JP2019014802A - A viscosity index improver and a lubricant composition - Google Patents

Abstract

To provide the viscosity index improver and the lubricant composition using the same, wherein the viscosity index improver can secure viscosity under a high temperature and a high shear condition and can lower the viscosity at a low temperature to a lower level.SOLUTION: The viscosity index improver containing a (meth) acrylate polymer has an intrinsic viscosity [η]at 100°C of 0.07 dL/g or more to 0.17 dL/g or less and the intrinsic viscosity [η]at 40°C of 0.01 dL/g or more to 0.08 or more in the group III base oil (viscosity index 122, kinematic viscosity 19.6 mm/s at 40°C) in the American Petroleum Institute (API) classification of the polymer.SELECTED DRAWING: Figure 1

Description

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

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

  As the viscosity index improver, those containing a polymer are known, and among them, a viscosity index improver composed of a (meth) acrylate polymer is said to exhibit a high viscosity index improving effect. On the other hand, since the viscosity index improver made of a (meth) acrylate polymer has poor shear stability, there has been a problem that fuel-saving properties are deteriorated (long life property is poor) during long-term use. Therefore, as means for achieving both a viscosity index improvement effect and shear stability, for example, Patent Documents 1 to 3 disclose a viscosity index improver comprising a polymer having a comb structure using a macromonomer as a monomer component. Patent Document 4 discloses a viscosity index improver made of a polymer having a star structure using divinylbenzene in the core.

JP2013-133460A Special table 2012-520358 gazette Special table 2010-532805 gazette JP 2012-197399 A

  The basic properties of the viscosity index improver are evaluated by the viscosity index. The viscosity index is an index representing the magnitude of the change in viscosity of the lubricating oil with temperature. The kinematic viscosity at 40 ° C. and 100 ° C. is measured, and the value of the viscosity index is determined by a predetermined method defined in JIS K 2283 (2000). calculate. It is generally recognized that the larger the value of the viscosity index, the smaller the change in viscosity due to temperature, and the more preferable as a lubricating oil. However, the present inventors have examined the effect of improving the viscosity characteristics of the viscosity index improver. As a result, simply increasing the value of the viscosity index may not sufficiently improve the viscosity characteristics of the lubricating oil. It was clarified that such a tendency is seen when used under conditions where a high shearing force is applied. That is, when used under high shear conditions, it has become clear that the effect of keeping the viscosity at low temperatures low while maintaining the lubricity at high temperatures may be insufficient.

  The present invention has been made in view of the above problems, and its purpose is to increase the viscosity index improver that can keep the viscosity at low temperature lower while ensuring the viscosity under high temperature and high shear conditions, And providing a lubricating oil composition using the viscosity index improver.

The present invention includes the following inventions.
[1] A viscosity index improver containing a (meth) acrylate polymer,
Intrinsic viscosity [η] ₁₀₀ at 100 ° C. in a group III base oil (viscosity index 122, 40 ° C. kinematic viscosity 19.6 mm ² / s) in the American Petroleum Institute (API) classification of the polymer is 0.07 dL / g or more. A viscosity index improver that is 0.17 dL / g or less and has an intrinsic viscosity [η] _{40 at} 40 ° C. of 0.01 dL / g or more and 0.08 dL / g or less.
[2] The viscosity index improver according to [1], wherein the thermal decomposition initiation temperature (Td) of the polymer is 275 ° C. or higher.
[3] The viscosity index improver according to [1] or [2], wherein the main chain SP value of the polymer is 9.20 or more and 9.50 or less.
[4] The viscosity index improver according to any one of [1] to [3], wherein the polymer has a weight average molecular weight (Mw) of 200,000 to 700,000.
[5] The viscosity index improver according to any one of [1] to [4], wherein the polymer has a structural unit derived from a macromonomer.
[6] The viscosity index improver according to any one of [1] to [5], wherein the polymer has a structural unit derived from a maleimide monomer.
[7] The viscosity index improver according to any one of [1] to [6], wherein the polymer has a structural unit derived from alkyl (meth) acrylate and having 2 to 6 carbon atoms in the alkyl group. .
[8] A lubricating oil composition comprising a lubricating base oil and the viscosity index improver according to any one of [1] to [7].

According to the viscosity index improver and lubricating oil composition of the present invention, the intrinsic viscosity [η] ₁₀₀ at 100 ° C. and the intrinsic viscosity [η] 40 ° C. of the (meth) acrylate polymer contained in the viscosity index improver ₄₀ By appropriately setting, the viscosity at a low temperature can be kept lower while ensuring the viscosity under a high temperature and high shear condition.

The graph which showed typically the relationship between the temperature of a lubricating oil under high shear conditions and low shear conditions and viscosity.

[1. (Viscosity index improver)
Lubricating oils are used in various fields including automobile applications in order to prevent machine wear and seizure. The lubricating oil is used in a wide temperature range from a low temperature to a high temperature. The viscosity is low at a high temperature and the viscosity is high at a low temperature, but it is desirable that the lubricating oil has a viscosity change as small as possible with respect to the temperature change. For example, in a lubricant for an internal combustion engine, if the viscosity is too low, the oil film of the lubricating oil becomes thin and the lubricity is lowered, so that problems such as wear and seizure of the cylinder and cylinder head are likely to occur, while if the viscosity is too high, Energy loss due to viscous resistance increases and fuel consumption deteriorates. A viscosity index improver is used to reduce such a change in viscosity with respect to a change in temperature of the lubricating oil.

The viscosity index improver is blended in the lubricating oil so that the viscosity at high temperature and high shear at which the oil film becomes the thinnest is maintained above a certain level. In particular, the lubricating oil for internal combustion engines is used in a situation where a high shearing force is applied between the cylinder and the cylinder head, but the present inventors have examined the effect of improving the viscosity characteristics by the viscosity index improver under high shear conditions. However, it has been clarified that there are cases where a sufficient viscosity characteristic improving effect cannot be obtained only by looking at the viscosity index, which is a basic performance index of the viscosity index improver. Under such circumstances, the present inventors have found that it is effective to use intrinsic viscosity as an index for a viscosity index improver used under high shear conditions. It was revealed that the viscosity at a low temperature can be suppressed to a lower level while maintaining the lubricity. Specifically, by setting the intrinsic viscosity [η] _{100 at 100} ° C. and the intrinsic viscosity [η] ₄₀ at 40 ° C. within appropriate ranges, the use environment of the lubricating oil for internal combustion engines, for example, a temperature of 150 ° C. In the following, it has been clarified that a favorable effect of improving viscosity characteristics can be obtained at both high shear and low shear.

  FIG. 1 schematically shows a graph of the relationship between temperature and viscosity under high shear conditions and low shear conditions in order to explain the effect of the viscosity index improver of the present invention. Although the viscosity of the lubricating oil decreases as the temperature increases, the temperature dependence of the viscosity decreases by adding a viscosity index improver. The viscosity index is used as an index representing the difference between the viscosity VL1 at low temperature T1 and the viscosity VL2 at high temperature T2 under low shear conditions. The larger the viscosity index, the smaller the temperature dependency of the viscosity. That is, the larger the viscosity index, the smaller the difference between the viscosity VL1 at the low temperature T1 and the viscosity VL2 at the high temperature T2. On the other hand, the lubricating oil viscosity also changes depending on the shearing conditions, and the viscosity tends to decrease as the shearing rate increases. The degree of viscosity change due to the difference in shear conditions varies depending on the viscosity index improver blended in the lubricating oil, but it is difficult to predict this from the viscosity index, which is an index representing the temperature dependence of viscosity. For this reason, a viscosity index improver that is excellent in the effect of improving the viscosity index does not always reduce the viscosity change due to the difference in shear conditions.

Considering the actual use conditions of the lubricating oil, the viscosity index improver is blended in the lubricating oil so that the viscosity at high temperature and high shear at which the oil film becomes the thinnest becomes a certain level or more. In FIG. 1, a necessary amount is blended in the lubricating oil so that the viscosity VH2 at high temperature and high shear is not less than a predetermined value. On the other hand, when the viscosity index improver is blended in this way, it is desirable that the viscosity VH1 at low temperature and high shear and the viscosity VL1 at low temperature and low shear are kept as low as possible from the viewpoint of improving fuel efficiency. Thus, the viscosity index improver of the present invention is excellent in the effect of improving the viscosity characteristics in consideration of shear conditions. Specifically, the intrinsic viscosity at 100 ° C. [η] ₁₀₀ and the intrinsic viscosity at 40 ° C. [η ] By appropriately setting ₄₀ , the viscosity at a low temperature can be kept lower while ensuring the viscosity under a high temperature and high shear condition. Hereinafter, the viscosity index improver of the present invention will be described in detail.

  The viscosity index improver of the present invention contains a (meth) acrylate polymer. The (meth) acrylate polymer is not particularly limited as long as it is a polymer having a structural unit derived from a (meth) acrylate monomer. As the (meth) acrylate monomer, an alkyl (meth) acrylate that may have a substituent, an aryl (meth) acrylate that may have a substituent, and a hetero that may have a substituent An aryl (meth) acrylate etc. are mentioned.

The (meth) acrylate polymer contained in the viscosity index improver is an intrinsic property at 100 ° C. in a group III base oil (viscosity index 122, kinematic viscosity at 40 ° C. 19.6 mm ² / s) in the American Petroleum Institute (API) classification. The viscosity [η] ₁₀₀ is 0.07 dL / g or more and 0.17 dL / g or less, and the intrinsic viscosity [η] _{40 at} 40 ° C. is 0.01 dL / g or more and 0.08 dL / g or less. Intrinsic viscosity is generally used as an index representing the spread of a polymer in a solution. As a result of studies by the present inventors, the values of intrinsic viscosity [η] _{100 at 100} ° C. and intrinsic viscosity [η] ₄₀ at 40 ° C. It was clarified that the viscosity index improver exhibiting a preferable effect of improving the viscosity characteristics at both high shear and low shear is obtained by setting the above in such a range. Specifically, when a viscosity index improver is added to a lubricating oil (base oil) so that the viscosity at high temperature and high shear at which the oil film becomes the thinnest is greater than a certain level, It becomes possible to keep the viscosity lower. By setting the intrinsic viscosity to an appropriate range in this way, it is assumed that the polymer spreads appropriately in the lubricating oil even under high temperature and high shear conditions, deformation due to shear is small, and the decrease in the thickening effect is small. Is done.

The intrinsic viscosity [η] _{100 at} 100 ° C. is preferably 0.08 dL / g or more, more preferably 0.09 dL / g or more, and preferably 0.16 dL / g or less, 0.15 dL / g or less. Is more preferable. The intrinsic viscosity [η] _{40 at} 40 ° C. is preferably 0.02 dL / g or more, more preferably 0.03 dL / g or more, and preferably 0.07 dL / g or less, 0.06 dL / g or less. Is more preferable. The intrinsic viscosity [η] _{100 at 100} ° C. is preferably larger than the intrinsic viscosity [η] _{40 at} 40 ° C. As a group III base oil having a viscosity index of 122 and a kinematic viscosity of 19.6 mm ² / s at 40 ° C., YUBASE4 manufactured by SK can be used.

The intrinsic viscosity ratio [η] ₁₀₀ / [η] ₄₀ of the (meth) acrylate polymer is preferably 1.7 or more, more preferably 1.9 or more, further preferably 2.1 or more, and 7.0 or less. Is preferably 4.7 or less, more preferably 3.8 or less, and even more preferably 3.5 or less. If the intrinsic viscosity ratio [η] ₁₀₀ / [η] ₄₀ is in such a range, when the viscosity index improver is added to the lubricating oil, the viscosity at high temperature and high shear is secured above a certain level, while at low temperatures. It becomes easy to keep the viscosity of the resin low.

In the viscosity index improver of the present invention, the value of the viscosity index is not particularly limited as long as the intrinsic viscosities [η] ₁₀₀ and [η] ₄₀ are in the above range. In the present invention, it is preferable that the viscosity index of the viscosity index improver is high to some extent, but it is not necessarily preferable that the viscosity index improver is higher. The (meth) acrylate polymer contained in the viscosity index improver has, for example, a viscosity index of a base oil solution of a polymer diluted with a base oil so that the high-temperature high-shear viscosity is 1.75 mPa · s is 200 or more. Preferably, it is 210 or more, more preferably 225 or more, more preferably 280 or less, more preferably 265 or less, and further preferably 250 or less. The high-temperature high-shear viscosity and viscosity index are 150 ° C. and shear rate of 1 × 10 ⁶ / s, group III base oil (viscosity index 122, 40 ° C. kinematic viscosity 19.6 mm ² ) in the American Petroleum Institute (API) classification. The base oil solution of the polymer diluted at / s) is determined by measuring based on the method of JIS K 2283 (2000).

The (meth) acrylate polymer comprises 78% by mass of Group III base oil (viscosity index 122, 40 ° C. kinematic viscosity 19.6 mm ² / s) in the American Petroleum Institute (API) classification, and 22% by mass of the polymer. The viscosity of the solution is preferably 8000 mPa · s or less when measured at 25 ° C. with a viscometer (manufactured by Toki Sangyo Co., Ltd., TVB-10, rotor: SPINDLE No. M3, rotation speed 6 rpm), and is 7000 mPa · s. s or less is more preferable, and 6000 mPa · s or less is more preferable. If the base oil solution of the polymer has such a viscosity, the fluidity of the viscosity index improver near room temperature is increased, and handling properties are improved. The minimum of the said viscosity is not specifically limited, For example, what is necessary is just 20 mPa * s or more. In addition, YUBASE4 made by SK is used as a group III base oil having a viscosity index of 122 and a kinematic viscosity of 40 ° C. of 19.6 mm ² / s.

  The (meth) acrylate polymer preferably has a weight average molecular weight (Mw) of 200,000 or more, more preferably 250,000 or more, further preferably 300,000 or more, even more preferably 350,000 or more, and 700,000. The following is preferable, and 600,000 or less is more preferable. When the weight average molecular weight of the polymer is small, the viscosity index of the lubricating oil to which the polymer is added, that is, the base oil solution of the viscosity index improver is likely to be lowered. The amount used is increased, which is disadvantageous in terms of cost. Further, when a viscosity index improver is added to the lubricating oil so that the viscosity at high temperature and high shear is not less than a certain level, the viscosity at low temperature tends to increase. On the other hand, when the weight average molecular weight of the polymer is excessively large, the solubility of the viscosity index improver in the base oil is lowered, or the shear stability of the viscosity index improver is easily lowered. As the polymerization average molecular weight increases, the intrinsic viscosity described above tends to increase overall.

  The number average molecular weight (Mn) of the (meth) acrylate polymer is preferably 100,000 or more, more preferably 120,000 or more, further preferably 140,000 or more, preferably 500,000 or less, more preferably 400,000 or less, 30 Even less than 10,000 is more preferable.

  The molecular weight distribution (Mw / Mn) calculated from Mw and Mn of the polymer is preferably 4.0 or less, more preferably 3.5 or less, and even more preferably 3.0 or less. When the molecular weight distribution exceeds 4.0, the solubility of the viscosity index improver in the base oil is insufficient, and the shear stability of the lubricating oil composition tends to be lowered. On the other hand, the lower limit of the molecular weight distribution is preferably 1.0, but the molecular weight distribution (Mw / Mn) is preferably 1.5 or more and more preferably 1.8 or more from the viewpoint of easy synthesis of the polymer. In addition, the weight average molecular weight (Mw) and number average molecular weight (Mn) of a polymer are calculated | required by the method as described in an Example.

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

  The glass transition temperature (Tg) of the (meth) acrylate polymer is preferably −50 ° C. or higher, more preferably −40 ° C. or higher, further preferably −30 ° C. or higher, and preferably 0 ° C. or lower, and −10 ° C. or lower. Is more preferable, and −20 ° C. or lower is more preferable. If the Tg of the (meth) acrylate polymer is in such a range, when the viscosity index improver is added to the lubricating oil, the solubility of the viscosity index improver in the lubricating oil (base oil) is secured, While maintaining a high viscosity index, the fluidity near room temperature can be easily improved.

  The thermal decomposition start temperature (Td) of the (meth) acrylate polymer is preferably 275 ° C. or higher, more preferably 278 ° C. or higher, and further preferably 280 ° C. or higher. When the Td of the (meth) acrylate polymer is 275 ° C. or higher, the heat resistance is improved, and the thermal decomposition stability and shear stability are improved. Therefore, when this is added to a lubricating oil and used, it becomes easy to ensure a desired viscosity over a long period of time under high temperature and high shear conditions. The upper limit of the Td of the (meth) acrylate polymer is not particularly limited. However, when the heat resistance is excessively improved, the solubility of the viscosity index improver in the base oil is insufficient or the viscosity index is decreased. Therefore, it is preferably 500 ° C. or lower, more preferably 450 ° C. or lower, still more preferably 400 ° C. or lower, and even more preferably 380 ° C. or lower.

The main chain SP value (main chain solubility parameter) of the (meth) acrylate polymer is preferably 9.20 or more, more preferably 9.22 or more, further preferably 9.25 or more, and 9.50 or less. Preferably, 9.45 or less is more preferable, and 9.40 or less is more preferable. The SP value of the base oil generally shows a value of about 8.0 to 8.5, but if the main chain SP value of the (meth) acrylate polymer is 9.20 or more, the viscosity of the base oil solution of the viscosity index improver It becomes easy to increase the viscosity index, and if the main chain SP value is 9.50 or less, it becomes easy to ensure the solubility of the viscosity index improver in the base oil. The main chain SP value is determined by the Fedors method, and details thereof are described in the examples. The unit of the main chain SP value is (cal / cm ³ ) ^1/2 . When the main chain SP value is low, the intrinsic viscosity tends to increase overall.

The shear stability (SSI) of the (meth) acrylate polymer is preferably 35 or less, more preferably 30 or less, and even more preferably 25 or less, whereby the shear stability and storage stability of the viscosity index improver are improved. improves. The lower limit of the SSI of the viscosity index improver is not particularly limited, but is preferably 0.1 or more, more preferably 0.5 or more, still more preferably 2 or more, and even more preferably 5 or more. is there. When SSI is less than 0.1, the viscosity index improving effect of the viscosity index improver tends to decrease. SSI is obtained by diluting a (meth) acrylate polymer in a base oil so that the kinematic viscosity at 100 ° C. is 7.0 mm ² / sec, and the kinematic viscosity before and after the shearing treatment by an ultrasonic homogenizer and the base oil at 100 ° C. The kinematic viscosity is measured and determined by the following formula: SSI = {1− (kinematic viscosity after shearing process−dynamic viscosity of base oil) / (kinematic viscosity before shearing process−dynamic viscosity of base oil)} × 100.

The (meth) acrylate polymer used in the present invention is not particularly limited in its structure as long as the intrinsic viscosities [η] ₁₀₀ and [η] ₄₀ are within the specific ranges described above. It is preferable to have a structural unit (A) derived from a macromonomer. If the (meth) acrylate polymer has a structural unit derived from a macromonomer, the base oil solubility is increased, and the viscosity index of the base oil solution of the viscosity index improver can be easily improved. Further, when the viscosity index improver is made highly polar and the intrinsic viscosity [η] ₄₀ is reduced, it becomes easy to ensure the base oil solubility. Furthermore, since it becomes easy to increase the shear stability of the polymer while increasing the weight average molecular weight of the (meth) acrylate polymer, the viscosity of the base oil solution of the viscosity index improver under high shear conditions is reduced. It becomes easy to secure for a long time.

  The structural unit (A) derived from the macromonomer can be introduced into the polymer by copolymerizing the macromonomer with a (meth) acrylate monomer or the like. The macromonomer can be used without particular limitation as long as it is a polymer having a polymerizable functional group, but preferably has a hydrocarbon group having 50 or more carbon atoms from the viewpoint of enhancing the base oil solubility of the polymer. The carbon number is more preferably 70 or more, still more preferably 100 or more, and even more preferably 150 or more. The upper limit of the carbon number of the hydrocarbon group of the macromonomer is not particularly limited, but is preferably 3500 or less, more preferably 1500 or less, and even more preferably 700 or less.

  The hydrocarbon group of the macromonomer preferably includes a repeating structure derived from a hydrocarbon monomer or a hydride thereof. Examples of the hydrocarbon monomer include ethylene, propylene, 1-butene, isobutene, and 1-tetradecene. Monoolefins such as 1-octadecene; 1,3-butadiene, 2-methyl-1,3-butadiene, 1,3-pentadiene, 1,4-pentadiene, 1,5-hexadiene, 2,5-dimethyl- Alkadienes such as 1,5-hexadiene (also known as diisobutene); styrene monomers such as styrene, α-methylstyrene and vinyltoluene. Of these, monoolefins, alkadienes and the like are preferable as the hydrocarbon monomer, and therefore the hydrocarbon group of the macromonomer is preferably an aliphatic hydrocarbon group. In the case where the hydrocarbon monomer is an alkadiene, the repeating structure derived from the alkadiene may contain an unsaturated bond. In this case, the unsaturated bond may be hydrogenated (hydrogenated). . These monoolefins and alkadienes preferably have 2 or more carbon atoms, more preferably 3 or more, more preferably 20 or less, still more preferably 10 or less, and still more preferably 6 or less.

  The aliphatic hydrocarbon group may be a straight chain or a branched chain, but from the point of preventing thickening by suppressing crystallization at low temperature of the (meth) acrylate polymer, It is preferably branched. The hydrocarbon group of the branched macromonomer preferably includes a branched alkylene group as a repeating unit, and preferably includes both a branched alkylene group and a linear alkylene group as a repeating unit. . Examples of the branched alkylene group include 1,2-propylene group, 1,2-butylene group, 1,3-butylene group, 2,3-butylene group, 1,2-hexylene group and the like. Examples of the linear alkylene group include ethylene, 1,3-propylene group, 1,4-butylene group, 1,5-pentylene group, 1,6-hexylene group and the like.

  It is preferable that the hydrocarbon group of the macromonomer does not contain an unsaturated bond. Therefore, the hydrocarbon group of the macromonomer is particularly preferably an aliphatic saturated hydrocarbon group.

As the structural unit (A) derived from the macromonomer, from the viewpoint of easy production and availability of the macromonomer, and easy copolymerization with other monomer components to obtain a (meth) acrylate polymer. What is represented by following formula (1) is preferable. In the following formula (1), R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X represents a urethane bond (—NH—CO—O—) or a urea bond (—NH—CO—NH—). , An ester bond (—CO—O—), an amide bond (—NH—CO—), a sulfonate ester bond (—SO ₂ —O—), or a sulfonamide bond (—SO ₂ —NH—) R ² represents a hydrocarbon group.

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

The direction of each bond of the urethane bond, urea bond, ester bond, amide bond, sulfonic acid ester bond, or sulfonamide bond contained in the X linking group of formula (1) is not particularly limited. Taking a urethane bond as an example, the urethane bond may have a nitrogen atom located on the R ² side and an oxygen atom located on the R ² side. As long as the linking group X includes the bond, it may have two or more of the bonds, and may have another divalent linking group such as a methylene group or an ether bond (—O—). Also good. The linking group X is more preferably one containing a urethane bond, urea bond, ester bond or amide bond.

For the hydrocarbon group of R ^{2 in} the formula (1), the description of the hydrocarbon group of the macromonomer is referred to. For example, the hydrocarbon group of R ² preferably has 50 or more carbon atoms, and preferably includes a repeating structure derived from a hydrocarbon monomer or a hydride thereof.

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

  The number average molecular weight of the structural unit (A) derived from the macromonomer is preferably 750 or more, more preferably 1000 or more, further preferably 1500 or more, and more preferably 2000 or more, from the viewpoint of base oil solubility, viscosity index, and shear stability. More preferably, it is preferably 50000 or less, more preferably 20000 or less, and even more preferably 10,000 or less.

  When the (meth) acrylate polymer has the structural unit (A), the content of the unit (A) is preferably 6 parts by mass or more, more preferably 7 parts by mass or more, and 8 parts by mass in 100 parts by mass of the polymer. Part or more is more preferable, 25 parts by mass or less is preferable, 22 parts by mass or less is more preferable, 18 parts by mass or less is further preferable, and 16 parts by mass or less is even more preferable. If the unit (A) is contained in such a content, when the viscosity index improver is added to the lubricating oil, the viscosity at high temperature and high shear is secured above a certain level, while at low temperature and high shear or at low temperature It becomes easy to keep the viscosity at low shear low. In addition, when the structural components other than the unit (A) in the polymer are the same, when the content of the unit (A) increases, the intrinsic viscosity of the (meth) acrylate polymer tends to decrease as a whole.

  The (meth) acrylate polymer preferably has a structural unit (B) derived from a maleimide monomer. In this case, a succinimide ring structure is introduced into the main chain of the polymer derived from the maleimide monomer. Thus, by introducing a ring structure into the main chain of the polymer, it is possible to increase the shear stability and heat resistance of the viscosity index improver while ensuring the solubility of the viscosity index improver in the base oil. . Therefore, when the viscosity index improver is added to the lubricating oil, the viscosity at high temperature and high shear is easily secured over a long period of time. Further, the lubricating oil thus obtained is expected to have an effect of improving the clean dispersibility of sludge and the like and suppressing wear on the metal surface. The unit (B) can be introduced into the polymer by copolymerizing maleimide optionally having a substituent at the N-position with a (meth) acrylate monomer or the like.

As the unit (B), those represented by the following formula (2) are preferable. In formula (2), R ³ and R ⁴ each independently represent a hydrogen atom or an alkyl group, and R ⁵ represents a hydrogen atom or an organic group having 1 to 40 carbon atoms.

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

Examples of the organic group represented by R ^{5 in} the formula (2) include an alkyl group, an aryl group, an aralkyl group, and a group in which a part of —CH ₂ — contained in the alkyl group is replaced by —O—. A substituent such as a hydroxyl group, a halogen group, a nitro group, an alkyl group (in the case of an aryl group or an aralkyl group), an alkoxy group, or a carboxy group may be bonded to the group. The organic group of R ⁵ preferably has 1 to 24 carbon atoms, more preferably 1 to 18 carbon atoms, and still more preferably 1 to 12 carbon atoms, from the viewpoint of increasing the solubility of the viscosity index improver in the base oil.

Examples of the alkyl group for R ⁵ include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group, isopentyl group, n-hexyl group, isohexyl group. Linear or branched alkyl groups such as xyl group, n-heptyl group, isoheptyl group, n-octyl group, 2-ethylhexyl group, cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cyclononyl group, Examples thereof include cyclic alkyl groups such as a cyclodecyl group, a dicyclopentanyl group, and an adamantyl group. Examples of the aryl group for R ⁵ include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and a biphenyl group. Examples of the aralkyl group for R ⁵ include a benzyl group and a naphthylmethyl group. Examples of the group in which a part of —CH ₂ — contained in the alkyl group of R ⁵ is replaced by —O— include polyoxyalkylene groups such as a polyoxyethylene group and a polyoxypropylene group.

  Specific examples of the maleimide monomer include, for example, maleimide, N-methylmaleimide, N-isopropylmaleimide, N-butylmaleimide, N-isobutylmaleimide, Nt-butylmaleimide, N-cyclohexylmaleimide, N-octyl Maleimide, N-2-ethylhexylmaleimide, N-decylmaleimide, N-laurylmaleimide, N-tetradecylmaleimide, N-stearylmaleimide, N-2-decyltetradecylmaleimide, N-phenylmaleimide, N-benzylmaleimide, N -Chlorophenylmaleimide, N-methylphenylmaleimide, N-naphthylmaleimide, N-hydroxylethylmaleimide, N-hydroxylphenylmaleimide, N-methoxyphenylmaleimide, N-carboxyphenylmaleimide Bromide, N- nitro-phenyl maleimide, N- tribromophenyl maleimide and the like. Among these, N-phenylmaleimide, N-cyclohexylmaleimide can be used as the maleimide monomer from the viewpoint of easy availability of maleimide monomers and ease of improving the base oil solubility of the viscosity index improver. N-isopropylmaleimide, N-benzylmaleimide, N-laurylmaleimide, and N-stearylmaleimide are preferable.

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

  When the (meth) acrylate polymer has the structural unit (B), the content of the unit (B) is preferably 1 part by mass or more, more preferably 2 parts by mass or more, in 100 parts by mass of the polymer, and 3 parts by mass. Part or more is more preferable, 20 parts by mass or less is preferable, 15 parts by mass or less is more preferable, and 10 parts by mass or less is more preferable. Thereby, the effect of including a unit (B) in a polymer becomes easy to be effective. In addition, when the content of the unit (B) increases, the intrinsic viscosity of the (meth) acrylate polymer tends to decrease as a whole.

  The (meth) acrylate polymer preferably has a structural unit (C) derived from alkyl (meth) acrylate and having 2 to 6 carbon atoms in the alkyl group. If the (meth) acrylate polymer has a unit (C), for example, the viscosity index is improved compared to the case where a structural unit derived from methyl (meth) acrylate is introduced into the polymer instead of the unit (C). Even when the concentration of the base oil solution of the agent is high, the viscosity tends to be low, which is advantageous in terms of handling properties. In addition, the viscosity index tends to increase.

As the unit (C), those represented by the following formula (3) are preferable. In formula (3), R ⁶ represents a hydrogen atom or a methyl group, and R ⁷ represents an alkyl group having 2 to 6 carbon atoms.

Examples of the alkyl group having 2 to 6 carbon atoms of R ^{7 in} the formula (3) include linear groups such as ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, pentyl group, and hexyl group. And cyclic alkyl groups such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. The alkyl group for R ⁷ is preferably linear or branched, and more preferably linear. Moreover, as for the carbon number, 3-5 are preferable. Among them, the alkyl group of R ⁷ is preferably a butyl group from the viewpoint of easy availability of the alkyl (meth) acrylate that gives the unit (C) and excellent fluidity at around room temperature of the viscosity index improver, An n-butyl group or an isobutyl group is more preferable.

  The (meth) acrylate polymer may contain only one type of structural unit (C) derived from an alkyl (meth) acrylate having 2 to 6 carbon atoms in the alkyl group, or two or more types. May be.

  When the (meth) acrylate polymer has the structural unit (C), the content of the unit (C) is preferably 35 parts by mass or more, more preferably 40 parts by mass or more, and 45 parts by mass in 100 parts by mass of the polymer. Is more preferably 50 parts by mass or more, more preferably 75 parts by mass or less, more preferably less than 74 parts by mass, still more preferably 72 parts by mass or less, still more preferably 70 parts by mass or less, and 68 parts by mass. Part or less is particularly preferable. If the unit (C) is contained in such a content, for example, compared with the case where a structural unit derived from methyl (meth) acrylate is introduced into the polymer instead of the unit (C), the viscosity index improver Even when the concentration of the base oil solution is high, the viscosity tends to be low and the handling property is excellent. In addition, it is easy to improve the viscosity index of the base oil solution of the viscosity index improver by increasing the solubility of the viscosity index improver in the base oil. In addition, when the content of the unit (C) increases, the intrinsic viscosity of the (meth) acrylate-based polymer increases as a whole as compared with the case where a structural unit derived from methyl (meth) acrylate is introduced. The amount of change tends to increase.

  The total content of the unit (A) and the unit (C) is 100 parts by mass of the polymer from the viewpoint of increasing the viscosity index of the base oil solution of the viscosity index improver and increasing the shear stability of the viscosity index improver. Among them, 46 parts by mass or more is preferable, 50 parts by mass or more is more preferable, 53 parts by mass or more is further preferable, 56 parts by mass or more is even more preferable, and 60 parts by mass or more is particularly preferable. Further, from the viewpoint of increasing the base oil solubility of the viscosity index improver, the total content of the unit (A) and the unit (C) is preferably 82 parts by mass or less and less than 80 parts by mass in 100 parts by mass of the polymer. More preferred is 79 parts by mass or less.

  The (meth) acrylate polymer preferably has a structural unit (D) derived from alkyl (meth) acrylate and having 7 to 40 carbon atoms in the alkyl group. If the (meth) acrylate polymer has the unit (D), it becomes easy to increase the solubility of the viscosity index improver in the base oil.

As the unit (D), those represented by the following formula (4) are preferable. In formula (4), R ⁸ represents a hydrogen atom or a methyl group, and R ⁹ represents an alkyl group having 7 to 40 carbon atoms.

As the alkyl group having 7 to 40 carbon atoms of R ^{9 in} the formula (4), heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group Group, octadecyl group, nonadecyl group, icosyl group, tetracosyl group, 2-decyltetradecyl group, etc., linear or branched alkyl group, cycloheptyl group, cyclooctyl group, cyclononyl group, cyclodecyl group, dicyclo And cyclic alkyl groups such as a pentanyl group and an adamantyl group. The alkyl group for R ⁹ is preferably linear or branched, and more preferably linear. Moreover, the carbon number is preferably 11 or more, more preferably 12 or more, further preferably 14 or more, and is preferably 35 or less, and more preferably 30 or less.

  The (meth) acrylate polymer may contain only one type of structural unit (D) derived from alkyl (meth) acrylate having 7 to 40 carbon atoms in the alkyl group, and contains two or more types. May be.

  The content of the unit (D) of the (meth) acrylate polymer may be 0 part by mass or more in 100 parts by mass of the polymer. When the (meth) acrylate polymer has a unit (D), the content of the unit (D) is preferably 3 parts by mass or more, more preferably 6 parts by mass or more, in 100 parts by mass of the polymer. It is more preferably at least 40 parts by mass, more preferably at most 40 parts by mass, more preferably at most 35 parts by mass, and even more preferably at most 30 parts by mass. If the unit (D) is contained in the polymer with such a content, it becomes easy to increase the solubility of the viscosity index improver in the base oil. Furthermore, it becomes easy to ensure the fluidity of the base oil solution of the viscosity index improver even at a low temperature.

  The total content of the unit (A), the unit (B), the unit (C), and the unit (D) in the (meth) acrylate polymer is preferably 49 parts by mass or more, and 60 parts by mass in 100 parts by mass of the polymer. Part or more is more preferable, 70 parts by mass or more is more preferable, and 80 parts by mass or more is even more preferable. The upper limit of the total content of the unit (A), the unit (B), the unit (C) and the unit (D) in the polymer is not particularly limited, and the polymer is substantially composed of only these units. In addition, in 100 parts by mass of the polymer, the total content may be 98 parts by mass or less, or 95 parts by mass or less.

  The (meth) acrylate polymer may have a structural unit derived from a monomer other than the units (A) to (D) described above (hereinafter referred to as “unit (E)”). The units (A) to (D) can be introduced as constituent units of the polymer by radical copolymerization of the corresponding macromonomer, maleimide monomer, and alkyl (meth) acrylate. E) is also preferably a structural unit derived from a radical polymerizable monomer. The radical polymerizable monomer forming the unit (E) includes a monofunctional monomer having one radical polymerizable group in the molecule and a polyfunctional monomer having two or more radical polymerizable groups in the molecule. Can be classified as body.

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

  Examples of the (meth) acrylate other than the alkyl (meth) acrylate forming the unit (C) and the unit (D) include methyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, and 2-hydroxyethyl. (Meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, morpholinoalkylene (meth) acrylate , Α-hydroxymethyl methyl acrylate, polyethylene glycol mono (meth) acrylate and the like.

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

  Among these monofunctional monomers, the unit (E) is preferably a (meth) acrylate or N-vinyl compound other than the alkyl (meth) acrylate that forms the unit (C) or the unit (D). More preferred are hydroxyethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, methyl α-hydroxymethyl acrylate, and N-vinylpyrrolidone.

  Examples of the polyfunctional monomer forming the unit (E) include polyfunctional (meth) acrylate, vinyl ether group-containing (meth) acrylate, allyl group-containing (meth) acrylate, and polyfunctional (meth) acryloyl group-containing isocyanurate. And polyfunctional (meth) acrylic compounds such as polyfunctional urethane (meth) acrylates, polyfunctional maleimide compounds, polyfunctional vinyl ethers, polyfunctional allyl compounds, polyfunctional aromatic vinyls, and the like. As for the unit (E) formed from these polyfunctional monomers, only 1 type may be sufficient and 2 or more types may be sufficient.

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

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

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

  The content of the unit (E) in the (meth) acrylate polymer may be 0 part by mass or more in 100 parts by mass of the polymer. When the polymer contains the unit (E), the content thereof is preferably 1 part by mass or more, more preferably 2 parts by mass or more, further preferably 3 parts by mass or more, and 50 parts by mass in 100 parts by mass of the polymer. Part or less, preferably 40 parts by weight or less, more preferably 30 parts by weight or less, still more preferably 20 parts by weight or less, and particularly preferably 10 parts by weight or less.

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

  In addition, vinyl ethers, olefins, and the like are less radically copolymerizable with (meth) acrylate, and therefore, from the viewpoint of ease of production of the polymer, it is preferable that the polymer does not contain many structural units derived from these. . For example, the total content of the structural units (E) derived from these monomers is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less with respect to 100 parts by mass of the polymer.

  It is preferable that the (meth) acrylate polymer does not contain excessively many constituent units derived from methyl (meth) acrylate. Thereby, even if it is a base oil solution of a high-concentration viscosity index improver, the viscosity becomes low, handling properties are easily secured, and the viscosity index is easily increased. For example, in 100 parts by mass of the polymer, the content of the constituent unit derived from methyl (meth) acrylate is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, further preferably 20 parts by mass or less, Even more preferred are parts by weight or less. In addition, when content of the structural unit derived from methyl (meth) acrylate increases, the intrinsic viscosity of a (meth) acrylate type polymer shows the tendency to fall entirely.

  The content of the structural unit (E) derived from the polyfunctional monomer in the (meth) acrylate polymer is preferably 0 part by mass or more and 5 parts by mass or less, and more preferably 3 parts by mass or less in 100 parts by mass of the polymer. Preferably, 2 parts by mass or less is more preferable. When the content of the structural unit derived from the polyfunctional monomer exceeds the above range, gelation proceeds during polymerization or the solubility of the viscosity index improver containing the polymer in the base oil decreases. There is. However, 2,2 ′-[oxybis (methylene)] bisacrylic acid, dialkyl-2,2 ′-[oxybis (methylene)] bis-2-propenoate, methyl α-allyloxymethyl acrylate, α-allyloxymethyl In the case of a polyfunctional monomer in which polymerization proceeds while cyclizing, such as stearyl acrylate and α-allyloxymethyl acrylate 2-decyltetradecyl, the structural unit derived from the polyfunctional monomer in the polymer The content of may be 0 to 30 parts by mass, 20 or less, or 15 or less parts by mass with respect to 100 parts by mass of the polymer. In this case, the effect of the ring structure introduced into the main chain can improve the heat resistance of the viscosity index improver and improve the shear stability.

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

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

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

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

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

  The content (total content) of the branch unit derived from the polyfunctional chain transfer agent and / or polyfunctional initiator in the (meth) acrylate polymer may be 0 part by mass or more in 100 parts by mass of the polymer. 0.01 parts by mass or more, preferably 0.02 parts by mass or more, more preferably 0.05 parts by mass or more, further preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and 1 part by mass or less. Is more preferable. By setting the content of the branch unit in such a range, the molecular weight distribution of the polymer becomes narrow and the shear stability can be improved. In the (meth) acrylate polymer, a branch unit derived from a polyfunctional chain transfer agent and / or a polyfunctional initiator may not be contained.

  The viscosity index improver of the present invention contains a (meth) acrylate polymer as a main component, and preferably in 100% by mass of the viscosity index improver, the polymer is 70% by mass or more, more preferably 90% by mass or more, More preferably 95% by mass or more, particularly preferably 99% by mass or more. The viscosity index improver may be composed only of a (meth) acrylate polymer. Components other than the (meth) acrylate polymer contained in the viscosity index improver include polyisobutylene, ethylene-propylene copolymer, styrene-diene hydrogenated copolymer, these graft polymers, comb polymers, and star polymers. Etc.

  The (meth) acrylate polymer can be obtained by a production method having a step (polymerization step) for radical polymerization of a monomer component containing (meth) acrylate. As the monomer component, a macromonomer that forms the structural unit (A) described above, a maleimide monomer that forms the structural unit (B), a structural unit (C), and a structural unit (D) are formed. Alkyl (meth) acrylates, radical polymerizable monomers that form the structural unit (E), and the like can be used.

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

  The solvent used for the polymerization is not particularly limited as long as it is inactive to the polymerization reaction. The polymerization mechanism, the type and amount of the monomer used, the type and amount of the polymerization initiator and the polymerization catalyst, etc. What is necessary is just to set suitably according to the polymerization conditions. From the viewpoint of ensuring the solubility of the polymer and from the viewpoint of easy solvent substitution with the base oil after polymerization, toluene, xylene, hexane, cyclohexane, methyl ethyl ketone, and tetrahydrofuran are preferred as the solvent used for the polymerization. A lubricating base oil can also be suitably used as the solvent. In this case, solvent replacement after polymerization is unnecessary, and the process is simplified, which is more preferable. These solvents may be used alone or in combination of two or more. The amount of the solvent used is not particularly limited, but it is preferably such that the concentration of the total amount of the monomer component, the polymerization initiator, and other components is 40% by mass or more and 100% by mass or less.

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

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

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

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

  As the lubricating base oil, known lubricating base oils can be used without particular limitation, and preferred examples include mineral base oils and synthetic base oils. Examples of the mineral oil base oil include paraffinic and naphthenic base oils. Mineral base oils include those obtained by subjecting raw material base oils to solvent refining, hydrocracking or hydroisomerization. Examples of synthetic base oils include hydrocarbon, ester, ether, silicone, and fluorine base oils. As described above, the lubricant base oil can be used as a polymerization reaction solvent for the (meth) acrylate polymer.

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

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

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

  As the lubricating base oil blended in the lubricating oil composition, the base oil selected from the base oils (1) to (7) or the lubricating oil fraction recovered from the base oil is subjected to the above treatment. The resulting base oil (8) or (9) is preferred. It is also preferred to use a base oil belonging to Group III based on classification by the American Petroleum Institute (API). A synthetic base oil may be used as the lubricating base oil to be blended in the lubricating oil composition.

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

The viscosity index of the lubricating base oil is preferably 100 or more, more preferably 120 or more, and preferably 160 or less. For example, when the viscosity index is less than 100, the viscosity-temperature characteristics, thermal / oxidative stability, and volatilization prevention properties are likely to deteriorate, the friction coefficient increases, and the wear prevention properties tend to decrease. On the other hand, when the viscosity index exceeds 160, the low-temperature viscosity characteristic tends to be lowered. The viscosity index is measured based on JIS K 2283 (2000). The kinematic viscosity at 100 ° C. of the lubricating base oil is preferably 1 to ²⁰ mm ² / s.

  The content of the (meth) acrylate polymer in the lubricating oil composition is not particularly limited. For example, in 100 parts by mass of the lubricating oil composition, 0.01 parts by mass or more is preferable, and 0.1 parts by mass or more is more preferable. Preferably, 0.5 parts by mass or more is more preferable, 70 parts by mass or less is preferable, 60 parts by mass or less is more preferable, and less than 50 parts by mass is further preferable. When the lubricating oil composition is used as a lubricating oil without further dilution with a lubricating base oil, the content of the (meth) acrylate polymer in the lubricating oil composition is 100 parts by weight of the lubricating oil composition. 0.01 parts by mass or more, preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, more preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and 10 parts by mass or less. Is more preferable. When the lubricating oil composition is used as the base oil composition, the content of the (meth) acrylate polymer in the base oil composition is preferably 5 parts by mass or more, for example, in 100 parts by mass of the lubricating oil composition. More than mass part is more preferable, 20 mass part or more is more preferable, 70 mass part or less is preferable, 60 mass part or less is more preferable, Less than 50 mass part is further more preferable.

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

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

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

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

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

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

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

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

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

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

  Examples of the demulsifier include polyalkylene glycol nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and polyoxyethylene alkyl naphthyl ether.

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

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

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

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

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

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

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

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

(1-2) Content of constitutional unit derived from each monomer component excluding macromonomer Content of constitutional unit derived from each monomer component excluding macromonomer in the polymer was measured by gas chromatography (manufactured by Shimadzu Corporation). , GC-2010plus). Specifically, a calibration curve solution in which each monomer and tridecane were dissolved in methyl isobutyl ketone was prepared, measured by gas chromatography, and a calibration curve was created from the peak area. Next, a sample solution in which the polymer solution (reaction solution) and tridecane were dissolved in methyl isobutyl ketone was prepared, and similarly measured by gas chromatography. By determining the content of each monomer component in the polymer solution by an internal standard method and determining the ratio (polymerization rate) to the amount of each monomer component charged into the system, each monomer in the polymer The content of constituent units derived from the components was determined. The measurement conditions for gas chromatography are as follows.
Column: Inert Cap1 (liquid phase film thickness: 0.25 μm, length: 30 m, inner diameter: 0.25 mm) manufactured by GL Science
-Temperature: 40 ° C (5 min hold) + 40 ° C to 170 ° C (10 ° C / min) + 170 ° C to 210 ° C (5 ° C / min) + 210 ° C to 330 ° C (15 ° C / min) + 330 ° C (20 min hold)
-Vaporization chamber temperature: 200 ° C
-Detector temperature: 350 ° C (FID)
-Carrier gas: helium (column flow rate 1.33 mL / min)
Injection volume: 0.5 μL (split method, split ratio: 30.0)
-Internal standard sample: Tridecane-Diluting solvent: Methyl isobutyl ketone

(1-3) Content of constituent unit derived from macromonomer The content of constituent unit derived from macromonomer in the polymer was determined using gel permeation chromatography (HLC-8320GPC ECOSEC, manufactured by Tosoh Corporation). Specifically, a calibration curve solution in which a macromonomer was dissolved in tetrahydrofuran was prepared, measured by gel permeation chromatography, and a calibration curve was created from the peak area. Next, a sample solution in which the polymer solution (reaction solution) was dissolved in tetrahydrofuran was prepared, and similarly measured by gel permeation chromatography. The macromonomer content in the polymer solution is determined from the peak area of the macromonomer in the obtained chromatogram, and the ratio (polymerization rate) to the amount of macromonomer charged in the system is determined. The content of the derived structural unit was determined. The measurement conditions of gel permeation chromatography are as follows.
-Column: manufactured by Tosoh Corporation, two TSKgel GMHXL-developing solvent: tetrahydrofuran-flow rate of developing solvent: 1.0 mL / min-standard sample: TSK standard polystyrene (PS-oligomer kit manufactured by Tosoh Corporation)
-Column temperature: 40 ° C
-Sample concentration: 0.5%
-Injection volume: 200 μL

(1-4) High shear viscosity (HTHS viscosity)
The HTHS viscosity was measured using a USV high shear viscometer (manufactured by PCS Instruments) under the condition of a shear rate of 1 × 10 ⁶ / s. The polymer was diluted with a base oil (manufactured by SK, YUBASE4) so that the viscosity at 150 ° C. was 1.75 mPa · s, and the viscosity at 40 ° C. was measured.

(1-5) Kinematic Viscosity and Viscosity Index A polymer is added to a base oil (manufactured by SK, YUBASE4) such that the HTHS viscosity at a shear rate of 1 × 10 ⁶ / s at 150 ° C. is 1.75 mPa · s. After dilution, the kinematic viscosity at 100 ° C. and 40 ° C. was measured using a Stabinger viscometer (manufactured by Anton Paar, SVM (registered trademark) 3000) to determine the viscosity index.

(1-6) Intrinsic Viscosity Diluted in base oil (SKBASE, YUBASE4) so that the polymer concentration becomes 0.25% by mass, 0.5% by mass, 0.75% by mass, and 1.0% by mass. About base oil solution of polymer and base oil (manufactured by SK, YUBASE4) (kinematic viscosity at 40 ° C, 60 ° C, 80 ° C, 100 ° C using (Anton Paar, SVM (registered trademark) 3000)) And the density was measured. When the concentration of the base oil solution of the polymer is c (g / dL), the kinematic viscosity is η (mm ² / s), and the kinematic viscosity of the base oil is η0, {(η / η0) -1} at each concentration The approximate straight line was calculated by plotting / c, and the value when c = 0 was determined as the intrinsic viscosity [η].

(1-7) Thermal decomposition start temperature (Td)
The thermal decomposition start temperature (Td) was determined from dynamic TG measurement of the polymer. Specifically, the base oil solution of the polymer was diluted with tetrahydrofuran, dropped into ethanol for reprecipitation, and heated at 100 ° C. overnight under vacuum. 10 g of the solid obtained by repeating this operation twice was measured, and the temperature was raised from normal temperature to 500 ° C. in a nitrogen gas atmosphere using a differential type differential thermal balance apparatus (Rigaku Corporation, Thermo Plus2 TG-8120). Then, thermogravimetric (TG) measurement was performed. At this time, if the weight reduction rate of the sample is 0.005% by weight / second or less, the rate of temperature increase is 10 ° C./minute, and the rate of weight reduction of the sample during temperature rise exceeds 0.005% by weight / second The temperature was raised by stepwise isothermal control so that the speed was kept at 0.005 wt% / second or less. The temperature at which the stepwise isothermal control was first performed in order to maintain the weight reduction rate (the lowest temperature at which the stepwise isothermal control was performed) was defined as the thermal decomposition start temperature of the polymer.

(1-8) Main chain solubility parameter (main chain SP value)
The main chain solubility parameter (main chain SP value) of the polymer was measured using Materials Studio (registered trademark) Ver. 6.1 Calculated using the MS-Synthia module. First, a monomer structure constituting the main chain was created, and a repeating structure was defined. Polymer physical properties (solubility parameters, etc.) were calculated with the MS-Synthia module using the defined monomer structure. The MS-Synthia module is software that can calculate the physical properties of a polymer by using a quantitative structure property relationship (QSPR) and uses a binding index obtained from graph theory to determine the polymer properties. The physical properties of can be calculated. The detailed theory is described in the following literature, which is incorporated herein by reference: Published by Josef Bicerano, “Prediction of Polymer Properties, 3rd Edition”, published by Marcel Dekker. Among the solubility parameters (SP values) of the Fedors method and van Krevelen method improved by Bicerano and calculated by MS-Synthia, the values of the Fedors method were used.

(1-9) Shear stability (SSI)
The base oil (SKBASE, YUBASE4) was diluted so that the kinematic viscosity at 100 ° C. was 7.0 mm ² / s to prepare a base oil solution of the polymer, and this was maintained at 100 ° C. Then, using an ultrasonic homogenizer (manufactured by Ultrasonics, Hielscher UP400S), ultrasonic treatment was applied for 10 minutes under the conditions of Amplitude = 70% and Cycle = 1, and shear treatment was performed. The kinematic viscosity at 100 ° C. of the base oil solution and base oil of the polymer before and after the shearing treatment was measured, and the shear stability (SSI) was determined by the following formula: SSI = {1− (kinematic viscosity after shearing treatment− Base oil kinematic viscosity) / (kinematic viscosity before shearing-base oil kinematic viscosity)} × 100.

(1-10) Viscosity A solution consisting of 78% by mass of a Group III base oil (viscosity index 122, 40 ° C. kinematic viscosity 19.6 mm ² / s) in the American Petroleum Institute (API) classification and 22% by mass of a polymer (Toki Sangyo Co., Ltd., TVB-10, rotor: SPINDLE No. M3, rotational speed 6 rpm) was measured at 25 ° C.

(2) Viscosity index improver production example (2-1) Example 1
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe, and a dropping funnel, 50 parts by mass of a one-terminal hydroxyl group-containing polymer of hydrogenated polybutadiene (manufactured by TOTAL, KrasolHLBH-5000M), 2-isocyanato 1.6 parts by weight of ethyl methacrylate (manufactured by Showa Denko KK, Karenz MOI), 20 parts by weight of toluene, and 0.1 parts by weight of dibutyltin dilaurate are charged and heated to 65 ° C. in an oil bath while introducing nitrogen gas. The mixture was stirred for 6 hours. After completion of the reaction, 50 parts by mass of water was added and the supernatant was recovered with a separatory funnel. After raising the temperature to 65 ° C., toluene was removed under reduced pressure to obtain 48 parts by mass of the macromonomer shown in Table 1. The obtained macromonomer was dissolved in deuterated chloroform (manufactured by Wako Pure Chemical Industries, Ltd.), and ¹ H-NMR measurement was carried out using a nuclear magnetic resonance spectrometer (manufactured by Varian, Unity Plus 400). A peak near 3.9 ppm attributed to the alcohol group of the raw material was not confirmed, and a peak near 4.9 ppm attributed to the generated urethane group was confirmed.

  Next, in a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe, and a dropping funnel, 12 parts by mass of the macromonomer obtained above as a monomer component, n-butyl methacrylate (BMA) 65 parts by mass, 18 parts by mass of stearyl methacrylate (SMA), 5 parts by mass of N-phenylmaleimide (PMI), 207.3 parts by mass of base oil (manufactured by SK, YUBASE4), and pentaerythritol tetrakis (mercaptoacetate) 0 .05 mass parts was charged, and the contents were heated to 105 ° C. while stirring while introducing nitrogen gas. Thereto, 0.052 parts by mass of t-amylperoxyisononanoate (manufactured by Arkema Yoshitomi Co., Ltd., Luperox (registered trademark) 570) and 5.1 parts by mass of a base oil (manufactured by SK, YUBASE4) as a polymerization initiator. While adding the mixed solution, the solution polymerization was advanced while dropping a solution prepared by dissolving 0.21 part by mass of the polymerization initiator in 13.7 parts by mass of base oil (manufactured by SK, YUBASE4) over 4 hours. Further, aging was performed for 2 hours. Subsequently, 74.0 parts by mass of base oil (manufactured by SK, YUBASE4) was added thereto and diluted to obtain a base oil solution of polymer 1 (polymer concentration: 25% by mass). Table 2 shows the composition of the structural units derived from the respective monomers of the obtained polymer 1 and the results of analysis / evaluation.

(2-2) Example 2
In Example 1, except that the amount of the base oil charged into the reaction vessel during the polymerization reaction was changed to 138.7 parts by mass, and the amount of the base oil added after the aging of the polymerization reaction was changed to 140.0 parts by mass, By performing the same operation as in Example 1, a base oil solution of polymer 2 (polymer concentration: 25% by mass) was obtained. Table 2 shows the composition of structural units derived from the respective monomers of the obtained polymer 2 and the results of analysis and evaluation.

(2-3) Example 3
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen introduction tube, and a dropping funnel, 12 parts by mass of the macromonomer obtained in Example 1 as a monomer component, n-butyl methacrylate (BMA) 40 parts by mass, lauryl methacrylate / tridecyl methacrylate mixture (mass ratio = 54/46) (SLMA) 18 parts by mass, N-phenylmaleimide (PMI) 3 parts by mass, and base oil (manufactured by SK, YUBASE4) 150 0.0 parts by mass and 0.05 parts by mass of pentaerythritol tetrakis (mercaptoacetate) were charged, and the contents were heated to 105 ° C. with stirring while introducing nitrogen gas. Thereto, 0.052 parts by mass of t-amylperoxyisononanoate (manufactured by Arkema Yoshitomi Co., Ltd., Luperox (registered trademark) 570) and 5.1 parts by mass of a base oil (manufactured by SK, YUBASE4) as a polymerization initiator. While adding a mixed solution, 0.21 part by mass of the polymerization initiator was dissolved in 13.7 parts by mass of base oil (manufactured by SK, YUBASE4), and 2 parts by mass of N-phenylmaleimide (PMI) Solution polymerization was allowed to proceed while dropping a solution dissolved in 25 parts by mass of n-butyl methacrylate (BMA) over 4 hours, followed by further aging for 2 hours. Subsequently, 131.0 parts by mass of base oil (manufactured by SK, YUBASE4) was added thereto and diluted to obtain a base oil solution of polymer 3 (polymer concentration: 25% by mass). Table 2 shows the composition of structural units derived from the respective monomers of the obtained polymer 3 and the results of analysis and evaluation.

(2-4) Comparative Example 1
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe, and a dropping funnel, 30 parts by mass of methyl methacrylate (MMA), 30 parts by mass of stearyl methacrylate (SMA), a lauryl methacrylate / tridecyl methacrylate mixture (mass) Ratio = 54/46) (SLMA) 40 parts by mass, toluene 53.33 parts by mass, pentaerythritol tetrakis (mercaptoacetate) 0.05 part by mass, and nitrogen gas was introduced into this, and the contents were raised to 105 ° C. Allowed to warm. As a polymerization initiator, a solution prepared by mixing 0.0258 parts by mass of t-amylperoxyisononanoate (manufactured by Arkema Yoshitomi Corp., Luperox (registered trademark) 570) and 0.46 parts by mass of toluene was added, and the polymerization was started. The solution polymerization was allowed to proceed while dropwise adding a solution prepared by dissolving 0.103 parts by mass of the agent in 10.3 parts by mass of toluene over 4 hours, followed by further aging for 4 hours. Subsequently, the cooling pipe was replaced with a U-shaped pipe connected to the cooling pipe and a distillate receiver, and 233 parts by mass of base oil (YUBASE4 manufactured by SK) was added to the reaction vessel. After raising the bath temperature of the reaction vessel to 150 ° C., the inside of the reaction vessel was gradually decompressed using a vacuum pump to remove toluene. 30 minutes after the temperature in the reaction vessel reached 142 ° C., the pressure was released and cooled to obtain a base oil solution of polymer 4 (polymer concentration: 30% by mass). Table 2 shows the composition of structural units derived from the respective monomers of the obtained polymer 4 and the results of analysis and evaluation.

(2-5) Comparative Example 2
The results of analysis and evaluation of the viscosity index improver VISCOPLEX (registered trademark) 3-201 commercially available from Evonik Industries are shown in Table 2 as Comparative Example 2. VISCOPLEX 3-201 is a viscosity index improver containing a polymer having a structural unit derived from a macromonomer, and measured each physical property as containing substantially only the polymer.

(3) Results Table 2 shows the compositions of the polymers obtained in the respective production examples and the physical property measurement results. In the polymers of Examples 1 to 3, the intrinsic viscosity [η] _{100 at} 100 ° C. is in the range of 0.07 dL / g to 0.17 dL / g, and the intrinsic viscosity [η] _{40 at} 40 ° C. is 0.01 dL. / G to 0.08 dL / g. On the other hand, in the polymer of Comparative Example 1, both the intrinsic viscosity [η] _{100 at 100} ° C. and the intrinsic viscosity [η] ₄₀ at 40 ° C. are outside the range, and the polymer of Comparative Example 2 has an intrinsic viscosity at 100 ° C. Viscosity [η] ₁₀₀ was out of the range. The polymer base oil solutions of the examples were maintained at a high temperature and high shear viscosity, that is, 150 ° C. HTHS viscosity at 1.75 mPa · s, while a low temperature high shear viscosity, ie, 40 ° C. HTHS viscosity, and a low temperature, low shear, viscosity. The viscosity of the polymer, that is, the kinematic viscosity at 40 ° C., could be kept lower than the base oil solution of the polymer of the comparative example. The polymer of an Example can be used as a viscosity index improver which shows a suitable viscosity characteristic improvement effect in both high shear and low shear.

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

Claims (8)

A viscosity index improver containing a (meth) acrylate polymer,
Intrinsic viscosity [η] ₁₀₀ at 100 ° C. in a group III base oil (viscosity index 122, 40 ° C. kinematic viscosity 19.6 mm ² / s) in the American Petroleum Institute (API) classification of the polymer is 0.07 dL / g or more. A viscosity index improver that is 0.17 dL / g or less and has an intrinsic viscosity [η] _{40 at} 40 ° C. of 0.01 dL / g or more and 0.08 dL / g or less.   The viscosity index improver according to claim 1, wherein the thermal decomposition starting temperature (Td) of the polymer is 275 ° C or higher.   The viscosity index improver according to claim 1 or 2, wherein a main chain SP value of the polymer is 9.20 or more and 9.50 or less.   The viscosity index improver according to any one of claims 1 to 3, wherein the polymer has a weight average molecular weight (Mw) of 200,000 or more and 700,000 or less.   The viscosity index improver according to any one of claims 1 to 4, wherein the polymer has a structural unit derived from a macromonomer.   The viscosity index improver according to any one of claims 1 to 5, wherein the polymer has a structural unit derived from a maleimide monomer.   The viscosity index improver according to any one of claims 1 to 6, wherein the polymer has a structural unit derived from an alkyl (meth) acrylate and having 2 to 6 carbon atoms in the alkyl group.   A lubricating oil composition comprising a lubricating base oil and the viscosity index improver according to any one of claims 1 to 7.

Images