Oxidation-stable hydraulic oil

Abstract

A synthetic ester comprising a reaction product of: (a) a polyol corresponding to formula I: wherein R 1 is a hydrogen atom, a methyl group or a hydroxyl group and R 2 and R 3 independently of one another, represent a methyl group or a group CH 2 —OH, with the proviso that at least two hydroxyl groups are present in the molecule, and (b) an unsaturated fatty acid having from about 16 to 18 carbon atoms, and wherein the synthetic ester has an iodine value of from about 65 to 100, a saponification value of from about 160 to 200, and an acid value of at most 3.

1 . Synthetic esters of 
 a) polyols corresponding to general formula (I):                          in which R 1  is a hydrogen atom, a methyl group or a hydroxyl group and R 2  and R 3  independently of one another represent a methyl group or a group CH 2 —OH, with the proviso that at least two hydroxyl groups must be present in the molecule, and    b) unsaturated fatty acids containing 16 to 18 carbon atoms,    characterized in that the synthetic esters have an iodine value (to DGF—C—V 11b) of 65 to 100, a saponification value (to DGF C—V 3) of 160 to 200 and an acid value (to DGF C—V 2) of at most 3):    
     
     
         2 . Synthetic esters as claimed in  claim 1 , characterized in that the esters have a kinematic viscosity at 40° C. of 40 to 70 mm 2 /s 2  and a kinematic viscosity at 100° C. (as measured to DIN 51562) of 5 to 20 mm 2 /s 2 .  
     
     
         3 . Synthetic esters as claimed in  claims 1  to  2 , characterized in that the polyol a) is selected from the group consisting of neopentyl glycol, trimethylol propane, trimethylol ethane and/or pentaerythritol.  
     
     
         4 . Synthetic esters as claimed in  claims 1  to  3 , characterized in that component b) is oleic acid.  
     
     
         5 . A process for the production of synthetic polyol esters in which polyols corresponding to general formula (I) in  claim 1  are reacted under nitrogen with oleins for at least 3 hours at temperatures of >200° C., after which the excess fatty acid is removed by distillation under reduced pressure, characterized in that the oleins have an iodine value (DGF C—V11B) in the range from 60 to 130 and a cloud point (DGF D III) of less than 11° C. and contain more than 65% by weight oleic acid and less than 20% by weight linoleic acid.  
     
     
         6 . A hydraulic oil containing 90 to 99% by weight of a synthetic ester according to  claims 1  to  5  and 1 to 10% by weight of additives.  
     
     
         7 . A hydraulic oil as claimed in  claim 6 , characterized in that it contains additives selected from the classes of antioxidants, extreme-pressure and anti-wear additives, corrosion inhibitors, demulsifiers and/or defoamers.  
     
     
         8 . A hydraulic oil as claimed in claims  6  and  7 , characterized in that it contains an additive which in turn contains alkylamines, tolyltriazole, alkyl phosphate and/or succinic acid semiester.  
     
     
         9 . A hydraulic oil as claimed in  claim 8 , characterized in that it contains the additive in quantities of 0.5 to 2.0% by weight.  
     
     
         10 . The use of the synthetic esters claimed in  claims 1  to  5  as basic fluid in hydraulic oils.  
     
     
         11 . The use of an additive mixture containing alkylamines, tolyltriazole, alkyl phosphate and succinic acid semiester for improving the oxidation stability of the synthetic polyolesters claimed in  claim 1.