JP6748593B2 - Viscosity index improver and lubricating oil composition - Google Patents

Description

The present invention relates to a viscosity index improver and a lubricating oil composition containing the viscosity index improver.

Lubricating oils and hydraulic oils used in automobiles and the like have lower viscosities at higher temperatures, but in practice it is desirable that the viscosities do not change as much as possible over a wide range from low to high temperatures. Therefore, a method of adding a viscosity index improver to the lubricating oil to improve the temperature dependence of the viscosity is widely used. As such viscosity index improvers, methacrylic acid ester copolymers (Patent Documents 1 to 4), olefin copolymers (Patent Document 5), macromonomer copolymers (Patent Document 6) and the like are known. ..
However, the above-mentioned viscosity index improvers have a problem that the effect of improving the viscosity index is not yet sufficient, and the shear stability after long-time operation is not sufficient in practical use.

Japanese Patent No. 2732187 Japanese Patent No. 2941392 JP, 7-62372, A JP, 2004-307551, A JP, 2005-2004454, A Japanese Patent Publication No. 2008-546894

An object of the present invention is to provide a viscosity index improver having a high viscosity index improving effect and excellent shear stability and stability of a lubricating oil composition.

［Ｒ^１は水素原子又はメチル基；−Ｘ^１−は−Ｏ−、−Ｏ（ＡＯ）_ｍ−又は−ＮＨ−で表される基であって、Ａは炭素数２〜４のアルキレン基であり、ｍは１〜１０の整数であり、ｍが２以上の場合のＡは同一でも異なっていてもよく、（ＡＯ）_ｍ部分はランダム結合でもブロック結合でもよい；Ｒ^２はイソブチレン及び／又は１，２−ブチレンを必須構成単位とする炭化水素重合体から水素原子を１つ除いた残基；ｐは０又は１の数。］

［Ｒ ^３ は水素原子又はメチル基；−Ｘ ^２ −は−Ｏ−又は−ＮＨ−で表される基；Ｒ ^４ は炭素数２〜４の直鎖又は分岐アルキレン基；Ｒ ^５ 、Ｒ ^６ はそれぞれ独立に炭素数８〜２４の直鎖アルキル基；ｑは０〜２０の整数であり、ｑが２以上の場合のＲ ^４ は同一でも異なっていてもよく、（Ｒ ^４ Ｏ） _ｑ 部分はランダム結合でもブロック結合でもよい。］
As a result of intensive studies, the present inventors have reached the present invention. That is, the present invention relates to a monomer (a) represented by the following general formula (1) and a (meth)acrylic acid alkyl ester (b) having an alkyl group having 1 to 4 carbon atoms as essential constituent monomers. A viscosity index improver containing a polymer (A), wherein (A) is a monomer (c) represented by the following general formula (2) as a constituent monomer of (A), and/or carbon. A copolymer containing a (meth)acrylic acid alkyl ester (d) having a linear alkyl group of the number 12 to 36, wherein the weight average molecular weight of (A) is 20,000 to 150,000, A viscosity index improver in which the weight average molecular weight of the monomer (a) is 1,000 to 4,000; a lubricating oil composition comprising the viscosity index improver and a base oil.

[R ¹ is a hydrogen atom or a methyl group; -X ¹ -is a group represented by -O-, -O(AO) _m -, or -NH-, and A is an alkylene group having 2 to 4 carbon atoms. And m is an integer of 1 to 10, and when m is 2 or more, A may be the same or different, and the (AO) _m portion may be a random bond or a block bond; R ² is isobutylene and/or Residue obtained by removing one hydrogen atom from a hydrocarbon polymer having 1,2-butylene as an essential constituent unit; p is a number of 0 or 1. ]

[R ³ is a hydrogen atom or a methyl group; -X ² is a group represented by -O- or -NH-; R ⁴ is a linear or branched alkylene group having 2 to ⁴ carbon atoms; R ⁵ and R ⁶ are Each independently a straight-chain alkyl group having 8 to 24 carbon atoms; q is an integer of 0 to 20, R ^{4 s} when q is 2 or more may be the same or different, and the (R ⁴ O) _q moiety is Random connection or block connection may be used. ]

The lubricating oil composition containing the viscosity index improver of the present invention has a high effect of improving the viscosity index and an effect of excellent shear stability.

The viscosity index improver of the present invention comprises (a) represented by the general formula (1) and (meth)acrylic acid alkyl ester (b) having an alkyl group having 1 to 4 carbon atoms as essential constituent monomers. It contains a copolymer (A). In addition, (meth)acrylic acid means acrylic acid or methacrylic acid.

R ¹ in the general formula (1) is a hydrogen atom or a methyl group. Of these, a methyl group is preferable from the viewpoint of viscosity index.

Formula (1) in the ^-X 1 - is, -O -, - is or NH- group represented by - O _{(AO) m.}
A is an alkylene group having 2 to 4 carbon atoms.
Examples of the alkylene group having 2 to 4 carbon atoms include ethylene group, 1,2- or 1,3-propylene group, and 1,2-, 1,3- or 1,4-butylene group.
When m is 1 or more, m is an integer of 1 to 10, preferably an integer of 1 to 4, and more preferably an integer of 1 to 2 from the viewpoint of the viscosity index.
When m is 2 or more, A may be the same or different, and the (AO) _m portion may be a random bond or a block bond.
Among —X ¹ —, a group represented by —O— and —O(AO) _m — is preferable from the viewpoint of viscosity index, and more preferably —O— and —O(CH ₂ CH ₂ O). )-Is a group represented by.

p is a number of 0 or 1.

R ² in the general formula (1) has one hydrogen atom from a hydrocarbon polymer (hereinafter abbreviated as “hydrocarbon polymer”) having isobutylene and/or 1,2-butylene as an essential constituent monomer. It is the removed residue.
Examples of the hydrocarbon polymer include polymers having the following (1) to (3) as constituent monomers in addition to isobutylene and/or 1,2-butylene.
The hydrocarbon polymer may be a block polymer or a random polymer.
(1) Aliphatic unsaturated hydrocarbons [olefins having 2 to 36 carbon atoms (for example, ethylene, propylene, 2,3-butylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, triacocene and hexatriacocene) and Dienes having 2 to 36 carbon atoms (such as butadiene, isoprene, 1,4-pentadiene, 1,5-hexadiene and 1,7-octadiene), etc.]
(2) Alicyclic unsaturated hydrocarbons [eg cyclohexene, (di)cyclopentadiene, pinene, limonene, indene, vinylcyclohexene and ethylidene bicycloheptene]
(3) Aromatic group-containing unsaturated hydrocarbon (for example, styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene, crotyl). Benzene, vinylnaphthalene, divinylbenzene, divinyltoluene, divinylxylene, trivinylbenzene, etc.) and the like.
When the hydrocarbon polymer has a double bond, a part or all of the double bond may be hydrogenated by hydrogenation.

Based on the total number of constituent monomers of the hydrocarbon polymer, the total ratio of isobutylene groups and/or 1,2-butylene groups is preferably 30 mol% or more, and more preferably from the viewpoint of viscosity index and shear stability. Is 40 mol% or more, particularly preferably 50 mol% or more, and most preferably 60 mol% or more.

The monomer (a) represented by the general formula (1) is an ester of (meth)acrylic acid with a hydroxyl group-containing (co)polymer (Y) having a hydroxyl group introduced at one terminal of a hydrocarbon polymer. It can be obtained by a chemical reaction. In addition, "(meth)acryl" means methacryl or acryl.

Specific examples of the one-terminal hydroxyl group-containing (co)polymer (Y) include the following.
Alkylene oxide adduct (Y1); alkylene oxide (ethylene oxide, propylene oxide, etc.) in (co)polymer obtained by polymerizing unsaturated hydrocarbon (x) in the presence of ionic polymerization catalyst (sodium catalyst, etc.) And the like obtained by adding.
Hydroboration compound (Y2); Hydroboration reaction product of (co)polymer of (x) having a terminal double bond (for example, those described in US Pat. No. 4,316,973) and the like.
Maleic anhydride-ene-amino alcohol adduct (Y3); The reaction product obtained by the ene reaction of the (co)polymer of (x) having a terminal double bond with maleic anhydride is imidized with amino alcohol. Things obtained from.
Hydroformyl-hydride (Y4); a product obtained by hydroformylating a (co)polymer of (x) having a terminal double bond and then hydrogenating it (for example, those described in JP-A-63-175096). )etc.
Among (Y), (Y1), (Y2) and (Y3) are preferable from the viewpoint of viscosity index and shear stability, and more preferable is (Y1).

The weight average molecular weight (hereinafter abbreviated as Mw) of the monomer (a) is 1,000 to 4,000, preferably 1,500 to 3,000, and more preferably from the viewpoint of viscosity index and shear stability. Is 1,500 to 2,500. The Mw of the monomer (a), the one-terminal hydroxyl group-containing (co)polymer (Y) and the copolymer (A) can be measured by gel permeation chromatography under the following conditions.
<Mw measurement conditions of (a), (Y) and (A)>
Device: "HLC-802A" [manufactured by Tosoh Corporation]
Column: "TSK gel GMH6" [manufactured by Tosoh Corporation] 2 Measuring temperature: 40°C
Sample solution: 0.5 wt% tetrahydrofuran solution Injection volume: 200 μl
Detector: Refractive index detector Reference substance: Standard polystyrene (TSK standard POLYSTYRENE) 12 points (molecular weight: 500, 1,050, 2,800, 5,970, 9,100, 18,100, 37,900, 96,400) , 190,000, 355,000, 1,090,000, 2,890,000) [manufactured by Tosoh Corporation]

From the viewpoint of solubility in lubricating oil, (Y) preferably has a specific solubility parameter (hereinafter abbreviated as SP value). The range of the SP value is preferably 7.0 to 9.0 (cal/cm ³ ) ^1/2 , and more preferably 7.3 to 8.5 (cal/cm ³ ) ^1/2 . The SP value in the present invention is a value calculated by the method described in the Fedors method (Polymer Engineering and Science, February, 1974, Vol. 14, No. 2 P. 147 to 154).
The SP value of (Y) is calculated by calculating the SP value of each of the monomers constituting (Y) by the above method, and the SP value of each monomer is calculated based on the mole fraction of the constituent monomer units. The average value.
The SP value of (Y) can be set within a desired range by appropriately adjusting the SP value and the mole fraction of the monomer used.

The crystallization temperature of (Y) is preferably −40° C. or lower, more preferably −50° C. or lower, particularly preferably −55° C. or lower, most preferably −60° C., from the viewpoint of low temperature viscosity of the lubricating oil composition. It is the following.
The crystallization temperature of (Y) and the (co)polymer (A) can be measured using a differential scanning calorimeter "Unix (registered trademark) DSC7" (manufactured by PERKIN-ELMER), It is a crystallization temperature observed when Y) and 5 mg of (A) are sampled and cooled from 100°C to -80°C at an isothermal rate of 10°C/min.

The copolymer (A) in the present invention contains a (meth)acrylic acid alkyl ester (b) having a linear alkyl group having 1 to 4 carbon atoms as an essential constituent monomer.

Examples of the (meth)acrylic acid alkyl ester (b) having a linear alkyl group having 1 to 4 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate and (meth ) N-butyl acrylate may be mentioned.
Preferred among (b) are (meth)acrylic acid esters having a linear alkyl group having 1 to 3 carbon atoms, more preferred are methyl (meth)acrylate and ethyl (meth)acrylate, Particularly preferred is methyl (meth)acrylate.

The (co)polymer (A) in the present invention is, in addition to the monomers (a) and (b), a monomer (c) represented by the following general formula (2) and/or a carbon number of 12 to 36. From the viewpoints of viscosity index and shear stability, a copolymer having the (meth)acrylic acid alkyl ester (d) having a linear alkyl group as a constituent monomer is preferable.

［Ｒ^３は水素原子又はメチル基；−Ｘ^２−は−Ｏ−又は−ＮＨ−で表される基；Ｒ^４は炭素数２〜４の直鎖又は分岐アルキレン基；Ｒ^５、Ｒ^６はそれぞれ独立に炭素数８〜２４の直鎖アルキル基；ｑは０〜２０の整数であり、ｑが２以上の場合のＲ^４は同一でも異なっていてもよく、（Ｒ^４Ｏ）_ｑ部分はランダム結合でもブロック結合でもよい。］

[R ³ is a hydrogen atom or a methyl group; -X ² -is a group represented by -O- or -NH-; R ⁴ is a linear or branched alkylene group having 2 to ⁴ carbon atoms; R ^{5 and} R ⁶ are Each independently a straight-chain alkyl group having 8 to 24 carbon atoms; q is an integer of 0 to 20, R ^{4 s} when q is 2 or more may be the same or different, and the (R ⁴ O) _q moiety is Random connection or block connection may be used. ]

R ³ in the general formula (2) is a hydrogen atom or a methyl group. Of these, the methyl group is preferable from the viewpoint of the effect of improving the viscosity index.

-X ² in the general formula (2) - is a group represented by -O- or -NH-. Of these, the group represented by —O— is preferable from the viewpoint of the effect of improving the viscosity index.

R ⁴ in the general formula (2) is an alkylene group having 2 to 4 carbon atoms. The alkylene group having 2 to 4 carbon atoms includes ethylene group, isopropylene group, 1,2- or 1,3-propylene group, isobutylene group, and 1,2-, 1,3- or 1,4-butylene group. Is mentioned.

Q in the general formula (2) is an integer of 0 to 20, preferably an integer of 0 to 5, and more preferably an integer of 0 to 2, from the viewpoint of the viscosity index improving effect and low temperature viscosity.
When q is 2 or more, A may be the same or different, and the (R ⁴ O) _q portion may be a random bond or a block bond.

R ⁵ and R ⁶ in the general formula (2) are each independently a linear alkyl group having 8 to 24 carbon atoms. Specifically, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tetradecyl group, n-hexadecyl group, n-octadecyl group, n-eicosyl group and An n-tetracosyl group is mentioned.
Among the linear alkyl groups having 8 to 24 carbon atoms, the linear alkyl groups having 8 to 20 carbon atoms are preferable, and the linear alkyl groups having 9 to 18 carbon atoms are more preferable from the viewpoint of viscosity index and shear stability. A group, particularly preferably a linear alkyl group having 10 to 16 carbon atoms.

Specific examples of the monomer (c) include 2-octyldecyl (meth)acrylate, ester of ethylene glycol mono-2-octyl pentadecyl ether and (meth)acrylic acid, and 2-octyl (meth)acrylate. Dodecyl, 2-decyltetradecyl (meth)acrylate, 2-dodecylhexadecyl (meth)acrylate, 2-tetradecyloctadecyl (meth)acrylate, 2-dodecylpentadecyl (meth)acrylate, (meth)acrylic Acid 2-tetradecylheptadecyl, (meth)acrylic acid 2-hexadecylheptadecyl, (meth)acrylic acid 2-heptadecylicosyl, (meth)acrylic acid 2-hexadecyldocosyl, (meth)acrylic acid 2 -Eicosyl docosyl, 2-(meth)acrylic acid 2-tetracosyl hexacosyl, N-2-octyl decyl (meth)acrylamide, etc. are mentioned.
Of the monomers (b), from the viewpoint of viscosity index and shear stability, 2-octyldodecyl (meth)acrylate, 2-decyltetradecyl (meth)acrylate, 2-dodecyl (meth)acrylate are preferable. Hexadecyl and 2-tetradecyl octadecyl (meth)acrylate.

Examples of the (meth)acrylic acid alkyl ester (d) having a linear alkyl group having 12 to 36 carbon atoms include (meth)acrylic acid n-dodecyl, (meth)acrylic acid n-tridecyl, and (meth)acrylic acid n-. Tetradecyl, n-pentadecyl (meth)acrylate, n-hexadecyl (meth)acrylate, n-octadecyl (meth)acrylate, n-icosyl (meth)acrylate, n-tetracosyl (meth)acrylate, (meth) Examples thereof include n-triacontyl acrylate and n-hexatriacontyl (meth)acrylate.
Among (d), a (meth)acrylic acid alkyl ester having a linear alkyl group having 12 to 32 carbon atoms is preferable, and a (meth)acrylic acid having a linear alkyl group having 16 to 30 carbon atoms is more preferable. Esters, particularly preferably (meth)acrylic acid esters having a linear alkyl group having 18 to 24 carbon atoms.

The (co)polymer (A) in the present invention is a nitrogen atom-containing monomer (e) other than the monomers (a) and (c), a hydroxyl group in addition to the monomers (a) to (d). From the viewpoint of viscosity index and shear stability, it is a copolymer having at least one selected from the group consisting of the containing monomer (f) and the phosphorus atom-containing monomer (g) as a constituent monomer. preferable.
Examples of the nitrogen atom-containing monomer (e) include the following monomers (e1) to (e4) excluding the monomers (a) and (c).

Amide group-containing monomer (e1):
(Meth)acrylamide, monoalkyl(meth)acrylamide [one nitrogen atom having one alkyl group having 1 to 4 carbon atoms; for example, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-isopropyl (Meth)acrylamide and Nn- or isobutyl (meth)acrylamide, etc.], N-(N'-monoalkylaminoalkyl)(meth)acrylamide [one nitrogen-bonded alkyl group having 1 to 4 carbon atoms] Those having an aminoalkyl group (having 2 to 6 carbon atoms); for example, N-(N'-methylaminoethyl)(meth)acrylamide, N-(N'-ethylaminoethyl)(meth)acrylamide, N-(N' -Isopropylamino-n-butyl)(meth)acrylamide and N-(N'-n- or isobutylamino-n-butyl)(meth)acrylamide, etc.], dialkyl(meth)acrylamide [having 1 to 4 carbon atoms at the nitrogen atom] Having two alkyl groups bonded thereto; 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 [aminoalkyl group in which two alkyl groups having 1 to 4 carbon atoms are bonded to the nitrogen atom of the aminoalkyl group (carbon Having a number of 2 to 6); 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 amide [N-vinylformamide, N -Vinylacetamide, N-vinyl-n- or isopropionic acid amide, N-vinylhydroxyacetamide and the like] and the like.

Nitro group-containing monomer (e2):
4-nitrostyrene etc. are mentioned.

Primary to tertiary amino group-containing monomer (e3):
Primary amino group-containing monomer {alkenylamine having 3 to 6 carbon atoms [(meth)allylamine and crotylamine, etc.], aminoalkyl (2 to 6 carbon atoms) (meth)acrylate [aminoethyl (meth)acrylate, etc.]} A secondary amino group-containing monomer {monoalkylaminoalkyl(meth)acrylate [having an aminoalkyl group (having 2 to 6 carbon atoms) in which one alkyl group having 1 to 6 carbon atoms is bonded to a nitrogen atom; Nt-butylaminoethyl (meth)acrylate and N-methylaminoethyl (meth)acrylate, etc.], C 6-12 dialkenylamine [di(meth)allylamine, etc.]; tertiary amino group-containing unit amount Body {dialkylaminoalkyl(meth)acrylate [having an aminoalkyl group (2 to 6 carbon atoms) in which two alkyl groups having 1 to 6 carbon atoms are bonded to a nitrogen atom; for example, N,N-dimethylaminoethyl (meth ) Acrylate and N,N-diethylaminoethyl (meth)acrylate, etc.], alicyclic (meth)acrylate having a nitrogen atom [morpholinoethyl (meth)acrylate, etc.], aromatic monomer [N-(N′, N′-diphenylaminoethyl)(meth)acrylamide, N,N-dimethylaminostyrene, 4-vinylpyridine, 2-vinylpyridine, N-vinylpyrrole, N-vinylpyrrolidone and N-vinylthiopyrrolidone]}, and These hydrochlorides, sulfates, phosphates, lower alkyl (C1-8) monocarboxylic acid (acetic acid, propionic acid, etc.) salts and the like can be mentioned.

Nitrile group-containing monomer (e4):
(Meth)acrylonitrile and the like can be mentioned.

Among (e), (e1) and (e3) are preferable, and N-(N′,N′-diphenylaminoethyl)(meth)acrylamide and N-(N′,N′-dimethyl) are more preferable. Aminoethyl)(meth)acrylamide, N-(N',N'-diethylaminoethyl)(meth)acrylamide, N-(N',N'-dimethylaminopropyl)(meth)acrylamide, N,N-dimethylaminoethyl (Meth)acrylate and N,N-diethylaminoethyl (meth)acrylate.

Hydroxyl group-containing monomer (f):
Hydroxyl group-containing aromatic monomer (p-hydroxystyrene etc.), hydroxyalkyl (C2-6) (meth)acrylate [2-hydroxyethyl (meth)acrylate, and 2- or 3-hydroxypropyl (meth)acrylate Etc.], mono- or bis-hydroxyalkyl (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, alkenol having 3 to 12 carbon atoms [(meth)allyl alcohol, crotyl alcohol, isocrotyl alcohol, 1-octenol and 1 -Undecenol and the like], alkene monool or alkene diol having 1 to 12 carbon atoms [1-buten-3-ol, 2-buten-1-ol and 2-butene-1,4-diol and the like], hydroxyalkyl (carbon 1 to 6) alkenyl (3 to 10 carbon atoms) ether (2-hydroxyethylpropenyl ether etc.), polyhydric (3 to 8 valent) alcohol (glycerin, pentaerythritol, sorbitol, sorbitan, diglycerin, sugar and sucrose etc. ) Alkenyl (C3-10) ether or (meth)acrylate [sucrose (meth)allyl ether, etc.];
Polyoxyalkylene glycol (alkylene group having 2 to 4 carbon atoms, degree of polymerization 2 to 50), polyoxyalkylene polyol [polyoxyalkylene ether of the above trivalent to octavalent alcohol (alkylene group having 2 to 4 carbon atoms, degree of polymerization) 2 to 100)], mono(meth)acrylates of alkyl (C1-4) ethers of polyoxyalkylene glycols or polyoxyalkylene polyols [polyethylene glycol (Mn: 100 to 300) mono(meth)acrylate, polypropylene glycol ( Mn: 130 to 500) mono(meth)acrylate, methoxypolyethylene glycol (Mn: 110 to 310) (meth)acrylate, lauryl alcohol ethylene oxide adduct (2 to 30 mol) (meth)acrylate and mono(meth)acrylic acid. Polyoxyethylene (Mn: 150 to 230) sorbitan, etc.] and the like;

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

Phosphoric acid ester group-containing monomer (g1):
(Meth)acryloyloxyalkyl (C2-4) phosphoric acid ester [(meth)acryloyloxyethyl phosphate and (meth)acryloyloxyisopropyl phosphate] and phosphoric acid alkenyl ester [vinyl phosphate, allyl phosphate, Propenyl phosphate, isopropenyl phosphate, butenyl phosphate, pentenyl phosphate, octenyl phosphate, decenyl phosphate, dodecenyl phosphate, etc.] and the like. In addition, "(meth)acryloyloxy" means acrylyloxy or methacryloyloxy.

Phosphono group-containing monomer (g2):
(Meth)acryloyloxyalkyl (C2-4) phosphonic acid [(meth)acryloyloxyethylphosphonic acid, etc.] and alkenyl (C2-12) phosphonic acid [vinylphosphonic acid, allylphosphonic acid and octenyl] Phosphonic acid and the like] and the like.

Among (g), (g1) is preferable, (meth)acryloyloxyalkyl (C2-4) phosphate ester is more preferable, and (meth)acryloyloxyethyl phosphate is particularly preferable.

The viscosity index (A) is a copolymer containing, in addition to the monomers (a) to (g), a monomer (h) having two or more unsaturated groups as a constituent monomer. And preferable from the viewpoint of shear stability.

Examples of the monomer (h) having two or more unsaturated groups include divinylbenzene, alkadienes having 4 to 12 carbon atoms (butadiene, isoprene, 1,4-pentadiene, 1,6-heptadiene and 1,7- Octadiene, etc.), (di)cyclopentadiene, vinylcyclohexene and ethylidene bicycloheptene, limonene, ethylene di(meth)acrylate, polyalkylene oxide glycol di(meth)acrylate, pentaerythritol triallyl ether, trimethylolpropane tri(meth)acrylate. The esters of unsaturated carboxylic acids and glycols and the esters of unsaturated alcohols and carboxylic acids described in International Publication No. WO01/009242, and the esters having Mn of 500 or more are mentioned.

In addition to the monomers (a) to (h), (A) may have the following monomers (i) to (o) as constituent monomers.

Aliphatic hydrocarbon monomer (i):
Examples thereof include alkenes having 2 to 20 carbon atoms (ethylene, propylene, butene, isobutene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.).

Alicyclic hydrocarbon-based monomer (j):
Examples thereof include cyclopentene, cyclohexene, cycloheptene, cyclooctene and pinene.

Aromatic hydrocarbon monomer (k):
Styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, 4-ethylstyrene, 4-isopropylstyrene, 4-butylstyrene, 4-phenylstyrene, 4-cyclohexylstyrene, 4-benzylstyrene, 4-chlorostyrene. Examples include chillbenzene, indene, 2-vinylnaphthalene and the like.

Vinyl ester, vinyl ether, vinyl ketones (l):
Vinyl ester of saturated fatty acid having 2 to 12 carbon atoms (vinyl acetate, vinyl propionate, vinyl butyrate, vinyl octanoate, etc.), alkyl, aryl or alkoxyalkyl vinyl ether 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 and vinyl-2-butoxyethyl ether, etc.) and C1-C8 alkyl or aryl vinyl ketones (methyl vinyl ketone, ethyl vinyl ketone and Phenyl vinyl ketone etc.) and the like.

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

Halogen element-containing monomer (n):
Examples thereof include vinyl chloride, vinyl bromide, vinylidene chloride, (meth)allyl chloride, and styrene halides (dichlorostyrene etc.).

Esters of unsaturated polycarboxylic acids (o):
Alkyl, cycloalkyl or aralkyl ester of unsaturated polycarboxylic acid [C1-C8 alkyl diester of unsaturated dicarboxylic acid (maleic acid, fumaric acid, itaconic acid, etc.) (dimethyl maleate, dimethyl fumarate, diethyl maleate And dioctyl maleate)] and the like.

The proportion of (a) constituting (A) is preferably 1 to 25% by weight, and more preferably 5 to 20% by weight, based on the weight of (A), from the viewpoint of viscosity index and shear stability. %, particularly preferably 5 to 17% by weight, most preferably 5 to 15% by weight.
The proportion of (b) constituting (A) is preferably 20 to 60% by weight, more preferably 30 to 55% by weight, based on the weight of (A), from the viewpoint of viscosity index and shear stability. , Particularly preferably 35 to 50% by weight, most preferably 40 to 50% by weight.
The proportion of (c) constituting (A) is preferably 20 to 70% by weight, more preferably 30 to 65% by weight, based on the weight of (A), from the viewpoint of viscosity index and shear stability. And particularly preferably 35 to 60% by weight.
The proportion of (d) constituting (A) is preferably 1 to 40% by weight based on the weight of (A), if necessary, from the viewpoint of viscosity index and shear stability. It is preferably 5 to 35% by weight, particularly preferably 10 to 30% by weight.
From the viewpoint of viscosity index and shear stability, the proportion of each of (e) to (g) constituting (A) is, if necessary, preferably 1 to 15 weight based on the weight of (A). %, more preferably 1 to 12% by weight, particularly preferably 2 to 10% by weight.
The proportion of (h) constituting (A) is preferably 0.01 to 200 ppm based on the weight of (A) from the viewpoint of viscosity index and shear stability, and further, if necessary. It is preferably 0.05 to 50 ppm, particularly preferably 0.1 to 20 ppm.
From the viewpoint of the viscosity index improving effect and the low temperature viscosity of the lubricating oil composition, the respective proportions of (i) to (o) constituting (A) are, if necessary, based on the weight of (A), It is preferably 1 to 10% by weight, more preferably 1 to 7% by weight, and particularly preferably 2 to 5% by weight.

The SP value of (A) is preferably 8.5 to 9.6 (cal/cm ³ ) ^1/2 from the viewpoint of the effect of improving the viscosity index and the low temperature viscosity of the lubricating oil composition, and more preferably 8. 8 to 9.6 (cal/cm ³ ) ^1/2 , particularly preferably 9.0 to 9.5 (cal/cm ³ ) ^1/2 , and most preferably 9.2 to 9.5 (cal/cm ^{3 ).} ) ^1/2 .
The SP value of (A) is calculated by calculating the SP value of each of the monomers constituting (A) by the above method, and the SP value of each monomer is calculated based on the mole fraction of the constituent monomer units. The average value.
The SP value of (A) can be adjusted to 8.5 to 9.6 (cal/cm ³ ) ^1/2 by appropriately adjusting the SP value and the mole fraction of the monomer used.

The absolute value of the difference between the SP value of (A) and the SP value of the base oil is preferably 0.5 to 1.6 (cal/cm ³ ) from the viewpoint of the viscosity index improving effect and the low temperature viscosity of the lubricating oil composition. ^1/2 , more preferably 0.8 to 1.6 (cal/cm ³ ) ^1/2 , and particularly preferably 1.0 to 1.6 (cal/cm ³ ) ^1/2 .

Mw of (A) is usually 20,000 to 150,000, and from the viewpoint of viscosity index and shear stability, the lower limit is preferably 30,000 or more, more preferably 40,000 or more, and the upper limit is preferable. Is 130,000, more preferably 120,000 or less, particularly preferably 100,000 or less, most preferably 80,000 or less. If Mw is less than 20,000, the viscosity index may be small, and if Mw is more than 150,000, shear stability may be deteriorated.

(A) can be obtained by a known production method, and specific examples thereof include a method of performing solution polymerization of the above monomer in a solvent in the presence of a polymerization catalyst.
Examples of the solvent include toluene, xylene, alkylbenzene having 9 to 10 carbon atoms, methyl ethyl ketone, mineral oil and the like.
As the polymerization catalyst, an azo catalyst (2,2′-azobis(2-methylbutyronitrile) and 2,2′-azobis(2,4-dimethylvaleronitrile), etc.), a peroxide catalyst (benzoylperoxide) Oxide, cumyl peroxide, lauryl peroxide, etc.) and a redox catalyst (a mixture of benzoyl peroxide and a tertiary amine, etc.). Further, if necessary, a known chain transfer agent (such as an alkylmercaptan having 2 to 20 carbon atoms) can be used.
The polymerization temperature is preferably 25 to 140°C, more preferably 50 to 120°C. In addition to the solution polymerization described above, (A) can be obtained by bulk polymerization, emulsion polymerization or suspension polymerization.
When (A) is a copolymer, the polymerization form may be either a random addition polymer or an alternating copolymer, and may be a graft copolymer or a block copolymer.

The viscosity index improver of the present invention may use (A) and an alkyl (meth)acrylic acid ester (co)polymer (B) other than (A) in combination.
(B) is not particularly limited as long as it is an alkyl (meth)acrylic acid ester (co)polymer other than (A), but is a (meth)acrylic acid alkyl ester having a linear alkyl group having 1 to 18 carbon atoms. Examples thereof include (co)polymers.
Specific examples of (B) include an n-octadecyl methacrylate/n-dodecyl methacrylate (molar ratio 10 to 30/90 to 70) copolymer, an n-tetradecyl methacrylate/n-dodecyl methacrylate (molar ratio 10). -30/90-70) copolymer, n-hexadecyl methacrylate/n-dodecyl methacrylate/methyl methacrylate (molar ratio 20-40/55-75/0-10) copolymer and n-dodecyl acrylate /N-dodecyl methacrylate (molar ratio 10 to 40/90 to 60) copolymer and the like can be mentioned, and these may be used alone or in combination of two or more kinds.

When using (A) and (B) together, the amount of (B) used is preferably 0.01 to 30% by weight, and more preferably 0, from the viewpoint of low temperature viscosity, based on the weight of (A). 0.01 to 20% by weight, particularly preferably 0.01 to 10% by weight.

The lubricating oil composition of the present invention comprises the viscosity index improver of the present invention and a base oil. As the base oil, mineral oil (solvent refined oil, paraffin oil, high viscosity index oil containing isoparaffin, high viscosity index oil by hydrocracking of isoparaffin, naphthene oil, etc.), synthetic lubricating oil [hydrocarbon-based synthetic lubricating oil (Poly α-olefin-based synthetic lubricating oil and the like) and ester-based synthetic lubricating oil and the like] and mixtures thereof. Of these, mineral oil is preferred.

Kinematic viscosity at 100 ° C. of the base oil (as measured by JIS-K2283) is preferably from the viewpoint of the HTHS viscosity at effective temperature is 1 to 15 mm ² / s, more preferably is 2 to 5 mm ² / s ..
The viscosity index of the base oil (measured by JIS-K2283) is preferably 110 or more from the viewpoint of the HTHS viscosity in the effective temperature range.

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

The content of the viscosity index improver in the lubricating oil composition of the present invention is preferably 1 to 30% by weight, based on the weight of the base oil and converted to the weight of (A) in the viscosity index improver. ..
When the lubricating oil composition is used as an engine oil, it is preferable that the base oil having a kinematic viscosity at 100° C. of 4 to 10 mm ² /s contains 2 to 10% by weight of (A).
When the lubricating oil composition is used as a gear oil, it is preferable that the base oil having a kinematic viscosity at 100° C. of ² to 10 mm ² /s contains 3 to 30% by weight of (A).
When the lubricating oil composition is used as an automatic transmission oil (ATF, belt-CVTF, etc.), (A) is added in an amount of 3 to 25% by weight to a base oil having a kinematic viscosity of ² to 6 mm ² /s at 100° C. Those containing are preferable.
When the lubricating oil composition is used as a traction oil, a base oil having a kinematic viscosity at 100° C. of 1 to 5 mm ² /s and containing 0.5 to 10% by weight of (A) is preferable. ..

The lubricating oil composition of the present invention may contain various additives. The following are mentioned as an additive.
(1) Detergent:
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;
(2) Dispersant:
Succinimides (bis- or mono-polybutenyl succinimides), Mannich condensation products, borates, etc.;
(3) Antioxidant:
Hindered phenols and aromatic secondary amines, etc.;
(4) Oiliness improver:
Long-chain fatty acids and their esters (such as oleic acid and oleic acid esters), long-chain amines and their amides (such as oleylamine and oleylamide);
(5) Friction and wear modifier:
Molybdenum-based and zinc-based compounds (molybdenum dithiophosphate, molybdenum dithiocarbamate, zinc dialkyldithiophosphate, etc.) and the like;
(6) Extreme pressure agent:
Sulfur-based compounds (mono- or disulfides, sulfoxides and sulfur-phosphides), phosphides and chlorine-based compounds (chlorinated paraffins, etc.);
(7) Defoaming agent:
Silicone oil, metallic soap, fatty acid ester and phosphate compound etc.;
(8) Demulsifier:
Quaternary ammonium salts (tetraalkylammonium salts, etc.), sulfated oils and phosphates (polyoxyethylene-containing nonionic surfactant phosphates, etc.), etc.;
(9) Corrosion inhibitor:
Nitrogen atom-containing compounds (benzotriazole, 1,3,4-thiodiazolyl-2,5-bisdialkyldithiocarbamate, etc.) and the like.

A lubricating oil composition containing the viscosity index improver of the present invention is a drive system lubricating oil [MTF (manual transmission oil), differential gear oil, ATF (automatic transmission oil) and belt-CVTF (belt-continuous continuous oil). Variable transmission oil, etc.), hydraulic oil (machine hydraulic oil, power steering oil, shock absorber oil, etc.), engine oil (gasoline, diesel, etc.), and traction oil. Among these applications, from the viewpoint of viscosity index and shear stability, drive system lubricating oils (MTF, differential gear oil, ATF, belt-CVTF, etc.) are preferable.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

<Production Example 1> Production of one-terminal hydroxyl group-containing (co)polymer In a reactor, 330 parts by weight of n-hexane was charged and cooled to -40°C. To this, 28 parts by weight of a cyclohexane solution of sec-butyllithium (concentration: 15.6% by weight) was added, then 84 parts by weight of butadiene liquefied at -78° C., stirred for 2 hours, and then 18 parts by weight of tetrahydrofuran (THF). Parts were added and stirred at −20° C. for 30 minutes. After 1.5 hours, 125 parts by weight of ethylene oxide (1.1 mol/l, THF solution) was added. The reaction solution was warmed to room temperature and stirred for 40 minutes, and then 122 parts by weight of methanol was added.
This solution was washed twice with 300 parts by weight of 0.3% by weight hydrochloric acid, and then twice with 300 parts by weight of pure water. 11 parts by weight of anhydrous magnesium sulfate was added to the organic layer, and the mixture was left standing for 30 minutes. A filtration operation was performed, the filtrate was concentrated, and the solvent was distilled off to obtain 89 parts by weight of a highly viscous (co)polymer having one terminal hydroxyl group (Y1-1).
The physical properties of the obtained (co)polymer (Y1-1) were as follows.
Proportion of 1,2 adduct of butadiene based on the sum of 1,2 adduct and 1,4 adduct of 91.9 mol %, Mw=2,160.

<Production Example 2>
The reactor was charged with 250 parts by weight of n-hexane and cooled to -40°C. 12 parts by weight of an n-hexane solution of n-butyllithium (concentration: 20.4% by weight), and then a THF solution of potassium t-butoxy (concentration of potassium t-butoxide: 10.2% by weight, addition amount: n- 96 parts by weight of twice the molar amount of butyllithium) was added, and the mixture was stirred at -40°C for 30 minutes. 14 parts by weight of butadiene liquefied at -78°C was added dropwise thereto, and the mixture was stirred at -20°C for 1 hour. Further, 35 parts by weight of 35 parts by weight of liquefied butadiene was added dropwise and stirred at -20°C for 1 hour. 125 parts by weight of ethylene oxide (1.1 mol/l, THF solution) was added. The reaction solution was warmed to room temperature and stirred for 40 minutes, and then 122 parts by weight of methanol was added.
This solution was washed twice with 200 parts by weight of pure water, three times with 200 g of 0.2% by weight hydrochloric acid, further diluted with 180 parts by weight of toluene, and then washed four times with 300 parts by weight of pure water. The organic layer was concentrated and the solvent was distilled off to obtain 48 parts by weight of a hydroxyl group-containing (co)polymer at one end (Y1-3).
The physical properties of the obtained (co)polymer (Y1-3) were as follows.
The butadiene 1,2 adduct ratio is 45 mol% based on the sum of the 1,2 and 1,4 adducts, Mw=2,309.

<Production Example 3>
(Y1-1) and (Y1-3) were mixed in the mass ratio shown in Table 1 to obtain (Y1-2).

<Production Example 4>
28 parts by weight of 12 parts by weight of an n-hexane solution of n-butyllithium (concentration: 20.4% by weight) in Production Example 2 and a THF solution of potassium t-butoxide (concentration of potassium t-butoxide is 10.2 parts by weight). %, and the addition amount was changed to 96 parts by weight of double the amount of n-butyllithium) to 180 parts by weight and 125 parts by weight of ethylene oxide (1.1 mol/l, THF solution) to 250 parts by weight. Was carried out in the same manner as above to obtain 59 parts by weight of a hydroxyl group-containing (co)polymer at one end (Y1-4).
The physical properties of the obtained (co)polymer (Y1-4) were as follows.
The ratio of butadiene 1,2-adducts is 47 mol %, Mw=1,151, based on the sum of 1,2-adducts and 1,4 adducts.

<Production Example 5>
7 parts by weight of 12 parts by weight of n-hexane solution of n-butyllithium (concentration: 20.4% by weight) in Production Example 2 and a THF solution of potassium t-butoxide (concentration of potassium t-butoxide is 10.2 parts by weight). %, the addition amount was 96 parts by weight of twice the n-butyllithium) to 56 parts by weight, and 125 parts by weight of ethylene oxide (1.1 mol/l, THF solution) was changed to 75 parts by weight. The same procedure as in (4) was performed to obtain 45 parts by weight of a hydroxyl group-containing (co)polymer at one end (Y1-5).
The physical properties of the obtained (co)polymer (Y1-5) were as follows.
Ratio of 1,2 adduct of butadiene based on the sum of 1,2 adduct and 1,4 adduct of 45.1 mol %, Mw=3,811.

<Production Example 6> Production of hydrogenated one-terminal hydroxyl group-containing (co)polymer 50 parts by weight of (co)polymer (Y1-1) obtained in Production Example 1 in a reactor equipped with a gas introduction tube, and 100 parts by weight of THF. Part was charged and uniformly dissolved. A mixture of 5 parts by weight of palladium carbon and 10 parts by weight of ethanol was added thereto and stirred for 10 minutes, then hydrogen gas was introduced into the solution at a flow rate of 20 ml/minute, and the mixture was reacted at room temperature for 5 hours. After the reaction, palladium carbon was removed by filtration, the filtrate was stirred under reduced pressure, the solvents THF and ethanol were removed, and 45 parts by weight of a highly viscous hydrogenated one-terminal hydroxyl group-containing copolymer (Y1-6) Got
The physical properties of the obtained (co)polymer (Y1-6) were as follows. The results are shown in Table 1.
The total ratio of isobutylene groups and 1,2-butylene groups is 91.9 mol %, Mw=2,240.

<Production Examples 7 to 10> Production of hydrogenated one-terminal hydroxyl group-containing (co)polymer (Y1-2), (Y1-3), (Y1-4), and (Y1-5) Similarly, hydrogenation reaction was performed to obtain hydrogenated one-terminal hydroxyl group-containing (co)polymers (Y1-7), (Y1-8), (Y1-9) and (Y1-10).
The respective physical property values were as follows. The results are shown in Table 1.
(Y1-7): total ratio of isobutylene group and 1,2-butylene group 73 mol%, Mw=2,300.
(Y1-8): total ratio of isobutylene group and 1,2-butylene group of 45 mol%, Mw=2,390.
(Y1-9): Total ratio of isobutylene group and 1,2-butylene group of 47 mol %, Mw=1,190.
(Y1-10): total ratio of isobutylene group and 1,2-butylene group of 45 mol%, Mw=3,930.

<Examples 1 to 6, Comparative Examples 1 to 4>
Base oil A (SP value: 8.3, kinematic viscosity at 100° C.: 2.2 mm ² /s, in a reaction vessel equipped with a stirrer, a heating and cooling device, a thermometer, a dropping funnel, a nitrogen blowing tube, and a decompression device. Viscosity index: 105) 100 parts were put into another glass beaker, 100 parts by weight of the monomer shown in Table 2, 0.6 part by weight of dodecyl mercaptan as a chain transfer agent, and 2,2-azobis(2,2). 0.5 parts by weight of 4-dimethylvaleronitrile) and 0.2 parts by weight of 2,2-azobis(2-methylbutyronitrile) were added, and the mixture was stirred and mixed at 20° C. to prepare a monomer solution. It was put into a dropping funnel. After performing nitrogen substitution (vapor-phase oxygen concentration: 100 ppm or less) in the gas-phase portion of the reaction vessel, the monomer solution was added dropwise over 2 hours while maintaining the internal system temperature at 70 to 85°C under the closed condition. After aging at 85° C. for 2 hours from the end, the temperature was raised to 120 to 130° C., unreacted monomers were removed under reduced pressure (0.027 to 0.040 MPa) at the same temperature for 2 hours, and Viscosity index improvers (R1) to (R9) and (S1) to (S4) composed of the polymers (A1) to (A9) and (H1) to (H4) were obtained. The SP values of the obtained copolymers (A1) to (A9) and (H1) to (H4) were calculated by the above method, and Mw was measured by the above method. The base oil solubility of the viscosity index improver was evaluated by the following method. The results are shown in Table 2.

<Method for evaluating base oil solubility of viscosity index improver>
10 parts by weight of viscosity index improvers (R1) to (R9) and (S1) to (S4) were added to base oil A, the appearance at room temperature was visually observed, and the solubility of base oil was evaluated according to the following evaluation criteria. did.
[Evaluation criteria]
◯: The appearance is uniform and there is no insoluble matter of the copolymer. x: The appearance is not uniform and insoluble matter of the copolymer is observed.

The compositions of the monomers (a) to (f) shown in Table 2 are as described below.
(A-1): Methacrylic acid esterified product of (Y1-6) (Mw2,310)
(A-2): Methacrylic ester of (Y1-7) (Mw2,370)
(A-3): Methacrylic acid esterified product of (Y1-8) (Mw2,460)
(A-4): Methacrylic acid esterified product of (Y1-9) (Mw1, 260)
(A-5): Methacrylic ester of (Y1-10) (Mw3,990)
(A'-1): Polymer containing hydrogenated polybutadiene at one end hydroxyl group (trade name: Krasol HLBH-5000M, manufactured by Cray Valley, 1,2-butylene ratio: 65 mol%, hydroxyl value: 10.4 mgKOH/g, Mw 8,000, Mw/Mn=1.10)
(B-1): Methyl methacrylate (c-1): 2-decyl tetradecyl methacrylate (c-2): 2-dodecyl hexadecyl methacrylate (c-3): 2-tetradecyl octadecyl methacrylate (d -1): hexadecyl methacrylate (d-2): octadecyl methacrylate (e-1): N,N-dimethylaminoethyl methacrylate (f-1): 2-hydroxyethyl methacrylate (g-1): methacryloyloxy Ethyl phosphate

<Examples 10 to 18, Comparative Examples 5 to 7>
Base oil A (SP value: 8.3, kinematic viscosity at 100° C.: 2.2 mm ² /s, viscosity index: 105) was put into a stainless steel container equipped with a stirrer to obtain a lubricating oil composition. Viscosity index improvers (R1) to (R9) and (S1) to (S4) were added so that the kinematic viscosity at 100°C was 5.00 ± 0.02 (mm ² /s), and the lubricating oil composition was added. Products (V1) to (V9) and (W1) to (W4) were obtained.
Lubricating oil compositions (V1) to (V9), (W1), (W2) and (W4) viscosity index, 40°C kinematic viscosity, shear stability, low temperature viscosity (-40°C) were measured by the following methods. .. The results are shown in Table 3. The lubricating oil composition (W3) was not evaluated because insoluble matter of the copolymer was found in the base oil A.

<Measurement method of viscosity index and 40° C. kinematic viscosity of lubricating oil composition>
It was measured by the method of JIS-K2283.

<Method for measuring low temperature viscosity of lubricating oil composition>
The viscosity at -40°C was measured by the method of ASTM D 2983.
<Method of measuring shear stability (SS) of lubricating oil composition>
Lubricating oil composition for gear oil: measured by the method of ASTM D 2603.

表３の結果から明らかなように、本発明の粘度指数向上剤を含有してなる潤滑油組成物（実施例１０〜１８）は、比較例５〜７の潤滑油組成物と比較して、粘度指数向上効果が高い。また本発明の粘度指数向上剤を含有してなる潤滑油組成物は剪断安定度が低く、低温粘度が低く、いずれにも優れる。

As is clear from the results in Table 3, the lubricating oil compositions (Examples 10 to 18) containing the viscosity index improver of the present invention were compared with the lubricating oil compositions of Comparative Examples 5 to 7, Highly effective in improving viscosity index. The lubricating oil composition containing the viscosity index improver of the present invention has low shear stability and low temperature viscosity, and is excellent in both cases.

The lubricating oil composition containing the viscosity index improver of the present invention is a drive system lubricating oil (MTF, differential gear oil, ATF, belt-CVTF, etc.), hydraulic oil (machine hydraulic oil, power steering oil and shock). It is suitable as absorber oil, engine oil (for gasoline and diesel, etc.) and traction oil.

Claims (6)

Copolymer (A) containing as an essential constituent monomer a monomer (a) represented by the following general formula (1) and a (meth)acrylic acid alkyl ester (b) having an alkyl group having 1 to 4 carbon atoms. A viscosity index improver containing (A) , wherein (A) is a monomer (c) represented by the following general formula (2) as a constituent monomer of (A), and/or having 12 to 36 carbon atoms. A copolymer containing a (meth)acrylic acid alkyl ester (d) having a linear alkyl group, wherein the weight average molecular weight of (A) is 20,000 to 150,000, and the monomer (a The viscosity index improver having a weight average molecular weight of 1,000 to 4,000.

[R ¹ is a hydrogen atom or a methyl group; -X ¹ -is a group represented by -O-, -O(AO) _m -, or -NH-, and A is an alkylene group having 2 to 4 carbon atoms. And m is an integer of 1 to 10, and when m is 2 or more, A may be the same or different, and the (AO) _m portion may be a random bond or a block bond; R ² is isobutylene and/or Residue obtained by removing one hydrogen atom from a hydrocarbon polymer having 1,2-butylene as an essential constituent unit; p is a number of 0 or 1. ]

[R ³ is a hydrogen atom or a methyl group; -X ² is a group represented by -O- or -NH-; R ⁴ is a linear or branched alkylene group having 2 to ⁴ carbon atoms; R ⁵ and R ⁶ are Each independently a straight-chain alkyl group having 8 to 24 carbon atoms; q is an integer of 0 to 20, R ^{4 s} when q is 2 or more may be the same or different, and the (R ⁴ O) _q moiety is Random connection or block connection may be used. ] The viscosity index improver according to claim 1, wherein the solubility parameter of (A) is 8.5 to 9.6. (A) is further selected from the group consisting of a nitrogen atom-containing monomer (e) other than the monomers (a) and (c), a hydroxyl group-containing monomer (f) and a phosphorus atom-containing monomer (g). The viscosity index improver according to claim 1 or 2 , which is a copolymer having at least one selected from constituent monomers. (A) is 1 to 25% by weight of (a), 20 to 60% by weight of (b), 20 to 70% by weight of (c) and (d) based on the weight of (A) as a constituent monomer. 4. The viscosity index improver according to claim 1, which is a copolymer containing 1 to 40% by weight. A lubricating oil composition comprising a viscosity index improver and a base oil according to any one of claims 1-4, the absolute value of the difference between the solubility parameter and base oil solubility parameter of (A) Is 0.5 to 1.6. Further, it contains one or more additives selected from the group consisting of detergents, dispersants, antioxidants, oiliness improvers, friction and wear modifiers, extreme pressure agents, defoamers, demulsifiers and corrosion inhibitors. The lubricating oil composition according to claim 5 , wherein