JP7623350B2 - Lubricating Oil Composition - Google Patents

Description

The present invention relates to a lubricating oil composition.

In recent years, there has been a demand for improved fuel economy in vehicles such as automobiles in order to reduce the environmental impact. One method for improving fuel economy is known to be to reduce the viscosity of a lubricating oil composition to reduce viscous resistance and energy loss (see, for example, Patent Document 1).

JP 2004-137317 A

However, when the viscosity of a lubricating oil composition is reduced, the amount of evaporation of the lubricating oil composition tends to increase, making it difficult to maintain a sufficient amount of oil required to lubricate engine parts. In addition, it becomes difficult to properly maintain an oil film on sliding parts inside the engine. As a result, engine parts and the like are easily damaged by fatigue and wear. This problem is particularly likely to become evident in lubricating oil compositions used in environments with high thermal loads, such as engines equipped with turbochargers.

Therefore, there is a demand for a lubricating oil composition that has low viscosity, low volatility, and excellent performance in properly maintaining an oil film on sliding parts inside an engine (hereinafter also referred to as "oil film retention ability"). In addition, from the viewpoint of providing a lubricating oil composition with excellent long drain properties, high temperature detergency is also required.
Furthermore, lubricating oil compositions are required to have high compatibility with rubber materials used in sealing materials and the like, and to suppress swelling and hardening of the rubber materials.
However, a lubricating oil composition that satisfies all of these requirements has not yet been fully investigated.

The objective of the present invention is to provide a lubricating oil composition that has low viscosity, low volatility, excellent oil film retention, and excellent high-temperature detergency and compatibility with rubber materials.

In order to solve the above problems, the present inventors have conducted extensive research into low-viscosity lubricating oil compositions having a kinetic viscosity at 100° C. in the range of 5.0 mm ² /s or more and less than 7.1 mm ² /s, and have completed the present invention.
The present invention relates to the following [1] and [2].
[1] A lubricating oil composition comprising a base oil (A) containing an olefin polymer (A1), a viscosity index improver (B), and an imide-based dispersant (C),
The olefin polymer (A1) includes a first olefin polymer (A1-1) having a kinetic viscosity at 100° C. of 3.0 mm ² /s or more, and the content of the first olefin polymer (A1-1) is 30 mass% or more based on the total amount of the base oil (A);
the olefin polymer (A1) does not contain a second olefin polymer (A1-2) having a kinetic viscosity at 100° C. of less than 3.0 mm ² /s, or if it does contain one, the amount of the second olefin polymer (A1-2) is less than 18.5 mass % based on the total amount of the base oil (A);
the content of the resin component (B1) derived from the viscosity index improver (B) is 0.01 mass% or more based on the total amount of the lubricating oil composition;
The nitrogen atom content derived from the imide-based dispersant (C) is 0.06 mass% or more based on the total amount of the lubricating oil composition;
a content ratio [(B1)/(A1-1)] of the resin component (B1) derived from the viscosity index improver (B) to the first olefin polymer (A1-1) is greater than 0.001 in terms of mass ratio,
The kinetic viscosity at 100°C is 5.0 ^mm2 /s or more and less than 7.1 ^mm2 /s;
A lubricating oil composition having an aniline point of 95° C. or higher.
[2] A method for lubricating an internal combustion engine using the lubricating oil composition according to [1] above.

According to the present invention, it is possible to provide a lubricating oil composition that has low viscosity, low volatility, excellent oil film retention, and excellent high-temperature detergency and compatibility with rubber materials.

In this specification, the lower limit and upper limit described in stages for the preferred numerical range (e.g., the range of the content, etc.) can be independently combined. For example, the description "preferably 10 to 90, more preferably 30 to 60" can be combined with the "preferable lower limit (10)" and the "more preferable upper limit (60)" to form "10 to 60."
In this specification, the numerical values in the examples are numerical values that can be used as upper or lower limits.
In this specification, a numerical range expressed as "AA to BB" means "at least AA and not more than BB," unless otherwise specified.

In this specification, the mass average molecular weight (Mw) and number average molecular weight (Mn) of each component are values calculated as standard polystyrene measured by gel permeation chromatography (GPC), and specifically, mean values measured by the method described in the Examples.
In this specification, for example, "(meth)acrylate" is used as a term indicating both "acrylate" and "methacrylate", and the same applies to other similar terms and similar labels.

In this specification, "kinematic viscosity at 40°C" is also referred to as "40°C kinematic viscosity." Also, "kinematic viscosity at 100°C" is also referred to as "100°C kinematic viscosity."

[Embodiments of the lubricating oil composition of the present invention]
The lubricating oil composition of the present invention is a lubricating oil composition containing a base oil (A) containing an olefin polymer (A1), a viscosity index improver (B), and an imide-based dispersant (C),
The olefin polymer (A1) includes a first olefin polymer (A1-1) having a kinetic viscosity at 100° C. of 3.0 mm ² /s or more, and the content of the first olefin polymer (A1-1) is 30 mass% or more based on the total amount of the base oil (A);
the olefin polymer (A1) does not contain a second olefin polymer (A1-2) having a kinetic viscosity at 100° C. of less than 3.0 mm ² /s, or if it does contain one, the amount of the second olefin polymer (A1-2) is less than 18.5 mass % based on the total amount of the base oil (A);
the content of the resin component (B1) derived from the viscosity index improver (B) is 0.01 mass% or more based on the total amount of the lubricating oil composition;
The nitrogen atom content derived from the imide-based dispersant (C) is 0.06 mass% or more based on the total amount of the lubricating oil composition;
a content ratio of the resin component (B1) to the first olefin polymer (A1) [(B1)/(A1-1)] is more than 0.001 in terms of mass ratio,
The kinetic viscosity at 100°C is 5.0 ^mm2 /s or more and less than 7.1 ^mm2 /s;
The lubricating oil composition has an aniline point of 95° C. or higher.

In order to solve the above problems, the present inventors have conducted extensive research into a low-viscosity lubricating oil composition having a kinetic viscosity at 100° C. in the range of 5.0 mm ² /s or more and less than 7.1 mm ² /s.
As a result, it was found that the above-mentioned problems can be solved by a lubricating oil composition which uses a base oil containing a specific amount of a specific olefin polymer while having a small content of other olefin polymers different from the specific olefin polymer, adjusts the resin content derived from the viscosity index improver and the specific olefin polymer to a specific ratio, adjusts the content of the resin content derived from the viscosity index improver and the content of the imide dispersant, etc. to specific ranges, and further adjusts the aniline point to a specific range. Based on this finding, the present inventors further conducted various studies and have completed the present invention.

In the following description, the “base oil (A)”, the “viscosity index improver (B)”, and the “imide-based dispersant (C)” will also be referred to as “component (A)”, “component (B)”, and “component (C)”, respectively.
The lubricating oil composition of one embodiment of the present invention may be composed only of component (A), component (B), and component (C), but may also contain components other than component (A), component (B), and component (C) as long as the effects of the present invention are not impaired.
In the lubricating oil composition of one embodiment of the present invention, the total content of components (A), (B), and (C) is preferably 70 mass % to 100 mass %, more preferably 75 mass % to 100 mass %, and even more preferably 80 mass % to 100 mass %, based on the total amount of the lubricating oil composition.
Each component contained in the lubricating oil composition of the present invention will now be described in detail.

<<Base oil (A)>>
The lubricating oil composition of the present invention contains a base oil (A) containing an olefin polymer (A1).
The lubricating oil composition of the present invention contains, as the olefin polymer (A1), a first olefin polymer (A1-1) having a kinematic viscosity of 3.0 mm ² /s or more at 100° C. The content of the first olefin polymer (A1-1) is 30 mass % or more based on the total amount of the base oil (A).
When the content of the first olefin polymer (A1-1) is less than 30 mass % based on the total amount of the base oil (A), the lubricating oil composition cannot be made low volatility.

From the viewpoint of facilitating the preparation of a low-volatility lubricating oil composition, the 100°C kinetic viscosity of the first olefin polymer (A1-1) is preferably 3.1 ^mm2 /s or more, more preferably 3.2 ^mm2 /s or more, and even more preferably 3.3 ^mm2 /s or more. From the viewpoint of facilitating the preparation of a low-volatility lubricating oil composition, the 100°C kinetic viscosity of the olefin polymer (A1) is preferably 7.0 ^mm2 /s or less, more preferably 5.0 ^mm2 /s or less, even more preferably 4.0 ^mm2 /s or less, and even more preferably 3.7 ^mm2 /s or less.
The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, the range is preferably 3.1 mm ^{2 /} s to 7.0 mm ² /s, more preferably 3.2 mm ² /s to 5.0 mm ² /s, even more preferably 3.3 mm ^{2 /s} to 4.0 mm ² /s, and still more preferably 3.3 mm ^{2 /} s to 3.7 mm ² /s.
In this specification, the 100° C. kinematic viscosity of the base oil is a value measured in accordance with JIS K2283:2000.

From the viewpoint of facilitating the preparation of a low-volatility lubricating oil composition, the content of the first olefin polymer (A1-1) is preferably 40% by mass to 100% by mass, more preferably 50% by mass to 100% by mass, and even more preferably 60% by mass to 100% by mass, based on the total amount of the base oil (A).
The first olefin polymer (A1-1) will be described in detail below.

<First olefin polymer (A1-1)>
The first olefin polymer (A1-1) is a polymer containing a structural unit (a1) (hereinafter, also referred to as "monomer (a1)") derived from an α-olefin.
The first olefin polymer (A1-1) may be used alone or in combination of two or more kinds.
The number of carbon atoms in the monomer (a1) is preferably 6 or more, more preferably 8 or more, from the viewpoint of easily exerting the effects of the present invention. The number is also preferably 20 or less, more preferably 16 or less, and even more preferably 12 or less. The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, the number is preferably 6 to 20, more preferably 8 to 16, and even more preferably 8 to 12. The number is even more preferably 10. The monomer (a1) may be linear or branched.
Specific examples of the monomer (a1) include preferably 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, and 1-eicosene. Among these, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, and 1-heptadecene are more preferred, 1-octene, 1-nonene, 1-decene, 1-undecene, and 1-dodecene are even more preferred, and 1-decene is even more preferred.
The monomer (a1) may be used alone or in combination of two or more kinds.

Here, from the viewpoint of making it easier to exert the effects of the present invention, the first olefin polymer (A1-1) preferably contains 1-decene as the monomer (a1).
The content of 1-decene is preferably 80 to 100 mass%, more preferably 90 to 100 mass%, even more preferably 95 to 100 mass%, and still more preferably 100 mass%, based on the total amount of monomers constituting the first olefin polymer (A1-1).
In addition, when the first olefin polymer (A1-1) contains an α-olefin other than 1-decene as the monomer (a1), the α-olefin other than 1-decene may be one or more selected from the α-olefins other than 1-decene among the above α-olefins exemplified as the monomer (a1).

In order to facilitate the exertion of the effects of the present invention, the first olefin polymer (A1-1) preferably contains a dimer to a pentamer of the monomer (a1), more preferably a dimer to a tetramer, and even more preferably a trimer. For example, when the monomer (a1) is 1-decene, the first olefin polymer (A1-1) preferably contains a decene trimer.

In addition, from the viewpoint of easily achieving the effects of the present invention and easily ensuring the performance as an engine oil, it is preferable that the first olefin polymer (A1-1) has terminal vinylidene double bonds reduced by hydrogenation. That is, the first olefin polymer (A1-1) is preferably a partially hydrogenated product, and more preferably a fully hydrogenated product.

(Polymerization method for first olefin polymer (A1-1))
The polymerization method for the first olefin polymer (A1-1) is not particularly limited, and any known method capable of polymerizing the first olefin polymer (A1-1) by a polymerization reaction of an α-olefin (for example, a polymerization method using an acid catalyst such as a _BF3 catalyst) can be appropriately adopted.
Here, from the viewpoint of increasing the content (purity) of a desired polymer (e.g., decene trimer) in the first olefin polymer (A1-1) and making it easier to exhibit the effects of the present invention, it is preferable to employ a polymerization method using a metallocene catalyst.

Metallocene Catalyst As the metallocene catalyst, a complex containing a Group 4 element and having a five-membered conjugated carbon ring is preferable.
The Group 4 element may be one or more selected from titanium, zirconium, and hafnium, with zirconium being preferred among these.
As the complex having a conjugated five-membered carbon ring, a complex having a substituted or unsubstituted cyclopentadienyl ligand is preferable.
Specific examples of metallocene catalysts include bis(n-octadecylcyclopentadienyl)zirconium dichloride, bis(trimethylsilylcyclopentadienyl)zirconium dichloride, bis(tetrahydroindenyl)zirconium dichloride, bis[(t-butyldimethylsilyl)cyclopentadienyl]zirconium dichloride, bis(di-t-butylcyclopentadienyl)zirconium dichloride, (ethylidene-bisindenyl)zirconium dichloride, biscyclopentadienylzirconium dichloride, ethylidenebis(tetrahydroindenyl)zirconium dichloride, and bis[3,3(2-methyl-benzindenyl)]dimethylsilanediylzirconium dichloride.
The metallocene catalyst may be used alone or in combination of two or more kinds.

Co-catalyst When a polymerization method using a metallocene catalyst is employed, an oxygen-containing organoaluminum compound may be used as a co-catalyst together with the metallocene catalyst.
Specific examples of oxygen-containing organoaluminum compounds include methylalumoxane, ethylalumoxane, and isobutylalumoxane.
The oxygen-containing organoaluminum compounds may be used alone or in combination of two or more.

Blending Ratio of Co-catalyst to Metallocene Catalyst The blending ratio of the co-catalyst to the metallocene catalyst (co-catalyst/metallocene catalyst) is, in terms of a molar ratio, preferably 5 to 1,000, more preferably 7 to 500, and even more preferably 10 to 200, from the viewpoint of obtaining a first olefin polymer (A1-1) that can more easily exhibit the effects of the present invention.

(Production method of first olefin polymer (A1-1))
The first olefin polymer (A1-1) is preferably produced through the following steps (i) to (iii).
Step (i): A step of polymerizing the monomer (a1) using a metallocene catalyst.
Step (ii): A step of treating the polymer obtained in step (i) with an alkali.
Step (iii): A step of subjecting the polymer after the alkali treatment in step (ii) to a hydrogen treatment.

Step (i)
Step (i) may be carried out in a batchwise or continuous manner.
The above-mentioned oxygen-containing organoaluminum compound may be used as a co-catalyst together with the metallocene catalyst.
In step (i), the polymerization of monomer (a1) may proceed in the presence of one or more organic solvents selected from benzene, ethylbenzene, toluene, and the like.
The polymerization reaction in the step (i) is preferably carried out under conditions of a reaction temperature of 15 to 100° C. and a reaction pressure of atmospheric pressure to 0.2 MPa.
After the polymerization has progressed sufficiently, the reaction can be stopped by adding water or alcohol.

Step (ii)
The step (ii) is a step in which the polymer obtained in the step (i) is treated with an alkali to remove catalyst components such as the metallocene catalyst and the oxygen-containing organoaluminum compound.
The alkali used in step (ii) may be, for example, one or more selected from sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, and the like.
The catalyst component can be removed by adding a solution of these alkalis dissolved in water or an alcohol such as methanol, ethanol, or propanol to a reaction liquid containing a polymer, thoroughly stirring the mixture, separating the mixture, and taking out the organic layer.
The pH of the solution is preferably at least 9. The temperature of the solution is preferably 20 to 100°C.

Step (iii)
The step (iii) is a step of subjecting the polymer after the alkali treatment in the step (ii) to a hydrogenation treatment to convert the polymer into a hydrogenated product. The hydrogenated product may be a partial hydrogenated product, but is preferably a fully hydrogenated product.
The hydrogenation treatment in the step (iii) is carried out by filling a system containing the polymer with hydrogen gas and heating it in the presence of a metal catalyst.
The metal catalyst used in the hydrogenation treatment may be, for example, one or more selected from nickel-based catalysts, cobalt-based catalysts, palladium-based catalysts, platinum-based catalysts, and the like. Specific examples of the metal catalyst include one or more selected from diatomaceous earth-supported nickel catalysts, cobalt trisacetylacetonate/organoaluminum catalysts, activated carbon-supported palladium catalysts, alumina-supported platinum catalysts, and the like.

The temperature condition of the hydrogenation treatment is usually 200° C. or less, and is appropriately set depending on the type of metal catalyst used. For example, when a nickel-based catalyst is used, the temperature is preferably 150 to 200° C. When a palladium-based catalyst or a platinum-based catalyst is used, the temperature is preferably 50 to 150° C. When a homogeneous reducing agent such as cobalt trisacetylacetonate/organoaluminum is used, the temperature is preferably 20 to 100° C.
The hydrogen pressure during the hydrogenation treatment is preferably from normal pressure to 20 MPa.

After the hydrogenation treatment, it is preferable to carry out a distillation treatment to remove by-products.
The distillation treatment is preferably carried out under conditions of a temperature of 180 to 450° C. and a pressure of 0.01 to 100 kPa.

<Second Olefin Polymer (A1-2)>
In the lubricating oil composition of the present invention, the olefin polymer (A1) does not contain a second olefin polymer (A1-2) having a kinetic viscosity at 100°C of less than 3.0 ^mm2 /s, or if it does contain one, the amount is less than 18.5 mass% based on the total amount of the base oil (A).
If the content of the second olefin polymer (A1-2) is 18.5 mass % or more based on the total amount of the base oil (A), the lubricating oil composition cannot be made low volatility.

The lower the kinematic viscosity at 100° C. of the second olefin polymer (A1-2) (that is, less than 2.5 mm ² /s, further less than 2.3 mm ² /s, particularly less than 2.1 mm ² /s), the more difficult it becomes to ensure low volatility of the lubricating oil composition.
Therefore, from the viewpoint of facilitating the preparation of a low-volatility lubricating oil composition, the content of the second olefin polymer (A1-2) is preferably as small as possible. Specifically, the content of the second olefin polymer (A1-2) is preferably 0% by mass to 15% by mass, more preferably 0% by mass to 10% by mass, even more preferably 0% by mass to 5% by mass, still more preferably 0% by mass to 1% by mass, and even more preferably no second olefin polymer (A1-2) is contained, based on the total amount of the base oil (A).

The second olefin polymer (A1-2) may be used alone or in combination of two or more kinds.
The second olefin polymer (A1-2) can be produced, for example, by using the same method as the above-mentioned method for producing the first olefin polymer (A1-1) but changing the distillation temperature or the like.

<Other base oils>
In the lubricating oil composition of one embodiment of the present invention, the base oil (A) may contain a base oil different from the above-mentioned base oils. For example, in the lubricating oil composition of one embodiment of the present invention, the base oil (A) may contain one or more selected from the group consisting of mineral oils (A2) and synthetic oils (A3) other than the first olefin polymer (A1-1) and the second olefin polymer (A1-2).
The content of the other base oil is 70 mass% or less based on the total amount of base oil (A). From the viewpoint of making it easier to exhibit the effects of the present invention, the content is preferably 0 mass% to 60 mass%, more preferably 0 mass% to 50 mass%, and even more preferably 0 mass% to 40 mass%.
The mineral oil (A2) and the synthetic oil (A3) will be described in detail below.

(Mineral oil (A2))
As the mineral oil (A2), any mineral oil commonly used as a lubricating base oil can be used without any particular limitation, so long as it does not impair the effects of the present invention.
Specific examples of the mineral oil (A2) include atmospheric residual oil obtained by atmospheric distillation of crude oil such as paraffinic crude oil, intermediate base crude oil, naphthenic crude oil, etc.; distillate oil obtained by vacuum distillation of such atmospheric residual oil; mineral oil obtained by subjecting such distillate oil to one or more treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, etc.; wax isomerized mineral oil, etc.
The mineral oil (A2) may be used alone or in combination of two or more kinds.

Here, from the viewpoint of facilitating the preparation of a low-volatility lubricating oil composition, the content of mineral oil (A2) is preferably 50 mass% or less, more preferably 40 mass% or less, and even more preferably 35 mass% or less, based on the total amount of base oil (A).

On the other hand, in the lubricating oil composition of one embodiment of the present invention, it is preferable to blend a certain amount or more of mineral oil (A2) within a range in which the content of mineral oil (A2) does not exceed the above upper limit value. This makes it easier to adjust the aniline point of the lubricating oil composition to 95 ° C. or higher, to improve compatibility with rubber materials, and to easily exert the effect of suppressing swelling and the effect of rubber materials while suppressing the cost of base oil (A). From this viewpoint, the content of mineral oil (A2) is preferably 10 mass % or more, more preferably 20 mass % or more, and even more preferably 25 mass % or more based on the total amount of base oil (A).
In this case, the total content of the first olefin polymer (A1-1) and the mineral oil (A2) is preferably 70% by mass to 100% by mass, more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, still more preferably 95% by mass to 100% by mass, and even more preferably 100% by mass, based on the total amount of the base oil (A).
In this case, the content ratio of the first olefin polymer (A1-1) to the mineral oil (A2) [(A1-1)/(A2)] is preferably 50/50 or more, more preferably 60/40 or more, and even more preferably 65/35 or more, in terms of mass ratio. It is also preferably 90/10 or less, more preferably 80/20 or less, and even more preferably 75/25 or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 50/50 to 90/10, more preferably 60/40 to 80/20, and even more preferably 65/35 to 75/25.

As the mineral oil (A2), a mineral oil classified as Group II or III of the American Petroleum Institute (API) base oil category is preferred.
From the viewpoint of easily exerting the effects of the present invention, the 100°C kinematic viscosity of the mineral oil (A2) is preferably 1.0 ^mm2 /s or more, more preferably 1.5 ^mm2 /s or more, and even more preferably 2.0 ^mm2 /s or more. Also, it is preferably 7.5 ^mm2 /s or less, more preferably 5.0 ^mm2 /s or less, and even more preferably 3.5 ^mm2 /s or less. The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 1.0 mm2 ^/s to 7.5 ^mm2 /s, more preferably 1.5 mm2 ^/s to 5.0 ^mm2 /s, and even more preferably 2.0 mm2 ^/s to 3.5 ^mm2 /s.
The viscosity index of the mineral oil (A2) is preferably 90 or more, more preferably 95 or more, and even more preferably 100 or more.
When the mineral oil (A2) is a mixture of two or more kinds, the kinematic viscosity and viscosity index of the mixture need only be within the above ranges.

(Synthetic oil (A3))
As the synthetic oil (A3), any synthetic oil generally used as a lubricating base oil can be used without any particular limitation, so long as it does not impair the effects of the present invention.
Specific examples of the synthetic oil (A3) include polyphenyl ether, alkylbenzene, alkylnaphthalene, polyphenyl-based hydrocarbon, ester-based oil, naphthene-based synthetic oil, glycol-based synthetic oil, and GTL base oil obtained by isomerizing wax produced from natural gas by the Fischer-Tropsch process or the like (GTL wax (Gas To Liquids WAX)).

Here, from the viewpoint of easily achieving the effects of the present invention, the content of the synthetic oil (A3) is 70 mass% or less based on the total amount of the base oil (A), but from the viewpoint of more easily achieving the effects of the present invention, it is preferably 0 mass% to 60 mass%, more preferably 0 mass% to 50 mass%, and even more preferably 0 mass% to 40 mass%.

Here, from the viewpoint of easily adjusting the aniline point to 95° C. or higher, easily improving compatibility with rubber materials, and easily exerting the effect of suppressing swelling and the like of rubber materials, it is preferable that the base oil (A) does not contain an ester-based oil (A3-1). Or, even if the base oil (A3-1) is contained, its content is preferably 15 mass % or less, and more preferably 10 mass % or less, based on the total amount of the base oil (A).
From the same viewpoint, it is preferable that the base oil (A) does not contain a naphthenic synthetic oil (A3-2). Or, even if the base oil (A) contains a naphthenic synthetic oil (A3-2), the content of the naphthenic synthetic oil (A3-2) is preferably 15 mass% or less, and more preferably 10 mass% or less, based on the total amount of the base oil (A).

<<Viscosity index improver (B)>>
The lubricating oil composition of the present invention contains a viscosity index improver (B). In the lubricating oil composition of the present invention, the content of the resin component (B1) derived from the viscosity index improver (B) is 0.01 mass % or more based on the total amount of the lubricating oil composition.
When the content of the resin component (B1) derived from the viscosity index improver (B) is less than 0.01 mass % based on the total amount of the lubricating oil composition, oil film retention cannot be sufficiently ensured.
Here, from the viewpoint of making it easier to improve the oil film retention, the content of the resin component (B1) derived from the viscosity index improver (B) is preferably 0.10 mass% or more, more preferably 0.30 mass% or more, and even more preferably 0.50 mass% or more, based on the total amount of the lubricating oil composition. Also, from the viewpoint of the shear stability of the viscosity index improver (B), it is preferably 5.0 mass% or less, more preferably 4.0 mass% or less, even more preferably 3.0 mass% or less, and even more preferably 1.5 mass% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 0.10 mass% to 5.0 mass%, more preferably 0.30 mass% to 4.0 mass%, even more preferably 0.50 mass% to 3.0 mass%, and even more preferably 0.50 to 1.5 mass%.

The term "resin component (B1) derived from viscosity index improver (B)" refers to a polymer having a mass average molecular weight (Mw) of 1,000 or more and having a certain repeating unit.
In the lubricating oil composition of one embodiment of the present invention, the mass average molecular weight (Mw) of the resin component (B1) derived from the viscosity index improver (B) is preferably from 200,000 to 1,000,000, more preferably from 200,000 to 800,000, and even more preferably from 200,000 to 700,000, from the viewpoint of providing a lubricating oil composition that can stably exhibit excellent fuel saving properties even when used in a wide range of temperature environments from low temperature to high temperature, and from the viewpoint of providing excellent oil film retention properties.
In the lubricating oil composition of one embodiment of the present invention, the molecular weight distribution (Mw/Mn) (wherein Mw is the mass average molecular weight of the resin component (B1) and Mn is the number average molecular weight of the resin component (B1)) of the resin component (B1) derived from the viscosity index improver (B) is preferably 8.00 or less, more preferably 7.00 or less, more preferably 6.50 or less, even more preferably 6.00 or less, even more preferably 5.00 or less, and even more preferably 3.00 or less, from the viewpoint of improving the fuel saving performance of the lubricating oil composition. Note that the smaller the molecular weight distribution of the resin component (B1), the more the fuel saving performance of the lubricating oil composition containing the resin component (B1) together with the base oil (A) tends to be improved.
The molecular weight distribution of the resin component (B1) is not particularly limited in terms of its lower limit, but is usually 1.01 or more, preferably 1.05 or more, and more preferably 1.10 or more.

In one embodiment of the lubricating oil composition of the present invention, the resin component (B1) derived from the viscosity index improver (B) contains, for example, one or more selected from non-dispersant polymethacrylate, dispersant polymethacrylate, comb polymer, etc. The resin component (B1) may contain other resin components, etc., as long as the effects of the present invention are not impaired.

From the viewpoint of making it easier to exert the effects of the present invention and of lowering the viscosity of the lubricating oil composition in the low temperature region, it is preferred that the resin component (B1) derived from the viscosity index improver (B) is a comb polymer (B1-1).
The comb polymer (B1-1) will be described in detail below.

<Comb polymer (B1-1)>
In the present invention, the "comb polymer (B1-1)" refers to a polymer having a structure in which the main chain has many three-way branching points from which high molecular weight side chains extend.
The mass average molecular weight (Mw) of the comb polymer (B1-1) is preferably 100,000 or more, more preferably 200,000 or more, even more preferably 250,000 or more, even more preferably 300,000 or more, and even more preferably 350,000 or more, from the viewpoint of improving fuel efficiency. Also, it is preferably 1,000,000 or less, more preferably 800,000 or less, even more preferably 750,000 or less, even more preferably 700,000 or less, and even more preferably 650,000 or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 100,000 to 1,000,000, more preferably 200,000 to 800,000, even more preferably 250,000 to 750,000, even more preferably 300,000 to 700,000, and even more preferably 350,000 to 650,000.

The molecular weight distribution (Mw/Mn) of the comb polymer (B1-1) (wherein Mw is the mass average molecular weight of the comb polymer (B1-1) and Mn is the number average molecular weight of the comb polymer (B1-1)) is, from the viewpoint of improving the fuel saving performance of the lubricating oil composition, preferably 8.00 or less, more preferably 7.00 or less, more preferably 6.50 or less, even more preferably 6.00 or less, even more preferably 5.00 or less, and still more preferably 3.00 or less. Note that the smaller the molecular weight distribution of the comb polymer (B1-1), the more the fuel saving performance of the lubricating oil composition containing the comb polymer (B1-1) together with the base oil (A) tends to be improved.
The molecular weight distribution of the comb polymer (B1-1) is not particularly limited in terms of its lower limit, but is usually 1.01 or more, preferably 1.05 or more, and more preferably 1.10 or more.

In the lubricating oil composition of one embodiment of the present invention, the content of comb polymer (B1-1) is preferably 0.10 mass % or more, more preferably 0.30 mass % or more, and even more preferably 0.50 mass % or more, based on the total amount of the lubricating oil composition.
In the lubricating oil composition of one embodiment of the present invention, the content of comb polymer (B1-1) is preferably 5.0 mass % or less, more preferably 4.0 mass % or less, and even more preferably 3.0 mass % or less, based on the total amount of the lubricating oil composition.

The SSI (shear stability index) of the comb polymer (B1-1) is preferably 12.0 or less, more preferably 10.0 or less, even more preferably 5.0 or less, still more preferably 3.0 or less, and even more preferably 1.0 or less.
The SSI of the comb polymer (B1-1) has no particular lower limit, but is usually 0.1 or more, preferably 0.2 or more.

In this specification, the SSI (shear stability index) of the comb polymer (B1-1) indicates the viscosity reduction due to shear caused by the resin content in the comb polymer (B1-1) as a percentage, and is a value measured in accordance with ASTM D6278. More specifically, it is a value calculated by the following calculation formula (1).

In the above formula (1), Kv ₀ is the value of the kinetic viscosity at 100°C of a sample oil obtained by diluting a viscosity index improver containing a resin component with mineral oil, and Kv ₁ is the value of the kinetic viscosity at 100°C after the sample oil obtained by diluting the viscosity index improver containing a resin component with mineral oil is passed through a 30-cycle high-shear diesel injector according to the procedure of ASTM D6278. Also, Kv _oil is the value of the kinetic viscosity at 100°C of the mineral oil used to dilute the viscosity index improver.

The SSI value of the comb polymer (B1-1) varies depending on the structure of the comb polymer (B1-1). Specifically, there are the following tendencies, and the SSI value of the comb polymer (B1-1) can be easily adjusted by taking these factors into consideration. The following factors are merely examples, and the SSI value can also be adjusted by taking other factors into consideration.
A comb polymer in which the side chains of the comb polymer (B1-1) are constituted by a macromonomer (x1) and the content of the structural unit (X1) derived from the macromonomer (x1) is 0.5 mol % or more based on the total amount of the structural units, tends to have a low SSI value.
The larger the molecular weight of the macromonomer (x1) constituting the side chain of the comb polymer (B1-1), the lower the SSI value tends to be.

<Structural Units of Comb Polymer (B1-1)>
The structural units of the comb polymer (B1-1) used in one embodiment of the present invention will now be described.
The comb polymer (B1-1) is preferably a polymer having at least a structural unit (X1) derived from a macromonomer (x1). This structural unit (X1) corresponds to the above-mentioned "high molecular weight side chain."
In the present invention, the above-mentioned "macromonomer" means a high molecular weight monomer having a polymerizable functional group, and is preferably a high molecular weight monomer having a polymerizable functional group at its terminal.

The longer the main chain is relative to the side chains of the comb polymer (B1-1), the lower its shear stability. This property is thought to contribute to improved fuel efficiency even at low temperatures around 50°C.

From the above viewpoints, the content of the structural unit (X1) in the comb polymer (B1-1) used in one embodiment of the present invention is preferably at least 0.1 mol % and less than 10 mol %, more preferably 0.2 to 7 mol %, even more preferably 0.3 to 5 mol %, and still more preferably 0.5 to 3 mol %, based on the total amount of the structural units of the comb polymer (B1-1).
In this specification, the content of each structural unit in the comb polymer (B1-1) means a value calculated by analyzing a ¹³ C-NMR quantitative spectrum.

From the above viewpoints, the number average molecular weight (Mn) of the macromonomer (x1) is preferably 300 or more, more preferably 500 or more, even more preferably 1,000 or more, still more preferably 2,000 or more, particularly preferably 4,000 or more, and is preferably 100,000 or less, more preferably 50,000 or less, even more preferably 20,000 or less, and still more preferably 10,000 or less.

Examples of the polymerizable functional group possessed by the macromonomer (x1) include an acryloyl group (CH ₂ ═CH—COO—), a methacryloyl group (CH ₂ ═CCH ₃ —COO—), an ethenyl group (CH ₂ ═CH—), a vinyl ether group (CH ₂ ═CH—O—), an allyl group (CH ₂ ═CH—CH ₂ —), an allyl ether group (CH ₂ ═CH—CH ₂ —O—), a group represented by CH ₂ ═CH—CONH—, and a group represented by CH ₂ ═CCH ₃ —CONH—.

The macromonomer (x1) may have, in addition to the above polymerizable functional group, one or more repeating units represented by the following general formulae (i) to (iii).

In the above general formula (i), R ^b1 represents a linear or branched alkylene group having 1 to 10 carbon atoms, and specific examples thereof include a methylene group, an ethylene group, a 1,2-propylene group, a 1,3-propylene group, a 1,2-butylene group, a 1,3-butylene group, a 1,4-butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group, and a 2-ethylhexylene group.
In the above general formula (ii), R ^b2 represents a linear or branched alkylene group having 2 to 4 carbon atoms, and specific examples thereof include an ethylene group, a 1,2-propylene group, a 1,3-propylene group, a 1,2-butylene group, a 1,3-butylene group, and a 1,4-butylene group.
In the above general formula (iii), R ^b3 represents a hydrogen atom or a methyl group.
Furthermore, R ^b4 represents a linear or branched alkyl group having 1 to 10 carbon atoms, and specific examples thereof include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an isopropyl group, an isobutyl group, a sec-butyl group, a t-butyl group, an isopentyl group, a t-pentyl group, an isohexyl group, a t-hexyl group, an isoheptyl group, a t-heptyl group, a 2-ethylhexyl group, an isooctyl group, an isononyl group, and an isodecyl group.
When the compound has a plurality of repeating units represented by each of the above general formulae (i) to (iii), R ^b1 , R ^b2 , R ^b3 , and R ^b4 may be the same or different from each other.

In one embodiment of the present invention, the macromonomer (x1) is preferably a polymer having a repeating unit represented by the general formula (i), and more preferably a polymer having a repeating unit (X1-1) in which R ^b1 in the general formula (i) is a 1,2-butylene group and/or a 1,4-butylene group.

The content of the repeating unit (X1-1) is preferably 1 to 100 mol%, more preferably 20 to 95 mol%, even more preferably 40 to 90 mol%, and even more preferably 50 to 80 mol%, based on the total amount (100 mol%) of the constituent units of the macromonomer (x1).

In addition, when the macromonomer (x1) is a copolymer having two or more repeating units selected from the general formulas (i) to (iii), the form of the copolymerization may be a block copolymer or a random copolymer.

The comb polymer (B1-1) used in one embodiment of the present invention may be a homopolymer consisting of only structural units (X1) derived from one type of macromonomer (x1), or it may be a copolymer containing structural units (X1) derived from two or more types of macromonomers (x1).
Furthermore, the comb polymer (B1-1) used in one embodiment of the present invention may be a copolymer that contains, in addition to a structural unit derived from the macromonomer (x1), a structural unit (X2) derived from a monomer (x2) other than the macromonomer (x1).
A specific structure of such a comb polymer (B1-1) is preferably a copolymer having a main chain containing the structural unit (X2) derived from the monomer (x2) and a side chain containing the structural unit (X1) derived from the macromonomer (x1). More preferably, the main chain contains the structural unit (X2) derived from the monomer (x2) and also contains the structural unit (X1) derived from the macromonomer (x1) as a main chain.

Examples of monomer (x2) include monomer (x2-a) represented by the following general formula (a1), alkyl (meth)acrylate (x2-b), nitrogen atom-containing vinyl monomer (x2-c), hydroxyl group-containing vinyl monomer (x2-d), phosphorus atom-containing monomer (x2-e), aliphatic hydrocarbon vinyl monomer (x2-f), alicyclic hydrocarbon vinyl monomer (x2-g), vinyl esters (x2-h), vinyl ethers (x2-i), vinyl ketones (x2-j), epoxy group-containing vinyl monomer (x2-k), halogen element-containing vinyl monomer (x2-l), ester of unsaturated polycarboxylic acid (x2-m), (di)alkyl fumarate (x2-n), (di)alkyl maleate (x2-o), and aromatic hydrocarbon vinyl monomer (x2-p).

As the monomer (x2), a monomer other than the nitrogen atom-containing vinyl monomer (x2-c), the phosphorus atom-containing monomer (x2-e), and the aromatic hydrocarbon vinyl monomer (x2-p) is preferable.
The monomer (x2) preferably includes one or more selected from the group consisting of a monomer (x2-a) represented by the following general formula (a1), an alkyl (meth)acrylate (x2-b), and a hydroxyl group-containing vinyl monomer (x2-d), and more preferably includes at least a hydroxyl group-containing vinyl monomer (x2-d).

(Monomer (x2-a) represented by the following general formula (a1))

In the above general formula (a1), R ^b11 represents a hydrogen atom or a methyl group.
R ^b12 represents a single bond, a linear or branched alkylene group having 1 to 10 carbon atoms, -O-, or -NH-.
R ^b13 represents a linear or branched alkylene group having 2 to 4 carbon atoms. Furthermore, n represents an integer of 1 or more (preferably an integer of 1 to 20, more preferably an integer of 1 to 5). When n is an integer of 2 or more, multiple R ^b13 may be the same or different, and further, the (R ^b13 O) _n portion may be a random bond or a block bond.
R ^b14 represents a linear or branched alkyl group having 1 to 60 carbon atoms (preferably 10 to 50, more preferably 20 to 40).
Specific examples of the above "linear or branched chain alkylene group having 1 to 10 carbon atoms", "linear or branched chain alkylene group having 2 to 4 carbon atoms", and "linear or branched chain alkyl group having 1 to 60 carbon atoms" include the same groups as exemplified in the description of the above general formulas (i) to (iii).

(Alkyl (meth)acrylate (x2-b))
Examples of the alkyl (meth)acrylate (x2-b) include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, 2-t-butylheptyl (meth)acrylate, octyl (meth)acrylate, and 3-isopropylheptyl (meth)acrylate.

The alkyl group in the alkyl (meth)acrylate (x2-b) preferably has 4 to 30 carbon atoms, more preferably 4 to 24 carbon atoms, and even more preferably 4 to 18 carbon atoms.
The alkyl group may be a straight chain alkyl group or a branched chain alkyl group.

The content ratio [(α)/(β)] of the structural unit (α) derived from butyl (meth)acrylate to the structural unit (β) derived from an alkyl (meth)acrylate having an alkyl group having 12 to 20 carbon atoms is, in molar ratio, preferably 7.00 or more, more preferably 8.50 or more, even more preferably 10.00 or more, and is preferably 20 or less.

The content of the structural unit (α) derived from butyl (meth)acrylate is preferably 40 to 95 mol%, more preferably 50 to 90 mol%, and even more preferably 60 to 85 mol%, based on the total amount (100 mol%) of the structural units of the comb polymer.

The content of the structural unit (β) derived from an alkyl (meth)acrylate having an alkyl group having 12 to 20 carbon atoms is preferably 1 to 30 mol %, more preferably 3 to 25 mol %, and even more preferably 5 to 20 mol %, based on the total amount (100 mol %) of the structural units of the comb polymer.

(Nitrogen atom-containing vinyl monomer (x2-c))
Examples of the nitrogen atom-containing vinyl monomer (x2-c) include an amide group-containing vinyl monomer (x2-c1), a nitro group-containing monomer (x2-c2), a primary amino group-containing vinyl monomer (x2-c3), a secondary amino group-containing vinyl monomer (x2-c4), a tertiary amino group-containing vinyl monomer (x2-c5), and a nitrile group-containing vinyl monomer (x2-c6).

Examples of the amide group-containing vinyl monomer (x2-c1) include (meth)acrylamide; monoalkylamino(meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-n-butyl(meth)acrylamide, and N-isobutyl(meth)acrylamide; monoalkylaminoalkyl(meth)acrylamides such as N-methylaminoethyl(meth)acrylamide, N-ethylaminoethyl(meth)acrylamide, N-isopropylamino-n-butyl(meth)acrylamide, N-n-butylamino-n-butyl(meth)acrylamide, and N-isobutylamino-n-butyl(meth)acrylamide; N,N-dimethyl(meth)acrylamide; dialkylamino(meth)acrylamides such as N,N-dimethylaminoethyl(meth)acrylamide, N,N-diethylaminoethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, and N,N-di-n-butylaminobutyl(meth)acrylamide; dialkylaminoalkyl(meth)acrylamides such as N,N-dimethylaminoethyl(meth)acrylamide, N,N-diethylaminoethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, and N,N-di-n-butylaminobutyl(meth)acrylamide; N-vinylcarboxylic acid amides such as N-vinylformamide, N-vinylacetamide, N-vinyl-n-propionylamide, N-vinylisopropionylamide, and N-vinylhydroxyacetamide.

Examples of nitro group-containing monomers (x2-c2) include nitroethylene and 3-nitro-1-propene.

Examples of primary amino group-containing vinyl monomers (x2-c3) include alkenylamines having an alkenyl group having 3 to 6 carbon atoms, such as (meth)allylamine and crotylamine; aminoalkyl (meth)acrylates having an alkyl group having 2 to 6 carbon atoms, such as aminoethyl (meth)acrylate; and the like.

Examples of secondary amino group-containing vinyl monomers (X2-C4) include monoalkylaminoalkyl (meth)acrylates such as t-butylaminoethyl (meth)acrylate and methylaminoethyl (meth)acrylate; dialkenylamines having 6 to 12 carbon atoms such as di(meth)allylamine; and the like.

Examples of tertiary amino group-containing vinyl monomers (x2-c5) include dialkylaminoalkyl (meth)acrylates such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate; alicyclic (meth)acrylates having a nitrogen atom such as morpholinoethyl (meth)acrylate; and their hydrochlorides, sulfates, phosphates, or lower alkyl (carbon number 1 to 8) monocarboxylic acid (acetic acid, propionic acid, etc.) salts.

Examples of nitrile group-containing vinyl monomers (x2-c6) include (meth)acrylonitrile, etc.

In the comb polymer used in one embodiment of the present invention, the content of constitutional units derived from the nitrogen atom-containing vinyl monomer (x2-c) is preferably as small as possible.
Specifically, the content of the constituent units derived from the nitrogen atom-containing vinyl monomer (x2-c) is, based on the total amount (100 mol%) of the constituent units of the comb polymer, preferably less than 1.0 mol%, more preferably less than 0.5 mol%, even more preferably less than 0.1 mol%, still more preferably less than 0.01 mol%, and particularly preferably 0 mol%.

(Hydroxyl-containing vinyl monomer (x2-d))
Examples of the hydroxyl group-containing vinyl monomer (x2-d) include a hydroxyl group-containing vinyl monomer (x2-d1) and a polyoxyalkylene chain-containing vinyl monomer (x2-d2).

Examples of the hydroxyl group-containing vinyl monomer (x2-d1) include hydroxyalkyl (meth)acrylates having an alkyl group having 2 to 6 carbon atoms, such as 2-hydroxyethyl (meth)acrylate and 2- or 3-hydroxypropyl (meth)acrylate; mono- or di-hydroxyalkyl-substituted (meth)acrylamides having an alkyl group having 1 to 4 carbon atoms, such as N,N-dihydroxymethyl (meth)acrylamide, N,N-dihydroxypropyl (meth)acrylamide, and N,N-di-2-hydroxybutyl (meth)acrylamide; vinyl alcohol; alkenyl monomers having 3 to 12 carbon atoms, such as (meth)allyl alcohol, crotyl alcohol, isocrotyl alcohol, 1-octenol, and 1-undecenol. alkenols; alkene monools or alkene diols having 4 to 12 carbon atoms, such as 1-buten-3-ol, 2-buten-1-ol, and 2-butene-1,4-diol; hydroxyalkyl alkenyl ethers having an alkyl group having 1 to 6 carbon atoms and an alkenyl group having 3 to 10 carbon atoms, such as 2-hydroxyethylpropenyl ether; compounds in which an unsaturated group, such as an alkenyl group or the above-mentioned polymerizable functional group possessed by the macromonomer (x1), has been introduced into a polyhydric alcohol, such as glycerin, pentaerythritol, sorbitol, sorbitan, diglycerin, sugars, and sucrose; and compounds in which an unsaturated group, such as an alkenyl group or the above-mentioned polymerizable functional group possessed by the macromonomer (x1), has been introduced into glyceric acid or a glycerin fatty acid ester.
Among these, hydroxyl-containing vinyl monomers having two or more hydroxyl groups are preferred, and compounds in which the above-mentioned unsaturated groups have been introduced into polyhydric alcohols or glyceric acid are more preferred.

Examples of the polyoxyalkylene chain-containing vinyl monomer (x2-d2) include polyoxyalkylene glycols (alkylene group having 2 to 4 carbon atoms, polymerization degree 2 to 50), polyoxyalkylene polyols (polyoxyalkylene ethers of the above-mentioned polyhydric alcohols (alkylene group having 2 to 4 carbon atoms, polymerization degree 2 to 100)), and compounds in which the above-mentioned unsaturated group is introduced into a compound selected from alkyl (carbon number 1 to 4) ethers of polyoxyalkylene glycols or polyoxyalkylene polyols.
Specific examples include polyethylene glycol (Mn: 100 to 300) mono(meth)acrylate, polypropylene glycol (Mn: 130 to 500) mono(meth)acrylate, methoxypolyethylene glycol (Mn: 110 to 310) (meth)acrylate, lauryl alcohol ethylene oxide adduct (2 to 30 mol) (meth)acrylate, and polyoxyethylene mono(meth)acrylate (Mn: 150 to 230) sorbitan.

The content of the structural units derived from the hydroxyl group-containing vinyl monomer (x2-d) is preferably 0.1 to 30 mol%, more preferably 0.5 to 20 mol%, even more preferably 1 to 15 mol%, and even more preferably 3 to 10 mol%, based on the total amount (100 mol%) of the structural units of the comb polymer.

(Phosphorus Atom-Containing Monomer (x2-e))
Examples of the phosphorus atom-containing monomer (x2-e) include a phosphate ester group-containing monomer (x2-e1) and a phosphono group-containing monomer (x2-e2).

Examples of the phosphate ester group-containing monomer (x2-e1) include (meth)acryloyloxyalkyl phosphate esters having an alkyl group having 2 to 4 carbon atoms, such as (meth)acryloyloxyethyl phosphate and (meth)acryloyloxyisopropyl phosphate; alkenyl phosphate esters having an alkenyl group having 2 to 12 carbon atoms, such as vinyl phosphate, allyl phosphate, propenyl phosphate, isopropenyl phosphate, butenyl phosphate, pentenyl phosphate, octenyl phosphate, decenyl phosphate, and dodecenyl phosphate; and the like.

Examples of the phosphono group-containing monomer (x2-e2) include (meth)acryloyloxyalkylphosphonic acids having an alkyl group with 2 to 4 carbon atoms, such as (meth)acryloyloxyethylphosphonic acid; alkenylphosphonic acids having an alkenyl group with 2 to 12 carbon atoms, such as vinylphosphonic acid, allylphosphonic acid, and octenylphosphonic acid; and the like.

In the comb polymer used in one embodiment of the present invention, the content of constitutional units derived from the phosphorus atom-containing monomer (x2-e) is preferably as small as possible.
Specifically, the content of the constituent units derived from the phosphorus atom-containing monomer (x2-e) is, based on the total amount (100 mol%) of the constituent units of the comb polymer, preferably less than 1.0 mol%, more preferably less than 0.5 mol%, even more preferably less than 0.1 mol%, still more preferably less than 0.01 mol%, and particularly preferably 0 mol%.

(Aliphatic Hydrocarbon Vinyl Monomer (x2-f))
Examples of the aliphatic hydrocarbon vinyl monomer (x2-f) include alkenes having 2 to 20 carbon atoms, such as ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, and octadecene; and alkadienes having 4 to 12 carbon atoms, such as butadiene, isoprene, 1,4-pentadiene, 1,6-heptadiene, and 1,7-octadiene.
The aliphatic hydrocarbon vinyl monomer (x2-f) preferably has 2 to 30 carbon atoms, more preferably 2 to 20 carbon atoms, and further preferably 2 to 12 carbon atoms.

(Alicyclic Hydrocarbon Vinyl Monomer (x2-g))
Examples of the alicyclic hydrocarbon vinyl monomer (x2-g) include cyclohexene, (di)cyclopentadiene, pinene, limonene, vinylcyclohexene, and ethylidenebicycloheptene.
The alicyclic hydrocarbon vinyl monomer (x2-g) preferably has 3 to 30 carbon atoms, more preferably 3 to 20 carbon atoms, and further preferably 3 to 12 carbon atoms.

(Vinyl esters (x2-h))
Examples of the vinyl esters (x2-h) include vinyl esters of saturated fatty acids having 2 to 12 carbon atoms, such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl octanoate.

(Vinyl ethers (x2-i))
Examples of the vinyl ethers (x2-i) include alkyl vinyl ethers having 1 to 12 carbon atoms, such as methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, and 2-ethylhexyl vinyl ether; alkoxyalkyl vinyl ethers having 1 to 12 carbon atoms, such as vinyl-2-methoxyethyl ether and vinyl-2-butoxyethyl ether; and the like.

(Vinyl ketones (x2-j))
Examples of the vinyl ketones (x2-j) include alkyl vinyl ketones having 1 to 8 carbon atoms, such as methyl vinyl ketone and ethyl vinyl ketone; and the like.

(Epoxy Group-Containing Vinyl Monomer (x2-k))
Examples of the epoxy group-containing vinyl monomer (x2-k) include glycidyl (meth)acrylate and glycidyl (meth)allyl ether.

(Halogen-containing vinyl monomer (x2-l))
Examples of the halogen-containing vinyl monomer (x2-l) include vinyl chloride, vinyl bromide, vinylidene chloride, and (meth)allyl chloride.

(Ester of unsaturated polycarboxylic acid (x2-m))
Examples of the ester of an unsaturated polycarboxylic acid (x2-m) include an alkyl ester of an unsaturated polycarboxylic acid, a cycloalkyl ester of an unsaturated polycarboxylic acid, and an aralkyl ester of an unsaturated polycarboxylic acid. Examples of the unsaturated carboxylic acid include maleic acid, fumaric acid, and itaconic acid.

((Di)alkyl fumarate (x2-n))
Examples of the (di)alkyl fumarate (x2-n) include monomethyl fumarate, dimethyl fumarate, monoethyl fumarate, diethyl fumarate, methylethyl fumarate, monobutyl fumarate, dibutyl fumarate, dipentyl fumarate, and dihexyl fumarate.

((Di)alkyl maleate (x2-o))
Examples of the (di)alkyl maleate (x2-o) include monomethyl maleate, dimethyl maleate, monoethyl maleate, diethyl maleate, methylethyl maleate, monobutyl maleate, and dibutyl maleate.

(Aromatic Hydrocarbon Vinyl Monomer (x2-p))
Examples of the aromatic hydrocarbon vinyl monomer (x2-p) include styrene, α-methylstyrene, α-ethylstyrene, vinyltoluene, 2,4-dimethylstyrene, 4-ethylstyrene, 4-isopropylstyrene, 4-butylstyrene, 4-phenylstyrene, 4-cyclohexylstyrene, 4-benzylstyrene, p-methylstyrene, monochlorostyrene, dichlorostyrene, tribromostyrene, tetrabromostyrene, 4-crotylbenzene, indene, and 2-vinylnaphthalene.
The aromatic hydrocarbon vinyl monomer (x2-p) preferably has 8 to 30 carbon atoms, more preferably 8 to 20 carbon atoms, and further preferably 8 to 18 carbon atoms.

In the comb polymer (B1-1) used in one embodiment of the present invention, the content of structural units derived from the aromatic hydrocarbon vinyl monomer (x2-p) is preferably as small as possible.
The content of the structural units derived from the specific aromatic hydrocarbon vinyl monomer (x2-p) is, based on the total amount (100 mol%) of the structural units of the comb polymer, preferably less than 1.0 mol%, more preferably less than 0.5 mol%, even more preferably less than 0.1 mol%, still more preferably less than 0.01 mol%, and particularly preferably 0 mol%.

<<Content Ratio of Resin Component (B1) Derived from Viscosity Index Improver (B) and First Olefin Polymer (A1-1)>>
In the lubricating oil composition of the present invention, the content ratio [(B1)/(A1-1)] of the resin component (B1) derived from the viscosity index improver (B) to the first olefin polymer (A1-1) is greater than 0.001 in mass ratio.
[(B1)/(A1-1)] means the amount of the resin component (B1) derived from the viscosity index improver (B) relative to the first olefin polymer (A1-1). If this value is 0.001 or less, the lubricating oil composition will have poor oil film retention.
Here, in the lubricating oil composition of one embodiment of the present invention, from the viewpoint of easily preparing a lubricating oil composition having excellent oil film retention, [(B1)/(A1-1)] is preferably 0.002 or more, more preferably 0.003 or more, even more preferably 0.004 or more, and even more preferably 0.005 or more. Also, from the viewpoint of shear stability, it is preferably 0.10 or less, more preferably 0.05 or less, and even more preferably 0.02 or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 0.002 to 0.10, more preferably 0.003 to 0.05, even more preferably 0.004 to 0.02, and even more preferably 0.005 to 0.02.

<<Imide-based dispersant (C)>>
The lubricating oil composition of the present invention contains an imide-based dispersant (C).
In the lubricating oil composition of the present invention, the content of nitrogen atoms derived from the imide-based dispersant (C) is 0.06 mass % or more based on the total amount of the lubricating oil composition.
If the nitrogen atom content derived from the imide-based dispersant (C) is less than 0.06 mass %, the high-temperature detergency of the lubricating oil composition cannot be ensured, and the oil film retention cannot be sufficient.

In the lubricating oil composition of one embodiment of the present invention, from the viewpoint of improving high-temperature detergency and oil film retention, the nitrogen atom content derived from the imide-based dispersant (C) is preferably 0.08 mass% or more, more preferably 0.10 mass% or more, and even more preferably 0.11 mass% or more. Also, it is preferably 1.00 mass% or less, more preferably 0.50 mass% or less, and even more preferably 0.20 mass% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 0.08 mass% to 1.00 mass%, more preferably 0.10 mass% to 0.50 mass%, and even more preferably 0.11 mass% to 0.20 mass%.
In addition, in the lubricating oil composition of one embodiment of the present invention, the content of the imide-based dispersant (C) may be adjusted so that the nitrogen atom content derived from the imide-based dispersant (C) satisfies the above range. The content of the imide-based dispersant (C) is preferably 1.0 mass% or more, more preferably 5.0 mass% or more, and even more preferably 7.5 mass% or more, based on the total amount of the lubricating oil composition. Also, it is preferably 20.0 mass% or less, more preferably 15.0 mass% or less, and even more preferably 12.5 mass% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 1.0 mass% to 20.0 mass%, more preferably 5.0 mass% to 15.0 mass%, and even more preferably 7.5 mass% to 12.5 mass%.

Examples of the imide-based dispersant (C) include one or more compounds selected from the group consisting of succinic acid monoimides such as alkenyl succinic acid monoimides and alkyl succinic acid monoimides; boron-modified succinic acid monoimides; succinic acid bisimides such as alkenyl succinic acid bisimides and alkyl succinic acid bisimides; and boron-modified succinic acid bisimides.
Among these, at least one selected from the group consisting of succinic acid monoimides (non-boron modified) and succinic acid bisimides (non-boron modified) is preferred.
The imide-based dispersant (C) may be used alone or in combination of two or more kinds.

Examples of the alkenyl succinic acid monoimide or alkyl succinic acid monoimide include the compounds represented by the following general formula (c-1). Examples of the alkenyl succinic acid bisimide or alkyl succinic acid bisimide include the compounds represented by the following general formula (c-2).

In general formula (c-1) and formula (c-2), R ^3C , R ^5C , and R ^6C are an alkenyl group or an alkyl group, and each has a mass average molecular weight (Mw) of preferably 500 to 3,000, more preferably 1,000 to 3,000.
When the mass average molecular weight of ^R3C , ^R5C , and ^R6C is 500 or more, the solubility in the base oil (A) can be improved. When the mass average molecular weight is 3,000 or less, the effects of the present invention can be more easily exhibited. ^R5C and ^R6C may be the same or different.
R ^4C , R ^7C , and R ^8C are each an alkylene group having 2 to 5 carbon atoms, and R ^7C and R ^8C may be the same or different. n1 represents an integer of 1 to 10, and n2 represents 0 or an integer of 1 to 10. Here, n1 is preferably 2 to 5, more preferably 2 to 4. When n1 is 2 or more, the effects of the present invention can be more easily exhibited. When n1 is 5 or less, the solubility in the base oil (A) is further improved.
In the general formula (c-2), n2 is preferably 1 to 6, more preferably 2 to 6. When n2 is 1 or more, the effects of the present invention can be more easily exhibited. When n2 is 6 or less, the solubility in the base oil (A) is further improved.

Examples of alkenyl groups that can be selected as R ^3C , R ^5C , and R ^6C include polybutenyl groups, polyisobutenyl groups, and ethylene-propylene copolymers, and preferably polybutenyl groups or polyisobutenyl groups. The polybutenyl group is preferably a mixture of 1-butene and isobutene or a polymer of high-purity isobutene.
Examples of the alkyl group that can be selected as R ^3C , R ^5C , and R ^6C include a polybutenyl group, a polyisobutenyl group, a hydrogenated ethylene-propylene copolymer, etc., and preferably a hydrogenated polybutenyl group or a polyisobutenyl group.

The above alkenylsuccinimides or alkylsuccinimides can be produced by reacting an alkenylsuccinic anhydride, which is usually obtained by reacting a polyolefin with maleic anhydride, or an alkylsuccinic anhydride obtained by hydrogenating the alkenylsuccinic anhydride, with a polyamine. Monoimides or bisimides can be produced by changing the ratio of alkenylsuccinic anhydride or alkylsuccinic anhydride to polyamine.
The alkenyl succinimide or alkyl succinimide succinimide may be a boron-modified product, which can be produced, for example, by reacting a boron-free alkenyl succinic acid monoimide or alkyl succinic acid monoimide, or an alkenyl succinic acid bisimide or alkyl succinic acid bisimide with a boron compound.

As the olefin monomer forming the polyolefin, for example, one or more types selected from α-olefins having 2 to 8 carbon atoms can be used, and a mixture of isobutene and 1-butene can be preferably used.
On the other hand, examples of polyamines include single diamines such as ethylenediamine, propylenediamine, butylenediamine, and pentylenediamine; polyalkylenepolyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, di(methylethylene)triamine, dibutylenetriamine, tributylenetetramine, and pentapentylenehexamine; piperazine derivatives such as aminoethylpiperazine, etc. One type of polyamine may be used alone, or two or more types may be used in combination.

The boron compounds include boric acid, borates, and borate esters.
Examples of boric acid include orthoboric acid, metaboric acid, and paraboric acid.
Borates include ammonium borates such as ammonium metaborate, ammonium tetraborate, ammonium pentaborate, and ammonium octaborate.
Examples of borate esters include monomethyl borate, dimethyl borate, trimethyl borate, monoethyl borate, diethyl borate, triethyl borate, monopropyl borate, dipropyl borate, tripropyl borate, monobutyl borate, dibutyl borate, and tributyl borate.

<<Metal-based detergent (D)>>
The lubricating oil composition of one embodiment of the present invention may contain a metallic detergent (D).
By including the metallic detergent (D) in the lubricating oil composition of one embodiment of the present invention, the high temperature detergency of the lubricating oil composition can be further improved.
In the lubricating oil composition of one embodiment of the present invention, the content of metal atoms derived from the metallic detergent (D) is, from the viewpoint of improving high-temperature detergency and keeping the sulfated ash content low, preferably 0.01 mass % to 0.20 mass %, more preferably 0.05 mass % to 0.18 mass %, and even more preferably 0.08 mass % to 0.15 mass %, based on the total amount of the lubricating oil composition.
In the lubricating oil composition of one embodiment of the present invention, the content of the metallic detergent (D) may be adjusted so that the content of metal atoms derived from the metallic detergent (D) falls within the above range, preferably 0.1 mass% to 10.0 mass%, more preferably 0.5 mass% to 5.0 mass%, and even more preferably 0.75 mass% to 2.0 mass%, based on the total amount of the lubricating oil composition.

Examples of the metallic detergent (D) include alkali metal detergents and alkaline earth metal detergents, and among these, alkaline earth metal detergents are preferred.
Examples of alkaline earth metals constituting the alkaline earth metal-based detergent include magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Among these, calcium (Ca) and magnesium (Mg) are preferred.
That is, the metal-based detergent (D) is preferably at least one selected from the group consisting of calcium-based detergents (D1) and magnesium-based detergents (D2).
The calcium-based detergent (D1) and the magnesium-based detergent (D2) will be described in detail below.

<Calcium-based detergent (D1)>
Examples of the calcium-based detergent (D1) include calcium salts such as calcium sulfonate, calcium phenate, and calcium salicylate.
Among these, from the viewpoint of improving high-temperature detergency, calcium phenate and calcium salicylate are preferred, and calcium salicylate is more preferred.
As the calcium sulfonate, a metal sulfonate represented by the following general formula (d1-1) in which M is a calcium atom is preferable. As the calcium phenate, a metal phenate represented by the following general formula (d1-2) in which M' is a calcium atom is preferable. As the calcium salicylate, a metal salicylate represented by the following general formula (d1-3) in which M is a calcium atom is preferable.
The calcium-based detergent (D1) may be used alone or in combination of two or more kinds.

In the above general formulas (d1-1) to (d1-3), M is a metal atom selected from alkali metals and alkaline earth metals, and M' is an alkaline earth metal. p is the valence of M and is 1 or 2. R is a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms. q is an integer of 0 or more, and preferably an integer of 0 to 3.
Examples of the hydrocarbon group that can be selected as R include an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 18 ring carbon atoms, an aryl group having 6 to 18 ring carbon atoms, an alkylaryl group having 7 to 18 carbon atoms, and an arylalkyl group having 7 to 18 carbon atoms.

The calcium-based detergent (D1) may be any of neutral, basic, and overbased. From the viewpoint of making it easier to improve the base number maintenance, the calcium-based detergent (D1) is preferably basic or overbased, and more preferably overbased.
In this specification, the basic or overbased metal-based detergent means a detergent obtained by reacting a metal with an acidic organic compound and containing an excess of the metal compared to the stoichiometric amount required for neutralizing the metal with the acidic organic compound. That is, when the total chemical equivalent of the metal in the metal-based detergent is defined as the "metal ratio" relative to the chemical equivalent of the metal in the metal salt (neutral salt) obtained by reacting the metal with the acidic organic compound according to the stoichiometric amount required for neutralizing the metal, the metal ratio of the basic or overbased metal-based detergent is greater than 1. The metal ratio of the basic or overbased metal-based detergent used in this embodiment is preferably greater than 1.3, more preferably 5 to 30, and even more preferably 7 to 22. Specific examples of the basic or overbased metal-based detergent include those containing one or more selected from the group consisting of the above-mentioned metal salicylates, metal phenates, and metal sulfonates, and containing an excess of metal.
In this specification, a base number measured by the measurement method described below of less than 50 mgKOH/g is defined as "neutral," a base number of 50 mgKOH/g or more and less than 150 mgKOH/g is defined as "basic," and a base number of 150 mgKOH/g or more is defined as "overbased."

The base number of the calcium-based detergent (D1) is preferably 5 mgKOH/g or more, more preferably 100 mgKOH/g or more, even more preferably 150 mgKOH/g or more, still more preferably 200 mgKOH/g or more, and is preferably 500 mgKOH/g or less, more preferably 450 mgKOH/g or less, even more preferably 400 mgKOH/g or less.
In this specification, the "base number" of the metallic detergent (D) means a base number measured by a perchloric acid method in accordance with JIS K 2501:2003.

In the lubricating oil composition of one embodiment of the present invention, the content of calcium atoms derived from the calcium-based detergent (D1) is, from the viewpoint of improving high-temperature detergency and keeping the sulfated ash content low, preferably 0.01 mass % to 0.75 mass %, more preferably 0.02 mass % to 0.30 mass %, and even more preferably 0.05 mass % to 0.15 mass %, based on the total amount of the lubricating oil composition.
In the lubricating oil composition of one embodiment of the present invention, the content of the calcium-based detergent (D1) may be adjusted so that the content of calcium atoms derived from the calcium-based detergent (D1) falls within the above range, preferably 0.01 to 10.0 mass%, more preferably 0.10 to 5.0 mass%, and even more preferably 0.80 to 2.00 mass%, based on the total amount of the lubricating oil composition.

<Magnesium-based detergent (D2)>
Examples of the magnesium-based detergent (D2) include magnesium salts such as magnesium sulfonate, magnesium phenate, and magnesium salicylate.
Among these, magnesium sulfonate is preferred from the viewpoint of improving high-temperature detergency.
The magnesium sulfonate is preferably a metal sulfonate represented by the above general formula (d1-1) in which M is a magnesium atom. The magnesium phenate is preferably a metal phenate represented by the above general formula (d1-2) in which M' is a magnesium atom. The magnesium salicylate is preferably a metal salicylate represented by the above general formula (d1-3) in which M is a magnesium atom.
The magnesium-based detergent (D2) may be used alone or in combination of two or more kinds.

The magnesium-based detergent (D2) may be neutral, basic or overbased, but from the viewpoint of detergency, it is preferably basic or overbased.
The base number of the magnesium-based detergent (D2) is preferably 5 mgKOH/g or more, more preferably 100 mgKOH/g or more, even more preferably 150 mgKOH/g or more, still more preferably 200 mgKOH/g or more, and is preferably 500 mgKOH/g or less, more preferably 450 mgKOH/g or less, even more preferably 400 mgKOH/g or less.

In the lubricating oil composition of one embodiment of the present invention, the content of magnesium atoms derived from the magnesium-based detergent (D2) is, from the viewpoint of improving high-temperature detergency and keeping the sulfated ash content low, preferably 0.001 mass % to 0.1 mass %, more preferably 0.010 mass % to 0.050 mass %, and even more preferably 0.015 mass % to 0.025 mass %, based on the total amount of the lubricating oil composition.
In the lubricating oil composition of one embodiment of the present invention, the content of the magnesium-based detergent (D2) may be adjusted so that the content of magnesium atoms derived from the magnesium-based detergent (D2) falls within the above range. The content of the magnesium-based detergent (D2) is preferably 0.001 mass% to 2.000 mass%, more preferably 0.005 mass% to 1.000 mass%, and even more preferably 0.01 mass% to 0.300 mass%, based on the total amount of the lubricating oil composition.

<<Zinc dithiophosphate (E)>>
The lubricating oil composition of one embodiment of the present invention may contain zinc dithiophosphate (E).
By including the zinc dithiophosphate (E) in the lubricating oil composition of one embodiment of the present invention, the wear resistance of the lubricating oil composition can be further improved.

The zinc dithiophosphate (E) used in the lubricating oil composition of one embodiment of the present invention is preferably represented by the following general formula (e-1):

In general formula (e-1), R ^21E to R ^24E each independently represent a hydrocarbon group. The hydrocarbon group is not particularly limited as long as it is a monovalent hydrocarbon group, and from the viewpoint of improving oxidation stability, preferred examples thereof include an alkyl group, an alkenyl group, a cycloalkyl group, and an aryl group, with an alkyl group and an aryl group being more preferred, and an alkyl group being even more preferred. That is, the zinc dithiophosphate used in one embodiment of the present invention is preferably a zinc dialkyldithiophosphate.

The alkyl and alkenyl groups that can be selected as R ^21E to R ^24E may be either linear or branched, but from the viewpoint of obtaining better oxidation stability, primary and secondary groups are preferred, and among these, primary alkyl and secondary alkyl groups are preferred. That is, as the zinc dialkyldithiophosphate, primary zinc dialkyldithiophosphate and secondary zinc dialkyldithiophosphate are preferred.
Furthermore, when the monovalent hydrocarbon group is an alkyl group, the number of carbon atoms in the hydrocarbon group that can be selected from R ^21E to R ^24E is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more, with the upper limit being preferably 24 or less, more preferably 18 or less, and even more preferably 12 or less. When the monovalent hydrocarbon group is an alkenyl group, the number of carbon atoms is preferably 2 or more, more preferably 3 or more, and the upper limit is preferably 24 or less, more preferably 18 or less, and even more preferably 12 or less.

The cycloalkyl group and aryl group that can be selected as R ^21E to R ^24E may be polycyclic groups such as ^decalyl and ^naphthyl . When the monovalent hydrocarbon group is a cycloalkyl group, the carbon number is preferably 5 or more and the upper limit is preferably 20 or less. When the monovalent hydrocarbon group is an aryl group, the carbon number is preferably 6 or more and the upper limit is preferably 20 or less.

The monovalent hydrocarbon group may be partially substituted with a group containing an oxygen atom and/or a nitrogen atom, such as a hydroxyl group, a carboxy group, an amino group, an amide group, a nitro group, or a cyano group, or may be partially substituted with a nitrogen atom, an oxygen atom, a halogen atom, or the like. When the monovalent hydrocarbon group is a cycloalkyl group or an aryl group, it may further have a substituent such as an alkyl group or an alkenyl group.

From the viewpoint of making it easier to improve the wear resistance of the lubricating oil composition, and from the viewpoint of suppressing the amount of phosphorus in the lubricating oil composition and suppressing poisoning of an exhaust gas purification catalyst provided in an exhaust gas purification device, the lubricating oil composition of one embodiment of the present invention preferably has a content of phosphorus atoms derived from the zinc dithiophosphate (E) of 0.005 mass % to 0.200 mass %, more preferably 0.010 mass % to 0.150 mass %, and even more preferably 0.05 mass % to 0.100 mass %, based on the total amount of the lubricating oil composition.
From the same viewpoint, the content of zinc atoms derived from the zinc dithiophosphate (E) is preferably 0.005 mass % to 0.200 mass %, more preferably 0.010 mass % to 0.150 mass %, and even more preferably 0.06 mass % to 0.110 mass %, based on the total amount of the lubricating oil composition.
In the lubricating oil composition of one embodiment of the present invention, the content of zinc dithiophosphate (E) may be adjusted so that the phosphorus atom content and zinc atom content derived from zinc dithiophosphate (E) are within the above ranges. The content of zinc dithiophosphate (E) is preferably 0.10 mass% to 5.00 mass%, more preferably 0.50 mass% to 2.50 mass%, and even more preferably 0.75 mass% to 1.25 mass%, based on the total amount of the lubricating oil composition.

<<Other lubricating oil additives>>
The lubricating oil composition of one embodiment of the present invention may contain lubricating oil additives (hereinafter simply referred to as "lubricating oil additives") other than the above-mentioned components, as necessary, within the scope of not impairing the effects of the present invention.
Examples of the lubricating oil additives include antioxidants, extreme pressure agents, friction modifiers, antifoaming agents, rust inhibitors, corrosion inhibitors, metal deactivators, etc. Also included are antiwear agents other than zinc dithiophosphate (E).
The lubricating oil additives may be used either alone or in combination of two or more.

The content of each of these lubricating oil additives can be appropriately adjusted within a range that does not impair the effects of the present invention, but is usually 0.001 mass % or more, preferably 0.005 mass % or more, more preferably 0.01 mass % or more, and preferably 30 mass % or less, more preferably 27 mass % or less, and even more preferably 24 mass % or less, based on the total amount of the lubricating oil composition.
In the lubricating oil composition of one embodiment of the present invention, the total content of these lubricating oil additives, based on the total amount (100 mass%) of the lubricating oil composition, is preferably 5 mass% or more, more preferably 10 mass% or more, even more preferably 15 mass% or more, and is preferably 35 mass% or less, preferably 30 mass% or less, more preferably 27 mass% or less, even more preferably 25 mass% or less.

<Antioxidants>
The antioxidant may be any one appropriately selected from known antioxidants that have been conventionally used as antioxidants for lubricating oils, and examples of such antioxidants include amine-based antioxidants and phenol-based antioxidants.
The antioxidants may be used alone or in combination of two or more.

<Extreme pressure agent>
Examples of the extreme pressure agent include sulfur-based extreme pressure agents such as sulfides, sulfoxides, sulfones, and thiophosphinates; halogen-based extreme pressure agents such as chlorinated hydrocarbons; and organometallic extreme pressure agents.
The extreme pressure agents may be used alone or in combination of two or more.

<Friction modifier>
Examples of the friction modifier include ashless friction modifiers having at least one alkyl or alkenyl group having 6 to 30 carbon atoms in the molecule, such as aliphatic amines, fatty acid esters, fatty acid amides, fatty acids, aliphatic alcohols, and aliphatic ethers; fats and oils; amines; amides; sulfide esters; phosphate esters; phosphites; and phosphate amine salts.
The friction modifiers may be used alone or in combination of two or more.

<Antifoaming agent>
Examples of the defoaming agent include silicone oil, fluorosilicone oil, and fluoroalkyl ether.
The defoaming agent may be used alone or in combination of two or more kinds.

<Rust inhibitor>
Examples of the rust inhibitor include fatty acids, alkenyl succinic acid half esters, fatty acid soaps, alkyl sulfonates, polyhydric alcohol fatty acid esters, fatty acid amines, paraffin oxide, and alkyl polyoxyethylene ethers.
The rust inhibitors may be used alone or in combination of two or more.

<Corrosion inhibitors, metal deactivators>
Examples of corrosion inhibitors and metal deactivators include benzotriazole-based compounds, tolyltriazole-based compounds, thiadiazole-based compounds, imidazole-based compounds, and pyrimidine-based compounds.
These may be used alone or in combination of two or more.

<Anti-wear agents other than zinc dithiophosphate (E)>
Examples of anti-wear agents include sulfur-containing compounds such as zinc phosphates other than zinc dithiophosphate (E), zinc dithiocarbamates, disulfides, sulfurized olefins, sulfurized oils and fats, sulfurized esters, thiocarbonates, thiocarbamates, and polysulfides; phosphorus-containing compounds such as phosphites, phosphates, phosphonates, and amine salts or metal salts thereof; and sulfur- and phosphorus-containing anti-wear agents such as thiophosphites, thiophosphates, thiophosphonates, and amine salts or metal salts thereof.
These may be used alone or in combination of two or more.

<Molybdenum compounds>
The lubricating oil composition of one embodiment of the present invention may contain a molybdenum-based compound, but the content of the molybdenum-based compound is preferably small.The lubricating oil composition of one embodiment of the present invention has excellent wear resistance even without containing a molybdenum-based compound.Therefore, excellent effects are exhibited even without blending a molybdenum-based compound that causes a decrease in high-temperature detergency.
The content of Mo atoms derived from molybdenum-based compounds is preferably less than 0.10 mass%, more preferably less than 0.05 mass%, even more preferably less than 0.04 mass%, based on the total amount of the lubricating oil composition, and even more preferably the lubricating oil composition does not contain any molybdenum-based compounds.
Examples of the molybdenum compounds include dinuclear organomolybdenum compounds such as dinuclear molybdenum dithiocarbamates; and trinuclear organomolybdenum compounds.

<Mist prevention agent>
The lubricating oil composition according to one embodiment of the present invention may contain a mist inhibitor, but the content of the mist inhibitor is preferably small.
The content of the anti-mist agent is preferably less than 0.01 mass %, more preferably less than 0.001 mass %, based on the total amount of the lubricating oil composition, and even more preferably the lubricating oil composition is free of any anti-mist agent.
As the mist suppressant, a hydrocarbon-based polymer compound such as polyisobutylene, ethylene-propylene copolymer, etc. The number average molecular weight of the polymer compound is preferably 100,000 to 3,000,000, and more preferably 200,000 to 2,000,000.

[Physical properties of lubricating oil composition]
<Kinematic Viscosity at 100°C>
The lubricating oil composition of the present invention has a 100° C. kinematic viscosity of 5.0 mm ² /s or more and less than 7.1 mm ² /s.
If the 100° C. kinetic viscosity is less than 5.0 mm ² /s, it becomes difficult to maintain an oil film and the NOACK evaporation amount is liable to increase, whereas if the 100° C. kinetic viscosity is 7.1 mm ² /s or more, fuel economy decreases.
From this viewpoint, the lubricating oil composition of one embodiment of the present invention has a 100°C kinematic viscosity of preferably 5.1 ^mm2 /s or more, more preferably 5.2 ^mm2 /s or more, and even more preferably 5.3 ^mm2 /s or more. Also, it is preferably 6.8 ^mm2 /s or less, more preferably 6.6 ^mm2 /s or less, and even more preferably 6.4 ^mm2 /s or less. The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 5.1 ^mm2 /s or more and 6.8 ^mm2 /s or less, more preferably 5.2 ^mm2 /s or more and 6.6 ^mm2 /s or less, and even more preferably 5.3 ^mm2 /s or more and 6.4 ^mm2 /s or less.
In this specification, the 100° C. kinematic viscosity of the lubricating oil composition is a value measured in accordance with JIS K2283:2000.

<HTHS Viscosity at 150° C.>
The lubricating oil composition of one embodiment of the present invention preferably has an HTHS viscosity at 150° C. of 2.0 mPa·s or more and less than 2.3 mPa·s.
When the HTHS viscosity at 150° C. is 2.0 mPa·s or more, the oil film is easily maintained. On the other hand, when the HTHS viscosity at 150° C. is less than 2.3 mPa·s, the fuel economy is easily improved.
From this viewpoint, the lubricating oil composition of one embodiment of the present invention more preferably has an HTHS viscosity at 150° C. of 2.0 mPa·s or more and 2.2 mPa·s or less.
In this specification, the HTHS viscosity at 150° C. is a value measured in accordance with ASTM D4683 using a TBS high temperature viscometer (Tapered Bearing Simulator Viscometer) at a temperature of 150° C. and a shear rate of 10 ⁶ /s.

<Kinematic Viscosity at 40°C>
The lubricating oil composition of one embodiment of the present invention preferably has a 40° C. kinematic viscosity of 15.0 mm ^{2 /s} to 30.0 mm ² /s.
When the 40° C. kinetic viscosity is 15.0 mm ² /s or more, the oil film is easily maintained and the NOACK evaporation amount is easily suppressed. On the other hand, when the 40° C. kinetic viscosity is 30 mm ² /s or less, the fuel economy is easily improved.
From this viewpoint, the lubricating oil composition of one embodiment of the present invention more preferably has a 40° C. kinematic viscosity of 18.0 mm ^{2 /} s to 29.0 mm ² /s, more preferably 20.0 mm ² /s to 28.0 mm ² /s, and even more preferably 21.0 mm ² /s to 27.0 mm ² /s.
In this specification, the 40° C. kinematic viscosity of the lubricating oil composition is a value measured in accordance with JIS K2283:2000.

<Viscosity index>
The lubricating oil composition of one embodiment of the present invention has a viscosity index of preferably 150 or more, more preferably 160 or more, and even more preferably 170 or more. Also, it is preferably 230 or less, more preferably 220 or less, and even more preferably 210 or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 150 to 230, more preferably 160 to 220, and even more preferably 170 to 210.
In this specification, the viscosity index of a lubricating oil composition is a value calculated in accordance with JIS K2283:2000.

<NOACK Evaporation Amount>
The lubricating oil composition of one embodiment of the present invention has a NOACK evaporation amount (250° C., 1 hour) of less than 23% by mass. If the NOACK evaporation amount is 23% by mass or more, the lubricating oil composition will thicken, which will cause a decrease in fuel economy.
From this viewpoint, the lubricating oil composition of one embodiment of the present invention preferably has a NOACK evaporation amount of 22 mass % or less, more preferably 21 mass % or less, and even more preferably 20 mass % or less. Also, it is usually 0.1 mass % or more.
In this specification, the NOACK evaporation amount is a value measured in accordance with JPI-5S-41-2004 under conditions of 250° C. and 1 hour.

<Aniline point>
The lubricating oil composition of the present invention has an aniline point of 95° C. or higher.
If the aniline point of the lubricating oil composition is less than 95° C., there is a risk that the rubber material will swell or harden.
Here, from the viewpoint of further improving compatibility with rubber materials without swelling or hardening the rubber materials, the aniline point is preferably 100° C. or higher, more preferably 110° C. or higher.
In this specification, the aniline point is a value measured in accordance with JIS K 2256:2013.

<High temperature cleanliness>
The lubricating oil composition of the present invention has excellent high-temperature detergency properties, specifically, the score of the hot tube test carried out by the method described in the examples below is preferably 2.5 or more.

<Oil film retention>
The lubricating oil composition of the present invention has excellent oil film retention properties, specifically, the oil film thickness measured by the method described in the Examples below is preferably 60 nm or more.

<Molybdenum atom content>
The lubricating oil composition of one embodiment of the present invention has a molybdenum (Mo) atom content, based on the total amount of the lubricating oil composition, of preferably less than 0.10 mass%, more preferably less than 0.05 mass%, even more preferably less than 0.04 mass%, still more preferably less than 0.02 mass%, and particularly preferably no molybdenum (Mo) atoms.
The molybdenum atom content can be measured in accordance with JIS-5S-38-03.

[Method of producing lubricating oil composition]
The method for producing the lubricating oil composition of the present invention is not particularly limited.
For example, a method for producing a lubricating oil composition according to one embodiment of the present invention includes a step of mixing a base oil (A) containing an olefin polymer (A1), a viscosity index improver (B), and an imide-based dispersant (C),
The olefin polymer (A1) includes a first olefin polymer (A1-1) having a kinetic viscosity at 100° C. of 3.0 mm ² /s or more, and the content of the first olefin polymer (A1-1) is 30 mass% or more based on the total amount of the base oil (A);
the olefin polymer (A1) does not contain a second olefin polymer (A1-2) having a kinetic viscosity at 100° C. of less than 3.0 mm ² /s, or if it does contain one, the amount of the second olefin polymer (A1-2) is less than 18.5 mass % based on the total amount of the base oil (A);
the content of the resin component (B1) derived from the viscosity index improver (B) is 0.01 mass% or more based on the total amount of the lubricating oil composition;
The nitrogen atom content derived from the imide-based dispersant (C) is 0.06 mass% or more based on the total amount of the lubricating oil composition;
a content ratio [(B1)/(A1-1)] of the resin component (B1) derived from the viscosity index improver (B) to the first olefin polymer (A1-1) is greater than 0.001 in terms of mass ratio,
The kinetic viscosity at 100°C is 5.0 ^mm2 /s or more and less than 7.1 ^mm2 /s;
A method for producing a lubricating oil composition having an aniline point of 95° C. or higher.
The method of mixing the above components is not particularly limited, and may be, for example, a method having a step of blending a viscosity index improver (B) and an imide-based dispersant (C) into a base oil (A) containing an olefin-based polymer (A1). The viscosity index improver (B) and the imide-based dispersant (C) may be blended simultaneously or separately into the base oil (A) containing the olefin-based polymer (A1). The same applies to blending other components other than the viscosity index improver (B) and the imide-based dispersant (C). Each component may be blended after being made into a solution (dispersion) by adding a diluent oil or the like. After blending each component, it is preferable to stir and uniformly disperse the components by a known method.

[Uses of the lubricating oil composition]
The lubricating oil composition of one embodiment of the present invention can be preferably used as a lubricating oil composition for internal combustion engines such as gasoline engines, diesel engines, gas engines, etc. of automobiles such as two-wheeled and four-wheeled vehicles, generators, ships, etc., and can be particularly preferably used as a lubricating oil composition used in environments with high thermal loads, such as internal combustion engines such as engines equipped with a supercharger such as a turbocharger.
The lubricating oil composition of one embodiment of the present invention is preferably filled into these internal combustion engines, particularly internal combustion engines equipped with a turbocharger (engines equipped with a turbocharger), and used to lubricate various parts associated with these internal combustion engines.
Therefore, according to one aspect of the present invention, there is provided a method for lubricating an internal combustion engine by using the lubricating oil composition. Also provided is a method for lubricating an internal combustion engine equipped with a turbocharger (a turbocharged engine) by using the lubricating oil composition.

[One aspect of the present invention provided]
In one aspect of the present invention, the following [1] to [11] are provided.
[1] A lubricating oil composition comprising a base oil (A) containing an olefin polymer (A1), a viscosity index improver (B), and an imide-based dispersant (C),
The olefin polymer (A1) includes a first olefin polymer (A1-1) having a kinetic viscosity at 100° C. of 3.0 mm ² /s or more, and the content of the first olefin polymer (A1-1) is 30 mass% or more based on the total amount of the base oil (A);
the olefin polymer (A1) does not contain a second olefin polymer (A1-2) having a kinetic viscosity at 100° C. of less than 3.0 mm ² /s, or if it does contain one, the amount of the second olefin polymer (A1-2) is less than 18.5 mass % based on the total amount of the base oil (A);
the content of the resin component (B1) derived from the viscosity index improver (B) is 0.01 mass% or more based on the total amount of the lubricating oil composition;
The nitrogen atom content derived from the imide-based dispersant (C) is 0.06 mass% or more based on the total amount of the lubricating oil composition;
a content ratio [(B1)/(A1-1)] of the resin component (B1) derived from the viscosity index improver (B) to the first olefin polymer (A1-1) is greater than 0.001 in terms of mass ratio,
The kinetic viscosity at 100°C is 5.0 ^mm2 /s or more and less than 7.1 ^mm2 /s;
A lubricating oil composition having an aniline point of 95° C. or higher.
[2] The lubricating oil composition according to the above item [1], wherein the base oil (A) further comprises one or more selected from the group consisting of mineral oils (A2) and synthetic oils (A3) other than the first olefin polymer (A1-1) and the second olefin polymer (A1-2).
[3] The lubricating oil composition according to the above [2], wherein the content of the mineral oil (A2) is 50 mass% or less based on the total amount of the base oil (A).
[4] The lubricating oil composition according to any one of the above [1] to [3], having a high temperature high shear viscosity (HTHS viscosity) at 150°C of 2.0 mPa·s or more and less than 2.3 mPa·s.
[5] The lubricating oil composition according to any one of the above [1] to [4], wherein the mass average molecular weight (Mw) of the resin component (B1) is 200,000 or more.
[6] The lubricating oil composition according to any one of the above [1] to [5], further comprising a metallic detergent (D).
[7] The lubricating oil composition according to any one of the above [1] to [6], further comprising a zinc dithiophosphate (E).
[8] The lubricating oil composition according to any one of the above [1] to [7], which is used in an internal combustion engine.
[9] The lubricating oil composition according to any one of the above [1] to [7], which is used in an internal combustion engine equipped with a turbocharger.
[10] A method for lubricating an internal combustion engine using the lubricating oil composition according to any one of [1] to [7] above.
[11] The lubrication method according to the above [10], wherein the internal combustion engine is an internal combustion engine equipped with a turbocharger.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples.

[Methods for measuring various physical properties]
The properties of the raw materials used in each Example and Comparative Example and the lubricating oil compositions in each Example and Comparative Example were measured according to the procedures described below.

(1) Kinematic Viscosity at 40° C. and Kinematic Viscosity at 100° C. The kinematic viscosities at 40° C. and 100° C. of the base oil and lubricating oil composition were measured in accordance with JIS K2283:2000.
(2) Viscosity Index The viscosity index of the base oil and the lubricating oil composition was calculated from the measured values of kinematic viscosity at 40°C and kinematic viscosity at 100°C measured in accordance with JIS K2283:2000.
(3) HTHS Viscosity at 150° C. The HTHS viscosity of the lubricating oil composition at 150° C. was measured in accordance with ASTM D4683 using a TBS high temperature viscometer (Tapered Bearing Simulator Viscometer) at a temperature of 150° C. and a shear rate of 10 ⁶ /s.
(4) NOACK Evaporation Amount The NOACK evaporation amount of a lubricating oil composition was measured at 250° C. for 1 hour in accordance with JPI-5S-41-2004.
(5) Aniline Point The aniline point of the lubricating oil composition was measured in accordance with JIS K 2256:2013.
(6) Mass average molecular weight (Mw), number average molecular weight (Mn)
Measurements were carried out using a gel permeation chromatograph (Agilent Technologies, "1260 Model HPLC") under the following conditions, and values measured in terms of standard polystyrene were used.
(Measurement conditions)
- Column: Two "Shodex LF404" columns connected in series.
Column temperature: 35°C
Developing solvent: chloroform Flow rate: 0.3 mL/min

[Examples 1 to 4 and Comparative Examples 1 to 6]
The lubricating oil compositions of Examples 1 to 4 and Comparative Examples 1 to 6 were prepared by thoroughly mixing the base oil (A), viscosity index improver (B), imide-based dispersant (C), and various additives shown below in the amounts (unit: mass %) shown in Table 1.
Details of the base oil (A), viscosity index improver (B), imide-based dispersant (C), and various additives used in the preparation of the lubricating oil compositions of Examples 1 to 4 and Comparative Examples 1 to 6 are as follows.
The blending amount of the viscosity index improver (B) shown in Table 1 is the blending amount of the active ingredient (resin component (B1)) excluding the diluent oil.

<Base oil (A)>
(First olefin polymer (A1-1)-1)
Olefin polymer produced in Production Example 1 described later: 40° C. kinematic viscosity: 13.61 mm ² /s, 100° C. kinematic viscosity: 3.42 mm ² /s, viscosity index: 129
(First olefin polymer (A1-1)-2)
Manufactured by Ineos, product name "Durasyn 133"
40°C kinematic viscosity: 13.41mm ² /s, 100°C kinematic viscosity: 3.36mm ² /s, viscosity index: 125
(Second Olefin Polymer (A1-2)-1)
Manufactured by Ineos, product name "Durasyn 162"
40°C kinematic viscosity: 5.10mm ² /s, 100°C kinematic viscosity: 1.80mm ² /s
(Second Olefin Polymer (A1-2)-2)
Poly-α-olefin oligomer synthesized from 1-decene, the raw material monomer, using a BF ₃ catalyst. Kinematic viscosity at 40°C: 5 mm ² /s, Kinematic viscosity at 100°C: 1.7 mm ² /s
(Mineral oil (A2)-1)
Mineral oil classified as Group III in the API category. Kinematic viscosity at 40°C: 19 mm ² /s, Kinematic viscosity at 100°C: 4.2 mm ² /s, Viscosity index: 126
(Mineral oil (A2)-2)
Mineral oil classified as Group II in the API category. Kinematic viscosity at 40°C: 12 ^mm2 /s, Kinematic viscosity at 100°C: 3.0 ^mm2 /s, Viscosity index: 106
(Ester-based oil (A3-1))
Dioctyl sebacate Kinematic viscosity at 40°C: 12 ^mm2 /s, Kinematic viscosity at 100°C: 3.2 ^mm2 /s, Viscosity index: 151

<Production Example 1: Production of First Olefin Polymer (A1-1)-1>
(1) Polymerization of 1-decene In a 5-L three-neck flask, 4 L (21.4 mol) of 1-decene (manufactured by Idemitsu Kosan Co., Ltd., product name "Linearene 10") was added under a nitrogen stream, and then a solution of biscyclopentadienylzirconium dichloride (complex mass: 1,168 mg (4 mmol)) as a metallocene catalyst dissolved in toluene and a solution of methylalumoxane (Al equivalent: 40 mmol) as a co-catalyst dissolved in toluene were further added.
After the addition, the mixture was stirred at 40° C. for 20 hours to allow the oligomerization of the decene monomer to proceed, and then 20 ml of methanol was added to terminate the oligomerization reaction.
Next, the reaction mixture was taken out of the three-neck flask, 4 liters of a 5 mol/L aqueous sodium hydroxide solution was added, and the mixture was stirred at room temperature (25° C.) for 4 hours to carry out a liquid separation operation. Then, the upper organic layer was taken out to obtain a solution of decene trimer.

(2) Hydrogenation Treatment In a 5-liter autoclave, 3 liters of the decene oligomer solution obtained in (1) above was added under a nitrogen stream, and then a solution of cobalt trisacetylacetonate (catalyst mass: 3.0 g) dissolved in toluene and a solution of triisobutylaluminum (30 mmol) dissolved in toluene were further added.
After the addition, the system was replaced with hydrogen twice, and then the temperature was raised and the hydrogenation reaction was allowed to proceed while maintaining the reaction temperature at 80° C. and the hydrogen pressure at 0.9 MPa. Then, 4 hours after the start of the reaction, the temperature was lowered to room temperature (25° C.) to terminate the hydrogenation reaction.
The autoclave was then depressurized, and the reaction product was removed from the autoclave. A fraction having a distillation temperature of 240 to 270° C. and a pressure of 530 Pa was separated by simple distillation to obtain a first olefin polymer (A1-1)-1 consisting of a hydrogenated product of decene trimer.

<Viscosity index improver (B)>
(Resin component (B1)-1: Comb polymer)
Mass average molecular weight (Mw): 600,000, Mw/Mn: 2.9, SSI: 1, and at least one structural unit derived from a macromonomer having an Mn of 500 or more.
(Resin content (B1)-2: PMA)
Polymethacrylate (manufactured by Sanyo Chemical Industries, Ltd., product name "Aclub 740"), mass average molecular weight (Mw): 230,000, Mw/Mn: 2.1.

<Imide-based dispersant (C)>
Polybutenyl succinic acid bisimide (non-boron modified): Nitrogen content 1.2% by mass

<Other lubricating oil additives>
(Metal-Based Detergent (D))
Calcium salicylate, magnesium salicylate In Examples 1 to 4, Comparative Examples 1 to 4, and Comparative Example 6, calcium salicylate and magnesium salicylate were blended so that the Ca content in the lubricating oil composition was 0.11 mass % and the Mg content was 0.02 mass %.
In Comparative Example 5, calcium salicylate was blended so that the Ca content in the lubricating oil composition was 0.23 mass %.
(Zinc dithiophosphate (E))
ZnDTP of the first grade, ZnDTP of the second grade
In Examples 1 to 4, Comparative Examples 1 to 4, and Comparative Example 6, first-class ZnDTP and second-class ZnDTP were blended so that the P content in the lubricating oil composition was 0.07 mass % and the Zn content was 0.08 mass %.
In Comparative Example 5, first class ZnDTP and second class ZnDTP were blended so that the P content in the lubricating oil composition was 0.08 mass % and the Zn content was 0.09 mass %.
(Antioxidants)
An amine-based antioxidant was added to each of Examples 1 to 4 and Comparative Examples 1 to 6. The amount of the amine-based antioxidant added to the lubricating oil composition was 0.5% by mass.

[Evaluation of high-temperature detergency]
The lubricating oil compositions of Examples 1 to 4 and Comparative Examples 1 to 6 were evaluated for high temperature detergency.
First, the lubricating oil compositions of Examples 1 to 4 and Comparative Examples 1 to 6 were subjected to an aging treatment by blowing _NOX gas with a concentration of 4,000 ppm by volume into the lubricating oil compositions for 72 hours at an oil temperature of 150°C. This aging treatment resulted in the lubricating oil compositions in a state equivalent to that after driving about 16,000 km. The volume of the test container was 300 mL, and 100 mL of the lubricating oil composition was used.
The aged lubricating oil composition was subjected to a hot tube test at a temperature of 260°C.
A lubricating oil composition that received a rating of 2.5 or more out of a range of 0 to 10 in the hot tube test was evaluated as having high-temperature detergency properties that could be maintained for a long period of time.

[Evaluation of oil film retention]
The oil film thickness of the obtained lubricating oil composition was measured under the following conditions. The oil film thickness was measured three times under the same conditions, and the average of the three measurements was taken as the EHL oil film thickness of the lubricating oil composition. If the EHL oil film thickness was 60 nm or more, the lubricating oil composition was evaluated as having excellent oil film retention properties.
- Device name: EHD2 (manufactured by PCS Instruments)
・Test piece: Steel Ball (diameter: 7.5mm)
Disc: SiO ₂ /Cr coated Glass Disc
Oil temperature: 100℃
Load: 20N (surface pressure: 0.5GPa)
・Speed: 100mm/s
Slip ratio (SRR): 200%

The results are shown in Table 1.

From Table 1, the following can be seen:
It is seen that the lubricating oil compositions of Examples 1 to 4 have low volatility, excellent oil film retention, and excellent high-temperature detergency. In addition, they have aniline points of 95°C or higher, and are also excellent in compatibility with rubber materials.
In contrast, the lubricating oil composition of Comparative Example 1 has a content of the second olefin polymer (A1-2) of 18.5 mass % or more based on the total amount of the base oil (A), and therefore is found to have poor low volatility.
The lubricating oil composition of Comparative Example 2 has an aniline point at room temperature, and therefore is poor in compatibility with rubber materials.
It is clear that the lubricating oil composition of Comparative Example 3 is inferior in terms of low volatility since it does not contain the first olefin polymer (A1-1).
The lubricating oil compositions of Comparative Examples 4 and 5 have a nitrogen atom content derived from the imide-based dispersant (C) of less than 0.06% by mass, and therefore are inferior in high-temperature detergency. They also have inferior oil film retention. The lubricating oil composition of Comparative Example 5 has a content ratio [(B1)/(A1-1)] of the resin component (B1) derived from the viscosity index improver (B) to the first olefin polymer (A1-1) of 0.001 or less by mass, and therefore is inferior in oil film retention compared to Comparative Example 4.
The lubricating oil composition of Comparative Example 6 does not contain a viscosity index improver (B), and the content ratio [(B1)/(A1-1)] of the resin component (B1) derived from the viscosity index improver (B) to the first olefin polymer (A1-1) is 0.001 or less in mass ratio, and therefore it is clear that the lubricating oil composition of Comparative Example 6 has poor oil film retention.

Claims (11)

A lubricating oil composition comprising a base oil (A) containing an olefin polymer (A1), a viscosity index improver (B), and an imide-based dispersant (C),
The olefin polymer (A1) includes a first olefin polymer (A1-1) having a kinetic viscosity at 100° C. of 3.0 mm ² /s or more, and the content of the first olefin polymer (A1-1) is 30 mass% or more based on the total amount of the base oil (A);
the olefin polymer (A1) does not contain a second olefin polymer (A1-2) having a kinetic viscosity at 100° C. of less than 3.0 mm ² /s, or if it does contain one, the amount of the second olefin polymer (A1-2) is less than 18.5 mass % based on the total amount of the base oil (A);
the content of the resin component (B1) derived from the viscosity index improver (B) is 0.01 mass% or more based on the total amount of the lubricating oil composition;
The nitrogen atom content derived from the imide-based dispersant (C) is 0.06 mass% or more based on the total amount of the lubricating oil composition;
a content ratio [(B1)/(A1-1)] of the resin component (B1) derived from the viscosity index improver (B) to the first olefin polymer (A1-1) is greater than 0.001 in terms of mass ratio,
The kinetic viscosity at 100°C is 5.0 ^mm2 /s or more and less than 7.1 ^mm2 /s;
A lubricating oil composition having an aniline point of 95° C. or higher. The lubricating oil composition according to claim 1, wherein the base oil (A) further comprises one or more selected from the group consisting of mineral oil (A2) and synthetic oil (A3) other than the first olefin polymer (A1-1) and the second olefin polymer (A1-2). The lubricating oil composition according to claim 2, wherein the content of the mineral oil (A2) is 50 mass% or less based on the total amount of the base oil (A). A lubricating oil composition according to any one of claims 1 to 3, having a high temperature, high shear viscosity (HTHS viscosity) at 150°C of 2.0 mPa·s or more and less than 2.3 mPa·s. A lubricating oil composition according to any one of claims 1 to 4, wherein the mass average molecular weight (Mw) of the resin component (B1) is 200,000 or more. A lubricating oil composition according to any one of claims 1 to 5, further comprising a metal-based detergent (D). The lubricating oil composition according to any one of claims 1 to 6, further comprising zinc dithiophosphate (E). A lubricating oil composition according to any one of claims 1 to 7, for use in an internal combustion engine. A lubricating oil composition according to any one of claims 1 to 7, for use in an internal combustion engine equipped with a turbocharger. A method for lubricating an internal combustion engine using the lubricating oil composition according to any one of claims 1 to 7. The lubrication method according to claim 10, wherein the internal combustion engine is an internal combustion engine equipped with a turbocharger.