CN104411811A - Poly(meth)acrylate viscosity index improver, and lubricating oil composition and lubricating oil additive containing said viscosity index improver - Google Patents

Abstract

The present invention provides a poly(meth)acrylate viscosity index improver that has a polymer chain containing a structural unit represented by general formula (1), and that has a weight average molecular weight (Mw) of at least 100,000 and a ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of at most 1.6. [In formula (1), R1 represents hydrogen or a methyl group, and R2 represents a C1-36 alkyl group.]

Description

Poly(meth)acrylate viscosity index improver, and lubricating oil additive and lubricating oil composition containing the viscosity index improver

technical field

The present invention relates to a poly(meth)acrylate viscosity index improver, a lubricating oil additive and a lubricating oil composition containing the viscosity index improver.

Background technique

Conventionally, in the field of lubricating oil, studies have been made on improvement of lubricating oil from the viewpoint of energy saving. Especially in recent years, the tendency to protect the global environment has been increasing, and the demand for improving the energy-saving performance of lubricating oils has further increased.

For example, in the case of lubricating oil used in internal combustion engines such as automobile engines (also referred to as "lubricating oil for internal combustion engines" or "engine oil"), as one of means for improving fuel economy, it is known that by adding A method in which a viscosity index improver is added to an oil base oil to increase the viscosity index of a lubricating oil.

In addition, for example, in the case of lubricating oils such as ATF, MTF, and CVTF used in automobile transmissions (also called "transmission lubricating oil" or "drive system oil"), as a means of improving fuel efficiency One of them is a method of lowering the viscosity of lubricating oil for a transmission to reduce viscous resistance. However, reducing the viscosity of lubricating oil for transmissions may cause other problems such as oil leakage and seizing.

Therefore, as another method of improving fuel efficiency, there is a method of using a viscosity index improver. This method raises the viscosity index of the lubricating oil for a transmission by using a viscosity index improver, maintains the viscosity in a high-temperature region, and suppresses an increase in viscosity in a low-temperature region.

Regarding viscosity index improvers, the use of various viscosity index improvers has been proposed so far, and in particular, the use of many poly(meth)acrylate-based viscosity index improvers has been proposed (for example, refer to Patent Documents 1 to 7).

prior art literature

patent documents

Patent Document 1: Japanese Patent Application Laid-Open No. 7-48421

Patent Document 2: Japanese Patent Application Laid-Open No. 7-62372

Patent Document 3: Japanese Patent Application Laid-Open No. 6-145258

Patent Document 4: Japanese Patent Application Laid-Open No. 3-100099

Patent Document 5: Japanese Patent Laid-Open No. 2002-302687

Patent Document 6: Japanese Patent Laid-Open No. 2004-124080

Patent Document 7: Japanese Patent Laid-Open No. 2005-187736

Contents of the invention

The problem to be solved by the invention

However, for example, in lubricating oils for internal combustion engines, when the above-mentioned conventional poly(meth)acrylate-based viscosity index improvers are used, there is room for improvement in terms of high-shear viscosity in order to achieve practically sufficient fuel economy. In particular, in 0W-20, which requires high fuel efficiency, it is necessary to maintain the high-shear viscosity at 150°C at a somewhat high level while reducing the high-shear viscosity at 100°C. On the other hand, with the conventional poly(meth)acrylate-based viscosity index improvers, it is difficult to maintain the high-shear viscosity at 150°C and reduce the high-shear viscosity at 100°C.

In addition, for example, in lubricating oils for transmissions, friction loss during transmission of gears in a drive unit can be cited as one of the causes of poor fuel efficiency. Therefore, if a lubricating oil with low viscous resistance under high-shear conditions can be realized, friction loss can be reduced and fuel economy can be further improved.

However, the conventional viscosity index improvers described above are not sufficient in terms of the frictional loss reduction effect to improve the viscosity characteristics in the high-temperature region and the low-temperature region by increasing the viscosity index.

Therefore, an object of the present invention is to provide a viscosity index improver capable of achieving fuel economy, and a lubricating oil additive and lubricating oil composition containing the viscosity index improver.

In addition, another object of the present invention is to provide a viscosity index improver capable of maintaining a high shear viscosity at 150°C and sufficiently reducing a high shear viscosity at 100°C, and a lubricating oil additive containing the viscosity index improver and lubricating oil composition.

Another object of the present invention is to provide a viscosity index improver capable of imparting a sufficient friction loss reducing effect to lubricating oil, and a lubricating oil additive and lubricating oil composition containing the viscosity index improver.

solutions to problems

The inventors of the present invention conducted in-depth studies and found that by having a specific structure, the weight-average molecular weight and the ratio Mw/Mn of the weight-average molecular weight Mw to the number-average molecular weight Mn satisfy specific conditions. The viscosity index improver (hereinafter referred to as "the first poly(meth)acrylate viscosity index improver") can maintain the high-shear viscosity at 150°C and sufficiently reduce the high-shear viscosity at 100°C, thereby The present invention has been accomplished.

That is, the present invention provides a poly(meth)acrylate viscosity index improver having a polymer chain containing a structural unit represented by the following general formula (1), the poly(meth)acrylate viscosity index The weight average molecular weight Mw of the improver is 100,000 or more, and the ratio Mw/Mn of the weight average molecular weight Mw to the number average molecular weight Mn is 1.6 or less.

[In formula (1), R ¹ represents hydrogen or a methyl group, and R ² represents an alkyl group having 1 to 36 carbon atoms. ]

In addition, the inventors of the present invention conducted intensive studies and found that poly(meth)acrylic acid having a specific structure, a weight-average molecular weight, and a ratio Mw/Mn of the weight-average molecular weight Mw to the number-average molecular weight Mn satisfies specific conditions. The ester-based viscosity index improver (hereinafter referred to as "the first poly(meth)acrylate-based viscosity index improver") is capable of imparting a frictional loss reduction effect, and completed the present invention.

That is, the present invention provides a poly(meth)acrylate viscosity index improver having a polymer chain containing a structural unit represented by the following general formula (1), the poly(meth)acrylate viscosity index The weight average molecular weight Mw of the improver is less than 100,000, and the ratio Mw/Mn of the weight average molecular weight Mw to the number average molecular weight Mn is 1.6 or less.

[In formula (1), R ¹ represents hydrogen or a methyl group, and R ² represents an alkyl group having 1 to 36 carbon atoms. ]

In addition, the present invention provides a lubricating oil additive containing at least one of the above-mentioned first poly(meth)acrylate viscosity index improvers and second poly(meth)acrylate viscosity index improvers. .

In addition, the present invention provides a lubricating oil composition comprising a lubricating oil base oil, and a viscosity index improver selected from the first poly(meth)acrylate-based viscosity index improver and the second poly(meth)acrylate-based viscosity index improver. At least one of the improvers.

The effect of the invention

According to the present invention, it is possible to provide a viscosity index improver capable of achieving fuel economy, and a lubricating oil additive and lubricating oil composition containing the viscosity index improver.

In addition, according to the present invention, a viscosity index improver capable of maintaining a high shear viscosity at 150°C and sufficiently reducing a high shear viscosity at 100°C, and a lubricating oil additive and a lubricating oil combination containing the viscosity index improver can be provided things.

Also, according to the present invention, a viscosity index improver capable of reducing friction loss, and a lubricating oil additive and a lubricating oil composition containing the viscosity index improver can be provided.

Detailed ways

Hereinafter, preferred embodiments of the present invention will be described in detail, but the present invention is not limited at all by the following embodiments.

[First Embodiment: First Poly(meth)acrylate Viscosity Index Improver]

The poly(meth)acrylate viscosity index improver of 1st Embodiment has a polymer chain containing the structural unit represented by following General formula (1). The poly(meth)acrylate-based viscosity index improver has a weight-average molecular weight Mw (hereinafter, sometimes simply referred to as "Mw") of 100,000 or more, and the weight-average molecular weight Mw and the number-average molecular weight Mn (hereinafter, sometimes simply referred to as "Mn".) The ratio Mw/Mn (hereinafter, may be simply referred to as "Mw/Mn") is 1.6 or less.

[In formula (1), R ¹ represents hydrogen or a methyl group, and R ² represents an alkyl group having 1 to 36 carbon atoms. ]

R ¹ can be either hydrogen or methyl, preferably methyl.

The number of carbon atoms of the alkyl group represented by ^R2 is 1 to 36 as described above, preferably 1 to 30, more preferably 1 to 26, and even more preferably 1 to 22 from the viewpoint of handleability and ease of manufacture. . In addition, the alkyl group represented by R ² may be linear or branched.

When the polymer chain contains two or more structural units represented by the above general formula (1), R ¹ and R ² may be the same or different between the structural units. In the case of containing two or more structural units with different R ² , from the viewpoint of fuel-saving properties and solubility, based on the total amount of structural units contained in the polymer chain, the structural unit in which R ² is a methyl group preferably contains 10 to 45% by mass, more preferably 15 to 45% by mass, still more preferably 20 to 45% by mass. In addition, from the viewpoint of fuel-saving characteristics, based on the total amount of structural units contained in the polymer chain, the structural unit in which ^R is an alkyl group with 18 or more carbon atoms preferably contains 10% by mass or more, more preferably contains 15% by mass or more, more preferably 20% by mass or more.

The polymer chain may contain only the structural unit represented by the above general formula (1), or may contain structures other than the structural unit represented by the above general formula (1) in addition to the structural unit represented by the above general formula (1) unit. In addition, the terminal of the polymer chain is not particularly limited. It is preferable that such a polymer chain contains only the structural unit represented by the above-mentioned general formula (1) and has a terminal hydrogen atom, that is, a polymer chain represented by the following general formula (2).

In formula (2), R ¹ represents hydrogen or a methyl group, R ² represents an alkyl group having 1 to 36 carbon atoms, and n is an integer selected so that Mw and Mw/Mn satisfy the above conditions. n is, for example, an integer of 400 to 2,000.

The weight-average molecular weight Mw is 100,000 or more, preferably 125,000 or more, more preferably 150,000 or more, and still more preferably 175,000 or more from the viewpoint of fuel efficiency. The upper limit of Mw is not particularly limited, and Mw is, for example, 500,000 or less.

The number average molecular weight Mn is appropriately selected so that Mw/Mn satisfies the above conditions. From the viewpoint of reducing the HTHS viscosity at 100°C, Mn is preferably 75,000 or more, more preferably 94,000 or more, and still more preferably 110,000 or more. The upper limit of Mn is not particularly limited, and Mn is, for example, 300,000 or less.

Mw/Mn is 1.6 or less, preferably 1.5 or less, more preferably 1.4 or less, and still more preferably 1.2 or less from the viewpoint of fuel efficiency. Moreover, from a viewpoint of the yield of poly(meth)acrylate, Mw/Mn becomes like this. Preferably it is 1.0 or more, More preferably, it is 1.01 or more, More preferably, it is 1.02 or more.

It should be noted that the "weight average molecular weight Mw", "number average molecular weight Mn" and "ratio Mw/Mn of weight average molecular weight Mw to number average molecular weight Mn" referred to in the present invention refer to the Mw obtained by GPC analysis. , Mn and Mw/Mn (polystyrene (standard sample) conversion value). Specifically, for example, it can be measured as follows.

As a solvent, tetrahydrofuran was used and diluted to prepare a solution having a sample concentration of 2% by mass. This sample solution was analyzed using a GPC device (Waters Alliance 2695). The flow rate of the solvent was 1 ml/min, and the analysis was carried out using a column with an analyzable molecular weight of 10,000 to 256,000 with a refractive index as a detector. It should be noted that the relationship between the column retention time and the molecular weight was obtained using standard polystyrene with a definite molecular weight, and a calibration curve was prepared separately, and the molecular weight was determined from the obtained retention time.

The method for producing the poly(meth)acrylate-based viscosity index improver of this embodiment is not particularly limited, and examples include adding an initiator to a mixed solution containing an alkyl (meth)acrylate, a polymerization reagent, and a solvent, A method of polymerizing alkyl (meth)acrylates at a specified temperature.

As the alkyl (meth)acrylate, an alkyl (meth)acrylate represented by the following general formula (3) can be used.

In formula (3), R ¹ represents hydrogen or a methyl group, and R ² represents an alkyl group having 1 to 36 carbon atoms.

R ¹ is preferably methyl. The number of carbon atoms in the alkyl group represented by R ² is preferably 1-30, more preferably 1-26, even more preferably 1-22.

As the alkyl (meth)acrylate, one kind can be used alone or two or more kinds of alkyl (meth)acrylates represented by the general formula (3) can be used in combination, and two or more kinds can be used in combination. When two or more are used in combination, the content of methyl (meth)acrylate in which ^R2 is a methyl group is preferably 5 to 50% by mass, more preferably 10% by mass, based on the total amount of alkyl (meth)acrylates. -50% by mass, more preferably 20-45% by mass. In addition, based on the total amount of alkyl (meth)acrylates, the content of alkyl (meth)acrylates in which ^R is an alkyl group with 18 or more carbon atoms is preferably 10% by mass or more, more preferably 15% by mass. Mass % or more, More preferably, it is 20 mass % or more.

As a polymerization reagent, for example, a compound having a thiocarbonyl group such as cumyl dithiobenzoate can be used. Cumyl dithiobenzoate can be illustrated as a preferable polymerization reagent.

As the solvent, for example, highly purified mineral oil, anisole, and toluene can be used. As a preferable solvent, highly purified mineral oil can be illustrated.

As the initiator, for example, azobisisobutyronitrile, azobismethylvaleronitrile and azobismethylbutyronitrile can be used. As a preferable initiator, azobisisobutyronitrile can be illustrated.

As reaction temperature at the time of superposing|polymerizing an alkyl (meth)acrylate, Preferably it is 70-120 degreeC, More preferably, it is 80-110 degreeC, More preferably, it is 90-100 degreeC. When the reaction temperature is within the above range, Mw/Mn of the obtained poly(meth)acrylate-based viscosity index improver is likely to be 1.6 or less. For example, when the reaction temperature is 90-100°C, Mw/Mn tends to be 1.0-1.2; when the reaction temperature is 100-110°C, Mw/Mn tends to be 1.2-1.4; Mn tends to be 1.4 to 1.6.

The reaction time can be appropriately selected according to reaction conditions such as the alkyl (meth)acrylate used as a raw material, the type and amount of the polymerization reagent, solvent, and initiator, the reaction temperature, and the Mw and Mw/Mn of the target poly(meth)acrylate. . As a preferable reaction time, 10 to 14 hours can be illustrated.

The polymerization of the alkyl (meth)acrylate is preferably performed under a nitrogen atmosphere.

[Second Embodiment: Lubricating Oil Additive]

The lubricating oil additive according to the second embodiment of the present invention contains a poly(meth)acrylate viscosity index improver having a structure represented by the above general formula (1) The poly(meth)acrylate-based viscosity index improver has a weight-average molecular weight Mw of 100,000 or more, and a ratio Mw/Mn of the weight-average molecular weight Mw to the number-average molecular weight Mn of 1.6 or less. It should be noted that the poly(meth)acrylate-based viscosity index improver in this embodiment is the same as the viscosity index improver in the above-mentioned first embodiment, and repeated descriptions are omitted here.

The lubricating oil additive may contain only the above-mentioned poly(meth)acrylate viscosity index improver, or may be a mixture of the viscosity index improver and other additives (ie, an additive composition). When the lubricating oil additive is a mixture of the viscosity index improver and other additives, their mixing ratio is not particularly limited, and can be appropriately selected according to the application.

Examples of other additives include viscosity index improvers other than the aforementioned poly(meth)acrylate-based viscosity index improvers, antioxidants, antiwear agents (or extreme pressure agents), anticorrosion agents, rust inhibitors, viscosity index improvers, etc. Additives such as additives, pour point depressants, demulsifiers, metal deactivators, defoamers, ashless friction modifiers, etc. These additives may be used alone or in combination of two or more.

Examples of viscosity index improvers other than the aforementioned poly(meth)acrylate viscosity index improvers include poly(meth)acrylate viscosity index improvers other than the aforementioned poly(meth)acrylate viscosity index improvers. agent, polyisobutylene-based viscosity index improver, ethylene-propylene copolymer-based viscosity index improver, hydrogenated styrene-butadiene copolymer-based viscosity index improver, etc.

Examples of the antioxidant include ashless antioxidants such as phenol-based and amine-based antioxidants, and metal-based antioxidants such as zinc-based, copper-based, and molybdenum-based antioxidants.

Examples of phenolic antioxidants include 4,4'-methylenebis(2,6-di-tert-butylphenol), 4,4'-bis(2,6-di-tert-butylphenol), 4 ,4'-bis(2-methyl-6-tert-butylphenol), 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 2,2'-methylene Bis(4-methyl-6-tert-butylphenol), 4,4'-butylenebis(3-methyl-6-tert-butylphenol), 4,4'-isopropylidenebis(2, 6-di-tert-butylphenol), 2,2'-methylenebis(4-methyl-6-nonylphenol), 2,2'-isobutylenebis(4,6-dimethylphenol) , 2,2'-methylenebis(4-methyl-6-cyclohexylphenol), 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethane phenylphenol, 2,4-dimethyl-6-tert-butylphenol, 2,6-di-tert-α-dimethylamino-p-cresol, 2,6-di-tert-butyl-4-(N, N-dimethylaminomethylphenol), 4,4'-thiobis(2-methyl-6-tert-butylphenol), 4,4'-thiobis(3-methyl-6-tert-butyl phenylphenol), 2,2'-thiobis(4-methyl-6-tert-butylphenol), bis(3-methyl-4-hydroxy-5-tert-butylbenzyl)sulfide, bis( 3,5-di-tert-butyl-4-hydroxybenzyl)sulfide, 2,2'-thio-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], tridecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate], octyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octadecyl 3-(3,5-di-tert-butyl- 4-hydroxyphenyl)propionate, octyl-3-(3-methyl-5-di-tert-butyl-4-hydroxyphenyl)propionate, and the like. These may be used in combination of two or more.

Examples of amine-based antioxidants include aromatic amine compounds, alkyldiphenylamines, alkylnaphthylamines, phenyl-α-naphthylamines, and alkylphenyl-α-naphthylamines, which are commonly used for lubricating oils. known amine antioxidants.

Examples of anticorrosion agents include benzotriazole-based, tolyltriazole-based, thiadiazole-based, and imidazole-based compounds.

Examples of the rust preventive include petroleum sulfonic acid (ester) salts, alkylbenzenesulfonic acid (ester) salts, dinonylnaphthalenesulfonic acid (ester) salts, alkenyl succinic acid esters, polyol esters, and the like.

Examples of metal deactivators include imidazolines, pyrimidine derivatives, alkylthiadiazoles, mercaptobenzothiazoles, benzotriazoles or derivatives thereof, 1,3,4-thiadiazole polysulfides, 1,3,4-Thiadiazolyl-2,5-dialkyldithiocarbamate, 2-(alkyldithio)benzimidazole, or β-(o-carboxybenzylthiocarbamate ) propionitrile etc.

Examples of antifoaming agents include silicone oils having a kinematic viscosity of 1,000 to 100,000 mm ² /s at 25°C, alkenyl succinic acid derivatives, esters of polyhydric aliphatic alcohols and long-chain fatty acids, and methyl salicylic acid Salt and o-hydroxybenzyl alcohol, etc.

As the ashless friction modifier, any compound generally used as an ashless friction modifier for lubricating oil can be used, for example, an alkyl or alkenyl group having at least one carbon number of 6 to 30 in the molecule, especially Ashless friction modifiers such as straight-chain alkyl or straight-chain alkenyl amine compounds, fatty acid esters, fatty amides, fatty acids, aliphatic alcohols, and aliphatic ethers with 6 to 30 carbon atoms. In addition, various ashless friction modifiers such as nitrogen-containing compounds and their acid-modified derivatives described in JP-A-2009-286831 and exemplified in International Publication No. 2005/037967 can also be used.

In addition, the lubricating oil additive of this embodiment may further contain a solvent. As a solvent, highly purified mineral oil, anisole, and toluene can be used. Among these, highly refined mineral oil is preferably used. When the lubricating oil additive contains a solvent, the content of the solvent is preferably 5 to 75% by mass, more preferably 30 to 60% by mass, based on the total amount of the lubricating oil additive, from the viewpoint of handling properties of the additive.

[Third Embodiment: Lubricating Oil Composition]

The lubricating oil composition of the third embodiment contains a lubricating oil base oil and a poly(meth)acrylate viscosity index improver, and the poly(meth)acrylate viscosity index improver has The polymer chain of the structural unit shown, the weight average molecular weight Mw of the poly(meth)acrylate viscosity index improver is 100,000 or more, and the ratio Mw/Mn of the weight average molecular weight Mw to the number average molecular weight Mn is 1.6 or less. Here, the lubricating oil composition of the present embodiment includes an embodiment including the lubricating oil base oil and the lubricating oil additive of the above-mentioned second embodiment. The poly(meth)acrylate-based viscosity index improver in this embodiment is the same as the poly(meth)acrylate-based viscosity index improver in the above-mentioned first embodiment and second embodiment, and in addition, in the lubricating oil composition The other additives and solvents contained are the same as those in the second embodiment, and repeated descriptions are omitted here.

The lubricating oil base oil is not particularly limited, and lubricating oil base oils used in general lubricating oils can be used. Specifically, a mineral oil-based lubricating oil base oil, a synthetic oil-based lubricating oil base oil, or a mixture of two or more lubricating oil base oils selected from these in an arbitrary ratio can be used.

Examples of mineral oil-based lubricating oil base oils include, for example, distilling crude oil at atmospheric pressure to obtain an atmospheric residual oil, subjecting the atmospheric residual oil to vacuum distillation to obtain a lubricating oil fraction, and performing solvent removal on the obtained lubricating oil fraction. Base oil refined by one or more of asphalt, solvent extraction, hydrocracking, solvent dewaxing, hydrofining, etc.; or by isomerizing wax isomerized mineral oil and GTL wax (Gas toliquid wax) The base oil and the like manufactured by the method.

Examples of synthetic oil-based lubricating oils include polybutene or its hydrogenated products; poly-α-olefins such as 1-octene oligomers and 1-decene oligomers or their hydrogenated products; Trialkyl ester, bis(2-ethylhexyl) adipate, diisodecyl adipate, ditridecyl adipate, bis(2-ethylhexyl) sebacate, etc. Esters; trimethylolpropane octanoate, trimethylolpropane nonanoate, pentaerythritol-2-ethylhexanoate, pentaerythritol nonanoate and other polyol esters; alkylnaphthalene, alkylbenzene and other aromatics Synthetic oils or their mixtures etc.

The kinematic viscosity at 100°C of the lubricating base oil is preferably 2.5 to 10.0 mm ² /s, more preferably 3.0 to 8.0 mm ² /s, and still more preferably 3.5 to 6.0 mm ² /s. In addition, the viscosity index of the lubricating base oil is preferably 90-165, more preferably 100-155, and still more preferably 120-150.

In order to easily exert the effect of additives such as the poly(meth)acrylate viscosity index improver of the first embodiment, the saturated content of the lubricating base oil by chromatographic analysis is preferably 80% or more, more preferably 85% or more, More preferably, it is 90% or more, and most preferably, it is 95% or more.

Based on the total amount of the lubricating oil composition, the content of the poly(meth)acrylate viscosity index improver according to the first embodiment is preferably 0.1 to 20.0% by mass, more preferably 0.5 to 15.0% by mass, and even more preferably 1.0% by mass. ~10.0% by mass. When this content is more than the said lower limit, sufficient addition effect is easy to be acquired, and on the other hand, when this content is below the said upper limit, shear stability improves and fuel consumption sustainability improves.

The kinematic viscosity at 100°C of the lubricating oil composition is preferably 3.0 to 16.3 mm ² /s, more preferably 3.5 to 12.5 mm ² /s, and still more preferably 4.0 to 9.3 mm ² /s. When the kinematic viscosity at 100° C. is not less than the above lower limit, it is easy to ensure lubricity, while on the other hand, when the kinematic viscosity at 100° C. is not more than the above upper limit, fuel efficiency is further improved. In addition, the kinematic viscosity at 100 degreeC in this invention means the kinematic viscosity at 100 degreeC prescribed|regulated by JISK-2283-1993.

The viscosity index of the lubricating oil composition is preferably 150-250, more preferably 160-240, even more preferably 170-230. When the viscosity index is more than the above lower limit, the fuel economy can be further improved while maintaining the HTHS viscosity, and the low-temperature viscosity can be easily lowered. On the other hand, when the viscosity index is not more than the above-mentioned upper limit, low-temperature fluidity, solubility of additives, and compatibility with sealing materials can be ensured. It should be noted that the viscosity index in the present invention refers to the viscosity index specified in JIS K-2283-1993.

The HTHS viscosity at 150° C. of the lubricating oil composition is preferably 1.7 mPa·s or higher, more preferably 2.0 mPa·s or higher, still more preferably 2.3 mPa·s or higher, most preferably 2.6 mPa·s or higher. When the HTHS viscosity at 150° C. is more than the above lower limit, evaporation of the lubricating oil composition can be suppressed and lubricity can be ensured. In addition, the HTHS viscosity at 100° C. of the lubricating oil composition is preferably 5.2 mPa·s or less, more preferably 5.1 mPa·s or less, even more preferably 5.0 mPa·s or less. When the HTHS viscosity at 100° C. is not more than the above upper limit, higher fuel efficiency can be obtained. It should be noted that the HTHS viscosity at 150°C or 100°C in the present invention refers to the high-temperature high-shear viscosity at 150°C or 100°C specified in ASTM D-4683.

The viscosity index improver of the first embodiment described above, the lubricating oil additive of the second embodiment, and the lubricating oil composition of the third embodiment can be used in a wide range of fields such as lubricating oils for internal combustion engines and lubricating oils for driving systems. It is useful in the field of lubricating oil for internal combustion engines. For the fuel of the internal combustion engine in this case, either gasoline or diesel fuel can be used.

[Fourth Embodiment: Second Poly(meth)acrylate-based Viscosity Index Improver]

The poly(meth)acrylate viscosity index improver of 4th Embodiment has a polymer chain containing the structural unit represented by following General formula (1). The weight average molecular weight Mw (hereinafter, sometimes simply referred to as "Mw") of this poly(meth)acrylate viscosity index improver is less than 100,000, and the weight average molecular weight Mw and the number average molecular weight Mn (hereinafter, sometimes simply referred to as " Mn".) The ratio Mw/Mn (Hereinafter, it may only be referred to as "Mw/Mn".) is 1.6 or less.

[In formula (1), R ¹ represents hydrogen or a methyl group, and R ² represents an alkyl group having 1 to 36 carbon atoms. ]

R ¹ can be either hydrogen or methyl, preferably methyl.

The number of carbon atoms of the alkyl group represented by ^R2 is 1 to 36 as described above, preferably 1 to 30, more preferably 1 to 26, and even more preferably 1 to 22 from the viewpoint of handleability and ease of manufacture. . In addition, the alkyl group represented by R ² may be linear or branched.

When the polymer chain contains two or more structural units represented by the above general formula (1), R ¹ and R ² may be the same or different between the structural units. In the case of containing two or more structural units with different R ² , from the viewpoint of viscosity temperature characteristics, based on the total amount of structural units contained in the polymer chain, the structural unit in which R ² is a methyl group preferably contains 10 to 45 mass %, more preferably 15 to 45% by mass, still more preferably 20 to 45% by mass. In addition, from the viewpoint of fuel-saving characteristics, based on the total amount of structural units contained in the polymer chain, the structural unit in which ^R is an alkyl group with 18 or more carbon atoms preferably contains 10% by mass or more, more preferably contains 15% by mass or more, more preferably 20% by mass or more.

The polymer chain may contain only the structural unit represented by the above general formula (1), or may contain structures other than the structural unit represented by the above general formula (1) in addition to the structural unit represented by the above general formula (1) unit. In addition, the terminal of the polymer chain is not particularly limited. It is preferable that such a polymer chain contains only the structural unit represented by the above-mentioned general formula (1) and has a terminal hydrogen atom, that is, a polymer chain represented by the following general formula (2).

In formula (2), R ¹ represents hydrogen or a methyl group, R ² represents an alkyl group having 1 to 36 carbon atoms, and n is an integer selected so that Mw and Mw/Mn satisfy the above conditions. n is an integer of 40-450, for example.

The weight average molecular weight Mw is less than 100,000, and is preferably 80,000 or less, more preferably 70,000 or less, and still more preferably 60,000 or less from the viewpoint of fuel-saving characteristics. The lower limit of Mw is not particularly limited, and Mw is, for example, 10,000 or more.

The number average molecular weight Mn is appropriately selected so that Mw/Mn satisfies the above conditions. From the viewpoint of fuel-saving characteristics, Mn is preferably 6,000 or more, more preferably 10,000 or more, and still more preferably 12,500 or more. The upper limit of Mn is not particularly limited, and Mn is, for example, 60,000 or less.

Mw/Mn is 1.6 or less, preferably 1.5 or less, more preferably 1.4 or less, and still more preferably 1.3 or less from the viewpoint of fuel efficiency. In addition, from the viewpoint of fuel efficiency, Mw/Mn is preferably 1.0 or more, more preferably 1.01 or more, and still more preferably 1.02 or more.

It should be noted that the "weight average molecular weight Mw", "number average molecular weight Mn" and "ratio Mw/Mn of weight average molecular weight Mw to number average molecular weight Mn" referred to in the present invention refer to the Mw obtained by GPC analysis. , Mn and Mw/Mn (polystyrene (standard sample) conversion value). Specifically, for example, it can be measured as follows.

As a solvent, tetrahydrofuran was used and diluted to prepare a solution having a sample concentration of 2% by mass. This sample solution was analyzed using a GPC device (Waters Alliance 2695). The flow rate of the solvent was 1 ml/min, and the analysis was carried out using a column with an analyzable molecular weight of 10,000 to 256,000 with a refractive index as a detector. It should be noted that the relationship between the column retention time and the molecular weight was obtained using standard polystyrene with a definite molecular weight, and a calibration curve was prepared separately, and the molecular weight was determined from the obtained retention time.

The method for producing the poly(meth)acrylate-based viscosity index improver of this embodiment is not particularly limited, and examples include adding an initiator to a mixed solution containing an alkyl (meth)acrylate, a polymerization reagent, and a solvent, A method of polymerizing alkyl (meth)acrylates at a specified temperature.

As the alkyl (meth)acrylate, an alkyl (meth)acrylate represented by the following general formula (3) can be used.

In formula (3), R ¹ represents hydrogen or a methyl group, and R ² represents an alkyl group having 1 to 36 carbon atoms.

R ¹ is preferably methyl. The number of carbon atoms in the alkyl group represented by R ² is preferably 1-36, more preferably 1-30, even more preferably 1-22.

As the alkyl (meth)acrylate, one kind can be used alone or two or more kinds of alkyl (meth)acrylates represented by the general formula (3) can be used in combination, and two or more kinds can be used in combination. When two or more are used in combination, the content of methyl (meth)acrylate in which ^R2 is a methyl group is preferably 5 to 50% by mass, more preferably 10% by mass, based on the total amount of alkyl (meth)acrylates. -50% by mass, more preferably 20-45% by mass. In addition, based on the total amount of alkyl (meth)acrylates, the content of alkyl (meth)acrylates in which ^R is an alkyl group with 18 or more carbon atoms is preferably 10% by mass or more, more preferably 15% by mass. Mass % or more, More preferably, it is 20 mass % or more.

As a polymerization reagent, for example, cumyl dithiobenzoate and a thiocarbonyl group-containing substance can be used. Cumyl dithiobenzoate can be illustrated as a preferable polymerization reagent.

As the solvent, for example, highly purified mineral oil, anisole, and toluene can be used. As a preferable solvent, highly purified mineral oil can be illustrated.

As the initiator, for example, azobisisobutyronitrile, azobisdimethylvaleronitrile and azobismethylbutyronitrile can be used. As a preferable initiator, azobisisobutyronitrile can be illustrated.

As reaction temperature at the time of superposing|polymerizing an alkyl (meth)acrylate, Preferably it is 70-120 degreeC, More preferably, it is 80-110 degreeC, More preferably, it is 80-120 degreeC. When the reaction temperature is within the above range, Mw/Mn of the obtained poly(meth)acrylate-based viscosity index improver is likely to be 1.6 or less. For example, when the reaction temperature is 90-100°C, Mw/Mn tends to be 1.0-1.2; when the reaction temperature is 100-110°C, Mw/Mn tends to be 1.2-1.4; Mn tends to be 1.4 to 1.6.

The reaction time can be appropriately selected according to reaction conditions such as the alkyl (meth)acrylate used as a raw material, the type and amount of the polymerization reagent, solvent, and initiator, the reaction temperature, and the Mw and Mw/Mn of the target poly(meth)acrylate. . As a preferable reaction time, 10 to 14 hours can be illustrated.

The polymerization of the alkyl (meth)acrylate is preferably performed under a nitrogen atmosphere.

[Fifth Embodiment: Lubricating Oil Additive]

The lubricating oil additive according to the fifth embodiment of the present invention contains a poly(meth)acrylate viscosity index improver having a structure represented by the above general formula (1) The poly(meth)acrylate-based viscosity index improver has a weight-average molecular weight Mw of less than 100,000 and a ratio Mw/Mn of the weight-average molecular weight Mw to the number-average molecular weight Mn of 1.6 or less. It should be noted that the poly(meth)acrylate-based viscosity index improver in this embodiment is the same as the viscosity index improver in the fourth embodiment described above, and repeated descriptions are omitted here.

The lubricating oil additive may contain only the above-mentioned poly(meth)acrylate viscosity index improver, or may be a mixture of the viscosity index improver and other additives (ie, an additive composition). When the lubricating oil additive is a mixture of the viscosity index improver and other additives, their mixing ratio is not particularly limited, and can be appropriately selected according to the application. As other additives, they are the same as those in the above-mentioned second embodiment, and repeated descriptions are omitted here.

In addition, the lubricating oil additive of this embodiment may further contain a solvent. As the solvent, highly refined mineral oil, solvent refined mineral oil, and synthetic oil can be used. Among these, highly refined mineral oil is preferably used. When the lubricating oil additive contains a solvent, the content of the solvent is preferably 5 to 75% by mass, more preferably 30 to 60% by mass, based on the total amount of the lubricating oil additive.

[Sixth Embodiment: Lubricating Oil Composition]

The lubricating oil composition according to the sixth embodiment contains a lubricating oil base oil and a poly(meth)acrylate viscosity index improver, and the poly(meth)acrylate viscosity index improver has The poly(meth)acrylate-based viscosity index improver has a weight average molecular weight Mw of less than 100,000, and the ratio Mw/Mn of the weight average molecular weight Mw to the number average molecular weight Mn is 1.6 or less. Here, the lubricating oil composition of the present embodiment includes an embodiment including the lubricating oil base oil and the lubricating oil additive of the fifth embodiment described above. The poly(meth)acrylate-based viscosity index improver in this embodiment is the same as the poly(meth)acrylate-based viscosity index improver in the above-mentioned fourth embodiment and fifth embodiment. In addition, in the lubricating oil composition Other additives and solvents that may be contained are the same as those in the fifth embodiment, and repeated descriptions are omitted here.

The lubricating oil base oil is the same as the lubricating oil base oil in the above-mentioned third embodiment, and repeated description is omitted here.

Based on the total amount of the lubricating oil composition, the content of the poly(meth)acrylate viscosity index improver according to the fourth embodiment is preferably 0.1 to 20.0% by mass, more preferably 0.5 to 15.0% by mass, and even more preferably 1.0% by mass. ~10.0% by mass. When this content is more than the said lower limit, sufficient addition effect is easy to be acquired, and on the other hand, when this content is below the said upper limit, shear stability improves and fuel consumption sustainability improves.

The kinematic viscosity at 100°C of the lubricating oil composition is preferably 2.0 to 16.3 mm ² /s, more preferably 2.5 to 12.5 mm ² /s, and still more preferably 3.0 to 10.0 mm ² /s. When the kinematic viscosity at 100° C. is not less than the above lower limit, it is easy to ensure lubricity, while on the other hand, when the kinematic viscosity at 100° C. is not more than the above upper limit, fuel efficiency is further improved. In addition, the kinematic viscosity at 100 degreeC in this invention means the kinematic viscosity at 100 degreeC prescribed|regulated by JISK-2283-1993.

The viscosity index of the lubricating oil composition is preferably 130-250, more preferably 140-240, even more preferably 160-230. When the viscosity index is more than the above lower limit, the fuel economy can be further improved while maintaining the HTHS viscosity, and the low-temperature viscosity can be easily lowered. On the other hand, when the viscosity index is not more than the above-mentioned upper limit, low-temperature fluidity, solubility of additives, and compatibility with sealing materials can be ensured. It should be noted that the viscosity index in the present invention refers to the viscosity index specified in JIS K-2283-1993.

The viscosity index improver of the fourth embodiment described above, the lubricating oil additive of the fifth embodiment, and the lubricating oil composition of the sixth embodiment can be used in a wide range of fields such as lubricating oils for internal combustion engines and lubricating oils for driving systems. is useful in the field of drive system lubricants. The drive device in this case may be any one of an automatic transmission (AT), a continuously variable automatic transmission (CVT), and a manual transmission (TM).

Example

Hereinafter, examples are given and the present invention will be described more specifically, but the present invention is not limited at all by the following examples.

[Example 1-1]

The poly(meth)acrylate viscosity index improver was synthesized under the following conditions ("synthesis conditions 1-1").

Add methyl methacrylate (formula (3 ) in which both R ¹ and R ² are methyl. Hereinafter described as "C1-MA".) 12 g, stearyl methacrylate (R ¹ in formula (3) is methyl, R ² is stearyl Aliphatic group (straight chain alkyl with 18 carbon atoms). Hereinafter described as "C18-MA".) 18g, cumyl dithiobenzoate (CDTBA) 0.030g, and the height of the solvent 30g of refined mineral oil was stirred to form a homogeneous solution. The solution was cooled to 0° C. in an ice bath, and vacuum degassing/nitrogen purging of the reaction system was performed 5 times using a diaphragm pump. Further, 0.052 g of azobisisobutyronitrile (AIBN) as a free radical initiator was dropped from the sample inlet under a nitrogen stream, and then polymerized for 12 hours at a solution temperature of 110° C. under a nitrogen atmosphere to obtain base) solution of acrylate viscosity index improver.

About the obtained poly(meth)acrylate viscosity index improver, the weight average molecular weight Mw and the number average molecular weight Mn were measured by GPC analysis. As a result, the weight average molecular weight Mw was 230,000, the number average molecular weight Mn was 152,000, and Mw/Mn was 1.51. The procedure of GPC analysis is as follows.

As a solvent, tetrahydrofuran was used and diluted to prepare a solution having a sample concentration of 2% by mass. This sample solution was analyzed using a GPC device (Waters Alliance 2695). The flow rate of the solvent was 1 ml/min, and the analysis was carried out using a column with an analyzable molecular weight of 10,000 to 256,000 with a refractive index as a detector. It should be noted that the relationship between the column retention time and the molecular weight was obtained using standard polystyrene with a definite molecular weight, and a calibration curve was prepared separately, and the molecular weight was determined from the obtained retention time.

[Example 1-2]

The poly(meth)acrylate viscosity index improver was synthesized under the following conditions ("synthesis conditions 1-2").

Throw methyl methacrylate (C1-MA ) 12g, stearyl methacrylate (C18-MA) 18g, cumyl dithiobenzoate (CDTBA) 0.031g, and highly refined mineral oil 30g as a solvent, and stirred to form a uniform solution. The solution was cooled to 0° C. in an ice bath, and vacuum degassing/nitrogen purging of the reaction system was performed 5 times using a diaphragm pump. Further, 0.051 g of azobisisobutyronitrile (AIBN) as a free radical initiator was dropped from the sample introduction port under a nitrogen stream, and then polymerized at a solution temperature of 100° C. under a nitrogen atmosphere for 12 hours to obtain base) solution of acrylate viscosity index improver.

As a result of GPC analysis of the obtained poly(meth)acrylate viscosity index improver in the same manner as in Example 1-1, the weight average molecular weight Mw was 220,000, the number average molecular weight Mn was 167,000, and the Mw/Mn was 1.32. .

[Example 1-3]

The poly(meth)acrylate viscosity index improver was synthesized under the following conditions ("synthesis conditions 1-3").

Throw methyl methacrylate (C1-MA ) 12g, stearyl methacrylate (C18-MA) 18g, cumyl dithiobenzoate (CDTBA) 0.033g, and highly refined mineral oil 30g as a solvent, and stirred to form a uniform solution. The solution was cooled to 0° C. in an ice bath, and vacuum degassing/nitrogen purging of the reaction system was performed 5 times using a diaphragm pump. Further, 0.055 g of azobisisobutyronitrile (AIBN) as a free radical initiator was dropped from the sample inlet under a nitrogen stream, and then polymerized for 12 hours at a solution temperature of 90° C. under a nitrogen atmosphere to obtain base) solution of acrylate viscosity index improver.

As a result of GPC analysis of the obtained poly(meth)acrylate viscosity index improver in the same manner as in Example 1-1, the weight average molecular weight Mw was 210,000, the number average molecular weight Mn was 186,000, and the Mw/Mn was 1.13 .

[Comparative Example 1-1]

The poly(meth)acrylate viscosity index improver was synthesized under the following conditions ("synthesis conditions 1-4").

Add 30 g of highly refined mineral oil as a solvent to a 300 ml four-neck reaction flask equipped with a stirring blade (with a vacuum seal), a serpentine condenser, a three-way piston for nitrogen introduction, and a dropping funnel for sample introduction, and place at 85° C. The mixture was stirred for 1 hour while purging nitrogen gas in an oil bath. Into the dropping funnel for sample introduction, 12 g of methyl methacrylate (C1-MA) and 18 g of stearyl methacrylate (C18-MA) as raw material monomers, and azobisisobutylene as a radical initiator Nitrile (AIBN) 0.12 g was mixed as a raw material, and this raw material was dripped in the reaction flask over 70 minutes. Then, it superposed|polymerized while keeping stirring at 85 degreeC under nitrogen flow for 8 hours, and obtained the solution containing the poly(meth)acrylate viscosity index improver. Then, vacuum distillation was implemented at 130 degreeC and 1 mmHg for 3 hours, and the unreacted monomer was removed from the said solution.

As a result of GPC analysis of the obtained poly(meth)acrylate viscosity index improver in the same manner as in Example 1-1, the weight average molecular weight Mw was 260,000, the number average molecular weight Mn was 158,000, and the Mw/Mn was 1.65 .

[Examples 1-4 to 1-15, Comparative Examples 1-2 to 1-4]

The compounding quantity of the raw material was changed as shown in Table 1, 3, 5, 7, and the poly(meth)acrylate system was synthesized in the same manner as any of the above-mentioned synthesis conditions 1-1 to 1-4. Viscosity index improver. It should be noted that, in the table, C12-MA represents the compound in which R in formula (3) ^is a methyl group and ^R is a dodecyl group (straight-chain alkyl group with 12 carbon atoms). In addition, C22- MA represents a compound in which R ¹ in formula (3) is a methyl group and R ² is a docosyl group (straight-chain alkyl group having 22 carbon atoms). Mw, Mn, and Mw/Mn of the obtained poly(meth)acrylate viscosity index improver are shown in Tables 2, 4, 6, and 8.

<Preparation of lubricating oil composition>

The poly(meth)acrylate-based viscosity index improvers obtained in Examples 1-1 to 1-15 and Comparative Examples 1-1 to 1-4 respectively contained metal-based (calcium sulfonate-based) scavenger, no Performance additives for ash dispersants (succinimide), friction modifiers (glyceryl monooleate) and antiwear agents (zinc dithiophosphate), and highly refined mineral oils (GroupIII base oils, kinematic viscosity at 100°C : 4.2 mm ² /s, VI: 125) were blended at the ratios shown in Tables 2, 4, 6, and 8 to prepare lubricating oil compositions.

<Evaluation of lubricating oil composition>

For each lubricating oil composition of Examples 1-1 to 1-15 and Comparative Examples 1-1 to 1-4, the kinematic viscosity at 100°C, viscosity index, and 100°C and The HTHS viscosity at 150°C was measured. The results are shown in Tables 2, 4, 6, and 8.

Kinematic viscosity: JIS K-2283-1993

Viscosity index: JIS K 2283-1993

HTHS Viscosity: ASTM D-4683

[Table 1]

[Table 2]

[table 3]

[Table 4]

[table 5]

[Table 6]

[Table 7]

[Table 8]

[Example 2-1]

A poly(meth)acrylate viscosity index improver was synthesized under the following conditions ("synthesis conditions 2-1").

Add methyl methacrylate (formula (3 ) in which both R ¹ and R ² are methyl. Hereinafter described as "C1-MA".) 12 g, stearyl methacrylate (R ¹ in formula (3) is methyl, R ² is stearyl Aliphatic group (straight chain alkyl with 18 carbon atoms). Hereinafter described as "C18-MA".) 18g, cumyl dithiobenzoate (CDTBA) 0.081g, and the height of the solvent 30g of refined mineral oil was stirred to form a homogeneous solution. The solution was cooled to 0° C. in an ice bath, and vacuum degassing/nitrogen purging of the reaction system was performed 5 times using a diaphragm pump. Further, 0.014 g of azobisisobutyronitrile (AIBN) as a free radical initiator was dropped from the sample inlet under a nitrogen stream, and then polymerized at a solution temperature of 110° C. under a nitrogen atmosphere for 12 hours to obtain base) solution of acrylate viscosity index improver.

About the obtained poly(meth)acrylate viscosity index improver, the weight average molecular weight Mw and the number average molecular weight Mn were measured by GPC analysis. As a result, the weight average molecular weight Mw was 83,000, the number average molecular weight Mn was 55,000, and Mw/Mn was 1.51. The procedure of GPC analysis is as follows.

As a solvent, tetrahydrofuran was used and diluted to prepare a solution having a sample concentration of 2% by mass. This sample solution was analyzed using a GPC device (Waters Alliance 2695). The flow rate of the solvent was 1 ml/min, and the analysis was carried out using a column with an analyzable molecular weight of 10,000 to 256,000 with a refractive index as a detector. It should be noted that the relationship between the column retention time and the molecular weight was obtained using standard polystyrene with a definite molecular weight, and a calibration curve was prepared separately, and the molecular weight was determined from the obtained retention time. The molecular weights (Mw and Mn) of the arms can be calculated by dividing the obtained molecular weights (Mw and Mn) by the number of functional groups of the initiator.

[Example 2-2]

The poly(meth)acrylate viscosity index improver was synthesized under the following conditions ("synthesis conditions 2-2").

Throw methyl methacrylate (C1-MA ) 12g, stearyl methacrylate (C18-MA) 18g, cumyl dithiobenzoate (CDTBA) 0.085g, and highly refined mineral oil 30g as a solvent, and stirred to form a uniform solution. The solution was cooled to 0° C. in an ice bath, and vacuum degassing/nitrogen purging of the reaction system was performed 5 times using a diaphragm pump. Further, 0.013 g of azobisisobutyronitrile (AIBN) as a free radical initiator was dropped into the sample inlet under a nitrogen stream, and then polymerized at a solution temperature of 100° C. under a nitrogen atmosphere for 12 hours to obtain base) solution of acrylate viscosity index improver.

As a result of GPC analysis of the obtained poly(meth)acrylate viscosity index improver in the same manner as in Example 2-1, the weight average molecular weight Mw was 78,000, the number average molecular weight Mn was 59,000, and the Mw/Mn was 1.32 .

[Example 2-3]

The poly(meth)acrylate viscosity index improver was synthesized under the following conditions ("synthesis conditions 2-3").

Throw methyl methacrylate (C1-MA ) 12g, stearyl methacrylate (C18-MA) 18g, cumyl dithiobenzoate (CDTBA) 0.084g, and highly refined mineral oil 30g as a solvent, and stirred to form a uniform solution. The solution was cooled to 0° C. in an ice bath, and vacuum degassing/nitrogen purging of the reaction system was performed 5 times using a diaphragm pump. Further, 0.014 g of azobisisobutyronitrile (AIBN) as a free radical initiator was dropped from the sample introduction port under a nitrogen stream, and then polymerized at a solution temperature of 90° C. under a nitrogen atmosphere for 12 hours to obtain base) solution of acrylate viscosity index improver.

As a result of GPC analysis of the obtained poly(meth)acrylate viscosity index improver in the same manner as in Example 2-1, the weight average molecular weight Mw was 85,000, the number average molecular weight Mn was 75,000, and Mw/Mn was 1.13 .

[Comparative Example 2-1]

The poly(meth)acrylate viscosity index improver was synthesized under the following conditions ("synthesis conditions 2-4").

Add 30 g of highly refined mineral oil as a solvent to a 300 ml four-neck reaction flask equipped with a stirring blade (with a vacuum seal), a serpentine condenser, a three-way piston for nitrogen introduction, and a dropping funnel for sample introduction, and place at 85° C. The mixture was stirred for 1 hour while purging nitrogen gas in an oil bath. Into the dropping funnel for sample introduction, 12 g of methyl methacrylate (C1-MA) and 18 g of stearyl methacrylate (C18-MA) as raw material monomers, and azobisisobutylene as a radical initiator Nitrile (AIBN) 0.068 g of the mixed raw material was dropped into the reaction flask over 70 minutes. Then, it superposed|polymerized while keeping stirring at 85 degreeC under nitrogen flow for 8 hours, and obtained the solution containing the poly(meth)acrylate viscosity index improver. Then, vacuum distillation was implemented at 130 degreeC and 1 mmHg for 3 hours, and the unreacted monomer was removed from the said solution.

As a result of GPC analysis of the obtained poly(meth)acrylate viscosity index improver in the same manner as in Example 2-1, the weight average molecular weight Mw was 18,000, the number average molecular weight Mn was 11,000, and Mw/Mn was 1.65 .

[Examples 2-4 to 2-14, Comparative Examples 2-2 to 2-5]

The compounding quantity of raw materials was changed as shown in Table 9, 11, 13, and 15, and the poly(meth)acrylate system was synthesized in the same manner as any of the above-mentioned synthesis conditions 2-1 to 2-4. Viscosity index improver. It should be noted that, in the table, C12-MA represents the compound in which R in formula (3) ^is a methyl group and ^R is a dodecyl group (straight-chain alkyl group with 12 carbon atoms). In addition, C22- MA represents a compound in which R ¹ in formula (3) is a methyl group and R ² is a docosyl group (straight-chain alkyl group having 22 carbon atoms). Mw, Mn, and Mw/Mn of the obtained poly(meth)acrylate viscosity index improver are shown in Tables 2, 4, 6, and 8.

<Preparation of lubricating oil composition>

The poly(meth)acrylate-based viscosity index improvers obtained in Examples 2-1 to 2-14 and Comparative Examples 2-1 to 2-5 respectively contained metal-based (calcium sulfonate-based TBN300mgKOH/g) Cleaning agent, ash-free residual agent (succinimide), friction modifier (oleamide), anti-wear agent (phosphoric acid), antioxidant (diphenylamine), metal deactivator (thiadiazole) and sulfur additives ( sulfurized ester) and highly refined mineral oil (Group III base oil, kinematic viscosity at 100°C: 3.3mm ² /s, VI: 110) at the ratios shown in Tables 10, 12, 14, and 16, A lubricating oil composition is prepared.

<Evaluation of lubricating oil composition>

For each lubricating oil composition of Examples 2-1 to 2-14 and Comparative Examples 2-1 to 2-5, the kinematic viscosity and viscosity index at 100° C. were measured by the following standard method, respectively. The results are shown in Tables 10, 12, 14, and 16.

Kinematic viscosity: JIS K-2283-1993

Viscosity index: JIS K 2283-1993

In addition, regarding the friction characteristics of the lubricating oil compositions of Examples 2-1 to 2-14 and Comparative Examples 2-1 to 2-5, using a double-cylinder rotary sliding friction tester, the friction coefficient under a constant load condition Make an evaluation. Specifically, under the conditions of a test temperature of 80° C., a load of 142 N, a surface pressure of 0.48 GPa, a peripheral velocity of 1.0 m/s, and a slip coefficient of 5.1%, the friction coefficients within 10 minutes from the start of the test were averaged. The results are shown in Tables 10, 12, 14, and 16.

[Table 9]

[Table 10]

[Table 11]

[Table 12]

[Table 13]

[Table 14]

[Table 15]

[Table 16]

Claims (4)

1. poly-(methyl) acrylic ester viscosity index improver, it has the polymeric chain containing the structural unit shown in following general formula (1), the weight-average molecular weight Mw of this poly-(methyl) acrylic ester viscosity index improver is more than 100000, weight-average molecular weight Mw is less than 1.6 with the ratio Mw/Mn of number-average molecular weight Mn

In formula (1), R ¹represent hydrogen or methyl, R ²represent that carbonatoms is the alkyl of 1 ~ 36.

2. poly-(methyl) acrylic ester viscosity index improver, it has the polymeric chain containing the structural unit shown in following general formula (1), the weight-average molecular weight Mw of this poly-(methyl) acrylic ester viscosity index improver is less than 100000, weight-average molecular weight Mw is less than 1.6 with the ratio Mw/Mn of number-average molecular weight Mn

In formula (1), R ¹represent hydrogen or methyl, R ²represent that carbonatoms is the alkyl of 1 ~ 36.

3. a lubricating oil additive, it contains poly-(methyl) acrylic ester viscosity index improver described in claim 1 or 2.

4. a lubricating oil composition, it contains poly-(methyl) acrylic ester viscosity index improver described in lubricant base and claim 1 or 2.