Lubricating oil composition and methods for controlling foam tendency and/or foam stability

Abstract

Provided is a lubricating oil composition and methods for controlling one or more of foam tendency and foam stability in such composition using as the oil a mixture of at least two base stocks. The at least two base stocks have a surface tension difference between them such that, when the surface tension difference is greater than 1.0 dynes/cm, then one or more of foam tendency and foam stability are enhanced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture. When the surface tension difference between them is less than 1.0 dynes/cm, then one or more of foam tendency and foam stability are reduced or equivalent as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture. Two low-foaming base stocks can produce a significant high foam response that reduces or eliminates the need for pro-foaming additives.

What is claimed is: 
     
         1 . A method for controlling one or more of foam tendency and foam stability in a lubricating oil comprising: providing as the lubricating oil a mixture of at least two base stocks; wherein the at least two base stocks have a surface tension difference between them such that, when the surface tension difference is greater than 1.0 dynes/cm, then one or more of foam tendency and foam stability are enhanced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture; and, when the surface tension difference is less than 1.0 dynes/cm, then one or more of foam tendency and foam stability are reduced or equivalent as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture. 
     
     
         2 . The method of  claim 1  wherein the at least two base stocks are selected from Group I, II, III, IV or V base oil stocks. 
     
     
         3 . The method of  claim 1  wherein the at least two base stocks comprise a poly alpha olefin (PAO) or gas-to-liquid (GTL) oil base stock. 
     
     
         4 . The method of  claim 1  wherein the mixture comprises from 5 weight percent to 95 weight percent of a first base stock and from 5 weight percent to 95 weight percent of a second base stock, based on the total weight of the lubricating oil. 
     
     
         5 . The method of  claim 1  wherein the at least two base stocks are selected from poly alpha olefin (PAO) and a metallocene catalyzed poly alpha olefin (mPAO) base stocks such that one or more of foam tendency and foam stability are enhanced or reduced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture. 
     
     
         6 . The method of  claim 1  wherein the at least two base stocks are mixed in a ratio such that one or more of foam tendency and foam stability are enhanced or reduced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture. 
     
     
         7 . The method of  claim 1  wherein the at least two base stocks comprise a poly alpha olefin (PAO) and a metallocene catalyzed poly alpha olefin (mPAO). 
     
     
         8 . The method of  claim 1  wherein the at least two base stocks comprise metallocene catalyzed poly alpha olefins (mPAO) having similar viscosities and different chain length olefin feedstocks. 
     
     
         9 . The method of  claim 1  wherein the at least two base stocks have a surface tension difference between them of greater than 2.0 dynes/cm. 
     
     
         10 . The method of  claim 1  wherein the lubricating oil further comprises one or more of a viscosity improver, antioxidant, detergent, dispersant, pour point depressant, corrosion inhibitor, metal deactivator, seal compatibility additive, inhibitor, and anti-rust additive. 
     
     
         11 . A lubricating oil comprising a mixture of at least two base stocks, wherein the at least two base stocks have a surface tension difference between them such that, when the surface tension difference is greater than 1.0 dynes/cm, then one or more of foam tendency and foam stability are enhanced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture; and, when the surface tension difference is less than 1.0 dynes/cm, then one or more of foam tendency and foam stability are reduced or equivalent as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture. 
     
     
         12 . The lubricating oil of  claim 11  wherein the lubricating oil base stock comprises a Group I, II, III, IV or V base oil stock. 
     
     
         13 . The lubricating oil of  claim 11  wherein the lubricating oil base stock comprises a poly alpha olefin (PAO) or gas-to-liquid (GTL) oil base stock. 
     
     
         14 . The lubricating oil of  claim 11  wherein the mixture comprises from 5 weight percent to 95 weight percent of a first base stock and from 5 weight percent to 95 weight percent of a second base stock, based on the total weight of the lubricating oil. 
     
     
         15 . The lubricating oil of  claim 11  wherein the at least two base stocks are selected from poly alpha olefin (PAO) and a metallocene catalyzed poly alpha olefin (mPAO) base stocks such that one or more of foam tendency and foam stability are enhanced or reduced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture. 
     
     
         16 . The lubricating oil of  claim 11  wherein the at least two base stocks are mixed in a ratio such that one or more of foam tendency and foam stability are enhanced or reduced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture. 
     
     
         17 . The lubricating oil of  claim 11  wherein the at least two base stocks comprise a poly alpha olefin (PAO) and a metallocene catalyzed poly alpha olefin (mPAO). 
     
     
         18 . The lubricating oil of  claim 11  wherein the at least two base stocks comprise metallocene catalyzed poly alpha olefins (mPAO) having similar viscosities and different chain length olefin feedstocks. 
     
     
         19 . The lubricating oil of  claim 11  wherein the at least two base stocks have a surface tension difference between them of greater than 2.0 dynes/cm. 
     
     
         20 . The lubricating oil of  claim 11  wherein the lubricating oil further comprises one or more of a viscosity improver, antioxidant, detergent, dispersant, pour point depressant, corrosion inhibitor, metal deactivator, seal compatibility additive, inhibitor, and anti-rust additive.