Hydraulic fluids with erosion resistance

Abstract

The erosion resistance of phosphate ester based hydraulic fluids has been found to be enhanced by incorporating in the fluid a minor amount of an alkali metal perfluorophosphate and a mono epoxycyclohexane carboxylate.

1 . A fluid composition comprising: 
 a major amount of a phosphate ester base stock and a minor amount of an alkali metal perfluorophosphate or mixture of alkali metal perfluorophosphates and a mono epoxycyclohexane carboxylate.    
   
   
       2 . The composition of  claim 1  wherein the alkali metal perfluorophosphate or mixtures of alkali metal perfluorophosphates are present in an amount of from about 0.01 wt % to about 0.5 wt % based on the weight of the composition.  
   
   
       3 . The composition of  claim 2  wherein the mono epoxycyclohexane carboxylate is represented by the formula  
     
       
         
         
             
             
         
       
     
     where R is an alkyl group of 1 to 10 carbon atoms or —(CH 2 ) n —OR, where n is an integer of 1 to 3 and R 1  is an alkyl group of 1 to 10 and wherein said mono epoxycyclohexane carboxylate is present from about 1 wt % to about 10 wt % based on the weight of the composition.  
   
   
       4 . A hydraulic fluid composition comprising: 
 (a) a major amount of a phosphate ester base stock comprising, based on the weight of base stock; 
 (i) from 10 to 100 wt % of trialkyl phosphate;  
 (ii) from 0 to 75 wt % of dialkyl aryl phosphates;  
 (iii) from 0 to 30 wt % of alkyldiaryl phosphates; and  
 (iv) from 0 to 20 wt % of alkylated triaryl phosphates, and wherein the alkyl groups of (i) to (iv) have from 3 to 8 carbon atoms; and  
   (b) both 
 (i) from about 0.01 wt % to about 0.5 wt %, based on the weight of the composition of an alkali metal perfluorophosphate or mixtures of alkali-metal perfluorophosphate; and  
 (ii) from about 1 wt % to about 10 wt %, based on the weight of the composition, of a compound having the formula  
                     
 where R is an alkyl group of 1 to 10 carbon atoms or —(CH 2 ) n OR, where n is an integer of 1 to 3 and R is an alkyl group of 1 to 10 carbon atoms.  
   
   
   
       5 . The composition of  claim 4  wherein the alkali metal of the perfluorophosphate is potassium and R is a branched alkyl group of 4 to 8 carbon atoms.  
   
   
       6 . The composition of  claim 5  including a poly(alkylacrylate) or poly(alkylmethacrylate) viscosity index improver (VII).  
   
   
       7 . The composition of  claim 6  wherein the VII is present at from about 3 wt % to about 10 wt % based on the weight of the composition.