Lubricating oil composition for shock absorber

Abstract

The lubricating oil composition for a shock absorber of the present invention contains (A) a base oil composed of a mineral oil and/or a synthetic oil, (B) a tertiary amine represented by the following general formula (I), and (C) a zinc dithiophosphate represented by the following general formula (II): ##STR00001## wherein R.sup.1 and R.sup.2 each independently represent an aliphatic hydrocarbon group having from 1 to 5 carbon atoms, and R.sup.3 represents an aliphatic hydrocarbon group having from 12 to 24 carbon atoms in the general formula (I), ##STR00002## wherein R.sup.4 to R.sup.7 each independently represent one selected from an alkyl group and an alkenyl group each having 1 to 24 carbon atoms in the general formula (II).

Claims

1. A lubricating oil composition for a shock absorber, comprising (A) a base oil composed of a mineral oil and/or a synthetic oil, (B) from 0.01 to 3% by mass of a tertiary amine represented by the following general formula (I), (C) from 0.01 to 3% by mass of a zinc dithiophosphate represented by the following general formula (II): ##STR00009## wherein R.sup.1 and R.sup.2 each independently represent an aliphatic hydrocarbon group having from 1 to 5 carbon atoms, and R.sup.3 represents is a linear, branched or cyclic alkyl group having from 16 to 20 carbon atoms in the general formula (I), ##STR00010## wherein R.sup.4 to R.sup.7 each independently represent one selected from a linear, branched or cyclic alkyl group having from 6 to 10 carbon atoms in the general formula (II), (D) from 0.001 to 0.1% by mass of a polydimethylsiloxane foaming agent having a kinematic viscosity at 20° C. of from 0.5 to 15 mm.sup.2/s, and (E) from 0.0001 to 0.01% by mass of a fluorinated polysiloxane anti-foaming agent having a kinematic viscosity at 20° C. of from 200 to 2,000 mm.sup.2/s.

2. The lubricating oil composition for a shock absorber according to claim 1, wherein R.sup.3 in the general formula (I) is a stearyl group.

3. The lubricating oil composition for a shock absorber according to claim 1, which is a lubricating oil composition for a shock absorber for cars.

4. The lubricating oil composition for a shock absorber according to claim 1, wherein R.sup.1 and R.sup.2 in the general formula (I) each have 1 or 2 carbon atoms.

5. The lubricating oil composition for a shock absorber according to claim 1, wherein R.sup.1 and R.sup.2 each have one or two carbon atoms, and R.sup.3 is a stearyl group in general formula (I).

6. The lubricating oil composition for a shock absorber according to claim 1, wherein the lubricating oil composition does not contain stearic acid.

7. The lubricating oil composition for a shock absorber according to claim 1, wherein the lubricating oil composition does not contain a non-fluorinated silicon antifoaming agent.

8. The lubricating oil composition for a shock absorber according to claim 1, having a friction coefficient μ to bronze of from 0.072 to 0.075.

9. The lubricating oil composition for a shock absorber according to claim 1, having a worn area in a bronze wear test of from 0.028 to 0.030 mm.sup.2.

10. A shock absorber comprising the lubricating oil composition of claim 1.

Description

EXAMPLES

(1) Next, the present invention is described in more detail by Examples, but the present invention is not whatsoever restricted by these Examples.

(2) Evaluations of physical properties in the present invention were carried out according to the following methods.

(3) [Evaluation Methods]

(4) 1. Kinematic Viscosity

(5) Measured according to JIS K2283.

(6) 2. Friction Coefficient μ to Bronze

(7) Using a Bowden type reciprocating friction tester, the friction coefficient μ to bronze was measured under the following test conditions.

(8) Test Conditions

(9) Temperature: 80° C.

(10) Load: 0.5 kgf

(11) Rate: 0.2 mm/s

(12) Amplitude: 10 mm

(13) Test piece: phosphor-bronze ball (ball having a diameter 12.7 mm)/chromium-plated plate (50×1,000×5 mm)

(14) 3. Worn Area

(15) Using a Bowden type reciprocating friction tester, the worn area of bronze was measured according to a bronze wear test under the following test conditions.

(16) Test Conditions

(17) Temperature: 80° C.

(18) Load: 0.5 kgf

(19) Rate: 5 mm/s

(20) Amplitude: 10 mm

(21) Test piece: phosphor-bronze ball (ball having a diameter of 12.7 mm)/chromium-plated plate (50×1,000×5 mm)

(22) Test time: 30 minutes

(23) Measurement of the above friction coefficient μ and worn area was performed, after a few drops of a sample oil were put onto the plate and running-in operation (at a rate of 20 mm/s for 2 minutes) was performed.

(24) 4. Amplitude in Bronze Wear Test

(25) In the above bronze wear test, the amplitude of the friction coefficient at the center position of displacement was measured.

(26) 5. Solubility

(27) Various additives were added to the base oil at 60° C., and mixed to prepare a lubricating oil composition for a shock absorber. This was statically left at room temperature (23° C.) for 24 hours, and the appearance thereof was observed.

(28) 6. Foaming Characteristics Evaluation Test

(29) Each lubricating oil composition for a shock absorber was stirred by jetting for 5 minutes, and then the foaming amount immediately after stopping the stirring was referred to as initial foaming. The time taken until the disappearance of the foams was referred to as a defoaming time. The foaming characteristics were evaluated at 20° C. and 100° C.

Examples 1 and 2 and Comparative Examples 1 to 4

(30) Lubricating oil compositions for a shock absorber of Examples 1 and 2 and Comparative Examples 1 to 4 as shown in Table 1 were prepared, and evaluated for the friction coefficient μ to bronze, the worn area and the solubility.

(31) TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Comparative Example 1 Example 2 Example 1 Example 2 Example 3 Example 4 Lubricating (A) Base Oil 1 93.589 93.589 93.599 93.599 94.099 94.099 Oil (B) Tertiary Amine 1 0.500 — — — — — Composition (B) Tertiary Amine 2 — 0.500 — — — — Stearic Acid — — 0.500 — — — Isostearic Acid — — — 0.500 — — Dioleyl Acid Phosphate — — — — 0.800 — Distearyl Acid Phosphate — — — — — 0.800 (C) Zinc Dithiophosphate 0.800 0.800 0.800 0.800 — — (D) Silicone Foaming Agent 0.010 0.010 — — — — (E) Fluorinated Silicone 0.001 0.001 — — — — Antifoaming Agent Silicone Antifoaming Agent — — 0.001 0.001 0.001 0.001 Viscosity Index Improver 1.400 1.400 1.400 1.400 1.400 1.400 Sulfur-Based Seal Sweller 0.400 0.400 0.400 0.400 0.400 0.400 Pentaerythritol Dioleate 3.000 3.000 3.000 3.000 3.000 3.000 (friction regulator) Monooleyl Glyceride 0.300 0.300 0.300 0.300 0.300 0.300 (friction regulator) Evaluation 40° C. Kinematic Viscosity 12.1 12.1 12.3 12.3 12.0 12.3 Results of Composition Friction Coefficient μ 0.072 0.075 0.054 0.280 0.140 0.240 to Bronze Worn Area (mm.sup.2) 0.028 0.030 0.072 0.198 0.040 0.181 in Bronze Wear Test Amplitude in Bronze 0.001 0.001 0.001 0.001 0.005 0.008 Wear Test Solubility in Mineral Oil transparent transparent cloudy transparent transparent transparent

(32) Mineral oil and additives in Tables 1 and 2 are as follows. Base oil 1: paraffinic mineral oil, 40° C. kinematic viscosity: 9.067 mm.sup.2/s, viscosity index: 109, density (15° C.): 0.828 g/mm.sup.3. Tertiary amine 1: dimethylstearylamine. Tertiary amine 2: diethylstearylamine. Zinc dithiophosphate: zinc 2-ethylhexyldithiophosphate of the general formula (II) where R.sup.4 to R.sup.7 are all 2-ethylhexyl. Silicone foaming agent: polydimethylsiloxane having a 20° C. kinematic viscosity of 5 mm.sup.2/s. Fluorinated silicone antifoaming agent: fluorinated polysiloxane having a 20° C. kinematic viscosity of 1,000 mm.sup.2/s. Silicone antifoaming agent: polydimethylsiloxane having a 20° C. kinematic viscosity of 12500 mm.sup.2/s. Viscosity index improver: polymethacrylate compound.

Examples 1 to 6

(33) Next, as shown in Table 2, lubricating oil compositions for a shock absorber of Examples 3 to 6 were prepared in addition to Examples 1 and 2, and evaluated for the solubility and the foaming characteristics thereof.

(34) TABLE-US-00002 TABLE 2 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Formulation (A) Base Oil 1 93.589 93.589 93.600 93.599 93.599 93.590 (B) Tertiary Amine 1 0.500 — 0.500 0.500 0.500 0.500 (B) Tertiary Amine 2 — 0.500 — — — — (C) Zinc Dithiophosphate 0.800 0.800 0.800 0.800 0.800 0.800 (D) Silicone Foaming Agent 0.010 0.010 — — — 0.010 (E) Fluorinated Silicone 0.001 0.001 — — 0.001 — Antifoaming Agent Silicone Antifoaming Agent — — — 0.001 — — Viscosity Index Improver 1.400 1.400 1.400 1.400 1.400 1.400 Sulfur-Based Seal Sweller 0.400 0.400 0.400 0.400 0.400 0.400 Pentaerythritol Dioleate 3.000 3.000 3.000 3.000 3.000 3.000 (friction regulator) Monooleyl Glyceride (friction regulator) 0.300 0.300 0.300 0.300 0.300 0.300 Evaluation 40° C. Kinematic Viscosity 12.1 12.1 12.1 12.1 11.9 11.7 Results of Composition Solubility in Mineral Oil transparent transparent transparent transparent transparent transparent Foaming Characteristics Initial Foaming 120 125 250 62 61 221 (20° C.) Amount (ml) Defoaming 125 128 52 232 26 121 Time (sec) Foaming Characteristics Initial Foaming 121 122 211 262 21 312 (100° C.) Amount (ml) Defoaming 21 23 31 52 12 80 Time (sec)

(35) As obvious from the results of Examples 1 and 2 in Table 1, by blending the tertiary amine (B) and the zinc dithiophosphate (C) in the base oil, the friction coefficient to bronze was lowered and the worn area was reduced, and therefore, the wear-resistant properties were bettered, and in addition, the solubility of various additives in mineral oil was good. On the other hand, when stearic acid was used in place of the tertiary amine (B), the friction coefficient was lowered, but the worn area was increased and thus the wear-resistant properties could not be bettered. Further, the solubility of the additives in the base oil was not sufficient. In addition, in Comparative Example 2 where isostearic acid was used in place of the tertiary amine (B), the wear-resistant properties could not be bettered and the friction coefficient μ could not be reduced sufficiently. Further, also in Comparative Examples 3 and 4 using a phosphate in place of the tertiary amine (B) and the zinc dithiophosphate (C), neither the friction coefficient nor the worn area could be lowered.

(36) As obvious from the results of Examples 1 and 2 in Table 2, by blending the silicone foaming agent (D) and the silicone antifoaming agent (E), the initial foaming amount at each of 20° C. and 100° C. was controlled to fall within a range of from 100 to 150 ml, and further the defoaming time at each of 20° C. and 100° C. was controlled to be from 100 to 150 seconds, and shorter than 50 seconds, respectively. Thus, the oil compositions had good foaming characteristics. Consequently, it can be understood that the lubricating oil compositions for a shock absorber of Examples 1 and 2 can further better the riding comfort performance by foaming.

INDUSTRIAL APPLICABILITY

(37) The lubricating oil composition for a shock absorber of the present invention can be used in various shock absorbers, and for example, can be favorably used in both a multi-cylinder shock absorber and a single-cylinder shock absorber, and in addition, can be used in shock absorbers for both cars and motorcycles. Especially preferred is use for cars.