JP2009013380A - Lubricating oil composition for shock absorbers - Google Patents

Abstract

[PROBLEMS] To increase the frictional force of a sliding part such as a piston rod and an oil seal or a piston band and a cylinder in a shock absorber without deteriorating corrosion resistance and sludge resistance while maintaining good wear resistance. Provided is a lubricating oil composition for a shock absorber that is compatible with handling stability and riding comfort at a high level.
A base oil composed of mineral oil and / or synthetic oil, (A) 0.3 to 2% by mass of zinc dialkyldithiophosphate having 7 to 12 carbon atoms in the alkyl group, and (B) fatty acid amides 0.05. The content of the ester having -COO- bond in the base oil is 0.6 as -COO-, and -2 mass% and (C) 0.1-1 mass% of the monocyclic phenol-based antioxidant. It is a lubricating oil composition for shock absorbers with a mass% or less.
[Selection figure] None

Description

  The present invention relates to a lubricating oil composition for shock absorbers. More specifically, the present invention maintains the frictional force of the sliding portion of the shock absorber (shock absorber) such as the piston rod and the oil seal, the piston band and the cylinder, etc. while maintaining good wear resistance, Lubricant composition for shock absorbers mainly used for four wheels (hereinafter referred to as shock absorber oil), which enhances sludge resistance without impairing, and achieves a high level of handling stability and ride comfort. Is).

  Lubricants for automobile shock absorbers are mainly used for the purpose of suppressing vibrations in order to exhibit an optimum damping force for a vehicle and maintain steering stability. In particular, recently, the highway network has been completed, and the rate of high-speed travel has increased compared to the past. Therefore, there is an increasing demand for vehicles that exhibit high-speed running stability and excellent performance in avoiding danger. However, in current vehicles in Japan, unstable rolling occurs when the steering wheel is turned to change the lane at a speed of 100 to 200 km / h, and the stability of the vehicle body is deteriorated or danger is avoided. The problem is that the necessary avoidance distance is long.

As a result of research, it has been clarified that this cause is related to the magnitude of the frictional force in the sliding portion such as the oil seal and the piston rod, piston band and cylinder when the amplitude is very small in the shock absorber. In high-speed running, vibrations are transferred to tires, springs, shock absorbers, and vehicle bodies, resulting in slight vibrations. This vibration usually has a stroke length of about 0.4 to 2.0 mm and a repetition rate of about 1.5 to 15.0 Hz. Such a condition is a condition in which the damping force of the shock absorber is unlikely to be generated, so that the vibration damping action is not sufficiently exhibited. As a result, if the frictional force at the beginning of sliding of the sliding portion such as the oil seal and the piston rod or the piston band and the cylinder is small, the posture of the vehicle body easily deteriorates the tilt stability.
Therefore, in order to solve such a problem, it is conceivable that the frictional force of the sliding portion such as the oil seal of the shock absorber lubricating oil, the piston rod, the piston band, and the cylinder may be increased.

In Patent Document 1, as a lubricating oil composition for automobile shock absorbers, based on the total weight of the composition, (A) an amine salt of acidic phosphoric acid monoester 0.05 to 0.3% by weight based on the total weight of the lubricating oil, What blended 0.1-0.6 weight% of (B) polyalkenyl succinimide and 0.3-0.8 weight% of (C) acidic phosphorous acid diester is disclosed.
However, in a lubricating oil composition using such a phosphorus-based additive, the corrosion resistance (particularly when mixed with water) has a Zn-based additive such as zinc dialkyldithiophosphate (hereinafter sometimes abbreviated as ZnDTP). There was a problem that it was inferior to the high friction oil using the agent. On the other hand, it is known that the high friction oil using the Zn-based additive is inferior in sludge resistance to the high friction oil using the phosphorus-based additive as described above.

When sludge is generated in the shock absorber, the smooth reciprocating motion is hindered due to the clogging of the valve portion and the sticking to the seal portion. Also, many metal parts such as iron (tubes and valves) and copper (guide bushes) are used for the shock absorber, and a large amount of water may be mixed into the shock absorber when traveling on the road when the snow melts. Shock absorber oil is required to have sludge resistance and corrosion resistance.
On the other hand, based on the total amount of the composition with respect to a base oil of 5% C _A or less, (A) 0.01 to 5% by weight of an amine antioxidant, and (B) 0.01 to 5% by weight of a phenolic antioxidant. (C) Phosphate ester 0.01 to 5% by weight and (D) Fatty acid amide and / or polyhydric alcohol ester 0.001 to 5% by weight of hydraulic fluid composition (Patent Document 2) A lubricating composition comprising a base oil, (A) at least one selected from a phenolic antioxidant and an amine antioxidant, and (B) an ester compound having a disulfide structure (see Patent Document 3) In addition, a hydraulic fluid composition for a shock absorber (see Patent Document 4) is disclosed in which a base oil contains a specific nitrogen-containing compound and a specific phosphate ester, all of which contain ZnDTP. Does not contain.

JP 2003-147379 A Japanese Patent Laid-Open No. 9-111277 JP 2007-63431 A JP 2002-194376 A

  Under such circumstances, the present invention maintains good wear resistance as well as anti-corrosion characteristics and resistance to friction between the piston rod and the oil seal, the piston band and the cylinder sliding portion of the shock absorber. The purpose of the present invention is to provide a lubricating oil composition for shock absorbers mainly used for four-wheel vehicles, which enhances sludge characteristics without impairing, and achieves a high level of handling stability and riding comfort. .

As a result of intensive research to develop a lubricating oil composition for a shock absorber having the above preferred properties, the present inventor has, as a base oil, a mineral oil having a content of an ester compound having a —COO— bond of a certain value or less. A lubricating oil composition using a synthetic oil and containing ZnDTP having a specific number of carbon atoms in an alkyl group, a fatty acid amide, and a monocyclic phenol-based antioxidant in a predetermined ratio is provided for that purpose. It was found that it can be adapted. The present invention has been completed based on such findings.
That is, the present invention
(1) Base oil composed of mineral oil and / or synthetic oil, (A) 0.3 to 2% by mass of zinc dialkyldithiophosphate having 7 to 12 carbon atoms in the alkyl group, (B) fatty acid amides 0.05 to 2% by mass and (C) 0.1 to 1% by mass of a monocyclic phenolic antioxidant, and the content of the ester having —COO— bonds in the base oil is 0.6 mass as —COO—. %, A lubricating oil composition for shock absorbers,
(2) The lubricating oil composition for a shock absorber according to the above (1), wherein the base oil is mineral oil,
(3) The above (1), wherein the base oil is a hydrocarbon-based synthetic oil and / or an ether-based synthetic oil
Is a lubricating oil composition for shock absorbers according to (2),
(4) The lubricating oil composition for a shock absorber according to (3), wherein the base oil is a hydrocarbon-based synthetic oil,
(5) The lubricating oil composition for a shock absorber according to any one of the above (1) to (4), wherein the content of the zinc dialkyldithiophosphate as the component (A) is 0.5 to 1.5% by mass,
(6) The lubricating oil composition for a shock absorber according to any one of (1) to (5), wherein the fatty acid amide content of the component (B) is 0.08 to 1% by mass,
(7) The content of the monocyclic phenolic antioxidant as the component (C) is 0.1 to 0.8% by mass.
The lubricant composition for a shock absorber according to any one of the above (1) to (6), and (8) the lubricant for a shock absorber according to any one of the above (1) to (7) used for four wheels. Oil composition,
Is to provide.

  According to the present invention, the frictional force of the sliding portion of the shock absorber, such as the piston rod and the oil seal, the piston band and the cylinder, maintains good wear resistance, and impairs the corrosion resistance and sludge resistance. It is possible to provide a lubricating oil composition for a shock absorber mainly used for four-wheel vehicles, which is improved to a high level and has both high handling stability and riding comfort at a high level.

The shock absorber oil of the present invention is a lubricating oil composition comprising a base oil composed of mineral oil and / or synthetic oil, and (A) ZnDTP, (B) fatty acid amides, and (C) a monocyclic phenolic antioxidant. is there.
[Base oil]
As the base oil in the shock absorber oil of the present invention, a base oil that is a mineral oil and / or a synthetic oil and has a content of an ester having a —COO— bond of 0.6% by mass or less as —COO— is used. . If the ester content exceeds 0.6 mass% as -COO-, the corrosion resistance to metal may be deteriorated when water is mixed in the buffer. The preferable ester content is 0.4% by mass or less as —COO—, and it is more preferable that the ester is not substantially contained.
Examples of the mineral oil of the base oil include paraffin-based mineral oil, intermediate-based mineral oil, and naphthenic-based mineral oil obtained by usual purification methods such as solvent refining and hydrogenation refining.
The synthetic oil is preferably a hydrocarbon synthetic oil or an ether synthetic oil. Examples of the hydrocarbon synthetic oil include polybutene, polyisobutylene, 1-octene oligomer, 1-decene oligomer, and ethylene-propylene copolymer. An α-olefin oligomer such as a coalescence or a hydride thereof, alkylbenzene, alkylnaphthalene, and the like can be given. Examples of the ether-based synthetic oil include polyoxyalkylene glycol and polyphenyl ether.
Of these, mineral oil and hydrocarbon-based synthetic oil are preferred in the present invention.
In the present invention, as the base oil, one kind of the above mineral oil may be used, or two or more kinds may be used in combination, and one kind of the above synthetic oil may be used, or two or more kinds may be used in combination. Good. Further, one or more mineral oils and one or more synthetic oils may be used in combination.
The viscosity of the base oil is preferably in the range of 2.0 to 15.0 mm ² / s at a viscosity of 40 ° C. in the case of a four-wheel shock absorber oil for riding purposes. 0 mm ² / s is more preferable.

[(A) ZnDTP]
In the shock absorber oil of the present invention, as a component (A), ZnDTP having 7 to 12 carbon atoms in an alkyl group is used in order to improve the friction coefficient of the seal and to improve the wear resistance. As the ZnDTP, the following general formula (I)

(In the formula, R ¹ and R ² each independently represent a linear, branched or cyclic alkyl group having 7 to 12 carbon atoms.)
The compound represented by these can be mentioned.
In the general formula (I), specific examples of the alkyl group represented by R ¹ and R ² include a heptyl group, an isoheptyl group, a cyclohexylmethyl group, an octyl group, a 2-ethylhexyl group, an isooctyl group, a cyclooctyl group, Nonyl group, isononyl group, 3,5,5-trimethylhexyl group, cyclooctylmethyl group, decyl group, 3,7-dimethyloctyl group, 2-propylheptyl group, isodecyl group, undecyl group, dodecyl group, 2-butyl An octyl group, an isododecyl group, etc. are mentioned. Among these, those having 7 to 10 carbon atoms are more preferable.
R ¹ and R ² may be the same or different from each other, but are preferably the same from the viewpoint of ease of production.
In the shock absorber oil of the present invention, the content of the component (A) ZnDTP needs to be 0.3 to 2% by mass from the viewpoint of the effect of improving the friction coefficient of the seal and the wear resistance. , Preferably it is 0.5-1.5 mass%.

[(B) Fatty acid amides]
In the shock absorber oil of the present invention, fatty acid amides are used as the component (B). These fatty acid amides have a corrosion prevention effect and an effect of improving sludge resistance.
Examples of the fatty acid amides include linear or branched saturated or unsaturated monocarboxylic acids having 7 to 31 carbon atoms and the following general formula (II):
H ₂ N— (R ³ —NH) _m —H (II)
(In the formula, R ³ represents an alkylene group having 2 to 4 carbon atoms, and m represents an integer of 2 to 6).
What was obtained by making it react with the polyalkylene polyamine represented by these can be used.

(Monocarboxylic acid)
Examples of the monocarboxylic acid having 7 to 31 carbon atoms include heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, Saturated fatty acids such as nonadecanoic acid, icosanoic acid, henicosanoic acid, docosanoic acid, tricosanoic acid, tetracosanoic acid, pentacosanoic acid, hexacosanoic acid, heptacosanoic acid, octacosanoic acid, nonacosanoic acid, triacontanoic acid, etc. Heptenoic acid, octenoic acid, nonenoic acid, decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, pentadecenoic acid, hexadecenoic acid, heptadecenoic acid, octadecenoic acid (including oleic acid), nonadedecenoic acid, Icosenoic acid, f Unsaturated fatty acids such as icosenoic acid, docosenoic acid, tricosenoic acid, tetracosenoic acid, pentacosenoic acid, hexacosenoic acid, heptacosenoic acid, octacosenoic acid, nonacosenoic acid, triacontenoic acid (these unsaturated fatty acids may be linear or branched, In addition, among these, those having 10 to 24 carbon atoms are preferable, and specifically, lauric acid, myristic acid, palmitic acid, stearic acid, isostearin Examples include acids and oleic acid.
(Polyalkylene polyamine)
Examples of the polyalkylene polyamine represented by the general formula (II) to be reacted with the monocarboxylic acid include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, tetrapropylenepentamine, hexa Examples include butylene heptamine.

The required fatty acid amides can be obtained by reacting the polyalkylene polyamine with the monocarboxylic acid described above at a temperature of about 200 to 220 ° C. for about 2 to 3 hours. In this case, the amount of the monocarboxylic acid used is preferably (m + 1) mol or less with respect to 1 mol of the polyalkylene polyamine.
In the shock absorber oil of the present invention, as the component (B), the fatty acid amides obtained as described above may be used singly or in combination of two or more. Moreover, the content needs to be 0.05-2 mass% from a viewpoint of a corrosion prevention effect and a sludge-proof characteristic improvement effect, and it is preferable that it is 0.08-1 mass%.

[(C) Monocyclic phenolic antioxidant]
In the shock absorber oil of the present invention, a monocyclic phenol-based antioxidant is used as the component (C). This monocyclic phenolic antioxidant exhibits an effect of improving sludge resistance.
Examples of the monocyclic phenol-based antioxidant include 2,6-di-tert-butyl-p-cresol, 2,6-di-tert-butyl-4-ethylphenol, (3-methyl-5-tert- (Butyl-4-hydroxyphenyl) acetic acid n-hexyl, (3-methyl-5-tert-butyl-4-hydroxyphenyl) isohexyl acetate, (3-methyl-5-tert-butyl-4-hydroxyphenyl) acetic acid n- Heptyl, (3-methyl-5-tert-butyl-4-hydroxyphenyl) isoheptyl acetate, (3-methyl-5-tert-butyl-4-hydroxyphenyl) acetate n-octyl, (3-methyl-5-tert -Butyl-4-hydroxyphenyl) isooctyl acetate, (3-methyl-5-tert-butyl-4-hydroxyphenyl) N) 2-ethylhexyl acetate, (3-methyl-5-tert-butyl-4-hydroxyphenyl) acetate n-nonyl, (3-methyl-5-tert-butyl-4-hydroxyphenyl) acetonate isononyl, (3- Methyl-5-tert-butyl-4-hydroxyphenyl) acetate n-decyl, (3-methyl-5-tert-butyl-4-hydroxyphenyl) acetate isodecyl, (3-methyl-5-tert-butyl-4- Hydroxyphenyl) acetate n-undecyl, (3-methyl-5-tert-butyl-4-hydroxyphenyl) isoundecyl acetate, (3-methyl-5-tert-butyl-4-hydroxyphenyl) acetate n-dodecyl, (3 -Methyl-5-tert-butyl-4-hydroxyphenyl) isododecyl acetate, (3-methyl-5 tert-butyl-4-hydroxyphenyl) n-hexyl propionate, (3-methyl-5-tert-butyl-4-hydroxyphenyl) isohexyl propionate, (3-methyl-5-tert-butyl-4-hydroxyphenyl) ) N-heptyl propionate, (3-methyl-5-tert-butyl-4-hydroxyphenyl) isoheptyl propionate, (3-methyl-5-tert-butyl-4-hydroxyphenyl) n-octyl propionate, ( Isooctyl 3-methyl-5-tert-butyl-4-hydroxyphenyl) propionate, 2-ethylhexyl (3-methyl-5-tert-butyl-4-hydroxyphenyl) propionate, (3-methyl-5-tert- Butyl-4-hydroxyphenyl) propionic acid n- Nonyl, isononyl (3-methyl-5-tert-butyl-4-hydroxyphenyl) propionate, n-decyl (3-methyl-5-tert-butyl-4-hydroxyphenyl) propionate, (3-methyl-5 -Tert-butyl-4-hydroxyphenyl) isodecyl propionate, n-undecyl (3-methyl-5-tert-butyl-4-hydroxyphenyl) propionate, (3-methyl-5-tert-butyl-4-hydroxy) Phenyl) isoundecyl propionate, (3-methyl-5-tert-butyl-4-hydroxyphenyl) n-dodecyl propionate, (3-methyl-5-tert-butyl-4-hydroxyphenyl) isododecyl propionate, (3 , 5-Di-tert-butyl-4-hydroxyphenyl) vinegar n-hexyl, (3,5-di-tert-butyl-4-hydroxyphenyl) isohexyl acetate, (3,5-di-tert-butyl-4-hydroxyphenyl) acetate n-heptyl, (3,5-di- -Tert-butyl-4-hydroxyphenyl) isoheptyl acetate, (3,5-di-tert-butyl-4-hydroxyphenyl) acetate n-octyl, (3,5-di-tert-butyl-4-hydroxyphenyl) Isooctyl acetate, (3,5-di-tert-butyl-4-hydroxyphenyl) acetic acid 2-ethylhexyl, (3,5-di-tert-butyl-4-hydroxyphenyl) acetic acid n-nonyl, (3,5- Di-tert-butyl-4-hydroxyphenyl) isononyl acetate, (3,5-di-tert-butyl-4-hydroxyphenyl) N-decyl acid, (3,5-di-tert-butyl-4-hydroxyphenyl) isodecyl acetate, (3,5-di-tert-butyl-4-hydroxyphenyl) acetate n-undecyl, (3,5- Di-tert-butyl-4-hydroxyphenyl) isoundecyl acetate, (3,5-di-tert-butyl-4-hydroxyphenyl) acetate n-dodecyl, (3,5-di-tert-butyl-4-hydroxyphenyl) ) Isododecyl acetate, n-hexyl (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, isohexyl (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, (3,5 -Di-tert-butyl-4-hydroxyphenyl) n-heptyl propionate, (3,5-di-tert-butyl-4 -Hydroxyphenyl) isoheptyl propionate, (3,5-di-tert-butyl-4-hydroxyphenyl) n-octyl propionate, (3,5-di-tert-butyl-4-hydroxyphenyl) isooctyl propionate, 2-ethylhexyl (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, n-nonyl (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, (3,5-di -Tert-butyl-4-hydroxyphenyl) isononyl propionate, (3,5-di-tert-butyl-4-hydroxyphenyl) n-decyl propionate, (3,5-di-tert-butyl-4-hydroxy) Phenyl) isodecyl propionate, (3,5-di-tert-butyl-4-hydroxy) Nenyl) propionate n-undecyl, (3,5-di-tert-butyl-4-hydroxyphenyl) isoundecyl propionate, (3,5-di-tert-butyl-4-hydroxyphenyl) propionate n-dodecyl, And (3,5-di-tert-butyl-4-hydroxyphenyl) isododecyl propionate. These may be used individually by 1 type, and may be used in combination of 2 or more types.

The monocyclic phenol-based antioxidant is superior in sludge resistance effect as compared with the polycyclic phenol-based antioxidant, and 2,6-di-tert-butyl is preferable as the monocyclic phenol-based antioxidant. -P-cresol and 2,6-di-tert-butyl-4-ethylphenol, and particularly from the viewpoint of effect and availability, 2,6-di-tert-butyl-p-cresol is Is preferred.
In the shock absorber oil of the present invention, the content of the monocyclic phenolic antioxidant of the component (C) needs to be in the range of 0.1 to 1% by mass from the viewpoint of the sludge resistance effect. The range is preferably from 0.1 to 0.8% by mass.

[Optional components]
In the shock absorber oil of the present invention, as optional additional components, other ashless detergent dispersants, metal detergents, other lubricity improvers, other antioxidants, rust inhibitors, metal deactivators, viscosity At least one selected from an index improver, a pour point depressant and an antifoaming agent can be appropriately contained as long as the object of the present invention is not impaired.
Examples of the ashless detergent dispersant include succinimides, boron-containing succinimides, benzylamines, boron-containing benzylamines, and divalent carboxylic acid amides represented by succinic acid. Examples of metal detergents include neutral metal sulfonates, neutral metal phenates, neutral metal salicylates, neutral metal phosphonates, basic sulfonates, basic phenates, basic salicylates, overbased sulfonates, and overbased salicylates. And overbased phosphonates.

Examples of other lubricity improvers include extreme pressure agents, antiwear agents, and oiliness agents. For example, phosphoric acid esters, amine salts of acidic phosphoric acid monoesters, phosphorus ester compounds such as acidic phosphorous acid diesters, Organometallic compounds such as zinc dithiocarbamate (ZnDTC), sulfurized oxymolybdenum organophosphorodithioate (MoDTP), and sulfurized oxymolybdenum dithiocarbamate (MoDTC) can be mentioned.
In addition, sulfur-based extreme pressure agents such as sulfurized fats and oils, sulfurized fatty acids, sulfurized esters, sulfurized olefins, dihydrocarbyl polysulfides, thiadiazole compounds, alkylthiocarbamoyl compounds, triazine compounds, thioterpene compounds, and dialkylthiodipropionate compounds are exemplified.
Further, aliphatic saturated and unsaturated monocarboxylic acids such as stearic acid and oleic acid, polymerized fatty acids such as dimer acid and hydrogenated dimer acid, hydroxy fatty acids such as ricinoleic acid and 12-hydroxystearic acid, lauryl alcohol and oleyl alcohol Oily agents such as aliphatic saturated and unsaturated monoalcohols, aliphatic saturated and unsaturated monoamines such as stearylamine and oleylamine, aliphatic saturated and unsaturated monocarboxylic amides such as lauric acid amide and oleic acid amide .

  Examples of other antioxidants include polycyclic phenols such as 4,4′-methylenebis (2,6-di-tert-butylphenol) and 2,2′-methylenebis (4-ethyl-6-tert-butylphenol). Antioxidants; monoalkyldiphenylamine compounds such as monooctyldiphenylamine and monononyldiphenylamine, 4,4′-dibutyldiphenylamine, 4,4′-dipentyldiphenylamine, 4,4′-dihexyldiphenylamine, 4,4′-di Dialkyldiphenylamine compounds such as heptyldiphenylamine, 4,4'-dioctyldiphenylamine, 4,4'-dinonyldiphenylamine, tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, tetranonyl Polyalkyldiphenylamine compounds such as phenylamine, α-naphthylamine, phenyl-α-naphthylamine, butylphenyl-α-naphthylamine, pentylphenyl-α-naphthylamine, hexylphenyl-α-naphthylamine, heptylphenyl-α-naphthylamine, octylphenyl Amine-based antioxidants such as naphthylamine compounds such as -α-naphthylamine and nonylphenyl-α-naphthylamine; 2,6-di-tert-butyl-4- (4,6-bis (octylthio) -1,3 Sulfur acids such as 5-triazin-2-ylamino) phenol, thioterpene compounds such as a reaction product of phosphorus pentasulfide and pinene, dialkylthiodipropionates such as dilauryl thiodipropionate and distearyl thiodipropionate Inhibitor; and the like.

Examples of the rust inhibitor include metal sulfonates and succinates, and examples of the metal deactivator include benzotriazole and thiadiazole.
As the viscosity index improver, for example, polymethacrylate, dispersed polymethacrylate, olefin copolymer (for example, ethylene-propylene copolymer), dispersed olefin copolymer, styrene copolymer (for example, Styrene-diene hydrogenated copolymer, etc.).
As the pour point depressant, polymethacrylate having a weight average molecular weight of about 50,000 to 150,000 can be used.
As the antifoaming agent, a high molecular silicone antifoaming agent is preferable, and by including this high molecular silicone antifoaming agent, the antifoaming property is effectively exhibited and the riding comfort is improved.
Examples of the polymer silicone antifoaming agent include organopolysiloxane, and fluorine-containing organopolysiloxane such as trifluoropropylmethyl silicone oil is particularly suitable.

The shock absorber oil of the present invention uses, as a base oil, a mineral oil and / or a synthetic oil in which the content of an ester having a —COO— bond is defined, and ZnDTP having a specific number of carbon atoms in the alkyl group and fatty acid amides And a monocyclic phenol-based antioxidant at a predetermined ratio, the frictional force of the piston rod and the oil seal, the piston band and the cylinder sliding portion of the shock absorber, the corrosion resistance and The sludge resistance can be improved without impairing the sludge, and good wear resistance can be maintained, and the handling stability and ride comfort can be achieved at a high level.
The shock absorber oil of the present invention can be used for both a double-cylinder shock absorber and a single-cylinder shock absorber, and can be used for either a four-wheel or a two-wheel shock absorber. It is preferably used as an application.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
In addition, the measurement of a friction coefficient, the immersion test of iron and copper, and the oxidation stability test were implemented by the method shown below.
(1) Measurement of rubber friction coefficient Test machine: Bounden reciprocating friction tester Test conditions Load: 9.8N
Stroke: 10mm
Speed: 3.3mm / s
Temperature: 60 ° C
Number of friction: 30
Friction material: upper rubber (A727),
Lower chrome plated plate (50x1000x5mm)
The rubber was tested by cutting a rubber plate into a circle with a diameter of 15 mm, extruding it with a 12.7 mm ball, and dropping a few drops of sample oil on the plate.
(2) Immersion test of iron and copper at the time of mixing with water 100 mL of sample oil and 2 mL of distilled water were placed in a 500 mL glass bottle, and the mixture was stirred with a homogenizer at 2000 rpm for 1 minute. Next, a copper piece (pure copper plate for copper plate corrosion test) and an iron piece (bearing race: WS1730) were put into this, covered with aluminum foil, and allowed to stand in a constant temperature bath at 100 ° C. for 48 hours.
The copper piece and iron piece after the test were observed, and the mass loss of the copper piece was measured. The discoloration of the copper piece was determined based on JIS 2513. The criterion is (no discoloration) 1a>1b...> 4c (large discoloration).
Then, it left still at room temperature for 20 hours, and the presence or absence of sludge was confirmed before and after hexane washing | cleaning. In addition, hexane washing | cleaning was performed by putting 50 mL of hexane in a 500 mL glass bottle, removing lightly, and stirring hexane.
(3) Oxidation stability test The oxidation stability test was performed based on the CEC L-48-A-00 / B method.
Air was blown into a test oil amount of 100 mL at 160 ° C. for 96 hours at 5.0 L / h, and the presence or absence of deposits on the wall surface of the glass container was observed, and n-pentane insoluble matter (Method A) was measured.

Examples 1 to 3 and Comparative Examples 1 to 11
A lubricating oil composition (shock absorber oil) containing each component shown in Table 1 was prepared, and a coefficient of friction measurement, an iron and copper immersion test, and an oxidation stability test were performed. The results are shown in Table 1.

[note]
1) Base oil A: mineral oil 35N
2) Base oil B: Mineral oil 40N
3) Base oil C: Mineral oil 60N
4) Base oil D: Dioleyl ester of pentaerythritol, —COO— content in the molecule = 13% by mass
5) ZnDTP-A: “OLOA5660” manufactured by Chevron Japan, alkyl group = 2-ethylhexyl group, S = 12.6 mass%, P = 6.15 mass%, Zn = 7.62 mass%
6) ZnDTP-B: “OLOA267” manufactured by Chevron Japan, alkyl group = C3-C6 mixed alkyl group, S = 15.03 mass%, P = 7.50 mass%, Zn = 8.50 mass%
7) Antioxidant A: “Sumilyzer BHT” manufactured by Sumitomo Chemical Co., Ltd., 2,6-di-tert-butyl-p-cresol 8) Antioxidant B: “ANTIOXIDANT 702ND” manufactured by Albemarle Asano Co., 4, 4′- Methylene bis (2,6-di-tert-butylphenol)
9) Fatty acid amide A: “OLOA 340D” manufactured by Chevron Japan, isostearic acid and tetraethylenepentamine reaction product, N = 6.20% by mass, total base number = 81.0 mgKOH / g
10) Fatty acid amide B: Isostearic acid and triethylenetetramine reactant 11) Polybutenyl succinimide A: “OLOA 1200N” manufactured by Chevron Japan, Monomer, N = 1.85% by mass, Total base number = 33. 0mgKOH / g
12) Polybutenyl succinimide B: “Hitec 646” manufactured by Ethyl Japan, Mono, N = 1.75% by mass, total base number = 40.0 mgKOH / g
13) Ca Sulfonate: Crompton Corporation Ltd. "Bryton _{C-500", (RC 6 H 4 SO 3} ) 2 Ca
14) Phosphorus extreme pressure agent A: “VANLUBE672” manufactured by Vanderbilt, acidic phosphate ester amine salt (mainly monoethylamine salt and monomethylamine salt), P = 9.5% by mass, N = 4.95% by mass
15) Phosphorus extreme pressure agent B: “JP-218-OR” manufactured by Johoku Chemical Industry Co., Ltd., Dioleyl hydrogen phosphite, P = 5.34% by mass
16) Viscosity index improver A: “Acruve 806T” manufactured by Sanyo Chemical Industries, Ltd. 17) Polymethylmethacrylate having a weight average molecular weight of 61,000 17) Viscosity index improver B: “Acrub 504” manufactured by Sanyo Chemical Industries, Ltd., weight average molecular weight 140,000 polymethyl methacrylate 18) Metal deactivator: “HiTEC 4313” manufactured by Ethyl Japan, 2,5-bis (1,1,3,3-tetramethylbutyldithio) -1,3,4-thiadiazole 19 ) Antifoaming agent: “FL100” manufactured by Shin-Etsu Chemical Co., Ltd., fluorine-containing organopolysiloxane The content of the ester in the base oil in Comparative Example 1 is 0.79% by mass as —COO—.

When comparing Comparative Example 1 and Examples 1 to 3, Comparative Example 1 is 0.79 mass% in which the ester content in the base oil is more than 0.6 mass% as -COO- In the iron / copper immersion test, the copper weight loss rate is larger than in Examples 1 to 3.
When comparing Comparative Example 3 and Examples 1 to 3, Comparative Example 3 uses ZnDTP having 3 to 6 mixed alkyl groups having an alkyl group with less than 7 carbon atoms. In the copper immersion test, the discoloration and weight loss rate of the copper pieces are larger than those in Examples 1-3.
Since Comparative Examples 2 and 4 to 11 do not contain any one or more of ZnDTP, monocyclic phenolic antioxidant and fatty acid amide according to the present invention, rust is generated on the iron piece in the iron / copper immersion test. Or the copper pieces discolor, sludge is generated, or sludge is generated in the oxidation stability test.

The shock absorber oil of the present invention increases the frictional force of the piston rod and oil seal or the sliding part of the piston band and cylinder, etc. in the shock absorber without impairing the corrosion resistance and sludge resistance, and has good wear resistance. Maintain stability and achieve a high level of handling stability and ride comfort.
The shock absorber oil of the present invention is particularly preferably used for four wheels.

Claims (8)

  Base oil composed of mineral oil and / or synthetic oil, and (A) 0.3 to 2% by mass of zinc dialkyldithiophosphate having 7 to 12 carbon atoms in the alkyl group, and (B) 0.05 to 2% by mass of fatty acid amides. And (C) 0.1 to 1% by mass of a monocyclic phenol-based antioxidant, and the content of the ester having a —COO— bond in the base oil is 0.6% by mass or less as —COO— A lubricating oil composition for a shock absorber.   The lubricating oil composition for a shock absorber according to claim 1, wherein the base oil is mineral oil.   The lubricating oil composition for a shock absorber according to claim 1 or 2, wherein the base oil is a hydrocarbon-based synthetic oil and / or an ether-based synthetic oil.   The lubricating oil composition for a shock absorber according to claim 3, wherein the base oil is a hydrocarbon-based synthetic oil.   The lubricating oil composition for a shock absorber according to any one of claims 1 to 4, wherein the content of the component (A) zinc dialkyldithiophosphate is 0.5 to 1% by mass.   The content of fatty acid amides as the component (B) is 0.08 to 1% by mass, and the lubricating oil composition for a shock absorber according to any one of claims 1 to 5. (C) Content of monocyclic phenolic antioxidant of component is 0.1-0.8 mass%
The lubricating composition for a shock absorber according to any one of claims 1 to 6.   The lubricating oil composition for a shock absorber according to any one of claims 1 to 7, which is used for four wheels.