JP7779164B2 - lubricating oil composition - Google Patents

Description

The present invention relates to a lubricating oil composition.

In recent years, efforts to improve fuel economy have led to demands for improved power transmission efficiency and smaller, lighter automobile transmissions. As a result, some vehicles have moved from manual transmissions to automatic transmissions, and more recently to continuously variable transmissions. Meanwhile, electric vehicles equipped with lead-acid batteries, nickel-metal hydride batteries, lithium-ion batteries, fuel cells, etc., and fitted with electric motors, as well as hybrid vehicles that use these batteries in conjunction with internal combustion engines, have been developed, and these vehicles use separate transmission oils and electric motor oils.

Recently, in the field of electric vehicles or hybrid vehicles, there has been a demand for standardization of these oils and for packaging the transmission and electric motor to reduce size and weight, and there has been a demand for new oils that not only have the lubricating properties of manual transmission oils, automatic transmission oils, or continuously variable transmission oils, but also the insulating properties and cooling properties of electric motor oils.
Transmission fluids are required to have thermal and oxidation stability, detergent-dispersant properties, anti-wear properties, anti-seizure properties, etc. To meet these requirements, transmission fluids are generally made by adding various additives (antioxidants, detergent-dispersants, anti-wear agents, rust inhibitors, metal deactivators, friction modifiers, scavengers, colorants, seal expansion agents, viscosity index improvers, etc.) to mineral oil or synthetic base oils. Since such transmission fluids have low volume resistivity and insufficient insulating properties, when used as electric motor oils, they can cause problems such as short circuits in electric motors, and poor cooling and power loss due to their high kinematic viscosity.

On the other hand, electric motor oils are required to have insulating properties, cooling properties, etc., but not lubricity, and therefore contain almost no additives. Therefore, when electric motor oils are used in transmissions, there is a problem of significant wear of bearings, gears, etc. In addition, with the progress of miniaturization and high rotation speeds in electric motors, expectations are increasing for the cooling properties of lubricating oils. In other words, for vehicles equipped with electric motors, such as electric vehicles or hybrid vehicles, there is a demand for automotive transmission oil compositions that have the anti-seizure performance, anti-wear performance, and low-temperature flow performance required for transmission oils, as well as better insulating properties and cooling properties than conventional transmission oils.
It is known to use an ester-based synthetic oil with high thermal conductivity, such as an ester of a monohydric alcohol and a monobasic acid and/or an ester of a monohydric alcohol and a polybasic acid, as an automotive transmission oil composition that also has cooling properties (Patent Documents 1 and 2).
However, although the above-mentioned composition has a low viscosity, a good heat transfer coefficient, and a high cooling property, the low viscosity results in a thin oil film thickness, which increases the coefficient of friction and deteriorates lubricity.

Japanese Patent Application Laid-Open No. 2009-242547 JP 2014-25081 A

The object of the present invention is to provide a lubricating oil composition that combines cooling and lubricating properties.

As a result of extensive research, the present inventors have arrived at the present invention, which is a lubricating oil composition comprising a copolymer (A) having, as essential constituent monomers , a monomer (a) represented by the following general formula (1) , a monomer (b) represented by the following general formula (2), and a hydroxyl group-containing monomer (e) other than the monomer (a), and an ester oil (B):
[In formula (1), A ¹ represents a monovalent radically polymerizable group; -X ¹ -, -X ² -, and -X ³ - each independently represent a group represented by -O- or -NH-; R ¹ represents an alkylene group having 1 to 4 carbon atoms; R ² each independently represent an alkylene group having 2 to 20 carbon atoms, and when there are multiple R ^2s , they may be the same or different; R ³ represents a hydrogen atom, an alkyl group having 1 to 44 carbon atoms, an acyl group having 2 to 45 carbon atoms, or a phenyl group or benzoyl group optionally substituted with an alkyl group having 1 to 44 carbon atoms; and p represents an integer from 1 to 100.]
[In formula (2), R ⁴ represents a hydrogen atom or a methyl group; —X ⁴ — represents a group represented by —O— or —NH—; and R ⁵ represents a linear or branched alkyl group having 5 to 44 carbon atoms.]

The lubricating oil composition of the present invention has the effect of achieving both cooling properties and lubrication properties.

1 shows the relationship between rotational speed and MTM friction coefficient in the MTM friction coefficient measurement at 100° C. for the lubricating oil compositions (V-1) to (V-4) of Examples 1 to 4. This shows the relationship between rotational speed and MTM friction coefficient in the MTM friction coefficient measurement at 100°C for lubricating oil compositions (V'-1), (V'-3), (V'-5) to (V'-8) of Comparative Examples 1, 3, and 5 to 8.

The lubricating oil composition of the present invention is a lubricating oil composition comprising a copolymer (A) having, as essential constituent monomers, a monomer (a) represented by the following general formula (1), and a monomer (b) represented by the following general formula (2) and/or a monomer (c) represented by the following general formula (3), and an ester oil (B):
[In formula (1), A ¹ represents a monovalent radically polymerizable group; -X ¹ -, -X ² -, and -X ³ - each independently represent a group represented by -O- or -NH-; R ¹ represents an alkylene group having 1 to 4 carbon atoms; R ² each independently represent an alkylene group having 2 to 20 carbon atoms, and when there are multiple R ^2s , they may be the same or different; R ³ represents a hydrogen atom, an alkyl group having 1 to 44 carbon atoms, an acyl group having 2 to 45 carbon atoms, or a phenyl group or benzoyl group optionally substituted with an alkyl group having 1 to 44 carbon atoms; and p represents an integer from 1 to 100.]
[In formula (2), R ⁴ represents a hydrogen atom or a methyl group; —X ⁴ — represents a group represented by —O— or —NH—; and R ⁵ represents a linear or branched alkyl group having 5 to 44 carbon atoms.]
[In formula (3), R ⁶ is a hydrogen atom or a methyl group; -X ⁵ - is a group represented by -O-, -O(AO) _m -, or -NH-, A is an alkylene group having 2 to 4 carbon atoms, m is an integer from 1 to 10, and when m is 2 or more, As may be the same or different; R ⁷ is a residue in which one hydrogen atom has been removed from a hydrocarbon polymer having 43 or more carbon atoms and containing isobutylene groups and/or 1,2-butylene groups as essential structural units; and q is the number 0 or 1.]

The copolymer (A) and the ester oil (B) may each be used alone or in combination of two or more thereof.
In the present invention, it has been found that by combining copolymer (A) and ester oil (B), it is possible to achieve excellent power transmission characteristics, with a high MTM (mini-traction) friction coefficient of 0.070 or more at low speed (measured under the conditions described below, the same applies hereinafter) (100°C, speed: ¹⁰ mm/s) without reducing the cooling ability of ester oil (B) {a heat transfer coefficient of 2.10 W/(m2/K) or more at 40°C}, and at high speed the MTM friction coefficient (100°C, speed: 100 mm/s) can be rapidly reduced to 0.055 or less, thereby achieving high lubricity.

<Copolymer (A)>
In the present invention, the copolymer (A) contains the monomer (a) represented by the above general formula (1) as an essential constituent monomer.
In the general formula (1), A ¹ is a monovalent radically polymerizable group, specifically a vinyl group, a (meth)acryloyl group, or the like.
From the viewpoint of lubricity, ^A1 is preferably a vinyl group or a (meth)acryloyl group, and more preferably a (meth)acryloyl group.

In formula (1), —X ¹ —, —X ² — and —X ³ — each independently represent a group represented by —O— or —NH—.
From the viewpoint of lubricity, these —X ¹ —, —X ² — and —X ³ — are preferably —O—.

In the general formula (1), R ¹ is an alkylene group having 1 to 4 carbon atoms.
Examples of alkylene groups having 1 to 4 carbon atoms include methylene, ethylene, 1,2- and 1,3-propylene, and 1,2-, 1,3- and 1,4-butylene groups. Of these, from the viewpoint of lubricity, ethylene, 1,2-propylene, and 1,3-propylene groups are preferred, and ethylene is more preferred.

In the general formula (1), p is an integer of 1 to 100, and from the viewpoint of reducing friction at high speeds and solubility in a base oil (such as an ester oil (B), the same applies hereinafter), p is preferably an integer of 1 to 70, more preferably an integer of 1 to 40, and particularly preferably an integer of 1 to 20.
When p is 2 or more, the multiple (-C(=O)-R ² -X ³ -) groups may be the same or different.

In the general formula (1), R ² is an alkylene group having 2 to 20 carbon atoms, and when there are a plurality of R ^{2 s} , they may be the same or different.
Examples of alkylene groups having 2 to 20 carbon atoms include ethylene, 1,2- or 1,3-propylene, isobutylene, 1,2-, 1,3-, or 1,4-butylene, isopentylene, 1,2-, 1,3-, 1,4-, or 1,5-pentylene, isohexylene, 1,2-, 1,3-, 1,4-, 1,5-, or 1,6-hexylene, isoheptylene, 1,2-, 1,3-, 1,4-, 1,5-, 1,6-, or 1,7-heptylene, isooctylene, 1,8-octylene, isononylene, 1,9-nonylene, isodecylene, and 1,10-decylene. Examples of the alkyl group include an alkyl group, an alkyl acrylate ...
From the viewpoint of reducing friction at high speeds, ^R2 is preferably an alkylene group having 2 to 17 carbon atoms, more preferably an alkylene group having 2 to 15 carbon atoms, particularly preferably an alkylene group having 2 to 13 carbon atoms, and most preferably an alkylene group having 2 to 10 carbon atoms.

In general formula (1), ^R3 is a hydrogen atom, an alkyl group having 1 to 44 carbon atoms, an acyl group having 2 to 45 carbon atoms, a phenyl group which may be substituted with an alkyl group having 1 to 44 carbon atoms, or a benzoyl group.

Alkyl groups having 1 to 44 carbon atoms include linear or branched alkyl groups, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, n-hexyl, isohexyl, n-heptyl, isoheptyl, n-octyl, 2-ethylhexyl, isooctyl, n-nonyl, and isononyl. group, n-decyl group, isodecyl group, n-undecyl group, isoundecyl group, n-dodecyl group, isododecyl group, n-tridecyl group, isotridecyl group, n-tetradecyl group, 2-ethyldodecyl group, n-pentadecyl group, 2-methyltetradecyl group, n-hexadecyl group, isohexadecyl group, n-heptadecyl group, isoheptadecyl group, 2-ethylpentadecyl group, 2-octylnonyl group, 2-(3-methylhexyl )-7-methyl-nonyl group, n-octadecyl group, isooctadecyl group, 2-hexylundecyl group, 2-ethylheptadecyl group, 1-hexyltridecyl group, n-icosyl group, 2-octylundecyl group, isoicosyl group, 1-undecyldodecyl group, 1-octylpentadecyl group, 2-decyltridecyl group, n-tetraicosyl group, 2-decyltetradecyl group, 2-dodecylpentadecyl group, 2-heptylicosyl group Examples include a 2-dodecylhexadecyl group, an n-triacontyl group, a 2-tetradecyloctadecyl group, an n-hexatriacontyl group, an n-tetracontyl group, a 2-ethyltetracontyl group, and residues obtained by removing the hydroxyl group from oxoalcohols obtained from olefins [such as propylene oligomers (dimer to tetradecamer), ethylene/propylene oligomers (dimer to 20mer), and isobutene oligomers (dimer to 10mer)].

Acyl groups include those derived from carboxylic acids having 2 to 45 carbon atoms and having the aforementioned alkyl group having 1 to 44 carbon atoms, such as acetyl, propionyl, butanoyl, pentanoyl, hexanoyl, heptanoyl, octanoyl, nonanoyl, decanoyl, lauryl, myristoyl, and palmitoyl groups.

Examples of phenyl or benzoyl groups that may be substituted with an alkyl group having 1 to 44 carbon atoms include phenyl, benzoyl, phenyl groups in which some or all of the hydrogen atoms have been substituted with alkyl groups having 1 to 44 carbon atoms (such as tolyl), and benzoyl groups in which some or all of the hydrogen atoms have been substituted with alkyl groups having 1 to 44 carbon atoms.

Of these ^R3s , from the viewpoint of reducing friction at high speeds, a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an acyl group having 2 to 13 carbon atoms, a phenyl group or a benzoyl group which may be substituted with an alkyl group having 1 to 12 carbon atoms is preferred, and a hydrogen atom and an acyl group having 4 to 12 carbon atoms are more preferred.

The structural unit derived from the monomer (a) (a structure in which the radically polymerizable carbon-carbon double bond of the monomer (a) has reacted to form a single bond) preferably has a specific solubility parameter (hereinafter sometimes abbreviated as SP value) from the viewpoint of solubility in the base oil.
The SP value range is preferably 9.0 to 12.5 (cal/cm ³ ) ^1/2 , more preferably 9.3 to 12.3 (cal/cm ³ ) ^1/2 , and particularly preferably 9.5 to 12.0 (cal/cm ³ ) ^1/2 .

Furthermore, when copolymer (A) uses two or more types of monomers (a) in combination, it is preferable that the SP values of the respective monomers constituting (a) are calculated by the above-mentioned method, and the arithmetic mean of the SP values of the respective monomers (a) based on the weight fractions of the constituent monomer units satisfies the range of the SP values of the monomers (a).
When the SP value of the constituent unit derived from the monomer (a) is within the above range, friction at high speeds tends to be reduced and solubility in the base oil tends to be good.
The SP value in the present invention refers to the value calculated by formula (28) on page 153 of the Fedors method (Polymer Engineering and Science, February 1974, Vol. 14, No. 2, pp. 147-154) using the values (heat of vaporization and molar volume at 25°C of atoms or functional groups) described on page 152 (Table 5). Specifically, the SP value can be calculated from the values of Δe _i and v _i described in Table 1 below, which are parameters of the Fedors method, by applying the values corresponding to the types of atoms and atomic groups in the molecular structure to the following formula:
SP value = (ΣΔe _i /Σv _i ) ^1/2

The molecular formula weight or number average molecular weight (hereinafter abbreviated as Mn) of the monomer (a) is preferably 150 to 20,000, more preferably 150 to 10,000, particularly preferably 150 to 7,000, and most preferably 150 to 4,000, from the viewpoint of reducing friction at high speeds.
The Mn of (a), the weight average molecular weight (hereinafter abbreviated as Mw) and Mn of (c), and the Mw and Mn of the copolymer (A) described later can be measured by gel permeation chromatography (hereinafter abbreviated as GPC) under the following conditions.
<Measurement conditions for Mn of (a), Mw and Mn of (c), and Mw and Mn of (A)>
Device: "HLC-802A" [manufactured by Tosoh Corporation]
Column: 2 "TSK gel GMH6" [manufactured by Tosoh Corporation] Measurement temperature: 40°C
Sample solution: 0.25 wt% tetrahydrofuran solution Solution injection amount: 100 μl
Detector: Refractive index detector Reference material: Standard polystyrene (TSKstandard POLYSTYRENE)
12 points (molecular weight: 500, 1,050, 2,800, 5,970, 9,100, 18,100, 37,900, 96,400, 190,000, 355,000, 1,090,000, 2,890,000) [manufactured by Tosoh Corporation]

As the monomer (a), from the viewpoint of reducing friction at high speeds, preferred examples include (a1) an adduct of 1 to 100 moles of lactone of a hydroxyalkyl (meth)acrylate, (a2-1) an esterification product of (a1) with a monocarboxylic acid having 2 to 45 carbon atoms, (a2-2) an esterification product of (a1) with benzoic acid (in which some of the hydrogen atoms bonded to the aromatic ring of benzoic acid may be substituted with an alkyl group having 1 to 44 carbon atoms), (a2-3) an etherification product of (a1) with an alkyl alcohol having 1 to 44 carbon atoms, (a3) an adduct of 1 to 100 moles of lactam of a hydroxyalkyl (meth)acrylate, and (a4) an amidation product of (a3) with a monocarboxylic acid having 2 to 45 carbon atoms.
These monomers (a) can be obtained by known production methods.

Examples of the monomer (a) include the following:
Hydroxyalkyl (meth)acrylate lactone adduct (a1):
Examples include ring-opening addition of lactones (having 3 to 21 carbon atoms, for example, β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, etc.) to hydroxyalkyl (hydroxyalkyl group having 1 to 4 carbon atoms) (meth)acrylates {for example, hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), etc.}.
The reaction temperature when the lactone is subjected to the ring-opening addition reaction with the hydroxyalkyl (meth)acrylate is preferably 80°C to 150°C, more preferably 100°C to 140°C, from the viewpoint of reaction time. The reaction time is preferably 2 to 24 hours, more preferably 3 to 10 hours. The reaction is mainly carried out in the presence of a catalyst.
The catalyst for the above reaction may be any known catalyst, such as p-toluenesulfonic acid, tetrapropyl titanate, or stannous octoate. The amount of catalyst used is preferably 0.01 to 5 mass % relative to the amount of the reaction product, and more preferably 0.03 to 0.5 mass %. After completion of the ring-opening addition reaction, the catalyst is desirably treated by a method of adsorbing and filtering with an adsorbent, removing the catalyst, or by a method of neutralizing and inactivating the catalyst.

(a2-1) an esterification product of (a1) with a monocarboxylic acid having 2 to 45 carbon atoms, and (a2-2) an esterification product of (a1) with benzoic acid (in which some of the hydrogen atoms bonded to the aromatic ring of the benzoic acid may be substituted with alkyl groups having 1 to 44 carbon atoms):
The reaction temperature when the (a1) is esterified with a carboxylic acid (such as a monocarboxylic acid having 2 to 45 carbon atoms or benzoic acid) is preferably 80°C to 150°C, more preferably 90°C to 130°C, from the viewpoints of reaction time and preventing polymerization of (meth)acrylic acid. The reaction pressure during the esterification reaction may be reduced in order to remove the water produced. From the viewpoints of reaction time and preventing polymerization, the reaction pressure is preferably 0.007 to 0.095 MPa, more preferably 0.01 to 0.092 MPa. The reaction time is preferably 2 to 24 hours, more preferably 3 to 10 hours. The esterification reaction is desirably carried out in the presence of a catalyst.
The catalyst for the esterification reaction may be a known catalyst, such as sulfuric acid, p-toluenesulfonic acid, etc. A solvent may also be used in the esterification reaction, and examples of the solvent include water-insoluble solvents having a boiling point of 150° C. or less, such as cyclohexane and toluene.
Examples of monocarboxylic acids having 2 to 45 carbon atoms include saturated aliphatic monocarboxylic acids (e.g., ethanoic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, etc.), unsaturated aliphatic monocarboxylic acids (e.g., oleic acid, linoleic acid, linolenic acid, arachidonic acid, docosahexanoic acid, etc.), etc. Among these, saturated aliphatic monocarboxylic acids are preferred, and saturated aliphatic monocarboxylic acids having 2 to 13 carbon atoms are more preferred.

Etherification product (a2-3) of (a1) with alkyl alcohol having 1 to 44 carbon atoms:
The compound (a1) can be obtained by reacting the compound (a1) with an alkylating agent having 1 to 44 carbon atoms (an alkyl chloride such as methyl chloride, ethyl chloride, propyl chloride, butyl chloride, isopropyl chloride, or allyl chloride; an alkyl bromide such as methyl bromide, ethyl bromide, propyl bromide, butyl bromide, or isopropyl bromide) in the presence of an alkali (for example, an amine, a quaternary ammonium salt, or sodium hydroxide) under general conditions.

1 to 100 mole adduct of hydroxyalkyl (meth)acrylate with lactam (a3):
Examples include those obtained by ring-opening addition of a lactam (having 3 to 21 carbon atoms, for example, β-lactam, γ-lactam, δ-lactam, ε-lactam, etc.) to a hydroxyalkyl (hydroxyalkyl group having 1 to 4 carbon atoms) (meth)acrylate {for example, hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), etc.}.
The reaction temperature when the lactam is subjected to the ring-opening addition reaction to the hydroxyalkyl (meth)acrylate is preferably 80°C to 150°C, more preferably 100°C to 140°C, from the viewpoint of reaction time. The reaction time is preferably 2 to 24 hours, more preferably 3 to 10 hours. The reaction is mainly carried out in the presence of a catalyst.
The catalyst for the above reaction may be a known catalyst, such as tetrapropyl titanate, stannous octoate, etc. The amount of the catalyst used is preferably 0.01 to 5 mass %, more preferably 0.03 to 0.5 mass %, based on the amount of the reaction product.
After the ring-opening addition reaction is completed, the catalyst is desirably treated by a method such as adsorption using an adsorbent, filtration and removal, or neutralization to inactivate the catalyst.

Amidation product (a4) of (a3) with a monocarboxylic acid having 2 to 45 carbon atoms:
The reaction temperature when the (a3) is subjected to the amidation reaction with a monocarboxylic acid having 2 to 45 carbon atoms is preferably 80°C to 150°C, more preferably 90°C to 130°C, from the viewpoints of reaction time and prevention of polymerization of (meth)acrylic acid. Furthermore, the reaction pressure during the amidation reaction may be reduced in order to remove the water produced. From the viewpoints of reaction time and prevention of polymerization, the preferred reaction pressure is preferably 0.007 to 0.095 MPa, more preferably 0.01 to 0.092 MPa. The reaction time is preferably 2 to 24 hours, more preferably 3 to 10 hours.
Examples of monocarboxylic acids having 2 to 45 carbon atoms include saturated aliphatic monocarboxylic acids (e.g., ethanoic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, etc.), unsaturated aliphatic monocarboxylic acids (e.g., oleic acid, linoleic acid, linolenic acid, arachidonic acid, docosahexanoic acid, etc.), etc. Among these, saturated aliphatic monocarboxylic acids are preferred, and saturated aliphatic monocarboxylic acids having 2 to 13 carbon atoms are more preferred.

Among the monomers (a), from the viewpoint of reducing friction at high speeds, preferred are (a1) an adduct of 1 to 100 moles of lactone with hydroxyalkyl (meth)acrylate and (a2-1) an ester of (a1) with a monocarboxylic acid having 2 to 45 carbon atoms, with (a1) being more preferred, and (a1) in which the number of moles of lactone added is 1 to 20 moles being particularly preferred.

In the spectrum obtained by nuclear magnetic resonance analysis ( ¹³ C-NMR), the monomer (a) preferably has a ratio (M1/M2) of the total area ratio of peaks with a chemical shift of 170-180 ppm to the total area of all peaks (M1) to the total area ratio of peaks with a chemical shift of 160-170 ppm to the total area of all peaks (M2) of 0.01 or more, more preferably 0.02 or more, next more preferably 0.03 or more, particularly preferably 0.04 or more, and most preferably 0.05 or more. Furthermore, the ratio (M1/M2) is preferably 200 or less, more preferably 180 or less, particularly preferably 150 or less, and most preferably 130 or less. When the ratio (M1/M2) is 0.01 or more, lubricity and fuel economy tend to be improved, and when it is 200 or less, compatibility with the ester oil (B) tends to be good and storage stability tends to be improved.

The total area (M1) of peaks with chemical shifts between 170 and 180 ppm relative to the total area of ^all peaks means the ratio of the integrated intensity attributable to a specific carbonyl structure of (meth)acrylate relative to the total integrated intensity of all carbons measured by ^{13 C-NMR. The total area (M2) of peaks with chemical shifts between 160 and 170 ppm relative to the total area of all peaks means the ratio of the integrated intensity attributable to a specific carbonyl structure of (meth)acrylate relative to the total integrated intensity of all carbons measured by 13} C-NMR.

The ratio (M1/M2) means the proportion of a specific carbonyl structure in the (meth)acrylate, but other methods may be used as long as equivalent results are obtained. For the ^13C -NMR measurement, a sample prepared by diluting 0.1 g of the sample with 2 ml of deuterated chloroform is used, the measurement temperature is room temperature, the resonance frequency is 100 MHz, and the measurement method is the inverse gate decoupling method.

From the above analysis,
(a) the sum of the integrated intensities at chemical shifts of 160-180 ppm (the sum of the integrated intensities attributable to all carbons in hydrocarbons), and (b) the sum of the integrated intensities at chemical shifts of 170-180 ppm (the sum of the integrated intensities attributable to a specific carbonyl structure).
(c) Sum of integrated intensities at chemical shifts of 160-170 ppm (sum of integrated intensities attributable to a specific carbonyl structure)
Each of these is measured, and the ratio (%) of (b) when (a) is taken as 100% is calculated and designated as M1. Similarly, the ratio (%) of (c) when (a) is taken as 100% is calculated and designated as M2.

The copolymer (A) of the present invention contains, as constituent monomers, the monomer (b) represented by the general formula (2) and/or the monomer (c) represented by the general formula (3).

In the monomer (b), —X ⁴ — in the general formula (2) is a group represented by —O— or —NH—, and is preferably —O— from the viewpoint of reducing friction at high speeds.

In the monomer (b), R ⁴ in the general formula (2) is a hydrogen atom or a methyl group, and is preferably a methyl group from the viewpoint of reducing friction at high speeds.

In the monomer (b), ^R5 in the general formula (2) is a linear or branched alkyl group having 5 to 44 carbon atoms. Specific examples include an n-pentyl group, an isopentyl group, an n-hexyl group, an isohexyl group, an n-heptyl group, an isoheptyl group, an n-octyl group, a 2-ethylhexyl group, an isooctyl group, an n-nonyl group, an isononyl group, an n-decyl group, an isodecyl group, an n-undecyl group, an isoundecyl group, an n-dodecyl group, an isododecyl group, an n-tridecyl group, an isotridecyl group, an n-tetra ... tetradecyl group, 2-ethyldodecyl group, n-pentadecyl group, 2-methyltetradecyl group, n-hexadecyl group, isohexadecyl group, n-heptadecyl group, isoheptadecyl group, 2-ethylpentadecyl group, 2-octylnonyl group, 2-(3-methylhexyl)-7-methyl-nonyl group, n-octadecyl group, isooctadecyl group, 2-hexylundecyl group, 2- Examples thereof include an ethylheptadecyl group, a 1-hexyltridecyl group, an n-icosyl group, a 2-octylundecyl group, an isoicosyl group, a 1-undecyldodecyl group, a 1-octylpentadecyl group, a 2-decyltridecyl group, an n-tetraicosyl group, a 2-decyltetradecyl group, a 2-dodecylpentadecyl group, a 2-heptylicosyl group, a 2-dodecylhexadecyl group, an n-triacontyl group, a 2-tetradecyloctadecyl group, an n-hexatriacontyl group, an n-tetracontyl group, a 2-ethyltetracontyl group, and a residue obtained by removing a hydroxyl group from an oxoalcohol obtained from an olefin [for example, a propylene oligomer (dimer to 14-mer), an ethylene/propylene oligomer (dimer to 20-mer), an isobutene oligomer (dimer to 10-mer), and the like].

Of ^R5 , from the viewpoint of solubility in base oil, preferred is a linear or branched alkyl group having 10 to 34 carbon atoms, more preferred is a linear or branched alkyl group having 12 to 32 carbon atoms, particularly preferred is a linear or branched alkyl group having 16 to 32 carbon atoms, and most preferred are a linear or branched alkyl group having 16 to 22 carbon atoms and a branched alkyl group having 18 to 32 carbon atoms.

The SP value of the structural unit derived from the monomer (b) (a structure in which the carbon-carbon double bond of the monomer (b) has reacted to form a single bond) is preferably 7.0 to 9.5 (cal/cm ³ ) ^1/2 , and more preferably 7.3 to 9.2 (cal/cm ³ ) ^1/2 , from the viewpoint of solubility in the base oil.

In the monomer (c), ^R6 in the general formula (3) is a hydrogen atom or a methyl group, and is preferably a methyl group from the viewpoint of reducing friction at high speeds.

In the monomer (c), —X ⁵ — in the general formula (3) is a group represented by —O—, —O(AO) _m — or —NH—.
A is an alkylene group having 2 to 4 carbon atoms.
Examples of the alkylene group having 2 to 4 carbon atoms include an ethylene group, a 1,2- or 1,3-propylene group, and a 1,2-, 1,3-, or 1,4-butylene group.
m is an integer of 1 to 10, and is preferably an integer of 1 to 4, more preferably an integer of 1 or 2, from the viewpoint of solubility in the base oil.
When m is 2 or more, As may be the same or different, and the (AO) _m portion may be a random bond or a block bond.
From the viewpoint of lubricity, —X ⁵ — is preferably a group represented by —O— or —O(AO) _m —, and more preferably a group represented by —O— or —O(CH ₂ CH ₂ O) _m —.

In monomer (c), q in general formula (3) is a number of 0 or 1, and 0 is preferred from the viewpoint of solubility in base oil.

In the monomer (c), R ⁷ in the general formula (3) is a residue in which one hydrogen atom has been removed from a hydrocarbon polymer having 43 or more carbon atoms and containing an isobutylene group and/or a 1,2-butylene group as a structural unit.
An isobutylene group is a group represented by —CH ₂ C(CH ₃ ) ₂ — or —C(CH ₃ ) ₂ CH ₂ —, and a 1,2-butylene group is a group represented by —CH ₂ CH(CH ₂ CH ₃ )— or —CH(CH ₂ CH ₃ )CH ₂ —.
Examples of hydrocarbon polymers having an isobutylene group and/or a 1,2-butylene group as a constituent unit include polymers using isobutene and 1-butene as constituent monomers (unsaturated hydrocarbon (x)), and polymers in which the double bonds of 1,2-addition products obtained by polymerizing 1,3-butadiene are hydrogenated.
Furthermore, the hydrocarbon polymer may contain, as a constituent monomer, one or more of the following (1) to (3) as the unsaturated hydrocarbon (x), in addition to isobutene, 1-butene, and 1,3-butadiene:
(1) Aliphatic unsaturated hydrocarbons [olefins having 2 to 36 carbon atoms (e.g., ethylene, propylene, 2-butene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, triacosene, hexatriacosene, etc.) and dienes having 4 to 36 carbon atoms (e.g., isoprene, 1,4-pentadiene, 1,5-hexadiene, 1,7-octadiene, etc.)]
(2) Alicyclic unsaturated hydrocarbons [e.g., cyclohexene, (di)cyclopentadiene, pinene, limonene, indene, vinylcyclohexene, ethylidenebicycloheptene, etc.]
(3) Aromatic group-containing unsaturated hydrocarbons (e.g., styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene, crotylbenzene, vinylnaphthalene, divinylbenzene, divinyltoluene, divinylxylene, trivinylbenzene, etc.)
The hydrocarbon polymer formed by these may be a block polymer or a random polymer. Furthermore, when the hydrocarbon polymer has double bonds, the double bonds may be partially or completely hydrogenated by hydrogenation. In one embodiment, the hydrocarbon polymer in ^R7 may be a hydrocarbon polymer using only monomers having 4 carbon atoms as constituent monomers, and the monomer having 4 carbon atoms may be at least one selected from the group consisting of isobutene, 1-butene, and 1,3-butadiene.

The Mn of monomer (c) is preferably 800 to 10,000, more preferably 1,000 to 9,000, and even more preferably 1,200 to 8,500. If the Mn of monomer (c) is 800 or higher, it tends to have good lubricity, and if it is 10,000 or lower, it tends to have good copolymerizability with other monomers.

Monomer (c) can be obtained by esterifying polymer (Y), which is obtained by introducing a hydroxyl group to one end of a hydrocarbon polymer, with (meth)acrylic acid, or by transesterification with an alkyl (meth)acrylate (preferably having 1 to 4 carbon atoms) ester, such as methyl (meth)acrylate. Note that "(meth)acrylic" means "acrylic and/or methacrylic."

Specific examples of the polymer (Y) containing a hydroxyl group at one end include the following (Y1) to (Y4).
Alkylene oxide adduct (Y1): a compound obtained by adding an alkylene oxide (ethylene oxide, propylene oxide, etc.) to a hydrocarbon polymer obtained by polymerizing an unsaturated hydrocarbon (x) in the presence of an ionic polymerization catalyst (sodium catalyst, etc.) (in this case, the monomer (c) is a compound of general formula (3) in which -X ⁵ - is -(AO) _m - and q=0).
Hydroboration product (Y2): a hydroboration reaction product of a hydrocarbon polymer of an unsaturated hydrocarbon (x) having a double bond at one end (for example, those described in U.S. Pat. No. 4,316,973) (in this case, the monomer (c) is a compound of the general formula (3) in which —X ⁵ — is —O— and q=0).
Maleic anhydride-ene-aminoalcohol adduct (Y3): a product obtained by imidizing, with an aminoalcohol, a reaction product obtained by an ene reaction between a hydrocarbon polymer of an unsaturated hydrocarbon (x) having a double bond at one end and maleic anhydride (in this case, the monomer (c) is a compound of the general formula (3) in which —X ⁵ — is —O— and q=1).
Hydroformyl-hydride (Y4): a compound obtained by hydroformylating a hydrocarbon polymer of an unsaturated hydrocarbon (x) having a double bond at one end, followed by a hydrogenation reaction (for example, the compound described in JP-A-63-175096) (in this case, the monomer (c) is a compound of the general formula (3) in which —X ⁵ — is —O— and q=0).
Among these polymers (Y) containing a hydroxyl group at one end, from the viewpoint of lubricity, the alkylene oxide adduct (Y1), the hydroboronate (Y2) and the maleic anhydride-ene-amino alcohol adduct (Y3) are preferred, and the alkylene oxide adduct (Y1) is more preferred.

The proportion of butadiene in all monomers constituting ^R7 in general formula (3) (the weight proportion of 1,3-butadiene in all constituent monomers in a hydrocarbon polymer containing an isobutylene group and/or a 1,2-butylene group as a constituent unit) is, from the viewpoint of lubricity, preferably 50% by weight or more, more preferably 75% by weight or more, even more preferably 85% by weight or more, and particularly preferably 90% by weight or more.

In the hydrocarbon polymer of general formula (3) containing isobutylene groups and/or 1,2-butylene groups as essential structural units, the total amount of isobutylene groups and 1,2-butylene groups is, from the viewpoint of lubricity, preferably 30 mol % or more, more preferably 40 mol % or more, and even more preferably 50 mol % or more, based on the total number of moles of structural units of the hydrocarbon polymer.
As a method for increasing the ratio of the total amount of isobutylene groups and 1,2-butylene groups in a hydrocarbon polymer, for example, the following methods can be employed. In the case of the above alkylene oxide adduct (Y1), for example, in anionic polymerization using 1,3-butadiene, the ratio of the total amount of isobutylene groups and 1,2-butylene groups in the hydrocarbon polymer can be increased by setting the reaction temperature to the boiling point of 1,3-butadiene (-4.4°C) or lower and reducing the amount of polymerization initiator added relative to the 1,3-butadiene. In the case of the above hydroboronated product (Y2), maleic anhydride-ene-aminoalcohol adduct (Y3), and hydroformyl-hydride product (Y4), the ratio can be increased by increasing the degree of polymerization of the hydrocarbon polymer having a double bond at one end.

The total amount of isobutylene groups and 1,2-butylene groups in a hydrocarbon polymer of general formula (3) containing isobutylene groups and/or 1,2-butylene groups as essential structural units can be measured by ^C -NMR. Specifically, for example, when only monomers having four carbon atoms are used, the hydrocarbon polymer can be analyzed by ^C -NMR and calculated using the following mathematical formula (1), to determine the total mole percentage of isobutylene groups and 1,2-butylene groups based on the total mole number of structural units of the hydrocarbon polymer. In ^13C -NMR, a peak derived from the methyl group of the isobutylene group appears _at an integral value of 30 to 32 ppm (integral value A), and a peak derived from the branched methylene group of the 1,2-butylene group ( _-CH2CH ( _CH2CH3 )- or _-CH ( _CH2CH3 ) _CH2- ) appears at an integral value of 26 to 27 ppm (integral value B). The combined mole percentage of isobutylene groups and 1,2-butylene groups based on the total number of moles of structural units of the hydrocarbon polymer can be determined from the integral value of the above peak and the integral value of the peak for all carbon in the hydrocarbon polymer (integral value C).
Total amount of isobutylene groups and 1,2-butylene groups (mol %)=100×{(integral value A)×2+(integral value B)×4}/(integral value C) (1)

When the hydrocarbon polymer in ^R7 contains butadiene or butadiene and 1-butene as constituent monomers, in the structure derived from butadiene or butadiene and 1-butene constituting part or all of ^R7 in general formula (3), the molar ratio of the 1,2-adduct to the 1,4-adduct (1,2-adduct/1,4-adduct) is preferably 5/95 to 95/5, more preferably 20/80 to 80/20, and even more preferably 30/70 to 70/30, from the viewpoints of lubricity and copolymerizability with other monomers.

When the hydrocarbon polymer in ^R7 contains butadiene or butadiene and 1-butene as constituent monomers, the molar ratio of 1,2-adduct/1,4-adduct in the structure derived from butadiene or butadiene and 1-butene constituting part or all of ^R7 in general formula (3) can be measured by ^1H -NMR, ^13C -NMR, Raman spectroscopy, or the like.

The SP value of the structural unit derived from the monomer (c) (a structure in which the carbon-carbon double bond of the (meth)acryloyl group in the monomer (c) has reacted to form a single bond) is preferably 7.0 to 9.0 (cal/cm ³ ) ^1/2 , and more preferably 7.3 to 8.5 (cal/cm ³ ) ^1/2 , from the viewpoint of solubility in the base oil.

The copolymer (A) of the present invention may further contain, as a constituent monomer, a (meth)acrylic acid alkyl ester (d) in which the alkyl group is a linear alkyl group having 1 to 4 carbon atoms.

Examples of the (meth)acrylic acid alkyl ester (d) in which the alkyl group is a linear alkyl group having 1 to 4 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and n-butyl (meth)acrylate.
Among (d), from the viewpoint of lubricity, preferred are (meth)acrylic acid esters having a linear alkyl group having 1 to 3 carbon atoms, more preferred are methyl (meth)acrylate and ethyl (meth)acrylate, and particularly preferred is methyl (meth)acrylate.

In the present invention, from the viewpoint of reducing friction at high speeds (particularly at 100°C and speeds of 100 mm/s and 1000 mm/s), the copolymer (A) preferably contains a hydroxyl group-containing monomer (e) other than the monomer (a) as a constituent monomer.
Specific examples of the hydroxyl group-containing monomer (e) include the following.
Hydroxyl group-containing aromatic monomers (e.g., p-hydroxystyrene), hydroxyalkyl (2 to 6 carbon atoms) (meth)acrylates [2-hydroxyethyl (meth)acrylate, 2- or 3-hydroxypropyl (meth)acrylate, 2-, 3- or 4-hydroxybutyl (meth)acrylate, 2-hydroxyisobutyl (meth)acrylate, etc.], mono- or di-hydroxyalkyl (1 to 4 carbon atoms) substituted (meth)acrylamides [N,N-dihydroxymethyl (meth)acrylamide, N,N-dihydroxypropyl (meth)acrylamide, N,N-di-2-hydroxybutyl (meth)acrylamide, etc.], vinyl alcohol, alkenols having 3 to 12 carbon atoms [( (meth)allyl alcohol, crotyl alcohol, isocrotyl alcohol, 1-octenol, 1-undecenol, etc.], alkene monools or alkene diols having 4 to 12 carbon atoms [1-buten-3-ol, 2-buten-1-ol, 2-butene-1,4-diol, etc.], hydroxyalkyl (having 1 to 6 carbon atoms) alkenyl (having 3 to 10 carbon atoms) ethers (2-hydroxyethylpropenyl ether, etc.), alkenyl (having 3 to 10 carbon atoms) ethers or (meth)acrylates of polyhydric (tri- to octahydric) alcohols (glycerin, pentaerythritol, sorbitol, sorbitan, diglycerin, sugars, sucrose, etc.) [sucrose (meth)allyl ether, etc.], and the like.
Of these, from the viewpoint of reducing friction at high speeds, hydroxyalkyl (2 to 6 carbon atoms) (meth)acrylates are preferred, and 2-hydroxyethyl (meth)acrylate is more preferred.

The copolymer (A) may be a copolymer containing at least one constituent monomer selected from the group consisting of a phosphorus atom-containing monomer (f) and a nitrogen atom-containing monomer (g) (excluding monomer (a), monomer (b), and monomer (c)).

Examples of the phosphorus atom-containing monomer (f) used in combination with monomer (a) include the following monomers (f1) to (f2).

Phosphate ester group-containing monomer (f1):
Examples include (meth)acryloyloxyalkyl (C2 to C4) phosphate esters [(meth)acryloyloxyethyl phosphate and (meth)acryloyloxyisopropyl phosphate] and alkenyl phosphate esters [vinyl phosphate, allyl phosphate, propenyl phosphate, isopropenyl phosphate, butenyl phosphate, pentenyl phosphate, octenyl phosphate, decenyl phosphate, dodecenyl phosphate, and the like].

Phosphono group-containing monomer (f2):
Examples thereof include (meth)acryloyloxyalkyl (C2-4) phosphonic acids [(meth)acryloyloxyethyl phosphonic acid, etc.] and alkenyl (C2-12) phosphonic acids [vinylphosphonic acid, allylphosphonic acid, octenylphosphonic acid, etc.].

Of the phosphorus atom-containing monomers (f), (f1) is preferred, (meth)acryloyloxyalkyl (carbon number 2 to 4) phosphate esters are more preferred, and (meth)acryloyloxyethyl phosphate is particularly preferred.

The nitrogen atom-containing monomer (g) [excluding the monomer (a), the monomer (b) and the monomer (c)] includes the following monomers (g1) to (g4).
Amide group-containing monomer (g1):
(Meth)acrylamide, monoalkylamino(meth)acrylamide [one having one alkyl group having 1 to 4 carbon atoms bonded to a nitrogen atom; for example, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, and N-n- or isobutyl(meth)acrylamide, etc.], monoalkylaminoalkyl(meth)acrylamide [one having an aminoalkyl group (having 2 to 6 carbon atoms) in which one alkyl group having 1 to 4 carbon atoms bonded to a nitrogen atom; for example, N-methylaminoethyl(meth)acrylamide, N-ethylaminoethyl(meth)acrylamide, N-isopropylamino-n-butyl(meth)acrylamide, and N-n- or isobutylamino-n-butyl(meth)acrylamide, etc.], dialkylamino(meth)acrylamide [one having two alkyl groups having 1 to 4 carbon atoms bonded to a nitrogen atom; for example Examples include those having a nitrogen atom only in the amide group, such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, and N,N-di-n-butyl(meth)acrylamide, dialkylaminoalkyl(meth)acrylamides [those having an aminoalkyl group (having 2 to 6 carbon atoms) in which two alkyl groups having 1 to 4 carbon atoms are bonded to a nitrogen atom; for example, N,N-dimethylaminoethyl(meth)acrylamide, N,N-diethylaminoethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, and N,N-di-n-butylaminobutyl(meth)acrylamide, and N-vinylcarboxylic acid amides [N-vinylformamide, N-vinylacetamide, N-vinyl-n- or isopropionylamide, and N-vinylhydroxyacetamide, etc.].

Nitro group-containing monomer (g2):
4-nitrostyrene and the like.

Monomer containing primary to tertiary amino groups (g3):
Primary amino group-containing vinyl monomers {C3-C6 alkenylamines [(meth)allylamine, crotylamine, etc.], aminoalkyl (C2-C6) (meth)acrylates [aminoethyl (meth)acrylate, etc.]}; secondary amino group-containing vinyl monomers {monoalkylaminoalkyl (meth)acrylates [those having an aminoalkyl group (C2-C6) in which one alkyl group having 1-6 carbon atoms is bonded to a nitrogen atom; for example, t-butylaminoethyl (meth)acrylate, methylaminoethyl (meth)acrylate, etc.], dialkenylamines having 6-12 carbon atoms [di(meth)allylamine, etc.]}; tertiary amino group-containing vinyl monomers {dialkylaminoalkyl (meth)acrylates [nitrogen atom and those having an aminoalkyl group (having 2 to 6 carbon atoms) in which two alkyl groups having 1 to 6 carbon atoms are bonded to the aminoalkyl group; for example, dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate, etc.], alicyclic (meth)acrylates having a nitrogen atom [morpholinoethyl (meth)acrylate, etc.], aromatic vinyl monomers [N,N-diphenylaminoethyl (meth)acrylamide, N,N-dimethylaminostyrene, 4-vinylpyridine, 2-vinylpyridine, N-vinylpyrrole, N-vinylpyrrolidone, N-vinylthiopyrrolidone, etc.]}, and their hydrochlorides, sulfates, phosphates, or lower alkyl (having 1 to 8 carbon atoms) monocarboxylic acid (acetic acid, propionic acid, etc.) salts.

Nitrile group-containing monomer (g4):
(Meth)acrylonitrile and the like.

Of the nitrogen-containing vinyl monomers (g), (g1) and (g3) are preferred, and N,N-diphenylaminoethyl (meth)acrylamide, dimethylaminoethyl (meth)acrylamide, diethylaminoethyl (meth)acrylamide, dimethylaminopropyl (meth)acrylamide, dimethylaminoethyl (meth)acrylate, and diethylaminoethyl (meth)acrylate are more preferred.

Copolymer (A) may contain the following monomers (h) to (o) as constituent monomers.

Aliphatic hydrocarbon monomer (h):
Examples include alkenes having 2 to 20 carbon atoms (ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, and octadecene) and alkadienes having 4 to 12 carbon atoms (butadiene, isoprene, 1,4-pentadiene, 1,6-heptadiene, and 1,7-octadiene).

Alicyclic hydrocarbon monomer (i):
Examples include cyclohexene, (di)cyclopentadiene, pinene, limonene, vinylcyclohexene, and ethylidenebicycloheptene.

Aromatic hydrocarbon monomer (j):
Examples include styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, 4-ethylstyrene, 4-isopropylstyrene, 4-butylstyrene, 4-phenylstyrene, 4-cyclohexylstyrene, 4-benzylstyrene, indene, 4-crotylbenzene, and 2-vinylnaphthalene.

Vinyl esters, vinyl ethers, vinyl ketones (k):
Examples include vinyl esters of saturated fatty acids having 2 to 12 carbon atoms (vinyl acetate, vinyl propionate, vinyl butyrate, vinyl octanoate, etc.), alkyl, aryl, or alkoxyalkyl vinyl ethers having 1 to 12 carbon atoms (methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, 2-ethylhexyl vinyl ether, phenyl vinyl ether, vinyl-2-methoxyethyl ether, vinyl-2-butoxyethyl ether, etc.), and alkyl or aryl vinyl ketones having 1 to 8 carbon atoms (methyl vinyl ketone, ethyl vinyl ketone, phenyl vinyl ketone, etc.).

Epoxy group-containing monomer (l):
Examples include glycidyl (meth)acrylate and glycidyl (meth)allyl ether.

Halogen-containing monomer (m):
Examples include vinyl chloride, vinyl bromide, vinylidene chloride, (meth)allyl chloride, and halogenated styrenes (such as dichlorostyrene).

Esters of unsaturated polycarboxylic acids (n):
Examples include alkyl, cycloalkyl, or aralkyl esters of unsaturated polycarboxylic acids [C1 to C8 alkyl diesters of unsaturated dicarboxylic acids (maleic acid, fumaric acid, itaconic acid, etc.) (dimethyl maleate, dimethyl fumarate, diethyl maleate, and dioctyl maleate)].

Alkoxyalkyl ether monomer (o);
Methoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, methoxybutyl (meth)acrylate, methoxyheptyl (meth)acrylate, methoxyhexyl (meth)acrylate, methoxypentyl (meth)acrylate, methoxyoctyl (meth)acrylate, ethoxyethyl (meth)acrylate, ethoxypropyl (meth)acrylate, ethoxybutyl (meth)acrylate, ethoxyheptyl (meth)acrylate, ethoxyhexyl (meth)acrylate, ethoxypentyl (meth)acrylate, ethoxyoctyl (meth)acrylate, propoxymethyl (meth)acrylate, propoxyethyl (meth)acrylate, propoxypropyl (meth)acrylate, propoxybutyl (meth)acrylate, propoxyheptyl (meth)acrylate, propoxyhexyl (meth)acrylate, propoxypentyl (meth)acrylate, propoxyoctyl (meth)acrylate, butoxymethyl (meth)acrylate, butoxyethyl (meth)acrylate, butoxypropyl (meth)acrylate, butoxybutyl (meth)acrylate, butoxyheptyl (meth)acrylate, butoxyhexyl (meth)acrylate, butoxypentyl (meth)acrylate, butoxyoctyl (meth)acrylate, and the like.
Of the monomers (o), preferred are methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and butoxyethyl (meth)acrylate.

The proportion of the monomer (a) constituting the copolymer (A) is preferably 2 to 50% by weight, more preferably 5 to 45% by weight, and particularly preferably 5 to 40% by weight, based on the total weight of the constituent monomers of (A), from the viewpoints of lubricity and viscosity index.
From the viewpoint of lubricity and viscosity index, the total proportion of the monomers (b) and (c) constituting (A) is preferably 20 to 97% by weight, more preferably 40 to 94% by weight, and particularly preferably 50 to 90% by weight, based on the total weight of the constituent monomers of (A).
From the viewpoint of reducing friction at high speeds, the proportion of the monomer (a) constituting the copolymer (A) is preferably 2 to 90% by weight, more preferably 5 to 80% by weight, even more preferably 10 to 70% by weight, particularly preferably 15 to 60% by weight, and most preferably 15 to 55% by weight, based on the total weight of the constituent monomers of (A).
The total proportion of the monomers (b) and (c) constituting (A) is preferably 10 to 98% by weight, more preferably 20 to 95% by weight, even more preferably 30 to 90% by weight, and particularly preferably 40 to 85% by weight, based on the total weight of the constituent monomers of (A), from the viewpoints of reducing friction at high speeds and solubility in the base oil.
From the viewpoint of reducing friction at high speeds, the proportion of the monomer (d) constituting (A) is preferably 50% by weight or less, more preferably 45% by weight or less, even more preferably 40% by weight or less, and particularly preferably 10% by weight or less, based on the total weight of the constituent monomers of (A).
From the viewpoint of reducing friction at high speeds, the proportion of the monomer (e) constituting (A) is preferably 1.0 to 20.0% by weight, more preferably 1.0 to 15.0% by weight, and particularly preferably 5.0 to 10.0% by weight, based on the total weight of the constituent monomers of (A).
From the viewpoint of reducing friction at high speeds, the total content of (f) to (g) constituting (A) is preferably 20% by weight or less, more preferably 1 to 15% by weight, and particularly preferably 2 to 10% by weight, based on the total weight of the constituent monomers of (A).
From the viewpoint of reducing friction at high speeds, the total content of (h) to (o) constituting (A) is preferably 10% by weight or less, more preferably 1 to 7% by weight, and particularly preferably 2 to 5% by weight, based on the total weight of the constituent monomers of (A).

From the viewpoint of reducing friction at high speeds and improving lubricity, the SP value of (A) is preferably 8.5 to 11.5 (cal/cm ³ ) ^1/2 , more preferably 8.7 to 11.0 (cal/cm ³ ) ^1/2 , even more preferably 8.9 to 10.5 (cal/cm ³ ) ^1/2 , and particularly preferably 9.2 to 10.2 (cal/cm ³ ) ^1/2 .
The SP value of (A) refers to the arithmetic average of the SP values of the constituent units derived from each monomer constituting (A) (structures in which the vinyl groups contained in each monomer constituting (A) have become single bonds through polymerization) calculated using the SP value calculation method described above, based on the weight fraction of each constituent monomer at the time of charging. For example, when the monomer is methyl methacrylate, the constituent units derived from methyl methacrylate have two _CH3 , one _CH2 , one C, and one _CO2 atomic groups, so the SP value of the constituent units derived from methyl methacrylate can be found to be 9.933 (cal/ ^cm3 ) ^1/2 from the following formula. Similarly, the SP value of the constituent units derived from ethyl methacrylate can be found to be 9.721 (cal/ ^cm3 ) ^1/2 .
ΣΔe _i =1125×2+1180+350+4300=8080
Σv _i =33.5×2+16.1-19.2+18.0=81.9
δ=(8080/81.9) ^1/2 =9.933(cal/cm ³ ) ^1/2
When the polymer is a polymer of 50% by weight of methyl methacrylate and 50% by weight of ethyl methacrylate, the SP value of the polymer is calculated by taking an arithmetic average based on the weight fraction of the SP values of the constituent units derived from each monomer, as follows:
SP value of polymer = (9.933 x 50 + 9.721 x 50) / 100 = 9.827
The SP value of polymer (A) can be adjusted to a desired range by appropriately adjusting the weight fraction of the monomers used. Specifically, the SP value can be reduced by using a large amount of monomers having a long alkyl group carbon number, and the SP value can be increased by using a large amount of monomers having a short alkyl group carbon number.

Furthermore, when two or more types of copolymer (A) are used, it is preferable that the weight fraction be calculated based on the SP value of each polymer (A), and the arithmetic average value satisfies the above SP value.

From the viewpoints of reducing friction at high speeds, improving the viscosity index, and achieving a high low-temperature viscosity of the lubricating oil composition, the Mw of (A) is preferably 5,000 to 2,000,000, more preferably 7,000 to 1,000,000, even more preferably 10,000 to 600,000, particularly preferably 15,000 to 500,000, and most preferably 20,000 to 250,000.

(A) can be obtained by a known production method, specifically a method in which the above-mentioned monomers are solution polymerized in a solvent in the presence of a polymerization catalyst.
Examples of the solvent include toluene, xylene, alkylbenzene having 9 to 10 carbon atoms, methyl ethyl ketone, ethyl acetate, 2-propanol, and ester oil.
Examples of the polymerization catalyst include azo catalysts (azobisisobutyronitrile, azobisvaleronitrile, etc.), peroxide catalysts (benzoyl peroxide, cumyl peroxide, lauryl peroxide, etc.), and redox catalysts (mixtures of benzoyl peroxide and tertiary amines, etc.). If necessary, known chain transfer agents (such as alkyl mercaptans having 2 to 20 carbon atoms) can also be used.
The polymerization temperature is preferably 25 to 140° C., more preferably 50 to 120° C. In addition to the above solution polymerization, (A) can also be obtained by bulk polymerization, emulsion polymerization or suspension polymerization.
When (A) is a copolymer, the polymerization form may be either a random addition polymer or an alternating copolymer, and may also be either a graft copolymer or a block copolymer.

<Ester oil (B)>
The ester oil (B) is not particularly limited as long as it is an ester compound having a lubricating function and has been conventionally used as a lubricating oil. Examples thereof include a diesterification product of a dicarboxylic acid (x1) and a monohydric alcohol (y1), a diesterification product of a monocarboxylic acid (x2) and a dihydric alcohol (y2), an esterification product of a monocarboxylic acid (x2) and a monohydric alcohol (y1), an esterification product of a monocarboxylic acid (x1) and a trihydric or higher polyhydric alcohol (y3), and an esterification product of a trihydric or higher polyhydric carboxylic acid (x3) and a monohydric alcohol (y1).
From the viewpoint of cooling properties, the ester oil (B) is preferably at least one selected from the group consisting of a diesterification product of a dicarboxylic acid (x1) and a monohydric alcohol (y1), a diesterification product of a monocarboxylic acid (x2) and a dihydric alcohol (y2), and an esterification product of a monocarboxylic acid (x2) and a monohydric alcohol (y1).

The dicarboxylic acid (x1) may be an aliphatic dicarboxylic acid having 2 to 24 carbon atoms [linear saturated aliphatic dicarboxylic acid {for example, ethanedioic acid (oxalic acid), propanedioic acid (malonic acid), n-butanedioic acid (succinic acid), n-heptanedioic acid (glutaric acid), n-hexanedioic acid (adipic acid), n-heptanedioic acid, n-octanedioic acid, n-nonanedioic acid (azelaic acid), n-decanedioic acid (sebacic acid), n-undecanedioic acid, n-dodecanedioic acid, n-tridecanedioic acid, n-tetradecanedioic acid, n n-pentadecanedioic acid and n-hexadecanedioic acid}, branched saturated aliphatic dicarboxylic acids {for example, 3-methyladipic acid}, unsaturated aliphatic dicarboxylic acids {for example, maleic acid, fumaric acid}, alicyclic saturated dicarboxylic acids {for example, 1,2- or 1,3-cyclopentanedicarboxylic acid, 1,2-, 1,3-, or 1,4-cyclohexanedicarboxylic acid}, and aromatic ring-containing dicarboxylic acids having 8 to 24 carbon atoms {for example, phthalic acid, isophthalic acid, terephthalic acid}.
Among these, from the viewpoint of thermal conductivity, aliphatic dicarboxylic acids having 2 to 24 carbon atoms are preferred, linear saturated aliphatic dicarboxylic acids having 2 to 24 carbon atoms are more preferred, and linear saturated aliphatic dicarboxylic acids having 6 to 10 carbon atoms are particularly preferred.

Examples of the monocarboxylic acid (x2) include aliphatic monocarboxylic acids having 2 to 25 carbon atoms [linear saturated aliphatic monocarboxylic acids {for example, acetic acid, propionic acid, n-butanoic acid, n-pentanoic acid, n-hexanoic acid, n-heptanoic acid, n-octanoic acid, n-nonanoic acid, n-decanoic acid, n-undecanoic acid, n-dodecanoic acid, n-tridecanoic acid, n-tetradecanoic acid, n-pentadecanoic acid, n-hexadecanoic acid, n-heptadecanoic acid, n-octadecanoic acid, n-nonadecanoic acid, eicosanoic acid, docosanoic acid, and tetradecanoic acid, trachosanoic acid, etc.}, branched saturated aliphatic monocarboxylic acids having 4 to 25 carbon atoms {for example, isobutyric acid, 2-ethylhexanoic acid, isononanoic acid, isodecanoic acid, isoundecanoic acid, isododecanoic acid, isotridecanoic acid, isotetradecanoic acid, isopentadecanoic acid, isohexadecanoic acid, isoheptadecanoic acid, isooctadecanoic acid, isononadecanoic acid, etc.}, alicyclic monocarboxylic acids {for example, cyclohexanecarboxylic acid, etc.}, and aromatic ring-containing monocarboxylic acids {for example, benzoic acid, etc.}.
Among these, from the viewpoint of thermal conductivity and lubricity, aliphatic monocarboxylic acids having 2 to 25 carbon atoms are preferred, more preferably compounds having a linear or branched alkyl group with 1 to 24 carbon atoms in the alkyl group (linear or branched saturated aliphatic monocarboxylic acids), and particularly preferably linear saturated aliphatic monocarboxylic acids with an alkyl group with 5 to 14 carbon atoms.

Examples of the monohydric alcohol (y1) include aliphatic monoalcohols having 1 to 24 carbon atoms [straight-chain saturated aliphatic monoalcohols {e.g., n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, n-undecyl alcohol, n-dodecyl alcohol, n-tridecyl alcohol, n-tetradecyl alcohol, n-pentadecyl alcohol, n-hexadecyl alcohol, n-heptadecyl alcohol, n-octadecyl alcohol, n-nonadecyl alcohol, n-icosanol, n-heneicosanol, n-docosanol, and n-tetracosanol, etc.}, branched saturated aliphatic monoalcohols {e.g., 2-ethylhexyl alcohol, cyclohexanol, isononyl alcohol, isodecyl alcohol, isoundecyl alcohol, isododecyl alcohol, isotridecyl alcohol, isotetradecyl alcohol, isopentadecyl alcohol, isohexadecyl alcohol, isoheptadecyl alcohol, isooctadecyl alcohol, isononadecyl alcohol, etc.}, alicyclic monoalcohols {for example, cyclohexanol, 2-, 3-, or 4-t-butylcyclohexanol, menthol, cyclohexaneethanol, 2-, 3-, or 4-isopropylcyclohexanol, etc.}, and aromatic ring-containing monoalcohols having 7 to 24 carbon atoms {for example, benzyl alcohol, etc.}.
Of these, from the viewpoint of thermal conductivity, aliphatic monoalcohols having 1 to 24 carbon atoms are preferred, more preferably compounds having a linear or branched alkyl group with 1 to 24 carbon atoms in the alkyl group (linear or branched saturated aliphatic monoalcohols), and particularly preferably compounds having a linear or branched alkyl group with 4 to 16 carbon atoms in the alkyl group (linear or branched saturated aliphatic monoalcohols).

Examples of the dihydric alcohol (y2) include aliphatic dihydric alcohols having 2 to 24 carbon atoms [linear saturated aliphatic diols {e.g., ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,15-pentadecanediol, and 1,16-hexadecanediol, etc.}, branched saturated aliphatic diols {e.g., 2-methyl-1,3-propanediol, 2-methyl-1, 4-butanediol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 3-methyl-1,5-pentanediol, 1,2-heptanediol, 1,2-octanediol, 1,2-nonanediol, 1,2-decanediol, 1,2-undecanediol, 1,2-dodecanediol, 1,2-tridecanediol, 1,2-tetradecanediol, 1,2-pentadecanediol, 1,2-hexadecanediol, and the like}, alicyclic diols {for example, 1,2-, 1,3-, or 1,4-cyclohexanediol, and the like}, aromatic ring-containing dihydric alcohols having 8 to 24 carbon atoms {for example, ethylene oxide adducts of dihydroxybenzene, and the like}, and the like.
Among these, from the viewpoint of heat transfer coefficient, aliphatic dihydric alcohols having 2 to 24 carbon atoms are preferred, linear saturated aliphatic diols having 2 to 24 carbon atoms are more preferred, and linear or branched saturated aliphatic diols having 4 to 12 carbon atoms are particularly preferred.

From the viewpoints of cooling property, lubricity and solubility of (A), the SP value of the ester oil (B) is preferably 8.1 to 10.1 (cal/cm ³ ) ^1/2 , more preferably 8.2 to 9.5 (cal/cm ³ ) ^1/2 , and particularly preferably 8.4 to 9.2 (cal/cm ³ ) ^1/2 .
When two or more types of ester oils (B) are used, it is preferable that the SP value and weight fraction of each ester oil are calculated and the arithmetic mean value satisfies the above SP value.

The kinematic viscosity (measured in accordance with JIS-K2283) (unit: mm ² /s, hereinafter abbreviated) of the ester oil (B) at 40° C. is preferably 3 to 30, more preferably 3 to 15, from the viewpoints of cooling property and lubrication property.
The kinematic viscosity of the ester oil (B) at 40°C can be adjusted by the carbon number and branching degree of the carboxylic acid and alcohol used when synthesizing the ester oil (B). For example, the kinematic viscosity tends to be high when a carboxylic acid with a large carbon number is used, and low when a carboxylic acid with a small carbon number is used. Furthermore, the kinematic viscosity tends to be high when a carboxylic acid with a small branching degree is used, and low when a carboxylic acid with a large branching degree is used.
As the ester oil (B), from the viewpoint of lubrication and cooling properties, an ester compound having 10 to 40 carbon atoms is preferred, and an ester compound having 15 to 26 carbon atoms is more preferred.
From the viewpoint of lubrication and cooling properties, the ester oil (B) is preferably a diester of a linear saturated aliphatic dicarboxylic acid having 6 to 10 carbon atoms with a branched saturated aliphatic monoalcohol having 4 to 16 carbon atoms, a diester of a linear saturated aliphatic monocarboxylic acid having 5 to 14 carbon atoms with a branched saturated aliphatic diol having 4 to 12 carbon atoms, or an ester of a linear saturated aliphatic monocarboxylic acid in which the alkyl group has 5 to 14 carbon atoms with a branched saturated aliphatic monoalcohol having 4 to 16 carbon atoms.
From the viewpoint of lubrication and cooling properties, the ester oil (B) preferably has 2 to 6 methyl groups, more preferably 3 to 4 methyl groups.
Examples of compounds having three methyl groups include diesters of 3-methyl-1,5-pentanediol and linear saturated aliphatic monocarboxylic acids.
An example of a compound having four methyl groups is a diester of 2-ethylhexyl alcohol and a linear saturated aliphatic dicarboxylic acid.

Specific examples of the ester oil (B) include diesters of dicarboxylic acids (x1) and monohydric alcohols (y1) {for example, bis(2-ethylhexyl) sebacate (kinematic viscosity at 100°C: 3.19, kinematic viscosity at 40°C: 11.3), bis(2-ethylhexyl) dodecanedioate (kinematic viscosity at 100°C: 3.7, kinematic viscosity at 40°C: 13.7), ditridecyl dodecanedioate (kinematic viscosity at 100°C: 5.1, kinematic viscosity at 40°C: 24.0), bis(n-octyl) adipate (kinematic viscosity at 100°C: 2.6, kinematic viscosity at 40°C: 2.6, ℃ kinematic viscosity: 8.2), bis(2-ethylhexyl) adipate (100℃ kinematic viscosity: 2.4, 40℃ kinematic viscosity: 7.8), bis(2-ethylhexyl) azelaate (100℃ kinematic viscosity: 3.0, 40℃ kinematic viscosity: 10.4), 2-ethylhexyl-n-octyl azelaate (100℃ kinematic viscosity: 3.1, 40℃ kinematic viscosity: 10.8), 2-ethylhexyl-n-octyl sebacate (100℃ kinematic viscosity: 3.6, 40℃ kinematic viscosity: 11.7), etc.}, monocarboxylic acids (x2) and dicarboxylic acids Diesters with coal (y2) {for example, 3-methyl-1,5-pentanediyl bis(pentanoate) (kinematic viscosity at 100°C: 1.5, kinematic viscosity at 40°C: 3.7), 3-methyl-1,5-pentanediyl bis(octanoate) (kinematic viscosity at 100°C: 2.41, kinematic viscosity at 40°C: 7.4), 3-methyl-1,5-pentanediyl bis(nonanoate) (kinematic viscosity at 100°C: 2.7, kinematic viscosity at 40°C: 8.9), 3-methyl-1,5-pentanediyl bis(decanoate) (kinematic viscosity at 100°C: 3 2, 40°C kinematic viscosity: 10.7), diester of neopentyl glycol and isooctanoic acid (100°C kinematic viscosity: 2.9, 40°C kinematic viscosity: 11.4), diester of neopentyl glycol and 2-ethylhexanoic acid (100°C kinematic viscosity: 2.0, 40°C kinematic viscosity: 7.5), etc.), monoester of monohydric alcohol (y1) and monocarboxylic acid (x2) {for example, isooctanol oleate (100°C kinematic viscosity: 2.7, 40°C kinematic viscosity: 8.3), etc.}.

The kinematic viscosity of the ester oil (B) at 100°C (measured according to JIS-K2283) is preferably 1 to 15 mm ² /s, more preferably 2 to 5 mm ² /s, from the viewpoint of cooling property and lubrication property, and particularly preferably 2.4 to 3.2 mm ² /s from the viewpoint of viscosity index.
The viscosity index (measured in accordance with JIS-K2283) of the ester oil (B) is preferably 90 or more, more preferably 100 or more, from the viewpoint of lubricity.

The cloud point of the ester oil (B) (measured according to JIS-K2269) is preferably -5°C or lower, and more preferably -15°C or lower. When the cloud point of the base oil is within this range, the lubricating oil composition has good low-temperature viscosity.

<Lubricating oil composition>
The lubricating oil composition of the present invention contains the copolymer (A) and the ester oil (B).
The weight ratio (A/B) of the copolymer (A) to the ester oil (B) in the lubricating oil composition is preferably 0.001 to 0.43, more preferably 0.001 to 0.11, from the viewpoints of reducing friction at high speeds, cooling properties, and lubrication properties.
The content of copolymer (A) in the lubricating oil composition is preferably 0.1 to 30% by weight, more preferably 0.1 to 10% by weight, based on the weight of the lubricating oil composition, from the viewpoints of reducing friction at high speeds, cooling properties, and lubrication properties.
The content of the ester oil (B) in the lubricating oil composition is preferably 40% by weight or more, more preferably 60% by weight or more, even more preferably 70 to 99.9% by weight, and particularly preferably 90.0 to 99.9% by weight, based on the weight of the lubricating oil composition, from the viewpoint of cooling properties.

The lubricating oil composition of the present invention may contain a base oil other than the ester oil (B).
Examples of base oils include mineral oils (solvent refined oils, paraffin oils, high viscosity index oils containing isoparaffins, high viscosity index oils obtained by hydrocracking isoparaffins, and naphthenic oils), synthetic lubricating oils (hydrocarbon-based synthetic lubricating oils (poly-α-olefin-based synthetic lubricating oils, etc.)), and the like.
As the base oil other than the ester oil (B), a mineral oil is preferred from the viewpoint of insulating properties and solubility of (A).
From the viewpoint of cooling properties, the base oil other than the ester oil (B) preferably has a kinematic viscosity at 40° C. of 6 to 20 mm ² /s, more preferably 6 to 15 mm ² /s.
From the viewpoint of lubricity, the base oil other than the ester oil (B) preferably has a kinematic viscosity at 100° C. of 1 to 6 mm ² /s, more preferably 2 to 5 mm ² /s.
The content of base oils other than the ester oil (B) in the lubricating oil composition is preferably 80% by weight or less, more preferably 50% by weight or less, and even more preferably 30% by weight or less, based on the weight of the lubricating oil composition, from the viewpoints of cooling property, insulating property, and thermal conductivity.

From the viewpoints of friction reduction and solubility, the absolute value of the difference between the SP value of the copolymer (A) and the SP value of the ester oil (B) is preferably 3.4 (cal/cm ³ ) ^1/2 or less, more preferably 2.3 (cal/cm ³ ) ^1/2 or less, and particularly preferably 1.8 (cal/cm ³ ) ^1/2 or less.
When two or more types of copolymer (A) and ester oil (B) are used in combination, it is preferable that the difference between the calculated arithmetic mean of the SP value and weight fraction of (A) and the calculated arithmetic mean of the SP value and weight fraction of (B) falls within the above range.

From the viewpoints of reducing friction at high speeds and solubility in the base oil, the absolute value of the difference between the SP value of the structural unit derived from monomer (a) in the monomers constituting copolymer (A) and the SP value of ester oil (B) is preferably 4.4 (cal/cm ³ ) ^1/2 or less, more preferably 4.1 (cal/cm ³ ) ^1/2 or less, and particularly preferably 3.6 (cal/cm ³ ) ^1/2 or less, and the lower limit is preferably 0.3 (cal/cm ³ ) ^1/2 or more, more preferably 0.9 (cal/cm ³ ) ^1/2 or more. Preferred ranges include, for example, 0.3 to 4.4 (cal/cm ³ ) ^1/2 and 0.9 to 4.4 (cal/cm ³ ) ^1/2 .
In addition, when the copolymer (A) has structural units derived from multiple types of monomers (a) or when two or more types of ester oils (B) are used in combination, it is preferable that the difference from the arithmetic mean value based on the respective weight fractions satisfies the above range.

The ratio (N1/N2) of the number of carbon atoms (N1) of the alkyl group of the monohydric alcohol (y1) constituting the ester oil (B) or the alkyl group of the monovalent carboxylic acid (x2) to the number of carbon atoms (N2) of ^R5 in the monomer (b) or ^R7 in the monomer (c) constituting the copolymer (A) is preferably 0.01 to 4.80, more preferably 0.01 to 1.33, from the viewpoint of solubility in the base oil.

The thermal conductivity of the lubricating oil composition at 25°C (measured with a thermal property meter under conditions described below) is preferably 0.14 to 0.16 W/(m·K), and more preferably 0.15 to 0.16 W/(m·K), from the viewpoint of cooling properties.
The heat transfer coefficient of the lubricating oil composition at 80° C. (calculated under conditions described below) is preferably 2.35 to 2.80 W/(m ² /K), more preferably 2.45 to 2.70 W/(m ² /K), from the viewpoint of cooling ability.
From the viewpoint of cooling performance, the heat transfer coefficient of the lubricating oil composition at 40° C. (calculated under conditions described below) is preferably 2.10 W/(m ² /K) or more, and more preferably 2.10 to 2.45 W/(m ² /K).
From the viewpoint of insulating properties, the volume resistivity of the lubricating oil composition is preferably 10 ¹⁰ Ω·cm or more, and more preferably 10 ¹¹ Ω·cm or more.

The MTM friction coefficient of the lubricating oil composition (measured under the conditions described below, the same applies hereinafter) (100°C, speed: 10 mm/s) is preferably 0.070 to 0.095, more preferably 0.070 to 0.090, from the viewpoint of lubricity.
From the viewpoint of lubricity, the MTM friction coefficient (100° C., speed: 100 mm/s) of the lubricating oil composition is preferably 0.055 or less, and more preferably 0.030 to 0.055.
From the viewpoint of lubricity, the MTM friction coefficient (100° C., speed: 1000 mm/s) of the lubricating oil composition is preferably 0.025 or less, more preferably 0.005 to 0.023, and particularly preferably 0.008 to 0.020.
The ratio (10/100) of the MTM friction coefficient (100°C, speed: 10 mm/s) to the MTM friction coefficient (100°C, 100 mm/s) of the lubricating oil composition is preferably 1.60 to 2.50, more preferably 1.80 to 2.32, from the viewpoint of lubricity.
The ratio (10/1000) of the MTM friction coefficient (100°C, speed: 10 mm/s) to the MTM friction coefficient (100°C, 1000 mm/s) of the lubricating oil composition is preferably 3.0 to 12, more preferably 5.5 to 7.5, from the viewpoint of lubricity.

The kinematic viscosity of the lubricating oil composition at 40° C. (measured according to JIS-K2283) is preferably 4.0 to 30.0 mm ² /s, more preferably 7.0 to 20.0 mm ² /s, from the viewpoint of lubrication and cooling properties.
The kinematic viscosity of the lubricating oil composition at 80° C. (measured according to JIS-K2283) is preferably 1.5 to 19.0 mm ² /s, more preferably 3.0 to 8.0 mm ² /s, from the viewpoints of lubrication and cooling properties.
The kinematic viscosity of the lubricating oil composition at 100° C. (measured according to JIS-K2283) is preferably 1.0 to 15.0 ^{mm 2} /s, more preferably 2.0 to 5.0 mm ² /s, from the viewpoints of lubrication and cooling properties.
The viscosity index of the lubricating oil composition (measured in accordance with JIS-K2283) is preferably 160 or greater, more preferably 170 or greater, from the viewpoint of lubricity.

The lubricating oil composition of the present invention may further contain at least one additive selected from the group consisting of viscosity index improvers, detergents, dispersants, antioxidants, oiliness improvers, friction and wear modifiers, extreme pressure agents, antifoaming agents, demulsifiers, corrosion inhibitors, and pour point depressants.

(1) Viscosity index improver:
(C1 to C7) alkyl (meth)acrylate/(C8 to C40) linear or branched alkyl (meth)acrylate copolymer, dispersing monomer (amine monomer, etc.)/(C1 to C7) alkyl (meth)acrylate/(C8 to C40) linear or branched alkyl (meth)acrylate copolymer, hydroxy group-containing monomer/(C1 to C7) alkyl (meth)acrylate/(C8 to C40) linear or branched alkyl (meth)acrylate copolymer, comb polymer [(C1 to C7) alkyl (meth)acrylate/(C8 to C40) linear or branched alkyl (meth)acrylate/polyolefin macromonomer], ethylene/(C1 to C18) alkyl (meth)acrylate copolymer, polyisobutylene, polyalkylstyrene, ethylene/propylene copolymer, styrene/maleic acid ester copolymer, styrene/hydrogenated isoprene copolymer, etc.;

(2) Detergent:
Basic, overbased or neutral metal salts [such as overbased or alkaline earth metal salts of sulfonates (petroleum sulfonates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, etc.)], salicylates, phenates, naphthenates, carbonates, phosphonates, and mixtures thereof;
(3) Dispersant:
Succinimides (bis- or mono-polybutenyl succinimides), Mannich condensation products, borates, and the like;
(4) Antioxidant:
hindered phenols and aromatic secondary amines, etc.;
(5) Oiliness improver:
Long-chain fatty acids and their esters (oleic acid and oleic acid esters, etc.), long-chain amines and their amides (oleylamine and oleylamide, etc.), etc.;
(6) Friction and wear modifier:
Molybdenum and zinc compounds (molybdenum dithiophosphate, molybdenum dithiocarbamate, zinc dialkyldithiophosphate, etc.);
(7) Extreme pressure agents:
Sulfur-based compounds (monosulfides or disulfides, sulfoxides, and sulfur phosphide compounds), phosphide compounds, and chlorine-based compounds (chlorinated paraffins, etc.);
(8) Antifoaming agent:
Silicon oil, metal soap, fatty acid ester, phosphate compound, etc.;
(9) Demulsifier:
Quaternary ammonium salts (such as tetraalkylammonium salts), sulfated oils and phosphates (such as phosphates of polyoxyethylene-containing nonionic surfactants), etc.;
(10) Corrosion inhibitor:
Nitrogen atom-containing compounds (benzotriazole, 1,3,4-thiodiazolyl-2,5-bisdialkyldithiocarbamate, etc.);
(11) Pour point enhancers:
Polyalkyl methacrylate, polyalkyl acrylate, polyalkyl styrene, polyvinyl acetate, etc.

The lubricating oil composition of the present invention is suitable for use in gear oils (differential oils, industrial gear oils, etc.), MTFs, transmission oils [ATFs, belt-CVTFs, etc.], traction oils (toroidal-CVTFs, etc.), shock absorber oils, power steering oils, hydraulic oils (construction machinery hydraulic oils, industrial hydraulic oils, etc.), engine oils, etc. From the perspective of easily demonstrating its effectiveness, it is preferably used as transmission oils, electric motor oils, and dual-purpose oils for both transmissions and electric motors in electric vehicles or hybrid vehicles, and particularly preferably as dual-purpose oils for both transmissions and electric motors in electric vehicles or hybrid vehicles.

The present invention will be explained in detail below using examples, but the present invention is not limited to these examples.

<Production Example 1> [Production of Monomer (a-1)]
A reaction vessel equipped with a temperature controller, a vacuum stirring blade, a pressure reducing device, a Dimroth condenser, a fractionating column, a distillate receiving flask, and a nitrogen inlet and outlet was charged with 260.3 parts by weight (2.0 parts by mole) of 2-hydroxyethyl methacrylate (HEMA), 1141.4 parts by weight (10.0 parts by mole) of ε-caprolactone, 3.7 parts by weight (0.03 parts by mole) of hydroquinone monomethyl ether, and 0.27 parts by weight of butyl tris(2-ethylhexanoyloxy)tin, and the mixture was heated to 115°C with stirring while passing air through. The mixture was then reacted at 115°C for 8 hours, and the distillate water was separated. The mixture was further cooled to 25°C, and the esterification reaction product was confirmed by ^1H -NMR (yield: 98 mol%).
(a-1) is a monomer represented by general formula (1) in which ^A1 is a methacryloyl group, ^R1 is an ethylene group, p=5, ^R2 is a pentylene group, and ^R3 is a hydrogen atom, and the SP value of the structural unit derived from (a-1) is 10.75.

<Production Example 2> [Production of Monomer (a-2)]
A reaction vessel equipped with a temperature controller, a vacuum stirring blade, a pressure reducing device, a Dimroth condenser, a fractionating column, a distillate receiving flask, and a nitrogen inlet and outlet was charged with 520.8 parts by weight of lauric acid, 711.0 parts by weight of (a-1), 3.7 parts by weight (0.03 parts by mole) of hydroquinone monomethyl ether, 300 parts by weight of toluene, and 20.7 parts by weight of paratoluenesulfonic acid, and the temperature was raised to 115°C with stirring. Next, an esterification reaction was carried out at 115°C for 8 hours, and the distillate water was separated. The mixture was further cooled to 25°C, and the esterification reaction product was confirmed by ^1H -NMR (yield: 98 mol%). 200 parts by weight of a 10 wt% aqueous sodium hydroxide solution was charged and stirred to sufficiently neutralize the paratoluenesulfonic acid. The supernatant was collected in a separatory funnel, heated to 120° C., and then the toluene was removed at the same temperature under reduced pressure (0.027 to 0.040 MPa) over 2 hours to obtain (a-2).
(a-2) is a monomer represented by the general formula (1) in which ^A1 is a methacryloyl group, ^R1 is an ethylene group, p=5, ^R2 is a pentylene group, and ^R3 is a lauroyl group having 12 carbon atoms, and the SP value of the structural unit derived from (a-2) is 9.68.

<Production Example 3> [Production of Monomer (a-3)]
A reaction vessel equipped with a temperature controller, a vacuum stirring blade, a pressure reducing device, a Dimroth condenser, a fractionating column, a distillate receiving flask, and a nitrogen inlet and outlet was charged with 232.2 parts by weight (2.0 parts by mole) of 2-hydroxyethyl acrylate (HEA), 2,282.8 parts by weight (20.0 parts by mole) of ε-caprolactone, 3.7 parts by weight (0.03 parts by mole) of hydroquinone monomethyl ether, and 0.27 parts by weight of butyl tris(2-ethylhexanoyloxy)tin, and the mixture was heated to 115°C with stirring while air was passed through. The mixture was then reacted at 115°C for 8 hours, and the distillate water was separated. The mixture was then cooled to 25°C, and the esterification reaction product was confirmed by ^1H -NMR (yield: 98 mol%).
(a-3) is a monomer represented by general formula (1) in which ^A1 is an acryloyl group, ^R1 is an ethylene group, p=10, ^R2 is a pentylene group, and ^R3 is a hydrogen atom, and the SP value of the structural unit derived from (a-3) is 10.68.

<Production Examples 4 to 24, Comparative Production Examples 1 to 4>
A reaction vessel equipped with a stirrer, a heating/cooling device, a thermometer, and a nitrogen inlet tube was charged with 185 parts by weight of ethyl acetate, 100 parts by weight of a blend of various monomers shown in Tables 2 to 4, and dodecyl mercaptan and 2,2′-azobis(2-methylbutyronitrile) as chain transfer agents in the amounts shown in Tables 2 to 4. After nitrogen substitution (gas phase oxygen concentration: 100 ppm), the vessel was sealed and heated to 76° C. with stirring, and polymerization reaction was carried out at the same temperature for 6 hours.
150 parts by weight of a base oil shown in Tables 2 to 4 was added, and the temperature was raised to 120 to 130°C. Unreacted monomers and ethyl acetate were then removed at the same temperature under reduced pressure (0.027 to 0.040 MPa) over 2 hours to obtain copolymer solutions containing the copolymers (A-1) to (A-12) of the present invention or the copolymers (A'-1) to (A'-2) for comparison.

<Comparative Production Examples 5 to 9>
The base oils listed in Table 5 were used as solutions as they were.

The various monomers and base oils listed in Tables 2-5 are as follows:
(a-4): 1-mol ε-caprolactone adduct of HEMA (a-5): 20-mol ε-caprolactone adduct of HEMA (a-6): Terminal butyl ester of 4-mol ε-caprolactone adduct of HEMA (a-7): 2-mol ε-caprolactone adduct of HEA (a-8): 14-mol ε-caprolactone adduct of HEA (a-9): Terminal butyl ester of 7-mol ε-caprolactone adduct of HEA (b-1): n-dodecyl methacrylate (b-2): Mixture of linear and branched alkyl methacrylates having 12 to 15 carbon atoms (esterification product of Neodol 23 (manufactured by Shell Chemicals) and methacrylic acid)
(b-3): n-hexadecyl methacrylate (b-4): n-octadecyl methacrylate (b-5): 2-decyltetradecyl methacrylate (b-6): 2-docylhexadecyl methacrylate (b-7): 2-tetradecyloctadecyl methacrylate (b-8): n-dodecyl acrylate (b-9): n-octadecyl acrylate (c-1): Polybutadiene macromonomer (ester of L-1203 [1,2-adduct/1,4-adduct=45/55] manufactured by Kuraray Co., Ltd. and methacrylic acid, Mn=6960)
(c-2): Polybutadiene macromonomer (ester of L-3203 [1,2-adduct/1,4-adduct=65/35] manufactured by Kuraray Co., Ltd. and methacrylic acid, Mn=6960)
(d-1): Methyl methacrylate (d-2): Butyl methacrylate (e-1): 2-hydroxyethyl acrylate (e-2): 2-hydroxyethyl methacrylate (e-3): 2-hydroxyisobutyl methacrylate (g-1): N,N-dimethylaminoethyl methacrylate (B-1): Diester of 3-methyl-1,5-pentanediol and octanoic acid (40°C kinematic viscosity: 7.38 mm ² /s, 100°C kinematic viscosity: 2.41 mm ² /s, SP value: 8.98
(B-2): Diester of 3-methyl-1,5-pentanediol and nonanoic acid (kinematic viscosity at 40°C: 8.93 mm ² /s, kinematic viscosity at 100°C: 2.73 mm ² /s, SP value: 8.95)
(B-3): Diester of 2-ethylhexyl alcohol and adipic acid (kinematic viscosity at 40°C: 7.80 mm ² /s, kinematic viscosity at 100°C: 2.40 mm ² /s, SP value: 8.91)
(B-4): Monoester of isooctanol and oleic acid (kinematic viscosity at 40°C: 8.20 mm ² /s, kinematic viscosity at 100°C: 2.68 mm ² /s, SP value: 8.61)
(B-5): Diester of 3-methyl-1,5-pentanediol and pentanoic acid (kinematic viscosity at 40°C: 3.74 mm ² /s, kinematic viscosity at 100°C: 1.49 mm ² /s, SP value: 9.11)
(B-6): Diester of 2-ethylhexyl alcohol and zebaic acid (kinematic viscosity at 40°C: 11.32 mm ² /s, kinematic viscosity at 100°C: 3.19 mm ² /s, SP value: 8.87)
(B-7): Diester of n-octanol and adipic acid (kinematic viscosity at 40°C: 8.21 mm ² /s, kinematic viscosity at 100°C: 2.58 mm ² /s, SP value: 9.04)
(B-8): Diester of neopentyl glycol and 2-ethylhexanoic acid (kinematic viscosity at 40°C: 7.49 mm ² /s, kinematic viscosity at 100°C: 2.03 mm ² /s, SP value: 8.79)
(C-1): Mineral oil (SK Lubricants YUBASE2, kinematic viscosity at 40°C: 8.65 mm ² /s, kinematic viscosity at 100°C: 2.41 mm ² /s, SP value: 8.20)

<Examples 1 to 21 and Comparative Examples 1 to 9>
The solutions obtained in Production Examples 4 to 24 and Comparative Production Examples 1 to 9 were blended in the amounts shown in Tables 2 to 5 to obtain lubricating oil compositions (V-1) to (V-21) and (V'-1) to (V'-9).
Using the resulting lubricating oil compositions (V-1) to (V-21) and (V'-1) to (V'-9), the kinematic viscosity, viscosity index, thermal conductivity, heat transfer coefficient, volume resistivity, and MTM friction coefficient at various temperatures were measured by the following methods. In Comparative Examples 5 to 9, the base oils listed in Table 5 were used as lubricating oil compositions (V'-5) to (V'-9) as they were.

<Method for calculating viscosity index of lubricating oil composition>
The kinematic viscosities were measured at 100°C, 80°C and 40°C by the method of ASTM D 445, and the viscosity index was calculated from the kinematic viscosities at 100°C and 40°C by the method of ASTM D 2270.

<Measurement of thermal conductivity>
Measurement was carried out at room temperature of 25°C using a thermal property meter KD2pro manufactured by Decagon Corporation with a single needle sensor.

<Calculation method for heat transfer coefficient>
The heat transfer coefficients at 40°C and 80°C were calculated using the following equation from the kinematic viscosity, thermal conductivity, density and constant pressure specific heat of the lubricating oil composition at each temperature (40°C or 80°C).

Heat transfer coefficient (W/m ² K) = (density [kg/m ³ ]) ^0.33 × (specific heat at constant pressure [kJ/kgK]) ^0.33 × (thermal conductivity [W/mK]) ^0.67 / (kinetic viscosity [mm ² /s]) ^0.17

<Measurement of volume resistivity>
The measurement was carried out in accordance with JIS C 2101, 24 (volume resistivity test) at room temperature of 25°C.

<MTM (Mini Traction) Friction Coefficient>
Measurements were carried out using an MTM (mini traction) testing machine under the following measurement conditions to obtain Stribeck curves, and the friction coefficients at various speeds of 10 mm/s, 100 mm/s, 500 mm/s, and 1,000 mm/s are shown in Tables 2 to 5.
Equipment: PCS Instruments MTM-2
Disc: MTM polished disc (standard) (0.01 micron)
Ball: Drilled 3/4 AISI52100 precision steel ball
Speed: 10mm/s ~ 3,000mm/s
Temperature: 100℃
Sliding/rolling ratio: 50%
Load: 30N

Tables 2 to 5 show that the lubricating oil composition of the present invention has a heat transfer coefficient of 2.10 W/(m ² /K) or more at 40°C without reducing the cooling ability of the ester oil (B), has a high MTM friction coefficient (100°C, speed: 10 mm/s) of 0.070 or more at low speed, and is excellent in power transmission characteristics, and can rapidly reduce the MTM friction coefficient (100°C, speed: 100 mm/s) to 0.055 or less at high speed, thereby providing high lubricity.

The lubricating oil composition of the present invention has excellent cooling and lubrication properties and is therefore suitable for use in gear oils (differential oils, industrial gear oils, etc.), MTFs, transmission oils [ATFs, belt-CVTFs, etc.], traction oils (toroidal-CVTFs, etc.), shock absorber oils, power steering oils, hydraulic oils (construction machinery hydraulic oils, industrial hydraulic oils, etc.), engine oils, etc. It is particularly useful as a transmission oil, electric motor oil, or dual-purpose oil for both transmissions and electric motors in electric vehicles or hybrid vehicles, and is extremely useful as a dual-purpose oil for both transmissions and electric motors in electric vehicles or hybrid vehicles.

Claims (14)

A lubricating oil composition comprising a copolymer (A) having, as essential constituent monomers, a monomer (a) represented by the following general formula (1) , a monomer (b) represented by the following general formula (2), and a hydroxyl group-containing monomer (e) other than the monomer (a), and an ester oil (B).
[In formula (1), A ¹ represents a monovalent radically polymerizable group; -X ¹ -, -X ² -, and -X ³ - each independently represent a group represented by -O- or -NH-; R ¹ represents an alkylene group having 1 to 4 carbon atoms; R ² each independently represent an alkylene group having 2 to 20 carbon atoms, and when there are multiple R ^2s , they may be the same or different; R ³ represents a hydrogen atom, an alkyl group having 1 to 44 carbon atoms, an acyl group having 2 to 45 carbon atoms, or a phenyl group or benzoyl group optionally substituted with an alkyl group having 1 to 44 carbon atoms; and p represents an integer from 1 to 100.]
[In formula (2), R ⁴ represents a hydrogen atom or a methyl group; —X ⁴ — represents a group represented by —O— or —NH—; and R ⁵ represents a linear or branched alkyl group having 5 to 44 carbon atoms.] The lubricating oil composition according to claim 1, wherein the weight-average molecular weight of the copolymer (A) is 5,000 to 2,000,000. 3. The lubricating oil composition according to claim 1, wherein the solubility parameter of the copolymer (A) is 8.5 to 11.5 (cal/cm ³ ) ^1/2 . The lubricating oil composition according to any one of claims 1 to 3, wherein the ester oil (B) has a kinematic viscosity at 40°C of 3 to 30 mm ² /s. The lubricating oil composition according to any one of claims 1 to 4, wherein the ester oil (B) has a solubility parameter of 8.1 to 10.1 (cal/cm ³ ) ^1/2 . The lubricating oil composition according to any one of claims 1 to 5, wherein the content of copolymer (A) is 0.1 to 10% by weight, based on the weight of the lubricating oil composition. The lubricating oil composition according to any one of claims 1 to 6, wherein the copolymer (A) contains, as a constituent monomer , a monomer (c) represented by the following general formula (3):
[In formula (3), R ⁶ is a hydrogen atom or a methyl group; -X ⁵ - is a group represented by -O-, -O(AO) _m -, or -NH-, A is an alkylene group having 2 to 4 carbon atoms, m is an integer from 1 to 10, and when m is 2 or more, As may be the same or different; R ⁷ is a residue in which one hydrogen atom has been removed from a hydrocarbon polymer having 43 or more carbon atoms and containing isobutylene groups and/or 1,2-butylene groups as essential structural units; and q is the number 0 or 1.] The lubricating oil composition according to any one of claims 1 to 7, wherein the absolute value of the difference between the solubility parameter of the copolymer (A) and the solubility parameter of the ester oil (B) is 3.4 (cal/cm ³ ) ^1/2 or less. The lubricating oil composition according to any one of claims 1 to 8, wherein the ester oil (B) is at least one selected from the group consisting of a diesterification product of a dicarboxylic acid (x1) and a monohydric alcohol (y1), a diesterification product of a monocarboxylic acid (x2) and a dihydric alcohol (y2), and an esterification product of a monocarboxylic acid (x2) and a monohydric alcohol (y1), wherein the monohydric alcohol (y1) is a compound having a linear or branched alkyl group with 1 to 24 carbon atoms in the alkyl group, and the monocarboxylic acid (x2) is a compound having a linear or branched alkyl group with 1 to 24 carbon atoms in the alkyl group. The lubricating oil composition according to claim 9, wherein the ester oil (B) is a diester of the dicarboxylic acid (x1) and the monohydric alcohol (y1) and/or a diester of the monocarboxylic acid (x2) and the dihydric alcohol (y2). The lubricating oil composition according to any one of claims 1 to 10, wherein the absolute value of the difference between the solubility parameter of the constituent unit derived from the monomer (a) and the solubility parameter of the ester oil (B) is 0.9 to 4.4 (cal/cm ³ ) ^1/2 . The lubricating oil composition according to any one of claims 1 to 11, which is a lubricating oil composition for electric vehicles or hybrid vehicles. The lubricating oil composition according to any one of claims 1 to 12, which is a dual-purpose oil for the transmission and electric motor in an electric vehicle or hybrid vehicle. The lubricating oil composition according to any one of claims 1 to 13, further comprising at least one additive selected from the group consisting of viscosity index improvers, detergents, dispersants, antioxidants, oiliness improvers, friction and wear modifiers, extreme pressure agents, antifoaming agents, demulsifiers, corrosion inhibitors, and pour point depressants.