JP6742829B2 - Viscosity index improver and lubricating oil composition - Google Patents

Description

The present invention relates to a viscosity index improver having a specific structure, and a lubricating oil composition containing the same. In particular, the present invention relates to a viscosity index improver containing a polymer having a high viscosity index and good shear stability and having a high fluidity at room temperature and easy handling when used as a base oil composition.

In recent years, lubricating oils for internal combustion engines have been strongly demanded to have improved fuel economy characteristics, and as one means, reduction of viscous resistance by lowering the viscosity of lubricating oils is mentioned. However, since simply lowering the viscosity causes problems such as liquid leakage and seizure, it is effective to add a viscosity index improver having an effect of keeping the viscosity at high temperature low while keeping the viscosity at low temperature low.

It is known that the viscosity index improver contains a polymer, and there are various types. Among them, the viscosity index improver composed of an alkyl (meth)acrylate polymer exhibits a high effect of improving the viscosity index. On the other hand, the viscosity index improver made of an alkyl (meth)acrylate polymer has poor shear stability, and therefore has a problem that fuel consumption characteristics are deteriorated during long-term use (long life is poor).

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 susceptible to shearing and the smaller the decrease range of the molecular weight. Therefore, it is possible to suppress the viscosity decrease after shearing by using a low molecular weight viscosity index improver (Patent Document 1 and Non-Patent Document 1). Patent Document 1). In addition, it has been reported that a polymer having a star structure using divinylbenzene in the core portion is attempted to improve shear stability (Patent Document 2).

JP, 2013-104032, A JP 2012-197399 A

Nakata, "Viscosity index improver for high-performance engine oils", Sanyo Chemical News, Sanyo Chemical Industry Co., Ltd., 2013, No. 476

However, generally, the lower the molecular weight, the lower the effect of improving the viscosity index. Therefore, when a low molecular weight viscosity index improver is used, the viscosity index becomes low. Further, in order to adjust the viscosity to a desired value, it is necessary to increase the amount of the viscosity index improver used, which tends to be disadvantageous in terms of cost. Further, even when a polymer having a star structure using divinylbenzene is used in the core part, there is still room for improvement in achieving both the viscosity index and shear stability, and it is high while maintaining good shear stability. A viscosity index improver having a viscosity index has been desired.

The lubricating oil composition contains a lubricating base oil and various additives, a viscosity index improver, and the like. Among them, the viscosity index improver is generally handled as a base oil composition dissolved in a base oil. When the viscosity index improver concentration in the base oil composition is high, not only does the flexibility of formulation when forming the lubricating oil composition increase, but also the amount of the lubricating base oil used per unit mass in the viscosity index improver. However, the viscosity of the base oil composition increases, making it difficult to handle near room temperature, and heating or special heat when mixing and dissolving with other components. There was a case where the equipment was required and the productivity was lowered.

The present invention has been made in view of the above problems, and its object is to have a high viscosity index and good shear stability, and to have high fluidity near room temperature when used as a base oil composition. It is an object of the present invention to provide a viscosity index improver containing an easy polymer and a lubricating oil composition using the viscosity index improver.

The inventors of the present invention 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 relates to a unit derived from a maleimide-based monomer (hereinafter referred to as “(a) unit”) and a unit derived from an alkyl(meth)acrylate having an aliphatic hydrocarbon group having 2 to 6 carbon atoms (hereinafter referred to as “(a) unit”). , (B) units are essential constituent units, and the viscosity index improver contains a polymer having a viscosity of 30 Pa·s or less at 25° C. measured under the following conditions.
<Measurement conditions>
A solution consisting of 80% by mass of Group III base oil (viscosity index 122, 40° C. kinematic viscosity 19.6 mm ² /s) and 20% by mass of the polymer in the American Petroleum Institute (API) classification was used as an E-type viscometer (East Viscometer). Koki Sangyo: TVE-35H 3° x R9.7 rotor).

The polymer is a unit derived from an alkyl (meth)acrylate having an aliphatic hydrocarbon group having 7 to 40 carbon atoms (hereinafter, referred to as "(c) unit" in addition to the units (a) and (b)). Referred to).

In 100 parts by mass of the polymer, the (a) unit is preferably 0.5 parts by mass or more and 35 parts by mass or less, and the (b) unit is preferably 0.5 parts by mass or more and 60 parts by mass or less.

In 100 parts by mass of the polymer, the total of the units (a), (b) and units derived from methyl (meth)acrylate is preferably 10 parts by mass or more and less than 70 parts by mass.

In 100 parts by mass of the polymer, the unit (c) is preferably 30 parts by mass or more and less than 90 parts by mass.

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

By using the viscosity index improver of the present invention, it is possible to achieve both a high viscosity index and good shear stability as compared with conventional lubricating oil compositions. Further, since the viscosity index improver of the present invention has high fluidity at room temperature and is easy to handle when it is used as a base oil composition, it is possible to improve workability and productivity during production of the lubricating oil composition. it can.

The present invention will be described in detail below. In the following description, "part" means "part by mass" and "%" means "% by mass", respectively, unless otherwise specified. Further, “A to B” indicating the range indicates that it 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 in which the units (a) and (b) are essential constituent units, and the viscosity measured under the following conditions is 30 Pa·s or less at 25°C. It is a viscosity index improver.
<Measurement conditions>
A solution consisting of 80% by mass of Group III base oil (viscosity index 122, 40° C. kinematic viscosity 19.6 mm ² /s) and 20% by mass of the polymer in the American Petroleum Institute (API) classification was used as an E-type viscometer (East Viscometer). Koki Sangyo: TVE-35H 3° x R9.7 rotor).

The unit (a) is specifically a unit represented by the general formula (1).

(In the formula (1), R ¹ and R ² are each independently a hydrogen atom or an alkyl group, and X is a hydrogen atom or an organic group having 1 to 40 carbon atoms.)
X in the general formula (1) is not particularly limited as long as it is a hydrogen atom or an organic group having 1 to 40 carbon atoms, and any substituent may be bonded. 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 solubility of the base oil. Examples of the organic group include linear or branched, cyclic alkyl groups, aryl groups, H(CH ₂ ) ₆ -O-(CH ₂ ) _2- O-(CH ₂ ) ₄ -. Oxaalkyl group.

Specific examples of the maleimide-based monomer include, for example, maleimide, N-methylmaleimide, N-iso-propylmaleimide, N-butylmaleimide, N-iso-butylmaleimide, Nt-butylmaleimide, N-cyclohexylmaleimide. , N-octyl maleimide, N-2-ethylhexyl maleimide, N-decyl maleimide, N-lauryl maleimide, N-tetradecyl maleimide, N-stearyl maleimide, N-2-decyl tetradecyl maleimide, N-phenyl maleimide, N- Benzylmaleimide, N-chlorophenylmaleimide, N-methylphenylmaleimide, N-naphthylmaleimide, N-hydroxylethylmaleimide, N-hydroxylphenylmaleimide, N-methoxyphenylmaleimide, N-carboxyphenylmaleimide, N-nitrophenylmaleimide, N -Tribromophenyl maleimide and the like. Among these, N-phenylmaleimide, N-cyclohexylmaleimide, N-isopropylmaleimide, N-benzylmaleimide, N-laurylmaleimide, and N-stearyl are available from the viewpoints of availability and economical efficiency and high solubility in base oil. Maleimide is preferred. The above monomers for constituting the unit (a) may be used alone or in combination of two or more kinds.

The content of the unit (a) is preferably 0.5 parts by mass or more, more preferably 2 parts by mass or more, still more preferably 5 parts by mass or more, and preferably 35 parts by mass or less, in 100 parts by mass of the polymer. It is more preferably 30 parts by mass or less. The viscosity index improver having the unit (a) in the above range can improve the shear stability and heat resistance due to the ring structure of the main chain while ensuring the solubility in the base oil. Further, effects such as improvement of clean dispersibility of sludge and the like and suppression of wear of metal surface are expected.

The unit (b) is specifically a unit derived from a monomer represented by the general formula (2).

(In the formula (2), R ³ is a hydrogen atom or a methyl group, and R ⁴ is an aliphatic hydrocarbon group having 2 to 6 carbon atoms.)
Specific examples of the general formula (2) include, for example, 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 (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylbutyl Examples thereof include (meth)acrylate and cyclohexyl (meth)acrylate. Among these, n-butyl (meth)acrylate and iso-butyl (meth)acrylate are preferable from the viewpoints of availability and economical efficiency and the fact that the base oil composition greatly enhances the fluidity at around room temperature. The above-mentioned monomers for forming the unit (b) may be used alone or in combination of two or more kinds.
The content of the unit (b) is preferably 0.5 parts by mass or more, more preferably 2 parts by mass or more, further preferably 5 parts by mass or more, and 60 parts by mass or less, in 100 parts by mass of the polymer. Are preferred, 55 parts by mass or less are more preferred, and 50 parts by mass or less are even more preferred. The viscosity index improver containing a polymer having the unit (b) in the above numerical range has good solubility in base oils of various compositions, and has high fluidity at room temperature when formed into a base oil composition. Therefore, the productivity of the lubricating oil composition is excellent, and the viscosity index of the resulting lubricating oil composition is high.

Moreover, the viscosity index improver in the present invention may contain a unit derived from methyl (meth)acrylate. The unit derived from methyl (meth)acrylate is preferably 0.5 parts by mass or more, more preferably 2 parts by mass or more, further preferably 5 parts by mass or more, and less than 30 parts by mass in 100 parts by mass of the polymer. The amount is preferably 28 parts by mass or less, more preferably 25 parts by mass or less.

The total of units (a), units (b), and units derived from methyl (meth)acrylate is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and 30 parts by mass or more in 100 parts by mass of the polymer. More preferred is 35 parts by mass or more, particularly preferred is less than 70 parts by mass, more preferred is less than 65 parts by mass, and further preferred is less than 60 parts by mass. A viscosity index improver containing a polymer in which the total of units (a), units (b), and units derived from methyl (meth)acrylate is in the above range has a fluidity near room temperature when made into a base oil composition. Since it is high, the productivity of the lubricating oil composition is excellent, and the viscosity index and shear stability of the resulting lubricating oil composition are high.

The polymer contained in the viscosity index improver of the present invention preferably has a unit (c) in addition to the units (a), (b) and units derived from methyl (meth)acrylate.
The unit (c) is specifically a unit derived from a monomer represented by the general formula (3).

(In the formula (3), R ⁵ represents a hydrogen atom or a methyl group, and R ⁶ is an aliphatic hydrocarbon group having 7 to 40 carbon atoms.)
Specific examples of the general formula (3) include, for example, n-heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, 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, menthyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth) Examples thereof include acrylate and adamantyl (meth)acrylate. Among them, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, eicosyl (meth)acrylate, behenyl (behenyl (from the viewpoints of availability and economical efficiency and high solubility in base oil). Preferred are (meth)acrylate, tetracosyl (meth)acrylate and 2-decyltetradecyl (meth)acrylate. The above monomers for constituting the unit (c) may be used alone or in combination of two or more kinds.

The content of the unit (c) is, in 100 parts by mass of the polymer, preferably 30 parts by mass or more, more preferably 35 parts by mass or more, further preferably 40 parts by mass or more, and preferably less than 90 parts by mass, 80 parts by mass. It is more preferably less than 70 parts by mass, and further preferably 70 parts by mass or less. The viscosity index improver containing the polymer having the unit (c) in the above numerical range has good solubility in base oils of various compositions.

The polymer of the present invention may contain units (hereinafter referred to as “(d) units”) other than (a) units, (b) units, (c) units, and units derived from methyl (meth)acrylate. it can. Radical polymerization is advantageous in terms of productivity and cost in order to form the units (a), (b), (c), units derived from methyl (meth)acrylate, and units (d). 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 (meth)acrylates other than the general formulas (2) and (3), unsaturated mono- or dicarboxylic acid esters, unsaturated carboxylic acids, Examples thereof 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) and methyl (meth)acrylate include 2-hydroxyethyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 2-methoxyethyl. (Meth)acrylate, tetrahydrofurfuryl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, morpholino alkylene (meth)acrylate, methyl α-hydroxymethyl acrylate, polyethylene glycol mono(meth)acrylate, etc. Can be mentioned.

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

Examples of unsaturated carboxylic acids include (meth)acrylic acid, maleic acid, fumaric acid, and maleic anhydride.

Examples of the vinyl aromatic compound include styrene-based 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 vinyl ethers 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 and diisobutene.

Examples of vinyl cyanide include acrylonitrile and methacrylonitrile.

Examples of the N-vinyl compound include N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylimidazole, N-vinylmorpholine, N-vinylacetamide and the like.

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

The monofunctional monomer for constituting the unit (d) 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 in 100 parts by mass of the polymer. ..

Examples of the polyfunctional monomer for forming the unit (d) include polyfunctional (meth)acrylate, vinyl ether group-containing (meth)acrylate, allyl group-containing (meth)acrylate, and polyfunctional (meth)acryloyl group-containing. Examples thereof include polyfunctional (meth)acrylic compounds such as isocyanurate and polyfunctional urethane (meth)acrylate, polyfunctional maleimide compounds, polyfunctional vinyl ethers, polyfunctional allyl compounds, and polyfunctional aromatic vinyls. The above polyfunctional monomers may be used alone or in combination of two or more.

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

Examples of vinyl ether group-containing (meth)acrylates include 2-vinyloxyethyl (meth)acrylate, 4-vinyloxybutyl (meth)acrylate, and 2-(vinyloxyethoxy)ethyl (meth)acrylate.

Examples of the allyl group-containing (meth)acrylates include allyl (meth)acrylate, methyl α-allyloxymethyl acrylate, stearyl α-allyloxymethyl acrylate, and 2-decyl tetradecyl α-allyloxymethyl acrylate. Is mentioned.

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

Examples of polyfunctional urethane (meth)acrylates include polyfunctional isocyanates such as tolylene diisocyanate, isophorone diisocyanate, and xylylene diisocyanate, and hydroxyl groups such as 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate. Examples thereof include polyfunctional urethane (meth)acrylates obtained by reaction with contained (meth)acrylic acid ester.

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

Examples of polyfunctional vinyl ethers 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 the polyfunctional allyl compound 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, and ditrimethylolpropane tetraallyl ether. Polyfunctional allyl ethers; polyfunctional allyl group-containing isocyanurates such as triallyl isocyanurate; polyfunctional allyl esters such as diallyl phthalate and diallyl diphenate; bisallylnadiimide compounds and the like; bisallylnadiimide compounds and the like. ..

Examples of the polyfunctional aromatic vinyl include divinylbenzene and the like.

The content of the polyfunctional monomer for constituting the unit (d) is preferably 0 parts 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 the monomer components. It is preferably 2 parts by mass or less and more preferably 2 parts by mass or less. The content of the polyfunctional monomer-derived unit 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. It is more preferably 2 parts by mass or less. In this case, when the polymer has a branched structure or the like, the shear stability of the viscosity index improver containing the polymer can be improved without significantly 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 2-decyltetradecyl α-allyloxymethyl acrylate, the inclusion of units derived from the polyfunctional monomer in the polymer The amount is preferably 0 parts 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 based on 100 parts by mass of all the 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 can be 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 above monomer component is polymerized by a radical polymerization mechanism, it is industrially advantageous and preferable to use a radical polymerization initiator in combination. As the radical polymerization initiator, there are a thermal radical polymerization initiator that generates a polymerization initiation radical by heating, and a photoradical polymerization initiator that generates a polymerization initiation radical by irradiation with an active energy ray. Alternatively, two or more kinds 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, if necessary.

Specific examples of the thermal radical polymerization initiator include methyl ethyl ketone peroxide, cyclohexanone peroxide, methyl cyclohexanone peroxide, methyl acetoacetate peroxide, acetyl acetate peroxide, 1,1-bis(t-hexylperoxide). 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-menthane hydroperoxide, 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-butyl Cumyl 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, succinic acid peroxide, m-toluoyl benzoyl peroxide, benzoyl peroxide, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, bis(4 -T-butylcyclohexyl)peroxydicarbonate, di-2-ethoxyethylperoxydicarbonate, di-2-ethoxyhexylperoxydicarbonate, di-3-methoxybutylperoxydicarbonate, di-s-butylpercarbonate Oxydicarbonate, di(3-methyl-3-methoxybutyl)peroxydicarbonate, α,α′-bis(neodecanoylperoxy)diisopropylbenzene, cumylperoxy neodecanoate, 1,1,3 3,-Tetramethylbutylperoxy neodecanoate, 1-cyclohexyl-1 -Methylethyl peroxy neodecanoate, t-hexyl peroxy neodecanoate, t-butyl peroxy neodecanoate, t-hexyl peroxypivalate, t-butyl peroxypivalate, 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-hexylperoxyisopropyl monocarbonate, t-butylperoxyisobutyrate , T-butylperoxymaleate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxylaurate, t-butylperoxyisopropylmonocarbonate, t-butylperoxy-2. -Ethylhexyl monocarbonate, t-butylperoxyacetate, t-butylperoxy-m-toluylbenzoate, 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-butyltrimethylsilylperoxide Oxide, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 3,3′,4,4′-tetra(t-butylperoxycarbonyl)benzophenone, t-amylperoxyiso Peroxide initiators such as nanoate, t-amylperoxy-2-ethylhexanoate, sodium persulfate, potassium persulfate, ammonium persulfate, hydrogen peroxide; 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)dihi Drochloride, 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, 2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride,2,2′-azobis[ 2-(4,5,6,7-Tetrahydro-1H-1,3-diazepin-2-yl)propane]dihydrochloride, 2,2′-azobis[2-(3,4,5,6-tetrahydropyrimidine 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)propionitrile] and other azo-based initiators, and 2,3-dimethyl-2,3-diphenylbutane.

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, potassium; Amine compounds; quaternary ammonium salts; thiourea compounds; ketone compounds, and the like. Specific examples include cobalt octylate, cobalt naphthenate, copper octylate, copper naphthenate, manganese octylate, and naphthenic acid. Examples thereof include manganese, dimethylaniline, triethanolamine, triethylbenzylammonium chloride, di(2-hydroxyethyl)p-toluidine, ethylenethiourea, acetylacetone and methyl acetoacetate.

Specific examples of the photoradical polymerization initiator include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, and 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-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]- Alkylphenone compounds such as 1-butanone; benzophenone, 4,4'-bis(dimethylamino)benzophenone, benzophenone compounds such as 2-carboxybenzophenone; benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, etc. Benzoin-based compounds; thioxanthone-based compounds such as thioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, and 2,4-diethylthioxanthone; 2-(4-methoxyphenyl)- 4,6-bis(trichloromethyl)-s-triazine, 2-(4-methoxynaphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-ethoxynaphthyl)-4,6- Halomethylated triazine compounds such as bis(trichloromethyl)-s-triazine and 2-(4-ethoxycarboquinylnaphthyl)-4,6-bis(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 other halomethylated oxadiazole compounds; 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 ,5'-Tetraphenyl-1,2'-biimidazole and other biimidazole compounds; 1,2-octanedione, 1-[4-(phenylthio)-,2-(O-benzoyloxime)], ethanone, Oxime ester compounds such as 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyloxime); bis(η5-2,4-cyclo) Pentadiene-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium and other titanocene compounds; p-dimethylaminobenzoic acid, p-diethylaminobenzoic acid and the like. Benzoic acid ester compounds; acridine compounds such as 9-phenylacridine; and the like.

When the above-mentioned monomer component is polymerized by a radical polymerization mechanism, a known chain transfer agent may be used if necessary, and it is more preferably used in combination with a radical polymerization initiator. A common monofunctional chain transfer agent is used as the chain transfer agent. As such a chain transfer agent, for example, mercaptoacetic acid, mercaptocarboxylic acids such as 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 acid esters such as pentaerythritol hexakis (3-mercaptopropionate); alkyl mercaptans such as ethyl mercaptan, t-butyl mercaptan, n-dodecyl mercaptan, 1,2-dimercaptoethane; 2-mercaptoethanol , 4-mercapto-1-butanol and other mercapto alcohols; benzenethiol, m-toluenethiol, p-toluenethiol, 2-naphthalenethiol and other aromatic mercaptans; tris[(3-mercaptopropionyloxy)-ethyl ] Mercaptoisocyanurates such as isocyanurate; disulfides such as 2-hydroxyethyl disulfide and tetraethylthiuram disulfide; dithiocarbamates such as benzyl diethyldithiocarbamate; monomer dimers such as α-methylstyrene dimer; tetrabromide Examples thereof include halogenated alkyls such as carbon. Among these, mercaptocarboxylic acids, mercaptocarboxylic acid esters, alkylmercaptans, mercaptoalcohols, aromatic mercaptans; mercaptoisocyanurates, from the viewpoints of availability, ability to prevent crosslinking, and a small degree of decrease in polymerization rate. Compounds having a mercapto group, such as the classes, are preferred. These may be used alone or in combination of two or more.

The amount of the monofunctional chain transfer agent (total amount added) may be appropriately set according to the type and amount of the monomer used, the polymerization conditions such as the polymerization temperature and the polymerization concentration, and the target molecular weight of the polymer. Well, it is not particularly limited. 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 the monofunctional chain transfer agent used is 100 parts by mass of the monomer component. 0.001 mass part or more is preferable, 0.005 mass part or more is more preferable, 0.5 mass part or less is preferable, 0.3 mass part or less is more preferable, 0.2 mass part or less is further more preferable.

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, for example, trimethylolpropane trimercaptoacetate, trimethylolpropane tri(3-mercaptopropionate), pentaerythritol tetrakismercaptoacetate, pentaerythritol tetrakis(3-mercaptopropionate), Compounds having three or more hydroxyl groups and carboxyl group-containing mercaptan polyester compounds such as dipentaerythritol hexakis mercaptoacetate and dipentaerythritol hexakis (3-mercaptopropionate), triazine polythiols, and polyepoxy compounds A compound obtained by adding hydrogen sulfide to a plurality of epoxy groups to introduce three or more mercapto groups per molecule, and three compounds per molecule obtained by esterifying a plurality of carboxyl groups of a polycarboxylic acid and mercaptoethanol Examples thereof include compounds having a mercapto group. Trifunctional or higher polyvalent mercaptans can be used alone or in combination (for example, as a mixture).

The amount of the trifunctional or higher polyvalent mercaptan used (total amount added) is appropriately determined depending on the type and amount of the monomers used, polymerization conditions such as polymerization temperature and polymerization concentration, and the target molecular weight of the polymer. It may be set, and is not particularly limited. 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 the trifunctional or higher polyvalent mercaptan is 100 parts by mass of the monomer component. On the other hand, 0.01 part by mass or more is preferable, 0.05 part by mass or more is more preferable, 5 parts by mass or less is preferable, 3 parts by mass or less is more preferable, and 2 parts by mass or less is further preferable. Within this range, the molecular weight distribution is narrowed and the shear stability can be improved.

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

The amount of the trifunctional or higher polyfunctional initiator to be used (total amount added) may be appropriately set depending on the purpose and application, and is not particularly limited. From the standpoint of obtaining a viscosity index improver containing a polymer having a weight average molecular weight of 100,000 or more, which has a high viscosity index and a high base oil solubility, in consideration of the balance between polymerizability, adverse effects of decomposed products, and economy. The amount of the trifunctional or higher polyfunctional initiator to be used 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, 10 parts by mass or less, preferably 5 parts by mass or less, more preferably 2 parts by mass or less.

A polymer obtained by radically polymerizing 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. Will have. That is, the polymer contained in the viscosity index improver of the present invention has a trifunctional or higher functional polyvalent mercaptan-derived branch unit and/or a trifunctional or higher functional polyfunctional initiator-derived branch unit. Since the polymer contained in the viscosity index improver has such a structure, it is possible to improve the shear stability of the viscosity index improver containing the polymer without significantly impairing the solubility in the base oil. it can.

When the polymer contained in the viscosity index improver has a trifunctional or higher functional polyvalent mercaptan-derived branching unit, the polymer should have a branching 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 trifunctional or higher functional polyfunctional initiator-derived branching unit, the polymer preferably has a trifunctional or higher functional peroxide-derived branching unit. Preferably has a branching 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 0-5.

The polymer contained in the viscosity index improver may contain only one of a trifunctional or higher functional polyvalent mercaptan-derived branch unit and a trifunctional or higher functional polyfunctional initiator-derived branch unit, or both of them. Good. The trifunctional or higher functional polyvalent mercaptan-derived branching unit may be contained alone or in combination of two or more. The branch unit derived from a trifunctional or higher polyfunctional initiator may be contained in only one kind or in two or more kinds.

The content of the trifunctional or more 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. The amount is preferably 1 part or less, more preferably 3 parts by mass or less, still more preferably 2 parts by mass or less. Within this range, the molecular weight distribution of the polymer becomes narrow, and the shear stability can be improved. The content of the trifunctional or higher polyvalent mercaptan-derived branching unit is determined by dividing the amount of the trifunctional or higher polyvalent mercaptan used by the mass of the polymer.

The content of branch units derived from a trifunctional or higher polyfunctional initiator in the polymer is a point at which a viscosity index improver containing a polymer having a high viscosity index and base oil solubility and a weight average molecular weight of 100,000 or more is obtained. Therefore, with respect to 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 further 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 further preferable. The content of the branching unit derived from a trifunctional or higher polyfunctional initiator is determined by dividing the amount of the trifunctional or higher polyfunctional initiator used by the mass of the polymer.

The method for polymerizing the polymer contained in the viscosity index improver of the present invention can be obtained by a production method having a step of polymerizing a monomer component (polymerization step). The method of polymerizing the component of the monomer in the polymerization step may be, for example, bulk polymerization, solution polymerization, suspension polymerization or emulsion polymerization, but is not particularly limited. When a dispersion medium, an emulsifier, a dispersant, etc. are used, known ones can be used without particular limitation.

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

In the polymerization step, as a monomer component, a component for constituting the (a) unit represented by the above-mentioned general formula (1) and a general formula (2) for constituting the (b) unit are represented. It is preferable to essentially use the alkyl (meth)acrylate component represented by the general formula (3) for constituting the unit (c) as an essential component. As the monomer component, methyl (meth)acrylate or the component for forming the unit (d) described above may be used in combination. Suitable conditions such as the type and usage amount of each of these monomer components are as described above.

The solvent used for the polymerization is not particularly limited as long as it is inert to the polymerization reaction, the polymerization mechanism, the type and amount of the monomer used, the type and amount of the polymerization initiator and the polymerization catalyst, etc. It may be appropriately set according to the polymerization conditions of. From the viewpoint of ensuring the solubility of the polymer, and from the viewpoint of easy solvent substitution to the base oil after the polymerization, the solvent used for the polymerization, toluene, xylene, hexane, cyclohexane, methyl ethyl ketone, tetrahydrofuran, ethyl acetate, Butyl acetate is preferred. Further, the lubricating base oil described below 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 the 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 total concentration of the monomer component, the polymerization initiator, and the other components is 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 depending on the polymerization mechanism, the type and amount of the monomer used, the type and amount of the polymerization initiator/polymerization catalyst, and is not particularly limited. However, the temperature is preferably 0° C. or higher, more preferably 25° C. or higher, preferably 200° C. or lower, and more preferably 150° C. or lower. If the polymerization temperature is less than 0°C, the polymerization reaction will be extremely slow, and if it exceeds 200°C, the reaction will be so violent that control will be difficult.

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, It is more preferably 300,000 or more, less than 500,000, preferably 490,000 or less, and more preferably 480,000 or less. When the weight average molecular weight of the polymer is less than the above lower limit value, not only the viscosity index of the lubricating oil composition becomes low, but also it is necessary to increase the amount of the viscosity index improver used to adjust the viscosity to a desired value. However, it 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, and 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 80,000 or more, preferably 90,000 or more, more preferably 90,000 to 220,000, and further 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 further preferably 3.0 or less. If the molecular weight distribution exceeds 4.0, the solubility of the viscosity index improver in the base oil will be insufficient, and the shear stability of the lubricating oil composition will decrease, 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 the present invention can be measured using a 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 kind of the polymerization initiator/polymerization catalyst, the polymerization temperature, and the kind and amount of the chain transfer agent. Living Radical Polymerization can also be used as a method for controlling the molecular weight distribution. RAFT method, NMP method, ATRP method and the like are famous as specific methods. For details, see Aldrich Material Matters, Vol. 5, No. 1, 2010. As an example of use, in the case of the RAFT method, in JP 2012-197399 A, 2,2'-azobisisobutyronitrile is used as a polymerization initiator and cumyl dithiobenzoate is used as a polymerization catalyst.

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, 4 It is more preferably 0.0 or less. When the branching degree is less than 1.0, the branched structure of the polymer is not sufficient, and improvement in shear stability cannot be expected. The branching degree in the present invention corresponds to the average number of branching points per polymer molecule, and theoretically, for example, a straight-chain polymer having no branching has a branching degree of 0, and only one branching point is obtained. The degree of branching of a polymer in which three polymer chains extend from the point is 1, and the degree of branching of a polymer in which four polymer chains extend is 2 and that of a polymer in which five polymer chains extend. The degree of branching is 3.

The glass transition temperature (Tg) of the polymer contained in the viscosity index improver of the present invention is a value determined by the method described in Examples below. Tg is preferably −50° C. or higher, more preferably −40° C. or higher, further preferably −30° C. or higher, preferably 0° C. or lower, more preferably −10° C. or lower, and further preferably −20° C. or lower. When the Tg of the polymer is within this range, it becomes easy to increase the fluidity at around room temperature in the case of a base oil composition while maintaining the solubility in the base oil and the high viscosity index.

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. It is preferably 9.5 or less, more preferably 9.4 or less. The SP value of the base oil generally shows a value of about 8.0 to 8.5, but 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 value of the polymer is increased. When the value is 9.6 or less, it becomes easy to secure 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 high viscosity index improving effect and a high shear stability. As specific numerical values of the shear stability, for example, PSSI (Permanent Shear Stability Index: ASTM D 6022), SSI obtained by the method shown below, or decomposition start temperature is used as an index.
The SSI in the present invention is a value measured by the method described in Examples below. That is, the polymer was diluted in a base oil (YUBASE4 manufactured by SK) so that the kinematic viscosity at 100° C. was 7.0 mm ² /sec, and ultrasonic waves were irradiated under the following conditions.
Device: Hielscher Ultrasonics UP400S
Settings: Amplitude=70%, Cycle=1
Time: 10 minutes Temperature: 100°C
The kinematic viscosities of the base oil before and after shearing and at 100° C. were measured, and SSI={1-(kinematic viscosity after shearing−kinematic viscosity of base oil)/(kinematic viscosity before shearing−kinematic viscosity of base oil)}×100 Calculated by the formula.
In the present invention, the SSI of the viscosity index improver, which is an index of shear stability, is preferably 45 or less, more preferably 40 or less, and further preferably 38 or less. Further, the SSI is preferably 0.1 or more, more preferably 0.5 or more, further 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 may be small and the cost may increase, and if the SSI is more than 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 further 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 and the viscosity index tends to decrease.

The viscosity index improver of the present invention contains the above-mentioned polymer as a main component, preferably 70% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass of the polymer in 100% by mass of the viscosity index improver. It is contained in an amount of not less than 100% by mass, particularly preferably not less than 99% by mass and not more than 100% by mass.

As the components other than the above-mentioned polymer contained in the viscosity index improver of the present invention, polymethacrylate, polyisobutylene, ethylene-propylene copolymer, styrene-diene hydrogenated copolymer, these graft polymers and comb polymers, Star polymers and the like can be mentioned. These other polymers are preferably 0% by mass or more and 30% by mass or less, more preferably 10% by mass or less, further preferably 5% by mass or less, and particularly preferably 1% 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 give a lubricating oil composition. The lubricating oil composition may be used as a lubricating oil without further diluting it with a lubricating base oil, or may be further diluted with a lubricating base oil and used 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 "base oil composition".

As the lubricant base oil, known lubricant 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-based base oil include paraffin-based and naphthene-based base oils. The mineral base oil also includes solvent-refined, hydrocracked or hydroisomerized raw material base oil. Examples of synthetic base oils include hydrocarbon-based, ester-based, ether-based, silicon-based, and fluorine-based base oils. The lubricating base oil can also be used as a polymerization reaction solvent for the polymer contained in the viscosity index improver, as described above.

As a preferred specific example of the mineral oil-based base oil, the following base oils (1) to (7) are used as raw materials, and the raw oil and/or the lubricating oil fraction recovered from the raw oil is subjected to a predetermined refining method. A base oil obtained by refining by the above method and recovering a lubricating oil fraction can be mentioned. Further, the following base oil (8) or (9) obtained by subjecting a base oil selected from (1) to (7) or a lubricating oil fraction recovered from the base oil to a predetermined treatment is particularly preferable.
(1) Normal pressure distillation of paraffin-based crude oil and/or mixed base-based crude oil Distillate oil by vacuum distillation of residual oil (WVGO)
(2) Wax (slack wax, etc.) obtained by the lubricating oil dewaxing step and/or synthetic wax (Fischer-Tropsch wax, GTL wax, etc.) obtained by a gas to liquid (GTL) process, etc.
(3) One or two or more kinds of mixed oil selected from base oils (1) to (2) and/or mild hydrocracking treated oil (4) base oil (1) to (3) Two or more types of mixed oil (5) Base oil (1) to (4) any deasphalted oil (DAO)
(6) Base oil (5) Mild hydrocracking treated oil (MHC)
(7) Two or more kinds of mixed oils selected from base oils (1) to (6).
(8) The base oil selected from the above base oils (1) to (7) or the lubricating oil fraction recovered from the base oil is hydrocracked, and the product or the product is recovered by distillation or the like. A hydrocracked mineral oil obtained by subjecting a lubricating oil fraction to dewaxing treatment such as solvent dewaxing or catalytic dewaxing, or by performing dewaxing treatment and then distilling.
(9) The base oil selected from the above base oils (1) to (7) or the lubricating oil fraction recovered from the base oil is hydroisomerized, and the product or the product is recovered by distillation or the like. A hydroisomerized mineral oil obtained by subjecting a lubricating oil fraction to dewaxing treatment such as solvent dewaxing or catalytic dewaxing, or distilling after the dewaxing treatment.

The kinematic viscosity of the mineral oil-based base oil at 100° C. is preferably 1 to ²⁰ mm ² /s.

Specific examples of synthetic base oils include poly α-olefins or hydrides thereof, isobutene oligomers or hydrides thereof, isoparaffin, 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 Examples thereof include glycol, dialkyldiphenyl ether, polyphenyl ether and the like, and among them, poly α-olefin is preferable. As the poly α-olefin, typically, an oligomer or cooligomer of α-olefin having 2 to 32 carbon atoms, preferably 6 to 16 carbon atoms (1-octene oligomer, decene oligomer, ethylene-propylene cooligomer, etc.) and those The hydride of is mentioned. The kinematic viscosity of the synthetic base oil at 100° C. is preferably 1 to ²⁰ mm ² /s.

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

In the lubricating oil composition of the present invention, the above-mentioned lubricating base oil may be used alone, or may be used in combination with one or more kinds of other base oils. When the lubricating base oil is used in combination with another base oil to form a mixed base oil, the mixed base oil is the above-mentioned lubricating base oil (8) or (for the reason of increasing the viscosity index of the lubricating oil composition. It is preferable to include at least 9). The proportion 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. More preferable.

The viscosity index of the lubricating base oil is preferably 100 or more, more preferably 120 or more, and preferably 160 or less. If the viscosity index is less than the above lower limit value, not only the viscosity-temperature characteristics, heat/oxidation stability, and volatility prevention properties deteriorate, but also the friction coefficient tends to increase, and the wear prevention property decreases. There is a tendency. Further, when the viscosity index exceeds the above upper limit value, the low temperature viscosity characteristic tends to deteriorate. The viscosity index as referred to in the present invention means the viscosity index measured according to JIS K 2283.

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, 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 for example, 0.01% by mass or more is preferable, and 0.1% by mass or more is based on the total amount of the lubricating oil composition. It is more preferably 0.5% by mass or more, further preferably 70% by mass or less, more preferably 60% by mass or less, and further preferably less than 50% by mass. When the lubricating oil composition is used as a lubricating oil without further diluting it 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. 0.01 mass% or more is preferable, 0.1 mass% or more is more preferable, 0.5 mass% or more is further preferable, 20 mass% or less is preferable, 15 mass% or less is more preferable, and 10 mass% is 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, 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 preferable.

The base oil composition of the present invention has a viscosity of 30 Pa·s or less at 25° C. measured under the following conditions from the viewpoint of being advantageous in terms of productivity and handleability in producing a lubricating oil composition. It has a viscosity index improver containing coalesce.
<Measurement conditions>
A solution consisting of 80% by mass of Group III base oil (viscosity index 122, 40° C. kinematic viscosity 19.6 mm ² /s) and 20% by mass of the polymer in the American Petroleum Institute (API) classification was used as an E-type viscometer (East Viscometer). Koki Sangyo: TVE-35H 3° x R9.7 rotor).

Within the above viscosity range, good fluidity is maintained when the content of the viscosity index improver in the base oil composition is in the above range, and a lubricating oil composition is obtained by adding a lubricating base oil or additives. It is possible to improve the productivity when manufacturing a product.

The lubricating oil composition of the present invention contains the viscosity index improver of the present invention and a lubricating base oil as essential components, and may further contain optional additives and the like. The lubricating oil composition is selected, for example, from the group consisting of pour point depressants, antiwear agents, metallic detergent dispersants, ashless detergent dispersants, antioxidants, corrosion inhibitors, defoamers and friction modifiers. 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 the pour point depressant include polymethacrylates, naphthalene-chlorinated paraffin condensation products, phenol-chlorinated paraffin condensation products, and the like. Of 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, a sulfur-based, phosphorus-based, sulfur-phosphorus-based extreme pressure agent or the like can be used. Specifically, zinc dialkyldithiophosphate (ZnDTP), phosphite ester , Thiophosphite esters, dithiophosphite esters, trithiophosphite esters, phosphoric acid esters, thiophosphoric acid esters, dithiophosphoric acid esters, trithiophosphoric acid esters, amine salts thereof, these Examples thereof include metal salts, derivatives thereof, dithiocarbamates, zinc dithiocarbamates, MoDTC, disulfides, polysulfides, sulfurized olefins, 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-based detergent dispersant include normal salts or basic salts such as alkali metal/alkaline earth metal sulfonates, alkali metal/alkaline earth metal phenates, and alkali metal/alkaline earth metal salicylates. 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 oils 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 benzylamine having at least one alkenyl group in the molecule, polyamine having at least one alkyl group or alkenyl group having 40 to 400 carbon atoms in the molecule, or modification thereof with a boron compound, carboxylic acid, phosphoric acid or the like. Examples include products. At the time of use, one kind or two or more kinds arbitrarily selected from these can be blended.

Examples of the antioxidant include ashless antioxidants such as phenol and amine, and metal antioxidants such as copper and molybdenum. Specific examples of the antioxidant include 4,4′-methylenebis(2,6-di-tert-butylphenol) and 4,4′-bis(2,4) as phenol-based ashless antioxidants. 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-based, tolyltriazole-based, thiadiazole-based, and imidazole-based 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, alkenylsuccinic acid derivative, ester of polyhydroxy fatty alcohol and long chain fatty acid, and methyl salicylate. Examples thereof include rate and o-hydroxybenzyl alcohol.

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

The lubricating oil composition is one selected from the group consisting of pour point depressants, antiwear agents, metallic detergent dispersants, ashless detergent dispersants, antioxidants, corrosion inhibitors, defoamers and friction modifiers. Alternatively, when two or more kinds are contained, the content of each is preferably 0.01% by mass or more and 10% by mass or less based on the total amount of the lubricating oil composition. When the lubricating oil composition contains an antifoaming agent, its content is preferably 0.0001 mass% or more and 0.01 mass% or less. When the lubricating oil composition is used as a base oil composition, the base oil composition may consist essentially of a viscosity index improver and a lubricating base oil. In this case, 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 more preferably 99.5% by mass, based on the total amount of the base oil composition. The above is more preferable.

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 in addition to the above components.

The viscosity index improver other than the polymer of the present invention is specifically a non-dispersion type or dispersion type ester group-containing viscosity index improving agent, and as an example, a non-dispersion type or dispersion type poly(meth)acrylate viscosity index improving agent Agents, non-dispersed or dispersed olefin-(meth)acrylate copolymer-based viscosity index improvers, styrene-maleic anhydride copolymer-based viscosity index improvers, and mixtures thereof. Among these, the non-dispersion type or dispersion type poly(meth)acrylate-based viscosity index improver is preferable, and the non-dispersion type or dispersion type polymethacrylate-based viscosity index improver is more preferable. Other examples include non-dispersed or dispersed ethylene-α-olefin copolymers or hydrogenated products thereof, polyisobutylene or hydrogenated products thereof, styrene-diene hydrogenated copolymers and polyalkylstyrenes.

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

Examples of the demulsifier include polyalkylene glycol-based nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, and polyoxyethylene alkylnaphthyl ether.

Examples of the metal deactivator include imidazoline, pyrimidine derivative, alkylthiadiazole, mercaptobenzothiazole, benzotriazole or a derivative thereof, 1,3,4-thiadiazole polysulfide, 1,3,4-thiadiazolyl-2,5-bis. Examples thereof include dialkyldithiocarbamate, 2-(alkyldithio)benzimidazole, β-(o-carboxybenzylthio)propionnitrile, and the like.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto. In addition, "%" and "part" in Examples and Comparative Examples represent "mass%" and "part by mass", respectively, unless otherwise specified.

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

PMI: N-phenylmaleimide MMA: methyl methacrylate BMA: n-butyl methacrylate SMA: stearyl methacrylate SLMA: lauryl methacrylate/tridecyl methacrylate = 54/46 (mass ratio) mixture (1) Analytical method (polymerization rate)
The polymerization rate of each monomer component of the present invention was determined by using gas chromatography (manufactured by Shimadzu Corporation, GC-2010plus).

The measurement conditions are as follows.
-Column: GL Science Inert Cap1 (liquid phase film thickness: 0.25 μm, length: 30 m, inner diameter: 0.25 mm)
-Temperature: 40°C (hold for 5 minutes) +40°C to 170°C (10°C/minute) +170°C to 210°C (5°C/minute) +210°C to 330°C (15°C/minute) +330°C (hold for 20 minutes)
-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, and they were measured by gas chromatography to prepare a calibration curve from the peak area. Next, a sample solution was prepared by dissolving the polymerization solution and tridecane in ethyl acetate, and the same measurement was performed. The polymerization rate of each monomer component was determined by the internal standard method.

(Weight average molecular weight and number average molecular weight)
The weight average molecular weight and the number average molecular weight of the polymer were measured under the following conditions.
-Device: GPC system HLC-8320GPC ECOSEC manufactured by Tosoh Corporation
-Column: Tosoh Corporation, TSKgel GMHXL 2 bottles-Developing solvent: Tetrahydrofuran-Flow rate of developing solvent: 1.0 ml/min-Standard sample: TSK standard polystyrene (Tosoh Corporation, PS-oligomer kit)
-Column temperature: 40°C
-Sample concentration: 0.5%
-Injection volume: 200 μl
(Viscosity index)
As kinematic viscosity of 7.0 mm ² / s at 100 ° C., the base oil (SK manufactured: YUBASE4 American Petroleum Institute (API) Group III base oil in the classification (viscosity index 122,40 ° C. kinematic viscosity 19.6 mm ² / The polymer was diluted with s)) and measured by the method of JIS K2283. When the viscosity index was 230 or more, it was evaluated as ◯, and when it was less than 230, it was evaluated as x.

(Shear stability)
The polymer was diluted in a base oil (YUBASE4 manufactured by SK) so that the kinematic viscosity at 100° C. was 7.0 mm ² /sec, and ultrasonic waves were irradiated under the following conditions.
Device: Hielscher Ultrasonics UP400S
Setting: Amplitude=70%, Cycle=1
Time: 10 minutes Temperature: 100°C
The kinematic viscosities of the base oil before and after shearing and at 100° C. were measured, and SSI={1-(kinematic viscosity after shearing−kinematic viscosity of base oil)/(kinematic viscosity before shearing−kinematic viscosity of base oil)}×100 When the value calculated by the formula is 45 or less, it is indicated by O, and when it exceeds 45, it is indicated by x.

(Viscosity measurement)
A base oil (manufactured by SK: YUBASE4 group III base oil (viscosity index 122, 40° C. kinematic viscosity 19.6 mm ² /s) in the American Petroleum Institute (API) classification) 80% by mass and a solution containing 20% by mass of the polymer. Was measured with an E-type viscometer (manufactured by Toki Sangyo: TVE-35H 3°×R9.7 rotor).
At 25° C., the case where the viscosity was 30 Pa·s or less was marked with ◯, and the case where it exceeded 30 Pa·s was marked with x.

(Dilution speed)
The polymer was diluted with a base oil (manufactured by SK: YUBASE4) so that the solid content concentration was 20% by mass. 1.5 parts by mass of the obtained 20% by mass base oil solution was placed in a glass screw tube, and a base oil (manufactured by SK: YUBASE4) was further added at room temperature to make a total amount of 10 parts by mass (solid content concentration 3% by mass). And

The above mixture is dissolved at room temperature under the following conditions, and when the time required for complete dissolution by visual observation is less than 1 hour, it is ⊚, and when it is 1 hour or more and less than 1.5 hours, it is 1. The case where the time was 5 hours or more was marked with x.
Device: MIX-ROTAR VWR-3 Made by Inouchi Seieido Co., Ltd. Setting: 80 rpm
(SP value)
The SP value (solubility parameter) of the polymer was measured by Materials Studio (registered trademark) Ver. 6.1 Calculated using MS-Synthia module. First, a monomer structure was created and a repeating structure was defined. Polymer properties (such as solubility parameters) were calculated by MS-Synthia module using the defined monomer structure. The MS-Synthia module is software that can calculate physical properties of a polymer by using quantitative structure-property relationship (QSPR: Quantitative Structure Property Relationships). Physical properties can be calculated. The detailed theory is described in the following documents, which are incorporated herein by reference: Josef Bicerano, "Prediction of Polymer Properties, 3rd Edition", published by Marcel Dekker. This time, of the SP values (solubility parameter) of the Feders method and van Krevelen method improved by Bicerano that can be calculated by MS-Synthia, the value of the Fedors method was used.
(Tg)
In the present invention, the glass transition temperature (Tg) is
FOX formula: 1/Tg=W1/Tg1+W2/Tg2+...
(Tg: glass transition temperature to be obtained, W1: weight fraction of component 1, Tg1: glass transition temperature of homopolymer of component 1)
It was obtained by calculation according to. As the value of the glass transition temperature of the homopolymer of each component, the value described in "Adhesive Technology Handbook" by Nikkan Kogyo Shimbun Co., Ltd. or "Polymer Handbook" by Wiley-Interscience shall be adopted. In the present invention, the glass transition temperatures of homopolymers of PMI, SLMA, and SMA are 337°C, -65°C, and -70°C, respectively.

(2) Production Example of Base Oil Solution of Polymer (Example 1)
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introducing pipe, and a dropping funnel, 32 parts by mass of BMA, 30 parts by mass of SMA, 10 parts by mass of PMI, 28 parts by mass of SLMA, and 124.2 parts by mass of base oil (YUBASE4 manufactured by SK). Parts, and 0.05 parts by mass of pentaerythritol tetrakis (mercaptoacetate) were charged, and the content was heated to 105° C. while introducing nitrogen gas. As a polymerization initiator, a solution prepared by mixing 0.1161 parts by mass of t-amyl peroxyisononanoate (Arkema Yoshitomi Co., Luperox (registered trademark) 570) and 8.2 parts by mass of base oil (SK YUBASE4) was added. In addition, 0.051 parts by mass of t-amylperoxy-2-ethylhexanoate (Arkema Yoshitomi Co., Luperox (registered trademark) 575) as a polymerization initiator was added to 3.4 parts by mass of base oil (YUBASE4 manufactured by SK). While the solution dissolved in was added dropwise over 2 hours, solution polymerization was allowed to proceed, and further aging was carried out for 4 hours. Subsequently, 97.3 parts by mass of base oil (YUBASE4 manufactured by SK) was added and diluted to obtain a base oil solution of polymer 1 (polymer concentration 30% by mass). The results of various evaluations are shown in Table 1.

(Example 2)
In Example 1, the same operation as in Example 1 was performed except that 32 parts by mass of BMA was changed to 30 parts by mass of SLMA and 28 parts by mass of SLMA was changed to 30 parts by mass. 30% by weight) was obtained. The results of various evaluations are shown in Table 1.

(Example 3)
In Example 2, 0.1161 parts by mass of t-amylperoxyisononanoate (manufactured by Arkema Yoshitomi Co., Luperox (registered trademark) 570) was added to 0.0774 parts by mass, and t-amylperoxy-2-ethylhexano was prepared. Except that 0.051 parts by mass of ate (manufactured by Arkema Yoshitomi, Luperox (registered trademark) 575) was changed to 0.034 parts by mass of t-amylperoxyisononanoate (manufactured by Arkema Yoshitomi, Luperox (registered trademark) 570). In the same manner as in Example 2, a base oil solution of the polymer 3 (polymer concentration 30% by mass) was obtained. The results of various evaluations are shown in Table 1.
(Example 4)
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introducing pipe, and a dropping funnel, 20 parts by mass of MMA, 5 parts by mass of BMA, 30 parts by mass of SMA, 10 parts by mass of PMI, 35 parts by mass of SLMA, and base oil (YUBASE4 manufactured by SK). 143.6 parts by mass and pentaerythritol tetrakis (mercaptoacetate) 0.05 parts by mass were charged, and the content was heated to 105° C. while introducing nitrogen gas. As a polymerization initiator, a solution prepared by mixing 0.0774 parts by mass of t-amyl peroxyisononanoate (Arkema Yoshitomi Co., Luperox (registered trademark) 570) and 6.3 parts by mass of base oil (SK YUBASE4) was added. In addition, 0.034 parts by mass of t-amyl peroxyisononanoate (Arkema Yoshitomi Co., Luperox (registered trademark) 570) as a polymerization initiator was dissolved in 3.4 parts by mass of base oil (YUBASE4 manufactured by SK). The solution polymerization was allowed to proceed while the solution was added dropwise over 2 hours, followed by aging for 4 hours. Subsequently, 78.9 parts by mass of a base oil (YUBASE4 manufactured by SK) was added and diluted to obtain a base oil solution of the polymer 4 (polymer concentration 30% by mass). The results of various evaluations are shown in Table 1.

(Comparative Example 1)
Regarding Example 3, the same operation as in Example 3 was carried out except that 30 parts by mass of BMA was changed to 30 parts by mass of MMA to obtain a base oil solution of the polymer 5 (polymer concentration 30%). Since the polymer 5 had poor solubility in the base oil and insoluble matter was generated, the viscosity index and the 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 pipe, a nitrogen introduction pipe, and a dropping funnel, 30 parts by mass of MMA, 30 parts by mass of SMA, 40 parts by mass of SLMA, 53.33 parts by mass of toluene, pentaerythritol tetrakis (mercaptoacetate) 0 The content was heated to 105° C. while introducing nitrogen gas into the mixture. As a polymerization initiator, 0.0258 parts by mass of t-amyl peroxyisononanoate (Arkema Yoshitomi Co., Luperox (registered trademark) 570) and 0.46 parts by mass of toluene were added, and the polymerization was started. A solution prepared by dissolving 0.103 parts by mass of the agent in 10.3 parts by mass of toluene was added dropwise over 4 hours to allow solution polymerization to proceed, followed by aging for 4 hours.

Subsequently, the cooling pipe was replaced with a V-shaped pipe connected to the cooling pipe and the distillate receiver, and 233 parts by mass of base oil (YUBASE4 manufactured by SK) 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. Thirty minutes after the internal temperature reached 142° C., decompression and cooling were performed to obtain a base oil solution of polymer 6 (polymer concentration 30 mass %). The results are shown in Table 1.

The viscosity index improver containing the units (a) and (b) as essential constituent units not only exhibits good shear stability and high viscosity index while maintaining solubility in the base oil, but was also measured under specific conditions. It was suggested that when the viscosity of the base oil composition is not more than a certain value, the base oil composition can be easily handled at room temperature and can be rapidly diluted, so that the productivity of the lubricating oil composition is excellent.

The lubricating oil composition using the viscosity index improver containing the polymer of the present invention exhibits good shear stability and a high viscosity index while maintaining the solubility of the base oil, as compared with the conventional lubricating oil composition. Therefore, since it can meet future demands for fuel economy and long life of automobiles, it can be suitably used as drive system lubricating oil, hydraulic oil, and engine oil. In addition, since the base oil composition has a high fluidity at room temperature, it can be diluted quickly and the productivity of the lubricating oil composition can be improved.

Claims (5)

A unit derived from a maleimide-based monomer represented by the following formula (1) (hereinafter referred to as “(a) unit”) ,

[In the formula (1), R ¹ and R ² are each independently a hydrogen atom or an alkyl group, and X is a hydrogen atom or an organic group having 1 to 40 carbon atoms. ]
A unit derived from an alkyl (meth)acrylate having an aliphatic hydrocarbon group having 2 to 6 carbon atoms (hereinafter referred to as a unit (b)) ,
A polymer containing an alkyl (meth)acrylate-derived unit having an aliphatic hydrocarbon group having 7 to 40 carbon atoms (hereinafter referred to as "(c) unit") as an essential constituent unit,
In 100 parts by mass of the polymer, (a) unit is 0.5 parts by mass or more and 35 parts by mass or less, (b) unit is 0.5 parts by mass or more and 60 parts by mass or less, and (c) unit is 30 parts by mass or more and 90 parts by mass or more. Less than 50 parts by mass, the total of (a) units, (b) units, and units derived from methyl (meth)acrylate is 35 parts by mass or more and less than 70 parts by mass,
A viscosity index improver comprising a polymer having a viscosity of 4.1 Pa·s or more and 30 Pa·s or less at 25° C. measured under the following conditions.
<Measurement conditions>
A solution consisting of 80% by mass of Group III base oil (viscosity index 122, 40° C. kinematic viscosity 19.6 mm ² /s) and 20% by mass of the polymer in the American Petroleum Institute (API) classification was used as an E-type viscometer (East Viscometer). Koki Sangyo: TVE-35H 3° x R9.7 rotor). The viscosity index improver according to claim 1, wherein a molecular weight distribution (Mw/Mn) calculated from the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polymer is 4.0 or less. The viscosity index improver according to claim 1 or 2 , except that the polymer has a unit derived from styrene. The polymer is further viscosity index improver according to any one of claims 1 to 3 having a trifunctional or higher polyvalent mercaptan derived branching units and / or trifunctional or more branching units derived from polyfunctional initiator .. A lubricant base oil, the lubricating oil composition characterized by containing a viscosity index improver according to any one of claims 1-4.