Engine oil composition

Abstract

To provide an engine oil composition with excellent fuel efficiency and coking resistance. [Solution] An engine oil composition comprising a base oil containing a mineral oil-based base oil and a synthetic oil-based base oil, wherein the traction coefficient at 60°C is 0.045 or less, and a viscosity index improver containing a star-shaped polymer and a comb-shaped polymer.

Description

Technical Field

[0001] The present disclosure relates to an engine oil composition.

[0002] In recent years, as a response to environmental issues such as global warming, engine units such as diesel engines for large commercial vehicles are required to both reduce CO₂ emissions and comply with exhaust gas regulations. Therefore, latest engines adopt technologies such as downsizing or high-efficiency turbocharging.

[0003] Engine oils (i.e., engine oil compositions) used in diesel engines and the like are also required to contribute not only to reliability but also to fuel efficiency improvement.

[0004] A lubricating oil composition for use in a diesel engine equipped with a supercharger is known, which contains a base oil (A) containing poly-α-olefin (A1) and a viscosity index improver (B) having an SSI (shear stability index) of 20 or less, and has a distillate amount of light fractions at 496°C or lower in a gas chromatography distillation test of less than 80% by volume (see Patent Document 1). Further, as an engine oil composition having excellent fuel-saving performance, an engine oil composition containing a specific viscosity index improver and having a viscosity index of 185 to 230 is known (see Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of Invention

Problem to be Solved by the Invention

[0006] From the perspective of improving fuel efficiency, distillation characteristics such as a distillation volume of light fractions below 496°C of less than 80% by volume in gas chromatography distillation tests may not provide sufficient fuel efficiency. Furthermore, even when improving fuel efficiency, it is required that the system also maintains reliability.

[0007] The problem that one embodiment of this invention aims to solve is to provide an engine oil composition that is excellent in fuel efficiency and resistance to coking. [Means for solving the problem]

[0008] This disclosure includes the following embodiments: <1> An engine oil composition comprising a base oil containing a mineral oil-based base oil and a synthetic oil-based base oil, wherein the traction coefficient at 60°C is 0.045 or less, and a viscosity index improver containing a star-shaped polymer and a comb-shaped polymer. <2> The base oil contains synthetic oil-based base oil at a ratio of 50% or less by mass, based on the total mass of the base oil. <1> The engine oil composition described above. <3> The base oil has an aniline point A (°C) and a kinematic viscosity B (mm²) at 100°C. 2 / s) satisfies the following equation (1) <1> or <2> The engine oil composition described above. (A / 10)-B≦8.0 (1) <4> The viscosity index improver contains comb-shaped polymers in a mass ratio of 4.0 to 5.5 times the mass of star-shaped polymers, calculated based on the amount of active ingredients. <1> ~ <3> An engine oil composition as described in any one of the following. <5> The base oil has a kinematic viscosity B(mm) at 100°C. 2 / s) is 4.3mm 2 / s or less <1> ~ <4> An engine oil composition as described in any one of the following. <6> The SAE viscosity grade specified in SAE J300 is 0W-30 or 5W-30. <1> ~ <5> An engine oil composition as described in any one of the following. [Effects of the Invention]

[0009] According to one embodiment of the present disclosure, an engine oil composition is provided that is excellent in fuel efficiency and coking resistance. [Modes for carrying out the invention]

[0010] The engine oil compositions relating to this disclosure will be described in detail below. The following description may be based on representative embodiments, but the engine oil compositions relating to this disclosure are not limited to such embodiments.

[0011] In this disclosure, a numerical range indicated using "~" means a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages within this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described within this disclosure, the upper or lower limit of that range may be replaced with the values ​​shown in the examples. In this disclosure, the amount of each component in a composition means the total amount of multiple substances corresponding to each component present in the composition, unless otherwise specified. In this disclosure, "mass%" and "weight%" are synonymous. In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0012] In this disclosure, the weight-average molecular weight (Mw), number-average molecular weight (Mn), and Z-average molecular weight (Mz) are values ​​measured by gel permeation chromatography (GPC). The weight-average molecular weight (Mw), number-average molecular weight (Mn), and Z-average molecular weight (Mz) in this disclosure are measured using a Shodex GPC-101 measuring instrument (manufactured by Showa Denko Corporation), three Shodex GPC LF-804 measuring columns (manufactured by Showa Denko Corporation), a differential refractive index (RI) detector, THF (tetrahydrofuran) mobile phase, a flow rate of 1 ml / min, a sample concentration of 1.0 mass% / vol, and an injection volume of 100 μL. The weight-average molecular weight (Mw), number-average molecular weight (Mn), and Z-average molecular weight (Mz) are calculated from these measurement results using molecular weight distribution curves prepared from monodisperse polystyrene standard samples.

[0013] In this disclosure, "polyalkyl (meth)acrylate" means a polymer comprising constituent units derived from alkyl esters of acrylic acid, alkyl esters of methacrylic acid, and / or both thereof. In this disclosure, "JIS" is used as an abbreviation for Japanese Industrial Standards. In this disclosure, "ASTM" refers to the international standards developed by ASTM International.

[0014] <Engine oil composition> The engine oil composition relating to this disclosure is It contains a base oil comprising a mineral oil-based base oil and a synthetic oil-based base oil, and having a traction coefficient of 0.045 or less at 60°C, and a viscosity index improver comprising a star-shaped polymer and a comb-shaped polymer.

[0015] The engine oil composition according to this disclosure exhibits excellent fuel efficiency and coking resistance. The reasons for the excellent fuel efficiency and coking resistance of the engine oil composition according to this disclosure are presumed to be friction reduction due to a low traction coefficient, the effect of viscosity index improvers containing a combination of star-shaped polymers and comb-shaped polymers, and the synergistic effect of the base oil and viscosity index improvers.

[0016] Regarding friction reduction due to a low traction coefficient, it is estimated that the base oil having a low traction coefficient of 0.045 or less at 60°C significantly reduces resistance in the fluid lubrication range, thereby improving fuel efficiency. Regarding the effects of the viscosity index improver, it is presumed that by including a combination of star-shaped polymers and comb-shaped polymers, viscosity fluctuations due to changes in oil temperature are suppressed and shear stability is enhanced, thereby maintaining the performance of the engine oil over a long period of time. For example, it is presumed that this prevents the decomposition and shortening of polymer molecules in high-temperature environments and contributes to suppressing deposit formation (i.e., coking). Regarding the synergistic effect of the base oil and viscosity index improver, it is presumed that blending mineral oil-based and synthetic oil-based base oils combines the advantages of each, such as the stability of mineral oil-based base oils and the low-temperature fluidity of synthetic oil-based base oils, resulting in desirable physical properties. Furthermore, it is presumed that achieving both a low traction coefficient and high shear stability will result in a balance between fuel efficiency and coking resistance. Thus, by reducing friction through a low traction coefficient and incorporating viscosity index improvers that utilize the high shear stability of star-shaped and comb-shaped polymers, the overall performance of the engine oil composition is improved, and it is estimated that both fuel efficiency and coking resistance will be achieved.

[0017] (1) Base oil The engine oil composition according to this disclosure includes a base oil. The base oil includes a mineral oil-based base oil and a synthetic oil-based base oil, and has a traction coefficient of 0.045 or less at 60°C. In a base oil that is a mixed oil containing a mineral oil-based base oil and a synthetic oil-based base oil, it is sufficient that the traction coefficient at 60°C is 0.045 or less, and the mineral oil-based base oil or the synthetic oil-based base oil can be selected from various types, and the respective amounts can also be selected as appropriate.

[0018] In this disclosure, "traction coefficient at 60°C" refers to the result obtained using a PCS Instruments MTM (i.e., The Mini Traction Machine) at an oil temperature of 60°C and a sliding speed of 1000 mm. 2This value refers to the measurement taken during 60 minutes of operation with a load of 30N and a slip ratio of 50%.

[0019] Mineral oil-based base oils can be obtained through various manufacturing methods. Examples of mineral oil-based base oils include those obtained by refining the lubricating oil fraction of crude oil using a combination of refining methods such as solvent refining, hydrorefining, hydrocracking, and hydrodeswaxing. Alternatively, the mineral oil-based base oil may be a paraffinic mineral oil (i.e., a high viscosity index mineral oil-based lubricating oil base oil) that has been highly refined by subjecting hydrorefined oil, catalytic isomerized oil, etc., to solvent dewaxing or hydrodeswaxing.

[0020] Examples of synthetic oil-based base oils include isoparaffins synthesized from natural gas such as methane, α-olefin oligomers, dialkyldiesters, polyols, alkylbenzenes, polyglycols, and phenyl ethers.

[0021] The base oil may be a single mineral oil-based base oil or a synthetic oil-based base oil, or a mixture of two or more types. For example, as the mineral oil-based base oil, a mixture of multiple types of mineral oil-based base oils having different kinematic viscosities at 100°C may be used. Furthermore, a mixed oil can be used that has been adjusted to the above properties by mixing a Group II base oil (i.e., a base oil having a sulfur content of 0.03% by mass or less, a saturation content of 90% by mass or more, and a viscosity index of 80 or more and less than 120) and a Group III base oil (i.e., a base oil having a sulfur content of 0.03% by mass or less, a saturation content of 90% by mass or more, and a viscosity index of 120 or more) according to the American Petroleum Institute (API) base oil classification. As for the mineral oil base oil, it is preferable to use a mineral oil base oil classified as Group III or higher, and it is more preferable to use a mineral oil base oil classified as Group III.

[0022] Regarding the blending amount of the mineral base oil or synthetic base oil, from the viewpoint that the traction coefficient at 60°C can be easily suppressed to 0.045 or less for the lower limit, and from the viewpoint of controlling the aniline point for the upper limit, it is preferred that the synthetic base oil is contained in a proportion of 25% by mass to 50% by mass based on the total mass of the base oil, and it is more preferred that the synthetic base oil is contained in a proportion of 30% by mass to 45% by mass.

[0023] In one embodiment of the present disclosure, from the viewpoint of achieving excellent fuel efficiency, the base oil has a traction coefficient of 0.045 or less at 60°C. The base oil preferably has a traction coefficient of 0.042 or less at 60°C, and more preferably 0.040 or less.

[0024] With regard to the properties of the base oil, as long as the traction coefficient at 60°C is 0.045 or less, other properties are not limited as long as they are properties suitable for an engine oil composition. In the base oil, the kinematic viscosity B at 100°C (mm 2 / s) is preferably 4.3 mm 2 / s or less, more preferably 3.5 mm 2 / s or more and 4.3 mm 2 / s or less, and even more preferably 3.8 mm 2 / s or more and 4.1 mm 2 / s or less. When the kinematic viscosity B at 100°C of the base oil is within the above range, the viscosity of the engine oil composition becomes appropriate, the fuel saving effect can be sufficiently exhibited, the evaporation characteristics of the base oil are excellent, and the practical performance of the engine oil composition can be ensured.

[0025] In the present disclosure, the kinematic viscosity of the base oil is a value measured according to ASTM D7042.

[0026] The viscosity index of the base oil is preferably 115 or more, more preferably 120 or more. By using the base oil exhibiting the above viscosity index, the viscosity characteristics of the engine oil composition can be improved, and the detergency can be enhanced.

[0027] In this disclosure, the viscosity index of the base oil is the value measured according to ASTM D7042.

[0028] Furthermore, if catalog values ​​for the kinematic viscosity and / or viscosity index of the base oil are available, these catalog values ​​will be used.

[0029] The base oil preferably has an aniline point of 110°C to 130°C, and more preferably 115°C to 125°C, as measured in accordance with JIS K 2256-2013 "Aniline Point Test Method".

[0030] Setting the aniline point above 110°C is preferable because it makes it easier to produce a base oil with a high viscosity index. Setting the aniline point below 130°C is also preferable because it tends to produce a base oil that easily ensures the solubility of additives. Furthermore, from the viewpoint of ensuring compatibility with rubber-based sealing materials used in engines, it is preferable to set the aniline point within an appropriate range, and from this viewpoint as well, an aniline point of 110°C to 130°C is preferable.

[0031] The base oil has an aniline point A (°C) and a kinematic viscosity B (mm²) at 100°C. 2 It is preferable that / s) and satisfy the following equation (1).

[0032] (A / 10)-B≦8.0 (1)

[0033] In the base oil, the aniline point A (°C) and the kinematic viscosity B (mm²) at 100°C are given. 2When the ratio of s) satisfies the above equation (1), it becomes possible to optimize the balance between the aromatic content of the base oil and the kinematic viscosity at 100°C. This improves oxidation stability and makes it easier to maintain the oil's performance over a long period of time. Furthermore, optimizing the balance between the aromatic content of the base oil and the kinematic viscosity at 100°C suppresses the formation of deposits that occur during operation, and a cleaning effect inside the engine can be expected. In addition, having the kinematic viscosity within an appropriate range ensures fluidity at low temperatures while forming a sufficient oil film at high temperatures, maintaining wear protection performance and improving reliability. As described above, the aniline point A (°C) and the kinematic viscosity B (mm²) at 100°C are 2 When the ratio of / s satisfies the above formula (1), the balance between the aromatic content of the base oil and the kinematic viscosity at 100°C is optimized, and as a result, the oxidation resistance, low-temperature fluidity, and deposition suppression effect of the entire engine oil composition can be improved.

[0034] The base oil has an aniline point A (°C) and a kinematic viscosity B (mm²) at 100°C. 2 It is preferable that / s) and satisfy the following equation (2).

[0035] (A / 10)-B≦7.5 (2)

[0036] In the base oil, the aniline point A (°C) and the kinematic viscosity B (mm²) at 100°C are given. 2 By satisfying equation (2) above, the effects described above for equation (1) can be realized to a more advanced degree.

[0037] (2) Viscosity index improvers The engine oil composition relating to this disclosure contains a viscosity index improver. The viscosity index improver includes star-shaped polymers and comb-shaped polymers. Star-shaped polymers are polymers with a structure in which multiple linear molecular chains (i.e., arms) radiate outwards from a central core. Comb-shaped polymers, on the other hand, are polymers that have multiple extended side chains arranged in a comb-like fashion relative to the polymer main chain. The viscosity index improver may include one or more types for each of the star-shaped polymer and comb-shaped polymer.

[0038] The engine oil composition according to this disclosure contains a star-shaped polymer and a comb-shaped polymer as viscosity index improvers. The star-shaped polymer has a structure in which multiple branched chains radiate from the center, and it is presumed that this three-dimensional structure suppresses the breakage of molecular chains under shear, thereby minimizing the decrease in oil viscosity. On the other hand, the comb-shaped polymer has numerous side chains arranged along the main chain, which is presumed to improve compatibility or dispersibility with the base oil, thereby enhancing the overall uniformity and viscosity adjustment effect of the additive. Furthermore, by incorporating these two types of polymers in combination as a viscosity index improver, it is presumed that the engine oil composition according to this disclosure containing the viscosity index improver will synergistically exhibit the effects of the viscosity index improver, including improved shear stability, suppression of deposit formation, and improved compatibility with additives.

[0039] It is estimated that the improved shear stability will be achieved by maintaining stable viscosity even under high temperature and high shear conditions, thereby preserving the protective performance of the oil film. To suppress deposit formation, for example, it is estimated that preventing the breakage or modification of molecular chains in star-shaped polymers and comb-shaped polymer polymers can prevent deposit formation in the compressor, thereby improving engine durability and efficiency. Regarding improved compatibility with additives, it is presumed that the presence of comb-shaped polymers allows for the uniform dispersion of other additives, thereby optimizing the overall performance of the lubricating oil composition. These effects suggest that the combined use of star-shaped polymers and comb-shaped polymers makes it possible to achieve both fuel efficiency and engine protection (e.g., wear resistance and caulking resistance).

[0040] Star-shaped polymers have a so-called star-shaped structure in which polymer chains branch out from the center of the polymer. In other words, star-shaped polymers have a structure in which polymer chains are bonded to the center of the polymer. Star-shaped polymers are preferably olefin copolymers, and are polymers obtained by copolymerization and hydrogenation of vinyl aromatic compound monomers and conjugated diene monomers.

[0041] Examples of star-shaped polymers include those obtained by copolymerizing one or more monomers selected from vinyl aromatic compound monomers with one or more monomers selected from conjugated diene monomers to obtain a copolymer of vinyl aromatic compound monomers and conjugated diene monomers, then reacting this copolymer with a polyalkenyl coupling agent, and further hydrogenating it. In the star-shaped polymer obtained in this way, the structural site derived from the polyalkenyl coupling agent after reaction with the copolymer of vinyl aromatic compound monomers and conjugated diene monomers and further hydrogenation, or a part of the copolymer of vinyl aromatic compound monomers and conjugated diene monomers with the structural site derived from the polyalkenyl coupling agent after hydrogenation, forms the center of the star-shaped polymer, and polymer chains obtained by copolymerization and hydrogenation of vinyl aromatic compound monomers and conjugated diene monomers branch out from this center.

[0042] Vinyl aromatic compound monomers are aromatic compounds having a vinyl group or alkylates thereof, such as styrene, methylstyrene, ethylstyrene, vinylnaphthalene, and their alkylates. Of these, styrene is preferred as the vinyl aromatic compound monomer.

[0043] Examples of conjugated diene monomers include butadiene, isoprene, 2-methyl-butadiene, 2,3-dimethyl-butadiene, 2-ethyl-butadiene, 2,3-diethyl-butadiene, pentadiene, 2-methyl-pentadiene, and 3-methyl-pentadiene. Of these, butadiene and isoprene are examples of conjugated diene monomers. preferable.

[0044] When copolymerizing a vinyl aromatic compound monomer with a conjugated diene monomer, the copolymerization ratio of the vinyl aromatic compound monomer is preferably 5% to 35% by mass, and particularly preferably 5% to 25% by mass, relative to the total mass of the monomers, and the copolymerization ratio of the conjugated diene monomer is preferably 65% ​​to 95% by mass, and particularly preferably 75% to 95% by mass, relative to the total mass of the monomers.

[0045] Examples of polyalkenyl coupling agents include polyalkenyl aliphatic compounds such as polyvinylacetylene, polyallylacetylene, diacetylene, and dimethacrylate, and polyalkenyl aromatic compounds such as divinylbenzene, trivinylbenzene, tetravinylbenzene, divinyl-o-xylene, m-xylene, p-xylene, trivinyl-o-xylene, trivinyl-m-xylene, trivinyl-p-xylene, tetravinyl-o-xylene, tetravinyl-m-xylene, tetravinyl-p-xylene, divinylnaphthalene, divinylethylbenzene, divinylbiphenyl, diisobutenylbenzene, diisopropenylbenzene, and diisopropenylbiphenyl. Polyalkenyl aromatic compounds are preferred, and divinylbenzene is particularly preferred.

[0046] Examples of star-shaped polymers include styrene-butadiene-isoprene star polymers, in which the polymer chains are obtained by copolymerization and hydrogenation of styrene, butadiene, and isoprene, and styrene-isoprene star polymers, in which the polymer chains are obtained by copolymerization and hydrogenation of styrene and isoprene. Styrene-butadiene-isoprene star polymers are obtained by copolymerizing styrene, butadiene, and isoprene to obtain a copolymer, then reacting this copolymer with a polyalkenyl coupling agent such as divinylbenzene, and further hydrogenating it. Similarly, styrene-isoprene star polymers are obtained by copolymerizing styrene and isoprene to obtain a copolymer, then reacting this copolymer with a polyalkenyl coupling agent such as divinylbenzene, and further hydrogenating it. Such styrene-butadiene-isoprene star polymers or styrene-isoprene star polymers contain divinylbenzene at the center of their molecular structure.

[0047] As mentioned above, polymers containing styrene monomer (hereinafter also referred to as styrene-based star polymers) are preferred as star-shaped polymers. Examples include copolymers such as styrene block copolymers (SBCs) and styrene-ethylene / butylene-styrene copolymers (SEBS). The star polymer may contain one of these structures or two or more.

[0048] The star-shaped polymer is obtained by copolymerizing a vinyl aromatic compound monomer and a conjugated diene monomer, then reacting it with a polyalkenyl coupling agent, and finally undergoing a hydrogenation treatment. Therefore, it has few unsaturated bonds derived from the conjugated diene, but it may also have unsaturated bonds derived from the conjugated diene. It is preferable that the degree of unsaturation derived from the conjugated diene in the star-shaped polymer be low, and it is particularly preferable that the repeating units based on conjugated diene having unsaturated bonds be 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, relative to the total amount of repeating units based on conjugated diene.

[0049] Star-shaped polymers have a structure in which polymer chains, consisting of hydrogenated copolymers of vinyl aromatic compound monomers and conjugated diene monomers, branch out from the center of the polymer, a so-called "star structure." The number of polymer chains in a star-shaped polymer is three or more, preferably five or more, and particularly preferably seven or more. By having five or more polymer chains in a star-shaped polymer, it is easier to keep the weight-average molecular weight within the range described later, and good shear stability tends to be easily obtained.

[0050] From the viewpoint of the effect of viscosity index improvers, the star-shaped polymer is preferably having the following weight-average molecular weight (Mw), number-average molecular weight (Mn), or molecular weight distribution (Mw / Mn). The star-shaped polymer preferably has a weight-average molecular weight (Mw) of 500,000 or more, and more preferably 550,000 or more. The star-shaped polymer preferably has a number-average molecular weight (Mn) of 500,000 or more, and more preferably 530,000 or more. The star-shaped polymer preferably has a molecular weight distribution (Mw / Mn) of 1.00 to 1.20, and more preferably 1.03 to 1.15.

[0051] From the viewpoint of the effect of viscosity index improvers, the star-shaped polymer preferably has a shear stability index (SSI) of 0 to 30, and more preferably 0 to 10.

[0052] SSI is defined in ASTM D 6022-19. SSI is calculated using the following formula (B) based on data measured by the diesel injector method (ASTM D 6278-17), which is one of the shear stability tests.

[0053] Formula (B): SSI = 100 × (KV100) 新油 -KV100 せん断安定性試験後油 ) / (KV100 新油 -KV100 基油 ) In formula (B), KV100 新油 , KV100 せん断安定性試験後油, and KV100 基油 These values ​​represent the kinematic viscosity at 100°C for new oil, oil after shear stability testing, and base oil, respectively. Kinematic viscosity at 100°C (KV100) refers to the kinematic viscosity at 100°C as measured according to JIS K-2283-2000 (ASTM D445-19).

[0054] Furthermore, if catalog values ​​are available for the quantity-average molecular weight (Mw), number-average molecular weight (Mn), molecular weight distribution (Mw / Mn), or SSI of star-shaped polymers, the catalog values ​​will be used.

[0055] The viscosity index improver may contain one type of star-shaped polymer alone, or a combination of two or more types. Commercially available star-shaped polymers may be used.

[0056] The comb-shaped polymer is preferably one in which the high molecular weight polyolefin macromonomer portion extends from the main chain, exhibiting a comb-like structure. The comb-shaped polymer is preferably one in which the main chain contains repeating units based on polyolefin macromonomers, repeating units based on alkyl (meth)acrylate having an alkyl group with 1 to 30 carbon atoms, and repeating units based on styrene monomers.

[0057] Examples of polyolefins used in the comb-shaped polymer include polymers of alkenes with 2 to 10 carbon atoms or alkadienes with approximately 4 to 10 carbon atoms. Examples of alkenes with 2 to 10 carbon atoms include ethylene, propylene, n-butene, and isobutene. Examples of alkadienes with 4 to 10 carbon atoms include butadiene and isoprene. If the polyolefin group of the polyolefin macromonomer has an unsaturated bond, it is preferable to ultimately hydrogenate it to remove the unsaturated bond. Among these olefins, polybutadiene and polyisoprene are suitable examples of comb-shaped polymers, with polybutadiene being the most suitable.

[0058] The polyolefin macromonomer preferably contains polyolefin-derived repeating units in an amount of 70% by mass or more, and more preferably 90% by mass or more, relative to the total mass of the polyolefin macromonomer. The polyolefin macromonomer may also contain structures derived from monomers other than the aforementioned polyolefins, such as alkyl (meth)acrylates or styrene monomers, but these are preferably in an amount of 30% by mass or less, and more preferably 15% by mass or less, relative to the total mass of the polyolefin macromonomer.

[0059] The number-average molecular weight (Mn) of the polyolefin macromonomer is preferably in the range of 1,000 to 10,000, more preferably 1,500 to 8,500, even more preferably 2,000 to 7,000, and most preferably 3,000 to 6,000.

[0060] Polyolefin macromonomers have a functional group that confers radical polymerizability. Preferably, one of these functional groups is contained at the terminal end of the polyolefin macromonomer, thereby providing the polyolefin macromonomer with a single polymerization site, allowing a comb-like structure to be obtained by copolymerization with a specific low molecular weight monomer. A (meth)acryloyl group can preferably be used as the radical polymerizability functional group, with the methacryloyl group being particularly preferred. A common method for imparting (meth)acryloyl groups is to obtain them by transesterification or aminolysis of polyolefins functionalized with hydroxyl or amino groups at their terminal ends using methyl (meth)acrylate or ethyl (meth)acrylate. These hydroxyl or amino-functionalized polyolefins can be manufactured by known methods or are available as products from the market.

[0061] The ratio of structural units derived from polyolefin macromonomers to the total mass of the comb-shaped polymer is preferably in the range of 10% to 40% by mass, more preferably 15% to 35% by mass, even more preferably 17% to 32% by mass, and most preferably 20% to 30% by mass.

[0062] Comb-shaped polymers are obtained by copolymerizing the aforementioned polyolefin macromonomers with specific low molecular weight monomers by radical polymerization. As low molecular weight monomers, alkyl (meth)acrylates having alkyl groups with 1 to 30 carbon atoms, styrene monomers, and monomers obtained from mixtures thereof can be used.

[0063] The number of carbon atoms in the alkyl(meth)acrylate is preferably in the range of 1 to 30, more preferably 1 to 20, even more preferably 1 to 16, and most preferably 1 to 14. The alkyl(meth)acrylate having the above range of carbon atoms may be a single molecule or a combination of alkyl(meth)acrylates with different alkyl groups may be used, but it is preferable to mix alkyl(meth)acrylates with 1 to 10 carbon atoms and alkyl methacrylates with 11 to 30 carbon atoms. Furthermore, the ratio of structural units derived from alkyl(meth)acrylate monomers with 1 to 30 carbon atoms is preferably 50% by mass or more, more preferably 60% by mass or more, and most preferably 70% by mass or more, based on the total mass of the comb-shaped polymer.

[0064] Examples of styrene-based monomers contained in the comb-shaped polymer include styrene, α-methylstyrene, and α-ethylstyrene, with styrene being preferred among these. These styrene-based monomers may be a single type or a mixture of multiple types. The ratio of structural units derived from styrene-based monomers is preferably 0.5 to 20% by mass, more preferably 0.5 to 15% by mass, and most preferably 1.0 to 10% by mass, relative to the total mass of the comb-shaped polymer.

[0065] In addition to the structural units derived from the monomers mentioned above, comb-shaped polymers may contain structural units derived from other types of monomers in their structure. A suitable ratio of structural units derived from other types of monomers to the total mass of the comb-shaped polymer is 20% by mass or less, more preferably 10% by mass or less, and most preferably 5% by mass or less. This includes functional groups such as amino groups and hydroxyl groups, as well as alkyl (meth)acrylates having nitrogen-containing heterocyclic structures such as imidazole groups and morpholine groups, so-called "dispersed" alkyl (meth)acrylate structures.

[0066] From the viewpoint of the effect of viscosity index improvers, the comb-shaped polymer is preferably having the following weight-average molecular weight (Mw), number-average molecular weight (Mn), molecular weight distribution (Mw / Mn or Mz / Mw), or Z-average molecular weight (Mz). The comb-shaped polymer preferably has a weight-average molecular weight (Mw) of 450,000 or more, and more preferably 500,000 or more. The comb-shaped polymer preferably has a number-average molecular weight (Mn) of 150,000 or more, and more preferably 200,000 or more. The comb-shaped polymer preferably has a molecular weight distribution (Mw / Mn) of 2.00 to 4.00, and more preferably 2.50 to 3.50.

[0067] From the viewpoint of the effect of viscosity index improvers, the comb-shaped polymer preferably has a shear stability index (SSI) of 0 to 30, and more preferably 0 to 10. The method for calculating SSI is the same as described above.

[0068] Furthermore, if catalog values ​​are available for the weight-average molecular weight (Mw), number-average molecular weight (Mn), molecular weight distribution (Mw / Mn or Mz / Mw), Z-average molecular weight (Mz), or SSI of the comb-shaped polymer, the catalog values ​​will be used.

[0069] The viscosity index improver may contain one type of comb-shaped polymer alone, or a combination of two or more types. Commercially available comb-shaped polymers may be used.

[0070] The engine oil composition relating to this disclosure may contain only one viscosity index improver, or it may contain two or more.

[0071] From the viewpoint of maximizing the effects of the engine oil composition according to this disclosure, the content of the viscosity index improver is preferably 1.0% to 5.0% by mass, more preferably 1.2% to 4.0% by mass, and most preferably 1.4% to 3.0% by mass, based on the amount of active ingredients per 100% by mass of the engine oil composition.

[0072] From the viewpoint of the effects of the viscosity index improver, the viscosity index improver preferably contains comb-shaped polymers in a mass ratio of 4.0 to 5.5 times the mass of star-shaped polymers, and more preferably in a mass ratio of 4.5 to 5.5 times, in terms of the amount of active ingredients.

[0073] In addition to the viscosity index improvers described above, the engine oil compositions relating to this disclosure may also contain other viscosity index improvers in combination, depending on the purpose, to the extent that the effects relating to this disclosure can be obtained. The other viscosity index improvers are compounds different from the star-shaped polymers and comb-shaped polymers contained in the viscosity index improvers.

[0074] Other viscosity index improvers include known viscosity index improvers commonly used in lubricating oils for internal combustion engines. Examples of other viscosity index improvers include olefin copolymers, polyisobutylenes, polyalkylstyrenes, styrene-butadiene hydrogenated copolymers, styrene-isoprene hydrogenated copolymers, styrene-maleic anhydride copolymers, and polymers containing dispersing groups. Note that styrene-butadiene hydrogenated copolymers refer to polymers obtained by hydrogenating styrene-butadiene copolymers to replace the remaining double bonds with saturated bonds. Styrene-isoprene hydrogenated copolymers refer to polymers obtained by hydrogenating styrene-isoprene copolymers to replace the remaining double bonds with saturated bonds.

[0075] When using viscosity index improvers in combination with other viscosity index improvers, one or more types selected from the viscosity index improvers may be used in combination with one or more types selected from the other viscosity index improvers mentioned above.

[0076] However, adding other viscosity index improvers in excess of what is necessary may reduce the high fuel efficiency and excellent coking resistance exhibited by the engine oil composition of this disclosure. Therefore, when other viscosity index improvers are included, it is preferable that the total amount of other viscosity index improvers is less than the amount of viscosity index improvers, and that, in terms of the amount of active ingredients, does not exceed the range described above as the preferred amount of viscosity index improvers.

[0077] If the viscosity index improver content is excessive, the viscosity index will improve, but the viscosity of the engine oil composition tends to increase more than necessary, which may result in a failure to achieve fuel efficiency. Furthermore, excessive viscosity index improvers can lead to a deterioration in coking resistance. From this perspective, and from the viewpoint of easily obtaining the effects of the engine oil composition according to this disclosure, it is preferable to prepare the engine oil composition with the viscosity index improver content within the above-mentioned preferred range.

[0078] In addition to the viscosity index improver described above, the engine oil composition according to this disclosure may further contain various additives as needed.

[0079] (3) Succinimide-based dispersants The engine oil composition relating to this disclosure may contain a succinimide-based dispersant. As the succinimide-based dispersant, for example, a succinimide-based dispersant represented by the following general formula (3) or general formula (4) can be used. Alternatively, a boron-modified succinimide represented by the following general formula (3) or general formula (4) can also be used.

[0080] [ka]

[0081] In general formulas (3) and (4), R 1 and R 3 Each independently represents an alkyl group or an alkenyl group, R 2 Each of these independently represents an alkylene group. n represents an integer from 1 to 10.

[0082] As the succinimide-based dispersant, one or more succinimide-based dispersants selected from those represented by general formula (3) and general formula (4) may be used in combination with one or more compounds selected from those obtained by boron modification of succinimide-based dispersants of general formula (3) and general formula (4).

[0083] While there are no particular restrictions on the amount of succinimide-based dispersant that can be included, succinimide-based dispersants are generally very viscous and affect the viscosity characteristics of the engine oil composition. Therefore, from the perspective of maintaining high fuel efficiency, it is desirable to limit their content to the minimum amount necessary to obtain the expected effects of the succinimide-based dispersant.

[0084] (4) Zinc dialkyldithiophosphate From the viewpoint of wear prevention performance, the engine oil composition relating to this disclosure preferably contains zinc dialkyldithiophosphate.

[0085] The alkyl group in zinc dialkyldithiophosphate may be derived from a primary alcohol, a secondary alcohol, or a combination of both. There are no particular restrictions on the number of carbon atoms in the alkyl group, but from the viewpoint of wear prevention performance, it is preferably in the range of 3 to 12.

[0086] The content of zinc dialkyldithiophosphate is preferably 0.01% to 0.20% by mass, and more preferably 0.031% to 0.14% by mass, based on phosphorus, relative to the total amount of the engine oil composition.

[0087] When the zinc dialkyldithiophosphate content is 0.01% by mass or more, the expected wear prevention performance tends to be sufficiently obtained. On the other hand, when the zinc dialkyldithiophosphate content is 0.20% by mass or less, it is preferable because the decrease in the oxidation stability of the engine oil composition due to sulfuric acid and other substances generated from its decomposition products is effectively suppressed.

[0088] (5) Metal-type cleaning agents The engine oil composition relating to this disclosure may contain a metallic detergent. Examples of metal-type cleaning agents include alkaline earth metal salicylates, alkaline earth metal sulfonates, and alkaline earth metal phenates.

[0089] Metallic cleaning agents may be used individually or in combination of two or more. For example, when using alkaline earth metal salicylate, alkaline earth metal sulfonate, and alkaline earth metal phenate, one of these three components may be used individually, or two or three may be used in combination as needed. From the viewpoint of fuel efficiency, alkaline earth metal salicylate is preferred as the metallic cleaning agent.

[0090] From the viewpoint of ensuring sufficient cleanliness and more effectively avoiding adverse effects on exhaust gas aftertreatment devices, the content of the metal-type detergent is preferably 0.05% to 0.4% by mass, and more preferably 0.15% to 0.3% by mass, in terms of alkaline earth metal equivalent.

[0091] (6) Antioxidants The engine oil composition relating to this disclosure may contain an antioxidant. Examples of antioxidants include phenolic antioxidants, amine-based antioxidants, and organic molybdenum-based antioxidants. Antioxidants may be used individually or in combination of two or more as needed. Furthermore, when using phenolic antioxidants, amine-based antioxidants, and organic molybdenum-based antioxidants, each of these three components may be used individually or in combination of two or more.

[0092] Examples of phenolic antioxidants include alkylphenols such as 2,6-di-tert-butyl-p-cresol, bisphenols such as 4,4'-methylenebis-(2,6-di-t-butylphenol), and phenolic compounds such as n-octadecyl-3-(4'-hydroxy-3',5'-di-tert-butylphenol)propionate. Examples of amine antioxidants include aromatic amine compounds such as naphthylamines and dialkyldiphenylamines. Examples of organic molybdenum antioxidants include organic molybdenum compounds such as molybdenamines.

[0093] The antioxidant content is preferably 0.05% to 5.0% by mass, and more preferably 0.5% to 3.0% by mass, relative to the total amount of the engine oil composition.

[0094] (7) Friction modifiers The engine oil composition according to this disclosure can further improve fuel efficiency by including a friction modifier, from the viewpoint of reducing friction in the boundary lubrication zone. Examples of friction modifiers include organic molybdenum compounds and ashless friction modifiers.

[0095] Examples of organic molybdenum compounds include molybdenum dithiophosphate, molybdenum dithiocarbamate, molybdenum amine compounds, and molybdenum long-chain aliphatic amine compounds. The molybdenum compound content is preferably 100 ppm by mass or more and 1,200 ppm by mass or less as the metallic molybdenum concentration in the engine oil composition.

[0096] Examples of ashless friction modifiers include long-chain aliphatic amines, long-chain fatty acid esters, long-chain aliphatic alcohols, amide compounds of aliphatic amines and fatty acids, and aliphatic polyglyceryl ethers. The preferred content of the ashless friction modifier is preferably 500 ppm to 5% by mass, more preferably 1,000 ppm to 4% by mass, and even more preferably 3,000 ppm to 3% by mass, based on the total amount of the engine oil composition.

[0097] When the engine oil composition according to this disclosure contains friction modifiers (for example, the above-mentioned organic molybdenum compound and ashless friction modifier), these friction modifiers may be used individually or in combination as necessary. However, as mentioned above, when applying the engine oil composition according to this disclosure to a diesel engine, the organic molybdenum compound may not be able to exert a satisfactory effect due to the influence of soot, so it is desirable to include an ashless friction modifier.

[0098] (8) Other additives The engine oil composition according to this disclosure may contain various additives in addition to the components described above. Specifically, the engine oil composition may contain, as needed, additives that are effective in imparting engine oil performance, such as metal deactivators, rust inhibitors, pour point depressants, and antifoaming agents. Furthermore, a single additive may perform two or more functions.

[0099] <Method for preparing engine oil composition> The method for preparing the engine oil composition according to this disclosure is not particularly limited, and the base oil, viscosity index improver, and the various components mentioned above, which may be added as needed, can be appropriately mixed. The mixing order of the components is not particularly limited.

[0100] <Properties of engine oil composition> [Viscosity properties] From the viewpoint of obtaining sufficient fuel efficiency, it is preferable that the viscosity properties of the engine oil composition according to this disclosure be adjusted to a specific range.

[0101] The viscosity index of the engine oil composition is preferably in the range of 150 to 300, more preferably 160 to 270, even more preferably 170 to 250, and most preferably 180 to 240.

[0102] A viscosity index of 150 or higher effectively suppresses the increase in viscosity of the engine oil composition under low oil temperature conditions, resulting in sufficient fuel efficiency. On the other hand, a viscosity index of 300 or lower allows for further improvement of fuel efficiency without excessive viscosity index improvers, while also suppressing cost increases and maintaining piston cleanliness better.

[0103] [Kinematic viscosity] The kinematic viscosity of engine oil compositions at 40°C (JIS-K-2283-2000 (ASTM D7042)) is typically 10 mm². 2 / s~70mm 2 / s is acceptable, preferably 20mm 2 / s~60mm 2 / s is more preferably 30mm 2 / s~55mm 2 It is / s.

[0104] The kinematic viscosity of engine oil compositions at 100°C (JIS-K-2283-2000 (ASTM D7042)) is typically 5.6 mm². 2 / s~12.5mm 2 / s is acceptable, preferably 8.5mm 2 / s~11.5mm 2 / s, more preferably 9.3mm 2 / s~11.0mm 2 The value is / s, and is particularly preferably 9.7mm 2 / s~10.8mm 2 It is / s.

[0105] [High-temperature high-shear viscosity (HTHS viscosity)] The high-temperature, high-shear viscosity of the engine oil composition is defined as oil temperature 100°C and shear rate 10 6The high-temperature high-shear viscosity at / s is preferably 7.0 mPa·s or less, more preferably 6.8 mPa·s or less, even more preferably 6.5 mPa·s or less, and most preferably 6.3 mPa·s or less.

[0106] Also, oil temperature 150℃, shear rate 10 6 The high-temperature, high-shear viscosity at / s is preferably 2.6 mPa·s or higher, more preferably 2.8 mPa·s or higher, and most preferably 2.9 mPa·s or higher, considering the high oil film retention required for high-load engines. (Oil temperature 150℃, shear rate 10 6 The upper limit of the high-temperature high-shear viscosity at / s may be, for example, 3.5 mPa·s.

[0107] Oil temperature 150°C, shear rate 10 6 The high-temperature high-shear viscosity at / s refers to the high-temperature high-shear viscosity measured according to the method described in ASTM D4683. Oil temperature 100°C, shear rate 10 6 The high-temperature high-shear viscosity at / s refers to the high-temperature high-shear viscosity measured according to the method described in ASTM D6616. Oil temperature 100℃, shear rate 10 6 The lower limit of the high-temperature high-shear viscosity at / s may be, for example, 5.5 mPa·s.

[0108] By adjusting the viscosity of the engine oil composition by combining the base oil and viscosity index improver so that the high-temperature, high-shear viscosity of the engine oil composition falls within the above range, excellent fuel efficiency can be expected even in high-load engines where the oil film environment is severe.

[0109] Furthermore, from the perspective of further improving fuel efficiency, in addition to the high temperature and high shear viscosity mentioned above, an oil temperature of 150°C and a shear rate of 10°C are also considered. 7The high-temperature, high-shear viscosity at / s is preferably 2.8 mPa·s or less, more preferably 2.7 mPa·s or less, even more preferably 2.6 mPa·s or less, and most preferably 2.5 mPa·s or less. (Oil temperature 150°C, shear rate 10 7 The lower limit of the high-temperature high-shear viscosity at / s may be, for example, 2.0 mPa·s.

[0110] Oil temperature 150℃, shear rate 10 7 By setting the high-temperature, high-shear viscosity at / s to the above-mentioned preferred value, the fuel efficiency performance of the engine oil composition can be further improved.

[0111] From the viewpoint of improving fuel efficiency, one preferred embodiment of the engine oil composition according to this disclosure is an oil temperature of 100°C and a shear rate of 10°C. 6 The high-temperature, high-shear viscosity at / s is 7.0 mPa·s or less, and the oil temperature is 150°C and the shear rate is 10 7 This embodiment has a high-temperature, high-shear viscosity at / s of 2.8 mPa·s or less.

[0112] Oil temperature 150℃, shear rate 10 7 High-temperature, high-shear viscosity at / s is defined using the PCS Instruments USV (The Ultra Shear Viscometer) at an oil temperature of 150°C and a shear rate of 1.0 × 10⁻⁶. 7 This refers to the high-temperature, high-shear viscosity measured under the condition of / s.

[0113] Also, 100℃, 1×10 6 The high-temperature high-shear viscosity in / s is 5.7 or less, and at 150°C, 1 × 10⁻⁶ 7 A high-temperature, high-shear viscosity of 2.1 or less per s, and a traction coefficient of 0.045 or less, are preferable because they provide a high fuel-saving effect. The fuel-saving effect of an engine oil composition is determined at 100°C, 1 × 10⁻⁶. 6 / s and 150℃, 1×10 7It is possible to predict to some extent from the high-temperature, high-shear viscosity of / s, and the lower these high-temperature, high-shear viscosities are, the greater the fuel-saving effect tends to be. Therefore, satisfying the above conditions tends to result in an engine oil composition with excellent fuel efficiency and coking resistance.

[0114] [SAE viscosity grade] The engine oil composition according to this disclosure preferably has an SAE viscosity grade of 0W-30 or 5W-30 as defined in SAE J300.

[0115] By having an SAE viscosity grade of 0W-30 or 5W-30, it is possible to maximize fuel efficiency while maintaining the oil film retention required for high-load engines. When adjusting the viscosity during the preparation of engine oil compositions, it is desirable to adjust the amount of each component to match these SAE viscosity grades.

[0116] [Sulfated ash] In engine oil compositions, the sulfated ash content, which serves as an indicator of the amount of metal-containing additives, is preferably 2% by mass or less, more preferably 1.5% by mass or less, even more preferably 1.2% by mass or less, and most preferably 1.1% by mass or less. Having the sulfated ash content within the above range ensures good compatibility with exhaust gas aftertreatment devices and effectively suppresses the possibility of excessive ash accumulating around the piston.

[0117] The sulfated ash content referred to here means the value obtained by the test method specified in JIS-K-2272-1998.

[0118] [NOACK evaporative] The NOACK evaporation rate of the engine oil composition is preferably 15% or less, and more preferably 13% or less. Having the NOACK evaporation rate of the engine oil composition within this range suppresses evaporation of the engine oil composition at high temperatures (i.e., during engine operation), thereby suppressing the formation of coking material. The lower limit of the NOACK evaporation rate is not particularly limited. The lower limit of the NOACK evaporation rate can be appropriately set considering the effects and costs related to this disclosure.

[0119] NOACK evaporability refers to the evaporability (%) of the base oil measured in accordance with JPI 5S-1 (2004).

[0120] <Application> The engine oil composition according to this disclosure can be applied to various engine engines. Examples of engine engines include, but are not limited to, gasoline engines, diesel engines, and gas engines. The engine engines to which the engine oil composition according to this disclosure is preferably applied are gasoline engines and diesel engines. In particular, the engine oil composition according to this disclosure can be suitably used in diesel engines, which are used under high loads and have relatively high thermal loads around the pistons. [Examples]

[0121] Next, the engine oil compositions relating to this disclosure will be described in more detail with reference to examples and comparative examples. However, the engine oil compositions relating to this disclosure are not limited in any way to the examples shown below.

[0122] In the following examples and comparative examples, the base oil, viscosity index improver, and other additives, as shown in the <Base Oil and Additives> section described later, were mixed in the amounts shown in Tables 1 to 3 to obtain the engine oil composition. Note that "mass%" in Tables 1 to 3 refers to mass% based on the total mass of the engine oil composition. A "-" in the composition column of Tables 1 to 3 indicates that the corresponding component is not included or does not apply.

[0123] Each engine oil composition meets the requirements of either 0W-30 or 5W-30 in SAE viscosity grades, and the kinematic viscosity at 100°C after shear testing, as specified in ASTM D6278-07, is 9.3 mmHg, as required by the JASO DH-2 standard, the domestic diesel engine oil standard. 2 It is prepared to be at least / s.

[0124] Also, 150℃, shear rate 1×10 6 The high-temperature, high-shear viscosity was adjusted to be 3.0 mPa·s or higher for all engine oil compositions.

[0125] Furthermore, in preparing each example and comparative example, care was taken to ensure that the amount of viscosity index improver added was the minimum necessary to satisfy the above conditions, taking into consideration its impact on fuel efficiency.

[0126] Regarding the properties of the base oil, the kinematic viscosity at 100°C, the traction coefficient at 60°C, and the aniline point were measured by the method described above. The value in equation (1) was calculated from these values.

[0127] <Base oil and additives> (1) Base oil A Hydrocracking-based mineral oil base oil (Group II base oil) 100℃ kinematic viscosity: 3.0mm 2 / s, viscosity index: 99 (2) Base oil B Hydrocracking-based mineral oil base oil (Group III base oil) 100℃ kinematic viscosity: 4.2mm 2 / s, viscosity index: 122 (3) Base oil C Hydrocracking-based mineral oil base oil (Group III base oil) 100℃ kinematic viscosity: 6.5mm 2 / s, viscosity index: 131 (4) Base oil D Synthetic oil-based base oil (Group IV base oil) 100℃ kinematic viscosity: 6.5mm 2 / s, viscosity index: 131 (5) Star-shaped polymer A (viscosity index improver) Active ingredient: Styrene copolymer, Amount of active ingredient: 8% by mass Mw:680000g / mol, Mn:640000g / mol, Mz:700000, Mw / Mn:1.06, Mz / Mw:1.05, SSI:1 (6) Star-shaped polymer B (viscosity index improver) Active ingredient: Styrene copolymer, Amount of active ingredient: 11% by mass Mw:600000g / molg / mol, Mn:550000g / mol, Mw / Mn:1.07, SSI:30 (7) Comb-shaped polymer (viscosity index improver) Active ingredient: Alkyl (meth)acrylate copolymer, Amount of active ingredient: 22% by mass Mw:530000g / mol, Mn:200000g / mol, Mz:790000, Mw / Mn:2.61, Mz / Mw:1.51, SSI:2 (8) Other additives This product includes viscosity index improvers other than viscosity index improvers A and B, anti-wear agents, dispersants, metallic detergents, friction modifiers, phenolic antioxidants, pour point depressants, and silicone-based defoamers.

[0128] <Evaluation Method> The engine oil compositions obtained in the examples and comparative examples were subjected to the evaluation tests described in items (1) to (9) below. The test methods are as follows.

[0129] (1) SAE viscosity grade The viscosity grade was determined according to SAE J300. (2)Kinematic viscosity Kinematic viscosity and viscosity index were measured at 40°C and 100°C in accordance with ASTM D7042. (3) Viscosity index The calculation was performed according to ASTM D7042. (4) Temperature 100°C, shear rate 1 × 10⁻⁶ 6 High-temperature high-shear viscosity (HTHS viscosity) at / s Measurements were taken according to ASTM D6616. (5) Temperature 150℃, shear rate 1×10 6 High-temperature high-shear viscosity (HTHS viscosity) at / s Measurements were taken according to ASTM D4683. (6) Temperature 150℃, shear rate 1×10 7 High-temperature high-shear viscosity (HTHS viscosity) at / s Measurements were taken using the USV (The Ultra Shear Viscometer) manufactured by PCS Instruments.

[0130] The engine oil composition of the example satisfies the preferred range described above for items (1) to (6). This indicates that the engine oil composition of the example is an engine oil composition with excellent fuel efficiency.

[0131] (7) Fuel-saving effect The Hino Motors, Ltd. "N04C-VH engine" as specified in JASO M362 was used. The test conditions were an oil temperature of 90°C and an engine speed of 1300 rpm. The maximum engine torque obtained under these conditions was defined as a 100% load, and the engine torque obtained by dividing it by 5 was defined as a 20% load. The fuel efficiency effect (%) was calculated by comparing it with the fuel consumption rate of the reference oil under the above conditions, and the obtained measured values ​​were used for evaluation. As the reference oil, a commercially available lubricating oil composition with an SAE viscosity grade of 10W-30 was used. -Evaluation Criteria- A: Fuel efficiency improvement of 2.5% or more at a load of 20%, and fuel efficiency improvement of 0.7% or more at a load of 100%. B: Fuel efficiency improvement at a load of 20% is less than 2.5%, or fuel efficiency improvement at a load of 100% is less than 0.7%.

[0132] (8) Panel caulking test Using 250 ml of engine oil composition (new oil and degraded oil), a panel caulking test was conducted using a panel caulking test machine manufactured by Rigosha Co., Ltd. for a test period of 3 hours (15 seconds of splashing operation, 45 seconds of operation pause x 180 cycles), with an aluminum panel (A2024P) as the test specimen, a panel temperature of 320°C, and an oil temperature of 100°C. The panel mass was measured before and after the test, and the difference was defined as the amount of caulking. The amount of caulking in Comparative Example 2 was set to 1, and the ratio to the amount of caulking in Comparative Example 2 was calculated. -Evaluation Criteria- A: The ratio value to the amount of caulking in Comparative Example 2 is 0.8 or less. B: The ratio value to the amount of caulking in Comparative Example 2 is greater than 0.8.

[0133] (9) NOACK evaporative NOACK evaporability (%) was measured based on JPI 5S-41 (2004). -Evaluation Criteria- A: NOACK evaporative rate (%) is 13% or less B: NOACK evaporability (%) greater than 13%

[0134] [Table 1]

[0135] [Table 2]

[0136] [Table 3]

[0137] As shown in Table 1, the engine oil compositions of Examples 1 and 2, which contain a base oil comprising a mineral oil-based base oil and a synthetic oil-based base oil, and a base oil having a traction coefficient of 0.045 or less at 60°C, and a viscosity index improver containing star-shaped polymers and comb-shaped polymers, were found to have excellent fuel efficiency and coking resistance. On the other hand, as shown in Tables 2 to 3, the engine oil compositions of Comparative Examples 1 to 8 were found to be inferior in either fuel efficiency or coking resistance, or both.

[0138] The fuel-saving effects in Comparative Examples 5 to 8 were estimated as follows. In other words, the fuel efficiency of an engine oil composition is determined by 100°C, 1 × 10⁻⁶ 6 / s and 150℃, 1×10 7 It is possible to predict this from the HTHS viscosity in / s, and it is known that the lower the HTHS viscosity, the greater the fuel-saving effect. Since the fuel-saving effect was evaluated as A in Example 1, Example 2, Comparative Example 2, and Comparative Example 4, the fuel-saving effect was estimated under the following conditions.

[0139] (conditions) 100℃, 1 × 10 6 HTHS viscosity at / s: 5.7 or less, and at 150°C, 1 × 10 7 If the HTHS viscosity at / s is 2.1 or less, and the traction coefficient is 0.045 or less, the fuel efficiency is as high as that of fuel efficiency rating A.

[0140] Based on the above, the fuel-saving effects of Comparative Example 5 and Comparative Example 7 were estimated as follows. Comparative Example 5: Since the HTHS viscosity satisfies the above conditions and the traction coefficient is 0.045 or less, the fuel efficiency effect was estimated to be A. Comparative Example 6: The HTHS viscosity did not meet the above conditions, and the traction coefficient was greater than 0.045, so the fuel efficiency effect was estimated to be B. Comparative Example 8: Although the traction coefficient is 0.045 or less, the HTHS viscosity does not meet the above conditions, so the fuel efficiency effect was estimated to be B.

[0141] As is clear from the above, it has been found that the engine oil composition according to this disclosure can achieve excellent fuel efficiency and coking resistance for the first time.

Claims

1. A base oil comprising a mineral oil-based base oil and a synthetic oil-based base oil, and having a traction coefficient of 0.045 or less at 60°C, A viscosity index improver containing star-shaped polymers and comb-shaped polymers, Engine oil composition.

2. The engine oil composition according to claim 1, wherein the base oil comprises the synthetic oil-based base oil in a proportion of 50% by mass or less, based on the total mass of the base oil.

3. The base oil has an aniline point A (°C) and a kinematic viscosity B (mm²) at 100°C. ２ The engine oil composition according to claim 1, wherein ( / s) satisfies the following formula (1). (A / 10)-B≦8.0 (1)

4. The engine oil composition according to claim 1, wherein the viscosity index improver comprises the comb-shaped polymer in a mass ratio of 4.0 to 5.5 times the mass of the star-shaped polymer, calculated in terms of the amount of active ingredients.

5. The base oil has a kinematic viscosity B (mm) at 100°C. ２ ( / s) is 4.3 mm ２ The engine oil composition according to claim 1, wherein the value is less than or equal to / s.

6. The engine oil composition according to claim 1, wherein the SAE viscosity grade as defined in SAE J300 is 0W-30 or 5W-30.

7. 100℃, 1 × 10 ６ The high-temperature high-shear viscosity at / s is 5.7 or less, and at 150°C, 1 × 10⁻⁶ ７ The engine oil composition according to claim 1, wherein the high-temperature high-shear viscosity at / s is 2.1 or less.

Images