Lubricating oil composition and method for producing same

Abstract

To provide a lubricant composition having a low pour point and a method for producing the same.SOLUTION: The lubricant composition containing an ester-based base oil and a polymer compound having no polar group in a constituent monomer has a ratio (PP1 / PP2) of less than 1 with respect to a flow point PP1 (K) of a composition (L1) to a flow point PP2 (K) of a composition (L2). The composition (L1) is composed of the ester-based base oil and the polymer compound having no polar group in the constituent monomer. The composition (L2) is composed of the ester-based base oil having the same mass as that contained in the composition (L1) and polymethacrylate having the same mass as the polymer compound having no polar group in the constituent monomer contained in the composition (L1).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a lubricating oil composition and a method for producing the same. [Background technology]

[0002] Lubricating oil is oil used to lubricate between mechanical elements, and is used in many mechanical devices. By placing this lubricating oil between the moving parts of the machine, friction between the solid objects in contact with each other is reduced, and the generation of frictional heat and wear are suppressed. This allows the machine to continue operating stably.

[0003] Lubricating oils are made by adding various additives to a base oil. For example, viscosity index improvers can suppress the viscosity change of base oil due to temperature, and suppress the decrease in lubricity of lubricating oil at high temperatures and the decrease in energy efficiency due to increased viscous resistance at low temperatures, etc. Known examples of viscosity index improvers include olefin copolymers, styrene-diene copolymers, polyisobutylene, polymethacrylate, etc. (see, for example, Patent Document 1). In addition, pour point depressants suppress the crystallization of wax in lubricating oils at low temperatures, lower the pour point of the lubricating oil, and broaden the range of temperatures at which the lubricating oil can be used. Known pour point depressants include polymethacrylates, alkylated aromatic compounds, and maleate / fumarate copolymer esters (see, for example, Patent Documents 1 and 2).

[0004] On the other hand, the use of an ester-based base oil as a base oil has also been investigated in order to reduce the viscosity and pour point of a lubricating oil (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2017-528588 [Patent Document 2] JP 2018-080216 A [Patent Document 3] JP 2014-189555 A Summary of the Invention [Problem to be solved by the invention]

[0006] When lubricating oils are used in low-temperature environments such as cold regions or high altitudes, further improvement of low-temperature properties is required. For lubricating oils using mineral oil-based base oils, it is known that the addition of pour point depressants such as polymethacrylates and alkylated aromatic compounds is an effective method for lowering the pour point. On the other hand, no effective pour point lowering method has been found for ester-based base oils. In some cases, it is possible to lower the pour point while maintaining the kinetic viscosity by changing the structural design of the ester-based base oil, but there is a problem in that the production cost increases. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lubricating oil composition having a low pour point and a method for producing the same. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention employs the following configuration. That is, a first aspect of the present invention is a lubricating oil composition containing an ester base oil and a polymer compound having no polar group in its constituent monomer, The lubricating oil composition has a ratio (PP1 / PP2) of a pour point PP1(K) of the following composition (L1) to a pour point PP2(K) of the following composition (L2) of less than 1. Composition (L1): A composition comprising the ester base oil and a polymer compound having no polar group in the constituent monomer. Composition (L2): A composition consisting of an ester base oil that is identical and of the same mass as the ester base oil contained in composition (L1), and a polymethacrylate of the same mass as the polymeric compound having no polar group in the constituent monomers contained in composition (L1).

[0008] A second aspect of the present invention is a method for producing a lubricating oil composition, comprising the steps of: The method includes a step of mixing an ester-based base oil with a polymer compound having no polar group in a constituent monomer, The method for producing a lubricating oil composition is characterized in that the ratio (PP1 / PP2) of the pour point PP1(K) of the following composition (L1) to the pour point PP2(K) of the following composition (L2) is less than 1. Composition (L1): A composition comprising the ester base oil and a polymer compound having no polar group in the constituent monomer. Composition (L2): A composition consisting of an ester base oil that is the same as and of the same mass as the ester base oil contained in composition (L1), and a polymethacrylate that is the same mass as the polymeric compound that does not have a polar group in the constituent monomers contained in composition (L1). Effect of the Invention

[0009] According to the present invention, it is possible to provide a lubricating oil composition having a low pour point and a method for producing the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] (Lubricating oil composition) The lubricating oil composition of this embodiment contains at least an ester-based base oil and a polymeric compound having no polar group in the constituent monomer, and may contain other components as necessary. The lubricating oil composition is characterized in that the ratio (PP1 / PP2) of the pour point PP1(K) of the following composition (L1) to the pour point PP2(K) of the following composition (L2) is less than 1, and various known lubricating oil compositions can be used for the other components. Composition (L1): A composition comprising the ester base oil and a polymer compound having no polar group in the constituent monomer. Composition (L2): A composition consisting of an ester base oil that is the same as and of the same mass as the ester base oil contained in composition (L1), and a polymethacrylate that is the same mass as the polymeric compound that does not have a polar group in the constituent monomers contained in composition (L1).

[0011] In the lubricating oil composition of this embodiment, the ratio (PP1 / PP2) of the pour point PP1(K) of the composition (L1) below to the pour point PP2(K) of the composition (L2) below is less than 1, preferably 0.995 or less, and more preferably 0.990 or less. By using a polymer compound having no polar group as a constituent monomer, it is possible to obtain a greater pour point reducing effect than with polymethacrylate.

[0012] The pour point PP1 and the pour point PP2 in the (PP1 / PP2) ratio are values ​​expressed in absolute temperature (K). In this specification, 0 degrees Celsius (0°C) is defined as 273.15 degrees Kelvin (K). In the present invention, the pour point PP1 and the pour point PP2 refer to pour points measured by a method in accordance with JIS K 2269 (1987). The pour point PP1 is not particularly limited, but is preferably 193.15 K (-80°C) or higher. The pour point PP1 is preferably 253.15 K (-20°C) or lower, and more preferably 248.15 K (-25°C) or lower. When the pour point PP1 is within the above preferred range, the lubricating oil composition can be easily used under cold conditions.

[0013] <Base oil> The lubricating oil composition of the present embodiment contains at least an ester-based base oil as a base oil. The ester-based base oil may include vegetable oil, synthetic oil, or a mixture thereof. Specifically, the ester-based base oil in the present embodiment may include organic acid ester-based base oil, phosphate ester-based base oil, silicate ester-based base oil, etc. Among them, from the viewpoint of pour point depression and viscosity index improvement, organic acid ester-based base oil is preferred, and monoester-based base oil is more preferred.

[0014] In the lubricating oil composition of this embodiment, the ester-based base oil may be used alone or in combination of two or more kinds.

[0015] The lubricating oil composition of the present embodiment may contain a base oil other than the ester-based base oil. Any of Groups I to V in the base oil classification can be used. In this embodiment, the content of the ester base oil is preferably 50 mass% or more, more preferably 70 mass% or more, and even more preferably 90 mass% or more, based on the total amount of the lubricating oil composition. When the content of the ester base oil is within the above preferred range, the pour point lowering effect is easily obtained.

[0016] (Polymer compounds with no polar groups in the constituent monomers) In this embodiment, the polymer compound having no polar group in the constituent monomer (hereinafter, may be referred to as "polymer compound (P)") is not particularly limited as long as the constituent monomer has no polar group. Examples of the polymer compound (P) include olefin copolymers such as ethylene-propylene copolymer and polyisobutylene. The mass average molecular weight (Mw) of the polymer compound (P) is not particularly limited, and is preferably 10000 or more, more preferably 30000 or more, and even more preferably 40000 or more. The mass average molecular weight (Mw) is preferably 5,000,000 or less, more preferably 4,000,000 or less, and even more preferably 3,000,000 or less. The weight average molecular weight (Mw) of the olefin copolymer can be measured by gel permeation chromatography (GPC).

[0017] In the lubricating oil composition of this embodiment, the mass average molecular weight of the polymethacrylate in composition (L2) is preferably in the range of 0.5 to 2 times the mass average molecular weight of the polymer compound in composition (L1) that does not have a polar group as a constituent monomer. When the mass average molecular weight of the polymethacrylate in the composition (L2) is within the above preferred range, the pour point lowering effect is more easily achieved.

[0018] In the lubricating oil composition of this embodiment, the polymer compound (P) may be used alone or in combination of two or more kinds.

[0019] In this embodiment, the content (mass basis) of the polymer compound (P) is appropriately determined depending on the type or application of the base oil, and is, for example, preferably 0.01 mass% or more, more preferably 0.03 mass% or more, and even more preferably 0.05 mass% or more, based on the total amount (100 mass%) of the lubricating oil composition. The content (mass basis) of the polymer compound (P) is preferably 50 mass% or less, more preferably 30 mass% or less, and even more preferably 20 mass% or less, based on the total amount (100 mass%) of the lubricating oil composition. If the content of the polymer compound (P) is equal to or greater than the lower limit of the above-mentioned preferred range, the pour point lowering effect is sufficiently exhibited. On the other hand, if the content of the polymer compound (P) exceeds the upper limit of the above-mentioned preferred range, it becomes difficult to obtain an improvement effect commensurate with the amount added.

[0020] The lubricating oil composition of this embodiment has a kinetic viscosity of 1 mm at 40°C. 2 / s or more is preferable, 1.5 mm 2 / s or more is preferable, and 1.8 mm 2 The lubricating oil composition of this embodiment has a 40°C kinematic viscosity of 500mm 2 / s or less is preferable, 490mm 2 / s or less is preferable, and 480 mm 2 When the 40°C kinematic viscosity of the lubricating oil composition is equal to or higher than the lower limit of the above-mentioned preferred range, the oil film forming ability is easily improved. On the other hand, when the 40°C kinematic viscosity of the lubricating oil composition is equal to or lower than the upper limit of the above-mentioned preferred range, the viscosity increase at low temperatures is easily suppressed. In the present invention, the "kinematic viscosity" refers to the kinematic viscosity at a temperature of 40°C measured by a method in accordance with JIS K 2283 (2000).

[0021] In the lubricating oil composition of this embodiment, the 40°C kinematic viscosity of composition (L1) is preferably within ±30% of the 40°C kinematic viscosity of composition (L2), more preferably within ±20%, and even more preferably within ±10%. When the 40°C kinematic viscosity of the composition (L1) is within the above-mentioned preferred range, the pour point lowering effect is more easily achieved even when the amount of a polymeric compound having no polar group among the constituent monomers contained in the lubricating oil composition is small.

[0022] The viscosity index of the lubricating oil composition in this embodiment is preferably 100 or greater, and more preferably 120 or greater. If the viscosity index of the lubricating oil composition is equal to or greater than the lower limit of the above-mentioned preferred range, viscosity changes due to temperature are easily suppressed, whereas if the viscosity index of the lubricating oil composition is equal to or less than the upper limit of the above-mentioned preferred range, the range of options for obtaining base oils is broadened, making production easier. In the present invention, the "viscosity index of a lubricating oil composition" can be measured by a method in accordance with JIS K 2283 (2000).

[0023] The lubricating oil composition of this embodiment may contain other components within the range that does not impair the effects of the present invention. Examples of other components that may be contained in the lubricating oil composition of this embodiment include rust inhibitors (rust inhibitors), antifoaming agents (defoamers), friction modifiers, viscosity index improvers, metal deactivators, pour point depressants, demulsifiers, metal-based detergents, ashless dispersants, antiwear agents or extreme pressure agents, and corrosion inhibitors.

[0024] It has been known that the addition of pour point depressants such as polymethacrylates and alkylated aromatic compounds is an effective method for lowering the pour point of lubricating oils that use mineral oil-based base oils. However, no effective pour point depressant has been found for ester-based base oils. In the lubricating oil composition of this embodiment, the ratio (PP1 / PP2) of the pour point PP1(K) of the composition (L1) to the pour point PP2(K) of the composition (L2) is less than 1. That is, the pour point PP1 of the composition (L1) consisting of an ester base oil and a polymer compound (polymer compound (P)) having no polar group in the constituent monomer is lower than the pour point PP2 of the composition (L2) consisting of the same and same mass of ester base oil as the ester base oil contained in the composition (L1) and the same mass of polymethacrylate as the polymer compound (P) contained in the composition (L1). Therefore, the lubricating oil composition of this embodiment has a low pour point and can be suitably used under cold conditions. The reason why the above-mentioned effects are obtained is not clear, but is presumed to be as follows. The lubricating oil composition of this embodiment contains an ester-based base oil and a polymer compound (P). The ester-based base oil has a polar group. On the other hand, the polymer compound (P) does not have a polar group in the constituent monomer. It is presumed that the polymer compound (P) therefore penetrates between the molecules of the ester-based base oil, preventing the ester-based base oil from crystallizing and lowering the pour point.

[0025] The lubricating oil composition of the present embodiment has a low pour point and can therefore be suitably used as a lubricating oil, particularly under cold conditions. EXAMPLES

[0026] The effects of the present invention will be described in detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0027] <Production of Lubricating Oil Composition> The components shown in Tables 1 to 5 were mixed to prepare the lubricating oil compositions of each example.

[0028] [Table 1]

[0029] [Table 2]

[0030] [Table 3]

[0031] [Table 4]

[0032] [Table 5]

[0033] In Tables 1 to 5, the abbreviations have the following meanings: The numbers in brackets [ ] are mass % relative to the total amount of the lubricating oil composition (100 mass %). BO-1: n-Butyl oleate BO-2: 2-Ethylhexyl myristate BO-3: Neopentyl glycol monooleate BO-4: Mineral oil (Group I. Kinematic viscosity: 6.5 mm 2 / s) BO-5: Mineral oil (Group I. Kinematic viscosity: 23 mm 2 / s) OCP-1: Ethylene-propylene copolymer (Mw (mass average molecular weight; hereafter the same) = 120,000) OCP-2: Ethylene-propylene copolymer (Mw=230,000) PMA-1: Polymethacrylate (Mw=170,000) PMA-2: Polymethacrylate (Mw=40,000) PIB: Polyisobutylene (Mw=2 million)

[0034] For each of the lubricating oil compositions obtained, the pour point and kinematic viscosity at 40° C. were measured by the following methods. The results are shown in Tables 6-10.

[0035] [Pour point] The pour point (° C. or K) of the lubricating oil composition was measured by a method in accordance with JIS K 2269 (1987).

[0036] [Pour point ratio] The pour point ratios (PP1 / PP2) of the lubricating oil compositions were as follows: For the lubricating oil compositions of Example 1 and Comparative Example 1, the pour point PP2 of the lubricating oil composition of Reference Example 2 was used as the standard. For the lubricating oil compositions of Examples 2 and 3 and Comparative Example 2, the pour point PP2 of the lubricating oil composition of Reference Example 3 was used as the standard. For the lubricating oil compositions of Examples 4 and 5, the pour point PP2 of the lubricating oil composition of Reference Example 5 was used as the standard. For the lubricating oil compositions of Comparative Examples 5 and 7, the pour point PP2 of the lubricating oil composition of Reference Example 7 was used as the standard. For the lubricating oil compositions of Comparative Examples 6 and 8, the pour point PP2 of the lubricating oil composition of Reference Example 8 was used as the standard. For the lubricating oil composition of Example 6, the pour point PP2 of the lubricating oil composition of Reference Example 10 was used as the standard. For the lubricating oil composition of Example 7, the pour point PP2 of the lubricating oil composition of Reference Example 11 was used as the standard. For the lubricating oil composition of Comparative Example 9, the pour point PP2 of the lubricating oil composition of Reference Example 13 was used as the standard. For the lubricating oil composition of Comparative Example 10, the pour point PP2 of the lubricating oil composition of Reference Example 14 was used as the standard.

[0037] [Kinematic viscosity at 40℃] The kinematic viscosity (mm 2 The kinematic viscosity at 40°C of composition (L1) was measured in accordance with JIS K 2283 (2000). The difference (%) between the kinematic viscosity at 40°C of composition (L2) and that of composition (L1) is also shown in each table as "L1 / L2 (%)."

[0038] [Table 6]

[0039] From the results shown in Table 6, it was confirmed that the pour point PP1 of the lubricating oil composition of Example 1 (composition (L1)) consisting of an ester-based base oil and an olefin copolymer was lower than the pour point PP2 of the lubricating oil composition of Reference Example 2 (composition (L2)) consisting of the same and same mass of ester-based base oil as the ester-based base oil contained in the lubricating oil composition of Example 1 and the same mass of polymethacrylate PMA-2 as the olefin copolymer contained in the lubricating oil composition of Example 1. It was also confirmed that the pour point PP1 of the lubricating oil composition of Example 1 was lower than the pour point of the lubricating oil composition of Comparative Example 1, which consisted of the olefin copolymer contained in the lubricating oil composition of Example 1 and the same mass of polymethacrylate PMA-1.

[0040] Similarly, it was confirmed that the pour point PP1 of the lubricating oil composition of Examples 2 and 4 (composition (L1)) consisting of an ester-based base oil and an olefin copolymer was lower than the pour point PP2 of the lubricating oil composition of Reference Example 3 (composition (L2)) consisting of the same and same mass of ester-based base oil as the ester-based base oil contained in the lubricating oil composition of Examples 2 and 4 and the same mass of polymethacrylate PMA-2 as the olefin copolymer contained in the lubricating oil composition of Examples 2 and 4. In addition, it was confirmed that the pour points PP1 of the lubricating oil compositions of Examples 2 and 4 were lower than the pour point of the lubricating oil composition of Comparative Example 2, which consisted of the olefin copolymer contained in the lubricating oil compositions of Examples 2 and 4 and the same mass of polymethacrylate PMA-1.

[0041] Furthermore, from the results shown in Table 6, it was confirmed that the lubricating oil compositions of Examples 1 to 3 had kinematic viscosities at 40°C equivalent to those of the lubricating oil compositions of Comparative Examples 1 to 2 and Reference Examples 1 to 3, regardless of the amount of additive added.

[0042] [Table 7]

[0043] From the results shown in Table 7, it was confirmed that the pour point PP1 of the lubricating oil composition of Examples 4 and 5 (composition (L1)) consisting of an ester-based base oil and an olefin copolymer was lower than the pour point PP2 of the lubricating oil composition of Reference Example 5 (composition (L2)) consisting of the same and same mass of ester-based base oil as the ester-based base oil contained in the lubricating oil composition of Examples 4 and 5 and the same mass of polymethacrylate PMA-2 as the olefin copolymer contained in the lubricating oil composition of Examples 4 and 5.

[0044] Furthermore, from the results shown in Table 7, it was confirmed that the lubricating oil compositions of Examples 4 and 5 had kinematic viscosities at 40° C. equivalent to those of the lubricating oil compositions of Reference Examples 4 and 5.

[0045] [Table 8]

[0046] From the results shown in Table 8, it was confirmed that the pour point PP1 of the lubricating oil composition of Comparative Examples 5 and 7 (composition (L1)) consisting of a mineral oil not corresponding to an ester-based base oil and an olefin copolymer is higher than the pour point PP2 of the lubricating oil composition of Reference Example 7 (composition (L2)) consisting of the same mineral oil and the same mass as the mineral oil contained in the lubricating oil composition of Comparative Examples 5 and 7 and the same mass of polymethacrylate PMA-2 as the olefin copolymer contained in the lubricating oil composition of Comparative Examples 5 and 7. In addition, it was confirmed that the pour point PP1 of the lubricating oil composition of Comparative Examples 6 and 8 (composition (L1)), which consists of a mineral oil not corresponding to an ester-based base oil and an olefin copolymer, is higher than the pour point PP2 of the lubricating oil composition of Reference Example 8 (composition (L2)), which consists of the same and the same mass of mineral oil as the mineral oil contained in the lubricating oil compositions of Comparative Examples 6 and 8, and the same mass of polymethacrylate PMA-2 as the olefin copolymer contained in the lubricating oil compositions of Comparative Examples 6 and 8.

[0047] [Table 9]

[0048] From the results shown in Table 9, it was confirmed that the pour point PP1 of the lubricating oil composition of Example 6 (composition (L1)) consisting of an ester-based base oil and an olefin copolymer was lower than the pour point PP2 of the lubricating oil composition of Reference Example 10 (composition (L2)) consisting of the same and same mass of ester-based base oil as the ester-based base oil contained in the lubricating oil composition of Example 6 and the same mass of polymethacrylate PMA-1 as the olefin copolymer contained in the lubricating oil composition of Example 6.

[0049] Similarly, it was confirmed that the pour point PP1 of the lubricating oil composition of Example 7 (composition (L1)) consisting of an ester-based base oil and an olefin copolymer was lower than the pour point PP2 of the lubricating oil composition of Reference Example 11 (composition (L2)) consisting of the same and same mass of ester-based base oil as the ester-based base oil contained in the lubricating oil composition of Example 7 and the same mass of polymethacrylate PMA-1 as the olefin copolymer contained in the lubricating oil composition of Example 7.

[0050] Furthermore, from the results shown in Table 9, it was confirmed that the lubricating oil compositions of Examples 6 and 7 had kinematic viscosities at 40° C. equivalent to those of the lubricating oil compositions of Reference Examples 9-11.

[0051] [Table 10]

[0052] From the results shown in Table 10, it was confirmed that the pour point PP1 of the lubricating oil composition of Comparative Example 9 (composition (L1)), which consists of a mineral oil that does not fall under the category of an ester-based base oil and an olefin copolymer, is higher than the pour point PP2 of the lubricating oil composition of Reference Example 13 (composition (L2)), which consists of the same mineral oil and the same mass as the mineral oil contained in the lubricating oil composition of Comparative Example 9 and the same mass of polymethacrylate PMA-1 as the olefin copolymer contained in the lubricating oil composition of Comparative Example 9. Similarly, it was confirmed that the pour point PP1 of the lubricating oil composition of Comparative Example 10 (composition (L1)), which consists of a mineral oil that does not fall under the category of ester-based base oil and an olefin copolymer, is higher than the pour point PP2 of the lubricating oil composition of Reference Example 14 (composition (L2)), which consists of the same mineral oil and the same mass as the mineral oil contained in the lubricating oil composition of Comparative Example 10 and the same mass of polymethacrylate PMA-1 as the olefin copolymer contained in the lubricating oil composition of Comparative Example 10.

[0053] From the above results, it was confirmed that the lubricating oil compositions of Examples 1 to 7 to which the present invention was applied had a sufficient pour point lowering effect.

Claims

1. A lubricating oil composition comprising an ester-based base oil which is a monoester-based base oil and a polymeric compound having no polar group in its constituent monomer, The content of the ester-based base oil is 90 mass% or more based on the total amount of the lubricating oil composition, A lubricating oil composition in which the ratio (PP1 / PP2) of the pour point PP1(K) of the following composition (L1) to the pour point PP2(K) of the following composition (L2) is less than 1 (however, excluding a drawing lubricant containing a base oil and a branched olefin polymer, wherein the content of the branched olefin polymer is 0.01 to 5 mass %, the branched olefin polymer is at least one selected from the group consisting of polyisobutylene, polyisoprene, ethylene-propylene copolymer, and styrene-butadiene copolymer, and the average molecular weight is 10,000 to 5,000,000, and the kinetic viscosity of the drawing lubricant at 40°C is 1 to 50 mm 2 / s). Composition (L1): A composition comprising the ester base oil and a polymer compound having no polar group in the constituent monomer. Composition (L2): A composition consisting of an ester base oil that is the same as and has the same mass as the ester base oil contained in composition (L1), and a polymethacrylate that is the same mass as the polymeric compound that does not have a polar group in the constituent monomers contained in composition (L1).

2. The lubricating oil composition according to claim 1, wherein the 40°C kinematic viscosity of the composition (L1) is within ±30% of the 40°C kinematic viscosity of the composition (L2).

3. The lubricating oil composition according to claim 1 or 2, wherein the mass average molecular weight of the polymethacrylate in the composition (L2) is in the range of 0.5 to 2 times the mass average molecular weight of the polymer compound in the composition (L1) that does not have a polar group as a constituent monomer.

4. A method for producing a lubricating oil composition, comprising the steps of: The method includes a step of mixing an ester-based base oil, which is a monoester-based base oil, with a polymer compound having no polar group in its constituent monomers, A method for producing a lubricating oil composition, wherein the ratio (PP1 / PP2) of a pour point PP1(K) of the following composition (L1) to a pour point PP2(K) of the following composition (L2) is less than 1, A method for producing a lubricating oil composition, the content of which is 90 mass% or more based on the total amount of the lubricating oil composition (excluding a lubricant for drawing containing a base oil and a branched olefin polymer, the content of which is 0.01 to 5 mass%, the branched olefin polymer being at least one selected from the group consisting of polyisobutylene, polyisoprene, ethylene-propylene copolymer, and styrene-butadiene copolymer, and having an average molecular weight of 10,000 to 5,000,000, and having a kinetic viscosity at 40°C of 1 to 50 mm2 / s). Composition (L1): A composition comprising the ester base oil and a polymer compound having no polar group in the constituent monomer. Composition (L2): A composition consisting of an ester base oil that is the same as and has the same mass as the ester base oil contained in composition (L1), and a polymethacrylate that is the same mass as the polymeric compound that does not have a polar group in the constituent monomers contained in composition (L1).

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