JP2011021111A - Hydraulic fluid composition for shock absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydraulic fluid composition having good low-temperature characteristics and low piping resistance, and a low rate of change in damping force with temperature change, moreover a low swelling rate (rate of volume change) of sealing materials. <P>SOLUTION: The hydraulic fluid composition comprises a base oil compounded of a polymethacrylate-based viscosity index improver whose weight-average molecular weight is 200,000-600,000 and an amine salt of an acidic phosphate ester, wherein the compounding ratio of the polymethacrylate-based viscosity index improver is 0.1-5.0 mass% to the total amount of the composition, and the compounding ratio of the amine salt of an acidic phosphate ester is 2.0-5.0 mass% to the total amount of the composition, and the other properties of the composition include a kinematic viscosity of 4-8 mm<SP>2</SP>/s at 40°C, a Brookfield viscosity of ≤1,000 mPa s at -30°C, an aniline point of 85-110°C, and a viscosity index of ≥150. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a hydraulic fluid composition for shock absorbers, and more particularly to a hydraulic fluid suitable for automobile shock absorbers.

Among automotive suspension components, shock absorbers are functional components that play an important role in maneuverability, stability and ride comfort. Various shock absorbers such as double tube type and gas-filled type are known as the structure of the shock absorber. Basically, it consists of a piston and a cylinder, and the hydraulic fluid for the shock absorber is sealed inside. In addition, the sliding surfaces of the cylinder, piston rod, and cylinder are sealed with a sealing material such as nitrile rubber so that the internal hydraulic fluid does not leak and the sliding portion is protected. The impact applied from the outside of the automobile is absorbed by the damping force using the flow resistance of the hydraulic fluid sealed inside. Various functions such as damping force characteristics, low temperature fluidity, wear resistance, low friction characteristics, seal compatibility, etc. are required for hydraulic fluids for shock absorbers having such functions. Hydraulic fluids for shock absorbers have been proposed (see, for example, Patent Document 1 and Patent Document 2).

By the way, in recent years, each shock absorber unit disposed on the right front wheel and the left rear wheel and between the left front wheel and the right rear wheel is about twice as large as the conventional piping through a shock absorber unit arranged between them. A shock absorber connected by a pipe having a length of 10 mm was developed. Since this shock absorber has the effect of simultaneously suppressing the rolling (pitch) and pitching (pitch) speeds, it is possible to obtain better ride comfort and steering stability than conventional shock absorbers. However, since this shock absorber has a longer pipe connecting each shock absorber unit than the conventional pipe, if the conventional hydraulic fluid for shock absorber is used as it is, the pipe resistance increases by the length of the pipe, and as a result the target There is a concern that the damping action cannot be obtained. In addition, even with conventional shock absorbers, the damping action tends to deteriorate due to an increase in the viscosity of the hydraulic fluid at low temperatures. However, in the above-mentioned new shock absorbers, pipe resistance due to long pipes also increases. There is a concern that the increase in the viscosity of the hydraulic fluid at low temperatures may further affect the damping action.

In order to reduce the impact on piping resistance and damping force at low temperatures, it is conceivable to reduce the viscosity of the hydraulic fluid for shock absorbers. The viscosity becomes too low, and this makes it difficult to obtain a sufficient damping force.
Therefore, even if each shock absorber is a new shock absorber connected to a long pipe, the hydraulic resistance fluid for the shock absorber has a sufficiently low pipe resistance, a good damping force, and a low rate of change in damping force due to temperature. It was sought after.
In general, when the viscosity is low, the swelling rate of the nitrile rubber of the sealing material tends to be high, and when the swelling rate is too high, there is a concern that the sealing performance may be lowered. There was a need for hydraulic oil.

JP-A-7-258675 JP-A-7-271886

In view of the above situation, the present invention is for a shock absorber having good low-temperature characteristics, low pipe resistance, a lower rate of change in damping force due to temperature change, and a smaller swelling rate (volume change rate) of the sealing material. The object is to provide a hydraulic fluid.

As a result of intensive research in order to solve the above problems, the present inventor has formulated a specific amount of a specific polymethacrylate viscosity index improver and an amine salt of an acidic phosphate ester in the base oil, and the properties of the composition The low temperature characteristics are good by making the kinematic viscosity at 40 ° C. 4-8 mm ² / s, Brookfield viscosity at −30 ° C. 1000 mPa · s or less, aniline point 85-110 ° C., and viscosity index 150 or more. Thus, it has been found that a hydraulic fluid composition for a shock absorber is obtained that has excellent low friction properties, low pipe resistance, low rate of change in damping force due to temperature change, and excellent seal compatibility.

That is, the present invention is a hydraulic fluid composition comprising a base oil and a polymethacrylate viscosity index improver having a weight average molecular weight of 200,000 to 600,000 and an amine salt of an acidic phosphate ester. The blending ratio of the polymethacrylate-based viscosity index improver is 0.1 to 5.0% by mass with respect to the total amount of the composition, and the blending ratio of the amine salt of the acidic phosphate ester is the composition. It is 2.0-5.0 mass% with respect to the whole quantity of a thing, As a property of this composition, the kinetic viscosity of 40 degreeC is 4-8 mm < ² > / s, and the Brookfield viscosity in -30 degreeC is 1000 mPa * s or less. The present invention provides a hydraulic fluid composition for a shock absorber having an aniline point of 85 to 110 ° C. and a viscosity index of 150 or more.

In the hydraulic fluid composition for a shock absorber according to the present invention, the base oil has (A) a kinematic viscosity at 40 ° C. of 10 to 15 mm ² / s, an aniline point of 100 to 115 ° C., and a pour point. A hydrocarbon base oil having a temperature of −40 ° C. or lower, and (B) a kinematic viscosity at 40 ° C. of 2.0 to 5.0 mm ² / s, an aniline point of 60 to 95 ° C., and a pour point of −20 to −50 ° C. The hydraulic base oil composition for a shock absorber, which is a base oil containing the hydrocarbon base oil of (A) in a proportion of 25 to 55 mass% with respect to the total mass of (A) and (B), is provided. Is.

The hydraulic fluid composition for a shock absorber according to the present invention has good low-temperature characteristics, excellent low friction, low pipe resistance, small change rate of damping force due to temperature change, and swelling rate (volume change rate) of the sealing material. ) Is small and has excellent compatibility with sealing materials.

(1) Properties of shock absorber hydraulic fluid composition The shock absorber hydraulic fluid composition of the present invention has the following properties.
(I) a kinematic viscosity of 40 ° C. is 4 to 8 mm ² / s, preferably from 5 to 7 mm ² / s.
Kinematic viscosity low enough piping resistance is low, but can also at a low temperature to obtain a good damping force is less than 4 mm 2 / ^s tend to damping force at high temperatures is lowered, the piston - wear between cylinder There is concern about oil leakage from the seal. On the other hand, if it exceeds 8 mm ² / s, the pipe resistance increases and the damping force tends to decrease in general, and it becomes difficult to obtain a good damping force particularly at low temperatures.

(Ii) Brookfield viscosity at −30 ° C. is 1000 mPa · s or less, preferably 300 mPa · s or less. When it exceeds 1000 mPa · s, the piping resistance at low temperatures increases and the damping force tends to decrease in general. On the other hand, there is no limitation on the lower limit value, but about 100 mPa · s is a realistic lower limit value.
(Iii) An aniline point is 85-110 degreeC, Preferably it is 90-105 degreeC, More preferably, it is 90-100 degreeC. When the aniline point exceeds 110 ° C., the rubber of the sealing material is hardened, and there is a concern that the sealing performance is lowered. On the other hand, if the aniline point is less than 85 ° C., the rubber of the sealing material swells too much, and there is a concern that the sealing performance is lowered. Alternatively, it may be necessary to change to an expensive sealing material that is more difficult to swell, resulting in an increase in cost.

(Iv) The viscosity index is 150 or more, preferably 160 or more. If the viscosity index is less than 150, the rate of change of the damping force due to temperature increases. The upper limit of the viscosity index is not limited, but in order to increase the viscosity index, it is necessary to increase the blending amount of polymethacrylate which is a viscosity index improver. Since the viscosity decreases due to use, it may be difficult to maintain the predetermined kinematic viscosity necessary for the composition of the present invention, so the practical upper limit is about 230, and if the shear stability is more important, the upper limit The value is more preferably about 200.

(2) Base oil The base oil used in the hydraulic fluid composition for a shock absorber according to the present invention is not particularly limited, and it can be used for the shock absorber according to the present invention from mineral base oils, synthetic base oils, and mixed base oils thereof. A base oil that satisfies the properties of the hydraulic fluid composition may be selected as appropriate, but in terms of easily obtaining the properties of the composition of the present invention,
(A) a kinematic viscosity of 40 ° C. is 10-15 mm ² / s, preferably 10.5~13.5mm ² / s, aniline point 100 to 115 ° C., preferably 102 - 112 ° C., and pour point - A hydrocarbon base oil having a temperature of 40 ° C. or lower, preferably −50 ° C. or lower;
(B) Kinematic viscosity at 40 ° C. is 2.0 to 5.0 mm ² / s, aniline point is 60 to 95 ° C., preferably 70 to 90 ° C., and pour point is −20 to −50 ° C., preferably − A hydrocarbon base oil having a temperature of 20 to −45 ° C.
Use what mixed so that the content rate of the base oil of (A) with respect to the total amount of the base oil of (A) and the base oil of (B) may be 25-55 mass%, Preferably it is 30-45 mass%. Is preferred.
In addition, the lower limit value of the pour point of the hydrocarbon base oil of component (A) is preferably as low as possible if it satisfies the above physical properties, but what is obtained within the above 40 ° C. kinematic viscosity range is The lower limit is about −70 ° C.

As the base oil (A), for example, vacuum gas oil, slack wax by solvent dewaxing, wax obtained by Fischer-Tropsch synthesis, etc. are used as raw materials, and these are hydrotreated, hydrocracked, and hydrogen Hydrocracked mineral oil, GTL base oil, and the like obtained by a method of hydroisomerization and dewaxing are preferred.
Examples of the base oil (B) include mineral oil obtained by removing aromatic components contained in a gasoline fraction having a boiling range of 150 to 200 ° C. obtained by atmospheric distillation of crude oil. It is mentioned as preferable.
Each of the base oil (A) and the base oil (B) may be used alone or in combination of two or more.
The content of the base oil in the hydraulic fluid composition for a shock absorber of the present invention is preferably 90 to 97% by mass, more preferably 92 to 95% by mass.

(3) Viscosity index improver The composition of the present invention is a polymethacrylate viscosity index improver having a weight average molecular weight of 200,000 to 600,000, and 0.1 to 5.0 mass relative to the total amount of the composition. %contains. In addition, the weight average molecular weight (Mw) in this invention is the standard polystyrene conversion for molecular weight calculation measured by the gel permeation chromatography (GPC).
When the weight average molecular weight of the polymethacrylate viscosity index improver is less than 200,000, it is difficult to obtain a predetermined viscosity index. On the other hand, when the weight average molecular weight of the polymethacrylate viscosity index improver exceeds 600,000, sufficient shear stability cannot be obtained, and secondary viscosity is lowered after long-term use, and the viscosity of the composition is increased. Therefore, there is a concern that the required kinematic viscosity that is required cannot be maintained.

  The structure of the polymethacrylate viscosity index improver used in the present invention is a structure having a polymer of a methacrylic acid ester represented by the following general formula (1), and even if the monomer is a polymer of only a methacrylic acid ester. The monomer may be a copolymer of a methacrylic acid ester and another monomer, or may contain a polymer compound other than polymethacrylate in a part of the structure. Further, a “dispersion type” having a polar group such as an amino group or a sulfonic acid group in the molecule or a “non-dispersion type” having no polar group may be used. Viscosity index improvers are “non-dispersed” with little impact on frictional properties.

(In the formula (1), ^{R 1} is a hydrogen atom or an alkyl group having a carbon number of 1 to 20, k is an integer of 1 or more.)
The compounding quantity of a polymethacrylate type viscosity index improver is 0.1 mass%-5 mass% with respect to the whole quantity of a composition, Preferably it is 0.5-3.0 mass%. When the blending amount is less than 0.1% by mass, it is difficult to obtain a predetermined viscosity index. On the other hand, if it exceeds 5.0% by mass, the shear stability is lowered and the viscosity is liable to be lowered, and there is a concern that the predetermined kinematic viscosity necessary for the composition of the present invention cannot be maintained.

(3) Amine salt of acidic phosphate ester The composition of the present invention contains 2.0 to 5.0% by mass of an amine salt of acidic phosphate ester based on the total amount of the composition.
The acid phosphate ester constituting the amine salt of the acid phosphate ester may be either a monoester or a diester. Examples of the alcohol residue include carbon such as butyl, octyl, lauryl, stearyl, and oleyl groups. Examples thereof include alkyl groups having 4 to 30 carbon atoms, aryl groups having 6 to 30 carbon atoms such as phenyl groups, and alkyl-substituted aryl groups having 7 to 30 carbon atoms such as methylphenyl and octylphenyl groups.

The compounding quantity of the amine salt of acidic phosphoric acid ester is 2.0-5 mass% with respect to the whole quantity of a composition, Preferably it is 3.0 mass%-4.0 mass%. When the blending amount is less than 2.0% by mass, friction between the piston and the cylinder or between the piston rod and the cylinder becomes large, and it is difficult to obtain a smooth damping force. On the other hand, even if it exceeds 5.0 mass%, there is no particular problem, but it is only up to about 5.0 mass% that an effect corresponding to the blending amount can be obtained.

(4) Other Additives Various known additives can be blended with the hydraulic fluid composition for a shock absorber of the present invention, if necessary, as long as the object of the present invention is not impaired. For example, antioxidants, extreme pressure agents, oily agents, detergent dispersants, rust inhibitors, metal deactivators, pour point depressants, foam depressants, demulsifiers and the like can be mentioned.
Antioxidants include phenol-based antioxidants such as 2,6-di-tert-butyl-p-cresol, amine-based antioxidants such as alkylated diphenylamine and alkylated phenyl-α-naphthylamine, phosphonic acid esters, etc. And phosphorus-based antioxidants.

Examples of the extreme pressure agent include phosphorus extreme pressure agents such as phosphate and phosphite, sulfur extreme pressure agents such as olefin sulfide, and organometallic extreme pressure agents such as ZnDTP and ZnDTC.
Examples of the oily agent include higher fatty acids such as oleic acid and stearic acid, higher alcohols such as oleyl alcohol, amines such as oleylamine, and esters such as butyl stearate.
Examples of the cleaning dispersant include ashless cleaning dispersants such as alkenyl succinimides and alkenyl succinic esters, and alkaline earth metal cleaning dispersants.

Examples of the rust inhibitor include carboxylic acid, metal soap, carboxylic acid amine salt, sulfonic acid metal salt, and partial ester of polyhydric alcohol.
Examples of metal deactivators include benzotriazole and derivatives thereof, and alkyl succinic acid derivatives.
Examples of the pour point depressant include polyalkyl methacrylate, polybutene, polyalkyl styrene, polyvinyl acetate, polyalkyl acrylate and the like.
Examples of antifoaming agents include silicone oil and ester-based antifoaming agents.
Examples of the demulsifier include demulsifiers such as an anionic surfactant, a cationic surfactant, and a nonionic surfactant.
These additives may be used alone or in combination of two or more.

EXAMPLES Next, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not restrict | limited at all by these examples.
The hydraulic fluid composition for a shock absorber according to Example 1 and Comparative Example 1 was prepared according to the composition shown in Table 1. These compositions were subjected to the following (1) damping force change rate measurement test, (2) frictional force measurement test, and (3) sealing material compatibility test.

* 1 Base oil A1: Hydrocarbon base oil (hydrocracking mineral oil) having the following properties.
Kinematic viscosity @ 40 ° C: 11.6 mm ² / s, aniline point: 107 ° C, pour point: <-50 ° C
* 2 Base oil A2: A mixture of three mineral oils that are hydrocarbon base oils and have the following properties.
(1) Neutral base oil; kinematic viscosity @ 40 ° C: 9.4 mm ² / s, aniline point: 96 ° C, pour point: -13 ° C
(2) Naphthenic base oil; Kinematic viscosity @ 40 ° C .: 11.6 mm ² / s, aniline point: 57 ° C., pour point: <−50 ° C.
(3) Naphthenic base oil; Kinematic viscosity @ 40 ° C: 8.6 mm ² / s, aniline point: 59 ° C, pour point: <-50 ° C

* 3 Base oil B1: Hydrocarbon base oil (obtained by removing aromatics from a gasoline fraction having a boiling range of 150 to 200 ° C. obtained by atmospheric distillation of crude oil) and having the following properties: A mixture of equal amounts of oil. Kinematic viscosity @ 40 ° C: 3.1 mm ² / s, aniline point: 85.9 ° C, pour point: -32.5 ° C
(1) Kinematic viscosity @ 40 ° C: 2.5 mm ² / s, aniline point: 78 ° C, pour point: -45 ° C, aromatic content 0.1% by mass,
(2) Kinematic viscosity @ 40 ° C: 4.1 mm ² / s, aniline point: 89 ° C, pour point: -35 ° C, aromatic content 0.2% by mass

* 4 Base oil B2: Hydrocarbon base oil (obtained by removing aromatics from a gasoline fraction having a boiling range of 150 to 200 ° C. obtained by atmospheric distillation of crude oil) and having the following properties. Kinematic viscosity @ 40 ° C: 4.1 mm ² / s, aniline point: 89 ° C, pour point: -35 ° C
* 5 Polymethacrylate A: non-dispersed, weight average molecular weight: 400,000
* 6 Polymethacrylate B: Dispersion type, weight average molecular weight: 150,000
* 7 Amine salt of acidic phosphate; Amine salt of oleyl acid phosphate

(1) Damping force change rate measurement test Using the hydraulic fluid composition for shock absorbers described in Example 1 and Comparative Example 1, a bench-top actual machine test was performed to measure the temperature change rate of the damping force.
The rate of change in damping force was calculated from the following formula based on the measured value at 20 ° C. for both the example and the comparative example. Specifically, in the experiment, a shock absorber for automobile in which test oil was sealed was vibrated under the following experimental conditions, and the damping force applied when the piston of the end shock absorber was extended was measured. The lower the rate of change in damping force, the smaller the change in damping force due to temperature change, which means that the ride comfort and steering stability of the car can be maintained.
The results are shown in Table 2.

"Damping force change rate measurement test conditions"
Example 1 Test condition temperature at the time of measurement: −30 ° C. ± 3 ° C., 20 ± 3 ° C., 80 ± 3 ° C.
Excitation waveform: sine wave piston speed: 0.05 m / s, 0.10 m / s, 0.30 m / s
Lateral force: 0N
Comparative Example 1 Test condition temperature during measurement: 20 ± 3 ° C., 50 ± 3 ° C., 80 ± 3 ° C.
Excitation waveform: sine wave piston speed: 0.05 m / s, 0.10 m / s, 0.30 m / s
Lateral force: 0N

(Damping force change rate calculation formula)
Damping force change rate (%) = {(damping force at T ° C.) − (Damping force at 20 ° C.)} / (Damping force at 20 ° C.) × 100

(Comparison 1 damping force change rate calculation formula at -30 ° C)
Damping force change rate (%) = {Viscosity change rate of 20 ° C. → -30 ° C. of Comparative Example 1} / {Viscosity change rate of 20 ° C. → -30 ° C. of Example 1}
× (Damping force change rate of Example 1 at −30 ° C.)

(2) Friction force measurement test Similar to the damping force change rate measurement test, the bench actual machine test was performed using the hydraulic fluid composition for shock absorbers described in Example 1 and Comparative Example 1, and the friction force was measured.
The results are shown in Table 3.
"Frictional force measurement test conditions"
Example 1 and Comparative Example 1 Experimental condition temperature during measurement: 20 ± 3 ° C.
Excitation waveform: Sine wave stroke: ± 5mm
Piston speed: 0.001m / s
Lateral force: 0N

(3) Sealing material compatibility test The sealing material was immersed in the hydraulic fluid composition for shock absorbers described in Example 1 and Comparative Example 1, and the volume change rate and the weight change rate were measured.
The results are shown in Table 4.
"Seal compatibility test conditions"
Sealing material: Nitrile rubber test oil temperature: 100 ° C
Test time: 70h

Claims (2)

A hydraulic fluid composition comprising a base oil and a polymethacrylate viscosity index improver having a weight average molecular weight of 200,000 to 600,000 and an amine salt of an acidic phosphate ester, the polymethacrylate The blending ratio of the viscosity index improver of the system is 0.1 to 5.0% by mass with respect to the total amount of the composition, and the blending ratio of the amine salt of the acidic phosphate is based on the total amount of the composition As the properties of the composition, the kinematic viscosity at 40 ° C. is 4 to 8 mm ² / s, the Brookfield viscosity at −30 ° C. is 1000 mPa · s or less, and the aniline point is 85 to 85%. A hydraulic fluid composition for a shock absorber, having a viscosity index of 110 ° C. or higher at 110 ° C. The base oil is (A) a hydrocarbon base oil having a kinematic viscosity at 40 ° C. of 10 to 15 mm ² / s, an aniline point of 100 to 115 ° C., and a pour point of −40 ° C. or less, and (B) Hydrocarbon base oils having a kinematic viscosity at 40 ° C. of 2.0 to 5.0 mm ² / s, an aniline point of 60 to 95 ° C., and a pour point of −20 to −50 ° C. are represented by (A) and (B). The hydraulic fluid composition for a shock absorber according to claim 1, which is a base oil containing (A) at a ratio of 25 to 55 mass% with respect to the total mass of the buffer.