Lubricant composition for internal combustion engines

Abstract

To provide a lubricating oil composition for internal combustion engines that suppresses the formation of caulking not only during the initial period of use but also as the engine deteriorates, resulting in excellent long-life performance. [Solution] Kinematic viscosity at 100°C is 12 mm 2 A lubricating oil composition for internal combustion engines, comprising a base oil X containing a base oil of 1 / s or higher, an alkaline earth metal-based detergent, a boron-based dispersant, a non-boron-based dispersant, a phenol-based antioxidant and / or an amine-based antioxidant, a molybdenum-based antioxidant, and a phosphorus-based anti-wear agent, wherein the base oil X content is 5.0% by mass or more and 20% by mass or less, the alkaline earth metal-based detergent has a base number of 100 mgKOH / g or more, the boron-based dispersant contains a boron-based dispersant with a B / N ratio of 0.4 or more, the ratio of nitrogen element content from the boron-based dispersant to nitrogen element content from the non-boron-based dispersant is 0.5 or more and 2.5 by mass, the alkaline earth metal content is more than 1000 ppm by mass and 1500 ppm by mass or less, and the boron element content from the boron-based dispersant is 200 ppm by mass or more.

Description

[Technical Field]

[0001] This disclosure relates to lubricating oil compositions for internal combustion engines. [Background technology]

[0002] In recent years, cogeneration systems have attracted attention from the perspective of energy conservation and diversification of power sources. In particular, gas cogeneration systems are seen as promising as environmentally friendly systems that use clean fuels. Because gas engines have high combustion temperatures, the concentration of NOx in blow-by gas is relatively high, which easily leads to sludge formation in the lubricating oil. Therefore, regular changes of the lubricating oil are necessary, but increasing the frequency of changes leads to higher maintenance costs, so there is a demand for lubricating oils with a longer lifespan (i.e., long drainability).

[0003] Recent gas cogeneration systems aim to minimize emissions of carbon dioxide, nitrogen oxides, and sulfur oxides through optimal fuel combustion, and to achieve energy savings by increasing the efficiency of power generation and heat utilization. Therefore, lubricating oil compositions used in gas engines are required to maintain excellent high-temperature stability without reducing power generation efficiency.

[0004] Gas cogeneration systems often employ relatively large gas engines, resulting in high maintenance costs. Therefore, reducing the frequency of maintenance inspections is a crucial issue. In this regard, the use of lubricating oil in gas engines presents a problem: ash contained in the lubricating oil accumulates on the top of the pistons and exhaust valves, reducing the cleanliness of the gas engine. As a result, it becomes necessary to perform the engine itself overhaul multiple times at regular intervals, requiring considerable effort for maintenance. Therefore, from the perspective of improving maintainability, low-ash content lubricating oil is necessary.

[0005] When a gas engine is operated continuously for a long period of time, the lubricating oil contained in the gas engine is constantly exposed to high temperatures and gradually undergoes thermal oxidative degradation. In addition, gas engines, which have a higher combustion temperature compared to diesel engines, tend to have a higher concentration of NOx contained in blow-by gas, and thus are prone to causing sludge generation in the lubricating oil. For this reason, regular replacement of the lubricating oil is necessary, but in order to reduce maintenance costs by extending the service life of the lubricating oil itself and prevent troubles caused by local coking in various parts of the engine, it is required to achieve both long service life and coking performance.

[0006] As a lubricating oil composition for gas engines, for example, Patent Document 1 discloses a lubricating oil composition for gas engines which contains a base oil having a flash point of 240°C or higher, a molybdenum-based antioxidant, and a viscosity modifier having a flash point of 270°C or higher, wherein the mass of molybdenum atoms is 20 ppm or more and 800 ppm or less relative to the total mass of the entire lubricating oil composition for gas engines. [Prior Art Documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2023-151487 [Summary of the Invention] [Problem to be Solved by the Invention]

[0008] The lubricating oil composition for gas engines disclosed in Patent Document 1 has improved coking resistance at the initial stage of use, but there is room for improvement in the sustainability of coking resistance when the composition is degraded through use.

[0009] An embodiment of the present disclosure is to provide a lubricating oil composition for internal combustion engines that suppresses the occurrence of coking not only at the initial stage of use but also when degraded, and has excellent long service life. [Means for Solving the Problem]

[0010] The present disclosure includes the following aspects.

[0011] <1> The kinematic viscosity at 100°C is 12 mm³. 2 A base oil containing base oil X with a value of / s or more, Alkaline earth metal-based cleaning agent, A boron-based dispersant containing boron and nitrogen, A non-boron dispersant that does not contain boron and contains nitrogen, At least one antioxidant selected from the group consisting of phenolic antioxidants and amine antioxidants, Molybdenum-based antioxidants, It contains a phosphorus-based anti-wear agent, The kinematic viscosity at 100°C is 12 mm³. 2 The content of base oil X of / s or more is 5% by mass or more and 20% by mass or less of the total amount of the lubricating oil composition. The base number of the alkaline earth metal-based detergent is 100 mg KOH / g or higher. The boron-based dispersant includes a boron-based dispersant with a B / N ratio of 0.4 or higher. The ratio of nitrogen elements derived from boron-based dispersants to nitrogen elements derived from non-boron-based dispersants is 0.5 or more and 2.5 or less by mass. The content of alkaline earth metals in the lubricating oil composition is greater than 1000 ppm by mass and less than or equal to 1500 ppm by mass, based on the total amount of the lubricating oil composition. The content of boron element derived from the boron-based dispersant is 200 ppm or more relative to the total amount of the lubricating oil composition. Lubricating oil composition for internal combustion engines. <2> It contains an olefin copolymer type viscosity index improver, and the viscosity index improver content is 5% by mass or less. <1> The lubricating oil composition for internal combustion engines described above. <3> The total content of phenolic antioxidants and amine-based antioxidants is 1% by mass or more and 5.5% by mass or less. <1> or <2> The lubricating oil composition for internal combustion engines described above. <4> The molybdenum-based antioxidant is at least one selected from the group consisting of amide-based molybdenum compounds, ester-based molybdenum compounds, molybdate amine compounds, molybdenum dithiocarbamate, and molybdenum dithiophosphate, and the content of molybdenum element derived from the molybdenum-based antioxidant is greater than 0 ppm by mass and 100 ppm or less based on the total amount of the lubricating oil composition. <1> ~ <3> A lubricating oil composition for internal combustion engines as described in any one of the following. <5> The phosphorus element content derived from the phosphorus-based anti-wear agent is greater than 0 ppm by mass and 500 ppm by mass or less, relative to the total amount of the lubricating oil composition. <1> ~ <4> A lubricating oil composition for internal combustion engines as described in any one of the following. <6> For gas engines, <1> ~ <5> A lubricating oil composition for internal combustion engines as described in any one of the following. [Effects of the Invention]

[0012] According to this disclosure, a lubricating oil composition for internal combustion engines is provided that suppresses the occurrence of coking not only during the initial period of use but also when the engine has deteriorated, and exhibits excellent long-life performance. [Modes for carrying out the invention]

[0013] The following describes an example of an embodiment of this disclosure. These descriptions and examples are illustrative and do not limit the scope of the invention. In this specification, a numerical range represented by "~" means a range that includes the numbers before and after "~" as the lower and upper limits, respectively. However, if the numbers before and after "~" are preceded by "greater than" or "less than", the numerical range means a range that does not include those numbers as the lower or upper limit. Regarding the content of ingredients, "%" means "mass%" unless otherwise specified. Regarding the content of ingredients, "ppm" refers to "mass ppm" unless otherwise specified. In the numerical ranges described stepwise in this specification, the upper limit of one stepwise numerical range may be replaced with the upper limit of another stepwise numerical range, or with the values ​​shown in the examples. Similarly, the lower limit of one stepwise numerical range may be replaced with the lower limit of another stepwise numerical range, or with the values ​​shown in the examples.

[0014] Each component may contain multiple types of the relevant substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it refers to the total amount of those multiple substances present in the composition.

[0015] <Lubricant composition for internal combustion engines> The lubricating oil composition for internal combustion engines relating to this disclosure (hereinafter also referred to as the "lubricating oil composition") is The kinematic viscosity at 100°C is 12 mm³. 2 It contains a base oil X with a viscosity of 1 / s or more, an alkaline earth metal-based detergent, a boron-based dispersant containing boron and nitrogen, a non-boron-based dispersant that does not contain boron but contains nitrogen, at least one antioxidant selected from the group consisting of phenol-based antioxidants and amine-based antioxidants, a molybdenum-based antioxidant, and a phosphorus-based anti-wear agent. The kinematic viscosity at 100°C is 12 mm³. 2 The content of base oil X of / s or more is 5% by mass or more and 20% by mass or less of the total amount of the lubricating oil composition. The boron-based dispersant includes a boron-based dispersant with a B / N ratio of 0.4 or higher. The ratio of nitrogen elements derived from boron-based dispersants to nitrogen elements derived from non-boron-based dispersants is 0.5 or more and 2.5 or less by mass. The content of alkaline earth metals in the lubricating oil composition is greater than 1000 ppm by mass and less than or equal to 1500 ppm by mass, based on the total amount of the lubricating oil composition. The content of boron element derived from the boron-based dispersant is 200 ppm by mass or more, relative to the total amount of the lubricating oil composition.

[0016] The lubricating oil composition according to the present disclosure has the above configuration, whereby coking is inhibited not only in the initial stage of use but also when the composition is deteriorated, and is excellent in long-life performance. In the present disclosure, the long-life performance of the lubricating oil composition is determined by the base number (mgKOH / g) and the increase rate (%) of the kinematic viscosity at 40°C obtained by subjecting the lubricating oil composition to an oxidation stability test (ISOT test). Details of the test method and test conditions for the ISOT test will be described in detail in the section of Examples described later.

[0017] Hereinafter, each component contained in the lubricating oil composition according to the present disclosure will be described in detail.

[0018] (Base Oil) The lubricating oil composition according to the present disclosure contains a base oil, and the base oil includes a base oil X having a kinematic viscosity at 100°C of 12 mm 2 / s or more (hereinafter, also simply referred to as "base oil X"). The base oil contained in the lubricating oil composition according to the present disclosure preferably includes the base oil X and a base oil Y having a kinematic viscosity at 100°C of less than 12 mm 2 / s.

[0019] The kinematic viscosity at 100°C of the base oil X is 12 mm 2 / s or more, and from the viewpoints of coking inhibition and long-life performance, it is preferably 12.5 mm 2 / s or more and 400 mm 2 / s or less, more preferably 13 mm 2 / s or more and 375 mm 2 / s or less, and still more preferably 13.5 mm 2 / s or more and 350 mm 2 / s or less.

[0020] In the present disclosure, the kinematic viscosity of the base oil at 100°C is measured in accordance with ASTM D7042.

[0021] In the lubricating oil composition according to the present disclosure, the content of the base oil X is 5.0% by mass or more and 20% by mass or less based on the total amount of the lubricating oil composition. From the viewpoint of long lifespan, the content of base oil X is preferably 20% by mass or less, and more preferably 17.5% by mass or less. From the viewpoint of coking resistance, the content of base oil X is preferably 6.0% by mass or more, and more preferably 8.0% by mass or more.

[0022] The base oil X may consist of only one type of base oil, or it may consist of two or more types. The base oil that makes up base oil X has a kinematic viscosity of 12 mm at 100°C. 2 There are no particular restrictions as long as the base oil is of / s or higher. The base oil constituting base oil X may be, for example, a base oil classified as API (American Petroleum Institute) Group I (Gr.I), API (American Petroleum Institute) Group II (Gr.II), API (American Petroleum Institute) Group III (Gr.III), and API (American Petroleum Institute) Group VI (Gr.VI), with a kinematic viscosity of 12 mm² at 100°C. 2 You can choose from base oils with a viscosity of / s or higher. In one embodiment, the base oil X may be at least one selected from base oils classified as API (American Petroleum Institute) Group I (Gr.I) and API Group IV (Gr.IV).

[0023] Examples of base oils classified as Group I include mineral oil-based base oils, such as API base oils obtained by combining the processes of atmospheric distillation, vacuum distillation, solvent desying, solvent extraction, hydrorefining, and solvent dewaxing from crude oil. Examples of base oils classified under Group IV include synthetic hydrocarbons such as α-olefin oligomers (polyalphaolefins: PAO), isoparaffin oligomers, propylene oligomers, isobutylene oligomers, butene oligomers, 1-octene oligomers, 1-decene oligomers, and ethylene-propylene oligomers; aromatic hydrocarbons such as alkylbenzenes and alkylnaphthalenes; esters such as di-2-ethylhexyl adipate and diisodecyl adipate; polyol esters such as trimethylolpropaneoleate and pentaerythritol-2-ethylhexanoate; polyglycols such as polyoxyalkylene glycols; and polyphenyl ethers.

[0024] In this disclosure, the viscosity index of the base oil is measured in accordance with JIS K2283 (2000).

[0025] Base oil Y has a kinematic viscosity of 12 mmHg at 100°C. 2 The base oil is less than / s. The base oil Y may consist of only one type of base oil, or it may consist of two or more types.

[0026] The base oil Y is preferably a base oil classified as API Group III (Gr.III) or API Group II (Gr.II), and more preferably a base oil classified as Group III.

[0027] Base oils classified as API Group III are preferred because they maintain a high flash point and do not contain low-boiling fractions that worsen coking when exposed to high temperatures. Examples of base oils classified as Group III include mineral oil-based base oils and synthetic base oils used in the lubricating oil field. From the viewpoint of using a base oil that contains as few low-boiling-point fractions as possible, which can cause coking, it is preferable to use a mineral oil-based base oil classified as Group III.

[0028] Examples of mineral oil-based base oils include base oils classified as API Group III, which are obtained by combining the following processes from crude oil: atmospheric distillation, vacuum distillation, solvent desying, solvent extraction, hydrorefining, and solvent dewaxing.

[0029] In the lubricating oil composition according to this disclosure, the content ratio of base oil X and base oil Y is preferably 5:95 to 25:75 by mass, more preferably 7:93 to 22:78, and even more preferably 10:90 to 20:80.

[0030] (Alkaline earth metal-based cleaning agent) The lubricating oil composition relating to this disclosure contains an alkaline earth metal-based detergent. The lubricating oil composition relating to this disclosure may contain only one alkaline earth metal-based detergent, or two or more.

[0031] Examples of alkaline earth metals contained in alkaline earth metal-based cleaning agents include calcium, magnesium, and other alkaline earth metals. Examples of alkaline earth metal-based cleaning agents include alkaline earth metal sulfonates, alkaline earth metal phenates, and alkaline earth metal salicylates.

[0032] From the viewpoint of extending the lifespan of the lubricating oil composition, the alkaline earth metal detergent is preferably a metal detergent containing calcium (hereinafter also referred to as "Ca-based metal detergent"). The Ca-based metal-based detergent is preferably at least one selected from the group consisting of calcium salicylate, calcium phenate, calcium sulfonate, magnesium salicylate, and magnesium sulfonate, with calcium salicylate being more preferred.

[0033] Ca-based metal-based detergents are preferably those with a base number of 100 mg KOH / g or higher.

[0034] In this disclosure, the base number of the Ca-based metal detergent is measured by the hydrochloric acid method in accordance with JIS K2501 (2003).

[0035] Ca-based metal detergents exhibit superior longevity when their base number is 100 mg KOH / g or higher. The base number of the Ca-based metal detergent is preferably 100 KOH / g or higher, and more preferably 150 KOH / g or higher. From the viewpoint of suppressing coking, the upper limit of the base number of the Ca-based metal detergent is, for example, 500 KOH / g.

[0036] The content of the alkaline earth metal-based detergent is preferably 1.2% by mass or more and 1.9% by mass or less, more preferably 1.3% by mass or more and 1.9% by mass or less, and even more preferably 1.4% by mass or more and 1.9% by mass or less, based on the total mass of the lubricating oil composition.

[0037] (Boron-based dispersant containing boron and nitrogen) The lubricating oil composition relating to this disclosure contains a boron-based dispersant containing boron and nitrogen. In this disclosure, a boron-based dispersant containing boron and nitrogen means a dispersant comprising a compound containing boron and nitrogen in its molecule. Hereinafter, boron-based dispersants containing boron and nitrogen will also be simply referred to as "boron-based dispersants."

[0038] The lubricating oil composition relating to this disclosure may contain only one boron-based dispersant or may contain two or more boron-based dispersants.

[0039] The boron-based dispersant contained in the lubricating oil composition relating to this disclosure includes a boron-based dispersant with a B / N ratio of 0.4 or higher. The B / N ratio of a boron-based dispersant refers to the mass ratio of the boron content to the nitrogen content in the boron-based dispersant. In this disclosure, the B / N ratio is calculated by dividing the boron content (mass%) in the boron-based dispersant by the nitrogen content (mass%) and rounding the result to two decimal places.

[0040] As the boron-based dispersant, boron-based dispersants used in the lubricating oil field can be used.

[0041] As a boron-based dispersant, a boron-containing imide-based dispersant is preferred. A boron-containing imide-based dispersant refers to a dispersant that contains boron and has an imide bond. In other words, the lubricating oil composition according to this disclosure preferably contains a boron-containing imide-based dispersant having a B / N ratio of 0.4 or higher as the boron-based dispersant. In this disclosure, boron-based dispersants with a B / N ratio of 0.4 or higher are also referred to as "high B / N ratio boron-based dispersants," and boron-based dispersants with a B / N ratio of less than 0.4 are also referred to as "low B / N ratio boron-based dispersants."

[0042] Examples of boron-containing imide-based dispersants include monoimide compounds of alkyl or alkenyl succinic acid, and boron-modified bisimide compounds thereof. Among these, boron-modified bisimide compounds of alkyl or alkenyl succinic acid are preferred from the viewpoint of extending the lifespan of the lubricating oil composition, wear resistance, and dispersibility.

[0043] The boron-based dispersant may be either a low-molecular-weight compound or a polymer, but from the viewpoint of clean dispersibility, a polymer is preferred. In this disclosure, a polymer means a compound having a weight-average molecular weight (Mw) of 1,000 or more on a polystyrene basis.

[0044] From the viewpoint of clean dispersibility, boron-based dispersants are preferably weight-average molecular weight (Mw) of 2,000 to 7,000. In this disclosure, the weight-average molecular weight (Mw) is a value measured by gel permeation chromatography (GPC).

[0045] The weight-average molecular weight (Mw) in this disclosure is 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 detector, THF (tetrahydrofuran) as the 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 is calculated from these measurement results using a molecular weight distribution curve prepared from a monodisperse polystyrene standard sample.

[0046] From the viewpoint of caulking resistance, long lifespan, and abrasion resistance, the content of the boron-based dispersant is preferably 2.5% by mass or more and 10% by mass or less, and more preferably 2.5% by mass or more and 5.5% by mass or less.

[0047] The lubricating oil composition relating to this disclosure contains a boron-free and nitrogen-containing non-boron dispersant. In this disclosure, a boron-free and nitrogen-containing non-boron dispersant means a dispersant comprising a compound that does not contain boron in its molecule and contains nitrogen. Non-boron dispersants are included in ashless dispersants. Hereinafter, boron-based dispersants containing boron and nitrogen will also be simply referred to as "non-boron-based dispersants."

[0048] The lubricating oil composition relating to this disclosure may contain only one non-boron dispersant or may contain two or more non-boron dispersants.

[0049] As non-boron dispersants, for example, polyamines containing one or more alkyl or alkenyl groups in their molecules, and acid-modified versions thereof can be used. As non-boron-based dispersants, for example, succinimide represented by general formula (1) or general formula (2) described in paragraphs 0029 to 0032 of Japanese Patent Application Publication No. 2018-048220 (however, boron-modified products are not included) and dispersant B described in paragraph 0048 can also be suitably used. As non-boron dispersants, suitable examples include polyisobutenyl succinimide compounds that do not contain boron.

[0050] From the viewpoint of long lifespan and wear resistance, the content of the non-boron dispersant is preferably 1.0% by mass or more and 10% by mass or less, more preferably 1.0% by mass or more and 6.0% by mass or less, and even more preferably 1.5% by mass or more and 4.0% by mass or less.

[0051] <Relationship between boron-based and non-boron-based dispersants> In the lubricating oil composition according to this disclosure, the ratio of nitrogen elements derived from the boron-based dispersant to nitrogen elements derived from the non-boron-based dispersant is 0.5 or more and 2.5 or less by mass. The ratio of nitrogen elements derived from boron-based dispersants to nitrogen elements derived from non-boron-based dispersants is preferably 0.6 to 2.4, and more preferably 0.6 to 2.2, from the viewpoint of coking resistance, long service life, and abrasion resistance.

[0052] (Phenol-based antioxidants and amine-based antioxidants) The lubricating oil composition relating to this disclosure contains at least one antioxidant selected from the group consisting of phenolic antioxidants and amine-based antioxidants, from the viewpoint of extending the lifespan. Phenolic antioxidants refer to antioxidants that consist of compounds having a phenol structure within their molecule. Amine-based antioxidants refer to antioxidant compounds that consist of compounds having an amine structure within their molecule.

[0053] The lubricating oil composition relating to this disclosure may contain one or more phenolic antioxidants selected from either phenolic antioxidants or amineic antioxidants, or it may contain one or more phenolic antioxidants and one or more amineic antioxidants selected from each. The lubricating oil composition relating to this disclosure preferably contains one or more selected phenolic antioxidants and amine-based antioxidants.

[0054] <Phenol-based antioxidants> Examples of phenolic antioxidants include alkylphenol compounds such as 2,6-di-tert-p-cresol; bisphenol compounds such as 4,4'-methylenebis-(2,6-di-tert-butylphenol); hindered phenol compounds such as esters of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid with alcohols having 8 or more carbon atoms; and phenolic compounds such as octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamic acid. These compounds may be isomers with different numbers of carbon atoms or structures in the alkyl group.

[0055] <Amine-based antioxidants> Examples of amine-based antioxidants include aromatic amine-based antioxidants and aliphatic amine-based antioxidants. Examples of amine-based antioxidants include amine compounds such as diphenylamine, 4-benzylamine, 2-aminobiphenyl, naphthylamine, allylaniline, 4-aminobinephenyl, o-toluidine, m-toluidine, p-toluidine, aniline, allylamine, their alkylated derivatives, hindered amine compounds, and their alkenylated derivatives. These compounds may also be isomers with different numbers of carbon atoms or structures of alkyl groups.

[0056] The aromatic amine antioxidant may be an amine compound that contains one or more amines selected from primary amines, secondary amines, primary diamines, and secondary diamines in its chemical structure, contains one or more aromatic rings, and has an acid dissociation constant of one or more of these amines of 8 or less.

[0057] The lubricating oil composition relating to this disclosure preferably contains an aromatic amine-based antioxidant.

[0058] In one embodiment, as an aromatic amine antioxidant, it is preferable to select and include one or more aromatic amine compounds represented by the following formulas (1) and (2) from the viewpoint of effectively inhibiting the oxidation of the amine portion.

[0059] [ka]

[0060] In formula (1), R1 to R6 each independently represent an alkyl group or an alkoxy group. n and m each independently represent an integer from 0 to 4. The alkyl groups represented by R1 to R6 are preferably alkyl groups having 1 to 16 carbon atoms, and more preferably alkyl groups having 1 to 14 carbon atoms. The alkyl groups may be linear or branched. Examples of alkyl groups include methyl, ethyl, and octyl groups. The alkoxy groups represented by R1 to R6 are preferably alkoxy groups having 1 to 16 carbon atoms, and more preferably alkoxy groups having 1 to 14 carbon atoms. Examples of alkoxy groups include methoxy groups, ethoxy groups, and octoxy groups. The alkyl or alkoxy groups represented by R1 to R6 may have further substituents. Examples of substituents include alkylamino groups, alkanoyl groups, and alkyl ester groups. n is preferably between 0 and 2, and more preferably between 0 and 1. m is preferably between 0 and 2, and more preferably between 0 and 1.

[0061] [ka]

[0062] In formula (2), R 21 ~R 28 Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, or a phenyl group. R 21 ~R 28The alkyl group represented is preferably an alkyl group having 1 to 16 carbon atoms. A C1-C12 alkyl group is preferred. The alkyl group may be a linear alkyl group or a branched alkyl group. Examples of alkyl groups include a methyl group, an ethyl group, an octyl group, and a dodecyl group. R 21 ~R 28 The alkoxy group represented by is preferably an alkoxy group having 1 to 16 carbon atoms, and preferably an alkoxy group having 1 to 12 carbon atoms. Examples of alkoxy groups include a methoxy group, an ethoxy group, and an octoxy group. R 21 ~R 28 The alkyl, alkoxy, or phenyl group represented by may have further substituents. Examples of substituents include alkylamino groups, alkanoyl groups, and alkyl ester groups.

[0063] In one embodiment, the amine-based antioxidant preferably contains one or more compounds selected from those represented by the following formulas (3A) and (3B) in order to effectively enhance the antioxidant effect of the amine portion.

[0064] [ka]

[0065] In equations (3A) and (3B), R 31 and R 32 Each of these independently represents an alkyl group or an alkoxy group. R 31 and R 32 The alkyl group represented by is preferably an alkyl group having 1 to 18 carbon atoms, and more preferably an alkyl group having 1 to 16 carbon atoms. Examples of alkyl groups include a methyl group, an ethyl group, an octyl group, and a dodecyl group. R 31 and R 32The alkoxy group represented by is preferably an alkoxy group having 1 to 18 carbon atoms, and more preferably an alkoxy group having 1 to 16 carbon atoms. Examples of alkoxy groups include a methoxy group, an ethoxy group, and an octoxy group. R 31 and R 32 The alkyl or alkoxy group represented by may have further substituents. Examples of substituents include alkenyl groups, alkylamino groups, alkanonyl groups, and alkyl ester groups.

[0066] Other specific examples of amine-based antioxidants are listed below, but are not limited to these. Examples of compounds represented by formula (3A) include R 31 However, one example is 2,2,6,6-tetramethylpiperidin-4-yl hexadecanoate, which has 8 carbon atoms, and is known as 2,2,6,6-tetramethylpiperidin-4-yloctadecanoate. Examples of compounds represented by formula (3B) include R 31 and R 32 However, independently of each other, didodecylamines, which have 12 carbon atoms, can be cited.

[0067] In the lubricating oil composition according to this disclosure, the total content of the phenolic antioxidant and the amine antioxidant is preferably 0.5% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 6% by mass or less, and even more preferably 1% by mass or more and 5.5% by mass or less, based on the total content of the lubricating oil composition.

[0068] (Molybdenum-based antioxidant) The lubricating oil composition relating to this disclosure contains a molybdenum-based antioxidant. Molybdenum-based antioxidants refer to compounds that contain molybdenum in their molecule and possess antioxidant properties.

[0069] Examples of molybdenum-based antioxidants include amide-type molybdenum compounds, ester-type molybdenum compounds, molybdate amine compounds, molybdenum dithiocarbamates, molybdenum dithiophosphates, and other organic molybdenum complexes.

[0070] From the viewpoint of improving wear resistance, it is preferable that the molybdenum-based antioxidant is at least one selected from the group consisting of amide-type molybdenum compounds, ester-type molybdenum compounds, molybdate amine compounds, molybdenum dithiocarbamates, and molybdenum dithiophosphates.

[0071] Amide-type molybdenum compounds are compounds that contain an amide group and molybdenum. From the viewpoint of improving wear resistance, it is preferable that the amide group in the amide-based molybdenum compound is bonded to an alkyl group. The alkyl group bonded to the amide group may be linear or branched. From the viewpoint of improving wear resistance, the number of carbon atoms in the alkyl group bonded to the amide group is preferably 4 to 12, more preferably 5 to 11, and even more preferably 5 to 10.

[0072] Ester-type molybdenum compounds are compounds that contain an ester group and molybdenum. From the viewpoint of improving wear resistance, it is preferable that the ester group of the ester-based molybdenum compound is bonded to an alkyl group. The alkyl group bonded to the ester group may be linear or branched. From the viewpoint of improving wear resistance, the number of carbon atoms in the alkyl group bonded to the ester group is preferably 4 to 12, more preferably 5 to 11, and even more preferably 5 to 10.

[0073] Amine molybdate compounds are molybdic acids that have an amino group. Specifically, examples of molybdate amine compounds include those obtained by reacting a compound containing a hexavalent molybdenum atom with an amine using the method described in Japanese Patent Publication No. 2003-252887.

[0074] Other organic molybdenum complexes are described, for example, in Japanese Patent Publication No. 62-108891. The following organic molybdenum complexes are examples.

[0075] From the viewpoint of improving wear resistance, it is preferable that the molybdenum-based antioxidant is at least one selected from the group consisting of amide-based molybdenum compounds and ester-based molybdenum compounds.

[0076] From the viewpoint of improving wear resistance, the amide-based molybdenum compound is preferably a compound represented by the following formula (4A).

[0077] [ka]

[0078] In formula (4A), R 41 This signifies an alkyl group. R 41 The alkyl group represented is preferably a primary alkyl group (i.e., an alkyl group in which the carbon atom bonded to the amide group is a primary carbon) or a secondary alkyl group (i.e., an alkyl group in which the carbon atom bonded to the amide group is a secondary carbon). R 41 The number of carbon atoms in the alkyl group represented by is preferably 3 to 20, more preferably 4 to 18, and even more preferably 5 to 16.

[0079] From the viewpoint of improving wear resistance, the ester-based molybdenum compound is preferably a compound represented by the following formula (4B).

[0080] [ka]

[0081] In formula (4B), R 42 This signifies an alkyl group. The alkyl group represented by R2 is preferably a primary alkyl group (i.e., an alkyl group in which the carbon atom bonded to the amide group is a primary carbon) or a secondary alkyl group (i.e., an alkyl group in which the carbon atom bonded to the amide group is a secondary carbon). R 42 The number of carbon atoms in the alkyl group represented by is preferably 3 to 20, more preferably 4 to 18, and even more preferably 5 to 16.

[0082] The molybdenum-based antioxidant may include the molybdenum compound described in Japanese Patent Application Publication No. 2003-252887, provided that it does not significantly impair the long lifespan and does not cause adverse effects such as the formation of precipitates.

[0083] The molybdenum-based antioxidant is preferably at least one selected from the group consisting of, for example, amide-type molybdenum compounds, ester-type molybdenum compounds, molybdate amine compounds, molybdenum dithiocarbamates, and molybdenum dithiophosphates.

[0084] In the lubricating oil composition according to this disclosure, the content of molybdenum elements derived from the molybdenum-based antioxidant is preferably greater than 0 ppm by mass and 800 ppm by mass or less, more preferably greater than 0 ppm by mass and 200 ppm by mass or less, and even more preferably greater than 0 ppm by mass and 100 ppm or less, based on the total amount of the lubricating oil composition. When the content of molybdenum elements is greater than 0 ppm by mass, coking in the gas engine can be further suppressed, and when it is 800 ppm by mass or less, the life characteristics in high-temperature environments and in the presence of NOx can be maintained to the same extent as when no molybdenum-based antioxidant is added.

[0085] From the viewpoint of improving coking resistance when the lubricating oil composition according to this disclosure is deteriorated with use, the molybdenum-based antioxidant is preferably at least one selected from the group consisting of amide-based molybdenum compounds, ester-based molybdenum compounds, molybdate amine compounds, molybdenum dithiocarbamate, and molybdenum dithiophosphate, and the content of molybdenum element derived from the molybdenum-based antioxidant is preferably greater than 0 ppm by mass and 100 ppm or less with respect to the total amount of the lubricating oil composition.

[0086] The molybdenum content relative to the total lubricating oil composition shall be determined by analytical values ​​obtained from ICP emission spectroscopy in accordance with JPI-5S-38-92.

[0087] The content of the molybdenum-based antioxidant is preferably more than 0% by mass and 1.0% by mass or less, more preferably 0.05% by mass or more and 0.25% by mass or less, and even more preferably 0.08% by mass or more and 0.15% by mass or less, based on the total amount of the lubricating oil composition.

[0088] (Phosphorus-based wear inhibitor) The lubricating oil composition relating to this disclosure contains a phosphorus-based anti-wear agent.

[0089] An example of a phosphorus-based anti-wear agent is zinc dialkyldithiophosphate (ZnDTP).

[0090] As the zinc dialkyldithiophosphate, for example, it is preferable to have a primary or secondary alkyl group. The primary or secondary alkyl group of the zinc dialkyldithiophosphate is preferably an alkyl group having 4 to 12 carbon atoms. That is, one preferred embodiment of the anti-wear agent is at least one selected from zinc dialkyldithiophosphate having two identical or different alkyl groups selected from primary or secondary alkyl groups having 4 to 12 carbon atoms.

[0091] Specific examples of zinc dialkyldithiophosphate include, but are not limited to, zinc dialkyldithiophosphate having a primary alkyl group with 8 carbon atoms and zinc alkyldithiophosphate having a secondary alkyl group with 4 carbon atoms.

[0092] From the viewpoint of wear resistance, the lubricating oil composition according to this disclosure preferably contains phosphorus elements derived from phosphorus-based anti-wear agents in an amount greater than 0 ppm by mass and 1000 ppm by mass or less, more preferably 100 ppm by mass or more and 700 ppm by mass or less, and even more preferably 300 ppm by mass or more and 600 ppm by mass or less, based on the total amount of the lubricating oil composition.

[0093] The phosphorus content relative to the total lubricating oil composition shall be determined by analytical values ​​obtained from ICP emission spectroscopy in accordance with JPI-5S-38-92.

[0094] (Viscosity index improver) The lubricating oil composition relating to this disclosure may contain an olefin copolymer type viscosity index improver.

[0095] Examples of olefin copolymer-type viscosity index improvers include non-dispersive and dispersed viscosity index improvers as described in JASO M355:2021.

[0096] Examples of non-dispersive viscosity index improvers include olefin copolymers such as ethylene-propylene copolymers.

[0097] Examples of dispersion-type viscosity index improvers include polymers such as random copolymers of olefins and methacrylates, block copolymers of olefins and methacrylates, and graft copolymers of polymethacrylates and olefin copolymers. Random copolymers of olefins and methacrylates include random copolymers of ethylene-alkyl methacrylate and random copolymers of propylene-alkyl methacrylate. Examples include isobutylene-alkyl methacrylate random copolymers. Examples of olefin and methacrylate block copolymers include ethylene-alkyl methacrylate block copolymers, propylene-alkyl methacrylate block copolymers, and isobutylene-alkyl methacrylate block copolymers. Examples of graft copolymers of polymethacrylate and olefin copolymer include polymers in which the main chain is polymethacrylate and the side chains are olefin copolymers.

[0098] When the olefin copolymer used as a viscosity index improver is an alkylated derivative having a side-chain alkyl group, the number of carbon atoms in the side-chain alkyl group is preferably 1 to 50.

[0099] In this disclosure, the olefin copolymer type viscosity index improver is preferably a polymer with a weight-average molecular weight of 10,000 or more that contributes to improving the viscosity index, and the content of the polymer is 1% by mass or more based on the total amount of the lubricating oil composition. The weight-average molecular weight of the olefin copolymer type viscosity index improver is preferably 100,000 or less, more preferably 80,000 or less, even more preferably 50,000 or less, and most preferably 25,000. The weight-average molecular weight of olefin copolymer-type viscosity index improvers is a value calculated using polystyrene as the standard, measured by gel permeation chromatography.

[0100] The content of the olefin copolymer type viscosity index improver is preferably 5% by mass or less. If the content of the olefin copolymer type viscosity index improver is 5% by mass or less, it contributes to improving the viscosity index without worsening the caulking resistance. From this viewpoint, the content of the olefin copolymer type viscosity index improver is preferably 0% by mass or more and 4.5% by mass or less.

[0101] (Other additives) The lubricating oil composition relating to this disclosure may contain other additives as needed. Other additives include pour point depressants, corrosion inhibitors (rust inhibitors), and defoamers. Examples of pour point depressants include polyalkyl methacrylates without polar groups, copolymers thereof, and alkyl group derivatives thereof. The weight-average molecular weight of a pour point depressant is measured by gel permeation chromatography and is calculated using polystyrene as the standard. Examples of corrosion inhibitors include thiadiazole derivatives, benzotriazole derivatives, and imidazole derivatives. Examples of defoaming agents include silicone oils such as polydimethylsiloxane, alkylated polydimethylsiloxane derivatives, and halogenated alkylated polydimethylsiloxane derivatives.

[0102] (Alkaline earth metal content) The lubricating oil composition relating to this disclosure has an alkaline earth metal content in the lubricating oil composition that is greater than 1,000 ppm by mass and less than or equal to 1,500 ppm by mass, based on the total amount of the lubricating oil composition. Alkaline earth metals in the lubricating oil composition are included from alkaline earth metal-based detergents (e.g., Ca-based metal detergents). From the viewpoint of low ash content, long lifespan, and cleanliness, the alkaline earth metal content in the lubricating oil composition is preferably more than 1000 ppm and less than or equal to 1500 ppm by mass, and more preferably between 1100 ppm and 1500 ppm relative to the total amount of the lubricating oil composition.

[0103] (Boron content derived from boron-based dispersants) The internal combustion engine lubricant composition relating to this disclosure contains a boron content derived from a boron-based dispersant, It is preferable that the boron content is 200 ppm or more by mass relative to the total amount of the lubricating oil composition. Having a boron content of 200 ppm or more derived from the boron-based dispersant in the lubricating oil composition effectively improves caulking resistance and long service life.

[0104] (Physical properties of lubricating oil compositions for internal combustion engines) -Kinematic viscosity- The kinematic viscosity of the lubricating oil composition relating to this disclosure at 100°C is 12.5 mm². 2 / s or more 16.3mm 2 Preferably, it is less than or equal to / s, and 13.0 mm 2 / s or more 16.0mm 2 / s or less is more preferable, and 14.0 mm 2 / s or more 16.0mm 2 / s or less is even more preferable.

[0105] (Uses of lubricating oil compositions for internal combustion engines) The lubricating oil composition according to this disclosure is preferably used as a lubricating oil for gas engines that are powered by gases such as hydrogen, autogas, and natural gas. It is preferable to use it as a lubricant for gas engines, hydrogen engines, or dual-fuel engines for ships that are used in total energy systems (systems that use gas as fuel to generate electricity, power, etc., using gas engines, turbines, etc., and simultaneously utilize the waste heat generated), among other gas engines. Gas engines, hydrogen engines, and dual-fuel engines used in total energy systems tend to have higher concentrations of NOx in their blow-by gases compared to other gas engines. Consequently, they are more prone to coking.

[0106] The lubricating oil composition according to this disclosure suppresses the occurrence of coking and has a long lifespan. Therefore, the lubricating oil composition according to this disclosure is suitable for hydrogen engines and dual-fuel engines for ships.

[0107] (Method for producing lubricating oil compositions for internal combustion engines) The method for producing the lubricating oil composition relating to this disclosure is not particularly limited. The lubricating oil composition according to this disclosure, for example, may contain a predetermined base oil, an alkaline earth metal-based detergent, a boron-based dispersant, a predetermined antioxidant, and a phosphorus-based anti-wear agent, in addition to an olefin copolymer-type viscosity index improver and other additives as needed. The mixing order of each component contained in the lubricating oil composition is not particularly limited and may be mixed sequentially with the base oil. [Examples]

[0108] The lubricating oil compositions for internal combustion engines according to this disclosure will be described in detail below with reference to examples. However, the lubricating oil compositions for internal combustion engines according to this disclosure are not limited in any way by these examples.

[0109] <Examples 1-11, Comparative Examples 1-12> The lubricating oil compositions of Examples 1 to 11 and Comparative Examples 1 to 12 were prepared by blending each component listed in the composition column of Table 1 or Table 2 in the blending ratio (mass%) shown in Table 1 or Table 2, and dissolving and dispersing them at 60°C. In the composition column of Tables 1 and 2, a blank space indicates that the target component is not present.

[0110] <Measurement and Evaluation> The following measurements and evaluations were performed using each of the obtained lubricating oil compositions. The results are shown in Table 1 or Table 2. In the evaluation columns of Tables 1 and 2, entries marked with "-" indicate that the corresponding evaluation was not performed.

[0111] (Kinematic viscosity at 100℃) The kinematic viscosity of each lubricating oil composition at 100°C was measured according to ASTM D 7042.

[0112] (element content) For each lubricating oil composition, the content (mass ppm) of calcium (Ca), boron (B), phosphorus (P), and molybdenum (Mo) was measured by ICP emission spectroscopy in accordance with JPI-5S-38-92. Calcium (Ca), boron (B), phosphorus (P), and molybdenum (Mo) are each expressed in mass ppm relative to the lubricating oil composition. The boron (B) content was determined by measuring the amount of boron in the boron-based dispersant and calculating the mass ppm relative to the lubricating oil composition.

[0113] (Panel caulking test (PCT): New oil) A 250 mL lubricating oil composition (new oil) was used in a panel caulking test machine manufactured by Rigosha Co., Ltd. The test was conducted for 3 hours (15 seconds of splashing operation, 45 seconds of rest x 180 cycles) on an aluminum panel (A2024P), with a panel temperature of 320°C and an oil temperature of 110°C. The panel mass was measured before and after the test, and the difference was defined as the amount of caulking. A caulking amount of 20.0 mg or less was considered acceptable, and the new oil was evaluated as having excellent caulking resistance.

[0114] (Performance evaluation after 72 hours of ISOT testing) Oxidation stability tests were conducted on lubricating oil compositions for internal combustion engines in accordance with JIS K 2514-1 (2013). Copper and steel plate catalysts were added to 250 mL each of gas engine oil compositions, and the tests were conducted at 165.5°C, 1300 rpm (revolutions per minute, hereafter the same), and for 72 hours. The following performance evaluations were performed on the lubricating oil compositions (degraded oil) after the tests.

[0115] Panel Caulking Test (PCT): Degraded Oil A panel caulking test (PCT) was performed using a lubricating oil composition (degraded oil) in the same manner as the panel caulking test (PCT) performed with new oil. A caulking amount of 30.0 mg or less was considered acceptable, and the oil was evaluated as having excellent resistance to caulking.

[0116] =Percentage increase in kinematic viscosity at 40°C (%)= The percentage increase in kinematic viscosity at 40°C was measured for the lubricating oil composition (degraded oil) after 72 hours of ISOT testing. The percentage increase in kinematic viscosity at 40°C is calculated by dividing the kinematic viscosity of degraded oil at 40°C by the kinematic viscosity of new oil at 40°C and expressing the result as a percentage. The kinematic viscosity at 40°C was measured for lubricating oil compositions (new oil and degraded oil) in accordance with ASTM D7042.

[0117] =base value= The base number of the lubricating oil composition (degraded oil) was measured using the hydrochloric acid method in accordance with JIS K2501 (2003).

[0118] The rate of increase in kinematic viscosity and the base number at 40°C are criteria for determining longevity. A lubricating oil composition was deemed acceptable if the increase in kinematic viscosity of the degraded oil at 40°C was 5.0% or less, and the base number was 0.8 mg KOH / g or higher, indicating excellent long-life performance.

[0119] (Shell abrasion test: Measurement of abrasion mark diameter) In a shell four-ball abrasion resistance test compliant with ASTM D4172, the test was conducted using a Phoenix Tribology TE92 shell four-ball abrasion tester under the conditions of a rotation speed of 1500 rpm, 30 minutes, 75°C, and a load of 30 kg. The abrasion mark diameter (μm) of the steel balls after the test was measured. Lubricating oil compositions with an abrasion mark diameter of 450 μm or less were deemed acceptable and evaluated as having excellent abrasion properties.

[0120] [Table 1]

[0121] [Table 2]

[0122] Details of the abbreviations used in Tables 1 and 2 are provided below.

[0123] (Base oil) • Base oil X1: A base oil belonging to API Group IV (Gr.IV) and exhibiting the following general properties. Kinematic viscosity (100℃): 303mm 2 / s, viscosity index: 241, flash point: 286℃ or higher • Base oil X2: A base oil belonging to API Group I (Gr.I) and exhibiting the following general properties. Kinematic viscosity (100℃): 13.9mm 2 / s, viscosity index: 93, flash point: 250℃ or higher • Base oil X3: A base oil belonging to API Group I (Gr.I) and exhibiting the following general properties. Kinematic viscosity (100℃): 32.9mm 2 / s, viscosity index: 97, flash point: 300℃ or more • Base oil Y1: Belongs to API Group III (Gr.III) and exhibits the following general properties. Kinematic viscosity (100℃): 7.6mm 2 / s, viscosity index: 130, flash point: 240℃ or higher • Base oil Y2: Belongs to API Group II (Gr.II) and exhibits the following general properties. Kinematic viscosity (100℃): 9.9mm 2 / s, viscosity index: 101, flash point: 240℃ or higher

[0124] (Alkaline earth metal-based cleaning agent) • Ca-containing cleaning agent A Calcium salicylate: Base number measured according to JIS K2501 (2003) is 228 mg KOH / g, calcium content is 8.0% by mass. • Ca-containing cleaning agent B Calcium salicylate: Base number measured according to JIS K2501 (2003) is 58.8 mg KOH / g, calcium content is 2.3% by mass.

[0125] (Boron-based dispersant) • Boron-based dispersant A Succinimide-based dispersant: Boron content 0.87% by mass, nitrogen content 1.7% by mass, base number 33 mgKOH / g, weight-average molecular weight 5500 g / mol, B / N ratio: 0.5, high B / N ratio boron-based dispersant • Boron-based dispersant B Succinimide-based dispersant: Boron content 1.42% by mass, nitrogen content 1.6% by mass, base number 36 mgKOH / g, weight-average molecular weight 4900 g / mol, B / N ratio: 0.9, high B / N ratio boron-based dispersant • Boron-based dispersant C Succinimide-based dispersant: Boron content 0.50% by mass, nitrogen content 1.5% by mass, base number 32 mgKOH / g, weight-average molecular weight 4400 g / mol, B / N ratio: 0.3, low B / N ratio boron-based dispersant

[0126] (Non-boron dispersants) Non-boron-based dispersant A Ashless dispersant: Nitrogen content 1.8% by mass, base number 41 mgKOH / g, weight-average molecular weight 4900 g / mol • Non-boron dispersant B Ashless dispersant: Nitrogen content 2.0% by mass, base number 47 mgKOH / g, weight-average molecular weight 4900 g / mol

[0127] (Antioxidant) • Phenolic antioxidant: Density 0.97 g / cm³ 3 (At 20°C), with a flash point of 152°C and a boiling point of 240°C, this phenolic compound (octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamic acid) is classified as CAS No. 125643-61-0. • Amine-based antioxidant: Density 0.97 g / cm³ 3 An aromatic amine compound classified as CAS No. 68411-46-1, with a kinematic viscosity of 401 cSt at 40°C, a flash point of 154°C, a basic nitrogen content of 4.5%, and a base number of 180 mg KOH / g, was used in combination with an aromatic amine compound classified as CAS No. 68259-36-9, with a flash point of 215°C. • Molybdenum-based antioxidants: A mixture of amide-type molybdenum compounds and ester-type molybdenum compounds. Density 1.08 g / cm³ 3 (At 15°C), the kinematic viscosity at 100°C is 55 cSt, the flash point is 193°C, the nitrogen content is 2.8% by mass, and the molybdenum content is 7.9% by mass. 41 Compounds represented by formula (4A) in which C3 is an alkyl group having 3 to 16 carbon atoms, and R 42A mixture of compounds represented by formula (4B), wherein the alkyl group has 3 to 16 carbon atoms. The composition column in Tables 1 and 2 shows the total percentage (by mass) of phenolic antioxidants and amine antioxidants.

[0128] (Phosphorus-based wear inhibitor) • Phosphorus-based anti-wear agent: ZnDTP (a zinc dialkyldithiophosphate compound having primary and secondary alkyl chains with a phosphorus content of 8.8%).

[0129] (Viscosity index improver) • Viscosity index improver: Density 0.85 g / cm³ 3 An olefin copolymer with a kinematic viscosity of 2000 cSt at 100°C (at 15°C), a flash point of 295°C, and a weight-average molecular weight of 15,000.

[0130] (Other additives) • Rust inhibitor: Benzotriazole • Pour point depressant: Polymethacrylate (density 0.92 g / cm³) 3 (25°C, pour point -42°C) • Antifoaming agent: Silicone-based (density 0.97 g / cm³) 3 (25℃), flash point 350℃)

[0131] As shown in Table 1, the lubricating oil compositions for internal combustion engines in the examples exhibited low coking levels in both new and degraded oil conditions, and also demonstrated excellent long-life performance. The lubricating oil compositions for internal combustion engines in the examples also exhibited excellent wear resistance. On the other hand, as shown in Table 2, the lubricating oil composition for internal combustion engines in the comparative example did not meet the acceptance criteria in either the evaluation of new oil or degraded oil.

Claims

1. The kinematic viscosity at 100°C is 12 mm². ２ A base oil containing a base oil X of / s or higher, Alkaline earth metal-based cleaning agent, A boron-based dispersant containing boron and nitrogen, A non-boron dispersant that does not contain boron and contains nitrogen, At least one antioxidant selected from the group consisting of phenolic antioxidants and amine antioxidants, Molybdenum-based antioxidants, It contains a phosphorus-based anti-wear agent, The kinematic viscosity at 100°C is 12 mm. ２ The content of base oil X with a ratio of / s or higher is 5.0% by mass or more and 20% by mass or less, relative to the total amount of the lubricating oil composition. The base number of the aforementioned alkaline earth metal-based detergent is 100 mg KOH / g or more. The boron-based dispersant comprises a boron-based dispersant with a B / N ratio of 0.4 or higher. The ratio of the nitrogen element content derived from the boron-based dispersant to the nitrogen element content derived from the non-boron-based dispersant is 0.5 or more and 2.5 or less by mass. The content of alkaline earth metals in the lubricating oil composition is greater than 1,000 ppm by mass and less than or equal to 1,500 ppm by mass, based on the total amount of the lubricating oil composition. The content of boron element derived from the boron-based dispersant is 200 ppm by mass or more relative to the total amount of the lubricating oil composition. Lubricating oil composition for internal combustion engines.

2. The lubricating oil composition for internal combustion engines according to claim 1, comprising an olefin copolymer type viscosity index improver, wherein the content of the viscosity index improver is 5% by mass or less.

3. The lubricating oil composition for internal combustion engines according to claim 1, wherein the total content of the phenolic antioxidant and the amine antioxidant is 1% by mass or more and 5.5% by mass or less.

4. The lubricating oil composition for an internal combustion engine according to claim 1, wherein the molybdenum-based antioxidant is at least one selected from the group consisting of amide-based molybdenum compounds, ester-based molybdenum compounds, molybdate amine compounds, molybdenum dithiocarbamate, and molybdenum dithiophosphate, and the content of molybdenum element derived from the molybdenum-based antioxidant is greater than 0 ppm by mass and 100 ppm or less with respect to the total amount of the lubricating oil composition.

5. The lubricating oil composition for an internal combustion engine according to claim 1, wherein the content of phosphorus elements derived from the phosphorus-based anti-wear agent is greater than 0 ppm by mass and 500 ppm by mass or less, relative to the total amount of the lubricating oil composition.

6. A lubricating oil composition for an internal combustion engine according to any one of claims 1 to 5, for use in a gas engine.

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