Viscosity index improver and lubricating oil composition

Abstract

The present invention aims to provide a viscosity index improver and a lubricating oil composition containing the viscosity index improver, wherein the lubricating oil composition to which the viscosity index improver is added has an excellent friction reduction effect. The present invention relates to a viscosity index improver, etc., which comprises a (co)polymer (A) containing a polyolefin monomer (a) represented by the following general formula (1) as an essential constituent monomer, and a (co)polymer (A) having a kinematic viscosity of 1.00 to 2.50 mm at 100°C. 2 / s ester oil (B1) and 100℃ kinematic viscosity of 2.51~5.00mm 2 / s of ester oil (B2). [In the general formula (1), R 1 is a hydrogen atom or a methyl group; 1 ‑is‑O‑,‑O(AO) m A is an alkylene group having 2 to 4 carbon atoms, m is an integer of 1 to 10, and when m is 2 or more, A may be the same or different; R 2 A residue obtained by removing one hydrogen atom from a hydrocarbon polymer containing a 1,2-butylene group as a structural unit; p is a number of 0 or 1.]

Description

Technical Field

[0001] The present invention relates to viscosity index improvers and lubricating oil compositions. Background Art

[0002] In recent years, in order to achieve the reduction of CO2 emissions and the protection of oil resources, there is a further demand for automobiles to be more fuel-efficient. As one of the measures for fuel efficiency, it is possible to reduce the viscosity of the engine oil to reduce the viscous resistance. However, if the viscosity is reduced, there will be risks related to mechanical protection such as leakage and burning. In the 0W-20 grade and 0W-16 grade in the SAE engine oil viscosity standard (SAE J300) in the United States, the viscosity at high temperature and high shear (HTHS viscosity) is stipulated as 2.6 mPa·s and 2.3 mPa·s or more at 150°C HTHS viscosity (ASTM D4683 or D5481) respectively. Regarding fuel efficiency, in addition to meeting the above viscosity standards, an engine oil with a lower HTHS viscosity in the effective temperature range of 80°C or 100°C is required. In addition, in order to suppress friction and wear of the engine, an engine oil with good friction characteristics is required.

[0003] Therefore, as a method for improving viscosity characteristics, a method of adding a viscosity index improver to lubricating oil has been widely used. As such a viscosity index improver, methacrylate copolymers (Patent Documents 1 to 4), olefin copolymers (Patent Document 5), and macromonomer copolymers (Patent Document 6) are known. In addition, a viscosity index improver in which an ester oil is used in combination with a diluent oil is also known (Patent Document 7).

[0004] However, the above-mentioned viscosity index improvers have problems such as a decrease in viscosity in an effective temperature range and insufficient friction characteristics when added to an engine oil composition.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 2732187

[0008] Patent Document 2: Japanese Patent No. 2941392

[0009] Patent Document 3: Japanese Patent Application Laid-Open No. 7-62372

[0010] Patent Document 4: Japanese Patent Application Publication No. 2004-307551

[0011] Patent Document 5: Japanese Patent Application Publication No. 2005-200454

[0012] Patent Document 6: Japanese Patent Application No. 2008-546894

[0013] Patent Document 7: Japanese Patent No. 5591327 Summary of the invention

[0014] Problems to be solved by the invention

[0015] An object of the present invention is to provide a viscosity index improver and a lubricating oil composition containing the viscosity index improver, wherein the lubricating oil composition to which the viscosity index improver is added has an excellent friction reducing effect.

[0016] Means for solving problems

[0017] The present inventors have conducted studies to achieve the above-mentioned object and have completed the present invention as a result.

[0018] That is, the present invention relates to a viscosity index improver comprising a (co)polymer (A) containing a polyolefin monomer (a) represented by the following general formula (1) as an essential constituent monomer, and a (co)polymer having a kinematic viscosity of 1.00 to 2.50 mm at 100°C. 2 / s ester oil (B1) and 100℃ kinematic viscosity of 2.51~5.00mm 2 / s ester oil (B2); a lubricating oil composition comprising the viscosity index improver and at least one additive selected from the group consisting of a detergent, a dispersant, an antioxidant, an oiliness improver, a pour point depressant, a friction and wear regulator, an extreme pressure agent, a defoamer, an anti-emulsifier, a metal passivator and a corrosion inhibitor.

[0019] [Chemistry 1]

[0020]

[0021] [In the general formula (1), R 1 is a hydrogen atom or a methyl group; -X 1 - is -O-, -O(AO) m - or -NH-, A is an alkylene group having 2 to 4 carbon atoms, m is an integer of 1 to 10, and when m is 2 or more, A may be the same or different; R 2 A residue obtained by removing one hydrogen atom from a hydrocarbon polymer containing a 1,2-butylene group as a structural unit; p is a number of 0 or 1.]

[0022] Effects of the Invention

[0023] The lubricating oil composition containing the viscosity index improver of the present invention exhibits an excellent friction reducing effect. DETAILED DESCRIPTION

[0024] The viscosity index improver of the present invention comprises a (co)polymer (A) containing a polyolefin monomer (a) represented by the following general formula (1) as an essential constituent monomer, and a (co)polymer (A) having a kinematic viscosity of 1.00 to 2.50 mm at 100° C. 2 / s ester oil (B1) and 100℃ kinematic viscosity of 2.51~5.00mm 2 / s of ester oil (B2).

[0025] [Chemistry 2]

[0026]

[0027] [In the general formula (1), R 1 is a hydrogen atom or a methyl group; -X 1 - is -O-, -O(AO) m - or -NH-, A is an alkylene group having 2 to 4 carbon atoms, m is an integer of 1 to 10, and when m is 2 or more, A may be the same or different; R 2 A residue obtained by removing one hydrogen atom from a hydrocarbon polymer containing a 1,2-butylene group as a structural unit; p is a number of 0 or 1.]

[0028] <(Co)polymer (A)>

[0029] The viscosity index improver of the present invention contains a (co)polymer (A) containing the polyolefin-based monomer (a) represented by the above-mentioned general formula (1) as a constituent monomer.

[0030] It should be noted that, in the present invention, "(co)polymer" means "homopolymer and / or copolymer".

[0031] The polyolefin monomer (a) represented by the above general formula (1) is described.

[0032] R in the general formula (1) 1 It is a hydrogen atom or a methyl group. Among these, a methyl group is preferred from the viewpoint of the viscosity index improvement effect.

[0033] -X in the general formula (1) 1 - is -O-, -O(AO) m - or NH-.

[0034] A is an alkylene group having 2 to 4 carbon atoms, and examples thereof include ethylene, 1,2-propylene or 1,3-propylene, isobutylene, and 1,2-butylene, 1,3-butylene or 1,4-butylene.

[0035] AO is an alkyleneoxy group having 2 to 4 carbon atoms, and examples thereof include ethyleneoxy, 1,2-propyleneoxy, 1,3-propyleneoxy, isobutyleneoxy, 1,2-butyleneoxy, 1,3-butyleneoxy, and 1,4-butyleneoxy.

[0036] m is the number of moles of the alkylene oxide added, and is an integer of 1 to 10, and is preferably an integer of 1 to 4, and more preferably an integer of 1 to 2, from the viewpoint of the viscosity index improvement effect.

[0037] When m is 2 or more, A may be the same or different, (AO) m The bonding form of the parts may be random or block-like.

[0038] -X 1 -, from the viewpoint of viscosity index improvement effect, -O- and -O(AO) are preferred. m The group represented by - is more preferably a group represented by -O- and -O(CH2CH2O)1-.

[0039] p is a number of 0 or 1.

[0040] R in the general formula (1) 2 It is a residue obtained by removing one hydrogen atom from a hydrocarbon polymer containing a 1,2-butylene group (-CH2CH(CH2CH3)- or -CH(CH2CH3)CH2-) as an essential structural unit.

[0041] In the hydrocarbon polymer containing a 1,2-butylene group as a structural unit, the ratio of the 1,2-butylene group in all structural units is preferably 10 to 90 mol %, more preferably 20 to 80 mol %, from the viewpoint of HTHS viscosity at 100°C.

[0042] When two polymers having different 1,2-butylene group ratios are used in combination in a hydrocarbon polymer containing 1,2-butylene groups as structural units, the absolute value of the difference between the two 1,2-butylene group ratios is preferably 10 to 80 mol %, more preferably 20 to 70 mol %, from the viewpoint of low temperature viscosity.

[0043] As the hydrocarbon polymer containing a 1,2-butylene group as a structural unit, a polymer having 37 or more carbon atoms is preferred, and examples thereof include a polymer obtained by hydrogenating the carbon-carbon double bond of a 1,2-addition product of a polymer obtained by using 1-butene as a constituent monomer (unsaturated hydrocarbon (x)) and a polymer obtained by using 1,3-butadiene.

[0044] In the hydrocarbon polymer containing 1,2-butylene groups as structural units in the general formula (1), the proportion of 1,2-butylene groups in all structural units can be expressed by 13C-NMR is used for determination. Specifically, 13 The hydrocarbon polymer was analyzed by C-NMR and determined by calculation using the following mathematical formula (1). 13 In C-NMR, the peak of the tertiary carbon atom derived from the 1,2-butylene group appears at an integrated value of 26 to 27 ppm (integral value B). The proportion of the 1,2-butylene group can be determined from the integrated value of the peak and the integrated value of all carbon peaks of the hydrocarbon polymer (integral value C).

[0045] Ratio of 1,2-butylene group (mol%) = {(integral value B) × 4} / (integral value C) × 100 (1)

[0046] It should be noted that in order to increase the proportion of 1,2-butylene groups, for example, in anionic polymerization using 1,3-butadiene, the reaction temperature is lowered to a temperature below the boiling point of 1,3-butadiene (-4.4°C), and the amount of polymerization initiator added is less than that of 1,3-butadiene; in order to reduce the proportion of 1,2-butylene groups, the reaction temperature is increased to a temperature above the boiling point of 1,3-butadiene, and the amount of polymerization initiator added is more than that of 1,3-butadiene.

[0047] Regarding R in the general formula (1) 2 The ratio of 1,3-butadiene in all monomers (the weight ratio of 1,3-butadiene in all constituent monomers in a hydrocarbon polymer containing a 1,2-butylene group as a structural unit) is preferably 50% by weight or more, more preferably 75% by weight or more, particularly preferably 85% by weight or more, and most preferably 90% by weight or more, from the perspective of the viscosity index improvement effect.

[0048] In the general formula (1), the 2 In the structure of a part or all of 1,3-butadiene, the molar ratio of 1,2-butylene (1,2-adduct) to 1,4-butylene (1,4-adduct) (1,2-adduct / 1,4-adduct) is preferably 1 / 99 to 99 / 1, more preferably 10 / 90 to 90 / 10, and particularly preferably 20 / 80 to 80 / 20, from the viewpoint of the viscosity index improvement effect and low-temperature viscosity.

[0049] In addition, as the monomer (a), it is preferred to use a monomer having a molar ratio (1,2-adduct / 1,4-adduct) of 1 / 99 to 50 / 50 and a monomer having a molar ratio of 51 / 49 to 99 / 1, and it is more preferred to use a monomer having a molar ratio of 10 / 90 to 50 / 50 and a monomer having a molar ratio of 55 / 45 to 90 / 10.

[0050] In the general formula (1), the 2The molar ratio of 1,2-adduct / 1,4-adduct in the structure of part or all of 1,3-butadiene can be determined by 1 H-NMR, 13 C-NMR, Raman spectroscopy, etc.

[0051] From the perspective of low temperature viscosity, R in the general formula (1) 2 Preferably, it is a residue obtained by removing one hydrogen atom from a hydrocarbon polymer containing an isobutylene group as a structural unit in addition to a 1,2-butylene group. As a method for producing a hydrocarbon polymer containing an isobutylene group as a structural unit, there can be mentioned a method using isobutylene as a constituent monomer (unsaturated hydrocarbon (x)).

[0052] The total ratio of the isobutylene group to the 1,2-butylene group in the hydrocarbon polymer is preferably 30 mol % or more, more preferably 40 mol % or more, particularly preferably 50 mol % or more, and most preferably 60 mol % or more based on the total number of structural units of the hydrocarbon polymer, from the perspective of low-temperature viscosity.

[0053] The total ratio of isobutylene groups to 1,2-butylene groups based on the total number of structural units of the hydrocarbon polymer can be determined by 13 The hydrocarbon polymer is analyzed by C-NMR spectroscopy and determined by calculation using the following mathematical formula (2). Specifically, for example, assuming that only monomers with 4 carbon atoms are used as monomers, 13 In the C-NMR spectrum, the peak derived from the methyl group of the isobutylene group appears at an integrated value of 30-32 ppm (integral value A), and the peak derived from the tertiary carbon atom of the 1,2-butylene group appears at an integrated value of 26-27 ppm (integral value B). The total ratio can be calculated from the integrated value of the above peaks and the integrated value of all carbon peaks of the hydrocarbon polymer (integral value C).

[0054] Total ratio of isobutylene group and 1,2-butylene group (mol%) = {(integral value A) × 2 + (integral value B) × 4} / (integral value C) × 100 (2)

[0055] The hydrocarbon polymer containing a 1,2-butylene group as a structural unit may contain the following (1) to (3) as a constituent monomer as the unsaturated hydrocarbon (x) in addition to 1-butene and 1,3-butadiene.

[0056] (1) Aliphatic unsaturated hydrocarbons [olefins having 2 to 36 carbon atoms (e.g., ethylene, propylene, 2-butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, tricosene, and hexacosene) and dienes having 4 to 36 carbon atoms (e.g., isoprene, 1,4-pentadiene, 1,5-hexadiene, and 1,7-octadiene)]

[0057] (2) Alicyclic unsaturated hydrocarbons [e.g. cyclohexene, (di)cyclopentadiene, pinene, limonene, indene, vinylcyclohexene and ethylidene bicycloheptene]

[0058] (3) Unsaturated hydrocarbons containing aromatic groups (e.g., styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene, crotylbenzene, vinylnaphthalene, divinylbenzene, divinyltoluene, divinylxylene, trivinylbenzene, etc.)

[0059] The hydrocarbon polymer composed of these may be a block polymer or a random polymer. In addition, when the hydrocarbon polymer has carbon-carbon double bonds, part or all of the double bonds may be hydrogenated by hydrogenation. 2 The hydrocarbon polymer may be a hydrocarbon polymer using only monomers having 4 carbon atoms as constituent monomers, and the monomers having 4 carbon atoms may be 1-butene and / or 1,3-butadiene, and may contain isobutylene as necessary.

[0060] The weight proportion of unsaturated hydrocarbons other than 1-butene, 1,3-butadiene and isobutylene in the monomer (a) is preferably 50% by weight or less, more preferably 25% by weight or less, further preferably 15% by weight or less, particularly preferably 10% by weight or less.

[0061] The weight average molecular weight (hereinafter abbreviated as Mw) and number average molecular weight (hereinafter abbreviated as Mn) of the monomer (a) can be measured by gel permeation chromatography (hereinafter abbreviated as GPC) under the following conditions.

[0062] <Measurement Conditions for Mw and Mn of Monomer (a)>

[0063] Device: "HLC-8320GPC" [manufactured by Tosoh Corporation]

[0064] Column: "TSKgel GMHXL" [manufactured by Tosoh Corporation] 2 pieces

[0065] "TSKgel Multipore H XL-M" [manufactured by Tosoh Corporation] 1 piece

[0066] Measurement temperature: 40℃

[0067] Sample solution: 0.25 wt% tetrahydrofuran solution

[0068] Solution injection volume: 10.0μl

[0069] Detection device: Refractive index detector

[0070] Reference material: Standard polystyrene (TS Reference material: Standard polystyrene (TSKstandardPOLYSTYRENE))

[0071] 12 types (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]

[0072] The Mn of the monomer (a) is preferably 800 to 10,000, more preferably 1,000 to 9,000, particularly preferably 1,200 to 8,500.

[0073] When the Mn of the monomer (a) is 800 or more, the viscosity index improving effect tends to be good, and when it is 10,000 or less, the shear stability during long-term use tends to be good.

[0074] From the viewpoint of low temperature viscosity, the Mw of the monomer (a) is preferably 900 to 13,000, more preferably 1,200 to 12,000, and particularly preferably 1,500 to 11,000.

[0075] The monomer (a) can be obtained by an esterification reaction of a polymer (Y) having a hydroxyl group at one end {a material obtained by introducing a hydroxyl group at one end of the above-mentioned hydrocarbon polymer} with (meth)acrylic acid, or an ester exchange reaction of the polymer (Y) with an alkyl (meth)acrylate (preferably the alkyl group has 1 to 4 carbon atoms) such as methyl (meth)acrylate.

[0076] In addition, "(meth)acrylic acid" means "acrylic acid and / or methacrylic acid".

[0077] From the viewpoint of solubility in lubricating oil, the solubility parameter (hereinafter also referred to as SP value) of the structural unit derived from the monomer (a) (a structure in which the vinyl portion of the monomer (a) reacts 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 .

[0078] It should be noted that the SP value in the present invention is a value calculated by the method described in the mathematical formula (28) on page 153 of the Fedors method (Polymer Engineering and Science, February, 1974, Vol. 14, No. 2 P. 147-154) using the numerical values ​​(heat of vaporization and molar volume of an atom or functional group at 25° C.) described on page 152 (Table 5). Specifically, the SP value can be calculated based on the Δe described in the following Table 1 as a parameter of the Fedors method. i and Δv i The numerical value of is calculated by substituting the numerical values ​​corresponding to the types of atoms and atomic groups in the molecular structure into the following mathematical formula.

[0079] SP value = (ΣΔe i / ΣΔv i ) 1 / 2

[0080] [Table 1]

[0081]

[0082] The SP value of the structural unit derived from the monomer (a) can be calculated using the above parameters based on the molecular structure of the structural unit derived from the monomer (a), and can be within a desired range by appropriately adjusting the monomer (unsaturated hydrocarbon (x)) and weight fraction used.

[0083] Specific examples of the polymer (Y) containing a hydroxyl group at one end include the following (Y1) to (Y4).

[0084] Alkylene oxide adduct (Y1): a product obtained by adding alkylene oxide (ethylene oxide, propylene oxide, etc.) to a polymer obtained by polymerizing an unsaturated hydrocarbon (x) in the presence of an ionic polymerization catalyst (lithium catalyst, sodium catalyst, etc.) (in the general formula (1), -X 1 -for-(AO) m -, p=0).

[0085] Borohydride (Y2): a borohydride reaction product of a polymer of an unsaturated hydrocarbon (x) having a double bond at one end (e.g., a substance described in U.S. Patent No. 4,316,973) etc. (In the general formula (1), -X 1 - is -O-, p=0).

[0086] Maleic anhydride-ene-amino alcohol adduct (Y3): a product obtained by imidizing a reaction product obtained by reacting a polymer of an unsaturated hydrocarbon (x) having a double bond at one end with an ene of maleic anhydride with an amino alcohol (in the general formula (1), -X 1- is -O-, p=1).

[0087] Hydroformylation hydrogenated product (Y4): a product obtained by hydroformylating a polymer of an unsaturated hydrocarbon (x) having a double bond at one end, followed by hydrogenation (e.g., the product described in Japanese Unexamined Patent Publication No. 175096-63) (in the general formula (1), -X 1 - is -O-, p=0).

[0088] Among these polymers (Y) containing a hydroxyl group at one end, alkylene oxide adducts (Y1), borohydrides (Y2) and maleic anhydride-ene-amino alcohol adducts (Y3) are preferred from the viewpoint of the HTHS viscosity and viscosity index improvement effect, and alkylene oxide adducts (Y1) are more preferred.

[0089] In the (co)polymer (A), from the aspects of low-temperature viscosity, shear stability, kinematic viscosity at 40°C, HTHS viscosity at 100°C and viscosity index improvement effect, the weight proportion of monomer (a) in the constituent monomers of the (co)polymer (A) is preferably 1 to 40 weight %, more preferably 5 to 30 weight % based on the total weight of the monomers constituting the (co)polymer (A).

[0090] In the present invention, the (co)polymer (A) may be a copolymer comprising a (meth)acrylic acid alkyl ester monomer (b) having an alkyl group with 1 to 4 carbon atoms (hereinafter sometimes referred to as monomer (b)) and / or a (meth)acryloyl monomer (c) having a linear or branched alkyl group with 9 to 36 carbon atoms (hereinafter sometimes referred to as monomer (c)) as constituent monomers. Monomer (b) and monomer (c) may be used singly or in combination of two or more. From the perspective of the viscosity index improvement effect, the (co)polymer (A) is preferably a copolymer comprising monomer (b) as a constituent monomer. In addition, from the perspective of solubility in base oil, the (co)polymer (A) is preferably a copolymer comprising monomer (c) as a constituent monomer.

[0091] The (meth)acrylate alkyl ester monomer (b) having an alkyl group having 1 to 4 carbon atoms includes esters of linear or branched alcohols having 1 to 4 carbon atoms and (meth)acrylic acid, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, sec-butyl (meth)acrylate and isobutyl (meth)acrylate.

[0092] Among the monomers (b), methyl (meth)acrylate, ethyl (meth)acrylate and n-butyl (meth)acrylate are preferred from the viewpoint of the viscosity index improving effect, and ethyl (meth)acrylate and n-butyl (meth)acrylate are particularly preferred.

[0093] Monomer (c) is a monomer other than monomer (a), and includes a (meth)acryloyl monomer (c1) having a linear alkyl group having 9 to 36 carbon atoms and a (meth)acryloyl monomer (c2) having a branched alkyl group having 9 to 36 carbon atoms represented by the following general formula (2).

[0094] In addition, the monomer (c) may be used alone or in combination of two or more.

[0095] [Chemistry 3]

[0096]

[0097] [In general formula (2), R 3 is a hydrogen atom or a methyl group; -X 2 - is a group represented by -O- or -NH-; R 4 O is an alkyleneoxy group having 2 to 4 carbon atoms; R 5 and R 6 are each independently a linear alkyl group having 1 to 24 carbon atoms, R 5 and R 6 The total number of carbon atoms is 7 to 34; s is an integer of 0 to 20, and when s is 2 or more, R 4 O may be the same or different.]

[0098] Examples of the (meth)acryloyl monomer (c1) having a linear alkyl group having 9 to 36 carbon atoms (hereinafter sometimes referred to as monomer (c1)) include (meth)acrylic acid alkyl esters {esters of linear alkyl alcohols having 9 to 36 carbon atoms and (meth)acrylic acid, such as n-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-undecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, n-pentadecyl (meth)acrylate, n-hexadec ... (meth)acrylate, alkyl esters, n-hexadecyl (meth)acrylate, n-octadecyl (meth)acrylate, n-eicosyl (meth)acrylate, n-tetracosyl (meth)acrylate, n-triacontyl (meth)acrylate and n-hexadecyl (meth)acrylate}, esters of 1 to 20 mol addition products of alkylene oxide (2 to 4 carbon atoms) to straight-chain alkyl alcohols having 9 to 36 carbon atoms and (meth)acrylic acid, and (meth)acrylic acid alkylamides {amides of straight-chain alkylamines having 9 to 36 carbon atoms and acrylic acid}, etc.

[0099] Among the monomers (c1), from the viewpoint of the viscosity index improving effect, an alkyl (meth)acrylate having a linear alkyl group having 12 to 28 carbon atoms is preferred, an alkyl (meth)acrylate having a linear alkyl group having 12 to 24 carbon atoms is more preferred, and an alkyl (meth)acrylate having a linear alkyl group having 12 to 20 carbon atoms is particularly preferred.

[0100] The monomer (c1) may be used alone or in combination of two or more.

[0101] In the monomer (c2), R in the general formula (2) 3 It is a hydrogen atom or a methyl group. Among these, a methyl group is preferred from the viewpoint of the viscosity index improvement effect.

[0102] -X in the general formula (2) 2 - is a group represented by -O- or -NH-. Among these, a group represented by -O- is preferred from the viewpoint of the viscosity index improvement effect.

[0103] R in the general formula (2) 4 It is an alkylene group having 2 to 4 carbon atoms. Examples of the alkylene group having 2 to 4 carbon atoms include ethylene, 1,2-propylene or 1,3-propylene, isobutylene, and 1,2-butylene, 1,3-butylene or 1,4-butylene.

[0104] R 4 O is an alkyleneoxy group having 2 to 4 carbon atoms, and examples thereof include ethyleneoxy, 1,2-propyleneoxy or 1,3-propyleneoxy, isobutyleneoxy, and 1,2-butyleneoxy, 1,3-butyleneoxy or 1,4-butyleneoxy.

[0105] s in the general formula (2) is an integer of 0 to 20, preferably an integer of 0 to 5, more preferably an integer of 0 to 2, from the viewpoint of the viscosity index improvement effect.

[0106] When s is 2 or more, R 4 O can be the same or different, (R 4 O) s The parts may be randomly bonded or block bonded.

[0107] R in the general formula (2) 5 and R 6Each is independently a straight-chain alkyl group having 1 to 24 carbon atoms. Specifically, there can be mentioned methyl, ethyl, n-propyl, n-butyl, n-heptyl, n-hexyl, n-pentyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tetradecyl, n-hexadecyl, n-octadecyl, n-eicosyl and n-tetracosyl. Among the straight-chain alkyl groups having 1 to 24 carbon atoms, from the viewpoint of the viscosity index improvement effect, a straight-chain alkyl group having 6 to 24 carbon atoms is preferred, a straight-chain alkyl group having 6 to 20 carbon atoms is further preferred, and a straight-chain alkyl group having 8 to 16 carbon atoms is particularly preferred.

[0108] R 5 and R 6 The total number of carbon atoms is 7 to 34, preferably 12 to 30, more preferably 14 to 26 from the viewpoint of the viscosity index improving effect.

[0109] Contains R 5 and R 6 The carbon chain consists of R 5 and R 6 A branched alkyl group having 9 to 36 carbon atoms, one of which is a branched chain.

[0110] The number of carbon atoms of the branched alkyl group is 9 to 36, preferably 14 to 32, more preferably 16 to 28 from the viewpoint of the viscosity index improving effect.

[0111] Specific examples of the monomer (c2) 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-dodecylpentadecyl (meth)acrylate, 2-n-tetradecylheptadecyl (meth)acrylate, 2-n-hexadecylheptadecyl (meth)acrylate, 2-n-hexadecyleicosyl (meth)acrylate, 2-n-hexadecylbehenyl (meth)acrylate, 2-n-tetradecylhexacosyl (meth)acrylate, and N-2-octyldecyl (meth)acrylamide.

[0112] The monomer (c2) may be used alone or in combination of two or more.

[0113] Among the monomers (c), from the viewpoint of solubility in the base oil and low-temperature viscosity, the (meth)acryloyl monomer (c2) having a branched alkyl group having 9 to 36 carbon atoms represented by the above-mentioned general formula (2) is preferred, and the (meth)acryloyl monomer having a branched alkyl group having 14 to 32 carbon atoms among the monomers (c2) is more preferred, and the (meth)acryloyl monomer having a branched alkyl group having 16 to 28 carbon atoms among the monomers (c2) is particularly preferred.

[0114] In the present invention, the (co)polymer (A) may be a copolymer comprising a monomer (d) represented by the following general formula (3) as a constituent monomer. One monomer (d) may be used, or two or more monomers may be used in combination. From the perspective of viscosity index improvement effect and HTHS viscosity reduction, the (co)polymer (A) preferably comprises monomer (d) as a constituent monomer.

[0115] [Chemistry 4]

[0116]

[0117] [In general formula (3), R 7 is a hydrogen atom or a methyl group; -X 3 - is a group represented by -O- or -NH-; R 8 is an alkylene group having 2 to 4 carbon atoms; R 9 is an alkyl group having 1 to 8 carbon atoms; r is an integer of 1 to 20, and when r is 2 or more, R 8 Can be the same or different.]

[0118] R in the general formula (3) 7 It is a hydrogen atom or a methyl group. Among these, a methyl group is preferred from the viewpoint of the viscosity index improvement effect.

[0119] -X in the general formula (3) 3 - is a group represented by -O- or -NH-. Among these, a group represented by -O- is preferred from the viewpoint of the viscosity index improvement effect.

[0120] R in the general formula (3) 8 It is an alkylene group having 2 to 4 carbon atoms.

[0121] Examples of the alkylene group having 2 to 4 carbon atoms include ethylene, 1,2-propylene or 1,3-propylene, isobutylene, and 1,2-butylene, 1,3-butylene or 1,4-butylene.

[0122] R 8 O is an alkyleneoxy group having 2 to 4 carbon atoms, and examples thereof include ethyleneoxy, 1,2-propyleneoxy or 1,3-propyleneoxy, isobutyleneoxy, and 1,2-butyleneoxy, 1,3-butyleneoxy or 1,4-butyleneoxy.

[0123] In the general formula (3), r is an integer of 1 to 20, and is preferably an integer of 1 to 5, and more preferably an integer of 1 to 2, from the viewpoint of the viscosity index improvement effect and the low-temperature viscosity.

[0124] When r is 2 or more, R 8 O can be the same or different, (R 8 O) r The bonding form of the parts may be random or block-like.

[0125] R in the general formula (3) 9 It is an alkyl group having 1 to 8 carbon atoms, including straight-chain or branched-chain alkyl groups, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-heptyl, isoheptyl, n-hexyl, 2-ethylhexyl, n-pentyl and n-octyl.

[0126] Among the alkyl groups having 1 to 8 carbon atoms, from the viewpoint of the viscosity index improving effect, an alkyl group having 1 to 7 carbon atoms is preferred, an alkyl group having 1 to 6 carbon atoms is more preferred, an alkyl group having 1 to 5 carbon atoms is particularly preferred, and an alkyl group having 2 or 4 carbon atoms is most preferred.

[0127] Specific examples of the monomer (d) include methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, pentyloxyethyl (meth)acrylate, hexyloxyethyl (meth)acrylate, heptyloxyethyl (meth)acrylate, octyloxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, ethoxypropyl (meth)acrylate, propoxypropyl (meth)acrylate, butoxypropyl (meth)acrylate, pentyloxypropyl (meth)acrylate, hexyloxypropyl (meth)acrylate, and octyloxyethyl (meth)acrylate. esters of (meth)acrylic acid and the like.

[0128] Among the monomers (d), ethoxyethyl (meth)acrylate and butoxyethyl (meth)acrylate are preferred from the viewpoint of the viscosity index improving effect.

[0129] In addition, in the present invention, "(meth)acrylate" means "acrylate and / or methacrylate".

[0130] In the (co)polymer (A), from the perspective of the viscosity index improvement effect, the weight proportion of the monomer (b) in the constituent monomers of the (co)polymer (A) is preferably 1 to 80 weight %, and more preferably 2 to 70 weight % based on the total weight of the monomers constituting the (co)polymer (A).

[0131] In the (co)polymer (A), from the perspective of improving the viscosity index and making the (co)polymer (A) have a preferred SP value, the weight proportion of the monomer (c) in the constituent monomers of the (co)polymer (A) is preferably 1 to 60 weight %, and more preferably 5 to 35 weight % based on the total weight of the monomers constituting the (co)polymer (A).

[0132] In the (co)polymer (A), from the aspects of HTHS viscosity at 100°C, kinematic viscosity at 40°C, shear stability and viscosity index improvement effect, the weight proportion of monomer (d) in the constituent monomers of the (co)polymer (A) is preferably 2 to 35 weight %, and more preferably 5 to 30 weight % based on the total weight of the monomers constituting the (co)polymer (A).

[0133] In the (co)polymer (A), from the perspective of HTHS viscosity at 100°C, kinematic viscosity at 40°C and viscosity index improvement effect, the weight ratio (a / d) of monomer (a) to monomer (d) in the constituent monomers of the (co)polymer (A) is preferably 95 / 5 to 1 / 99, and more preferably 90 / 10 to 5 / 95.

[0134] The (co)polymer (A) in the present invention may contain, in addition to the above-mentioned monomers (a) to (d), nitrogen atom-containing monomers (e), hydroxyl group-containing monomers (f), phosphorus atom-containing monomers (g), aromatic ring-containing vinyl monomers (h) and monomers (i) to (m) as constituent monomers.

[0135] The monomers (e) to (m) may be used alone or in combination of two or more.

[0136] Examples of the nitrogen atom-containing monomer (e) include the following monomers (e1) to (e4) other than the monomer (a), the monomer (c) and the monomer (d).

[0137] Amide group-containing monomer (e1):

[0138] Examples include (meth)acrylamide, monoalkyl (meth)acrylamide [(meth)acrylamide having one alkyl group having 1 to 4 carbon atoms bonded to the nitrogen atom; for example, N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, and N-n- or isobutyl (meth)acrylamide], N-(N'-monoalkylaminoalkyl) (meth)acrylamide [(meth)acrylamide having an aminoalkyl group (having 2 to 6 carbon atoms) bonded to the 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], dialkyl (meth)acrylamide [(meth)acrylamide having two alkyl groups having 1 to 4 carbon atoms bonded to the 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], (meth)acrylamide; 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 [(meth)acrylamide having an aminoalkyl group (having 2 to 6 carbon atoms) bonded to the nitrogen atom of the aminoalkyl group and having two alkyl groups having 1 to 4 carbon atoms; 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-vinylcarboxylic acid amides [N-vinylformamide, N-vinylacetamide, N-vinylpropionamide and N-vinylhydroxyacetamide, etc.], etc.

[0139] Nitro-containing monomers (e2):

[0140] Examples thereof include 4-nitrostyrene.

[0141] Monomers containing primary to tertiary amino groups (e3):

[0142] Examples include primary amino group-containing monomers {alkenylamines having 3 to 6 carbon atoms [(meth)allylamine and crotylamine, etc.], aminoalkyl(meth)acrylates (having 2 to 6 carbon atoms) [aminoethyl(meth)acrylate, etc.]}; secondary amino group-containing monomers {monoalkylaminoalkyl(meth)acrylates [(meth)acrylates having aminoalkyl(2 to 6 carbon atoms) groups having one alkyl group having 1 to 6 carbon atoms bonded to a nitrogen atom; for example, N-tert-butylaminoethyl(meth)acrylate and N-methylaminoethyl(meth)acrylate, etc.], dienylamines having 6 to 12 carbon atoms [di(meth)allylamine, etc.]}; tertiary amino group-containing monomers {dialkylaminoalkyl(meth)acrylates [having aminoalkyl(2 to 6 carbon atoms) groups having two alkyl ... (Meth)acrylates of aminoalkyl (carbon number 2 to 6) of an alkyl group having 1 to 6 carbon atoms; for example, N,N-dimethylaminoethyl (meth)acrylate and N,N-diethylaminoethyl (meth)acrylate, etc.], alicyclic (meth)acrylates having nitrogen atoms [morpholinoethyl (meth)acrylate, etc.], aromatic monomers [N-(N',N'-diphenylaminoethyl) (meth)acrylamide, N,N-dimethylaminostyrene, 4-vinylpyridine, 2-vinylpyridine, N-vinylpyrrole, N-vinylpyrrolidone and N-vinylthiopyrrolidone, etc.]}, and their hydrochlorides, sulfates, phosphates or lower alkyl (carbon number 1 to 8) monocarboxylic acid (acetic acid, propionic acid, etc.) salts, etc.

[0143] Nitrile group-containing monomer (e4):

[0144] (Meth)acrylonitrile and the like are mentioned.

[0145] Among the monomers (e), preferred are amide group-containing monomers (e1) and primary to tertiary amino group-containing monomers (e3), 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.

[0146] Hydroxyl-containing monomers (f):

[0147] Examples include hydroxyl-containing aromatic monomers (p-hydroxystyrene, etc.), hydroxyalkyl (meth)acrylates (having 2 to 6 carbon atoms) [2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate or 3-hydroxypropyl (meth)acrylate, etc.], monohydroxyalkyl or bishydroxyalkyl (having 1 to 4 carbon atoms) substituted (meth)acrylamide [N,N-bis(hydroxymethyl) (meth)acrylamide, N,N-bis(hydroxypropyl) (meth)acrylamide, N,N-bis(2-hydroxybutyl) (meth)acrylamide, etc.], vinyl alcohol, enols having 3 to 12 carbon atoms [(methyl ) allyl alcohol, crotyl alcohol, isocrotyl alcohol, 1-octenol and 1-undecenol, etc.], olefin monoalcohols or olefin diols having 4 to 12 carbon atoms [1-butene-3-ol, 2-butene-1-ol and 2-butene-1,4-diol, etc.], hydroxyalkyl (carbon number 1 to 6) alkenyl (carbon number 3 to 10) ethers (2-hydroxyethyl propenyl ether, etc.), alkenyl (carbon number 3 to 10) ethers of polyols (3 to 8 hydration) (glycerol, pentaerythritol, sorbitol, sorbitan, diglycerol, sugars and sucrose, etc.) or (meth) acrylates [sucrose (meth) allyl ether, etc.], etc.;

[0148] Polyoxyalkylene glycol (alkylene group having 2 to 4 carbon atoms and a degree of polymerization of 2 to 50), polyoxyalkylene polyol [polyoxyalkylene ethers of the above trivalent to octavalent alcohols (alkylene group having 2 to 4 carbon atoms and a degree of polymerization of 2 to 100), etc.], mono(meth)acrylates of alkyl (carbon number 1 to 4) ethers of polyoxyalkylene glycol or polyoxyalkylene polyol [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, etc.], etc.

[0149] Examples of the phosphorus atom-containing monomer (g) include the following monomers (g1) to (g2).

[0150] Monomer containing phosphate group (g1):

[0151] Examples include (meth)acryloyloxyalkyl (carbon number 2 to 4) phosphates [(meth)acryloyloxyethyl phosphate and (meth)acryloyloxyisopropyl phosphate] and alkenyl phosphates [vinyl phosphate, allyl phosphate, propylene phosphate, isopropylene phosphate, butyl phosphate, pentyl phosphate, octenyl phosphate, decenyl phosphate, and dodecenyl phosphate, etc.]. It should be noted that "(meth)acryloyloxy" means an acryloyloxy group or a methacryloyloxy group.

[0152] Phosphonyl-containing monomer (g2):

[0153] Examples thereof include (meth)acryloyloxyalkyl (carbon number 2-4)phosphonic acid [such as (meth)acryloyloxyethylphosphonic acid] and alkenyl (carbon number 2-12)phosphonic acid [such as vinylphosphonic acid, allylphosphonic acid and octenylphosphonic acid].

[0154] Among the monomers (g), the phosphoric acid ester group-containing monomer (g1) is preferred, (meth)acryloyloxyalkyl (carbon number 2 to 4) phosphoric acid ester is more preferred, and (meth)acryloyloxyethyl phosphoric acid ester is particularly preferred.

[0155] Aromatic vinyl monomers (h):

[0156] Examples thereof 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.

[0157] Among the monomers (h), styrene and α-methylstyrene are preferred, and styrene is more preferred.

[0158] Examples of the monomer (i) having two or more unsaturated groups include divinylbenzene, dienes 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, polyoxyalkylene glycol di(meth)acrylate, pentaerythritol triallyl ether, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, trimethylolpropane tri(meth)acrylate, esters of unsaturated carboxylic acids and diols having an Mn of 500 or more as described in International Publication No. WO01 / 009242, and esters of unsaturated alcohols and carboxylic acids.

[0159] Vinyl esters, vinyl ethers, vinyl ketones (j) (sometimes referred to as monomers (j)):

[0160] Examples include vinyl esters of saturated fatty acids having 2 to 12 carbon atoms (vinyl acetate, vinyl propionate, vinyl butyrate, vinyl octanoate, etc.), alkyl, aryl or alkoxyalkyl vinyl ethers having 1 to 12 carbon atoms (methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, 2-ethylhexyl vinyl ether, phenyl vinyl ether, vinyl-2-methoxyethyl ether, vinyl-2-butoxyethyl ether, etc.), and alkyl or aryl vinyl ketones having 1 to 8 carbon atoms (methyl vinyl ketone, ethyl vinyl ketone, phenyl vinyl ketone, etc.).

[0161] Epoxy-containing monomer (k) (sometimes referred to simply as monomer (k)):

[0162] Examples thereof include glycidyl (meth)acrylate and glycidyl (meth)allyl ether.

[0163] Monomer (l) containing a halogen element (sometimes referred to simply as monomer (l)):

[0164] Examples thereof include vinyl chloride, vinyl bromide, vinylidene chloride, (meth)allyl chloride, and halogenated styrene (such as dichlorostyrene).

[0165] Ester of unsaturated polycarboxylic acid (m) (sometimes referred to simply as monomer (m)):

[0166] Examples include alkyl, cycloalkyl or aralkyl esters of unsaturated polycarboxylic acids [alkyl diesters of unsaturated dicarboxylic acids (such as maleic acid, fumaric acid and itaconic acid) having 1 to 8 carbon atoms (such as dimethyl maleate, dimethyl fumarate, diethyl maleate and dioctyl maleate)] and the like.

[0167] In the (co)polymer (A), from the perspective of the HTHS viscosity at the effective temperature and the viscosity index improvement effect, the weight proportion of the monomer (e) in the constituent monomers of the (co)polymer (A) is preferably 50 weight % or less, and more preferably 1 to 40 weight % based on the total weight of the monomers constituting the (co)polymer (A).

[0168] In the (co)polymer (A), from the perspective of the HTHS viscosity at the effective temperature and the viscosity index improvement effect, the weight proportion of the monomer (f) in the constituent monomers of the (co)polymer (A) is preferably 40 weight % or less, and more preferably 1 to 30 weight % based on the total weight of the monomers constituting the (co)polymer (A).

[0169] In the (co)polymer (A), from the perspective of the HTHS viscosity at the effective temperature and the viscosity index improvement effect, the weight proportion of the monomer (g) in the constituent monomers of the (co)polymer (A) is preferably 30 weight % or less, and more preferably 1 to 20 weight % based on the total weight of the monomers constituting the (co)polymer (A).

[0170] In the (co)polymer (A), from the perspective of the HTHS viscosity at the effective temperature and the viscosity index improvement effect, the weight proportion of the monomer (h) in the constituent monomers of the (co)polymer (A) is preferably 20 weight % or less, and more preferably 1 to 15 weight % based on the total weight of the monomers constituting the (co)polymer (A).

[0171] In the (co)polymer (A), from the perspective of HTHS viscosity at the effective temperature, the weight proportion of the monomer (i) in the constituent monomers of the (co)polymer (A) is preferably 10 wt % or less, and more preferably 1 to 5 wt % based on the total weight of the monomers constituting the (co)polymer (A).

[0172] In the (co)polymer (A), from the perspective of the viscosity index improvement effect, the weight proportion of the monomer (j) in the constituent monomers of the (co)polymer (A) is preferably 5 weight % or less, and more preferably 0.5 to 2 weight % based on the total weight of the monomers constituting the (co)polymer (A).

[0173] In the (co)polymer (A), from the perspective of the viscosity index improvement effect, the weight proportion of the monomer (k) in the constituent monomers of the (co)polymer (A) is preferably 20 weight % or less, and more preferably 1 to 10 weight % based on the total weight of the monomers constituting the (co)polymer (A).

[0174] In the (co)polymer (A), from the perspective of the viscosity index improvement effect, the weight proportion of the monomer (l) in the constituent monomers of the (co)polymer (A) is preferably less than 5 weight %, and more preferably 0.1 to 2 weight % based on the total weight of the monomers constituting the (co)polymer (A).

[0175] In the (co)polymer (A), from the perspective of the viscosity index improvement effect, the weight proportion of the monomer (m) in the constituent monomers of the (co)polymer (A) is preferably 1 weight % or less, and more preferably 0.01 to 0.5 weight % based on the total weight of the monomers constituting the (co)polymer (A).

[0176] The Mw of the (co)polymer (A) is preferably 5,000 to 2,000,000, more preferably 5,000 to 1,000,000, particularly preferably 10,000 to 800,000, most preferably 15,000 to 700,000, and most preferably 30,000 to 600,000. When the Mw of the (co)polymer (A) is 5,000 or more, there is a tendency for the viscosity-temperature characteristics to be improved and the viscosity index to be improved. In addition, the amount of viscosity index improver added will not be too much, which is also advantageous in terms of cost. When the Mw is 2,000,000 or less, there is a tendency for the shear stability to be good.

[0177] The more preferred range of Mw of the (co)polymer (A) varies depending on the use of the viscosity index improver and the lubricating oil composition, but is the range described in Table 2.

[0178] [Table 2]

[0179]

[0180] *: Automatic transmission oil

[0181] **: Belt type continuously variable transmission oil

[0182] ***: Manual transmission fluid

[0183] The Mn of the (co)polymer (A) is preferably 2,500 or more, more preferably 5,000 or more, particularly preferably 7,500 or more, and most preferably 15,000 or more. It is preferably 300,000 or less, more preferably 150,000 or less, and particularly preferably 100,000 or less.

[0184] When Mn is 2,500 or more, the viscosity-temperature characteristics are improved and the viscosity index is improved. In addition, the amount of viscosity index improver added is not too much, which is also advantageous in terms of cost. When Mn is 300,000 or less, the shear stability is good.

[0185] The molecular weight distribution (Mw / Mn) of the (co)polymer (A) is preferably 1.0 to 4.0, more preferably 1.5 to 3.5, from the viewpoint of shear stability.

[0186] It should be noted that the measurement conditions of Mw, Mn and molecular weight distribution of the (co)polymer (A) are the same as the measurement conditions of Mw and Mn of the above-mentioned monomer (a).

[0187] The (co)polymer (A) can be obtained by a known production method, and specifically, there can be mentioned a method of obtaining the polymer by solution polymerization of the above-mentioned monomers in a solvent in the presence of a polymerization catalyst.

[0188] Examples of the solvent include toluene, xylene, alkylbenzenes having 9 to 10 carbon atoms, methyl ethyl ketone, mineral oil, synthetic oil, and mixtures thereof.

[0189] Examples of the polymerization catalyst include azo catalysts (2,2'-azobis(2-methylbutyronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile)), peroxide catalysts (benzoyl peroxide, cumyl peroxide, and lauryl peroxide), and redox catalysts (a mixture of benzoyl peroxide and a tertiary amine).

[0190] Furthermore, in order to adjust the molecular weight, a known chain transfer agent (such as an alkyl mercaptan having 2 to 20 carbon atoms) may be used as necessary.

[0191] 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.

[0192] The (co)polymer (A) may be in the form of a random addition polymer or an alternating copolymer, or may be in the form of a graft copolymer or a block copolymer.

[0193] From the viewpoint of solubility in the base oil, the SP value calculated based on the weight fraction of the monomers constituting the (co)polymer (A) is preferably 8.0 to 10.0 (cal / cm 3 ) 1 / 2 , more preferably 8.5 to 9.5 (cal / cm 3 ) 1 / 2 .

[0194] The SP value calculated based on the weight fraction of the monomers constituting the (co)polymer (A) (sometimes referred to as the SP value of the (co)polymer (A)) refers to the value obtained by calculating the SP value of the structural unit (a structure in which the vinyl group becomes a single bond through a polymerization reaction) derived from each monomer constituting the (co)polymer (A) using the above-mentioned SP value calculation method, and arithmetically averaging the weight fraction of each constituent monomer at the time of charging. For example, when the monomer is methyl methacrylate, in the structural unit derived from methyl methacrylate, in terms of atomic groups, CH3 is 2, CH2 is 1, C is 1, and CO2 is 1. Therefore, it can be seen from the following mathematical formula that the SP value of the structural unit derived from methyl methacrylate is 9.933 (cal / cm 3 ) 1 / 2 The same calculation shows that the SP value of the structural unit derived from ethyl methacrylate is 9.721 (cal / cm 3 ) 1 / 2 .

[0195] ΣΔe i =1125×2+1180+350+4300=8080

[0196] ΣΔv i =33.5×2+16.1-19.2+18.0=81.9

[0197] δ=(8080 / 81.9) 1 / 2 =9.933(cal / cm 3 ) 1 / 2

[0198] 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 the arithmetic mean based on the weight fraction of the SP value of the structural unit derived from each monomer as follows.

[0199] SP value of copolymer = (9.933 × 50 + 9.721 × 50) / 100 = 9.827

[0200] The SP value calculated based on the weight fraction of the monomers constituting the (co)polymer (A) can be within the desired range by appropriately adjusting the monomers used and the weight fractions of the monomers used. Specifically, the SP value can be reduced by using more monomers with a large number of carbon atoms in the alkyl group, and the SP value can be increased by using more monomers with a small number of carbon atoms in the alkyl group.

[0201] The shear stability index (SSI) of the (co)polymer (A) is preferably 70 or less, more preferably 60 or less, from the viewpoint of the service life of the lubricating oil composition.

[0202] It should be noted that in the present invention, the SSI of the (co)polymer (A) is a value expressed as a percentage of the viscosity reduction of the copolymer (A) due to shearing, and is a value measured in accordance with ASTM D6278. More specifically, it is a value calculated by the following mathematical formula (3).

[0203] SSI=(Kν0-Kν1) / (Kν0-Kν oil ) (3)

[0204] In the above mathematical formula (3), Kν0 is the value of the kinematic viscosity at 100°C of a sample oil obtained by diluting the viscosity index improver containing the (co)polymer (A) in mineral oil, and Kν1 is the value of the kinematic viscosity at 100°C of a sample oil obtained by diluting the viscosity index improver containing the (co)polymer (A) in mineral oil and passing the obtained sample oil through a high shear Bosch diesel injector for 30 cycles according to the process of ASTM D6278. In addition, Kν oil It is a value of the kinematic viscosity at 100° C. of the mineral oil used when diluting the viscosity index improver.

[0205] The viscosity index improver of the present invention may contain, in addition to the above-mentioned (co)polymer (A), an alkyl (meth)acrylate (co)polymer (C) other than the (co)polymer (A), and containing the (co)polymer (C) is preferred from the perspective of low-temperature viscosity.

[0206] The (co)polymer (C) includes a (co)polymer that does not contain the monomer (a), and examples thereof include a (co)polymer that contains a (meth)acryloyl monomer (c) having a linear and / or branched alkyl group having 9 to 36 carbon atoms as a constituent monomer. Specifically, there can be mentioned copolymers of n-dodecyl (meth)acrylate, n-tetradecyl (meth)acrylate, n-hexadecyl (meth)acrylate and n-octadecyl (meth)acrylate, copolymers of n-octadecyl (meth)acrylate / n-dodecyl (meth)acrylate (molar ratio of 10 to 30 / 90 to 70), copolymers of n-tetradecyl (meth)acrylate / n-dodecyl (meth)acrylate (molar ratio of 10 to 30 / 90 to 70), copolymers of n-hexadecyl (meth)acrylate / n-dodecyl (meth)acrylate / methyl (meth)acrylate (molar ratio of 20 to 40 / 55 to 75 / 0 to 10), and copolymers of n-dodecyl acrylate / n-dodecyl methacrylate (molar ratio of 10 to 40 / 90 to 60). These may be used alone or in combination of two or more.

[0207] In the viscosity index improver of the present invention, the content of the (co)polymer (C) is preferably 0.01 to 30% by weight, more preferably 0.01 to 10% by weight, based on the weight of the (co)polymer (A), from the perspective of low-temperature viscosity.

[0208] From the viewpoint of lowering the pour point temperature, the Mw of the (co)polymer (C) is preferably 5,000 to 100,000, more preferably 10,000 to 80,000.

[0209] From the viewpoint of solubility in the base oil, the SP value calculated based on the weight fraction of the monomer constituting the (co)polymer (C) is preferably 7.0 to 10, more preferably 8.0 to 9.5.

[0210] It should be noted that the measurement conditions of the Mw of the (co)polymer (C) are the same as the measurement conditions of the Mw of the above-mentioned monomer (a), and the calculation method of the SP value is the same as that of the (co)polymer (A).

[0211] In the viscosity index improver of the present invention, the (co)polymer (A) is preferably contained in an amount of 10% by weight or more and 40% by weight or less based on the weight of the viscosity index improver.

[0212] In the viscosity index improver of the present invention, the (co)polymer (C) is preferably contained in an amount of 0.01 to 5% by weight based on the weight of the viscosity index improver.

[0213] <Ester oil>

[0214] The viscosity index improver of the present invention comprises the above-mentioned (co)polymer (A), and a (co)polymer having a kinematic viscosity at 100° C. measured by JIS-K2283 (hereinafter also referred to as the 100° C. kinematic viscosity) of 1.00 to 2.50 mm 2 / s ester oil (B1) and 100℃ kinematic viscosity of 2.51~5.00mm 2 / s of ester oil (B2). The viscosity index improver of the present invention contains ester oil (B1) or ester oil (B2), and has low viscosity even when a (co)polymer (A) with a high molecular weight is contained at a high concentration, and has a tendency to have good handling properties of the viscosity index improver, and has a tendency to be easily taken out from the reaction tank after the viscosity index improver is manufactured. In addition, by using ester oil (B1) and ester oil (B2) together, when added to a lubricating oil composition, it has an effect of excellent friction characteristics. It is speculated that this is because ester oil (B1) has an adsorption effect on the metal surface, and the oil film thickness is increased by the expansion effect of the polymer chain caused by the interaction between the (co)polymer (A) and the ester oil (B2), thereby being able to exert an excellent friction reduction effect.

[0215] It should be noted that the kinematic viscosity at 100°C can be adjusted by changing the carbon number of the carboxylic acid and alcohol in the synthetic ester oil. For example, if a substance with a large carbon number is used, the kinematic viscosity at 100°C increases; if a substance with a small carbon number is used, the kinematic viscosity at 100°C decreases.

[0216] Examples of the ester oil (B1) include monoesters of a linear or branched saturated or unsaturated aliphatic monocarboxylic acid having 14 to 18 carbon atoms and a linear or branched saturated or unsaturated aliphatic monohydric alcohol having 1 to 8 carbon atoms, wherein the total number of carbon atoms is 16 to 22 {e.g., ethyl myristate, propyl myristate, butyl myristate, octyl myristate, ethyl myristoleate, propyl myristoleate, butyl myristoleate, octyl myristoleate, methyl palmitate, ethyl palmitate, propyl palmitate, butyl palmitate, methyl palmitoleate, ethyl palmitoleate, propyl palmitoleate, butyl palmitoleate, methyl stearate, ethyl stearate, propyl stearate, butyl stearate, methyl oleate (100° C. kinematic viscosity: 1.62 mm 2 / s), ethyl oleate (100℃ kinematic viscosity: 1.83mm 2 / s), propyl oleate (100℃ kinematic viscosity: 2.01mm 2 / s), butyl oleate (100℃ kinematic viscosity: 2.20mm 2 / s) etc.}, a diester of a linear saturated alkyl dicarboxylic acid having 6 to 10 carbon atoms and a saturated or unsaturated aliphatic monohydric alcohol having 4 to 8 carbon atoms, and having a total of 14 to 22 carbon atoms {e.g., di-n-butyl sebacate (100°C kinematic viscosity: 2.04 mm2 / s), di-n-butyl adipate (100℃ kinematic viscosity: 1.40mm 2 / s), bis(2-ethylhexyl) adipate (100℃ kinematic viscosity: 2.32mm 2 / s) etc.

[0217] Among these, propyl oleate, butyl oleate, di-n-butyl sebacate and bis(2-ethylhexyl) adipate are preferred, and butyl oleate and bis(2-ethylhexyl) adipate are more preferred from the viewpoints of HTHS viscosity, 40°C kinematic viscosity, volatility at 250°C and friction characteristics.

[0218] Examples of the ester oil (B2) include monoesters of a linear or branched saturated or unsaturated aliphatic monocarboxylic acid having 16 to 18 carbon atoms and a linear or branched saturated or unsaturated aliphatic monohydric alcohol having 8 to 10 carbon atoms, wherein the total number of carbon atoms is 24 to 28 {e.g., octyl palmitate, decyl palmitate, octyl palmitoleate, decyl palmitoleate, octyl stearate, decyl stearate, octyl oleate (100° C. kinematic viscosity: 2.60 mm 2 / s), decyl oleate, etc., a diester of a linear saturated alkyl dicarboxylic acid having 6 to 12 carbon atoms and a saturated or unsaturated aliphatic monohydric alcohol having 4 to 10 carbon atoms, and a total of 23 to 30 carbon atoms {e.g., di-n-octyl sebacate (100°C kinematic viscosity: 3.21 mm 2 / s), diisononyl adipate (100℃ kinematic viscosity: 3.05mm 2 / s), diisodecyl adipate (100℃ kinematic viscosity: 3.62mm 2 / s), diisodecyl sebacate (100℃ kinematic viscosity: 4.73mm 2 / s), bis(2-ethylhexyl) sebacate (100°C kinematic viscosity: 3.20 mm 2 / s), bis(2-ethylhexyl) dodecanedioate (100°C kinematic viscosity: 3.80 mm 2 / s) etc.

[0219] Among these, diisononyl adipate, di-n-octyl sebacate, diisodecyl adipate, diisodecyl sebacate, bis(2-ethylhexyl) sebacate and bis(2-ethylhexyl) dodecanedioate are preferred from the viewpoints of HTHS viscosity, 40°C kinematic viscosity, volatility at 250°C and friction characteristics, and di-n-octyl sebacate and diisodecyl adipate are more preferred.

[0220] The ester oil (B1) preferably has a kinematic viscosity of 2.00 to 2.40 mm at 100° C. from the viewpoints of HTHS viscosity, 40° C. kinematic viscosity, volatility at 250° C., and friction characteristics.2 / s.

[0221] The ester oil (B2) preferably has a kinematic viscosity of 3.00 to 3.90 mm at 100° C. from the viewpoints of HTHS viscosity, 40° C. kinematic viscosity, volatility at 250° C., and friction characteristics. 2 / s.

[0222] The difference in kinematic viscosity between the ester oil (B1) and the ester oil (B2) at 100°C ((B2) - (B1)) is preferably 0.8 to 1.5 mm in terms of volatility at 250°C and friction reduction effect. 2 / s.

[0223] The kinematic viscosity at 100° C. of the ester oil (B1) and the ester oil (B2) in the viscosity index improver can be measured by the following method.

[0224] The composition of the ester oil contained in the viscosity index improver is determined by subjecting the viscosity index improver subjected to the polymer separation operation to NMR analysis and / or mass analysis, etc. The kinematic viscosity at 100° C. of each ester oil in the viscosity index improver can be determined by measuring the kinematic viscosity at 100° C. of each ester oil identical to each ester oil component determined to be contained in the viscosity index improver in accordance with JIS-K2283.

[0225] The viscosity index of the ester oil (B1) is preferably 100 or more, more preferably 105 to 230, from the viewpoint of the viscosity index.

[0226] The viscosity index of the ester oil (B2) is preferably 100 or more, more preferably 105 to 190, from the viewpoint of the viscosity index.

[0227] The viscosity index (measured according to JIS-K2283) of ester oil (B1) and ester oil (B2) can be adjusted by changing the carbon number of carboxylic acid and alkyl alcohol when synthesizing the ester oil. Specifically, when a substance with a large carbon number is used, the viscosity index tends to increase.

[0228] From the viewpoint of solubility of various additives, the SP value of the ester oil (B1) is preferably 8.0 to 10.0 (cal / cm 3 ) 1 / 2 , more preferably 8.5 to 9.5 (cal / cm 3 ) 1 / 2 .

[0229] From the viewpoint of solubility of various additives, the SP value of the ester oil (B2) is preferably 8.0 to 10.0 (cal / cm 3 ) 1 / 2 , more preferably 8.5 to 9.5 (cal / cm3 ) 1 / 2 .

[0230] The absolute value of the difference between the SP value of the ester oil (B1) and the SP value of the ester oil (B2) is preferably 0.01 to 2.0 (cal / cm 3 ) 1 / 2 , more preferably 0.01 to 1.5 (cal / cm 3 ) 1 / 2 , particularly preferably 0.01 to 1.0 (cal / cm 3 ) 1 / 2 .

[0231] From the perspective of compatibility, the absolute value of the difference between the SP value calculated based on the weight fraction of the monomers constituting the (co)polymer (A) and the SP value of the ester oil {the weight average of (B1) and (B2)} is preferably 0.1 to 2.0 (cal / cm 3 ) 1 / 2 , more preferably 0.1 to 1.5 (cal / cm 3 ) 1 / 2 , particularly preferably 0.1 to 1.0 (cal / cm 3 ) 1 / 2 .

[0232] The weight ratio {(B1) / (B2)} of the ester oil (B1) to the ester oil (B2) contained in the viscosity index improver of the present invention is preferably 10 / 90 to 90 / 10, more preferably 20 / 80 to 80 / 20, from the viewpoints of friction characteristics, 100°C HTHS viscosity, 40°C kinematic viscosity and 250°C volatility.

[0233] Within this range, when a lubricating oil composition is prepared, the weight ratio of the ester oil (B1) to the ester oil (B2) in the lubricating oil composition is within the above range, and the friction characteristics, 100°C HTHS viscosity, 40°C kinematic viscosity and 250°C volatility of the lubricating oil composition tend to be good, and in particular, the friction characteristics and 250°C volatility tend to be more good.

[0234] From the aspects of the handling properties of the viscosity index improver, 100°C HTHS viscosity, 40°C kinematic viscosity and 250°C volatility, the weight ratio {(A) / ((B1)+(B2))} of the (co)polymer (A) to the ester oil (B1) and the ester oil (B2) contained in the viscosity index improver of the present invention is preferably 10 / 90 to 50 / 50, and more preferably 20 / 80 to 35 / 65.

[0235] When the viscosity index improver is within this range, the viscosity (for example, the viscosity at 90°C) of the viscosity index improver is low, and the handling property tends to be good. In addition, when the lubricating oil composition is prepared, the weight ratio of the (co)polymer (A) to the ester oil (B1) and the ester oil (B2) in the lubricating oil composition is within the above range, and the HTHS viscosity at 100°C, the kinematic viscosity at 40°C, and the volatility at 250°C of the lubricating oil composition tend to be good.

[0236] The total content of the ester oil (B1) and the ester oil (B2) in the viscosity index improver of the present invention is preferably 30 to 90% by weight, more preferably 40 to 85% by weight, and particularly preferably 45 to 83% by weight, based on the weight of the viscosity index improver, from the viewpoints of the handling properties of the viscosity index improver, 100°C HTHS viscosity, 40°C kinematic viscosity, and 250°C volatility.

[0237] From the aspects of the handling properties of the viscosity index improver, HTHS viscosity at 100°C, kinematic viscosity at 40°C and volatility at 250°C, the content of the (co)polymer (A) in the viscosity index improver of the present invention is preferably 10 to 70 wt %, more preferably 10 to 40 wt %, particularly preferably 13 to 40 wt %, based on the weight of the viscosity index improver.

[0238] The viscosity index improver of the present invention may further contain a base oil other than the ester oil (B1) and the ester oil (B2).

[0239] As a base oil other than ester oil (B1) and ester oil (B2), including a base oil having a kinematic viscosity of less than 1.00 mm at 100°C 2 / s ester oil, 100℃ kinematic viscosity greater than 5.00mm 2 / s of ester oil and hydrocarbon oil, and hydrocarbon oil is preferred from the viewpoint of oxidation stability.

[0240] Examples of the hydrocarbon oil include hydrocarbon oils of groups I to IV of the API classification.

[0241] From the viewpoint of solubility of various additives, the SP value of the hydrocarbon oil is preferably 7.8 to 9.5 (cal / cm 3 ) 1 / 2 , more preferably 8.0 to 9.0 (cal / cm 3 ) 1 / 2 .

[0242] It should be noted that, when a mixture of various hydrocarbon compounds such as mineral oil is used as the hydrocarbon oil, the molecular weight can be determined by GPC, 1 H-NMR and 13The constituent components and their molecular structures can be roughly known from molecular structure analysis such as C-NMR, and the SP value of the hydrocarbon oil can be calculated by arithmetic mean based on the mole fraction.

[0243] In the viscosity index improver of the present invention, the absolute value of the difference between the SP value of the ester oil {the weight average value of (B1) and (B2)} and the SP value of the hydrocarbon oil is preferably 0.1 to 2.0 (cal / cm 3 ) 1 / 2 , more preferably 0.2 to 1.5 (cal / cm 3 ) 1 / 2 , particularly preferably 0.3 to 1.0 (cal / cm 3 ) 1 / 2 .

[0244] In the viscosity index improver of the present invention, from the viewpoint of compatibility, the absolute value of the difference between the SP value calculated based on the weight fraction of the monomers constituting the (co)polymer (A) and the SP value of the hydrocarbon oil is preferably 0.8 to 2.0 (cal / cm 3 ) 1 / 2 , more preferably 0.8 to 1.3 (cal / cm 3 ) 1 / 2 , particularly preferably 0.9 to 1.2 (cal / cm 3 ) 1 / 2 .

[0245] The absolute value of the difference between the SP value calculated based on the weight fraction of the monomers constituting the (co)polymer (A) and the SP value of the hydrocarbon oil can be set to the desired range by appropriately adjusting the SP value and weight fraction of the monomers used to produce the (co)polymer (A).

[0246] The kinematic viscosity of the hydrocarbon oil at 100° C. (measured according to JIS-K2283) is preferably 1 to 15 mm 2 / s, more preferably 2 to 5 mm 2 / s.

[0247] The viscosity index (measured in accordance with JIS-K2283) of the hydrocarbon oil is preferably 100 or more from the viewpoint of the viscosity index and low-temperature fluidity of the lubricating oil composition.

[0248] From the viewpoints of the oxidation stability of the viscosity index improver, the HTHS viscosity, the 40°C kinematic viscosity and the low-temperature viscosity of the lubricating oil composition, the ratio of the total weight of the ester oil (B1) and the ester oil (B2) in the viscosity index improver to the weight of the hydrocarbon oil [{(B1)+(B2)} / hydrocarbon oil] is preferably 100 / 0 to 10 / 90, more preferably 99.9 / 0.1 to 20 / 80.

[0249] From the viewpoint of HTHS viscosity, the weight ratio of the (co)polymer (A) to the hydrocarbon oil in the viscosity index improver ((A) / hydrocarbon oil) is preferably 100 / 0 to 50 / 50, more preferably 90 / 10 to 80 / 20.

[0250] The content of the hydrocarbon oil in the viscosity index improver of the present invention is preferably 1 to 60% by weight, more preferably 2 to 30% by weight, based on the weight of the viscosity index improver, from the viewpoints of oxidation stability, 100°C HTHS viscosity, 40°C kinematic viscosity and low-temperature viscosity of the viscosity index improver.

[0251] From the viewpoint of the handling property of the viscosity index improver, the kinematic viscosity of the viscosity index improver at 90° C. (measured in accordance with JIS-K2283) is preferably 100 to 20,000 mm 2 / s, more preferably 300 to 12000 mm 2 / s.

[0252] The cloud point of the hydrocarbon oil (measured according to JIS-K2269) is preferably -5°C or lower, more preferably -15°C or lower. When the cloud point of the hydrocarbon oil is within this range, the low-temperature viscosity of the lubricating oil composition tends to be good.

[0253] <Lubricating Oil Composition>

[0254] The lubricating oil composition of the present invention contains the viscosity index improver of the present invention and at least one additive selected from the group consisting of a detergent, a dispersant, an antioxidant, an oiliness improver, a pour point depressant, a friction and wear modifier, an extreme pressure agent, a defoamer, an anti-emulsifier, a metal deactivator and a corrosion inhibitor.

[0255] The lubricating oil composition of the present invention preferably contains the (co)polymer (A) in an amount of 0.1 wt % to less than 10 wt %, more preferably 0.5 wt % to less than 10 wt %, based on the weight of the lubricating oil composition, from the perspective of fuel efficiency.

[0256] The lubricating oil composition of the present invention preferably contains the (co)polymer (C) in an amount of 0.01 to 2% by weight based on the weight of the lubricating oil composition, from the viewpoint of low-temperature viscosity.

[0257] In the lubricating oil composition of the present invention, the content of the (co)polymer (C) is preferably 0.01 to 30% by weight, more preferably 0.01 to 10% by weight, based on the weight of the (co)polymer (A), from the viewpoint of low temperature viscosity.

[0258] The lubricating oil composition of the present invention preferably contains the ester oil (B1) and the ester oil (B2) in a total amount of 1 to 99.9 wt %, more preferably 2 to 30 wt %, based on the weight of the lubricating oil composition, from the viewpoints of low temperature viscosity, HTHS viscosity at 100° C., and kinematic viscosity at 40° C.

[0259] The lubricating oil composition of the present invention preferably contains the hydrocarbon oil in an amount of 98.9% by weight or less, more preferably 50 to 90% by weight, based on the weight of the lubricating oil composition, from the viewpoint of oxidation stability.

[0260] When the lubricating oil composition is used as an engine oil, it is preferred that the kinematic viscosity at 100° C. be 2 to 10 mm 2 A lubricating oil composition containing 1 wt% or more and less than 10 wt% of a (co)polymer (A) in a base oil (a mixture of an ester oil (B1) and an ester oil (B2) and, if necessary, a hydrocarbon oil) having a molecular weight of 400 μm.

[0261] When the lubricating oil composition is used as a gear oil, it is preferred that the kinematic viscosity at 100° C. be 2 to 10 mm 2 A lubricating oil composition containing 3 to 20 wt% of a (co)polymer (A) in a base oil (a mixture of an ester oil (B1) and an ester oil (B2) and, if necessary, a hydrocarbon oil) having a molecular weight of 400 μm.

[0262] When the lubricating oil composition is used as an automatic transmission oil (ATF, belt-type CVTF, etc.), the kinematic viscosity at 100° C. is preferably 2 to 6 mm 2 A lubricating oil composition containing 3 to 20 wt% of a (co)polymer (A) in a base oil (a mixture of an ester oil (B1) and an ester oil (B2) and, if necessary, a hydrocarbon oil) having a molecular weight of 400 μm.

[0263] When the lubricating oil composition is used as traction oil, it is preferred that the kinematic viscosity at 100° C. be 1 to 5 mm 2 A lubricating oil composition containing 0.5 to 10 wt% of the (co)polymer (A) in a base oil (a mixture of the ester oil (B1) and the ester oil (B2) and, if necessary, a hydrocarbon oil) having a molecular weight of 400 μm.

[0264] From the viewpoints of friction characteristics, 100°C HTHS viscosity, 40°C kinematic viscosity and 250°C volatility, the weight ratio {(B1) / (B2)} of the ester oil (B1) to the ester oil (B2) contained in the lubricating oil composition of the present invention is preferably 10 / 90 to 90 / 10, more preferably 20 / 80 to 80 / 20.

[0265] From the aspects of low temperature viscosity, HTHS viscosity at 100°C and kinematic viscosity at 40°C, the ratio of the weight of the (co)polymer (A) contained in the lubricating oil composition of the present invention to the total weight of the ester oil (B1) and the ester oil (B2) [(A) / {(B1)+(B2)}] is preferably 10 / 90 to 50 / 50, more preferably 20 / 80 to 35 / 65.

[0266] From the viewpoints of oxidation stability, low temperature viscosity, HTHS viscosity at 100°C, kinematic viscosity at 40°C and volatility at 250°C of the lubricating oil composition, the ratio of the total weight of the ester oil (B1) and the ester oil (B2) contained in the lubricating oil composition to the weight of the hydrocarbon oil [{(B1)+(B2)} / hydrocarbon oil] is preferably 1 / 99 to 20 / 80, more preferably 2 / 98 to 15 / 85.

[0267] From the viewpoint of HTHS viscosity, the weight ratio of the (co)polymer (A) to the hydrocarbon oil {(A) / hydrocarbon oil} contained in the lubricating oil composition is preferably 0.1 / 99.9 to 20 / 80, more preferably 1 / 99 to 10 / 90.

[0268] The lubricating oil composition of the present invention contains various additives. Examples of the additives include the following.

[0269] (1) Cleaning agent:

[0270] Basic, overbased or neutral metal salts [overbased or alkaline earth metal salts of sulfonates (petroleum sulfonates, alkylbenzene sulfonates and alkylnaphthalene sulfonates, etc.)], salicylates, phenates, naphthenates, carbonates, phosphonates and mixtures thereof;

[0271] (2) Dispersant:

[0272] Succinimides (bis- or mono-polybutenyl succinimides), Mannich condensates and borates, etc.;

[0273] (3) Antioxidants:

[0274] Hindered phenols and aromatic secondary amines, etc.;

[0275] (4) Oiliness improver:

[0276] Long-chain fatty acids and their esters (oleic acid and oleic acid esters, etc.), long-chain amines and their amides (oleylamine and oleylamide, etc.), etc.;

[0277] (5) Pour point depressant

[0278] Polyalkyl methacrylate, ethylene-vinyl acetate copolymer, etc.;

[0279] (6) Friction and wear regulator:

[0280] Molybdenum and zinc compounds (molybdenum dithiophosphate, molybdenum dithiocarbamate and zinc dialkyl dithiophosphate, etc.);

[0281] (7) Extreme pressure agent:

[0282] Sulfur compounds (monosulfide or disulfide, sulfoxide and sulfur-phosphorus compounds), phosphorus compounds and chlorine compounds (chlorinated paraffins, etc.);

[0283] (8) Defoaming agent:

[0284] Silicone oil, metal soap, fatty acid ester and phosphate compounds, etc.;

[0285] (9) Anti-emulsifier:

[0286] Quaternary ammonium salts (tetraalkylammonium salts, etc.), sulfated oils and phosphate esters (phosphate esters of nonionic surfactants containing polyoxyethylene, etc.), hydrocarbon solvents (toluene, xylene, ethylbenzene), etc.;

[0287] (10) Metal passivator

[0288] Compounds containing nitrogen atoms (such as benzotriazole), chelated compounds containing nitrogen atoms (such as N,N'-disalicylidene-1,2-diaminopropane), compounds containing nitrogen and sulfur atoms (such as 2-(n-dodecylthio)benzimidazole), etc.;

[0289] (11) Anticorrosive agents:

[0290] Compounds containing nitrogen atoms (benzotriazole and 1,3,4-thiadiazolyl-2,5-bisdialkyldithiocarbamate, etc.)

[0291] Only one of these additives may be added, or two or more additives may be added as needed. In addition, additives obtained by mixing these additives are sometimes referred to as performance additives or package additives, and such additives may also be added.

[0292] The content of each of these additives is preferably 0.1 to 15% by weight based on the total weight of the lubricating oil composition, and the total content of the additives is preferably 0.1 to 30% by weight, more preferably 0.3 to 20% by weight, based on the total weight of the lubricating oil composition.

[0293] The lubricating oil composition of the present invention is suitable for use in gear oil (differential oil and industrial gear oil, etc.), MTF, transmission oil [ATF, DCTF and belt CVTF, etc.], traction oil (annular CVTF, etc.), shock absorber oil, power steering oil, hydraulic oil (hydraulic oil for construction machinery and industrial hydraulic oil, etc.) and engine oil (for gasoline engines and diesel engines).

[0294] Example

[0295] The present invention is further described below by way of examples and comparative examples, but the present invention is not limited thereto.

[0296] The ratio of 1,2-butylene groups in the structural units of hydrocarbon polymers is given by 13 The polymer was analyzed by C-NMR and the molecular weight was determined by the above method using the above mathematical formula (1).

[0297] The molar ratio of 1,2-adduct / 1,4-adduct in the hydrocarbon polymer (molar ratio in the structure derived from butadiene) is given by 13 The polymer was analyzed by C-NMR, and the value of the integrated value B and the integrated value C used in the above-mentioned mathematical formula (1) were determined by the following mathematical formula (3).

[0298] 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)

[0299] <Production Example 1>

[0300] Into a 1 L SUS pressure-resistant reaction vessel equipped with a temperature control device 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 polymerization was then carried out at a polymerization temperature of 50°C.

[0301] After the polymerization rate reached approximately 100%, 2 parts by weight of ethylene oxide was added and the reaction was further carried out at 50°C for 3 hours. To stop the reaction, 50 parts by weight of water and 25 parts by weight of 1N-hydrochloric acid aqueous solution were added and stirred at 80°C for 1 hour. The organic phase of the reaction solution was recovered with a separatory funnel, heated to 70°C, and the solvent was removed under a reduced pressure of 0.027 to 0.040 MPa for 2 hours.

[0302] The obtained polybutadiene containing a hydroxyl group at one end is transferred to a reaction vessel equipped with a temperature regulating device, a stirrer, and a hydrogen introduction tube, and 150 parts by weight of tetrahydrofuran is added to make it uniformly dissolved. After injecting a suspension prepared by premixing 10 parts by weight of palladium carbon and 50 parts by weight of tetrahydrofuran, hydrogen is supplied to the liquid at a flow rate of 30 mL / min through the hydrogen introduction tube, and the reaction is carried out at room temperature for 8 hours. After that, the palladium carbon is removed by filtration, the obtained filtrate is heated to 70°C, and tetrahydrofuran is removed under a reduced pressure of 0.027 to 0.040 MPa to obtain a polymer (Y-1) containing a hydroxyl group at one end of hydrogenated polybutadiene.

[0303] The molecular weight of (Y-1) obtained was measured by GPC, and the 13 The ratio of 1,2-butylene groups was measured by C-NMR. As a result, 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.

[0304] <Production Example 2>

[0305] Into a 1 L SUS pressure-resistant reaction vessel equipped with a temperature control device 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-butyl lithium were charged, and then polymerization was carried out at a polymerization temperature of -0°C.

[0306] After the polymerization rate reached approximately 100%, 2 parts by weight of ethylene oxide was added and the mixture was reacted at 50°C for 3 hours. To stop the reaction, 50 parts by weight of water and 25 parts by weight of a 1N hydrochloric acid aqueous solution were added and stirred at 80°C for 1 hour. The organic phase of the reaction solution was recovered with a separatory funnel, heated to 70°C, and the solvent was removed under a reduced pressure of 0.027 to 0.040 MPa for 2 hours.

[0307] The obtained polybutadiene containing a hydroxyl group at one end is transferred to a reaction vessel equipped with a temperature regulating device, a stirrer, and a hydrogen introduction tube, and 150 parts by weight of tetrahydrofuran is added to make it uniformly dissolved. After injecting a suspension prepared by premixing 10 parts by weight of palladium carbon and 50 parts by weight of tetrahydrofuran, hydrogen is supplied to the liquid at a flow rate of 30 mL / min through the hydrogen introduction tube, and the reaction is carried out at room temperature for 8 hours. After that, the palladium carbon is removed by filtration, the obtained filtrate is heated to 70°C, and tetrahydrofuran is removed under a reduced pressure of 0.027 to 0.040 MPa to obtain a polymer (Y-2) containing a hydroxyl group at one end of hydrogenated polybutadiene.

[0308] The molecular weight of (Y-2) obtained was measured by GPC. 13 The ratio of 1,2-butylene groups was measured by C-NMR. As a result, 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.

[0309] <Production Example 3: Production of Copolymer (C)>

[0310] A hydrocarbon oil (kinematic viscosity at 100° C.: 4.2 mm) was added to a reaction vessel equipped with a stirring device, a heating and cooling device, a thermometer, a dropping funnel, a nitrogen blowing tube, and a pressure reducing device. 2 / s, viscosity index: 128), 75 parts of n-dodecyl methacrylate, 24 parts by weight of n-tetradecyl methacrylate, 41 parts by weight of n-hexadecyl methacrylate, 16 parts by weight of n-octadecyl methacrylate, 0.6 parts by weight of dodecyl mercaptan as a chain transfer agent, 0.5 parts by weight of 2,2-azobis(2,4-dimethylvaleronitrile) and 0.2 parts by weight of 2,2-azobis(2-methylbutyronitrile) were added to another glass beaker, stirred and mixed at 20°C to prepare a monomer solution, which was then added to a dropping funnel.

[0311] After nitrogen substitution of the gas phase of the reaction vessel (gas phase oxygen concentration: 100 ppm or less), the monomer solution was added dropwise over 2 hours while the temperature in the system was kept at 70 to 85°C in a sealed manner. After the addition was completed, the temperature was raised to 120 to 130°C after aging at 85°C for 2 hours, and then the unreacted monomers were removed at the same temperature under reduced pressure (0.027 to 0.040 MPa) for 2 hours to obtain a copolymer composition (C-1) containing 65% by weight of the copolymer (C) in the base oil. The obtained copolymer (C) had an Mw of 53,000 and an SP value of 9.0.

[0312] <Examples 1 to 24, Comparative Examples 1 to 3>

[0313] Into a reaction vessel equipped with a stirring device, a heating and cooling device, a thermometer and a nitrogen inlet pipe, the base oil blend, the monomer blend and the catalyst of the type and amount listed in Table 3-1, 3-2 or Table 4 were added, and after nitrogen substitution (gas phase oxygen concentration 100 ppm), the temperature was raised to 76°C while stirring in a sealed state, and a polymerization reaction was carried out at this temperature for 4 hours. After the temperature was raised to 120 to 130°C, the unreacted monomer was removed at this temperature under reduced pressure (0.027 to 0.040 MPa) for 2 hours. The copolymer composition (C-1) obtained in Preparation Example 3 was further added in the amount listed in Table 3-1, 3-2 or Table 4, and the SP values ​​of the copolymers (A-1) to (A-10) among the viscosity index improvers (R-1) to (R-24) and (R'-1) to (R'-3) were calculated by the above method, and the Mw and Mn were measured by the above method. In addition, the base oil solubility of the copolymer (A) was evaluated by the following method. The oxidation stability of the viscosity index improver was evaluated by the following method. The kinematic viscosity of the viscosity index improver was evaluated by the following method. The results are shown in Tables 3-1, 3-2 and 4.

[0314] <Method for evaluating base oil solubility of copolymer (A)>

[0315] The appearance of the viscosity index improvers (R-1) to (R-24) and (R'-1) to (R'-3) which had been temperature-controlled at 25°C for one day was visually observed under a fluorescent white light at room temperature of 25°C, and the solubility of the copolymer (A) in the base oil was evaluated according to the following evaluation criteria.

[0316] [Evaluation criteria]

[0317] ○: Uniform appearance, no insoluble copolymer

[0318] ×: The appearance is uneven, and insoluble matter of the copolymer is observed

[0319] <Determination method of oxidation stability>

[0320] According to JIS-K2514, an oxidation stability test was conducted at 165.5°C ± 0.5°C for 120 hours, and the increase in the total acid value (mgKOH / g) of the viscosity index improver and the lubricating oil composition before and after the test was measured. The smaller the value, the better the oxidation stability.

[0321] [Evaluation criteria: Viscosity index improver]

[0322] ◎: The increase in the total acid value of the lubricating oil composition before and after the test is 30 mgKOH / g or less

[0323] ○: The increase in the total acid value of the lubricating oil composition before and after the test is greater than 30 mgKOH / g and less than 50 mgKOH / g

[0324] △: The increase in the total acid value of the lubricating oil composition before and after the test is greater than 50 mgKOH / g and less than 70 mgKOH / g

[0325] <Method for measuring kinematic viscosity of viscosity index improver>

[0326] The kinematic viscosity at 90° C. is measured by the method of JIS-K2283. A lower value means a lower viscosity and better handling properties.

[0327] [Table 3-1]

[0328]

[0329] [Table 3-2]

[0330]

[0331] [Table 4]

[0332]

[0333] The compositions of the base oils and monomers (a) to (d) described in Tables 3-1, 3-2 or 4 are as follows.

[0334] Ester oil 1: Bis(2-ethylhexyl) adipate (SP value: 8.93 (cal / cm 3 ) 1 / 2 , Kinematic viscosity at 100℃: 2.32mm 2 / s, viscosity index: 118)

[0335] Ester oil 2: bis(2-ethylhexyl) sebacate (SP value: 8.87 (cal / cm 3 ) 1 / 2 , Kinematic viscosity at 100℃: 3.20mm 2 / s, viscosity index: 151)

[0336] Ester oil 3: butyl oleate (SP value: 8.62 (cal / cm 3 ) 1 / 2 , Kinematic viscosity at 100℃: 2.20mm 2 / s, viscosity index: 232)

[0337] Ester oil 4: diisodecyl adipate (SP value: 8.97 (cal / cm 3 ) 1 / 2 , Kinematic viscosity at 100℃: 3.62mm 2 / s, viscosity index: 141)

[0338] Hydrocarbon oil 1: Kinematic viscosity at 100°C: 4.2 mm 2 / s, viscosity index: 122

[0339] Hydrocarbon oil 2: Kinematic viscosity at 100°C: 3.1 mm 2 / s, viscosity index: 106

[0340] (Y-1): Hydrogenated product of polybutadiene containing a hydroxyl group at one end of Production Example 1 (1,2-butene ratio = 45 mol%)

[0341] (Y-2): Hydrogenated product of polybutadiene containing a hydroxyl group at one end of Production Example 2 (1,2-butene ratio = 65 mol%)

[0342] (a-1): Methacrylate of (Y-1) [Mn: 6,600]

[0343] (a-2): Methacrylate of (Y-2) [Mn: 6,600]

[0344] (b-1): Ethyl methacrylate

[0345] (b-2): n-Butyl methacrylate

[0346] (b-3): Isopropyl methacrylate

[0347] (b-4): Isobutyl methacrylate

[0348] (c-1): a mixture of linear and branched alkyl methacrylates having 12 to 15 carbon atoms (esterified product of Neodol 23 (manufactured by Shell Chemicals) and methacrylic acid)

[0349] (c-2): A mixture of linear and branched alkyl methacrylates having 14 to 16 carbon atoms (esterified product of Neodol 45 (manufactured by Shell Chemicals) and methacrylic acid)

[0350] (d-1) Butoxyethyl methacrylate

[0351] <Examples 25 to 48 and Comparative Examples 4 to 6: 0W-20 Evaluation>

[0352] Hydrocarbon oil (SP value: 8.3 to 8.4 (cal / cm 3 ) 1 / 2 , Kinematic viscosity at 100℃: 4.2mm 2 / s, viscosity index: 128) 90 parts by weight of a lubricating oil composition and 10 parts by weight of a package additive "Infineum P5741" (base value = 84 mgKOH / g, calcium content = 2.49%, nitrogen content = 0.68%, phosphorus content = 0.78%, sulfated ash = 9.76%, zinc content = 0.86%), and viscosity index improvers (R-1) to (R-24) or (R'-1) to (R'-3) were added respectively so that the HTHS viscosity of the obtained lubricating oil composition at 150°C was 2.60±0.05 (mPa·s), thereby obtaining lubricating oil compositions (V-1) to (V-24) and (W-1) to (W-3).

[0353] The lubricating oil compositions (V-1) to (V-24) and (W-1) to (W-3) were measured for shear stability (BOSCH SSI, Sonic SSI), HTHS viscosity (150°C, 100°C, 80°C), kinematic viscosity (100°C, 40°C), viscosity index, low temperature viscosity (-40°C), volatility at 250°C, and friction coefficient by the following methods. The results are shown in Tables 5 and 6.

[0354] [Table 5]

[0355]

[0356] [Table 6]

[0357]

[0358] <Examples 49 to 72 and Comparative Examples 7 to 9: Evaluation of 0W-16>

[0359] Hydrocarbon oil (SP value: 8.3 to 8.4 (cal / cm 3 ) 1 / 2 , Kinematic viscosity at 100℃: 4.2mm 2 / s, viscosity index: 128) 90 parts by weight and 10 parts by weight of a package additive (Infineum P5741), viscosity index improvers (R-1) to (R-24) or (R'-1) to (R'-3) were added respectively so that the HTHS viscosity of the obtained lubricating oil composition at 150°C was 2.30±0.05 (mPa·s), to obtain lubricating oil compositions (V-25) to (V-48) and (W-4) to (W-6). The shear stability (BOSCH SSI, Sonic SSI), HTHS viscosity (150°C, 100°C, 80°C), kinematic viscosity (100°C, 40°C), viscosity index, low temperature viscosity (-40°C), volatility at 250°C and friction coefficient of the lubricating oil compositions (V-25) to (V-48) and (W-4) to (W-6) were measured by the following methods. The results are shown in Tables 7 and 8.

[0360] [Table 7]

[0361]

[0362] [Table 8]

[0363]

[0364] <Method for measuring HTHS viscosity of lubricating oil composition>

[0365] The measurement is performed by the method of ASTM D 4683 at 80° C., 100° C., and 150° C. The lower the HTHS viscosity at 80° C. and 100° C., the better it means.

[0366] <Method for measuring kinematic viscosity of lubricating oil composition and method for calculating viscosity index>

[0367] The kinematic viscosity at 40° C. and 100° C. was measured by the method of JIS-K2283, and the viscosity index was calculated by the method of JIS-K2283. A larger value of the viscosity index means a higher viscosity index improvement effect.

[0368] <Method for measuring and calculating shear stability (BOSCH SSI) of lubricating oil composition>

[0369] The shear stability is measured by the method of ASTM D 6278 and calculated by the method of ASTM D 6022. The smaller the value, the higher the shear stability.

[0370] <Method for measuring and calculating shear stability (Sonic SSI) of lubricating oil composition>

[0371] The shear stability is measured by using an ultrasonic shearing device according to the method of JPI-5S-29-2006 and calculated by the method of ASTM D 6022. The smaller the value, the higher the shear stability.

[0372] <Method for measuring low temperature viscosity of lubricating oil composition>

[0373] The viscosity at -40°C was measured by the method of JPI-5S-42-2004. The smaller the value, the lower the low-temperature viscosity.

[0374] <Determination method of evaporation>

[0375] The evaporation rate at 250° C. is measured by the method of ASTM D 5800. The smaller the value, the lower the evaporation rate of the lubricating oil, and the better it is as a motor oil.

[0376] <Method for measuring friction characteristics of lubricating oil composition-HFRR>

[0377] A high-frequency reciprocating tester (HFRR, manufactured by PCS Instruments) was used, the material of the test steel ball was SUJ2, the diameter of the test steel ball was 6 mm, and the material of the test disc was SUJ2. The test was conducted under the conditions of a test temperature of 80°C, a load of 3.92N (400g), a stroke of 1000μm, a frequency of 20Hz, and a test time of 60min to measure the friction coefficient.

[0378] The results in Tables 5 to 8 show that the viscosity index improver of the present invention has an excellent friction reducing effect and is also excellent in HTHS viscosity, 40°C kinematic viscosity, viscosity index, shear stability, low temperature viscosity and 250°C volatility.

[0379] On the other hand, it can be seen that the lubricating oil compositions of Comparative Examples 4 to 9 containing only one ester oil or no ester oil have a very high friction coefficient and inferior friction characteristics compared with otherwise identical Examples 26 and 50. In particular, the results of Comparative Examples 4 and 7 show that the lubricating oil compositions containing only ester oil having a kinematic viscosity of 1.00 to 2.50 mm / s at 100°C are inferior to those of Examples 26 and 50. 2 / s ester oil (B1), the evaporation at 250°C also deteriorated, and from the results of Examples 26 and 50, it was found that the kinematic viscosity at 100°C was 2.51 to 5.00 mm / s. 2 When used in combination with an ester oil (B2) having a viscosity of 1.5 W / s, the evaporation property at 250°C can be improved, and both the friction characteristics and the evaporation property at 250°C can be achieved.

[0380] Industrial Applicability

[0381] The lubricating oil composition containing the viscosity index improver of the present invention has excellent friction characteristics and is therefore suitable for use in gear oils (differential oils and industrial gear oils, etc.), MTFs, transmission oils [ATFs, DCTFs, belt-type CVTFs, etc.], traction oils (annular CVTFs, etc.), shock absorber oils, power steering oils, hydraulic oils (construction machinery hydraulic oils and industrial hydraulic oils, etc.), and engine oils (for gasoline engines and diesel engines).

Claims

1. A viscosity index improver comprising a copolymer (A) comprising a polyolefin monomer (a) represented by the following general formula (1), a (meth)acrylic acid alkyl ester monomer (b) having an alkyl group having 1 to 4 carbon atoms, and a (meth)acryloyl monomer (c) having a linear or branched alkyl group having 9 to 36 carbon atoms as essential constituent monomers, and a 100° C. kinematic viscosity of 1.00 mm 2 / s~2.50mm 2 / s ester oil (B1) and 100℃ kinematic viscosity of 2.51mm 2 / s~5.00mm 2 / s ester oil (B2), The weight ratio of ester oil (B1) to ester oil (B2) is (B1) / (B2) from 10 / 90 to 90 / 10. The difference in kinematic viscosity between ester oil (B1) and ester oil (B2) at 100°C (B2) - (B1) is 0.8 mm 2 / s~1.5mm 2 / s, [Chemistry 1] In the general formula (1), R 1 is a hydrogen atom or a methyl group; -X 1 - is -O-, -O(AO) m - or -NH-, A is an alkylene group having 2 to 4 carbon atoms, m is an integer of 1 to 10, and when m is 2 or more, A is the same or different; R 2 A residue obtained by removing one hydrogen atom from a hydrocarbon polymer containing a 1,2-butylene group as a structural unit; p is 0.

2. The viscosity index improver according to claim 1, wherein The ratio (A) / ((B1)+(B2)) of the weight of the copolymer (A) contained in the viscosity index improver to the total weight of the ester oil (B1) and the ester oil (B2) is 10 / 90 to 50 / 50.

3. The viscosity index improver according to claim 1 or 2, wherein The difference in kinematic viscosity at 100°C between the ester oil (B1) and the ester oil (B2) contained in the viscosity index improver (B2) - (B1) is 1.0 mm 2 / s~1.5mm 2 / s.

4. The viscosity index improver according to claim 1 or 2, wherein The solubility parameter calculated based on the weight fraction of the monomers constituting the copolymer (A) was 8.0 (cal / cm 3 ) 1 / 2 ~10.0(cal / cm 3 ) 1 / 2 .

5. The viscosity index improver according to claim 1 or 2, wherein The copolymer (A) is a copolymer containing a monomer (d) represented by the following general formula (3) as a constituent monomer, [Chemistry 2] In the general formula (3), R 7 is a hydrogen atom or a methyl group; -X 3 - is a group represented by -O- or -NH-; R 8 is an alkylene group having 2 to 4 carbon atoms; R 9 is an alkyl group having 1 to 8 carbon atoms; r is an integer of 1 to 20, and when r is 2 or more, R 8 Same or different.

6. The viscosity index improver according to claim 5, wherein The copolymer (A) is a copolymer containing the following monomers as constituent monomers: based on the total weight of the monomers constituting the copolymer (A), it contains 1% by weight to 80% by weight of the monomer (b), 1% by weight to 60% by weight of the monomer (c), and 2% by weight to 35% by weight of the monomer (d).

7. The viscosity index improver according to claim 1 or 2, wherein The weight average molecular weight of the copolymer (A) is 5,000 to 2,000,000.

8. The viscosity index improver according to claim 1 or 2, wherein The viscosity index improver contains 0.01% by weight to 30% by weight of the (meth)acrylate copolymer (C) other than the copolymer (A), based on the weight of the copolymer (A).

9. The viscosity index improver according to claim 1 or 2, wherein The viscosity index improver contains hydrocarbon oil.

10. A lubricating oil composition comprising the viscosity index improver according to any one of claims 1 to 9 and at least one additive selected from the group consisting of a detergent, a dispersant, an antioxidant, an oiliness improver, a pour point depressant, a friction and wear modifier, an extreme pressure agent, a defoamer, an anti-emulsifier, a metal deactivator and a corrosion inhibitor.

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