Viscosity index improving agent composition and lubricating oil composition

Abstract

The present invention provides a viscosity index improver that exhibits excellent solubility in hydrocarbon-based synthetic base oils and has a superior viscosity index improving effect, and a lubricating oil composition using the viscosity index improver. [Solution] A viscosity index improver comprising a copolymer (A) having an alkyl (meth)acrylate monomer (a) having an alkyl group having 1 to 4 carbon atoms and an alkyl (meth)acrylate monomer (b) having an alkyl group having 6 to 15 carbon atoms as essential constituent monomers, and a hydrocarbon-based synthetic base oil (B), wherein the ratio (Wa / Wb) of the weight Wa of monomer (a) to the weight Wb of monomer (b) is 1 / 5 to 1 / 1.

Description

Technical Field

[0001] The present invention relates to a viscosity index improver and a lubricating oil composition.

Background Art

[0002] Lubricating oils, hydraulic fluids, etc. used in automobiles and the like have a decreasing viscosity as the temperature rises. Practically, it is desirable that the viscosity hardly changes over a wide range from low temperature to high temperature. Therefore, as a method for improving the viscosity characteristics, a method of adding a viscosity index improver to the lubricating oil is widely practiced. As such viscosity index improvers, methacrylic acid ester copolymers (Patent Document 1), olefin copolymers, macromonomer copolymers (Patent Document 2), etc. are known. However, the above viscosity index improvers have a problem that there is room for improvement in the viscosity index improvement effect and the solubility in hydrocarbon-based synthetic base oils is not yet sufficient.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a viscosity index improver excellent in solubility in hydrocarbon-based synthetic base oils and excellent in viscosity index improvement effect, and a lubricating oil composition using the viscosity index improver.

Means for Solving the Problems

[0005] As a result of intensive studies, the present inventors have arrived at the present invention. That is, the present invention is as follows. [1] A viscosity index improver comprising a copolymer (A) having (meth)acrylic acid alkyl ester monomer (a) with an alkyl group having 1 to 4 carbon atoms and (meth)acrylic acid alkyl ester monomer (b) with an alkyl group having 6 to 15 carbon atoms as essential constituent monomers, and a hydrocarbon synthetic base oil (B), wherein the ratio (Wa / Wb) of the weight Wa of the monomer (a) to the weight Wb of the monomer (b) is 1 / 5 to 1 / 1. [2] The viscosity index improver composition according to [1], wherein the copolymer (A) further contains at least one monomer (c) selected from the group consisting of a monomer (c1) represented by the following general formula (1) and a (meth)acrylic acid alkyl ester monomer (c2) having an alkyl group having 16 to 20 carbon atoms as a constituent monomer.

[0006] [Chemical formula]

[0007] [R 1 is a hydrogen atom or a methyl group; -X 1 - is a group represented by -O- or -NH-; R 2 is an alkylene group having 2 to 4 carbon atoms; R 3 and R 4 are each independently a linear or branched alkyl group having 8 to 24 carbon atoms, and the sum of the carbon numbers of the alkyl groups of R 3 and the carbon number of the alkyl group of R 4 is 19 or more; p is an integer of 0 to 20, and when p is 2 or more, R 2 may be the same or different. [3] The lubricating oil composition according to [1] or [2], wherein the solubility parameter of the copolymer (A) is 8.5 to 9.5 (cal / cm 3 ) 1 / 2 . [4] The viscosity index improver composition according to any one of [1] to [3], wherein the weight average molecular weight of the copolymer (A) is 5,000 to 2,000,000. [5] The kinematic viscosity of the hydrocarbon synthetic base oil at 100 °C is 1 to 15 mm 2A viscosity index improver composition according to any one of the following [1] to [4], wherein the viscosity index of the base oil is 100 or more, and the viscosity index of the base oil is 100 or more. A lubricating oil composition comprising a viscosity index improving agent composition described in any one of items [6][1] to [5], and at least one additive selected from the group consisting of detergents, dispersants, antioxidants, oiliness improvers, pour point depressants, friction and wear modifiers, extreme pressure agents, anti-emulsifiers, metal deactivators, and corrosion inhibitors. [Effects of the Invention]

[0008] The viscosity index improver of the present invention exhibits excellent solubility in hydrocarbon-based synthetic base oils and provides excellent viscosity index improvement effects. [Modes for carrying out the invention]

[0009] The viscosity index improver of the present invention is a viscosity index improver comprising a copolymer (A) having an alkyl (meth)acrylate monomer (a) having an alkyl group having 1 to 4 carbon atoms and an alkyl (meth)acrylate monomer (b) having an alkyl group having 6 to 15 carbon atoms as essential constituent monomers, and a hydrocarbon-based synthetic base oil (B). In the present invention, the ratio (Wa / Wb) of the weight Wa of monomer (a) to the weight Wb of premer (b) is 1 / 5 to 1 / 1.

[0010] In the present invention, copolymer (A) comprises an alkyl (meth)acrylate monomer (a) having an alkyl group having 1 to 4 carbon atoms and an alkyl (meth)acrylate monomer (b) having an alkyl group having 6 to 15 carbon atoms as essential constituent monomers.

[0011] In the present invention, the monomer constituting copolymer (A) includes an alkyl (meth)acrylate monomer (a) having an alkyl group having 1 to 4 carbon atoms (hereinafter also referred to as monomer (a)) as an essential constituent monomer. Examples of alkyl (meth)acrylate esters (a) having an alkyl group with 1 to 4 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isobutyl (meth)acrylate, and n-butyl (meth)acrylate. Of monomer (a), preferred are methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate, with particular preference being methyl (meth)acrylate and n-butyl (meth)acrylate. Monomer (a) may be used alone, or two or more may be used in combination.

[0012] In the present invention, the monomer constituting copolymer (A) includes an alkyl (meth)acrylate monomer (b) having an alkyl group having 6 to 15 carbon atoms (hereinafter also referred to as monomer (b)) as an essential constituent monomer. The alkyl (meth)acrylate monomer (b) having an alkyl group having 6 to 15 carbon atoms includes esters of a linear or branched alkyl alcohol having 6 to 15 carbon atoms with (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, etc.; isooctyl (meth)acrylate, (meth) Examples include esters of branched alkyl alcohols having 6 to 15 carbon atoms, such as 2-ethylhexyl acrylic acid, isononyl (meth)acrylate, 3,5,5-trimethylhexyl (meth)acrylate, 2,4,6-trimethylheptyl (meth)acrylate, 2-methylnonyl (meth)acrylate, isodecyl (meth)acrylate, 2-ethylnonyl (meth)acrylate, isoundecyl (meth)acrylate, isododecyl (meth)acrylate, 2-ethyldodecyl (meth)acrylate, 2-ethyltridecyl (meth)acrylate, and 2-methyltetradecyl (meth)acrylate, with (meth)acrylic acid. Of the monomers (b), those preferred from the viewpoint of viscosity index improvement are alkyl (meth)acrylate esters having a linear alkyl group with 8 to 15 carbon atoms, those more preferred are (meth)acrylate esters having a linear alkyl group with 10 to 15 carbon atoms, and those particularly preferred are (meth)acrylate esters having a linear alkyl group with 12 to 20 carbon atoms. Monomer (b) may be used alone or in combination of two or more. As monomer (b), for example, an esterified product of an alcohol with a distributed carbon number (for example, an alcohol having an alkyl group with 12 to 15 carbon atoms) and (meth)acrylic acid may be used.

[0013] In the present invention, it is preferable from the viewpoint of viscosity index improvement effect that the copolymer (A) further comprises at least one monomer (c) selected from the group consisting of a monomer (c1) represented by the following general formula (1) and an alkyl (meth)acrylate monomer (c2) having an alkyl group having 16 to 20 carbon atoms. Hereinafter, the monomer (c1) represented by the general formula (1) will also be referred to as monomer (c1).

[0014] [ka]

[0015] [R 1 is a hydrogen atom or a methyl group; -X 1 - represents a group represented by -O- or -NH-; R 2 R is an alkylene group having 2 to 4 carbon atoms; 3 and R 4 Each of these is independently a linear or branched alkyl group having 8 to 24 carbon atoms, and R 3 The number of carbon atoms in the alkyl group and R 4 The sum of the number of carbon atoms in the alkyl group is 19 or more; p is an integer from 0 to 20, and R is 2 or greater. 2 They may be the same or different.

[0016] A monomer (c1) that can constitute the copolymer (A) is represented by the above general formula (1). R in general formula (1) 1 This is either a hydrogen atom or a methyl group. Of these, the methyl group is preferred from the viewpoint of improving viscosity index. -X in general formula (1) 1 - represents a group represented by -O- or -NH-. R in general formula (1) 2 This is an alkylene group having 2 to 4 carbon atoms. Examples of alkylene groups having 2 to 4 carbon atoms include ethylene groups, 1,2- or 1,3-propylene groups, and 1,2-, 1,3- or 1,4-butylene groups. Of these, the ethylene group is preferred from the viewpoint of improving the viscosity index. p is the number of moles of alkylene oxide added, and is an integer from 0 to 20. From the viewpoint of viscosity index improvement effect, it is preferably an integer from 0 to 4, and more preferably an integer from 0 to 2. When p is 2 or more, R 2 They may be the same or different, R 2 (R 2 O) p The chemical structure of the part can be either random or block bonds. R 3 and R 4 Each of these is independently a linear or branched alkyl group having 8 to 24 carbon atoms. Examples of linear or branched alkyl groups having 8 to 24 carbon atoms include: linear alkyl groups {n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-eicosyl group, n-heneicosyl group, n-docosyl group, n-tricosyl group and n-tetracosyl group, etc.}, and branched alkyl groups {isooctyl group, 2-ethylhexyl group, isononyl group, 3,5,5-trimethylhexyl group, 2,4,6 Examples include trimethylheptyl group, 2-methylnonyl group, isodecyl group, 2-ethylnonyl group, isoundecyl group, isododecyl group, 2-ethyldodecyl group, 2-ethyltridecyl group, 2-methyltetradecyl group, isohexadecyl group, 2-octylnonyl group, 2-hexylundecyl group, 2-ethylpentadecyl group, 2-(3-methylhexyl)-7-methylnonyl group, isooctadecyl group, 1-hexyltridecyl group, 2-ethylheptadecyl group, isoicosyl group, 1-octylpentadecyl group, and 2-decyltetradecyl group. Of these, linear or branched alkyl groups having 8 to 20 carbon atoms are preferred from the viewpoint of viscosity index improvement effect and shear stability, and linear or branched alkyl groups having 10 to 18 carbon atoms are more preferred. R 3 and R 4 The total number of carbon atoms is 19 or more. From the perspective of viscosity index, R 3 and R 4 The total number of carbon atoms is preferably 20 to 40, and more preferably 22 to 38.

[0017] Examples of monomers (c1) include esters of alcohols having a branched alkyl group with 21 to 40 carbon atoms and (meth)acrylic acid [e.g., 2-octyltetradecyl (meth)acrylic acid, 2-n-decyltetradecyl (meth)acrylic acid, 2-dodecylhexadecyl (meth)acrylic acid, 2-tetradecyloctadecyl (meth)acrylic acid, and 2-hexadecylicosyl (meth)acrylic acid], esters of alkylene oxide adducts (2 to 4 carbon atoms) of alcohols having a branched alkyl group with 21 to 40 carbon atoms and (meth)acrylic acid, and amidates of amines having a branched alkyl group with 21 to 40 carbon atoms and (meth)acrylic acid. As the monomer (c1), from the viewpoint of viscosity index, an ester of an alcohol having a branched alkyl group with 21 to 40 carbon atoms and (meth)acrylic acid is preferred, and 2-n-decyltetradecyl (meth)acrylic acid, 2-dodecylhexadecyl (meth)acrylic acid, and 2-tetradecyloctadecyl (meth)acrylic acid are more preferred. Monomer (c1) may be used alone, or two or more may be used in combination.

[0018] Examples of alkyl (meth)acrylate monomers (C2) having an alkyl group with 16 to 20 carbon atoms (hereinafter also referred to as monomer (C2)) include esterified products of alkyl alcohols with 16 to 20 carbon atoms and (meth)acrylic acid, such as n-pentadecyl (meth)acrylate, n-hexadecyl (meth)acrylate, n-octadecyl (meth)acrylate, n-icosyl (meth)acrylate, isohexadecyl (meth)acrylate, 2-octylnonyl (meth)acrylate, 2-hexylundecyl (meth)acrylate, 2-ethylpentadecyl (meth)acrylate, (2-(3-methylhexyl)-7-methylnonyl (meth)acrylate), isooctadecyl (meth)acrylate, 1-hexyltridecyl (meth)acrylate, 2-ethylheptadecyl (meth)acrylate, and isoicosyl (meth)acrylate. From the viewpoint of viscosity index, n-hexadecyl (meth)acrylate and n-octadecyl (meth)acrylate are preferred as monomer (c2). The monomer (c2) may be used alone, or two or more may be used in combination.

[0019] In the present invention, copolymer (A) may further contain as a constituent monomer at least one monomer selected from the group consisting of nitrogen atom-containing monomer (d), hydroxyl group-containing monomer (e), phosphorus atom-containing monomer (f), aromatic ring-containing vinyl monomer (g), monomer having two or more unsaturated groups (h), vinyl compound (i), epoxy group-containing monomer (j), halogen element-containing monomer (k), and ester of unsaturated polycarboxylic acid (l).

[0020] Examples of nitrogen atom-containing monomers (d) include the following monomers (d1) to (d4), excluding monomer (c1). Amide group-containing monomer (d1): (meth)acrylamide, monoalkyl(meth)acrylamide [a nitrogen atom to which one C1-C4 alkyl group is bonded; 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 [having an aminoalkyl group (C2-C6) to which one C1-C4 alkyl group is bonded to a nitrogen atom; for example, N-(N'-methylaminoethyl)(meth)acrylamide, N-(N'-ethylaminoethyl)(meth)acrylamide, N-(N'-isopropylamino-n-butyl)(meth)acrylamide, and N-(N'-n- or isobutylamino-n-butyl)(meth)acrylamide, etc.], dialkyl(meth)acrylamide [a nitrogen atom to which two C1-C4 alkyl groups are bonded; for example, N,N Examples include: -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 [those having an aminoalkyl group (with 2 to 6 carbon atoms) in which two alkyl groups with 1 to 4 carbon atoms are bonded to the nitrogen atom of the aminoalkyl group; for example, N-(N',N'-dimethylaminoethyl)(meth)acrylamide, N-(N',N'-diethylaminoethyl)(meth)acrylamide, N-(N',N'-dimethylaminopropyl)(meth)acrylamide, and N-(N',N'-di-n-butylaminobutyl)(meth)acrylamide, etc.]; N-vinyl carboxylic acid amide [N-vinylformamide, N-vinylacetamide, N-vinyl-n- or isopropionic acid amide, and N-vinylhydroxyacetamide, etc.].

[0021] Examples of nitro group-containing monomers (d2) include 4-nitrostyrene.

[0022] Monomers containing primary to tertiary amino groups (d3): Primary amino group-containing monomers {alkenylamines with 3-6 carbon atoms [(meth)allylamine and clotylamine, etc.], aminoalkyl (2-6 carbon atoms) (meth)acrylates [aminoethyl (meth)acrylate, etc.]}; Secondary amino group-containing monomers {monoalkylaminoalkyl (meth)acrylates [those having an aminoalkyl group (2-6 carbon atoms) with one C1-6 alkyl group bonded to the nitrogen atom; for example, Nt-butylaminoethyl (meth)acrylate and N-methylaminoethyl (meth)acrylate, etc.], dialkenylamines with 6-12 carbon atoms [di(meth)allylamine, etc.]}; Tertiary amino group-containing monomers {dialkylaminoalkyl (meth)acrylates [a group with 1-6 carbon atoms bonded to the nitrogen atom Examples include aminoalkyl groups (with 2 to 6 carbon atoms) with two hydroxyl groups bonded to them; for example, N,N-dimethylaminoethyl (meth)acrylate and N,N-diethylaminoethyl (meth)acrylate, etc., alicyclic (meth)acrylates having a nitrogen atom [such as morpholinoethyl (meth)acrylate], aromatic monomers [such as N-(N',N'-diphenylaminoethyl)(meth)acrylamide, N,N-dimethylaminostyrene, 4-vinylpyridine, 2-vinylpyridine, N-vinylpyrrole, N-vinylpyrrolidone and N-vinylthiopyrrolidone], and their hydrochloride salts, sulfates, phosphates, or lower alkyl (with 1 to 8 carbon atoms) monocarboxylic acid (such as acetic acid and propionic acid) salts.

[0023] Nitrile group-containing monomer (d4): Examples include (meth)acrylonitrile.

[0024] Of the nitrogen atom-containing monomers (d), (d1) and (d3) are preferred, and more preferably 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. Monomer (d) may be used alone, or two or more may be used in combination.

[0025] Hydroxyl group-containing monomer (e) Hydroxyl group-containing aromatic monomers (e.g., p-hydroxystyrene), hydroxyalkyl (meth)acrylates (2-6 carbon atoms) [e.g., 2-hydroxyethyl (meth)acrylate, 2- or 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxyisobutyl (meth)acrylate], mono- or bis-hydroxyalkyl (1-4 carbon atoms) substituted (meth)acrylamides [e.g., N,N-bis(hydroxymethyl)(meth)acrylamide, N,N-bis(hydroxypropyl)(meth)acrylamide, N,N-bis(2-hydroxybutyl)(meth)acrylamide], vinyl alcohol, alkenols with 3-12 carbon atoms [(meth)allyl alcohol, clotyl alcohol, isoclotyl alcohol, 1-octenol and 1-undecenol, etc.], C4-C12 alkene monools or alkene diols [1-buten-3-ol, 2-buten-1-ol and 2-buten-1,4-diol, etc.], hydroxyalkyl (C1-C6) alkenyl (C3-C10) ethers (2-hydroxyethylpropenyl ether, etc.), alkenyl (C3-C10) ethers or (meth)acrylates of polyhydric (3-8 hydric) alcohols (glycerin, pentaerythritol, sorbitol, sorbitan, diglycerin, sugars and sucrose, etc.) [sucrose (meth)allyl ether, etc.], etc.; Examples include polyoxyalkylene glycols (alkylene group with 2-4 carbon atoms, degree of polymerization 2-50), polyoxyalkylene polyols [polyoxyalkylene ethers of the above 3-8 valent alcohols (alkylene group with 2-4 carbon atoms, degree of polymerization 2-100)], and mono(meth)acrylates of alkyl (1-4 carbon atoms) ethers of polyoxyalkylene glycols or polyoxyalkylene polyols [polyethylene glycol (Mn: 100-300) mono(meth)acrylate, polypropylene glycol (Mn: 130-500) mono(meth)acrylate, methoxypolyethylene glycol (Mn: 110-310) (meth)acrylate, lauryl alcohol ethylene oxide adduct (2-30 mol) (meth)acrylate, and polyoxyethylene (Mn: 150-230) sorbitan mono(meth)acrylate, etc.].

[0026] Of the monomers (e), hydroxyalkyl (meth)acrylate (hydroxyalkyl group with 2 to 6 carbon atoms) is preferred from the viewpoint of viscosity index improvement effect, and hydroxyalkyl (meth)acrylate (hydroxyalkyl group with 2 to 4 carbon atoms) is more preferred. Monomer (e) may be used alone, or two or more may be used in combination.

[0027] Examples of phosphorus atom-containing monomers (f) include the following monomers (f1) to (f2).

[0028] Phosphate ester group-containing monomer (f1): Examples include (meth)acryloyloxyalkyl (C2-C4) phosphate esters [(meth)acryloyloxyethyl phosphate and (meth)acryloyloxyisopropyl phosphate] and alkenyl phosphate esters [vinyl phosphate, allyl phosphate, propenyl phosphate, isopropenyl phosphate, butenyl phosphate, pentenyl phosphate, octenyl phosphate, decenyl phosphate, and dodecenyl phosphate, etc.]. Note that "(meth)acryloyloxy" means acryloyloxy or methacryloyloxy.

[0029] Phosphono group-containing monomer (f2): Examples include (meth)acryloyloxyalkyl (2-4 carbon atoms) phosphonic acids [such as (meth)acryloyloxyethylphosphonic acid] and alkenyl (2-12 carbon atoms) phosphonic acids [such as vinylphosphonic acid, allylphosphonic acid, and octenylphosphonic acid].

[0030] Of (f), (f1) is preferred, (meth)acryloyloxyalkyl (2-4 carbon atoms) phosphate esters are preferred, and (meth)acryloyloxyethyl phosphate is particularly preferred. Monomer (f) may be of one type or two or more types may be used in combination.

[0031] Aromatic ring-containing vinyl monomer (g): Examples include styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, 4-ethylstyrene, 4-isopropylstyrene, 4-butylstyrene, 4-phenylstyrene, 4-cyclohexylstyrene, 4-benzylstyrene, 4-clotylbenzene, indene, and 2-vinylnaphthalene. Of the monomers (g), styrene and α-methylstyrene are preferred from the viewpoint of improving viscosity index, and styrene is even more preferred. You may use one type of monomer (g), or two or more types in combination.

[0032] Examples of monomers (h) having two or more unsaturated groups include divinylbenzene, C4-C12 alkadienes (butadiene, isoprene, 1,4-pentadiene, 1,6-heptadiene, and 1,7-octadiene, etc.), (di)cyclopentadiene, vinylcyclohexene, and ethylidenebicycloheptene, limonene, ethylene di(meth)acrylate, polyalkylene oxide glycol di(meth)acrylate, pentaerythritol trialyl ether, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, trimethylolpropane tri(meth)acrylate, and esters of unsaturated carboxylic acids with Mn of 500 or more and glycols, and esters of unsaturated alcohols and carboxylic acids, as described in International Publication WO01 / 009242. Monomer (h) may be used alone, or two or more may be used in combination.

[0033] Vinyl compounds (vinyl esters, vinyl ethers, vinyl ketones, etc.) (i): Examples include vinyl esters of saturated fatty acids having 2 to 12 carbon atoms (vinyl acetate, vinyl propionate, vinyl butyrate, and 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, and vinyl-2-butoxyethyl ether, etc.), and alkyl or aryl vinyl ketones having 1 to 8 carbon atoms (methyl vinyl ketone, ethyl vinyl ketone, and phenyl vinyl ketone, etc.). Monomer (i) may be of one type, or two or more types may be used in combination.

[0034] Epoxy group-containing monomer (j): Examples include glycidyl (meth)acrylate and glycidyl (meth)allyl ether. Monomer (j) may be used alone, or two or more may be used in combination.

[0035] Halogen element-containing monomer (k): Examples include vinyl chloride, vinyl bromide, vinylidene chloride, (meth)allyl chloride, and halogenated styrenes (such as dichlorostyrene). One type of monomer (k) may be used, or two or more types may be used in combination.

[0036] Ester (l) of unsaturated polycarboxylic acid: Examples include alkyl, cycloalkyl, or aralkyl esters of unsaturated polycarboxylic acids [alkyl diesters having 1 to 8 carbon atoms of unsaturated dicarboxylic acids (such as maleic acid, fumaric acid, and itaconic acid) (dimethyl maleate, dimethyl fumarate, diethyl maleate, and dioctyl maleate)]. One type of monomer (l) may be used, or two or more types may be used in combination.

[0037] The weight average molecular weight (hereinafter abbreviated as Mw) and number average molecular weight (hereinafter abbreviated as Mn) of the copolymer (A) can be measured by gel permeation chromatography (hereinafter abbreviated as GPC) under the following conditions. <Measurement conditions for Mw and Mn> Apparatus: "HLC-8320GPC" [manufactured by Tosoh Corporation] Column: "TSKgelguardcolumnSuperHZM-M" [manufactured by Tosoh Corporation] Three "TSKgel SuperHZM-M" columns [manufactured by Tosoh Corporation] Measurement temperature: 40 °C Sample solution: 0.25 wt% tetrahydrofuran solution Solution injection volume: 10.0 μl Detector: Refractive index detector Reference substance: Standard polystyrene (TS reference substance: Standard polystyrene (TSKstandard POLYSTYRENE) 12 points (Molecular weights: 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]

[0038] The Mw of copolymer (A) is preferably 5,000 to 2,000,000, more preferably 5,000 to 700,000, even more preferably 10,000 to 600,000, particularly preferably 15,000 to 550,000, and most preferably 18,000 to 500,000, from the viewpoint of viscosity index improvement effect, solubility, and shear stability. When Mw is 5,000 or higher, the viscosity-temperature characteristics and viscosity index improvement effects are excellent. Furthermore, because the amount of viscosity index improver composition added to the lubricating oil composition is appropriate, it is also advantageous in terms of cost. When Mw is 2,000,000 or lower, shear stability tends to be good.

[0039] The Mn content of copolymer (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 also preferably 300,000 or less, more preferably 250,000 or less, particularly preferably 240,000 or less, and most preferably 225,000 or less. When Mn is 2,500 or higher, it exhibits excellent effects in improving viscosity-temperature characteristics and viscosity index. Furthermore, because the amount of viscosity index improver added to the lubricating oil composition is appropriate, it is also advantageous in terms of cost. When Mn is 300,000 or lower, shear stability tends to be good.

[0040] From the viewpoint of solubility in lubricating oil, copolymer (A) is preferably one that has a specific solubility parameter (hereinafter abbreviated as SP value). The SP value of copolymer (A) is 8.5-9.5 (cal / cm³). 3 ) 1 / 2 Preferably, and more preferably 8.7 to 9.3 (cal / cm²) from the viewpoint of viscosity index improvement effect and solubility in lubricating oil compositions. 3 )1 / 2 Next, more preferably 8.8 to 9.2 (cal / cm²). 3 ) 1 / 2 Particularly preferably 8.9 to 9.2 (cal / cm³) 3 ) 1 / 2 That is the case.

[0041] In this invention, the SP value refers to the value calculated using formula (28) on page 153 of the Fedors method (Polymer Engineering and Science, February, 1974, Vol. 14, No. 2, pp. 147-154), using the numerical values ​​(heat of vaporization and molar volume of atoms or functional groups at 25°C) listed on page 152 (Table 5). Specifically, it refers to the Δe parameter of the Fedors method, as listed in Tables 1 and 2 below. i and v i The values ​​can be used to calculate the following formula by applying the values ​​corresponding to the types of atoms and atomic groups within the molecular structure. SP value = (ΣΔe i / Σv i ) 1 / 2

[0042] [Table 1]

[0043] [Table 2]

[0044] The SP value of copolymer (A) is calculated by determining the SP value of each constituent unit (structure in which vinyl groups become single bonds through polymerization) derived from each monomer constituting copolymer (A) using the SP value calculation method described above, and then weighting the values ​​based on the weight fraction of each constituent monomer at the time of preparation. For example, if the monomer is methyl methacrylate, the constituent units derived from methyl methacrylate consist of two CH3 atoms, one CH2 atom, one C atom, and one CO2 atom. Therefore, according to the following formula, the SP value of the constituent units derived from methyl methacrylate is 9.933 (cal / cm³). 3) 1 / 2 It can be seen that this is the case. ΣΔe i =1125×2+1180+350+4300=8080 ΣΔv i =33.5 × 2 + 16.1 - 19.2 + 18.0 = 81.9 δ = (8080 / 81.9) 1 / 2 = 9.933 (cal / cm 3 ) 1 / 2 Similarly, the SP value of the constituent unit derived from ethyl methacrylate is 9.721 (cal / cm³). 3 ) 1 / 2 It can be seen that this is the case. When the copolymer is a polymer of 50% by weight methyl methacrylate and 50% by weight butyl methacrylate, the SP value of the copolymer is calculated by weighting and averaging the SP values ​​of the constituent units derived from each monomer, as described below. SP value of copolymer = (9.933 × 50 + 9.721 × 50) / 100 = 9.827 Furthermore, the SP value calculated based on the weight fraction of copolymer (A) can be brought within a desired range by appropriately adjusting the monomers and their weight fractions used. Specifically, the SP value can be reduced by using more monomers with long alkyl groups, and increased by using more monomers with short alkyl groups.

[0045] The weight percentage of monomer (a) constituting copolymer (A) is preferably 5 to 20% by weight, more preferably 7 to 18% by weight, and particularly preferably 10 to 16% by weight, based on the weight of copolymer (A), from the viewpoint of viscosity index improvement effect and solubility in hydrocarbon-based synthetic base oils. The weight percentage of monomer (b) constituting copolymer (A) is preferably 5 to 50% by weight, more preferably 10 to 45% by weight, and particularly preferably 10 to 40% by weight, based on the weight of copolymer (A), from the viewpoint of viscosity index improvement effect and solubility in hydrocarbon-based synthetic base oils. When copolymer (A) contains monomer (c) as a constituent monomer, the weight percentage of monomer (c) is preferably 40 to 60% by weight, more preferably 40 to 55% by weight, and particularly preferably 44 to 55% by weight, based on the weight of copolymer (A), from the viewpoint of viscosity index improvement effect and solubility in hydrocarbon-based synthetic base oils.

[0046] In the present invention, the ratio (Wa / Wb) of the weight Wa of monomer (a) to the weight Wb of monomer (b) is 1 / 5 to 1 / 1. This makes it possible to provide a viscosity index improver that has excellent solubility in hydrocarbon-based synthetic base oils and excellent viscosity index improvement effect.

[0047] The total weight percentage of monomers (d) to (l) constituting copolymer (A) is preferably 0 to 10% by weight, more preferably 1 to 7% by weight, and particularly preferably 2 to 5% by weight, based on the weight of copolymer (A), from the viewpoint of improving viscosity index.

[0048] Copolymer (A) can be obtained by known manufacturing methods, specifically by solution polymerization of the monomer in a solvent in the presence of a polymerization catalyst. Examples of solvents include toluene, xylene, alkylbenzenes with 9 to 10 carbon atoms, methyl ethyl ketones, mineral oils, synthetic oils, and mixtures thereof. Examples of polymerization catalysts include azo catalysts (such as 2,2'-azobis(2-methylbutyronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile)), peroxide catalysts (such as benzoyl peroxide, cumyl peroxide, and lauryl peroxide), and redox catalysts (such as mixtures of benzoyl peroxide and tertiary amines). Furthermore, known chain transfer agents (such as alkyl mercaptans with 2 to 20 carbon atoms) can be used as needed to adjust the molecular weight. The polymerization temperature is preferably 25 to 140°C, and more preferably 50 to 120°C. In addition to the solution polymerization described above, copolymer (A) can also be obtained by bulk polymerization, emulsion polymerization, or suspension polymerization. The polymerization form of copolymer (A) may be either a random addition copolymer or an alternating copolymer, and may also be either a graft copolymer or a block copolymer.

[0049] The viscosity index improver of the present invention comprises a copolymer (A) and a hydrocarbon-based synthetic base oil (B). Examples of hydrocarbon-based synthetic base oils include poly-α-olefin-based synthetic base oils, cyclic olefin-based base oils, GTL base oils, and mixtures thereof. Of these, poly-α-olefin-based synthetic base oils are preferred.

[0050] The kinematic viscosity of hydrocarbon-based synthetic base oils at 100°C (measured according to JIS-K2283) is preferably 1 to 15 mm from the viewpoint of improving viscosity index. 2 / s, and more preferably 2-5 mm 2 It is / s. The viscosity index of the hydrocarbon-based synthetic base oil (measured according to JIS-K2283) is preferably 90 or higher, and more preferably 100 or higher, from the viewpoint of viscosity index improvement effect.

[0051] The lubricating oil composition of the present invention comprises the viscosity index improving agent composition of the present invention and one or more additives selected from the group consisting of detergents, dispersants, antioxidants, oiliness improvers, pour point depressants, friction and wear modifiers, extreme pressure agents, defoamers, anti-emulsifiers, metal deactivators, and corrosion inhibitors. From the viewpoint of viscosity index improvement effect and shear stability, the lubricating oil composition of the present invention preferably contains copolymer (A) in an amount of 0.1 to 20% by weight based on the weight of the lubricating oil composition.

[0052] The lubricating oil composition of the present invention may contain various additives. Examples of additives include the following: (1) Cleaning agent: Basic, overbasic, or neutral metal salts [overbasic sulfonates (petroleum sulfonates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, etc.) or alkaline earth metal salts, etc.], salicylates, phenates, naphthenates, carbonates, phosphonates, and mixtures thereof; (2) Dispersant: Succinimides (bis- or mono-polybutenyl succinimides), Mannich condensates, borates, etc.; (3) Antioxidants: Hindered phenols and aromatic secondary amines, etc. (4) Oiliness improvers: 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. (5) Pour point depressants Polyalkyl methacrylate, ethylene-vinyl acetate copolymer, etc. (6) Friction and wear modifiers: Molybdenum-based and zinc-based compounds (such as molybdenum dithiophosphate, molybdenum dithiocarbamate, and zinc dialkyldithiophosphate); (7) Extreme pressure agents: Sulfur compounds (mono- or disulfide, sulfoxide, and sulfur phosphide compounds), phosphide compounds, and chlorine compounds (such as chlorinated paraffins); (8) Antiemulsifiers: Quaternary ammonium salts (such as tetraalkylammonium salts), sulfated oils and phosphates (such as phosphates of polyoxyethylene-containing nonionic surfactants), hydrocarbon solvents (toluene, xylene, ethylbenzene), etc.; (9) Metal deactivators Nitrogen-containing compounds (such as benzotriazole), nitrogen-containing chelate compounds (such as N,N'-disalithidene-1,2-diaminopropane), nitrogen and sulfur-containing compounds (such as 2-(n-dodecylthio)benzimidazole), etc. (10) Corrosion inhibitors: Nitrogen atom-containing compounds (such as benzotriazole and 1,3,4-thiodiazolyl-2,5-bisdialkyldithiocarbamate), etc.

[0053] These additives may be added individually, or two or more may be added as needed. A mixture of these additives may also be called a performance additive or packaging additive, and this may also be added. The content of each of these additives is preferably 0.1 to 15% by weight based on the total amount of the lubricating oil composition. Furthermore, the total content of each additive is preferably 0.1 to 30% by weight, and more preferably 0.3 to 20% by weight, based on the total amount of the lubricating oil composition.

[0054] The lubricating oil composition of the present invention is suitably used in gear oil (differential oil and industrial gear oil, etc.), MTF, transmission oil [ATF, DCTF and belt-CVTF, etc.], engine oil, traction oil (toroidal-CVTF, etc.), shock absorber oil, power steering oil, hydraulic oil (hydraulic oil for construction machinery and industrial hydraulic oil, etc.). [Examples]

[0055] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0056] <Examples 1-6, Comparative Examples 1-2> 100 parts by weight of the base oil listed in Table 3 was added to a reaction vessel equipped with a stirrer, heating / cooling device, thermometer, dropping funnel, nitrogen inlet tube, and vacuum device. In a separate glass beaker, 100 parts by weight of monomers (a) to (c) of the types listed in Table 3, 0.02 parts by weight of a chain transfer agent (dodecyl mercaptan), and 0.12 parts by weight of a polymerization initiator (2,2'-azobis(2-methylbutyronitrile)) were added. The mixture was stirred and mixed at 20°C to prepare a monomer solution, which was then added to the dropping funnel. After purging the gas phase of the reaction vessel with nitrogen, the entire monomer solution was added dropwise over 3 hours while maintaining the internal temperature at 70-85°C under a sealed system. The mixture was then aged at 90°C for 2 hours after the end of the addition. Subsequently, the temperature was raised to 120°C, and then unreacted monomers were removed under reduced pressure (0.027~0.040 MPa) at the same temperature for 2 hours to obtain viscosity index improving compositions (R-1)~(R-6) and (R'-1)~(R'-2) containing copolymer (A) or (co)polymer (A'). The Mw of (co)polymers (A-1)~(A-6) and (A'-1)(A'-2) in the obtained viscosity index improving compositions was measured by the method described above (the method described in "Measurement conditions for Mw and Mn of copolymer (A) by GPC"). The results are shown in Table 3.

[0057] [Table 3]

[0058] The compositions of monomers (a) to (c) and hydrocarbon-based synthetic base oil (B) listed in Table 3 are as follows. (a-1): Methyl methacrylate (a-2): Butyl methacrylate (b-1): Ester of methacrylic acid with Neodol 23 (a mixture of linear or branched alkyl alcohols with 12-13 carbon atoms, manufactured by Shell Chemicals (weight ratio = linear C12:branched C12:linear C13:branched C13 = 40:10:40:10)) (b-2): Ester of acrylic acid with Neodol 45 (manufactured by Shell Chemicals, a mixture of linear or branched alkyl alcohols with 14-15 carbon atoms (weight ratio = linear C14:branched C14:linear C15:branched C15 = 40:10:40:10)) {tetradecyl acrylate / pentadecyl acrylate = 50 / 50 (weight ratio)} (c1-1): 2-decyltetradecyl methacrylate (c1-2): 2-dodecylhexadecyl methacrylate (c1-1): 2-tetradecyl octadecyl methacrylate (c2-1): n-hexadecyl methacrylate (c2-2): n-octadecyl methacrylate (B-1): ExxonMobil Spectrasyn4 (kinematic viscosity at 100°C: 4.1 mm) 2 kinematic viscosity at 40°C: 19 mm² / s 2 / s) (B-2): ExxonMobil Spectrasyn10 (kinematic viscosity at 100°C: 10.0 mm) 2 kinematic viscosity at 40°C: 66 mm² / s 2 / s)

[0059] <Method for evaluating the solubility of copolymer (A) or (co)polymer (A') in hydrocarbon-based synthetic base oil (B)> The compatibility of copolymer (A) or (co)polymer (A') in viscosity index improvers with hydrocarbon-based synthetic base oil (B) was evaluated according to the following evaluation criteria. The results are shown in Table 3. [Evaluation Criteria] ○: The appearance is uniform and free of insoluble matter. ×: Uneven appearance and / or insoluble material are observed.

[0060] <Method for measuring the viscosity of a lubricating oil composition> The kinematic viscosity at 40°C and 100°C was measured using the JIS-K2283 (2000) method, and the viscosity index was calculated using the JIS-K2283 (2000) method. A higher viscosity index value indicates a greater viscosity index improvement effect.

[0061] <Method for evaluating the low-temperature solubility of lubricating oil compositions> Lubricating oil compositions (1) to (6) and (1') were stored for 6 hours under 0°C conditions, and then their appearance was visually observed. Base oil solubility was evaluated according to the following evaluation criteria. [Evaluation Criteria] ○: The appearance is uniform and free of insoluble matter. ×: Uneven appearance and / or insoluble material are observed.

Claims

1. A viscosity index improver comprising a copolymer (A) having an alkyl (meth)acrylate monomer (a) having an alkyl group having 1 to 4 carbon atoms and an alkyl (meth)acrylate monomer (b) having an alkyl group having 6 to 15 carbon atoms as essential constituent monomers, and a hydrocarbon-based synthetic base oil (B), A viscosity index improver in which the ratio (Wa / Wb) of the weight Wa of monomer (a) to the weight Wb of monomer (b) is 1 / 5 to 1 / 1.

2. The viscosity index improving agent composition according to claim 1, wherein the copolymer (A) further comprises, as a constituent monomer, at least one monomer (c) selected from the group consisting of a monomer (c1) represented by the following general formula (1) and an alkyl (meth)acrylate monomer (c2) having an alkyl group having 16 to 20 carbon atoms. 【Chemistry 1】 [R １ is a hydrogen atom or a methyl group; -X １ - represents a group represented by -O- or -NH-; R ２ R is an alkylene group having 2 to 4 carbon atoms; ３ and R ４ Each of these is independently a linear or branched alkyl group having 8 to 24 carbon atoms, and R ３ The number of carbon atoms in the alkyl group and R ４ The sum of the number of carbon atoms in the alkyl group is 19 or more; p is an integer from 0 to 20, and R is 2 or more. ２ They may be the same or different.

3. The solubility parameter of the copolymer (A) is 8.5 to 9.5 (cal / cm ３ ). １／２ The lubricating oil composition according to claim 1 or 2, wherein the solubility parameter is as defined above.

4. The viscosity index improving agent composition according to claim 1 or 2, wherein the weight-average molecular weight of the copolymer (A) is 5,000 to 2,000,000.

5. The kinematic viscosity of the hydrocarbon-based synthetic base oil at 100°C is 1 to 15 mm². ２ The viscosity index improving agent composition according to claim 1 or 2, wherein the viscosity index of the base oil is 100 or more, and the viscosity index of the base oil is 100 or more.

6. A lubricating oil composition comprising the viscosity index improving agent composition according to claim 1 or 2, and at least one additive selected from the group consisting of a detergent, a dispersant, an antioxidant, an oiliness improving agent, a pour point depressant, a friction and wear modifier, an extreme pressure agent, an anti-emulsifier, a metal deactivator, and a corrosion inhibitor.

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