JP5078068B2 - Lubricating base oil - Google Patents

Description

  The present invention relates to a lubricating base oil and a lubricating oil including the case of containing the same.

  There has been proposed a lubricating base oil containing a synthetic ester that exhibits excellent lubricity over a long period of time in a wide range of operating temperatures from low to high temperatures (Patent Document 1). However, when the lubricating oil containing the lubricating base oil is used for a long time, the lubricity may be insufficient.

An ester of pentaerythritol and a carboxylic acid that exhibits excellent properties over a wide temperature range and exhibits stable lubricity even after long-term use. Acid, n-heptanoic acid and n-octanoic acid, the weight ratio of the content of 2-ethylhexanoic acid to the total content of n-heptanoic acid and n-octanoic acid [2-ethylhexanoic acid / (n-heptane Acid + n-octanoic acid)] in a ratio of 65/35 to 35/65 has been proposed (Patent Document 2).
Japanese Patent Laid-Open No. 11-80766 JP 2006-124429 A

  However, even with the lubricating base oil described in Patent Document 2, the viscosity is stable at a relatively low temperature, but under a high temperature load environment, the viscosity increases and the heat resistance is insufficient. there were.

  As the high heat-resistant base oil, a fluorine-based compound is conceivable. However, the fluorine-based compound is expensive and there is a possibility that hydrogen fluoride is generated during thermal decomposition. Although phenyl ether may be used, phenyl ether has a high viscosity and is not sufficiently lubricious.

  The present invention is a lubricating base oil that exhibits excellent properties over a wide temperature range, can suppress an increase in viscosity even when used for a long time under a high temperature load environment, exhibits stable and sufficient lubricity, and has good heat resistance. The purpose is to provide. Furthermore, an object of the present invention is to provide a lubricating oil including the case where the lubricating base oil is contained.

  That is, the present invention is a lubricating base oil containing a synthetic ester obtained by reacting pentaerythritol and carboxylic acid, wherein the carboxylic acid is 2-ethylhexanoic acid, n-heptanoic acid and n N-heptanoic acid and n-octanoic acid containing 95 to 100% by weight of total octanoic acid and containing 15 to 35% by weight of 2-ethylhexanoic acid in the carboxylic acid And a lubricating base oil having a total content of 65 to 85% by weight.

  The present invention also provides a lubricating oil comprising a synthetic ester obtained by reacting pentaerythritol and a carboxylic acid, wherein the carboxylic acid is 2-ethylhexanoic acid, n-heptanoic acid and n-octanoic acid. And the total content of n-heptanoic acid and n-octanoic acid in the carboxylic acid, and the content of 2-ethylhexanoic acid in the carboxylic acid is 15 to 35% by weight. This relates to a lubricating oil having a content of 65 to 85% by weight.

  In the present invention, a lubricating base oil containing a synthetic ester obtained by reacting pentaerythritol and a carboxylic acid, and a lubricating oil that may contain the lubricating base oil, the carboxylic acid as By using the one in which the content ratio of 2-ethylhexanoic acid is 15 to 35% by weight and the total content ratio of n-heptanoic acid and n-octanoic acid is 65 to 85% by weight The present invention has realized a lubricating base oil and lubricating oil that exhibit excellent properties over a wide temperature range, exhibit stable lubricity even when used for a long time under a high temperature load environment, and have good heat resistance. The lubricating base oil and the lubricating oil are, as carboxylic acids, controlled by controlling the content of 2-ethylhexanoic acid and the total content of n-heptanoic acid and n-octanoic acid within the above range. Lubricating base oil and the chemical structure of the lubricating oil are stable even under high temperature load environments, and the amount of high molecular weight substances generated in the lubricating base oil and lubricating oil can be suppressed even under high temperature load environments. It is thought that the property has improved. Moreover, according to the said lubricating base oil and lubricating oil, the volatilization amount in a high temperature load environment also becomes small, and it turns out that heat resistance is improving also from this point.

  As described above, the lubricating base oil of the present invention, or the lubricating oil that may contain the lubricating base oil, has good heat resistance and exhibits excellent lubricity in a wide temperature range from low temperature to high temperature. It can be used stably for a period.

  The lubricating base oil of the present invention contains a synthetic ester obtained by reacting pentaerythritol and a carboxylic acid, and the carboxylic acid contains 2-ethylhexanoic acid, n-heptanoic acid and n -Octanoic acid is contained in a total content of 95 to 100% by weight. That is, the lubricating base oil of the present invention is obtained by reacting a mixture of pentaerythritol and at least the three kinds of carboxylic acids, and each synthetic ester obtained by reacting pentaerythritol and each carboxylic acid is obtained. They are not blended.

  In addition, the carboxylic acid is 2-ethylhexane from the viewpoint of being able to be used stably for a long period of time, especially under a high temperature load environment, so that the lubricating base oil has excellent lubricity in a wide temperature range. The acid content is 15 to 35% by weight, and the total content of n-heptanoic acid and n-octanoic acid is controlled to 65 to 85% by weight. The weight ratio of the content of 2-ethylhexanoic acid to the total content of n-heptanoic acid and n-octanoic acid [2-ethylhexanoic acid / (n-heptanoic acid + n-octanoic acid)] is preferably 15 / 85 to 32/68, more preferably 20/80 to 30/70, and even more preferably 27/75 to 30/70.

  Furthermore, the content of 2-ethylhexanoic acid in the carboxylic acid is preferably 15 to 32% by weight, more preferably 20 to 30% by weight, and further preferably 25 to 30% by weight. The content of n-heptanoic acid in the carboxylic acid is preferably 30 to 50% by weight, more preferably 40 to 50% by weight, and still more preferably 40 to 45% by weight. In the carboxylic acid, the content of n-octanoic acid is preferably 20 to 50% by weight, more preferably 25 to 40% by weight, and further preferably 25 to 35% by weight.

  The carboxylic acid may optionally contain other carboxylic acids other than 2-ethylhexanoic acid, n-heptanoic acid and n-octanoic acid as long as the desired effects of the present invention are not inhibited. . Examples of other carboxylic acids include n-pentanoic acid, n-hexanoic acid, n-nonanoic acid, n-decanoic acid, and other branched chain fatty acids having 6 to 10 carbon atoms having an alkyl group at the α-position. .

  Esters of pentaerythritol and a carboxylic acid containing a predetermined amount of 2-ethylhexanoic acid, n-heptanoic acid, and n-octanoic acid can be obtained between both components according to a known method (for example, see JP-A-11-80766). Can be prepared by carrying out an esterification reaction.

  In the reaction of pentaerythritol and carboxylic acid, the equivalent ratio between the two is usually preferably adjusted so that the carboxyl group of the carboxylic acid is 1 to 1.3 equivalent to 1 equivalent of the hydroxyl group of pentaerythritol. In addition, when the ratio of the carboxyl group of carboxylic acid is made high, the reactivity of pentaerythritol and carboxylic acid becomes good, but it is necessary to remove excess carboxylic acid after completion of the reaction. When a large amount of carboxylic acid is used, excess carboxylic acid may be removed by methods such as distillation under reduced pressure, steaming, adsorption using an adsorbent, and removal.

  The lubricating base oil of the present invention preferably contains 80 to 100% by weight, more preferably 90 to 100% by weight of the ester. When 100% by weight is contained, the lubricating base oil is composed of the ester of the present invention itself. Examples of esters other than the esters used in the present invention include diester oils such as di-2-ethylhexyl sebacate, polyol ester oils produced from trimethylolpropane, neopentyl glycol and the like and carboxylic acids, pyromellitic acid, Aromatic ester oil produced from trimellitic acid and alcohol can be used. Examples of components other than esters in the lubricating base oil include hydrocarbon oils and ethers.

  The lubricating base oil of the present invention is considered to have an improved amount of high molecular weight generated in the lubricating base oil even under a high temperature load environment. As a result, the heat resistance is considered to be improved. Generation of a high molecular weight product having a molecular weight of 1500 or more measured by the molecular weight distribution measurement method, in particular, a molecular weight exceeding 3000, is suppressed more excellently than that of a conventional lubricating base oil.

  The volatilization amount of the lubricating base oil of the present invention is preferably 30% by weight or less from the viewpoint of heat resistance that can maintain excellent lubricity even when the lubricating base oil is used for a long period of time at a high temperature. More preferably, it is 25 weight% or less, More preferably, it is 20 weight% or less. The volatilization amount can be obtained by a method described later.

  In addition, the pour point of the lubricating base oil of the present invention is preferably −45 ° C. or less, preferably −50 ° C. or less, from the viewpoint of having a low temperature fluidity that is more excellent in lubricity at low temperatures. More preferably, the temperature is −52.5 ° C. or lower. The pour point is measured according to JISK2269. Lubricating base oil containing ester having such a pour point is used in, for example, air-conditioner fan motor bearings, automobile bearings, acoustic equipment bearings, computer bearings, spindle motor bearings, etc. Can be drastically reduced.

  Therefore, the lubricating base oil of the present invention is more preferably one having a pour point of −45 ° C. or lower and a volatilization amount of 30% by weight or lower.

Further, the kinematic viscosity at 40 ° C. of the lubricating base oil of the present invention is preferably 20 to 40 mm ² / sec from the viewpoint of ensuring lubricity such as motor startability and long-term use under high temperature load environment. More preferably, it is 22 to 36 mm ² / second, more preferably 24 to 32 mm ² / second, and the above value before the thermal load test is preferably 20 to 300 mm ² / ^second after the thermal load test. sec, more preferably 20 to 200 mm ² / sec, more preferably from 20 to 150 mm ² / sec, more preferably more a 20~120mm ² / sec. The kinematic viscosity at 40 ° C. is measured according to JIS K2283, and the thermal load test method will be described later. Even in a high-temperature load environment, from the viewpoint of such may be used stably for a long period of time, the difference in the kinematic viscosity (viscosity increase) is preferably 100 mm ² / sec or less, and more is 90 mm ² / sec Preferably, it is 80 mm ² / sec or less, more preferably 70 mm ² / sec or less.

  The acid value of the lubricating base oil of the present invention is preferably 0.5 mg KOH / g or less, more preferably flash point, oxidation stability, thermal stability, hydrolysis resistance, metal corrosion resistance, etc. Is 0.1 mg KOH / g or less. Further, the hydroxyl value of the lubricating base oil of the present invention is preferably 4 mg KOH / g or less, more preferably 3 mg KOH / g, because of its good flash point, low temperature fluidity, thermal stability, hydrolysis resistance and the like. It is as follows.

  The lubricating base oil of the present invention can be used as a lubricating oil as it is. The physical properties of the lubricating base oil of the present invention and the lubricating oil containing the lubricating base oil of the present invention reflect the physical properties of the synthetic ester according to the present invention, and these physical properties are common to each other. In the lubricating oil of the present invention, when the lubricating base oil of the present invention is used, the content thereof is preferably 80 to 100% by weight, more preferably 90 to 100% by weight.

  The lubricating oil of the present invention is a lubricating oil comprising a synthetic ester obtained by reacting pentaerythritol and carboxylic acid, and the carboxylic acid is 2-ethylhexanoic acid, n-heptanoic acid and The total content of n-octanoic acid is 95 to 100% by weight, and the content of 2-ethylhexanoic acid in the carboxylic acid is 15 to 35% by weight. n-heptanoic acid and n-octane The total content with the acid is 65 to 85% by weight. The ratio of each carboxylic acid and the like related to the synthetic ester used in the lubricating oil is the same as that of the lubricating oil base oil.

  As described above, the lubricating oil of the present invention contains the synthetic ester according to the present invention by containing the lubricating base oil of the present invention, or the synthetic ester according to the present invention prepared separately, according to the present invention. The synthetic ester which concerns on is contained. When the lubricating oil of the present invention contains components other than the synthetic ester according to the present invention, the lubricating oil of the present invention is prepared in advance using the lubricating base oil of the present invention containing the synthetic ester. Alternatively, the synthetic ester may be added separately from the lubricating base oil of the present invention to prepare the lubricating oil of the present invention. For example, the lubricating oil of the present invention may contain a lubricating base oil other than the synthetic ester according to the present invention. Or a lubricating base oil that does not contain the synthetic ester according to the present invention when the lubricating oil of the present invention is prepared (hereinafter also referred to as “second base oil” for convenience). ) May be added separately. Similarly, although the lubricating oil of the present invention can contain various additives, the additive may be previously contained in the lubricating base oil or the second base oil of the present invention, or You may add separately from the lubricating oil of this invention, or the 2nd base oil in the case of preparation of the lubricating oil of this invention. Furthermore, in the lubricating base oil of the present invention and the lubricating oil of the present invention, components other than the synthetic ester according to the present invention are derived from any of the lubricating base oil, the second base oil or the additive of the present invention. There is no particular limitation as to whether it is.

  Furthermore, the lubricating oil of the present invention can contain conventionally known lubricating oil additives as necessary in order to further enhance its performance. As such additives, antioxidants, extreme pressure agents, antiwear agents, rust inhibitors, antifoaming agents, demulsifiers, metal deactivators such as benzotriazole, oily agents such as fatty acids, viscosity index improvers, A pour point depressant, a cleaning dispersant, and the like may be prepared by appropriately mixing with the synthetic ester as desired in an amount within the range in which the object of the present invention is not impaired. These additives may be used individually by 1 type, and may be used in combination of 2 or more type. The content of these additives is preferably 10% by mass or less, more preferably 5% by mass or less, based on the total amount of the lubricating oil.

  Examples of the antioxidant include 2,6-di-t-butyl-4-methylphenol, 4,4′-methylenebis (2,6-di-t-butyl-4-methylphenol), bisphenol A, and the like. Phenolic antioxidants such as p, p'-dioctylphenylamine, monooctyldiphenylamine, phenothiazine, 3,7-dioctylphenothiazine, phenyl-1-naphthylamine, phenyl-2-naphthylamine, alkylphenyl-1-naphthylamine, alkyl Amine-based antioxidants such as phenyl-2-naphthylamine and N, N-di (2-naphthyl) -p-phenylenediamine; Sulfur-based antioxidants such as alkyl disulfide, thiodipropionic acid ester and benzothiazole; dialkyl Zinc dithiophosphate, diaryl dithiophosphate Examples include zinc. These antioxidants can be used alone or in admixture of two or more.

  Examples of the extreme pressure agent include zinc dialkyl dithiophosphate, zinc diaryl dithiophosphate, dialkyl polysulfide, triaryl phosphate, trialkyl phosphate, chlorinated paraffin, sulfur compound and the like. These extreme pressure agents can be used alone or in admixture of two or more.

  Examples of the rust preventive include alkenyl succinic acid, alkenyl succinic acid derivative, sorbitan monooleate, pentaerythritol monooleate, glycerin monooleate, and amine phosphate. These rust inhibitors can be used alone or in admixture of two or more.

  Examples of the antifoaming agent include silicone oils such as dimethylpolysiloxane and organosilicates such as diethyl silicate. These silicone-based antifoaming agents can be used alone or in admixture of two or more.

  Examples of the demulsifier include polyoxyalkylene glycol, polyoxyalkylene alkyl ether, polyoxyalkylene alkylamide, polyoxyalkylene fatty acid ester, and the like, but are not limited to such examples. These demulsifiers can be used alone or in admixture of two or more.

  In addition, when preparing a grease using the lubricating base oil of the present invention, additives such as thickeners, antioxidants, rust inhibitors, extreme pressure agents, oiliness agents, solid lubricants, etc. are added as necessary. What is necessary is just to mix. Examples of the thickener include soaps such as calcium soap, sodium soap, and lithium soap; complex soaps such as calcium complex soap, aluminum complex soap, and lithium complex soap; terephthalamidate, urea, silica airgel, and the like. It is done.

The kinematic viscosity at 40 ° C. of the lubricating oil of the present invention is preferably 20 to from the viewpoint of ensuring lubricity such as startability of the motor and long-term use under a high temperature load environment when designed as a liquid lubricating oil. 40 mm ² / sec, more preferably 22~36mm ² / sec, more preferably 24~32mm ² / sec, as was the said values before heat load test, after heat load test, preferably 20 to 300 mm ² / sec, more preferably 20 to 200 mm ² / sec, more preferably from 20 to 150 mm ² / sec, more preferably more a 20~120mm ² / sec.

  Further, the acid value of the lubricating oil of the present invention is preferably 0. 0 in order to prevent corrosion of the base material to which the lubricating oil is applied and to prevent decomposition of the synthetic ester contained in the lubricating oil of the present invention. 1 mgKOH / g or less, more preferably 0.05 mgKOH / g or less. In the present invention, the acid value was obtained by the measurement described later.

  Further, the ash content of the lubricating oil of the present invention is preferably 100 ppm or less, more preferably 50 ppm or less in order to enhance the stability of the lubricating oil of the present invention and suppress the generation of sludge and the like. In the present invention, ash means the value of ash measured based on JIS K 2272 “Testing method for ash and sulfated ash of crude oil and petroleum products”.

  The lubricating base oil of the present invention and the lubricating oil including the case of containing it are excellent in heat resistance, and are therefore preferably used even in a high temperature environment, such as air conditioner fan motor bearings, automotive bearings, acoustic equipment bearings, and computers. When used for grease used in parts that require heat resistance, such as bearings for motors and spindle motors, it can be used more stably for a long time. Also, it can be used stably for a long period of time even when it is used for an open system that can come into contact with moisture, such as external water or parts used in an environment where water generated by condensation can enter the lubricant. .

Example 1
A 2 liter four-necked flask was equipped with a stirrer, thermometer, nitrogen gas blowing tube and cooling tube. To this flask, 379 g of 2-ethylhexanoic acid, 568 g of n-heptanoic acid and 316 g of n-octanoic acid were added as carboxylic acid (fatty acid), and 250 g of pentaerythritol was added thereto. The ratio (weight ratio) of n-heptanoic acid: n-octanoic acid: 2-ethylhexanoic acid is 30:45:25, and the carboxyl group of the carboxylic acid is equivalent to 1 equivalent of the hydroxyl group of pentaerythritol. It set so that it might become 1.25 equivalent.

  Next, the reaction was carried out at 230 ° C. for 14 hours while blowing nitrogen gas into the flask, and the distilled water was removed. After completion of the reaction, excess carboxylic acid was removed under a reduced pressure of 0.13 kPa, and steaming was performed for 1 hour under a reduced pressure of 0.67 kPa. Adsorbent (Kyowa Chemical Industry Co., Ltd., trade name: KYOWARD 500SH) Then, the remaining carboxylic acid was adsorbed and filtered to obtain an ester. The acid value of the ester was 0.01 mgKOH / g, and the hydroxyl value was 0.50 mgKOH / g. The ester was used as a lubricating base oil. The ester can also be used as a lubricating oil, and the volatilization amount, pour point and kinematic viscosity at 40 ° C. are also indicators of the lubricating oil. The following Examples 2 to 4 and Comparative Examples 1 to 10 are similarly evaluated as a lubricating base oil and also evaluated as a lubricating oil.

Examples 2-4, Comparative Examples 1-10
Esters were synthesized in the same manner as in Example 1 except that the types and ratios of the carboxylic acids (fatty acids) used were changed as shown in Table 1. The ester was used as a lubricating base oil.

Comparative Example 11
Each ester obtained in Comparative Example 4, Comparative Example 5 and Comparative Example 6 was blended so that the ratio (weight ratio) of Comparative Example 4: Comparative Example 5: Comparative Example 6 was 45:25:30. A mixed ester was prepared. The mixed ester was used as a lubricating base oil.

<Evaluation>
The following evaluation was performed about the lubricating base oil obtained by the said Example and comparative example. The results are shown in Table 1.

(1) Volatilization amount: About 20 g of the obtained lubricant base oil is weighed as a sample oil in a 100 cc glass beaker having a diameter of about 55 mm, heated in a thermostatic chamber having an atmospheric temperature of 180 ° C. for 500 hours, and again. Weighing and obtaining the volatilization amount from the following formula.
Volatilization amount (% by weight) = {(weight of sample oil before heating) − (weight of sample oil after heating)} / (weight of sample oil before heating) × 100

  (2) Pour point: The pour point (° C.) was determined according to JIS K2269.

(3) Kinematic viscosity at 40 ° C .: The kinematic viscosity (mm ² / sec) at 40 ° C. was determined according to JIS K2283. As for the kinematic viscosity, a heat load test was performed on the lubricating base oil (new oil) immediately after preparation, and after putting 20 g of the new oil in a 100 ml beaker and leaving it at 180 ° C. in an air atmosphere for 500 hours. The thing was measured. Table 1 also shows the kinematic viscosity difference (increased viscosity) between the new oil and that after the heat load test.

  (4) Acid value and hydroxyl value: The acid value was determined according to JIS K0070 3.1. The hydroxyl value is determined according to JIS K0070 7.2.

(5) Molecular weight distribution: For the lubricating base oil (new oil) immediately after preparation, 20 g of fresh oil was put into a 100 ml beaker and left at 180 ° C. in an air atmosphere for 500 hours to conduct a thermal load test. The weight average molecular weight was less than 1500, less than 1500 and less than 3000, and the ratio of each component was measured.
The ratio of the weight average molecular weight is a value calculated based on the peak area ratio (%) in the chromatogram obtained by applying the gel permeation chromatography (GPC) method under the following conditions.
Column: G2000HXL + G1000HXL (Tosoh Corporation)
Eluent: THF
Flow rate: 1.0 mL / min
Column temperature: 40 ° C
Detector: RI detector Standard material: Polystyrene conversion

  In Table 1, nC7 is n-heptanoic acid. Kyowa Noic GH (manufactured by Kyowa Hakko) is 2-ethylpentanoic acid (17% by weight), 2-methylhexanoic acid (62% by weight), 2-ethylhexanoic acid (21% by weight) in the total amount of the product. Is a mixture containing as a main component. nC8 is n-octanoic acid. 2EH is 2-ethylhexanoic acid. iC9 acid is 3,5,5-trimethylhexanoic acid. Emazole 874 (produced by Emery) is a mixture in which the total amount of isostearic acid, isopalmitic acid, myristic acid, palmitic acid, stearic acid, oleic acid, and cyclic octadecanoic acid is 90% by weight or more in the total amount of the product. Note that Comparative Examples 1 to 3 in Table 1 correspond to Examples 1 to 3 in JP-A-2006-124429.

The lubricating base oils of Examples 1 to 4 have a volatility of 30% by weight, a pour point of −45 ° C. or less, a kinematic viscosity difference (viscosity increase) of 100 mm ² / sec or less, and excellent heat resistance. It has low temperature fluidity and high temperature lubricity.

  On the other hand, Comparative Examples 1 to 3 use a carboxylic acid (fatty acid) having the same composition as that of the example. However, since the ratio of 2EH is large, the increase in viscosity after heat load is remarkable, and the heat resistance is not satisfied. . Furthermore, the amount of evaporation is larger than that of the example, and it can be seen from this point that the heat resistance is not sufficient. In Comparative Examples 4 to 6, each carboxylic acid (fatty acid) used in Examples and Comparative Examples 1 to 3 is used alone, and has a high pour point and cannot be used as a lubricating base oil. Moreover, although the comparative example 10 mixes each ester obtained by Comparative Examples 4-6 and imitates the same carboxylic acid (fatty acid) as Example 2, it has a high pour point and cannot be used. Comparative Examples 7 to 9 are cases where a carboxylic acid (fatty acid) having a composition different from that of the Examples was used, but although the evaporation amount was low, the increase in viscosity after heat load was large and the heat resistance could not be satisfied.

Claims (5)

A lubricating base oil containing a synthetic ester obtained by reacting pentaerythritol and a carboxylic acid, the carboxylic acid containing a total of 2-ethylhexanoic acid, n-heptanoic acid and n-octanoic acid The content of 95 to 100% by weight, and the content of 2-ethylhexanoic acid in the carboxylic acid is 15 to 32 % by weight, and the total content of n-heptanoic acid and n-octanoic acid is 68-85 wt% der Ri, n- content of heptanoic acid is 30 to 50 wt%, the content of n- octanoic acid Ru 20-50 wt% der lubricating base oil. In the carboxylic acid, the weight ratio of the content of 2-ethylhexanoic acid to the total content of n-heptanoic acid and n-octanoic acid [2-ethylhexanoic acid / (n-heptanoic acid + n-octanoic acid)] is The lubricating base oil according to claim 1, which is 15/85 to 32/68 . 3. The lubricating base oil according to claim 1, wherein the 40 ° C. kinematic viscosity before the heat load test is 20 to 40 mm ² / sec and the 40 ° C. kinematic viscosity after the heat load test is 20 to 300 mm ² / sec. A lubricating oil comprising a synthetic ester obtained by reacting pentaerythritol and a carboxylic acid, wherein the carboxylic acid contains 2-ethylhexanoic acid, n-heptanoic acid and n-octanoic acid in a total content 95 to 100% by weight, the content of 2-ethylhexanoic acid in the carboxylic acid is 15 to 32 % by weight, and the total content of n-heptanoic acid and n-octanoic acid is 68 to 85 wt% der Ri, n- content of heptanoic acid is 30 to 50 wt%, the content of n- octanoic acid Ru 20-50 wt% der lubricating oil. In the carboxylic acid, the weight ratio of the content of 2-ethylhexanoic acid to the total content of n-heptanoic acid and n-octanoic acid [2-ethylhexanoic acid / (n-heptanoic acid + n-octanoic acid)] is The lubricating oil according to claim 4, which is 15/85 to 32/68 .