Lubricating compositions having improved shear stability

Abstract

A lubricating composition with improved shear stability having a kinematic viscosity (Kv 100 ) from 5 to 32.5 cSt at 100° C., and a viscosity index from 140 to 200. The lubricating composition includes: a bi-modal blend lubricating oil including from 20 to 99 weight percent of a low viscosity basestock having a Kv 100 from 2 to 8 cSt at 100° C., and from 1 to 20 weight percent of a high viscosity basestock having a Kv 100 from 40 to 600 cSt at 100° C.; a viscosity modifier including a copolymer having units derived from monomers of (i) an α-olefin and (ii) an ethylenically unsaturated carboxylic acid or derivatives thereof esterified with an alcohol; and an alkylated aromatic co-base stock in an amount from 1 to 8 weight percent and having a Kv 100 from 3 to 15 cSt at 100° C.

What is claimed is: 
     
         1 . A lubricating composition having a kinematic viscosity (Kv 100 ) from 5 to 32.5 cSt at 100° C., and a viscosity index (VI) from 140 to 200; said lubricating composition comprising:
 a bi-modal blend lubricating oil comprising from 20 to 99 weight percent, based on the total weight of the bi-modal blend lubricating oil, of a low viscosity basestock having a Kv 100  from 2 to 8 cSt at 100° C., and from 1 to 20 weight percent, based on the total weight of the bi-modal blend lubricating oil, of a high viscosity basestock having a Kv 100  from 40 to 600 cSt at 100° C.; 
 a viscosity modifier comprising a copolymer having units derived from monomers of (i) an α-olefin and (ii) an ethylenically unsaturated carboxylic acid or derivatives thereof esterified with an alcohol; and 
 an alkylated aromatic co-base stock in an amount form 1 to 12 weight percent, based on the total weight of the lubricating composition, and having a Kv 100  from 3 to 15 cSt at 100° C.; 
 wherein shear stability (as determined by CEC L-45-A-99) is improved in a driveline device lubricated with said lubricating composition as compared to shear stability achieved using a lubricating composition containing no co-base stock or a co-base stock other than the alkylated aromatic co-base stock. 
 
     
     
         2 . The lubricating composition of  claim 1  wherein the bi-modal blend lubricating oil comprises two or more Group I, II, III, IV, V and/or VI base oil stocks. 
     
     
         3 . The lubricating composition of  claim 1  wherein the bi-modal blend lubricating oil comprises at least two synthetic polyalphaolefin (PAO) fluids, said PAO independently comprising a polymer of one or more C 8  to C 12  alphaolefin monomers. 
     
     
         4 . The lubricating composition of  claim 1  having a kinematic viscosity (Kv 100 ) from 6 to 20 cSt at 100° C., and a VI from 150 to 190. 
     
     
         5 . The lubricating composition of  claim 1  wherein the viscosity modifier is represented by the formula: 
       
         
           
           
               
               
           
         
       
       wherein
 Formula (I) comprises a copolymer backbone (BB), and one or more pendant groups, wherein BB is derived from a copolymer of (i) an α-olefin and (ii) ethylenically unsaturated carboxylic acid or derivatives thereof; 
 X is a functional group which either (i) contains a carbon and at least one oxygen or nitrogen atom, or (ii) is an alkylene group with 1 to 5 carbon atoms, connecting the copolymer backbone and a branched hydrocarbyl group contained within ( ) y ; 
 w is the number of pendant groups attached to the copolymer backbone, which is in the range of 2 to 2000; 
 y is 0, 1, 2 or 3, provided that in at least 1 mol % of the pendant groups, y is not zero; and with the proviso that when y is 0, X is bonded to a terminal group in a manner sufficient to satisfy the valence of X, wherein the terminal group is selected from hydrogen, alkyl, aryl, a metal or ammonium cation, and mixtures thereof; 
 p may be an integer in the range of 1 to 15; and 
 R′ and R″ are independently linear or branched hydrocarbyl groups, and the combined total number of carbon atoms present in R′ and R″ is at least 12. 
 
     
     
         6 . The lubricating composition of  claim 1  wherein the α-olefin is selected from the group consisting of 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, -pentadecene, 1-hexadecene, 1-hepta-decene 1-octadecene, and mixtures thereof; the ethylenically unsaturated carboxylic acid or derivative thereof is selected from the group consisting of acrylic acid, methyl acrylate, methacrylic acid, maleic acid or anhydride, fumaric acid, itaconic acid or anhydride or mixtures thereof, and substituted equivalents thereof; and the alcohol is selected from the group consisting of 2-ethylhexanol, 2-butyloctanol, 2-hexyldecanol, 2-octyldodecanol, 2-decyltetradecanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, eicosanol, and mixtures thereof. 
     
     
         7 . The lubricating composition of  claim 1  wherein the viscosity modifier is a copolymer derived from monomers of (i) an α-olefin and (ii) an ethylenically unsaturated carboxylic acid or derivatives thereof,
 wherein 0.1 to 99.89 percent of the carboxylic acid units are esterified with a primary alcohol branched at the β- or higher position, 
 wherein 0.1 to 99.89 percent of the carboxylic acid units are esterified with a linear alcohol or an alpha-branched alcohol, and 
 wherein 0.01 to 10 percent of the carboxylic acid units has at least one of an amino-, amido- and/or imido-group. 
 
     
     
         8 . The lubricating composition of  claim 1  wherein the alkylated aromatic co-base stock is selected from the group consisting of alkyl benzenes, alkyl naphthalenes, alkyl diphenyl oxides, alkyl naphthols, alkyl diphenyl sulfides, alkylated bis-phenol A, and alkylated thiodiphenol. 
     
     
         9 . The lubricating composition of  claim 1  wherein the alkylated aromatic co-base stock comprises an alkylated naphthalene or alkylated benzene. 
     
     
         10 . The lubricating composition of  claim 1  wherein the alkylated aromatic co-base stock is mono-alkylated, dialkylated, or polyalkylated. 
     
     
         11 . The lubricating composition of  claim 1  wherein the alkylated aromatic co-base stock is an alkyl naphthalene selected from the group consisting of mono-, di-, tri-, tetra-, or penta-C 3  alkyl naphthalene, C 4  alkyl naphthalene, C 5  alkylnaphthalene, C 6  alkyl naphthalene, C 8  alkyl naphthalene, C 10  alkyl naphthalene, C 1-2  alkyl naphthalene, C 1-4  alkyl naphthalene, C 1-6  alkyl naphthalene, C 1-8  alkyl naphthalene, C 10 -C 14  mixed alkyl naphthalene, C 6 -C 18  mixed alkyl naphthalene, or mono-, di-, tri-, tetra-, or penta C 3 , C 4 , C 5 , C 6 , C 8 , C 10 , C 12 , C 14 , C 16 , C 18  or mixture thereof, alkyl monomethyl, dimethyl, ethyl, diethyl, or methylethyl naphthalene, or mixtures thereof. 
     
     
         12 . The lubricating composition of  claim 1  wherein the bi-modal blend lubricating oil is present in an amount of from 45 weight percent to 98 weight percent, the viscosity modifier is present in an amount of from 1 weight percent to 40 weight percent, and the alkylated aromatic co-base stock is present in an amount of from 4 weight percent to 12 weight percent, based on the total weight of the lubricating composition. 
     
     
         13 . A process for producing the lubricating composition of  claim 1 , said process comprising:
 providing a bi-modal blend lubricating oil comprising from 20 to 99 weight percent of a low viscosity basestock having a Kv 100  from 2 to 8 cSt 100° C., and from 1 to 20 weight percent of a high viscosity basestock having a Kv 100  from 40 to 600 cSt at 100° C.;   providing a viscosity modifier comprising a copolymer having units derived from monomers of (i) an α-olefin and (ii) an ethylenically unsaturated carboxylic acid or derivatives thereof esterified with an alcohol;   providing an alkylated aromatic co-base stock in an amount form 1 to 12 weight percent and having a Kv 100  from 3 to 15 cSt at 100° C.; and   blending the bimodal blend lubricating oil, viscosity modifier and alkylated aromatic co-base stock in amounts sufficient to produce the lubricating composition.   
     
     
         14 . A lubricant comprising the lubricating composition of  claim 1 . 
     
     
         15 . The lubricant of  claim 14  further comprising one or more of an antioxidant, detergent, dispersant, pour point depressant, corrosion inhibitor, metal deactivator, seal compatibility additive, anti-foam agent, inhibitor, antiwear, extreme pressure agent, friction modifier, and anti-rust additive. 
     
     
         16 . A method of lubricating a mechanical device comprising supplying to the device a lubricating composition of  claim 1 , wherein the mechanical device comprises a driveline device. 
     
     
         17 . The method of  claim 16  wherein the driveline device comprises gears or transmissions. 
     
     
         18 . The lubricant of  claim 14  which comprises an axle fluid or manual transmission fluid (MTF). 
     
     
         19 . A method for improving fuel efficiency, while maintaining or improving shear stability in a driveline device lubricated with a lubricating oil, by using as the lubricating oil a lubricant of  claim 14 . 
     
     
         20 . The method of  claim 19  wherein the lubricating composition comprises from 4 weight percent to 12 weight percent of the alkylated aromatic co-base stock, based on the total weight of the lubricating composition.