Thermally stable zinc-free antiwear agent

Abstract

There is disclosed a lubricant additive composition comprising a thermally stable, zinc-free, phosphorous-containing antiwear agent. Moreover, a lubricant composition comprising the disclosed additive composition is also disclosed. Methods for making and using the disclosed compositions are disclosed.

1 . A lubricant additive composition comprising
 at least one thermally stable dithiophosphate prepared by reacting a dithiophosphoric acid with an alkene; and   at least one polyalkylmethacrylate viscosity index improver,   wherein the additive composition provides a phosphorus content ranging from about 300 to about 700 parts per million when used in a lubricating composition.   
   
   
       2 . The additive of  claim 1 , wherein the alkene is a dicyclopentadiene or ethyl acrylate. 
   
   
       3 . A method of controlling sludge formation in a multigrade lubricating composition, said method comprising providing a major amount of a base oil, and a minor amount of an additive composition comprising at least one thermally stable dithiophosphate prepared by reacting a dithiophosphoric acid with an alkene; and at least one polyalkylmethacrylate viscosity index improver,
 wherein the lubricating composition has a phosphorus content ranging from about 300 to abut 700 parts per million.   
   
   
       4 . The method of  claim 3 , wherein the phosphorus content in the lubricating composition ranges from about 400 to about 500 parts per million. 
   
   
       5 . The method of  claim 3 , wherein the lubricating composition further comprises thermally unstable metal-free antiwear agents, with the proviso that the thermally unstable metal-free antiwear agents are present in an amount that does not contribute to sludge formation. 
   
   
       6 . The method of  claim 5 , wherein the metal-free antiwear agent is selected from the group consisting of thermally unstable dithiophosphates prepared by reacting a dithiophosphoric acid with an alkenoic acid, amine salts of sulfurized phosphate, and mixtures thereof. 
   
   
       7 . The method of  claim 3 , wherein the composition further comprises one or more materials selected from the group consisting of antioxidants, dispersants, detergents, rust inhibitors, corrosion inhibitors, demulsifiers, and supplemental viscosity index improvers. 
   
   
       8 . A method of controlling sludge formation in a monograde lubricating composition, said method comprising providing a base oil, and adding thereto at least one thermally stable dithiophosphate prepared by reacting a dithiophosphoric acid with an alkene,
 wherein the composition has a phosphorus content ranging from about 300 to abut 700 parts per million.   
   
   
       9 . The method of  claim 8 , wherein the phosphorus content in the composition ranges from about 400 to about 500 parts per million. 
   
   
       10 . The method of  claim 8 , wherein the composition further comprises thermally unstable metal-free antiwear agents, with the proviso that the thermally unstable antiwear agents are present in an amount that does not contribute to sludge formation. 
   
   
       11 . The method of  claim 10 , wherein the thermally unstable metal-free antiwear agent is selected from the group consisting of thermally unstable dithiophosphates prepared by reacting a dithiophosphoric acid with an alkenoic acid, amine salts of sulfurized phosphate, and mixtures thereof. 
   
   
       12 . The method of  claim 8 , wherein the composition further comprises one or more materials selected from the group consisting of antioxidants, dispersants, detergents, rust inhibitors, corrosion inhibitors, demulsifiers, and supplemental viscosity index improvers. 
   
   
       13 . A lubricant additive composition comprising
 at least one thermally stable triarylphosphate or dilaurylphosphate; and   at least one polyalkylmethacrylate viscosity index improver,   wherein the additive composition provides a phosphorus content ranging from about 300 to about 700 parts per million when used in a lubricating composition.   
   
   
       14 . The additive composition of  claim 13 , wherein the triarylphosphate is tricresylphosphate. 
   
   
       15 . A lubricating composition comprising:
 a major amount of a base oil; and   a minor amount of the additive composition of  claim 1 .   
   
   
       16 . The lubricating composition of  claim 15 , wherein the base oil is chosen from a Group I, Group II, and a Group III base oil. 
   
   
       17 . The lubricating composition of  claim 15 , wherein the phosphorus content in the composition ranges from about 400 to about 500 parts per million. 
   
   
       18 . The lubricating composition of  claim 15 , wherein the composition further comprises one or more materials selected from the group consisting of antioxidants, dispersants, detergents, rust inhibitors, corrosion inhibitors, demulsifiers, and viscosity index improvers. 
   
   
       19 . The lubricating composition of  claim 15 , wherein the composition is a hydraulic fluid. 
   
   
       20 . A method of improving the thermal stability of a lubricating composition, said method comprising formulating the lubricating oil comprising a major amount of a base oil and a minor amount of the additive composition of  claim 1 . 
   
   
       21 . A method of lubricating a hydraulic machine having a lubrication system, said method comprising adding to the lubrication system the lubricating composition of  claim 1 .