JP2017160310A - Viscosity index improver and lubricant composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubricant composition based on a viscosity index improver containing a polymer which has a high viscosity index and good shear stability and exhibits sufficient solubility in a lubricant base oil.SOLUTION: The viscosity index improver contains a polymer comprising a unit represented by general formula (1) as an essential constitutional unit, where the weight average molecular weight (Mw) of the polymer is greater than or equal to 20000 and less than 500000. The lubricant composition contains a lubricant and the viscosity index improver.SELECTED DRAWING: None

Description

  The present invention relates to a viscosity index improver having a specific structure, a method for producing the same, and a lubricating oil composition containing the same. In particular, the present invention relates to a viscosity index improver that has a high viscosity index and good shear stability and exhibits sufficient solubility in a lubricating oil.

  In recent years, lubricating oil for internal combustion engines has been strongly required to improve fuel-saving characteristics, and one means is to reduce viscosity resistance by reducing the viscosity of the lubricating oil. However, simply reducing the viscosity causes problems such as liquid leakage and seizure. Therefore, it is effective to add a viscosity index improver having an effect of keeping the viscosity at a low temperature while keeping the viscosity at a high temperature high.

  Viscosity index improvers are known to contain polymers, and there are various types. Especially, the viscosity index improver which consists of an alkyl (meth) acrylate polymer shows a high viscosity index improvement effect. On the other hand, since the viscosity index improver made of an alkyl (meth) acrylate polymer has poor shear stability, there has been a problem that fuel-saving properties are deteriorated (long life property is poor) during long-term use.

  Examples of means for improving the shear stability include reducing the molecular weight of the polymer contained in the viscosity index improver. In general, the lower the molecular weight, the less the influence of shearing, and the lower the molecular weight reduction range. Therefore, by using a low molecular weight viscosity index improver, it is possible to suppress the viscosity reduction after shearing (Patent Document 1 and Non-Patent Document 1). Patent Document 1). There has also been a report of attempts to improve shear stability with a polymer having a star structure using divinylbenzene in the core (Patent Document 2).

JP 2013-104032 A JP 2012-197399 A

Nakata, “Viscosity index improver for high performance engine oils”, Sanyo Kasei News, Sanyo Chemical Industries, 2013, No. 476

  However, generally, the lower the molecular weight, the lower the viscosity index improving effect tends to be low. Therefore, when a low molecular weight viscosity index improver is used, there arises a problem that the viscosity index decreases. Furthermore, in order to adjust to a desired viscosity, it is necessary to increase the usage-amount of a viscosity index improver, and it tends to be disadvantageous in cost. Even when a polymer having a star structure using divinylbenzene in the core is used, there is still room for improvement in coexistence of the viscosity index and the shear stability, which is high while maintaining good shear stability. A viscosity index improver that exhibits a viscosity index has been desired.

  The present invention has been made in view of the above problems, and its object is to provide a viscosity index improver containing a polymer exhibiting a high viscosity index while maintaining good shear stability, and the viscosity index improver. It is providing the lubricating oil composition using this.

  The inventors of the present application have conducted extensive studies and have found a viscosity index improver that achieves the above object by the following method.

  That is, the present invention contains a polymer having a unit represented by the general formula (1) (hereinafter referred to as “(a) unit”) as an essential constituent unit, and the weight average molecular weight (Mw) of the polymer is 20000. The viscosity index improver is less than 500,000.

(In the formula, R ¹ and R ² are each independently a hydrogen atom or an alkyl group, and X is an organic group having 8 to 40 carbon atoms.)
In addition to the unit (a), the polymer has a unit derived from an alkyl (meth) acrylate having an aliphatic hydrocarbon group having 6 to 40 carbon atoms (hereinafter referred to as “(b) unit”) and carbon number. Preferably have a unit derived from an alkyl (meth) acrylate having 1 to 5 aliphatic hydrocarbon groups (hereinafter referred to as “(c) unit”).

  The amount of the unit (a) is preferably 5 parts by mass or more and 65 parts by mass or less with respect to 100 parts by mass of the polymer.

  The total amount of (a) units and (c) units is preferably 30 parts by mass or more and less than 95 parts by mass with respect to 100 parts by mass of the polymer.

  The present invention also provides a lubricating oil composition containing the viscosity index improver.

  By using the viscosity index improver of the present invention, shear stability and heat resistance can be improved as compared with conventional lubricating oil compositions. Moreover, since the viscosity index improver of the present invention is easy to ensure sufficient solubility in a base oil while having a high molecular weight, a lubricating oil composition having a high viscosity index can be provided.

  The present invention is described in detail below. In the following description, “part” means “part by mass” and “%” means “mass%” unless otherwise specified. In addition, “A to B” indicating a range indicates that the range is A or more and B or less.

[1. (Viscosity index improver)
The polymer contained in the viscosity index improver of the present invention contains a polymer having the unit (a) represented by the general formula (1) as an essential constituent unit, and the weight average molecular weight (Mw) of the polymer is 20000. The viscosity index improver is less than 500,000.

(In the formula, R ¹ and R ² are each independently a hydrogen atom or an alkyl group, and X is an organic group having 8 to 40 carbon atoms.)
In order to make the unit (a) an essential constituent unit, it is preferable to polymerize a maleimide monomer. X in the general formula (1) is not particularly limited as long as it is an organic group having 8 to 40 carbon atoms, and an arbitrary substituent may be bonded thereto. However, the number of atoms other than carbon atoms and hydrogen atoms in the organic group is preferably 0 or more and 10 or less from the viewpoint of ensuring base oil solubility. Examples of the organic group include linear or branched, cyclic alkyl groups, aryl groups, and H (CH ₂ ) ₆ —O— (CH ₂ ) ₂ —O— (CH ₂ ) ₄ —. An oxaalkyl group.

  Specific examples of the maleimide monomer include, for example, N-octylmaleimide, N-2-ethylhexylmaleimide, N-decylmaleimide, N-laurylmaleimide, N-tetradecylmaleimide, N-stearylmaleimide, N-2- Examples include decyltetradecylmaleimide. Among these, N-laurylmaleimide, N-stearylmaleimide, N-2-ethylhexylmaleimide, and N-2-decyltetradecylmaleimide are preferable because they are highly available and economical and have high solubility in base oils. In addition, the said monomer for comprising (a) unit may be used independently, and may use 2 or more types together.

  (A) The content of the unit is preferably 5 parts by mass or more, preferably 65 parts by mass or less, more preferably 50 parts by mass or less, and still more preferably 40 parts by mass or less with respect to 100 parts by mass of the polymer. The viscosity index improver having the unit (a) in the above range can increase the solubility in the base oil due to the effect of the organic group on the nitrogen atom, and has shear stability and heat resistance due to the ring structure of the main chain. Can be increased. Furthermore, effects such as improvement in clean dispersibility of sludge and the like and suppression of wear on the metal surface are expected.

The polymer contained in the viscosity index improver of the present invention includes the (b) unit derived from an alkyl (meth) acrylate having an aliphatic hydrocarbon group having 6 to 40 carbon atoms in addition to the above (a) unit and the carbon number. Preferably have (c) units derived from an alkyl (meth) acrylate having 1 to 5 aliphatic hydrocarbon groups.
In order to constitute the (b) unit, it is preferable to polymerize an alkyl (meth) acrylate represented by the following general formula (2). In the following general formula (2), R ³ represents a hydrogen atom or a methyl group, and R ⁴ is an alkyl group having 6 to 40 carbon atoms (preferably an alkyl group having 6 to 24 carbon atoms, more preferably 12 carbon atoms). To 24 alkyl groups). The alkyl group of R ⁴ may be any of a chain, a ring, and a branch, and may have a substituent.

In the (meth) acrylate represented by the general formula (2), R ³ and R ⁴ may each be a single monomer, or two or more monomers having different R ³ and / or R ⁴ It may be a mixture of From the viewpoint of reactivity, R ³ is preferably a hydrogen atom or a methyl group.

  Specific examples of the alkyl (meth) acrylate represented by the general formula (2) include, for example, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, and nonyl (meth). Acrylate, decyl (meth) acrylate, undecyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, Stearyl (meth) acrylate, nonadecyl (meth) acrylate, eicosyl (meth) acrylate, behenyl (meth) acrylate, tetracosyl (meth) acrylate, 2-decyltetradecyl (meth) acrylate Over DOO, cyclohexyl (meth) acrylate, menthyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, adamantyl (meth) acrylate. Among these, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, eicosyl (meth) acrylate, behenyl (behind from the viewpoint of availability and economy and high solubility in base oils. (Meth) acrylate, tetracosyl (meth) acrylate, 2-decyltetradecyl (meth) acrylate, and cyclohexyl (meth) acrylate are preferred. The (meth) acrylate represented by the general formula (2) may be used alone or in combination of two or more.

The content of the (meth) acrylate represented by the general formula (2) is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, and preferably less than 90 parts by mass with respect to 100 parts by mass of the polymer. 80 parts by mass or less is more preferable, and 70 parts by mass or less is more preferable. The viscosity index improver containing the polymer having the unit (b) in the above numerical range has good solubility in base oils having various compositions.
In order to constitute the unit (c), it is preferable to polymerize an alkyl (meth) acrylate represented by the following general formula (3). In the following general formula (3), R ⁵ represents a hydrogen atom or a methyl group, and R ⁶ represents an aliphatic hydrocarbon group having 1 to 5 carbon atoms (preferably an alkyl group having 1 to 5 carbon atoms). The aliphatic hydrocarbon group for R ⁶ may be linear, cyclic or branched, and may have a substituent.

In the alkyl (meth) acrylate represented by the general formula (3), R ⁵ and R ⁶ may each be a single monomer, and R ⁵ and / or R ⁶ are different from one another. It may be a mixture of bodies. From the viewpoint of reactivity, R ⁵ is preferably a hydrogen atom or a methyl group. In view of improving the viscosity index, the aliphatic hydrocarbon group represented by R ⁶ is preferably linear or branched.

  Specific examples of the alkyl (meth) acrylate represented by the general formula (3) include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, t-butyl (meth) acrylate, n-amyl (meth) acrylate, iso-amyl (meth) acrylate, t-amyl (meth) acrylate, neopentyl ( And (meth) acrylate. Especially, it is preferable that at least methyl (meth) acrylate is included as (meth) acrylate represented by General formula (3). When the (meth) acrylate represented by the general formula (3) contains methyl (meth) acrylate, it becomes a viscosity index improver having a large effect of improving the viscosity index and having high heat resistance and high shear stability. The (meth) acrylate represented by the general formula (3) may be used alone or in combination of two or more.

  (C) The content of the unit is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, preferably 40 parts by mass or less, more preferably 35 parts by mass or less, relative to 100 parts by mass of the polymer. 30 parts by mass or less is more preferable. When the content of the unit (c) is in the above range, the copolymerization with other components is good, the polymerization rate is good, the polymerization rate is high, and the productivity is good. Moreover, the shear stability and base oil solubility of the viscosity index improver obtained by copolymerization become better.

  The polymer contained in the viscosity index improver of the present invention is preferably such that the total amount of (a) units and (c) units is 30 parts by mass or more with respect to 100 parts by mass of the polymer. The amount is more preferably 40 parts by mass or more, preferably less than 95 parts by mass, and more preferably less than 80 parts by mass. If the total of the amount of (a) unit and (c) unit is in the above range, high shear stability due to the ring structure of the main chain and high by (c) unit while ensuring solubility in base oil The viscosity index can be compatible.

  In the polymer contained in the viscosity index improver of the present invention, the mass ratio of the units (a) and (c) is such that the former / the latter is, for example, 65 / 5-5 / 40, preferably 50 / 10-5 / 35. More preferably, it is 40/10 to 5/30. If the mass ratio of the unit (a) to the unit (c) is in the above range, high shear stability due to the ring structure of the main chain and high viscosity index due to the unit (c) are ensured while ensuring solubility in the base oil. It can be compatible.

  The polymer of the present invention is represented by the (a) unit represented by the general formula (1), the (b) unit derived from the alkyl (meth) acrylate represented by the general formula (2), and the general formula (3). Units other than the (c) unit derived from alkyl (meth) acrylate (hereinafter referred to as “(d) unit”) can be contained. In order to constitute the units (a), (b), (c) and (d), radical polymerization is advantageous from the viewpoint of productivity and cost. The radical polymerizable monomer can be classified into a monofunctional monomer having one radical polymerizable group in the same molecule and a polyfunctional monomer having two or more radical polymerizable groups in the same molecule.

  Examples of the monofunctional monomer for constituting the unit (d) include other (meth) acrylates other than the general formulas (2) and (3), unsaturated mono- or dicarboxylic acid esters, unsaturated carboxylic acids, Examples include vinyl aromatic compounds, vinyl esters, vinyl ethers, olefins, vinyl cyanide, N-vinyl compounds and the like. These monofunctional monomers may be used alone or in combination of two or more.

  Examples of other (meth) acrylates other than the general formulas (2) and (3) include 2-hydroxyethyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, and tetrahydro Examples include furfuryl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, morpholinoalkylene (meth) acrylate, methyl α-hydroxymethyl acrylate, and polyethylene glycol mono (meth) acrylate.

  Examples of the unsaturated mono- or dicarboxylic acid ester include butyl crotonate, octyl crotonate, dibutyl maleate, dilauryl maleate, dioctyl fumarate, distearyl fumarate, and the like.

  Examples of the unsaturated carboxylic acids include (meth) acrylic acid, maleic acid, fumaric acid, maleic anhydride, N-substituted maleimide and the like.

  Examples of the vinyl aromatic compound include styrene monomers such as styrene, α-methylstyrene, vinyltoluene, and methoxystyrene, 2-vinylpyridine, 4-vinylpyridine, and the like.

  Examples of the vinyl ester include vinyl acetate, vinyl propionate, vinyl octylate and the like.

  Examples of the vinyl ether include methyl vinyl ether, butyl vinyl ether, octyl vinyl ether, dodecyl vinyl ether, and the like.

  Examples of olefins include ethylene, propylene, 1-butene, isobutene, 1-tetradecene, 1-octadecene, diisobutene and the like.

  Examples of vinyl cyanide include acrylonitrile and methacrylonitrile.

  Examples of the N-vinyl compound include N-vinyl pyrrolidone, N-vinyl caprolactam, N-vinyl imidazole, N-vinyl morpholine, N-vinyl acetamide and the like.

  Of these monofunctional monomers, 2-hydroxyethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, methyl α-hydroxymethyl acrylate, and N-vinylpyrrolidone are preferred.

  (D) The monofunctional monomer for constituting the unit is preferably 0 part by mass or more and 30 parts by mass or less, more preferably 25 parts by mass or less, and 20 parts by mass or less with respect to 100 parts by mass of the polymer. Further preferred.

  (D) Examples of polyfunctional monomers for constituting units include polyfunctional (meth) acrylates, vinyl ether group-containing (meth) acrylates, allyl group-containing (meth) acrylates, polyfunctional (meth) acryloyl group-containing Examples include polyfunctional (meth) acrylic compounds such as isocyanurate and polyfunctional urethane (meth) acrylate, polyfunctional maleimide compounds, polyfunctional vinyl ethers, polyfunctional allyl compounds, polyfunctional aromatic vinyls, and the like. The said polyfunctional monomer may be used independently and may use 2 or more types together.

  Examples of the polyfunctional (meth) acrylate (polyfunctional (meth) acrylic acid ester) include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and hexanediol di (meth). Acrylate, bisphenol A alkylene oxide di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 2,2 '-[oxybis (methylene)] bisacrylic acid, dialkyl-2,2'-[oxybis (methylene)] bis -2-propenoate and the like.

  Examples of the vinyl ether group-containing (meth) acrylate (vinyl ether group-containing (meth) acrylic acid ester) include 2-vinyloxyethyl (meth) acrylate, 4-vinyloxybutyl (meth) acrylate, and 2- (vinyl) (meth) acrylate. Roxyethoxy) ethyl and the like.

  Examples of the allyl group-containing (meth) acrylate (allyl group-containing (meth) acrylic ester) include, for example, allyl (meth) acrylate, methyl α-allyloxymethyl acrylate, stearyl α-allyloxymethyl acrylate, α- Examples include 2-decyltetradecyl allyloxymethyl acrylate.

  Examples of the polyfunctional (meth) acryloyl group-containing isocyanurate include tri (acryloyloxyethyl) isocyanurate, tri (methacryloyloxyethyl) isocyanurate, and the like.

  As polyfunctional urethane (meth) acrylate (polyfunctional urethane (meth) acrylic acid ester), for example, polyfunctional isocyanate such as tolylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate and 2-hydroxyethyl (meth) acrylate, ( Examples thereof include polyfunctional urethane (meth) acrylates obtained by a reaction with a hydroxyl group-containing (meth) acrylic ester such as 2-hydroxypropyl (meth) acrylate.

  Examples of the polyfunctional maleimide compound include 4,4′-diphenylmethane bismaleimide, m-phenylene bismaleimide, bisphenol A diphenyl ether bismaleimide, 1,6-bismaleimide- (2,2,4-trimethyl) hexane, and the like. Can be mentioned.

  Examples of the polyfunctional vinyl ether include ethylene glycol divinyl ether, diethylene glycol divinyl ether, polyethylene glycol divinyl ether, hexanediol divinyl ether, bisphenol A alkylene oxide divinyl ether, trimethylolpropane trivinyl ether, and the like.

  Examples of polyfunctional allyl compounds include ethylene glycol diallyl ether, diethylene glycol diallyl ether, polyethylene glycol diallyl ether, hexanediol diallyl ether, bisphenol A alkylene oxide diallyl ether, trimethylolpropane triallyl ether, ditrimethylolpropane tetraallyl ether, and the like. Polyfunctional allyl ethers; polyfunctional allyl group-containing isocyanurates such as triallyl isocyanurate; polyfunctional allyl esters such as diallyl phthalate and diallyl diphenate; bisallyl nadiimide compounds; bisallyl nadiimide compounds and the like .

  Examples of the polyfunctional aromatic vinyl include divinylbenzene.

  (D) The content of the polyfunctional monomer for constituting the unit is preferably 0 part by mass or more and 5 parts by mass or less, and more preferably 3 parts by mass or less with respect to 100 parts by mass in total of all monomer components. Preferably, 2 parts by mass or less is more preferable. Further, the content of the unit derived from the polyfunctional monomer in the polymer is preferably 0 parts by mass or more and 5 parts by mass or less, more preferably 3 parts by mass or less, with respect to 100 parts by mass of the polymer. 2 parts by mass or less is more preferable. In this case, when the polymer has a branched structure, the shear stability of the viscosity index improver containing the polymer can be improved without greatly impairing the solubility in the base oil.

  However, 2,2 ′-[oxybis (methylene)] bisacrylic acid, dialkyl-2,2 ′-[oxybis (methylene)] bis-2-propenoate, methyl α-allyloxymethyl acrylate, α-allyloxymethyl In the case of a polyfunctional monomer in which polymerization proceeds while cyclizing, such as stearyl acrylate and α-allyloxymethyl acrylate 2-decyltetradecyl, the inclusion of units derived from the polyfunctional monomer in the polymer The amount is preferably 0 part by mass or more and 30 parts by mass or less, more preferably 25 parts by mass or less, and further preferably 20 parts by mass or less with respect to 100 parts by mass of the polymer. The same applies to the content of the polyfunctional monomer with respect to a total of 100 parts by mass of all monomer components. In this case, due to the effect of the ring structure introduced into the main chain, the heat resistance of the viscosity index improver containing the polymer is improved, and the shear stability can be improved.

  If the unit derived from the polyfunctional monomer exceeds the above range, gelation may proceed during polymerization, or the solubility of the viscosity index improver containing the polymer in the base oil may decrease.

  When the monomer component is polymerized by a radical polymerization mechanism, it is industrially advantageous to use a radical polymerization initiator in combination. The radical polymerization initiator includes a thermal radical polymerization initiator that generates a polymerization initiating radical by heating and a photo radical polymerization initiator that generates a polymerization initiating radical by irradiation with an active energy ray. Or 2 or more types can be used. It is also preferable to add one or more conventionally known thermal radical polymerization accelerators, photosensitizers, photoradical polymerization accelerators, and the like as necessary.

  Specific examples of the thermal radical polymerization initiator include methyl ethyl ketone peroxide, cyclohexanone peroxide, methylcyclohexanone peroxide, methyl acetoacetate peroxide, acetyl acetate peroxide, 1,1-bis (t-hexyl peroxide). Oxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-hexylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1, 1-bis (t-butylperoxy) -2-methylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) cyclododecane, 1,1-bis (T-Butylperoxy) butane, p-menthan high Loperoxide, diisopropylbenzene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, t-hexyl hydroperoxide, t-butyl hydroperoxide, α, α'-bis (T-butylperoxy) diisopropylbenzene, dicumyl peroxide, 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane, t-butylcumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-bis (t-butylperoxy) hexyne-3, isobutyryl peroxide, 3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide Oxide, sc Acid peroxide, m-toluoylbenzoyl peroxide, benzoyl peroxide, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, bis (4-t-butylcyclohexyl) peroxydicarbonate, di-2 -Ethoxyethyl peroxydicarbonate, di-2-ethoxyhexyl peroxydicarbonate, di-3-methoxybutyl peroxydicarbonate, di-s-butyl peroxydicarbonate, di (3-methyl-3-methoxybutyl ) Peroxydicarbonate, α, α′-bis (neodecanoylperoxy) diisopropylbenzene, cumylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, 1 -Cyclohexyl-1- Tylethyl peroxyneodecanoate, t-hexylperoxyneodecanoate, t-butylperoxyneodecanoate, t-hexylperoxypivalate, t-butylperoxypivalate, 1,1,3 , 3-tetramethylbutylperoxy-2-ethylhexanoate, 2,5-dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexanoate, 1-cyclohexyl-1-methylethylperoxy-2 -Ethylhexanoate, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-hexylperoxyisopropylmonocarbonate, t-butylperoxyisobutyrate, t-butyl peroxymalate, t-butyl peroxy-3,5,5-tri Tylhexanoate, t-butyl peroxylaurate, t-butyl peroxyisopropyl monocarbonate, t-butyl peroxy-2-ethylhexyl monocarbonate, t-butyl peroxyacetate, t-butyl peroxy-m-toluyl Benzoate, t-butylperoxybenzoate, bis (t-butylperoxy) isophthalate, 2,5-dimethyl-2,5-bis (m-toluylperoxy) hexane, t-hexylperoxybenzoate, 2,5 -Dimethyl-2,5-bis (benzoylperoxy) hexane, t-butylperoxyallyl monocarbonate, t-butyltrimethylsilyl peroxide, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) Propane, 3,3 ', 4,4'-teto La (t-butylperoxycarbonyl) benzophenone, t-amylperoxyisonanoate, t-amylperoxy-2-ethylhexanoate, sodium persulfate, potassium persulfate, ammonium persulfate, hydrogen peroxide, etc. Oxide-based initiator; 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile, 1-[(1-cyano-1-methylethyl) azo] formamide, 1,1′-azobis (cyclohexane-1- Carbonitrile), 2,2′-azobis (2-methylbutyronitrile), 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2 '-Azobis (2,4-dimethyl-4-methoxyvaleronitrile), 2,2'-azobis (2-methylpropionamidine) dihydride Chloride, 2,2′-azobis (2-methyl-N-phenylpropionamidine) dihydrochloride, 2,2′-azobis [N- (4-chlorophenyl) -2-methylpropionamidine] dihydrochloride, 2,2 ′ -Azobis [N- (4-hydrophenyl) -2-methylpropionamidine] dihydrochloride, 2,2'-azobis [2-methyl-N- (phenylmethyl) propionamidine] dihydrochloride, 2,2'-azobis [2-Methyl-N- (2-propenyl) propionamidine] dihydrochloride, 2,2′-azobis [N- (2-hydroxyethyl) -2-methylpropionamidine] dihydrochloride, 2,2′-azobis [ 2- (5-methyl-2-imidazolin-2-yl) propane] dihydrochloride, 2, '-Azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (4,5,6,7-tetrahydro-1H-1,3-diazepine-2- Yl) propane] dihydrochloride, 2,2′-azobis [2- (3,4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (5-hydroxy) -3,4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} Dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane], 2,2′-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) ) -2-Hydroxyethyl] propionamide}, 2,2′-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) ethyl] propionamide}, 2,2′-azobis [2-methyl -N- (2-hydroxyethyl) propionamide], 2,2'-azobis (2-methylpropionamide), 2,2'-azobis (2,4,4-trimethylpentane), 2,2'-azobis (2-methylpropane), dimethyl-2,2-azobis (2-methylpropionate), 4,4′-azobis (4-cyanopentanoic acid), 2,2′-azobis [2- (hydroxymethyl) Azo initiators such as propionitrile], 2,3-dimethyl-2,3-diphenylbutane, and the like.

  Examples of the thermal radical polymerization accelerator that can be used together with the thermal radical polymerization initiator include metal soaps such as cobalt, copper, tin, zinc, manganese, iron, zirconium, chromium, vanadium, calcium, and potassium; Quaternary ammonium salts; thiourea compounds; ketone compounds, etc., specifically, for example, cobalt octylate, cobalt naphthenate, copper octylate, copper naphthenate, manganese octylate, naphthenic acid Manganese, dimethylaniline, triethanolamine, triethylbenzylammonium chloride, di (2-hydroxyethyl) p-toluidine, ethylenethiourea, acetylacetone, methyl acetoacetate and the like can be mentioned.

  Specific examples of the radical photopolymerization initiator include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1 -Phenylpropan-1-one, 1- [4- (2-hydroxyethoxy) phenyl] -2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1- {4- [4- ( 2-hydroxy-2-methylpropionyl) benzyl] phenyl} -2-methylpropan-1-one, 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one, 2-benzyl-2 -Dimethylamino-1- (4-morpholinophenyl) -butanone-1,2- (dimethylamino) -2-[(4-methyl Alkylphenone compounds such as phenyl) methyl] -1- [4- (4-morpholinyl) phenyl] -1-butanone; benzophenones such as benzophenone, 4,4′-bis (dimethylamino) benzophenone and 2-carboxybenzophenone Compound: Benzoin compounds such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether; thioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4 -Thioxanthone compounds such as diethylthioxanthone; 2- (4-methoxyphenyl) -4,6-bis (trichloromethyl) -s-triazine, 2- (4-methoxynaphthyl) -4,6 Bis (trichloromethyl) -s-triazine, 2- (4-ethoxynaphthyl) -4,6-bis (trichloromethyl) -s-triazine, 2- (4-ethoxycarboquinylnaphthyl) -4,6-bis ( Halomethylated triazine compounds such as trichloromethyl) -s-triazine; 2-trichloromethyl-5- (2′-benzofuryl) -1,3,4-oxadiazole, 2-trichloromethyl-5- [β- ( 2'-benzofuryl) vinyl] -1,3,4-oxadiazole, 4-oxadiazole, 2-trichloromethyl-5-furyl-1,3,4-oxadiazole and the like halomethylated oxadiazoles Compound; 2,2′-bis (2-chlorophenyl) -4,4 ′, 5,5′-tetraphenyl-1,2′-biimidazole, 2,2′-bis (2 4-dichlorophenyl) -4,4 ′, 5,5′-tetraphenyl-1,2′-biimidazole, 2,2′-bis (2,4,6-trichlorophenyl) -4,4 ′, 5 Biimidazole compounds such as 5′-tetraphenyl-1,2′-biimidazole; 1,2-octanedione, 1- [4- (phenylthio)-, 2- (O-benzoyloxime)], ethanone, 1 Oxime ester compounds such as [9-ethyl-6- (2-methylbenzoyl) -9H-carbazol-3-yl]-, 1- (O-acetyloxime); bis (η5-2,4-cyclopentadiene -1-yl) -bis (2,6-difluoro-3- (1H-pyrrol-1-yl) -phenyl) titanium compounds such as titanium; p-dimethylaminobenzoic acid, p-diethylaminoacetate Benzoic acid ester compounds such as benzoic acid; acridine compounds such as 9-phenylacridine; and the like.

  When the monomer component is polymerized by a radical polymerization mechanism, a known chain transfer agent may be used as necessary, and it is more preferable to use in combination with a radical polymerization initiator. Specific examples of such chain transfer agents include mercaptocarboxylic acids such as mercaptoacetic acid and 3-mercaptopropionic acid; methyl mercaptoacetate, methyl 3-mercaptopropionate, 2-ethylhexyl 3-mercaptopropionate, N-octyl 3-mercaptopropionate, methoxybutyl 3-mercaptopropionate, stearyl 3-mercaptopropionate, trimethylolpropane tris (3-mercaptopropionate), pentaerythritol tetrakis (3-mercaptopropionate), di Mercaptocarboxylic esters such as pentaerythritol hexakis (3-mercaptopropionate); ethyl mercaptan, t-butyl mercaptan, n-dodecyl mercaptan, 1,2-dimercaptoethane, etc. Alkyl mercaptans; mercaptoalcohols such as 2-mercaptoethanol and 4-mercapto-1-butanol; aromatic mercaptans such as benzenethiol, m-toluenethiol, p-toluenethiol and 2-naphthalenethiol; tris [(3 -Mercaptopropionyloxy) -ethyl] mercaptoisocyanurates such as isocyanurate; disulfides such as 2-hydroxyethyl disulfide and tetraethylthiuram disulfide; dithiocarbamates such as benzyldiethyldithiocarbamate; simple units such as α-methylstyrene dimer Monomeric dimers; alkyl halides such as carbon tetrabromide; Among these, mercaptocarboxylic acids, mercaptocarboxylic esters, alkyl mercaptans, mercaptoalcohols, aromatic mercaptans; mercaptoisocyanurates in terms of availability, ability to prevent crosslinking, and low degree of polymerization rate reduction. Compounds having a mercapto group, such as catechol, are preferred. These may be used alone or in combination of two or more.

  When the monomer component is polymerized by a radical polymerization mechanism, radical polymerization may be performed in the presence of a trifunctional or higher polyvalent mercaptan and / or a trifunctional or higher polyfunctional initiator.

  Examples of the trifunctional or higher polyvalent mercaptan include trimethylolpropane trimercaptoacetate, trimethylolpropane tri (3-mercaptopropionate), pentaerythritol tetrakismercaptoacetate, pentaerythritol tetrakis (3-mercaptopropionate), Dipentaerythritol hexakis mercaptoacetate, dipentaerythritol hexakis (3-mercaptopropionate) and other compounds having three or more hydroxyl groups and carboxyl group-containing mercaptans polyester compounds, triazine polyvalent thiols, polyvalent epoxy compounds A compound obtained by adding hydrogen sulfide to a plurality of epoxy groups and introducing three or more mercapto groups per molecule, a plurality of carboxyl groups and mercapto of polyvalent carboxylic acid Ethanol to can be such compounds include having esterified three or more mercapto groups per molecule comprising. The trifunctional or higher polyvalent mercaptan can be used alone or in combination (for example, mixed).

  The amount (total amount added) of the trifunctional or higher polyvalent mercaptan is appropriately determined according to the type and amount of the monomer used, the polymerization conditions such as polymerization temperature and polymerization concentration, the molecular weight of the target polymer, and the like. What is necessary is just to set, and it does not specifically limit. From the viewpoint of obtaining a viscosity index improver containing a polymer having a high base oil solubility and a weight average molecular weight of 100,000 or more, the amount of trifunctional or higher polyvalent mercaptan used is 100 parts by mass of the monomer component. On the other hand, 0.01 mass part or more is preferable, 0.05 mass part or more is more preferable, 5 mass part or less is preferable, 3 mass part or less is more preferable, and 2 mass part or less is further more preferable. By setting it as this range, molecular weight distribution becomes narrow and shear stability can be improved.

  Examples of the trifunctional or higher polyfunctional initiator include 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, tris (t-butylperoxy) triazine, 3,3 ′, 4,4. Trifunctional or higher functional organic peroxides such as' -tetra (t-butylperoxycarbonyl) benzophenone are exemplified, but not particularly limited.

  The usage amount (addition amount total amount) of the trifunctional or higher polyfunctional initiator is not particularly limited, and may be appropriately set according to the purpose and application. From the viewpoint of obtaining a viscosity index improver containing a polymer having a weight average molecular weight of 100,000 or more, which has high viscosity index and base oil solubility, taking into consideration the balance between polymerizability, adverse effects of degradation products, and economic efficiency. The amount of the trifunctional or higher polyfunctional initiator is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, and 0.05 parts by mass or more with respect to 100 parts by mass of the monomer component. More preferably, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and further preferably 2 parts by mass or less.

  A polymer obtained by radical polymerization of a monomer component in the presence of a trifunctional or higher polyvalent mercaptan and / or a trifunctional or higher polyfunctional initiator has a structure in which a polymer chain is branched from the center. It will have. That is, the polymer contained in the viscosity index improver of the present invention has a branch unit derived from a trifunctional or higher polyvalent mercaptan and / or a branch unit derived from a trifunctional or higher polyfunctional initiator. When the polymer contained in the viscosity index improver has such a structure, the shear stability of the viscosity index improver containing the polymer can be improved without greatly impairing the solubility in the base oil. it can.

When the polymer contained in the viscosity index improver has a branched unit derived from a trifunctional or higher polyvalent mercaptan, the polymer has a branched unit (chain transfer agent residue) represented by the following formula (4). Is preferred. In the following formula (4), L _T represents an m-valent organic residue, m represents a number of 0 or more. m is preferably 0-5.

When the polymer contained in the viscosity index improver has a branch unit derived from a trifunctional or higher polyfunctional initiator, the polymer preferably has a branch unit derived from a trifunctional or higher functional peroxide. Preferably has a branch unit represented by the following formula (5). In the following formula (5), L _S represents an n-valent organic residue (initiator residue), and n represents a number of 0 or more. n is preferably 0 to 5.

  The polymer contained in the viscosity index improver may contain only one or both of a branched unit derived from a polyfunctional mercaptan having a functionality of 3 or more and a branched unit derived from a polyfunctional initiator having a functionality of 3 or more. Also good. Only one type of trifunctional or higher polyvalent mercaptan-derived branch unit may be contained, or two or more types may be contained. Only one type of branch unit derived from a trifunctional or higher polyfunctional initiator may be contained, or two or more types may be contained.

  The content of the trifunctional or higher polyfunctional mercaptan-derived branch unit in the polymer is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and 5 parts by mass with respect to 100 parts by mass of the polymer. Part or less, preferably 3 parts by weight or less, more preferably 2 parts by weight or less. By setting it as this range, the molecular weight distribution of the polymer becomes narrow, and the shear stability can be improved. The content of the branch unit derived from the trifunctional or higher polyvalent mercaptan is obtained by dividing the amount of the trifunctional or higher polyvalent mercaptan used by the polymer mass.

  The content of the branch unit derived from the trifunctional or higher polyfunctional initiator in the polymer is a viscosity index and a viscosity index improver containing a polymer having a high base oil solubility and a weight average molecular weight of 100,000 or more. From 100 parts by mass of the polymer, 0.01 parts by mass or more is preferable, 0.02 parts by mass or more is more preferable, 0.05 parts by mass or more is more preferable, and 10 parts by mass or less is preferable, and 5 parts by mass is preferable. The following is more preferable, and 2 parts by mass or less is more preferable. The content of the branch unit derived from the trifunctional or higher polyfunctional initiator is obtained by dividing the amount of the trifunctional or higher polyfunctional initiator used by the polymer mass.

  The polymerization method of the polymer contained in the viscosity index improver of the present invention can be obtained by a production method having a step of polymerizing monomer components (polymerization step). The polymerization method of the monomer component in the polymerization step may be any of bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization and the like, but is not particularly limited. When using a dispersion medium, an emulsifier, a dispersant, etc., there is no particular limitation and a known one can be used.

  In the case of using a trifunctional or higher polyvalent mercaptan and / or a trifunctional or higher polyfunctional initiator in the polymerization step, suitable conditions such as the type and amount of use thereof are as described above. In the polymerization, the trifunctional or higher polyvalent mercaptan and / or the trifunctional or higher polyfunctional initiator may be added all at once or in divided portions. Further, a bifunctional or lower functional mercaptan or a bifunctional or lower functional initiator may be used in combination.

  In the polymerization step, the monomer component is represented by (a) a component for constituting the unit represented by the general formula (1) described above, and (b) represented by the general formula (2) for constituting the unit. It is preferable to essentially use the alkyl (meth) acrylate component represented by the general formula (3) for constituting the alkyl (meth) acrylate component and (c) unit. As a monomer component, you may use together the component for comprising the (d) unit demonstrated above. Suitable conditions such as the type and amount of each monomer component are as described above.

  The solvent used for the polymerization is not particularly limited as long as it is inactive to the polymerization reaction, the polymerization mechanism, the type and amount of the monomer used, the type and amount of the polymerization initiator / polymerization catalyst, etc. What is necessary is just to set suitably according to the polymerization conditions. In addition, from the viewpoint of ensuring the solubility of the polymer, and from the viewpoint of easy solvent substitution to the base oil after polymerization, the solvent used for the polymerization is toluene, xylene, hexane, cyclohexane, methyl ethyl ketone, tetrahydrofuran, ethyl acetate, Butyl acetate is preferred. Further, a lubricating base oil described later can also be suitably used as the solvent. In this case, solvent replacement after polymerization is unnecessary, and the process is simplified, which is more preferable. These solvents may be used alone or in combination of two or more. The amount of solvent used is not particularly limited, but from the viewpoint of obtaining a polymer having a high viscosity index and a weight average molecular weight of 100,000 or more, the concentration of the total amount of the monomer component, polymerization initiator and other components is The degree which becomes 20 mass% or more and 80 mass% or less is preferable.

  The polymerization temperature at the time of polymerizing the monomer component may be appropriately set according to the polymerization mechanism, the type and amount of the monomer used, the type and amount of the polymerization initiator / polymerization catalyst, and the like. However, 0 ° C. or higher is preferable, 25 ° C. or higher is more preferable, 200 ° C. or lower is preferable, and 150 ° C. or lower is more preferable. If the polymerization temperature is less than 0 ° C., the polymerization reaction is very slow, and if it exceeds 200 ° C., the reaction is so intense that it is difficult to control.

  The polymer contained in the viscosity index improver of the present invention has a weight average molecular weight (Mw) of 20,000 or more, preferably 100,000 or more, more preferably 200,000 or more, further preferably 250,000 or more, 300,000 or more is even more preferable, less than 500,000, 490,000 or less is preferable, and 480,000 or less is more preferable. When the weight average molecular weight of the polymer is less than the above lower limit, not only the viscosity index of the lubricating oil composition is lowered, but it is necessary to increase the amount of the viscosity index improver used to adjust to the desired viscosity. This is disadvantageous in terms of cost. When the weight average molecular weight of the polymer is excessively large, the solubility of the viscosity index improver in the base oil tends to be insufficient or the shear stability of the lubricating oil composition tends to decrease.

  The number average molecular weight (Mn) of the polymer contained in the viscosity index improver of the present invention is preferably 8,000 or more, preferably 90,000 or more, more preferably 90,000 to 220,000, and still more preferably 90,000. ~ 200,000.

  The molecular weight distribution (Mw / Mn) calculated from Mw and Mn is preferably 4.0 or less, more preferably 3.5 or less, and even more preferably 3.0 or less. When the molecular weight distribution exceeds 4.0, the solubility of the viscosity index improver in the base oil is insufficient, and the shear stability of the lubricating oil composition is decreased, which is not preferable. On the other hand, the lower limit of the molecular weight distribution is preferably 1.0, but from the viewpoint of easy synthesis of the polymer, the molecular weight distribution (Mw / Mn) is preferably 1.5 or more, more preferably 2.0 or more, and 2.3. The above is more preferable. In addition, Mw and Mn in this invention can be measured using a well-known method.

  A known method can be used as a method for controlling the molecular weight. For example, it can be controlled by adjusting the amount and type of the polymerization initiator / polymerization catalyst, the polymerization temperature, and the type and amount of the chain transfer agent. Living Radical Polymerization can also be used as a method for controlling the molecular weight distribution. As specific methods, RAFT method, NMP method, ATRP method and the like are well known. For details, see Aldrich Material Matters, Vol. 5, no. 1, 2010. For example, in the case of the RAFT method, 2,2′-azobisisobutyronitrile is used as a polymerization initiator and cumyl dithiobenzoate is used as a polymerization catalyst in JP2012-197399A.

  The degree of branching of the polymer contained in the viscosity index improver of the present invention is preferably 1.0 or more, more preferably 1.4 or more, and preferably 10.0 or less, more preferably 6.0 or less. 0.0 or less is more preferable. When the degree of branching is less than 1.0, the branched structure of the polymer is not sufficient, and improvement in shear stability cannot be expected. The degree of branching in the present invention corresponds to the average number of branch points per molecule of the polymer, and logically, for example, the degree of branching of a straight-chain polymer without branching is 0, and the only branching From the point, the degree of branching of the polymer in which three polymer chains are extended is 1, the degree of branching of the polymer in which four polymer chains are extended is 2, and the degree of branching of the polymer in which five polymer chains are extended The degree of branching is 3.

  The content of the above-described polymer in the viscosity index improver is not particularly limited as long as it does not impair the effects of the present invention, but the viscosity index improver of the present invention may contain the above-mentioned polymer as a main component. preferable. The content of the polymer in the viscosity index improver is, for example, preferably 50 parts by mass or more, more preferably 80 parts by mass or more, and still more preferably 90 parts by mass or more with respect to 100 parts by mass of the viscosity index improver.

  The SP value (solubility parameter) of the polymer contained in the viscosity index improver of the present invention is preferably 8.8 or more, more preferably 8.9 or more, further preferably 9.0 or more, and 9.6 or less. Preferably, 9.5 or less is more preferable, and 9.4 or less is more preferable. The SP value of the base oil generally shows a value of about 8.0 to 8.5. However, if the SP value of the polymer is 8.8 or more, the viscosity index of the lubricating oil composition is easily increased, and the SP of the polymer is increased. If the value is 9.6 or less, it becomes easy to ensure the solubility of the viscosity index improver in the base oil. The SP value can be obtained using a known method.

The viscosity index improver of the present invention can achieve both a viscosity index improving effect and shear stability at a high level. As specific values of the shear stability, for example, PSSI (Permanent Cystability Index: ASTM D 6022), SSI obtained by the method shown below, or decomposition start temperature is an index.
The SSI in the present invention is a value measured by the method described in Examples described later. That is, the polymer was diluted in a base oil (manufactured by SK: YUBASE4) so that the kinematic viscosity at 100 ° C. was 7.0 mm ² / sec, and ultrasonic waves were irradiated under the following conditions.
Apparatus: UP400S manufactured by Hielscher Ultrasonics
Setting: Amplitude = 70%, Cycle = 1
Time: 10 minutes Temperature: 100 ° C
The kinematic viscosity before and after shearing and at 100 ° C. of the base oil was measured. It was calculated by the following formula.

  In the present invention, the SSI of the viscosity index improver as an index of shear stability is preferably 45 or less, more preferably 40 or less, and still more preferably 38 or less. The SSI is preferably 0.1 or more, more preferably 0.5 or more, still more preferably 2 or more, and particularly preferably 5 or more. If the SSI is less than 0.1, the effect of improving the viscosity index is small and the cost may increase. If the SSI exceeds 45, the shear stability and storage stability may be deteriorated.

  The decomposition start temperature of the viscosity index improver is preferably 290 ° C or higher, more preferably 295 ° C or higher, further preferably 300 ° C or higher, particularly preferably 310 ° C or higher, and preferably 500 ° C or lower, 450 ° C or lower. Is more preferable, 400 ° C. or lower is more preferable, and 380 ° C. or lower is particularly preferable. By increasing the decomposition start temperature of the viscosity index improver, heat resistance is improved, and thermal decomposition stability and shear stability are improved. On the other hand, when the heat resistance is excessively improved, the solubility in the base oil tends to be insufficient or the viscosity index tends to decrease.

  The viscosity index improver of the present invention contains the above-mentioned polymer as a main component, and preferably, in 100% by mass of the viscosity index improver, the polymer is 70% by mass or more, more preferably 90% by mass or more, and still more preferably 95%. It is contained by mass% or more, particularly preferably 99% by mass or more and 100% by mass or less.

[2. (Composition containing viscosity index improver and base oil)
The present invention also provides a lubricating oil composition containing the viscosity index improver of the present invention. The viscosity index improver of the present invention can be blended with a lubricating base oil to form a lubricating oil composition. The lubricating oil composition may be used as a lubricating oil without further dilution with a lubricating base oil, or may be further diluted with a lubricating base oil as a lubricating oil. In the latter case, the lubricating oil composition is used as a stock solution, which may hereinafter be referred to as a “base oil composition”.

  As the lubricating base oil, known lubricating base oils can be used without particular limitation, and mineral oil base oils and synthetic base oils can be preferably mentioned. Examples of the mineral oil base oil include paraffinic and naphthenic base oils. Mineral base oils include those obtained by subjecting raw material base oils to solvent refining, hydrocracking or hydroisomerization. Examples of synthetic base oils include hydrocarbon, ester, ether, silicon, and fluorine base oils. As described above, the lubricating base oil can also be used as a polymerization reaction solvent for the polymer contained in the viscosity index improver.

As a preferred specific example of the mineral oil base oil, the following base oils (1) to (7) are used as raw materials, and the raw oil and / or a lubricating oil fraction recovered from the raw oil is used as a predetermined refining method. And base oils obtained by recovering the lubricating oil fraction. Further, the following base oil (8) or (9) obtained by performing a predetermined treatment on a base oil selected from (1) to (7) or a lubricating oil fraction recovered from the base oil is particularly preferable.
(1) Distilled oil (WVGO) by distillation under reduced pressure of paraffin base crude oil and / or mixed base crude oil at atmospheric distillation residue
(2) Wax (such as slack wax) obtained by the lubricant dewaxing process and / or synthetic wax (Fischer-Tropsch wax, GTL wax, etc.) obtained by the gas-liquid (GTL) process, etc.
(3) One or two or more mixed oils selected from base oils (1) to (2) and / or mild hydrocracked oils of the mixed oils (4) selected from base oils (1) to (3) 2 or more kinds of mixed oils (5) Base oils (1) to (4)
(6) Mild hydrocracking treatment oil (MHC) of base oil (5)
(7) Two or more mixed oils selected from base oils (1) to (6).
(8) Hydrocracking a base oil selected from the base oils (1) to (7) or a lubricating oil fraction recovered from the base oil, and recovering the product or the product by distillation or the like Hydrocracked mineral oil obtained by performing dewaxing treatment such as solvent dewaxing or catalytic dewaxing on the lubricating oil fraction, or by performing distillation after the dewaxing treatment.
(9) A base oil selected from the base oils (1) to (7) or a lubricating oil fraction recovered from the base oil is hydroisomerized and recovered from the product or the product by distillation or the like. Hydroisomerized mineral oil obtained by subjecting a lubricating oil fraction to dewaxing treatment such as solvent dewaxing or catalytic dewaxing, or distillation after the dewaxing treatment.

Specific examples of synthetic base oils include poly α-olefins or hydrides thereof, isobutene oligomers or hydrides thereof, isoparaffins, alkylbenzenes, alkylnaphthalenes, diesters (ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl). Adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, etc.), polyol ester (trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate, etc.), polyoxyalkylene Glycol, dialkyl diphenyl ether, polyphenyl ether and the like can be mentioned, and among them, poly α-olefin is preferable. As the poly α-olefin, typically, an oligomer or co-oligomer (1-octene oligomer, decene oligomer, ethylene-propylene co-oligomer, etc.) having 2 to 32 carbon atoms, preferably 6 to 16 carbon atoms, and those. Of the hydrides. The kinematic viscosity at 100 ° C. of the synthetic base oil is preferably 1 to ²⁰ mm ² / sec.

  As the lubricating base oil blended in the lubricating oil composition, the base oil selected from the above base oils (1) to (7) or the lubricating oil fraction recovered from the base oil, the viscosity index of the lubricating oil composition The base oil (8) or (9) obtained by carrying out the above-mentioned treatment is particularly preferred for the reason of increasing the viscosity. It is also preferred to use a base oil belonging to Group III based on classification by the American Petroleum Institute (API). As the lubricating base oil blended in the lubricating oil composition, the above-described synthetic base oil may be used.

  In the lubricating oil composition of the present invention, the above lubricating base oil may be used alone or in combination with one or more other base oils. When a lubricating base oil and another base oil are used in combination to obtain a mixed base oil, the mixed base oil is used for the above lubricating base oil (8) or ( 9) is preferably included. The ratio of the lubricating base oil (8) or (9) in the mixed base oil is preferably 30% by mass or more, more preferably 50% by mass or more, and 70% by mass or more. Further preferred.

  The viscosity index of the lubricating base oil is preferably 100 or more, more preferably 120 or more, and preferably 160 or less. When the viscosity index is less than the above lower limit, not only the viscosity-temperature characteristics, thermal / oxidative stability, and volatilization prevention properties deteriorate, but also the friction coefficient tends to increase, and the wear prevention properties decrease. There is a tendency. On the other hand, when the viscosity index exceeds the above upper limit, the low-temperature viscosity characteristics tend to deteriorate. In addition, the viscosity index as used in the field of this invention means the viscosity index measured based on JISK2283.

  The viscosity index of the lubricating oil composition is preferably 200 or more and 400 or less, and more preferably 230 or more and 300 or less. When the viscosity index is within the above range, the fuel economy, heat / oxidation stability, and storage stability are excellent.

  The content of the viscosity index improver of the present invention in the lubricating oil composition is not particularly limited, and is preferably 0.01% by mass or more, for example, 0.1% by mass or more based on the total amount of the lubricating oil composition. More preferably, 0.5% by mass or more is further preferable, 70% by mass or less is preferable, 60% by mass or less is more preferable, and less than 50% by mass is further preferable. When the lubricating oil composition is used in lubricating oil without further dilution with a lubricating base oil, the content of the viscosity index improver of the present invention in the lubricating oil composition is based on the total amount of the lubricating oil composition. Is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, further preferably 0.5% by mass or more, more preferably 20% by mass or less, more preferably 15% by mass or less, and more preferably 10% by mass. The following is more preferable. When the lubricating oil composition of the present invention is used as a base oil composition, the content of the viscosity index improver of the present invention in the base oil composition is, for example, preferably 5% by mass or more, and more preferably 10% by mass or more. 20 mass% or more is more preferable, 70 mass% or less is preferable, 60 mass% or less is more preferable, and less than 50 mass% is further more preferable.

  The lubricating oil composition of the present invention contains the viscosity index improver of the present invention and a lubricating oil base oil as essential components, and may further contain optional additives and the like. The lubricating oil composition is selected from the group consisting of, for example, a pour point depressant, an antiwear agent, a metallic detergent dispersant, an ashless detergent dispersant, an antioxidant, a corrosion inhibitor, an antifoaming agent, and a friction modifier. It is preferable to further contain at least one additive.

  As the pour point depressant, any pour point depressant used for lubricating oil can be used. Examples of pour point depressants include polymethacrylates, naphthalene-chlorinated paraffin condensation products, phenol-chlorinated paraffin condensation products, and the like. Among these, addition of polymethacrylates is preferable.

  As the antiwear agent (or extreme pressure agent), any antiwear agent / extreme pressure agent used for lubricating oil can be used. As the antiwear agent (or extreme pressure agent), for example, sulfur-based, phosphorus-based, sulfur-phosphorus-based extreme pressure agents and the like can be used. Specifically, zinc dialkyldithiophosphate (ZnDTP), phosphite Thiophosphites, dithiophosphites, trithiophosphites, phosphate esters, thiophosphate esters, dithiophosphate esters, trithiophosphate esters, amine salts thereof, these Examples thereof include metal salts, derivatives thereof, dithiocarbamate, zinc dithiocarbamate, MoDTC, disulfides, polysulfides, sulfurized olefins, and sulfurized fats and oils. Among these, addition of a sulfur-based extreme pressure agent is preferable, and sulfurized fats and oils are particularly preferable.

  Examples of the metal detergent / dispersant include normal salts or basic salts such as alkali metal / alkaline earth metal sulfonate, alkali metal / alkaline earth metal phenate, and alkali metal / alkaline earth metal salicylate. Examples of the alkali metal include sodium and potassium, and examples of the alkaline earth metal include magnesium, calcium and barium. Magnesium or calcium is preferable, and calcium is particularly preferable.

  As the ashless detergent / dispersant, any ashless detergent / dispersant used for lubricating oil can be used. Examples of the ashless detergent / dispersant include mono- or bissuccinimide having at least one linear or branched alkyl group or alkenyl group having 40 to 400 carbon atoms in the molecule, and alkyl group having 40 to 400 carbon atoms. Or a benzylamine having at least one alkenyl group in the molecule, a polyamine having at least one alkyl group or alkenyl group having 40 to 400 carbon atoms in the molecule, or a modification thereof by a boron compound, carboxylic acid, phosphoric acid or the like. Examples include products. In use, one kind or two or more kinds arbitrarily selected from these can be blended.

  Examples of the antioxidant include ashless antioxidants such as phenols and amines, and metal antioxidants such as copper and molybdenum. Specific examples of the antioxidant include, for example, 4,4′-methylenebis (2,6-di-tert-butylphenol), 4,4′-bis (2, 6-di-tert-butylphenol) and the like, and amine-based ashless antioxidants include phenyl-α-naphthylamine, alkylphenyl-α-naphthylamine, dialkyldiphenylamine and the like.

  Examples of the corrosion inhibitor include benzotriazole, tolyltriazole, thiadiazole, or imidazole compounds.

Examples of the defoaming agent include silicone oil having a kinematic viscosity at 25 ° C. of 1000 to 100,000 mm ² / s, fluorosilicone oil, alkenyl succinic acid derivative, ester of polyhydroxy aliphatic alcohol and long chain fatty acid, methyl salicy Rate and o-hydroxybenzyl alcohol.

  Friction modifiers include succinimide molybdenum complexes such as molybdenum dithiocarbamate and molybdenum dithiophosphate, organic molybdenum compounds such as amine salts of organic molybdic acid, and linear alkyl and metal having 8 to 30 carbon atoms as the basic structure. And having a polar group that can be adsorbed on the same molecule in the same molecule. Examples of polar groups include amines, polyamines, amides, urea compounds and alkenyls such as amine compounds, fatty acid esters, fatty acid amides, fatty acids, fatty alcohols, aliphatic ethers, urea compounds, hydrazide compounds having these simultaneously in the molecule. Examples thereof include succinimide type, ester, alcohol and diol, or monoalkyl glycerol ester having ester and hydroxyl group at the same time. In addition, there are various types such as an alkylamine afucosyl alcohol having an amine and a hydroxyl group in the same molecule.

  The lubricating oil composition is one selected from the group consisting of a pour point depressant, an antiwear agent, a metallic detergent dispersant, an ashless detergent dispersant, an antioxidant, a corrosion inhibitor, a defoamer, and a friction modifier. Or when it contains 2 or more types, it is preferable that each content is 0.01 mass% or more and 10 mass% or less on the basis of the whole quantity of a lubricating oil composition. Moreover, when a lubricating oil composition contains an antifoamer, the content becomes like this. Preferably it is 0.0001 mass% or more and 0.01 mass% or less. When the lubricating oil composition is used as the base oil composition, the base oil composition may substantially consist of a viscosity index improver and a lubricating base oil. In this case, in the base oil composition The total content of the viscosity index improver and the lubricating base oil is, for example, preferably 98% by mass or more, more preferably 99% by mass or more, and 99.5% by mass based on the total amount of the base oil composition. The above is more preferable.

  In addition to the above components, the lubricating oil composition may further contain a viscosity index improver other than the polymer of the present invention, a rust inhibitor, a demulsifier, a metal deactivator, and the like.

  The viscosity index improver other than the polymer of the present invention is specifically a non-dispersed or dispersed ester group-containing viscosity index improver, for example, a non-dispersed or dispersed poly (meth) acrylate viscosity index improver. Agents, non-dispersed or dispersed olefin- (meth) acrylate copolymer viscosity index improvers, styrene-maleic anhydride copolymer viscosity index improvers, and mixtures thereof. Among these, a non-dispersed or dispersed poly (meth) acrylate viscosity index improver is preferable, and a non-dispersed or dispersed polymethacrylate viscosity index improver is more preferable. In addition, a non-dispersed or dispersed ethylene-α-olefin copolymer or a hydrogenated product thereof, polyisobutylene or a hydrogenated product thereof, a styrene-diene hydrogenated copolymer, a polyalkylstyrene, and the like can be given.

  Examples of the rust inhibitor include petroleum sulfonate, alkylbenzene sulfonate, dinonylnaphthalene sulfonate, alkenyl succinic acid ester, and polyhydric alcohol ester.

  Examples of the demulsifier include polyalkylene glycol nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, or polyoxyethylene alkyl naphthyl ether.

  Examples of metal deactivators include imidazoline, pyrimidine derivatives, alkylthiadiazoles, mercaptobenzothiazoles, benzotriazoles or derivatives thereof, 1,3,4-thiadiazole polysulfide, 1,3,4-thiadiazolyl-2,5-bis. Examples thereof include dialkyldithiocarbamate, 2- (alkyldithio) benzimidazole, and β- (o-carboxybenzylthio) propiononitrile.

  The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. In the examples and comparative examples, “%” and “parts” represent “% by mass” and “parts by mass”, respectively, unless otherwise specified.

  In the Examples, for convenience, the following abbreviations are used for compounds.

LMI: laurylmaleimide (monomer synthesized in Production Example 1)
SMI: Stearylmaleimide (monomer synthesized in Production Example 2)
MMA: Methyl methacrylate SMA: Stearyl methacrylate SLMA: Mixture of lauryl methacrylate / tridecyl methacrylate = 54/46 (mass ratio) (1) Analytical method (polymerization rate)
The polymerization rate of each monomer component of the present invention was determined using gas chromatography (manufactured by Shimadzu Corporation, GC-2010plus).

The measurement conditions are as follows.
Column: Inert Cap1 (liquid phase film thickness: 0.25 μm, length: 30 m, inner diameter: 0.25 mm) manufactured by GL Science
-Temperature: 40 ° C (5 min hold) + 40 ° C to 170 ° C (10 ° C / min) + 170 ° C to 210 ° C (5 ° C / min) + 210 ° C to 330 ° C (15 ° C / min) + 330 ° C (20 min hold)
-Vaporization chamber temperature: 200 ° C
-Detector temperature: 350 ° C (FID)
-Carrier gas: helium (column flow rate 1.33 ml / min)
Injection volume: 0.5 μl (split method, split ratio: 30.0)
-Internal standard sample: tridecane-diluting solvent: ethyl acetate A calibration curve solution was prepared by dissolving each monomer and tridecane in ethyl acetate, measured by gas chromatography, and a calibration curve was created from the peak area. Next, a sample solution in which the polymerization solution and tridecane were dissolved in ethyl acetate was prepared and measured in the same manner. The polymerization rate of each monomer component was determined by an internal standard method.

(Weight average molecular weight and number average molecular weight)
The weight average molecular weight and number average molecular weight of the polymer were measured under the following conditions.
-Equipment: Tosoh GPC system HLC-8320GPC ECOSEC
-Column: manufactured by Tosoh Corporation, two TSKgel GMHXL-developing solvent: tetrahydrofuran-flow rate of developing solvent: 1.0 ml / min-standard sample: TSK standard polystyrene (PS-oligomer kit manufactured by Tosoh Corporation)
-Column temperature: 40 ° C
-Sample concentration: 0.5%
Injection volume: 200 μl
(Viscosity index)
The polymer was diluted with a base oil (manufactured by SK: YUBASE4) so that the kinematic viscosity at 100 ° C. was 7.0 mm ² / sec, and the measurement was performed by the method of JIS K2283. The case where the viscosity index was 230 or more was rated as ◯, and the case where it was less than 230 was rated as x.

(Shear stability)
The polymer was diluted in a base oil (manufactured by SK: YUBASE4) so that the kinematic viscosity at 100 ° C. was 7.0 mm ² / second, and ultrasonic waves were irradiated under the following conditions.
Apparatus: UP400S manufactured by Hielscher Ultrasonics
Setting: Amplitude = 70%, Cycle = 1
Time: 10 minutes Temperature: 100 ° C
The kinematic viscosity before and after shearing and at 100 ° C. of the base oil was measured, and SSI = {1− (kinematic viscosity after shearing−dynamic viscosity of base oil) / (dynamic viscosity before shearing−dynamic viscosity of base oil)} × 100 The case where the value calculated by the above formula was less than 45 was marked with ◯, and the case where it was 45 or more was marked with ×.

(2) Production Example of Polymer Base Oil Solution (Production Example 1) Synthesis of LMI In a 500 ml flask equipped with a thermometer, a condenser and a stirrer, 51.48 g (0.525 mol) of maleic anhydride, xylene 272. 88 g was added and stirred and dissolved at 80 ° C. Next, a mixed solution of 134.76 g (0.50 mol) of laurylamine and 92.68 g of xylene was added over 1 hour using a dropping funnel, followed by stirring and aging at 80 ° C. for 1 hour. The mousse-like reaction liquid was filtered, and the collected solid was further washed with xylene and then dried under reduced pressure at 60 ° C. to obtain lauryl maleamic acid as a white solid.
Next, 42.5 g (0.15 mol) of the obtained lauryl maleamic acid, 168 mg of calcium oxide, 5.3 g of triethylamine, and 20.4 g (0.2 mol) of acetic anhydride were added to a 300 ml flask equipped with a thermometer, a condenser and a stirrer. It was thrown into. The reaction was stirred at 80 ° C. for 3 hours, and the resulting solid was washed with water and filtered. Furthermore, after recrystallizing with methanol, it was dried under reduced pressure at 40 ° C. to obtain 15.88 g of slightly yellow LMI (39.9% in terms of lauryl maleamic acid, 12.0% in terms of laurylamine).

(Production Example 2) SMI synthesis 12.87 g (0.131 mol) of maleic anhydride and 200 g of xylene were charged into a 500 ml flask equipped with a thermometer, a condenser and a stirrer, and stirred and dissolved at 100 ° C. Next, a mixed solution of stearylamine 33.69 g (0.125 mol) and xylene 70 g heated to 50 ° C. was added through a dropping funnel over 1 hour, and then stirred and aged at 100 ° C. for 6 hours. The reaction solution was filtered at 70 ° C., and the filtered solid was further washed with xylene, and then dried under reduced pressure at 60 ° C. to obtain stearyl maleamic acid as a white solid.
Next, 29.41 g (0.08 mol) of the obtained stearyl maleamic acid, 14.7 g of 85% phosphoric acid, and 100 g of xylene were charged into a 300 ml flask equipped with a thermometer, a water separation tube, a cooling tube, and a stirrer. The reaction was stirred at 150 ° C. for 3 hours, and the resulting reaction solution was separated, and the oil layer was washed with water. After washing with water, xylene was distilled off from the oil layer, recrystallized with methanol, and then dried under reduced pressure at 40 ° C. to give 12.91 g of slightly yellow stearylmaleimide (46.2% in terms of stearylmaleamic acid, 29. in terms of stearylamine). 6%).

Example 1
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen introduction tube, and a dropping funnel, MMA 30 parts by mass, SMA 30 parts by mass, LMI 10 parts by mass, SLMA 30 parts by mass, toluene 53.33 parts by mass, antioxidant ( ADK STAB (registered trademark) 2112 (manufactured by ADEKA) 0.05 parts by mass, 0.40 parts by mass of acetic anhydride, 0.05 parts by mass of pentaerythritol tetrakis (mercaptoacetate), and contents while introducing nitrogen gas The temperature was raised to 105 ° C. As a polymerization initiator, a solution prepared by mixing 0.0258 parts by mass of t-amylperoxyisononanoate (manufactured by Arkema Yoshitomi Corp., Luperox (registered trademark) 570) and 0.46 parts by mass of toluene was added, and the polymerization was started. The solution polymerization was allowed to proceed while dropwise adding a solution prepared by dissolving 0.103 parts by mass of the agent in 10.3 parts by mass of toluene over 4 hours, followed by further aging for 4 hours.

  Subsequently, the cooling pipe was replaced with a U-shaped pipe connected to the cooling pipe and a distillate receiver, and 233 parts by mass of base oil (manufactured by SK: YUBASE4) was charged into the reaction vessel. After raising the bath temperature to 150 ° C., the pressure was gradually reduced using a vacuum pump to remove toluene. 30 minutes after the internal temperature reached 142 ° C., the pressure was released and cooled to obtain a base oil solution of polymer 1 (polymer concentration: 30% by mass). The results are shown in Table 1.

(Example 2)
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen introduction tube, and a dropping funnel, MMA 35 parts by mass, SMA 30 parts by mass, SMI 10 parts by mass, SLMA 25 parts by mass, toluene 32.3 parts by mass, antioxidant ( Adeka Stub (registered trademark) 2112 (manufactured by ADEKA) 0.05 parts by mass, acetic anhydride 0.40 parts by mass, n-dodecyl mercaptan 0.05 parts by mass, and nitrogen gas was introduced into this, the content was 105 ° C The temperature was raised to. As a polymerization initiator, a solution prepared by mixing 0.0258 parts by mass of t-amylperoxyisononanoate (manufactured by Arkema Yoshitomi Corp., Luperox (registered trademark) 570) and 0.46 parts by mass of toluene was added, and the polymerization was started. The solution polymerization was allowed to proceed while dropwise adding a solution prepared by dissolving 0.103 parts by mass of the agent in 10.3 parts by mass of toluene over 4 hours, followed by further aging for 4 hours.

  Subsequently, the cooling pipe was replaced with a U-shaped pipe connected to the cooling pipe and a distillate receiver, and 233 parts by mass of base oil (manufactured by SK: YUBASE4) was charged into the reaction vessel. After raising the bath temperature to 150 ° C., the pressure was gradually reduced using a vacuum pump to remove toluene. 30 minutes after the internal temperature reached 142 ° C., the pressure was released and cooled to obtain a base oil solution of polymer 2 (polymer concentration: 30% by mass). The results are shown in Table 1.

(Comparative Example 1)
About Example 1, except having used phenylmaleimide instead of LMI, operation similar to Example 1 was performed and the base oil solution (polymer concentration 30%) of the polymer 3 was obtained. Since the polymer 3 had poor solubility in the base oil and insoluble matter was generated, the viscosity index and shear stability could not be evaluated. The results are shown in Table 1.

(Comparative Example 2)
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen introduction tube, and a dropping funnel, 20 parts by mass of MMA, 30 parts by mass of SMA, 46.7 parts by mass of toluene, antioxidant (ADK STAB (registered trademark) 2112, ADEKA) 0.05 parts by mass) and 0.75 parts by mass of n-dodecyl mercaptan were charged, and the contents were heated to 85 ° C. while introducing nitrogen gas. As a polymerization initiator, a solution prepared by mixing 0.25 parts by mass of 2,2-azobisdimethylvaleronitrile (ADVN) and 2.25 parts by mass of toluene was added, and ADVN 0.25 parts by mass, n-dodecyl mercaptan 0. A mixed solution of 75 parts by mass, MMA 20 parts by mass, SMA 30 parts by mass, toluene 46.7 parts by mass and toluene 50 parts by mass was added dropwise over 4 hours. After aging for 2 hours, 0.3 part by weight of ADVN dissolved in 2.3 parts by weight of toluene was added to the reaction vessel and allowed to react for another 3 hours.
Subsequently, the cooling pipe was replaced with a U-shaped pipe connected to the cooling pipe and a distillate receiver, and 233 parts by mass of base oil (manufactured by SK: YUBASE4) was charged into the reaction vessel. After raising the bath temperature to 150 ° C., the pressure was gradually reduced using a vacuum pump to remove toluene. 30 minutes after the internal temperature reached 142 ° C., the pressure was released and cooled to obtain a base oil solution of polymer 4 (polymer concentration: 30% by mass). The results are shown in Table 1.

  (A) By using the polymer which has a unit and Mw exists in the specific range, the viscosity index improver which shows favorable shear stability and a high viscosity index was obtained, maintaining base oil solubility.

  The lubricating oil composition using the viscosity index improver containing the polymer of the present invention exhibits good shear stability and high viscosity index while maintaining the base oil solubility as compared with the conventional lubricating oil composition. Therefore, since it can meet the future demands for fuel saving and long life of automobiles, it can be suitably used for drive system lubricating oil, hydraulic oil, and engine oil.

Claims (5)

A polymer having a unit represented by the following general formula (1) (hereinafter referred to as “(a) unit”) as an essential constituent unit, and having a weight average molecular weight (Mw) of 20,000 or more and less than 500,000 A viscosity index improver.

(In the formula, R ¹ and R ² are each independently a hydrogen atom or an alkyl group, and X is an organic group having 8 to 40 carbon atoms.)   In addition to the unit (a), the polymer has an alkyl (meth) acrylate-derived unit having an aliphatic hydrocarbon group having 6 to 40 carbon atoms and an aliphatic hydrocarbon group having 1 to 5 carbon atoms. The viscosity index improver according to claim 1, which has a unit derived from an alkyl (meth) acrylate (hereinafter referred to as "(c) unit").   The viscosity index improver according to claim 1 or 2, wherein the amount of the unit (a) is 5 parts by mass or more and 65 parts by mass or less with respect to 100 parts by mass of the polymer.   The viscosity index improvement according to any one of claims 1 to 3, wherein the total amount of (a) units and (c) units is 30 parts by mass or more and less than 95 parts by mass with respect to 100 parts by mass of the polymer. Agent.   A lubricating oil composition comprising a lubricating base oil and the viscosity index improver according to claim 1.