Shock absorber fluid

Abstract: A hydraulic working oil composition for buffers which comprises a lubricating oil as a base oil, (A) a phosphoric acid ester such as dioleyl acid phosphate and/or a phosphorous acid ester such as dioleyl hydrogen phophite, and (B) an adduct of an aliphatic amine such as oleyl amine with an alkylene oxide such as ethylene oxide, the compounds (A) and (B) being the essential components added to said base oil; and, in one embodiment, a process for lubricating buffers which comprises adding said compounds (A) and (B) to said base oil to prepare a hydraulic working oil composition and using the thus prepared oil composition in buffers.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to hydraulic working oil compositions for use in buffers and more particularly to such oil compositions suitable for car suspension devices such as shock absorbers. 2. Prior Art As conventional hydraulic working oils which have hitherto been used in car buffer devices such as shock absorbers, active suspensions, stay dampers and engine dampers, there have been known those which incorporate a phosphoric acid ester and/or a phosphorus acid ester to provide them with friction-reducing properties and wear-preventing properties. In addition, there have also widely used such hydraulic working oils in which a fatty acid, aliphatic alcohol, fatty acid ester, aliphatic amine and other oily agents are used to further improve the working oils in friction-reducing properties. Hydraulic working oils are those which are required to be capable of reducing friction at friction surfaces simultaneously with preventing wear of the friction surfaces. Recently, there have been increasingly used bush members impregnated with a Teflon resin in attempts to reduce friction at friction surfaces from the standpoint of material or substance used. Further, particularly gas-sealed type and damping force-variable type buffers have increasingly been used and, therefore, load applied to the friction surfaces of buffers has been increased and conditions under which the buffers are used have be come severe. With a change in such conditions or circumstances under which hydraulic working oils are used, conventional oils incorporating only a phosphoric acid ester and/or a phosphorous acid ester, or those in which a fatty acid, aliphatic alcohol, a fatty acid ester and other oily agents are used, have raised problems in that they allow friction surfaces to be come considerably worn since their friction-reducing effects are low and poor. In addition, it has been found that the conventional working oils in which is used a phophoric acid ester and/or a phosphorous acid ester as well as an aliphatic amine which is an oily agent, will exhibit somewhat excellent wear-preventing and friction-reducing effects on the friction surfaces of a suspension device at the initial time when the working oils are used therein but the conventional working oils will raise problems that they cannot keep such effects durably and will greatly increase in frictional coefficient during their use whereupon spherical particles produced by the wear of the friction surfaces are attached to the friction surfaces which are the surfaces of a Teflon resin-impregnated bush member. EP-A-351 964 and EP-A-348 236 each discloses a lubricating oil composition, comprising a lubricating oil and additives including a hydroxyl amine compound and an organic phosphite ester. These power transmission fluids can control the friction characteristics but not necessarily lower it. US-A-4 634 543 discloses a fluid composition for use in a shock absorber, comprising as an essential component a phosphoric acid ester and a boron containing detergent in a lubricating base oil. There have been eagerly desired the developments of novel hydraulic working oils for a buffer which meet new requirements such as excellent applicability to Teflon resin-impregnated bush members and excellent durability (little degradation during the use) of friction-reducing and wear-preventing effects, in addition to the conventional requirements, since said new requirements have come to be made much of. SUMMARY OF THE INVENTION The primary object of this invention is to provide shock absorber fluids which are excellent in applicability to Teflon resin-impregnated bush members as well as durability (little degradation with the time of use) of friction-reducing and wear-preventing effects. The present inventors made intensive studies to achieve the object of this invention and, as the result of their studies, found that the combined use of (A) a phosphoric acid ester and/or a phosphorous acid ester and (B) an alkylene oxide of an aliphatic amine in a lubricating oil as a base oil will exert their synergistic effect thereby to obtain a new hydraulic working oil exhibiting excellent performances when used, thus completing this invention. The primary object of this invention is achieved by providing a shock absorber fluid prepared by adding to a lubricating oil as a base oil the following ingredients as essential components (A) a phosphoric acid ester and/or a phosphorous acid ester and (B) an alkylene oxide adduct of an aliphatic amine. This invention will be explained below in more detail. The lubricating oils used as a base oil in this invention are not particularly limited, and both mineral oils and synthetic oils which are usually used as a base oil for lubricating oils may be used as the base oil in this invention. The mineral oil-type lubricating oils which may be used as a base oil, include paraffinic and naphthenic oils obtained by refining, for example, lubricating oil fractions obtained by the atmospheric and reduced-pressure distillation of a crude oil, by means of a suitable combination of solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing and clay treatment. The synthetic oil-type lubricating oils which may be used as a base oil, include poly α-olefins (polybutene, 1-octene oligomers, 1-decene oligomers, etc.), alkylbenzenes, alkylnaphthalenes, diesters (ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, etc.), polyol esters (trimethylolpropane caprylate, trimethylolpropane peralgonate, pentaerithritol 2-ethyl hexanoate, pentaerithritol peralgonate, etc.), polyoxyalkylene glycol, polyphenyl ethers, silicone oil and perfluoroalkyl ethers. The lubricating oils used as a base oil are hereinafter sometimes referred to as "base lubricating oils" for simplicity. The base lubricating oils may be used singly or jointly, but the mineral oil-type base lubricating oils are preferably used from the standpoint of their adaptability to, or compatibility with, gum sealants in this invention. The base lubricating oils used in this invention are optional in viscosity, but those having a viscosity of 8 - 60 cSt, preferably 10 - 40 cSt, at 40°C are usually used from necessity for their applicability to damping force required in general buffers. The component (A) which is an essential additive to be added to a base lubricating oil according to this invention is a phosphoric acid ester and/or a phosphorous acid ester. The phosphoric acid ester defined here is a compound represented by the following formula (1) and the phosphorous acid ester defined here is a compound represented by the following formula (2) In the formula (1) R 1 and R 2 are each a straight-chain or branched-chain alkyl or alkenyl group having 8 - 20 carbon atoms, and R 3 is hydrogen; in the formula (2) R 4 and R 5 are each a straight-chain ore branched-chain alkyl or alkenyl group having 8 - 20 carbon atoms, and R 6 is hydrogen. R 1 , R 2 , R 4 and R 5 each include an alkyl group such as butyl groups (including all isomeric groups), pentyl groups (including all isomeric groups), hexyl groups (including all isomeric groups), heptyl groups (including all isomeric groups), octyl groups (including all isomeric groups), nonyl groups (including all isomeric groups), decyl groups (including all isomeric groups), undecyl groups (including all isomeric groups), dodecyl groups (including all isomeric groups), tridecyl groups (including all isomeric groups), tetradecyl groups (including all isomeric groups), pentadecyl groups (including all isomeric groups), hexadecyl groups (including all isomeric groups), heptadecyl groups (including all isomeric groups), octadecyl groups (including all isomeric groups), nonadecyl groups (including all isomeric groups), eicosyl groups (including all isomeric groups), heneicosyl groups (including all isomeric groups) and docosyl groups (including all isomeric groups); an alkenyl group such as butenyl groups (including all isomeric groups), pantenyl groups (including all isomeric groups), hexenyl groups (including all isomeric groups), heptenyl groups (including all isomeric groups), octenyl groups (including all isomeric groups), nonenyl groups (including all isomeric groups), decenyl groups (including all isomeric groups), undecenyl groups (including all isomeric groups), dodecenyl groups (including all isomeric groups), tridecenyl groups (including all isomeric groups), tetradecenyl groups (including all isomeric groups), pentadecenyl groups (including all isomeric groups), hexadecenyl groups (including all isomeric groups), heptadecenyl groups (including all isomeric groups), octadecenyl groups (including all isomeric groups), nonadecenyl groups (including all isomeric groups), eicosenyl groups (including all isomeric groups), heneicosenyl groups (including all isomeric groups) and docosenyl groups (including all isomeric groups). From the standpoint of excellency particularly in wear-preventing and friction-reducing effects, the phosphoric acid ester of the component (A) used in this invention is preferably a compound of the formula (1) wherein R 1 and R 2 are each a member selected from a straight-chain alkyl or alkenyl group, and R 3 is hydrogen. From the standpoint of excellency particularly in wear-preventing and friction-reducing effects in the same manner as in the phosphoric acid ester of the formula (1), the phosphorous acid ester of the component (A) used in this invention is preferably a compound of the formula (2) wherein R 4 and R 5 are each a straight-chain alkyl or alkenyl group, and R 6 is hydrogen. The phosphoric acid ester which is among the components (A) used in this invention includes dioctyl acid phosphate (dicapryl acid phosphate), didecyl acid phosphate, didodecyl acid phosphate (dilauril acid phosphate), ditetradecyl acid phosphate (dimyristyl acid phosphate), dihexadecyl acid phosphate (dipalmityl acid phosphate), dioctadecyl acid phosphate (distearyl acid phosphate) and di-9-octadecenyl acid phosphate (dioleyl phosphate). The phosphorous acid ester which is among the components (A), includes dioctyl hydrogen phosphite (dicapryl hydrogen phosphite), didecyl hydrogen phosphite, didodecyl hydrogen phosphite (dilauril hydrogen phosphite), ditetradecyl hydrogen phosphite (dimyristyl hydrogen phosphite), dihexadecyl hydrogen phosphite (dipalmityl hydrogen phosphite), dioctadecyl hydrogen phosphite (distearyl hydrogen phosphite), di-9-octadecenyl hydrogen phosphite (dioleyl hydrogen phosphite) and a mixture thereof. In the shock absorber fluid of this invention, the amount of the phosphoric acid ester and/or phosphorous acid ester added may be arbitrary, but it is an amount of preferably 0.05 to 10% by weight, more preferably 0.1 to 5% by weight, based on the total weight of the composition. Further, the component (B) which is another essential component used in this invention is an adduct of an aliphatic amine with an alkylene oxide. The alkylene oxide adduct of an aliphatic amine defined in this invention means a compound represeted by the following general formula (3) wherein R 7 represents a straight-chain or branched-chain alkyl or alkenyl group having 8 - 22 carbon atoms, R 8 and R 9 may be identical with, or different from, each other and are each a straight-chain or branched-chain alkylene group having 2 - 4 carbon atoms; and m and n may be identical with, or different from, each other and are each an integer of 0-10 with the proviso that m plus n equals 1-10, prefereably 1-5. R 7 is exemplified by an alkyl group such as octyl groups (including all isomeric groups), nonyl groups (including all isomeric groups), decyl groups (including all isomeric groups), undecyl groups (including all isomeric groups), dodecyl groups (including all isomeric groups), tridecyl groups (including all isomeric groups), tetradecyl groups (including all isomeric groups), pentadecyl groups (including all isomeric groups), hexadecyl groups (including all isomeric groups), heptadecyl groups (including all isomeric groups), octadecyl groups (including all isomeric groups), nonadecyl groups (including all isomeric groups), eicosyl groups (including all isomeric groups), heneicosyl groups (including all isomeric groups) and docosyl groups (including all isomeric groups); and an alkenyl group such as octenyl groups (including all isomeric groups), nonenyl groups (including all isomeric groups), decenyl groups (including all isomeric groups), undecenyl groups (including all isomeric groups), docenyl groups (including all isomeric groups), tridecenyl groups (including all isomeric groups), tetradecenyl groups (including all isomeric groups), pentadecenyl groups (including all isomeric groups), hexadecenyl groups (including all isomeric groups), peptadecenyl groups (including all isomeric groups), octadecenyl groups (including all isomeric groups), nonadecenyl groups (including all isomeric groups), eicosenyl groups (including all isomeric groups), heneicosenyl groups (including all isomeric groups) and docosenyl groups (including all isomeric groups). R 8 and R 9 include an ethylene group, trimethylene group, 1-methylethylene group, 2-methylethylene group, tetramethylene group, 1-methyltrimethylene group, 2-methyltrimethylene group, 3-methyltrimethylene group, 1-ethylethylene group, 2-ethylethylene 1,2-dimethylethylene group, 1,1-dimethylethylene group, group and 2,2-dimethylethylene group. The alkylene oxide adduct of an aliphatic amine, which is represented by formula (3) and is the component (B) used in this invention, is preferably a compound of the formula (3) in which R 7 is a straight-chain alkyl or alkenyl group having 12-18 carbon atoms, and R 8 and R 9 are each an ethylene group, in view of excellent wear-reducing effects. The particularly preferable alkylene oxide adducts of an aliphatic amine, which are the component (B) used in this invention, include ethylene oxide adducts of an aliphatic amine and a mixture of the adducts, and more particularly they are alkylene oxide adducts of an aliphatic amine such as octyl amine (capryl amine), decyl amine, dodecyl amine (lauril amine), tetradecyl amine (mylystyl amine), hexadecyl amine (palmitil amine), octadecyl amine (stearyl amine) or 9-octadecenyl amine (oleyl amine). In the shock absorber fluid of this invention, the amount added of the alkylene oxide adduct of an aliphatic amine, which is the component (B), may be arbitrary, but it is desirable to add the adduct in an amount of preferably 0.05 to 10% by weight, more preferably 0.1 to 5% by weight, based on the total weight of the composition. As described above, although the shock absorber fluid of this invention having excellent performances can be obtained by only adding to the base lubricating oil the phosphoric ester and/or phosphorous ester which is the component (A), and the alkylene oxide adduct of an aliphatic amine, which is the component (B), into the base lubricating oil. To further enhance the thus obtained hydraulic working oil composition in such performances, heretofore known additives for lubricating oils may be used singly or jointly. These additives include friction-reducing agents other than the components of the oil composition of this invention, such as an aliphatic alcohol, aliphatic acid, aliphatic amine and aliphatic amide; antioxidants such as phenol-, amine-, sulphur-, zinc dithiophosphate- and phenothiazine-based compounds; extreme-pressure agents such as sulfurized fats and oils, sulfides and zinc dithiophosphate; rust preventives such as petroleum sulfonates and dinonylnaphthalene sulfonate; metal deactivators such as benzotriazole and thiadiazole; metallic detergents such as alkaline earth metal sulfonates, alkaline earth metal phenates, alkaline earth metal salicylates and alkaline earth metal phosphonates; ashless dispersants such as succinic imide, succinic esters and benzyl amine; antifoaming agents such as methylsilicone and fluorosilicone; viscosity index improvers such as polymethacrylate, polyisobutylene and polystyrene; and pour point depressants. Although the amount of these additives added may be arbitrary, the contents of the antifoaming agent, the viscosity index improver, the metal inactivator and each of the other additives in the oil composition are ordinarily 0.0005 - 1% by weight, 1 - 30% by weight, 0.005 - 1% by weight and 0.1 - 15% by weight in this order, based on the total amount of the oil composition, respectively. The process for preparing the hydraulic working oil compositions of this invention is not particularly limited. This process, however, may usually comprise mixing a base lubricating oil and additives including the essential components (A) and (B) together, heating the resulting mixture to 30 - 100°C and then maintaining it at this temperature under agitation for 20 minutes to 5 hours, or may comprise separately heating all the additives (solid additives having beforehand been solved in a small amount of the base lubricating oil) to 30 - 100°C, mixing these additives in portions or in full into the base lubricating oil heated to 20 - 80°C and then maintaining the resulting mixture at 30 - 100°C under agitation for 20 minutes to 5 hours. DESCRIPTION OF PREFERRED EMBODIMENTS This invention will be better understood by the non-limitative Examples and Comparative Examples. Examples 1 - 3 and Comparative Examples 1 - 4 In each of the Examples, the ingredients shown in Table 1 were mixed together and the resulting mixture was heated to 50°C under stirring for two hours thereby to prepare a hydraulic working oil composition of this invention (Examples 1 - 3). The oil compositions of this invention so prepared were subjected to a duration test using an actual device to evaluate them for their friction-reducing effects and wear-preventing effects. Comparative hydraulic working oil compositions were prepared by following the procedure of the above Examples except that the component (A) was used singly (Comp. Example 1), except that the component (B) was used singly (Comp. Example 2), except that an aliphatic amine was substituted for the component (B) (Comp. Example 3) or except that a fatty acid was substituted for the component (A) (Comp. Example 4). The comparative oil compositions so prepared were subjected to the same duration test as above. Duration Test Using Actual Device Using two commercially available strut-type shock absorbers, duration tests were made under the following conditions until the end of two million frequency of oscillation application. Temperature of a test oil 80°C Amount of a test oil used 330 ml/one shock absorber Lateral load 200 kgf Entire amplitude of oscillation applied 50 mm Velocity of oscillation applied 0.5 m/s (1) Friction-reducing effects The shock absorbers were measured for their frictional coefficients at their surfaces at the time of oscillation application frequency of zero (at the initial stage of the duration test) and at the time of oscillation application frequency of two million (at the time of completion of the duration test), respectively. The frictional coefficients so measured are as shown in Table 1. (2) Wear-preventing effects After the completion of the duration test, the shock absorbers were disassembled to visually evaluate the surface state of their friction surfaces (cylinders, pistons, rods and oil seals of the shock absorbers) with the results being as shown in Table 1. The degrees of the wear-preventing effects are represented in terms of six numerals 0 - 5 (numeral 5 being the best). As is apparent from the results of the Examples, the hydraulic working oil compositions (Examples 1 - 3) are excellent in friction-reducing effects at the initial stage of the duration test and exhibit less degradation of their friction-reducing performances with the lapse of time. In addition, they exhibit less wear at the friction surfaces even at the time of end of the duration test whereby they are also excellent in wear-preventing effects. The comparative hydraulic working oil compositions (Comp. Examples 1 - 4), on the other hand, are excellent in friction-reducing effects at the initial stage of the duration test but they exhibit much more degradation of their friction-reducing performances with the lapse of time. In addition, they are very also inferior in wear-preventing effects to those of this invention. Effects of this Invention As is apparent from the foregoing, the hydraulic working oil compositions of this invention are excellent not only in applicability to Teflon resin-impregnated bush members but also in durability (less degradation with the time) of friction-reducing effects and wear-preventing effects.

Claims: Shock absorber fluid comprising a lubricating oil as a base oil and (A) at least one ester selected from the group consisting of a phosphoric acid ester and a phosphorous acid ester and (B) an adduct of an aliphatic amine with an alkylene oxide as essential components, wherein the phosphoric acid ester, the phosphorous acid ester and the adduct of an aliphatic amine with an alkylene oxide are represented respectively by the following formulae (1), (2) and (3) and wherein in the formula (1) the R 1 and R 2 are each a straight-chain or branched-chain alkyl or alkenyl group having 8 - 20 carbon atoms, and R 3 is hydrogen; in the formula (2) the R 4 and R 5 are each a straight-chain or branched-chain alkyl or alkenyl group having 8 - 20 carbon atoms, and the R 6 is hydrogen; and in the formula (3) the R 7 is a straight-chain or branched-chain alkyl or alkenyl group having 8 - 22 carbon atoms, and the R 8 and R 9 may be identical with, or different from, each other and they are each a straight-chain or branched-chain alkylene group having 2 - 4 carbon atoms; m and n may be identical with, or different from, each other and they are each an integer of 0-10 with the proviso that m plus n equals 1-10. Shock absorber fluid according to claim 1, wherein said R 1 , R 2 , R 4 and R 5 are each a straight-chain alkyl or alkenyl group. Shock absorber fluid according to claim 1, wherein the phosphoric acid ester is dioctyl acid phosphate (dicapryl acid phosphate), didecyl acid phosphate, didodecyl acid phosphate (dilauryl acid phosphate), ditetradecyl acid phosphate (dimyristyl acid phosphate), dihexadecyl acid phosphate (dipalmityl acid phosphate), dioctadecyl acid phosphate (distearyl acid phosphate) and di-9-octadecenyl acid phosphate (dioleyl acid phosphate) or a mixture thereof; the phosphorous acid ester is dioctyl hydrogen phosphite (dicapryl hydrogen phosphite), didecyl hydrogen phosphite, didodecyl hydrogen phosphite (dilauryl hydrogen phosphite), ditetradecyl hydrogen phosphite (dimyristyl hydrogen phosphite), dihexadecyl hydrogen phosphite (dipalmityl hydrogen phosphite), dioctadecyl hydrogen phosphite (distearyl hydrogen phosphite), di-9-octadecenyl hydrogen phosphite (dioleyl hydrogen phosphite) or a mixture thereof; and the alkylene oxide adduct of an aliphatic amine is an ethylene oxide adduct of octyl amine (capryl amine), decyl amine, dodecyl amine (lauryl amine), tetradecyl amine (mylystyl amine), hexadecyl amine (palmityl amine), octadecyl amine (stearyl amine) or 9-octadecenyl amine (oleyl amine). Shock absorber fluid according to any one of claims 1 to 3, wherein said R 7 is a straight-chain alkyl or alkenyl group having 12 - 18 carbon atoms. Shock absorber fluid according to any one of claims 1 to 4, wherein said R 8 and R 9 are each an ethylene group. Shock absorber fluid according to claims 1 to 5, wherein the m plus n equals 1 - 5. Shock absorber fluid according to any one of claims 1 to 6, wherein the base oil is a paraffinic or naphthenic oil refined by subjecting lubricating oil fractions produced by the atmospheric and reduced-pressure distillation of a crude oil to refining steps selected from solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric washing and clay treatment, or is a synthetic oil selected from the group consisting of polybutene, 1-octene oligomers, 1-decene oligomers, alkylbenzenes, alkylnaphthalenes, tridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, trimethylolpropane caprilate, trimethylolpropane peralgonate, pentaerithritol 2-ethyl hexanoate, pentaerithritol peralgonate, polyoxyalkylene glycol, polyphenyl ethers, silicone oil and perfluoroalkyl ethers. Shock absorber fluid according to any one of claims 1 to 7, wherein the base oil has a viscosity of 8 - 60 cSt at 40°C. Shock absorber fluid according to any one of claims 1 to 8, wherein the phosphoric acid ester and/or phosphorous acid ester is added to the base oil in an amount of 0.05 - 10% by weight of the total amount of the oil composition, and the alkylene oxide adduct of an aliphatic amine is added to the base oil in an amount of 0.05 - 10% by weight of the total amount of the oil composition. Preparation of a shock absorber fluid described in at least one of the foregoing claims 1 to 9, by adding component (A) and component (B) to the basis oil. Use of the fluid, comprising the basis oil, component (A) and component (B), described in at least one of the claims 1 to 9, as shock absorber fluid.

Inventors: HIRATA SHIGEAKI, MIYAGAWA TORU, OKADA MITSUO, HIRATA, SHIGEAKI, MIYAGAWA, TORU, OKADA, MITSUO, Hirata, Shigeaki, c/o Nippon Oil Co., Ltd., Miyagawa, Toru, c/o Nippon Oil Co., Ltd., Okada, Mitsuo, c/o Nippon Oil Co., Ltd.
Applicants: NIPPON OIL CO LTD, NIPPON OIL COMPANY, LIMITED
Application year: 1993
Main classification: C10M141
IPC codes: C10M161, C10N30, C10M141, C10M169, C10N40