JP2015013958A - Poly(meth)acrylate-based viscosity index improver, and lubricating oil additive and lubricating oil composition containing viscosity index improver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a viscosity index improver capable of imparting a sufficient friction loss reducing effect to a lubricating oil and to provide a lubricating oil additive and a lubricating oil composition containing the viscosity index improver.SOLUTION: There is provided a poly(meth)acrylate-based viscosity index improver having a polymer chain containing a structural unit represented by the following general formula (1), where the weight average molecular weight (Mw) of the poly(meth)acrylate-based viscosity index improver is less than 100000 and the ratio (Mw/Mn) between the weight average molecular weight (Mw) and the number average molecular weight (Mn) is 1.6 or less. [where, Rrepresents a hydrogen atom or a methyl group; and Rrepresents an alkyl group having 1 to 36 carbon atoms.]

Description

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

  Conventionally, in the field of lubricating oil, improvement of lubricating oil has been studied from the viewpoint of energy saving. In particular, in recent years, the trend of protecting the global environment has increased, and the demand for an energy saving improvement effect on lubricating oil has become even stronger.

  For example, in the case of lubricating oils such as ATF, MTF, CVTF, etc. (also referred to as “transmission lubricating oil” or “driving system oil”) used in automobile transmissions, as one means for improving fuel efficiency. And a method of reducing viscosity resistance by reducing the viscosity of transmission lubricating oil. However, when the viscosity of the transmission lubricating oil is lowered, other problems such as oil leakage and seizure may occur.

  Therefore, as another method for improving fuel economy, there is a method using a viscosity index improver. In this method, the viscosity index of the transmission lubricant is increased by using a viscosity index improver, and the increase in the viscosity in the low temperature region is suppressed while the viscosity in the high temperature region is maintained. Regarding the viscosity index improver, various types of viscosity index improvers have been proposed so far, but in particular, the use of poly (meth) acrylate viscosity index improvers has been proposed (for example, Patent Documents 1 to 7). reference).

JP 7-48421 A JP-A-7-62372 JP-A-6-145258 JP-A-3-100099 JP 2002-302687 A JP 2004-124080 A JP 2005-187736 A

  By the way, as one of the causes of the deterioration of fuel efficiency, there is a friction loss at the time of power transmission of a gear in the drive device. Therefore, if a lubricating oil with low viscous resistance can be realized under high shear conditions, friction loss can be reduced and fuel economy can be further improved.

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

  Accordingly, the present invention provides a viscosity index improver capable of imparting a sufficient friction loss reducing effect to a lubricant, and a lubricant additive and a lubricant composition containing the viscosity index improver. Objective.

  As a result of intensive studies, the inventors of the present invention have a specific structure, and a poly (meth) acrylate system having a weight average molecular weight and a ratio Mw / Mn between the weight average molecular weight Mw and the number average molecular weight Mn satisfying a specific condition. The present inventors have found that a friction loss reducing effect can be imparted by the viscosity index improver and have completed the present invention.

［式（１）中、Ｒ^１は水素又はメチル基を示し、Ｒ^２は炭素数１〜３６のアルキル基を示す。］ That is, the present invention has a polymer chain containing a structural unit represented by the following general formula (1), has a weight average molecular weight Mw of less than 100,000, and a ratio Mw between the weight average molecular weight Mw and the number average molecular weight Mn. A poly (meth) acrylate viscosity index improver having / Mn of 1.6 or less is provided.

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

  Moreover, this invention provides the lubricating oil additive containing the said poly (meth) acrylate type viscosity index improver.

  The present invention also provides a lubricating oil composition comprising a lubricating base oil and the poly (meth) acrylate viscosity index improver.

  ADVANTAGE OF THE INVENTION According to this invention, the viscosity index improver which can reduce a friction loss, and the lubricating oil additive and lubricating oil composition containing this viscosity index improver can be provided.

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

[First Embodiment: Poly (meth) acrylate viscosity index improver]
The poly (meth) acrylate viscosity index improver according to the first embodiment has a polymer chain including a structural unit represented by the following general formula (1). The poly (meth) acrylate viscosity index improver has a weight average molecular weight Mw (hereinafter, simply referred to as “Mw” in some cases) of less than 100,000, and a weight average molecular weight Mw and a number average molecular weight Mn (hereinafter, sometimes, The ratio Mw / Mn (hereinafter simply referred to as “Mw / Mn”) is 1.6 or less.

［式（１）中、Ｒ^１は水素又はメチル基を示し、Ｒ^２は炭素数１〜３６のアルキル基を示す。］

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

R ¹ may be either hydrogen or a methyl group, but is preferably a methyl group.

The number of carbon atoms of the alkyl group represented by R ² is 1 to 36 as described above, and is preferably 1 to 30 and more preferably 1 to 26 from the viewpoint of handleability and manufacturability. More preferably, it is 1-22. Further, the alkyl group represented by R ² may be linear or branched.

When the structural unit represented by the general formula (1) contained in the polymer chain is 2 or more, R ¹ and R ² may be the same or different among the structural units. When two or more types of structural units different in R ² are contained, from the viewpoint of viscosity temperature characteristics, the structural unit in which R ² is a methyl group is 10 to 45 masses based on the total amount of structural units contained in the polymer chain. %, Preferably 15 to 45% by mass, more preferably 20 to 45% by mass. From the viewpoint of fuel saving properties, it is preferable that the structural unit in which R ² is an alkyl group having 18 or more carbon atoms is contained in an amount of 10% by mass or more based on the total amount of structural units contained in the polymer chain, % Or more is more preferable, and 20% by mass or more is more preferable.

  The polymer chain may contain only the structural unit represented by the general formula (1), or represented by the general formula (1) in addition to the structural unit represented by the general formula (1). A structural unit other than the structural unit to be formed may be further included. The terminal of the polymer chain is not particularly limited. Among such polymer chains, the polymer chain contains only the structural unit represented by the general formula (1) and has a terminal hydrogen atom, that is, a polymer chain represented by the following general formula (2). It is preferable.

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 such that Mw and Mw / Mn satisfy the above-described conditions. . n is an integer of 40 to 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 further preferably 60,000 or less from the viewpoint of fuel saving characteristics. preferable. The lower limit of Mw is not particularly limited, but 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. Mn is preferably 6,000 or more, more preferably 10,000 or more, and further preferably 12,500 or more, from the viewpoint of fuel saving characteristics. The upper limit of Mn is not particularly limited, but Mn is, for example, 60,000 or less.

  Mw / Mn is 1.6 or less, but from the viewpoint of fuel economy, it is preferably 1.5 or less, more preferably 1.4 or less, and further preferably 1.3 or less. preferable. Further, Mw / Mn is preferably 1.0 or more, more preferably 1.01 or more, and further preferably 1.02 or more, from the viewpoint of fuel economy.

  In the present invention, “weight average molecular weight Mw”, “number average molecular weight Mn” and “ratio Mw / Mn of weight average molecular weight Mw and number average molecular weight Mn” are Mw, Mn and Mw obtained by GPC analysis. / Mn (polystyrene (standard sample) conversion value). Specifically, for example, it is measured as follows.

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

  The production method of the poly (meth) acrylate viscosity index improver according to the present embodiment is not particularly limited. For example, an initiator is added to a mixed solution containing an alkyl (meth) acrylate, a polymerization reagent, and a solvent, A method of polymerizing alkyl (meth) acrylate at a temperature is mentioned.

  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 a methyl group. The number of carbon atoms of the alkyl group represented by R ² is preferably 1 to 36, more preferably 1 to 30, and still more preferably 1 to 22.

As the alkyl (meth) acrylate, one of the alkyl (meth) acrylates represented by the general formula (3) can be used alone, or two or more kinds can be used in combination. Are preferably used. When using 2 or more types mixedly, it is preferable that content of methyl (meth) acrylate whose R < ² > is a methyl group is 5-50 mass% on the basis of alkyl (meth) acrylate whole quantity, and 10-50 More preferably, it is mass%, and it is still more preferable that it is 20-45 mass%. Further, the content of R ² is alkyl (meth) acrylate is an alkyl group having 18 or more carbon atoms, an alkyl (meth) acrylate total amount of preferably 10 mass% or more and 15 mass% or more Is more preferable, and it is still more preferable that it is 20 mass% or more.

  As the polymerization reagent, for example, cumyldithiobenzoic acid or a substance containing a thiocarbonyl group can be used. As a preferable polymerization reagent, cumyldithiobenzoic acid can be exemplified.

  As the solvent, for example, highly refined mineral oil, anisole, and toluene can be used. As a preferred solvent, highly refined mineral oil can be exemplified.

  As the initiator, for example, azobisisobutyronitrile, azobisdimethylvaleronitrile, azobismethylbutylnitrile can be used. As a preferred initiator, azobisisobutyronitrile can be exemplified.

  The reaction temperature for polymerizing the alkyl (meth) acrylate is preferably 70 to 120 ° C, more preferably 80 to 110 ° C, and still more preferably 80 to 120 ° C. By setting the reaction temperature within the above range, the Mw / Mn of the resulting poly (meth) acrylate viscosity index improver tends to be 1.6 or less. For example, when the reaction temperature is 90 to 100 ° C., Mw / Mn tends to be 1.0 to 1.2, and when the reaction temperature is 100 to 110 ° C., Mw / Mn is 1.2 to 1.4. When the reaction temperature is 110 to 120 ° C., Mw / Mn tends to be 1.4 to 1.6.

  The reaction time depends on the reaction conditions such as the raw material alkyl (meth) acrylate, polymerization reagent, solvent and initiator, reaction temperature, and the like, and the desired poly (meth) acrylate Mw and Mw / Mn. It can be selected as appropriate. As preferable reaction time, 10 to 14 hours can be illustrated, for example.

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

[Second Embodiment: Lubricating Oil Additive]
The lubricating oil additive according to the second embodiment of the present invention has a polymer chain containing the structural unit represented by the general formula (1), has a weight average molecular weight Mw of less than 100,000, and a weight average molecular weight. A poly (meth) acrylate viscosity index improver having a ratio Mw / Mn of Mw to number average molecular weight Mn of 1.6 or less is contained. The poly (meth) acrylate-based viscosity index improver in the present embodiment is the same as the viscosity index improver in the first embodiment, and a duplicate description is omitted here.

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

  Other additives include viscosity index improvers other than the above poly (meth) acrylate viscosity index improvers, antioxidants, antiwear agents (or extreme pressure agents), corrosion inhibitors, rust inhibitors, viscosity indexes Examples thereof include additives such as improvers, pour point depressants, demulsifiers, metal deactivators, antifoaming agents, and ashless friction modifiers. These additives can be used individually by 1 type or in combination of 2 or more types.

  As the viscosity index improver other than the above poly (meth) acrylate viscosity index improver, poly (meth) acrylate viscosity index improver other than the above poly (meth) acrylate viscosity index improver, polyisobutene viscosity index Examples thereof include an improver, an ethylene-propylene copolymer viscosity index improver, and a styrene-butadiene hydrogenated copolymer viscosity index improver.

  Examples of the antioxidant include ashless antioxidants such as phenols and amines, and metal antioxidants such as zinc, copper, and molybdenum.

  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'-methylenebis (4-methyl-6-tert-butylphenol), 4,4′-butylidenebis (3-methyl-6-tert-butylphenol), 4,4′-isopropylidenebis (2,6-di-tert-butylphenol), 2,2′-methylenebis (4-methyl-6) -Nonylphenol), 2,2'-isobutylidenebis (4,6-dimethylphenol), 2,2'-methylenebis (4-methyl-6-silane) (Rohexylphenol), 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, 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-butylphenol), 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, pentaerythrityl Tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, stearyl 3- ( 3,5-di-tert-butyl-4-hydroxyphenyl) propionate, octyl-3- (3-methyl-5-di-tert-butyl-4-hydroxyphenyl) propionate, and the like. You may use these in mixture of 2 or more types.

  As the amine-based antioxidant, for example, known amine-based antioxidants generally used for lubricating oils such as aromatic amine compounds, alkyldiphenylamines, alkylnaphthylamines, phenyl-α-naphthylamines, alkylphenyl-α-naphthylamines, etc. Agents.

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

  Examples of the rust preventive include petroleum sulfonate, alkylbenzene sulfonate, dinonylnaphthalene sulfonate, alkenyl succinic acid ester, and polyhydric alcohol ester.

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

Examples of antifoaming agents include silicone oils having a kinematic viscosity at 25 ° C. of 1,000 to 100,000 mm ² / s, alkenyl succinic acid derivatives, esters of polyhydroxy aliphatic alcohols and long chain fatty acids, and methyl salicylates. o-Hydroxybenzyl alcohol and the like can be mentioned.

  As the ashless friction modifier, any compound usually used as an ashless friction modifier for lubricating oils can be used, for example, an alkyl group or alkenyl group having 6 to 30 carbon atoms, particularly 6 to 30 carbon atoms. And ashless friction modifiers such as amine compounds, fatty acid esters, fatty acid amides, fatty acids, aliphatic alcohols and aliphatic ethers having at least one linear alkyl group or linear alkenyl group in the molecule. Various ashless friction modifiers exemplified in International Publication No. 2005/037967 pamphlet such as nitrogen-containing compounds and acid-modified derivatives thereof described in JP-A-2009-286831 can also be used.

  Moreover, the lubricating oil additive according to 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, it is preferable to use highly refined mineral oil. When the lubricating oil additive contains a solvent, the content of the solvent is preferably 5 to 75 mass%, more preferably 30 to 60 mass%, based on the total amount of the lubricating oil additive.

[Third Embodiment: Lubricating Oil Composition]
The lubricating oil composition according to the third embodiment has a lubricating base oil and a polymer chain containing the structural unit represented by the general formula (1), and the weight average molecular weight Mw is less than 100,000, And a poly (meth) acrylate viscosity index improver having a ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn of 1.6 or less. Here, the lubricating oil composition according to the present embodiment includes a mode including the lubricating base oil and the lubricating oil additive according to the second embodiment. The poly (meth) acrylate-based viscosity index improver in the present embodiment is the same as the poly (meth) acrylate-based viscosity index improver in the first embodiment and the second embodiment, and is included in the lubricating oil composition. The other additives and solvents to be obtained are the same as the other additives and solvents in the second embodiment, and redundant description is omitted here.

  The lubricating base oil is not particularly limited, and a lubricating base oil used for ordinary lubricating oil can be used. Specifically, a mineral oil base oil, a synthetic oil base oil, or a mixture of two or more kinds of lubricant base oils selected from these can be used.

  Examples of mineral oil base oils include, for example, solvent oil removal, solvent extraction, hydrocracking, solvent removal of lubricating oil fractions obtained by distillation under reduced pressure of atmospheric residual oil obtained by atmospheric distillation of crude oil. Examples thereof include those refined by performing one or more treatments such as dewaxing and hydrorefining, or base oils produced by a method of isomerizing wax isomerized mineral oil or GTL wax (gas-tuly wax).

  Synthetic oil-based lubricating oils include, for example, polybutene or hydrides thereof; poly-α-olefins such as 1-octene oligomers and 1-decene oligomers or hydrides thereof; ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl Diesters such as adipate, ditridecyl adipate, di-2-ethylhexyl sebacate; polyol esters such as trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate, pentaerythritol pelargonate; alkylnaphthalene And aromatic synthetic oils such as alkylbenzene or mixtures thereof.

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

  The saturated content of the lubricating base oil by chromatographic analysis is preferably 80% or more, more preferably, in order to facilitate the effects of additives such as the poly (meth) acrylate viscosity index improver according to the first embodiment. 85% or more, more preferably 90% or more, and most preferably 95% or more.

  The content of the poly (meth) acrylate viscosity index improver according to the first embodiment is preferably 0.1 to 20.0 mass%, more preferably 0.5 to 15 based on the total amount of the lubricating oil composition. It is 0.0 mass%, More preferably, it is 1.0-10.0 mass%. When the content is equal to or higher than the lower limit value, it is easy to obtain a sufficient addition effect. On the other hand, when the content is equal to or lower than the upper limit value, shear stability is increased and fuel consumption sustainability is improved.

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, 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 value, it becomes easy to ensure lubricity, while when the kinematic viscosity at 100 ° C. is not more than the above upper limit value, fuel economy is further improved. The kinematic viscosity at 100 ° C. in the present invention means the kinematic viscosity at 100 ° C. defined in JIS K-2283-1993.

  The viscosity index of the lubricating oil composition is preferably 130 to 250, more preferably 140 to 240, and still more preferably 160 to 230. When the viscosity index is equal to or higher than the lower limit, fuel economy can be further improved while maintaining the HTHS viscosity, and the low temperature viscosity is easily lowered. On the other hand, when the viscosity index is less than or equal to the above upper limit, low temperature fluidity, solubility of additives, and compatibility with sealing materials can be ensured. In addition, the viscosity index in this invention means the viscosity index prescribed | regulated to JISK2283-1993.

  The viscosity index improver according to the first embodiment described above, the lubricating oil additive according to the second embodiment, and the lubricating oil composition according to the third embodiment include a lubricating oil for an internal combustion engine, a drive system lubricating oil, and the like. Although it can be used in a wide range of fields, it is particularly useful in the field of drive system lubricants. The driving device in this case may be any of an automatic transmission (AT), a continuously variable automatic transmission (CVT), and a stepped transmission (TM).

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to a following example at all.

[Example 1]
A poly (meth) acrylate viscosity index improver was synthesized under the following conditions (referred to as “synthesis condition 1”).

A 300 ml five-neck separable flask equipped with a vertical metal stirring blade (with vacuum seal), a Dimroth cooler, a three-way cock for introducing nitrogen and a sample inlet was charged with methyl methacrylate (R ^{1 in} formula (3) and Compound in which R ² is both a methyl group, hereinafter referred to as “C1-MA”) 12 g, stearyl methacrylate (R ¹ in formula (3) is a methyl group, R ² is a stearyl group (straight chain of 18 carbon atoms) A compound that is an alkyl group), hereinafter referred to as “C18-MA”.) 18 g, cumyldithiobenzoic acid (CDTBA) 0.081 g, and 30 g of highly purified mineral oil as a solvent were added to obtain a homogeneous solution under stirring. This 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. Furthermore, 0.014 g of azobisisobutyronitrile (AIBN) was added as a radical initiator from the sample inlet under a nitrogen flow, and then polymerization was carried out at a solution temperature of 110 ° C. for 12 hours in a nitrogen atmosphere. A solution containing a (meth) acrylate viscosity index improver was obtained.

  About the obtained poly (meth) acrylate type 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.

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

[Example 2]
A poly (meth) acrylate viscosity index improver was synthesized under the following conditions (referred to as “synthesis condition 2”).

  A 300 ml 5-neck separable flask equipped with a vertical metal stirring blade (with vacuum seal), a Dimroth cooler, a three-way cock for introducing nitrogen and a sample inlet, 12 g of methyl methacrylate (C1-MA), stearyl methacrylate (C18) -MA) 18 g, cumyldithiobenzoic acid (CDTBA) 0.085 g, and highly refined mineral oil 30 g as a solvent were added to obtain a homogeneous solution under stirring. This 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. Furthermore, 0.013 g of azobisisobutyronitrile (AIBN) was added as a radical initiator from the sample introduction port under a nitrogen flow, and then polymerization was performed at a solution temperature of 100 ° C. for 12 hours in a nitrogen atmosphere. A solution containing a (meth) acrylate viscosity index improver was obtained.

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

[Example 3]
A poly (meth) acrylate viscosity index improver was synthesized under the following conditions (referred to as “synthesis condition 3”).

  A 300 ml five-neck separable flask equipped with a vertical metal stirring blade (with vacuum seal), a Dimroth cooler, a three-way cock for introducing nitrogen and a sample inlet, 12 g of methyl methacrylate (C1-MA), stearyl methacrylate ( C18-MA) 18 g, cumyldithiobenzoic acid (CDTBA) 0.084 g, and highly refined mineral oil 30 g as a solvent were added to obtain a homogeneous solution under stirring. This 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. Furthermore, 0.014 g of azobisisobutyronitrile (AIBN) was added as a radical initiator from the sample introduction port under a nitrogen flow, and then polymerization was performed at a solution temperature of 90 ° C. for 12 hours in a nitrogen atmosphere. A solution containing a (meth) acrylate viscosity index improver was obtained.

  The obtained poly (meth) acrylate viscosity index improver was subjected to GPC analysis in the same manner as in Example 1. As a result, 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 1]
A poly (meth) acrylate viscosity index improver was synthesized under the following conditions (referred to as “synthesis condition 4”).

  A 300 ml four-necked reaction flask equipped with a stirring blade (with vacuum seal), a Dimroth cooler, a three-way cock for introducing nitrogen, and a dropping funnel for introducing sample was charged with 30 g of highly purified mineral oil as a solvent, and an oil at 85 ° C. The mixture was stirred for 1 hour while purging with nitrogen in the bath. Into the dropping funnel for sample introduction, a raw material in which 12 g of methyl methacrylate (C1-MA) and 18 g of stearyl methacrylate (C18-MA) are mixed as raw materials and 0.068 g of azobisisobutyronitrile (AIBN) as a radical initiator is added. This raw material was dropped into the reaction flask over 70 minutes. Thereafter, polymerization was carried out for 8 hours while maintaining stirring at 85 ° C. under a nitrogen flow to obtain a solution containing a poly (meth) acrylate viscosity index improver. Thereafter, vacuum distillation was performed at 130 ° C. and 1 mmHg for 3 hours to remove unreacted monomers from the solution.

  The obtained poly (meth) acrylate viscosity index improver was subjected to GPC analysis in the same manner as in Example 1. As a result, 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 4 to 14, Comparative Examples 2 to 5]
The blending amount of the raw materials was changed as shown in Tables 1, 3, 5, and 7, and a poly (meth) acrylate viscosity index improver was synthesized in the same manner as in any of the above synthesis conditions 1 to 4 except that. . In the table, C12-MA is a compound in which R ¹ in the formula (3) is a methyl group and R ² is a dodecyl group (a linear alkyl group having 12 carbon atoms), and C22-MA is a compound in the formula (3). Compounds in which R ¹ is a methyl group and R ² is a docosanyl group (a linear alkyl group having 22 carbon atoms) are respectively represented. Tables 2, 4, 6, and 8 show Mw, Mn, and Mw / Mn of the obtained poly (meth) acrylate viscosity index improvers.

<Preparation of lubricating oil composition>
Poly (meth) acrylate viscosity index improvers obtained in Examples 1 to 15 and Comparative Examples 1 to 4, respectively, metal (TBN 300 mg KOH / g calcium sulfonate) detergent, ashless residue (succinimide) ), A friction modifier (oleylamide), an antiwear agent (phosphoric acid), an antioxidant (diphenylamine), a metal deactivator (thiadiazole), and a sulfur-based additive (sulfurized ester), and a performance additive, Highly refined mineral oil (Group ^II base oil, kinematic viscosity at 100 ° C .: 3.3 mm ² / s, VI: 110) was blended in the ratios shown in Tables 2, 4, 6, and 8 to prepare lubricating oil compositions. .

<Evaluation of lubricating oil composition>
About each lubricating oil composition of Examples 1-14 and Comparative Examples 1-5, the kinematic viscosity and viscosity index in 100 degreeC were measured by the method based on the following, respectively. The results are shown in Tables 2, 4, 6, and 8.
Kinematic viscosity: JIS K-2283-1993
Viscosity index: JIS K 2283-1993

  Moreover, the friction characteristic of each lubricating oil composition of Examples 1-14 and Comparative Examples 1-5 was evaluated by the coefficient of friction under a constant load condition using a two-cylinder rolling sliding friction tester. Specifically, the friction coefficient for 10 minutes from the start of the test was averaged under the conditions of a test temperature of 80 ° C., a load of 142 N, a surface pressure of 0.48 GPa, a peripheral speed of 1.0 m / s, and a slip ratio of 5.1%. The results are shown in Tables 2, 4, 6, and 8.

Claims (3)

It has a polymer chain containing a structural unit represented by the following general formula (1), 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 is 1. A poly (meth) acrylate viscosity index improver that is 6 or less.

[In formula (1), ^{R 1} represents hydrogen or a methyl group, ^{R 2} represents an alkyl group having 1 to 36 carbon atoms. ]   A lubricating oil additive comprising the poly (meth) acrylate viscosity index improver according to claim 1.   A lubricating oil composition comprising a lubricating base oil and the poly (meth) acrylate viscosity index improver according to claim 1.