JP2018162433A - Viscosity index-improving agent and lubricating oil composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a viscosity index-improving agent having a high viscosity index and good shear stability and having a high fluidity at around a room temperature when used as base oil solution thereby handled easily, and a lubricating oil composition using the same.SOLUTION: A viscosity index-improving agent of the present invention comprises a copolymer comprising a unit (a) derived from a maleimide monomer and a unit (b) derived from a macromonomer. A base oil solution which accounts for 22 mass% of concentration of the copolymer has a viscosity of 8000 mPa s or less.SELECTED DRAWING: None

Description

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

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

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

  Examples of means for improving the shear stability include reducing the molecular weight of the polymer contained in the viscosity index improver. In general, the lower the molecular weight of the polymer, the less affected by shearing, and the lowering of the molecular weight decreases, so the use of a low molecular weight polymer as a viscosity index improver can suppress a decrease in viscosity after shearing. Yes (Patent Document 1 and Non-Patent Document 1). In addition, a report of trying to improve shear stability with a polymer having a star-shaped structure using divinylbenzene in the core (Patent Document 2), a report using a comb-shaped polymer as a component of a lubricating oil composition. (Patent Documents 3 and 4).

JP 2013-104032 A JP 2012-197399 A Special table 2010-532805 gazette Special table 2012-520358 gazette

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

  However, generally, the lower the molecular weight of the polymer, the lower the viscosity index improving effect. Therefore, when a low molecular weight polymer is used as a viscosity index improver, the problem that the viscosity index decreases is generated. Furthermore, in order to adjust to a desired viscosity, it is necessary to increase the usage-amount of a viscosity index improver, and it tends to be disadvantageous in terms of cost. The lubricating oil composition includes a lubricating base oil, various additives, a viscosity index improver, and the like. Among these, the viscosity index improver is generally handled as a base oil composition dissolved in the base oil. When the viscosity index improver concentration in the base oil composition is high, not only the degree of freedom of blending when making the lubricating oil composition is increased, but the amount of lubricating base oil used per unit mass in the viscosity index improver This is advantageous in terms of manufacturing and transportation costs, but the viscosity of the base oil composition is increased, making it difficult to handle near room temperature, and when mixing and dissolving with other components, heating and special Equipment may be required and productivity may be reduced.

  The present invention has been made in view of the above problems, and its purpose is to have a high viscosity index and good shear stability, and when it is used as a base oil solution, it has high fluidity near room temperature and is easy to handle. And a lubricating oil composition using the viscosity index improver.

The viscosity index improver of the present invention that has solved the above problems is a viscosity index containing a copolymer having units (a) derived from maleimide monomers and units (b) derived from macromonomers. It is an improver and is characterized in that the viscosity measured by the following method is 8000 mPa · s or less.
(Viscosity measurement)
A solution consisting of 78% by mass of Group III base oil (viscosity index 122, kinematic viscosity 19.6 mm ² / s) in the American Petroleum Institute (API) classification and 22% by mass of the copolymer was converted into a viscometer Sangyo Co., Ltd., TVB-10, rotor: SPINDLE No. M3, 6 rpm, measured at 25 ° C.

  In the viscosity index improver of the present invention, the content of the unit (a) is preferably 1 part by mass or more and 20 parts by mass or less in 100 parts by mass of the copolymer.

  In the viscosity index improver of the present invention, the content of the macromonomer is preferably 18 parts by mass or less with respect to 100 parts by mass of the macromonomer-derived unit (b) and the macromonomer.

  The copolymer preferably has a weight average molecular weight (Mw) of 200,000 to 700,000 and a number average molecular weight (Mn) of 120,000 to 500,000.

  It is preferable that the copolymer further has a unit (c) derived from alkyl (meth) acrylate and having 1 to 6 carbon atoms in the alkyl group of the alkyl (meth) acrylate, and the copolymer has a mass of 100 mass. Part, the content of the unit (b) is 6 parts by mass or more and less than 20 parts by mass, the content of the unit (c) is 40 parts by mass or more and less than 74 parts by mass, the unit (b) and the unit (c). The total content of is preferably 46 parts by mass or more and less than 80 parts by mass. The copolymer also has a unit (d) derived from alkyl (meth) acrylate, wherein the alkyl group of the alkyl (meth) acrylate has 11 to 40 carbon atoms, and 100 parts by mass of the copolymer Among them, the content of the unit (d) is also preferably 3 parts by mass or more and 40 parts by mass or less. The unit (b) of the copolymer preferably has a urethane bond in the monomer.

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

  When the viscosity index improver of the present invention is used, a high viscosity index and good shear stability can be obtained when a base oil solution is obtained. Further, the base oil solution of the viscosity index improver of the present invention has high fluidity near room temperature and is easy to handle, so that workability and productivity in preparing a lubricating oil composition are improved.

[1. (Viscosity index improver)
The viscosity index improver of the present invention contains a copolymer having units (a) derived from maleimide monomers and units (b) derived from macromonomers. The viscosity index improver of the present invention contains a copolymer having units (a) and (b), so that it has excellent solubility in base oil, and is high when used as a base oil solution. In addition to exhibiting a viscosity index, shear stability can also be improved. Therefore, if the viscosity index improver of the present invention is used, it is possible to improve both the viscosity index and the shear stability which are in a contradictory relationship with the molecular weight of the polymer. Further, the viscosity index improver of the present invention has high fluidity and excellent handling properties when used as a base oil solution.

  The copolymer used for the viscosity index improver of the present invention can be obtained by copolymerizing a maleimide monomer and a macromonomer, but by copolymerizing the macromonomer with the maleimide monomer. In addition, the residual amount of unreacted monomers, particularly macromonomers whose polymerization rate tends to decrease greatly upon copolymerization can be suppressed, and the polymerization rate can be increased. Macromonomers generally have low copolymerizability relative to other monomers and tend to decrease the polymerization rate, but in this case, macromonomer-derived units are not efficiently introduced into the copolymer. There is a discrepancy between the charge composition at the time of copolymerization (that is, the design composition of the copolymer) and the composition of the actually obtained copolymer, and the viscosity characteristics of the copolymer and the viscosity index improver containing the copolymer. And durability and base oil solubility are likely to decrease. On the other hand, there is a possibility that such performance degradation can be reduced by using the macromonomer in excess of the design composition, but the amount of unreacted macromonomer remaining in the system increases, which is the cause. There remains concern that the viscosity properties will change. Further, since the macromonomer is relatively more expensive than the other monomers, the cost of the copolymer and the viscosity index improver containing it is undesirably high. However, by copolymerizing the macromonomer with the maleimide monomer, it is possible to efficiently introduce macromonomer-derived units into the copolymer, facilitating the production of the copolymer, and each unit of the copolymer. The composition control of the monomer component is also facilitated. When using the reaction liquid subjected to the polymerization reaction as a viscosity index improver, it is possible to prevent the viscosity characteristics of the viscosity index improver from greatly changing due to the influence of unreacted monomer components (particularly macromonomers).

  The copolymer contained in the viscosity index improver has a succinimide ring structure in the main chain of the copolymer as a unit (a) derived from a maleimide monomer. By introducing a ring structure into the main chain of the copolymer, the shear stability and heat resistance of the viscosity index improver can be enhanced while ensuring the solubility of the viscosity index improver in the base oil. Furthermore, when a lubricating oil composition is used, effects such as improvement in the clean dispersibility of sludge and the like and suppression of wear on the metal surface are expected. The unit (a) can be introduced into the copolymer by copolymerizing a maleimide optionally having a substituent at the N-position with a monomer component such as a macromonomer.

The unit (a) is preferably a unit represented by the following formula (1). In formula (1), R ¹ and R ² each independently represents a hydrogen atom or an alkyl group, and R ³ represents a hydrogen atom or an organic group having 1 to 40 carbon atoms.

The alkyl group of R ¹ and R ² in Formula (1) preferably has 1 to 8 carbon atoms, more preferably 1 to 4 carbon atoms, and still more preferably 1 to 3 carbon atoms. R ¹ and R ² are more preferably a hydrogen atom, a methyl group or an ethyl group, and even more preferably a hydrogen atom or a methyl group.

Examples of the organic group represented by R ^{3 in} the formula (1) include an alkyl group, an aryl group, an aralkyl group, a group in which a part of —CH ₂ — contained in the alkyl group is replaced by —O—, and the like. A substituent such as a hydroxyl group, a halogen group, a nitro group, an alkyl group (in the case of an aryl group or an aralkyl group), an alkoxy group, or a carboxy group may be bonded to the group. The organic group of R ³ preferably has 1 to 24 carbon atoms, more preferably 1 to 18 carbon atoms, and still more preferably 1 to 12 carbon atoms from the viewpoint of increasing the solubility of the viscosity index improver in the base oil.

Examples of the alkyl group for R ³ include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group, isopentyl group, n-hexyl group, isohexyl group. Linear or branched alkyl groups such as xyl group, n-heptyl group, isoheptyl group, n-octyl group, 2-ethylhexyl group, cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cyclononyl group, Examples thereof include cyclic alkyl groups such as a cyclodecyl group, a dicyclopentanyl group, and an adamantyl group. Examples of the aryl group for R ³ include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and a biphenyl group. Examples of the aralkyl group for R ³ include a benzyl group and a naphthylmethyl group. Examples of the group in which a part of —CH ₂ — contained in the alkyl group of R ³ is replaced by —O— include polyoxyalkylene groups such as a polyoxyethylene group and a polyoxypropylene group. From the viewpoint of easily improving the shear stability of the viscosity index improver, R ³ is preferably an aryl group. From the viewpoint of easily improving the viscosity index, R ³ is cycloalkyl. It is preferably a group.

  Specific examples of the maleimide monomer that provides the unit (a) derived from the maleimide monomer include, for example, maleimide, N-methylmaleimide, N-isopropylmaleimide, N-butylmaleimide, N-isobutylmaleimide, N- t-butylmaleimide, N-cyclohexylmaleimide, N-octylmaleimide, N-2-ethylhexylmaleimide, N-decylmaleimide, N-laurylmaleimide, N-tetradecylmaleimide, N-stearylmaleimide, N-2-decyltetradecyl Maleimide, N-phenylmaleimide, N-benzylmaleimide, N-chlorophenylmaleimide, N-methylphenylmaleimide, N-naphthylmaleimide, N-hydroxylethylmaleimide, N-hydroxylphenylmaleimide, N-methoxyph Cycloalkenyl maleimide, N- carboxyphenyl maleimide, N- nitro-phenyl maleimide, N- tribromophenyl maleimide and the like. Among these, N-phenylmaleimide, N-cyclohexylmaleimide can be used as the maleimide monomer from the viewpoint of easy availability of maleimide monomers and ease of improving the base oil solubility of the viscosity index improver. N-isopropylmaleimide, N-benzylmaleimide, N-laurylmaleimide, and N-stearylmaleimide are preferable. Among these, N-phenylmaleimide is preferable as the maleimide monomer from the viewpoint of improving the shear stability of the viscosity index improver, and N-cyclohexylmaleimide is preferable from the viewpoint of improving the viscosity index.

  The copolymer may contain only one type of maleimide monomer-derived unit (a), or may contain two or more types.

  The content of the unit (a) in the copolymer is preferably 1 part by mass or more, more preferably 2 parts by mass or more, further preferably 3 parts by mass or more, and 20 parts by mass or less in 100 parts by mass of the copolymer. Is preferably 15 parts by mass or less, and more preferably 10 parts by mass or less. The copolymer contains a unit (b) derived from a macromonomer. By containing the unit (a) in such a content in the copolymer, the monomer component is copolymerized and copolymerized. When manufacturing a polymer, the polymerization rate of the macromonomer which brings a unit (b) improves, and the residual amount of a macromonomer can be suppressed. In addition, the solubility of the copolymer in the base oil is improved, and when it is used as a base oil solution, it has a high viscosity index, and can improve the shear stability, has high fluidity and excellent handling properties. It becomes.

  The unit (b) derived from the macromonomer is a structural unit that can be introduced into the copolymer by copolymerizing the macromonomer. As the macromonomer, any polymer having a polymerizable functional group can be used without particular limitation, but has a repeating structure derived from a hydrocarbon monomer from the viewpoint of enhancing the base oil solubility of the copolymer. Is preferred. Examples of the hydrocarbon monomer include ethylene, propylene, 1-butene, isobutene, 1-tetradecene, 1-octadecene and other monoolefins; 1,3-butadiene, 2-methyl-1,3-butadiene, 1, Alkadienes such as 3-pentadiene, 1,4-pentadiene, 1,5-hexadiene, 2,5-dimethyl-1,5-hexadiene (also called diisobutene); styrene-based units such as styrene, α-methylstyrene, vinyltoluene Examples include a polymer. The alkadienes preferably complete the polymerization reaction with one remaining ethylenic carbon-carbon double bond, and this unreacted ethylenic carbon-carbon double bond portion is hydrogenated after polymerization. Is preferred. As the hydrocarbon monomer, monoolefins, alkadienes and the like are preferable, and the carbon number of these monoolefins and alkadienes is preferably about 2 to 20, more preferably about 2 to 10. 3 to 6 is more preferable.

As the unit (b) derived from the macromonomer, those represented by the following formula (2) are preferable from the viewpoint of easy production and availability of the macromonomer. In the following formula (2), R ⁴ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X ¹ is a single bond, an alkylene group, —O—, —CO—, —NH— or a combination thereof. R ⁵ represents a macromolecular structure of a macromonomer.

The alkyl group having 1 to 4 carbon atoms R ⁴ of formula (2), a methyl group, an ethyl group, a propyl group, an isopropyl group, n- butyl group, an isobutyl group, and a t- butyl group and the like are. The carbon number of the alkyl group of R ⁴ is more preferably 1 to 3, 1 to 2 is more preferred. Of these, R ⁴ is preferably a hydrogen atom or a methyl group.

When X ^{1 in} formula (2) is a single bond, the polymer structure of R ⁵ is directly bonded to the ester group in formula (2), and X ^{1 in} formula (2) is a linking group such as an alkylene group. In this case, the polymer structure part of R ⁵ is bonded to the ester group of the formula (2) through a linking group. When an alkylene group is contained in the linking group for X ^1, the alkylene group is preferably linear or branched, and the number of carbon atoms is preferably 1 to 6, more preferably 1 to 4, and more preferably 1 to 3. Is more preferable. The linking group for X ¹ includes an ester bond (—CO—O—), an amide bond (—CO—NH—), a urethane bond (—NH—CO—O—), etc., other than those containing an alkylene group. X ¹ includes one or two or more selected from these bonds from the viewpoint that the viscosity of the base oil solution of the viscosity index improver is lowered at around room temperature and handling properties are improved. Those having a urethane bond are particularly preferred.

The polymer structure portion of R ^{5 in} the formula (2) preferably includes a repeating structure derived from a hydrocarbon monomer, and examples of the hydrocarbon monomer include those exemplified above. The polymer structure portion is preferably a hydrocarbon group, specifically, a polymer of monoolefins and / or alkadienes, and if the unsaturated bond remains after polymerization, the unsaturated structure More preferably, the bond is hydrogenated. Since such a preferable polymer structure part is formed of carbon and hydrogen as a whole, it is referred to as a macro hydrocarbon group in the present specification. Similarly, when an unsaturated bond is not included, it is called a macroalkyl group.

  The macro hydrocarbon group or macroalkyl group may be linear or branched, but it suppresses crystallization at low temperatures when used as a viscosity index improver and prevents thickening. From the viewpoint, it is preferably branched. The branched macrohydrocarbon group or macroalkyl group preferably includes a branched alkylene group as a repeating unit, and includes both a branched alkylene group and a linear alkylene group as a repeating unit. Is more preferable. Examples of the branched alkylene group include 1,2-propylene group, 1,2-butylene group, 1,3-butylene group, 2,3-butylene group, 1,2-hexylene group and the like. Examples of the linear alkylene group include ethylene, 1,3-propylene group, 1,4-butylene group, 1,5-pentylene group, 1,6-hexylene group and the like.

  The copolymer may contain only one type of macromonomer-derived unit (b), or may contain two or more types.

The number average molecular weight of the unit (b) derived from the macromonomer is preferably 500 or more, more preferably 1000 or more, further preferably 1500 or more, and more preferably 2000 or more, from the viewpoints of base oil solubility, viscosity index, and shear stability. More preferably, it is preferably 50000 or less, more preferably 20000 or less, and still more preferably 10,000 or less. In the unit represented by the above formula (2), the number of carbon atoms of the hydrocarbon group of R ⁵ is preferably 35 or more, more preferably 50 or more, still more preferably 70 or more, still more preferably 100 or more, Moreover, 3500 or less are preferable, 1500 or less are more preferable, and 700 or less are further more preferable.

  The content of the unit (b) in the copolymer is preferably 6 parts by mass or more, more preferably 7 parts by mass or more, further preferably 8 parts by mass or more, and less than 20 parts by mass in 100 parts by mass of the copolymer. Is preferable, 18 mass parts or less are more preferable, and 16 mass parts or less are more preferable. If the copolymer contains the unit (b) in such a content, the base oil solubility of the viscosity index improver can be enhanced, and the shear stability can be enhanced.

  The viscosity index improver preferably has a macromonomer content of 18 parts by mass or less, and more preferably 16 parts by mass or less, with respect to 100 parts by mass in total of the unit (b) and the macromonomer. That is, it is preferable that the viscosity index improver does not have much macromonomer that gives the unit (b). The viscosity index improver of the present invention can be produced, for example, by blending a reaction solution obtained by polymerization reaction with a base oil or other additives, and a maleimide monomer and a macromonomer during the polymerization reaction. , The residual amount of unreacted macromonomer can be suppressed. Therefore, the viscosity index improver obtained in this way is suppressed from greatly changing the viscosity characteristics of the viscosity index improver due to a large amount of unreacted macromonomer remaining, base oil solubility, viscosity index, It is excellent in shear stability and handling properties when used as a base oil solution. The total amount of the unit (b) and the macromonomer is equal to the total amount of the macromonomer charged into the polymerization system and the macromonomer charged into the polymerization system, and the content of the macromonomer is determined by the method described in the examples.

  The copolymer contained in the viscosity index improver may have a unit (c) derived from alkyl (meth) acrylate and having 1 to 6 carbon atoms in the alkyl group. The unit (c) can be introduced into the copolymer by copolymerizing an alkyl (meth) acrylate having 1 to 6 carbon atoms in the alkyl group with the macromonomer described above.

The unit (c) is preferably a unit represented by the following formula (3). In formula (3), R ⁶ represents a hydrogen atom or a methyl group, and R ⁷ represents an alkyl group having 1 to 6 carbon atoms.

Examples of the alkyl group having 1 to 6 carbon atoms of R ^{7 in} the formula (3) include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a pentyl group, and a hexyl group. And a linear or branched alkyl group, and a cyclic alkyl group such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. The alkyl group for R ⁷ is preferably linear or cyclic, and more preferably linear. The number of carbon atoms in the alkyl group represented by R ⁷ is preferably 2 or more, preferably 5 or less, more preferably 4 or less, and more preferably 5 or more if it is cyclic. Among them, the alkyl group of R ⁷ is a butyl group or a cyclohexyl group from the viewpoint of easy availability of alkyl (meth) acrylate that gives the unit (c) and excellent viscosity index improver near room temperature. Are preferable, and an n-butyl group or an isobutyl group is more preferable.

  The copolymer may contain only one type of unit (c) derived from an alkyl (meth) acrylate having 1 to 6 carbon atoms in the alkyl group, or may contain two or more types.

  The content of the unit (c) in the copolymer may be 0 part by mass or more in 100 parts by mass of the copolymer. When the copolymer contains the unit (c), the content is preferably 40 parts by mass or more, more preferably 45 parts by mass or more, further preferably 50 parts by mass or more, and even more preferably 55 parts by mass or more. If the unit (c) is contained in such a content, the viscosity index of the base oil solution of the viscosity index improver is improved, and the shear stability of the viscosity index improver is also improved. On the other hand, the content of the unit (c) in the copolymer is preferably less than 74 parts by mass, more preferably 72 parts by mass or less, still more preferably 70 parts by mass or less, and 68 parts by mass in 100 parts by mass of the copolymer. The following are even more preferred: If unit (c) is contained with such content, the solubility to the base oil of a viscosity index improver can be improved.

  In addition, while increasing the viscosity index of the base oil solution of the viscosity index improver and increasing the shear stability of the viscosity index improver, the total content of units (b) and units (c) in the copolymer is: In 100 parts by mass of the copolymer, it is preferably 46 parts by mass or more, more preferably 50 parts by mass or more, further preferably 53 parts by mass or more, still more preferably 56 parts by mass or more, and particularly preferably 60 parts by mass or more. . Moreover, from the point which improves the base oil solubility of a viscosity index improver, the total content of the unit (b) and the unit (c) is preferably less than 80 parts by mass in 100 parts by mass of the copolymer, and 79 parts by mass or less. Is more preferable.

  The copolymer contained in the viscosity index improver may have a unit (d) derived from alkyl (meth) acrylate and having 11 to 40 carbon atoms in the alkyl group. By including the unit (d) in the copolymer, it becomes easy to increase the solubility of the viscosity index improver in the base oil. The unit (d) can be introduced into the copolymer by copolymerizing an alkyl (meth) acrylate having an alkyl group having 11 to 40 carbon atoms with the macromonomer described above.

The unit (d) is preferably a unit represented by the following formula (4). In formula (4), R ⁸ represents a hydrogen atom or a methyl group, and R ⁹ represents an alkyl group having 11 to 40 carbon atoms.

As the alkyl group having 11 to 40 carbon atoms of R ^{9 in} the formula (4), undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, icosyl group, tetracosyl group Group, a linear or branched alkyl group such as 2-decyltetradecyl group, and a cyclic alkyl group such as cycloheptyl group, cyclooctyl group, cyclononyl group, cyclodecyl group, dicyclopentanyl group, adamantyl group, etc. Etc. The alkyl group for R ⁹ is preferably linear or branched, and more preferably linear. The number of carbon atoms is preferably 12 or more, more preferably 14 or more, and preferably 35 or less, more preferably 30 or less.

  The copolymer may contain only one type (d) derived from an alkyl (meth) acrylate having 11 to 40 carbon atoms in the alkyl group, or may contain two or more types.

  Content of the unit (d) in a copolymer should just be 0 mass part or more in 100 mass parts of copolymers. When the copolymer contains the unit (d), the content thereof is preferably 3 parts by mass or more, more preferably 6 parts by mass or more, further preferably 10 parts by mass or more, in 100 parts by mass of the copolymer. It is preferably 40 parts by mass or less, more preferably 35 parts by mass or less, and further preferably 30 parts by mass or less. If the unit (d) is contained in the copolymer with such a content, it becomes easy to increase the solubility of the viscosity index improver in the base oil.

  The total content of unit (a), unit (b), unit (c) and unit (d) in the copolymer is preferably 49 parts by mass or more, and 50 parts by mass or more in 100 parts by mass of the copolymer. More preferably, 60 parts by mass or more is further preferable, 70 parts by mass or more is further more preferable, and 80 parts by mass or more is particularly preferable. The upper limit of the total content of the unit (a), the unit (b), the unit (c) and the unit (d) in the copolymer is not particularly limited, and the copolymer is substantially composed of the unit (a) and the unit ( b), unit (c) and unit (d) may be used alone, and the total content of unit (a), unit (b), unit (c) and unit (d) in the copolymer may be In 100 parts by mass of the copolymer, it may be 98 parts by mass or less, or 95 parts by mass or less.

  The copolymer contained in the viscosity index improver may have a unit derived from a monomer other than the units (a) to (d) described above (hereinafter referred to as “unit (e)”). Good. The units (a) to (d) can be introduced as constituent units of the copolymer by radical copolymerization of the corresponding maleimide monomers, macromonomers, and alkyl (meth) acrylates. (E) is also preferably a unit derived from a radical polymerizable monomer. The radical polymerizable monomer forming the unit (e) includes a monofunctional monomer having one radical polymerizable group in the molecule and a polyfunctional monomer having two or more radical polymerizable groups in the molecule. Can be classified as body.

  Examples of monofunctional monomers include units (c) and (meth) acrylates other than alkyl (meth) acrylates forming units (d), unsaturated mono- or dicarboxylic esters, unsaturated carboxylic acids, vinyl aromatics. Examples thereof include compounds, vinyl esters, vinyl ethers, olefins, vinyl cyanide and N-vinyl compounds. The unit (e) formed from these monofunctional monomers may be only one type or two or more types.

  Examples of the (meth) acrylate other than the alkyl (meth) acrylate forming the unit (c) and the unit (d) include benzyl (meth) acrylate, phenyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2 -Hydroxybutyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, morpholinoalkylene (meth) acrylate, α-hydroxymethylacrylic Examples include methyl acid and polyethylene glycol mono (meth) acrylate.

Examples of the unsaturated mono- or dicarboxylic acid ester include butyl crotonate, octyl crotonate, dibutyl maleate, dilauryl maleate, dioctyl fumarate, distearyl fumarate and the like.
Examples of the unsaturated carboxylic acids include (meth) acrylic acid, maleic acid, fumaric acid, maleic anhydride and the like.
Examples of the vinyl aromatic compound include styrene monomers such as styrene, α-methylstyrene, vinyltoluene, and methoxystyrene, 2-vinylpyridine, 4-vinylpyridine, and the like.
Examples of the vinyl ester include vinyl acetate, vinyl propionate, vinyl octylate and the like.
Examples of the vinyl ether include methyl vinyl ether, butyl vinyl ether, octyl vinyl ether, dodecyl vinyl ether and the like.
Examples of olefins include ethylene, propylene, 1-butene, isobutene, 1-tetradecene, 1-octadecene, diisobutene and the like.
Examples of vinyl cyanide include acrylonitrile and methacrylonitrile.
Examples of the N-vinyl compound include N-vinyl pyrrolidone, N-vinyl caprolactam, N-vinyl imidazole, N-vinyl morpholine, N-vinyl acetamide and the like.

  Among these monofunctional monomers, the unit (e) is preferably a (meth) acrylate or N-vinyl compound other than the alkyl (meth) acrylate that forms the unit (c) or the unit (d). Hydroxyethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, methyl α-hydroxymethyl acrylate, and N-vinylpyrrolidone are particularly preferred.

  Examples of the polyfunctional monomer forming the unit (e) include polyfunctional (meth) acrylate, vinyl ether group-containing (meth) acrylate, allyl group-containing (meth) acrylate, and polyfunctional (meth) acryloyl group-containing isocyanurate. And polyfunctional (meth) acrylic compounds such as polyfunctional urethane (meth) acrylates, polyfunctional maleimide compounds, polyfunctional vinyl ethers, polyfunctional allyl compounds, polyfunctional aromatic vinyls, and the like. The unit (e) formed from these polyfunctional monomers may be only one type or two or more types.

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

Examples of the vinyl ether group-containing (meth) acrylate include 2-vinyloxyethyl (meth) acrylate, 4-vinyloxybutyl (meth) acrylate, 2- (vinyloxyethoxy) ethyl (meth) acrylate, and the like.
Examples of the allyl group-containing (meth) acrylate include, for example, allyl (meth) acrylate, methyl α-allyloxymethyl acrylate, stearyl α-allyloxymethyl acrylate, α-allyloxymethyl acrylate 2-decyltetradecyl etc. Is mentioned.
Examples of the polyfunctional (meth) acryloyl group-containing isocyanurate include tri (acryloyloxyethyl) isocyanurate, tri (methacryloyloxyethyl) isocyanurate, and the like.
Examples of the polyfunctional urethane (meth) acrylate 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. The polyfunctional urethane (meth) acrylate obtained by reaction with containing (meth) acrylic acid ester, etc. are mentioned.

Examples of the polyfunctional maleimide compound include 4,4′-diphenylmethane bismaleimide, m-phenylene bismaleimide, bisphenol A diphenyl ether bismaleimide, 1,6-bismaleimide- (2,2,4-trimethyl) hexane, and the like. Can be mentioned.
Examples of the polyfunctional vinyl ether include ethylene glycol divinyl ether, diethylene glycol divinyl ether, polyethylene glycol divinyl ether, hexanediol divinyl ether, bisphenol A alkylene oxide divinyl ether, trimethylolpropane trivinyl ether, and the like.
Examples of polyfunctional allyl compounds include ethylene glycol diallyl ether, diethylene glycol diallyl ether, polyethylene glycol diallyl ether, hexanediol diallyl ether, bisphenol A alkylene oxide diallyl ether, trimethylolpropane triallyl ether, ditrimethylolpropane tetraallyl ether, and the like. Polyfunctional allyl ethers; polyfunctional allyl group-containing isocyanurates such as triallyl isocyanurate; polyfunctional allyl esters such as diallyl phthalate and diallyl diphenate; bisallyl nadiimide compounds; bisallyl nadiimide compounds and the like .
Examples of the polyfunctional aromatic vinyl include divinylbenzene.

  Content of the unit (e) in a copolymer should just be 0 mass part or more in 100 mass parts of copolymers. When the copolymer contains the unit (e), the content thereof is preferably 1 part by mass or more, more preferably 2 parts by mass or more, further preferably 3 parts by mass or more, in 100 parts by mass of the copolymer. 50 parts by mass or less is preferable, 40 parts by mass or less is more preferable, 30 parts by mass or less is further preferable, 20 parts by mass or less is even more preferable, and 10 parts by mass or less is particularly preferable.

  In addition, it is preferable that a copolymer does not contain many units derived from a styrenic monomer. This is because when the content of the unit derived from the styrene monomer is increased, the solubility of the viscosity index improver in the base oil is likely to be lowered, and the viscosity index is likely to be lowered. Therefore, in 100 parts by mass of the copolymer, the content of the unit derived from the styrene monomer is preferably less than 3 parts by mass, more preferably 2 parts by mass or less, and further preferably 1 part by mass or less. Styrene monomers include not only styrene but also those having a substituent bonded to the benzene ring or vinyl group of styrene, such as styrene, α-methylstyrene, vinyltoluene, and methoxystyrene.

  In addition, vinyl ethers, olefins, and the like are less radically copolymerizable with (meth) acrylates, so from the viewpoint of ease of production of the copolymer, the copolymer may not contain many units derived from these. preferable. For example, the total content of these monomer-derived units (e) is preferably 5 parts by mass or less and more preferably 3 parts by mass or less with respect to 100 parts by mass of the copolymer.

  The content of the unit (e) derived from the polyfunctional monomer in the copolymer is preferably 0 part by mass or more and 5 parts by mass or less, more preferably 3 parts by mass or less, in 100 parts by mass of the copolymer. Part or less is more preferable. When the content of the unit derived from the polyfunctional monomer exceeds the above range, gelation proceeds during polymerization, or the solubility of the viscosity index improver containing the copolymer in the base oil decreases. There is.

  However, 2,2 ′-[oxybis (methylene)] bisacrylic acid, dialkyl-2,2 ′-[oxybis (methylene)] bis-2-propenoate, methyl α-allyloxymethyl acrylate, α-allyloxymethyl In the case of a polyfunctional monomer in which polymerization proceeds while cyclizing, such as stearyl acrylate and α-allyloxymethyl acrylate 2-decyltetradecyl, the unit derived from the polyfunctional monomer in the copolymer The content of may be 0 to 30 parts by mass, 20 or less parts by mass, or 15 or less parts by mass with respect to 100 parts by mass of the copolymer. In this case, the effect of the ring structure introduced into the main chain can improve the heat resistance of the viscosity index improver and improve the shear stability.

  The copolymer contained in the viscosity index improver may have a branch unit derived from a polyfunctional chain transfer agent or a polyfunctional polymerization initiator. If the copolymer has such a branch unit, the shear stability of the viscosity index improver can be improved without greatly impairing the solubility of the viscosity index improver in the base oil.

As the polyfunctional chain transfer agent, a trifunctional or higher polyvalent mercaptan is preferably used. When such a chain transfer agent is used for radical copolymerization of a monomer component, a branch represented by the following formula (5) is used. Units (chain transfer agent residues) are introduced into the copolymer. In the following formula (5), L ¹ represents an m-valent organic residue, and m represents a number of 0 or more. m is preferably 0-5.

  Examples of the trifunctional or higher polyvalent mercaptan include trimethylolpropane trimercaptoacetate, trimethylolpropane tri (3-mercaptopropionate), pentaerythritol tetrakismercaptoacetate, pentaerythritol tetrakis (3-mercaptopropionate), Dipentaerythritol hexakis mercaptoacetate, dipentaerythritol hexakis (3-mercaptopropionate) and other compounds having three or more hydroxyl groups and carboxyl group-containing mercaptans polyester compounds, triazine polyvalent thiols, polyvalent epoxy compounds A compound obtained by adding hydrogen sulfide to a plurality of epoxy groups and introducing three or more mercapto groups per molecule, a plurality of carboxyl groups and mercapto of polyvalent carboxylic acid Compounds and the like having per molecule three or more mercapto groups obtained by esterification of ethanol. In the copolymer, only one type of branch unit derived from a trifunctional or higher polyfunctional chain transfer agent may be contained, or two or more types may be contained.

It is preferable to use a trifunctional or higher functional peroxide as the polyfunctional polymerization initiator. When such a polyfunctional polymerization initiator is used as a radical polymerization initiator, a branch unit represented by the following formula (6) (initiation) Agent residue) is introduced into the copolymer. In the following formula (6), L ² represents an n-valent organic residue, and n represents a number of 0 or more. n is preferably 0 to 5.

  Examples of the trifunctional or higher polyfunctional initiator include 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, tris (t-butylperoxy) triazine, 3,3 ′, 4,4. And trifunctional or higher functional organic peroxides such as' -tetra (t-butylperoxycarbonyl) benzophenone. In the copolymer, only one type of branch unit derived from a polyfunctional initiator having three or more functions may be included, or two or more types of branch units may be included.

  The content (total content) of branch units derived from the polyfunctional chain transfer agent and / or polyfunctional initiator in the copolymer is preferably 0.01 parts by mass or more in 100 parts by mass of the copolymer. 02 parts by mass or more is more preferable, 0.05 parts by mass or more is more preferable, 3 parts by mass or less is preferable, 2 parts by mass or less is more preferable, and 1 part by mass or less is more preferable. By setting the content of the branch unit in such a range, the molecular weight distribution of the copolymer is narrowed and the shear stability is improved. In the copolymer, a branch unit derived from a polyfunctional chain transfer agent and / or a polyfunctional initiator may not be contained.

The copolymer contained in the viscosity index improver of the present invention contains 78% by mass of Group III base oil (viscosity index 122, kinematic viscosity 19.6 mm ² / s) in the American Petroleum Institute (API) classification, When a solution consisting of 22% by mass of a polymer was measured at 25 ° C. with a viscometer (manufactured by Toki Sangyo Co., Ltd., TVB-10, rotor: SPINDLE No. M3, rotation speed 6 rpm), the viscosity was 8000 mPa · s or less. It will be. If the base oil solution of the copolymer has such a viscosity, the fluidity of the viscosity index improver near room temperature is increased, and handling properties are improved. The viscosity is preferably 7000 mPa · s or less, more preferably 6000 mPa · s or less. The lower limit of the viscosity is not particularly limited, and may be, for example, 1 mPa · s or more. YUBASE4 manufactured by SK is used as a group III base oil having a viscosity index of 122 and a kinematic viscosity of 40 ° C. of 19.6 mm ² / s.

  The viscosity index improver may contain a part of the raw material for producing the copolymer together with the copolymer, as long as the performance is not greatly impaired. For example, the copolymer obtained by the polymerization reaction In the case of producing a viscosity index improver without particularly refining or highly purifying the copolymer raw material (for example, monomer component, polymerization initiator, chain transfer agent) in the viscosity index improver Etc.). In such a case, the copolymer concentration of the base oil solution of the copolymer used in the above viscosity measurement may be regarded as the concentration of the copolymer including the copolymer raw material in addition to the copolymer. it can. That is, a solution comprising a total of 22% by mass of the copolymer and the copolymer raw material and 78% by mass of group III base oil may be used for viscosity measurement. For example, the copolymer concentration including the copolymer raw material can be determined by measuring the content of the base oil in the sample using gel permeation chromatography.

  The copolymer contained in the viscosity index improver preferably has a weight average molecular weight (Mw) of 200,000 or more, more preferably 250,000 or more, further preferably 300,000 or more, and preferably 700,000 or less, 65 10,000 or less is more preferable, and 600,000 or less is more preferable. When the weight average molecular weight of the copolymer is small, the viscosity index of the base oil solution of the viscosity index improver tends to decrease, so the amount of the viscosity index improver used to adjust to the desired viscosity increases, and the cost side Is disadvantageous. When the weight average molecular weight of the copolymer is excessively large, the solubility of the viscosity index improver in the base oil decreases, and the shear stability of the viscosity index improver tends to decrease.

  The number average molecular weight (Mn) of the copolymer contained in the viscosity index improver is preferably 120,000 or more, more preferably 130,000 or more, preferably 500,000 or less, more preferably 400,000 or less.

  The molecular weight distribution (Mw / Mn) calculated from Mw and Mn of the copolymer is preferably 4.0 or less, more preferably 3.5 or less, and even more preferably 3.0 or less. When the molecular weight distribution exceeds 4.0, the solubility of the viscosity index improver in the base oil is insufficient, and the shear stability of the lubricating oil composition tends to be lowered. 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 copolymer, the molecular weight distribution (Mw / Mn) is preferably 1.5 or more, and more preferably 1.8 or more. In addition, the weight average molecular weight (Mw) and number average molecular weight (Mn) of a copolymer are calculated | required by the method as described in an Example.

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

  The glass transition temperature (Tg) of the copolymer contained in the viscosity index improver is preferably −50 ° C. or higher, more preferably −40 ° C. or higher, further preferably −30 ° C. or higher, and preferably 0 ° C. or lower, − 10 degrees C or less is more preferable, and -20 degrees C or less is still more preferable. If the Tg of the copolymer is in such a range, when it is used as a base oil solution of a viscosity index improver, the solubility in the base oil is ensured and the flow around room temperature is maintained while maintaining a high viscosity index. It becomes easy to improve sex.

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

  The viscosity index improver of the present invention can achieve both a viscosity index improving effect and shear stability at a high level. As specific numerical values of the shear stability, SSI and decomposition start temperature obtained by the following method are used as indexes.

The SSI of the viscosity index improver is obtained by diluting the viscosity index improver (copolymer) in the base oil so that the kinematic viscosity at 100 ° C. is 7.0 mm ² / sec, and before and after the shear treatment by the ultrasonic homogenizer. And the base oil at 100 ° C. are measured and determined by the following formula: SSI = {1− (dynamic viscosity after shearing process−dynamic viscosity of base oil) / (dynamic viscosity before shearing process−dynamics of base oil) Viscosity)} × 100. The SSI of the viscosity index improver is preferably 38 or less, more preferably 36 or less, and even more preferably 34 or less, which improves the shear stability and storage stability of the viscosity index improver. The lower limit of the SSI of the viscosity index improver is not particularly limited, but is preferably 0.1 or more, more preferably 0.5 or more, still more preferably 2 or more, and even more preferably 5 or more. is there. When SSI is less than 0.1, the viscosity index improving effect of the viscosity index improver tends to decrease.

The viscosity index improver is a viscosity index improver (copolymer) in the base oil that gives a kinematic viscosity of 7.0 mm ² / sec at 100 ° C. when the viscosity index improver (copolymer) is diluted in the base oil. The higher the concentration is, the higher the viscosity index and shear stability tend to be, and the concentration is preferably 3.0% by mass or more, and more preferably 3.5% by mass or more. On the other hand, the upper limit of the concentration is not particularly limited, but may be, for example, 10.0% by mass or less.

  The decomposition start temperature of the copolymer contained in the viscosity index improver is preferably 270 ° C or higher, more preferably 275 ° C or higher, further preferably 280 ° C or higher, preferably 500 ° C or lower, and 450 ° C or lower. More preferred is 400 ° C. or lower. 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 of the viscosity index improver in the base oil tends to be insufficient, or the viscosity index tends to decrease.

The viscosity index improver preferably has a viscosity index of 200 or more when the viscosity index improver (copolymer) is diluted in the base oil so that the kinematic viscosity at 100 ° C. is 7.0 mm ² / s. 230 or more, more preferably 255 or more, and preferably 350 or less, more preferably 330 or less, and even more preferably 310 or less. When the viscosity index of the viscosity index improver is within the above range, the fuel economy, heat / oxidation stability, and storage stability are excellent. The viscosity index is measured according to the method of JIS K 2283.

  The viscosity index improver of the present invention contains the above-mentioned copolymer as a main component, and preferably, in 100% by mass of the viscosity index improver, the copolymer is 70% by mass or more, more preferably 90% by mass or more, and still more preferably. Contains 95% by mass or more, particularly preferably 99% by mass or more. The viscosity index improver may be composed only of the above-described copolymer. Components other than the above-mentioned copolymer contained in the viscosity index improver of the present invention include polymethacrylate, polyisobutylene, ethylene-propylene copolymer, styrene-diene hydrogenated copolymer, and these graft polymers and comb polymers. And star polymers.

  The copolymer contained in the viscosity index improver of the present invention is a step of polymerizing a monomer component containing a maleimide monomer forming unit (a) and a macromonomer forming unit (b) (polymerization). It can obtain by the manufacturing method which has a process. A commercially available thing may be used for the macromonomer which forms unit (b), and a macromonomer may be synthesize | combined by providing a macromonomer synthetic | combination process prior to a superposition | polymerization process.

  The polymerization method of the monomer component in the polymerization step may be any of bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc., but considering the handleability of the resulting polymer as a viscosity index improver, Polymerization is preferably performed by polymerization. In addition, when using a dispersion medium, an emulsifier, a dispersing agent, etc., there is no restriction | limiting in particular and a well-known thing can be used.

  In the polymerization step, a maleimide monomer that forms unit (a) and a macromonomer that forms unit (b) are used as monomer components, and alkyl (meth) that further forms unit (c). An acrylate, an alkyl (meth) acrylate that forms the unit (d), and a monomer that forms the unit (e) may be used as the monomer component.

  The solvent used for the polymerization is not particularly limited as long as it is inactive to the polymerization reaction. The polymerization mechanism, the type and amount of the monomer used, the type and amount of the polymerization initiator and the polymerization catalyst, etc. What is necessary is just to set suitably according to the polymerization conditions. From the viewpoint of ensuring the solubility of the polymer and from the viewpoint of easy solvent substitution with the base oil after polymerization, toluene, xylene, hexane, cyclohexane, methyl ethyl ketone, and tetrahydrofuran are preferred as the solvent used for the polymerization. Further, a lubricating base oil described later can also be suitably used as the solvent. In this case, solvent replacement after polymerization is unnecessary, and the process is simplified, which is more preferable. These solvents may be used alone or in combination of two or more. The amount of the solvent used is not particularly limited, but is preferably such that the concentration of the total amount of the monomer component, the polymerization initiator, and other components is 20% by mass or more and 100% by mass or less of the whole.

  In the polymerization, it is preferable to use a polymerization initiator. A known polymerization initiator may be used as the polymerization initiator. For example, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-amidinopropane) dihydrochloride, dimethyl-2, Azo compounds such as 2′-azobis (2-methylpropionate) and 4,4′-azobis (4-cyanopentanoic acid); persulfates such as potassium persulfate; cumene hydroperoxide, diisopropylbenzene hydroperoxide , Di-t-butyl peroxide, lauroyl peroxide, benzoyl peroxide, t-butyl peroxyisopropyl carbonate, t-amyl peroxy-2-ethyl hexanoate, t-amyl peroxy octoate, t-amyl per Peroxides such as oxyisononanoate can be used. Moreover, the polyfunctional initiator demonstrated above can also be used. These may use only 1 type and may use 2 or more types together. It is preferable that the usage-amount of a polymerization initiator shall be 0.01-3 mass parts with respect to 100 mass parts of monomer components, for example.

  In the polymerization step, a chain transfer agent or the like may be used. By using a chain transfer agent, it becomes easy to obtain a copolymer having a small molecular weight distribution. In addition, thermal decomposition due to depolymerization is easily suppressed. Chain transfer agents include butanethiol, octanethiol, octadecanthiol, dodecanethiol, cyclohexyl mercaptan, thiophenol, octyl thioglycolate, octyl 2-mercaptopropionate, octyl 3-mercaptopropionate, 2-ethylhexyl ester of mercaptopropionate , Mercaptans such as 2-mercaptoethyl ester of octanoic acid, 1,8-dimercapto-3,6-dioxaoctane, dodecyl mercaptan, ethylene glycol bisthioglycolate; carbon tetrachloride, carbon tetrabromide, methylene chloride, bromoform, Halogen compounds such as bromotrichloroethane; α-methylstyrene dimer and the like. Moreover, the polyfunctional chain transfer agent demonstrated above can also be used. The amount of the chain transfer agent used is preferably 0.01 to 3 parts by mass with respect to 100 parts by mass of the monomer component, for example.

  The temperature of the polymerization reaction may be appropriately adjusted according to the type of the polymerization solvent and the degree of progress of the polymerization reaction. The following is more preferable. The polymerization reaction time may be appropriately adjusted according to the degree of progress of the polymerization reaction. For example, the polymerization reaction time may be 1 to 48 hours (preferably 3 to 24 hours).

  In the polymerization step, all monomers may be charged into the system and polymerization may be started, or a part of the monomers may be added continuously or intermittently during the polymerization. Only one type of monomer may be added during the polymerization, or two or more types may be used.

  At the end of the polymerization step, the polymerization rate of the maleimide monomer is preferably 95% or more, more preferably 97% or more, and even more preferably 99% or more. This suppresses the volatilization of the maleimide monomer during handling and reduces the concern of affecting the human body and the environment. At the end of the polymerization step, the polymerization rate of the macromonomer is preferably 82% or more, more preferably 83% or more, and still more preferably 84% or more. This improves the base oil solubility, viscosity index, shear stability, and handling properties when used as a base oil solution.

  When performing the macromonomer synthesis step, the compound having the macro hydrocarbon group described above and a functional group selected from a hydroxyl group, an amino group, a carboxy group, a carboxylic acid ester group, an isocyanate group, and a sulfo group (hereinafter referred to as “a macromonomer group”) A macromonomer by reacting a reactive group with the functional group and a compound having a polymerizable double bond (hereinafter referred to as “counter compound”). preferable. By reacting the macro compound with the counter compound (addition reaction or condensation reaction) and polymerizing the obtained macro monomer together with other monomer components in the polymerization step, macro carbonization derived from the macro compound in the copolymer Hydrogen groups are incorporated.

  The functional group possessed by the macro compound is preferably a hydroxyl group, a carboxy group, or a carboxylic acid ester group from the viewpoint of ease of production and availability. The macro compound preferably has only one such functional group, and more preferably has such a functional group at the end of the macro compound.

  Examples of the reactive group possessed by the counter compound include a hydroxyl group, an amino group, a carboxy group, a carboxylic acid ester group, an isocyanate group, a sulfo group, and an oxazoline group. The counter compound preferably has only one such reactive group. Examples of the counter compound include (meth) acrylates such as 2-isocyanatoethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, and 3-sulfopropyl (meth) acrylate; (meth) acrylic acid; 2-hydroxyethyl Vinyl ethers such as vinyl ether and 2,2-dimethyl-2-isocyanatoethyl vinyl ether; styrenes such as 4-aminostyrene and 4-vinylbenzenesulfonic acid; 2-isopropenyl-2-oxazoline and the like.

  The reaction between the macro compound and the counter compound includes urethanation reaction in which an isocyanate group and a hydroxyl group react, urea formation reaction in which an isocyanate group and an amino group react, esterification reaction in which a carboxy group and a hydroxyl group react, a carboxy group and an amino group Amidation reaction in which a group reacts, sulfonic acid esterification reaction in which a sulfo group and a hydroxyl group react, sulfonamidation reaction in which a sulfo group and an amino group react, transesterification reaction in which an esterified product of a hydroxyl group and a carboxy group reacts Amide esterification reaction in which an oxazoline group and a carboxy group react. Among these, a urethanization reaction, a urealation reaction, an esterification reaction, a transesterification reaction, or an amidation reaction is preferable, and a urethanization reaction is particularly preferable from the viewpoint of excellent reactivity.

  In the macromonomer synthesis step, the reaction between the macro compound and the counter compound is preferably performed in the presence of a metal catalyst. This makes it possible to efficiently produce a macromonomer from the macro compound and the counter compound, and to shorten the reaction time. Furthermore, in the subsequent polymerization step, even if the metal derived from the metal catalyst remains in the reaction solution, the polymerization reaction of the monomer component including the macromonomer can be suitably performed.

  The metal catalyst is not particularly limited as long as it promotes the reaction between the macro compound and the counter compound, but the metal catalyst contains one or more metal elements selected from the group consisting of titanium, zirconium, zinc, tin, and bismuth. It is preferable to use a titanium catalyst and / or a tin catalyst. If a titanium catalyst and / or a tin catalyst are used, in the macromonomer synthesis process, the reaction between the macro compound and the counter compound proceeds rapidly, and the metal derived from these catalysts remains in the reaction liquid in the subsequent polymerization process. Even if it does, the polymerization rate of a macromonomer can be raised and it becomes easy to obtain a higher molecular weight polymer.

  The metal catalyst preferably has a group or ligand containing a Group 16 element. In this case, the group 16 element contained in the group or ligand is preferably bonded or coordinated to the metal atom of the metal catalyst. Examples of the Group 16 element include oxygen, sulfur, selenium, tellurium and the like, and among them, a group or ligand containing oxygen or sulfur is preferable. Examples of such a group or ligand include an alkoxy group, an aryloxy group, an acyloxy group, an acylate group, a catecholate group, a thiol group, and a thiocyanate group. Particularly, a group or ligand containing oxygen is preferably used. .

  The synthesis of the macromonomer is preferably performed in a solvent. As the solvent, a solvent that can be used in the polymerization reaction can be used, and a lubricating base oil can also be preferably used. The amount of the reaction solvent used in the macromonomer synthesis step is not particularly limited, but is preferably such that the total concentration of the macro compound and the counter compound in the reaction solution is 5% by mass or more and 70% by mass or less.

  When the synthesis of the macromonomer is performed in a lubricating base oil, the lubricating base oil can also be used as a reaction solvent in the polymerization step. As a result, the macromonomer synthesis step and the polymerization step can be simplified, and solvent replacement after polymerization is not necessary, so that the viscosity index improver of the present invention can be easily produced. In this case, in the presence of the metal derived from the metal catalyst used in the macromonomer synthesis step, the polymerization step of polymerizing the monomer component containing the macromonomer in the solvent (lubricant base oil) used in the macromonomer synthesis step You may go.

  The temperature at which the macro compound and the counter compound are reacted may be appropriately adjusted according to the type of reaction solvent and the progress of the reaction, but is preferably 0 ° C. or higher, more preferably 25 ° C. or higher, and 180 ° C or lower is preferable, and 155 ° C or lower is more preferable. The reaction time may be appropriately adjusted according to the degree of progress of the reaction. For example, the reaction time may be 20 minutes to 16 hours (preferably 30 minutes to 12 hours).

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

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

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

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

The kinematic viscosity at 100 ° C. of the lubricating base oil such as the mineral base oil or the synthetic base oil described above is preferably 1 to ²⁰ mm ² / s.

  As the lubricating base oil blended with the viscosity index improver, a mineral base oil is preferred from the viewpoint of cost and availability. Among the mineral oil base oils, the base oil (8) or the base oil obtained by performing the above-described treatment on the base oil selected from the base oils (1) to (7) or the lubricating oil fraction recovered from the base oil (9) is preferred. It is also preferred to use a base oil belonging to Group III based on classification by the American Petroleum Institute (API). As the lubricating base oil blended in the viscosity index improver, the above-described synthetic base oil may be used.

  In the lubricating oil composition of the present invention, the above lubricating base oil may be used alone or in combination with one or more other base oils. In addition, when using together lubricating base oil and another base oil, it is preferable that the said mixed base oil contains the said lubricating base oil (8) or (9) at least. The ratio of the lubricating base oil (8) or (9) in the mixed base oil is preferably 30% by mass or more, more preferably 50% by mass or more, and 70% by mass or more. Further preferred.

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

  The viscosity index of the lubricating oil composition is preferably 200 or more, more preferably 230 or more, further preferably 255 or more, more preferably 400 or less, more preferably 350 or less, and even more preferably 300 or less. When the viscosity index is within the above range, the fuel economy, heat / oxidation stability, and storage stability are excellent.

  The content of the copolymer according to the present invention in the lubricating oil composition is not particularly limited. For example, in 100 parts by mass of the lubricating oil composition, 0.01 parts by mass or more is preferable, and 0.1 parts by mass or more is more preferable. Preferably, 0.5 parts by mass or more is more preferable, 70 parts by mass or less is preferable, 60 parts by mass or less is more preferable, and less than 50 parts by mass is further preferable. In addition, when the lubricating oil composition is used for lubricating oil without further dilution with a lubricating base oil, the content of the copolymer according to the present invention in the lubricating oil composition is 100 parts by mass of the lubricating oil composition. 0.01 parts by mass or more, preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, more preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and 10 parts by mass or less. Is more preferable. When the lubricating oil composition of the present invention is used as a base oil composition, the content of the copolymer according to the present invention in the base oil composition is, for example, 5 parts by mass or more in 100 parts by mass of the lubricating oil composition. Preferably, 10 parts by mass or more is more preferable, 20 parts by mass or more is more preferable, 70 parts by mass or less is preferable, 60 parts by mass or less is more preferable, and less than 50 parts by mass is further preferable.

  The lubricating oil composition of the present invention contains the viscosity index improver of the present invention and a lubricating oil base oil as essential components, and may further contain optional additives and the like. Lubricating oil compositions include, for example, pour point depressants, antiwear agents, metallic detergents, ashless detergents, antioxidants, corrosion inhibitors, foam inhibitors, friction modifiers, rust inhibitors, It is preferable that at least one additive selected from the group consisting of an emulsifier and a metal deactivator is blended.

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

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

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

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

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

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

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

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

  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 nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and polyoxyethylene alkyl naphthyl ether.

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

  Lubricating oil compositions include pour point depressants, antiwear agents, metal detergents, ashless detergents, antioxidants, corrosion inhibitors, foam inhibitors, friction modifiers, rust inhibitors, demulsifiers, And one or more selected from the group consisting of metal deactivators, for example, each content is 0.01 parts by mass or more and 10 parts by mass or less in 100 parts by mass of the lubricating oil composition. If it is.

  When the lubricating oil composition contains a metallic detergent / dispersant, the content thereof is preferably 0.01 parts by mass or more and less than 30 parts by mass in 100 parts by mass of the lubricating oil composition. If the content is less than 0.01 parts by mass, the fuel saving effect may last only for a short period of time, and if it is 30 parts by mass or more, it is difficult to obtain an effect commensurate with the content.

  When the lubricating oil composition contains an antifoaming agent, the content is preferably 0.0001 parts by mass or more and 0.01 parts by mass or less in 100 parts by mass of the lubricating oil composition.

  When the lubricating oil composition contains a friction modifier, the content thereof is preferably 0.01 parts by mass or more and 3 parts by mass or less in 100 parts by mass of the lubricating oil composition. If the content of the friction modifier is less than 0.01 parts by mass, the effect of reducing friction due to the addition tends to be insufficient, and if it exceeds 3 parts by mass, the effects of other additives are likely to be hindered. Or the solubility of the additive tends to deteriorate.

  When the lubricating oil composition is used as a base oil composition, the base oil composition may substantially consist of a viscosity index improver and a lubricating base oil. In this case, the viscosity in the base oil composition The total content of the index improver and the lubricating base oil is preferably 98 parts by weight or more, more preferably 99 parts by weight or more, and more preferably 99.5 parts by weight or more in 100 parts by weight of the base oil composition. preferable. In particular, the base oil composition is preferably configured so that the total content of the above-described copolymer and lubricating base oil falls within such a range.

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

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

(1) Analysis and evaluation method (1-1) Weight average molecular weight and number average molecular weight The weight average molecular weight and number average molecular weight of a copolymer are calculated | required using a gel permeation chromatography (the Tosoh company make, HLC-8320GPC ECOSEC). It was. The measurement conditions are as follows.
-Column: manufactured by Tosoh Corporation, two TSKgel GMHXL-developing solvent: tetrahydrofuran-flow rate of developing solvent: 1.0 mL / min-standard sample: TSK standard polystyrene (PS-oligomer kit manufactured by Tosoh Corporation)
-Column temperature: 40 ° C
-Sample concentration: 0.5%
-Injection volume: 200 μL

(1-2) Polymerization rate of each monomer component excluding the macromonomer The polymerization rate of each monomer component excluding the macromonomer was determined using gas chromatography (manufactured by Shimadzu Corporation, GC-2010plus). Specifically, a calibration curve solution in which each monomer and tridecane were dissolved in ethyl acetate was prepared, measured by gas chromatography, and a calibration curve was created from the peak area. Next, a sample solution in which the copolymer solution and tridecane were dissolved in ethyl acetate was prepared, and similarly measured by gas chromatography. The polymerization rate of each monomer component was determined by an internal standard method. The measurement conditions for gas chromatography are shown below.
Column: Inert Cap1 (liquid phase film thickness: 0.25 μm, length: 30 m, inner diameter: 0.25 mm) manufactured by GL Science
-Temperature: 40 ° C (5 min hold) + 40 ° C to 170 ° C (10 ° C / min) + 170 ° C to 210 ° C (5 ° C / min) + 210 ° C to 330 ° C (15 ° C / min) + 330 ° C (20 min hold)
-Vaporization chamber temperature: 200 ° C
-Detector temperature: 350 ° C (FID)
-Carrier gas: helium (column flow rate 1.33 mL / min)
Injection volume: 0.5 μL (split method, split ratio: 30.0)
-Internal standard: Tridecane-Diluting solvent: Ethyl acetate

(1-3) Macromonomer Content and Polymerization Rate The macromonomer content and polymerization rate were determined using gel permeation chromatography (HLC-8320GPC ECOSEC, manufactured by Tosoh Corporation). Specifically, a calibration curve solution in which a macromonomer was dissolved in tetrahydrofuran was prepared, measured by gel permeation chromatography, and a calibration curve was created from the peak area. Next, a sample solution in which the copolymer solution was dissolved in tetrahydrofuran was prepared and measured in the same manner. The content of the macromonomer in the copolymer solution was determined from the peak area of the obtained macromonomer, and the content (mass%) of the macromonomer relative to the total amount of the macromonomer charged in the system was determined. The polymerization rate of the macromonomer depends on the content of the macromonomer in the copolymer solution, the amount of the copolymer solution used for analyzing the macromonomer content in the copolymer solution, and the amount of macromonomer added to the polymerization system. From the total amount and the total amount of the solution in the polymerization system, it was calculated by the following formula: Macromonomer polymerization rate (mass%) = [1-{(macromonomer content in copolymer solution × total solution amount in polymerization system / Copolymer solution amount used for analysis) / total amount of macromonomer added to the polymerization system}] × 100. The measurement conditions are as follows.
-Column: manufactured by Tosoh Corporation, two TSKgel GMHXL-developing solvent: tetrahydrofuran-flow rate of developing solvent: 1.0 mL / min-standard sample: TSK standard polystyrene (PS-oligomer kit manufactured by Tosoh Corporation)
-Column temperature: 40 ° C
-Sample concentration: 0.5%
-Injection volume: 200 μL

(1-4) Base oil solubility 4 parts by mass of copolymer and 96 parts by mass of base oil (manufactured by SK, YUBASE4) were prepared to prepare a base oil solution of the copolymer, which was stirred at room temperature for 1 hour. . The presence or absence of precipitates was visually confirmed, and the solubility when no precipitate or insoluble matter was confirmed was evaluated as ◯. When precipitates and insolubles were confirmed, the solution was heated at 80 ° C. for 30 minutes while stirring. Thereafter, the base oil solution of the copolymer was cooled to room temperature, and the presence or absence of precipitates was visually confirmed. The solubility when the precipitate was confirmed was evaluated as x, and the solubility when the precipitate was not confirmed was evaluated as Δ. YUBASE4 manufactured by SK is a Group III base oil (viscosity index 122, 40 ° C. kinematic viscosity 19.6 mm ² / s) in the American Petroleum Institute (API) classification.

(1-5) Viscosity 78% by mass of a group III base oil (manufactured by SK Corporation, YUBASE4, viscosity index 122, kinematic viscosity at 1400 mm ² / s at 40 ° C.) in the American Petroleum Institute (API) classification, A solution consisting of 22% by mass (including coalesced raw materials) was measured at 25 ° C. with a viscometer (manufactured by Toki Sangyo Co., Ltd., TVB-10, rotor: SPINDLE No. M3, rotational speed 6 rpm). The case where the viscosity was 8000 mPa · s or less was evaluated as ◯, and the case where the viscosity exceeded 8000 mPa · s was evaluated as x.

(1-6) Viscosity Index The copolymer was diluted with a base oil (manufactured by SK Corporation, YUBASE4) so that the kinematic viscosity at 100 ° C. was 7.0 mm ² / s, and measured by the method of JIS K 2283.

(1-7) Shear Stability A base oil solution of a copolymer is prepared by diluting the copolymer in a base oil (SKBASE, YUBASE4) so that the kinematic viscosity at 100 ° C. is 7.0 mm ² / s. Then, while maintaining this at 100 ° C., an ultrasonic homogenizer (Ultrasonics, Hielscher UP400S) was subjected to shear treatment by applying ultrasonic waves for 10 minutes under the conditions of Amplitude = 70% and Cycle = 1. The kinematic viscosity at 100 ° C. of the copolymer base oil solution and base oil before and after shearing was measured, and the shear stability (SSI) was determined by the following formula: SSI = {1− (kinematic viscosity after shearing) -Kinematic viscosity of base oil) / (Kinematic viscosity before shearing-Kinematic viscosity of base oil)} × 100. The case where the value of SSI was 40 or less was evaluated as ◯, and the case where it exceeded 40 was evaluated as x.

(2) Production Example of Macromonomer One end hydroxyl group-containing copolymer of hydrogenated polybutadiene (manufactured by TOTAL, KrasolHLBH-5000M) in a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen introduction tube, and a dropping funnel. ) 50 parts by mass, 1.6 parts by mass of 2-isocyanatoethyl methacrylate (manufactured by Showa Denko KK, Karenz MOI), 20 parts by mass of toluene, 0.1 parts by mass of dibutyltin dilaurate, and nitrogen gas was introduced into this. The mixture was stirred for 6 hours while being heated to 65 ° C. in an oil bath. After completion of the reaction, 50 parts by mass of water was added and the supernatant was recovered with a separatory funnel. After raising the temperature to 65 ° C., toluene was removed under reduced pressure to obtain 48 parts by mass of the macromonomer shown in Table 1.

The obtained macromonomer was dissolved in deuterated chloroform (manufactured by Wako Pure Chemical Industries, Ltd.), and ¹ H-NMR measurement was performed using a nuclear magnetic resonance spectrometer (manufactured by Varian, Unity Plus 400). A peak near 3.9 ppm attributed to the alcohol group of the raw material was not confirmed, and a peak near 4.9 ppm attributed to the generated urethane group was confirmed.

(3) Production Example of Polymer Base Oil Solution (3-1) Example 1
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe, and a dropping funnel, 12 parts by mass of a macromonomer, 65 parts by mass of n-butyl methacrylate (BMA), stearyl methacrylate ( SMA) 18 parts by mass, N-phenylmaleimide (PMI) 5 parts by mass, base oil (SK Corporation, YUBASE4) 138.7 parts by mass and pentaerythritol tetrakis (mercaptoacetate) 0.05 parts by mass, The contents were heated to 105 ° C. with stirring while introducing nitrogen gas. Thereto, 0.052 parts by mass of t-amylperoxyisononanoate (manufactured by Arkema Yoshitomi Co., Ltd., Luperox (registered trademark) 570) and 5.1 parts by mass of a base oil (manufactured by SK, YUBASE4) as a polymerization initiator. 12. While adding the mixed solution, 0.21 parts by mass of t-amyl peroxyisononanoate (manufactured by Arkema Yoshitomi, Luperox (registered trademark) 570) as a polymerization initiator is used as a base oil (manufactured by SK, YUBASE4). Solution polymerization was allowed to proceed while dripping the solution dissolved in 7 parts by mass over 4 hours, followed by further aging for 2 hours. Subsequently, 140.0 parts by mass of a base oil (manufactured by SK, YUBASE4) was added and diluted to obtain a base oil solution of copolymer 1 (copolymer concentration: 25% by mass). Tables 2 and 4 show the composition ratios of the units derived from the respective monomers of the obtained copolymer 1 and the results of analysis and evaluation.

(3-2) Example 2
As a monomer component, 12 parts by mass of a macromonomer, 10 parts by mass of methyl methacrylate (MMA), 52 parts by mass of BMA, SMA21 as a monomer component in a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe, and a dropping funnel 1 part by mass, 5 parts by mass of PMI, 124.2 parts by mass of base oil (manufactured by SK, YUBASE4) and 0.05 parts by mass of pentaerythritol tetrakis (mercaptoacetate) were added, and the mixture was stirred while introducing nitrogen gas. The contents were heated up to 105 ° C. Thereto, 0.12 parts by mass of t-amylperoxyisononanoate (manufactured by Arkema Yoshitomi Co., Ltd., Luperox (registered trademark) 570) and 8.2 parts by mass of a base oil (manufactured by SK, YUBASE4) as a polymerization initiator. While adding the mixed solution, 0.051 parts by mass of t-amylperoxy-2-ethylhexanoate (manufactured by Arkema Yoshitomi, Luperox (registered trademark) 575) as a polymerization initiator was added to the base oil (manufactured by SK, YUBASE4) Solution polymerization was allowed to proceed while dropping a solution dissolved in 3.4 parts by mass over 2 hours, followed by further aging for 4 hours. Subsequently, 97.3 parts by mass of base oil (manufactured by SK, YUBASE4) was added thereto and diluted to obtain a base oil solution of copolymer 2 (copolymer concentration: 30% by mass). Tables 2 and 4 show the composition ratios of the units derived from the respective monomers of the obtained copolymer 2 and the results of analysis and evaluation.

(3-3) Example 3
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe, and a dropping funnel, as a monomer component (initial), 12 parts by mass of macromonomer, 40 parts by mass of BMA, 12 parts by mass of SMA, lauryl methacrylate / 6 parts by mass of tridecyl methacrylate mixture (mass ratio = 54/46) (SLMA), 3 parts by mass of N-phenylmaleimide (PMI), 130.4 parts by mass of base oil (manufactured by SK, YUBASE4) and penta 0.05 parts by mass of erythritol tetrakis (mercaptoacetate) was charged, and the contents were heated to 105 ° C. while stirring while introducing nitrogen gas. Thereto, 0.052 parts by mass of t-amylperoxyisononanoate (manufactured by Arkema Yoshitomi Co., Ltd., Luperox (registered trademark) 570) and 5.1 parts by mass of a base oil (manufactured by SK, YUBASE4) as a polymerization initiator. 12. While adding the mixed solution, 0.21 parts by mass of t-amyl peroxyisononanoate (manufactured by Arkema Yoshitomi, Luperox (registered trademark) 570) as a polymerization initiator is used as a base oil (manufactured by SK, YUBASE4). Solution polymerization was allowed to proceed while dropping a solution dissolved in 7 parts by mass and a mixed solution of 25 parts by mass of BMA and 2 parts by mass of PMI as dropwise monomer components over 4 hours, followed by further aging for 4 hours. Subsequently, 149.0 parts by mass of base oil (manufactured by SK, YUBASE4) was added and diluted to obtain a base oil solution of copolymer 3 (copolymer concentration: 25% by mass). Tables 2 and 4 show the composition ratio of units derived from the respective monomers of the obtained copolymer 3 and the results of analysis and evaluation.

(3-4) Example 4
In Example 3, among the monomer components initially charged, 45 parts by mass of BMA is changed to 40 parts by mass, 12 parts by mass of SMA is changed to 0 parts by mass, and 6 parts by mass of SLMA is changed to 23 parts by mass. The same operation as in Example 3 was performed except that the amount of oil was changed from 130.4 parts by mass to 150.0 parts by mass and the amount of base oil added after aging was changed from 149.0 parts by mass to 130 parts by mass. By performing, the base oil solution of copolymer 4 (copolymer concentration 25 mass%) was obtained. Table 2 and Table 4 show the composition ratio of each monomer-derived unit of the obtained copolymer 4 and the results of analysis / evaluation.

(3-5) Example 5
In Example 4, the same procedure as in Example 4 was performed except that 40 parts by mass of BMA was changed to 45 parts by mass and 23 parts by mass of SLMA were changed to 18 parts by mass. A base oil solution of polymer 5 (copolymer concentration: 25% by mass) was obtained. Tables 2 and 4 show the composition ratios of the units derived from the respective monomers of the obtained copolymer and the results of analysis and evaluation.

(3-6) Example 6
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe, and a dropping funnel, 11.7 parts by mass of a one-terminal hydroxyl group-containing polymer of hydrogenated polybutadiene (manufactured by TOTAL, KrasolHLBH-5000M), 2- Isocyanatoethyl methacrylate (manufactured by Showa Denko KK, Karenz MOI) 0.38 parts by mass, base oil (manufactured by SK, YUBASE4) 73.6 parts by mass, tetraoctyl titanate (manufactured by Matsumoto Fine Chemicals Co., Ltd., Orugatix TA-30) 0 .024 parts by mass was added, and this was stirred for 30 minutes while heating to 75 ° C. in an oil bath while introducing nitrogen gas, to obtain 85.7 parts by mass of a macromonomer base oil solution shown in Table 1.
Next, 85.7 parts by mass of the obtained macromonomer base oil solution, 60 parts by mass of BMA, 23 parts by mass of SLMA, in a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe, and a dropping funnel, Charge 5 parts by mass of N-cyclohexylmaleimide (CHMI), add 117.7 parts by mass of base oil (manufactured by SK, YUBASE4) and 0.05 parts by mass of pentaerythritol tetrakis (mercaptoacetate), and introduce nitrogen gas into this. While stirring, the contents were heated to 105 ° C. Thereto, 0.0521 parts by mass of t-amylperoxyisononanoate (manufactured by Arkema Yoshitomi, Luperox (registered trademark) 570) and 2.6 parts by mass of base oil (manufactured by SK, YUBASE4) as a polymerization initiator. While adding the mixed solution, t-amyl peroxy isononanoate (manufactured by Arkema Yoshitomi Co., Ltd., Luperox (registered trademark) 570) as a polymerization initiator, 0.205 parts by mass of base oil (manufactured by SK, YUBASE4) 13. Solution polymerization was allowed to proceed while dripping the solution dissolved in 7 parts by mass over 4 hours, followed by further aging for 2 hours. Subsequently, 92.0 parts by mass of base oil (manufactured by SK, YUBASE4) was added and diluted to obtain a base oil solution of copolymer 6 (copolymer concentration: 25% by mass). Tables 2 and 4 show the composition ratio of the units derived from the respective monomers of the obtained copolymer 6 and the results of analysis / evaluation.

(3-7) Example 7
In Example 6, the BMA 60 parts by mass was changed to 65 parts by mass, the SLMA 23 parts by mass to 18 parts by mass, and the amount of base oil charged before the start of polymerization was changed from 117.7 parts by mass to 136.1 parts by mass. A base oil solution of copolymer 7 (copolymer concentration: 25 mass) was carried out in the same manner as in Example 6 except that the amount of the base oil added was changed from 92.0 mass parts to 73.6 mass parts. %). Tables 2 and 4 show the composition ratio of units derived from the respective monomers of the obtained copolymer 7 and the results of analysis and evaluation.

(3-8) Example 8
In Example 6, among the monomer components initially charged, 60 parts by mass of BMA was changed to 55 parts by mass, 5 parts by mass of N-phenylmaleimide (PMI) was newly added, and the base oil charged before the start of polymerization was added. The same operation as in Example 6 is performed except that the amount is changed from 117.7 parts by mass to 136.1 parts by mass and the amount of the base oil added after aging is changed from 92.0 parts by mass to 73.6 parts by mass. Thus, a base oil solution of copolymer 8 (copolymer concentration: 25% by mass) was obtained. Tables 2 and 4 show the composition ratio of the monomer-derived units of the obtained copolymer 8 and the results of analysis and evaluation.

(3-9) Example 9
In Example 8, except that 5 parts by mass of CHMI was changed to 5 parts by mass of cyclohexyl methacrylate (CHMA), by performing the same operation as in Example 8, a base oil solution of copolymer 9 (copolymer concentration: 25 masses) %). Tables 2 and 4 show the composition ratio of units derived from each monomer of the obtained copolymer 9 and the results of analysis and evaluation.

(3-10) Example 10
In Example 6, BMA 60 parts by mass was changed to 67 parts by mass, SLMA 23 parts by mass to SMA 13 parts by mass, CHMI 5 parts by mass to 8 parts by mass, and the amount of base oil added after aging was 92.0 to 49. A base oil solution of copolymer 10 (copolymer concentration: 28% by mass) was obtained by performing the same operation as in Example 6 except that the amount was changed to 1 part by mass. Tables 2 and 4 show the composition ratio of units derived from each monomer of the obtained copolymer 10 and the results of analysis and evaluation.

(3-11) Comparative Example 1
In Example 1, copolymer 11 was prepared by performing the same operation as in Example 1 except that 65 parts by mass of BMA was changed to 70 parts by mass and 5 parts by mass of PMI were changed to 0 parts by mass. A base oil solution (copolymer concentration 25% by mass) was obtained. Tables 3 and 5 show the composition ratio of the units derived from the respective monomers of the obtained copolymer 11 and the results of analysis and evaluation.

(3-12) Comparative Example 2
In Example 2, the same operation as in Example 2 was performed except that 12 parts by mass of macromonomer, 71 parts by mass of BMA, 5 parts by mass of lauryl methacrylate (LMA), and 12 parts by mass of styrene were used as monomer components. Thus, a base oil solution of copolymer 12 (copolymer concentration: 30% by mass) was obtained. Tables 3 and 5 show the composition ratio of units derived from each monomer of the obtained copolymer 12 and the results of analysis and evaluation.

(3-13) Comparative Example 3
In Example 2, the same operation as in Example 2 was performed except that 10 parts by mass of macromonomer, 40 parts by mass of MMA, 20 parts by mass of SMA, and 30 parts by mass of decyltetradecyl methacrylate (DTDMA) were used as the monomer component. By performing, the base oil solution of copolymer 13 (copolymer concentration 30 mass%) was obtained. Tables 3 and 5 show the composition ratio of the units derived from the respective monomers of the obtained copolymer 13 and the results of analysis and evaluation.

(3-14) Comparative Example 4
In Example 2, the base oil solution of copolymer 14 (copolymer concentration 30) was obtained by performing the same operation as in Example 2 except that 71 parts by mass of BMA and 29 parts by mass of SLMA were used as monomer components. Mass%). Tables 3 and 5 show the composition ratios of the units derived from the monomers of the copolymer 14 and the results of analysis and evaluation.

(4) Results Tables 2 to 5 show the composition ratio (mass basis) of units derived from each monomer of each copolymer produced in Examples and Comparative Examples, polymerization rate, molecular weight, physical property evaluation results, and the like. Indicated. In Tables 2 and 3, the polymerization rate means the polymerization rate of each monomer at the end of the polymerization. The macromonomer content means the content of the macromonomer relative to 100 parts by mass of the total amount of the macromonomer-derived unit (b) and macromonomer in the copolymer base oil solution. “Measured polymer concentration” in the physical property evaluation of Table 4 and Table 5 is the base oil so that the kinematic viscosity at 100 ° C. is 7.0 mm ² / s when measuring the shear stability. It means the copolymer concentration of the base oil solution prepared by diluting to YUBASE4 (manufactured by SK).
Although the copolymer used in Comparative Examples 1 and 3 has the unit (b) but does not have the unit (a) derived from the maleimide monomer, the polymerization rate of the macromonomer is low, and the base oil The base oil solution viscosity at room temperature increased. In Comparative Example 2 in which units derived from styrene were introduced instead of units derived from maleimide monomers (a), the base oil solubility was poor and precipitation occurred during polymerization. In Comparative Example 4 having no unit (b), the base oil solubility was poor and precipitation occurred during polymerization. On the other hand, since the copolymer used in Examples 1 to 10 had a unit (a) derived from a maleimide monomer in addition to the unit (b), the base oil solubility was excellent. The base oil solution viscosity at room temperature was low, and the handling property was excellent.

  The viscosity index improver of the present invention can be used as a lubricating oil composition, and can be suitably used for drive system lubricating oil, hydraulic oil, engine oil and the like.

Claims (8)

Containing a copolymer having units (a) derived from maleimide monomers and units (b) derived from macromonomers;
A viscosity index improver having a viscosity measured by the following method of 8000 mPa · s or less.
(Viscosity measurement)
A solution consisting of 78% by mass of Group III base oil (viscosity index 122, kinematic viscosity 19.6 mm ² / s) in the American Petroleum Institute (API) classification and 22% by mass of the copolymer was converted into a viscometer (TOKI Sangyo Co., Ltd., TVB-10, rotor: SPINDLE No. M3, 6 rpm, measured at 25 ° C.   The viscosity index improver according to claim 1, wherein the content of the unit (a) is 1 part by mass or more and 20 parts by mass or less in 100 parts by mass of the copolymer.   The viscosity index improver according to claim 1 or 2, wherein the content of the macromonomer is 18 parts by mass or less with respect to a total of 100 parts by mass of the unit (b) and the macromonomer.   The viscosity index improvement according to any one of claims 1 to 3, wherein the copolymer has a weight average molecular weight (Mw) of 200,000 to 700,000 and a number average molecular weight (Mn) of 120,000 to 500,000. Agent. The copolymer further has a unit (c) derived from alkyl (meth) acrylate, wherein the alkyl group of the alkyl (meth) acrylate has 1 to 6 carbon atoms,
In 100 parts by mass of the copolymer, the content of the unit (b) is 6 parts by mass or more and less than 20 parts by mass, the content of the unit (c) is 40 parts by mass or more and less than 74 parts by mass, and the unit (b). The viscosity index improver according to claim 1, wherein the total content of the unit (c) is 46 parts by mass or more and less than 80 parts by mass. The copolymer further has a unit (d) derived from alkyl (meth) acrylate, wherein the alkyl group of the alkyl (meth) acrylate has 11 to 40 carbon atoms,
The viscosity index improver according to any one of claims 1 to 5, wherein the content of the unit (d) is 3 parts by mass or more and 40 parts by mass or less in 100 parts by mass of the copolymer.   The viscosity index improver according to any one of claims 1 to 6, wherein the unit (b) has a urethane bond.   A lubricating oil composition comprising a lubricating base oil and the viscosity index improver according to claim 1.