JP7513658B2 - Lubricating Oil Composition - Google Patents

Description

The present invention relates to a lubricating oil composition.

In recent years, there has been an increasing demand for fuel-efficient automobiles in order to reduce _CO2 emissions and conserve oil resources. One way to reduce fuel consumption is to reduce viscous resistance by lowering the viscosity of engine oil. However, lowering the viscosity can cause problems such as leakage and seizure. To address this issue, the minimum guaranteed viscosity is set by the US SAE engine oil viscosity standard (SAE J300), and for the 0W-20 grade, the 150°C HTHS viscosity (ASTM D4683 or D5481) is set to 2.6 mPa·s or more as the viscosity under high temperature and high shear (HTHS viscosity), and for the 0W-16 grade, it is set to 2.3 mPa·s or more.

For fuel saving, engine oils that satisfy the above standards and have a lower kinematic viscosity in the effective temperature range (especially 80°C and 60°C) are required. As a method for lowering the kinematic viscosity in the effective temperature range, various viscosity index improvers have been proposed, and a method of using a large amount of low-viscosity base oil is also known. However, there is a problem that the evaporation loss rate of engine oil (NOACK evaporation amount [engine oil evaporation test method, ASTM D5800]) worsens. On the other hand, hybrid cars and electric cars are rapidly becoming popular in order to reduce _CO2 emissions and protect petroleum resources. In particular, with the popularity of hybrid cars, the frequency of engine operation has decreased and the frequency of low oil temperature operation has increased. Therefore, while viscosity reduction on the low temperature side is important for improving fuel efficiency, reliability on the high temperature side (100°C) is also necessary from the viewpoint of reliability in high-speed driving, etc., even though it is less frequent. Therefore, it is necessary to ensure an appropriate high viscosity even on the high temperature side (Patent Documents 1 to 4).
On the other hand, conventional lubricating oil compositions have a problem in that their elasticity increases at low temperatures, resulting in poor startability in cold regions. It has been difficult to obtain a lubricating oil that has good startability in cold regions by reducing low-temperature elasticity while suppressing NOACK evaporation amount to a low level.

JP 2013-147608 A International Publication No. 2015/129732 JP 2017-57378 A JP 2020-105347 A

The object of the present invention is to provide a lubricating oil composition that can reduce viscosity in the effective temperature range (especially 80°C and 60°C) and reduce elasticity at low temperatures (-20°C) even when the NOACK evaporation rate is kept low, with the aim of reducing fuel consumption.

As a result of extensive investigations, the present inventors have arrived at the present invention.
That is, the present invention relates to a (co)polymer (A) having a main chain having a repeating unit derived from a polymerizable monomer and a side chain having a polyolefin structure,
GTL base oil (B),
A lubricating oil composition comprising a detergent and/or dispersant and an antioxidant,
The lubricating oil composition has an HTHS viscosity at 150°C of 2.25 to 2.54 mPa·s, a kinematic viscosity at 80°C of 7.8 to 8.2 mm ² /s, a kinematic viscosity at 60°C of 11.8 to 12.4 mm ² /s, and a NOACK evaporation amount of the lubricating oil composition of 15 to 25% by weight, wherein the (co)polymer (A) is a polyolefin monomer (a) represented by the following general formula (1), a monomer (b) represented by the following general formula (2) in which R ^{4 is an alkyl group having 2 to 4 carbon atoms, and a monomer (c) represented by the following general formula (3) in which R 5} is an alkyl group having 2 to 4 carbon atoms. and a monomer (c) in which ⁴ is an alkyl group having 12 to 16 carbon atoms, as constituent monomers, wherein the number average molecular weight of the monomer (a) is 6,600 to 8,500, the solubility parameter calculated based on the weight fraction of the ( co) polymer (A) is 9.23 to 9.25 (cal/ ^cm3 ) ^1/2 , the weight ratio of the monomer (a) is 12 to 21 wt%, the weight ratio of the monomer (b) is 54 to 75 wt%, and the weight ratio of the monomer (c) is 3 to 17 wt%, based on the total weight of the monomers constituting the (co)polymer (A), and the total weight ratio of the monomers (a), (b) and (c) is 70 wt% or more.
[In general formula (1), R ¹ is a hydrogen atom or a methyl group; -X ¹ - is a group represented by -O(AO) _m , A is an alkylene group having 2 carbon atoms, and m is an integer of 1; R ² is a residue obtained by removing one hydrogen atom from a hydrocarbon polymer containing 1,2-butylene groups as a structural unit, the constituent monomer of the hydrocarbon polymer is 1,3-butadiene, and the ratio of 1,2-butylene groups is 45 to 65 mol % based on the total number of moles of the constituent monomers of the hydrocarbon polymer; and p is 0.]
[In the general formula (2), R ³ is a hydrogen atom or a methyl group; -X ² - is a group represented by -O-; and R ⁴ is an alkyl group having 2 to 4 or 12 to 16 carbon atoms.]

The lubricating oil composition of the present invention has the effect of reducing the viscosity in the effective temperature range (especially 80°C and 60°C) and reducing the elasticity at low temperatures (-20°C), even when the NOACK evaporation rate is kept low, thereby reducing fuel consumption.

1 is a graph showing the relationship between the kinematic viscosity at 60° C. (horizontal axis) and the storage modulus (vertical axis) for the lubricating oil compositions obtained in the Examples and the lubricating oil compositions obtained in the Comparative Examples.

The lubricating oil composition of the present invention comprises: a (co)polymer (A) having a main chain having a repeating unit derived from a polymerizable monomer and a side chain having a polyolefin structure;
GTL base oil (B),
A lubricating oil composition comprising a detergent and/or dispersant and an antioxidant,
The lubricating oil composition has an HTHS viscosity at 150°C of 2.25 to 2.54 mPa·s, a kinematic viscosity at 80°C of 7.8 to 8.2 mm ² /s, and a kinematic viscosity at 60°C of 11.8 to 12.4 mm ² /s, and a NOACK evaporation amount of 15 to 25 wt%.

<(Co)polymer (A)>
In the present invention, the (co)polymer (A) has a main chain having a repeating unit derived from a polymerizable monomer and a side chain having a polyolefin structure.
The polymerizable monomer includes those having a radical polymerizable carbon-carbon double bond {vinyl group (H ₂ C=CH-), vinylidene group or vinylene group (-HC=CH-)}, such as monomers having a (meth)acryloyl group, a carbon-carbon double bond in a mono- or diester of maleic acid (anhydride) or fumaric acid {-OC(O)HC=CH-C(O)O-}, a vinyl ether group, a styryl group, etc. Of these, monomers having a (meth)acryloyl group are preferred. When the polymerizable monomer has a (meth)acryloyl group, the (co)polymer has a highly polar group (ester group, amide group, etc.) in the vicinity of the main chain skeleton and has a non-polar polyolefin structure as a side chain, and at low temperatures, the polymer chain of the (co)polymer (A) gathers small around the main chain against a base oil with low polarity, and when the HTHS viscosity at 150°C is adjusted to 2.25 to 2.54 mPa·s, the kinetic viscosity at low temperatures (80°C, 60°C) can be reduced, and the elasticity at low temperatures (−20°C) tends to be reduced.

In the present invention, the (co)polymer (A) is preferably a (co)polymer containing, as a constituent monomer, a monomer having a polyolefin structure having 50 to 1,000 carbon atoms at one end and a (meth)acryloyl group at the other end, and more preferably a (co)polymer containing, as a constituent monomer, a monomer (a) represented by the following general formula (1):
When the monomer (a) represented by the following general formula (1) is used as a constituent monomer, ^R2 of the monomer (a) becomes a "side chain having a polyolefin structure" in the (co)polymer (A). The monomer (a) may be used alone or in combination of two or more kinds.
[In general formula (1), R ¹ is a hydrogen atom or a methyl group; -X ¹ - 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 ² is a residue in which one hydrogen atom has been removed from a hydrocarbon polymer containing a 1,2-butylene group as a structural unit; and p is the number 0 or 1.]

R ¹ in the general formula (1) is a hydrogen atom or a methyl group, and from the viewpoint of increasing the molecular behavior of (A) with respect to temperature (reducing the kinetic viscosity at low temperatures (80° C., 60° C.) when the HTHS viscosity at 150° C. is adjusted to a constant value, the same applies hereinafter), a methyl group is preferable.

In formula (1), --X ¹ -- 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 from the viewpoint of solubility in a base oil (such as an ester oil (B), the same applies hereinafter), is preferably an integer of 1 to 4, and more preferably an integer of 1 or 2.
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 enhancing the molecular behavior of (A) with respect to temperature, -X ¹ - 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 general formula (1), p is a number of 0 or 1, and 0 is preferred from the viewpoint of solubility in the base oil.

^R2 in the general formula (1) is a residue in which one hydrogen atom has been removed from a hydrocarbon polymer containing a 1,2-butylene group as a structural unit. From the viewpoint of enhancing the molecular behavior of (A) with respect to temperature, it preferably has 50 to 1,000 carbon atoms.
The 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 the hydrocarbon polymer having a 1,2-butylene group as a constituent unit include a polymer using 1-butene as a constituent monomer (unsaturated hydrocarbon (x)), and a polymer obtained by hydrogenating the double bond of a 1,2-addition product obtained by polymerizing 1,3-butadiene.
Furthermore, the hydrocarbon polymer may contain, in addition to 1-butene and 1,3-butadiene, one or more of the following (1) to (3) as the unsaturated hydrocarbon (x) as a constituent monomer:
(1) Aliphatic unsaturated hydrocarbons [olefins having 2 to 36 carbon atoms (e.g., ethylene, propylene, isobutene, 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. When the hydrocarbon polymer has double bonds, the double bonds may be partially or entirely hydrogenated by hydrogenation. In one embodiment, the hydrocarbon polymer in ^R2 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 1-butene and 1,3-butadiene.

The number average molecular weight (hereinafter abbreviated as Mn) of monomer (a) is preferably 800 to 10,000, more preferably 1,000 to 9,000, and even more preferably 1,200 to 8,500, from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature. If Mn of monomer (a) is 800 or more, it tends to have good solubility in base oil, and if it is 10,000 or less, it tends to have good copolymerizability with other monomers.

In the present invention, the weight average molecular weight (hereinafter abbreviated as Mw) and Mn can be measured by gel permeation chromatography (hereinafter abbreviated as GPC) under the following conditions.
<Conditions for measuring Mw and Mn>
Apparatus: "HLC-8320GPC" [manufactured by Tosoh Corporation]
Column: 2 columns of "TSKgel GMHXL" [manufactured by Tosoh Corporation]
"TSKgel Multipore H _XL -M 1 piece Measurement temperature: 40°C
Sample solution: 0.25% by weight tetrahydrofuran solution. Solution injection amount: 10.0 μl
Detector: Refractive index detector Reference material: Standard polystyrene (TS Standard polystyrene (TSK standard POLYSTYRENE)
12 points (molecular weight: 589, 1,050, 2,630, 9,100, 19,500, 37,900, 96,400, 190,000, 355,000, 1,090,000, 2,110,000, 4,480,000) [manufactured by Tosoh Corporation]

Monomer (a) can be obtained by an esterification reaction between (meth)acrylic acid and polymer (Y) containing a hydroxyl group at one end, obtained by introducing a hydroxyl group at one end of a hydrocarbon polymer, or by an ester exchange reaction between (meth)acrylic acid and 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 (such as ethylene oxide or propylene oxide) to a hydrocarbon polymer obtained by polymerizing an unsaturated hydrocarbon (x) in the presence of an ionic polymerization catalyst (such as a sodium catalyst) (in this case, the monomer (a) is a compound of the general formula (1) in which -X ¹ - is -(AO) _m - and p=0).
Hydroboration product (Y2): a hydroboration reaction product of a hydrocarbon polymer of an unsaturated hydrocarbon (x) having a double bond at one end (e.g., those described in U.S. Pat. No. 4,316,973) (in this case, the monomer (a) is a compound of the general formula (1) in which -X ¹ - is -O- and p=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 (a) is a compound of the general formula (1) in which -X ¹ - is -O- and p=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 (e.g., the compound described in JP-A-63-175096) (in this case, the monomer (a) is a compound of the general formula (1) in which -X ¹ - is -O- and p=0).
Of these polymers (Y) containing a hydroxyl group at one end, from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature, the alkylene oxide adduct (Y1) and the hydroboronate (Y2) are preferred, and the alkylene oxide adduct (Y1) is more preferred,

The ratio of butadiene to all monomers constituting R ² in general formula (1) (the weight proportion of 1,3-butadiene to all constituent monomers in a hydrocarbon polymer containing 1,2-butylene groups as a constituent unit) is 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, from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature.

With regard to the structure of the hydrocarbon polymer in the general formula (1) derived from 1-butene and/or 1,3-butadiene, the ratio of 1,2-butylene groups (number of moles of 1,2-butylene groups/total number of moles of constituent monomers×100) is preferably 30 mol % or more, and more preferably 30 to 70 mol %, based on the total number of moles of constituent monomers of the hydrocarbon polymer, from the viewpoints of the viscosity index improving effect and copolymerizability with other monomers.
The ratio of 1,2-butylene groups can be measured by ¹³ C-NMR. Specifically, for example, when only monomers having 4 carbon atoms are used, the hydrocarbon polymer is analyzed by ¹³ C-NMR, and the mole percentage of 1,2-butylene groups based on the total mole number of constituent units of the hydrocarbon polymer is calculated and determined using the following mathematical formula (1). In ¹³ C-NMR, a peak derived from the tertiary carbon atom (-CH ₂ CH(CH ₂ CH ₃ )-) of the 1,2-butylene group appears at an integral value (integral value B) of 26 to 27 ppm. The mole percentage can be determined from the integral value of this peak and the integral value (integral value C) of the peak of all carbon in the hydrocarbon polymer.
Ratio of 1,2-butylene groups (mol%)={(integral value B)×4}/(integral value C)×100 (1)
In order to increase the ratio of 1,2-butylene groups, for example, in anionic polymerization using 1,3-butadiene, the reaction temperature should be set to the boiling point of 1,3-butadiene (−4.4° C.) or lower and the amount of polymerization initiator added should be reduced relative to that of 1,3-butadiene. In order to decrease the ratio of 1,2-butylene groups, the reaction temperature should be set to the boiling point of 1,3-butadiene or higher and the amount of initiator should be increased.

The hydrocarbon polymer of formula (1) containing 1,2-butylene groups as a constituent unit may contain isobutylene groups from the viewpoint of enhancing the molecular behavior of (A) relative to temperature.
From the viewpoint of enhancing the molecular behavior of (A) with respect to temperature, the total amount of isobutylene groups and 1,2-butylene groups is 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 the 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 the hydrocarbon polymer, for example, the following methods can be adopted. 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 lowering the reaction temperature (for example, the boiling point of 1,3-butadiene (-4.4°C) or less) and decreasing the amount of polymerization initiator added relative to 1,3-butadiene. In the case of the above hydroboration product (Y2), maleic anhydride-ene-aminoalcohol adduct (Y3) and hydroformyl-hydride product (Y4), the above 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 containing 1,2-butylene groups as a structural unit in general formula (1) can be measured by ¹³ C-NMR. Specifically, for example, when only monomers having 4 carbon atoms are used as monomers, the hydrocarbon polymer is analyzed by ¹³ C-NMR and 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 can be determined by calculating using the following mathematical formula (2). In ¹³ C-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 (-CH ₂ CH(CH ₂ CH ₃ )- or -CH(CH ₂ CH ₃ )CH ₂ -) 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 the structural units of the hydrocarbon polymer can be determined from the integral of the above peak and the integral of the peak for all carbon in the hydrocarbon polymer (integral C).
Total Amount of Isobutylene Groups and 1,2-Butylene Groups (mol%)=100×{(Integral Value A)×2+(Integral Value B)×4}/(Integral Value C) (2)

When the hydrocarbon polymer in R ² contains butadiene, or butadiene and 1-butene, as a constituent monomer, in the structure derived from butadiene, or butadiene and 1-butene constituting part or all of R ² in general formula (1), 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 increasing the molecular behavior of (A) with respect to temperature and copolymerizability with other monomers.

When the hydrocarbon polymer in ^R2 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 ^R2 in general formula (1) can be measured by ^1H -NMR, ^13C -NMR, Raman spectroscopy, or the like.

The solubility parameter (hereinafter abbreviated as SP value) of the constituent unit derived from monomer (a) (a structure in which vinyl in (a) has reacted to form a single bond) is preferably 7.0 to 9.0 (cal/cm 3 ) ^1/2 , more preferably 7.3 to 8.5 (cal/cm ³ ) ^1/2 , from the viewpoints of making the SP value calculated based on the weight fraction of ( ^A ) appropriate and of solubility in the base oil.
The SP value tends to be smaller, for example, when the degree of branching of ^R2 is large and the number of carbon atoms is large, and tends to be larger when the degree of branching is small and the number of carbon atoms is small.
The SP value in the present invention means a value calculated by the 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 by applying the values of Δe _i and v _i described in Table 1 below, which are parameters of the Fedors method, to the formula below using the values corresponding to the types of atoms and atomic groups in the molecular structure.
SP value=(ΣΔe _i /Σv _i ) ^1/2

The SP value of the constituent unit derived from monomer (a) can be calculated using the above parameters based on the molecular structure of the constituent unit derived from monomer (a), and can be adjusted to the desired range by appropriately adjusting the weight fraction of the monomer (unsaturated hydrocarbon (x)) and monomer (unsaturated hydrocarbon (x)) used. In addition, when the (co)polymer (A) uses two or more types of monomer (a) in combination, it is preferable that the SP value of each of the multiple constituent units constituting (a) is calculated by the above method, and the arithmetic mean value of the SP values of the constituent units derived from each monomer (a) based on the weight fraction of the constituent monomer units satisfies the range of the SP value of the constituent unit derived from monomer (a).

In the present invention, the (co)polymer (A) preferably contains, as constituent monomers, a monomer (b) represented by the following general formula (2), in which R ⁴ is an alkyl group having 2 to 4 carbon atoms, and a monomer (b) represented by the following general formula (2), in which R ⁴ is an alkyl group having 12 to 16 carbon atoms.
[In the general formula (2), R ³ is a hydrogen atom or a methyl group; -X ² - is a group represented by -O- or -NH-; and R ⁴ is an alkyl group having 2 to 4 or 12 to 16 carbon atoms.]

In the general formula (2) representing the monomer (b) or (c), ^R3 is a hydrogen atom or a methyl group, and from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature, a methyl group is preferred.
In the general formula (2) representing the monomer (b) or (c), -X ² - is a group represented by -O- or -NH-, and from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature, a group represented by -O- is preferred.

In the monomer (b), R ⁴ in the general formula (2) is an alkyl group having 2 to 4 carbon atoms. Examples of the alkyl group having 2 to 4 carbon atoms include an ethyl group, a propyl group (e.g., an n-propyl group, an isopropyl group, and an butyl group (e.g., an n-butyl group, a sec-butyl group, an isobutyl group, and a tert-butyl group).
Of these, from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature, preferred are ethyl, n-butyl and isobutyl groups, more preferred are ethyl and n-butyl groups, and particularly preferred is n-butyl group.

Examples of the monomer (b) include ethyl (meth)acrylate, n-propyl (meth)acrylate, isobutyl (meth)acrylate, n-butyl (meth)acrylate, 1-methylpropyl (meth)acrylate, 2-methylpropyl (meth)acrylate, 1,1-dimethylethyl (meth)acrylate, and N-butyl(meth)acrylamide.
Among these, from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature, ethyl (meth)acrylate, n-butyl (meth)acrylate, and isobutyl (meth)acrylate are preferred, more preferably ethyl (meth)acrylate and n-butyl (meth)acrylate, and particularly preferably n-butyl (meth)acrylate.

In the monomer (c), R ⁴ in the general formula (2) is an alkyl group having 12 to 16 carbon atoms, and examples thereof include linear alkyl groups (e.g., n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, etc.), branched alkyl groups (e.g., 2-methylundecyl group, isododecyl group, 2-methyldodecyl group, isotridecyl group, 2-methyltridecyl group, isotetradecyl group, 2-methyltetradecyl group, isopentadecyl group, 2-methylpentadecyl group, isohexadecyl group, etc.), and the like.
Specific examples of the monomer (c) include linear alkyl (meth)acrylates (e.g., n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, n-pentadecyl (meth)acrylate, n-hexadecyl (meth)acrylate, etc.), linear alkyl (meth)acrylamides (e.g., N-dodecyl (meth)acrylamide, N-tridecyl (meth)acrylamide, N-tetradecyl (meth)acrylamide, N-pentadecyl (meth)acrylamide, N-hexadecyl (meth)acrylamide, etc.), branched alkyl (meth)acrylates (e.g., 2-methylundecyl (meth)acrylate, isododecyl (meth)acrylate, 2-methyldodecyl (meth)acrylate, isotridecyl (meth)acrylate, 2-methyltridecyl (meth)acrylate, (meth)acrylate, isotetradecyl (meth)acrylate, 2-methyltetradecyl (meth)acrylate, isopentadecyl (meth)acrylate, 2-methylpentadecyl (meth)acrylate, isohexadecyl (meth)acrylate, etc.), branched alkyl (meth)acrylamides (for example, N-2-methylundecyl(meth)acrylamide, N-isododecyl(meth)acrylamide, N-2-methyldodecyl(meth)acrylamide, N-isotridecyl(meth)acrylamide, N-2-methyltridecyl(meth)acrylamide, N-isotetradecyl(meth)acrylamide, N-2-methyltetradecyl(meth)acrylamide, N-isopentadecyl(meth)acrylamide, N-2-methylpentadecyl(meth)acrylamide, N-isohexadecyl(meth)acrylamide, etc.).
As the monomer (c), from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature, linear alkyl (meth)acrylates and branched alkyl (meth)acrylates are preferred.
As the monomer (c), a (meth)acrylic acid ester of a mixture of alkyl alcohols such as Neodol (registered trademark) 23 (a mixture of linear and branched alkyl alcohols having 12 to 13 carbon atoms, manufactured by SHELL) and Neodol (registered trademark) 45 (a mixture of linear and branched alkyl alcohols having 14 to 15 carbon atoms, manufactured by SHELL) may be used.

In the present invention, the weight ratio (b/a) of the monomers (a) and (b) constituting the (co)polymer (A) is preferably 3.5 to 4.9, more preferably 3.8 to 4.5, and particularly preferably 4.0 to 4.4, from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature. If the weight ratio is 3.5 or more or 4.9 or less, the molecular behavior of (A) with respect to temperature tends to be enhanced, the kinetic viscosity at 40 to 100°C (particularly the kinetic viscosity at 60 to 80°C) tends to be lower when the HTHS viscosity at 150°C is constant, and the storage modulus at low temperatures tends to be lower.
In the present invention, the weight ratio (b/c) of the monomers (b) and (c) constituting the (co)polymer (A) is preferably 4.1 or more, more preferably 4.5 to 10.0, and particularly preferably 5.0 to 9.0, from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature. If it is 4.1 or more, the molecular behavior of (A) with respect to temperature tends to be enhanced, the kinetic viscosity at 40 to 100°C (particularly the kinetic viscosity at 60 to 80°C) tends to be low when the HTHS viscosity at 150°C is constant, and the storage modulus at low temperatures tends to be low.

In the present invention, the weight ratio of (b) to the total weight of the monomers (a) and (c) constituting the (co)polymer (A), {b/(a+c)}, is preferably 2.0 to 3.5 from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature.

In the (co)polymer (A), the weight ratio of the monomer (a) among the constituent monomers of (A) is preferably 1 to 22% by weight, more preferably 10 to 21% by weight, and particularly preferably 12 to 20% by weight, based on the total weight of the monomers constituting (A), from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature.

In the (co)polymer (A), the weight ratio of the monomer (b) among the constituent monomers of (A) is preferably 4.1 to 77% by weight, more preferably 35 to 75% by weight, and particularly preferably 42 to 75% by weight, based on the total weight of the monomers constituting (A), from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature.

In the (co)polymer (A), the weight ratio of the monomer (c) among the constituent monomers of (A) is preferably 1 to 17% by weight, more preferably 3 to 15% by weight, and particularly preferably 8 to 13% by weight, based on the total weight of the monomers constituting (A), from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature.

In (co)polymer (A), the total weight ratio of monomer (a), monomer (b) and monomer (c) among the constituent monomers of (A) is preferably 70% by weight or more, more preferably 70 to 97% by weight, and particularly preferably 78 to 95% by weight, based on the total weight of the monomers constituting (A), from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature.

In the present invention, the (co)polymer (A) may be a copolymer containing, in addition to the monomers (a) to (c), at least one selected from the group consisting of a monomer (d) represented by the following general formula (3), a monomer (e) represented by the above general formula (2) in which R ⁴ is an alkyl group having 1 carbon atom, and a (meth)acryloyl monomer (f) having a linear or branched alkyl group having 17 to 36 carbon atoms (hereinafter sometimes abbreviated as monomer (f)). From the viewpoint of reducing the HTHS viscosity at 100° C., it is preferable that the copolymer contains monomer (d) as a constituent monomer. In addition, monomer (e) has high polarity due to the short carbon number of the alkyl group relative to the polar group (ester group, etc.), and can increase the polarity of the (co)polymer (A). Monomer (f) has a carbon number of the alkyl group relative to the polar group (ester group, etc.) longer than (b) and (c) but shorter than (a), and therefore has intermediate polarity and can adjust the polarity of the (co)polymer (A).

[In the general formula (3), R ⁵ is a hydrogen atom or a methyl group; -X ³ - is a group represented by -O- or -NH-; R ⁶ is an alkylene group having 2 to 4 carbon atoms; q is an integer of 1 to 20, and when q is 2 or more, R ⁶ may be the same or different; and R ⁷ is a linear or branched alkyl group having 1 to 4 carbon atoms.]

In the general formula (3), ^R5 is a hydrogen atom or a methyl group. Among these, from the viewpoint of reducing the HTHS viscosity at 100°C, a methyl group is preferred.

In the general formula (3), -X ³ - is a group represented by -O- or -NH-. Of these, from the viewpoint of reducing the HTHS viscosity at 100°C, the group represented by -O- is preferred.

In the general formula (3), R ⁶ 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, an isopropylene group, a 1,2- or 1,3-propylene group, an isobutylene group, and a 1,2-, 1,3- or 1,4-butylene group.
R ⁶ O is an alkyleneoxy group having 2 to 4 carbon atoms, such as an ethyleneoxy group, a 1,2- or 1,3-propyleneoxy group, and a 1,2-, 1,3-, or 1,4-butyleneoxy group.
In the general formula (3), q is an integer of 1 to 20, and from the viewpoint of reducing the HTHS viscosity at 100° C., is preferably an integer of 1 to 5, and more preferably an integer of 1 or 2.
When q is 2 or more, R ⁶ O may be the same or different, and the bonding form of the (R ⁶ O) _q portion may be random or block.

^R7 in the general formula (3) is a linear or branched alkyl group having 1 to 4 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an s-butyl group, and a t-butyl group.
Among the linear or branched alkyl groups having 1 to 4 carbon atoms, from the viewpoint of reducing the HTHS viscosity at 100° C., a linear alkyl group having 1 to 4 carbon atoms is preferred, and a linear alkyl group having 4 carbon atoms (n-butyl group) is more preferred.

Specific examples of the monomer (d) include methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, ethoxypropyl (meth)acrylate, propoxypropyl (meth)acrylate, butoxypropyl (meth)acrylate, methoxybutyl (meth)acrylate, ethoxybutyl (meth)acrylate, propoxybutyl (meth)acrylate, and butoxybutyl (meth)acrylate, as well as esters of (meth)acrylic acid and a linear or branched alkyl alcohol having 1 to 4 carbon atoms to which 2 to 20 moles of at least one selected from the group consisting of ethylene oxide, propylene oxide, and butylene oxide have been added.
Of the monomers (d), from the viewpoint of reducing the HTHS viscosity at 100° C., preferred are ethoxyethyl (meth)acrylate and butoxyethyl (meth)acrylate, and more preferred is n-butoxyethyl (meth)acrylate.

In (co)polymer (A), the weight proportion of monomer (d) among the constituent monomers of (A) is preferably 25% by weight or less, more preferably 1 to 20% by weight, and particularly preferably 5 to 15% by weight, based on the total weight of the monomers constituting (A), from the viewpoint of reducing the HTHS viscosity at 100°C.

In the monomer (e), ^R3 in the general formula (2) is a hydrogen atom or a methyl group, and from the viewpoint of the viscosity index improving effect, a methyl group is preferable.
In formula (2), -X ² - is a group represented by -O- or -NH-, and from the viewpoint of the effect of improving the viscosity index, a group represented by -O- is preferred.
In the general formula (2), ^R4 is an alkyl group having one carbon atom, such as a methyl group.
Specific examples of the monomer (e) include methyl (meth)acrylate and N-methyl(meth)acrylamide. Among the monomers (e), methyl (meth)acrylate is preferred from the viewpoint of the viscosity index improving effect.

In the (co)polymer (A), the weight proportion of the monomer (e) among the constituent monomers of (A) is preferably less than 0.2% by weight, based on the total weight of the monomers constituting (A), from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature, and more preferably is 0.1% by weight or less.

The monomer (f) is other than (a), and includes a (meth)acryloyl monomer (f1) having a linear alkyl group having 17 to 36 carbon atoms, and a (meth)acryloyl monomer (f2) having a branched alkyl group having 17 to 36 carbon atoms, represented by the following general formula (4), and the like.
The monomer (f) may be used alone or in combination of two or more kinds.
[In the general formula (4), R ⁸ is a hydrogen atom or a methyl group; -X ⁴ - is a group represented by -O- or -NH-; R ⁹ O is an alkyleneoxy group having 2 to 4 carbon atoms; R ¹⁰ and R ¹¹ each independently are a linear alkyl group having 1 to 24 carbon atoms, the total number of carbon atoms of R ¹⁰ and R ¹¹ being 15 to 34; s is an integer of 0 to 20, and when s is 2 or more, R ⁹ O may be the same or different.]

Examples of the (meth)acryloyl monomer (f1) having a linear alkyl group having 17 to 36 carbon atoms (hereinafter, sometimes abbreviated as monomer (f1)) include (meth)acrylic acid alkyl esters {esters of linear alkyl alcohols having 17 to 36 carbon atoms and acrylic acid, such as n-heptadecyl (meth)acrylate, n-octadecyl (meth)acrylate, n-icosyl (meth)acrylate, n-docosyl (meth)acrylate, n-tetracosyl (meth)acrylate, n-triacontyl (meth)acrylate, and n-hexatriacontyl (meth)acrylate}, esters of (meth)acrylic acid and 1 to 20 moles of an alkylene oxide (having 2 to 4 carbon atoms) adduct of a linear alkyl alcohol having 17 to 36 carbon atoms, and (meth)acrylic acid, and (meth)acrylic acid alkylamides {amides of linear alkylamines having 17 to 36 carbon atoms and acrylic acid, etc.}.
Among the monomers (f1), from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature, preferred are (meth)acrylic acid alkyl esters having a linear alkyl group having 17 to 28 carbon atoms, more preferred are (meth)acrylic acid esters having a linear alkyl group having 17 to 24 carbon atoms, and particularly preferred are (meth)acrylic acid esters having a linear alkyl group having 17 to 20 carbon atoms.
The monomer (f1) may be used alone or in combination of two or more kinds.

In the monomer (f2), ^R8 in the general formula (4) is a hydrogen atom or a methyl group. Among these, from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature, a methyl group is preferred.
In the general formula (4), -X ⁴ - is a group represented by -O- or -NH-. Of these, from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature, the group represented by -O- is preferred.
^R9 in the general formula (4) 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, an isopropylene group, a 1,2- or 1,3-propylene group, an isobutylene group, and a 1,2-, 1,3-, or 1,4-butylene group.
R ⁹ O is an alkyleneoxy group having 2 to 4 carbon atoms, such as an ethyleneoxy group, a 1,2- or 1,3-propyleneoxy group, and a 1,2-, 1,3-, or 1,4-butyleneoxy group.
In the general formula (4), s is an integer of 0 to 20, and from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature, an integer of 0 to 5 is preferable, and an integer of 0 to 2 is more preferable.
When s is 2 or more, R ⁹ O may be the same or different, and the (R ⁹ O) _s portion may be a random bond or a block bond.
In the general formula (4), R ¹⁰ and R ¹¹ are each independently a linear alkyl group having 1 to 24 carbon atoms. Specific examples include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-heptyl group, an n-hexyl group, an n-pentyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tetradecyl group, an n-hexadecyl group, an n-octadecyl group, an n-eicosyl group, and an n-tetracosyl group. Among the linear alkyl groups having 1 to 24 carbon atoms, from the viewpoint of increasing the molecular behavior of (A) with respect to temperature, it is preferable that either one of them is a linear alkyl group having 6 to 24 carbon atoms, more preferably either one is a linear alkyl group having 6 to 20 carbon atoms, and particularly preferably either one is a linear alkyl group having 8 to 16 carbon atoms.
The total number of carbon atoms in R ¹⁰ and R ¹¹ is 15 to 34, and from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature, it is preferably 15 to 30, and more preferably 15 to 26.

Specific examples of the monomer (f2) include 2-octyldecyl (meth)acrylate, an ester of ethylene glycol mono-2-octylpentadecyl ether and (meth)acrylic acid, 2-n-octyldodecyl (meth)acrylate, 2-n-decyltetradecyl (meth)acrylate, 2-n-dodecylhexadecyl (meth)acrylate, 2-n-tetradecyloctadecyl (meth)acrylate, 2-n-tetradecyloctadecyl (meth)acrylate, 2-n-tetradecyloctadecyl (meth)acrylate, and 2-n-tetradecyloctadecyl (meth)acrylate. dodecylpentadecyl, 2-n-tetradecylheptadecyl (meth)acrylate, 2-n-hexadecylheptadecyl (meth)acrylate, 2-n-heptadecylicosyl (meth)acrylate, 2-n-hexadecyldocosyl (meth)acrylate, 2-n-eicosyldocosyl (meth)acrylate, 2-n-tetracosylhexacosyl (meth)acrylate, and N-2-octyldecyl (meth)acrylamide.
The monomer (f2) may be used alone or in combination of two or more kinds.

Among the monomers (f2), from the viewpoints of solubility in hydrocarbon oils (such as GTL base oil (B)) and reduction in low-temperature viscosity, preferred are (meth)acryloyl monomers having a branched alkyl group with 17 to 32 carbon atoms, and particularly preferred are (meth)acryloyl monomers having a branched alkyl group with 17 to 28 carbon atoms.

In the (co)polymer (A), the weight proportion of the monomer (f) among the constituent monomers of (A) is preferably 5% by weight or less based on the total weight of the monomers constituting (A), from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature and from the viewpoint of the SP value calculated based on the weight fraction of (co)polymer (A).

When the (co)polymer (A) contains at least one monomer selected from the group consisting of monomer (d), monomer (e) and monomer (f) as a constituent monomer, the total weight ratio of monomer (d), monomer (e) and monomer (f) among the constituent monomers of (A) is preferably 3 to 30% by weight, more preferably 5 to 22% by weight, based on the total weight of the monomers constituting (A), from the viewpoint of enhancing the molecular behavior of (A) with respect to temperature.

The (co)polymer (A) in the present invention may contain, as constituent monomers, other monomers such as a phosphorus atom-containing monomer (g), an aromatic ring-containing vinyl monomer (h), the monomers (i) to (m), a nitrogen atom-containing monomer (n) and a hydroxyl group-containing monomer (o) in addition to the above monomers (a) to (f).
The monomers (g) to (o) may each be used alone or in combination of two or more.

Examples of the phosphorus atom-containing monomer (g) include the following monomers (g1) to (g2).

Phosphate ester group-containing monomer (g1):
Examples of such phosphates include (meth)acryloyloxyalkyl (carbon number: 2 to 4) 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, etc.]. Note that "(meth)acryloyloxy" means acryloyloxy or methacryloyloxy.

Phosphono group-containing monomer (g2):
Examples of the phosphonic acid include (meth)acryloyloxyalkyl (having 2 to 4 carbon atoms) phosphonic acids (such as (meth)acryloyloxyethyl phosphonic acid) and alkenyl (having 2 to 12 carbon atoms) phosphonic acids (such as vinyl phosphonic acid, allyl phosphonic acid, and octenyl phosphonic acid).

Among the monomers (g), (g1) is preferred, (meth)acryloyloxyalkyl (having 2 to 4 carbon atoms) phosphate ester is more preferred, and (meth)acryloyloxyethyl phosphate is particularly preferred.

Aromatic ring-containing vinyl monomer (h):
Examples of the vinyl styrene include styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, 4-ethylstyrene, 4-isopropylstyrene, 4-butylstyrene, 4-phenylstyrene, 4-cyclohexylstyrene, 4-benzylstyrene, 4-crotylbenzene, indene, and 2-vinylnaphthalene.

Among the monomers (h), styrene and α-methylstyrene are preferred, and styrene is more preferred.

Monomers (i) include those having two or more unsaturated groups, such as divinylbenzene, alkadienes having 4 to 12 carbon atoms (such as butadiene, isoprene, 1,4-pentadiene, 1,6-heptadiene, and 1,7-octadiene), (di)cyclopentadiene, vinylcyclohexene, and ethylidene bicycloheptene, limonene, ethylene di(meth)acrylate, polyalkylene oxide glycol di(meth)acrylate, pentaerythritol triallyl ether, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, trimethylolpropane tri(meth)acrylate, and esters of unsaturated carboxylic acids and glycols having an Mn of 500 or more, and esters of unsaturated alcohols and carboxylic acids, as described in International Publication WO01/009242.

Vinyl esters, vinyl ethers, vinyl ketones (j) (sometimes abbreviated as monomer (j)):
Examples of the vinyl esters 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 (k) (sometimes abbreviated as monomer (k)):
Examples thereof include glycidyl (meth)acrylate and glycidyl (meth)allyl ether.

Halogen-containing monomer (l) (sometimes abbreviated as monomer (l)):
Examples of the vinyl chloride include vinyl chloride, vinyl bromide, vinylidene chloride, (meth)allyl chloride, and halogenated styrenes (such as dichlorostyrene).

Ester (m) of unsaturated polycarboxylic acid (sometimes abbreviated as monomer (m)):
Examples of the alkyl, cycloalkyl, or aralkyl esters of unsaturated polycarboxylic acids include C1-8 alkyl diesters of unsaturated dicarboxylic acids (maleic acid, fumaric acid, itaconic acid, etc.) (dimethyl maleate, dimethyl fumarate, diethyl maleate, and dioctyl maleate).

The nitrogen atom-containing monomer (n) includes the following monomers (n1) to (n4) excluding the monomers (a) to (f).
Amide group-containing monomer (n1):
(meth)acrylamide, N-(N'-monoalkylaminoalkyl)(meth)acrylamide [one having an aminoalkyl group (having 2 to 6 carbon atoms) with one alkyl group having 1 to 4 carbon atoms bonded to a nitrogen atom; for example, N-(N'-methylaminoethyl)(meth)acrylamide, N-(N'-ethylaminoethyl)(meth)acrylamide, N-(N'-isopropylamino-n-butyl)(meth)acrylamide, and N-(N'-n- or isobutylamino-n-butyl)(meth)acrylamide, etc.], dialkyl(meth)acrylamide [one having two alkyl groups having 1 to 4 carbon atoms bonded to a nitrogen atom; for example, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, and N, N-di-n-butyl(meth)acrylamide, etc.], N-(N',N'-dialkylaminoalkyl)(meth)acrylamide [one having an aminoalkyl group (having 2 to 6 carbon atoms) in which two alkyl groups having 1 to 4 carbon atoms are bonded to the nitrogen atom of the aminoalkyl group; for example, N-(N',N'-dimethylaminoethyl)(meth)acrylamide, N-(N',N'-diethylaminoethyl)(meth)acrylamide, N-(N',N'-dimethylaminopropyl)(meth)acrylamide, and N-(N',N'-di-n-butylaminobutyl)(meth)acrylamide, etc.]; N-vinyl carboxylic acid amide [N-vinyl formamide, N-vinyl acetamide, N-vinyl-n- or isopropionic acid amide, and N-vinyl hydroxyacetamide, etc.].

Nitro group-containing monomer (n2):
4-nitrostyrene and the like.

Primary to tertiary amino group-containing monomer (n3):
Primary amino group-containing monomers {alkenylamines having 3 to 6 carbon atoms [(meth)allylamine, crotylamine, etc.], aminoalkyl (meth)acrylates (having 2 to 6 carbon atoms) [aminoethyl (meth)acrylate, etc.]}; secondary amino group-containing monomers {monoalkylaminoalkyl (meth)acrylates [having an aminoalkyl group (having 2 to 6 carbon atoms) with one alkyl group having 1 to 6 carbon atoms bonded to a nitrogen atom; for example, N-t-butylaminoethyl (meth)acrylate and N-methylaminoethyl (meth)acrylate, etc.], dialkenylamines having 6 to 12 carbon atoms [di(meth)allylamine, etc.]}; tertiary amino group-containing monomers {dialkylaminoalkyl (meth)acrylates [having an aminoalkyl group (having 2 to 6 carbon atoms) with one alkyl group having 1 to 6 carbon atoms bonded to a nitrogen atom; for example, N-t-butylaminoethyl (meth)acrylate and N-methylaminoethyl (meth)acrylate, etc.] Those having an aminoalkyl group (having 2 to 6 carbon atoms) to which two alkyl groups are bonded; for example, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, etc.], alicyclic (meth)acrylates having a nitrogen atom [morpholinoethyl (meth)acrylate, etc.], aromatic monomers [N-(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, etc.

Nitrile group-containing monomer (n4):
(Meth)acrylonitrile and the like.

Among the monomers (n), preferred are (n1) and (n3), and more preferred are N-(N',N'-diphenylaminoethyl)(meth)acrylamide, N-(N',N'-dimethylaminoethyl)(meth)acrylamide, N-(N',N'-diethylaminoethyl)(meth)acrylamide, N-(N',N'-dimethylaminopropyl)(meth)acrylamide, N,N-dimethylaminoethyl(meth)acrylate, and N,N-diethylaminoethyl(meth)acrylate.

Hydroxyl-containing monomer (o):
Hydroxyl-containing aromatic monomers (e.g., p-hydroxystyrene), hydroxyalkyl (C2-6) (meth)acrylates (e.g., 2-hydroxyethyl (meth)acrylate, 2- or 3-hydroxypropyl (meth)acrylate), mono- or bis-hydroxyalkyl (C1-4) substituted (meth)acrylamides (e.g., N,N-bis(hydroxymethyl)(meth)acrylamide, N,N-bis(hydroxypropyl)(meth)acrylamide, N,N-bis(2-hydroxybutyl)(meth)acrylamide), vinyl alcohol, alkenols having 3 to 12 carbon atoms (e.g., (meth)allyl alcohol, crotyl acrylamide, etc.), 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 (trihydric to octahydric) alcohols (glycerin, pentaerythritol, sorbitol, sorbitan, diglycerin, sugars, sucrose, etc.) [sucrose (meth)allyl ether, etc.], and the like;
Examples thereof include polyoxyalkylene glycols (alkylene group having 2 to 4 carbon atoms, polymerization degree 2 to 50), polyoxyalkylene polyols [polyoxyalkylene ethers of the above tri- to octahydric alcohols (alkylene group having 2 to 4 carbon atoms, polymerization degree 2 to 100)], mono(meth)acrylates of alkyl (carbon number 1 to 4) ethers of polyoxyalkylene glycols or polyoxyalkylene polyols [polyethylene glycol (Mn: 100 to 300) mono(meth)acrylate, polypropylene glycol (Mn: 130 to 500) mono(meth)acrylate, methoxypolyethylene glycol (Mn: 110 to 310) (meth)acrylate, lauryl alcohol ethylene oxide adduct (2 to 30 mol) (meth)acrylate, and polyoxyethylene mono(meth)acrylate (Mn: 150 to 230) sorbitan].

In the (co)polymer (A), the weight proportion of the monomer (g) among the constituent monomers of (A) is preferably 5% by weight or less, and more preferably 1% by weight or less, based on the total weight of the monomers constituting (A), from the viewpoint of the viscosity index improving effect.
In the (co)polymer (A), the weight proportion of the monomer (h) among the constituent monomers of (A) is, from the viewpoint of the viscosity index improving effect, preferably 5 wt % or less, more preferably 1 wt % or less, and particularly preferably 0.1 wt % or less, based on the total weight of the monomers constituting (A).
In the (co)polymer (A), the weight proportion of the monomer (i) among the constituent monomers of (A) is preferably 5% by weight or less from the viewpoint of the HTHS viscosity reducing effect at the effective temperature.
In the (co)polymer (A), the weight proportion of the monomer (j) among the constituent monomers of (A) is preferably 5% by weight or less based on the total weight of the monomers constituting (A), from the viewpoint of the viscosity index improving effect.
In the (co)polymer (A), the weight proportion of the monomer (k) among the constituent monomers of (A) is preferably 5% by weight or less based on the total weight of the monomers constituting (A), from the viewpoint of the viscosity index improving effect.
In the (co)polymer (A), the weight proportion of the monomer (l) among the constituent monomers of (A) is preferably 5% by weight or less based on the total weight of the monomers constituting (A), from the viewpoint of the viscosity index improving effect.
In the (co)polymer (A), the weight proportion of the monomer (m) among the constituent monomers of (A) is preferably 1% by weight or less based on the total weight of the monomers constituting (A), from the viewpoint of the viscosity index improving effect.
In the (co)polymer (A), the weight proportion of the monomer (n) among the constituent monomers of (A) is, from the viewpoint of the HTHS viscosity reducing effect and the viscosity index improving effect at the operating temperature, preferably 5 wt % or less, more preferably 3 wt % or less, and particularly preferably 1 wt % or less, based on the total weight of the monomers constituting (A).
In the (co)polymer (A), the weight proportion of the monomer (o) among the constituent monomers of (A) is, from the viewpoint of the HTHS viscosity reducing effect and the viscosity index improving effect, preferably 5% by weight or less, and more preferably 1% by weight or less, based on the total weight of the monomers constituting (A).

The Mw of the (co)polymer (A) is preferably 480,000 to 600,000 from the viewpoint of increasing the molecular behavior of (A) with respect to temperature. If the Mw of the (co)polymer (A) is 480,000 or more and 600,000 or less, the molecular behavior of (A) with respect to temperature tends to increase, the HTHS viscosity (100°C) tends to decrease, the kinetic viscosity at 40 to 80°C tends to decrease, and the storage modulus at low temperatures tends to decrease.

The molecular weight distribution (Mw/Mn) of the (co)polymer (A) is preferably from 1.0 to 4.0, more preferably from 1.5 to 3.5, from the viewpoint of shear stability.
The conditions for measuring the Mw and molecular weight distribution (Mw/Mn) of the (co)polymer (A) are the same as those for measuring the Mw and Mn of the monomer (a).

The (co)polymer (A) can be obtained by a known production method, specifically, a method of solution polymerization of the above-mentioned monomers in a solvent in the presence of a polymerization catalyst can be mentioned.
Examples of the solvent include toluene, xylene, alkylbenzene having 9 to 10 carbon atoms, methyl ethyl ketone, hydrocarbon oils (mineral oils, etc.), synthetic oils, and mixtures thereof.
Examples of the polymerization catalyst include azo catalysts (2,2'-azobis(2-methylbutyronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile), etc.), peroxide catalysts (benzoyl peroxide, cumyl peroxide, lauryl peroxide, etc.) and redox catalysts (mixtures of benzoyl peroxide and tertiary amines, etc.). Furthermore, known chain transfer agents (alkyl mercaptans having 2 to 20 carbon atoms, etc.) can also be used as necessary for molecular weight adjustment.
The polymerization temperature is preferably 25 to 140° C., more preferably 50 to 120° C. In addition to the above-mentioned solution polymerization, the (co)polymer (A) can also be obtained by bulk polymerization, emulsion polymerization or suspension polymerization.
The polymerization form of the (co)polymer (A) may be either a random addition polymer or an alternating copolymer, and may also be either a graft copolymer or a block copolymer.

The SP value calculated based on the weight fraction of the (co)polymer (A) is preferably 9.23 to 9.25 (cal/cm ³ ) ^1/2 .
If the SP value calculated based on the weight fraction of the (co)polymer (A) is 9.23 (cal/cm ³ ) ^1/2 or more, the molecular behavior of (A) with respect to temperature tends to be large, the kinetic viscosity at 40 to 80° C. tends to be low, and the storage modulus at low temperatures tends to be low. If the SP value is 9.25 (cal/cm ³ ) ^1/2 or less, the copolymer tends to be easily dissolved in hydrocarbon oils (especially GTL base oils (B), etc.).
The SP value calculated based on the weight fraction of the (co)polymer (A) means the SP value of the constituent units (structures in which vinyl groups have become single bonds by polymerization reaction) derived from each monomer constituting (A) calculated using the above-mentioned SP value calculation method, and the arithmetic average value 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 as atomic groups, so the SP value of the constituent units derived from methyl methacrylate is found to be 9.933 (cal/ ^cm3 ) ^1/2 according to the following formula. Similarly, the SP value of the constituent units derived from ethyl methacrylate is 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 copolymer is a polymer of 50% by weight of methyl methacrylate and 50% by weight of ethyl methacrylate, the SP value of the copolymer 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 shown below.
SP value of copolymer = (9.933 x 50 + 9.721 x 50) / 100 = 9.827
The SP value calculated based on the weight fraction of (A) can be adjusted to a desired range by appropriately adjusting the monomers and weight fractions 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.

<(Co)polymer (C)>
The lubricating oil composition of the present invention may further contain, in addition to the above-mentioned (co)polymer (A), a (meth)acrylic acid alkyl ester (co)polymer (C) other than (A), and it is preferable for the composition to contain the (co)polymer (C) from the viewpoint of low-temperature viscosity.
The (co)polymer (C) includes a (co)polymer that does not contain the monomer (a), and examples thereof include a (co)polymer having, as an essential constituent monomer, a (meth)acrylic acid alkyl ester (d) having a linear or branched alkyl group having 9 to 36 carbon atoms. Specifically, n-dodecyl (meth)acrylate, n-tetradecyl (meth)acrylate, n-hexadecyl (meth)acrylate and n-octadecyl (meth)acrylate copolymers, n-octadecyl (meth)acrylate/n-dodecyl (meth)acrylate (molar ratio 10-30/90-70) copolymers, n-tetradecyl (meth)acrylate/n-dodecyl (meth)acrylate (molar ratio 10-30/90-70) copolymers, n-hexadecyl (meth)acrylate/n-dodecyl (meth)acrylate/methyl (meth)acrylate (molar ratio 20-40/55-75/0-10) copolymers and n-dodecyl acrylate/n-dodecyl methacrylate (molar ratio 10-40/90-60) copolymers can be mentioned, and these may be used alone or in combination of two or more.

From the viewpoint of low-temperature viscosity, the content of (co)polymer (C) is preferably 0.01 to 30% by weight, more preferably 0.01 to 10% by weight, based on the weight of (co)polymer (A).

The Mw of the (co)polymer (C) is preferably from 5,000 to 100,000, and more preferably from 10,000 to 80,000, from the viewpoint of decreasing the pour point temperature.
The SP value calculated based on the weight fraction of the (co)polymer (C) is preferably 7.0 to 10, more preferably 8.0 to 9.5, from the viewpoint of solubility in the base oil.
The conditions for measuring the Mw of the (co)polymer (C) are the same as those for measuring the Mw of the above-mentioned monomer (a).

<GTL base oil (B)>
The lubricating oil composition of the present invention contains a GTL (Gas to Liquid) base oil (B). The GTL base oil is a base oil synthesized by the Fischer-Tropsch process for converting natural gas into liquid fuel.
Generally, base oils used in lubricating oils tend to have higher NOACK evaporation rates when their viscosity is low. However, GTL base oil (B) has an extremely low sulfur content and aromatic content, an extremely high paraffin composition ratio, excellent oxidation stability, and a tendency to have a low NOACK evaporation rate, as compared with, for example, mineral oils (oils refined from crude oil) of the same viscosity. It is presumed that the use of GTL base oil (B) tends to make it easier to adjust the kinetic viscosity (80°C, 60°C) in the effective temperature range low while keeping the NOACK evaporation rate low. In addition, by containing a GTL base oil (B) as a base oil, the temperature dependence of the behavior of the polymer chain of the (co)polymer (A) in the base oil (at low temperatures, the polyolefin chains aggregate so as to cover up the portions (e.g., ester groups) that are highly polar relative to the base oil, and at high temperatures, the polyolefin chains spread) becomes greater compared to the case where only a base oil other than a GTL base oil, such as mineral oil, is used as the base oil, and it is presumed that it is possible to lower the kinetic viscosity (80°C, 60°C) in the effective temperature range when the HTHS viscosity at 150°C is adjusted, and to lower the elasticity at low temperatures (-20°C).
The GTL base oil (B) may be used alone or in combination of two or more kinds, preferably in combination of two kinds.

The SP value of the GTL base oil (B) is preferably from 6 to 9 (cal/cm ³ ) ^1/2 , more preferably from 7 to 9 (cal/cm 3 ) ^1/2 , and particularly preferably from 8 to 9 (cal/cm ³ ) ^1/2 , from the viewpoint of the solubility of the (co)polymer (A ⁾ .
When a mixture of multiple hydrocarbon compounds is used as the GTL base oil (B), the approximate constituent components and their molecular structures can be determined by measuring the molecular weight by GPC and analyzing the molecular structure by ¹ H-NMR, ¹³ C-NMR, or the like, and the SP value of the GTL base oil (B) can be calculated from the arithmetic mean based on the molar fraction.

The kinetic viscosity (measured according to JIS-K2283, the same applies hereinafter) (unit: mm ² /s, hereinafter abbreviated) of the GTL base oil (B) at 100° C. is preferably 2.0 to 4.5, more preferably 2.0 to 3.5, from the viewpoint of reducing fuel consumption.
The lubricating oil composition preferably contains 80 wt % or more, more preferably 90 wt % or more, and particularly preferably 95 wt % or more, of a GTL base oil (B) having a kinematic viscosity at 100° C. in the above range, based on the weight of the GTL base oil (B) contained in the lubricating oil composition.
When two types of GTL base oils (B) are used in combination, from the viewpoint of reducing fuel consumption and maintaining a moderate amount of NOACK evaporation, it is preferable to use a GTL base oil having a kinetic viscosity at 100°C of 2.00 to 3.50 mm ² /s in combination with a GTL base oil having a kinetic viscosity at 100°C of 3.51 to 5.00 mm ² /s, and more preferably a GTL base oil having a kinetic viscosity at 100°C of 2.50 to 3.00 mm ² /s in combination with a GTL base oil having a kinetic viscosity at 100°C of 3.80 to 4.50 mm ² /s.

The kinematic viscosity (measured according to JIS-K2283, the same applies hereinafter) (unit: mm ² /s, hereinafter abbreviated) of the GTL base oil (B) at 40° C. is preferably 5.0 to 20.0, more preferably 8.0 to 19.0, from the viewpoint of reducing fuel consumption.

The viscosity index (measured according to JIS-K2283, the same applies below) of the GTL base oil (B) is preferably 90 or more, and more preferably 100 or more, from the viewpoint of the viscosity index improving effect of the lubricating oil composition.

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

The lubricating oil composition of the present invention may contain a base oil (G) other than the above GTL base oil (B).
Examples of the base oil (G) include hydrocarbon oils other than GTL base oils {mineral oils (solvent refined oils, paraffin oils, high viscosity index oils containing isoparaffin, high viscosity index oils obtained by hydrocracking isoparaffin, naphthenic oils, hydrocarbon-based synthetic lubricating oils (poly-α-olefin-based synthetic lubricating oils, etc.)}, non-hydrocarbon-based synthetic oils (ether-based synthetic lubricating oils, ester oils, silicon-based synthetic lubricating oils, etc.), and mixtures thereof. Of these, from the viewpoint of the solubility of the (co)polymer (A), preferred are hydrocarbon oils, and more preferred are mineral oils and poly-α-olefin-based synthetic lubricating oils.

The 40° C. kinematic viscosity (mm ² /s) of the base oil (G) is preferably 12-25, more preferably 15-22, from the viewpoint of reducing fuel consumption.
The 100° C. kinematic viscosity (mm ² /s) of the base oil (G) is preferably from 3.0 to 5.5, and more preferably from 3.5 to 5.0, from the viewpoint of reducing fuel consumption.
The content of the base oil (G) in the lubricating oil composition is preferably 5.0 to 15.0% by weight, more preferably 7.0 to 13.0% by weight, and particularly preferably 8.0 to 11.0% by weight, based on the weight of the lubricating oil composition, from the viewpoint of the solubility of the (co)polymer (A).

The 40°C kinematic viscosity ( ^mm2 /s) of the base oil (GTL base oil (B) or a mixture of (B) and base oil (G)) in the lubricating oil composition is preferably 7.0 to 15.0, more preferably 8.0 to 12.0, from the viewpoint of reducing fuel consumption.
The 100°C kinematic viscosity ( ^mm2 /s) of the base oil (GTL base oil (B) or a mixture of (B) and base oil (G)) in the lubricating oil composition is preferably 3.0 to 4.0, more preferably 3.3 to 3.8, from the viewpoint of reducing fuel consumption.

The SP value {(cal/cm ³ ) ^1/2 } of the base oil (GTL base oil (B) or a mixture of (B) and base oil (G)) in the lubricating oil composition is preferably 8.0 to 8.7, more preferably 8.1 to 8.6, and particularly preferably 8.2 to 8.5, from the viewpoint of the solubility of the (co)polymer (A).
When two or more types of base oils are used, it is preferable that the SP value of each base oil is calculated and the arithmetic mean value according to the weight fraction satisfies the above SP value.

<Additives>
The lubricating oil composition of the present invention contains a detergent and/or dispersant and an antioxidant.
In general, when a lubricating oil composition is used as an engine oil or the like, it is essential to contain a detergent and/or dispersant and an antioxidant in the lubricating oil composition from the viewpoint of effects other than the storage modulus at low temperatures (for example, oxidation stability, etc.), which is the effect of the present invention. However, even if the kinetic viscosity at 40 to 100 ° C. when the HTHS viscosity at 150 ° C. is adjusted to within a certain range in a composition that does not contain a detergent and/or dispersant and an antioxidant is within the numerical range of the present invention, the addition of a detergent and/or dispersant and an antioxidant increases the kinetic viscosity at 40 to 100 ° C. On the other hand, in the present invention, when a detergent and/or dispersant and an antioxidant are contained, the NOACK evaporation amount is kept low, while the kinetic viscosity (80 ° C., 60 ° C.) when the HTHS viscosity at 150 ° C. is adjusted to within a certain range is adjusted low, thereby making it possible to reduce the elasticity at low temperatures (-20 ° C.) and reduce fuel consumption.
The detergent and/or dispersant and the antioxidant may be included in the lubricating oil composition as a lubricating oil additive package in which multiple additives are combined.
The lubricating oil additive package may contain, in addition to the detergent, dispersant, and antioxidant, other additives (at least one selected from the group consisting of oiliness improvers, friction and wear modifiers, extreme pressure agents, antifoaming agents, demulsifiers, corrosion inhibitors, and pour point depressants).
"Containing a detergent and/or dispersant and an antioxidant" means containing a detergent and an antioxidant, containing a dispersant and an antioxidant, or containing a detergent, a dispersant and an antioxidant. In addition, an example of a lubricating oil additive package is a DI (Detergent Inhibitor) package.
As DI packages, those manufactured by Lubrizol Corporation {for example, the LUBRIZOL PV series (product name PV1510, etc.) for gasoline vehicles}, those manufactured by Chevron Corporation {for example, product names OLOA55501, OLOA55503, etc. for passenger car motor oils}, those manufactured by Afton Chemical Co. {for example, the HiTEC 9800 series, etc. for engine oils}, those manufactured by Infinium Corporation {for example, product name "P5741"}, etc. are commercially available and available.

Examples of the additive components include the following:
(1) Detergent:
Basic, overbased or neutral metal salts [such as overbased or alkaline earth metal salts of sulfonates (such as petroleum sulfonates, alkylbenzene sulfonates and alkylnaphthalene sulfonates)], salicylates, phenates, naphthenates, carbonates, phosphonates and mixtures thereof;
(2) Dispersant:
Succinimides (bis- or mono-polybutenyl succinimides), Mannich condensation products, and borates, etc.;
(3) Antioxidants:
Hindered phenols and aromatic secondary amines, etc.;
(4) Oiliness improver:
Long-chain fatty acids and their esters (such as oleic acid and oleic acid esters), long-chain amines and their amides (such as oleylamine and oleylamide), etc.;
(5) Pour point depressants: polyalkyl methacrylates, ethylene-vinyl acetate copolymers, 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) Defoaming agent:
Silicon oils, metal soaps, fatty acid esters, phosphate compounds, etc.;
(9) Demulsifier:
Quaternary ammonium salts (such as tetraalkylammonium salts), sulfated oils and phosphates (such as phosphates of polyoxyethylene-containing nonionic surfactants), hydrocarbon solvents (toluene, xylene, ethylbenzene), and the like;
(10) Metal deactivators Nitrogen atom-containing compounds (benzotriazole, etc.), nitrogen atom-containing chelate compounds (N,N'-disalicidene-1,2-diaminopropane, etc.), nitrogen and sulfur atom-containing compounds (2-(n-dodecylthio)benzimidazole, etc.), etc.;
(11) Corrosion inhibitor:
Nitrogen atom-containing compounds (such as benzotriazole and 1,3,4-thiodiazolyl-2,5-bisdialkyldithiocarbamate).

<Lubricating Oil Composition>
The lubricating oil composition of the present invention contains the (co)polymer (A), the ester oil (B), a detergent and/or dispersant and an antioxidant, and has an HTHS (high temperature high shear) viscosity at 150°C of 2.25 to 2.54 mPa·s, a kinematic viscosity at 80°C of 7.8 to 8.2 mm ² /s, a kinematic viscosity at 60°C of 11.8 to 12.4 mm ² /s, and a NOACK evaporation amount of 15 to 25 wt%.
The HTHS viscosity of the lubricating oil composition at 150°C of 2.25 to 2.54 mPa·s means that the viscosity is in accordance with the SAE standard 0W-16 ("0W" means the viscosity index (Winter Grade) at low temperature (when the engine is started), and "16" means the engine oil viscosity when the engine is warmed up).
In the present invention, although the lubricating oil composition contains additives that increase viscosity, such as a detergent and/or dispersant and an antioxidant, by combining the (co)polymer (A) with the GTL base oil (B), the NOACK evaporation amount of the lubricating oil composition is kept low, at 15 to 25% by weight, while the kinetic viscosities at 80°C and 60°C are adjusted to the above ranges, making it possible to reduce the elasticity at low temperatures (-20°C), thereby contributing to reduced fuel consumption.
The NOACK evaporation amount of the lubricating oil composition (measured by the method of ASTM D5800, a value measured at 250°C for 1 hour) is 15 to 25% by weight, and from the viewpoint of damage to the engine due to a decrease in the volatile residual amount of engine oil, it is preferably 17 to 25% by weight, and more preferably 19 to 24% by weight. The NOACK evaporation amount can be reduced by using a large amount of a base oil with a high viscosity, and can be increased by using a large amount of a base oil with a low viscosity.

The lubricating oil composition has an HTHS viscosity at 150° C. (according to ASTM D4683) of 2.25 to 2.54 mPa·s.
The HTHS viscosity at 150°C is the viscosity of the lubricating oil composition when it is subjected to shearing in a narrow gap between metals at a high temperature of 150°C, and the polymer chains of the (co)polymer (A) are oriented in the direction of flow and become elongated. It can be adjusted by the content of the (co)polymer (A), the molecular weight of the (co)polymer (A), the SP value calculated based on the weight fraction of the (co)polymer (A), the viscosity of the base oil contained, etc. For example, it can be lowered by reducing the content of (A), reducing the molecular weight of (A), increasing the SP value calculated based on the weight fraction of the (co)polymer (A), or using a base oil with a low viscosity (such as one with a small carbon number), and it can be increased by increasing the content of (A), increasing the molecular weight of (A), decreasing the SP value calculated based on the weight fraction of the (co)polymer (A), or using a base oil with a high viscosity.

The lubricating oil composition has a kinematic viscosity at 80°C (measured according to JIS-K2283, the same applies hereinafter) of 7.8 to 8.2 ^mm2 /s, and from the viewpoint of the elastic modulus at low temperature (-20°C), preferably 7.85 to 8.20 ^mm2 /s. If the kinematic viscosity at 80°C exceeds 8.2 ^mm2 /s, the elasticity at low temperature (-20°C) will be high, and if it is less than 7.8 ^mm2 /s, the NOACK evaporation amount will be high.
The lubricating oil composition has a kinetic viscosity at 60°C (measured according to JIS-K2283, the same applies below) of 11.8 to 12.4 ^mm2 /s, and from the viewpoint of the elastic modulus at low temperature (-20°C), preferably 12.0 to 12.4 ^mm2 /s. If the kinetic viscosity at 60°C exceeds 12.4 ^mm2 /s, the elasticity at low temperature (-20°C) will be high, and if it is less than 11.8 ^mm2 /s, the NOACK evaporation amount will be high.
In the present invention, when the HTHS viscosity at 150°C is adjusted to the above range, the kinematic viscosity (80°C, 60°C) is preferably low to the above range. Examples of the method of adjusting in this way include a method of adjusting (A) in the lubricating oil composition so that it spreads when sheared at 150°C (HTHS viscosity) but rapidly aggregates at temperatures below 80°C. Examples of the method of adjusting in this way include a method of adjusting the SP value calculated based on the weight fraction of (A) to the above range, a method of adjusting the weight ratio (b/a) or the weight ratio (b/c) to the above range, a method of adjusting the total weight ratio of the monomers (a), (b) and (c) constituting (A) to the above range, a method of adjusting the Mw of (A) to the above range, a method of adjusting the weight ratio (A/B) to the range described below, and a combination of these methods.

From the viewpoint of reducing fuel consumption, the ratio of the kinetic viscosity of the lubricating oil composition at 60°C to the kinetic viscosity at 80°C (60°C kinetic viscosity/80°C kinetic viscosity) is preferably 1.3 to 1.7, and more preferably 1.35 to 1.6.

From the viewpoint of reducing fuel consumption, the lubricating oil composition preferably has a kinematic viscosity at 100° C. of 6.00 to 6.70 mm ² /s, more preferably 6.10 to 6.60 mm ² /s.
The kinematic viscosity at 100° C. is the viscosity of the lubricating oil composition at 100° C. when the HTHS viscosity at 150° C. is adjusted to fall within the above range, and when the viscosity of the base oil is the same, it can be adjusted by adjusting the ease of aggregation or spreading of the (co)polymer (A) in the base oil at 100° C. For example, it can be lowered by using a large amount of highly polar monomers (e.g., monomers (b) and (d)) as constituent monomers of (A) within the above range to increase the SP value calculated based on the weight fraction of (A) and make aggregation easier, or by increasing the difference between the SP value calculated based on the weight fraction of (A) and the SP value of the base oil within the range described below to make aggregation easier. In addition, the SP value can be increased by using a large amount of monomers with low polarity (e.g., monomers (a) and (c)) as constituent monomers of (A) within the above range to lower the SP value calculated based on the weight fraction of (A) and make it difficult to aggregate, or by reducing the difference between the SP value calculated based on the weight fraction of (A) and the SP value of the base oil within the range described below to make it difficult to aggregate. In addition, when the SP value calculated based on the same weight fraction of (A) is the same, the SP value can be increased by increasing the Mw, and can be decreased by decreasing the Mw. In addition, the SP value can be decreased by using a large amount of base oil with a low 100°C kinetic viscosity, and can be increased by using a large amount of base oil with a high 100°C kinetic viscosity.

The lubricating oil composition preferably has a kinematic viscosity at 40° C. of 21.0 to 22.5 mm ² /s, more preferably 21.5 to 22.0 mm ² /s, from the viewpoint of the storage modulus at low temperatures.
The kinematic viscosity at 40 ° C. is the viscosity of the lubricating oil composition at 40 ° C. when the HTHS viscosity at 150 ° C. is adjusted to the above range, and when the viscosity of the base oil is the same, it can be adjusted by adjusting the ease of aggregation or spreading of the (co)polymer (A) in the base oil at 40 ° C. For example, it can be lowered by using a large amount of monomers with high polarity as the constituent monomers of (A) to make aggregation easier, or by increasing the difference between the SP value calculated based on the weight fraction of (A) and the SP value of the base oil to make aggregation easier. It can also be increased by using a large amount of monomers with low polarity as the constituent monomers of (A) to make aggregation harder, or by reducing the difference between the SP value calculated based on the weight fraction of (A) and the SP value of the base oil to make aggregation harder. It can also be lowered by using a large amount of base oil with a low kinematic viscosity at 40 ° C. within the amount range that can make the NOACK evaporation amount within the above range.
In the present invention, when the HTHS viscosity at 150° C. is adjusted to fall within the above range, it is preferable to adjust the kinetic viscosity at 40° C. low (preferably 21.0 to 22.5 mm ² /s) while keeping the kinetic viscosity at 100° C. to 6.00 mm ² /s or more. One method for such adjustment is to use a base oil that has a relatively high kinetic viscosity at 100° C. and a relatively low kinetic viscosity at 40° C. (a base oil with a high viscosity index).
Further, there is a method of adjusting (A) in the lubricating oil composition so that it spreads at 100° C. but aggregates at 40° C. Examples of such adjustment methods include a method of adjusting the SP value calculated based on the weight fraction of (A) to the above range, a method of adjusting the molecular weight of (A) to the above range, a method of adjusting the weight ratio (b/a) to the above range, a method of adjusting the weight ratio (b/c) to the above range, and a method of adjusting the total weight ratio of the monomers (a), (b) and (c) constituting (A) to the above range, which tend to increase the molecular behavior of (A) spreading at 100° C. but aggregating at 40° C.

The ratio of the kinetic viscosity at 40° C. to the kinetic viscosity at 100° C. (40° C. kinetic viscosity/100° C. kinetic viscosity) of the lubricating oil composition is preferably 3.0 to 4.0, more preferably 3.1 to 3.7, from the viewpoint of reducing fuel consumption.
From the viewpoint of reducing fuel consumption, the ratio of the kinetic viscosity at 60° C. to the kinetic viscosity at 100° C. of the lubricating oil composition (60° C. kinetic viscosity/100° C. kinetic viscosity) is preferably 1.8 to 2.1, and more preferably 1.8 to 2.0.
The ratio can be lowered, for example, by adjusting the molecular behavior of (A) in the lubricating oil composition relative to temperature (for example, spreading at 100° C. but coagulating at 40° C.).

The lubricating oil composition preferably has an HTHS viscosity at 100° C. (based on ASTM D4683) of 3.50 to 4.10 mPa·s, more preferably 3.60 to 4.00 mPa·s, from the viewpoint of reducing fuel consumption.
The HTHS viscosity at 100°C is the viscosity at 100°C in a state where the lubricating oil composition is subjected to shear (the oil is sheared in a narrow gap between metals, and (A) is oriented in the direction of flow and elongated) when the HTHS viscosity at 150°C is adjusted to the above range, and can be adjusted by adjusting the ease of aggregation or spreading of the (co)polymer (A) in the base oil at 100°C. For example, the viscosity can be lowered by using a large amount of highly polar monomers as the constituent monomers of (A) to make aggregation easier, or by increasing the difference between the SP value calculated based on the weight fraction of (A) and the SP value of the base oil to make aggregation easier, and can be increased by using a large amount of less polar monomers as the constituent monomers of (A) to make aggregation harder, or by decreasing the difference between the SP value calculated based on the weight fraction of (A) and the SP value of the base oil to make aggregation harder.
In addition, if the molecular weight of the (co)polymer (A) is increased, the amount of (A) added decreases and the HTHS viscosity (100°C), which is the viscosity under shear stress, tends to decrease, but the kinetic viscosity (100°C) tends to increase because the thickening effect due to the increased molecular weight outweighs the viscosity decrease due to the decreased amount added. Therefore, when the constituent monomers of (A) are the same, it is possible to increase the kinetic viscosity (100°C) while decreasing the HTHS viscosity (100°C) by adjusting the molecular weight.

From the viewpoint of reducing fuel consumption, the viscosity index of the lubricating oil composition is preferably 250 or more, more preferably 250 to 290, and particularly preferably 260 to 280.

The storage modulus G' of the lubricating oil composition (measurement temperature -20°C, measurement conditions are described below) is preferably 125 Pa or less, and more preferably 90 to 120 Pa, from the viewpoint of reducing fuel consumption.

The content of the (co)polymer (A) in the lubricating oil composition is, from the viewpoints of the storage modulus at low temperatures, the effect of improving the viscosity index, and costs, preferably from 0.1 to 10% by weight, more preferably from 0.1 to 5% by weight, even more preferably from 0.5 to less than 3% by weight, and particularly preferably from 0.8 to 2.8% by weight, based on the weight of the lubricating oil composition.
The content of the GTL base oil (B) in the lubricating oil composition is preferably 70 to 94 wt %, more preferably 75 to 90 wt %, and particularly preferably 78 to 85 wt %, based on the weight of the lubricating oil composition, from the viewpoints of reducing fuel consumption and costs.
The content of the base oil (G) in the lubricating oil composition is preferably 2 to 15 wt %, more preferably 5 to 13 wt %, and particularly preferably 8 to 12 wt %, based on the weight of the lubricating oil composition, from the viewpoints of reducing fuel consumption and costs.
The content of additives (the total of detergents, dispersants, antioxidants and other additives) in the lubricating oil composition is, from the viewpoints of fuel consumption reduction and cost, preferably 3 to 12% by weight, more preferably 4 to 12% by weight, and particularly preferably 5 to 12% by weight, based on the weight of the lubricating oil composition.
The weight ratio (B/A) of the GTL base oil (B) to the (co)polymer (A) in the lubricating oil composition is preferably 20 to 50, more preferably 25 to 45, and particularly preferably 28 to 40, from the viewpoints of reducing fuel consumption and costs.
The weight ratio (G/A) of the (co)polymer (A) to the base oil (G) in the lubricating oil composition is preferably 2.0 to 7.0, more preferably 3.0 to 6.0, and particularly preferably 3.5 to 5.0, from the viewpoints of reducing fuel consumption and costs.
The weight ratio (B/G) of the GTL base oil (B) to the base oil (G) in the lubricating oil composition is preferably 6.0 to 12.0, more preferably 7.0 to 11.0, and particularly preferably 7.5 to 10.0, from the viewpoints of reducing fuel consumption and costs.

The lubricating oil composition of the present invention can be particularly suitably used as a lubricating oil composition for internal combustion engines, and in particular as a lubricating oil composition for hybrid vehicles.

The present invention will be further explained below with reference to examples and comparative examples, but the present invention is not limited to these.

The ratio of 1,2-butylene groups in the structural units of the hydrocarbon polymer was determined by analyzing the polymer by ^13C -NMR and using the above-mentioned formula (1) according to the method described above, and the total ratio of isobutylene groups and 1,2-butylene groups was determined by analyzing the polymer by ^13C -NMR and using the above-mentioned formula (2) according to the method described above.
The molar ratio of 1,2-adduct/1,4-adduct in a hydrocarbon polymer (the molar ratio in a structure derived from butadiene) was calculated by analyzing the polymer by ^13C -NMR and using the values of integral values B and C used in the above formula (1) according to the following formula (3):
Molar ratio of 1,2-adduct/1,4-adduct={100×integral value B×4/integral value C}/{100−(100×integral value B×4/integral value C)} (3)

<Production Example 1>
Into a 1 L SUS pressure-resistant reaction vessel equipped with a temperature controller and a stirrer, 400 parts by weight of degassed and dehydrated hexane, 0.5 parts by weight of tetrahydrofuran, 90 parts by weight of 1,3-butadiene, and 0.9 parts by weight of n-butyllithium were charged, and then polymerization was carried out at a polymerization temperature of 50° C.
After the polymerization rate reached nearly 100%, 2 parts by weight of ethylene oxide was added and the reaction was allowed to proceed for an additional 3 hours at 50° C. To terminate the reaction, 50 parts by weight of water and 25 parts by weight of a 1N aqueous hydrochloric acid solution were added and stirred for 1 hour at 80° C. The organic phase of the reaction solution was recovered in a separatory funnel and heated to 70° C., after which the solvent was removed under a reduced pressure of 0.027 to 0.040 MPa over 2 hours.
The obtained polybutadiene containing a hydroxyl group at one end was transferred to a reaction vessel equipped with a temperature control device, a stirrer, and a hydrogen inlet tube, and 150 parts by weight of tetrahydrofuran was added to dissolve it uniformly. A suspension of 10 parts by weight of palladium carbon and 50 parts by weight of tetrahydrofuran was poured thereinto, and then the mixture was reacted at room temperature for 8 hours while hydrogen was supplied to the liquid from the hydrogen inlet tube at a flow rate of 30 mL/min. The palladium carbon was then removed by filtration, and the obtained filtrate was heated to 70°C and tetrahydrofuran was removed under reduced pressure of 0.027 to 0.040 MPa to obtain a hydrogenated polybutadiene containing a hydroxyl group at one end polymer (Y1).
The molecular weight of the obtained (Y1) was measured by GPC, and the ratio of 1,2-butylene groups was measured by ^13C -NMR, with the results being Mw=7,000, Mn=6,500, the ratio of 1,2-butylene groups=45 mol%, and the molar ratio (1,2-adduct/1,4-adduct)=45/55.

<Production Example 2>
Into a 1 L SUS pressure-resistant reaction vessel equipped with a temperature controller and a stirrer, 400 parts by weight of degassed and dehydrated hexane, 2 parts by weight of tetrahydrofuran, 90 parts by weight of 1,3-butadiene, and 0.9 parts by weight of n-butyllithium were charged, and then polymerization was carried out by lowering the polymerization temperature to minus 0°C.
After the polymerization rate reached nearly 100%, 2 parts by weight of ethylene oxide was added and reacted at 50° C. for 3 hours. To terminate the reaction, 50 parts by weight of water and 25 parts by weight of a 1N aqueous hydrochloric acid solution were added and stirred at 80° C. for 1 hour. The organic phase of the reaction solution was recovered in a separatory funnel and heated to 70° C., after which the solvent was removed under a reduced pressure of 0.027 to 0.040 MPa over 2 hours.
The obtained polybutadiene containing a hydroxyl group at one end was transferred to a reaction vessel equipped with a temperature control device, a stirrer, and a hydrogen inlet tube, and 150 parts by weight of tetrahydrofuran was added to dissolve it uniformly. A suspension of 10 parts by weight of palladium carbon and 50 parts by weight of tetrahydrofuran was poured thereinto, and then the mixture was reacted at room temperature for 8 hours while hydrogen was supplied to the liquid from the hydrogen inlet tube at a flow rate of 30 mL/min. The palladium carbon was then removed by filtration, and the obtained filtrate was heated to 70°C and tetrahydrofuran was removed under a reduced pressure of 0.027 to 0.040 MPa to obtain a hydrogenated polybutadiene containing a hydroxyl group at one end polymer (Y2).
The molecular weight of the obtained (Y2) was measured by GPC, and the ratio of 1,2-butylene groups was measured by ^13C -NMR, giving the following results: Mw=7,000, Mn=6,500, the ratio of 1,2-butylene groups=65 mol%, and the molar ratio (1,2-adduct/1,4-adduct)=65/35.

<Examples 1 to 13 and Comparative Examples 1 to 8>
<Preparation of composition containing copolymers (A-1) to (A-19)>
In a reaction vessel equipped with a stirrer, a heating/cooling device, a thermometer, and a nitrogen inlet tube, 400 parts of mineral oil 1 described below, a total amount of 100 parts by weight of the monomer blends described in Tables 2-3, and 2,2-azobis(2,4-dimethylvaleronitrile), 2,2-azobis(2-methylbutyronitrile), and t-butylperoxy-2-ethylhexyl monocarbonate as catalysts were added in the amounts described in Tables 2-3, and nitrogen replacement (gas phase oxygen concentration 100 ppm) was performed. The mixture was then heated to 76°C while stirring under a sealed condition, and polymerization reaction was carried out at the same temperature for 4 hours. After heating to 120-130°C, unreacted monomers were removed at the same temperature under reduced pressure (0.027-0.040 MPa) over 2 hours to obtain a composition containing copolymer (A) and mineral oil 1. The SP value (SP value of (A)) calculated based on the weight fraction of the resulting copolymer (A) was calculated by the above-mentioned method, and Mw was measured by the above-mentioned method.

<Preparation of Lubricating Oil Composition>
The copolymer (A)-containing composition obtained above, other additives, and base oil were blended in the amounts shown in Tables 2 and 3 to obtain lubricating oil compositions. The content of copolymer (A) in the tables refers to the pure content (wt%) of copolymer (A) contained in the lubricating oil composition, with the total amount of the lubricating oil composition taken as 100 wt%. The obtained lubricating oil compositions were evaluated for various physical properties. The results are shown in Tables 2 and 3.

The compositions of the monomers (a) to (d) shown in Tables 2 and 3 are as follows.
(a-1): Methacrylic acid ester of the one-terminal hydroxyl group-containing polymer (1,2-butylene ratio=45 mol%) (Y1) of the hydrogenated polybutadiene obtained in Production Example 1 [Mn: 6,600, p=0 in the general formula (1), -X ¹ -=-O(CH ₂ CH ₂ O) ₁ -]
(a-2): Methacrylic acid ester of the one-terminal hydroxyl group-containing polymer (1,2-butylene ratio=65 mol%) (Y2) of the hydrogenated polybutadiene obtained in Production Example 2 [Mn: 6,600, p=0 in the general formula (1), -X ¹ -=-O(CH ₂ CH ₂ O) ₁ -]
(a-3): An esterification product of one-terminal hydroxyl group-containing hydrogenated polybutadiene (trade name: Krasol HLBH-5000M, 1,2-butylene ratio = 65 mol%, molar ratio (1,2-adduct/1,4-adduct) = 65/35, crystallization temperature -60°C or lower) manufactured by Cray Valley (Paris, France) and methacrylic acid (Mn: 4,800, p = 0 in general formula (1), -X ¹ - = -O-)
(b-1): n-butyl methacrylate (b-2): ethyl methacrylate (c-1): methacrylic acid ester of Neodol 23 (Shell Chemicals, a mixture of linear or branched alkyl alcohols having 12 to 13 carbon atoms (weight ratio = linear C12: branched C12: linear C13: branched C13 = 40:10:40:10))
(c-2): Methacrylic acid ester of Neodol 45 (Shell Chemicals, a mixture of linear or branched alkyl alcohols having 14 to 15 carbon atoms (weight ratio = linear C14: branched C14: linear C15: branched C15 = 40:10:40:10)) (d-1): Ethoxyethyl methacrylate (d-2): Butoxyethyl methacrylate

The base oils and DI packages listed in Tables 2-3 are as follows:
Mineral oil 1: SK Lubricants, product name "Yubase 4", Group III (SP value: 8.3, kinetic viscosity at 100°C: 4.2 mm ² /s, kinetic viscosity at 40°C: 19.6 mm ² /s)
Mineral oil 2: SK Lubricants, product name "Yubase 3", Group III (SP value: 8.3, kinetic viscosity at 100°C: 3.1 mm ² /s, kinetic viscosity at 40°C: 12.3 mm ² /s)
GTL base oil 1: Group III (SP value: 8.3, kinematic viscosity at 100°C: 4.1 ^mm2 /s, kinematic viscosity at 40°C: 18 ^mm2 /s)
GTL base oil 2: Group III (SP value: 8.3, kinematic viscosity at 100°C: ^2.7 mm2/s, kinematic viscosity at 40°C: 9.9 ^mm2 /s)
P5741: Infinium Co., Ltd., a package additive containing detergents, dispersants, antioxidants, etc. PV1510: Lubrizol Co., Ltd., a DI package, a package additive containing detergents, dispersants, antioxidants, etc.

The SP value of the constitutional unit derived from each monomer (a structure in which a carbon-carbon double bond has reacted to form a single bond) was calculated based on the following formula.
Structural unit derived from (a-1)
Structure (1) ΣΔe _i = 1125 (CH ₃ ) + 1180 (CH ₂ ) + 350 (C) + 4300 (CO ₂ ) = 6955
Σv _i = 33.5 (CH ₃ ) + 16.1 (CH ₂ ) - 19.2 (C) + 18.0 (CO ₂ ) = 48.4
Structure (2) ΣΔe _i = 1180 (CH ₂ ) × 2 + 800 (O) = 3160
Σv _i = 16.1(CH ₂ ) × 2 + 3.8(O) = 36
Structure (3) ΣΔe _i = 1180 (CH ₂ ) × 2 + 1125 (CH ₃ ) + 820 (CH) = 4305
Σv _i = 16.1 (CH ₂ ) × 2 + 33.5 (CH ₃ ) - 1.0 (CH) = 64.7
Structure (4) ΣΔe _i = 1180 (CH ₂ ) × 4 = 4720
Σv _i =16.1(CH ₂ )×4=64.4
Here, the total number of 1,2-butylene groups and 1,4-butylene groups is as follows:
Total number of 1,2-butylene groups (structure (3)) and 1,4-butylene groups (structure (4))=(6600−86(structure (1))−44(structure (2)))/56=115.55
Therefore, the parameters of the constitutional unit derived from (a-1) are as follows.
ΣΔe _i = 6955 + 3160 + 4305 × 115.55 × 0.45 + 4720 × 115.55 × 0.55 = 533948.2
Σv _i = 48.4 + 36 + 64.7 × 115.55 × 0.45 + 64.4 × 115.55 × 0.55 = 7541.6497
SP value = (ΣΔe _i /Σv _i ) ^1/2 = (533948.2/7541.6497) ^1/2 = 8.414

Structural unit derived from (a-2)
Total number of 1,2-butylene groups and 1,4-butylene groups=(6600−85−44)/56=115.55
ΣΔe _i = 6955 + 3160 + 4305 × 115.55 × 0.65 + 4720 × 115.55 × 0.35 = 524357.3
Σv _i = 48.4 + 36 + 64.7 × 115.55 × 0.65 + 64.4 × 115.55 × 0.35 = 7548.583
SP value = (ΣΔe _i /Σv _i ) ^1/2 = (524357.3/7548.583) ^1/2 = 8.335

Structural unit derived from (a-3)
Total number of 1,2-butylene groups and 1,4-butylene groups=(4800−85)/56=84.20
ΣΔe _i = 6955 + 4305 × 84.20 × 0.65 + 4720 × 84.20 × 0.35 = 381650.2
Σv _i = 48.4 + 64.7 × 84.20 × 0.65 + 64.4 × 84.20 × 0.35 = 5487.068
SP value = (ΣΔe _i /Σv _i ) ^1/2 = (381650.2/5487.068) ^1/2 = 8.340

Structural unit derived from (b-1) ΣΔe _i = 6955 + 1180 × 3 + 1125 = 11620
Σv _i = 48.4 + 16.1 × 3 + 33.5 = 130.2
SP value = (ΣΔe _i /Σv _i ) ^1/2 = (11620/130.2) ^1/2 = 9.447
Structural unit derived from (b-2) ΣΔe _i = 6955 + 1180 + 1125 = 9260
Σv _i = 48.4 + 16.1 + 33.5 = 98
SP value = (ΣΔe _i /Σv _i ) ^1/2 = (9260/98) ^1/2 = 9.721

Straight chain C12 structural unit derived from (c-1)
ΣΔe _i = 6955 + 1180 × 11 + 1125 = 21060
Σv _i = 48.4 + 16.1 × 11 + 33.5 = 259
SP value = (ΣΔe _i /Σv _i ) ^1/2 = (21060/259) ^1/2 = 9.017
Branch C12
ΣΔe _i = 6955 + 1180 × 9 + 1125 × 2 + 820 = 20645
Σv _i = 48.4 + 16.1 × 9 + 33.5 × 2 − 1.0 = 259.3
SP value = (ΣΔe _i /Σv _i ) ^1/2 = (20645/259.3) ^1/2 = 8.923
Linear C13
ΣΔe _i = 6955 + 1180 × 12 + 1125 = 22240
Σv _i = 48.4 + 16.1 × 12 + 33.5 = 275.1
SP value = (ΣΔe _i /Σv _i ) ^1/2 = (22240/275.1) ^1/2 = 8.991
Branch C13
ΣΔe _i = 6955 + 1180 × 10 + 1125 × 2 + 820 = 21825
Σv _i = 48.4 + 16.1 × 10 + 33.5 × 2 - 1.0 = 275.4
SP value = (ΣΔe _i /Σv _i ) ^1/2 = (21825/275.4) ^1/2 = 8.902
SP value of the constitutional unit derived from (c-1)=(9.017×40+8.923×10+8.991×40+8.902×10)/100=8.986

Straight chain C14 structural unit derived from (c-2)
ΣΔe _i = 6955 + 1180 × 13 + 1125 = 23420
Σv _i = 48.4 + 16.1 × 13 + 33.5 = 291.2
SP value = (ΣΔe _i /Σv _i ) ^1/2 = (23420/291.2) ^1/2 = 8.968
Branch C14
ΣΔe _i = 6955 + 1180 × 11 + 1125 × 2 + 820 = 23005
Σv _i = 48.4 + 16.1 × 11 + 33.5 × 2 - 1.0 = 291.5
SP value = (ΣΔe _i /Σv _i ) ^1/2 = (23005/291.5) ^1/2 = 8.884
Linear C15
ΣΔe _i = 6955 + 1180 × 14 + 1125 = 24600
Σv _i = 48.4 + 16.1 × 14 + 33.5 = 307.3
SP value = (ΣΔe _i /Σv _i ) ^1/2 = (24600/307.3) ^1/2 = 8.947
Branch C15
ΣΔe _i = 6955 + 1180 × 12 + 1125 × 2 + 820 = 24185
Σv _i = 48.4 + 16.1 × 12 + 33.5 × 2 - 1.0 = 307.6
SP value = (ΣΔe _i /Σv _i ) ^1/2 = (24185/307.6) ^1/2 = 8.867
SP value of the constitutional unit derived from (c-2)=(8.968×40+8.884×10+8.947×40+8.867×10)/100=8.941

Structural unit derived from (d-1) ΣΔe _i = 6955 + 3160 + 1180 + 1125 = 12420
Σv _i = 48.4 + 36 + 16.1 + 33.5 = 134
SP value = (ΣΔe _i /Σv _i ) ^1/2 = (12420/134) ^1/2 = 9.627
Structural unit derived from (d-2) ΣΔe _i = 6955 + 3160 + 1180 × 3 + 1125 = 14780
Σv _i = 48.4 + 36 + 16.1 × 3 + 33.5 = 166.2
SP value = (ΣΔe _i /Σv _i ) ^1/2 = (14780/166.2) ^1/2 = 9.430

<Method for measuring NOACK evaporation amount of lubricating oil composition>
Measurement was performed according to the method of ASTM D 5800 (measurement conditions: 250° C., 1 hour).

<Method for measuring HTHS viscosity of lubricating oil composition>
Measured at 100°C and 150°C according to the method of ASTM D 4683.

<Method of measuring kinematic viscosity of lubricating oil composition and method of calculating viscosity index>
The kinematic viscosity was measured at 40° C., 60° C., 80° C. and 100° C. according to the method of JIS-2283, and the viscosity index was calculated according to the method of JIS-2283. A higher viscosity index value means a higher viscosity index improving effect.

<Method for measuring storage modulus (-20°C) of lubricating oil composition--Rheometer>
The measurements were performed using a rheometer "Physica MCR302" manufactured by Anton Paar, in the following manner. First, the target sample oil was inserted into a cone plate (diameter 50 mm, inclination angle 1°) and held at -20°C for 10 minutes. At this time, care was taken not to distort the inserted solution. Then, the storage modulus G' was measured at -20°C, a frequency of 1 Hz, shear strain of 0.00996 to 100%, and in vibration mode. In the above measurements, the value of the storage modulus G' (Pa) at a shear strain of 0.0096% is shown in the table.

The results in Tables 2 and 3 show that the lubricating oil composition of the present invention maintains appropriate volatility at 250°C, while reducing kinetic viscosity in the effective temperature range (particularly 80°C and 60°C), and exhibits low viscoelasticity at low temperatures (-20°C), making it excellent.
On the other hand, it is clear that the lubricating oil compositions of Comparative Examples 1 to 8, which have high kinetic viscosities in the effective temperature range (particularly 80°C and 60°C), are inferior in storage modulus at low temperature (-20) compared to the Examples.

The lubricating oil composition of the present invention has excellent elasticity at low temperatures (-20°C) and is therefore expected to have a fuel consumption reducing effect. Therefore, the composition is suitably used in gear oils (differential oils, industrial gear oils, etc.), MTFs, transmission fluids [ATFs, DCTFs, belt-CVTFs, etc.], traction oils (toroidal-CVTFs, etc.), shock absorber oils, power steering oils, hydraulic oils (hydraulic oils for construction machinery, hydraulic oils for industrial use, etc.) and engine oils (for gasoline and diesel engines), and can be particularly suitably used as a lubricating oil composition for internal combustion engines, in particular as a lubricating oil composition for hybrid vehicles.

Claims (7)

a (co)polymer (A) having a main chain having a repeating unit derived from a polymerizable monomer and a side chain having a polyolefin structure;
GTL base oil (B),
A lubricating oil composition comprising a detergent and/or dispersant and an antioxidant,
The lubricating oil composition has an HTHS viscosity at 150°C of 2.25 to 2.54 mPa·s, a kinematic viscosity at 80°C of 7.8 to 8.2 mm ² /s, a kinematic viscosity at 60°C of 11.8 to 12.4 mm ² /s, and a NOACK evaporation amount of the lubricating oil composition of 15 to 25% by weight, wherein the (co)polymer (A) is a polyolefin monomer (a) represented by the following general formula (1), a monomer (b) represented by the following general formula (2) in which R ^{4 is an alkyl group having 2 to 4 carbon atoms, and a monomer (c) represented by the following general formula (3) in which R 5} is an alkyl group having 2 to 4 carbon atoms. and a monomer (c) in which ⁴ is an alkyl group having 12 to 16 carbon atoms, as constituent monomers, wherein the number average molecular weight of the monomer (a) is 6,600 to 8,500, the solubility parameter calculated based on the weight fraction of the (co) polymer (A) is 9.23 to 9.25 (cal/ ^cm3 ) ^1/2 , the weight percentage of the monomer (a) is 12 to 21 wt%, the weight percentage of the monomer (b) is 54 to 75 wt%, and the weight percentage of the monomer (c) is 3 to 17 wt%, based on the total weight of the monomers constituting the (co)polymer (A), and the total weight percentage of the monomers (a), (b) and (c) is 70 wt% or more.
[In general formula (1), R ¹ is a hydrogen atom or a methyl group; -X ¹ - is a group represented by -O(AO) _m , A is an alkylene group having 2 carbon atoms, and m is an integer of 1; R ² is a residue obtained by removing one hydrogen atom from a hydrocarbon polymer containing 1,2-butylene groups as a structural unit, the constituent monomer of the hydrocarbon polymer is 1,3-butadiene, and the ratio of 1,2-butylene groups is 45 to 65 mol % based on the total number of moles of the constituent monomers of the hydrocarbon polymer; and p is 0.]
[In the general formula (2), R ³ is a hydrogen atom or a methyl group; -X ² - is a group represented by -O-; and R ⁴ is an alkyl group having 2 to 4 or 12 to 16 carbon atoms.] The lubricating oil composition according to claim 1, wherein the weight average molecular weight of the (co)polymer (A) is 480,000 to 600,000. The lubricating oil composition according to claim 1 or 2, which is a copolymer in which the weight ratio (b/a) of the monomer (a) to the monomer (b) constituting the (co)polymer (A) is 3.5 to 4.9, and the weight ratio (b/c) of the monomer (b) to the monomer (c) is 4.1 or more. The lubricating oil composition according to claim 1 or 2, containing 0.1 to 10% by weight of the (co)polymer (A). The lubricating oil composition according to claim 1 or 2, wherein the GTL base oil (B) has a 100° C. kinematic viscosity of 2.0 to 4.5 mm ² /s. The lubricating oil composition according to claim 1 or 2, further comprising at least one additive selected from the group consisting of an oiliness improver, a friction and wear modifier, an extreme pressure agent, an antifoaming agent, an antiemulsifier, a corrosion inhibitor, and a pour point depressant. The lubricating oil composition according to claim 1 or 2, wherein the lubricating oil composition has a viscosity index of 250 or more.