Abstract:
The present invention relates to hydraulic fluids which are particularly intended for shock absorption and level controlling applications in vehicles. Hydraulic fluids are provided which substantially consist of esterification products of monosaturated fatty acids and 2-alkyl-1-alkanols. The claimed fluids comply with the requirements made on industrial hydraulic media and are particularly outstanding by their good biodegradability.

Description:
FIELD OF THE INVENTION 
     The present invention relates to non-polluting shock absorber and level controller fluids which are particularly intended for use in vehicles and which consist of one or more base stocks and additives. 
     BACKGROUND OF THE INVENTION 
     Prior-art shock absorber and level controller fluids, particularly used in vehicles, are select mineral oil fractions in combination with suitable lubricant additives. Said fluids are also termed in the following `automotive hydraulic fluids`. Generally, these fluids meet the requirements with respect to shock absorption and ageing resistance. However, their biodegradation is not sufficiently rapid and their ecotoxicological characteristics are unsatisfactory so that they have a considerably polluting impact on the environment. Since, particularly with shock absorbers, uncontrollable oil leakage frequently occurs, environmentally acceptable shock absorber fluids are badly required. 
     Therefore, it was first attempted to substitute the petroleum products in question with natural materials, e.g. vegetable oils. 
     PCT publication WO 88/08808 describes hydraulic fluids based on natural triglycerides and a combination of vegetable oils with synthetic esters as adjusting agents for lowering or increasing the viscosity. However, the low-temperature behavior of these products, too, remains significantly above the values required of automotive hydraulic fluids. 
     For instance, rape and sunflower oil have high lubricating powers and excellent viscosity temperature (VT) behaviors, whereas their ageing and low-temperature properties are unsatisfactory so that these materials were inappropriate as substitutes. 
     Polyethylene glycols are used to a limited extend in universal industrial hydraulic applications, but such fluids are not suitable for automotive applications because their low-temperature fluidities and compatibilities with conventional lubricants are unsatisfactory. 
     Finally, for use in shock absorbers, saturated dicarboxylic acid esters and polyol esters have been examined which, although they presented yet sufficient degradation rates and good thermal stabilities, had viscosity indices (VI) which were significantly lower than the values obtained with natural oleic acid esters. Furthermore, when using NBR (nitrile butadiene rubber), a material which is normally used in technical applications, the elastomer swelling behavior is inacceptable. 
     U.S. Pat. No. 2,757,139 of the year 1953 discloses synthetic ester oils as lubricants for use in aircraft gas turbines. The experimental part of said patent publication only relates to esters of coconut fatty acids with C 16 , C 26  Guerbet alcohols tested as turbine lubricating oils. The esters described in said publication have insufficient VI indices for the application of the invention (max. 148) so that considerable amounts of VI improvers have to be added to reach values of higher than 150. In addition, the fluidities and low-temperature behaviors of said esters are unsatisfactory. No ecological requirements are made on the products. 
     SUMMARY OF THE INVENTION 
     Therefore, it was the object of this invention to provide shock absorber and level controller fluids which fulfill the technical and strict ecological demands made on such products, particularly with respect to biodegradability. 
     In carrying out these and other objects of the invention, there is provided, in one form, hydraulic fluids for shock absorption and level controlling in vehicles having (1) esterification products of oleic acid and 2-alkyl-1-alkanols with 12 to 20 carbon atoms as biologically degradable base fluids; and (2) ecologically compatible additives. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a viscosity-temperature curve of the inventive fluid of Example 3 ranging from -40° C. to +120° C. in comparison with a conventional shock absorber oil. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to the present invention, the problem is solved by using esterification products of oleic acid and 2-alkyl-1-alkanols comprising 12 to 20 carbon atoms as biodegradable base stocks and ecologically compatible additives as fluids for the shock absorption and level control, particularly of vehicles. 
     The alkanol components preferably comprise 12 to 16 carbon atoms. In particular, oleates are used the alkanol component of which is a mixture of said alcohols. 
     According to an embodiment of the present invention, the fluids also contain prior-art base stocks besides the base stock(s) of this invention. 
     It was surprisingly found that the products obtained by esterification of oleic acid with the aforesaid 2-alkyl-1-alkanols not only present highly satisfactory biodegradabilities and excellent ecological compatibilities but also comply in an exceptionally satisfactory way with the technical requirements when used as hydraulic fluids. In particular, the following criteria are relevant: 
     a) viscosity range at 20° C.: from about 20 to 35 mm 2  /s 
     b) optimum viscosity-temperature (VT) behavior, viscosity index (VT)=at least 150 
     c) good low-temperature fluidity at -40° C., max. 2,000 mPa.s, pour point below -40° C. 
     d) low volatility, 1 h/150° C./&lt;5% 
     e) sufficient thermal ageing stability up to at least 130° C. 
     f) sufficient sealing material resistance 
     With respect to the ecological compatibility, the following demands are made: 
     a) highest possible biodegradability in conformity with CEC-L-33-T82, at least 80% 
     b) water contamination rating: 0 (zero) 
     c) none of the constituents of such fluids is allowed to have a hazardous material classification or a water contamination rating of &gt;1 
     The aforementioned requirements are met by the hydraulic fluids of the present invention. Special attention is drawn to the following characteristics: 
     exceptionally high biodegradability 
     surprisingly good thermal ageing resistance 
     favorable viscosity-temperature behavior 
     excellent low-temperature fluidity at -40° C. 
     The exceptionally high biodegradability of the branched esters used according to this invention is surprising since, in general. C-chain branching is said to inhibit degradation. 
     The base stocks according to the present invention are manufactured as known per se by esterification, e.g. in the presence of zirconium or titanium catalysts and entraining agents, and by a stripping process. They are preferably comprised of ester mixtures of oleic acid. The oleic acid may contain small amounts of linoleic acid and of linolenic acid. 
     The following compounds of the group of 2-alkyl-1-alkanols are preferably used: 
     2-butyl octanol, 2-hexyl decanol, 2-butyl decanol, 2-octyl decanol, 2-hexal octanol, 2-hexyl dodecanol, 2-octyl dodecanol. 
     The general formula of the 2-alkyl-1-alkanols used is: ##STR1## wherein R 1  is the linear main chain, an alkyl with 8 to 12 carbon atoms, preferably 8 to 10 carbon atoms, and branched with the linear side chain R 2 , an alkyl with 4 to 8 carbon atoms, preferably 4 to 6 carbon atoms. They are known as Guebet alcohols and are accessible by technical processes. 
     In order to improve in the individual case the specific properties of the hydraulic fluids, customary additives are added to the esterification products, particularly up to 5 percent by weight of ecologically compatible additives, referring to the total quantity of hydraulic fluid, among others antiageing agents, antiwear agents, corrosion inhibitors and antifoaming agents. These constituents are selected according to the requirements of the field of application, e.g. shock absorbing systems for automobiles, industrial vehicles, railroad cars. 
     In another embodiment of the invention, the hydraulic fluids of the invention contain 0.1 to 5 weight percent of the ecologically compatible additives, related to the total composition of the hydraulic fluids. 
     EXAMPLES 
     In each of the following examples ecotoxicologically acceptable additives (water contamination rating=max. 1) were added, namely 1% of an antioxidant, a commercial mixture of hydroxylated aromatic hydrocarbons, and 1% of an antiwear agent, a commercial phosphoric acid ester. 
     The esters used and the results of the comparative experiments have been compiled in Tables 1 and 2. Listed in the following are the characteristics and the test methods used for determination: 
     
         ______________________________________Viscosity               DIN 51562Viscosity index (VI)    DIN-ISO 2909Pour point (PP)         DIN-ISO 3016Evaporation (Noack Test Procedure)                   DIN 51581Standard reference elastomer: NBR-1,swelling in volume over a period of168 hours at 100° C.Wear characteristics (four-ball tester)                   DIN 51350 T5Biodegradability after 21 days                   CEC L-33-T-82Artificial ageing of lubricating oilsat 120° C. in the presence of iron chips______________________________________ 
    
     EXAMPLE 1 (Comparison) 
     In comparison with the hydraulic fluids according to the present invention, refined rape oil presented an excellent viscosity-temperature behavior (viscosity index), but the low-temperature properties (Table 1) were not acceptable for outdoor use. 
     EXAMPLE 2 (Comparison) 
     A synthetic, commercial polyoleate based on a polyololeic acid ester having an iodine number of 48 and a saponification number of 265 (oleate ester A) only barely missed the viscosity range and low-temperature requirements (Table 1). However, considerable ageing symptoms and a higher tendency to swelling (Table 2) were found. 
     EXAMPLE 3 (according to the invention) 
     The synthetic oleate ester B based on technical-grade oleic acid of the following characteristics: 
     
         ______________________________________Analysis          Test Method Value______________________________________Acid number, mg KOH             DGF C-V 2   200Iodine number, gJ/100 g             DGF C-V 11b 95Unsaponifiables, %             DGF C-III 1a                         0.9______________________________________C-Chain Distribution (Gas Chromatographic)______________________________________C.sub.12 -C.sub.16         --         6.0%C.sub.18     Stearic acid                    1.0%C.sub.18 &#39;   Oleic acid  80.0%C.sub.18 &#39;&#39;  Linoleic acid                    11.5%C.sub.18 &#39;&#39;&#39; Linolenic acid                    0.5%&gt;C.sub.18     --         1.0%______________________________________ 
    
     has the following alkanol composition: 
     2-Butyloctanol oleate: 15% 
     2-Butyldecanol oleate: 50% 
     2-Hexyldecanol oleate: 35% 
     Biodegradability is almost 100%. 
     The measurements showed results which met the technical requirements. Depicted in FIG. 1 is the viscosity-temperature curve ranging from -40° C. to +120° C. In comparison with a conventional shock absorber oil (series oil). 
     Moreover, long-time shock absorber test runs were carried out at 85° C. (1 million strokes). The oil ageing was found to be low. In a triple test the following results were obtained: 
     a) Low-Temperature Function/Sealing Test 
     Filled shock absorbers were stored during 24 hours at -40° C. and then were actuated at max. 0.52 m/s up to a temperature of +120° C. The test was passed by the inventive fluid. 
     b) Friction/Graunz Test 
     Filler shock absorbers were examined for frictional noise by slowly moving the piston rod in and out at short strokes. The test was passed by the inventive fluid. 
     c) Shock Absorption 
     Filled shock absorbers were exposed to stroke rates of between 0.01 and 0.52 m/s at temperatures of from -40° C. to 180° C. 
     d) Long-Time Test Run 
     Filled shock absorbers were subjected to a beat frequency of 1/12 Hz over a period of 500 hours. Mechanical wear, changes in the absorbing power and possible oil losses were evaluated. 
     1×10 6  strokes at 85° C. 
     Oil loss 1%. 
     Increase in viscosity +4.5% at 40° C. 
     The other comparative examples were carried out using the following commercially available fluids: 
     Example 4 (Comparison) Diisodecylazelaic acid ester 
     Example 5 (Comparison) Di-ethylhexylsebacate 
     Example 6 (Comparison) Dialkylazelaic acid ester 
     Example 7 (Comparison) Trimethylolpropane complex ester 
     Example 8 (Comparison) Polyethylene glycol 
     
                                           TABLE 1__________________________________________________________________________Hydraulic Oils for Motor VehiclesBiodegradable Products (I)            Viscosity  Viscosity            20° C.                100° C.                       -20° C.                            -30° C.                                 -40° C.                                      PPExampleType        mm.sup.2 /s                mm.sup.2 /s                    VI mm.sup.2 /s                            mm.sup.2 /s                                 mm.sup.2 /s                                      °C.__________________________________________________________________________1    Vegetable oil, modified            68  7.5 214                       775  2,976                                 --   -332    Synthetic oleate ester A            50  5.2 170                       680  1,650                                 --   -453    Synthetic oleate ester B            -27 3.8 183                       230    490                                 1,140                                      -484    All-synthetic esters A            21  3.0 143                       195    450                                 1,250                                      -705    All-synthetic esters B            24  3.2 146                       230    540                                 1,500                                      -706    All-synthetic esters C            40  4.6 160                       520  1,380                                 4,400                                      -707    All-synthetic esters D            33  3.7 134                       360    860                                 1,860                                      -518    Polyglycol ether            79  5.4 123                       2,250                            8,720                                 47,730                                      -50__________________________________________________________________________ 
    
     
                                           TABLE 2__________________________________________________________________________Hydraulic Oils for Motor VehiclesBiodegradable Products (II)            Noack    Four-Ball   Ageing                                      Ageing            150° C.                     Tester                           CEC   312 h,                                      624 h,            1 h NBR-1                     630 N L-33-T-82                                 120° C.                                      120° C.ExampleType        %   %-vol.                     mm    %     %-visc.                                      %-visc.__________________________________________________________________________1    Vegetable oil, modified            -0.6                +9.2 0.53  97    +9.2 +24.42    Synthetic oleate ester A            -0.6                +27  1.0   ˜92                                 +10.5                                      +42.93    Synthetic oleate ester B            -0.5                +9.1 0.86  99    +4.0 +11.84    All-synthetic esters A            -0.6                +40  0.66  ˜91                                 +0.1 +0.15    All-synthetic esters B            -0.6                +35  0.63  ˜90                                 +/-0 +0.76    All-synthetic esters C            -0.6                +31  0.71  97    +/-0 +2.47    All-synthetic esters D            -0.9                +35  0.75  99    +/-0 +0.18    Polyglycol ether            -2.3                +10.7                     0.50  ˜85                                 +0.9 +4.6__________________________________________________________________________