds, sulfurized olefins, sulfurized oils and fats, sulfurized esters, thiocarbonates, thiocarbamates, polysulfides and other compounds containing sulfur atoms can be cited.

[0074] In one embodiment of the present invention, from the viewpoint of preparing a lubricating oil composition with improved wear resistance and high component protection with a small wear width in the sliding part, the acid value of the phosphorus-containing compound (C) is 1.0 mgKOH / g or more, and the acid value is preferably 2.0 mgKOH / g or more, 3.0 mgKOH / g or more, 4.0 mgKOH / g or more, 4.8 mgKOH / g or more, 5.0 mgKOH / g or more, 10.0 mgKOH / g or more, 20.0 mgKOH / g or more, 30.0 mgKOH / g or more, 40.0 mgKOH / g or more, 50.0 mgKOH / g or more, 58.0 mgKOH / g or more, 60.0 mgKOH / g or more, 70.0 mgKOH / g or more, 80.0 mgKOH / g or more, 90.0 mgKOH / g or more, 100 mgKOH / g or more, 110 mgKOH / g or more, 120 mgKOH / g or more, 128 mgKOH / g or more, or 130 mgKOH / g or more.

[0075] The upper limit value of the acid value is not particularly limited, and examples thereof include 300 mgKOH / g or less, 250 mgKOH / g or less, or 200 mgKOH / g or less.

[0076] It should be noted that in this specification, the acid value refers to the value measured in accordance with JIS K2501:2003 (indicator method).

[0077] In addition, the lubricating oil composition according to one embodiment of the present invention may contain a phosphorus-containing compound other than the phosphorus-containing compound (C) having an acid value of 1.0 mgKOH / g or more. Examples of such a phosphorus-containing compound include neutral phosphorus-based compounds having an acid value of less than 1.0 mgKOH / g. Specifically, examples thereof include tricresyl phosphate, xylenyl diphenyl phosphate, tolyl diphenyl phosphate, triethylphenyl phosphate, di(ethylphenyl)phenyl phosphate, ethylphenyl diphenyl phosphate, tri-n-propylphenyl phosphate, di(n-propylphenyl)phenyl phosphate, n-propylphenyl diphenyl phosphate, triisopropylphenyl phosphate, di(isopropylphenyl)phenyl phosphate, and isopropylphenyl diphenyl phosphate.

[0078] In the lubricating oil composition according to one embodiment of the present invention, from the viewpoint of making a lubricating oil composition with improved abrasion resistance and high component protection with a small wear width in the sliding part, based on the total amount (100% by mass) of the lubricating oil composition, the content of component (C) is preferably more than 0.2% by mass, more preferably 0.25% by mass or more, further preferably 0.3% by mass or more, still more preferably 0.4% by mass or more, particularly preferably 0.5% by mass or more. In addition, from the viewpoint of improving thermal stability, it is preferably 5.0% by mass or less, more preferably 4.0% by mass or less, further preferably 3.0% by mass or less.

[0079] In addition, in the lubricating oil composition according to one embodiment of the present invention, from the viewpoint of making a lubricating oil composition with improved abrasion resistance and high component protection with a small wear width in the sliding part, based on the total amount (100% by mass) of the lubricating oil composition, the content of component (C) in terms of phosphorus atoms is preferably 100 mass ppm or more, more preferably 120 mass ppm or more, further preferably 140 mass ppm or more, still more preferably 160 mass ppm or more, particularly preferably 180 mass ppm or more. In addition, it may be 200 mass ppm or more, 250 mass ppm or more, 300 mass ppm or more, 350 mass ppm or more, or 400 mass ppm or more.

[0080] On the other hand, from the viewpoint of improving thermal stability, the content of component (C) in terms of phosphorus atoms is preferably 1200 mass ppm or less, more preferably 1000 mass ppm or less, still more preferably 800 mass ppm or less, and even more preferably 600 mass ppm or less.

[0081] <Component (D): Fatty Acid Ester>

[0082] The lubricating oil composition of the present invention contains a fatty acid ester (D) as component (D). By containing component (D), the friction coefficient of the lubricating oil composition of the present invention is reduced, the generation of high resistance in the sliding part can be suppressed, and a lubricating oil composition with high hydraulic responsiveness can be obtained.

[0083] The fatty acid ester (D) is a condensate of an aliphatic carboxylic acid and an alcohol. Examples of the aliphatic carboxylic acid include saturated or unsaturated aliphatic monocarboxylic acids, aliphatic dicarboxylic acids, aliphatic tricarboxylic acids, aliphatic tetracarboxylic acids, and the like. The lubricating oil composition of one embodiment of the present invention contains at least an unsaturated fatty acid ester (D1) as component (D). In addition, the aliphatic carboxylic acid may be either a linear aliphatic carboxylic acid or a cyclic aliphatic carboxylic acid. Furthermore, the number of carbon atoms of the aliphatic carboxylic acid is preferably 6 to 40, more preferably 8 to 32, and still more preferably 12 to 24.

[0084] Examples of the saturated aliphatic carboxylic acid include saturated aliphatic monocarboxylic acids such as capric acid, neodecanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, and lignoceric acid; and saturated aliphatic dicarboxylic acids such as adipic acid, azelaic acid, and sebacic acid.

[0085] In addition, examples of the unsaturated aliphatic carboxylic acid include undecenoic acid, oleic acid, elaidic acid, erucic acid, nervonic acid, linoleic acid, ricinoleic acid, γ-linolenic acid, arachidonic acid, α-linolenic acid, octadecatetraenoic acid, eicosapentaenoic acid, and docosahexaenoic acid.

[0086] Examples of the alcohol include aliphatic alcohols. The aliphatic alcohol may be a monohydric alcohol or a polyhydric alcohol, and may be either saturated or unsaturated. In addition, it may be linear or branched. The number of carbon atoms of the alcohol is preferably 1 to 30, more preferably 2 to 24.

[0087] In addition, specific examples of the alcohol include methanol, ethanol, allyl alcohol, propanol, butanol, pentanol, hexanol, octanol, decanol, dodecanol, tetradecanol, hexadecanol, octadecanol, butenol, pentenol, hexenol, octenol, decenol, dodecenol, tetradecenol, hexadecenol, octadecenol, ethylene glycol, propylene glycol, neopentyl glycol, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, and sorbitol anhydride.

[0088] In one embodiment of the present invention, as the component (D), specifically, when the alcohol is glycerol, examples include monoglyceride fatty acid esters (monoglycerides) and diglyceride fatty acid esters (diglycerides).

[0089] In addition, when the alcohol is sorbitan, examples include sorbitan fatty acid esters such as sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, and sorbitan trioleate.

[0090] In addition, when the alcohol is pentaerythritol, examples include pentaerythritol fatty acid esters such as pentaerythritol monooleate, pentaerythritol dioleate, and pentaerythritol tetraoleate.

[0091] In the lubricating oil composition of one embodiment of the present invention, from the viewpoint of producing a lubricating oil composition with a low coefficient of friction and high hydraulic responsiveness, based on the total amount (100% by mass) of the lubricating oil composition, the content of the component (D) is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and still more preferably 0.3% by mass or more. In addition, from the viewpoint of maintaining good compatibility with elastic members such as rubber, it is preferably 5.0% by mass or less, more preferably 4.0% by mass or less, and still more preferably 3.0% by mass or less.

[0092] <General Additives>

[0093] The lubricating oil composition of one embodiment of the present invention can contain general additives (hereinafter also referred to as "general additives") that are usually contained in lubricating oil compositions and that do not belong to the above components (B) to (D) within the range that does not impair the effects of the present invention.

[0094] Examples of such general additives include antioxidants, ashless dispersants, metal detergents, viscosity index improvers, fluidity improvers, extreme pressure agents, rust inhibitors, friction modifiers, antiwear agents, etc. These general additives can be used alone or in combination of multiple types.

[0095] In addition, the lubricating oil composition of one embodiment of the present invention can use an additive package containing a combination of multiple of these general additives.

[0096] Based on the total amount (100% by mass) of the lubricating oil composition, the blending amount of each of these general additives is preferably 0.001 to 10% by mass, more preferably 0.01 to 5% by mass.

[0097] In addition, based on the total amount (100% by mass) of the lubricating oil composition, the total blending amount of the general additives is preferably 0.01 to 40% by mass, more preferably 0.1 to 35% by mass.

[0098] The lubricating oil composition of one embodiment of the present invention may contain a defoaming agent or may not contain a defoaming agent, but preferably contains substantially no defoaming agent from the viewpoint of suppressing bubbles generated in the oil. "Substantially containing no defoaming agent" excludes lubricating oil compositions that intentionally contain a defoaming agent, but does not exclude embodiments that contain such a defoaming agent unavoidably, but the content of such a defoaming agent is preferably as small as possible.

[0099] The content of the defoaming agent contained in the lubricating oil composition of one embodiment of the present invention is preferably less than 0.05% by mass, more preferably less than 0.03% by mass, further preferably less than 0.01% by mass, and particularly preferably less than 0.001% by mass, based on the total amount of the lubricating oil composition (100% by mass). Generally, the defoaming agent is added for the purpose of suppressing the foaming of the lubricating oil composition, destroying bubbles, etc., but in the present invention, it was found that if the defoaming agent is added, the bubbles in the oil are increased. Therefore, in order to suppress the bubbles generated in the oil, the content of the defoaming agent is preferably controlled within the above range.

[0100] In addition, as an antifoaming agent, silicone type antifoaming agents, such as an alkyl silicone type antifoaming agent and a fluorosilicone type antifoaming agent, are mentioned, for example.

[0101] <Method for producing lubricating oil composition>

[0102] The method for producing the lubricating oil composition according to one embodiment of the present invention is not particularly limited, but is preferably a method having a step of blending components (B) to (D) and, if necessary, various additives into component (A) from the viewpoint of productivity.

[0103] The order of blending the components can be appropriately set. From the viewpoint of compatibility with component (A), the resin component such as component (B) is preferably in the form of a solution dissolved in a diluent oil and the solution is blended with component (A).

[0104] [Properties of Lubricating Oil Composition]

[0105] The lubricating oil composition of one embodiment of the present invention preferably has a kinematic viscosity of 1.0 mm at 100°C. 2 / s or more, more preferably 1.2 mm 2 / s or more, more preferably 1.4 mm 2 / s or more, and preferably 6.0 mm from the viewpoint of suppressing an unexpected increase in resistance in the buffer and maintaining appropriate fluid resistance. 2 / s or less, more preferably 5.5mm 2 / s or less, more preferably 5.0 mm 2 / s or less, more preferably 4.5mm 2 / s or less, particularly preferably 4.0 mm 2 / s or less.

[0106] In addition, the viscosity index of the lubricating oil composition according to one embodiment of the present invention is preferably 70 or more, more preferably 80 or more, still more preferably 90 or more, and particularly preferably 100 or more.

[0107] [Characteristics and Uses of Lubricating Oil Composition]

[0108] The lubricating oil composition of the present invention has excellent hydraulic responsiveness and component protectiveness. As specific indices for evaluating hydraulic responsiveness, the number of bubbles in oil measured by the method described in the examples below and the rubber friction coefficient during the reciprocating sliding test described in the examples below can be cited.

[0109] In addition, as a specific index for evaluating component protectiveness, the wear width during the reciprocating motion friction test described in the examples below can be cited.

[0110] When using the lubricating oil composition according to one embodiment of the present invention, the number of bubbles in oil measured by the method described in the examples below is preferably 80 or less, more preferably 75 or less, still more preferably 70 or less, even more preferably 65 or less, and particularly preferably 60 or less. If there are bubbles in the oil, the bulk modulus of the lubricating oil composition decreases, and there is concern about a decrease in responsiveness in hydraulic mechanisms such as shock absorbers. Therefore, the fewer the number of bubbles in the oil in this evaluation, the better the hydraulic responsiveness of the lubricating oil composition can be said to be.

[0111] The rubber friction coefficient during the reciprocating sliding test described in the examples below when using the lubricating oil composition according to one embodiment of the present invention is preferably 0.70 or less, more preferably 0.65 or less, still more preferably 0.60 or less, and particularly preferably 0.50 or less. If the rubber friction coefficient is high, high resistance is generated in mechanisms where sliding occurs between an oil seal (rubber) and a metal material, such as in a shock absorber, and there is concern about a decrease in responsiveness. Therefore, the smaller the rubber friction coefficient, the better the hydraulic responsiveness of the lubricating oil composition can be said to be.

[0112] The wear width during the reciprocating motion friction test described in the examples below when using the lubricating oil composition according to one embodiment of the present invention is preferably 0.57 mm or less, more preferably 0.55 mm or less, still more preferably 0.50 mm or less, and particularly preferably 0.45 mm or less. The smaller the wear width, the better the wear resistance, and in mechanisms that accompany reciprocating motion and sliding, such as shock absorbers, it can be said that the lubricating oil composition has high component protectiveness.

[0113] Due to the above characteristics, the lubricating oil composition of one embodiment of the present invention can be suitably applied to the lubrication of various devices. For example, it can be applied to lubricating oils for buffers, hydraulic working oils, working oils for construction machinery, power steering oils, turbine oils, compressor oils, lubricating oils for machine tools, cutting oils, gear oils, fluid bearing oils, rolling bearing oils, etc. Among them, the lubricating oil composition of one embodiment of the present invention can be suitably used for buffers. More specifically, the lubricating oil composition of one embodiment of the present invention can be used for either a twin-tube shock absorber or a monotube shock absorber, and can also be suitably used for shock absorbers for either two-wheel or four-wheel vehicles.

[0114] Therefore, the present invention also provides the use of the buffer of the following [I] and the lubricating oil composition of the following [II].

[0115] [I] A buffer filled with the lubricating oil composition of one embodiment of the present invention described above.

[0116] [II] The use of the lubricating oil composition of one embodiment of the present invention described above for the lubrication of a buffer.

[0117] Examples

[0118] Next, the present invention will be described in more detail by way of examples, but the present invention is not limited by any of these examples. It should be noted that the various physical property values of the respective components used in the examples and comparative examples and the obtained lubricating oil compositions were measured according to the following methods.

[0119] (1) Kinematic viscosity, viscosity index

[0120] Measured and calculated according to JIS K2283:2000.

[0121] (2) Weight-average molecular weight (Mw)

[0122] Measured using a gel permeation chromatography device (manufactured by Agilent, "1260 type HPLC") under the following conditions, and the values measured by conversion with standard polystyrene were used.

[0123] (Measurement conditions)

[0124] · Column: Two "Shodex LF404" were connected in series.

[0125] · Column temperature: 35 °C

[0126] · Eluent: Chloroform

[0127] · Flow rate: 0.3 mL / min

[0128] (3) Acid value

[0129] The measurement is carried out in accordance with JIS K2501:2003 (indicator method).

[0130] (4)Hydroxyl value

[0131] The measurement is carried out in accordance with JIS K 0070:1992.

[0132] (5)Bubble characteristics in oil

[0133] In a rectangular glass container with a bottom area of 5 cm (length) × 5 cm (width), heat the lubricating oil composition to be measured to 100 °C and fill 50 mL. Oscillate it for 60 seconds with an amplitude of ±10 mm and a vibration frequency of 10 Hz. Use a high-speed camera to take pictures of the state in the lubricating oil composition (in the oil) 40 seconds after the end of oscillation from the side of the glass container, and measure the number of bubbles in the oil. Regarding the shooting range of the high-speed camera, observe from the side of the glass container and take a square range with a side length of 0.5 cm centered at a position 2.5 cm above the bottom of the container. The case where the number of bubbles in the oil measured by the above method is 80 or less is judged as qualified. For samples with the number of bubbles in the oil exceeding 80, the measurements in (3) and (4) below are not carried out. In this evaluation, the fewer the number of bubbles in the oil, the better the hydraulic responsiveness of the lubricating oil composition can be said to be.

[0134] (6)Rubber friction coefficient

[0135] Use a reciprocating friction testing machine to make a chromium-plated steel plate and nitrile rubber (manufactured by NOK, A437) covering a 1 / 2 steel ball reciprocate and slide in the state of dropping 0.1 mL of the lubricating oil composition to be measured, and record the maximum friction coefficient detected at the 100th reciprocation. The load is 4 N, the amplitude is ±3 mm, the vibration frequency is 1 Hz, and the chromium-plated steel plate is heated to 40 °C. The case where the rubber friction coefficient measured by the above method is 0.70 or less is judged as qualified. For samples with a rubber friction coefficient exceeding 0.70, the measurement in (2) above is not carried out. The smaller the rubber friction coefficient, the better the hydraulic responsiveness of the lubricating oil composition can be said to be.

[0136] (7)Wear resistance

[0137] Using a Bauden reciprocating friction testing machine, a SPCC-SB steel plate heated to 100 °C and a 1 / 2-inch SUJ2 steel ball were reciprocally moved and slid in a state where 0.1 mL of the lubricating oil composition to be measured was dropped, and the wear scar width at the sliding center of the SPCC-SB steel plate after 400 reciprocating movements was recorded. The load was set at 20 N, the amplitude was set at ±5 mm, the speed was set at 50 mm / s, and the reciprocating movement was performed at a constant speed. A sample with a wear width measured by the above method of 0.57 mm or less was judged to be qualified, and for a sample with a wear width exceeding 0.57 mm, the measurement in (2) above was not performed. The smaller the wear width, the better the wear resistance, and it can be said that in mechanisms accompanied by reciprocating movement and sliding such as shock absorbers, the lubricating oil composition has higher component protection.

[0138] Examples 1 to 11, Comparative Examples 1 to 5

[0139] The components (A) to (D) shown in Table 1 were added and mixed in the blending amounts shown in Table 1 to prepare lubricating oil compositions respectively. The prepared lubricating oil compositions substantially did not contain olefin copolymers with Mw less than 100,000 and defoamers (their contents were less than 0.05% by mass respectively). It should be noted that the blending amount of component (B) in Table 1 is recorded as the blending amount in terms of the resin component after removing the diluting solvent.

[0140] The details of each component used in the preparation of this lubricating oil composition are as follows.

[0141] <Base oil (A)>

[0142] · Mineral oil (a1): A mineral oil classified as Group III in the API base oil category with a kinematic viscosity at 100 °C = 2.2 mm 2 / s and a viscosity index = 109, and a density (15 °C) = 0.82 g / cm 3 .

[0143] · Mineral oil (a2): A mineral oil classified as Group III in the API base oil category with a kinematic viscosity at 100 °C = 2.7 mm 2 / s and a viscosity index = 111, and a density (15 °C) = 0.81 g / cm 3 .

[0144] · Mineral oil (a3): A mineral oil classified as Group III in the API base oil category with a kinematic viscosity at 100 °C = 6.0 mm 2 / s and a viscosity index = 132, and a density (15 °C) = 0.84 g / cm 3 .

[0145] <Poly(alkyl)acrylate (B)>

[0146] · PMA (b1): Polyalkyl methacrylate with Mw = 190,000.

[0147] · PMA (b2): Polyalkyl methacrylate with Mw = 540,000.

[0148] · PMA (b3): Polyalkyl methacrylate with Mw = 36,000.

[0149] <Phosphorus-containing compound (C)>

[0150] · Phosphorus-containing compound (c1): Dioleyl hydrogen phosphite, acid value (indicator) = 4.8 mg KOH / g

[0151] · Phosphorus-containing compound (c2): Mixture of dilauryl hydrogen phosphite and monolauryl hydrogen phosphite, acid value (indicator) = 58 mg KOH / g

[0152] · Phosphorus-containing compound (c3): Zinc dialkyldithiophosphate, acid value (indicator) = 128 mg KOH / g

[0153] · Phosphorus-containing compound (c4): Tricresyl phosphate, acid value (indicator) = 0.01 mg KOH / g

[0154] · Phosphorus-containing compound (c5): Triaryl isopropyl phosphate compound, acid value (indicator) = 0.05 mg KOH / g

[0155] <Fatty acid ester (D)>

[0156] · Fatty acid ester (d1): Monoglyceryl oleate, hydroxyl value = 156 mg KOH / g

[0157] · Fatty acid ester (d2): Sorbitan monooleate, hydroxyl value = 235 mg KOH / g

[0158] · Fatty acid ester (d3): Pentaerythritol dioleate, hydroxyl value = 156 mg KOH / g

[0159] For the lubricating oil compositions prepared in the examples and comparative examples, various physical property values were measured and calculated according to the above-mentioned measurement methods. These results are shown in Table 1.

[0160]

Table 1

[0161]

[0162] According to Table 1, containing a kinematic viscosity at 100 °C of 5.8 mm 2The lubricating oil compositions of Examples 1 to 11 containing base oil (A) with a kinematic viscosity of 10 mm2 / s or less, poly(alkyl methacrylate) (B) with a weight-average molecular weight of 100,000 or more, a phosphorus-containing compound (C) with an acid value of 1.0 mgKOH / g or more, and fatty acid ester (D) have excellent hydraulic responsiveness and component protectiveness as compared with Comparative Examples 1 to 5. Specifically, the lubricating oil compositions of Examples 1 to 11 have fewer bubbles in the oil and good hydraulic responsiveness as compared with the lubricating oil compositions of Comparative Examples 1 and 2. In addition, the lubricating oil compositions of Examples 1 to 11 have both small rubber friction coefficients and wear widths and good hydraulic responsiveness and component protectiveness as compared with the lubricating oil compositions of Comparative Examples 3 to 5.

Claims

1. A lubricating oil composition for lubricating a buffer, the lubricating oil composition containing a base oil (A) having a kinematic viscosity at 100 °C of 5.8 mm 2 / s or less, a poly(alkyl) acrylate (B) having a weight-average molecular weight of 100,000 or more, a phosphorus-containing compound (C) having an acid value of 1.0 mgKOH / g or more, and a fatty acid ester (D).

2. The lubricating oil composition according to claim 1, wherein, Based on the total amount of the lubricating oil composition, the content of the poly(alkyl) methacrylate (B) is 0.1% by mass or more.

3. The lubricating oil composition according to claim 1 or 2, wherein, Based on the total amount of the lubricating oil composition, the content of the olefin copolymer having a weight average molecular weight of less than 100,000 is less than 0.05% by mass.

4. The lubricating oil composition according to any one of claims 1 to 3, wherein, The phosphorus-containing compound (C) contains one or more selected from acidic phosphates (C1) and acidic phosphites (C2).

5. The lubricating oil composition according to any one of claims 1 to 4, wherein The fatty acid ester (D) contains an unsaturated fatty acid ester (D1).

6. The lubricating oil composition according to any one of claims 1 to 5, wherein, The content ratio of the phosphorus-containing compound (C) to the fatty acid ester (D), i.e., (C) / (D), is 0.3 to 10 in terms of mass ratio.

7. The lubricating oil composition according to any one of claims 1 to 6, wherein, Based on the total amount of the lubricating oil composition, the content of the antifoaming agent is less than 0.05% by mass.

8. The lubricating oil composition according to any one of claims 1 to 7 has a kinematic viscosity at 100 °C of 6.0 mm 2 / s or less.

9. Use of the lubricating oil composition according to any one of claims 1 to 8 for lubricating a buffer.

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