Lubricating base oil, lubricating oil composition containing lubricating base oil, and method for producing lubricating oil composition

Abstract

Provided is a method of lubricating a sliding part by applying a lubricating base oil containing an ester compound to the sliding part. The ester compound contains a mixture of one or more compounds represented by a general formula (1) wherein R.sup.1 and R.sup.2 independently represent a hydrogen, a methyl, a benzoyloxy, a naphthoyloxy, or general formula (2) (—O—C(═O)—R.sup.5), R.sup.3 and R.sup.4 independently represent a benzoyloxy group, a naphthoyloxy group, or general formula (2), and R.sup.5 represents a linear C5-21 alkyl group, a branched chain C9-21 alkyl group, or a C5-21 cycloalkyl group that may also be substituted with an alkyl chain. The mixture contains a compound in which at least one among R.sup.1 to R.sup.4 is general formula (2), and the proportion, in the mixture, of a compound in which at least one among R.sup.1 to R.sup.4 is a benzoyloxy group or a naphthoyloxy group is 5-100 mole %.

Claims

1. A method of lubricating a sliding part, comprising: applying a lubricant base oil comprising a mixture of ester compounds to the sliding part, wherein the mixture of ester compounds comprises compounds each represented by a general formula (1): ##STR00007## wherein R.sup.1 and R.sup.2 each independently represent a hydrogen atom, a methyl group, a benzoyloxy, a naphthoyloxy or a general formula (2): —O—C(═O)—R.sup.5, and R.sup.3 and R.sup.4 each independently represent a benzoyloxy, a naphthoyloxy or the general formula (2): —O—C(═O)—R.sup.5; wherein R.sup.5 represents a linear alkyl group having 5 to 21 (both inclusive) carbon atoms, a branched alkyl group having 9 to 21 (both inclusive) carbon atoms, or a cycloalkyl group having 5 to 21 (both inclusive) carbon atoms and optionally substituted with an alkyl chain, the mixture comprises compounds wherein at least two of R.sup.1 to R.sup.4 are the general formula (2): —O—C(═O)—R.sup.5, wherein at least one R.sup.5 is a linear alkyl group having 5 to 21 (both inclusive) carbon atoms and the other R.sup.5 is a branched alkyl group having 9 to 21 (both inclusive) carbon atoms, and further wherein a ratio by mole of the linear alkyl group having 5 to 21 (both inclusive) carbon atoms (c) to the branched alkyl group having 9 to 21 (both inclusive) carbon atoms (d) (ratio (c)/(d)) is from 0.1 or more to 2 or less, and a proportion of a compound about which at least one of R′ to R.sup.4 is the benzoyloxy or the naphthoyloxy in the mixture is from 5% or more by mole to 100% or less by mole.

2. The method according to claim 1, wherein a proportion by mass of the mixture in the lubricant base oil is from 50% or more by mass to 100% or less by mass.

3. A method of lubricating a sliding part, comprising: applying a lubricant oil composition to the sliding part, wherein the lubricant oil composition comprises the lubricant base oil according to claim 1.

4. The method according to claim 1, wherein the compound(s) represented by the general formula (1) is yielded by condensing one or more alcohols and one or more carboxylic acids, and each represented by the general formula (1), wherein the alcohol(s) comprise(s) a polyhydric alcohol represented by a general formula (3): ##STR00008## wherein R.sup.6 to R.sup.9 each independently represent a hydrogen atom, a methyl group or a hydroxyl group, and further at least two of R.sup.6 to R.sup.9 each represent the hydroxyl group, the carboxylic acid(s) comprise(s) one or more aromatic carboxylic acids and one or more aliphatic carboxylic acids, the aromatic carboxylic acid(s) comprise(s) benzoic acid and/or naphthoic acid, and the aliphatic carboxylic acid(s) comprise(s) at least one monocarboxylic acid selected from linear alkyl aliphatic acids each having 6 to 22 (both inclusive) carbon atoms, branched alkyl aliphatic acids each having 10 to 22 (both inclusive) carbon atoms, and cycloalkanecarboxylic acids each having 6 to 22 (both inclusive) carbon atoms and each optionally substituted with an alkyl chain.

5. The method according to claim 4, wherein the aromatic carboxylic acid(s) comprise(s) benzoic acid, and the linear alkyl aliphatic acids each having 6 to 22 (both inclusive) carbon atoms comprise n-heptanoic acid.

6. The method according to claim 4, wherein the aromatic carboxylic acid(s) comprise(s) benzoic acid, and the branched alkyl aliphatic acids each having 10 to 22 (both inclusive) carbon atoms comprise isostearic acid.

7. The method according to claim 4, wherein the aromatic carboxylic acid(s) comprise(s) benzoic acid, the linear alkyl aliphatic acids each having 6 to 22 (both inclusive) carbon atoms comprise n-heptanoic acid, and the branched alkyl aliphatic acids each having 10 to 22 (both inclusive) carbon atoms comprise isostearic acid.

8. The method according to claim 4, wherein for 100 equivalents of the polyhydric alcohol, an amount of carboxyl groups of the aromatic carboxylic acid(s) is from 10 to 90 equivalents both inclusive, an amount of carboxyl groups of the aliphatic carboxylic acid(s) is from 60 to 140 equivalents both inclusive, and further a total amount of the carboxyl groups of the aromatic carboxylic acid(s) and the aliphatic carboxylic acid(s) is from 100 to 150 equivalents both inclusive.

9. The method according to claim 1, wherein a ratio by mole of the general formula (2): —O—C(═O)—R.sup.5 (a) to the whole of the benzoyloxy and naphthoyloxy (ratio (a)/(b)) is from 0.1 or more to 10 or less.

10. The method according to claim 1, wherein a ratio by mole of the linear alkyl group having 5 to 21 (both inclusive) carbon atoms (c) to the whole of the benzoyloxy and naphthoyloxy (ratio (c)/(b)) is from 0.3 or more to 2 or less.

11. The method according to claim 1, wherein the proportion of the compound about which at least one of R.sup.1 to R.sup.4 is a benzoyloxy or naphthoyloxy group in the mixture is from 35% or more by mole to 99% or less by mole.

12. The method according to claim 1, wherein a proportion by mass of the compound about which at least one of R.sup.1 to R.sup.4 is a benzoyloxy or naphthoyloxy in the mixture is from 30% or more by mass to 95% or less by mass.

13. The method according to claim 1, wherein the 40° C. kinetic viscosity of a condensed ester comprising the compound(s) represented by the general formula (1) is from 30 mm.sup.2/s or more to 1500 mm.sup.2/s or less, and the 100° C. kinetic viscosity of the condensed ester is from 5 mm.sup.2/s or more to 20 mm.sup.2/s or less.

14. The method according to claim 1, wherein the pour point of a condensed ester comprising the compound(s) represented by the general formula (1) measured by a measuring method according to JIS K2269 is −20° C. or lower.

15. The method according to claim 4, wherein the polyhydric alcohol is at least one species selected from the group consisting of pentaerythritol, trimethylolpropane, and neopentyl glycol.

16. The method according to claim 4, wherein a proportion of the aromatic carboxylic acid(s) in the carboxylic acid(s) is from 10% or more by mole to 90% or less by mole.

17. The method according to claim 4, wherein a proportion of the linear alkyl aliphatic acid(s) having 6 to 22 (both inclusive) carbon atoms in the carboxylic acid(s) is from 20% or more by mole to 70% or less by mole.

18. The method according to claim 4, wherein a proportion of the branched alkyl aliphatic acids each having 10 to 22 (both inclusive) carbon atoms in the carboxylic acid(s) is from 10% or more by mole to 50% or less by mole.

19. The method according to claim 4, wherein a proportion of the cycloalkanecarboxylic acids each having 6 to 22 (both inclusive) carbon atoms and each optionally substituted with an alkyl chain in the carboxylic acid(s) is from 10% or more by mole to 70% or less by mole.

20. The method according to claim 3, wherein a proportion by mass of the lubricant base oil in the lubricant oil composition is from 90% or more by mass.

Description

EXAMPLES

(1) Hereinafter, the present invention will be described in more detail by way of working examples thereof. However, the invention is not limited only to these working examples.

Example 1

Synthesis of Ester Compounds

(2) Into a 1-L four-necked flask equipped with a stirrer, a thermometer, a nitrogen-blowing tube and a condenser were added 378.6 g of enantoic acid (n-heptanoic acid), and 118.3 g of benzoic acid as carboxylic acids, and then thereto was added 110.0 g of pentaerythritol as an alcohol. The addition amount of the carboxylic acids was adjusted to set the amount of all carboxyl groups of the carboxylic acids to 1.2 equivalents per equivalent of hydroxyl groups of the alcohol.

(3) Next, nitrogen gas was blown into the flask. While the reaction system was stirred, the temperature thereof was raised to 250° C. The system was kept at 250° C. for 18 hours. The condenser was used to remove water distilled off therefrom to the outside of the flask. After the end of the reaction, an excess of the carboxylic acid components was distilled off under a reduced pressure of 0.13 kPa. Under the reduced pressure of 0.13 kPa, the system was subjected to steaming for one hour to cause remaining fractions of the carboxylic acid components to be adsorbed on an adsorbent (trade name: KYOWAAD 500SH, manufactured by Kyowa Chemical Industry Co., Ltd.). Thereafter, the production system was filtrated to yield ester compounds in Example 1. About the resultant ester compounds, evaluations described below were obtained. The evaluation results are shown in Table 1.

Evaluation of Respective Proportions of Components in Ester Compounds

(4) The respective component proportions (% by mole) of the ester compounds yielded as described above were measured by a method described below.

(5) The resultant ester compounds were dissolved in deuterium chloroform. A nuclear magnetic resonance machine (trade name: system Agilent 400-MR DD2, manufactured by the company Agilent Technologies) was used to make a .sup.1H-NMR measurement of the solution. On the basis of proton intensities of peaks originating from ester groups, which made their appearance near 4 ppm, the percentage by mole of each of the respective numbers of ester groups each having in the molecule thereof an aromatic ring was calculated out. On the basis of the number of the ester groups in the molecule, peaks thereof, the number of which is “the number of the ester groups”ד2”, make their appearance. When the number is, for example, 4, peaks originating from 0, 1, 2, 1, 3, 2, 3 and 4 groups make their appearance toward lower values in the magnetic field. When the number is 3, peaks originating from 0, 1, 2, 1, 2, and 3 groups make their appearance toward lower values in the magnetic field. When the number is 2, peaks originating from 0, 1, 1, and 2 groups make their appearance toward lower values in the magnetic field. The intensity of protons is in proportional to the number of moles thereof. Thus, from the proportion of the proton intensity of each of the peaks gained in the measurement, the % by mole of each of the respective numbers of the ester groups each having an aromatic ring was calculated out.

(6) The total component proportion (% by mass) of compounds each having a benzoyloxy or naphthoyloxy group in the mixture of the ester compounds yielded as described above was calculated out by gaining the theoretical molecular weights of each of the resultant ester compounds from the charge ratio between the used alcohols and carboxylic acids, and then using the component proportion (% by mole) of each of the ester compounds.

Evaluation of Hydrolysis Resistance

(7) In an evaluation of the hydrolysis resistance of the ester compounds yielded as described, 10 mL of a 2% by mass of sodium hydroxide in water and 10 mL of the ester compounds were added to a 25-mL test tube with a screw cap. The screw cap was tightened. The test tube was turned upside down three times to mix the water phase and the oil phase preliminarily with each other, and then shaken upward and downward with a shaking-width of about 30 cm 30 times in one minute. After the shaking, the test tube was allowed to stand still, and the inside of the test tube was observed after 5 minutes and 10 minutes. The sample was evaluated in accordance with a criterion described below. According to this test, the superiority or inferiority of the hydrolysis resistance of the sample is understood in accordance with the following mechanism: The matter that the interface between the water phase and the oil phase is emulsified so that the boundary becomes unclear is to demonstrate that in a short time, the sample is hydrolyzed to produce a soap, or that the sample is easily mixed with water to be easily hydrolyzed. Accordingly, evaluation 1, in which after the shaking, the sample is immediately separated into the two phases, shows excellent hydrolysis resistance.

(8) 1: Within 5 minutes, the boundary between the water phase and the oil phase is clear, and these phases are each separated into a volume of 10 mL.

(9) 2: In a time of 5 to 10 minutes, the boundary between the water phase and the oil phase becomes clear, and these phases are each separated into a volume of 10 mL.

(10) 3: Even when 10 minutes or longer elapse, the boundary between the water phase and the oil phase does not become clear.

Evaluation of Heat Resistance

(11) In an evaluation of the heat resistance of the sample, a differential thermo-gravity simultaneously-measuring device (trade name: TG/DTA6200, manufactured by Seiko Instruments Inc.) was used to raise the temperature of the sample from 35° C. to 550° C. at 10° C./minute in a 250-mL/minute nitrogen-air atmosphere. Under conditions that the sample was kept at the temperature of 550° C. for 10 minutes, the thermal response of the ester compounds was measured, and the residual percentage (% by mass) thereof was calculated out in accordance with an expression described below. It is demonstrated that as the residual percentage is larger, the heat resistance is better.
residual percentage (% by mass)=“the mass of the sample at 350° C.”/“the mass thereof at 35° C.”×100  Expression:

Evaluation of Kinetic Viscosity

(12) In an evaluation of the kinetic viscosity of the sample, the 40° C. kinetic viscosity and the 100° C. kinetic viscosity (mm.sup.2/s) thereof were measured, using a Stabinger kinetic viscometer (trade name: SVM3000, manufactured by Anton Paar GmbH) satisfying a precision required in ASTM D7042.

Evaluation of Pour Point

(13) In an evaluation of the pour point of the sample, the pour point (° C.) was measured by a measuring method according to JIS K2269.

Examples 2 to 16, and Comparative Examples 1 to 3>

(14) In each of the examples, ester compounds were prepared and evaluated in the same way as in Example 1 except that the species and the blend amounts of the individual raw materials were changed as shown in Table 1. The evaluation results are shown in Table 1.

(15) TABLE-US-00001 TABLE 1 Charged components Carboxylic acids (% by mole) Carboxylic acids (% by mass) Aliphatic Aromatic carboxylic Aliphatic carboxylic Aromatic carboxylic carboxylic acids acids Others acids acids Alcohol Ph α-Naph β-Naph nC7 nC8 nC9 iC18 Cy nC5 iC9 2EH Ph α-Naph β-Naph nC7 Example 1 PET 25 75 23.8 76.2 Example 2 PET 25 75 22.0 Example 3 PET 25 75 20.5 Example 4 PET 50 50 48.4 51.6 Example 5 PET 75 25 73.8 26.2 Example 6 PET 25 50 25 18.3 39.0 Example 7 PET 37.5 50 12.5 31.3 44.4 Example 8 PET 12.5 50 37.5 8.2 34.8 Example 9 PET 25 37.5 37.5 16.4 26.2 Example 10 PET 37.5 37.5 25 27.6 29.5 Example 11 PET 12.5 62.5 25 9.1 48.5 Example 12 PET 25 62.5 12.5 20.7 55.2 Example 13 PET 12.5 25 62.5 9.2 Example 14 TMP 25 37.5 37.5 16.4 26.2 Example 15 PET 25 37.5 37.5 21.7 24.6 Example 16 PET 25 37.5 37.5 21.7 24.6 Comparative PET 100 100 Example 1 Comparative PET 25 75 22.0 Example 2 Comparative PET 25 54 21 25.7 Example 3 Evaluations Component proportion of each ester compound having one or Charged components more benzoyloxy or naphthoyloxy Carboxylic acids (% by mass) groups (a) in ester compound mixture Aliphatic carboxylic % by mole acids Others No One Two Three nC8 nC9 iC18 Cy nC5 iC9 2EH groups (a) group (a) groups (a) groups (a) Example 1 31.8 40.6 20.2 6.5 Example 2 78.0 34.0 40.3 19.0 6.4 Example 3 79.5 34.4 40.5 18.4 6.4 Example 4 6.3 25.2 37.9 24.7 Example 5 0.5 5.1 22.4 44.2 Example 6 42.7 35.0 43.4 19.2 2.2 Example 7 24.3 18.4 40.7 29.3 10.9 Example 8 57.0 69.8 26.7 3.5 0.0 Example 9 57.4 38.5 42.3 16.2 2.9 Example 10 42.9 19.9 40.2 27.7 11.4 Example 11 42.4 62.3 31.5 6.0 0.3 Example 12 24.1 37.7 43.4 17.0 1.5 Example 13 42.7 48.1 64.6 29.9 5.4 0.1 Example 14 57.4 46.3 42.0 10.7 1.0 Example 15 53.7 34.6 42.8 17.1 5.5 Example 16 53.7 38.4 39.2 15.5 6.9 Comparative 100.0 0.0 0.0 0.0 Example 1 Comparative 78.0 27.2 41.2 20.8 10.6 Example 2 Comparative 46.4 27.9 34.9 43.7 17.8 3.5 Example 3 Evaluations Component proportion of each ester compound having one or more benzoyloxy or naphthoyloxy groups (a) in ester compound mixture % by mole % by mass Total of Total of components components 40° C. 100° C. with one with one Residual Kinetic Kinetic Pour Four or more or more Hydrolysis percentage viscosity viscosity point groups (a) groups (a) groups (a) resistance (% by mass) (mm.sup.2/s) (mm.sup.2/s) (° C.) Example 1 0.8 68.2 67.7 1 60.9 49.4 6.5 −41 Example 2 0.4 66.0 64.8 1 76.5 51.5 7.2 −43 Example 3 0.3 65.6 63.8 1 78.4 62.1 8.1 −40 Example 4 5.8 93.7 93.5 1 82.7 207.0 12.1 −24 Example 5 27.8 99.5 99.5 1 92.1 1363.2 22.6 −24 Example 6 0.2 65.0 62.5 1 81.1 88.4 10.8 −39 Example 7 0.7 81.6 80.1 1 59.5 98.2 10.3 −31 Example 8 0.0 30.2 28.0 1 85.8 70.6 10.3 −36 Example 9 0.0 61.5 58.1 1 83.1 99.6 12.1 −40 Example 10 0.8 80.1 77.6 1 81.0 119.4 12.2 −32 Example 11 0.0 37.7 35.8 1 81.9 59.9 9.0 −44 Example 12 0.3 62.3 60.7 1 70.9 59.8 8.3 −43 Example 13 0.0 35.4 33.6 1 88.3 450.5 25.8 −24 Example 14 0.0 53.7 49.6 1 73.3 68.0 9.4 −45 Example 15 0.0 65.4 62.0 1 77.9 164.2 15.7 −30 Example 16 0.0 61.6 58.0 1 79.1 178.7 16.5 −28 Comparative 0.0 0.0 0.0 2 55.4 22.3 4.7 −35 Example 1 Comparative 0.2 72.8 71.7 1 25.5 115.5 9.6 −27 Example 2 Comparative 0.1 65.1 65.3 3 18.2 72.7 8.0 −29 Example 3

(16) In Table 1, individual symbols show the following:

(17) PET: pentaerythritol (manufactured by Tokyo Chemical Industry Co., Ltd.),

(18) TMP: trimethylolpropane (manufactured by Tokyo Chemical Industry Co., Ltd.),

(19) Ph: benzoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.)

(20) α-Naph: 1-naphthoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.),

(21) β-Naph: 2-naphthoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.),

(22) nC7: enantoic acid (n-heptanoic acid, manufactured by Tokyo Chemical Industry Co., Ltd.),

(23) nC8: caprylic acid (n-octanoic acid, manufactured by Tokyo Chemical Industry Co., Ltd.),

(24) nC9: pelargonic acid (n-nonanoic acid, manufactured by Tokyo Chemical Industry Co., Ltd.),

(25) iC18: isostearic acid (Prisorine 3501, manufactured by Croda Japan K.K.),

(26) Cy: cyclohexanecarboxylic acid (manufactured by Tokyo Chemical Industry Co., Ltd.),

(27) nC5: valeric acid (manufactured by Tokyo Chemical Industry Co., Ltd.),

(28) iC9: isononanoic acid (3,5,5-trimethylhexanoic acid, manufactured by Tokyo Chemical Industry Co., Ltd.), and

(29) 2EH: 2-ethylhexanoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.).