JP2002069471A - Lubricating oil composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubricating oil composition having a high viscosity index, excellent low-temperature fluidity and lubricating properties, and having little change in viscosity and change in viscosity index due to shearing. The polyorganosiloxanes comprising A an aryl group, the general formula _{R-O-CO- (CH 2} ) n -OC-O-R '(R, R' represents an alkyl group having 8 to 18 carbon atoms, R and R 'may be the same or different, and n is an integer of 4 to 13).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lubricating oil composition having excellent low-temperature fluidity, exhibiting stable lubricating performance over a wide temperature range, and having little change in viscosity characteristics due to shearing and having a high viscosity index. .

[0002]

2. Description of the Related Art In recent years, not only for special applications such as lubricating oil for aircraft, but also for engine oil for vehicles, automatic transmission oil, gear oil, hydraulic oil, precision machine oil, etc.
It is desired that oil film formation in a high temperature range is high, and a lubricating oil capable of exhibiting stable lubricating performance in a wide temperature range is required. Such lubricating oils need to have a high viscosity index. Conventionally, silicone oil (polyorganosiloxane) has been known as a base material having a high viscosity index. However, since silicone oil has extremely poor lubricity and the additives are hardly soluble, lubricity is improved by an antiwear agent or the like. Was difficult. On the other hand, it is possible to increase the viscosity index by blending high molecular compounds such as PMA polymers and olefin copolymers with mineral oil, etc., but in the case of lubricating oils blended with these polymers, the temporary viscosity decreases due to shearing. In addition, there is a problem that the permanent viscosity is reduced due to the breakage of the polymer, and as a result, the viscosity / viscosity index is reduced.

[0003]

SUMMARY OF THE INVENTION The present invention provides a lubricating oil composition having a high viscosity index, excellent low-temperature fluidity and lubricity, and little change in viscosity and change in viscosity index due to shearing. That is.

[0004]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the above-mentioned problems can be solved by blending a specific ester with a polyorganosiloxane containing an aryl group. Was found.

The present invention has been made based on this finding. An aryl group-containing polyorganosiloxane has the general formula R—O—CO— (CH ₂ ) _n —OC—O—
The dicarboxylic acid ester represented by R ′ (R and R ′ represent an alkyl group having 8 to 18 carbon atoms, R and R ′ may be the same or different, and n is an integer of 4 to 13) 80% lubricating oil composition

[0006] 2. 3. The lubricating oil composition according to the above 1 or 2, further comprising an antiwear agent and / or an antioxidant.

[0007] 3. 4. The lubricating oil composition according to any one of the above items 1 to 3, wherein the lubricating oil composition has a viscosity index of 250 or more.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As a silicone oil used for a substrate in the present invention, a polyorganosiloxane containing an aryl group is used. That is, it is a siloxane polymer represented by the following general formula.

[0009]

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Here, R and R 'represent an alkyl group or an aryl group, which may be the same or different. Here, the aryl group represents a substituent containing at least one benzene ring. R and R 'may be different for each adjacent siloxane unit. n is an integer that varies depending on the degree of polymerization, and is not particularly limited. However, if the degree of polymerization is too large, the desired performance may not be obtained, for example, the low-temperature viscosity becomes too high. Further, at the end of the polyorganosiloxane molecule, up to three hydrocarbon groups are attached to the Si atom, and these substituents may be either an alkyl group or an aryl group. Typically, the alkyl group is a methyl group,
Preferably, the aryl group is a phenyl group.

The content of the aryl group must be at least 1% or more, preferably 3% or more. When the content of the aryl group is less than 1%, the characteristics of the aryl group are not exhibited, and the solubility with the dicarboxylic acid ester becomes insufficient. Here, the “content of the aryl group” refers to the ratio of the number of aryl groups to the total number of substituents bonded to Si atoms contained in the polyorganosiloxane structure. / Means the number of all substituents. That is, as this number increases, the ratio of aryl groups increases.

Since the viscosity index of the dicarboxylic acid ester to be mixed is generally about 100 to 180, of the polyorganosiloxanes containing these aryl groups,
In particular, those having a viscosity index of 300 or more are preferably used.

The polyorganosiloxane containing an aryl group is mixed with a dicarboxylic acid ester in an amount of 10 to 80%. As the dicarboxylic acid ester, an ester composed of a monohydric alcohol having 8 to 18 carbon atoms and a dicarboxylic acid having 6 to 15 carbon atoms is preferably used. Dicarboxylic esters other than those described above are not suitable because they are inferior in volatility, low-temperature fluidity, viscosity index and solubility. Specific examples include sebacic acid ester, adipic acid ester, azelaic acid ester and the like. In particular, di-2-ethylhexyl adipate, di-isononyl adipate, di-2-ethylhexyl sebacate, di-2 azelate
-Ethylhexyl and the like are preferred.

The mixing ratio of the dicarboxylic acid ester is set to be 10 to 80% based on the total amount of the lubricating oil. If it is less than 10%, although it has a high viscosity index, sufficient lubricity and solubility of additives cannot be expected. On the other hand, if it exceeds 80%, the viscosity index becomes 200 or less, which is not preferable for the original purpose.

The base material in which a dicarboxylic acid ester is blended with the above-mentioned polyorganosiloxane containing an aryl group includes:
Various additives may be added as an antiwear agent and / or an antioxidant.

For example, as an antiwear agent, sulfur-based,
Phosphorus, an additive such as zinc dialkyldithiophosphate can be added, preferably, dibenzyl sulfide, sulfurized oil and fat, phosphate ester, thiophosphate ester,
Examples thereof include phosphate amine salts and zinc dialkyldithiophosphates.

Examples of the antioxidant include phenolic antioxidants (such as di-t-butylparacresol and bisphenol), amines (such as diphenylamine and phenyl α-naphthylamine), and phosphorous (such as phosphite).
And the like.

The lubricating oil composition of the present invention described above is characterized by a very high viscosity index of 250 or more, so that it can be used in a wide temperature range. In addition, it has excellent lubricity and low-temperature fluidity. In addition, additives such as anti-wear agents and anti-oxidants dissolve, and by adding these various additives, properties such as lubricity and oxidation stability can be further enhanced. It is. In addition, unlike a high-viscosity index base oil in which a dicarboxylic acid ester is blended with a polyorganosiloxane containing an aryl group, a high-viscosity index base oil in which a high-molecular polymer that is a viscosity index improver is blended, the viscosity and viscosity index decrease due to shearing. rare. Therefore, it is stable against the shearing of each sliding portion in actual use, and has a small change over time in viscosity and viscosity index, and can exhibit stable performance for a long period of time.

[0019]

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

1. Base oil The following polyorganosiloxane and ester were blended as a base oil. (Polyorganosiloxane) A1: Methylphenylpolysiloxane Phenyl group content 5% Viscosity index: 391 Kinematic viscosity (40 ° C.): 71 mm ² / s Kinematic viscosity (100 ° C.): 27 mm ² / s Was prepared. A2: Dimethylpolysiloxane Viscosity index: 423 Kinematic viscosity (40 ° C.) 75 mm ² / s Kinematic viscosity (100 ° C.) 31 mm ² / s (ester) B1: Di-2-ethylhexyl sebacate B2: Di-2-ethylhexyl adipate B3: di-isononyl adipate B4: di-tridecyl adipate B5: di-2-ethylhexyl azelate Also, as a comparative example for shear stability test, PMA polymer (molecular weight 20) was added to mineral oil (viscosity index 75) as a comparative example. 10,000).
A mixture containing 5% was prepared.

2. Additive (Anti-wear agent) Phosphorus-based tricresyl phosphate was prepared as an anti-wear agent. (Antioxidant) The following compounds were prepared as antioxidants. Antioxidant 1: di-t-butyl paracresol Antioxidant 2: dialkyldiphenylamine

3. Test Method The lubricating oil compositions of the above Examples and Comparative Examples were tested for dissolution stability, lubricity, oxidation stability, and shear stability.

(Solution stability) The solubility of the polyorganosiloxane and the fatty acid ester was evaluated by the following procedure. The polyorganosiloxane and the fatty acid ester were weighed and mixed at room temperature with stirring. The mixture was transferred to a test tube, and left still in a -30 ° C low-temperature bath for one day. The solubility was visually observed immediately after stirring at room temperature and at low temperature to determine whether or not uniform dissolution had occurred, and whether or not there was any separation between two layers or turbidity.

(Pour point) The low temperature fluidity is determined by the pour point (JIS
K2269).

(Lubricity) As a desk lubrication test, a shell 4-ball wear resistance test (ASTM D4172) was performed.
The test conditions were 1200 rpm, 40 kgf / cm ² , 8
The temperature was set to 0 ° C. for 30 minutes, and the wear scar diameter after the test was measured.

(Oxidation stability) Oxidation stability was measured using a rotating cylinder type oxidation stability (RBOT, JIS K2514).

(Shear stability) Shear stability was measured in accordance with JPI-5.
The evaluation was made based on the change in viscosity (40 ° C.) by the S-29 ultrasonic method (10 Kc, 40 ° C., 60 min).

4. Test Results Tables 1 to 4 show the composition and test results of each sample.

[0029]

[Table 1]

Table 1 shows viscosity characteristics, pour points, solubility, lubricity, and RBOT values when the mixing ratio of methylphenylpolysiloxane and di-2-ethylhexyl sebacate was changed. 10% to 80% of di-2-ethylhexyl sebacate
Has a viscosity index of 250 or more, and is excellent in solubility, low-temperature fluidity, and lubricity.

[0031]

[Table 2]

Table 2 shows the viscosity characteristics, pour points, solubility, lubricity, and RBOT values when various dicarboxylic esters are mixed in equal amounts to methylphenylpolysiloxane. Sebacic acid-di-2 against methylphenylpolysiloxane
Similarly to ethylhexyl, dicarboxylic acid esters such as di-2-ethylhexyl adipate, di-isononyl adipate, di-tridecyl adipate, and di-2-ethylhexyl azelate can be suitably used. In addition, by adding an anti-wear agent and an anti-oxidant, lubricity and
Oxidation stability can be improved.

[0033]

[Table 3]

Table 3 shows a comparative example. In the case of 100% methylphenylpolysiloxane, although the viscosity index was high, seizure occurred in the lubrication test. The miscibility of dicarboxylic acid esters with dimethylpolysiloxane as a polyorganosiloxane was studied. When dimethylpolysiloxane is mixed with an equal amount of di-2-ethylhexyl sebacate,
Although dissolved uniformly at room temperature, two layers were separated at low temperature. When dimethylpolysiloxane was mixed with di-isononyl adipate, it was not uniformly dissolved even at room temperature.

[0035]

[Table 4]

Table 4 shows the results of shear stability. A test oil obtained by adding an antiwear agent and an antioxidant to a mixed base oil of methylphenylpolysiloxane and di-2-ethylhexyl sebacate, and a test oil obtained by blending PMA polymer as a viscosity index improver with mineral oil, The shear stability was compared. The test oil composed of methylphenylpolysiloxane and di-2-ethylhexyl sebacate did not change in viscosity even by shearing, and maintained a high viscosity index. On the other hand, in the test oil in which the PMA polymer was blended with the mineral oil, a decrease in viscosity and a decrease in viscosity index were observed.

[0037]

The lubricating oil composition of the present invention has a high viscosity index, is excellent in lubricity, and has a viscosity change due to shearing.
The change in the viscosity index is small, and the lubricating property and the oxidative stability can be further improved by compounding the additive. The lubricant is expected to be applicable to various uses as a lubricant usable in a wide temperature range.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) C10N 30:06 C10N 30:06 30:08 30:08 30:10 30:10 F term (reference) 4H104 BB05C BB33A BE07C BG04C BG12C BH03C BH05C BH06C BH07C CJ06A EA02A EB08 EB09 FA02 LA01 LA03 LA04 LA05

Claims (3)

[Claims] 1. A polyorganosiloxane containing an aryl group is represented by a general formula R—O—CO— (CH ₂ ) _n —OC—O—R ′ (R and R ′ each represent an alkyl group having 8 to 18 carbon atoms. , R and R ′ may be the same or different, and n is an integer of 4 to 13), wherein 10 to 80% of a dicarboxylic acid ester represented by the formula (I) is blended. 2. The lubricating oil composition according to claim 1, further comprising an antiwear agent and / or an antioxidant. 3. The lubricating oil composition according to claim 1, having a viscosity index of 250 or more.