JP6676381B2 - Method for producing maleimide-based monomer copolymer, viscosity index improver, and method for producing lubricating oil composition - Google Patents

Description

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

  In recent years, lubricating oils for internal combustion engines have been strongly required to have improved fuel-saving characteristics, and one means is to reduce the viscous drag by reducing the viscosity of the lubricating oil. However, mere lowering of 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 high temperature low while keeping the viscosity at a high temperature high.

As the viscosity index improver, those containing a polymer are known, and there are various types. Above all, a viscosity index improver comprising an alkyl (meth) acrylate polymer exhibits a high viscosity index improvement effect. On the other hand, the viscosity index improver composed of an alkyl (meth) acrylate polymer has poor shear stability, and thus has a problem that fuel saving characteristics are deteriorated (long life property is poor) during long-term use. Means for improvement include, for example, reducing the molecular weight of the viscosity index improver. In general, the lower the molecular weight, the less likely to be affected by shearing, and the smaller the molecular weight reduction width. Therefore, by using a low molecular weight viscosity index improver, it is possible to suppress the decrease in viscosity after shearing (Patent Document 1 and Non-Patent Document 1). Patent Document 1).

  From the viewpoint of improving shear stability and thermal stability, a method has been proposed in which a specific amount of a maleimide monomer is introduced into the main chain skeleton of a polymethacrylate-based viscosity index improver (Patent Document 2).

JP 2013-104032 A JP-A-2015-86314 JP 2001-233919 A Sanyo Chemical News 2013 New Year issue No. 476

  The present invention provides a maleimide-based copolymer having a high viscosity index and good shear stability, and exhibiting sufficient solubility in a lubricating base oil, with a high polymerization rate and a small number of steps. The purpose is to do.

  As described above, since the polymethacrylate-based viscosity index improver is a polymer, it is subjected to a decrease in molecular weight due to shearing, and the viscosity of the lubricating oil composition is reduced and fuel economy is reduced. Sex improves. On the other hand, in general, the lower the molecular weight, the lower the viscosity index improving effect tends to be. Therefore, when a low molecular weight viscosity index improver is used, there is a problem that the viscosity index decreases. 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, a polymethacrylate-based viscosity index improver in which a specific amount of a maleimide-based monomer is introduced into the main chain skeleton has a high viscosity index and good shear stability. It is known that in the polymerization of a maleimide copolymer, the addition of an acid component is effective for improving the conversion of the maleimide-based monomer (Patent Document 3). However, when the above-mentioned method is used, odor derived from an acid component may be generated at the time of production, and there is a problem in workability. In addition, there was a concern about equipment corrosion due to acid components.

  The copolymer is obtained by a method such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. When a solvent is used, when a solvent insoluble in a lubricating base oil is used, there is a problem that solvent replacement after polymerization is required, and the number of steps is increased.

  As a result of intensive studies, the present inventors have found that a monomer containing a maleimide-based monomer is copolymerized in a lubricating base oil, and have reached the present invention.

That is, the present invention provides a copolymer having a step of polymerizing a monomer containing a maleimide monomer (hereinafter, referred to as “component (a)”) as an essential component in a lubricating base oil to obtain a polymer. In the case of using a styrene monomer , the copolymer is characterized in that the unit derived from the styrene monomer is 2 parts by mass or less based on 100 parts by mass of the polymer. It is a manufacturing method.
In the method for producing a copolymer, the content of the component (a) is preferably 5 parts by mass or more and 35 parts by mass or less based on 100 parts by mass of all the monomer components in total.

The monomer is, in addition to the component (a), (b) an alkyl (meth) acrylate having an aliphatic hydrocarbon group having 1 to 5 carbon atoms (hereinafter referred to as “component (b)”), (c) A) a monomer containing an alkyl (meth) acrylate having an aliphatic hydrocarbon group having 6 to 40 carbon atoms (hereinafter referred to as “component (c)”).
The copolymer is preferably obtained in a step of polymerizing the monomer in a lubricating base oil in the presence of a trifunctional or higher polyfunctional mercaptan and / or a trifunctional or higher polyfunctional initiator.
The present invention comprises a copolymer production step of producing a copolymer by the production method , and a step of producing a viscosity index improver containing 70% by mass or more of the copolymer obtained in the copolymer production step. It is also a method for producing a viscosity index improver.
The present invention provides a viscosity index improver producing step of producing a viscosity index improver by the production method, and mixing the viscosity index improver obtained in the viscosity index improver producing step with a base oil to form a lubricating oil composition. And a step of producing a lubricating oil composition.

  By using the production method of the present invention, the polymerization rate of the maleimide-based monomer can be improved without using an acid component, a shear stability suitable as a viscosity index improver, a copolymer having a high viscosity index, and A lubricating oil composition can be obtained without a solvent replacement step.

Hereinafter, the present invention will be described in detail. In the following description, “parts” means “parts by mass” and “%” means “% by mass” unless otherwise specified. Further, “A to B” indicating a range indicates that the range is A or more and B or less.
The present invention relates to a method for producing a copolymer, comprising a step of polymerizing a monomer containing a monomer (a) as an essential component in a lubricating base oil to obtain a polymer. In the case of using a copolymer, a method for producing a copolymer is characterized in that the unit derived from a styrene monomer is 2 parts by mass or less based on 100 parts by mass of the polymer .

  The monomer (a) component used in the present invention is a maleimide-based monomer represented by the following general formula (1).

(Wherein, R ¹ and R ² are each independently a hydrogen atom or an alkyl group, and X is a hydrogen atom, a linear, branched, or cyclic alkyl group, a substituted alkyl group, an aryl group, or a substituted aryl group. is there.)
As the monomer (a) component, of the above X, the branched alkyl group may have an alkyl group having an aromatic ring. As the cyclic alkyl group, an alkyl group having an aromatic ring such as a benzyl group and a cycloalkyl group such as a cyclohexyl group are preferable. As the aryl group, a phenyl group, a naphthyl group, or an aryl group in which hydrogen of an aromatic ring is substituted is preferable.

Specific examples of the monomer (a) component include maleimide, N-methylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, N-butylmaleimide, N-isobutylmaleimide, N-tert-butylmaleimide, and N-cyclohexyl. Maleimide, N-laurylmaleimide, N-stearylmaleimide, N-phenylmaleimide, N-benzylmaleimide, N-chlorophenylmaleimide, N-methylphenylmaleimide, N-naphthylmaleimide, N-hydroxylethylmaleimide, N-hydroxylphenylmaleimide, N-methoxyphenylmaleimide, N-carboxyphenylmaleimide, N-nitrophenylmaleimide, N-tribromophenylmaleimide, and the like, and one or more of these compounds are used. . Among these, N-phenylmaleimide, N-cyclohexylmaleimide, N-isopropylmaleimide, N-benzylmaleimide, N-laurylmaleimide, and N-stearyl are preferable from the viewpoints of availability and economy and high solubility in base oil. Maleimide is preferred, N-phenylmaleimide, N-cyclohexylmaleimide, and N-benzylmaleimide are more preferred, and N-cyclohexylmaleimide is even more preferred. In addition, the said monomer (a) may be used independently and may use 2 or more types together.
The content of the monomer (a) component is 0.5 parts by mass or more and 35 parts by mass or less, preferably 2 parts by mass or more and 35 parts by mass or less, with respect to 100 parts by mass of the total of all the monomer components. It is preferably from 5 parts by mass to 35 parts by mass, particularly preferably from 5 parts by mass to 30 parts by mass. The viscosity index improver containing a polymer using the monomer (a) component in the above numerical range can increase the shear stability while ensuring the solubility in the base oil. Furthermore, effects such as improvement in clean dispersibility of sludge and the like and suppression of wear on the metal surface are expected.

  The monomer used in the present invention includes, in addition to the component (a), (b) an alkyl (meth) acrylate having an aliphatic hydrocarbon group having 1 to 5 carbon atoms (hereinafter, referred to as “component (b)”). And (c) a monomer containing an alkyl (meth) acrylate having an aliphatic hydrocarbon group having 6 to 40 carbon atoms (hereinafter, referred to as “component (c)”).

Specifically, the component (b) has a structure represented by the following general formula (2), wherein R ³ is a hydrogen atom or a methyl group, and R ⁴ is a carbon atom. (Meth) acrylates which are 1 to 5 aliphatic hydrocarbon groups. Note that R ⁴ may be linear, cyclic, or branched, and may have a substituent.

In the monomer (b) component, R ³ and R ⁴ may each be a single monomer, or R ³ and / or R ⁴ may be a mixture of two or more different monomers. Good. From the viewpoint of reactivity, R ³ is preferably a hydrogen atom or a methyl group. Further, from the viewpoint of improving the viscosity index, R ⁴ is preferably linear or branched.

  Specific examples of the monomer (b) component include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate, and 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 and the like. . Especially, it is preferable to contain at least methyl (meth) acrylate as the monomer (b) component. When the component (b) contains methyl (meth) acrylate, the viscosity index improving effect is large, and the viscosity index improver has high heat resistance and high shear stability. In addition, the said monomer (b) may be used independently and may use 2 or more types together.

    The content of the monomer (b) component is preferably from 2 parts by mass to 40 parts by mass, more preferably from 5 parts by mass to 35 parts by mass, and particularly preferably from 100 parts by mass in total of all the monomer components. Is from 5 parts by mass to 30 parts by mass. When the content of the monomer (b) is in the above range, the copolymerizability with other components is good, the polymerization rate is good, the polymerization rate is high, and the productivity is good. Further, the viscosity stability improver and the base oil solubility of the viscosity index improver obtained by copolymerization become more favorable.

The monomer (c) component used in the present invention has a structure represented by the following general formula (3), wherein R ⁵ is a hydrogen atom or a methyl group, and R ⁶ is a carbon atom. (Meth) acrylates which are an alkyl group of the number 6 to 40, preferably an alkyl group of 6 to 24, and particularly preferably an alkyl group of 12 to 24 are exemplified. R ⁶ may be linear, cyclic, or branched, and may have a substituent.

In the monomer (c) component, R ⁵ and R ⁶ may each be a single monomer, or R ⁵ and / or R ⁶ may be a mixture of two or more different monomers. Good. From the viewpoint of reactivity, R ⁵ is preferably a hydrogen atom or a methyl group.
Specific examples of the monomer (c) component include n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, and undecyl (Meth) acrylate, dodecyl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) A) acrylate, nonadecyl (meth) acrylate, eicosyl (meth) acrylate, behenyl (meth) acrylate, tetracosyl (meth) acrylate, 2-decyltetradecyl (meth) acrylate, Hexyl (meth) acrylate, menthyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, adamantyl (meth) acrylate. Among them, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, eicosyl (meth) A) acrylate, behenyl (meth) acrylate, tetracosyl (meth) acrylate, 2-decyltetradecyl (meth) acrylate, and cyclohexyl (meth) acrylate. In addition, the said monomer (b) may be used independently and may use 2 or more types together.

  The content of the monomer (c) component is preferably 20 parts by mass or more and less than 95 parts by mass, more preferably 25 parts by mass or more and 85 parts by mass or less, particularly preferably 100 parts by mass based on 100 parts by mass of all the monomer components. Is 30 parts by mass or more and 75 parts by mass or less. The viscosity index improver containing a polymer using the monomer (c) component in the above numerical range has good solubility in base oils having various compositions.

  By using the component (c) having a low-polarity long-chain alkyl group, a polymer having high oil solubility can be obtained. The component (a) is preferably at least 2 parts by mass, more preferably at least 5 parts by mass, per 100 parts by mass of the polymer. The upper limit is preferably 33 parts by mass or less, particularly preferably 30 parts by mass or less. If the amount of the component (a) is less than 0.5 part by mass, the effect of introducing the component (a) cannot be sufficiently obtained, and the shear stability cannot be sufficiently improved. Further, the clean dispersibility of sludge or the like derived from the highly polar structure of the component (a) may be reduced, or the metal surface may be worn or the fatigue life may be reduced. If the amount exceeds 35 parts by mass, the solubility in the lubricating base oil tends to decrease and the viscosity index tends to decrease. When the weight-average molecular weight is less than 200,000, not only does the viscosity index of the lubricating oil composition decrease, but also it is necessary to increase the amount of the viscosity index improver used to adjust the viscosity to a desired viscosity. At a disadvantage.

  Further, as a monomer component for synthesizing the polymer of the present invention, a radical polymerizable monomer (d) other than the essential components (a), (b) and (c) can be contained. The monomer (d) 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 include (meth) acrylates other than the components (b) and (c), unsaturated mono- or dicarboxylic esters, unsaturated carboxylic acids, vinyl aromatics, vinyl esters, vinyl ethers, olefins, Examples thereof include vinyl cyanide, an N-vinyl compound, and (meth) acrylamide. These monofunctional monomers may be used alone or in combination of two or more.

  Examples of the (meth) acrylate other than the components (b) and (c) include benzyl (meth) acrylate, phenyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 3 -Hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) ) Acrylate, 2-phenoxyethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, morpholinoalkylene (meth) acrylate, α-hydroxymethylacryl Methyl, polyethylene glycol mono (meth) acrylate.

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

  Examples of the unsaturated carboxylic acids include (meth) acrylic acid, crotonic acid, cinnamic acid, vinylbenzoic acid, maleic acid, fumaric acid, itaconic acid, maleic anhydride, and itaconic anhydride.

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

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

  Examples of the vinyl ether include methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, hexyl vinyl ether, octyl vinyl ether, decyl vinyl ether, dodecyl vinyl ether, and octadecyl vinyl ether.

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

  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.

Examples of (meth) acrylamide include N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N, N-dipropyl (meth) acrylamide, N, N-dibutyl (meth) acrylamide, N -Methylol (meth) acrylamide, acryloyl morpholine and the like.
Among these monofunctional monomers, 2-hydroxyethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, α-hydroxymethyl acrylate, N-vinylpyrrolidone, N, N-dimethyl ( (Meth) acrylamide and acryloylmorpholine are preferred.

  The unit derived from the monofunctional monomer contained in the radical polymerizable monomer (d) other than the essential components (a), (b) and (c) is 0 parts by mass relative to 100 parts by mass of the polymer. It is 30 parts by mass or less, preferably 0 parts by mass or more and 25 parts by mass or less, more preferably 0 parts by mass or more and 20 parts by mass or less.

However when using the styrene monomer, the unit derived from the styrene monomer to the polymer 100 parts by weight is not more than 2 parts by weight, it is favorable preferable is not more than 1 part by weight. When units derived from styrene monomer exceeds 2 parts by mass, solubility and viscosity index of the base oil viscosity index improvers containing polymer is you decrease.

  When an olefin is used as a monomer, the unit derived from the olefin is preferably at most 5 parts by mass, more preferably at most 3 parts by mass, per 100 parts by mass of the polymer. When the unit derived from olefins exceeds 5 parts by mass, the viscosity index of the viscosity index improver containing the polymer tends to decrease.

  Examples of the polyfunctional monomer include polyfunctional (meth) acrylate, vinyl ether group-containing (meth) acrylate, allyl group-containing (meth) acrylate, polyfunctional (meth) acryloyl group-containing isocyanurate, and polyfunctional urethane (meth). Examples include polyfunctional (meth) acrylic compounds such as acrylates, 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 the polyfunctional (meth) acrylate include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, butylene glycol di (meth) acrylate, Hexanediol di (meth) acrylate, cyclohexanedimethanol di (meth) acrylate, bisphenol A alkylene oxide di (meth) acrylate, bisphenol F alkylene oxide di (meth) acrylate, trimethylolpropane tri (meth) acrylate, ditrimethylolpropane tetra (Meth) acrylate, glycerin tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaeryth Tall penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, 2,2 ′-[oxybis (methylene)] bis acrylate, dialkyl-2,2 ′-[oxybis (methylene)] bis-2-propenoate, etc. No.

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

  As the allyl group-containing (meth) acrylate, for example, allyl (meth) acrylate, methyl-α-allyloxymethyl (meth) acrylate, stearyl-α-allyloxymethyl (meth) acrylate, 2-decyltetradecyl-α- Allyloxymethyl (meth) acrylate and the like can be mentioned.

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

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

  Examples of the polyfunctional maleimide-based compound include, for example, 4,4′-diphenylmethanebismaleimide, m-phenylenebismaleimide, bisphenol A diphenylether bismaleimide, 3,3′-dimethyl-5,5′-diethyl-4,4′- Examples include diphenylmethane bismaleimide, 4-methyl-1,3-phenylene bismaleimide, and 1,6-bismaleimide- (2,2,4-trimethyl) hexane.

  Examples of the polyfunctional vinyl ether include ethylene glycol divinyl ether, diethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, butylene glycol divinyl ether, hexanediol divinyl ether, bisphenol A alkylene oxide divinyl ether, and bisphenol F alkylene oxide divinyl ether. And trimethylolpropane trivinyl ether, ditrimethylolpropane tetravinyl ether, glycerin trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, and dipentaerythritol hexavinyl ether.

  Examples of the polyfunctional allyl compound include, for example, ethylene glycol diallyl ether, diethylene glycol diallyl ether, polyethylene glycol diallyl ether, propylene glycol diallyl ether, butylene glycol diallyl ether, hexanediol diallyl ether, bisphenol A alkylene oxide diallyl ether, bisphenol F alkylene oxide Multifunctional allyl ethers such as diallyl ether, trimethylolpropane triallyl ether, ditrimethylolpropane tetraallyl ether, glycerin triallyl ether, pentaerythritol tetraallyl ether, dipentaerythritol pentaallyl ether, dipentaerythritol hexaallyl ether; triallyl Isocyanurate Polyfunctional allyl group-containing isocyanurate; diallyl phthalate, polyfunctional allyl ester such as diphenic diallyl like; bis-allyl-nadi-imide compound; bis-allyl-nadi-imide compound and the like.

Examples of the polyfunctional aromatic vinyl include divinylbenzene.
The unit derived from the polyfunctional monomer contained in the radical polymerizable monomer (d) other than the essential components (a), (b) and (c) is 0 parts by mass relative to 100 parts by mass of the polymer. The content is preferably from 5 to 5 parts by mass, more preferably from 0 to 3 parts by mass, and still more preferably from 0 to 2 parts by mass. In this case, since the polymer has a star structure or a crosslinked structure, 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, 0 to 30 parts by mass relative to 100 parts by mass of the polymer The content is preferably at most 0 part by mass and at most 25 parts by mass, more preferably at least 0 part by mass and at most 20 parts by mass. 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 progress 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. Examples of the radical polymerization initiator include 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 active energy rays. 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, for example, 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-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 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, screen Acid peroxide, m-toluoylbenzoyl peroxide, benzoyl peroxide, di-n-propylperoxydicarbonate, diisopropylperoxydicarbonate, bis (4-t-butylcyclohexyl) peroxydicarbonate, di-2 -Ethoxyethyl peroxydicarbonate, di-2-ethoxyhexylperoxydicarbonate, di-3-methoxybutylperoxydicarbonate, di-s-butylperoxydicarbonate, di (3-methyl-3-methoxybutyl) ) Peroxydicarbonate, α, α'-bis (neodecanoylperoxy) diisopropylbenzene, cumylperoxyneodecanoate, 1,1,3,3, -tetramethylbutylperoxyneodecanoate, 1 -Cyclohexyl-1- Tyl ethyl peroxy neodecanoate, t-hexyl peroxy neodecanoate, t-butyl peroxy neodecanoate, t-hexyl peroxy pivalate, t-butyl peroxy pivalate, 1,1,3 1,3-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-butyl peroxymalate, t-butyl peroxy-3,5,5-tri Tyl hexanoate, t-butyl peroxy laurate, t-butyl peroxyisopropyl monocarbonate, t-butyl peroxy-2-ethylhexyl monocarbonate, t-butyl peroxy acetate, 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'-tet 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) dialdehyde 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-based initiators such as [propionitrile], 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, and potassium; Grade 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. Manganese, dimethylaniline, triethanolamine, triethylbenzylammonium chloride, di (2-hydroxyethyl) p-toluidine, ethylenethiourea, acetylacetone, methyl acetoacetate and the like can be mentioned.

  Specific examples of the photoradical polymerization initiator include, for example, 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-methyl Alkylphenone compounds such as phenyl) methyl] -1- [4- (4-morpholinyl) phenyl] -1-butanone; benzophenone compounds such as benzophenone, 4,4'-bis (dimethylamino) benzophenone and 2-carboxybenzophenone Compounds: Benzoin-based compounds such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and 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-ethoxycarbokinylnaphthyl) -4,6-bis ( Halomethylated triazine compounds such as trichloromethyl) -s-triazine; 2-trichloromethyl-5- (2′-benzofuryl) -1,3,4-oxadiazole, 2-trichloromethyl-5- [β- ( Halomethylated oxadiazoles such as 2'-benzofuryl) vinyl] -1,3,4-oxadiazole, 4-oxadiazole, 2-trichloromethyl-5-furyl-1,3,4-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 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) Titanocene compounds such as -1-yl) -bis (2,6-difluoro-3- (1H-pyrrol-1-yl) -phenyl) titanium; p-dimethylaminobenzoic acid, p-diethylamido Benzoic acid ester compounds such as benzoic acid; acridine compounds such as 9-phenyl acridine; and the like.

  In the case where the above monomer component is polymerized by a radical polymerization mechanism, a known chain transfer agent may be used, if necessary, and it is more preferable to use it together with a radical polymerization initiator. Specific examples of such a chain transfer agent include, for example, 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), dimer Mercaptocarboxylic acid esters such as pentaerythritol hexakis (3-mercaptopropionate); ethylmercaptan, t-butylmercaptan, n-dodecylmercaptan, 1,2-dimercaptoethane, etc. Alkyl mercaptans; Mercapto alcohols 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] isocyanurate and the like; dihydroxyls and the like such as 2-hydroxyethyl disulfide and tetraethylthiuram disulfide; dithiocarbamates and the like such as benzyldiethyldithiocarbamate; and α-methylstyrene dimer and the like. Dimer; alkyl halides such as carbon tetrabromide. Among these, mercaptocarboxylic acids, mercaptocarboxylic esters, alkyl mercaptans, mercapto alcohols, aromatic mercaptans; mercapto isocyanurate; Compounds having a mercapto group, such as a group, are preferred. These may be used alone or in combination of two or more.

  When the above monomer component is polymerized by a radical polymerization mechanism, it is more preferable to carry out the radical polymerization in the presence of a trifunctional or higher functional polyvalent mercaptan and / or a trifunctional or higher functional polyfunctional initiator.

  Examples of the trifunctional or higher polyvalent mercaptan include trimethylolpropane trimercaptoacetate, trimethylolpropanetri (3-mercaptopropionate), pentaerythritol tetrakismercaptoacetate, pentaerythritol tetrakis (3-mercaptopropionate), Polyester compounds such as dipentaerythritol hexakismercaptoacetate, dipentaerythritol hexakis (3-mercaptopropionate), compounds having three or more hydroxyl groups and carboxyl group-containing mercaptans, triazine polyvalent thiols, polyepoxy compounds A compound obtained by adding hydrogen sulfide to a plurality of epoxy groups to introduce three or more mercapto groups per molecule, a plurality of carboxyl groups of a polycarboxylic acid and a mercapto group Ethanol to can be such compounds include having esterified three or more mercapto groups per molecule comprising. One or more of trifunctional or higher polyvalent mercaptans can be used alone or in combination (for example, by mixing).

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

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

  The amount of use of the trifunctional or higher polyfunctional initiator (total amount of addition) may be appropriately set depending on the purpose and application, and is not particularly limited. In addition, considering the balance of polymerizability, the adverse effect of decomposed products, and economic efficiency, from the viewpoint of obtaining a viscosity index improver containing a polymer having a viscosity index and a high weight-average molecular weight of 100,000 or more having high solubility in base oil, The use 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 preferably 0.05 parts by mass or more based on 100 parts by mass of the monomer component. It is still more preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more 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 becomes what has. That is, the polymer included in the viscosity index improver of the present invention has a branch unit derived from a trifunctional or higher polyfunctional 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, 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 trivalent or higher functional polyvalent mercaptan-derived branch unit, the polymer has a branch 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 from 0 to 5.

When the polymer included in the viscosity index improver has a trifunctional or higher functional branch unit derived from a polyfunctional initiator, the polymer preferably has a trifunctional or higher functional peroxide-derived branch unit, and 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 residues), 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 of a trifunctional or higher functional branch unit derived from a polyvalent mercaptan and a trifunctional or higher functional polyfunctional initiator, or may contain both. Is also good. The branch unit derived from a trifunctional or higher-functional polyvalent mercaptan 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 alone or in combination of two or more.

  The content of the trifunctional or higher-functional polyvalent mercaptan-derived branch unit in the polymer is preferably 0.01 part by mass or more, more preferably 0.05 part by mass or more, and 5 parts by mass with respect to 100 parts by mass of the polymer. Or less, more preferably 3 parts by mass or less, even 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 trivalent or higher functional polyvalent mercaptan-derived branch unit is determined by dividing the amount of the trifunctional or higher functional polyvalent mercaptan by the mass of the polymer.

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

  When a polyfunctional mercaptan having three or more functional groups and / or a polyfunctional initiator having three or more functional groups are used in the polymerization step, the suitable conditions such as the type and amount of the initiator are as described above. At the time of the polymerization, the trifunctional or higher polyhydric mercaptan and / or the trifunctional or higher polyfunctional initiator may be added all at once or in portions. Further, a bifunctional or lower functional mercaptan or a bifunctional or lower initiator may be used in combination.

Since narrowing the molecular weight distribution of the copolymer obtained according to the present invention is very advantageous from the viewpoint of improving the viscosity index and the shear stability, Living Radical Polymerization can also be used as the polymerization method. As specific methods, the RAFT method, the NMP method, the ATRP method and the like are well known. Details are outlined in Aldrich Material Materials Volume 5, Number 1, 2010. As an example of use, for example, in the case of the RAFT method, JP-A-2012-197399 uses 2,2′-azobisisobutyronitrile as a polymerization initiator and cumyl dithiobenzoate as a polymerization catalyst.
The polymerization temperature at the time of polymerization of 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 and the polymerization catalyst, and is particularly limited. However, it is preferably from 0 ° C to 200 ° C, and particularly preferably from 25 ° C to 150 ° C. When the polymerization temperature is lower than 0 ° C., the polymerization reaction becomes extremely slow. When the polymerization temperature is higher than 200 ° C., the reaction is so severe that it is difficult to control.

  The monomer component is polymerized by a solution polymerization method. The solvent used for the polymerization is a lubricating base oil.

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

As a preferred specific example of the mineral base oil, base oils (1) to (7) shown below are used as raw materials, and the raw oil and / or the lubricating oil fraction recovered from the raw oil are subjected to a predetermined purification method. And a base oil obtained by recovering a lubricating oil fraction. Further, the following base oils (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 are particularly preferable.
(1) Distillate (WVGO) obtained by vacuum distillation of atmospheric distillation residue of paraffin-based crude oil and / or mixed-base crude oil
(2) Wax (slack wax, etc.) obtained by a lubricating oil dewaxing step and / or synthetic wax (Fischer-Tropsch wax, GTL wax, etc.) obtained by a gas-to-liquid (GTL) process or the like.
(3) One or more mixed oils selected from base oils (1) and (2) and / or mild hydrocracked oils of the mixed oils (4) Base oils (1) to (3) (5) Base oil (1) to (4) of any of the mixed oils (DAO)
(6) Mild hydrocracking treated oil (MHC) of base oil (5)
(7) Two or more mixed oils selected from base oils (1) to (6).
(8) The base oil selected from the 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 contact dewaxing, or distilling after the dewaxing treatment.
(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 contact dewaxing, or distillation after the dewaxing treatment.
Specific examples of the synthetic base oil include poly-α-olefin or hydride thereof, isobutene oligomer or hydride thereof, isoparaffin, alkylbenzene, alkylnaphthalene, diester (ditridecylglutarate, di-2-ethylhexyl adipate). , Diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, etc.), polyol esters (trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate, etc.), poly Oxyalkylene 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 cooligomer (1-octene oligomer, decene oligomer, ethylene-propylene cooligomer, etc.) of α-olefin having 2 to 32 carbon atoms, preferably 6 to 16 carbon atoms and the like Hydride. The kinematic viscosity at 100 ° C. of the synthetic base oil is preferably 1 to ²⁰ mm ² / sec.

The lubricating base oil used when the copolymer obtained by the present invention is used as a viscosity index improver to form a lubricating oil composition is a base oil selected from the above base oils (1) to (7) or The base oil (8) or (9) obtained by performing the above-described treatment on the lubricating oil fraction recovered from the base oil is particularly preferable. It is also preferable to use a base oil belonging to Group III based on the classification by the American Petroleum Institute (API). As the lubricating base oil to be blended in the lubricating oil composition, the above-mentioned synthetic base oil may be used.
The lubricating base oil used in the present invention preferably has a paraffin content of 60 to 90 parts by mass, more preferably 65 to 85 parts by mass, out of 100 parts by mass of the lubricating base oil. And it is particularly preferable that the amount is 70 parts by mass or more and 80 parts by mass or less. Further, in 100 parts by mass of the lubricating base oil, the content of naphthene is preferably from 15 parts by mass to 40 parts by mass, more preferably from 20 parts by mass to 35 parts by mass, and further preferably from 25 parts by mass to 30 parts by mass. It is particularly preferred that the amount is not more than parts by mass. When the composition of the lubricating base oil is within these ranges, not only is the thermal stability and light stability excellent, but it is easy to adjust the viscosity to a desired value. Further, the balance between the viscosity index of the lubricating base oil and the low-temperature characteristics is improved.

  In the lubricating oil composition obtained according to the present invention, the above-mentioned 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 together to form a mixed base oil, the mixed base oil preferably contains at least the lubricating base oil (8) or (9). 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 preferably 70% by mass or more. More 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 100, not only the viscosity-temperature characteristics, heat / oxidation stability, and volatilization prevention property deteriorate, but also the friction coefficient tends to increase, and the abrasion prevention property tends to decrease. . When the viscosity index exceeds 160, the low-temperature viscosity characteristics tend to decrease. In addition, the viscosity index referred to in the present invention means a viscosity index measured according to JIS K 2283.

  The pour point of the lubricating base oil is preferably 0C or lower, more preferably -5C or lower, and more preferably -10C or lower. In addition, the pour point in the present invention means a viscosity index measured in accordance with JIS K 2269.

  The weight average molecular weight (Mw) of the polymer obtained by the present invention is preferably 100,000 or more, more preferably 200,000 or more and 600,000 or less, more preferably more than 250,000 and 600,000 or less, further preferably. It is 270,000 or more and 550,000 or less. When the weight average molecular weight of the polymer is less than the lower limit, not only does the viscosity index of the lubricating oil composition decrease, but it is necessary to increase the amount of the viscosity index improver used to adjust the viscosity to a desired value. 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. In addition, the molecular weight distribution of the polymer obtained by the present invention is preferably 4.0 or less, more preferably 3.0 or less, more preferably 2.8 or less, from the viewpoint of improving the viscosity index and shear stability. . The weight average molecular weight and the molecular weight distribution (Mw / Mn) in the present invention are values measured by the methods described in Examples described later.

  The degree of branching of the polymer obtained by 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, and further preferably 4.0 or less. preferable. When the degree of branching is less than 1.0, the polymer has a insufficient branched structure, and improvement in shear stability cannot be expected. The degree of branching in the present invention corresponds to the average of the number of branch points per polymer molecule. Logically, for example, the degree of branching of a linear polymer having no branch is 0, and The degree of branching of the polymer having three polymer chains extending from the point becomes 1, and the degree of branching of the polymer having four polymer chains extends becomes 2, and the degree of branching of the polymer having five polymer chains extends. The branching degree is 3.

  The SP value (solubility parameter) of the polymer obtained by the present invention is preferably 8.8 or more, more preferably 8.9 or more, still more preferably 9.0 or more, and preferably 9.6 or less, and 9.5. The following is more preferable, and 9.4 or less is still more preferable. The SP value of the base oil generally shows a value of about 8.0 to 8.5. However, when 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 is easy to ensure the solubility of the viscosity index improver in the base oil. The SP value can be measured using a known method.

  The copolymer obtained according to the present invention can achieve both a viscosity index improving effect and a high shear stability at a high level. PSSI (permanent shearability index: ASTM D6022) and decomposition start temperature are used as indices as specific numerical values of shear stability. The viscosity index improver according to the present embodiment contains the above-described polymer as a main component, and is preferably 70% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the viscosity index improver of the present invention. % By mass, most preferably 99% by mass or more and 100% by mass or less. The PSSI of the viscosity index improver is preferably 50 or less, more preferably 45 or less, and particularly preferably 40 or less. Further, the PSSI is preferably 0.1 or more, more preferably 0.5 or more, further preferably 2 or more, and particularly preferably 5 or more. When the PSSI is less than 0.1, the effect of improving the viscosity index is small and the cost may increase. When the PSSI exceeds 50, the shear stability and the storage stability may be deteriorated. In addition, PSSI in the present invention is a value measured by a method described in Examples described later.

In the production method of the viscosity index improver according to the present invention comprises as main components a polymer described above, in viscosity index improver 100 wt%, polymer 70 wt% or more, good Mashiku is more than 90 wt% , more preferably 95 mass% or more, more preferably to at least 99% by weight, containing 100 mass% or less.

The present invention provides a viscosity index improver producing step of producing a viscosity index improver by the above production method, and a lubricating oil composition obtained by mixing the viscosity index improver obtained in the viscosity index improver producing step with a base oil. And a step of producing a lubricating oil composition. The lubricating oil composition of the present invention can be obtained by adding the above-mentioned lubricating base oil and the additives described below to the viscosity index improver of the present invention. The viscosity index of the lubricating oil composition obtained by the present invention is preferably from 200 to 400, more preferably from 230 to 300. When the viscosity index is within the above range, fuel economy, heat / oxidation stability, and storage stability are excellent.

  In the lubricating oil composition according to the present embodiment, the content of the viscosity index improver of the present invention described above is preferably 0.01% by mass or more and 20% by mass or less, more preferably 0.01% by mass or less, based on the total amount of the lubricating oil composition. Is from 0.1% by mass to 15% by mass, more preferably from 0.5% by mass to 10% by mass.

  The lubricating oil composition obtained by the present invention contains the above-mentioned copolymer obtained by the present invention as an essential component. More preferably, it contains at least one additive selected from a pour point depressant, an antiwear agent, a metal detergent / dispersant, an ashless detergent / dispersant, an antioxidant, a corrosion inhibitor, a foam inhibitor and a friction modifier. Is preferred.

  As the pour point depressant, any pour point depressant used in lubricating oils can be used. For example, polymethacrylates, naphthalene-chlorinated paraffin condensation products, phenol-chlorinated paraffin condensation products, and the like can be mentioned. Among these, addition of polymethacrylates is preferred.

  As the anti-wear agent (or extreme pressure agent), any anti-wear and extreme pressure agent used for lubricating oil can be used. For example, sulfur-based, phosphorus-based, sulfur-phosphorus-based extreme pressure agents and the like can be used, and specifically, zinc dialkyldithiophosphate (ZnDTP), phosphites, thiophosphites, dithiophosphorus Acid esters, trithiophosphites, phosphates, thiophosphates, dithiophosphates, trithiophosphates, their amine salts, their metal salts, their derivatives, dithiocarbamates, zinc dithio Carbamates, MoDTC, disulfides, polysulfides, sulfurized olefins, sulfurized fats and the like can be mentioned. Of these, the addition of sulfur-based extreme pressure agents is preferred, and sulfurized fats and oils are particularly preferred.

  Examples of the metal-based detergent / dispersant include normal or basic salts such as alkali metal / alkaline earth metal sulphonate, 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. Of these, magnesium or calcium is preferable, and calcium is more preferable.

  As the ashless detergent / dispersant, any ashless detergent / dispersant used for lubricating oils can be used. For example, at least one linear or branched alkyl or alkenyl group having 40 to 400 carbon atoms per molecule is used. Mono- or bis-succinimide, benzylamine having at least one alkyl group or alkenyl group having 40 to 400 carbon atoms in the molecule, or having at least one alkyl group or alkenyl group having 40 to 400 carbon atoms in the molecule Examples thereof include polyamines and modified products thereof using boron compounds, carboxylic acids, phosphoric acids, and the like. Upon use, one or more 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. Specifically, for example, phenol-based ashless antioxidants include 4,4′-methylenebis (2,6-di-tert-butylphenol) and 4,4′-bis (2,6-di-tert-butylphenol). Butylphenol) 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 antifoaming agent include silicone oil having a kinematic viscosity at 25 ° C. of 1,000 to 100,000 mm 2 / s, fluorosilicone oil, alkenyl succinic acid derivative, ester of polyhydroxy aliphatic alcohol and long chain fatty acid, and methyl salicylate. And o-hydroxybenzyl alcohol.

  Examples of the friction modifier include imidomolybdenum succinate complexes such as molybdenum dithiocarbamate and molybdenum dithiophosphate, and organic molybdenum compounds such as amine salts of organic molybdic acid. Having a polar group capable of adsorbing on the same molecule in the same molecule. Examples of the polar group include amines, polyamines, amides, and urea and alkenyl such as amine compounds, fatty acid esters, fatty acid amides, fatty acids, aliphatic alcohols, aliphatic ethers, urea compounds, and hydrazide compounds having these in the molecule at the same time. Examples include succinimide type, esters, alcohols and diols, and monoalkyl glycerin esters having both an ester and a hydroxyl group. In addition, there are various compounds having an amine and a hydroxyl group in the same molecule, such as an alkylamine afkoshki alcohol.

  The lubricating oil composition according to this embodiment is one of a pour point depressant, an antiwear agent, a metal-based detergent / dispersant, an ashless detergent / dispersant, an antioxidant, a corrosion inhibitor, a foam inhibitor, and a friction modifier. 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 according to the present embodiment contains an antifoaming agent, the content is preferably 0.0001% by mass or more and 0.01% by mass or less.

  Further, the lubricating oil composition according to the present embodiment further contains, in addition to the above components, a viscosity index improver other than the polymer of the present invention, a rust inhibitor, a demulsifier, a metal deactivator, and the like. Can be.

  The viscosity index improver other than the polymer of the present invention according to the above embodiment is specifically a non-dispersible or dispersed ester group-containing viscosity index improver. ) Acrylate-based viscosity index improvers, non-dispersible or dispersed olefin- (meth) acrylate copolymer-based viscosity index improvers, styrene-maleic anhydride copolymer-based viscosity index improvers, and mixtures thereof, and the like. Among these, a non-dispersed or dispersed poly (meth) acrylate-based viscosity index improver is preferred. In particular, a non-dispersed or dispersed polymethacrylate-based viscosity index improver is preferred. Other examples include a non-dispersed or dispersed ethylene-α-olefin copolymer or a hydride thereof, polyisobutylene or a hydride thereof, a styrene-diene hydrogenated copolymer, and a polyalkylstyrene.

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

  Examples of the demulsifier include a polyalkylene glycol-based nonionic surfactant such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and polyoxyethylene alkyl naphthyl ether.

  Examples of the metal deactivator include imidazoline, pyrimidine derivatives, alkylthiadiazole, mercaptobenzothiazole, benzotriazole 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) propionnitrile.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto. The percentages and parts in the examples and comparative examples represent% by mass and parts by mass.
Analysis and evaluation of the polymer were performed by the following methods.
(Maleimide monomer polymerization rate)
For the measurement of the polymerization rate, gas chromatography (GC2010, manufactured by Shimadzu Corporation) was used. The measurement conditions are as follows.

Column: Inert Cap® 1 (inner diameter 0.25 mm, length 30 m)
temperature:
Inlet temperature: 200 ° C
Detector temperature: 350 ° C
Carrier gas: helium (column flow rate 1.39 mL / min)
Injection volume: 0.5 μL
Internal standard sample: Tridecane Diluent solvent: p-xylene Specifically, a calibration curve solution in which each monomer used for polymerization and tridecane were dissolved in p-xylene was prepared, and the solution was subjected to the above measurement conditions. A calibration curve was created from the peak areas obtained by gas chromatography. Next, a measurement sample was prepared by dissolving the polymer solution to be measured and tridecane in p-xylene, and the sample was measured by gas chromatography under the above measurement conditions. The content of the residual monomer in the polymerization solution was determined by a standard method, and the polymerization rate was calculated from the ratio to the monomer content before the start of the polymerization.
(Weight average molecular weight)
System: Tosoh GPC system HLC-8220
Measurement column configuration:
・ Guard column: TSKguardcolumn SuperHZ-L, manufactured by Tosoh
-Separation column: TSKgel SuperHZM-M, manufactured by Tosoh
Reference column configuration / Reference column: TSKgel SuperH-RC manufactured by Tosoh
Developing solvent: chloroform (Wako Pure Chemical Industries, special grade)
Flow rate of developing solvent: 0.6 mL / min Standard sample: TSK standard polystyrene (Tosoh, PS-oligomer kit)
Column temperature: 40 ° C
(Viscosity index)
The polymer was diluted with a base oil (YUBASE 4 manufactured by SK) so that the kinematic viscosity at 100 ° C. became 7.0 mm ² / s, and the measurement was performed according to the method of JIS K2283.
(Shear stability)
The polymer was diluted in a base oil (YUBASE 4 manufactured by SK) so that the kinematic viscosity at 100 ° C. became 7.0 mm ² / s, and the polymer was irradiated with ultrasonic waves under the following conditions.
Apparatus: UP400S manufactured by Hielscher Ultrasonics
Setting: Amplitude = 70%, Cycle = 1
Time: 5 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 It was calculated by the following equation.
(Odor)
Take 10 g of the liquid after the polymerization was completed in a 100 ml screw tube, cover and heat it at 120 ° C. for 1 hour. Then, remove the lid and check the odor. Was evaluated as ○.
(SP value)
The SP value (solubility parameter) of the polymer was measured using Materials Studio (registered trademark) Ver. 6.1 Calculated using MS-Synthia module. First, a monomer structure was created, and a repeating structure was defined. Using the defined monomer structure, polymer properties (solubility parameters and the like) were calculated using an MS-Synthia module. The MS-Synthia module is software that can calculate the physical properties of a polymer by using Quantitative Structure Properties Relationships (QSPR). The MS-Synthia module can convert a polymer structure from a monomer structure using a binding index obtained from graph theory. Physical properties can be calculated. The detailed theory is described in the following document, which is incorporated herein by reference: Jozef Bicerano, "Prediction of Polymer Properties, 3rd Edition", published by Marcel Dekker. In this case, of the SP values (solubility parameters) of the Fedors method and van Krevelen method improved by Bicerano that can be calculated by MS-Synthia, the value of the Fedors method was used.
(Example 1)
20 parts by mass of methyl methacrylate (MMA), 30 parts by mass of stearyl methacrylate (StMA), 10 parts by mass of N-phenylmaleimide (PMI) in a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introducing pipe, and a dropping funnel. Part, lauryl methacrylate / tridecyl methacrylate = 54/46 (mass ratio) mixture (SLMA) 40 parts by mass, base oil (YUBASE 4 manufactured by SK) 143.6 parts by mass, pentaerythritol tetrakis (mercaptoacetate) 0.05 part by mass The content was heated up to 105 ° C. while introducing nitrogen gas into it. A solution obtained by mixing 0.0774 parts by mass of t-amyl peroxy isononanoate (Lupelox (registered trademark) 570, manufactured by Arkema Yoshitomi Co., Ltd.) as a polymerization initiator and 1.38 parts by mass of a base oil (YUBASE 4 manufactured by SK) was used. A solution obtained by dissolving 0.034 parts by mass of the polymerization initiator in 3.40 parts by mass of base oil (YUBASE 4 manufactured by SK) was added dropwise over 2 hours, and the solution polymerization was allowed to proceed. Aging was performed.

  Subsequently, the cooling pipe was replaced with a C-shaped pipe connected to the cooling pipe and the distillate receiver, and 83.3 parts by mass of base oil (YUBASE 4 manufactured by SK) was charged into the reaction vessel. After the bath temperature was raised to 150 ° C., the pressure was gradually reduced using a vacuum pump to remove volatile components. After 30 minutes from the time when the internal temperature reached 142 ° C., the pressure was released and cooled to obtain a polymer base oil solution (polymer concentration: 30% by mass). Table 1 shows the results.

(Example 2)
In Example 1, the same operation was performed except that 10 parts by mass of PMI was changed to 10 parts by mass of cyclohexylmaleimide (CHMI), 25 parts by mass of MMA, and 35 parts by mass of SLMA, and a base oil solution (polymer (Coalescing concentration 30% by mass). Table 1 shows the results.
(Example 3)
20 parts by mass of MMA, 30 parts by mass of StMA, 10 parts by mass of PMI, 40 parts by mass of SLMA, base oil (YUBASE 4 manufactured by SK) 61.2 were placed in a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe, and a dropping funnel. Parts by mass and 0.05 parts by mass of pentaerythritol tetrakis (mercaptoacetate) were charged, and the content was heated to 105 ° C. while introducing nitrogen gas into the mixture. A solution prepared by mixing 0.0258 parts by mass of t-amyl peroxyisononanoate (Lupelox (registered trademark) 570, manufactured by Arkema Yoshitomi Co., Ltd.) and 0.46 parts by mass of a base oil (YUBASE 4 manufactured by SK) as a polymerization initiator was used. Along with the addition, a solution in which 0.205 parts by mass of the polymerization initiator was dissolved in 10.3 parts by mass of the base oil was added dropwise over 4 hours to proceed the solution polymerization, and aging was further performed for 4 hours.

  Subsequently, the cooling pipe was replaced with a C-shaped pipe connected to the cooling pipe and the distillate receiver, and 166.6 parts by mass of base oil (YUBASE 4 manufactured by SK) was charged into the reaction vessel. After the bath temperature was raised to 150 ° C., the pressure was gradually reduced using a vacuum pump to remove volatile components. After 30 minutes from the time when the internal temperature reached 142 ° C., the pressure was released and cooled to obtain a polymer base oil solution (polymer concentration: 30% by mass). Table 1 shows the results.

(Comparative Example 1)
20 parts by mass of MMA, 30 parts by mass of StMA, 10 parts by mass of PMI, 40 parts by mass of SLMA, an antioxidant (ADEKA STAB (registered trademark) 2112, ADEKA), 0.05 parts by mass of acetic anhydride, 0.4 parts by mass of acetic anhydride, 0.05 parts by mass of pentaerythritol tetrakis (mercaptoacetate), and 60.8 parts by mass of toluene. The contents were heated to 105 ° C. As a polymerization initiator, a solution prepared by mixing 0.0258 parts by mass of t-amyl peroxyisononanoate (Lupelox (registered trademark) 570, manufactured by Arkema Yoshitomi) with 0.46 parts by mass of toluene was added, and the polymerization was started. A solution prepared by dissolving 0.205 parts by mass of the agent in 20.5 parts by mass of toluene was added dropwise over 4 hours to advance solution polymerization, and aging was further performed for 4 hours.

  Subsequently, the cooling pipe was replaced with a C-shaped pipe connected to the cooling pipe and the distillate receiver, and 233 parts by mass of base oil (YUBASE 4 manufactured by SK) was charged into the reaction vessel. After the bath temperature was raised to 150 ° C., the pressure was gradually reduced using a vacuum pump to remove toluene. After 30 minutes from the time when the internal temperature reached 142 ° C., the pressure was released and cooled to obtain a polymer base oil solution (polymer concentration: 30% by mass). Table 1 shows the results.

(Comparative Example 2)
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen inlet pipe, and a dropping funnel, 25 parts by weight of MMA, 40 parts by weight of StMA, 10 parts by weight of PMI, 25 parts by weight of SLMA, an antioxidant (ADEKA STAB (registered trademark) 2112, ADEKA), 0.05 parts by mass, acetic anhydride 0.40 parts by mass, n-dodecyl mercaptan 0.05 parts by mass, and toluene 27.4 parts by mass. The temperature was raised to 105 ° C. As a polymerization initiator, a solution prepared by mixing 0.0258 parts by mass of t-amyl peroxyisononanoate (Lupelox (registered trademark) 570, manufactured by Arkema Yoshitomi) with 0.46 parts by mass of toluene was added, and the polymerization was started. A solution in which 0.103 parts by mass of the agent was dissolved in 10.3 parts by mass of toluene was added dropwise over 4 hours to advance solution polymerization, and aging was further performed for 4 hours.

  Subsequently, the cooling pipe was replaced with a C-shaped pipe connected to the cooling pipe and the distillate receiver, and 233 parts by mass of base oil (YUBASE 4 manufactured by SK) was charged into the reaction vessel. After the bath temperature was raised to 150 ° C., the pressure was gradually reduced using a vacuum pump to remove toluene. The pressure was released and cooled 30 minutes after the internal temperature reached 142 ° C., to obtain a polymer base oil solution (polymer concentration: 30% by mass). Table 1 shows the results.

(Comparative Example 3)
In Comparative Example 2, the same operation was performed except that acetic anhydride was not added, to obtain a polymer base oil solution (polymer concentration: 30% by mass). Table 1 shows the results.

  When polymerization was carried out in Examples, a high polymerization rate was exhibited without using an acid component.When the obtained copolymer was used as a viscosity index improver, a high viscosity index and sufficient shear stability were obtained. showed that.

  By using the production method of the present invention, a maleimide-based copolymer can be obtained at a high polymerization rate without fear of odor and corrosion. A lubricating oil composition using a viscosity index improver containing the obtained copolymer exhibits a high viscosity index and sufficient shear stability, and can meet the demands for future fuel economy and long life of automobiles. Therefore, it can be suitably used for drive system lubricating oil, hydraulic oil, and engine oil.

Claims (6)

A method for producing a copolymer, comprising a step of polymerizing a monomer containing a maleimide-based monomer (hereinafter, referred to as “component (a)”) as an essential component in a lubricating base oil to obtain a polymer. When a styrene monomer is used, the amount of the unit derived from the styrene monomer is 2 parts by mass or less based on 100 parts by mass of the polymer . The method for producing a copolymer according to claim 1, wherein the content of the component (a) is 5 parts by mass or more and 35 parts by mass or less based on 100 parts by mass in total of all the monomer components. In addition to the component (a), (b) an alkyl (meth) acrylate having an aliphatic hydrocarbon group having 1 to 5 carbon atoms, (c) an alkyl (having an aliphatic hydrocarbon group having 6 to 40 carbon atoms) method for producing a copolymer according to claim 1 or 2 characterized by having a step of polymerizing the monomer containing meth) acrylate with a lubricating oil base oil. One of claims 1 to 3 in which the trifunctional or higher polyhydric mercaptan and / or 3, wherein the presence of functional or higher polyfunctional initiator monomer and characterized as having a step of polymerizing with a lubricating oil base oil The method for producing a copolymer according to claim 1 . A copolymer manufacturing process for manufacturing a co-polymer in the production method according to any one of claims 1-4,
Producing a viscosity index improver containing 70% by mass or more of the copolymer obtained in the copolymer production step;
A method for producing a viscosity index improver, comprising: A viscosity index improver producing step of producing a viscosity index improver by the production method according to claim 5 ,
Mixing the viscosity index improver obtained in the viscosity index improver manufacturing step with a base oil to produce a lubricating oil composition;
A method for producing a lubricating oil composition, comprising: