JP2019194284A - Viscosity index improver and production method thereof - Google Patents

Abstract

To provide: a viscosity index improver which comprises a polymer having a unit derived from a monomer having an aliphatic hydrocarbon group with a large number of carbon atoms, which can improve polymerization conversion of the monomer having an aliphatic hydrocarbon group with a large number of carbon atoms when polymerizing the polymer; and a production method thereof.SOLUTION: The viscosity index improver comprises a polymer having: (A) a constitutional unit derived from an acrylate monomer; (B) a constitutional unit derived from a methacrylate monomer having an aliphatic hydrocarbon group of 30 or more carbons, where, relative to 100 mass% of the polymer, the content of the constitutional unit (A) is 1-70 mass%. The production method for the viscosity index improver comprises a step of performing copolymerization of a monomer component comprising (a) an acrylate monomer and (b) a methacrylate monomer having an aliphatic hydrocarbon group of 30 or more carbons. The used amount of the monomer (a) is 1-70 pts.mass relative to 100 pts.mass of the monomer component.SELECTED DRAWING: None

Description

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

  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, so it is effective to use a lubricating oil additive that has a viscosity index improving effect that keeps the viscosity at low temperature while keeping the viscosity at high temperature low, Such lubricating oil additives are known as viscosity index improvers.

  It is known that a viscosity index improver contains a polymer, and among them, a viscosity index improver made of an alkyl methacrylate polymer is said to exhibit a high viscosity index improving effect. On the other hand, since the viscosity index improver made of an alkyl methacrylate polymer has poor shear stability, there has been a problem that fuel-saving properties are deteriorated during long-term use (long life property is poor). In view of this, a method using a polymer using a macromonomer as a monomer component has been proposed as a means for achieving both a viscosity index improvement effect and shear stability. Patent Documents 1 to 3 disclose the use of methacrylate having a long-chain aliphatic hydrocarbon group in the structure as such a macromonomer.

JP2013-133460A Special table 2012-520358 gazette International Publication No. 2018/056316

  A monomer having an aliphatic hydrocarbon group usually has a tendency that the higher the carbon number, the lower the polymerizability and the lower the polymerization rate. As a result, the composition of the resulting polymer tends to deviate from the composition of the monomer component used for the polymerization, making it difficult to impart the desired properties to the polymer. A decrease in the polymerization rate also causes an increase in the amount of unreacted monomer remaining in the produced polymer. However, since such a monomer having an aliphatic hydrocarbon group having a large number of carbon atoms has a high boiling point and is difficult to separate from the polymer, in order to reduce the amount of unreacted monomer, It is desired to increase the polymerization rate during the reaction.

  The present invention has been made in view of the above circumstances, and its purpose is a viscosity index improver containing a polymer having a monomer-derived unit having an aliphatic hydrocarbon group having a large number of carbon atoms, An object of the present invention is to provide a viscosity index improver capable of increasing the polymerization rate of a monomer having an aliphatic hydrocarbon group having a large number of carbon atoms and a method for producing the same when polymerizing the polymer.

The present invention includes the following inventions.
[1] A polymer having a structural unit (A) derived from an acrylate monomer and a structural unit (B) derived from a methacrylate monomer having an aliphatic hydrocarbon group having 30 or more carbon atoms, In 100% by mass, the content of the structural unit (A) is 1% by mass or more and 70% by mass or less.
[2] The viscosity according to [1], wherein the polymer has, as a structural unit (A), a structural unit (A1) derived from an alkyl acrylate monomer and having 2 to 8 carbon atoms in the alkyl group. Index improver.
[3] The viscosity index improver according to [2], wherein the content of the structural unit (A1) is 1% by mass or more and 70% by mass or less in 100% by mass of the polymer.
[4] The polymer according to any one of [1] to [3], wherein the polymer further includes a structural unit (C2) derived from an alkyl methacrylate monomer, wherein the alkyl group has 9 to 20 carbon atoms. Viscosity index improver.
[5] The polymer is derived from a structural unit (A1) in which the alkyl group is derived from an alkyl acrylate monomer and the alkyl group has 2 to 8 carbon atoms, and / or is derived from an alkyl methacrylate monomer. It has a structural unit (C1) having 2 to 8 carbon atoms, and in 100% by mass of the polymer, the total content of the structural unit (A1) and the structural unit (C1) is 45% by mass to 75% by mass. The viscosity index improver according to any one of [1] to [4].
[6] The viscosity index improver according to any one of [1] to [5], wherein the polymer further has a structural unit (D) derived from a maleimide monomer.
[7] A step of copolymerizing a monomer component containing an acrylate monomer (a) and a methacrylate monomer (b) having an aliphatic hydrocarbon group having 30 or more carbon atoms, The method for producing a viscosity index improver, wherein the amount of the monomer (a) used is from 1 part by weight to 70 parts by weight with respect to 100 parts by weight.
[8] The method for producing a viscosity index improver according to [7], wherein the monomer (a) is an alkyl acrylate and the monomer (a1) having 2 to 8 carbon atoms in the alkyl group.
[9] The method for producing a viscosity index improver according to [8], wherein the amount of the monomer (a1) used is 1 part by mass or more and 70 parts by mass or less with respect to 100 parts by mass of the monomer component.
[10] The viscosity index according to any one of [7] to [9], further including a monomer (c2) in which the monomer component is an alkyl methacrylate and the alkyl group has 9 to 20 carbon atoms. A method for producing an improver.
[11] A lubricating oil composition comprising the viscosity index improver according to any one of [1] to [6] and a lubricating base oil.

  The viscosity index improver of the present invention contains a polymer having a structural unit derived from a methacrylate monomer having an aliphatic hydrocarbon group having 30 or more carbon atoms and a structural unit derived from an acrylate monomer. When polymerizing the polymer, the polymerization rate of the methacrylate monomer having an aliphatic hydrocarbon group having 30 or more carbon atoms can be increased. Therefore, the composition control of the polymer becomes easy, and the residual amount of the methacrylate monomer having an aliphatic hydrocarbon group having 30 or more carbon atoms can be reduced.

[1. (Viscosity index improver)
The viscosity index improver of the present invention contains a polymer having a structural unit derived from an acrylate monomer and a structural unit derived from a methacrylate monomer, and the composition derived from a methacrylate monomer of the polymer An aliphatic hydrocarbon group having 30 or more carbon atoms is bonded to at least a part of the side chain of the unit. When such a polymer having a long-chain aliphatic hydrocarbon group in the side chain is used as a viscosity index improver, it becomes easy to obtain a viscosity index improver excellent in shear stability and solubility in a lubricating base oil. Moreover, it becomes easy to improve the viscosity index of the base oil solution.

  By the way, when producing a polymer having a long-chain aliphatic hydrocarbon group in the side chain, the polymerizability usually tends to decrease as the number of carbon atoms of the aliphatic hydrocarbon group increases. Therefore, in the production of a viscosity index improver containing such a polymer, the polymerization rate in the polymerization reaction is lowered, making it difficult to control the composition of the polymer, and the remaining long-chain aliphatic hydrocarbon Due to the influence of the monomer component having a group, it may be difficult to impart desired properties to the viscosity index improver. However, in the present invention, by using a polymer having a structural unit derived from an acrylate monomer together with a structural unit derived from a methacrylate monomer having a long-chain aliphatic hydrocarbon group as a viscosity index improver, The polymerization rate of the monomer component having an aliphatic hydrocarbon group can be increased. Therefore, the composition control of the polymer becomes easy, and the residual amount of the monomer component having a long-chain aliphatic hydrocarbon group can be reduced. Hereinafter, the viscosity index improver of the present invention and the production method thereof will be described in detail.

  The viscosity index improver of the present invention is a polymer having a structural unit (A) derived from an acrylate monomer and a structural unit (M) derived from a methacrylate monomer (hereinafter referred to as “(meth) acrylate polymer”). In some cases). The structural unit (A) derived from the acrylate monomer of the (meth) acrylate polymer is not particularly limited as long as it is a structural unit formed by polymerizing the acrylate monomer (a). The structural unit (M) derived from the methacrylate monomer contained in the (meth) acrylate polymer is not particularly limited as long as it is a structural unit formed by polymerizing the methacrylate monomer (m). The (meth) acrylate polymer has at least a structural unit (B) derived from a methacrylate monomer having an aliphatic hydrocarbon group having 30 or more carbon atoms as the structural unit (M) derived from the methacrylate monomer. The said structural unit (B) can be formed by polymerizing the monomer component containing the methacrylate monomer (b) which has a C30 or more aliphatic hydrocarbon group.

The (meth) acrylate polymer contains 1% by mass or more and 70% by mass or less of the structural unit (A) derived from the acrylate monomer in 100% by mass of the polymer. If the structural unit (A) is contained in such a content, a methacrylate monomer (b) having an aliphatic hydrocarbon group having 30 or more carbon atoms is formed when the (meth) acrylate polymer is polymerized. ) Polymerization rate can be increased. As will be described later, when the C _9-20 alkyl methacrylate monomer (c2) is contained in the monomer component, the polymerization rate of the monomer (c2) can also be increased. The content of the structural unit (A) in the (meth) acrylate polymer is preferably 2% by mass or more, more preferably 3% by mass or more, and preferably 65% by mass or less, more preferably 60% by mass or less. From the viewpoint of increasing the weight average molecular weight of the (meth) acrylate polymer, the content of the structural unit (A) in the (meth) acrylate polymer is preferably 50% by mass or less, and more preferably 40% by mass or less. 30% by mass or less is more preferable, and 20% by mass or less is particularly preferable.

As the structural unit (A) derived from an acrylate monomer, a structural unit derived from an acrylate monomer having an aliphatic hydrocarbon group is preferable, and a structural unit derived from an alkyl acrylate monomer is more preferable. The structural unit derived from the alkyl acrylate monomer is preferably a structural unit that is an alkyl acrylate and the alkyl group has 29 or less carbon atoms, the carbon number of the alkyl group is more preferably 24 or less, and further 20 or less. preferable. In addition, it is alkyl (meth) acrylate and the thing whose carbon number of the said alkyl group is ab means the (meth) acrylate ester of the alkyl group of carbon number ab, in other words, carbon number. It means an esterified product of a saturated aliphatic alcohol a to b and (meth) acrylic acid. In this specification, such (meth) acrylate is represented as C _ab alkyl (meth) acrylate. Examples of the structural unit (A) derived from an acrylate monomer include a structural unit (A1) derived from a C _2-8 alkyl acrylate monomer and a structural unit (A2) derived from a C _9-20 alkyl acrylate monomer. Is mentioned. Details of these will be described later.

  The (meth) acrylate polymer preferably contains 25% by mass or more and 97% by mass or less of the structural unit (M) derived from the methacrylate monomer in 100% by mass of the polymer. The content of the structural unit (M) derived from the methacrylate monomer in the (meth) acrylate polymer is more preferably 30% by mass or more, further preferably 35% by mass or more, and more preferably 95% by mass or less, 92 mass% or less is more preferable.

As described above, the (meth) acrylate polymer is a structural unit (B) derived from a methacrylate monomer having an aliphatic hydrocarbon group having 30 or more carbon atoms as the structural unit (M) derived from the methacrylate monomer. As the structural unit (M) derived from a methacrylate monomer other than that, a structural unit derived from a methacrylate monomer having an aliphatic hydrocarbon group having 29 or less carbon atoms is preferably used. And the structural unit whose carbon number of the said alkyl group is 29 or less is more preferable. The alkyl group preferably has 24 or less carbon atoms, more preferably 20 or less. Examples of the structural unit derived from the alkyl methacrylate monomer include a structural unit (C1) derived from a C _2-8 alkyl methacrylate monomer and a structural unit (C2) derived from a C _9-20 alkyl methacrylate monomer. It is done. Details of these will be described later.

  The structural unit (B) derived from a methacrylate monomer having an aliphatic hydrocarbon group having 30 or more carbon atoms will be described in detail. The aliphatic hydrocarbon group of the structural unit (B) may be a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group, but the viscosity index improver is crystallized at a low temperature. Saturated aliphatic hydrocarbon group is preferable from the viewpoint of suppressing the increase in viscosity. The aliphatic hydrocarbon group of the structural unit (B) may be linear, branched or cyclic, but is preferably linear or branched.

The aliphatic hydrocarbon group of the structural unit (B) is directly bonded to an ester group (ester bond) included in a structure derived from a methacryloxy group (CH ₂ ═C (CH ₃ ) —CO—O—). Or may be indirectly bonded. In the latter case, the aliphatic hydrocarbon group includes a urethane bond (—NH—CO—O—), a urea bond (—NH—CO—NH—), an ester bond (—CO—O—), an amide bond (—NH It is bonded to the ester group via a linking group containing at least one selected from —CO—), sulfonic acid ester bond (—SO ₂ —O—), and sulfonamide bond (—SO ₂ —NH—). It is preferable. In addition, the direction of each bond of a urea bond, an ester bond, an amide bond, a sulfonic acid ester bond, or a sulfonamide bond is not particularly limited. Taking a urethane bond as an example, in the structural unit (B), in the urethane bond, the nitrogen atom may be located on the ester group side of the structure derived from the methacryloxy group, and the oxygen atom is located on the ester group side. Also good. In addition to these bonds, the linking group may include, for example, an alkylene group having 1 to 4 carbon atoms.

  The aliphatic hydrocarbon group of the structural unit (B) preferably has 50 or more carbon atoms from the viewpoint of enhancing the base oil solubility of the viscosity index improver and facilitating the improvement of the viscosity index of the viscosity index improver. , 70 or more is more preferable, 100 or more is more preferable, and 150 or more is even more preferable. The upper limit of the number of carbon atoms of the aliphatic hydrocarbon group of the structural unit (B) is not particularly limited, but from the viewpoint of securing a certain degree of polymerizability of the methacrylate monomer (b) giving the structural unit (B), for example, 3500 or less. Preferably, 1500 or less is more preferable, and 700 or less is more preferable.

  As the methacrylate monomer (b) giving the structural unit (B), it is convenient to use a so-called macromonomer. From such a viewpoint, the aliphatic hydrocarbon group of the structural unit (B) preferably includes a repeating structure derived from a hydrocarbon monomer or a hydride thereof. 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, Examples include alkadienes such as 3-pentadiene, 1,4-pentadiene, 1,5-hexadiene, and 2,5-dimethyl-1,5-hexadiene (also called diisobutene). In the case where the hydrocarbon monomer is an alkadiene, the repeating structure derived from the alkadiene may contain an unsaturated bond. In this case, the unsaturated bond may be hydrogenated (hydrogenated). . These monoolefins and alkadienes preferably have 2 or more carbon atoms, more preferably 3 or more, more preferably 20 or less, still more preferably 10 or less, and still more preferably 6 or less.

  The aliphatic hydrocarbon group of the structural unit (B) is preferably linear or branched, and is branched from the viewpoint of inhibiting crystallization of the (meth) acrylate polymer at low temperatures and preventing thickening. More preferably. In this case, the aliphatic hydrocarbon group preferably includes a branched alkylene group as a repeating unit, and preferably includes both a branched alkylene group and a linear alkylene group as a repeating unit. 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. Further, the aliphatic hydrocarbon group of the structural unit (B) preferably does not contain an unsaturated bond, and therefore is particularly preferably an aliphatic saturated hydrocarbon group.

  The structural unit (B) is included in the structure derived from the methacryloxy group through the linking group described above for the aliphatic hydrocarbon group from the viewpoint of ease of production of the monomer (b) that gives the structural unit (B). It is preferably bonded to an ester group. As such a structural unit (B), a unit represented by the following formula (1) is preferably shown.

In the above formula (1), R ¹ represents an aliphatic hydrocarbon group having 30 or more carbon atoms, and X is a linking group containing a urethane bond, a urea bond, an ester bond, an amide bond, a sulfonic acid ester bond, or a sulfonamide bond. Represents. For the details of the aliphatic hydrocarbon group of R ¹ and the linking group of X, the above description is referred to. The linking group X is more preferably one containing a urethane bond, a urea bond or an amide bond from the viewpoint of ease of production of the monomer (b) as a macromonomer.

  The number average molecular weight of the aliphatic hydrocarbon group of the structural unit (B) is preferably 750 or more, more preferably 1000 or more, further preferably 1500 or more, from the viewpoint of base oil solubility, viscosity index, and shear stability. The above is more preferable, 50000 or less is preferable, 20000 or less is more preferable, and 10,000 or less is more preferable.

  In the (meth) acrylate polymer, only one type of structural unit (B) may be contained, or two or more types may be contained.

  The content of the structural unit (B) in the (meth) acrylate polymer is preferably 6% by mass or more, more preferably 7% by mass or more, further preferably 8% by mass or more, in 100% by mass of the polymer. 25 mass% or less is preferable, 22 mass% or less is more preferable, 18 mass% or less is further more preferable, and 16 mass% or less is still more preferable. Thereby, it becomes easy to increase the viscosity index improving effect of the viscosity index improver or to increase the shear stability.

The (meth) acrylate-based polymer preferably has a structural unit derived from a relatively short-chain alkyl (meth) acrylate monomer from the viewpoint of enhancing heat resistance and enhancing the polymerizability at the time of polymerization. For example, the (meth) acrylate polymer has a structural unit derived from a C _1-8 alkyl acrylate monomer as the structural unit (A), or a C _1-8 alkyl methacrylate as the structural unit (M). It is preferable to have a structural unit derived from a monomer. In addition, it is preferable that a (meth) acrylate type polymer has a structural unit derived from a _C2-8 alkyl (meth) acrylate monomer from the point which improves the handleability of a viscosity index improver. That is, the structural unit (A) has a structural unit (A1) derived from a C _2-8 alkyl acrylate monomer and / or the structural unit (M) is derived from a C _2-8 alkyl methacrylate monomer. It is preferable to have a structural unit (C1). In this case, for example, when the polymer concentration in the viscosity index improver is increased compared to the case where a structural unit derived from methyl (meth) acrylate is introduced instead of the structural unit (A1) or the structural unit (C1). The base oil solution of the viscosity index improver tends to have a low viscosity, and handling properties are improved. In addition, the viscosity index tends to increase.

As the structural unit (A1), a structure represented by the following formula (2) is specifically shown, and as the structural unit (C1), a structure represented by the following formula (3) is specifically shown. In formula (2) and formula (3), R ² and R ³ represent an alkyl group having 2 to 8 carbon atoms.

The R ² alkyl group of 2-8 carbon atoms R ³ of formula (3) in equation (2), ethyl group, propyl group, isopropyl group, n- butyl group, an isobutyl group, t- butyl group, a pentyl Group, hexyl group, heptyl group, octyl group and other linear or branched alkyl groups, and cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group and other cyclic alkyl groups Is mentioned. The alkyl groups of R ² and R ³ are preferably linear or branched, and more preferably linear. Moreover, 3-6 are preferable and 3-5 are more preferable. Of these, the alkyl group of R ² and R ³ is preferably a butyl group, more preferably an n-butyl group or an isobutyl group, from the viewpoint that the viscosity index improver is excellent in fluidity around room temperature.

  The (meth) acrylate polymer may contain only one of the structural unit (A1) and the structural unit (C1), or both. In addition, the (meth) acrylate polymer may contain only one type of structural unit (A1), may contain two or more types, and contains only one type of structural unit (C1). Or two or more of them may be contained.

  When the (meth) acrylate polymer has the structural unit (A1) and / or the structural unit (C1), the total content of the structural unit (A1) and the structural unit (C1) is 45% in 100% by mass of the polymer. % By mass or more is preferred, 50% by mass or more is more preferred, 55% by mass or more is more preferred, 75% by mass or less is preferred, 70% by mass or less is more preferred, 68% by mass or less is further preferred, and 65% by mass or less. Is even more preferred. If the structural unit (A1) and / or the structural unit (C1) is contained in such a content, a structural unit derived from methyl (meth) acrylate is used instead of the structural unit (A1) or the structural unit (C1). Compared with the case where it introduce | transduces, when the base oil solution of a viscosity index improver is made into high concentration, it becomes easy to become a low viscosity and becomes excellent in handling property. Moreover, it becomes easy to improve the viscosity index of the base oil solution of the viscosity index improver by increasing the solubility of the (meth) acrylate polymer in the base oil.

The (meth) acrylate polymer preferably has at least the structural unit (A1). When the (meth) acrylate polymer is polymerized, the acrylate monomer (a) tends to have a lower polymerization rate than the methacrylate monomer (m). Therefore, as the acrylate monomer (a) giving the structural unit (A), it is preferable to use an acrylate monomer (a) having a relatively low molecular weight, thereby separating the acrylate monomer (a) from the (meth) acrylate polymer. It becomes easy to do. That is, when an acrylate monomer (a1) that gives the structural unit (A1) is used as the acrylate monomer (a) when the (meth) acrylate polymer is polymerized, a relatively low molecular weight acrylate monomer Even if the body (a1) remains, it becomes easy to separate the acrylate monomer (a1) from the (meth) acrylate polymer by separation means such as distillation or extraction. Further, even if such a low molecular weight acrylate monomer (a1) remains in the viscosity index improver, it does not significantly affect the performance characteristics of the viscosity index improver, and the viscosity index improver is used as a lubricating oil. When added and used, it is easily removed by volatilization. From such a viewpoint, it is preferable to use the acrylate monomer (a1) as much as possible as the acrylate monomer (a) which tends to have a low polymerization rate. That is, the (meth) acrylate polymer preferably has the structural unit (A1) as the structural unit (A). It is also preferred that the (meth) acrylate polymer has only a structural unit derived from a C _1-8 alkyl acrylate monomer as the structural unit (A).

  The content of the structural unit (A1) in the (meth) acrylate polymer is preferably 1% by mass or more, more preferably 2% by mass or more, further preferably 3% by mass or more, in 100% by mass of the polymer. 70 mass% or less is preferable, 65 mass% or less is more preferable, and 60 mass% or less is further more preferable. From the viewpoint of increasing the weight average molecular weight of the (meth) acrylate polymer, the content of the structural unit (A1) in the (meth) acrylate polymer is preferably 50% by mass or less, and more preferably 40% by mass or less. 30% by mass or less is more preferable, and 20% by mass or less is particularly preferable.

  The (meth) acrylate polymer preferably includes both the structural unit (A1) and the structural unit (C1) as a structural unit derived from a relatively short-chain alkyl (meth) acrylate monomer. Thereby, it becomes easy to raise the weight average molecular weight of the (meth) acrylate type polymer obtained, improving the polymerizability at the time of polymer-forming a (meth) acrylate type polymer. In this case, the (meth) acrylate polymer preferably contains more structural unit (C1) than structural unit (A1). For example, the content of the structural unit (C1) is preferably 60 parts by mass or more with respect to 100 parts by mass of the total content of the structural unit (A1) and the structural unit (C1) in the (meth) acrylate polymer. 70 parts by mass or more, more preferably 80 parts by mass or more, more preferably 99 parts by mass or less, more preferably 97 parts by mass or less, and still more preferably 95 parts by mass or less.

The (meth) acrylate polymer preferably has a structural unit derived from a C _9-20 alkyl (meth) acrylate monomer from the viewpoint of enhancing the base oil solubility of the viscosity index improver. That is, the structural unit (A) has a structural unit (A2) derived from a C _9-20 alkyl acrylate monomer and / or the structural unit (M) is derived from a C _9-20 alkyl methacrylate monomer. It is preferable to have a structural unit (C2).

As the structural unit (A2), a structure represented by the following formula (4) is specifically shown, and as the structural unit (C2), a structure represented by the following formula (5) is specifically shown. In formula (4) and formula (5), R ⁴ and R ⁵ represent an alkyl group having 9 to 20 carbon atoms.

Examples of the alkyl group having a carbon number of 9 to 20 of the R ⁵ of R ⁴ and Equation (5) in equation (4), nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl A linear or branched alkyl group such as heptadecyl group, octadecyl group, nonadecyl group, icosyl group, cycloheptyl group, cyclooctyl group, cyclononyl group, cyclodecyl group, dicyclopentanyl group, adamantyl group, etc. Examples thereof include a cyclic alkyl group. The alkyl groups of R ⁴ and R ⁵ are preferably linear or branched, and more preferably linear. Further, the number of carbon atoms is preferably 10 or more, more preferably 11 or more, and preferably 19 or less, more preferably 18 or less.

  The (meth) acrylate polymer may contain only one of the structural unit (A2) and the structural unit (C2), or both. In addition, the (meth) acrylate polymer may contain only one type of structural unit (A2), may contain two or more types, and contains only one type of structural unit (C2). Or two or more of them may be contained.

  When the (meth) acrylate polymer has the structural unit (A2) and / or the structural unit (C2), the total content of the structural unit (A2) and the structural unit (C2) is 5% in 100% by mass of the polymer. % By mass or more is preferable, 10% by mass or more is more preferable, 15% by mass or more is more preferable, 40% by mass or less is preferable, 35% by mass or less is more preferable, and 30% by mass or less is more preferable. When the structural unit (A2) and / or the structural unit (C2) is contained in the polymer with such a content, it becomes easy to increase the base oil solubility of the viscosity index improver. Furthermore, it becomes easy to ensure the fluidity of the base oil solution of the viscosity index improver even at a low temperature.

The (meth) acrylate polymer preferably contains more structural units (C2) than structural units (A2) as structural units derived from C _9-20 alkyl (meth) acrylate monomers. As explained above, the acrylate monomer (a) tends to have a lower polymerization rate than the methacrylate monomer (m). However, when the (meth) acrylate polymer is polymerized, the structural unit ( When a large amount of the acrylate monomer (a2) that gives A2) is used, a large amount of the acrylate monomer (a2) tends to remain in the (meth) acrylate polymer. In this case, since the acrylate monomer (a2) is an acrylate having a relatively long chain alkyl group, separation from the (meth) acrylate polymer is likely to be difficult. Further, if a large amount of the acrylate monomer (a2) remains in the viscosity index improver, there is a concern that the performance characteristics of the viscosity index improver may be affected. The content of the structural unit (A2) and the structural unit (C2) in the (meth) acrylate polymer is, for example, based on 100 parts by mass of the total content of the structural unit (A2) and the structural unit (C2). The content of the unit (C2) is preferably 70 parts by mass or more, more preferably 80 parts by mass or more, still more preferably 90 parts by mass or more, and even more preferably 95 parts by mass or more.

  It is also preferred that the structural unit (A2) is not substantially contained in the (meth) acrylate polymer. In this case, the content of the structural unit (C2) in the (meth) acrylate polymer is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 15% by mass or more in 100% by mass of the polymer. It is preferably 40% by mass or less, more preferably 35% by mass or less, and further preferably 30% by mass or less.

  The (meth) acrylate polymer preferably has a structural unit (D) derived from a maleimide monomer. In this case, a succinimide ring structure is introduced into the main chain of the polymer derived from the maleimide monomer. Thus, by introducing a ring structure into the main chain of the polymer, it is possible to enhance the shear stability and heat resistance of the viscosity index improver while ensuring the base oil solubility of the viscosity index improver. Furthermore, when added to lubricating oil, effects such as improvement in clean dispersibility of sludge and the like and suppression of wear on the metal surface are expected. The structural unit (D) can be introduced into the polymer by copolymerizing the maleimide monomer (d), which may have a substituent at the N-position, with a (meth) acrylate monomer or the like. .

As the structural unit (D), those represented by the following formula (6) are preferable. In formula (6), R ⁶ and R ⁷ each independently represent a hydrogen atom or an alkyl group, and R ⁸ represents a hydrogen atom or an organic group having 1 to 40 carbon atoms.

The alkyl group of R ⁶ and R ⁷ in Formula (6) preferably has 1 to 8 carbon atoms, more preferably 1 to 4 carbon atoms, and still more preferably 1 to 3 carbon atoms. R ⁶ and R ⁷ 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 ^{8 in} the formula (6) include an alkyl group, an aryl group, an aralkyl group, and a group in which a part of —CH ₂ — contained in the alkyl group is replaced by —O—. 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 ⁸ 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 base oil solubility of the viscosity index improver.

Examples of the alkyl group for R ⁸ 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 ⁸ include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and a biphenyl group. Examples of the aralkyl group for R ⁸ 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 ⁸ is replaced by —O— include polyoxyalkylene groups such as a polyoxyethylene group and a polyoxypropylene group.

Specific examples of the maleimide monomer (d) include, for example, maleimide, N-methylmaleimide, N-isopropylmaleimide, N-butylmaleimide, N-isobutylmaleimide, Nt-butylmaleimide, N-cyclohexylmaleimide, N -Octylmaleimide, N-2-ethylhexylmaleimide, N-decylmaleimide, N-laurylmaleimide, N-tetradecylmaleimide, N-stearylmaleimide, N-2-decyltetradecylmaleimide, N-phenylmaleimide, N-benzylmaleimide N-chlorophenylmaleimide, N-methylphenylmaleimide, N-naphthylmaleimide, N-hydroxylethylmaleimide, N-hydroxylphenylmaleimide, N-methoxyphenylmaleimide, N-carboxyphenyl Reimido, N- nitro-phenyl maleimide, N- tribromophenyl maleimide and the like. Among these, from the viewpoint of easy availability of the maleimide monomer (d) and easy improvement of the base oil solubility of the viscosity index improver, as the maleimide monomer (d), N-phenylmaleimide, N-cyclohexylmaleimide, N-isopropylmaleimide, N-benzylmaleimide, N-laurylmaleimide, and N-stearylmaleimide are preferable. Therefore, in Formula (6), R ⁶ and R ⁷ are preferably hydrogen atoms, and R ⁸ is preferably a phenyl group, a cyclohexyl group, an isopropyl group, a benzyl group, a lauryl group, or a stearyl group.

  In the (meth) acrylate polymer, only one type of structural unit (D) may be contained, or two or more types may be contained.

  When the (meth) acrylate polymer has the structural unit (D), the content of the structural unit (D) is preferably 1% by mass or more, more preferably 2% by mass or more, in 100% by mass of the polymer. % By mass or more is more preferable, 20% by mass or less is preferable, 15% by mass or less is more preferable, and 10% by mass or less is more preferable. Thereby, the effect of including a structural unit (D) in a polymer becomes easy to be effective.

  The (meth) acrylate polymer may have a structural unit derived from a monomer other than the structural units (A) to (D) described above (hereinafter referred to as “structural unit (E)”). Good. The structural units (A) to (D) can be introduced as a structural unit of the polymer by radical copolymerization of the corresponding (meth) acrylate monomer or maleimide monomer. E) is also preferably a structural unit derived from a radical polymerizable monomer. The radical polymerizable monomer forming the structural 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. It can be classified as a mass.

  Examples of monofunctional monomers include structural units (A1), (A2) and (meth) acrylates other than alkyl (meth) acrylates that form structural units (C1), (C2), unsaturated mono- or dicarboxylic acids Examples include esters, unsaturated carboxylic acids, vinyl aromatic compounds, vinyl esters, vinyl ethers, olefins, vinyl cyanide, and N-vinyl compounds. The structural 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 that forms the structural units (A1) and (A2) and the structural units (C1) and (C2) include, for example, methyl (meth) acrylate, benzyl (meth) acrylate, Phenyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, N, N-dimethylaminoethyl (meta ) Acrylate, morpholinoalkylene (meth) acrylate, methyl α-hydroxymethyl acrylate, polyethylene glycol mono (meth) acrylate, and the like.

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, as the structural unit (E), (meth) other than the alkyl (meth) acrylate other than the structural units (A1) and (A2) and the structural units (C1) and (C2). Acrylate and N-vinyl compound are preferable, and 2-hydroxyethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, methyl α-hydroxymethyl acrylate, and N-vinylpyrrolidone are more preferable.

  Examples of the polyfunctional monomer that forms the structural unit (E) include polyfunctional (meth) acrylate, vinyl ether group-containing (meth) acrylate, allyl group-containing (meth) acrylate, and polyfunctional (meth) acryloyl group-containing isocyanate. Examples thereof include polyfunctional (meth) acrylic compounds such as nurate and polyfunctional urethane (meth) acrylate, polyfunctional maleimide compounds, polyfunctional vinyl ethers, polyfunctional allyl compounds, and polyfunctional aromatic vinyls. The structural 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 structural unit (E) in a (meth) acrylate type polymer should just be 0 mass% or more in 100 mass% of polymers. When the structural unit (E) is contained in the polymer, the content thereof is preferably 1% by mass or more, more preferably 2% by mass or more, and further preferably 3% by mass or more, in 100% by mass of the polymer. % By mass or less is preferred, 40% by mass or less is more preferred, 30% by mass or less is more preferred, 20% by mass or less is even more preferred, and 10% by mass or less is particularly preferred.

  In addition, it is preferable that a (meth) acrylate type polymer does not contain many structural units derived from a styrene-type monomer. This is because when the content of the structural unit derived from the styrene monomer increases, the solubility of the viscosity index improver in the base oil tends to decrease and the viscosity index tends to decrease. Therefore, in 100% by mass of the polymer, the content of the structural unit derived from the styrene monomer is preferably less than 3% by mass, more preferably 2% by mass or less, and further preferably 1% 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) acrylate, and therefore, from the viewpoint of ease of production of the polymer, it is preferable that the polymer does not contain many structural units derived from these. . For example, the total content of the structural units (E) derived from these monomers is preferably 5% by mass or less, more preferably 3% by mass or less, in 100% by mass of the polymer.

  It is preferable that the (meth) acrylate polymer does not contain excessively many constituent units derived from methyl (meth) acrylate. Thereby, even if it is a base oil solution of a high-concentration viscosity index improver, the viscosity becomes low, handling properties are easily secured, and the viscosity index is easily increased. For example, in 100% by mass of the polymer, the content of the structural unit derived from methyl (meth) acrylate is preferably 30% by mass or less, more preferably 20% by mass or less, further preferably 10% by mass or less. Even more preferred is less than or equal to mass%.

  The content of the structural unit (E) derived from the polyfunctional monomer in the (meth) acrylate polymer is preferably 0% by mass to 5% by mass and more preferably 3% by mass or less in 100% by mass of the polymer. Preferably, 2 mass% or less is more preferable. When the content of the structural unit derived from the polyfunctional monomer exceeds the above range, gelation proceeds during polymerization or the solubility of the viscosity index improver containing the polymer 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 structural unit derived from the polyfunctional monomer in the polymer The content of may be 0% by mass to 30% by mass with respect to 100% by mass of the polymer, 20% by mass or less, or 15% by mass or less. 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 (meth) acrylate polymer may have a branch unit derived from a polyfunctional chain transfer agent or a polyfunctional polymerization initiator. If the polymer has such a branch unit, the shear stability of the viscosity index improver can be improved without significantly impairing the base oil solubility of the viscosity index improver.

As the polyfunctional chain transfer agent, it is preferable to use a trifunctional or higher polyvalent mercaptan. When such a chain transfer agent is used for radical copolymerization of the monomer component, a branch represented by the following formula (7) is used. Units (chain transfer agent residues) are introduced into the polymer. In the following formula (7), 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 mercaptans 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 polymer, 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 (8) (start) Agent residue) is introduced into the polymer. In the following formula (8), 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 polymerization initiator include 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, tris (t-butylperoxy) triazine, 3,3 ′, 4, Trifunctional or higher functional organic peroxides such as 4′-tetra (t-butylperoxycarbonyl) benzophenone are exemplified. In the polymer, only one type of branch unit derived from a polyfunctional polymerization 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 the branch unit derived from the polyfunctional chain transfer agent and / or polyfunctional polymerization initiator in the (meth) acrylate polymer is 0% by mass or more in 100% by mass of the polymer. Well, 0.01 mass% or more is preferable, 0.02 mass% or more is more preferable, 0.05 mass% or more is more preferable, 3 mass% or less is preferable, 2 mass% or less is more preferable, 1 mass% The following is more preferable. By setting the content of the branch unit in such a range, the molecular weight distribution of the polymer becomes narrow and the shear stability can be improved. In the (meth) acrylate polymer, a branch unit derived from a polyfunctional chain transfer agent and / or a polyfunctional polymerization initiator may not be contained.

  The weight average molecular weight (Mw) of the (meth) acrylate polymer is preferably 100,000 or more, more preferably 150,000 or more, further preferably 250,000 or more, still more preferably 350,000 or more, and 700,000 or less. Is preferable, 650,000 or less is more preferable, and 600,000 or less is more preferable. In order to adjust to a desired viscosity when the weight average molecular weight of the polymer is small, the viscosity index improving effect of the polymer is reduced, or the thickening effect when the polymer is added to the base oil is likely to be reduced. The amount of the viscosity index improver used is increased, which is disadvantageous in terms of cost. When the weight average molecular weight of the polymer is excessively large, the base oil solubility of the polymer is lowered, and the shear stability of the polymer is liable to be lowered.

  The number average molecular weight (Mn) of the (meth) acrylate polymer is preferably 50,000 or more, more preferably 80,000 or more, further preferably 110,000 or more, more preferably 300,000 or less, and more preferably 250,000 or less.

  The molecular weight distribution (Mw / Mn) calculated from Mw and Mn of the (meth) acrylate polymer is preferably 4.0 or less, more preferably 3.5 or less, and even more preferably 3.2 or less. When the molecular weight distribution exceeds 4.0, the solubility of the polymer in the base oil is insufficient, and the shear stability of the polymer tends to be lowered. On the other hand, the lower limit of the molecular weight distribution is preferably 1.0, but the molecular weight distribution (Mw / Mn) is preferably 1.5 or more and more preferably 1.8 or more from the viewpoint of easy synthesis of the polymer. In addition, the weight average molecular weight (Mw) and number average molecular weight (Mn) of a polymer are calculated | required by the method as described in an Example.

  The glass transition temperature (Tg) of the (meth) acrylate polymer is preferably −50 ° C. or higher, more preferably −40 ° C. or higher, further preferably −30 ° C. or higher, and preferably 0 ° C. or lower, and −10 ° C. or lower. Is more preferable, and −20 ° C. or lower is more preferable. When the Tg of the polymer is in such a range, the solubility of the polymer in the base oil is ensured, and the fluidity near room temperature is easily improved while maintaining a high viscosity index.

  The decomposition start temperature of the (meth) acrylate polymer is preferably 290 ° C or higher, more preferably 295 ° C or higher, further preferably 300 ° C or higher, particularly preferably 310 ° C or higher, and preferably 500 ° C or lower, 450 ° C. or lower is more preferable, 400 ° C. or lower is further preferable, and 380 ° C. or lower is particularly preferable. By increasing the decomposition start temperature of the polymer, 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 tends to be insufficient or the viscosity index tends to decrease when the polymer is added to the lubricating oil.

  The SP value (solubility parameter) of the (meth) acrylate polymer is preferably 8.8 or more, more preferably 8.9 or more, further preferably 9.0 or more, and more preferably 9.6 or less, 9.5 The following is more preferable, and 9.4 or less is more preferable. The SP value of the lubricating base oil generally shows a value of about 8.0 to 8.5. If the SP value of the polymer is 8.8 or higher, the viscosity index is increased when this is added to the lubricating oil. It becomes easy. On the other hand, if the SP value of the polymer is 9.6 or less, it becomes easy to ensure the solubility of the polymer in the base oil.

  When the (meth) acrylate polymer is applied to a viscosity index improver, it is preferable that the viscosity index improving effect and shear stability can be achieved at a high level. As a specific numerical value of the shear stability, SSI obtained by the following method is an index.

The SSI of the viscosity index improver is preferably 38 or less, more preferably 36 or less, and even more preferably 34 or less, thereby improving the shear stability and storage stability of the polymer. The lower limit of the SSI of the polymer 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. When SSI is less than 0.1, the effect of improving the viscosity index of the polymer tends to decrease. The SSI of the polymer is obtained by diluting the polymer in the base oil so that the kinematic viscosity at 100 ° C. is 7.0 mm ² / sec, and the kinematic viscosity before and after the shear treatment by the ultrasonic homogenizer and the kinematic viscosity at 100 ° C. of the base oil. Is obtained by the following formula: SSI = {1- (kinematic viscosity after shearing process−dynamic viscosity of base oil) / (kinematic viscosity before shearing process−dynamic viscosity of base oil)} × 100.

  The viscosity index improver contains the above-described (meth) acrylate polymer as a main component, and preferably in 100% by mass of the viscosity index improver, the polymer is 70% by mass or more, more preferably 90% by mass or more. More preferably, it is 95% by mass or more, particularly preferably 99% by mass or more. The viscosity index improver may be composed only of a (meth) acrylate polymer. Components other than the (meth) acrylate polymer contained in the viscosity index improver include polyisobutylene, ethylene-propylene copolymer, styrene-diene hydrogenated copolymer, these graft polymers, comb polymers, and star polymers. Etc. The viscosity index improver may also contain a part of the raw material for producing the polymer together with the (meth) acrylate polymer, as long as the performance is not greatly impaired. For example, when the viscosity index improver is produced without particularly purifying or highly purifying the polymer obtained by the polymerization reaction, the polymer raw material (eg, monomer component) is contained in the viscosity index improver. , Polymerization initiators, chain transfer agents, etc.).

  The viscosity index improver of the present invention can be obtained by a production method having a step (polymerization step) of copolymerizing a monomer component containing an acrylate monomer (a) and a methacrylate monomer (m). The acrylate monomer (a) gives the structural unit (A) derived from the acrylate monomer, and the methacrylate monomer (m) gives the structural unit (M) derived from the methacrylate monomer. In the present invention, as the methacrylate monomer (m), at least a methacrylate monomer (b) having an aliphatic hydrocarbon group having 30 or more carbon atoms is used, and the monomer (b) is a structural unit described above ( B) is given. As the monomer component, the acrylate monomer (a1) that gives the structural unit (A1) described above is preferably used as the acrylate monomer (a), and the structural unit (A2) described above is further used. An acrylate monomer (a2) that gives Further, as the methacrylate monomer (m), the methacrylate monomer (c1) that gives the structural unit (C1) described above is preferably used, and the methacrylate monomer that gives the structural unit (C2) described above. It is preferable to use (c2). For details such as preferred embodiments of these monomers, reference is made to the description of the monomers giving the units derived from the respective monomers.

For example, the monomer (b) is preferably a methacrylate monomer represented by the following formula (9). In the formula (9), the explanation of X and R ¹ in the formula (1) is referred to for the explanation of X and R ¹ .

The monomer (a1) is preferably an acrylate monomer represented by the following formula (10), and the monomer (c1) is a methacrylate monomer represented by the following formula (11). Is preferably shown. In the formula (10) and (11), the description of R ² and R ^3, description of R ² and R ³ of formula (3) of the above formula (2) is referred to.

As the monomer (a2), an acrylate monomer represented by the following formula (12) is preferably shown, and as the monomer (c2), a methacrylate monomer represented by the following formula (13) Is preferably shown. In the formula (12) and (13), the description of R ⁴ and R ^5, the description of R ⁴ and R ⁵ of formula (5) of the above formula (4) are referred to.

  The amount of the acrylate monomer (a) used is preferably 1 part by mass or more, more preferably 2 parts by mass or more, still more preferably 3 parts by mass or more, based on 100 parts by mass of all monomer components. 70 mass parts or less are preferable, 65 mass parts or less are more preferable, and 60 mass parts or less are more preferable. From the viewpoint of increasing the weight average molecular weight of the (meth) acrylate polymer, the amount of the acrylate monomer (a) used is preferably 50 parts by mass or less, based on 100 parts by mass of the monomer component, and 40 parts by mass. The following is more preferable, 30 parts by mass or less is further preferable, and 20 parts by mass or less is particularly preferable. Moreover, it is also preferable that the usage-amount of an acrylate monomer (a1) exists in such a range.

  The amount of the methacrylate monomer (m) used is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, still more preferably 35 parts by mass or more, and 97 parts by mass with respect to 100 parts by mass of the monomer component. Or less, more preferably 95 parts by mass or less, and still more preferably 92 parts by mass or less.

  The amount of the methacrylate monomer (b) having an aliphatic hydrocarbon group having 30 or more carbon atoms is preferably 6 parts by mass or more, more preferably 7 parts by mass or more, with respect to 100 parts by mass of the monomer component. 8 parts by mass or more is more preferable, 25 parts by mass or less is preferable, 22 parts by mass or less is more preferable, 18 parts by mass or less is further preferable, and 16 parts by mass or less is even more preferable.

  When a relatively short-chain alkyl (meth) acrylate monomer, that is, an acrylate monomer (a1) and / or a methacrylate monomer (c1) is used as the monomer component, the monomer (a1) and the monomer 45 mass parts or more are preferable with respect to 100 mass parts of monomer components, and, as for the total usage-amount of a body (c1), 50 mass parts or more are more preferable, 55 mass parts or more are more preferable, and 75 mass parts or less are more. Preferably, 70 parts by mass or less is more preferable, 68 parts by mass or less is more preferable, and 65 parts by mass or less is even more preferable. Moreover, it is preferable that there are many usage-amounts of a methacrylate monomer (c1) rather than an acrylate monomer (a1), for example with respect to 100 mass parts of total usage-amounts of a monomer (a1) and a monomer (c1). The amount of the monomer (c1) used is preferably 60 parts by mass or more, more preferably 70 parts by mass or more, further preferably 80 parts by mass or more, more preferably 99 parts by mass or less, and more preferably 97 parts by mass or less. 95 parts by mass or less is more preferable.

  When a relatively long-chain alkyl (meth) acrylate monomer, that is, an acrylate monomer (a2) and / or a methacrylate monomer (c2) is used as the monomer component, the monomer (a2) and a single amount The total amount used of the body (c2) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, further preferably 15 parts by mass or more, and 40 parts by mass or less with respect to 100 parts by mass of the monomer component. Preferably, 35 parts by mass or less is more preferable, and 30 parts by mass or less is more preferable. Moreover, it is also preferable that the usage-amount of a methacrylate monomer (c2) exists in such a range. Moreover, it is preferable that there is much usage-amount of a methacrylate monomer (c2) rather than an acrylate monomer (a2), for example with respect to 100 mass parts of total usage-amounts of a monomer (a2) and a monomer (c2). The amount of the monomer (c2) used is preferably 70 parts by mass or more, more preferably 80 parts by mass or more, still more preferably 90 parts by mass or more, and still more preferably 95 parts by mass or more. Moreover, it is also preferable to use only the methacrylate monomer (c2) without using the acrylate monomer (a2) as the relatively long-chain alkyl (meth) acrylate monomer.

  As the monomer component, it is also preferred to use a maleimide monomer (d). In this case, the amount of the maleimide monomer (d) used is preferably 1 part by mass or more, more preferably 2 parts by mass or more, further preferably 3 parts by mass or more, with respect to 100 parts by mass of the monomer component. 20 mass parts or less are preferable, 15 mass parts or less are more preferable, and 10 mass parts or less are further more preferable. For details of the maleimide monomer (d), reference is made to the description of the maleimide monomer (d) that gives the structural unit (D) derived from the maleimide monomer.

The maleimide monomer (d) is preferably a maleimide monomer represented by the following formula (14). In the formula (14), the description of R ^{6 to} R ^{8 in} the above formula (6) is referred to for the description of R ^{6 to} R ⁸ .

  As a monomer component, the radically polymerizable monomer which gives the structural unit (E) demonstrated above can also be used.

  The polymerization method of the monomer component in the polymerization step may be any of bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization and the like, and is not particularly limited. When using a dispersion medium, an emulsifier, a dispersant, etc., there is no particular limitation and a known one can be used. Among these, it is preferable to perform polymerization by solution polymerization because the polymerization reaction can be easily controlled and the viscosity index improver can be easily obtained as a base oil solution.

  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. In addition, from the viewpoint of ensuring the solubility of the polymer, and from the viewpoint of easy solvent substitution into the base oil after polymerization, the solvent used for the polymerization includes aromatic hydrocarbons such as toluene and xylene; hexane, cyclohexane, etc. Aliphatic hydrocarbons; ketones such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; ethers such as tetrahydrofuran, dioxane, diethyl ether and dibutyl ether are preferably used. These solvents may be used alone or in combination of two or more. A lubricating base oil 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 it is preferably such that the concentration of the total amount of the monomer component, the polymerization initiator, and other components is 40% by mass or more and 100% by mass or less.

  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 polymerization 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 polymer having a small molecular weight distribution. In addition, thermal decomposition due to depolymerization is easily suppressed. Chain transfer agents include butanethiol, octanethiol, octadecanethiol, 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.

  In the polymerization step, the polymerization reaction is preferably performed in the presence of a metal alkoxide. Thereby, the polymerizability of the monomer component is increased, and the polymerization rate can be increased or the reaction rate of the polymerization reaction can be increased. The metal alkoxide is not particularly limited as long as it is a compound in which an alkoxy group is bonded to a metal element. It is sufficient that at least one alkoxy group is bonded to the metal element of the metal alkoxide, and a group other than the alkoxy group (for example, alkyl group, aryl group, aralkyl group, acyloxy group, acylate group, aryloxy group, etc.) is bonded. You may do it. Note that it is preferable that two or more alkoxy groups are bonded to the metal element of the metal alkoxide. In this case, the plurality of alkoxy groups bonded to the metal element may be the same as or different from each other.

  The alkyl group of the alkoxy group bonded to the metal element is preferably linear or branched. Moreover, 1-10 are preferable and, as for the carbon number, 1-8 are more preferable.

  As the metal alkoxide, it is preferable to use at least one transition metal alkoxide selected from Group 4 elements, Group 5 elements, Group 12 elements, Group 14 elements and Group 15 elements. Among these, as the metal alkoxide, it is preferable to use an alkoxide of at least one metal element selected from titanium, zirconium, zinc, tin, and bismuth.

  Specific examples of the metal alkoxide include, for example, tetraisopropoxy titanium, tetra n-butoxy titanium, tetra tert-butoxy titanium, tetraoctyl titanate, titanium diisopropoxy bisethyl acetoacetate, tri n-butoxy titanium monostearate. , Di n-butoxy titanium distearate, tetra n-butoxy zirconium, tetra tert-butoxy zirconium, bis tert-butoxy zinc, tetra n-butoxy tin, tetra tert-butoxy tin, tri-n-butoxy bismuth, pentaethoxy tantalum, pentaethoxy Niobium, tetra tert-butoxy hafnium, tetraethoxy germanium and the like can be mentioned.

  The amount of metal alkoxide used is, for example, preferably 0.001 part by mass or more, more preferably 0.005 part by mass or more, further preferably 0.01 part by mass or more, relative to 100 parts by mass of the monomer component. It is preferably no greater than 1 part by mass, more preferably no greater than 1 part by mass, and even more preferably no greater than 0.5 part by mass.

  The metal alkoxide may be supplied to the polymerization reaction system (reactor) together with the monomer component during the polymerization reaction, or may be supplied to the polymerization reaction system in the middle of the polymerization reaction of the monomer component. Alternatively, a metal alkoxide may be present in the polymerization reaction system in advance, and then the monomer component may be supplied to carry out the polymerization reaction. For example, the metal alkoxide is charged in the step before the polymerization step and an arbitrary operation is performed, and then the polymerization step can be performed.

  In the polymerization step, the polymerization reaction may be performed in the presence of an acidic substance. Thereby, the initial polymerization rate can be increased. As the acidic substance, an organic phosphorus compound or an organic acid is preferably used. Examples of the organic phosphorus compound include alkyl (aryl) phosphonous acid and its monoester, dialkyl (aryl) phosphinic acid, alkyl (aryl) phosphonic acid and its monoester, alkylphosphinic acid, phosphorous acid di or monoester And phosphoric acid di or monoester. Examples of the organic acid include saturated or unsaturated fatty acids, aromatic carboxylic acids, hydroxy acids and the like. Fatty acids and aromatic carboxylic acids may be anhydrides. Among these, it is preferable to use a fatty acid having 6 or more carbon atoms as the acidic substance. The number of carbon atoms of the fatty acid is preferably 8 or more, more preferably 10 or more, 35 or less is preferable, 25 or less is more preferable, and 20 or less is more preferable. The amount of the acidic substance used is, for example, preferably 0.005 parts by mass or more, more preferably 0.01 parts by mass or more, further preferably 0.02 parts by mass or more with respect to 100 parts by mass of the monomer component. It is preferably no greater than 0.5 parts by mass, more preferably no greater than 0.5 parts by mass, and even more preferably no greater than 0.3 parts by mass.

  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).

[2. Lubricating oil composition)
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 being further diluted with a base oil, or may be further diluted with a 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 preferred examples include mineral base oils and synthetic base oils. 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 lubricant base oil can be used as a polymerization reaction solvent for the (meth) acrylate polymer.

  As specific examples of the mineral oil base oil, the following oils (1) to (7) are used as raw materials, and the raw oil and / or lubricating oil fraction recovered from the raw oil is refined by a predetermined refining method. And a base oil obtained by recovering the lubricating oil fraction. Considering that it is easy to improve the quality of the resulting viscosity index improver, as a lubricating base oil, a base oil selected from (1) to (7) or a lubricating oil fraction recovered from the base oil The following base oil (8) or (9) obtained by performing a predetermined treatment is preferably used.

(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.

  As the lubricating base oil blended in the lubricating oil composition, the base oil selected from the base oils (1) to (7) or the lubricating oil fraction recovered from the base oil is subjected to the above treatment. The resulting base oil (8) or (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). A synthetic base oil may be used as the lubricating base oil to be blended in the lubricating oil composition.

  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. For example, when the viscosity index is less than 100, the viscosity-temperature characteristics, thermal / oxidative stability, and volatilization prevention properties are likely to deteriorate, the friction coefficient increases, and the wear prevention properties tend to decrease. On the other hand, when the viscosity index exceeds 160, the low-temperature viscosity characteristic tends to be lowered. The viscosity index is measured based on JIS K 2283 (2000). The kinematic viscosity at 100 ° C. of the lubricating base oil is preferably 1 to ²⁰ mm ² / s.

  The content of the (meth) acrylate polymer 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. When the lubricating oil composition is used as a lubricating oil without further dilution with a lubricating base oil, the content of the (meth) acrylate polymer in the lubricating oil composition is 100 parts by weight 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 is used as the base oil composition, the content of the (meth) acrylate polymer in the base oil composition is preferably 5 parts by mass or more, for example, in 100 parts by mass of the lubricating oil composition. More than mass part is more preferable, 20 mass part or more is more preferable, 70 mass part or less is preferable, 60 mass part or less is more preferable, Less than 50 mass part is further more preferable.

  The lubricating oil composition contains a viscosity index improver and a lubricating base oil as essential components, and may further contain optional additives. 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. Among these, magnesium or calcium is preferable, and calcium is more 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.

  The friction modifier includes organic molybdenum compounds such as succinimide molybdenum complexes such as molybdenum dithiocarbamate and molybdenum dithiophosphate, and amine salts of organic molybdic acid, as well as linear alkyl and metal having 8 to 30 carbon atoms as the basic structure. And having a polar group that can be adsorbed on the same molecule in the same molecule. Examples of polar groups include amines, polyamines, amides, urea compounds and alkenyls such as amine compounds, fatty acid esters, fatty acid amides, fatty acids, fatty alcohols, aliphatic ethers, urea compounds, hydrazide compounds having these simultaneously in the molecule. Examples thereof include succinimide type, ester, alcohol and diol, or monoalkyl glycerol ester having ester and hydroxyl group at the same time. In addition, there are various types such as an alkylamine 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, 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 such that the total content of the (meth) acrylate polymer and the lubricating base oil falls within such a range.

  The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

(1) Analysis and evaluation method (1-1) Polymerization rate of macromonomer The polymerization rate of the macromonomer was determined using gel permeation chromatography (manufactured by Tosoh Corporation, HLC-8320GPC ECOSEC). Specifically, a calibration curve solution in which the macromonomer was dissolved in tetrahydrofuran was prepared and measured by gel permeation chromatography to prepare a calibration curve from the peak area. Next, a sample solution in which the polymerization solution was dissolved in tetrahydrofuran was prepared, and similarly measured by gel permeation chromatography. From the relationship between the peak area and the macromonomer concentration in the solution, the polymerization rate of the macromonomer was determined. The measurement conditions of gel permeation chromatography are shown below.
-Column: Tosoh Corporation, TSKgel GMHXL 2-Developing solvent: Tetrahydrofuran (THF)
-Flow rate of developing solvent: 1.0 mL / min-Standard sample: TSK standard polystyrene (manufactured by Tosoh Corporation, PS-oligomer kit)
-Column temperature: 40 ° C
-Sample concentration: 0.5%
-Injection volume: 200 μL

(1-2) Polymerization rate of monomer components other than 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 methyl isobutyl ketone was prepared, measured by gas chromatography, and a calibration curve was created from the peak area. Next, a sample solution in which the polymerization solution and tridecane were dissolved in methyl isobutyl ketone 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 sample: Tridecane-Diluting solvent: Methyl isobutyl ketone (MIBK)

(1-3) Average polymerization rate The polymerization rate of each monomer was multiplied by the mass ratio of each monomer added to the polymerization system, and the average polymerization rate was determined from the sum of these. For example, there are three types of monomers used for the polymerization, the blending ratio (mass%) of each monomer with respect to the total amount of monomers is A, B, and C, and the polymerization rate (mass%) of each monomer. ) Is a, b, c, the average polymerization rate is calculated as (Aa + Bb + Cc) / 100 (mass%).

(1-4) Weight average molecular weight and number average molecular weight The weight average molecular weight and the number average molecular weight were determined using gel permeation chromatography (manufactured by Tosoh Corporation, HLC-8320GPC ECOSEC). The measurement conditions are as follows.
-Column: Tosoh Corporation, TSKgel GMHXL 2-Developing solvent: Tetrahydrofuran (THF)
-Flow rate of developing solvent: 1.0 mL / min-Standard sample: TSK standard polystyrene (manufactured by Tosoh Corporation, PS-oligomer kit)
-Column temperature: 40 ° C
-Sample concentration: 0.5%
-Injection volume: 200 μL

(1-5) Viscosity Index Base oil (manufactured by SK, YUBASE4: Group III base oil in the American Petroleum Institute (API) classification so that the kinematic viscosity at 100 ° C. is 7.0 mm ² / s (viscosity index 122, 40 The polymer was diluted to 1 ° C. and kinematic viscosity 19.6 mm ² / s)), and measured by the method of JIS K 2283.

(1-6) Base oil solubility The appearance of the polymer base oil solution (polymer concentration 25% by weight) was visually observed, and the base oil solubility was evaluated according to the following evaluation criteria.
○: Appearance is uniform and there is no polymer insoluble matter. ×: Appearance is inhomogeneous and polymer insoluble matter is observed.

(2) Production example of base oil solution (viscosity index improver) of (meth) acrylate polymer (2-1) Production example 1
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen introduction tube, and a dropping funnel, a one-terminal hydroxyl group-containing polymer of hydrogenated polybutadiene (manufactured by TOTAL, Krasol (registered trademark) HLBH-5000M, number average molecular weight) 8200) 11.7 parts by mass, 2-isocyanatoethyl methacrylate (manufactured by Showa Denko KK, Karenz MOI (registered trademark)) 0.38 parts by mass, base oil (manufactured by SK, YUBASE4) 73.6 parts by mass, metal catalyst 0.024 parts by mass of tetraoctyl titanate (manufactured by Matsumoto Fine Chemical Co., Ltd.) was added, and this was stirred for 1 hour while heating to 75 ° C. in an oil bath while introducing nitrogen gas. A base oil solution was obtained. The macromonomer concentration of this base oil solution was 14% by mass, and the reaction rate was 100%. 85.7 parts by mass of the macromonomer base oil solution thus obtained, 10 parts by mass of n-butyl acrylate (BA), 50 parts by mass of n-butyl methacrylate (BMA), lauryl methacrylate / tridecyl methacrylate mixture ( (Mass ratio = 54/46) (SLMA) 23 parts by mass, N-phenylmaleimide (PMI) 5 parts by mass, base oil (manufactured by SK, YUBASE4) 86.8 parts by mass, pentaerythritol tetrakis (mercaptoacetate) 0.05 A mass part was charged into a reaction vessel, and the contents were heated to 105 ° C. with stirring while introducing nitrogen gas into the reaction vessel. As a polymerization initiator, 0.052 parts by mass of t-amylperoxoisononanoate (manufactured by Arkema Yoshitomi Co., Ltd., Luperox (registered trademark) 570) was dissolved in 2.56 parts by mass of base oil (manufactured by SK, YUBASE4). The solution was added, and 0.205 parts by mass of t-amylperoxoisononanoate (manufactured by Arkema Yoshitomi, Luperox (registered trademark) 570) as a polymerization initiator was added to 13.7 parts by mass of base oil (manufactured by SK, YUBASE4). Solution polymerization was allowed to proceed while dripping the dissolved solution over 4 hours, followed by aging for 2 hours. The base oil solution (polymer concentration 25 mass%) of the polymer 1 was obtained by adding and diluting 123.0 mass parts of base oil (the SKBASE make, YUBASE4) there.

(2-2) Production Example 2
In Production Example 1, 10 parts by weight of BA is 5 parts by weight, 50 parts by weight of BMA is 55 parts by weight, 86.8 parts by weight of base oil charged before polymerization is 73.6 parts by weight, and 123.0 A base oil solution of polymer 2 (polymer concentration 25% by mass) was obtained by performing the same operation as in Production Example 1, except that the part by mass was changed to 136.1 parts by mass.

(2-3) Production Example 3
In Production Example 1, 10 parts by mass of BA is 57 parts by mass, 50 parts by mass of BMA is 0 parts by mass, 23 parts by mass of SLMA is 26 parts by mass, and 86.8 parts by mass of base oil charged before polymerization is 117.74 parts by mass. The base oil solution of polymer 3 (polymer concentration 30% by mass) is the same as in Production Example 1 except that 123.0 parts by mass of base oil added after aging is changed to 25.32 parts by mass. Got

(2-4) Production Example 4
In Production Example 1, 10 parts by weight of BA is 0 parts by weight, 50 parts by weight of BMA is 60 parts by weight, 86.8 parts by weight of base oil to be charged before polymerization is 151.9 parts by weight, base oil 123.0 added after aging A base oil solution of polymer 4 (polymer concentration 25% by mass) was obtained by performing the same operation as in Production Example 1, except that the part by mass was changed to 66.7 parts by mass.

(3) Results Table 1 shows the polymerization conditions of each production example and the physical property evaluation results of the obtained polymers. In Production Examples 1 to 3, n-butyl acrylate (BA) was used as the acrylate monomer, and the macromonomer, n-butyl methacrylate (BMA), lauryl methacrylate / tridecyl methacrylate mixture (SLMA) were used as the methacrylate monomer. Was used. In Production Example 4, a macromonomer, n-butyl methacrylate (BMA), a lauryl methacrylate / tridecyl methacrylate mixture (SLMA) is used as the methacrylate monomer, and no acrylate monomer is used. In all of Production Examples 1 to 3, the polymerization rate of methacrylate monomers such as macromonomer and SLMA was higher than that of Production Example 4, and the overall polymerization rate was also higher.

  The viscosity index improver of the present invention can be used by adding to a lubricating oil, and the lubricating oil composition thus obtained can be suitably used for a drive system lubricating oil, a working oil, an engine oil and the like. .

Claims (11)

A polymer having a structural unit derived from an acrylate monomer (A) and a structural unit derived from a methacrylate monomer having an aliphatic hydrocarbon group having 30 or more carbon atoms (B),
The viscosity index improver, wherein the content of the structural unit (A) is 1% by mass to 70% by mass in 100% by mass of the polymer.   The viscosity index improvement according to claim 1, wherein the polymer has, as the structural unit (A), a structural unit (A1) derived from an alkyl acrylate monomer and having 2 to 8 carbon atoms in the alkyl group. Agent.   The viscosity index improver according to claim 2, wherein the content of the structural unit (A1) is 1% by mass or more and 70% by mass or less in 100% by mass of the polymer.   The viscosity index improvement according to any one of claims 1 to 3, wherein the polymer further has a structural unit (C2) derived from an alkyl methacrylate monomer, wherein the alkyl group has 9 to 20 carbon atoms. Agent. The polymer is derived from a structural unit (A1) in which the alkyl group is derived from an alkyl acrylate monomer and the alkyl group has 2 to 8 carbon atoms, and / or is derived from an alkyl methacrylate monomer, and the alkyl group has a carbon number. Having a structural unit (C1) of 2 to 8,
Viscosity as described in any one of Claims 1-4 whose total content of the said structural unit (A1) and the said structural unit (C1) is 45 to 75 mass% in the said polymer 100 mass%. Index improver.   The viscosity index improver according to any one of claims 1 to 5, wherein the polymer further has a structural unit (D) derived from a maleimide monomer. Copolymerizing a monomer component containing an acrylate monomer (a) and a methacrylate monomer (b) having an aliphatic hydrocarbon group having 30 or more carbon atoms,
The method for producing a viscosity index improver, wherein the monomer (a) is used in an amount of 1 to 70 parts by mass with respect to 100 parts by mass of the monomer component.   The method for producing a viscosity index improver according to claim 7, wherein a monomer (a1) which is an alkyl acrylate and has 2 to 8 carbon atoms in the alkyl group is used as the monomer (a).   The method for producing a viscosity index improver according to claim 8, wherein the amount of the monomer (a1) used is 1 part by mass or more and 70 parts by mass or less with respect to 100 parts by mass of the monomer component.   The viscosity index improver according to any one of claims 7 to 9, wherein the monomer component further comprises a monomer (c2) which is alkyl methacrylate and the alkyl group has 9 to 20 carbon atoms. Manufacturing method.   A lubricating oil composition comprising the viscosity index improver according to any one of claims 1 to 6 and a lubricating base oil.