JP2020122119A - Viscosity index improver for lubricant and lubricant composition - Google Patents

Abstract

To provide a viscosity index improver for lubricant that gives a lubricant composition having a high viscosity index improvement capability and high thickening properties, and having a transparent appearance.SOLUTION: A viscosity index improver for lubricant contains solid matter (S). The solid matter (S) contains a graft copolymer (X). The graft copolymer (X) has a main chain part derived from an ethylene-α-olefin copolymer (A), and a graft part derived from a (meth) acrylate copolymer (B), and has a grafting rate of 15-400%. The (meth) acrylate copolymer (B) is a copolymer of two or more (meth) acrylates. The (meth) acrylate has an alkyl group with an average carbon number of 8 or more.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a viscosity index improver for lubricating oil having a high viscosity index improving ability and a thickening property, and a lubricating oil composition containing the same.

Petroleum products generally have a so-called temperature dependence of viscosity, in which the viscosity changes greatly with temperature changes, but lubricating oils used as engine oils for automobiles, gear oils, hydraulic oils, etc., range from low temperature to high temperature. It is practically desirable that the viscosity does not change as much as possible over a wide range. The viscosity index is used as this measure, and the larger the viscosity index, the higher the stability against temperature changes. Therefore, for the purpose of reducing the temperature dependence of the viscosity of the lubricating oil, a certain polymer soluble in a lubricating base oil such as mineral oil is used as a viscosity index improver. As such a polymer, for example, polymethacrylate (PMA) (see Patent Document 1), olefin copolymer (OCP) (see Patent Document 2), polyisobutylene (PIB) and the like are used.

Each of the lubricating oils containing these polymers has its own characteristics. For example, PMA is excellent in improving the viscosity index and also has a pour point depressing action, but is low in thickening effect and shear stability. There is a method of increasing the molecular weight of PMA in order to improve the thickening effect, but in this case, the stability against shearing force becomes extremely poor, and the decrease in viscosity during driving becomes a problem. PIB has a large thickening effect, but is inferior in the viscosity index improving property. Although OCP is inferior to PMA in improving the viscosity index, it has a large thickening effect and is excellent in shear stability.

Further, PMA has poor compatibility with mineral oil, and when alkyl (meth)acrylate having a high polarity is used as a monomer, a compounded oil that does not dissolve or becomes cloudy when blended with mineral oil is obtained, and is practically useful. do not do. Patent Document 3 describes that when the average number of carbon atoms in the side chain of the alkyl (meth)acrylate is less than 7, the solubility in the base oil is poor and the compound does not function as a dispersant viscosity modifier.

As a method of improving the physical properties of OCP, a method of adjusting the kind and molar ratio of monomers, a method of changing a monomer sequence such as random or block, a method of blending polymers having different compositions, an ethylene/α-olefin copolymer There is also a method of graft-copolymerizing a polar monomer, and various methods have been tried so far.

For example, Patent Document 4 discloses a blend of ethylene/α-olefin copolymers having different ethylene contents, and shows that when used as a viscosity index improver of a lubricating oil, excellent low temperature properties can be obtained. Has been done. On the other hand, other devises that take advantage of the characteristics of living polymerization have been made. For example, in Patent Document 5, a random copolymer of ethylene and α-olefin having a narrow molecular weight distribution and different compositions in the molecule, a block copolymer Coalescence is disclosed. These copolymers have shear stability and thickening properties, and excellent low temperature properties, and have been shown to be suitable as viscosity index improvers.

In this way, various attempts have been made to improve performance, but in recent years, improvement of temperature-viscosity characteristics for the purpose of energy saving, and long life (shear stability, thermal oxidation resistance) for the purpose of reducing waste lubricating oil, etc. Stability) requirements are increasing, and further improvement in the performance balance is required for viscosity index improvers.

As a further measure for improving the balance of performance, it is considered to combine an ethylene/α-olefin copolymer having excellent thickening and heat resistance with a poly(meth)acrylate having excellent temperature-viscosity characteristics. A graft copolymer obtained by reacting a (meth)acrylate in the presence of a radical initiator is disclosed. However, it is difficult to obtain a sufficient reaction rate by radical grafting reaction, and the resulting grafted product contains a large amount of unmodified polyolefin and homopolymer of (meth)acrylate, and therefore the amount of active ingredient is small and Performance improvement cannot be expected.

As a method for producing a graft copolymer having a high graft ratio (grafting rate), a macromonomer having a radically polymerizable functional group added to a polyolefin chain is copolymerized with (meth)acrylate. A method of obtaining the copolymer is conceivable. As a method for producing a polyolefin macromonomer for synthesizing such a graft copolymer, for example, in Patent Document 7, a polymerizable acryloyl group or methacryloyl group is added to the end of polyethylene synthesized by using a living polymerization method. The method of introducing is described.

In the method using living polymerization described above, only one polymer can be obtained from one catalytically active site. However, from the viewpoint of productivity, the larger the number of polymers obtained from one catalyst active point, the more preferable. Therefore, it is hard to say that the use of living polymerization is economically sufficiently satisfactory in view of industrial mass production. Moreover, since the method described in Patent Document 6 uses the anionic polymerization method using alkyllithium, the polyolefin that can be produced as a macromonomer is polyethylene having a relatively low molecular weight of about 1000-mer at the maximum, and the lubricating oil It is difficult to apply to ethylene/α-olefin copolymer having a molecular weight of 500 to 20,000 which is useful as an additive.

JP, 7-62372, A JP-B-46-34508 JP-A-5-287028 U.S. Pat. No. 3,697,429 JP-A-60-35009 JP 61-181528 A JP-A-6-329720

The problem to be solved by the present invention is such that, from the viewpoint of low fuel consumption and energy saving of automobiles and industrial machines, a transparent appearance is obtained when blended oil having a high viscosity index and a high viscosity increase. The purpose of the present invention is to provide a viscosity index improver for lubricating oil.

As a result of intensive studies to solve the above problems, it was found that a specific copolymer has excellent viscosity index improving ability, viscosity increasing property and base oil solubility as a viscosity index improving agent for lubricating oil.
That is, the present invention is specified by the following [1] to [7].

[1] A viscosity index improver for a lubricating oil containing a solid matter (S),
The solid matter (S) contains a graft copolymer (X),
The graft copolymer (X) is
A main chain portion derived from an ethylene/α-olefin copolymer (A) which is a copolymer of ethylene and an α-olefin having 3 to 8 carbon atoms;
A graft portion derived from a (meth)acrylic acid ester copolymer (B), and having a grafting ratio defined by the following formula (I) of 15 to 400%,
The (meth)acrylic acid ester copolymer (B) is a copolymer of two or more kinds of (meth)acrylic acid ester,
A viscosity index improver for lubricating oil, wherein the alkyl group of the (meth)acrylic acid ester (that is, an alkyl group bonded to an acryloyloxy group or a methacryloyloxy group) has an average carbon number of 8 or more.
Grafting rate (%)={(mass of graft copolymer (X))-(mass of ethylene/α-olefin copolymer (A))}/(ethylene/α-olefin copolymer (A) Mass)×100 (I)
[2] The viscosity index improver for lubricating oil according to the above [1], wherein the α-olefin is one or more selected from propylene and butene.
[3] The intrinsic viscosity [η] of the graft copolymer (X) measured in a decalin solvent at 135° C. is 0.05 to 15 dL/g, [1] or [2] ] The viscosity index improver for lubricating oils described in.
[4] The (meth)acrylic acid ester copolymer (B) is a copolymer of C1-6 alkyl (meth)acrylate and C7-36 alkyl (meth)acrylate, The viscosity index improver for lubricating oil according to any one of 1] to [3].
[5] The lubricating oil according to any one of [1] to [4], wherein the proportion of the graft copolymer (X) in the solid matter (S) is 95% by mass or more. Viscosity index improver.
[6] The viscosity index improver for lubricating oil according to any one of the above [1] to [5], which contains 80% by mass or more of the solid matter (S).
[7] (i) 0.2 to 50 parts by mass of the viscosity index improver for lubricating oil according to any one of [1] to [6],
(Ii) 50 to 99.8 parts by mass of base oil consisting of at least one kind selected from mineral oil, synthetic hydrocarbon oil and ester oil, and having a kinematic viscosity at 100° C. in the range of 1 to ²⁰ mm ² /s (however, , The total of (i) and (ii) is 100 parts by mass), and optionally,
(Iii) selected from the group consisting of a detergent dispersant, a viscosity index improver, an antioxidant, a corrosion inhibitor, an antiwear agent, a friction modifier, a pour point depressant, a rust preventive, an antifoaming agent and an extreme pressure agent. A lubricating oil composition comprising at least one additive selected from the group consisting of:

INDUSTRIAL APPLICABILITY The viscosity index improver for lubricating oil of the present invention has excellent viscosity-temperature characteristics, thickening property, and base oil solubility as compared with conventional viscosity index improving agents for lubricating oil. Therefore, by blending with a lubricating base oil such as mineral oil and α-olefin oligomer and other additives, a lubricating oil composition having high viscosity-temperature characteristics and thickening properties and excellent in fuel efficiency is provided. be able to.

Hereinafter, the present invention will be described in detail.
<Viscosity index improver for lubricating oil>
The viscosity index improver for lubricating oil of the present invention contains a solid matter (S), and the solid matter (S) has a main chain portion derived from the ethylene/α-olefin copolymer (A), and (meth). The graft copolymer (X) having a graft portion derived from the acrylic acid ester copolymer (B) is included.

<Solid matter (S)>
The solid (S) is a solid component that does not have fluidity at room temperature, and may be in the form of particles such as powder or pellets, or in the form of various molded products such as bales, films, sheets and fibers.
The solid (S) contains the graft copolymer (X), and preferably contains the graft copolymer (X) as a main component. Specifically, in the solid (S), the graft copolymer (X) preferably accounts for 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more. Examples of the component other than the graft copolymer (X) in the solid (S) include an antioxidant and the like. Further, depending on the method for producing the graft copolymer (X), The simple substance of the ethylene/α-olefin copolymer (A) and the simple substance of the (meth)acrylic acid ester copolymer (B) to be described are also included.

<Graft copolymer (X)>
The graft copolymer (X) used in the present invention is
A main chain portion derived from an ethylene/α-olefin copolymer (A) which is a copolymer of ethylene and an α-olefin having 3 to 8 carbon atoms;
And a graft portion derived from the (meth)acrylic acid ester copolymer (B).
In addition, in this invention, (meth)acryl means acryl or methacryl.

That is, the graft copolymer (X) used in the present invention is an ethylene/α-olefin copolymer (A), which is a copolymer of ethylene and an α-olefin having 3 to 8 carbon atoms, and (meth)acrylic. It is a graft copolymer with the acid ester copolymer (B).

Ethylene/α-olefin copolymer (A)
The ethylene/α-olefin copolymer (A) used in the present invention is a copolymer of ethylene and an α-olefin having 3 to 8 carbon atoms.
Examples of the α-olefin having 3 to 8 carbon atoms include propylene, butene-1, pentene-1, 2-methylbutene-1, 3-methylbutene-1, hexene-1, 3-methylpentene-1, 4-methylpentene-. 1,3,3-dimethylbutene-1, heptene-1, methylhexene-1, dimethylpentene-1, trimethylbutene-1, ethylpentene-1, octene-1, methylpentene-1, dimethylhexene-1, trimethyl Examples include pentene-1, ethylhexene-1, methylethylpentene-1, diethylbutene-1, propylpentene-1 and the like. These α-olefins may be used alone or in combination of two or more.

Among them, propylene, butene, hexene and octene are preferable as the α-olefin having 3 to 8 carbon atoms, propylene, butene and octene are more preferable, propylene or butene is further preferable, and propylene is particularly preferable.

The ethylene/α-olefin copolymer (A) used in the present invention may be a copolymer of ethylene and an α-olefin having 3 to 8 carbon atoms, preferably ethylene and 3 carbon atoms. It is a random copolymer with the (alpha)- olefin of (8). As the ethylene/α-olefin copolymer (A) used in the present invention, particularly preferable copolymers include, for example, ethylene/propylene random copolymer and ethylene/1-butene random copolymer.

The ethylene/α-olefin copolymer (A) used in the present invention is not particularly limited in the copolymerization ratio of ethylene and the α-olefin having 3 to 8 carbon atoms, but is preferably derived from ethylene. The content of the structural unit thus obtained is 50 to 90 mol %, more preferably 51 to 85 mol %, further preferably 55 to 80 mol %, and the content of the structural unit derived from the α-olefin is preferably 10 to 50. It is desirable that it is in the range of mol%, more preferably 15 to 45 mol%, and further preferably 20 to 40 mol%.

The content of the structural unit derived from ethylene and the content of the structural unit derived from α-olefin of the ethylene/α-olefin copolymer (A) used in the present invention are measured by, for example, ¹³ C-NMR method. It is possible to perform peak identification and quantification according to the method described in “Polymer Analysis Handbook” (P163-170, published by Asakura Shoten).

The ethylene/α-olefin copolymer (A) used in the present invention has an intrinsic viscosity [η] measured in a decalin solvent at 135° C. of preferably 0.05 to 15 dL/g, more preferably 0.1. It is desirable to be in the range of 10 to 10 dL/g, and more preferably 0.5 to 3 dL/g. The melt flow rate (MFR) measured at 190° C. under a load of 2.16 kgf is usually 0.01 to 200 g/10 minutes, preferably 0.1 to 180 g/10 minutes, more preferably 1 to 150 g/10 minutes. , Is desirable.

The ethylene/α-olefin copolymer (A) used in the present invention is not particularly limited and can be prepared by a conventionally known method. Further, a commercially available ethylene/α-olefin copolymer which is a copolymer of ethylene and an α-olefin having 3 to 8 carbon atoms can also be used.

(Meth)acrylic acid ester copolymer (B)
The graft copolymer (X) used in the present invention has a graft portion derived from the (meth)acrylic acid ester copolymer (B).
The (meth)acrylic acid ester copolymer (B) is a copolymer of two or more kinds of (meth)acrylic acid ester. The (meth)acrylic acid ester copolymer (B) may or may not contain a structural unit other than the structural unit derived from the (meth)acrylic acid ester as long as the effect of the present invention is not impaired. Good.

From the viewpoint of easy production by a method of graft-copolymerizing two or more kinds of (meth)acrylic acid ester with respect to the ethylene/α-olefin copolymer (A) described later, (meth)acrylic acid is used. The ester copolymer (B) is preferably a (meth)acrylic acid ester copolymer selected from the group consisting of copolymers of two or more kinds of acrylic acid esters and copolymers of two or more kinds of methacrylic acid esters. Is.

More preferably, the graft copolymer (X) comprises, as a graft part, substantially only a graft part derived from a copolymer of two or more kinds of acrylic acid esters, or a copolymer of two or more kinds of methacrylic acid esters. It has only a graft portion derived from a polymer.

The copolymer of two or more kinds of acrylic acid ester may or may not contain a structural unit other than the structural unit derived from two or more kinds of acrylic acid ester as long as the effect of the present invention is not impaired. However, preferably, as the structural unit, substantially only structural units derived from two or more kinds of acrylic acid esters are included.

The copolymer of two or more kinds of methacrylic acid ester may or may not contain a structural unit other than the structural unit derived from two or more kinds of methacrylic acid ester within a range not impairing the effect of the present invention. However, preferably, it has substantially only structural units derived from two or more kinds of methacrylic acid esters as structural units.

The two or more kinds of (meth)acrylic acid esters are preferably C1-6 alkyl (meth)acrylate (that is, an ester in which the alkyl group bonded to the (meth)acryloyloxy group has 1 to 6 carbon atoms) and C7-36 alkyl (meth)acrylate (that is, an ester having an alkyl group bonded to a (meth)acryloyloxy group having 7 to 36 carbon atoms), and C1-6 alkyl (meth)acrylate and (meth) The C7-36 alkyl acrylate may be one kind or two or more kinds.

The C1-6 alkyl (meth)acrylate is preferably C1-4 alkyl (meth)acrylate (the numerical range after C is the number of carbon atoms in the alkyl group, and the same applies hereinafter), More preferably, it is C1-2 alkyl (meth)acrylate, and particularly preferably methyl (meth)acrylate. The C7-36 alkyl (meth)acrylate is preferably C8-28 alkyl (meth)acrylate, and more preferably C8-24 alkyl (meth)acrylate.

Specific examples of the acrylate ester include methyl acrylate, propyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, 2-ethylhexyl acrylate. , Octyl acrylate, nonyl acrylate, decyl acrylate, undecyl acrylate, dodecyl acrylate, pentadecyl acrylate, stearyl acrylate, tridecyl acrylate and the like. Specific examples of the methacrylic acid ester include methyl methacrylate, propyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate and methacrylic acid 2 -Ethylhexyl, octyl methacrylate, nonyl methacrylate, decyl methacrylate, undecyl methacrylate, dodecyl methacrylate, pentadecyl methacrylate, stearyl methacrylate, tridecyl methacrylate and the like can be mentioned.

By using such acrylic acid ester or methacrylic acid ester as a monomer, it is possible to introduce many graft moieties into the graft copolymer (X).
The average carbon number of the alkyl group of the structural unit derived from the (meth)acrylic acid ester (the alkyl group bonded to the structural unit derived from the (meth)acryloyloxy group), which constitutes the graft part of the graft copolymer (X), is , 8 or more.

A viscosity index improver for a lubricating oil, which is a copolymer of two or more (meth)acrylic acid esters and contains a graft copolymer (X) in which the average carbon number of the alkyl group is in the above range, has a high viscosity index. It has a high viscosity and a high base oil solubility (in other words, a transparent lubricating oil composition can be obtained when blended with a lubricating base oil).

From the viewpoint of improving the viscosity index, the average carbon number is preferably 12 or less, more preferably 11 or less.
The average carbon number can be obtained, for example, by performing ¹³ C-NMR measurement on the graft copolymer (X), and based on the ratio of the areas of the obtained peaks.

Two or more kinds of (meth)acrylic acid esters are used in such a ratio that the average carbon number of the alkyl group falls within the above range. When the (meth)acrylate is C1-6 alkyl (meth)acrylate and C7-36 alkyl (meth)acrylate, the proportion of C1-6 alkyl (meth)acrylate in the entire (meth)acrylate ester Is preferably 3.0 mol% or more, and more preferably 5.0 mol% or more from the viewpoint of improving the viscosity index.

Graft copolymer (X)
The graft copolymer (X) used in the present invention is derived from the above-mentioned main chain portion derived from the ethylene/α-olefin copolymer (A) and the (meth)acrylic acid ester copolymer (B). And a graft portion. In the present invention, even when the chain length of the graft part is longer than the chain length of the main chain part, the part derived from the ethylene/α-olefin copolymer (A) is the main chain part and the (meth)acrylic acid ester. A portion derived from the copolymer (B) is treated as a graft portion.

In the present invention, the graft copolymer (X) may be obtained by introducing the (meth)acrylic acid ester copolymer (B) into the ethylene/α-olefin copolymer (A), , Obtained by polymerizing an acrylic acid ester or a methacrylic acid ester which is a monomer of the (meth)acrylic acid ester copolymer (B) in the presence of the ethylene/α-olefin copolymer (A). Good.

Such a graft copolymer (X) has a high graft ratio of the graft portion, and the grafting ratio defined by the following formula (I) is 15% or more and 400% or less. The grafting ratio of the graft copolymer (X) is preferably 20% or more, more preferably 25% or more, and preferably 350% or less, more preferably 300% or less.
Grafting rate (%)={(mass of graft copolymer (X))-(mass of ethylene/α-olefin copolymer (A))}/(ethylene/α-olefin copolymer (A) Mass)×100 (I)

The mass of the ethylene/α-olefin copolymer (A) can be determined, for example, by the following procedures (i) to (iv).
(I) An ethylene/α-olefin copolymer (A) and a (meth)acrylic acid ester copolymer (B) (both of which may have any composition) are prepared.
(Ii) A blend resin is prepared by mixing these copolymers. At this time, the blending ratio of each copolymer is changed to prepare a plurality of kinds of blend resins.
(Iii) For each blend resin, the absorbance ratio (the ratio of the absorption A ₄₃₂₂ derived from the ethylene/α-olefin copolymer and the absorption A ₉₆₇ derived from the ester moiety) was measured by infrared spectroscopy (IR), A calibration curve showing the relationship between the ratio of the α-olefin copolymer and the absorbance ratio is prepared.
(Iv) The absorbance ratio of the graft copolymer (X) is measured, and the ratio of the ethylene/α-olefin copolymer (A) in the graft copolymer (X) is determined from the measured value and the calibration curve. From the mass of the graft copolymer (X) and the ratio, the mass of the ethylene/α-olefin copolymer (A) is calculated.

The graft copolymer (X) used in the present invention is not particularly limited, but the intrinsic viscosity [η] measured in a decalin solvent at 135° C. is preferably 0.05 to 15 dL/g, It is preferably 0.1 to 10 dL/g, more preferably 0.5 to 3 dL/g.

The graft copolymer (X) used in the present invention is not particularly limited, but the weight average molecular weight (Mw) is usually 60,000 to 600,000, preferably 70,000 to 500,000. More preferably, the range is 80,000 to 450,000.

Further, the graft copolymer (X) used in the present invention preferably has a molecular weight distribution (Mw/Mn) value determined from a weight average molecular weight (Mw) and a number average molecular weight molecule (Mn) of 1.5 to It is preferable to satisfy the range of 8.0, more preferably 2.0 to 7.5, and further preferably 2.5 to 7.0.

In the present invention, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are values determined by gel permeation chromatography (GPC) under the conditions described in Examples described later.

In the graft copolymer (X) used in the present invention, the main chain portion derived from the ethylene/α-olefin copolymer (A) is highly modified, and the graft portion having a polar group is introduced at a high ratio. Therefore, even when preparing a composition having a high affinity for both a hydrophilic substance and a hydrophobic substance and containing both the hydrophilic substance and the hydrophobic substance, the graft copolymer (X By coexisting with), a homogeneous composition can be easily prepared.

Method for Producing Graft Copolymer (X) As described above, the graft copolymer (X) used in the present invention is a (meth)acrylic acid ester with respect to the ethylene/α-olefin copolymer (A). It may be obtained by introducing the copolymer (B), and is a monomer of the (meth)acrylic acid ester copolymer (B) with respect to the ethylene/α-olefin copolymer (A). It may be obtained by graft-copolymerizing an acrylic ester or a methacrylic ester.

Among these, an acrylic acid ester or a methacrylic acid ester which is a monomer of the (meth)acrylic acid ester copolymer (B) is added to the ethylene/α-olefin copolymer (A) which is the main chain. The method of graft copolymerization can be preferably adopted.

In the production of the graft copolymer (X) used in the present invention, the ethylene/α-olefin copolymer (A) and the acrylic acid ester or the methacrylic acid ester are subjected to a graft copolymerization reaction using alkylboron. It is preferable to have a graft copolymerization step. Graft copolymer of ethylene/α-olefin copolymer (A) and acrylic acid ester or methacrylic acid ester, which is a monomer constituting the (meth)acrylic acid ester copolymer (B), using alkyl boron. When polymerized, a graft part derived from the (meth)acrylic acid ester copolymer (B) with a high grafting ratio to the main chain part derived from the ethylene/α-olefin copolymer (A). It is possible to preferably produce the graft copolymer (X) having

Specific aspects, preferable aspects, etc. of the (meth)acrylic acid ester, which is a monomer of the (meth)acrylic acid ester copolymer (B), are as described above, and the monomer is (meth)acrylic acid. Two or more kinds are used in combination so that a graft portion derived from the (meth)acrylic acid ester copolymer (B) in which the average carbon number of the alkyl group in the ester is 8 or more can be obtained.

In the graft copolymerization step using alkylboron, an initiator that reacts alkylboron with oxygen to form a peroxide can be used. Such a graft copolymerization reaction using an alkylboron is described in, for example, US3141862, Macromolecules 2005, 38, 8966-8970, J. APPL. POLYM. SCI. 2015, 42186 and Journal of Polymer Science: Part A: Polymer Chemistry. , Vol. 47, 6163-6167 (2009) and the like.

The alkyl boron is not particularly limited, but for example, triisobutyl boron can be preferably used.
The solvent used in the graft polymerization reaction, in addition to water, benzene, toluene, aromatic hydrocarbon solvents such as xylene, pentane, hexane, heptane, octane, nonane, aliphatic hydrocarbon solvents such as decane, cyclohexane, Alicyclic hydrocarbon solvents such as methylcyclohexane and decahydronaphthalene, chlorinated hydrocarbon solvents such as chlorobenzene, dichlorobenzene, trichlorobenzene, methylene chloride, chloroform, carbon tetrachloride and tetrachloroethylene, 1-methyl 2-pyrrolidone, ethylene carbonate, propylene carbonate, γ-butyrolactone, N-methyl-2-pyrrolidone, propylene glycol monomethyl ether acetate, acetyl citrate tributyl, 2,4-pentadiene, dimethyl sulfoxide, n-alkyl adipate, Ketones such as 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, 3-methoxy-3-methyl-1-butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetophenone, benzophenone and cyclohexanone; benzyl alcohol , 1-butanol, 2-butanol, t-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-ethyl-1-hexanol, normal propyl alcohol, isopropyl alcohol, ethanol, methanol and other alcohols; Examples thereof include ethers such as ethyl ether, ethylene glycol monomethyl ether, anisole, phenyl ether, dioxane, and tetrahydrofuran; esters such as ethyl acetate and butyl acetate. These solvents may be used alone or in combination of two or more.

In carrying out the graft copolymerization reaction, there is no particular limitation on the method of contacting the ethylene/α-olefin copolymer (A), the acrylic acid ester or methacrylic acid ester, which is a graft monomer, and the alkylboron, and the contacting order. Various methods can be adopted. The ethylene/α-olefin copolymer (A) may be impregnated with an acrylic acid ester or a methacrylic acid ester or an alkylboron in advance. In the graft copolymerization reaction, a known chain transfer agent may be used in combination for adjusting the molecular weight of the graft polymer.

On the other hand, the order of contacting alkylboron and oxygen is the starting point of the reaction. Therefore, it is preferable to charge alkylboron into the reaction system first, and then introduce oxygen to bring them into contact. The acrylic acid ester or methacrylic acid ester, which is a graft monomer, is preferably subjected to a nitrogen bubbling treatment in advance to sufficiently purge residual oxygen.

Further, within a range not hindering the object of the present invention, known additives, for example, antioxidants such as hindered phenol compounds, process stabilizers, heat stabilizers, heat aging agents, weathering stabilizers, antistatic agents, slips. Radical scavengers represented by nitroxy radicals such as inhibitors, antiblocking agents, antifog agents, lubricants, pigments, dyes, nucleating agents, plasticizers, hydrochloric acid absorbents, flame retardants, antiblooming agents, piperidines, etc. Various additives such as known softeners, tackifiers, processing aids, adhesion promoters, carbon fibers, glass fibers, and fillers such as whiskers can be used in combination. It is also possible to blend a small amount of another polymer compound without departing from the spirit of the present invention.

The above graft copolymerization reaction can be used without particular limitation as long as it is a device capable of mixing and heating. For example, both vertical and horizontal reactors can be used. Specifically, a fluidized bed, a moving bed, a loop reactor, a horizontal reactor with stirring blades, a vertical reactor with stirring blades, a rotating drum and the like can be mentioned. Further, a multi-spindle/revolution/revolution combination type mixer such as a planetary mixer, a kneader, a paddle dryer, a Henschel mixer, a static mixer, a V blender, a tumbler, and a Nauta mixer can also be used.

It is also preferable to have a washing step of washing the obtained graft copolymer with a solvent capable of dissolving unreacted acrylic acid ester or methacrylic acid ester after the completion of the graft copolymerization step.

The solvent used in the washing step is not particularly limited, but ketones and alcohols are preferable, and acetone and methanol are particularly preferable. The washing temperature is not limited as long as the produced graft copolymer (X) is not damaged, but is preferably 0 to 110°C, more preferably room temperature to 100°C.
Here, when the washing temperature is set higher than the boiling point of the washing solvent at atmospheric pressure, the washing step is preferably performed in a sealed state in order to prevent volatilization of the washing solvent.

<Viscosity index improver for lubricating oil>
The viscosity index improver for lubricating oil of the present invention contains the above-mentioned solid matter (S), and the solid matter (S) has a main chain portion derived from the ethylene/α-olefin copolymer (A), and ( A graft copolymer (X) having a graft part derived from a (meth)acrylic acid ester copolymer (B). Preferably, the solid content (S) of the viscosity index improver for lubricating oil accounts for 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more.

The viscosity index improver for lubricating oil of the present invention may be composed only of the solid matter (S), and may contain components other than the solid matter (S) as long as the effect of the present invention is not impaired. Absent. Examples of components other than the solid (S) include polymers conventionally used as viscosity index improvers for lubricating oils and various additives such as antioxidants.

The form of the viscosity index improver for lubricating oil of the present invention is not particularly limited, but it is preferably a solid form, for example, powder form, particle form such as pellet form, veil, film, sheet, It may be in the shape of various molded products such as fibers. The viscosity index improver for lubricating oils of the present invention can be suitably used for improving the viscosity index of lubricating oils by being added or dissolved or dispersed in a lubricating base oil which is usually a base oil.

<Lubricant composition>
The lubricating oil composition of the present invention is
(I) 0.2 to 50 parts by mass, preferably 0.2 to 25 parts by mass, more preferably 0.25 to 10 parts by mass of a viscosity index improver for lubricating oil containing the graft copolymer (X). Particularly preferably 0.25 to 5 parts by mass, and particularly preferably 0.3 to 2.5 parts by mass,
(Ii) 50 to 99.8 parts by mass of base oil consisting of at least one kind selected from mineral oil, synthetic hydrocarbon oil and ester oil, and having a kinematic viscosity at 100° C. in the range of 1 to ²⁰ mm ² /s (however, , The sum of (i) and (ii) is 100 parts by mass), and if necessary,
(Iii) selected from the group consisting of a detergent dispersant, a viscosity index improver, an antioxidant, a corrosion inhibitor, an antiwear agent, a friction modifier, a pour point depressant, a rust preventive, an antifoaming agent and an extreme pressure agent. At least one additive selected from the group consisting of:

Examples of the base oil (ii) used in the lubricating oil composition of the present invention include conventionally known mineral oils, synthetic hydrocarbon oils and ester oils having a kinematic viscosity at 100° C. in the range of 1 to ²⁰ mm ² /s. At least one base oil selected is used.

Mineral oils generally have several grades depending on how they are refined, but generally mineral oils containing 0.5-10% wax content are used. In the present invention, for example, a highly refined oil having a low pour point, a high viscosity index, and a composition mainly containing isoparaffin, which is produced by a hydrocracking refining method can be used.

Examples of synthetic hydrocarbon oils include α-olefin oligomers, alkylbenzenes, alkylnaphthalenes, and the like. These can be used alone or in combination of two or more. Among these, as the α-olefin oligomer, a low molecular weight oligomer of at least one olefin selected from olefins having 8 to 12 carbon atoms can be used. Such an α-olefin oligomer can be produced by Ziegler catalyst, cationic polymerization using Lewis acid as a catalyst, thermal polymerization, or radical polymerization.

Alkylbenzenes and alkylnaphthalenes are usually mostly dialkylbenzenes or dialkylnaphthalenes having an alkyl chain length of 6 to 14 carbon atoms. Such alkylbenzenes or alkylnaphthalenes are produced by the Friedel-Crafts alkylation reaction of benzene or naphthalene with an olefin. The alkylated olefins used in the production of alkylbenzenes or alkylnaphthalenes may be linear or branched olefins or combinations thereof. These manufacturing methods are described in, for example, US Pat. No. 3,909,432.

Ester oils include monoesters produced from monobasic acids and alcohols; diesters produced from dibasic acids and alcohols or diols and monobasic acids or acid mixtures; diols, triols (eg trimethylolpropane). , A polyol ester produced by reacting tetraol (for example, pentaerythritol), hexaol (for example, dipentaerythritol) and the like with a monobasic acid or an acid mixture. Examples of these esters include tridecyl pelargonate, di-2-ethylhexyl adipate, di-2-ethylhexyl azelate, trimethylolpropane triheptanoate, pentaerythritol tetraheptanoate and the like.

In the present invention, as the base oil (ii), any one of these mineral oils, synthetic hydrocarbon oils, and ester oils may be used alone, or two or more kinds may be used in combination.
The following can be illustrated as an additive used as needed in the lubricating oil composition of this invention, These can be used individually or in combination of 2 or more types.

Detergent dispersants: metal sulfonates, metal phenates, metal phosphanates, succinimides and the like can be exemplified, and they are usually used in the range of 0 to 15 mass %.
Pour point depressants: polymethacrylate, alkylnaphthalene and the like can be exemplified, and they are usually used in the range of 0 to 3 mass %.
Extreme pressure agents: Sulfur-based extreme pressure agents such as sulfides, sulfoxides, sulfones, thiophosphinates, thiocarbonates, sulfurized fats and oils, sulfurized olefins; phosphoric acid esters, phosphorous acid esters, phosphoric acid ester amine salts, Examples thereof include phosphoric acids such as phosphite amines; halogen compounds such as chlorinated hydrocarbons. The extreme pressure agent is used in a range of 0 to 15% by mass as needed.
Antiwear agents: inorganic or organic molybdenum compounds such as molybdenum disulfide, organic boron compounds such as alkylmercaptyl borate; graphite, antimony sulfide, boron compounds, polytetrafluoroethylene and the like. The antiwear agent is used in the range of 0 to 3% by mass as needed.
Antioxidant: Phenol-based or amine-based compounds such as 2,6-di-tert-butyl-4-methylphenol. The antioxidant is used in the range of 0 to 3% by mass as needed.
Anticorrosive: Examples include various amine compounds, carboxylic acid metal salts, polyhydric alcohol esters, phosphorus compounds, sulfonates and the like. The rust preventive agent is used in a range of 0 to 3 mass% as necessary.
Defoaming agents: dimethylsiloxane, silicone-based compounds such as silica gel dispersions, alcohol-based or ester-based compounds and the like can be exemplified. The antifoaming agent is used in the range of 0 to 0.2% by mass, if necessary.
In the lubricating oil composition according to the present invention, in addition to the above additives, demulsifiers, colorants, oiliness agents (oiliness improvers) and the like can be used if necessary.

Hereinafter, the present invention will be described more specifically based on Examples, but the present invention is not limited thereto.
In the following examples and the like, the measurement and evaluation methods are as follows.

<Weight average molecular weight (Mw), number average molecular weight (Mn), molecular weight distribution (Mw/Mn)>
The weight average molecular weight (Mw) and the number average molecular weight (Mn) were measured as follows using Tosoh Corporation HLC-8321 GPC/HT type gel permeation chromatograph (GPC).

As a separation column, TSKgel GMH6-HT (two) and GMH6-HTL (two) (each 7.5 mm ID×30 cm, manufactured by Tosoh Corp.) were used, the column temperature was 140° C., and the mobile phase was Using o-dichlorobenzene (containing 0.025% BHT), the development rate was 1.0 mL/min, the sample concentration was 0.1% (w/v), and the sample injection amount was 0.4 mL. A differential refractometer was used as. The instrument was calibrated using monodisperse polystyrene (Tosoh Corp., #3 std set). The molecular weight distribution (Mw/Mn) was calculated by dividing Mw measured by the above measuring method by Mn similarly measured by the above measuring method.

<Intrinsic viscosity [η]>
About 20 mg of the sample was dissolved in 15 ml of decalin, and the specific viscosity η _sp was measured in an oil bath at 135°C. To this decalin solution, 5 ml of decalin solvent was added and diluted, and then the specific viscosity η _sp was measured in the same manner. This dilution operation was repeated twice more, and the value of η _sp /C when the concentration (C) was extrapolated to 0 was determined as the intrinsic viscosity [η].
[Η]=lim(η _sp /C) (C→0)

<Grafting rate (%)>
The grafting ratio of the graft copolymer was determined by the following formula (I).
Grafting rate (%)={(mass of graft copolymer (X))-(mass of ethylene/α-olefin copolymer (A))}/(ethylene/α-olefin copolymer (A) Mass)×100 (I)

<Viscosity characteristics>
For the kinematic viscosity and the viscosity index, the kinematic viscosity at 100° C. and 40° C. was measured by the method described in JIS K2283, and the viscosity index was calculated.

<Cold Cranking Simulator (CCS) viscosity>
The measurement was carried out according to ASTM D 5293. The CCS viscosity is used for evaluating the slidability of the crankshaft at low temperature/starting, and the smaller the value, the better the low temperature characteristics of the lubricating oil.

<Appearance of compounded oil>
The appearance of the compounded oil at 25° C. was visually observed and evaluated according to the following criteria.
Transparent: It was transparent.
White turbidity: White turbidity was observed.

[Polymerization Example 1] (Production of Graft Copolymer (X-1))
As the ethylene/α-olefin copolymer (A), MFR=59.3 (g/10 minutes, 190° C., 2.16 kgf), ethylene content 78 mol%, intrinsic viscosity [η]=0.84 dL/g Using ethylene/propylene copolymer pellets (EP-1), methyl methacrylate (MMA), which is a methacrylic acid ester having an alkyl group having 1 carbon atom, and methacrylic acid having an alkyl group having 12 carbon atoms, are used as graft monomers. The ester dodecyl methacrylate (DMA) was used.

Under a nitrogen atmosphere, 25.0 g of ethylene/propylene copolymer pellets (EP-1) and 84.0 g of a mixed solution (MMA:DMA=10:90 (mol %)) of methyl methacrylate and dodecyl methacrylate were added to 500 mL of 500 mL. It was charged in a separable flask, the liquid temperature was adjusted to 60° C., and the ethylene/propylene copolymer pellets were dissolved. Separately, under a nitrogen atmosphere, 0.54 g of tributylboron (TBB) was added to 20 mL of hexane, 300 mL of air was aerated to prepare a solution, and the solution was charged into the polymer solution. The reaction was carried out at a temperature of 60° C. for 2 hours. After completion of the reaction, air was bubbled through the liquid at a rate of 2 L/min for 5 minutes. Then, acetone was added to precipitate the polymer.

Then, the polymer was filtered with a glass filter, washed sufficiently with acetone, and vacuum dried at 60° C. for 8 hours to obtain a graft copolymer (X-1). The yield of the graft copolymer (X-1) was 88.4 g, and the graft ratio was 253%. The average carbon number of the alkyl group of the structural unit derived from the methacrylic acid ester that constitutes the graft portion was 11. The intrinsic viscosity [η] of the graft copolymer (X-1) was 0.72 dL/g.

[Polymerization Example 2] (Production of Graft Copolymer (X-2))
The ethylene/propylene copolymer pellets (EP-1) used in Polymerization Example 1 were used as the ethylene/α-olefin copolymer (A), and methyl methacrylate (MMA) and dodecyl methacrylate (DMA) were used as graft monomers. ) Was used.

In a nitrogen atmosphere, 25 g of ethylene/propylene copolymer pellets (EP-1) and 72.8 g of a mixed liquid of methyl methacrylate and dodecyl methacrylate (MMA:DMA=30:70 (mol %)) are separated into 500 mL of separable. The flask was charged, the liquid temperature was adjusted to 60° C., and the ethylene/propylene copolymer pellets were dissolved. Separately, under a nitrogen atmosphere, 0.56 g of tributylboron (TBB) was added to 20 mL of hexane, 300 mL of air was aerated to prepare a solution, and the solution was charged into the polymer solution. The reaction was carried out at a temperature of 60° C. for 2 hours. After completion of the reaction, air was bubbled through the liquid at a rate of 2 L/min for 5 minutes. Then, acetone was added to precipitate the polymer.

Then, the polymer was filtered with a glass filter, washed sufficiently with acetone, and vacuum dried at 60° C. for 8 hours to obtain a graft copolymer (X-2). The yield of the graft copolymer (X-2) was 69.8 g, and the grafting rate was 179%. The average carbon number of the alkyl group of the structural unit derived from the methacrylic acid ester constituting the graft part was 9. The intrinsic viscosity [η] of the graft copolymer (X-2) was 0.74 dL/g.

[Polymerization Example 3] (Production of Graft Copolymer (X-3))
The ethylene/propylene copolymer pellets (EP-1) used in Polymerization Example 1 were used as the ethylene/α-olefin copolymer (A), and methyl methacrylate (MMA) and dodecyl methacrylate (DMA) were used as graft monomers. ) Was used.

Under a nitrogen atmosphere, 25 g of ethylene/propylene copolymer pellets (EP-1) and 63.0 g of a mixed liquid of methyl methacrylate and dodecyl methacrylate (MMA:DMA=36:64 (mol %)) are separated into 500 mL of separable. The flask was charged, the liquid temperature was adjusted to 60° C., and the ethylene/propylene copolymer pellets were dissolved. Separately, under a nitrogen atmosphere, 0.27 g of tributylboron (TBB) was added to 20 mL of heptane, 150 mL of air was aerated to prepare a solution, and the solution was charged into the polymer solution. The reaction was carried out at a temperature of 60° C. for 2 hours. After completion of the reaction, air was bubbled through the liquid at a rate of 2 L/min for 5 minutes. Then, acetone was added to precipitate the polymer.

Then, the polymer was filtered with a glass filter, sufficiently washed with acetone, and vacuum dried at 60° C. for 8 hours to obtain a graft copolymer (X-3). The yield of the graft copolymer (X-3) was 78.0 g, and the grafting ratio was 212%. The average carbon number of the alkyl group of the structural unit derived from the methacrylic acid ester that constitutes the graft portion was 8. The intrinsic viscosity [η] of the graft copolymer (X-3) was 0.84 dL/g.

[Polymerization Example 4] (Production of Graft Copolymer (X-4))
The ethylene/propylene copolymer pellets (EP-1) used in Polymerization Example 1 were used as the ethylene/α-olefin copolymer (A), and methyl methacrylate (MMA) and the carbon of the alkyl group were used as the graft monomers. Stearyl methacrylate (SMA), which is a number 18 methacrylate ester, was used.

In a nitrogen atmosphere, 25 g of ethylene/propylene copolymer pellets (EP-1) and 62.5 g of a mixed solution of methyl methacrylate and stearyl methacrylate (MMA:SMA=59:41 (mol %)) are separated into 500 mL of separable. The flask was charged, the liquid temperature was adjusted to 60° C., and the ethylene/propylene copolymer pellets were dissolved. Separately, under a nitrogen atmosphere, 0.30 g of tributylboron (TBB) was added to 20 mL of heptane, 150 mL of air was aerated to prepare a solution, and the solution was charged into the polymer solution. The reaction was carried out at a temperature of 60° C. for 2 hours. After completion of the reaction, air was bubbled through the liquid at a rate of 2 L/min for 5 minutes. Then, acetone was added to precipitate the polymer.

Then, the polymer was filtered with a glass filter, sufficiently washed with acetone, and vacuum dried at 60° C. for 8 hours to obtain a graft copolymer (X-4). The yield of the graft copolymer (X-4) was 81.4 g, and the grafting rate was 225%. The average carbon number of the alkyl group of the structural unit derived from the methacrylic acid ester that constitutes the graft portion was 8. The intrinsic viscosity [η] of the graft copolymer (X-4) was 1.13 dL/g.

[Polymerization Example 5] (Production of graft copolymer (X-5))
As the ethylene/α-olefin copolymer (A), the ethylene/propylene copolymer pellets (EP-1) used in Polymerization Example 1 were used, and as graft monomers, methyl methacrylate (MMA) and dodecyl methacrylate (DMA) were used. ) And stearyl methacrylate (SMA) were used.

Under nitrogen atmosphere, 25 g of ethylene/propylene copolymer pellets (EP-1) and a mixed solution of methyl methacrylate, dodecyl methacrylate and stearyl methacrylate (MMA:DMA:SMA=43:46:12 (mol %)) 62.5 g was charged into a 500 mL separable flask, the liquid temperature was adjusted to 60° C., and the ethylene/propylene copolymer pellets were dissolved. Separately, under a nitrogen atmosphere, 0.27 g of tributylboron (TBB) was added to 20 mL of heptane, 150 mL of air was aerated to prepare a solution, and the solution was charged into the polymer solution. The reaction was carried out at a temperature of 60° C. for 2 hours. After completion of the reaction, air was bubbled through the liquid at a rate of 2 L/min for 5 minutes. Then, acetone was added to precipitate the polymer.

Then, the polymer was filtered with a glass filter, washed sufficiently with acetone, and vacuum dried at 60° C. for 8 hours to obtain a graft copolymer (X-5). The yield of the graft copolymer (X-5) was 78.4 g, and the graft ratio was 213%. The average carbon number of the alkyl group of the structural unit derived from the methacrylic acid ester that constitutes the graft portion was 8. The intrinsic viscosity [η] of the graft copolymer (X-5) was 0.94 dL/g.

[Polymerization Example 6] (Production of graft copolymer (X-6))
As the ethylene/α-olefin copolymer (A), the ethylene/propylene copolymer pellets (EP-1) used in Polymerization Example 1 were used, and as graft monomers, methyl methacrylate (MMA) and dodecyl methacrylate (DMA) were used. ) And stearyl methacrylate (SMA) were used.

Under nitrogen atmosphere, 25 g of ethylene/propylene copolymer pellets (EP-1) and a mixed solution of methyl methacrylate, dodecyl methacrylate and stearyl methacrylate (MMA:DMA:SMA=48:31:21 (mol %)) 62.5 g was charged into a 500 mL separable flask, the liquid temperature was adjusted to 60° C., and the ethylene/propylene copolymer pellets were dissolved. Separately, under a nitrogen atmosphere, 0.29 g of tributylboron (TBB) was added to 20 mL of heptane, 150 mL of air was aerated to prepare a solution, and the solution was charged into the polymer solution. The reaction was carried out at a temperature of 60° C. for 2 hours. After completion of the reaction, air was bubbled through the liquid at a rate of 2 L/min for 5 minutes. Then, acetone was added to precipitate the polymer.

Then, the polymer was filtered with a glass filter, sufficiently washed with acetone, and vacuum dried at 60° C. for 8 hours to obtain a graft copolymer (X-6). The yield of the graft copolymer (X-6) was 71.2 g, and the grafting ratio was 185%. The average carbon number of the alkyl group of the structural unit derived from the methacrylic acid ester that constitutes the graft portion was 8.

The weight average molecular weight (Mw) of the graft copolymer (X-6) was 445,000, the number average molecular weight (Mn) was 67,000, and the molecular weight distribution (Mw/Mn) was 6.65. The intrinsic viscosity [η] was 1.05 dL/g.

[Polymerization Example 7] (Production of graft copolymer (X-7))
The ethylene/propylene copolymer pellets (EP-1) used in Polymerization Example 1 were used as the ethylene/α-olefin copolymer (A), and methyl methacrylate (MMA) was used as the graft monomer, and the carbon number of the alkyl group was used. 2-Ethylhexyl Methacrylate (2EHMA), which is a Methacrylic Acid Ester, and Stearyl Methacrylate (SMA) were used.

Under a nitrogen atmosphere, 25 g of ethylene/propylene copolymer pellets (EP-1), a mixed solution of methyl methacrylate, 2-ethylhexyl methacrylate and stearyl methacrylate (MMA:2EHMA:SMA=32:46:22( (Mol %)) 62.5 g was charged into a 500 mL separable flask, the liquid temperature was adjusted to 60° C., and the ethylene/propylene copolymer pellets were dissolved. Separately, under a nitrogen atmosphere, 0.30 g of tributylboron (TBB) was added to 20 mL of heptane, 150 mL of air was aerated to prepare a solution, and the solution was charged into the polymer solution. The reaction was carried out at a temperature of 60° C. for 2 hours. After completion of the reaction, air was bubbled through the liquid at a rate of 2 L/min for 5 minutes. Then, acetone was added to precipitate the polymer.

Then, the polymer was filtered through a glass filter, sufficiently washed with acetone, and vacuum dried at 60° C. for 8 hours to obtain a graft copolymer (X-7). The yield of the graft copolymer (X-7) was 67.8 g, and the graft ratio was 171%. The average carbon number of the alkyl group of the structural unit derived from the methacrylic acid ester that constitutes the graft portion was 8. The intrinsic viscosity [η] of the graft copolymer (X-7) was 1.04 dL/g.

[Polymerization Example 8] (Production of graft copolymer (X-8))
The ethylene/propylene copolymer pellets (EP-1) used in Polymerization Example 1 were used as the ethylene/α-olefin copolymer (A), and methyl methacrylate (MMA) and dodecyl methacrylate (DMA) were used as graft monomers. ) Was used.

Under a nitrogen atmosphere, 25 g of ethylene/propylene copolymer pellets (EP-1) and 52.5 g of a mixed liquid of methyl methacrylate and dodecyl methacrylate (MMA:DMA=67:33 (mol %)) are separated into 500 mL of a separable column. The flask was charged, the liquid temperature was adjusted to 60° C., and the ethylene/propylene copolymer pellets were dissolved. Separately, 0.51 g of tributylboron (TBB) was added to 20 mL of hexane under a nitrogen atmosphere to prepare a solution in which 300 mL of air was aerated, and the solution was charged into the polymer solution. The reaction was carried out at a temperature of 60° C. for 2 hours. After completion of the reaction, air was bubbled through the liquid at a rate of 2 L/min for 5 minutes. Then, acetone was added to precipitate the polymer.

Then, the polymer was filtered with a glass filter, sufficiently washed with acetone, and vacuum dried at 60° C. for 8 hours to obtain a graft copolymer (X-8). The yield of the graft copolymer (X-8) was 70.9 g, and the grafting ratio was 183%. The average carbon number of the alkyl group of the structural unit derived from the methacrylic acid ester that constitutes the graft portion was 5. The intrinsic viscosity [η] of the graft copolymer (X-8) was 0.64 dL/g.

[Polymerization Example 9] (Production of graft copolymer (X-9))
The ethylene/propylene copolymer pellets (EP-1) used in Polymerization Example 1 were used as the ethylene/α-olefin copolymer (A), and methyl methacrylate (MMA) and stearyl methacrylate (SMA) were used as graft monomers. ) Was used.

Under a nitrogen atmosphere, 25 g of ethylene/propylene copolymer pellets (EP-1) and 62.5 g of a mixed liquid of methyl methacrylate and stearyl methacrylate (MMA:SMA=65:35 (mol %)) are separated into 500 mL of separable. The flask was charged, the liquid temperature was adjusted to 60° C., and the ethylene/propylene copolymer pellets were dissolved. Separately, under a nitrogen atmosphere, 0.30 g of tributylboron (TBB) was added to 20 mL of heptane, 150 mL of air was aerated to prepare a solution, and the solution was charged into the polymer solution. The reaction was carried out at a temperature of 60° C. for 2 hours. After completion of the reaction, air was bubbled through the liquid at a rate of 2 L/min for 5 minutes. Then, acetone was added to precipitate the polymer.

Then, the polymer was filtered with a glass filter, sufficiently washed with acetone, and vacuum dried at 60° C. for 8 hours to obtain a graft copolymer (X-9). The yield of the graft copolymer (X-9) was 82.8 g, and the grafting ratio was 231%. The average carbon number of the alkyl group of the structural unit derived from the methacrylic acid ester that constitutes the graft portion was 7.

The weight average molecular weight (Mw) of the graft copolymer (X-9) was 416,000, the number average molecular weight (Mn) was 80,000, and the molecular weight distribution (Mw/Mn) was 5.21. The intrinsic viscosity [η] was 1.03 dL/g.
Table 1 shows the raw materials, reaction conditions, and properties of the graft copolymer in each polymerization example.

[Example 1]
A lubricating oil composition was prepared using the graft copolymer (X-1) obtained in Polymerization Example 1 as a viscosity index improver for lubricating oil.
(1) Preparation of Polymer Concentrate Yubase-4 (manufactured by SK Lubricants, kinematic viscosity (40° C.): 19.6 mm ² /s, kinematic viscosity (100° C.): 4.2 mm ² /s, viscosity index: 122) Using as a base oil, a 10 mass% solution of the graft copolymer X-1 obtained in Polymerization Example 1 was prepared to obtain a polymer concentrate-1.
(2) Preparation of Lubricating Oil Composition Yubase-4 (manufactured by SK Lubricants) was used as a base oil, and 0.3% by mass of a pour point depressant (Leblanc 165, manufactured by Toho Chemical Co., Ltd.) and an additive package ^* 8.15. After adding the mass%, the blending amount of the polymer concentrate-1 is adjusted and added so that a constant viscosity (about 10 mm ² /s) is obtained at 100° C., and a lubricating oil composition (100 mass%) as a blending oil is added. Was prepared. The performance of the obtained lubricating oil composition was evaluated. Table 2 shows the compounding ratio and the evaluation results.
Note: * Additive package = Ca and Na overbased detergents, N-containing dispersants, aminic and phenolic antioxidants, zinc dialkyldithiophosphates, friction modifiers, and defoamers. Including conventional engine lubricating oil package.

[Example 2]
Example 1 was repeated except that the graft copolymer (X-1) was replaced by the graft copolymer (X-2) obtained in Polymerization Example 2 as a viscosity index improver for lubricating oil. Polymer concentrates and lubricating oil compositions were prepared and evaluated as in Example 1. Table 2 shows the compounding ratio and the evaluation results.

[Example 3]
Example 1 was repeated except that the graft copolymer (X-3) obtained in Polymerization Example 3 was used as a viscosity index improver for lubricating oil instead of the graft copolymer (X-1). Polymer concentrates and lubricating oil compositions were prepared and evaluated as in Example 1. Table 2 shows the compounding ratio and the evaluation results.

[Example 4]
Example 1 was repeated except that the graft copolymer (X-1) was replaced by the graft copolymer (X-4) obtained in Polymerization Example 4 in Example 1 except that the viscosity index improver for lubricating oil was used. Polymer concentrates and lubricating oil compositions were prepared and evaluated as in Example 1. Table 2 shows the compounding ratio and the evaluation results.

[Example 5]
Example 1 was repeated except that the graft copolymer (X-5) obtained in Polymerization Example 5 was used as the viscosity index improver for lubricating oil in place of the graft copolymer (X-1). Polymer concentrates and lubricating oil compositions were prepared and evaluated as in Example 1. Table 2 shows the compounding ratio and the evaluation results.

[Example 6]
Example 1 was repeated, except that the graft copolymer (X-6) obtained in Polymerization Example 6 was used as the viscosity index improver for lubricating oil in place of the graft copolymer (X-1). Polymer concentrates and lubricating oil compositions were prepared and evaluated as in Example 1. Table 2 shows the compounding ratio and the evaluation results.

[Example 7]
Example 1 was repeated except that the graft copolymer (X-7) obtained in Polymerization Example 7 was used as the viscosity index improver for lubricating oil in place of the graft copolymer (X-1). Polymer concentrates and lubricating oil compositions were prepared and evaluated as in Example 1. Table 2 shows the compounding ratio and the evaluation results.

[Comparative Example 1]
Example 1 was repeated except that the graft copolymer (X-8) obtained in Polymerization Example 8 was used as a viscosity index improver for lubricating oil instead of the graft copolymer (X-1). Polymer concentrates and lubricating oil compositions were prepared and evaluated as in Example 1. Table 2 shows the compounding ratio and the evaluation results.

[Comparative example 2]
Example 1 was repeated except that the graft copolymer (X-9) obtained in Polymerization Example 9 was used as a viscosity index improver for lubricating oil instead of the graft copolymer (X-1). Polymer concentrates and lubricating oil compositions were prepared and evaluated as in Example 1. Table 2 shows the compounding ratio and the evaluation results.

[Comparison of Example and Comparative Example]
Compared with a lubricating oil composition [Comparative Example 1-Comparative Example 2] using a graft copolymer (X) having an average carbon number of the alkyl group of the (meth)acrylic acid ester of 7 or less as a viscosity index improver, ) The lubricating oil compositions of Examples 1 to 7 obtained by using the graft copolymer (X) in which the average carbon number of the alkyl group of the acrylate ester is 8 or more is a transparent compounding oil. And showed an excellent property of achieving a viscosity index equal to or higher than the above.

The viscosity index improver for lubricating oil of the present invention has an excellent balance of viscosity index improving ability and viscosity increasing as compared with conventional viscosity index improvers, and can be used as a lubricant additive adapted to fuel saving. is there.

Claims (7)

A viscosity index improver for a lubricating oil containing a solid matter (S),
The solid matter (S) contains a graft copolymer (X),
The graft copolymer (X) is
A main chain portion derived from an ethylene/α-olefin copolymer (A) which is a copolymer of ethylene and an α-olefin having 3 to 8 carbon atoms;
A graft portion derived from a (meth)acrylic acid ester copolymer (B), and having a grafting ratio defined by the following formula (I) of 15 to 400%,
The (meth)acrylic acid ester copolymer (B) is a copolymer of two or more kinds of (meth)acrylic acid ester,
The viscosity index improver for a lubricating oil, wherein the alkyl group of the (meth)acrylic acid ester has an average carbon number of 8 or more.
Grafting rate (%)={(mass of graft copolymer (X))-(mass of ethylene/α-olefin copolymer (A))}/(ethylene/α-olefin copolymer (A) Mass)×100 (I) The viscosity index improver for lubricating oil according to claim 1, wherein the α-olefin is one or more selected from propylene and butene. The intrinsic viscosity [η] of the graft copolymer (X) measured in a decalin solvent at 135° C. is 0.05 to 15 dL/g, and the lubricating oil according to claim 1 or 2. Viscosity index improver. 4. The (meth)acrylic acid ester copolymer (B) is a copolymer of (meth)acrylic acid C1-6 alkyl and (meth)acrylic acid C7-36 alkyl. The viscosity index improver for lubricating oil according to any one of 1. Ratio of the said graft copolymer (X) in the said solid (S) is 95 mass% or more, The viscosity index improvement for lubricating oils as described in any one of Claims 1-4 characterized by the above-mentioned. Agent. 80 mass% or more of said solid substance (S) is contained, The viscosity index improver for lubricating oils as described in any one of Claims 1-5 characterized by the above-mentioned. (I) 0.2 to 50 parts by mass of a viscosity index improver for lubricating oil according to any one of claims 1 to 6,
(Ii) 50 to 99.8 parts by mass of base oil consisting of at least one kind selected from mineral oil, synthetic hydrocarbon oil and ester oil, and having a kinematic viscosity at 100° C. in the range of 1 to ²⁰ mm ² /s (however, , The total of (i) and (ii) is 100 parts by mass, and optionally,
(Iii) selected from the group consisting of a detergent dispersant, a viscosity index improver, an antioxidant, a corrosion inhibitor, an antiwear agent, a friction modifier, a pour point depressant, a rust preventive, an antifoaming agent and an extreme pressure agent. A lubricating oil composition comprising at least one additive selected from the group consisting of: