Abstract:
A silicon elastomer compatible constant velocity joint grease comprises a urea grease composed of a lubricating oil and a urea thickener and an effective amount of a friction reducing additive package comprising vermiculite, molybdenum oxysulfide dithiocarbamate, polyphenylene sulfide and potassium triborate. The additive package solids have particle sizes below about 40 microns.

Description:
FIELD OF INVENTION 
     The present invention relates to a grease composition particularly useful in drive joints of front wheel drive vehicles. 
     BACKGROUND OF INVENTION 
     Front wheel drive vehicles employ front drive joints often referred to as constant velocity joints (CVJ) which require lubricating the joint to protect against wear, to reduce friction and vibration and to increase the life of the joint. 
     One type of CVJ lubricant is a grease composition comprising a purified mineral oil, as a base oil, and a lithium soap as a thickening agent. Another type of grease used for CVJ comprise a base oil and a urea type thickener. 
     CVJs experience significant pressures, torques and loads in use. Consequently, CVJ grease compositions typically contain extreme pressure additives such as molybdenum disulfide, molybdenum dithiocarbamates, sulfurized fats and oils and olefin sulfides. 
     A prime requirement for CVJ greases is that they be compatible with the elastomers and seals used in these joints. 
     To provide a CVJ grease with low friction properties additives such as ashless dithiophosphate and zinc dithiophosphate are often employed. These additives, however, are incompatible with silicone elastomers used and seals in many constant velocity joints. 
     One object of the present invention is to provide an improved, silicone elastomer compatible, grease, especially a low friction CVJ grease. 
     Other objects will become apparent upon a reading of the specification that follows. 
     SUMMARY OF INVENTION 
     The improved grease composition of the invention is compatible with silicone elastomers and is particularly useful for CVJs. The grease composition comprises a urea grease composed of a lubricating oil and a urea thickener and an effective amount of a friction reducing additive package comprising vermiculite, molybdenum oxysulfide dithiocarbamate and potassium triborate, the additive package solids having particles sizes below about 40 microns and preferably below about 10 microns. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The base oil used in the practice of the present invention may be a mineral oil or a synthetic hydrocarbon oil having a viscosity of a lubricant. Examples of mineral oil include 60 neutral oil, 100 neutral oil, 150 neutral oil, 300 neutral oil, 500 neutral oil, bright stock naphthenic oils and blends. Examples of synthetic oils include polyalphaolefin, polyglycol, polyolester, polyphosphoric acid ester, silicone oil, alkyldiphenyl, alkylbenzene, and dibasic acid ester. These base oils may be used alone or in the form of a mixture of two or more of them. It is particularly preferred in the practice of the present invention to use a mixture of bright stock and polyalpha olefin oils. 
     The base oil will comprise a major portion of the grease composition. For example the base oil typically will be in the range of about 65 to about 95 wt %, based on the total weight of the composition. 
     The grease composition of the present invention includes a urea thickener. Typical thickeners include diurea and triurea compounds and higher polyurea compounds. 
     Examples of diurea compounds include those obtained through a reaction of a monoamine with a diisocynate. Examples of diisocyanates include diphenyl diisocyanate, octadecene diisocynate and the like. Examples of monoamines include octylamine, dodecylamine, hexadecylamine and the like. 
     Among the higher polyurea compounds useful in the practice of the present invention are those obtained by the reaction of an amine with a diisocyante compound such as those mentioned above. 
     In the practice of the present invention it is preferred to use the urea thickener in an amount ranging from about 2.5 wt % to about 30 wt % based on the total weight of the composition. 
     The grease of the invention includes an effective amount of a friction reducing additive package comprising vermiculite, molybdenum oxysulfide dithiocarbamate, polyphenylene sulfide, and potassium triborate, the additive package having particle sizes below about 40 microns and preferably below about 10 microns, and even as low as 1 micron or less. 
     The vermiculite component of the additive package is a powdered thermally expanded magnesium-iron aluminum silicate. 
     The molybdenum oxysulfide dithiocarbamate of the additive package is a compound represented by the formula:                           
     wherein each of R 1  and R 2  are independently an alkyl group of from 1 to 24 carbon atoms, an aryl group or alkylaryl group of from 6 to 16 carbon atoms and wherein x and y are numerical values greater than zero and less than 4 and the sum of x and y is 4. 
     The polyphenylene sulfide or poly (1,4-phenylene sulfide) used in the additive package is a thermoplastic, injection molding resin available in powdered form. 
     The potassium triborate used in the additive package is an amorphous inorganic solid. A commercially available suspension of the triborate in an oil has been found to be a useful component in the additive package. 
     Typically the weight ratio of vermiculite:molybdenum oxysulfide dithiocarbamate:polyphenylene sulfide:potassium triborate will be in the range of about 0.5:2:1:1 to about 5:20:10:10, and preferably 1:3:2:2. 
     Also, the additive package will comprise about 0.5 to about 30 wt % of the total composition. 
    
    
     EXAMPLES 
     A grease was formulated by compounding the ingredients shown in Table 1. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Component 
                 Type 
                 Supplier 
                 Wt % 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Base Oil 
                 Bright stock/PAO 
                 NA 
                 71.74 
               
               
                 Thickener 
                 Polyruea 
                 NA 
                 12.26 
               
               
                 FPSV 
                 Vermiculite 
                 W. R. Grace 
                 2.0 
               
               
                   
                 Molybdenum 
               
               
                 Molyvan A 
                 Oxysulfide 
                 R. T. Vanderbilt 
                 6.0 
               
               
                   
                 Dithiocarbamate 
               
               
                 Oloa 9750 (1)   
                 Potassium triborate 
                 Chevron 
                 4.0 
               
               
                 Ryton Type VT 
                 Polyphenylene 
                 Phillips 66 
                 4.0 
               
               
                   
                 Sulfide 
               
               
                   
               
               
                 NA - not applicable  
               
               
                   (1) Oloa 9750 is a suspension of potassium borate in an oil.  
               
             
          
         
       
     
     The physical properties of the grease are set forth in Table 2. 
     
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Physical Properties 
                 Test Methods 
                 Test Results 
               
               
                   
               
             
             
               
                 Penetration, 60X 
                 ASTM D-217 
                 312 dmm 
               
               
                 Cold Penetration, 6 hours @ −40° C. 
                 ASTM D-217 (modified) 
                 165 dmm 
               
               
                 Dropping Point, ° C. (° F.) 
                 ASTM D-2265 
                 255° C. (491° F.) 
               
               
                 Oil Separation (%), 24 hours @ 100° C. 
                 FTM 791C/321.3 
                 2.0% 
               
               
                 Evaporation (%), 22 hours @ 99° C. 
                 ASTM D-972 
                 0.33% 
               
               
                 O 2  Stability, 100 hours KPa drop 
                 ASTM D-942 
                 21 KPa 
               
               
                 Copper Strip Corrosion, 1 hour @ 150° C. 
                 ASTM D-4048 
                 1B 
               
               
                 Low Temperature Torque, −40° C. starting N•m 
                 ASTM D-4693 
                 7.88 N•m 
               
               
                 Timken EP 
                 ASTM D-2509 
                 45 lbs. 
               
               
                 4 Ball EP 
                 ASTM D-2596 
                 315 kg 
               
               
                 Corrosion Prevention 
                 ASTM D-1743 
                 Pass 
               
               
                 4 Ball Wear @ 75° C. scar diameter, mm 
                 ASTM D-2266 
                 0.41 mm 
               
               
                 Base Oil Viscosity 
               
               
                 @100° C., cSt 
                 Calculated 
                 11.4 
               
               
                 @40° C., cSt 
                 Calculated 
                 107 
               
               
                 Viscosity index 
                 Calculated 
                 92 
               
               
                   
               
             
          
         
       
     
     The elastomer compatibility of the grease was determined by immersing elastomer samples in the grease for times and at the temperatures shown in Table 3 and thereafter measuring the change in elongation and tensile strength of the sample using an Instron tester at a load of 200 lbs. and a cross-head speed of 2 inches/minute for the Hytrel elastomer samples and 100 lbs. and 20 inches/minute for the silicon elastomer samples. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                 Test 
                 % Change, 
                 % Change, 
               
               
                   
                 Elastomer 
                 Conditions 
                 Elongation 
                 Tensile 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Silicone 
                 Total Immersion 
                 −9.09 
                 −13.17 
               
               
                   
                   
                 13 days @ 150° C. 
               
               
                   
                 Hytrel 
                 Total Immersion 
                 +1.33 
                 −11.49 
               
               
                   
                   
                 10 days @ 125° C.