JPH07150176A - Hydraulic fluid composition - Google Patents

Abstract

(57) [Summary] [Structure] A hydraulic fluid base oil containing long-chain zinc dithiophosphate and sorbitan fatty acid ester as essential components, and the average hydrocarbon group of the long-chain zinc dithiophosphate. A hydraulic fluid composition in which the chain length and the average chain length of the hydrocarbon groups of the sorbitan fatty acid ester are substantially in the same range. [Effect] It has excellent friction characteristics and wear resistance, and is used in hydraulic systems such as various hydraulic equipment and devices, and is particularly suitable for shock absorbers.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel hydraulic fluid composition, and more particularly, to excellent friction characteristics and wear resistance, for example, construction machines, machine tools, plastic processing machines, vehicles, ships and aircraft. The present invention relates to a hydraulic fluid composition that is used in a hydraulic system such as the hydraulic equipment and device, and is particularly suitable for a shock absorber.

[0002]

2. Description of the Related Art Hydraulic fluid is a power transmission fluid used for operations such as power transmission, force control and buffering in hydraulic systems such as hydraulic equipment and devices, and also fulfills the function of lubricating sliding parts. With respect to such hydraulic oil, (1) good lubrication performance is exhibited under the operating conditions of the hydraulic system, wear of the sliding portion is small, (2) viscosity change with operating temperature is small, (3) Having proper operating characteristics, (4) Stable use for a long period of time,
Many properties are required such as (5) no corrosiveness to metal, (6) not hardening or expanding the sealing material. As a hydraulic fluid, it is impossible to satisfy such a required performance only by improving a base oil component such as mineral oil or synthetic oil. Therefore, conventionally, various additives such as an antiwear agent, a friction modifier, The above performance is imparted by adding a viscosity index improver or the like. By the way, among the required performances, particularly low friction coefficient and excellent wear resistance are essential performances essential for hydraulic fluid. For example, hydraulic fluid for shock absorbers used in suspension systems for automobile bodies is designed to absorb vibrations to the vehicle body to secure ride comfort and maneuverability under severe driving conditions of automobiles, and to improve wear resistance. It is strongly demanded that the friction characteristics and the durability thereof be good. Therefore, in order to satisfy these required performances, for example, a lubricating base oil, zinc dithiophosphate (hereinafter referred to as Zn
(Also sometimes abbreviated as DTP), a hydraulic oil composition for a shock absorber (Japanese Patent Application Laid-Open No. 55-165996) and a lubricating oil base, in which a long-chain fatty acid is added as an oiliness agent and a detergent dispersant is further added. A hydraulic fluid for shock absorbers containing a boron-containing detergent dispersant and a phosphoric acid ester (Japanese Patent Publication No.
No. 44879) has already been proposed. However, the hydraulic fluid to which zinc dithiophosphate is added has a drawback that it has a high friction coefficient, although it has good wear resistance. Therefore, in order to reduce the coefficient of friction, zinc dithiophosphate is usually used in combination with other additives.However, oily agents such as long-chain fatty acids used in combination cause corrosion of the bearing material of the shock absorber. However, it has the drawback of promoting wear. On the other hand, phosphoric acid esters have a large effect of reducing the friction coefficient, but have insufficient wear resistance and some cause corrosive wear. Therefore, it has been studied to use a phosphoric acid ester having a small corrosion wear, for example, a phosphorous acid ester. In this case, although the wear resistance is improved, there is a drawback that the friction coefficient reducing effect is lowered.
Therefore, if these phosphoric acid esters and an oiliness agent are used together, the coefficient of friction is reduced, but a problem remains in terms of wear resistance. In recent years, the performance requirements for hydraulic fluids have become more and more severe, but in reality, it is extremely difficult to obtain a hydraulic fluid composition having a high degree of wear resistance and a low friction coefficient.

[0003]

Under the circumstances described above, the present invention has excellent wear resistance, low corrosion resistance, and excellent friction characteristics, such as various hydraulic equipment and devices. The present invention has been made for the purpose of providing a hydraulic fluid composition that is suitable for use as a shock absorber for automobiles and is particularly suitable for shock absorbers of automobiles.

[0004]

As a result of intensive studies to develop a hydraulic fluid composition having the above-mentioned preferable properties, the present inventor has found that long-chain zinc dithiophosphate having high wear resistance and friction adjustment When a long-chain zinc dithiophosphate and the average chain length of the hydrocarbon groups in the sorbitan fatty acid ester are used in combination with a sorbitan fatty acid ester as an agent, a good low friction coefficient is obtained. The inventors have found that the objects can be achieved, and have completed the present invention based on this finding. That is, the present invention comprises a hydraulic oil base oil containing long-chain zinc dithiophosphate and sorbitan fatty acid ester as essential components, and the average chain length of the hydrocarbon groups of the long-chain zinc dithiophosphate and The present invention provides a hydraulic fluid composition characterized in that the average chain length of the hydrocarbon groups of the sorbitan fatty acid ester is substantially in the same range. The greatest feature of the composition of the present invention is that the zinc dithiophosphate has a long-chain hydrocarbon group, and the average chain length of the hydrocarbon group and the average chain length of the hydrocarbon group of the sorbitan fatty acid ester are , Within a substantially equivalent range. Here, “within substantially the same range” means that the difference between the average carbon numbers of the two is less than 4, preferably 2 or less. As described above, it was found that, by using zinc dithiophosphate having a hydrocarbon group having a similar number of carbon atoms and sorbitan fatty acid ester in combination, a surprisingly remarkable effect of reducing the friction coefficient is exhibited, and the present invention is It has been completed.

The present invention will be described in detail below. The hydraulic oil base oil used in the composition of the present invention is not particularly limited, and various conventionally proposed mineral oils, that is, hydrocarbon oils, synthetic oils and the like can be used. As the mineral oil, for example, raffinate obtained by solvent refining using phenol, furfural or the like, or light neutral derived from hydrotreated oil obtained by hydrotreatment using a hydrotreating catalyst such as cobalt or molybdenum Oils, medium neutral oils, heavy neutral oils, bristock, and the like. On the other hand, examples of the synthetic oil include α-olefin oligomer, polybutene, alkylbenzene, ester of polyol and fatty acid, ester of dibasic acid and alcohol, silicone oil and the like. The mineral oil may be used alone, or two or more kinds may be used in combination, and the synthetic oil may be used one kind, or two or more kinds may be used in combination. Further, mineral oil and synthetic oil may be mixed and used.
The base oil used in the composition of the present invention varies depending on the use, but the kinematic viscosity at a temperature of 100 ° C. is usually 1 to
Those in the range of 30 mm ² / s are preferable. In the composition of the present invention, long-chain zinc dithiophosphate and sorbitan fatty acid ester are used as essential components. The long-chain zinc dithiophosphate has the general formula [1]

[0006]

[Chemical 1]

A compound represented by the formula: R ^{1 to} R ⁴ in the formula
Are each a hydrocarbon group having 1 to 30 carbon atoms, and their average carbon number is 8 or more, preferably 10 or more.
R ^{1 to} R ⁴ may be the same or different. R ^{1 to} R ⁴ are each an alkyl group having 1 to 30 carbon atoms, an alkenyl group having 2 to 30 carbon atoms, and 6 to 6 carbon atoms.
30 cycloalkyl group, C 6-30 aryl group, C 7-30 alkylaryl group, C 7-
Examples thereof include an arylalkyl group having 30 carbon atoms, a hydrocarbon group having 1 to 30 carbon atoms including an ester bond, an ether bond, an alcohol group or a carboxyl group.
Of these, an alkyl group having 8 to 20 carbon atoms, a cycloalkyl group having 8 to 18 carbon atoms, and an alkylaryl group having 8 to 18 carbon atoms are particularly preferable. Further, it is preferable that the secondary hydrocarbon group is present in an amount of 50 mol% or more based on the total amount of the hydrocarbon groups of R ^{1 to} R ⁴ . The long-chain zinc dithiophosphate includes various ones from the one in which all the hydrocarbon groups of R ^{1 to} R ^{4 in} the formula are the same to different ones,
One of these may be used, or two or more of them may be appropriately mixed and used. The long-chain zinc dithiophosphate is usually 0.1 to 7% by weight, preferably 0.1% by weight, based on the total weight of the composition.
It is mixed in a proportion of 2 to 3% by weight. This amount is 0.1
If it is less than 7% by weight, the effect of addition is not sufficiently exerted, and if it exceeds 7% by weight, the effect of addition is not so much improved for the amount.

On the other hand, as the sorbitan fatty acid ester, a mono-, di-, or triester whose ester group is a hydrocarbon group having 10 to 30 carbon atoms is preferably used. Typical examples of the ester group include a laurate group, an oleate group, a stearate group, a myristate group,
Examples thereof include palmitate group and phenyl stearate group. Therefore, as a typical sorbitan fatty acid ester, sorbitan monolaurate, sorbitan monooleate, sorbitan monostearate, sorbitan sesquioleate, sorbitan dioleate, etc. may be mentioned, and these may be used alone, Two or more kinds may be appropriately mixed and used, but as described above, a hydrocarbon group having an average carbon number within a range substantially equivalent to the average carbon number of the hydrocarbon group of the long-chain zinc dithiophosphate is used. It is necessary to select and use what you have. Thereby, the effect of reducing the friction coefficient is exhibited. As the sorbitan fatty acid ester, a commercially available sorbitan fatty acid ester can be used, or a boride compound of sorbitan fatty acid ester can also be used. Preferable examples of the boride include borated sorbitan monooleate obtained by reacting 2/3 to 1 mol of boric acid with 1 mol of sorbitan monooleate. By using such a borated sorbitan fatty acid ester, the corrosiveness of the bearing portion can be suppressed. In the composition of the present invention, the sorbitan fatty acid ester is generally added in a proportion of 0.05 to 5.0% by weight, preferably 0.1 to 2.0% by weight, based on the total weight of the composition. If the amount is less than 0.05% by weight, the effect of improving wear resistance and friction coefficient is not sufficiently exhibited, and if the amount is more than 5.0% by weight, the effect is not so much improved for the amount. .

The hydraulic fluid composition of the present invention may contain other additives, if necessary, such as a viscosity index improver, an antioxidant, an antifoaming agent, and a metal detergent within a range not impairing the object of the present invention. , A metal deactivator, a rust preventive and the like can be added appropriately. Examples of the viscosity index improver include polymethylmethacrylate-based, polyisobutylene-based, ethylene-
Examples thereof include a propylene copolymer system and a styrene-butadiene hydrogenated copolymer system, and they are usually used in a proportion of 0.5 to 35% by weight, preferably 1 to 15% by weight. Examples of the antioxidant include amine-based antioxidants such as alkylated diphenylamine, phenyl-α-naphthylamine, and alkylated-naphthylamine, 2,6-di-t-butylphenol, 4,4′-methylenebis (2,6 -Di-t-
Examples thereof include phenolic antioxidants such as butylphenol), and these are generally used in a proportion of 0.05 to 2% by weight, preferably 0.1 to 1% by weight. Examples of the defoaming agent include dimethylpolysiloxane and polyacrylate, and are usually added in a very small amount, for example, about 0.002% by weight. Examples of the metal detergent include Ca-sulfonate, Mg-sulfonate, Ba-sulfonate, Ca-phenate, Ba-phenate and the like, and these are usually 0.1 to 5% by weight.
Used in proportion. As the metal activator, for example,
Examples thereof include benzotriazole, benzotriazole derivative, benzothiazole, benzothiazole derivative, triazole, triazole derivative, dithiocarbamate, dithiocarbamate derivative, indazole and indazole derivative, and these are usually 0.005
Used in proportions of up to 0.3% by weight. As a rust preventive,
For example, alkenyl succinic acid or a partial ester thereof and the like can be mentioned, which can be appropriately added.

[0010]

The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto. The friction coefficient of the hydraulic fluid composition was determined according to the method described below. . (1) Coefficient of friction Using a Bowden tester, a few drops of sample oil were placed on the sliding surface of a nitrile rubber plate, and then a steel ball (3/4 inch) under a load of 3000 gf was applied at a low speed (3. 3 mm / s)
The friction coefficient was measured at room temperature and 50 ° C. by sliding. The friction coefficient was obtained by a method in which a strain gauge for detecting friction torque was attached to a steel ball cage that holds a steel ball, and the amount of strain was measured electrically. Example 1 As a hydraulic oil base oil, the kinematic viscosity at 100 ° C. is 2.5 mm ² /
s of highly hydrorefined mineral oil, 0.5% by weight of zinc dilauryldithiophosphate (C ₁₂ ) and sorbitan monolaurate (C ₁₂ ) as a friction modifier, based on the total weight of the composition. 5% by weight was added, and further, viscosity index improver (polymethacrylate type) 2.0% by weight, antioxidant (diphenylamine type) 0.2% by weight, metal deactivator (benzotriazole type) 0.1% by weight % And an antifoaming agent (silicone oil type) of 0.005% by weight were added to prepare a hydraulic fluid composition. The friction coefficient of the hydraulic oil composition was measured to be 0.120 at room temperature and 0.13 at 50 ° C.
It was 0. Comparative Examples 1 to 11 To the hydraulic oil base oil used in Example 1, zinc dithiophosphate and friction modifiers of the types shown in Table 1 were added in the amounts shown in Table 1, and other additives were added. The type and the addition amount of were prepared in the same manner as in Example 1, a hydraulic oil composition was prepared, and the friction coefficient thereof was determined. The results are shown in Table 1.

[0011]

[Table 1]

[0012]

[Table 2]

[0013]

The hydraulic fluid composition of the present invention contains, as essential components, zinc dithiophosphate having a long-chain hydrocarbon group and sorbitan fatty acid ester, and the hydrocarbon group of the zinc dithiophosphate is The average chain length and the average chain length of the hydrocarbon groups of the sorbitan fatty acid ester are substantially in the same range, and have excellent wear resistance and low friction coefficient, It is used as hydraulic fluid for hydraulic systems such as hydraulic equipment, and is particularly suitable as hydraulic fluid for shock absorbers.

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Claims (1)

[Claims] 1. A hydraulic fluid base oil, which comprises, as essential components, long-chain zinc dithiophosphate and sorbitan fatty acid ester, and the average chain length of hydrocarbon groups of said long-chain zinc dithiophosphate and A hydraulic fluid composition, wherein the average chain length of the hydrocarbon groups of the sorbitan fatty acid ester is substantially in the same range.