JP7570284B2 - Lubricating oil composition for internal combustion engines - Google Patents

Description

The present invention relates to a lubricating oil composition for internal combustion engines.

Since their invention, internal combustion engines have been the power source for various means of transportation for many years. In recent years, the fuel efficiency required of internal combustion engines has been increasing, and to meet this demand, high fuel efficiency performance is also required of lubricating oils for internal combustion engines.

Among various means of transportation, automobiles are responsible for much of land transportation, and improving their fuel efficiency has attracted great interest. In order to further improve the fuel efficiency of automobiles, hybrid automobiles equipped with a power unit combining an internal combustion engine and an electric motor have been proposed and have been commercially successful. Hybrid automobiles are classified into two types: series hybrid automobiles, in which only the electric motor is mechanically connected to the drive system and the automobile always runs on the output of the electric motor, and the internal combustion engine is operated to maintain a specified rotation speed that is the most efficient in order to generate electricity solely for driving the electric motor, and parallel hybrid automobiles, in which both the internal combustion engine and the electric motor are mechanically connected to the drive system and the automobile runs while appropriately allocating or switching the output load of the internal combustion engine and the electric motor according to the speed. Internal combustion engines have a most efficient rotation speed, and the lower the rotation speed, the lower the torque. Electric motors have high torque at low rotation speeds, but the higher the rotation speed, the lower the efficiency. With a parallel hybrid vehicle, the internal combustion engine and the electric motor can compensate for each other's shortcomings, making it possible to improve fuel efficiency over the entire speed range, from low to high.

JP 2015-196696 A International Publication No. 2014/136973 JP 2016-196667 A International Publication No. 2016/152679 International Publication No. 2014/136970 JP 2019-089938 A JP 2008-144019 A JP 2017-226793 A JP 2016-148004 A JP 2013-170217 A International Publication No. 2014/017557 International Publication No. 2014/017559

However, in hybrid vehicles, particularly parallel hybrid vehicles, the internal combustion engine may start and stop frequently. In such an operating mode, the engine oil does not reach a sufficiently high temperature, so moisture generated by the combustion of hydrocarbon fuel is likely to condense inside the internal combustion engine and accumulate in the engine oil. In addition, when there is a large temperature difference between the high-temperature and low-temperature parts of the engine, there is a concern that moisture will condense inside the internal combustion engine and accumulate in the engine oil, even in internal combustion engines of automobiles that are not hybrid vehicles and that generate driving force solely from the internal combustion engine.

The inventors have found that engine oil contaminated with water is prone to poor low-temperature fluidity. When the low-temperature viscosity of engine oil increases, the resistance to stirring of the engine oil increases under low-temperature conditions, leading to poor fuel economy.

The objective of the present invention is to provide a lubricating oil composition for internal combustion engines that can reduce the deterioration of low-temperature fluidity when water is mixed in.

The present invention includes the following embodiments [1] to [8].
[1] (A) a lubricating base oil consisting of one or more mineral base oils or one or more synthetic base oils or a combination thereof and having a kinematic viscosity at 100°C of 3.8 to 4.6 ^mm2 /s;
(B) a metal-based detergent including one or more metal salicylate detergents is present in an amount of 1,000 to 2,000 ppm by mass in terms of metal amount based on the total amount of the composition, and the amount of total salicylate soap groups per 1 kg of the composition is 10 mmol/kg or more;
(C) one or more comb-shaped poly(meth)acrylates having a weight average molecular weight of 350,000 to 1,000,000 and a polydispersity index of 4.0 or less, in an amount of 1.0 to 4.0 mass% based on the total mass of the composition as a resin content;
(D) a succinimide dispersant comprising one or more unmodified succinimide dispersants or one or more boric acid modified succinimide dispersants, or a combination thereof, wherein the ratio of the total nitrogen content of the unmodified succinimide dispersants and the boric acid modified succinimide dispersants to the total nitrogen content of the succinimide dispersant is 70 mass% or more, and the succinimide dispersant is 100 to 1000 mass ppm in terms of nitrogen content based on the total amount of the composition;
A lubricating oil composition for internal combustion engines, characterized in that the HTHS viscosity at 150°C is 2.25 mPa·s or more and less than 2.55 mPa·s.

In this specification, "kinematic viscosity at 100°C" means the kinematic viscosity at 100°C as specified in ASTM D445. "(Meth)acrylate" means "acrylate and/or methacrylate." "HTHS viscosity at 150°C" means the high temperature high shear viscosity at 150°C as specified in ASTM D4683.

[2] The lubricating oil composition according to [1], wherein the (A) lubricating base oil is one or more API base oil group III base oils, or one or more API base oil group IV base oils, or a combination thereof.

[3] The lubricating oil composition according to [1] or [2], in which the content of the component (B) is 15 mmol/kg or more in terms of the amount of total soap groups per kg of the composition.

[4] A lubricating oil composition according to any one of [1] to [3], in which the proportion of all salicylate soap groups in the total soap groups of component (B) is 50 mol% or more.

[5] The lubricating oil composition according to any one of [1] to [4], wherein the weight average molecular weight of the (C) component is more than 400,000 and not more than 1,000,000.

[6] The lubricating oil composition according to any one of [1] to [5], in which the mass ratio (B/N) of the total boron content (B) to the total nitrogen content (N) of the (D) component is 0 to 0.60.

[7] The lubricating oil composition according to any one of [1] to [6], in which the component (D) is a condensation reaction product of an alkyl or alkenyl succinic acid or anhydride thereof having an alkyl or alkenyl group having 40 to 400 carbon atoms and a polyamine, or a modified product thereof, or a combination thereof.

[8] A lubricating oil composition according to any one of [1] to [7], which is used to lubricate the internal combustion engine of a hybrid vehicle.

The lubricating oil composition for internal combustion engines of the present invention can reduce the deterioration of low-temperature fluidity when water is mixed in.

The present invention will be described in detail below. Unless otherwise specified, the expression "A to B" for the numerical values A and B means "A or more and B or less". In such an expression, when a unit is added only to the numerical value B, the unit is also applied to the numerical value A. Furthermore, the words "or" and "or" mean a logical sum unless otherwise specified. In this specification, the expression "E ₁ and/or E ₂ " for the elements E ₁ and E ₂ means "E ₁ or E ₂ , or a combination thereof", and the expression "E ₁ , ..., E N-1, and/or E _N " for the elements E ₁ , ..., E _N-1 , or E _N , or a combination thereof (N is an integer of 3 or more) means "E ₁ , ..., E _N-1 , or E _N , or a combination thereof". In addition, in this specification, "alkaline earth metal" also includes magnesium.

In this specification, unless otherwise specified, the contents of calcium, magnesium, zinc, phosphorus, sulfur, boron, barium, and molybdenum in the oil are measured by inductively coupled plasma atomic emission spectrometry (intensity ratio method (internal standard method)) in accordance with JIS K0116. The content of nitrogen in the oil is measured by a chemiluminescence method in accordance with JIS K2609. In addition, in this specification, the "weight average molecular weight" and "number average molecular weight" of a polymer mean the weight average molecular weight and number average molecular weight in terms of standard polystyrene measured by gel permeation chromatography (GPC). The measurement conditions for GPC are as follows.
[GPC measurement conditions]
Apparatus: ACQUITY (registered trademark) APC UV RI system manufactured by Waters Corporation Column: From the upstream side, two ACQUITY (registered trademark) APC XT900A manufactured by Waters Corporation (gel particle size 2.5 μm, column size (inner diameter x length) 4.6 mm x 150 mm) and one ACQUITY (registered trademark) APC XT200A manufactured by Waters Corporation (gel particle size 2.5 μm, column size (inner diameter x length) 4.6 mm x 150 mm) are connected in series. Column temperature: 40 ° C.
Sample solution: tetrahydrofuran solution with a sample concentration of 1.0% by mass. Solution injection amount: 20.0 μL.
Detector: Differential refractive index detector Reference material: Standard polystyrene (Agilent EasiCal (registered trademark) PS-1 manufactured by Agilent Technologies) 8 points (molecular weight: 2698000, 597500, 290300, 133500, 70500, 30230, 9590, 2970)
If the weight average molecular weight measured under the above conditions is less than 10,000, the column and the reference substance are changed to the following conditions and the measurement is repeated.
Columns: From the upstream side, one Waters Corporation ACQUITY (registered trademark) APC XT125A (gel particle size 2.5 μm, column size (inner diameter x length) 4.6 mm x 150 mm) and two Waters Corporation ACQUITY (registered trademark) APC XT45A (gel particle size 1.7 μm, column size (inner diameter x length) 4.6 mm x 150 mm) connected in series. Reference substance: Standard polystyrene (Agilent Technologies Agilent EasiCal (registered trademark) PS-1) 10 points (molecular weight: 30230, 9590, 2970, 890, 786, 682, 578, 474, 370, 266)

<(A) Lubricating base oil>
The lubricating oil composition for internal combustion engines of the present invention (hereinafter sometimes simply referred to as the "lubricating oil composition" or "composition") comprises a major amount of a lubricating base oil and one or more components other than the base oil. In the lubricating oil composition of the present invention, the lubricating base oil comprises one or more mineral base oils or one or more synthetic base oils or a combination thereof, A lubricating base oil (hereinafter sometimes referred to as "component (A)") having a kinetic viscosity of 3.8 to 4.6 mm ² /s at 20°C is used.

As the lubricant base oil, one or more mineral base oils, or one or more synthetic base oils, or a mixture thereof can be used. In one embodiment, as the lubricant base oil, Group I base oil (hereinafter sometimes referred to as "API Group I base oil"), Group II base oil (hereinafter sometimes referred to as "API Group II base oil"), Group III base oil (hereinafter sometimes referred to as "API Group III base oil"), Group IV base oil (hereinafter sometimes referred to as "API Group IV base oil"), or Group V base oil (hereinafter sometimes referred to as "API Group V base oil"), or a mixture thereof, of the API base oil classification can be used. API Group I base oil is a mineral base oil having a sulfur content of more than 0.03 mass% and/or a saturate content of less than 90 mass%, and a viscosity index of 80 to less than 120. API Group II base oil is a mineral oil-based base oil having a sulfur content of 0.03 mass% or less, a saturate content of 90 mass% or more, and a viscosity index of 80 or more and less than 120. API Group III base oil is a mineral oil-based base oil having a sulfur content of 0.03 mass% or less, a saturate content of 90 mass% or more, and a viscosity index of 120 or more. API Group IV base oil is a poly-α-olefin base oil. API Group V base oil is a base oil other than the above Groups I to IV, and a preferred example of such a base oil is an ester-based base oil. In this specification, the viscosity index means a viscosity index measured in accordance with JIS K 2283-2000. In this specification, the "sulfur content in the lubricating base oil" is measured in accordance with JIS K 2541-2003. In this specification, the "saturate content in the lubricating base oil" means a value measured in accordance with ASTM D 2007-93.

In one embodiment, the (A) component is preferably one or more API Group II base oils, or one or more API Group III base oils, or one or more API Group IV base oils, or a combination thereof, and more preferably one or more API Group III base oils, or one or more API Group IV base oils, or a combination thereof.

Examples of mineral oil base oils include paraffinic mineral oil base oils, normal paraffinic mineral oil base oils, isoparaffinic mineral oil base oils, and mixtures thereof, which are obtained by refining the lubricating oil fraction obtained by atmospheric distillation and/or vacuum distillation of crude oil through one or a combination of two or more refining processes selected from the group consisting of solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing, and clay treatment.

Preferred examples of mineral base oils include base oils obtained by using the following base oils (1) to (8) as raw materials, refining the raw material oil and/or a lubricating oil fraction recovered from the raw material oil by a predetermined refining method, and recovering the lubricating oil fraction.
(1) Distillate oil obtained by atmospheric distillation of paraffinic and/or mixed crude oils (2) Distillate oil obtained by vacuum distillation of residual oil obtained by atmospheric distillation of paraffinic and/or mixed crude oils (WVGO)
(3) Wax obtained by a lubricant dewaxing process (slack wax, etc.) and/or synthetic wax obtained by a Fischer-Tropsch (FT) process, etc. (FT wax, gas-to-liquid (GTL) wax, etc.)
(4) One base oil selected from base oils (1) to (3), or a mixed oil of two or more selected from base oils (1) to (3), or a mild hydrocracking treated oil thereof, or a mixed oil thereof; (5) A mixed oil of two or more selected from base oils (1) to (4); (6) A deasphalted oil (DAO) of base oil (1), (2), (3), (4) or (5);
(7) Mild hydrocracking treated oil (MHC) of base oil (6)
(8) A mixed oil of two or more types selected from the base oils (1) to (7).

The above-mentioned specified refining methods are preferably hydrorefining such as hydrocracking and hydrofinishing; solvent refining such as furfural solvent extraction; dewaxing such as solvent dewaxing and contact dewaxing; clay refining using acid clay or activated clay; and chemical (acid or alkali) washing such as sulfuric acid washing and caustic soda washing. One of these refining methods may be carried out alone, or two or more may be combined. When two or more refining methods are combined, the order is not particularly limited and can be selected as appropriate.

As the mineral base oil, the following base oil (9) or (10) obtained by subjecting a lubricating oil fraction recovered from the base oil selected from the above base oils (1) to (8) or a prescribed treatment to the base oil selected from the above base oils is particularly preferred.
(9) A hydrocracked base oil obtained by hydrocracking a base oil selected from the above base oils (1) to (8) or a lubricating oil fraction recovered from the base oil, and subjecting the product or the lubricating oil fraction recovered from the product by distillation or the like to a dewaxing treatment such as solvent dewaxing or catalytic dewaxing, or distilling the dewaxing treatment after the dewaxing treatment. (10) A hydroisomerized base oil obtained by hydroisomerizing a base oil selected from the above base oils (1) to (8) or a lubricating oil fraction recovered from the base oil, and subjecting the product or the lubricating oil fraction recovered from the product by distillation or the like to a dewaxing treatment such as solvent dewaxing or catalytic dewaxing, or distilling the dewaxing treatment after the dewaxing treatment. As the dewaxing process, a base oil produced through a catalytic dewaxing process is preferred.

When obtaining the lubricating base oil (9) or (10) above, a solvent refining process and/or a hydrofinishing process may be further carried out at an appropriate stage, if necessary.

The catalyst used for the hydrocracking and hydroisomerization is not particularly limited, but a hydrocracking catalyst in which a metal having hydrogenation ability (e.g., one or more metals of Group VIa or Group VIII of the periodic table) is supported on a carrier made of a composite oxide having cracking activity (e.g., silica alumina, alumina boria, silica zirconia, etc.) or a combination of one or more of the composite oxides bound with a binder, or a hydroisomerization catalyst in which a metal having hydrogenation ability including at least one metal of Group VIII of the periodic table is supported on a carrier containing zeolite (e.g., ZSM-5, zeolite beta, SAPO-11, etc.) is supported. The hydrocracking catalyst and the hydroisomerization catalyst may be used in combination by stacking or mixing.

The reaction conditions for hydrocracking and hydroisomerization are not particularly limited, but preferably are a hydrogen partial pressure of 0.1 to 20 MPa, an average reaction temperature of 150 to 450° C., an LHSV of 0.1 to 3.0 hr ⁻¹ , and a hydrogen/oil ratio of 50 to 20,000 scf/b.

The % _Cp of the mineral oil base oil is preferably 70 or more, more preferably 75 or more, from the viewpoint of improving the viscosity-temperature characteristics and fuel economy of the composition, and is preferably 99 or less, more preferably 95 or less, even more preferably 94 or less, from the viewpoint of improving the solubility of additives and further reducing deterioration of low-temperature fluidity when mixed with water, and in one embodiment, it may be 70 to 99, or 70 to 95, or 75 to 95, or 75 to 94.

From the viewpoint of improving the viscosity-temperature characteristics and fuel economy of the composition, the % _CA of the mineral base oil is preferably 2 or less, more preferably 1 or less, further preferably 0.8 or less, and particularly preferably 0.5 or less.

The % C _N of the mineral oil base oil is preferably 1 or more, more preferably 4 or more, from the viewpoint of increasing the solubility of the additives and further reducing the deterioration of low-temperature fluidity when mixed with water, and is preferably 30 or less, more preferably 25 or less, from the viewpoint of improving the viscosity-temperature characteristics and fuel economy of the composition, and in one embodiment, it may be 1 to 30, or 4 to 25.

In this specification, %C _P , %C _N and %C _A respectively mean the percentage of paraffin carbon number to the total carbon number, the percentage of naphthene carbon number to the total carbon number and the percentage of aromatic carbon number to the total carbon number, which are determined by a method (nd-M ring analysis) in accordance with ASTM D 3238-85. In other words, the preferred ranges of %C _P , %C _N and %C _A described above are based on the values determined by the above method, and even for example, even in the case of a lubricating base oil that does not contain naphthene content, the %C _N determined by the above method may show a value exceeding 0.

The content of saturated matter in the mineral oil-based base oil is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more, based on the total amount of the base oil, from the viewpoint of improving the viscosity-temperature characteristics of the composition. In this specification, saturated matter refers to a value measured in accordance with ASTM D 2007-93.

In addition, a similar method that can obtain similar results can be used to separate the saturates. For example, in addition to the method described in ASTM D 2007-93, the method described in ASTM D 2425-93, the method described in ASTM D 2549-91, a method using high performance liquid chromatography (HPLC), or an improvement of these methods can be used.

The aromatic content in the mineral oil-based base oil is preferably 0 to 10 mass%, more preferably 0 to 5 mass%, particularly preferably 0 to 1 mass%, based on the total amount of the base oil, and in one embodiment, may be 0.1 mass% or more. By having the aromatic content be equal to or less than the above upper limit, it is possible to improve the low-temperature viscosity characteristics and viscosity-temperature characteristics in a new oil state, further improve fuel efficiency, and further reduce the evaporation loss of the lubricating oil, thereby further reducing the consumption of the lubricating oil. In addition, when an additive is blended into the lubricating oil base oil, the effect of the additive can be effectively exerted. In addition, the lubricating oil base oil may not contain aromatic content, but by having the aromatic content be equal to or more than the above lower limit, the solubility of the additive can be further increased.

In this specification, the aromatic content refers to a value measured in accordance with ASTM D 2007-93. Aromatic content typically includes alkylbenzenes, alkylnaphthalenes, anthracene, phenanthrene and their alkylated derivatives, compounds with 4 or more condensed benzene rings, pyridines, quinolines, phenols, naphthols and other aromatic compounds with heteroatoms.

Examples of synthetic base oils include poly-α-olefins and their hydrogenated products, isobutene oligomers and their hydrogenated products, isoparaffins, alkylbenzenes, alkylnaphthalenes, diesters (ditridecyl glutarate, bis-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, bis-2-ethylhexyl sebacate, etc.), polyol esters (trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate, etc.), polyoxyalkylene glycols, dialkyl diphenyl ethers, polyphenyl ethers, and mixtures thereof. Of these, poly-α-olefin base oils are preferred. Typical examples of poly-α-olefin base oils include oligomers or co-oligomers of α-olefins having 2 to 32 carbon atoms, preferably 6 to 16 carbon atoms (1-octene oligomer, decene oligomer, ethylene-propylene co-oligomer, etc.) and their hydrogenated products.

The method for producing poly-α-olefins is not particularly limited, but an example is a method in which α-olefins are polymerized in the presence of a polymerization catalyst, such as a catalyst containing a complex of aluminum trichloride or boron trifluoride with water, an alcohol (ethanol, propanol, butanol, etc.), a carboxylic acid, or an ester.

The kinetic viscosity at 100°C of the lubricating base oil (total base oil) is 3.6 mm ^{2 /s or more, preferably 3.8 mm 2 /} s or more, from the viewpoint of improving wear resistance and seizure resistance and reducing evaporation loss of the lubricating oil composition to reduce lubricating oil consumption, and is 4.6 mm ² /s or less, preferably 4.4 mm ² /s or less, from the viewpoint of reducing deterioration of low-temperature fluidity when water is mixed in and improving fuel economy, and in one embodiment it may be 3.6 to 4.6 mm ² /s, or 3.6 to 4.4 mm ² /s, or 3.8 to 4.4 mm ² /s.

The kinetic viscosity at 40°C of the lubricating base oil (total base oil) is preferably 16.0 mm 2 /s or more, more preferably 16.3 mm ² /s or more, even more preferably 16.6 mm ² /s or more, and particularly preferably 16.9 mm ² /s or more, from the viewpoints of improving the wear resistance and seizure resistance, and of reducing the evaporation loss of the lubricating oil composition and thereby reducing the consumption of the lubricating oil; and from the viewpoints of improving the fuel economy and the low-temperature viscosity characteristics of the composition in a new oil state, and of further reducing the ^{deterioration} of the low-temperature fluidity when water is mixed in, the kinetic viscosity is preferably 25.0 mm ² /s or less, more preferably 23.0 mm ² /s or less, even more preferably 22.0 mm ² /s or less, and particularly preferably 21.0 ^mm 2 /s or less; and in one embodiment, it is 16.0 to 25.0 mm ² /s, or 16.3 to 23.0 mm ² /s, or 16.6 to 22.0 mm ^{2 /s} . In this specification, the "kinematic viscosity ^at 40°C" refers to the kinematic viscosity at 40°C specified in ASTM D445.

The viscosity index of the lubricating base oil (all base oils) is preferably 100 or more, more preferably 105 or more, even more preferably 110 or more, particularly preferably 115 or more, and most preferably 120 or more, from the viewpoints of improving the viscosity-temperature characteristics, wear resistance, and fuel economy of the composition, reducing the evaporation loss of the composition and reducing the consumption of lubricating oil, and further reducing the deterioration of low-temperature fluidity when water is mixed in. In this specification, the viscosity index means the viscosity index measured in accordance with JIS K 2283-2000.

The pour point of the lubricating base oil (all base oils) is preferably -10°C or lower, more preferably -12.5°C or lower, and even more preferably -15°C or lower. Having a pour point below the upper limit makes it possible to improve the low-temperature fluidity of the entire lubricating oil composition in a fresh oil state. In this specification, pour point refers to the pour point measured in accordance with JIS K 2269-1987.

The sulfur content in the base oil depends on the sulfur content of the raw material. For example, when a raw material that is substantially free of sulfur, such as a synthetic wax component obtained by the Fischer-Tropsch reaction, is used, a base oil that is substantially free of sulfur can be obtained. When a raw material that contains sulfur, such as slack wax obtained in the base oil refining process or microwax obtained in the refined wax process, is used, the sulfur content in the resulting base oil is usually 100 ppm by mass or more. From the viewpoint of reducing the sulfur content of the lubricating oil composition, the sulfur content in the lubricating oil base oil (total base oil) is preferably 100 ppm by mass or less, more preferably 50 ppm by mass or less, even more preferably 10 ppm by mass or less, and particularly preferably 5 ppm by mass or less. In this specification, the "sulfur content" in the base oil is measured in accordance with JIS K 2541-2003.

The nitrogen content in the lubricating base oil (total base oil) is preferably 10 ppm by mass or less, more preferably 5 ppm by mass or less, and even more preferably 3 ppm by mass or less. In this specification, nitrogen content means the nitrogen content measured in accordance with JIS K 2609-1998.

The lubricating base oil may be composed of a single base oil component or may contain multiple base oil components, so long as the base oil as a whole (total base oil) has a kinematic viscosity at 100° C. of 3.8 to 4.6 mm ² /s.

The content of lubricating base oil (total base oil) in the lubricating oil composition is usually 75 to 95 mass % based on the total amount of the composition, and preferably 85 to 95 mass %.

<(B): Metal-Based Detergent>
The lubricating oil composition of the present invention contains, as a metallic detergent, a metallic detergent (hereinafter sometimes referred to as "component (B)") containing one or more metallic salicylate detergents in an amount of 1000 to 2000 ppm by mass based on the total amount of the composition, and in an amount of 10 mmol/kg or more of total salicylate soap groups per kg of the composition. Examples of metallic detergents include salicylate-based detergents, sulfonate-based detergents, and phenate-based detergents. In addition, component (B) may contain only one type of metallic detergent, or may contain two or more types of metallic detergents.

Preferred examples of salicylate-based detergents include metal salicylates or their basic or overbased salts. Preferred examples of metal salicylates include alkali or alkaline earth metal salicylates represented by the following general formula (1):

In the general formula (1), R ¹ independently represents an alkyl or alkenyl group having 14 to 30 carbon atoms, M represents an alkali metal or an alkaline earth metal, a represents 1 or 2, and n represents 1 or 2 corresponding to the valence of M. When M is an alkali metal, n is 1, and when M is an alkaline earth metal, n is 2. As the alkali metal, sodium or potassium is preferred, and as the alkaline earth metal, calcium or magnesium is preferred. a is preferably 1. When a=2, R ¹ may be a combination of different groups.

A preferred embodiment of the salicylate detergent is an alkaline earth metal salicylate in which a=1 in the above general formula (1), or a basic salt or an overbased salt thereof.

The method for producing the alkali or alkaline earth metal salicylates is not particularly limited, and known methods for producing monoalkyl salicylates can be used. For example, a monoalkyl salicylic acid obtained by alkylating phenol as a starting material with an olefin and then carboxylating with carbon dioxide or the like, or a monoalkyl salicylic acid obtained by alkylating salicylic acid as a starting material with an equivalent amount of the above olefin, can be reacted with a metal base such as an oxide or hydroxide of an alkali or alkaline earth metal to obtain an alkali or alkaline earth metal salicylate. In another embodiment, the alkaline earth metal salicylate can be obtained by first converting these monoalkyl salicylates into alkali metal salts such as sodium salts or potassium salts, and then metal exchanging them with the alkaline earth metal salt.

Preferred examples of sulfonate detergents include alkali or alkaline earth metal salts of alkyl aromatic sulfonic acids obtained by sulfonating an alkyl aromatic compound, or basic or overbased salts thereof, more preferably alkaline earth metal salts or basic or overbased salts thereof. The weight average molecular weight of the alkyl aromatic compound is preferably 400 to 1500, more preferably 700 to 1300.
The alkali metal is preferably sodium or potassium, and the alkaline earth metal is preferably calcium or magnesium. Examples of alkyl aromatic sulfonic acids include so-called petroleum sulfonic acids and synthetic sulfonic acids. Examples of petroleum sulfonic acids include sulfonated alkyl aromatic compounds in the lubricating oil fraction of mineral oil, and mahogany acid, which is a by-product during the production of white oil. An example of a synthetic sulfonic acid is a sulfonated alkyl benzene having a linear or branched alkyl group obtained by recovering a by-product in an alkyl benzene production plant that is a raw material for detergents, or by alkylating benzene with a polyolefin. Another example of a synthetic sulfonic acid is a sulfonated alkyl naphthalene such as dinonyl naphthalene. The sulfonating agent used for sulfonating these alkyl aromatic compounds is not particularly limited, and for example, fuming sulfuric acid or sulfuric anhydride can be used.

Preferred examples of phenate detergents include overbased salts of alkali or alkaline earth metal salts of compounds having the structure shown in the following general formula (2), more preferably overbased salts of alkaline earth metal salts. The alkali metal is preferably sodium or potassium, and the alkaline earth metal is preferably calcium or magnesium.

In general formula (2), ^R2 represents a linear or branched, saturated or unsaturated alkyl or alkenyl group having 6 to 21 carbon atoms, m represents the degree of polymerization and is an integer from 1 to 10, A represents a sulfide (-S-) group or a methylene ( _-CH2- ) group, and x represents an integer from 1 to 3. ^R2 may be a combination of two or more different groups.

The number of carbon atoms in ^R2 in general formula (2) is preferably 9 or more from the viewpoint of increasing solubility in the base oil, and is preferably 18 or less, more preferably 15 or less, from the viewpoint of ease of production. In one embodiment, it may be 9 to 18, or 9 to 15.

The degree of polymerization m in general formula (2) is preferably 1 to 4.

The metallic detergent may be overbased with a carbonate (e.g., an alkali metal carbonate such as sodium carbonate or potassium carbonate, or an alkaline earth metal carbonate such as calcium carbonate or magnesium carbonate) or with a borate (e.g., an alkali metal borate such as sodium borate or potassium borate, or an alkaline earth metal borate such as calcium borate or magnesium borate).
The method for obtaining a metal-based detergent overbased with an alkali or alkaline earth metal carbonate is not particularly limited. For example, the metal-based detergent can be obtained by reacting a neutral salt of a metal-based detergent (e.g., an alkali or alkaline earth metal phenate, an alkali or alkaline earth metal sulfonate, an alkali or alkaline earth metal salicylate, etc.) with an alkali or alkaline earth metal base (e.g., an alkali or alkaline earth metal hydroxide, oxide, etc.) in the presence of carbon dioxide gas.
The method for obtaining a metal-based detergent overbased with an alkali or alkaline earth metal borate is not particularly limited, but it can be obtained by reacting a neutral salt of a metal-based detergent (e.g., an alkali or alkaline earth metal phenate, an alkali or alkaline earth metal sulfonate, an alkali or alkaline earth metal salicylate, etc.) with a base of an alkali or alkaline earth metal (e.g., an alkali or alkaline earth metal hydroxide, oxide, etc.) in the presence of boric acid or boric acid anhydride and optionally a borate. The boric acid may be orthoboric acid or a condensed boric acid (e.g., diboric acid, triboric acid, tetraboric acid, metaboric acid, etc.). As the borate, the sodium salt of these borates (when a sodium-based detergent overbased with a borate is obtained), the potassium salt (when a potassium-based detergent overbased with a borate is obtained), the calcium salt (when a calcium-based detergent overbased with a borate is obtained), or the magnesium salt (when a magnesium-based detergent overbased with a borate is obtained) can be preferably used. The borate may be a neutral salt or an acid salt. One type of boric acid and/or a borate may be used alone, or two or more types may be used in combination.

Component (B) comprises one or more metal salicylate detergents, preferably one or more alkaline earth metal salicylate detergents, more preferably one or more calcium or magnesium salicylate detergents. Component (B) preferably comprises one or more overbased calcium or magnesium salicylate detergents. The overbased calcium salicylate detergent may be overbased with calcium carbonate or may be overbased with calcium borate. The overbased magnesium salicylate detergent may also be overbased with magnesium carbonate or may be overbased with magnesium borate. In one embodiment, component (B) may further comprise, in addition to the metal salicylate detergent, an alkali or alkaline earth metal sulfonate detergent, or an alkali or alkaline earth metal phenate detergent, or a combination thereof. In one embodiment, component (B) may further contain, in addition to one or more metal salicylate detergents, a calcium or magnesium sulfonate detergent, or a calcium or magnesium phenate detergent, or a combination thereof. However, from the viewpoint of further reducing the deterioration of low-temperature fluidity when water is mixed, the proportion of all salicylate soap groups in all soap groups in component (B) is preferably 50 to 100 mol%, more preferably 60 to 100 mol%, even more preferably 70 to 100 mol%, particularly preferably 80 to 100 mol%, and in one embodiment may be 90 to 100 mol%, as the ratio of the substance amount (mol) of all soap groups in the salicylate detergent to the substance amount (mol) of all soap groups in component (B). From the same viewpoint, the ratio of the total salicylate soap groups to the total soap groups of component (B) is preferably 50 to 100 mass%, more preferably 60 to 100 mass%, even more preferably 70 to 100 mass%, particularly preferably 80 to 100 mass%, and in one embodiment may be 90 to 100 mass% as the ratio of the mass of all soap groups of the salicylate detergent, calculated as organic acid, to the mass of all soap groups of component (B), calculated as organic acid. In addition, in the field of lubricating oils, generally, as the metal-based detergent, an organic acid metal salt capable of forming micelles in a base oil (e.g., an alkali or alkaline earth metal alkyl salicylate, an alkali or alkaline earth metal alkyl benzene sulfonate, and an alkali or alkaline earth metal alkyl phenate, etc.), or a mixture of the organic acid metal salt and a basic metal salt (e.g., a hydroxide, carbonate, borate, etc. of the alkali or alkaline earth metal constituting the organic acid metal salt) is used. Such organic acids usually have at least one polar group (e.g., carboxyl group, sulfo group, phenolic hydroxyl group, etc.) having a Bronsted acidity capable of forming a salt with a metal base (typically a metal oxide and/or metal hydroxide) and at least one lipophilic group such as a linear or branched alkyl group (e.g., a linear or branched alkyl group having 6 or more carbon atoms, etc.) in one molecule. The soap group of a metal detergent means a conjugate base of an organic acid constituting the soap component of the metal detergent (e.g., an alkyl salicylate anion in a salicylate detergent, an alkyl benzene sulfonate anion in a sulfonate detergent, and an alkyl phenate anion in a phenate detergent). The substance amount of the soap group of a metal detergent is synonymous with the total amount of negative charges of the soap group. For example, in a metal salicylate represented by the above general formula (1), the total amount of negative charges per 1 mol of salicylate soap group is 1 mol. For example, in metal alkylbenzene sulfonates, the total amount of negative charges per 1 mol of sulfonate soap groups is 1 mol. For example, in metal alkyl phenates, the total amount of negative charges per 1 mol of phenate soap groups is 1 mol. For example, the phenolic compound represented by the above general formula (2) has m+1 phenolic hydroxy groups in one molecule that have Bronsted acidity capable of forming a salt with a metal base (typically a metal oxide and/or metal hydroxide). When all of the phenolic hydroxy groups form a metal salt, the total amount of negative charges is m+1 per molecule of the compound of general formula (2).

The metal content in component (B) can be, for example, 1.0 to 20 mass%, preferably 5.0 to 14 mass%.

The base number of the metal salicylate detergent may be, for example, preferably 150 to 350 mgKOH/g, more preferably 200 to 350 mgKOH/g, and particularly preferably 220 to 350 mgKOH/g. The base number of the metal sulfonate detergent may be, for example, 200 to 500 mgKOH/g, or 300 to 500 mgKOH/g, or 300 to 420 mgKOH/g. The base number of the metal phenate detergent may be, for example, 140 to 420 mgKOH/g, or 250 to 420 mgKOH/g, or 250 to 330 mgKOH/g. In this specification, the base number means the base number measured by the perchloric acid method in accordance with JIS K2501. Metal-based detergents are generally obtained by reaction in a diluent such as a solvent or a lubricating oil base oil. For this reason, metallic detergents are commercially distributed in a state diluted with a diluent such as a lubricating oil base oil. In this specification, the base number of a metallic detergent means the base number in a state including a diluent. Also, in this specification, the metal content of a metallic detergent means the metal content in a state including a diluent.

The metal ratio of the metal salicylate detergent is preferably 1.3 or more, more preferably 1.5 or more, even more preferably 1.7 or more, particularly preferably 2.5 or more, from the viewpoint of enhancing the cleaning performance and base number maintenance, and from the viewpoint of suppressing the ash content of the composition and improving the life of the exhaust gas aftertreatment device, it is preferably 7.0 or less, more preferably 5.5 or less, even more preferably 4.0 or less, and in one embodiment it may be 1.3 to 7.0, or 1.5 to 7.0, or 1.7 to 5.5, or 2.5 to 4.0. From the same viewpoint, the metal ratio of the metal sulfonate detergent is preferably 9.0 or more, or 11.0 or more, or 13.5 or more, and also preferably 35.0 or less, or 32.5 or less, or 28.0 or less, and in one embodiment it may be 9.0 to 35.0, or 11.0 to 32.5, or 13.5 to 28.0. In a similar respect, the metal ratio of the metal phenate detergent may be preferably 1.0 or more, or 2.0 or more, or 2.5 or more, and preferably 20 or less, or 15 or less, or 10 or less, and in one embodiment from 1.0 to 20, or from 2.0 to 15, or from 2.5 to 10.
In this specification, the metal ratio of a metal-based detergent is defined to be 1 when the metal-based detergent is a completely neutral salt, and is calculated according to the following formula:
Metal ratio = total amount of positive charges of all metal ions of a metal detergent (mol) / total amount of negative charges of all soap groups of a metal detergent (mol)
For example, there is 1 mol of positive charge per mol of alkali metal ion, and 2 mol of positive charge per mol of alkaline earth metal ion. The amount of negative charge on the soap group is as explained above.

The content of component (B) in the lubricating oil composition is 1000 ppm by mass or more, preferably 1100 ppm by mass or more, and in one embodiment 1200 ppm by mass or more, in terms of the metal amount based on the total amount of the composition, from the viewpoint of enhancing cleaning performance and base number maintenance, and from the viewpoint of suppressing an increase in ash in the composition and improving the life of the exhaust gas aftertreatment device, it is 2000 ppm by mass or less, preferably 1900 ppm by mass or less, and in one embodiment 1800 ppm by mass or less, and in one embodiment it may be 1000 to 2000 ppm by mass, or 1100 to 1900 ppm by mass, or 1200 to 1800 ppm by mass.

The content of component (B) in the lubricating oil composition is, in terms of the amount of substance of all salicylate soap groups per 1 kg of the composition, 10 mmol/kg or more, preferably 15 mmol/kg or more, and in one embodiment 18 mmol/kg or more, from the viewpoint of increasing the base number durability and reducing the deterioration of low-temperature fluidity when water is mixed in, and from the viewpoint of suppressing sludge, is preferably 70 mmol/kg or less, more preferably 60 mmol/kg or less, and in one embodiment 50 mmol/kg or less, and in one embodiment may be 10 to 70 mmol/kg, or 15 to 60 mmol/kg, or 18 to 50 mmol/kg. In this specification, the unit "mmol" means 10 ^-3 mol.

The content of component (B) in the lubricating oil composition is, in terms of the amount of substance of all soap groups per 1 kg of the composition, preferably 15 mmol/kg or more, more preferably 17 mmol/kg or more, and in one embodiment 18 mmol/kg or more, from the viewpoint of increasing the base number durability and further reducing the deterioration of low-temperature fluidity when mixed with water, and from the viewpoint of suppressing sludge, is preferably 70 mmol/kg or less, more preferably 60 mmol/kg or less, and in one embodiment 50 mmol/kg or less, and in one embodiment may be 15 to 70 mmol/kg, or 15 to 60 mmol/kg, or 18 to 50 mmol/kg.

<(C) Comb-shaped poly(meth)acrylate>
The lubricating oil composition of the present invention contains one or more comb-shaped poly(meth)acrylates (hereinafter sometimes referred to as "Component (C)") having a weight average molecular weight of 350,000 to 1,000,000 and a polydispersity index of 4.0 or less, in an amount of 1.0 to 4.0 mass% as a resin content based on the total amount of the composition. The comb-shaped poly(meth)acrylate may be a non-dispersed poly(meth)acrylate, a dispersed poly(meth)acrylate, or a combination thereof.

As the poly(meth)acrylate compound constituting component (C), for example, a poly(meth)acrylate compound in which the proportion of monomer units represented by the following general formula (3) in the total monomer units in the polymer is 10 mol % or more (hereinafter sometimes referred to as "poly(meth)acrylate (C1)" or "component (C1)") can be preferably used.

（一般式（３）中、Ｒ^３は水素又はメチル基を表し、Ｒ^４は炭素数１～５の直鎖または分岐鎖の炭化水素基、好ましくはアルキル基を表す。）

(In the general formula (3), ^R3 represents a hydrogen atom or a methyl group, and ^R4 represents a linear or branched hydrocarbon group having 1 to 5 carbon atoms, preferably an alkyl group.)

In the poly(meth)acrylate (C1), the proportion of the (meth)acrylate monomer units represented by the general formula (3) in the polymer is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 30 mol% or more, and particularly preferably 40 mol% or more, from the viewpoint of enhancing the effect of improving the viscosity-temperature characteristics, and from the viewpoint of enhancing the solubility in the base oil, the effect of improving the viscosity-temperature characteristics, and the low-temperature viscosity characteristics in a fresh oil state, it is preferably 90 mol% or less, more preferably 80 mol% or less, and even more preferably 70 mol% or less, and in one embodiment, it may be 10 to 90 mol%, or 20 to 90 mol%, or 30 to 80 mol%, or 40 to 70 mol%.

The viscosity index improver according to this embodiment may contain only the (meth)acrylate monomer units represented by general formula (3), or may be a copolymer containing other (meth)acrylate monomer units in addition to the (meth)acrylate monomer units represented by general formula (3). Such a copolymer can be obtained by copolymerizing one or more monomers represented by the following general formula (4) (hereinafter sometimes referred to as "monomer (M-1)") with one or more monomers other than monomer (M-1).

（一般式（４）中、Ｒ^３は水素又はメチル基を表し、Ｒ^４は炭素数１～５の直鎖または分岐鎖の炭化水素基、好ましくはアルキル基を表す。）

(In the general formula (4), ^R3 represents hydrogen or a methyl group, and ^R4 represents a linear or branched hydrocarbon group having 1 to 5 carbon atoms, preferably an alkyl group.)

The monomer to be combined with monomer (M-1) is not particularly limited, but for example, one or more monomers represented by the following general formula (5) (hereinafter sometimes referred to as "monomer (M-2)") or one or more monomers represented by the following general formula (6) (hereinafter sometimes referred to as "monomer (M-3)"), or a combination thereof, are preferred. A copolymer of monomer (M-1) and monomer (M-2) and/or monomer (M-3) is a so-called non-dispersed poly(meth)acrylate.

（一般式（５）中、Ｒ^５は水素原子又はメチル基を表し、Ｒ^６は炭素数６～１８の直鎖または分岐鎖の炭化水素基、好ましくはアルキル基を表す。）

(In the general formula (5), ^R5 represents a hydrogen atom or a methyl group, and ^R6 represents a linear or branched hydrocarbon group having 6 to 18 carbon atoms, preferably an alkyl group.)

（一般式（６）中、Ｒ^７は水素原子又はメチル基を表し、Ｒ^８は炭素数１９以上の直鎖または分岐鎖の炭化水素基、好ましくはアルキル基を表す。）

(In formula (6), ^R7 represents a hydrogen atom or a methyl group, and ^R8 represents a linear or branched hydrocarbon group having 19 or more carbon atoms, preferably an alkyl group.)

As described above, R ⁸ in the monomer (M-3) represented by the general formula (6) is a linear or branched chain hydrocarbon group having 19 or more carbon atoms, and is preferably a linear or branched chain hydrocarbon group having 20 to 50,000 carbon atoms, or a linear or branched chain hydrocarbon group having 22 to 500 carbon atoms, or a linear or branched chain hydrocarbon group having 24 to 100 carbon atoms, or a branched chain hydrocarbon group having 24 to 50 carbon atoms, or a branched chain hydrocarbon group having 24 to 40 carbon atoms.

In the poly(meth)acrylate (C1), the proportion of monomer units corresponding to monomer (M-2) represented by general formula (5) in the total monomer units in the polymer is preferably 3 mol% or more, more preferably 5 mol% or more, even more preferably 10 mol% or more, and particularly preferably 15 mol% or more, from the viewpoint of enhancing the effect of improving the viscosity-temperature characteristics, and from the viewpoint of enhancing the solubility in the base oil, the effect of improving the viscosity-temperature characteristics, and the low-temperature viscosity characteristics in a fresh oil state, it is preferably 75 mol% or less, more preferably 65 mol% or less, even more preferably 55 mol% or less, and particularly preferably 45 mol% or less, and in one embodiment, 35 mol% or less, and in one embodiment, it may be 3 to 75 mol%, or 5 to 65 mol%, or 10 to 55 mol%, or 15 to 45 mol, or 15 to 35 mol%.

In the poly(meth)acrylate (C1), the proportion of the monomer units corresponding to the monomer (M-3) represented by the general formula (6) in the total monomer units in the polymer is preferably 0.5 mol% or more, or 1 mol% or more, more preferably 3 mol% or more, even more preferably 5 mol% or more, and particularly preferably 10 mol% or more, from the viewpoint of enhancing the effect of improving the viscosity-temperature characteristics and the low-temperature viscosity characteristics in a fresh oil state, and is preferably 70 mol% or less, more preferably 60 mol% or less, even more preferably 50 mol% or less, and particularly preferably 40 mol% or less, and in one embodiment, 30 mol% or less, and in one embodiment, it may be 0.5 to 70 mol%, or 1 to 70 mol%, or 3 to 60 mol%, or 5 to 50 mol%, or 10 to 40 mol, or 10 to 30 mol%.

In one embodiment, the ratio of monomer units corresponding to monomers (M-1), (M-2), and (M-3) to the total monomer units in the polymer may be monomer (M-1):monomer (M-2):monomer (M-3) = 10-90 mol%: 3-75 mol%: 1-70 mol%, or 20-90 mol%: 5-65 mol%: 3-60 mol%, or 30-80 mol%: 10-55 mol%: 5-50 mol%, or 40-70 mol%: 15-45 mol%: 10-40 mol%.

As other monomers to be copolymerized with monomer (M-1), one or more monomers represented by the following general formula (7) (hereinafter sometimes referred to as "monomer (M-4)"), or one or more monomers represented by the following general formula (8) (hereinafter sometimes referred to as "monomer (M-5)"), or a combination thereof, are suitable. Copolymers of monomer (M-1) and, optionally, monomer (M-2) and/or monomer (M-3) with monomer (M-4) and/or (M-5) are so-called dispersion-type poly(meth)acrylate-based viscosity index improvers.

（一般式（７）中、Ｒ^９は水素原子又はメチル基を表し、Ｒ^１０は炭素数１～１８のアルキレン基を表し、Ｅ^１は窒素原子を１～２個、酸素原子を０～２個含有する、アミン残基又は複素環残基を表し、ｂは０又は１を表す。）

(In general formula (7), R ⁹ represents a hydrogen atom or a methyl group, R ¹⁰ represents an alkylene group having 1 to 18 carbon atoms, E ¹ represents an amine residue or a heterocyclic residue containing 1 to 2 nitrogen atoms and 0 to 2 oxygen atoms, and b represents 0 or 1.)

Examples of the alkylene group having 1 to 18 carbon atoms represented by R ¹⁰ include an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group, an undecylene group, a dodecylene group, a tridecylene group, a tetradecylene group, a pentadecylene group, a hexadecylene group, a heptadecylene group, and an octadecylene group (these alkylene groups may be linear or branched).

Examples of the group represented by ^E1 include a dimethylamino group, a diethylamino group, a dipropylamino group, a dibutylamino group, an anilino group, a toluidino group, a xylidino group, an acetylamino group, a benzoylamino group, a morpholino group, a pyrrolyl group, a pyrrolino group, a pyridyl group, a methylpyridyl group, a pyrrolidinyl group, a pyrrolidino group, a piperidinyl group, a piperidino group, a quinolyl group, a pyrrolidonyl group, a pyrrolidono group, an imidazolino group, and a pyrazinyl group.

（一般式（８）中、Ｒ^１１は水素原子又はメチル基を表し、Ｅ^２は窒素原子を１～２個、酸素原子を０～２個含有する、アミン残基または複素環残基を表す。）

(In the general formula (8), R ¹¹ represents a hydrogen atom or a methyl group, and E ² represents an amine residue or a heterocyclic residue containing 1 to 2 nitrogen atoms and 0 to 2 oxygen atoms.)

Examples of the group represented by ^E2 include a dimethylamino group, a diethylamino group, a dipropylamino group, a dibutylamino group, an anilino group, a toluidino group, a xylidino group, an acetylamino group, a benzoylamino group, a morpholino group, a pyrrolyl group, a pyrrolino group, a pyridyl group, a methylpyridyl group, a pyrrolidinyl group, a pyrrolidino group, a piperidinyl group, a piperidino group, a quinolyl group, a pyrrolidonyl group, a pyrrolidono group, an imidazolino group, and a pyrazinyl group.

Specific preferred examples of monomers (M-4) and (M-5) include dimethylaminomethyl methacrylate, diethylaminomethyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, 2-methyl-5-vinylpyridine, morpholinomethyl methacrylate, morpholinoethyl methacrylate, N-vinylpyrrolidone, and mixtures thereof.

The copolymerization ratio in the copolymer of monomer (M-1) and monomers (M-2) to (M-5) is not particularly limited, but the substance amount ratio is preferably monomer (M-1):monomers (M-2) to (M-5) = about 20:80 to 90:10 mol/mol, more preferably 30:70 to 80:20 mol/mol, and even more preferably 40:60 to 70:30 mol/mol.

The method for producing poly(meth)acrylate is not particularly limited. For example, a non-dispersed poly(meth)acrylate can be easily obtained by radical solution polymerization of one or more monomers selected from monomers (M-1) to (M-3) in the presence of a polymerization initiator (e.g., benzoyl peroxide, etc.). Also, for example, a dispersed poly(meth)acrylate compound can be easily obtained by radical solution polymerization of one or more monomers selected from monomers (M-1) to (M-3) and one or more nitrogen-containing monomers selected from monomers (M-4) and (M-5) in the presence of a polymerization initiator.

Component (C) is a comb-shaped poly(meth)acrylate. The comb-shaped polymer includes a trunk and two or more branches attached to the trunk. The trunk of the comb-shaped poly(meth)acrylate is a poly(meth)acrylate polymer chain. The branches of the comb-shaped poly(meth)acrylate may be a polymer chain other than a poly(meth)acrylate polymer chain, or may be a poly(meth)acrylate polymer chain.

A preferred example of a comb-shaped poly(meth)acrylate having a poly(meth)acrylate polymer chain as a branch portion is a poly(meth)acrylate (C1) (hereinafter sometimes referred to as a "comb-shaped poly(meth)acrylate (C1a)") obtained by polymerizing a poly(meth)acrylate macromonomer (M-6) (hereinafter sometimes referred to as "macromonomer (M-6)") having a polymerizable functional group, obtained by polymerizing one or more monomers selected from the above monomers (M-1) to (M-5), preferably one or more monomers selected from the above monomers (M-1), (M-2), (M-4), and (M-5), alone or together with one or more monomers selected from the above monomers (M-1) to (M-5). The macromonomer (M-6) preferably has a polymerizable functional group at the end of the polymer chain.

The number average molecular weight (Mn) of the macromonomer (M-6) is preferably 270 or more, more preferably 500 or more, even more preferably 600 or more, and particularly preferably 700 or more, from the viewpoint of further reducing deterioration of low-temperature fluidity when mixed with water, and is preferably 200,000 or less, more preferably 100,000 or less, even more preferably 50,000 or less, and particularly preferably 20,000 or less, and in one embodiment may be 270 to 200,000, or 500 to 100,000, or 600 to 50,000, or 700 to 20,000.

Examples of the polymerizable functional group contained in the macromonomer (M-6) include an acryloyl group, a methacryloyl group, a vinyl group, a vinyloxy group (CH ₂ ═CH—O— group), an allyl group, an allyloxy group (CH _{2 ═CH} —CH ₂ —O— group), an acroylamino group (CH _{2 ═CH} —CONH— group), and a methacryloylamino group (CH ₂ ═C(CH ₃ )—CONH— group).

The content of the monomer units corresponding to the macromonomer (M-6) in the comb-shaped poly(meth)acrylate (C1a) is preferably 30 to 100 mol%, more preferably 50 to 100 mol%, even more preferably 70 to 100 mol%, and particularly preferably 90 to 100 mol%, based on the total monomer units of the comb-shaped poly(meth)acrylate (C1a), in terms of further reducing the deterioration of low-temperature fluidity when water is mixed in. On the other hand, from the viewpoint of cost reduction, it is preferably 90 mol% or less, more preferably 70 mol% or less, and even more preferably 50 mol% or less, and in one embodiment, it may be 30 to 100 mol%, or 50 to 100 mol%, or 70 to 100 mol%, or 90 to 100 mol%, or 30 to 90 mol%, or 30 to 70 mol%, or 30 to 50 mol%, or 50 to 90 mol%, or 50 to 70 mol%.

A preferred example of a comb-shaped poly(meth)acrylate having a polymer chain other than a poly(meth)acrylate polymer chain as a branch portion is a copolymer of the above monomer (M-1) and the above monomer (M-3), and optionally the above monomers (M-2), (M-4), and/or (M-5), in which the monomer (M-3) contains a macromonomer (hereinafter sometimes referred to as "macromonomer (M-3a)") in which R ⁸ in general formula (6) has a number average molecular weight (Mn) of 1,000 or more (hereinafter sometimes referred to as "comb-shaped poly(meth)acrylate (C1b)"). In the comb-shaped poly(meth)acrylate (C1b), R ⁸ of the macromonomer (M-3a) constitutes the branch portion of the comb polymer.

In the comb-shaped poly(meth)acrylate (C1b), the number average molecular weight of R ⁸ (general formula (6)) in the macromonomer (M-3a) is 1,000 or more, preferably 1,500 or more, more preferably 2,000 or more, and is preferably 50,000 or less, more preferably 20,000 or less, and even more preferably 10,000 or less, and in one embodiment may be 1,000 to 50,000, or 1,500 to 20,000, or 2,000 to 10,000. Examples of such macromonomers (M-3a) include macromonomers having R ⁸ derived from a hydrogenated polyolefin obtained by copolymerizing butadiene and isoprene.

In the comb-shaped poly(meth)acrylate (C1b), the copolymerization ratio of the macromonomer (M-3a) is preferably 30 to 100 mol%, more preferably 50 to 100 mol%, even more preferably 70 to 100 mol%, and particularly preferably 90 to 100 mol%, based on the total monomer units of the poly(meth)acrylate, from the viewpoint of further reducing the deterioration of low-temperature fluidity when water is mixed in, while from the viewpoint of reducing costs, it is preferably 90 mol% or less, more preferably 80 mol% or less. mol% or less, more preferably 60 mol% or less, and particularly preferably 40 mol% or less, and in one embodiment, it may be 30 to 100 mol%, or 50 to 100 mol%, or 70 to 100 mol%, or 90 to 100 mol%, or 30 to 90 mol%, or 30 to 80 mol%, or 30 to 60 mol%, or 30 to 40 mol%, or 50 to 90 mol%, or 50 to 80 mol%, or 50 to 60 mol%, or 70 to 90 mol%, or 70 to 80 mol%.

The weight average molecular weight (Mw) of the (C) component is 350,000 or more, preferably 380,000 or more, and in one embodiment, more than 400,000, for example, 410,000 or more, from the viewpoint of reducing deterioration of low-temperature fluidity when water is mixed in. Also, from the viewpoint of improving fuel economy, storage stability, and shear stability, it is 1,000,000 or less, preferably 900,000 or less, and in one embodiment, 850,000 or less, for example, 800,000 or less, and in one embodiment, it may be 350,000 to 1,000,000, or 380,000 to 900,000, or more than 400,000 and 850,000 or less, or 410,000 to 800,000. When the (C) component contains a plurality of comb-shaped poly(meth)acrylates, it is preferable that the weight average molecular weight of each comb-shaped poly(meth)acrylate is within the above range.

The polydispersity index (PDI) of the (C) component is 4.0 or less from the viewpoint of reducing deterioration of low-temperature fluidity when water is mixed in, preferably 3.5 or less, more preferably 3.2 or less, and in one embodiment 3.1 or less, and is usually more than 1.0. From the viewpoint of ease of production, it is preferably 1.1 or more, more preferably 1.5 or more, and in one embodiment 2.0 or more, and in one embodiment it may be more than 1.0 and 4.0 or less, or 1.1 to 3.5, or 1.5 to 3.2, or 2.0 to 3.1. In this specification, the polydispersity of a polymer means the ratio (Mw/Mn) of the weight average molecular weight (Mw) of the polymer to the number average molecular weight (Mn) of the polymer. When the (C) component contains multiple comb-shaped poly(meth)acrylates, it is preferable that the polydispersity of each comb-shaped poly(meth)acrylate is within the above range.

The content of component (C) in the lubricating oil composition is 1.0 mass% or more, preferably 1.2 mass% or more, and in one embodiment 1.4 mass% or more, as resin content based on the total amount of the composition, from the viewpoint of reducing deterioration of low-temperature fluidity when water is mixed in, and from the viewpoint of maintaining the viscosity of the composition in a preferred range to improve fuel economy and to improve shear stability, it is 4.0 mass% or less, preferably 3.5 mass% or less, more preferably 3.0 mass% or less, and in one embodiment 2.5 mass% or less, and in one embodiment it may be 1.0 to 4.0 mass%, or 1.2 to 3.5 mass%, or 1.2 to 3.0 mass%, or 1.4 to 2.5 mass%. In this specification, "resin content" means a polymer component having a weight average molecular weight of 1,000 or more.

<(D) Succinimide Dispersant>
The lubricating oil composition of the present invention contains one or more unmodified succinimide dispersants or one or more boric acid modified succinimide dispersants or a succinimide dispersant containing a combination thereof (hereinafter sometimes referred to as "component (D)") in an amount of 100 to 1000 mass ppm in terms of nitrogen content based on the total amount of the composition. The ratio of the total nitrogen content of the unmodified succinimide dispersant and the boric acid modified succinimide dispersant to the total nitrogen content of component (D) is 70 mass% or more. As the succinimide dispersant, a succinimide having at least one alkyl group or alkenyl group in the molecule or a modified product thereof can be used. Examples of succinimides having at least one alkyl group or alkenyl group in the molecule include compounds represented by the following general formula (9) or (10).

In general formula (9), R ¹² represents an alkyl or alkenyl group having 40 to 400 carbon atoms, and c represents an integer of 1 to 5, preferably 2 to 4. The number of carbon atoms in R ¹² is 40 or more, preferably 60 or more, from the viewpoint of solubility in the base oil, and is 400 or less, preferably 350 or less, from the viewpoint of low-temperature fluidity of the composition in a fresh oil state, and in one embodiment, it may be 40 to 400, or 60 to 350.

In general formula (10), R ¹³ and R ¹⁴ each independently represent an alkyl or alkenyl group having 40 to 400 carbon atoms, and may be a combination of different groups. Furthermore, d represents an integer of 0 to 4, preferably 1 to 4, and more preferably 1 to 3. The carbon number of ^{R 13} and R ¹⁴ is 40 or more, preferably 60 or more, from the viewpoint of solubility in the base oil, and is 400 or less, preferably 350 or less, from the viewpoint of low-temperature fluidity of the composition in a fresh oil state, and in one embodiment, it may be 40 to 400, or 60 to 350.

In general formulas (9) and (10), when the carbon numbers of R ¹² to R ¹⁴ are equal to or greater than the lower limit, good solubility in the lubricating base oil can be obtained, whereas when the carbon numbers of R ¹² to R ¹⁴ are equal to or less than the upper limit, the low-temperature fluidity of the lubricating oil composition in a fresh oil state can be improved.

The alkyl or alkenyl groups (R ¹² to R ¹⁴ ) in the general formulae (9) and (10) may be linear or branched. Preferred examples thereof include branched alkyl groups and branched alkenyl groups derived from olefin oligomers such as propylene, 1-butene, and isobutene, and from cooligomers of ethylene and propylene. Among these, branched alkyl or alkenyl groups derived from an oligomer of isobutene commonly called polyisobutylene, and polybutenyl groups are most preferred.
The alkyl or alkenyl groups (R ¹² to R ¹⁴ ) in the general formulas (9) and (10) have a suitable number average molecular weight of 800 to 3,500, preferably 1,000 to 3,500.

Succinimides having at least one alkyl or alkenyl group in the molecule include so-called mono-type succinimides represented by general formula (9) in which succinic anhydride is added to only one end of the polyamine chain, and so-called bis-type succinimides represented by general formula (10) in which succinic anhydride is added to both ends of the polyamine chain. The lubricating oil composition may contain either mono-type succinimides or bis-type succinimides, or may contain both of them as a mixture. The content of bis-type succinimides or derivatives thereof in component (D) is preferably 50% by mass or more, more preferably 70% by mass or more, based on the total amount of component (D) (100% by mass).

The method for producing the succinimide having at least one alkyl or alkenyl group in the molecule is not particularly limited. The succinimide can be obtained, for example, as a condensation reaction product by reacting an alkyl or alkenyl succinic acid having an alkyl or alkenyl group having 40 to 400 carbon atoms or an anhydride thereof with a polyamine. As the (D) component, the condensation product may be used as it is (i.e., unmodified succinimide), or the condensation product may be converted into a modified product (derivative) described below and used. The condensation product of an alkyl or alkenyl succinic acid or anhydride thereof with a polyamine may be a bis-type succinimide (see general formula (10)) in which both ends of the polyamine chain are imidized, or a mono-type succinimide (see general formula (9)) in which only one end of the polyamine chain is imidized, or a mixture thereof. Here, an alkenylsuccinic anhydride having an alkenyl group having 40 to 400 carbon atoms can be obtained, for example, by reacting an olefin having 40 to 400 carbon atoms with maleic anhydride at 100 to 200°C. In addition, an alkylsuccinic anhydride having an alkyl group having 40 to 400 carbon atoms can be obtained by further subjecting the alkenylsuccinic anhydride to a hydrogenation reaction. Examples of polyamines include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine, as well as mixtures thereof, and a polyamine raw material containing one or more selected from these can be preferably used. The polyamine raw material may or may not further contain ethylenediamine, but from the viewpoint of improving the performance of the condensation product or its derivative as a dispersant, the content of ethylenediamine in the polyamine raw material is preferably 0 to 10 mass%, more preferably 0 to 5 mass%, based on the total amount of polyamine. The succinimide obtained as a condensation reaction product between an alkyl or alkenyl succinic acid or anhydride having an alkyl or alkenyl group having 40 to 400 carbon atoms and a mixture of two or more polyamines is a mixture of compounds having different c or d in the general formula (9) or (10).

Examples of modified succinimides (derivatives) include (i) boric acid modified products, (ii) phosphoric acid modified products, (iii) products modified with oxygen-containing organic compounds, (iv) sulfur modified products, and (v) products modified by a combination of two or more of these modifications.
(i) The boric acid modified product is a modified compound (boric acid modified succinimide) in which the above-mentioned succinimide is reacted with boric acid to neutralize or amidate a part or all of the remaining amino groups and/or imino groups.
(ii) The phosphoric acid modified product is a modified compound (phosphoric acid modified succinimide) in which the remaining amino groups and/or imino groups are partially or completely neutralized or amidated by reacting phosphoric acid with the above-mentioned succinimide.
(iii) The compound modified with an oxygen-containing organic compound is a modified compound (oxygen-containing organic compound-modified succinimide) in which the above-mentioned succinimide is reacted with a monocarboxylic acid having 1 to 30 carbon atoms such as a fatty acid, a polycarboxylic acid having 2 to 30 carbon atoms (e.g., oxalic acid, phthalic acid, trimellitic acid, pyromellitic acid, etc.), an anhydride or ester compound thereof, an alkylene oxide having 2 to 6 carbon atoms, or a hydroxy(poly)oxyalkylene carbonate, so that a part or all of the remaining amino groups and/or imino groups are neutralized or amidated.
(iv) The sulfur-modified product is a modified compound (sulfur-modified succinimide) obtained by reacting the above-mentioned succinimide with a sulfur compound.
(v) The modified compound obtained by combining two or more types of modifications can be obtained by subjecting the above-mentioned succinimide to a combination of two or more types of modifications selected from boron modification, phosphoric acid modification, modification with an oxygen-containing organic compound, and sulfur modification.
Among these modified products (derivatives) (i) to (v), boric acid modified succinimides, particularly boric acid modified products of bis-type alkenyl succinimides, can be preferably used.

There are no particular restrictions on the molecular weight of component (D), but a suitable weight average molecular weight is 1,000 to 20,000, more preferably 2,000 to 20,000, even more preferably 3,000 to 15,000, and particularly preferably 4,000 to 9,000.

Component (D) may contain only one or more unmodified succinimide dispersants, only one or more boric acid modified succinimide dispersants, or both. Component (D) may further contain the above-described modified succinimide other than the boric acid modified one in addition to the unmodified succinimide dispersant and/or boric acid modified succinimide. However, the ratio of the total nitrogen content of the unmodified succinimide dispersant and the boric acid modified succinimide dispersant to the total nitrogen content of component (D) is 70 to 100 mass%, preferably 80 to 100 mass%, more preferably 90 to 100 mass%, and particularly preferably 95 to 100 mass%, from the viewpoint of reducing deterioration of low-temperature fluidity when water is mixed.

The content of component (D) in the lubricating oil composition is preferably 100 ppm by mass or more, more preferably 200 ppm by mass or more, even more preferably 300 ppm by mass or more, and particularly preferably 400 ppm by mass or more, as nitrogen content based on the total amount of the composition, from the viewpoint of reducing deterioration of low-temperature fluidity when mixed with water, and from the viewpoint of increasing coking resistance and solubility of additives. Also, from the viewpoint of increasing fuel efficiency of the composition and low-temperature fluidity in a new oil state, it is 1000 ppm by mass or less, preferably 900 ppm by mass or less, more preferably 800 ppm by mass or less, and particularly preferably 700 ppm by mass or less, and in one embodiment, it may be 100 to 1000 ppm by mass, or 200 to 900 ppm by mass, or 300 to 800 ppm by mass, or 400 to 700 ppm by mass.

The boron content in the lubricating oil composition derived from component (D) is preferably 0 to 500 ppm by mass, more preferably 0 to 400 ppm by mass, even more preferably 0 to 350 ppm by mass, and particularly preferably 0 to 300 ppm by mass, based on the total amount of the composition, from the viewpoint of improving fuel economy and reducing the ash content of the composition.

The mass ratio (B/N) of the total boron content (B) to the total nitrogen content (N) of component (D) is preferably 0 to 0.69, more preferably 0 to 0.62, even more preferably 0 to 0.54, and particularly preferably 0 to 0.50, from the viewpoint of further reducing the deterioration of low-temperature fluidity when water is mixed in.

<(E) Zinc Dialkyldithiophosphate>
In one preferred embodiment, the lubricating oil composition of the present invention may further contain zinc dialkyldithiophosphate (ZnDTP; hereinafter, sometimes referred to as "Component (E)"). As Component (E), for example, a compound represented by the following general formula (11) can be used.

In the general formula (11), R ¹⁵ to R ¹⁸ each independently represent a linear or branched alkyl group having 1 to 24 carbon atoms, and may be a combination of different groups. The number of carbon atoms of R ¹⁵ to R ¹⁸ is preferably 3 to 12, more preferably 3 to 8. R ¹⁵ to R ¹⁸ may be any of a primary alkyl group, a secondary alkyl group, and a tertiary alkyl group, but is preferably a primary alkyl group, a secondary alkyl group, or a combination thereof, and further, the molar ratio of the primary alkyl group to the secondary alkyl group (primary alkyl group: secondary alkyl group) is preferably 0:100 to 30:70. This ratio may be a combination ratio of alkyl chains in the molecule, or may be a mixture ratio of ZnDTP having only a primary alkyl group and ZnDTP having only a secondary alkyl group. By being dominated by secondary alkyl groups, it is possible to further improve fuel efficiency.

The method for producing the zinc dialkyldithiophosphate is not particularly limited. For example, the zinc dialkyldithiophosphate can be synthesized by reacting an alcohol having an alkyl group corresponding to R ¹⁵ to R ¹⁸ with diphosphorus pentasulfide to synthesize a dithiophosphoric acid, and neutralizing the dithiophosphoric acid with zinc oxide.

The content of component (E) in the lubricating oil composition is preferably 0 to 1000 ppm by mass, more preferably 0 to 900 ppm by mass, and even more preferably 0 to 800 ppm by mass, based on the total amount of the composition, in terms of reducing catalyst poisoning in exhaust gas aftertreatment devices, and is preferably 400 ppm by mass or more, more preferably 500 ppm by mass or more, and even more preferably 600 ppm by mass or more in terms of improving wear resistance and pre-ignition suppression ability, and in one embodiment may be 700 to 800 ppm by mass, or 750 to 800 ppm by mass, or 770 to 800 ppm by mass.

<(F) Oil-soluble organomolybdenum compound>
In one preferred embodiment, the lubricating oil composition of the present invention may further contain an oil-soluble organo-molybdenum compound (hereinafter sometimes referred to as "Component (F)"). Component (F) acts as a molybdenum-based friction modifier.

As the (F) component, molybdenum dithiocarbamate (sulfurized molybdenum dithiocarbamate or sulfurized oxymolybdenum dithiocarbamate; hereinafter, sometimes referred to as "(F1) component") can be preferably used.

As component (F1), for example, a compound represented by the following general formula (12) can be used.

In the general formula (12), R ¹⁹ to R ²² may be the same or different and are an alkyl group having 2 to 24 carbon atoms or an (alkyl)aryl group having 6 to 24 carbon atoms, preferably an alkyl group having 4 to 13 carbon atoms or an (alkyl)aryl group having 10 to 15 carbon atoms. The alkyl group may be a primary alkyl group, a secondary alkyl group, or a tertiary alkyl group, and may be linear or branched. The term "(alkyl)aryl group" means an "aryl group or an alkylaryl group." In the alkylaryl group, the substitution position of the alkyl group on the aromatic ring is arbitrary. ^{Y 1} to Y ⁴ are each independently a sulfur atom or an oxygen atom, and at least one of Y ¹ to Y ⁴ is a sulfur atom.

Examples of oil-soluble organic molybdenum compounds other than component (F1) include, for example, molybdenum dithiophosphate; molybdenum compounds (for example, molybdenum oxides such as molybdenum dioxide and molybdenum trioxide; molybdic acids such as orthomolybdic acid, paramolybdic acid, and (poly)molybdic sulfide; metal salts of these molybdic acids; molybdates such as ammonium salts; molybdenum sulfides such as molybdenum disulfide, molybdenum trisulfide, molybdenum pentasulfide, and polymolybdenum sulfide; molybdic acid; metal or amine salts of molybdic sulfide; and halogenated compounds such as molybdenum chloride. molybdenum, etc.) and a sulfur-containing organic compound (e.g., alkyl(thio)xanthate, thiadiazole, mercaptothiadiazole, thiocarbonate, tetrahydrocarbyl thiuram disulfide, bis(di(thio)hydrocarbyl dithiophosphonate) disulfide, organic (poly)sulfide, sulfurized ester, etc.) or other organic compound; and sulfur-containing organic molybdenum compounds such as the above molybdenum sulfide, molybdic acid sulfide, and other sulfur-containing molybdenum compounds and alkenyl succinimide complexes. The organic molybdenum compound may be a mononuclear molybdenum compound or a polynuclear molybdenum compound such as a dinuclear molybdenum compound or a trinuclear molybdenum compound.

As an oil-soluble organomolybdenum compound other than component (F1), it is also possible to use an organomolybdenum compound that does not contain sulfur. Examples of organomolybdenum compounds that do not contain sulfur include molybdenum-amine complexes, molybdenum-succinimide complexes, molybdenum salts of organic acids, and molybdenum salts of alcohols. Of these, molybdenum-amine complexes, molybdenum salts of organic acids, and molybdenum salts of alcohols are preferred.

The content of component (F) in the lubricating oil composition is preferably 0 to 2000 ppm by mass, more preferably 0 to 1500 ppm by mass, and even more preferably 0 to 1200 ppm by mass, in terms of molybdenum content based on the total amount of the lubricating oil composition, from the viewpoint of improving the storage stability of the lubricating oil composition, and is preferably 50 ppm by mass or more, more preferably 200 ppm by mass or more, and even more preferably 300 ppm by mass or more, from the viewpoint of improving fuel economy and pre-ignition suppression ability, and in one embodiment may be 50 to 2000 ppm by mass, or 200 to 1500 ppm by mass, or 300 to 1200 ppm by mass.

<Other additives>
The lubricating oil composition of the present invention may further contain other additives generally used in lubricating oils depending on the purpose. Examples of such additives include antiwear agents or extreme pressure agents other than component (E), friction modifiers other than component (F), antioxidants other than component (E), corrosion inhibitors, rust inhibitors, metal deactivators, demulsifiers, antifoaming agents, etc.

As the antiwear agent or extreme pressure agent other than the component (E), antiwear agents or extreme pressure agents used in lubricating oils can be used without any particular restrictions. Examples of such agents include sulfur-based, phosphorus-based, and sulfur-phosphorus-based extreme pressure agents, and specifically, phosphites, thiophosphites, dithiophosphites, trithiophosphites, phosphates, thiophosphates, dithiophosphates, trithiophosphates, amine salts thereof, metal salts thereof, derivatives thereof, dithiocarbamates, zinc dithiocarbamates, disulfides, polysulfides, sulfurized olefins, and sulfurized oils and fats. Among these, sulfur-based extreme pressure agents are preferred, and sulfurized oils and fats are particularly preferred.
When the lubricating oil composition contains an antiwear agent or extreme pressure agent other than component (E), the content thereof may be, for example, 0.01 to 10 mass % based on the total amount of the composition.

As the friction modifier other than the component (F), compounds that are usually used as ashless friction modifiers for lubricating oils can be used without any particular restrictions. Examples of ashless friction modifiers include compounds having 6 to 50 carbon atoms, each having a hydrocarbon group having 6 or more carbon atoms and a functional group containing at least one hetero element selected from oxygen, nitrogen, and sulfur atoms in the molecule. More specific examples include compounds having at least one aliphatic hydrocarbyl or aliphatic hydrocarbyl carbonyl group having 8 to 36 carbon atoms in the molecule, such as aliphatic amines, fatty acid amides, fatty acid hydrazides, aliphatic imide compounds, aliphatic urea compounds, fatty acid esters, fatty acids, fatty acid metal salts, aliphatic alcohols, and aliphatic ethers.
When the lubricating oil composition contains a friction modifier other than component (F), the content thereof may usually be 0.1 to 1.0 mass %, for example 0.3 to 0.8 mass %, based on the total amount of the composition.

Examples of antioxidants other than component (E) include known ashless antioxidants such as aromatic amine antioxidants, hindered amine antioxidants, and phenolic antioxidants.

Examples of aromatic amine antioxidants include primary aromatic amine compounds such as alkylated α-naphthylamine; and secondary aromatic amine compounds such as alkylated diphenylamine, phenyl-α-naphthylamine, alkylated phenyl-α-naphthylamine, and phenyl-β-naphthylamine. As aromatic amine antioxidants, alkylated diphenylamine, alkylated phenyl-α-naphthylamine, or a combination thereof can be preferably used.

Examples of hindered amine antioxidants include compounds having a 2,2,6,6-tetraalkylpiperidine skeleton (2,2,6,6-tetraalkylpiperidine derivatives). As the 2,2,6,6-tetraalkylpiperidine derivative, a 2,2,6,6-tetraalkylpiperidine derivative having a substituent at the 4-position is preferred. In addition, two 2,2,6,6-tetraalkylpiperidine skeletons may be bonded via the respective substituents at the 4-position. In addition, the N-position of the 2,2,6,6-tetraalkylpiperidine skeleton may be unsubstituted, or the N-position may be substituted with an alkyl group having 1 to 4 carbon atoms. The 2,2,6,6-tetraalkylpiperidine skeleton is preferably a 2,2,6,6-tetramethylpiperidine skeleton.

Examples of the substituent at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton include an acyloxy group (R ²³ COO--), an alkoxy group (R ²³ O--), an alkylamino group (R ²³ NH--), an acylamino group (R ²³ CONH--), etc. ^{R 23} is preferably a hydrocarbon group having 1 to 30 carbon atoms, more preferably 1 to 24 carbon atoms, and even more preferably 1 to 20 carbon atoms. Examples of the hydrocarbon group include an alkyl group, an alkenyl group, a cycloalkyl group, an alkylcycloalkyl group, an aryl group, an alkylaryl group, an arylalkyl group, etc.

When two 2,2,6,6-tetraalkylpiperidine skeletons are bonded via a substituent at each 4-position, examples of the substituent include a hydrocarbylene bis(carbonyloxy) group (-OOC-R ²⁴ -COO-), a hydrocarbylene diamino group (-HN-R ²⁴ -NH-), a hydrocarbylene bis(carbonylamino) group (-HNCO-R ²⁴ -CONH-), etc. ^{R 24} is preferably a hydrocarbylene group having 1 to 30 carbon atoms, more preferably an alkylene group.

As the substituent at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton, an acyloxy group is preferred. An example of a compound having an acyloxy group at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton is an ester of 2,2,6,6-tetramethyl-4-piperidinol and a carboxylic acid. An example of the carboxylic acid is a linear or branched aliphatic carboxylic acid having 8 to 20 carbon atoms.

Examples of phenolic antioxidants include 4,4'-methylenebis(2,6-di-tert-butylphenol); 4,4'-bis(2,6-di-tert-butylphenol); 4,4'-bis(2-methyl-6-tert-butylphenol); 2,2'-methylenebis(4-ethyl-6-tert-butylphenol); 2,2'-methylenebis(4-methyl-6-tert-butylphenol); 4,4'-butyl 2,2'-methylenebis(4-methyl-6-nonylphenol); 2,2'-isobutylidenebis(4,6-dimethylphenol); 2,2'-methylenebis(4-methyl-6-cyclohexylphenol); 2,6-di-tert-butyl-4-methylphenol; 2,6- Examples of the hindered phenol compounds and bisphenol compounds include di-tert-butyl-4-ethylphenol; 2,4-dimethyl-6-tert-butylphenol; 2,6-di-tert-butyl-4-(N,N'-dimethylaminomethyl)phenol; 4,4'-thiobis(2-methyl-6-tert-butylphenol); 4,4'-thiobis(3-methyl-6-tert-butylphenol); 2,2'-thiobis(4-methyl-6-tert-butylphenol); bis(3-methyl-4-hydroxy-5-tert-butylbenzyl)sulfide; bis(3,5-di-tert-butyl-4-hydroxybenzyl)sulfide; 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid esters; and 3-methyl-5-tert-butyl-4-hydroxyphenol fatty acid esters. Examples of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid esters include octyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; decyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; dodecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; tetradecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. ester; hexadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; pentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; 2,2'-thio-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], etc.

When the lubricating oil composition contains an antioxidant other than component (E), the content thereof may usually be 0.1 to 5.0 mass %, for example 0.5 to 3.0 mass %, based on the total amount of the composition.

As the corrosion inhibitor, for example, a known corrosion inhibitor such as a benzotriazole-based compound, a tolyltriazole-based compound, a thiadiazole-based compound, or an imidazole-based compound can be used. When the lubricating oil composition contains a corrosion inhibitor, the content thereof can be, for example, 0.005 to 5 mass % based on the total amount of the composition.

As the rust inhibitor, known rust inhibitors such as petroleum sulfonates, alkylbenzene sulfonates, dinonylnaphthalene sulfonates, alkyl sulfonates, fatty acid soaps, fatty acids, alkenyl succinic acid half esters, polyhydric alcohol fatty acid esters, aliphatic amines, paraffin oxide, and alkyl polyoxyethylene ethers can be used. When the lubricating oil composition contains a rust inhibitor, the content thereof may be, for example, 0.005 to 5 mass% based on the total amount of the composition. In this specification, all organic acid metal salts capable of forming micelles in the base oil, even if they are not additives commercially available as metal detergents, are considered to contribute to the content of the above component (B), i.e., the metal detergent.

Examples of metal deactivators that can be used include known metal deactivators such as imidazoline, pyrimidine derivatives, alkyl thiadiazoles, mercaptobenzothiazoles, benzotriazoles and their derivatives, 1,3,4-thiadiazole polysulfides, 1,3,4-thiadiazolyl-2,5-bisdialkyldithiocarbamates, 2-(alkyldithio)benzimidazoles, and β-(o-carboxybenzylthio)propioninitrile. When the lubricating oil composition contains a metal deactivator, the content thereof can be, for example, 0.005 to 1 mass % based on the total amount of the composition.

As the demulsifier, a known demulsifier such as a polyalkylene glycol-based nonionic surfactant can be used. When the lubricating oil composition contains a demulsifier, the content thereof can be, for example, 0.005 to 5 mass % based on the total amount of the composition.

As the defoaming agent, for example, known defoaming agents such as silicone, fluorosilicone, and fluoroalkyl ether can be used. When the lubricating oil composition contains an defoaming agent, the content thereof can be, for example, 0.0001 to 0.1 mass % based on the total amount of the composition.

As the colorant, known colorants such as azo compounds can be used.

<Lubricating Oil Composition>
The lubricating oil composition has a kinematic viscosity at 100°C of preferably 6.1 mm ² /s or more, more preferably 6.2 mm ² /s or more, and even more preferably 6.3 mm ² /s or more, from the viewpoint of improving lubricity, and preferably 8.2 mm ² /s or less, more preferably 7.9 mm ² /s or less, and even more preferably 7.6 mm ² /s or less, from the viewpoint of improving fuel economy, and in one embodiment may be 6.1 to 8.2 mm ² /s, or 6.2 to 7.9 mm ² /s, or 6.3 to 7.6 mm ² /s.

The lubricating oil composition has a kinematic viscosity at 40°C of preferably 20.0 mm ² /s or more, more preferably 22.0 mm ² /s or more, and even more preferably 24.0 mm ² /s or more, from the viewpoint of enhancing lubricity, and preferably 35.0 mm ² /s or less, more preferably 32.0 mm ² /s or less, and even more preferably 29.0 mm ² /s or less, from the viewpoint of improving fuel economy and low-temperature viscosity characteristics in a fresh oil state, and in one embodiment may be 20.0 to 35.0 mm ² /s, or 22.0 to 32.0 mm ² /s, or 24.0 to 29.0 mm ² /s.

The viscosity index of the lubricating oil composition is preferably 140 or more, more preferably 160 or more, even more preferably 180 or more, particularly preferably 200 or more, and in one embodiment may be 210 or more, from the viewpoint of improving fuel economy while maintaining HTHS viscosity at 150°C, and from the viewpoint of reducing the viscosity of the composition in a fresh oil state at low temperatures (for example, -35°C, which is the measurement temperature for the CCS viscosity specified in SAE viscosity grade 0W-X, known as the viscosity grade of fuel-saving oils). The upper limit of the viscosity index of the lubricating oil composition is not particularly limited, and may be, for example, 250 or less, 240 or less, or 230 or less.

The HTHS viscosity of the lubricating oil composition at 150°C is 2.25 mPa·s or more from the viewpoint of enhancing lubricity, and less than 2.55 mPa·s, preferably 2.54 mPa·s or less, from the viewpoint of enhancing fuel economy, and in one embodiment may be 2.25 mPa·s or more and less than 2.55 mPa·s, or 2.25 to 2.54 mPa·s. In this specification, the HTHS viscosity at 150°C means the high temperature high shear viscosity at 150°C specified in ASTM D4683.

The HTHS viscosity of the lubricating oil composition at 100°C is preferably 3.7 mPa·s or more, more preferably 4.3 mPa·s or more, from the viewpoint of enhancing lubricity, and is preferably 5.2 mPa·s or less, more preferably 4.9 mPa·s or less, from the viewpoint of enhancing fuel economy, and in one embodiment may be 3.7 to 5.2 mPa·s, or 4.3 to 5.2 mPa·s, or 4.3 to 4.9 mPa·s. In this specification, "HTHS viscosity at 100°C" means the high temperature high shear viscosity at 100°C specified in ASTM D4683.

The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples.

<Examples 1 to 14 and Comparative Examples 1 to 13>
Using the base oils and additives shown below, lubricating oil compositions of the present invention (Examples 1 to 14) and comparative lubricating oil compositions (Comparative Examples 1 to 13) were prepared, respectively. The compositions of each composition are shown in Tables 1 to 6. In Tables 1 to 6, in the "base oil composition" section, "mass %" represents mass % based on the total amount of base oil (100%), in other sections, "mass %" represents mass % based on the total amount of the composition (100%), "mass % of resin content" represents mass % as the resin content based on the total amount of the composition (100%), "ppm by mass" represents ppm by mass based on the total amount of the composition, and for element X, "ppm by mass/X" represents ppm by mass as the amount of element X based on the total amount of the composition.

(Base oil)
O-1: API Group III base oil (hydrocracked mineral base oil, Yubase (registered trademark) 4 manufactured by SK Lubricants), kinematic viscosity (100°C) 4.2 mm ² /s, kinematic viscosity (40°C) 19.3 mm ² /s, viscosity index 125, % C _P 79.4, % C _N 20.6, % C _A 0.0, sulfur content less than 10 mass ppm O-2: API Group IV base oil (poly-α-olefin base oil, Durasyn (registered trademark) 164 manufactured by INEOS), kinematic viscosity (100°C) 3.9 mm ² /s, kinematic viscosity (40°C) 17.4 mm ² /s, viscosity index 122

(Metal-based detergent)
B-1: Calcium carbonate overbased calcium salicylate, Ca content 8.0 mass%, base number (perchloric acid method) 225 mg KOH/g, metal ratio 3.3
B-2: Magnesium carbonate overbased magnesium salicylate, Mg content 7.5% by mass, base number (perchloric acid method) 342 mg KOH/g, metal ratio 3.3
B-3 ^* : calcium carbonate overbased calcium sulfonate, Ca content 11.6 mass%, base number (perchloric acid method) 302 mg KOH/g, metal ratio 13.9
B-4 ^* : magnesium carbonate overbased magnesium sulfonate, Mg content 9.1% by mass, base number (perchloric acid method) 405 mg KOH/g, metal ratio 27.7

(polymer)
C-1: Comb-shaped poly(meth)acrylate, weight average molecular weight 770,000, polydispersity 2.31
C-2: Comb-shaped poly(meth)acrylate, weight average molecular weight 420,000, polydispersity 3.04
C-3 ^* : Comb-shaped poly(meth)acrylate, weight average molecular weight 430,000, polydispersity 5.16
C-4 ^* : Comb-shaped poly(meth)acrylate, weight average molecular weight 150,000, polydispersity 2.48
C-5 ^* : Linear poly(meth)acrylate, weight average molecular weight 560,000, polydispersity 2.31
C-6 ^* : Dispersed linear poly(meth)acrylate, weight average molecular weight 290,000, polydispersity 3.95
C-7 ^* : hydrogenated styrene-isoprene copolymer, weight average molecular weight 440,000, polydispersity index 1.55

(Succinimide dispersant)
D-1: Unmodified polybutenyl succinimide, N content 1.2% by mass
D-2: Boric acid modified polybutenyl succinimide, N content 5.5% by mass, B content 2.6% by mass
D-3 ^* : Formamide-modified polybutenyl succinimide, N content 1.1% by mass

(E) ZnDTP: Zinc dialkyldithiophosphate, P content 15.6% by mass, S content 32.3% by mass, Zn content 16.5% by mass, alkyl group: combination of primary C8 alkyl group, isopropyl group, and secondary C6 alkyl group

(F) MoDTC: Sulfide (oxy)molybdenum dithiocarbamate (ADEKA Corporation, Sakuralube (registered trademark) 515), Mo content 10.1% by mass

(Antioxidants)
G-1: Amine-based antioxidant (diphenylamine)
G-2: Hindered phenol antioxidant

(Other Additives)
Demulsifier (rust inhibitor): Vinyl acetate-alkyl fumarate copolymer

(Iron ball sinking test)
With respect to each lubricating oil composition, low-temperature fluidity when mixed with water was evaluated by the following test with reference to ASTM D7563.
Water and regular gasoline were added to the lubricating oil composition and mixed to prepare a water-mixed sample oil. The water content and regular gasoline content in the sample oil were each 15% by mass based on the total amount of the sample. 300 g of sample oil was placed in a 500 mL beaker, and the beaker and homogenizer (POLYTRON PT 10-35 GT, shaft PT-DA 20/2 EC-B193) were fixed so that the distance from the tip of the shaft of the homogenizer to the bottom of the beaker was 5 mm, and the sample oil was stirred for 13 minutes at a homogenizer shaft rotation speed of 12,000 rpm. The sample oil was then transferred from the beaker to a 500 mL graduated cylinder (inner diameter 52 mm). Within 10 minutes of stirring, the graduated cylinder was placed in a thermostatic bath and cooled from 25 ° C to -30 ° C at a cooling rate of -10 ° C / h, and cooled at -30 ° C for 40 hours. After cooling, within 10 seconds of removing the measuring cylinder from the thermostatic bath, an iron ball (mass 0.25 mg) was gently placed on the surface of the sample oil, and the iron ball was released to measure the time required for the iron ball to sink from the surface of the sample oil and reach the bottom of the measuring cylinder. The results are shown in Tables 1 to 6. The shorter the sinking time, the better the low-temperature fluidity when mixed with water. In Tables 1 to 6, the entry "not measurable" means that the sinking of the iron ball was not observed (the shear stress applied to the sample oil by the iron ball did not reach the yield stress of the sample oil).

(Evaluation Results)
The lubricating oil compositions of Examples 1 to 14 all showed fast sinking of the iron ball, that is, good low-temperature fluidity when mixed with water.
In the composition of Comparative Example 1, in which a comb-shaped poly(meth)acrylate having a polydispersity of more than 4.0 was used as the polymer, no sinking of the iron ball was observed in the iron ball sinking test.
In the composition of Comparative Example 2, in which a comb-shaped poly(meth)acrylate having a weight-average molecular weight of less than 350,000 was used as the polymer, no sinking of the iron ball was observed in the iron ball sinking test.
In the compositions of Comparative Examples 3 and 4, in which a non-comb-shaped poly(meth)acrylate was used as the polymer, no sinking of the iron ball was observed in the iron ball sinking test.
In the composition of Comparative Example 5, which used a hydrogenated styrene-isoprene copolymer as the polymer, no sinking of the iron ball was observed in the iron ball sinking test.
In the compositions of Comparative Examples 6 to 9, which used only a sulfonate detergent as the metal-based detergent, sinking of the iron ball was not observed in the iron ball sinking test, or the time required for sinking was significantly longer than that of the compositions of the Examples.
In the composition of Comparative Example 10, in which the content of the salicylate soap group of the metallic detergent was too low, the sinking of the iron ball was observed, but the time required for the sinking was significantly longer than that of the compositions of the Examples.
In the composition of Comparative Example 11, in which only a succinimide dispersant modified with a compound other than boric acid (formamide) was used as the succinimide dispersant, no sinking of the iron ball was observed in the iron ball sinking test.
In the compositions of Comparative Examples 12 and 13, in which the combined proportion of unmodified succinimide dispersant and boric acid-modified succinimide dispersant in the total nitrogen content of the succinimide dispersant was too low, either the iron ball was not observed to sink or the time required for the ball to sink was significantly longer than in the compositions of the Examples.

The lubricating oil composition for internal combustion engines of the present invention can reduce the deterioration of low-temperature fluidity when water is mixed in. Therefore, the lubricating oil composition for internal combustion engines of the present invention can be preferably used for lubricating internal combustion engines operated under conditions where water is likely to accumulate inside, particularly engines of hybrid automobiles, and especially engines of parallel-type hybrid automobiles.

Claims (8)

(A) a lubricating base oil consisting of one or more mineral base oils or one or more synthetic base oils or a combination thereof and having a kinematic viscosity at 100° C. of 3.8 to 4.6 mm ² /s;
(B) a metal-based detergent including one or more metal salicylate detergents is present in an amount of 1,000 to 2,000 ppm by mass in terms of metal amount based on the total amount of the composition, and the amount of total salicylate soap groups per 1 kg of the composition is 10 mmol/kg or more;
(C) one or more comb-shaped poly(meth)acrylates having a weight average molecular weight of 350,000 to 1,000,000 and a polydispersity index of 4.0 or less, in an amount of 1.0 to 4.0 mass% based on the total mass of the composition as a resin content;
(D) a succinimide dispersant comprising one or more unmodified succinimide dispersants or one or more boric acid modified succinimide dispersants, or a combination thereof, wherein the ratio of the total nitrogen content of the unmodified succinimide dispersants and the boric acid modified succinimide dispersants to the total nitrogen content of the succinimide dispersant is 70 mass% or more, and the succinimide dispersant is 100 to 1000 mass ppm in terms of nitrogen content based on the total amount of the composition;
A lubricating oil composition for internal combustion engines, characterized in that the HTHS viscosity at 150°C is 2.25 mPa·s or more and less than 2.55 mPa·s. The lubricating oil composition of claim 1, wherein the (A) lubricating base oil is one or more API base oil group III base oils, or one or more API base oil group IV base oils, or a combination thereof. The lubricating oil composition according to claim 1 or 2, wherein the content of component (B) is 15 mmol/kg or more in terms of the amount of total soap groups per kg of the composition. The lubricating oil composition according to any one of claims 1 to 3, wherein the proportion of all salicylate soap groups in the total soap groups of component (B) is 50 mol % or more. The lubricating oil composition according to any one of claims 1 to 4, wherein the weight average molecular weight of component (C) is more than 400,000 and not more than 1,000,000. The lubricating oil composition according to any one of claims 1 to 5, wherein the mass ratio (B/N) of the total boron content (B) to the total nitrogen content (N) of the (D) component is 0 to 0.60. The lubricating oil composition according to any one of claims 1 to 6, wherein the component (D) is a condensation reaction product of an alkyl or alkenyl succinic acid or anhydride thereof having an alkyl or alkenyl group having 40 to 400 carbon atoms with a polyamine, or a modified product thereof, or a combination thereof. The lubricating oil composition according to any one of claims 1 to 7, which is used to lubricate the internal combustion engine of a hybrid vehicle.