Lubricating oil composition for internal combustion engine

Abstract

To provide a lubricating oil composition for an internal combustion engine, which suppresses occurrence of coking not only in an early stage of use but also after deterioration, and which has an excellent demulsification property against moisture in blow-by-gas.SOLUTION: A lubricating oil composition for an internal combustion engine comprises: a base oil belonging to API Group III; a calcium-based detergent; a boron- and nitrogen-containing boron-based dispersant; one or more kinds of antioxidants selected from the group consisting of phenol-based antioxidants and amine-based antioxidants; a molybdenum-based antioxidant; a phosphorus-based anti-wear agent; and an olefin copolymer-type viscosity index improver. The calcium-based detergent has a base number of 100 mgKOH / g or less, and a content of a calcium element in the lubricating oil composition is more than 0 mass.ppm and 1500 mass.ppm or less, based on a total amount of the lubricating oil composition.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In recent years, cogeneration systems have been attracting attention from the perspective of energy conservation measures and the diversification of power sources. In particular, gas cogeneration systems are seen as promising as environmentally friendly systems that use clean fuel. Gas engines have high combustion temperatures, which means that the NOx concentration in the blow-by gas is relatively high, which can easily cause sludge to form in the lubricating oil. This requires periodic replacement of the lubricating oil, but increasing the number of replacements leads to higher maintenance costs, so there is a demand for longer-lasting lubricating oil (i.e., long-drain properties).

[0003] Recent gas cogeneration systems have been pursuing energy conservation through the optimization of fuel combustion to minimize emissions of carbon dioxide, nitrogen oxides, and sulfur oxides, and through the high efficiency of power generation and heat utilization. Therefore, lubricating oil compositions used in gas engines are also required to maintain excellent high-temperature stability without reducing power generation efficiency.

[0004] Gas cogeneration systems often use relatively large gas engines, which require high maintenance costs, making reducing the frequency of maintenance inspections an important issue. However, when using lubricating oil in gas engines, the ash contained in the lubricating oil accumulates on the top of the pistons and exhaust valves, reducing the cleanliness of the engine. As a result, the engine itself must be overhauled multiple times periodically, resulting in a significant amount of maintenance effort. Therefore, lubricating oils with low ash content are needed to improve maintainability.

[0005] When gas engines are operated continuously for long periods of time, the lubricating oil contained in the engine is constantly exposed to high temperatures, which gradually causes thermal oxidation degradation. Furthermore, gas engines, which have higher combustion temperatures than diesel engines, tend to have higher concentrations of NOx in their blow-by gas, which can easily cause sludge formation in the lubricating oil. Therefore, while regular replacement of the lubricating oil is necessary, there is a need for both long life and coking resistance to reduce maintenance costs by extending the life of the lubricating oil itself and to prevent problems caused by localized coking in various parts of the engine.

[0006] For example, Patent Document 1 discloses a lubricating oil composition for gas engines that contains a base oil with a flash point of 240°C or higher, a molybdenum-based antioxidant, and a viscosity modifier with a flash point of 270°C or higher, with the aim of suppressing the occurrence of coking, and that has a molybdenum atom content of 20 ppm or more and 800 ppm or less relative to the total mass of the lubricating oil composition for gas engines. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese 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 in the early stages of use, but there is room for improvement in the durability of coking resistance after deterioration due to use. Furthermore, lubricating oil compositions for gas engines are also required to have anti-emulsifying properties against moisture in blow-by gas.

[0009] Therefore, an object of the present disclosure is to provide a lubricating oil composition for internal combustion engines that suppresses the occurrence of coking not only in the early stages of use but also after deterioration, and that also has excellent demulsification properties against moisture in blow-by gas. [Means for solving the problem]

[0010] The means for solving the above problems include the following means. <1> base oils belonging to API Group III; a metal-based detergent containing calcium; a boron-based dispersant containing boron and nitrogen; one or more antioxidants selected from the group consisting of phenolic antioxidants and amine antioxidants; A molybdenum-based antioxidant, a phosphorus-based antiwear agent; Contains The base number of the calcium-containing metallic detergent is 100 mgKOH / g or less, The content of calcium element in the lubricating oil composition is more than 0 ppm by mass and 1500 ppm by mass or less, based on the total amount of the lubricating oil composition. A lubricating oil composition for an internal combustion engine. <2> The viscosity index improver contains an olefin copolymer type viscosity index improver, and the content of the viscosity index improver is 5% by mass or less. <1> The lubricating oil composition for internal combustion engines according to claim 1. <3> The content of boron element derived from the boron-based dispersant is 350 ppm by mass or more based on the total amount of the lubricating oil composition. <1> or <2> The lubricating oil composition for internal combustion engines according to claim 1. <4> the total content of the phenolic antioxidant and the amine antioxidant is 1% by mass or more and 5.5% by mass or less; <1> ~ <3> 1. A lubricating oil composition for internal combustion engines according to any one of the preceding claims. <5> 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 dithiocarbamates, and molybdenum dithiophosphates, and the content of molybdenum element derived from the molybdenum-based antioxidant is more than 0 ppm by mass and not more than 100 ppm by mass, based on the total amount of the lubricating oil composition; <1> ~ <4> 1. A lubricating oil composition for internal combustion engines according to any one of the preceding claims. <6> The content of phosphorus element derived from the phosphorus-based wear inhibitor is more than 0 ppm by mass and 500 ppm by mass or less, based on the total amount of the lubricating oil composition. <1> ~ <5> 1. A lubricating oil composition for internal combustion engines according to any one of the preceding claims. <7> For gas engines, <1> ~ <6> 1. A lubricating oil composition for internal combustion engines according to any one of the preceding claims. [Effects of the Invention]

[0011] According to the present disclosure, there is provided a lubricating oil composition for internal combustion engines that inhibits the occurrence of coking not only in the early stages of use but also after deterioration, and that also has excellent demulsification properties against moisture in blow-by gas. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present disclosure will be described. These descriptions and examples are intended to illustrate the embodiment and are not intended to limit the scope of the invention. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. However, when the numerical values ​​written before and after "to" are followed by "greater than" or "less than," the numerical range does not include these numerical values ​​as the lower or upper limit. Regarding the content of a component, "%" means "% by mass" unless otherwise specified. The same applies to "ppm." In addition, in the numerical ranges described in stages in this specification, the upper limit of a certain numerical range may be replaced by the upper limit of another numerical range described in stages, or may be replaced by a value shown in an Example. Furthermore, the lower limit of a certain numerical range may be replaced by the lower limit of another numerical range described in stages, or may be replaced by a value shown in an Example.

[0013] Each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified.

[0014] <Lubricating oil composition for internal combustion engines> The lubricating oil composition for internal combustion engines according to the present disclosure (sometimes simply referred to as the "lubricating oil composition" in this disclosure) comprises: base oils belonging to API Group III; a metal-based detergent containing calcium; a boron-based dispersant containing boron and nitrogen; one or more antioxidants selected from the group consisting of phenolic antioxidants and amine antioxidants; A molybdenum-based antioxidant, a phosphorus-based antiwear agent; Contains The base number of the calcium-containing metallic detergent is 100 mgKOH / g or less, The calcium content in the lubricating oil composition is more than 0 ppm by mass and not more than 1500 ppm by mass, based on the total amount of the lubricating oil composition. The inventors of the present disclosure have discovered that a lubricating oil composition comprising a combination of the above-described base oil, detergent, dispersant, antioxidant, anti-friction agent, and viscosity index improver improves coking resistance even when deteriorated with use, and also provides excellent demulsification properties against moisture in blow-by gas.

[0015] (base oil) The lubricating oil composition for internal combustion engines according to the present disclosure contains a base oil classified as API (American Petroleum Institute) Group III (Gr. III). Examples of base oils classified into Group III include mineral base oils and synthetic base oils used in the field of lubricating oils.

[0016] Examples of mineral base oils include base oils classified as API Group III, which are obtained from crude oil by combining atmospheric distillation, vacuum distillation, solvent deasphalting, solvent extraction, hydrorefining, and solvent dewaxing processes. Base oils classified as API Group III are preferred because they maintain a high flash point and do not contain low boiling fractions that exacerbate coking when exposed to high temperatures. The lubricating oil composition for internal combustion engines according to the present disclosure may contain a base oil other than that classified as API Group III.

[0017] Examples of synthetic base oils 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 trimethylolpropane oleate and pentaerythritol-2-ethylhexanoate; polyglycols such as polyoxyalkylene glycols; and polyphenyl ethers.

[0018] In order to obtain a base oil that contains as little low-boiling fractions as possible, which cause coking, it is preferable to use a mineral base oil as the base oil, but synthetic base oils may also be used to the extent that they do not interfere with sufficient dissolution of the additives.

[0019] The base oil may include other base oils besides mineral base oils and synthetic base oils.

[0020] The kinematic viscosity of the base oil at 40°C is not particularly limited, but from the viewpoint of evaporation performance and wear resistance, it is preferable that the kinematic viscosity be 10.0 mm 2 / s or more 60.0mm 2 / s or less is preferable, and 30.0 mm 2 / s or more 55.0mm 2 / s or less is more preferable, and 40.0 mm 2 / s or later Upper 50.0mm 2 / s or less is more preferable.

[0021] The kinematic viscosity of the base oil at 100°C is 4.0 mm 2 / s or more 10.0mm 2 / s or less is preferable, and 6.0 mm 2 / s or more 9.0mm 2 / s or less is more preferable, and 7.0 mm 2 / s or more 8.0mm 2 / s or less is more preferable.

[0022] The kinematic viscosity of the base oil at 40°C and at 100°C is measured in accordance with JIS K2283 (2000).

[0023] The viscosity index of the base oil is not particularly limited, but is preferably 100 or greater, more preferably 110 or greater, and even more preferably 120 or greater. By having a viscosity index within the above range, the viscosity stability of the lubricating oil composition for internal combustion engines with respect to temperature is improved, and performance such as wear resistance is more likely to be stably exhibited in a variety of external environments.

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

[0025] The content of the base oil belonging to Group III is preferably from 65 to 95 mass %, more preferably from 67 to 90 mass %, and even more preferably from 68 to 85 mass %, based on the total mass of the lubricating oil composition for internal combustion engines.

[0026] (Metallic detergents) The lubricating oil composition for internal combustion engines according to the present disclosure contains a metallic detergent containing calcium (hereinafter, sometimes referred to as a Ca-based metallic detergent). Examples of the Ca-based metal-based detergent include calcium salicylate, calcium phenate, and calcium sulfonate. It is preferable to use one or more selected from the group consisting of these Ca-based metal-based detergents, and it is most preferable to use calcium salicylate.

[0027] The Ca-based metal detergent preferably has a base number of 100 mgKOH / g or less. The base number of Ca-based metallic detergents is measured by the hydrochloric acid method in accordance with JIS K2501 (2003). When the base number of Ca-based metallic detergents is 2 mgKOH / g or more, it can effectively suppress oxidation of base oil and deterioration in the presence of NOx. When the base number of Ca-based metallic detergents is 100 mgKOH / g or less, it can effectively suppress the accumulation of ash on pistons and the occurrence of coking.

[0028] The content of the Ca-based metallic detergent is preferably 1% by mass or more and 30% by mass or less, more preferably 2% by mass or more and 20% by mass or less, and even more preferably 3% by mass or more and 10% by mass or less, based on the total mass of the lubricating oil composition for internal combustion engines.

[0029] (dispersant) The lubricating oil composition for internal combustion engines according to the present disclosure contains a boron-based dispersant containing boron and nitrogen as a dispersant. The lubricating oil composition for internal combustion engines according to the present disclosure may further contain a non-boron-based dispersant that does not contain boron but contains nitrogen.

[0030] The boron-based dispersant and the non-boron-based dispersant may each be contained in one kind or in two or more kinds, for example.

[0031] <Boron-based dispersant> By boron-based dispersant is meant a dispersant that contains boron and nitrogen. As the boron-based dispersant, a boron-based dispersant used in the field of lubricating oils can be used.

[0032] As the boron-based dispersant, a boron-containing imide-based dispersant is preferred. The boron-containing imide-based dispersant refers to a dispersant that is a compound containing boron and has an imide bond. Examples of the boron-containing imide-based dispersant include monoimides of alkyl or alkenyl succinic acid and boron-modified bisimides thereof. Among these, as the boron-containing imide-based dispersant, boron-modified bisimides of alkyl or alkenyl succinic acid are preferred from the viewpoints of extending the life, wear resistance, and dispersibility of the lubricating oil composition.

[0033] 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 the present disclosure, a polymer refers to a compound having a weight average molecular weight (Mw) of 1,000 or more in terms of polystyrene.

[0034] From the viewpoint of clean dispersibility, the boron-based dispersant preferably has a weight average molecular weight (Mw) of 2,000 to 7,000. In the present disclosure, the weight average molecular weight (Mw) is a value measured by gel permeation chromatography (GPC).

[0035] In this disclosure, the weight-average molecular weight (Mw) is measured using a Shodex GPC-101 (Showa Denko K.K.) measuring instrument, three Shodex GPC LF-804 (Showa Denko K.K.) measuring columns, a differential refractive index 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 is calculated from the measurement results using a molecular weight distribution curve prepared using a monodisperse polystyrene standard sample.

[0036] From the viewpoints of coking resistance, sludge dispersibility, and metal corrosion resistance, the content of the boron-based dispersant is preferably 3% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 9% by mass or less, and even more preferably 3.5% by mass or more and 8% by mass or less. However, the content of boron-based dispersant referred to here refers to the content of the active ingredient including the diluent oil when the boron-based dispersant contains diluent oil.

[0037] <Non-boron dispersant> The non-boron dispersant means a dispersant that does not contain boron but contains nitrogen, and is included, for example, in ashless dispersants.

[0038] Examples of non-boron dispersants that can be used include polyamines containing one or more alkyl or alkenyl groups in the molecule, and acid-modified products thereof. As non-boron-based dispersants, for example, succinimides (excluding boron-modified products) represented by general formula (1) or general formula (2) described in paragraphs 0029 to 0032 of JP 2018-048220 A and dispersant B described in paragraph 0048 can also be suitably used. A specific example of a suitable non-boron-based dispersant is a boron-free polyisobutenyl succinimide compound.

[0039] From the viewpoint of sludge dispersibility and metal corrosiveness, the content of the non-boron-based dispersant is preferably 0% by mass or more and 10% by mass or less, more preferably 0% by mass or more and 8% by mass or less, and even more preferably 0% by mass or more and 5% by mass or less. However, the content of the non-boron-based dispersant referred to here refers to the content of the active ingredient including the diluent oil when the non-boron-based dispersant contains diluent oil.

[0040] (antioxidant) The lubricating oil composition for internal combustion engines according to the present disclosure contains an antioxidant. Examples of the antioxidant include phenol-based antioxidants, amine-based antioxidants, and molybdenum-based antioxidants.

[0041] <Phenol-based antioxidant> Examples of phenolic antioxidants include alkylphenolic compounds such as 2,6-di-tert-p-cresol, bisphenolic compounds such as 4,4'-methylenebis-(2,6-di-tert-butylphenol), and hindered phenolic compounds such as esters of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid with alcohols having 8 or more carbon atoms. These compounds may be isomers differing in the number of carbon atoms or structure of the alkyl group.

[0042] <Amine-based antioxidants> Examples of the amine antioxidant include amine compounds such as diphenylamine, 4-benzylamine, 2-aminobiphenyl, naphthylamine, allylaniline, 4-aminobinephenyl, o-toluidine, m-toluidine, p-toluidine, aniline, allylamine, alkylated derivatives thereof, hindered amine compounds, and alkenylated derivatives thereof. These compounds may be isomers having different carbon atoms or structures in the alkyl group.

[0043] Examples of aromatic amine antioxidants include amine compounds that contain one or more amines selected from primary amines, secondary amines, primary diamines, and secondary diamines in their chemical structure, contain one or more aromatic rings, and have an acid dissociation constant of 8 or less for the one or more amines.

[0044] As the aromatic amine-based antioxidant, from the viewpoint of making the antioxidant effect of the amine moiety more effective, it is preferable to select and contain one or more types of compounds represented by the following formula (1) and formula (2).

[0045] [ka]

[0046] In formula (1), R1 to R6 each independently represent an alkyl group or an alkoxy group, and n and m each independently represent an integer of 0 to 4. The alkyl group represented by R1 to R6 is preferably an alkyl group having 1 to 16 carbon atoms, more preferably an alkyl group having 1 to 14 carbon atoms. The alkyl group may be a linear or branched alkyl group. Examples of the alkyl group include a methyl group, an ethyl group, and an octyl group. The alkoxy group represented by R1 to R6 is preferably an alkoxy group having 1 to 16 carbon atoms, more preferably an alkoxy group having 1 to 14 carbon atoms. Examples of the alkoxy group include a methoxy group, an ethoxy group, and an octoxy group. The alkyl group or alkoxy group represented by R1 to R6 may further have a substituent, such as an alkylamino group, an alkanonyl group, or an alkyl ester group. Examples of such groups include: n is preferably 0 to 2, and more preferably 0 to 1. m is preferably 0 to 2, and more preferably 0 to 1.

[0047] [ka]

[0048] In formula (2), R 21 ~R 28 each independently represents a hydrogen atom, an alkyl group, an alkoxy group, or a phenyl group. R 21 ~R 28 The alkyl group represented by the formula (I) is preferably an alkyl group having 1 to 16 carbon atoms, and more preferably an alkyl group having 1 to 12 carbon atoms. The alkyl group may be a linear or branched alkyl group. Examples of the alkyl group include a methyl group, an ethyl group, an octyl group, and a dodecyl group. R 21 ~R 28 The alkoxy group represented by the formula (I) is preferably an alkoxy group having 1 to 16 carbon atoms, more preferably an alkoxy group having 1 to 12 carbon atoms. Examples of the alkoxy group include a methoxy group, an ethoxy group, and an octoxy group. R 21 ~R 28The alkyl group, alkoxy group, or phenyl group represented by the formula (I) may further have a substituent, such as an alkylamino group, an alkanonyl group, or an alkyl ester group.

[0049] Other amine-based antioxidants The lubricating oil composition for gas engines according to the embodiment of the present disclosure may further contain other amine-based antioxidants. The other amine-based antioxidants include amine-based compounds containing one or more amines selected from primary amines, secondary amines, primary diamines, and secondary diamines in their chemical structure. The other amine-based antioxidants C do not include the above-mentioned aromatic amine-based antioxidants.

[0050] One embodiment of the other amine-based antioxidants includes aliphatic amine-based compounds that have one or more amines selected from primary amines, secondary amines, primary diamines, and secondary diamines in their chemical structure and do not contain an aromatic ring.

[0051] As other amine-based antioxidants, it is preferable to contain one or more compounds selected from the compounds represented by the following formulas (3A) and (3B) in order to make the antioxidant effect of the amine moiety more effective.

[0052] [ka]

[0053] In formulas (3A) and (3B), R 31 and R 32 each independently represents an alkyl group or an alkoxy group. R 31 and R 32 The alkyl group represented by the formula (I) is preferably an alkyl group having 1 to 18 carbon atoms, more preferably an alkyl group having 1 to 16 carbon atoms. Examples of the alkyl group include a methyl group, an ethyl group, an octyl group, and a dodecyl group. R 31 and R 32The alkoxy group represented by the formula (I) is preferably an alkoxy group having 1 to 18 carbon atoms, more preferably an alkoxy group having 1 to 16 carbon atoms. Examples of the alkoxy group include a methoxy group, an ethoxy group, and an octoxy group. R 31 and R 32 The alkyl group or alkoxy group represented by the formula (I) may further have a substituent, for example, an alkenyl group, an alkylamino group, an alkanonyl group, or an alkyl ester group.

[0054] Specific examples of other amine-based antioxidants include, but are not limited to, the following: Examples of the compound represented by formula (3A) include R 31 However, examples of the 2,2,6,6-tetramethylpiperidin-4-yl hexadecanoate include 2,2,6,6-tetramethylpiperidin-4-yloctadecanoate, which has 8 carbon atoms. Examples of the compound represented by formula (3B) include R 31 and R 32 wherein each independently has 12 carbon atoms, such as didodecylamine.

[0055] From the viewpoint of extending the life, the lubricating oil composition for internal combustion engines according to the present disclosure contains one or more antioxidants selected from the group consisting of phenolic antioxidants and amine antioxidants. 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 2% by mass or more and 5.5% by mass or less, based on the total amount of the lubricating oil composition for internal combustion engines.

[0056] (Molybdenum-based antioxidant) The lubricating oil composition for internal combustion engines according to the present disclosure further contains a molybdenum-based antioxidant as an antioxidant. The molybdenum-based antioxidant refers to an antioxidant containing molybdenum. Examples of the molybdenum antioxidant include amide-based molybdenum compounds, ester-based molybdenum compounds, molybdic acid amine compounds, molybdenum dithiocarbamates, molybdenum dithiophosphates, and other organic molybdenum complexes.

[0057] From the viewpoint of improving wear resistance, 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 dithiocarbamates, and molybdenum dithiophosphates.

[0058] The amide molybdenum compound is a compound containing an amide group and molybdenum. From the viewpoint of improving wear resistance, the amide group of the amide molybdenum compound is preferably 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 4 or more and 12 or less. It is preferable that the number of carbon atoms is 5 or more and 11 or less, more preferable that the number of carbon atoms is 5 or more and 10 or less.

[0059] The ester-based molybdenum compound is a compound containing an ester group and molybdenum. From the viewpoint of improving wear resistance, the ester group of the ester-based molybdenum compound is preferably bonded to an alkyl group. The alkyl group bonded to the ester group may be linear or branched. From the viewpoint of improving abrasion resistance, the alkyl group bonded to the ester group preferably has 4 or more and 12 or less carbon atoms, more preferably 5 or more and 11 or less carbon atoms, and even more preferably 5 or more and 10 or less carbon atoms.

[0060] The amine molybdate compound is molybdic acid having an amino group. Specific examples of the amine molybdate compound include those obtained by reacting a compound containing a hexavalent molybdenum atom with an amine by the method described in JP-A No. 2003-252887.

[0061] Other organic molybdenum complexes include, for example, those described in JP-A-62-108891. Examples of the organic molybdenum complexes include the organic molybdenum complexes described above.

[0062] From the viewpoint of improving wear resistance, the molybdenum-based antioxidant is preferably at least one selected from the group consisting of amide-based molybdenum compounds and ester-based molybdenum compounds.

[0063] From the viewpoint of improving wear resistance, the amide molybdenum compound is preferably a compound represented by the following general formula (1).

[0064] [ka]

[0065] In the general formula (1), R1 represents an alkyl group. The alkyl group represented by R1 is preferably a primary alkyl group (i.e., an alkyl group in which, among the carbon atoms contained in the alkyl group, the carbon atom bonded to the amide group is a primary carbon) or a secondary alkyl group (i.e., an alkyl group in which, among the carbon atoms contained in the alkyl group, the carbon atom bonded to the amide group is a secondary carbon). The alkyl group represented by R1 preferably has 3 or more and 20 or less carbon atoms, more preferably 4 or more and 18 or less carbon atoms, and even more preferably 5 or more and 16 or less carbon atoms.

[0066] From the viewpoint of improving wear resistance, the ester-based molybdenum compound is preferably a compound represented by the following general formula (2).

[0067] [ka]

[0068] In the general formula (2), R2 represents an alkyl group. The alkyl group represented by R2 is preferably a primary alkyl group (i.e., an alkyl group in which, among the carbon atoms contained in the alkyl group, the carbon atom bonded to the amide group is a primary carbon) or a secondary alkyl group (i.e., an alkyl group in which, among the carbon atoms contained in the alkyl group, the carbon atom bonded to the amide group is a secondary carbon). The alkyl group represented by R2 preferably has 3 or more and 20 or less carbon atoms, more preferably 4 or more and 18 or less carbon atoms, and even more preferably 5 or more and 16 or less carbon atoms.

[0069] The molybdenum-based antioxidant may contain the molybdenum compound described in JP-A-2003-252887 to the extent that it does not significantly impair the longevity of the antioxidant and does not cause adverse effects such as the formation of precipitates.

[0070] When the lubricating oil composition for internal combustion engines according to the present disclosure contains a molybdenum-based antioxidant, the mass of molybdenum relative to the total mass of the lubricating oil composition for internal combustion engines (hereinafter also simply referred to as the "specific molybdenum amount") is preferably 20 ppm or more and 800 ppm or less.

[0071] When the specific molybdenum content is 20 ppm or more, coking inside the gas engine can be further suppressed, and when it is 800 ppm or less, the life characteristics in high-temperature environments and in the presence of NOx can be maintained at the same level as when no molybdenum-based antioxidant is added.

[0072] From the viewpoint of improving wear resistance and coking resistance, the amount of molybdenum is preferably 0 ppm or more and 100 ppm or less.

[0073] The mass of molybdenum (specific molybdenum content) relative to the total mass of the lubricating oil composition for internal combustion engines is an analytical value obtained by ICP emission spectrometry in accordance with JPI-5S-38-92.

[0074] The content of the molybdenum-based antioxidant is preferably more than 0 mass% and not more than 5 mass%, more preferably 0.05 mass% or more and 2 mass% or less, and even more preferably 0.08 mass% or more and 1 mass% or less, relative to the total mass of the lubricating oil composition for internal combustion engines.

[0075] (anti-wear agent) The lubricating oil composition for internal combustion engines according to the present disclosure contains a phosphorus-based antiwear agent.

[0076] Phosphorus-based antiwear agents include zinc dialkyldithiophosphate (ZnDTP).

[0077] The zinc dialkyldithiophosphate is preferably, for example, a zinc dialkyldithiophosphate having a primary or secondary alkyl group. The primary or secondary alkyl group in the zinc dialkyldithiophosphate is preferably an alkyl group having 4 to 12 carbon atoms. That is, one suitable embodiment of the antiwear agent is at least one selected from zinc dialkyldithiophosphates having two identical or different alkyl groups selected from primary or secondary alkyl groups having 4 to 12 carbon atoms.

[0078] Specific examples of zinc dialkyldithiophosphates include, but are not limited to, zinc dialkyldithiophosphates having a primary alkyl group with 8 carbon atoms and zinc alkyldithiophosphates having a secondary alkyl group with 4 carbon atoms.

[0079] (viscosity index improver) The lubricating oil composition for internal combustion engines according to the present disclosure may contain an olefin copolymer type viscosity index improver.

[0080] Examples of olefin copolymer type viscosity index improvers include non-dispersant type viscosity index improvers and dispersant type viscosity index improvers described in JASO M355:2021.

[0081] Non-dispersant type viscosity index improvers include olefin copolymers such as ethylene-propylene copolymers.

[0082] Dispersant-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. Examples of the random copolymer of olefin and methacrylate include a random copolymer of ethylene-alkyl methacrylate, a random copolymer of propylene-alkyl methacrylate, and a random copolymer of isobutylene-alkyl methacrylate. Examples of the block copolymer of olefin and methacrylate include a block copolymer of ethylene-alkyl methacrylate, a block copolymer of propylene-alkyl methacrylate, and a block copolymer of isobutylene-alkyl methacrylate. Graft copolymers of polymethacrylate and olefin copolymer include polymers having a polymethacrylate main chain and an olefin copolymer side chain.

[0083] When the olefin copolymer serving as a viscosity index improver is an alkylated derivative having a side chain alkyl group, the side chain alkyl group preferably has 1 to 50 carbon atoms.

[0084] In the present disclosure, the olefin copolymer type viscosity index improver is preferably a polymer that contributes to improving the viscosity index and has a weight average molecular weight of 10,000 or more, and the content of the polymer is preferably 1 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 the olefin copolymer type viscosity index improver is a value measured by gel permeation chromatography and calculated using polystyrene as a standard.

[0085] 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 deteriorating the coking resistance. From this viewpoint, the content of the olefin copolymer type viscosity index improver is preferably 0% by mass or more and 5% by mass or less. However, when a diluent oil is included as a viscosity index improver, the content of the viscosity index improver referred to here refers to the content of the active ingredients including the diluent oil.

[0086] (Other additives) The lubricating oil composition for internal combustion engines according to the present disclosure may contain other additives as required. Other additives include pour point depressants, corrosion inhibitors, anti-foaming agents, and the like. Examples of pour point depressants include polyalkyl methacrylates having no polar group, copolymers thereof, and alkyl group derivatives thereof. The weight average molecular weight of the pour point depressant is determined by gel permeation chromatography and calculated using polystyrene as a standard. Examples of the corrosion inhibitor include thiadiazole derivatives, benzotriazole derivatives, and imidazole derivatives. Examples of the antifoaming agent include silicone oils such as polydimethylsiloxane, alkylated polydimethylsiloxane derivatives, and halogenated alkylated polydimethylsiloxane derivatives.

[0087] (Calcium content) The lubricating oil composition for internal combustion engines according to the present disclosure has a calcium (Ca) content of more than 0 ppm by mass and not more than 1500 ppm by mass, based on the total amount of the lubricating oil composition. The calcium contained in the lubricating oil composition is derived from a Ca-based metal detergent and the like. The calcium element content in the lubricating oil composition is, from the viewpoint of low ash content and ensuring long life and detergency, more than 0 ppm and not more than 1500 ppm, and preferably 1000 ppm or more and 1500 ppm or less, based on the total amount of the lubricating oil composition, by mass.

[0088] (Boron content derived from boron-based dispersants) The lubricating oil composition for internal combustion engines according to the present disclosure preferably contains 350 ppm by mass or more of boron derived from the boron-based dispersant, based on the total amount of the lubricating oil composition, which effectively improves sludge dispersancy at high temperatures.

[0089] (Physical Properties of Lubricating Oil Composition for Internal Combustion Engines) -Kinematic viscosity- The lubricating oil composition for internal combustion engines according to the present disclosure has a kinematic viscosity at 100°C of 7mm 2 / s or more 22mm 2 / s or less, and more preferably 11 mm 2 / s or more 18mm 2 / s or less, most preferably 12.5 mm 2 / s or more 16.3mm 2 / s or less.

[0090] The kinematic viscosity at 100°C of the lubricating oil composition for internal combustion engines is measured in accordance with JIS K2283 (2000).

[0091] -Sulfated ash content- The sulfated ash content of the lubricating oil composition for internal combustion engines is preferably 0.1 to 1.0 mass%, more preferably 0.3 to 0.8 mass%, and even more preferably 0.5 to 0.7 mass%. The amount of sulfated ash is measured by a method in accordance with JIS K2272 (1998). If the sulfated ash content is high, deposits on the piston head tend to interfere with normal fuel use, so it is desirable to keep it low within a range that does not significantly reduce base number retention, which is an indicator of life characteristics.

[0092] (Application) The lubricating oil composition for internal combustion engines according to the present disclosure is preferably used as a lubricating oil for gas engines that use gases such as hydrogen, autogas, and natural gas as fuel. Among gas engines, it is preferable to use it as a lubricant for gas engines, hydrogen engines, or dual-fuel engines for ships used in total energy systems (systems that use gas as fuel, gas engines, turbines, etc. to generate electricity, power, etc., and utilize the exhaust heat generated at the same time). Gas engines, hydrogen engines, and dual-fuel engines for ships used in total energy systems tend to have higher concentrations of NOx in their blow-by gases than other gas engines, which makes them more susceptible to coking.

[0093] The lubricating oil composition for internal combustion engines according to the present disclosure suppresses the occurrence of coking, and is therefore suitable for hydrogen engines and dual-fuel marine engines.

[0094] (Method of manufacturing a lubricating oil composition for internal combustion engines) There are no particular limitations on the method for producing the lubricating oil composition for internal combustion engines according to the present disclosure, and it is sufficient to appropriately mix a base oil belonging to Group III, a Ca-based metal-based detergent, a boron-based dispersant, an antioxidant, a phosphorus-based antiwear agent, and an olefin copolymer-type viscosity index improver, and further other additives as needed. The order of mixing the base oil belonging to Group III, the Ca-based metal-based detergent, the boron-based dispersant, the antioxidant, the phosphorus-based antiwear agent, the olefin copolymer type viscosity index improver, and other additives is not particularly limited, and they may be mixed sequentially with the base oil. [Example]

[0095] Examples of lubricating oil compositions for internal combustion engines according to the present disclosure will be described below, but the present disclosure is not limited to these examples in any way.

[0096] <Examples 1 to 5 and Comparative Examples 1 to 9> The base oil and additives were mixed in the blending ratios (mass %) shown in Table 1 below, and dissolved and dispersed at 60°C to prepare lubricating oil compositions for internal combustion engines.

[0097] <Evaluation> The lubricating oil compositions for internal combustion engines thus obtained were each subjected to the following evaluations, the results of which are shown in Table 1.

[0098] (ISOT test) An oxidation stability test was conducted on lubricating oil compositions for internal combustion engines in accordance with JIS K 2514-1 (2013). Copper and steel catalysts were added to 250 mL of each gas engine oil composition, and the test was conducted at 165.5°C, 1300 rpm (revolutions per minute, the same applies hereinafter), and for 72 hours. The ISOT test was conducted to obtain deteriorated oil, and the results of the ISOT test are not shown in Table 1.

[0099] (Panel Coking Test (PCT)) Using 250 mL of lubricating oil compositions for internal combustion engines (new oil and aged oil), tests were conducted using a panel coking tester manufactured by Rigo Co., Ltd., with a test time of 3 hours (15 seconds of splash operation, 45 seconds of rest × 180 cycles) on aluminum test panels (A2024P), a panel temperature of 320°C, and an oil temperature of 110°C. The panel masses were measured before and after the test, and the difference was taken as the amount of coking. Lubricating oil compositions for internal combustion engines with a coking amount of 20.0 mg or less for new oil and 30.0 mg or less for aged oil (acceptable standard) were evaluated as having excellent coking resistance. The deteriorated oil used was oil that had been in the ISOT test for 72 hours.

[0100] (Steam emulsification test) A steam emulsification test of internal combustion engine lubricating oil compositions was conducted for 72 hours. 50 mL of the internal combustion engine lubricating oil composition (new oil) was transferred to a glass container, and steam was blown into each glass container for 1 minute at a rate of 5.0 mL / min. The amount of highly viscous sludge (mL) remaining after 72 hours was measured. Lubricating oil compositions for internal combustion engines with an amount of highly viscous sludge of less than 10 mL (acceptable standard) were evaluated as having excellent steam emulsification properties.

[0101] <Physical properties> (Kinematic viscosity at 100℃) The kinematic viscosity at 100°C of the lubricating oil compositions for internal combustion engines was measured in accordance with ASTM D 7042.

[0102] [Table 1]

[0103] Details of the abbreviations in Table 1 are given below.

[0104] (base oil) Base oil A: A base oil that belongs to API Group III (Gr.III) and has the following general properties: Kinematic viscosity (100℃): 7.6mm 2 / s, viscosity index: 130, flash point: 240℃ or higher Base oil B: Base oil belonging to API Group IV and exhibiting the following general properties: Kinematic viscosity (100℃): 303mm 2 / s, viscosity index: 241, flash point: 286℃ or higher

[0105] (Ca-containing detergent) Calcium-containing detergent A Calcium salicylate: Base number measured according to JIS K2501 (2003) is 228 mg KOH / g, calcium content is 8.0 mass% Calcium-containing detergent B Calcium salicylate: Base number measured according to JIS K2501 (2003) is 58.8 mg KOH / g, calcium content is 2.3 mass%

[0106] (B-containing dispersant) Succinimide: boron content 0.87% by mass, nitrogen content 1.7% by mass, base number 33 mg KOH / g, weight average molecular weight 5500 g / mol

[0107] (antioxidant) Phenolic antioxidant: density 0.97g / cm 3 (20°C), flash point 152°C, boiling point 240°C, phenolic compound (octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamate) classified as CAS No. 125643-61-0 Amine antioxidant: Density 0.97g / cm 3 An aromatic amine compound classified as CAS No. 68411-46-1, which has a kinematic viscosity of 401 cSt at 40°C, a flash point of 154°C, basic nitrogen of 4.5%, and a base number of 180 mg KOH / g, and an aromatic amine compound classified as CAS No. 68259-36-9, which has a flash point of 215°C, were used in combination. Molybdenum antioxidant: A mixture of amide-type molybdenum compounds and ester-type molybdenum compounds. Density: 1.08 g / cm 3 (15°C), kinematic viscosity at 100°C of 55 cSt, flash point of 193°C, nitrogen content of 2.8 mass%, molybdenum content of 7.9 mass%, and a mixture of a compound represented by general formula (1) in which R1 is an alkyl group having 3 to 16 carbon atoms and a compound represented by general formula (2) in which R2 is an alkyl group having 3 to 16 carbon atoms.

[0108] (phosphorus-based anti-wear agent) ZnDTP: A zinc dialkyldithiophosphate compound with primary and secondary alkyl chains and a phosphorus content of 8.8%

[0109] (viscosity index improver) Viscosity index improver A: Density 0.85g / cm 3 (15°C), kinematic viscosity at 100°C of 2000cSt, flash point of 295°C, and weight average molecular weight of 15,000. Viscosity index improver C: Density 0.88g / cm 3(15°C), kinematic viscosity at 100°C of 2344 cSt, flash point of 220°C, and weight-average molecular weight of 150,000. The viscosity index improver content in Table 1 is the content of the diluent oil containing the viscosity index improver.

[0110] (others) Corrosion inhibitors, antifoaming agents, etc. Specifically, they are as follows: Silicone-based defoaming agent (density 0.97g / cm 3 (25℃), flash point 350℃) Amine-based corrosion inhibitor (40°C kinematic viscosity 48cSt, acid value 120mgKOH / g)

[0111] The calcium (Ca), boron (B), and phosphorus (P) contents were measured by ICP atomic emission spectroscopy in accordance with JPI-5S-38-92. The calcium (Ca), boron (B), phosphorus (P), and molybdenum (Mo) contents are expressed in ppm by mass relative to the lubricating oil composition. The boron content (B) was determined by measuring the amount of boron in the boron-based dispersant and calculating the mass ppm relative to the lubricating oil composition.

[0112] As shown in Table 1, the lubricating oil compositions for internal combustion engines of the examples suppressed the amount of coking to a low level in both the new oil and the deteriorated oil, and also suppressed steam emulsification to a low level. On the other hand, the lubricating oil compositions for internal combustion engines of the comparative examples did not meet the pass criteria in either or both of the amount of coking and steam emulsification.

Claims

1. a base oil belonging to API Group III; a metal-based detergent containing calcium; a boron-based dispersant containing boron and nitrogen; one or more antioxidants selected from the group consisting of phenol-based antioxidants and amine-based antioxidants; A molybdenum-based antioxidant, a phosphorus-based antiwear agent; Contains the base number of the calcium-containing metallic detergent is 100 mgKOH / g or less, The content of calcium element in the lubricating oil composition is more than 0 ppm by mass and 1500 ppm by mass or less, based on the total amount of the lubricating oil composition. A lubricating oil composition for an internal combustion engine.

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

3. 2. The lubricating oil composition for internal combustion engines according to claim 1, wherein the content of elemental boron derived from the boron-based dispersant is 350 ppm by mass or more, based on the total amount of the lubricating oil composition.

4. 2. 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 from 1% by mass to 5.5% by mass.

5. 2. The lubricating oil composition for internal combustion engines according to claim 1, wherein the molybdenum-based antioxidant is at least one selected from the group consisting of an amide-based molybdenum compound, an ester-based molybdenum compound, a molybdate amine compound, molybdenum dithiocarbamate, and molybdenum dithiophosphate, and the content of molybdenum element derived from the molybdenum-based antioxidant is more than 0 ppm by mass and not more than 100 ppm by mass, based on the total amount of the lubricating oil composition.

6. 2. The lubricating oil composition for internal combustion engines according to claim 1, wherein the content of phosphorus element derived from the phosphorus-based antiwear agent is more than 0 ppm by mass and not more than 500 ppm by mass, based on the total amount of the lubricating oil composition.

7. The lubricating oil composition for internal combustion engines according to any one of claims 1 to 6, which is for use in gas engines.

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