JP2015038194A - Viscosity index improver and lubricant composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a viscosity index improver having high viscosity index improvability, excellent shear stability of a lubricant composition and excellent storage stability at a low temperature.SOLUTION: There is provided a viscosity index improver containing a copolymer (A) composed of a monomer (a) represented by the following general formula (1) and a (meth)acrylic acid ester (b) having a linear alkyl group having 1 to 4 carbon atoms as essential constituent monomers, wherein (A) has a solubility parameter of 8.5 to 9.5 (cal/cm). There is provided a viscosity index improver for a hydrocarbon-based synthetic oil containing 70 to 90 mol% of (b) based on the total number of the constituent monomers of (A). [Ris a hydrogen atom or a methyl group; X is a group represented by -O- or -NH-; A is an alkylene group having 2 to 4 carbon atoms; n is an integer of 0 to 20; A may be the same or different when n is 2 or more; the (AO)moiety may be a random bond or a block bond; and Ris a branched alkyl group having 32 to 44 carbon atoms.]

Description

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

Lubricating oils and hydraulic oils used in automobiles and the like have a lower viscosity as the temperature increases, but in practice, it is desirable that the viscosity does not change as much as possible over a wide range from a low temperature to a high temperature. Therefore, a method for improving the temperature dependence of viscosity by adding a viscosity index improver to lubricating oil 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 improver is still insufficient in the effect of improving the viscosity index, and has a problem that the shear stability after long-time operation is not yet sufficient in practical use.

Japanese Patent No. 2732187 Japanese Patent No. 2941392 JP-A-7-62372 JP 2004-307551 A JP 2005-200454 A Special table 2008-546894 gazette

  An object of the present invention is to provide a viscosity index improver that has a high effect of improving the viscosity index and is excellent in the shear stability and storage stability at low temperatures of the lubricating oil composition.

As a result of intensive studies, the present inventors have arrived at the present invention. That is, the present invention uses (a) represented by the following general formula (1) and (meth) acrylic acid alkyl ester (b) having a linear alkyl group having 1 to 4 carbon atoms as essential constituent monomers. A viscosity index improver comprising a copolymer (A), wherein the solubility parameter of (A) is 8.5 to 9.5 (cal / cm ³ ) ^1/2 , Containing a viscosity index improver for hydrocarbon-based synthetic base oils containing 70 to 90 mol% of (b) based on the total number of constituent monomers, and the viscosity index improver and hydrocarbon-based synthetic base oil A lubricating oil composition.

R ¹ is a hydrogen atom or a methyl group; X is a group represented by —O— or —NH—;
An alkylene group of 4; n is an integer of 0 to 20, and when n is 2 or more, A may be the same or different, and (AO) _n part may be a random bond or a block bond; R ² is carbon It is a branched alkyl group of several 32 to 44.

  The lubricating oil composition containing the viscosity index improver of the present invention has a high effect of improving the viscosity index, and has the effect of being excellent in shear stability and storage stability at low temperatures.

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

The copolymer (A) in the present invention comprises (a) represented by the following general formula (1) as an essential constituent monomer. R ¹ in the general formula (1) is a hydrogen atom or a methyl group. Among these, a methyl group is preferable from the viewpoint of improving the viscosity index.

  X in the general formula (1) is a group represented by —O— or —NH—. Among these, the group represented by —O— is preferable from the viewpoint of the effect of improving the viscosity index.

A in General formula (1) is a C2-C4 alkylene group. Examples of the alkylene group having 2 to 4 carbon atoms include an ethylene group, 1,2- or 1,3-propylene group, and 1,2-, 1,3- or 1,4-butylene group. Among these, the ethylene group and the 1,2-propylene group are preferable from the viewpoint of the effect of improving the viscosity index.

N in the general formula (1) is a number from 0 to 20, preferably from 0 to 5, and more preferably from 0 to 2 from the viewpoint of the effect of improving the viscosity index and the low temperature viscosity.
When n is 2 or more, A may be the same or different, and (AO) _n part may be a random bond or a block bond.

R ² in the general formula (1) is a branched alkyl group having 32 to 44 carbon atoms.
Examples of the branched alkyl group having 32 to 44 carbon atoms include 2-tetradecyloctadecyl group, 2-tetradecylicosyl group, 2-hexadecyloctadecyl group, 2-hexadecylicosyl group, and 2-isohexadecylisoicosyl. Group, 2-octadecyl docosyl, 2-icosyl tetracosyl, olefin [for example, propylene oligomer (11 to 15 mer), ethylene / propylene oligomer (13 to 18 mer, molar ratio 16/1 to 1/11) And a residue obtained by removing a hydroxyl group from an oxo alcohol obtained from an isobutene oligomer (8 to 11-mer).
Of the branched alkyl groups having 32 to 44 carbon atoms, the branched alkyl group having 32 to 40 carbon atoms is preferred from the viewpoint of the effect of improving the viscosity index, and more preferred is a branched alkyl group having 32 to 36 carbon atoms. Preferable is a branched alkyl group having 32 to 36 carbon atoms which is branched at the 2-position of the alkyl group.

  The proportion of (a) constituting (A) is preferably 10 to 30 mol% from the viewpoint of improving the viscosity index, the shear stability of the lubricating oil composition, and the solubility in the hydrocarbon-based synthetic base oil. More preferably, it is 12 to 26 mol%, particularly preferably 14 to 22 mol%.

  The copolymer (A) in the present invention comprises (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.
Of these, (b) is preferably a (meth) acrylic acid ester having a linear alkyl group having 1 to 3 carbon atoms, more preferably methyl (meth) acrylate and ethyl (meth) acrylate, Particularly preferred is methyl (meth) acrylate.

  The proportion of (b) constituting (A) is 70 to 90 mol%, preferably from the viewpoint of improving the viscosity index, the shear stability of the lubricating oil composition, and the solubility in the hydrocarbon-based synthetic base oil. Is 72 to 89 mol%, more preferably 74 to 88 mol%, and particularly preferably 78 to 86 mol%.

  (A) is a co-polymer containing (meth) acrylic acid alkyl ester (c) having a branched alkyl group having 16 to 28 carbon atoms in addition to monomers (a) and (b). A coalescence is preferable from the viewpoints of solubility in a hydrocarbon-based synthetic base oil and storage stability at low temperatures.

Examples of the (meth) acrylic acid alkyl ester (c) having a branched alkyl group having 16 to 30 carbon atoms include isohexadecyl group, 2-octylnonyl group, 2-hexylundecyl group, 2-ethylpentadecyl group, 2 -(3-methylhexyl) -7-methyl-nonyl group, isooctadecyl group, 1-hexyltridecyl group, 2-ethylheptadecyl group, 2-octylundecyl group, isoicosyl group, 1-undecyldodecyl group, 1-octylpentadecyl group, 2-decyltridecyl group, 2-decyltetradecyl group, 2-dodecylpentadecyl group, 2-dodecylhexadecyl group, 2-dodecyloctadodecyl group, 2-tetradecylhexadecyl group, etc. It is done.
Among (c), a (meth) acrylic acid alkyl ester having a branched alkyl group having 18 to 26 carbon atoms is preferred, and (meth) acrylic acid having a branched alkyl group having 18 to 24 carbon atoms is more preferred. Esters, particularly preferred are (meth) acrylic acid esters having a branched alkyl group having 20 to 24 carbon atoms.

  The proportion of (c) constituting (A) is preferably 0 to 15 mol%, more preferably 1 to 12 in terms of solubility in a hydrocarbon-based synthetic base oil and storage stability at low temperatures. The mol%, particularly preferably 2 to 10 mol%.

(A) is a copolymer containing a monomer other than (a) a nitrogen atom-containing monomer (d), a hydroxyl group-containing monomer (e) and / or a phosphorus atom-containing monomer (f). A coalescence is preferable from the viewpoint of the effect of improving the viscosity index.
Examples of the nitrogen atom-containing monomer (d) include the following monomers (d1) to (d4) excluding the monomer (a).

Amide group-containing monomer (d1):
(Meth) acrylamide, monoalkyl (meth) acrylamide [one having an alkyl group having 1 to 4 carbon atoms bonded to a nitrogen atom; for example, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-isopropyl (Meth) acrylamide and Nn- or isobutyl (meth) acrylamide etc.], N- (N′-monoalkylaminoalkyl) (meth) acrylamide [one alkyl group having 1 to 4 carbon atoms bound to the nitrogen atom. Those having an aminoalkyl group (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 [nitrogen atom having two C1-C4 alkyl groups bonded; for example, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meta ) Acrylamide, N, N-diisopropyl (meth) acrylamide and N, N-di-n-butyl (meth) acrylamide etc.], N- (N ′, N′-dialkylaminoalkyl) (meth) acrylamide [aminoalkyl group Having an aminoalkyl group (2 to 6 carbon atoms) in which two alkyl groups having 1 to 4 carbon atoms are bonded to the nitrogen atom of, for example, N- (N ′, N′-dimethylaminoethyl) (meth) acrylamide, N- (N ′, N′-diethylaminoethyl) (meth) acrylamide, N- (N ′, N′-dimethylaminopropyl) (meth) acrylic 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 (d2):
4-nitrostyrene etc. are mentioned.

Monomers containing primary to tertiary amino groups (d3):
Primary amino group-containing monomer {C3-C6 alkenylamine [(meth) allylamine, crotylamine, etc.], Aminoalkyl (C2-C6) (meth) acrylate [Aminoethyl (meth) acrylate, etc.}} Secondary amino group-containing monomer {monoalkylaminoalkyl (meth) acrylate [having an aminoalkyl group (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.], C6-C12 dialkenylamine [di (meth) allylamine, etc.]}; tertiary amino group-containing single amount Body {dialkylaminoalkyl (meth) acrylate [an aminoalkyl group in which two alkyl groups having 1 to 6 carbon atoms are bonded to a nitrogen atom (carbon Having 2 to 6); for example, N, N-dimethylaminoethyl (meth) acrylate and N, N-diethylaminoethyl (meth) acrylate, etc.], alicyclic (meth) acrylate having a nitrogen atom [morpholinoethyl ( Meth) acrylates, etc.], aromatic monomers [N- (N ′, N′-diphenylaminoethyl) (meth) acrylamide, N, N-dimethylaminostyrene, 4-vinylpyridine, 2-vinylpyridine, N -Vinyl pyrrole, N-vinyl pyrrolidone, N-vinyl thiopyrrolidone, etc.]} and their hydrochlorides, sulfates, phosphates or lower alkyl (C1-8) monocarboxylic acids (such as acetic acid and propionic acid) Examples include salts.

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

  Of these, (e) is preferably (e1) and (e3), more preferably N- (N ′, N′-diphenylaminoethyl) (meth) acrylamide, N- (N ′, N′-dimethyl). 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.

  (D) is preferably (d1) and (d3), more preferably N- (N ′, N′-diphenylaminoethyl) (meth) acrylamide, N- (N ′, N′-dimethyl). 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 and the like), hydroxyalkyl (2 to 6 carbon atoms) (meth) acrylate [2-hydroxyethyl (meth) acrylate, and 2- or 3-hydroxypropyl (meth) acrylate Etc.], mono- or bis-hydroxyalkyl (C1-C4) 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], an alkene monool having 4 to 12 carbon atoms, or Lucenediol [1-buten-3-ol, 2-buten-1-ol, 2-butene-1,4-diol, etc.], hydroxyalkyl (C1-6) alkenyl (C3-10) ether (2 -Hydroxyethylpropenyl ether, etc.), polyvalent (3-8 valent) alcohols (glycerin, pentaerythritol, sorbitol, sorbitan, diglycerin, saccharides, sucrose, etc.) alkenyl (carbon number 3-10) ether or (meth) acrylate [Sucrose (meth) allyl ether etc.] etc .;
Polyoxyalkylene glycol (alkylene group having 2 to 4 carbon atoms, polymerization degree 2 to 50), polyoxyalkylene polyol [polyoxyalkylene ether of 3 to 8 valent alcohol (alkylene group having 2 to 4 carbon atoms, polymerization degree) 2-100)], mono (meth) acrylates of polyoxyalkylene glycol or polyoxyalkylene polyol alkyl (carbon number 1-4) ether [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 mono (meth) acryl Polyoxyethylene (Mn: 150 to 230), sorbitan, etc.] or the like; and the like.

  Among (e), 2-hydroxyethyl (meth) acrylate, 2- or 3-hydroxypropyl (meth) acrylate, and N, N-bis (hydroxypropyl) (meth) acrylamide are preferable.

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

Phosphate group-containing monomer (f1):
(Meth) acryloyloxyalkyl (2 to 4 carbon atoms) 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.]. “(Meth) acryloyloxy” means acryloyloxy or methacryloyloxy.

Phosphono group-containing monomer (f2):
(Meth) acryloyloxyalkyl (2 to 4 carbon atoms) phosphonic acid [(meth) acryloyloxyethylphosphonic acid etc.] and alkenyl (2 to 12 carbon atoms) phosphonic acid [vinyl phosphonic acid, allyl phosphonic acid and octenyl phosphone Acid, etc.].

  Of these, (f1) is preferred among (f), (meth) acryloyloxyalkyl (2 to 4 carbon atoms) phosphate is more preferred, and (meth) acryloyloxyethyl phosphate is particularly preferred. It is.

  In addition to the monomers (a) to (f), (A) may use the following monomers (g) to (n) as constituent monomers.

(Meth) acrylic acid alkyl ester having linear alkyl group having 8 to 18 carbon atoms (g):
N-octyl (meth) acrylate, n-nonyl (meth) acrylate, n-decyl (meth) acrylate, n-undecyl (meth) acrylate, n-dodecyl (meth) acrylate, (meth) acrylic acid Examples include n-tridecyl, n-tetradecyl (meth) acrylate, n-pentadecyl (meth) acrylate, n-hexadecyl (meth) acrylate, and n-octadecyl (meth) acrylate.

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

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

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

Vinyl esters, vinyl ethers, vinyl ketones (k):
Vinyl esters of saturated fatty acids having 2 to 12 carbon atoms (such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl octoate), 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) and alkyl or aryl vinyl ketones having 1 to 8 carbon atoms (methyl vinyl ketone, ethyl vinyl ketone and Phenyl vinyl ketone, etc.).

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

Halogen element-containing monomer (m):
Examples thereof include vinyl chloride, vinyl bromide, vinylidene chloride, (meth) allyl chloride and halogenated styrene (dichlorostyrene and the like).

Unsaturated polycarboxylic acid ester (n):
Alkyl, cycloalkyl or aralkyl ester of unsaturated polycarboxylic acid [alkyl diester having 1 to 8 carbon atoms of unsaturated dicarboxylic acid (such as maleic acid, fumaric acid and itaconic acid) (dimethyl maleate, dimethyl fumarate, diethyl maleate) And dioctyl maleate)] and the like.

  The ratio of (d) to (n) constituting (A) is preferably 0 to 10 mol%, more preferably 1 to 9 mol, respectively, independently from the viewpoint of the effect of improving the viscosity index. %, Particularly preferably 1 to 8 mol%.

* ：オートマチックトランスミッション油
** ：ベルト−コンティニュアスリーバリアブルトランスミッション油
*** ：マニュアルトランスミッション油 The weight average molecular weight (hereinafter abbreviated as Mw) of (A) is preferably 5,000 to 2,000,000 from the viewpoint of the effect of improving the viscosity index and the low temperature viscosity of the lubricating oil composition, and a more preferable range is Depends on the use of the lubricating oil composition, and is in the range shown in Table 1.

*: Automatic transmission oil
**: Belt-continuous variable transmission oil
***: Manual transmission oil

In addition, Mw of (A) can be measured on condition of the following by gel permeation chromatography.
<Measurement conditions of Mw>
Apparatus: “HLC-802A” [manufactured by Tosoh Corporation]
Column: 2 “TSK gel GMH6” Measurement temperature: 40 ° C.
Sample solution: 0.5 wt% tetrahydrofuran solution Solution injection amount: 200 μl
Detector: Refractive index detector Standard: Polystyrene

The solubility parameter (hereinafter abbreviated as SP value) of (A) is 8.5 to 9.5 (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 preferably 9.0 to 9.4 (cal / cm ³ ) ^1/2 , more preferably 9.1 to 9.3 (cal / cm ³ ) ^1/2 .
The SP value of (A) 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 (A) is calculated based on the SP value of each monomer constituting (A) by the above method, and the SP value of each monomer is based on the mole fraction of the constituent monomer units. The average value.
The SP value of (A) can be adjusted 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 hydrocarbon-based synthetic base oil is preferably 0.5 to 1.2 from the viewpoint of the effect of improving the viscosity index and the low temperature viscosity of the lubricating oil composition. More preferably, it is 0.6 to 1.0, and particularly preferably 0.7 to 0.9.

The crystallization temperature of (A) is preferably 0 ° C. or lower, more preferably −10 ° C. or lower, particularly preferably −20 ° C. or lower.
The crystallization temperature of (A) was determined by using a differential scanning calorimeter “UNIX (registered trademark) DSC7” (manufactured by PERKIN-ELMER), using 5 mg of a viscosity index improver as a sample, and an isothermal rate of 10 ° C./min. Is the crystallization temperature observed when cooled from 100 ° C. to −60 ° C.

(A) can be obtained by a known production method, and specifically includes a method obtained by solution polymerization of the 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, and mineral oil.
As radical polymerization initiators, known azo initiators (such as 2,2-azobis (2-methylbutyronitrile) and 2,2-azobis (2,4-dimethylvaleronitrile)), peroxide initiators Agents (benzoyl peroxide, cumyl peroxide, lauryl peroxide, etc.) and redox initiators (a mixture of benzoyl peroxide and tertiary amine, etc.). Furthermore, if necessary, a known chain transfer agent (such as an alkyl mercaptan having 2 to 20 carbon atoms) can also be used.
The polymerization temperature is preferably 25 to 140 ° C, more preferably 50 to 120 ° C. In addition to the above solution polymerization, (A) can be obtained by bulk polymerization, emulsion polymerization or suspension polymerization.
The polymerization form of (A) may be either a random addition polymer or an alternating copolymer, and may be either a graft copolymer or a block copolymer.

The viscosity index improver of the present invention may be used in combination with (A) and an alkyl (meth) acrylic acid ester (co) polymer (B) other than (A).
(B) is not particularly limited as long as it is an alkyl (meth) acrylate polymer other than (A), but (meth) acrylic acid alkyl ester having a linear alkyl group having 1 to 15 carbon atoms, etc. Can be mentioned.
Specific examples of (B) include n-octadecyl methacrylate / n-dodecyl methacrylate (molar ratio 10-30 / 90-70) copolymer, 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, and these may be used alone or in combination of two or more.

  When (A) and (B) are used in combination, the amount of (B) used is preferably 0.01 to 30% by weight and more preferably 0 based on the weight of (A) from the viewpoint of low temperature viscosity. 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 hydrocarbon-based synthetic base oil. Examples of the hydrocarbon-based synthetic base oil include poly α-olefin-based synthetic base oil, cyclic olefin-based base oil, GTL base oil, and mixtures thereof. Of these, poly α-olefin synthetic base oils and GTL base oils are preferred.

Kinematic viscosity at 100 ° C. of the hydrocarbon-based synthetic base oil (measured by JIS-K2283) is preferably from the viewpoint of the viscosity index improving effect is 1 to 15 mm ² / s, more preferably 2 to 5 mm ² / s It is.
The viscosity index (measured by JIS-K2283) of the hydrocarbon-based synthetic base oil is preferably 90 or more, more preferably 100 or more, from the viewpoint of the effect of improving the viscosity index.

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

The content of the viscosity index improver in the lubricating oil composition of the present invention is preferably 1 to 30 in terms of the weight of (A) in the viscosity index improver based on the weight of the hydrocarbon-based synthetic base oil. % By weight.
When the lubricating oil composition is used as an engine oil, it contains 2 to 10% by weight of (A) in a hydrocarbon-based synthetic base oil having a kinematic viscosity at 100 ° C. of 4 to 10 mm ² / s. Is preferred.
When the lubricating oil composition is used as gear oil, it contains 3 to 30% by weight of (A) in a hydrocarbon-based synthetic base oil having a kinematic viscosity at 100 ° C. of ² to 10 mm ² / s. Is preferred.
When the lubricating oil composition is used as an automatic transmission oil (ATF, belt-CVT, and MFT), a hydrocarbon-based synthetic base oil having a kinematic viscosity at 100 ° C. of ² to 6 mm ² / s is added to (A). What contains 3 to 25 weight% is preferable.
When the lubricating oil composition is used as a traction oil, it contains 0.5 to 10% by weight of (A) in a hydrocarbon-based synthetic base oil having a kinematic viscosity at 100 ° C. of 1 to 5 mm ² / s. Is preferred.

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 (such as petroleum sulfonates, alkylbenzene sulfonates and alkylnaphthalene sulfonates)], salicylates, phenates, naphthenates , Carbonates, phosphonates and mixtures thereof;
(2) Dispersant:
Succinimides (bis- or mono-polybutenyl succinimides), Mannich condensation products, borates and the like;
(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), etc .;
(5) Friction and wear modifier:
Molybdenum and zinc compounds (such as molybdenum dithiophosphate, molybdenum dithiocarbamate and zinc dialkyldithiophosphate);
(6) Extreme pressure agent:
Sulfur compounds (mono or disulfides, sulfoxides and sulfur phosphide compounds), phosphide compounds and chlorinated compounds (chlorinated paraffins, etc.);
(7) Antifoaming agent:
Silicon oil, metal 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.);
(9) Corrosion inhibitor:
Nitrogen atom-containing compounds (benzotriazole and 1,3,4-thiodiazolyl-2,5-
Bisdialkyldithiocarbamate, etc.).

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.

<Examples 1-6, Comparative Examples 1-4>
In a reaction vessel equipped with a stirrer, heating / cooling device, thermometer, dropping funnel, nitrogen blowing tube and decompression device, base oil A (α-olefin synthetic base oil) (SP value: 8.3, dynamic at 100 ° C.) Viscosity: 2.4 mm ² / s, viscosity index: 110) 100 parts are charged, and in another glass beaker, 100 parts by weight of the monomers listed in Table 2 and 0.6 parts by weight of dodecyl mercaptan as a chain transfer agent , 0.5 part by weight of 2,2-azobis (2,4-dimethylvaleronitrile) and 0.2 part by weight of 2,2-azobis (2-methylbutyronitrile) are added and stirred at 20 ° C. and mixed. A monomer solution was prepared and charged into a dropping funnel. After performing nitrogen substitution (gas phase oxygen concentration: 100 ppm or less) in the gas phase part of the reaction vessel, the monomer solution was dropped over 2 hours while maintaining the internal temperature of the system in a sealed state at 70 to 85 ° C. After aging at 85 ° C. for 2 hours after completion, the temperature was raised to 120 to 130 ° C., and unreacted monomers were removed at the same temperature under reduced pressure (0.027 to 0.040 MPa) over 2 hours. Viscosity index improvers (R1) to (R6) and (S1) to (S4) comprising the polymers (A1) to (A6) and (H1) to (H4) were obtained. The SP values of the obtained copolymers (A1) to (A6) and (H1) to (H4) were calculated by the above method, and Mw was measured by the above method. Moreover, the low temperature storage stability of the viscosity index improver was evaluated by the following method. The results are shown in Table 2. Table 3 shows the parts by weight of monomers converted to molar ratios.

<Examples 7-8, Comparative Examples 5-6>
Base oil B (α-olefin synthetic base oil) (SP value: 8.3, kinematic viscosity at 100 ° C .: 4.1 mm ²⁾ / S, Viscosity Index: 128) 400 parts by weight, 100 parts by weight of the monomer formulation described in Table 2, 0.05 parts by weight of 2,2-azobis (2,4-dimethylvaleronitrile) and 2,2- After 0.2 part by weight of azobis (2-methylbutyronitrile) was added and nitrogen substitution (gas phase oxygen concentration: 100 ppm or less) was performed, the temperature was raised to 76 ° C. with stirring and sealed, at the same temperature. The polymerization reaction was performed for 4 hours. After raising the temperature to 120 to 130 ° C., unreacted monomers are removed under reduced pressure (0.027 to 0.040 MPa) at the same temperature over 2 hours, and copolymers (A7) to (A8), (H5 ) To (H6) viscosity index improvers (R7) to (R8) and (S5) to (S6) were obtained. The SP values of the resulting copolymers (A7) to (A8) and (H5) to (H6) were calculated by the above method, and Mw was measured by the above method. Moreover, the low temperature storage stability of the viscosity index improver was evaluated by the following method. The results are shown in Table 2. Table 3 shows the parts by weight of monomers converted to molar ratios.

<Evaluation method of low temperature storage stability of viscosity index improver>
Viscosity index improvers (R1) to (R8) and (S1) to (S6) were added at 10% by weight with respect to the base oil B, and the appearance after storage for 24 hours at -25 ° C was visually observed. Low temperature storage stability was evaluated according to the evaluation criteria.
[Evaluation criteria]
○: Appearance is uniform and there is no insoluble matter in the copolymer ×: Appearance is inhomogeneous and insoluble matter in the copolymer is observed

The compositions of the monomers (a) to (f) described in Tables 2 and 3 are as described below.
(A-1): 2-tetradecyl octadecyl methacrylate (a-2): 2-hexadecylicosyl methacrylate (b-1): methyl methacrylate (c-1): 2-decyl tetradecyl methacrylate ( c-2): 2-dodecylhexadecyl methacrylate (d-1): N, N-dimethylaminoethyl methacrylate (e-1): 2-hydroxyethyl methacrylate (f-1): methacryloyloxyethyl phosphate (g -1): hexadecyl methacrylate (g-2): octadecyl methacrylate

<Examples 9-14, Comparative Examples 7-10 (Evaluation of Lubricating Oil Composition for Gear Oil)>
Into a stainless steel container equipped with a stirrer, the base oil A is charged, and the viscosity index is adjusted so that the resulting lubricating oil composition has a kinematic viscosity at 100 ° C. of 4.50 ± 0.02 (mm ² / s). Improvement agents (R1) to (R6) and (S1) to (S4) were added to obtain lubricating oil compositions (V1) to (V6) and (W1) to (W4).
The viscosity index, 40 ° C. kinematic viscosity, shear stability, and low temperature viscosity (−40 ° C.) of the lubricating oil compositions (V1) to (V6) and (W1) to (W4) were measured by the following methods. The results are shown in Table 3.

<Examples 15 to 16 and Comparative Examples 11 to 12 (Evaluation of Lubricating Oil Composition for Engine Oil)>
The base oil B is put into a stainless steel container equipped with a stirrer, and the resulting lubricating oil composition has an HTHS viscosity at 150 ° C. of 2.60 ± 0.05 (mm ² / s). Index improvers (R7) to (R8) and (S5) to (S6) were added to obtain lubricating oil compositions (V7) to (V8) and (W5) to (W6).
The viscosity index, HTHS viscosity (80 ° C.), shear stability, and low temperature viscosity (−40 ° C.) of the lubricating oil compositions (V7) to (V8) and (W5) to (W6) were measured by the following methods. The results are shown in Table 4.

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

<Method for Measuring HTHS Viscosity of Lubricating Oil Composition>
The measurement was performed at 80 ° C. by the method of ASTM D 5481.

<Method of measuring low temperature viscosity (−40 ° C.) of lubricating oil composition>
Lubricating oil composition for gear oil: Measured by the method of JPI-5S-26-2010.
Lubricating oil composition for engine oil: measured by the method of ASTM D 5293.

<Measurement Method of Shear Stability (SS) of Lubricating Oil Composition>
Lubricating oil composition for engine oil: measured by the method of ASTM D 6278.
Lubricating oil composition for gear oil: Measured by the method of ASTM D 2603.

  As is clear from the results of Tables 4 and 5, the lubricating oil compositions (Examples 9 to 16) containing the viscosity index improver of the present invention were compared with the lubricating oil compositions of Comparative Examples 7 to 12. Thus, the effect of improving the viscosity index is high, the shear stability is low, and the low-temperature viscosity is low.

  The lubricating oil composition containing the viscosity index improver of the present invention includes a drive system lubricating oil (MTF, differential gear oil, ATF, belt-CVTF, etc.), hydraulic oil (mechanical hydraulic oil, power steering oil, and shock). Absorber oil etc.), engine oil (gasoline and diesel etc.) and traction oil are suitable.

Claims (8)

The monomer (a) represented by the following general formula (1) and the (meth) acrylic acid alkyl ester (b) having 1 to 4 carbon atoms of the linear alkyl group are essential constituent monomers. A viscosity index improver comprising a copolymer (A), wherein the solubility parameter of (A) is 8.5 to 9.5 (cal / cm ³ ) ^1/2 , A viscosity index improver for hydrocarbon-based synthetic base oils containing 70 to 90 mol% of (b) based on the total number of constituent monomers.

[R ¹ is a hydrogen atom or a methyl group; X is a group represented by —O— or —NH—; A is an alkylene group having 2 to 4 carbon atoms; n is an integer of 0 to 20, and n is 2 or more. A in this case may be the same or different, and the (AO) _n moiety may be a random bond or a block bond; R ² is a branched alkyl group having 32 to 44 carbon atoms. ]   The viscosity index improver according to claim 1, wherein the absolute value of the difference between the solubility parameter of (A) and the solubility parameter of the hydrocarbon-based synthetic base oil is 0.5 to 1.2.   (A) is a copolymer having (meth) acrylic acid alkyl ester (c) having 16 to 30 carbon atoms of the branched alkyl group as a constituent monomer as constituent monomer of (A). Item 3. The viscosity index improver according to Item 1 or 2.   (A) further comprises a nitrogen atom-containing monomer (d) other than (a) as a constituent monomer of (A), a hydroxyl group-containing monomer (e), and a phosphorus atom-containing monomer (f). The viscosity index improver according to any one of claims 1 to 3, which is a copolymer comprising at least one selected from the group as a constituent monomer.   The weight index molecular weight of (A) is 5,000-2,000,000, The viscosity index improver in any one of Claims 1-4.   A lubricating oil composition comprising the viscosity index improver according to any one of claims 1 to 5 and a hydrocarbon-based synthetic base oil.   Furthermore, it contains one or more additives selected from the group consisting of detergents, dispersants, antioxidants, oiliness improvers, friction wear modifiers, extreme pressure agents, antifoaming agents, anti-emulsifiers and corrosion inhibitors. The lubricating oil composition according to claim 6. The lubricating oil composition according to claim 6 or 7, wherein the hydrocarbon-based synthetic base oil has a kinematic viscosity at 100 ° C of 1 to 15 mm ² / s, and the hydrocarbon-based synthetic base oil has a viscosity index of 100 or more.