Lubricating oil composition

Abstract

To provide a lubricating oil composition having excellent fuel economy and high shear stability; and a method for using the lubricating oil composition.SOLUTION: A lubricating oil composition includes: a comb-like polymer (A1) having a weight average molecular weight (Mw) of less than 300,000; and a comb-like polymer (A2) having a Mw of 400,000 or more, where a mass content ratio [(A1) / (A2)] of the comb-like polymer (A1) to the comb-like polymer (A2) in terms of resin content is 0.25 or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a lubricating oil composition, a diesel engine, and a method for using the lubricating oil composition. [Background technology]

[0002] In recent years, global environmental regulations have become increasingly stringent, and the situation surrounding automobiles has also become more challenging in terms of fuel efficiency regulations, exhaust gas regulations, and so on. In particular, improving the fuel efficiency of automobiles and other vehicles is a major challenge, and one way to solve this problem is to improve the fuel efficiency of lubricant compositions used in vehicles. To improve the fuel efficiency of lubricating oil compositions, polymethacrylate (PMA) is generally used as a viscosity index improver added to the lubricating oil composition.

[0003] It is known that lubricating oil compositions containing viscosity index improvers such as PMA suffer from reduced cleaning properties when used under high-temperature, high-shear conditions. Therefore, Patent Document 1 describes a lubricating oil composition containing a comb-shaped polymer with a weight-average molecular weight of 420,000 to 450,000 in the examples, with the aim of providing a lubricating oil composition having excellent cleaning properties and fuel efficiency. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2016 / 043333 [Overview of the project] [Problems that the invention aims to solve]

[0005] Under these circumstances, there is a need for a lubricating oil composition that can further improve fuel efficiency while being more suitably applied to internal combustion engines. The present invention has been made in view of the above, and aims to provide a lubricating oil composition having excellent fuel efficiency and high shear stability, and a method for using the lubricating oil composition. [Means for Solving the Problems]

[0006] As a result of intensive research, the inventors of the present invention have found that the above problems can be solved by using two types of comb polymers having different weight average molecular weights and adjusting their mass ratios within a specific range, and have completed the present invention. That is, the present invention provides the following aspects [1] to

[11] . [1] A lubricating oil composition comprising a base oil, a comb polymer (A1) having a weight average molecular weight (Mw) of less than 300,000, and a comb polymer (A2) having a Mw of 400,000 or more, wherein the content ratio [(A1) / (A2)] in terms of resin content of the comb polymer (A1) and the comb polymer (A2) is 0.25 or more in terms of mass ratio. [2] The lubricating oil composition according to [1], wherein the content of the comb polymer (A1) in terms of resin content is 0.01 to 3.50% by mass based on the total amount of the lubricating oil composition. [3] The lubricating oil composition according to [1] or [2], wherein the content of the comb polymer (A2) in terms of resin content is 0.01 to 2.40% by mass based on the total amount of the lubricating oil composition. [4] The lubricating oil composition according to any one of [1] to [3], wherein the kinematic viscosity of the lubricating oil composition at 100 °C is 9.3 mm 2 / s or more. [5] The lubricating oil composition according to any one of [1] to [4], wherein the high-temperature high-shear viscosity (HTHS viscosity) of the lubricating oil composition at 150 °C is 2.9 mPa·s or more. [6] The lubricating oil composition according to any one of [1] to [5], wherein the kinematic viscosity of the lubricating oil composition at 40 °C is 38.0 mm 2 / s or less. [7] Based on ASTM D6278, after passing through a 30-cycle high-shear Bosch diesel injector, the kinematic viscosity of the lubricating oil composition at 100 °C is 8.6 mm 2 / s or more. [8] The lubricating oil composition according to any one of [1] to [7], wherein the sulfuric acid ash content of the lubricating oil composition is 0.90% by mass or less. [9] A lubricating oil composition according to any one of [1] to [8] and used in a diesel engine.

[10] A diesel engine filled with a lubricating oil composition according to any one of [1] to [9].

[11] A method for using a lubricating oil composition, which comprises applying the lubricating oil composition according to any one of [1] to

[10] to lubricate a diesel engine. [Advantages of the Invention]

[0007] The lubricating oil composition of a preferred embodiment of the present invention has excellent fuel economy and high shear stability. [Modes for Carrying Out the Invention]

[0008] Regarding the numerical ranges described in this specification, the upper limit value and the lower limit value can be arbitrarily combined. For example, when 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 ranges described in this specification. Also, for example, when the numerical range is described as "preferably 30 or more, more preferably 40 or more, and 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 ranges described in this specification. In addition, as the numerical range described in this specification, for example, the description of "60 to 100" means a range of "60 or more and 100 or less". Furthermore, in the definition of the upper limit value and the lower limit value described in this specification, appropriate selection can be made from each option and arbitrarily combined to define a numerical range from the lower limit value to the upper limit value. In addition, various requirements described as preferred embodiments in this specification can be combined in plural.

[0009] [Composition of Lubricating Oil Composition] The lubricating oil composition of the present invention contains a comb-shaped polymer (A1) with a weight-average molecular weight (Mw) of less than 300,000 and a comb-shaped polymer (A2) with a Mw of 400,000 or more, and the content ratio of comb-shaped polymer (A1) to comb-shaped polymer (A2) in terms of resin content [(A1) / (A2)] is 0.25 or more by mass. To provide a lubricating oil composition with excellent fuel efficiency, viscosity index improvers with relatively large weight-average molecular weights are typically used. This allows the kinematic viscosity at 100°C, kinematic viscosity at 40°C, and high-temperature high-shear viscosity (HTHS viscosity), which are indicators of fuel efficiency, to be adjusted to below standard values. However, to meet the diesel engine oil standards (DL-1, DL-2), it was necessary to have high shear stability in addition to fuel efficiency. However, it was difficult to achieve high shear stability with viscosity index improvers with relatively large weight-average molecular weight alone, making it difficult to achieve both excellent fuel efficiency and high shear stability simultaneously. Furthermore, with commonly used viscosity index improvers such as PMA, even if the kinematic viscosity at 100°C and HTHS viscosity meet the standard values ​​and high shear stability can be achieved, it was difficult to adjust the kinematic viscosity at 40°C to within the standard value. To address these problems, the present inventors discovered that by blending a comb-shaped polymer with a relatively small weight-average molecular weight with a comb-shaped polymer with a relatively large weight-average molecular weight, a lubricating oil composition that satisfies the above-mentioned parameters can be obtained, thus completing the present invention. The details of each component contained in a lubricating oil composition according to one embodiment of the present invention will be described below.

[0010] <Base oil> The base oil contained in the lubricating oil composition according to one embodiment of the present invention may be mineral oil, synthetic oil, or a mixture of mineral oil and synthetic oil. Examples of mineral oils include atmospheric residue obtained by atmospheric distillation of crude oils such as paraffinic crude oil, intermediate-base crude oil, naphthenic crude oil, etc.; distillate oil obtained by vacuum distillation of these atmospheric residues; refined oil obtained by subjecting the distillate oil to one or more refining treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining; etc.

[0011] Examples of synthetic oils include poly-α-olefins such as α-olefins and their homopolymers, or α-olefin copolymers (e.g., α-olefin copolymers having 8 to 14 carbon atoms such as ethylene-α-olefin copolymers); isoparaffin; polyalkylene glycol; ester oils such as polyol ester, dibasic acid ester, and phosphate ester; ether oils such as polyphenyl ether; alkylbenzene; alkylnaphthalene; synthetic oils (GTL) obtained by isomerizing wax (GTL wax (Gas To Liquids WAX)) produced from natural gas by the Fischer-Tropsch method, etc.

[0012] Among these, the base oil used in one aspect of the present invention preferably contains at least one selected from mineral oils classified into Group 2 and Group 3 of the API (American Petroleum Institute) base oil category and synthetic oils. In one aspect of the present invention, these base oils may be used alone or in combination of two or more.

[0013] The kinematic viscosity at 100 °C of the base oil used in one aspect of the present invention is preferably 4.1 mm 2 / s or more, more preferably 4.2 mm 2 / s or more, still more preferably 4.3 mm 2 / s or more, and is preferably 4.5 mm 2 / s or less, more preferably 4.4 mm 2 / s or less. If the kinematic viscosity at 100 °C of the base oil is 4.1 mm 2 / s or more, it is preferable for oil film retention. On the other hand, if the kinematic viscosity at 100 °C of the base oil is 4.5 mm 2A value of / s or less is preferable because it suppresses power loss due to viscous resistance, resulting in improved fuel efficiency.

[0014] Furthermore, the viscosity index of the base oil used in one aspect of the present invention is preferably 70 or higher, more preferably 80 or higher, even more preferably 90 or higher, and even more preferably 100 or higher, from the viewpoint of suppressing viscosity changes due to temperature changes and improving fuel efficiency. In this specification, kinematic viscosity and viscosity index refer to values ​​measured or calculated in accordance with ASTM D455.

[0015] In a lubricating oil composition according to one aspect of the present invention, the base oil content is typically 55% by mass or more, preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, even more preferably 75% by mass or more, and particularly preferably 80% by mass or more, based on the total amount (100% by mass) of the lubricating oil composition, and also preferably 99.9% by mass or less, more preferably 98% by mass or less, and even more preferably 95% by mass or less.

[0016] <Viscosity index improver> The lubricating oil composition of the present invention comprises a comb-shaped polymer (A1) with a weight-average molecular weight (Mw) of less than 300,000 and a comb-shaped polymer (A2) with a Mw of 400,000 or more. The comb-shaped polymers (A1) and (A2) can be polymers having a structure in which the main chain has many tridental branching points from which high molecular weight side chains protrude. The comb-shaped polymers (A1) and (A2) used in one aspect of the present invention are preferably polymers having at least one constituent unit (X1) derived from a macromonomer (x1). This constituent unit (X1) corresponds to the "high molecular weight side chain" described above. In this invention, the above-mentioned "macromonomer (x1)" refers to 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 terminus.

[0017] The number-average molecular weight (Mn) of the macromonomer (x1) is preferably 300 or more, more preferably 400 or more, even more preferably 500 or more, and also preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 20,000 or less.

[0018] The comb-shaped polymers (A1) and (A2) used in one aspect of the present invention may be homopolymers consisting only of constituent units (X1) derived from one type of macromonomer (x1), or copolymers containing constituent units (X1) derived from two or more types of macromonomers (x1). Furthermore, the comb-shaped polymers (A1) and (A2) used in one aspect of the present invention may be copolymers that include structural units derived from a macromonomer (x1) as well as structural units (X2) derived from other monomers other than the macromonomer (x1). As for the specific structure of such comb-shaped polymers, a copolymer having a main chain containing a constituent unit (X2) derived from a monomer (x2) and side chains containing a constituent unit (X1) derived from a macromonomer (x1) is preferred.

[0019] Examples of monomers (x2) include alkyl (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, and aromatic carbon compounds. Examples include hydrogen-based vinyl monomers.

[0020] The lubricating oil composition of the present invention solves the above problems by setting the content ratio of comb-shaped polymer (A1) and comb-shaped polymer (A2) in terms of resin content to a specific numerical range. By adjusting the content ratio of these comb-shaped polymers in terms of resin content, a lubricating oil composition with excellent fuel efficiency and high shear stability can be obtained. In one embodiment of the present invention, the lubricating oil composition preferably has a content ratio [(A1) / (A2)] of comb-shaped polymer (A1) to comb-shaped polymer (A2) in terms of resin content, which is 0.25 or more by mass, more preferably 0.26 or more, even more preferably 0.27 or more, particularly preferably 0.28 or more, and also preferably 0.55 or less, more preferably 0.54 or less, even more preferably 0.53 or less, even more preferably 0.52 or less, even more preferably 0.51 or less, even more preferably 0.50 or less, even more preferably 0.49 or less, even more preferably 0.48 or less, even more preferably 0.47 or less, even more preferably 0.46 or less, and particularly preferably 0.45 or less.

[0021] Furthermore, the weight-average molecular weight (Mw) of the comb-shaped polymer (A1) used in one aspect of the present invention is preferably less than 300,000, more preferably 300,000 or less, even more preferably 290,000 or less, even more preferably 280,000 or less, and even more preferably 270,000 or less, and from the viewpoint of improving fuel efficiency, it is preferably 50,000 or more, more preferably 100,000 or more, even more preferably 120,000 or more, even more preferably 150,000 or more, even more preferably 170,000 or more, and particularly preferably 200,000 or more.

[0022] The weight-average molecular weight (Mw) of the comb-shaped polymer (A2) used in one aspect of the present invention is preferably 400,000 or more, more preferably 410,000 or more, even more preferably 420,000 or more, even more preferably 430,000 or more, even more preferably 440,000 or more, and particularly preferably 450,000 or more, and from the viewpoint of increasing fuel efficiency, it is preferably 900,000 or less, more preferably 800,000 or less, even more preferably 700,000 or less, even more preferably 600,000 or less, even more preferably 550,000 or less, and particularly preferably 500,000 or less.

[0023] In this specification, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are values ​​on a standard polystyrene basis measured by gel permeation chromatography (GPC), specifically, values ​​on a standard polystyrene basis measured using the following measuring apparatus and conditions. (Measuring device) Gel permeation chromatography system (Agilent, "Model 1260 HPLC") (Measurement conditions) • Column: Two "Shodex LF404" columns connected sequentially. • Column temperature: 35℃ • Developing solvent: Chloroform ·Flow rate: 0.3mL / min

[0024] In a lubricating oil composition according to one aspect of the present invention, the difference between the Mw of comb polymer (A2) and the Mw of comb polymer (A1) is preferably 50,000 or more, more preferably 70,000 or more, even more preferably 90,000 or more, even more preferably 100,000 or more, even more preferably 110,000 or more, even more preferably 120,000 or more, even more preferably 130,000 or more, even more preferably 140,000 or more, even more preferably 150,000 or more, even more preferably 160,000 or more, even more preferably 170,000 or more, even more preferably 180,000 or more, and particularly preferably 190,000 or more, from the viewpoint of making it easier to adjust parameters that serve as indicators of fuel efficiency and shear stability by using comb polymers with different SSI (shear stability index). Furthermore, from the same viewpoint as above, the difference between the Mw of comb-shaped polymer (A2) and the Mw of comb-shaped polymer (A1) is preferably 900,000 or less, more preferably 800,000 or less, even more preferably 700,000 or less, even more preferably 600,000 or less, even more preferably 500,000 or less, even more preferably 450,000 or less, even more preferably 400,000 or less, even more preferably 350,000 or less, and particularly preferably 300,000 or less. In this case, the Mw of the comb-shaped polymer (A2) is preferably at least 400,000, from the viewpoint of improving fuel efficiency.

[0025] The molecular weight distribution (Mw / Mn) (Mw: weight-average molecular weight of the comb-shaped polymer (A1), Mn: number-average molecular weight of the comb-shaped polymer (A1)) used in one aspect of the present invention is preferably 7.00 or less, more preferably 6.00 or less, even more preferably 5.00 or less, even more preferably 4.00 or less, particularly preferably 3.50 or less, and usually 1.01 or more, preferably 1.05 or more, and more preferably 1.10 or more.

[0026] The molecular weight distribution (Mw / Mn) (Mw: weight-average molecular weight of the comb-shaped polymer (A2), Mn: number-average molecular weight of the comb-shaped polymer (A2)) used in one aspect of the present invention is preferably 8.00 or less, more preferably 7.50 or less, even more preferably 7.00 or less, even more preferably 6.50 or less, particularly preferably 6.00 or less, and usually 1.01 or more, preferably 1.05 or more, and more preferably 1.10 or more.

[0027] Furthermore, in a lubricating oil composition according to one embodiment of the present invention, the content of the comb-shaped polymer (A1) in terms of resin content is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.10% by mass or more, even more preferably 0.20% by mass or more, even more preferably 0.25% by mass or more, even more preferably 0.30% by mass or more, even more preferably 0.35% by mass or more, even more preferably 0.40% by mass or more, even more preferably 0.45% by mass or more, even more preferably 0.50% by mass or more, and particularly preferably 0.55% by mass or more, based on the total amount (100% by mass) of the lubricating oil composition, from the viewpoint of obtaining high shear stability. On the other hand, from the viewpoint of providing a lubricating oil composition with good fuel efficiency, the content of the comb-shaped polymer (A1) in terms of resin content is preferably 3.50% by mass or less, more preferably 3.00% by mass or less, even more preferably 2.50% by mass or less, even more preferably 2.00% by mass or less, even more preferably 1.50% by mass or less, even more preferably 1.25% by mass or less, even more preferably 1.20% by mass or less, even more preferably 1.15% by mass or less, even more preferably 1.10% by mass or less, even more preferably 1.05% by mass or less, even more preferably 1.00% by mass or less, even more preferably 0.95% by mass or less, and particularly preferably 0.90% by mass or less.

[0028] On the other hand, in a lubricating oil composition according to one aspect of the present invention, the content of the comb-shaped polymer (A2) in terms of resin content is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.10% by mass or more, even more preferably 0.30% by mass or more, even more preferably 0.50% by mass or more, even more preferably 0.70% by mass or more, even more preferably 0.90% by mass or more, and even more preferably 1.00% by mass or more, based on the total amount (100% by mass) of the lubricating oil composition, from the viewpoint of improving fuel efficiency. More preferably 1.10% by mass or more, even more preferably 1.20% by mass or more, even more preferably 1.30% by mass or more, even more preferably 1.40% by mass or more, even more preferably 1.50% by mass or more, even more preferably 1.55% by mass or more, even more preferably 1.60% by mass or more, even more preferably 1.65% by mass or more, even more preferably 1.70% by mass or more, even more preferably 1.75% by mass or more, even more preferably 1.80% by mass or more, and particularly preferably 1.85% by mass or more. On the other hand, from the viewpoint of providing a lubricating oil composition with good shear stability, the content of the comb-shaped polymer (A2) in terms of resin content is preferably 2.40% by mass or less, more preferably 2.35% by mass or less, even more preferably 2.30% by mass or less, even more preferably 2.25% by mass or less, even more preferably 2.20% by mass or less, even more preferably 2.15% by mass or less, even more preferably 2.10% by mass or less, and particularly preferably 2.05% by mass or less, based on the total amount (100% by mass) of the lubricating oil composition.

[0029] In one embodiment of the present invention, the total content of comb-shaped polymer (A1) and comb-shaped polymer (A2) in terms of resin content is preferably 2.00% by mass or more, more preferably 2.10% by mass or more, even more preferably 2.15% by mass or more, even more preferably 2.20% by mass or more, even more preferably 2.25% by mass or more, even more preferably 2.30% by mass or more, even more preferably 2.35% by mass or more, particularly preferably 2.40% by mass or more, and also preferably 3.00% by mass or less, more preferably 2.95% by mass or less, even more preferably 2.90% by mass or less, even more preferably 2.85% by mass or less, even more preferably 2.80% by mass or less, particularly preferably 2.75% by mass or less.

[0030] Furthermore, viscosity index improvers such as comb-shaped polymers (A1) and (A2) are distributed in the form of solutions dissolved in diluent oils such as mineral oil, synthetic oil, and light oil, taking into consideration handling properties and solubility in base oils. When preparing lubricating oil compositions, they may be formulated in the form of a solution containing the diluent oil. However, in this specification, the viscosity index improver content is "content on a resin basis" as stated above, meaning the resin content excluding the diluent oil.

[0031] Here, the SSI value of a viscosity index improver is a physical property value that shows, as a percentage, the viscosity reduction due to shear originating from the polymer constituting the viscosity index improver. In other words, the SSI value indicates the polymer's ability to resist shear, and the larger the SSI value, the more unstable and easily decomposed the polymer is against shear.

[0032] The SSI of the comb-shaped polymer (A1) used in one aspect of the present invention is preferably 7.0 or less, more preferably 6.0 or less, even more preferably 5.0 or less, even more preferably 4.0 or less, particularly preferably 3.0 or less, and also preferably 0.1 or more, more preferably 0.5 or more, and even more preferably 0.7 or more.

[0033] The SSI of the comb-shaped polymer (A2) used in one aspect of the present invention is preferably 12.0 or less, more preferably 11.0 or less, even more preferably 10.0 or less, and also preferably 7.0 or more, more preferably 8.0 or more.

[0034] The SSI of the comb-shaped polymer mixture (A1) and (A2) used in one aspect of the present invention is preferably 10.0 or less, more preferably 9.0 or less, even more preferably 8.0 or less, and also preferably 0.1 or more, more preferably 0.5 or more, even more preferably 1.0 or more, even more preferably 2.0 or more, and even more preferably 5.0 or more. Furthermore, in one embodiment of the present invention, when viscosity index improvers other than the comb-shaped polymers (A1) and (A2) are used in combination, the SSI of the viscosity index improver is preferably within the above range as the SSI of the mixture.

[0035] Furthermore, in this specification, the SSI of a viscosity index improver refers to a value measured in accordance with ASTM D6278, and more specifically, a value calculated from the following formula (1).

number

[0036] Furthermore, the SSI value of a viscosity index improver varies depending on the structure of the polymer that makes up the viscosity index improver, and specifically, the following trends are observed. The more branched polymers there are compared to linear polymers, the lower the SSI value will be. The larger the molecular weight of the side chains in a branched polymer, the lower the SSI value will be. The more comb-shaped polymers there are compared to linear polymers, the lower the SSI value will be.

[0037] [Other viscosity index improvers] The viscosity index improver used in one aspect of the present invention may contain a viscosity index improver made of a polymer other than the above-described comb-shaped polymers (A1) and (A2), as long as it does not impair the effects of the present invention. Other polymers that fall under the category of comb-type polymers include, for example, polymethacrylates, dispersed polymethacrylates, olefin copolymers (e.g., ethylene-propylene copolymers), dispersed olefin copolymers, and styrene copolymers (e.g., styrene-diene copolymers, styrene-isoprene copolymers).

[0038] However, in one embodiment of the present invention, it is preferable that the content of viscosity index improvers other than the comb-shaped polymers (A1) and (A2) be kept as low as possible. Specifically, the total content of other viscosity index improvers other than the comb-shaped polymers (A1) and (A2) in terms of resin content may be 100 parts by mass or less, 70 parts by mass or less, 50 parts by mass or less, 20 parts by mass or less, 10 parts by mass or less, 5 parts by mass or less, 1 part by mass or less, 0.1 parts by mass or less, 0.01 parts by mass or less, or 0.001 parts by mass or less, relative to 100 parts by mass of the total resin content of the comb-shaped polymers (A1) and (A2).

[0039] <Various additives> A lubricating oil composition according to one aspect 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, wear-resistant agents, rust inhibitors, defoamers, and extreme pressure additives. These lubricating oil additives may be used individually or in combination of two or more types.

[0040] The content of each of these various 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.

[0041] Alternatively, commercially available additive packages containing multiple additives that comply with standards such as those set by the European Automobile Manufacturers' Association (ACEA) or API / ILSAC SN / GF-5 may be used as additives. Furthermore, compounds having multiple functions as additives (for example, compounds having functions as a wear-resistant agent and an extreme pressure additive) may be used. Furthermore, these lubricating oil additives may be used individually or in combination of two or more types.

[0042] [Pour point depressant] A lubricating oil composition according to one embodiment 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 copolymers, condensates of chlorinated paraffin and naphthalene, condensates of chlorinated paraffin and phenol, polymethacrylates, and polyalkylstyrenes. The mass-average molecular weight (Mw) of the pour point depressant used in one aspect of the present invention may be 5,000 or more, 7,000 or more, 10,000 or more, 15,000 or more, 20,000 or more, 25,000 or more, 30,000 or more, 35,000 or more, 40,000 or more, 45,000 or more, 50,000 or more, 55,000 or more, or 60,000 or more, or 150,000 or less, 120,000 or less, 100,000 or less, 90,000 or less, or 80,000 or less.

[0043] [Antioxidant] A lubricating oil composition according to one embodiment of the present invention may further contain an antioxidant. The antioxidant may be used alone or in combination of two or more types. Examples of antioxidants used in one aspect 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.

[0044] [Metal-based cleaning agent] 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. Furthermore, 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.

[0045] In a lubricating oil composition according to one embodiment of the present invention, the metal-based detergent preferably contains one or more selected from calcium sulfonate, calcium salicylate, and calcium phenate, and more preferably contains calcium sulfonate. The calcium sulfonate content is preferably 50-100% by mass, more preferably 60-100% by mass, even more preferably 70-100% by mass, and even more preferably 80-100% by mass, based on the total amount (100% by mass) of metal-based detergents contained in the lubricating oil composition.

[0046] The base number of the metal-based detergent is preferably 0 to 600 mg KOH / g. However, in a lubricating oil composition according to one aspect of the present invention, the metal-based detergent is preferably an overbasic metal-based detergent with a base number of 100 mg KOH / g or more. The base number of the overbasic metal-based detergent is 100 mg KOH / g or more, preferably 150 to 500 mg KOH / g, and more preferably 200 to 450 mg KOH / g. In this specification, "base number" refers to the base number measured by the perchloric acid method in accordance with JIS K2501:2003 "Petroleum products and lubricating oils - Neutralization number test method" 7.

[0047] [Ashless Dispersant] A 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 types. In one aspect of the present invention, alkenyl succinimide is preferred as the ashless dispersant, 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.

[0048] [Abrasion-resistant agent] A lubricating oil composition according to one embodiment 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 wear-resistant agents used in one aspect of the present invention include sulfur-containing compounds such as zinc dialkyldithiophosphate (ZnDTP), zinc phosphate, zinc dithiocarbamate, molybdenum dithiocarbamate, molybdenum dithiophosphate, 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 wear-resistant agents such as thiophosphite esters, thiophosphate esters, thiophosphonic acid esters, and their amine salts or metal salts.

[0049] [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.

[0050] [Antifoaming agent] A 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 defoaming agents used in one aspect of the present invention include alkyl silicone-based defoaming agents, fluorosilicone-based defoaming agents, and fluoroalkyl ether-based defoaming agents.

[0051] [Extreme pressure additives] A lubricating oil composition according to one embodiment of the present invention may further contain extreme pressure additives. The extreme pressure additives may be used alone or in combination of two or more types. Examples of extreme pressure additives used in one aspect of the present invention include chlorine-based extreme pressure additives such as chlorinated paraffin, chlorinated fatty acids, and chlorinated fatty oils; sulfur-based extreme pressure additives such as sulfurized olefins, sulfurized lard, alkyl polysulfides, and sulfurized fatty acids; and phosphorus-based extreme pressure additives such as phosphate esters, phosphite esters, thiophosphate esters, and their salts, phosphine-based additives, and tricresyl phosphate.

[0052] <Method for producing a lubricating oil composition> The method for producing a lubricating oil composition according to one embodiment of the present invention is not particularly limited, but it is preferable to have a step of blending a base oil with the viscosity index improver described above, and optionally other various additives. The order in which each component is blended can be set as appropriate.

[0053] [Properties of the lubricating oil composition] The kinematic viscosity of a lubricating oil composition according to one embodiment of the present invention at 100°C is preferably 9.3 mm. 2 / s or more, more preferably 9.4 mm 2 / s or more, more preferably 9.5 mm 2 The value is 1 / s or more, and preferably 10.0 mm 2 / s or less, more preferably 9.9 mm 2 It is less than or equal to / s.

[0054] The kinematic viscosity of a lubricating oil composition according to one embodiment of the present invention at 40°C is preferably 38.0 mm². 2 / s or less, more preferably 37.8 mm 2 / s or less, more preferably 37.6 mm 2 / s or less, more preferably 37.4 mm 2 / s or less, more preferably 37.2 mm 2 / s or less, more preferably 37.0 mm 2 / s or less, more preferably 36.8 mm 2 / s or less, more preferably 36.6 mm 2 / s or less, more preferably 36.4 mm 2 / s or less, particularly preferably 36.2 mm 2 It is less than or equal to / s.

[0055] The viscosity index of the lubricating oil composition according to one embodiment of the present invention is preferably 170 or higher, more preferably 180 or higher, even more preferably 190 or higher, even more preferably 200 or higher, even more preferably 210 or higher, even more preferably 220 or higher, even more preferably 230 or higher, even more preferably 240 or higher, even more preferably 250 or higher, even more preferably 260 or higher, and particularly preferably 270 or higher.

[0056] The HTHS viscosity of the lubricating oil composition according to one embodiment of the present invention is preferably 2.9 to 3.0 mPa·s at 150°C. In this specification, the HTHS viscosity of the lubricating oil composition is determined in accordance with ASTM D4683, with a shear rate of 10 6 This refers to the viscosity value after shearing at / s.

[0057] In a lubricating oil composition according to one aspect of the present invention, the kinematic viscosity at 100°C after passing through a 30-cycle high-shear Bosch diesel injector, according to ASTM D6278 (hereinafter also referred to as "Bosch 100°C kinematic viscosity" for convenience), is preferably 8.6 mm². 2 / s or more, more preferably 8.7 mm 2 / s or more, more preferably 8.8 mm 2 / s or more, more preferably 8.9 mm 2 / s or more, more preferably 9.0 mm 2 / s or more, more preferably 9.1 mm 2 / s or more, particularly preferably 9.2 mm 2 The value is 1 / s or more, and preferably 10.5 mm2 Less than / s, more preferably 10.4 mm 2 / s or less, more preferably 10.3 mm 2 / s or less, more preferably 10.2 mm 2 / s or less, more preferably 10.1 mm 2 / s or less, particularly preferably 10.0 mm 2 It is less than or equal to / s.

[0058] The sulfated ash content of the lubricating oil composition according to one embodiment of the present invention is preferably 0.90% by mass or less, more preferably 0.88% by mass or less, even more preferably 0.86% by mass or less, even more preferably 0.84% ​​by mass or less, even more preferably 0.82% by mass or less, and particularly preferably 0.80% by mass or less. Furthermore, preferably it is 0.61% by mass or more, more preferably 0.65% by mass or more, and even more preferably 0.70% by mass or more. In this specification, sulfated ash refers to a value measured or calculated in accordance with ASTM D874.

[0059] [Uses of lubricating oil compositions] The lubricating oil composition of the present invention has excellent fuel efficiency and high shear stability. Therefore, an engine filled with the lubricating oil composition of the present invention can have excellent fuel efficiency and other performance characteristics. The lubricating oil composition of the present invention can be suitably used in diesel engines. Therefore, the present invention also provides a diesel engine as described in [I] below, and a method for using the lubricating oil composition as described in [II] below. [I] A diesel engine filled with a lubricating oil composition according to one embodiment of the present invention described above. [II] A method of using a lubricating oil composition according to one aspect of the present invention described above, for the lubrication of a diesel engine. [Examples]

[0060] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In addition, the various physical property values of each component used in the examples, comparative examples, and reference examples and the obtained lubricating oil compositions were measured in accordance with the following methods.

[0061] <Kinematic viscosity> Measured and calculated in accordance with ASTM D455. <Viscosity index> Measured and calculated in accordance with ASTM D2270. <SSI (Shear stability index)> Measured in accordance with ASTM D6278. <Weight average molecular weight (Mw), number average molecular weight (Mn)> Using a gel permeation chromatograph (manufactured by Agilent Technologies, "1260型HPLC"), measurements were taken under the following conditions, and values measured in terms of standard polystyrene conversion were used. (Measurement conditions) · Column: Two "Shodex LF404" columns connected in series. · Column temperature: 35 °C · Developing solvent: Chloroform · Flow rate: 0.3 mL / min <HTHS viscosity> In accordance with ASTM D4683, at a measurement temperature of 150 °C, after shearing at a shear rate of 10 6 / s, the viscosity was measured. <Bosch 100 °C kinematic viscosity> In accordance with ASTM D6278, the kinematic viscosity at 100 °C after passing through a 30-cycle high-shear Bosch diesel injector was measured. <Sulfated ash> Measured in accordance with ASTM D874.

[0062] Examples 1 to 4, Comparative Examples 1 to 6, Reference Example 1 Lubricating oil compositions were prepared by adding and mixing the various components and other additives shown in Table 1 in the amounts shown in Table 1. Note that the amounts of viscosity index improvers in Table 1 are calculated based on the resin content, excluding the diluent solvent. Details of each component used in the preparation of the lubricating oil compositions are as follows.

[0063] <Base oil> ·Mineral oil: 100℃ kinematic viscosity = 4.3mm 2 Mineral oil classified as Group III in the API base oil category, with viscosity index = 124. <Viscosity index improver> • Comb-shaped polymer (A1): A comb-shaped polymer with a structure that has many tridental branching points in the main chain from which high molecular weight side chains emerge, Mw=260,000, Mw / Mn=3.1, SSI=1 • Comb-shaped polymer (A2): A comb-shaped polymer with a structure that has many tridental branching points in the main chain from which high molecular weight side chains emerge, Mw=450,000, Mw / Mn=5.5, SSI=9 PMA(1): Polymethacrylate, Mw=540,000, SSI=50 PMA(2): Polymethacrylate, Mw=230,000, SSI=25 PMA(3): Polymethacrylate, Mw=430,000, SSI=20 <Other additives> • An additive mixture comprising a cleaning agent, a dispersant, ZnDTP, an antifoaming agent, a pour point depressant, molybdenum dithiocarbamate (MoDTC), benzotriazole, and diethanolamide.

[0064] The lubricating oil compositions prepared in the examples, comparative examples, and reference examples were measured and calculated according to the measurement methods described above. These results are shown in Table 1. In Table 1, if even one of the physical properties is not within the range specified below, the composition is considered "fail," and if all of the physical properties are within the range specified below, the composition is considered "pass." ·40℃ kinematic viscosity: 38.0mm 2 / s or less ·Kinematic viscosity at 100℃: 9.3mm 2 / s or more, 10.0mm 2 / s or less ·HTHS viscosity (150℃): More than 2.8mPa·s, 3.0mPa·s or less ·Bosch 100℃ kinematic viscosity: 8.6mm 2 / s or more

[0065] [Table 1]

[0066] Table 1 shows that the lubricating oil compositions of Examples 1 to 4, in which the content ratio (mass ratio) of comb-shaped polymers (A1) and (A2) is above a predetermined value, all of their physical properties fall within the predetermined range. It can be said that lubricating oil compositions with such properties possess excellent fuel efficiency and high shear stability.

Claims

1. A lubricating oil composition comprising a base oil, a comb-shaped polymer (A1) with a weight-average molecular weight (Mw) of less than 300,000, and a comb-shaped polymer (A2) with a Mw of 400,000 or more, wherein the content ratio of comb-shaped polymer (A1) to comb-shaped polymer (A2) in terms of resin content [(A1) / (A2)] is 0.25 or more by mass.

2. The lubricating oil composition according to claim 1, wherein the content of the comb-shaped polymer (A1) on a resin basis is 0.01 to 3.50% by mass on a total basis of the lubricating oil composition.

3. The lubricating oil composition according to claim 1 or 2, wherein the content of the comb-shaped polymer (A2) on a resin basis is 0.01 to 2.40% by mass on a total basis of the lubricating oil composition.

4. The kinematic viscosity of the lubricating oil composition at 100°C is 9.3 mm. ２ A lubricating oil composition according to any one of claims 1 to 3, wherein the ratio is 1 / s or more.

5. The lubricating oil composition according to any one of claims 1 to 4, wherein the high-temperature high-shear viscosity (HTHS viscosity) of the lubricating oil composition at 150°C is 2.9 mPa·s or more.

6. The kinematic viscosity of the lubricating oil composition at 40°C is 38.0 mm². ２ A lubricating oil composition according to any one of claims 1 to 5, wherein the ratio is less than or equal to / s.

7. According to ASTM D6278, the kinematic viscosity of the lubricating oil composition at 100°C after passing it through a 30-cycle high-shear Bosch diesel injector is 8.6 mm². ２ A lubricating oil composition according to any one of claims 1 to 6, wherein the ratio is 1 / s or more.

8. The lubricating oil composition according to any one of claims 1 to 7, wherein the sulfated ash content of the lubricating oil composition is 0.90% by mass or less.

9. A lubricating oil composition according to any one of claims 1 to 8, for use in a diesel engine.

10. A diesel engine filled with the lubricating oil composition described in any one of claims 1 to 9.

11. A method for using a lubricating oil composition, wherein the lubricating oil composition described in any one of claims 1 to 9 is applied to the lubrication of a diesel engine.

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