JP2000109876A - Hydraulic oil composition for buffer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a hydraulic oil compsn, for buffers, which is excellent in low-temp. viscosity characteristics, vaporizability, and shear stability and has a stable damping power at from low to high temps. SOLUTION: This compsn. contains, based on the compsn., at least 80 wt.% base oil comprising (A)(a) a deeply dewaxed mineral oil or a mixed mineral oil consisting of (a) a deeply dewaxed mineral oil and (b) a low-viscosity mineral oil in a wt. ratio of (80/20)-(100/0) or comprising (B) a synthetic base oil consisting of at least either (c) a poly-α-olefin or (d) an ester compd., is prepd. by compounding the base oil with (C) 20 wt.% or lower additive comprising (e) a viscosity index improver and/or a flow point depressant, and has a kinematic viscosity of 1-20 mm2/s at 100 deg.C, a viscosity index of 140 or higher, and a Brookfield viscosity of 29 000 mPa.s or lower at -40 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a hydraulic oil composition for a shock absorber. More specifically, the present invention relates to a hydraulic fluid composition for a shock absorber having excellent damping force stability, and particularly having good riding comfort at low temperatures.

[0002]

2. Description of the Related Art In general, a hydraulic shock absorber (buffer) is used for a suspension (suspension device) of a vehicle body of an automobile in order to reduce vibration and improve ride comfort and steering stability. The structure of the shock absorber is basically a cylindrical structure using the flow resistance of oil, and usually a hydraulic piston having a small hole in a piston is used. In the shock absorber having this cylindrical structure, oil passes through the hole according to the up and down of the piston, and the resistance at that time is proportional to the speed of the piston. For this reason, a guide bush, which also serves as a guide, is provided in the sliding portion between the cylinder and the piston rod to prevent mutual wear, and the whole is sealed to prevent oil leakage. Various types of shock absorbers, such as a double-tube type and a gas-filled type, are known in addition to the above-mentioned cylindrical structure. In the case of the shock absorber having such a structure, as described above, a large number of combined frictions occur between the piston rod and the guide bush, between the piston rod and the seal, between the piston and the cylinder, and the like. In addition, in the case of a car, it is necessary to reduce the vibration to the car under severe driving conditions to ensure ride comfort and steering stability.
It is required that the hydraulic oil used for the shock absorber has good wear resistance and durability, and good friction characteristics. In automobiles, similar shock absorbers are also used in engine support devices, bumper shock absorbers, door checkers, and the like. Also, in an aircraft, a hydraulic shock absorber for absorbing impact during takeoff and landing is arranged. The same performance as described above is required for the hydraulic oil used in these shock absorbers.

[0003] Conventionally, as a hydraulic fluid for a shock absorber having good wear resistance, durability and friction characteristics, zinc dithiophosphate (Zn-DTP) in a lubricating base oil has been used as an oily agent such as a long-chain fatty acid. Hydraulic hydraulic oil composition for buffer added together with detergent dispersant (Japanese Patent Application Laid-Open No. 55-165996), and fluid composition for buffer containing lubricant base oil containing boron-containing detergent dispersant and phosphate ester JP-A-2-44879), a hydraulic oil composition for a buffer containing a phosphate ester or the like and an alkanolamine in a lubricating base oil (Japanese Patent Application Laid-Open No. HEI 5 (1993) -205).
JP-A-255683), a hydraulic fluid composition for a shock absorber in which a phosphate ester or the like and an aliphatic polyamine are blended in a lubricating base oil (JP-A-7-224293), and a phosphate ester or the like in the lubricating base oil. Hydraulic hydraulic oil composition for a shock absorber containing an aliphatic polyamine and an aliphatic monoamine
No. 258,673).

By the way, the shock absorber performs a vibration damping action, and the damping force is usually called a damping force, and the performance of the shock absorber is related to the operating speed and the damping force. In the case of shock absorbers, especially automobile shock absorbers, it is necessary to reduce the vibration to the car under severe driving conditions to ensure ride comfort and steering stability, so that the damping force should be stably maintained. Is the most important. The damping force is related to the flow resistance of the liquid, that is, the hydraulic oil, the frictional force of each sliding portion of the shock absorber, and the like, and is a combination of a plurality of resistances. Therefore, in order to keep the damping force within a certain range, it is necessary that the viscosity and friction characteristics of the hydraulic oil used are as stable as possible.
However, most of conventionally proposed hydraulic fluids for shock absorbers are related to abrasion resistance and friction characteristics, and few are related to viscosity characteristics. Lubricating oil for machine equipment having an orifice mechanism in which a viscosity index improver or a phosphorus-based extreme pressure agent is blended with a deeply dewaxed base oil having a pour point of -25 ° C or less and a cloud point of -25 ° C or less. There is only a composition (JP-A-63-280797).

[0005] Since the shock absorber is used in a relatively wide temperature range, it is necessary to reduce a change in viscosity due to temperature and to prevent a change in damping force. In particular, the viscosity of the hydraulic fluid for a shock absorber increases at low temperatures, and when the viscosity at low temperatures becomes too high, the damping force becomes large and smooth operation cannot be performed, and ride comfort and steering stability deteriorate. Therefore, recently, the requirement for maintaining the damping force at a low temperature has become strict, and for example, it is required to greatly reduce the damping force at a low temperature of -20 ° C to -40 ° C. Therefore, there is a strong demand for a hydraulic oil for a shock absorber having good low-temperature viscosity characteristics. However, conventional hydraulic fluids for shock absorbers contain a viscosity index improver or a pour point depressant in a low-viscosity base oil. And there is a disadvantage that the amount of evaporation increases and the damping force fluctuates due to cavitation. Furthermore, hydraulic fluids for shock absorbers containing a large amount of viscosity index improvers and pour point depressants are
The oil is sheared when the piston slides or the oil flows in the orifice, and the viscosity of the hydraulic oil for the shock absorber decreases.
A significant decrease in viscosity will result in a decrease in damping force. For these reasons, the development of hydraulic fluids for shock absorbers, which have excellent low-temperature viscosity characteristics, evaporative properties, and shear stability, and good damping force stability from high to low temperatures, has been strongly developed. Is desired.

[0006]

SUMMARY OF THE INVENTION In view of the above situation, an object of the present invention is to provide excellent low-temperature viscosity characteristics, excellent evaporability and shear stability, and good damping force stability from high to low temperatures. Another object of the present invention is to provide a hydraulic oil composition for a shock absorber.

[0007]

Means for Solving the Problems The present inventors have described the above-mentioned.
After intensive research to solve the problems of the prior art
Fruit, deep-dewaxed mineral oil of specific properties, and / or synthesis of specific properties
Oil lubricating base oil, polymethacrylate, olefin
Viscosity index improvers such as copolymers and star polymers;
/ Or acrylate, polymethacrylate, etc.
Hydraulic fluid for shock absorbers with specific amount of moving point depressant
Kinematic viscosity at 100 ° C, viscosity index, and -40 ° C
The Brookfield viscosity in the specified range
Low temperature viscosity required as hydraulic fluid for shock absorber
Excellent properties, evaporability and shear stability, from high to low temperatures
Hydraulic fluid composition for shock absorber with good damping force stability over the whole
Was obtained. The present invention is based on these findings.
It was completed based on. That is, the book
According to the invention, the following mineral oil (A) and / or synthetic oil
20 bases on the base oil consisting of (B) based on the total amount of the composition
% Or less of a viscosity index improver and / or a pour point depressant.
A hydraulic oil composition for a shock absorber, comprising:
The kinematic viscosity at 100 ° C. is 1 to 20 mm²/
s, viscosity index is 140 or more and at -40 ° C
Brookfield viscosity of 2000 mPa · s or less
A hydraulic fluid composition for a shock absorber characterized by
Provided. Mineral oil (A): kinematic viscosity at 100 ° C. is 2 to 3 mm²/
s, pour point of -30 ° C or less, and cloud point of -27.5 ° C
Or a deeply dewaxed mineral oil (a), or
And the kinematic viscosity at 40 ° C. is 1.0 to 6.0 mm²/ S
Mineral oil mixed with a low-viscosity mineral oil (b)
The mineral oil (b) content is 2% based on the total amount of the mixed mineral oil.
Less than 0% by weight). Synthetic oil (B): kinematic viscosity at 100 ° C. is 1.5 to 45.
mm²/ S of poly-α-olefin (c), and / or
Is a kinematic viscosity at 100 ° C. of 1.5 to 20 mm ²/ S and
And an ester compound (d) having a pour point of -30 ° C or lower.

[0008] As described above, the present invention provides a low-temperature viscosity property,
The present invention relates to a hydraulic fluid composition for a shock absorber having excellent evaporability and shear stability and good damping force stability from high to low temperatures. Preferred embodiments thereof include the following. . (A) the base oil has a kinematic viscosity at 100 ° C. of ² to 3 mm ^2;
/ S, a pour point of −30 ° C. or less, and a cloud point of −27.5.
The hydraulic oil composition for a shock absorber according to the above, which is a deep dewaxed mineral oil (a) having a temperature of not more than 0 ° C. (B) the base oil has a kinematic viscosity at 100 ° C. of ² to 3 mm ^2;
/ S, a pour point of −30 ° C. or less, and a cloud point of −27.5.
Deep-wax mineral oil (a) at a temperature of 40 ° C. or lower and low-viscosity mineral oil (b) having a kinematic viscosity at 40 ° C. of 1.0 to 6.0 mm ² / s.
(However, the content of the low-viscosity mineral oil (b) is less than 20% by weight based on the total amount of the mixed mineral oil)
The hydraulic oil composition for a shock absorber according to the above. (C) the base oil has a kinematic viscosity at 100 ° C of ² to 3 mm ^2;
/ S, a pour point of −30 ° C. or less, and a cloud point of −27.5.
And a low viscosity mineral oil (b ¹ ) having a kinematic viscosity of 1.0 to 2.5 mm ² / s at 40 ° C. (wherein the low viscosity mineral oil (a) b ¹ )
Is less than 20% by weight based on the total amount of the mixed mineral oil). (D) the base oil has a kinematic viscosity at 100 ° C. of ² to 3 mm ^2;
/ S, a pour point of −30 ° C. or less, and a cloud point of −27.5.
And a low viscosity mineral oil (b ² ) having a kinematic viscosity at 40 ° C. of 2.5 to 6.0 mm ² / s (provided that the low viscosity mineral oil (a) b ² )
Is less than 20% by weight based on the total amount of the mixed mineral oil). (E) any of the above (a) to (d), which is a deep dewaxed mineral oil having a kinematic viscosity at 100 ° C of ² to 3 mm ² / s, a pour point of -35 ° C or less, and a cloud point of -30 ° C or less. 3. The hydraulic oil composition for a shock absorber according to the item 1. (F) the base oil has a kinematic viscosity at 100 ° C of 1.5 to 45;
mm ² / s at which poly α- olefin (c), and / or 100 the kinematic viscosity at ° C. consists 1.5~20mm ² / s and an ester compound are pour point of -30 ° C. or less (d) synthetic oils The hydraulic oil composition for a shock absorber according to the above. (G) the mixing ratio of the poly α-olefin (c) and the ester compound (d) is (c) 70 to 90% by weight,
(D) The hydraulic oil composition for a shock absorber according to the above (f), which is 10 to 30% by weight. (H) the base oil has a kinematic viscosity at 100 ° C of ² to 3 mm ^2;
/ S, a pour point of −30 ° C. or less, and a cloud point of −27.5.
Deep-wax mineral oil (a) having a kinematic viscosity at 100 ° C. of 1.5 to 45 mm ² / s and / or a kinematic viscosity at 100 ° C. of 1.5 to 45 mm ² / s.
The hydraulic oil composition for a shock absorber as described above, which is a partially synthetic oil with an ester compound (d) having a flow point of 20 mm ² / s and a pour point of −30 ° C. or lower. (I) the base oil has a kinematic viscosity at 100 ° C of ² to 3 mm ^2;
/ S, a pour point of −30 ° C. or less, and a cloud point of −27.5.
Deep dewaxed mineral oil (a) having a kinematic viscosity of 1.0 to 6.0 mm ² / s at 40 ° C. or lower (b).
(However, the content of the low-viscosity mineral oil (b) is less than 20% by weight based on the total amount of the mixed mineral oil)
And the kinematic viscosity at 100 ° C. is 1.5 to 45 mm ² / s
And the kinematic viscosity at 100 ° C. is 1.5 to ²⁰ mm ² / s and the pour point is −
The hydraulic oil composition for a shock absorber according to the above, which is a partially synthetic oil with the ester compound (d) having a temperature of 30 ° C. or lower. (N) To reduce the viscosity index improver for general lubricating oils such as polymethacrylates, olefin copolymers and star polymers and / or pour point depressants (e) such as acrylates and polymethacrylates to 20% by weight or less. The blended hydraulic oil composition for a shock absorber as described above.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. (1) Lubricating oil base oil In the hydraulic oil composition for a shock absorber of the present invention, the deeply dewaxed mineral oil (a) used as the base oil is a distillate obtained by distilling a paraffinic crude oil or an intermediate base crude oil. It can be obtained by performing a deep dewaxing treatment after purifying according to a conventional method. The distillate refers to one obtained by distilling crude oil at normal pressure or distilling residual oil of normal pressure under reduced pressure. The purification method is not particularly limited, but can be obtained by any one of the following treatments. The distillate is subjected to a hydrotreating process or a hydrotreating process, followed by alkali distillation or sulfuric acid washing. The distillate is subjected to a solvent refining treatment or a solvent refining treatment, followed by alkali distillation or sulfuric acid washing. After hydrotreating the distillate, a second-stage hydrotreatment is performed. After hydrotreating the distillate, a second-stage hydrotreatment and a third-stage hydrotreatment are performed. After hydrotreating the distillate, a second-stage hydrotreatment is performed, followed by alkali distillation or sulfuric acid washing.

An example of the processing method will be described below. A crude lubricating oil raw material is prepared from a paraffinic crude oil or an intermediate base crude oil by an ordinary method and subjected to severe hydrotreating. By this treatment, a reaction is performed to remove components that are not desirable in the lubricating oil fraction such as aromatic components or to convert them into effective components. At this time, most of sulfur and nitrogen are also removed. Next, fractional distillation is performed to obtain the required viscosity by distillation under reduced pressure. Thereafter, known solvent dewaxing is performed to dewax to the pour point of ordinary paraffinic base oil, that is, about -15 to -10 ° C. After this dewaxing treatment, if necessary, further hydrogenation treatment is carried out to hydrogenate most of the aromatics to a saturated content, thereby improving the thermal and chemical stability of the base oil. However, since the pour point is still high, it is not suitable as a lubricating oil.
For this purpose, a deep dewaxing process is subsequently performed. This deep dewaxing treatment is carried out under a severe solvent dewaxing method, or by using a zeolite catalyst to selectively decompose paraffin (mainly normal paraffin) adsorbed in the pores of the catalyst under a hydrogen atmosphere to obtain a wax. A catalytic hydrogenation dewaxing method is applied to remove the components. The hydrotreating varies depending on the properties of the feedstock oil, etc., but usually the reaction temperature is from 200 to 480 ° C., preferably from 250 to 4 ° C.
80 ° C., hydrogen pressure 5 to 300 kg / cm ² , preferably 30 to 250 kg / cm ² , hydrogen introduction amount (per 1 kl of feed distillate) 30 to 3000 Nm ³ , preferably 100
It is performed under the condition of ２０００2000 Nm ³ . The catalyst used at this time uses alumina, silica, silica-alumina, zeolite, activated carbon, bauxite or the like as a carrier, and a metal such as Group VI or VIII of the periodic table, preferably cobalt, nickel, molybdenum, or the like. A catalyst component such as tungsten supported by a known method is used. Preferably, the catalyst is preliminarily sulfurized. As described above, the distillate is subjected to various treatments after the hydrotreating. When the second or third stage hydrotreating is performed, the hydrotreating conditions are set within the above range. The conditions in the first to third stages may be the same or different. However, usually, the conditions are set stricter in the second stage than in the first stage and in the third stage than in the second stage. Next, alkali distillation is performed as a step of improving the stability of the distillate by removing a trace amount of acidic substances,
This is performed by adding an alkali such as NaOH or KOH and performing distillation under reduced pressure. Sulfuric acid washing is generally performed as a finishing step for petroleum products, and removes aromatic hydrocarbons, particularly polycyclic aromatic hydrocarbons, olefins, sulfur compounds, and the like, to improve the properties of distillate oil. Applied to improve. In addition, there are the above-mentioned specific methods for the treatment of the distillate according to a combination of the above-mentioned operations, and among these methods, the method is particularly preferable.

The deeply dewaxed base oil (a) used in the present invention is:
It can be obtained by the above method,
Kinematic viscosity is 2-3mm²/ S, preferably 2 to 2.5
mm ²/ S, pour point of -30 ° C or less, preferably -35
° C or less, and the cloud point is -27.5 ° C or less, preferably -3.
It needs to be 0.0 ° C. or less. Kinematic viscosity at 100 ° C
Degree is 2mm²/ S, the abrasion resistance is reduced,
This is not preferable because the emission characteristics deteriorate. On the other hand, 3mm²/
If the viscosity exceeds s, viscosity characteristics at low temperature, that is, low-temperature fluidity,
It is not preferable because it lowers. In addition, the pour point is -30 ° C.
If the cloud point exceeds -27.5 ° C, the low-temperature fluidity decreases.
This is not preferred.

In the hydraulic fluid composition for a shock absorber according to the present invention, a low-viscosity base oil having a kinematic viscosity at 40.degree.
There is a low-viscosity mineral oil (b) that is 0-6.0 mm ² / s,
For example, the kinematic viscosity at 40 ° C. is 1.0 to 2.5 mm ²
/ S mineral oil (b ¹ ), preferably a mineral oil having a kinematic viscosity at 40 ° C. of 1.5 to 2.1 mm ² / s, or a mineral oil having a kinematic viscosity at 40 ° C. of 2.5 to 6.0 mm ² / s ( b ² ),
Preferably, the kinematic viscosity at 40 ° C. is 2.6 to 3.5 mm.
² / s mineral oil and the like. In the above deep dewaxed mineral oil,
By mixing these low-viscosity mineral oils, the low-temperature fluidity can be drastically improved as compared with the case of using deeply dewaxed mineral oil alone. If the kinematic viscosity at 40 ° C. is less than 1 mm ² / s, the abrasion resistance decreases and the evaporation characteristics deteriorate, which is not preferable. On the other hand, if it exceeds 6 mm ² / s, the viscosity characteristics at low temperature, that is, the low-temperature fluidity decreases, which is not preferable.
In the present invention, when a mixed mineral oil of the deeply dewaxed mineral oil (a) and the low-viscosity mineral oil (b) is used as a base oil of the hydraulic oil composition for a shock absorber, the low-viscosity mineral oil (b) The content should be less than 20% by weight based on the total amount of the mixed mineral oil. Preferably, it is at most 10% by weight. If the mixing ratio is outside the above range, the evaporation characteristics are inferior, and the lubricating characteristics and friction characteristics inherent to the hydraulic oil for shock absorbers are also unsatisfactory.

In the hydraulic fluid composition for a shock absorber according to the present invention, the poly α-olefin (c) used as the base oil is α
A synthetic lubricating oil, also called an olefin oligomer, having the following general formula [I]

[0014]

Embedded image

(Wherein, R represents an alkyl group having 4 to 12 carbon atoms, and m represents 0 to 30). Here, the poly-α-olefin has a kinematic viscosity at 100 ° C. of 1.5 to 45 mm ² / s, preferably 1.7.
の も の 40 mm ² / s is used. Here, when the kinematic viscosity is less than 1.5 mm ² / s, there is a disadvantage that the evaporation amount is large. On the other hand, when the kinematic viscosity exceeds 45 mm ² / s,
It is not preferable because the low-temperature viscosity characteristics deteriorate. Specifically, it is preferable to use a poly-α-olefin having a low polymerization degree such as a 2- to 10-mer of 1-octene, 1-decene, or 1-dodecene, preferably a 2- to 4-mer of 1-decene. Desirable in terms of pour point. Such a poly-α-olefin is
It can be produced by a known method comprising a polymerization step, a catalytic decomposition step, a distillation step, and a hydrogenation step. The degree of polymerization may be adjusted by changing the residence time of the reactor in the polymerization step.

In the hydraulic fluid composition for a shock absorber according to the present invention, the ester compound (d) used as the base oil is 100%.
An ester compound having a kinematic viscosity at 1.5 ° C. of 1.5 to ²⁰ mm ² / s and a pour point of −30 ° C. or less can be used, but a kinematic viscosity at 100 ° C. of 1.5 to 10 mm ² is preferable. / S and a pour point of -35 ° C or less. Such ester compounds include, for example,
Examples thereof include dibasic acid esters (diesters) and polyol esters (hindered esters), and dibasic acid esters (diesters) are particularly preferable from the viewpoints of high viscosity index, low-temperature fluidity, and the like. The dibasic acid ester is usually one obtained by subjecting one dibasic acid to an esterification reaction at a ratio of two alcohols. Dibasic acids which are the raw materials for dibasic acid esters include adipic acid, azelaic acid, sebacic acid,
Such as dodecanedioic acid is used as the alcohol, a primary alcohol is often used having a side chain with 7 to 13 carbon atoms, for example, the C ₂ 2-ethylhexanol, C
₁₂ of isodecanol _and tridecanol of _{C 13} and the like. As the dibasic acid ester, for example, di-
2-ethylhexyl sebacate (DOS), di-2-ethylhexyl siadipate (DOA), diisodecyl adipate (DIDA), diisooctyl adipate (D
IOA), di-2-ethylhexyl azelate (DO
Z) and the like. Polyol esters are usually
It is an ester of neopentyl polyol and a monobasic fatty acid. Neopentyl polyol, which is a raw material of polyol ester, includes neopentyl glycol (NPG) as a dihydric alcohol, and trimethylolpropane (TMP) or trimethylolethane (TM) as a trivalent alcohol.
E), pentaerythritol (P
E), dipentaerythritol (DP
E), and trimethylolpropane (TMP) and pentaerythritol (PE) are often used. As the raw material monobasic fatty acid, a linear or branched C ₃ -C ₁₃ fatty acid is often used. In order to improve the pour point, a mixture of several types of linear acids having different carbon numbers is used. Or a small amount of a branched acid.

In the present invention, the above-mentioned poly-α-olefin and / or ester compound can be used as the base oil of the hydraulic oil composition for a shock absorber. These can be used alone or in combination of both, but it is preferable to use a combination of a poly-α-olefin and an ester compound. Compounding ratio of poly α-olefin (c) and ester compound (d) (c: d)
Is usually 50:50 to 95: 5, preferably 70:30 to 90:10, and more preferably 75:25 by weight.
85:15. By being in this range, the compatibility with the seal rubber is excellent, the viscosity index is high, and the low-temperature viscosity characteristics can be improved. In the present invention, the mineral oil (A) and the synthetic oil (B) may be used alone or in combination as the base oil of the hydraulic oil composition for a shock absorber.

(2) Viscosity index improver and / or pour point depressant (e) The viscosity index improver and / or pour point depressant (e) incorporated in the hydraulic fluid composition for a shock absorber of the present invention are: The viscosity index improver and the pour point depressant are used alone or in combination. As the viscosity index improver, general viscosity index improvers for lubricating oils such as polymethacrylates, olefin copolymers, and star polymers can be used. As pour point depressants, acrylates, polymethacrylates, and the like can be used. Can be used. The viscosity index improver is preferably a polymethacrylate type,
Polymethacrylate-based viscosity index improvers include a dispersion type and a non-dispersion type, and any of them may be used. Those having a weight average molecular weight of 10,000 to 300,000 are preferably used, and particularly preferably 10,000 to 120,000.
0. When the weight average molecular weight is less than 10,000, the shear stability is good but the low-temperature viscosity reduction effect is small. On the other hand, when the weight average molecular weight exceeds 300,000, the low temperature viscosity reduction effect is large but the shear stability is poor. The compounding amount of the viscosity index improver and / or the pour point depressant (e) is 20% by weight or less based on the total amount of the composition. Preferably, 4-
10% by weight. If the amount is more than 20% by weight, the shear stability is deteriorated and the low-temperature viscosity is increased.

(3) Other additives In the hydraulic fluid composition for a shock absorber of the present invention, other additives, such as a friction modifier and an antiwear agent, may be added, if necessary, unless the object of the present invention is impaired. An antioxidant, an ashless detergent / dispersant, a metal detergent, a corrosion inhibitor, a rust inhibitor, an antifoaming agent, and the like can be appropriately added. Examples of the friction modifier include fatty acids (such as oleic acid and stearic acid), higher alcohols (such as oleyl alcohol), fatty acid esters, phosphate esters, phosphite esters, phosphate amine salts, oils and fats, polyhydric alcohol esters, Sorbitan esters, aliphatic amines and the like can be mentioned.
Usually, it is used in a proportion of 0.05 to 3.0% by weight. As antiwear agents, metal dithiophosphates (Zn, Pb, S
b, Mo, etc.), metal salts of dithiocarbamic acid (Zn, M
o etc.) Naphthenic acid metal salts (Pb etc.), fatty acid metal salts (Pb etc.), phosphate esters, phosphite esters, phosphate amine salts, sulfurized fats and oils, sulfur compounds, boron compounds, etc. , These are usually
It is used in a proportion of from 0.5 to 3.0% by weight. As antioxidants, alkylated diphenylamine, phenyl-α-
Amine antioxidants such as naphthylamine and alkylated phenyl-α-naphthylamine; phenolic antioxidants such as 2,6-di-t-butylphenol and 4,4′-methylenebis- (2,6-ditert-butylphenol) , Phosphite and other phosphorus antioxidants, dilauryl-
Sulfur-based antioxidants such as 3,3'-thiodipropionate and the like can be mentioned.
Used at a rate of 2.0% by weight. Examples of the ashless detergent / dispersant include succinimide-based, succinic amide-based, benzylamine-based and succinate-based detergents, and a boron-containing ashless detergent / dispersant can also be used. These are usually 0.05
It is used in a proportion of ~ 7.0% by weight. As the metal detergent, Ca-sulfonate, Mg-sulfonate, Ba-
Sulfonate, Ca-phenate, Mg-phenate,
There are Ba-phenate, Ca-salicylate, Mg-salicylate, Ba-salicylate and the like, which are usually used at a ratio of 0.1 to 5.0% by weight. Examples of the corrosion inhibitor include benzotriazole, benzotriazole derivatives, thiadiazole derivatives and the like.
Usually, it is used in a ratio of 0.01 to 2.0% by weight. Examples of the rust inhibitor include carboxylic acid, carboxylate, sulfonate, amine, alkenyl succinic acid and partial esters thereof, and the like can be added as appropriate. Examples of the antifoaming agent include dimethylpolysiloxane and polyacrylate, which can be added as appropriate.

(4) Hydraulic oil composition for shock absorber The hydraulic oil composition for shock absorber of the present invention has excellent viscosity stability, especially its viscosity characteristics in order to provide good riding comfort at low temperatures. Has a kinematic viscosity at 100 ° C. of 1 to 2
0 mm ² / s, a viscosity index of 140 or more, and −
Brookfield (BF) viscosity at 40 ° C. of 20
It is necessary to be not more than 00 mPa · s. Preferably, 1
The kinematic viscosity at 00 ° C is ² to 8 mm ² / s, the viscosity index is 145 or more, and the Brookfield viscosity at -40 ° C is 1700 mPa · s or less. 100
When the kinematic viscosity at 0 ° C is less than 1 mm ² / s, the amount of evaporation increases and the abrasion resistance deteriorates, while 20 mm ² / s
If it exceeds s, the low temperature viscosity becomes too large. When the viscosity index is less than 140, the low temperature viscosity becomes too large. -4
Brookfield viscosity at 0 ° C of 2000 mPa
If it exceeds s, the damping force at low temperatures becomes large, and the ride comfort and steering stability deteriorate.

[0021]

The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. The methods for measuring various physical properties of Brookfield viscosity, evaporability, and shear stability in Examples are as follows. (1) Brookfield Viscosity The Brookfield (B) at −40 ° C. was measured using a Brookfield viscometer specified in ASTM D2983.
F) The viscosity was measured. (2) Evaporability According to DIN51581, the NOACK evaporation amount was measured under the measurement conditions of a temperature of 120 ° C. and 3 hours, and the evaporability was evaluated. (3) Shear Stability According to ASTM D2603, a sample was irradiated with a sound wave to give shear, and the viscosity reduction rate at 100 ° C. was calculated from the viscosity before and after irradiation to evaluate the shear stability. The test conditions were as follows: sample 30 ml, sound wave output 10 kHz, irradiation time 3
The circulating water temperature was set to 38 ° C. for 0 minute.

Example 1 100 ° C. as lubricating base oil
Has a kinematic viscosity of 2.4 mm ² / s and a pour point of −35.
C. and a deep dewaxed mineral oil having a cloud point of -30.degree. C. or lower, and as an additive, a polymethacrylate-based viscosity index improver (weight average molecular weight 75,000) based on the total amount of the composition.
A required amount of 4.0% by weight and other additives such as an antioxidant and an antiwear agent was added to prepare a hydraulic oil composition for a shock absorber. The viscosity characteristics, viscosity index, evaporability, and shear stability of the hydraulic oil composition for a shock absorber obtained here were measured and evaluated. Table 1 shows the results. The hydraulic fluid composition for a shock absorber of Example 1 has a viscosity characteristic of a kinematic viscosity at 100 ° C. of 3.1 mm ² / s, a viscosity index of 149, and a Brookfield viscosity at −40 ° C. of 1650 mPa · s. As for the evaporating property, the NOACK evaporation amount was 4.3% by weight, and the shear stability was good because the sonication method viscosity reduction rate was 4.0%.

[0023]

[Table 1]

Examples 2 to 8 The lubricating base oil components shown in Table 1 were mixed with the viscosity index improver and other additive components in the proportions shown in the table to prepare hydraulic oil compositions for shock absorbers. . The mixing ratio of the base oil is based on the total amount of the base oil, and the adding ratio of the viscosity index improver and other additives is based on the total amount of the composition. The viscosity characteristics, viscosity index, evaporability and shear stability of the hydraulic fluid compositions for shock absorbers shown in Examples 2 to 8 were measured and evaluated. Table 1 shows the results. In any of the examples, it was found that high quality hydraulic oil for shock absorbers could be obtained.

[Comparative Examples 1 to 4] Lubricating base oil components and various additive components shown in Table 1 were blended in the proportions shown in the same table to prepare hydraulic working oil compositions for shock absorbers. Comparative Example 1 used a normal solvent dewaxed mineral oil (pour point -15 ° C, 100 ° C kinematic viscosity 2.7 mm ² / s) without using a deeply dewaxed mineral oil as a base oil, and based on the total amount of the composition. And 1.5 wt% of a polymethacrylate-based viscosity index improver (weight average molecular weight: 45,000). As a result, the Brookfield viscosity at −40 ° C. is 4700 mPa · s, and the low-temperature viscosity characteristic is low. Is bad. Comparative Example 2 used a deep dewaxed mineral oil having a kinematic viscosity at 100 ° C. of 2.4 mm ² / s as a base oil, and based on the total amount of the composition, a polymethacrylate-based viscosity index improver (weight average molecular weight 75,000). In the case where 21.0% by weight or the like is blended, the low-temperature viscosity exceeds 2000 mPa · s and the shear stability is poor. Comparative Example 3 used a synthetic oil of a poly-α-olefin and an ester compound as a base oil, and used a polymethacrylate-based viscosity index improver (weight average molecular weight of 100,000) 26.0% by weight based on the total amount of the composition. And a kinematic viscosity at 100 ° C. of 20.2
mm ² / s, but the low-temperature viscosity is 2000 m
Exceeds Pa · s and has poor shear stability. Comparative Example 4
As a base oil, 70% by weight of a deep-dewaxed mineral oil having a kinematic viscosity at 100 ° C. of 2.4 mm ² / s based on the total amount of the base oil was converted to
And 30% by weight of a low-viscosity mineral oil having a kinematic viscosity of 1.8 mm ² / s, and a polymethacrylate-based viscosity index improver (weight-average molecular weight of 75,000
0) 15.0% by weight or the like is blended. Although the low-temperature viscosity characteristics are good, the NOACK evaporation amount is clearly deteriorated and the shear stability is also deteriorated.

[0026]

The hydraulic fluid composition for a shock absorber according to the present invention comprises:
A specific amount of a viscosity index improver and / or a pour point depressant is blended with a base oil of a deep-dewaxed mineral oil having a specific property and / or a synthetic oil having a specific property, and the kinematic viscosity at 100 ° C. of a hydraulic fluid for a shock absorber. , Viscosity index, and Brookfield viscosity at −40 ° C. within the specified ranges, thereby exhibiting excellent low-temperature viscosity characteristics, evaporability, and shear stability required for hydraulic fluids for shock absorbers, and particularly from high to low temperatures. And excellent damping force stability.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C10M 145: 14) C10N 30:02 30:06 30:08 40:08 (72) Inventor Naoto Otsuka Saitama 1-3-1 Nishi-Tsurugaoka, Oi-machi, Iruma-gun F-term in Tonen Research Laboratory (reference) 4H104 BA07A BB33A BB34A CA05A DA02A EA02A EA02Z EA04A EB02 EB05 LA01 LA03 LA04 LA20 PA05

Claims (1)

[Claims] 1. The following mineral oil (A) and / or synthetic oil
20 bases on the base oil consisting of (B) based on the total amount of the composition
% Or less of a viscosity index improver and / or a pour point depressant.
A hydraulic oil composition for a shock absorber, comprising a kinematic viscosity at 100 ° C. of 1 to 20 m.
m²/ S, a viscosity index of 140 or more, and -40
Brookfield viscosity at 2000C
s or less, the hydraulic fluid composition for a shock absorber
object. Mineral oil (A): kinematic viscosity at 100 ° C. is 2 to 3 mm²/
s, pour point of -30 ° C or less, and cloud point of -27.5 ° C
Or a deeply dewaxed mineral oil (a), or
And the kinematic viscosity at 40 ° C. is 1.0 to 6.0 mm²/ S
Mineral oil mixed with a low-viscosity mineral oil (b)
The mineral oil (b) content is 2% based on the total amount of the mixed mineral oil.
Less than 0% by weight). Synthetic oil (B): kinematic viscosity at 100 ° C. is 1.5 to 45.
mm²/ S of poly-α-olefin (c), and / or
Is a kinematic viscosity at 100 ° C. of 1.5 to 20 mm ²/ S and
And an ester compound (d) having a pour point of -30 ° C or lower.