Use of comb copolymers for improving scuffing load capacity

Abstract

The present invention relates to the use of comb polymers comprising, in the main chain, repeat units derived from polyolefin-based macromonomers with a molecular weight of at least 500 g/mol, and repeat units derived from low molecular weight monomers with a molecular weight less than 500 g/mol, for improving the load-bearing capacity of hydraulic fluids. Furthermore, the present invention describes new hydraulic fluids.

1 - 17 . (canceled) 
     
     
         18 . A method for improving the load-bearing capacity of at least one hydraulic fluid, comprising
 mixing a comb polymer with the hydraulic fluid,   wherein the comb polymer comprises, in the main chain, at least one repeat unit corresponding to at least one polyolefin-based macromonomer with a molecular weight of at least 500 g/mol, and at least one repeat unit corresponding to at least one low molecular weight monomer with a molecular weight less than 500 g/mol,   wherein the comb polymer has a molar degree of branching in the range from 0.3 to 3.6 mol %, and   wherein the comb polymer comprises a total of at least 80% by weight, based on the weight of the repeat units, of the at least one repeat unit corresponding to at least one polyolefin-based macromonomer, and the at least one repeat unit corresponding to at least one low molecular weight monomer selected from the group consisting of a styrene monomer having 8 to 17 carbon atoms, an alkyl (meth)acrylate having 1 to 10 carbon atoms in the alcohol group, a vinyl ester having 1 to 11 carbon atoms in the acyl group, a vinyl ether having 1 to 10 carbon atoms in the alcohol group, a (di)alkyl fumarate having 1 to 10 carbon atoms in the alcohol group, and a (di)alkyl maleate having 1 to 10 carbon atoms in the alcohol group.   
     
     
         19 . The method of  claim 18 , wherein the comb polymer comprises 20 to 60% by weight of the at least one repeat unit corresponding to the at least one polyolefin-based macromonomer with a molecular weight of at least 500 g/mol. 
     
     
         20 . The method of  claim 18 , wherein the comb polymer comprises at least one repeat unit corresponding to styrene and at least one repeat unit corresponding to n-butyl methacrylate. 
     
     
         21 . The method of  claim 18 , wherein the comb polymer comprises at most 2% by weight of one or more dispersing monomers of formula (I) 
       
         
           
           
               
               
           
         
         in which R is hydrogen or methyl, X is oxygen, sulfur or an amino group of the formula —NH— or —NR a — in which R a  is an alkyl radical having 1 to 10 carbon atoms, R 1  is a radical comprising 2 to 50 carbon atoms and has at least one heteroatom, preferably at least two heteroatoms, R 2  and R 3  are each independently hydrogen or a group of the formula —COX′R 1′  in which X′ is oxygen or an amino group of the formula —NH— or —NR a ′— in which R a′  is an alkyl radical having 1 to 10 carbon atoms, and R 1′  is a radical comprising 1 to 50 carbon atoms. 
       
     
     
         22 . The method of  claim 21 , wherein the proportion of the dispersing monomers is at most 0.5% by weight. 
     
     
         23 . The method of  claim 18 , wherein the hydraulic fluid further comprises a lubricant oil. 
     
     
         24 . The method of  claim 18 , wherein the hydraulic fluid is present in a vane pump, a gear pump, a radial piston pump, an axial piston pump or a hydraulic motor. 
     
     
         25 . The method of  claim 18 , wherein the hydraulic fluid comprises 1 to 30% by weight of the comb polymer. 
     
     
         26 . The method of  claim 18 , wherein the comb polymer comprises 20 to 60% by weight of the at least one repeat unit corresponding to the at least one polyolefin-based macromonomer with a molecular weight of at least 500 g/mol. 
     
     
         27 . The method of  claim 18 , wherein the comb polymer comprises at least one repeat unit corresponding to styrene and at least one repeat unit corresponding to n-butyl methacrylate. 
     
     
         28 . The method of  claim 27 , wherein a weight ratio of the at least one repeat unit corresponding to styrene to the at least one repeat unit corresponding to n-butyl methacrylate is in the range from 4:1 to 1.5:1. 
     
     
         29 . The method of  claim 18 , wherein after the mixing the hydraulic fluid has a viscosity measured to ASTM D 445 at 40° C. in the range from 10 to 120 mm 2 /s. 
     
     
         30 . The method of  claim 18 , wherein the hydraulic fluid further comprises at least one defoamer which is a copolymer comprising at least one polyalkyl(meth)acrylate and at least one unit corresponding to at least one alkoxylated (meth)acrylate. 
     
     
         31 . The method of  claim 27 , wherein the at least one lubricant oil has a viscosity in the range from 3 mm 2 /s to 100 mm 2 /s, measured at 40° C. according to ASTM 445. 
     
     
         32 . The method of  claim 21 , wherein the comb polymer is free of dispersing monomers. 
     
     
         33 . The method of  claim 18 , wherein the comb polymer comprises 35% to 60% by weight of at least one repeat unit corresponding to the polyolefin-based macromonomer.