Bearing grease composition

Abstract

A bearing grease composition used under clean atmosphere, as in a bearing of hard disc drive, which has small dust generation (scatter), a long life, excellent acoustic performance and low torque. It has been found that especially the bearing grease composition comprising a carbonate having a branched alkyl group of 13 to 15 carbon atoms and a metallic soap shows remarkable characteristics.

What is claimed is:  
     
         1 . A grease composition for a bearing for a spindle motor comprising: 
 (a) a base oil including a carbonate compound represented by the following formula (I):                           wherein R and R′, which may be the same or different, are each represented by the following formula (II):                           wherein n is a number from 13 to 15 and m is a number from 0 to 6; and    (b) at least one of lithium stearate and lithium 12-hydroxystearate,    wherein said grease composition comprises 70 to 95 parts by weight of component (a) and 5 to 30 parts by weight of component (b).    
     
     
         2 . The grease composition of  claim 1 , wherein said component (a) includes two or more carbonate compounds, each represented by said formula (I), wherein said carbonate compounds may be the same compound or a mixture of compounds.  
     
     
         3 . The grease composition of  claim 1 , wherein said grease composition includes a lubricant and/or additives.  
     
     
         4 . The grease composition of  claim 3 , wherein said lubricant is selected from the group consisting of a mineral oil, synthesized hydrocarbon oil, ether oil and ester oil.  
     
     
         5 . The grease composition of  claim 3 , wherein said additives are an antioxidant and a rust inhibitor.  
     
     
         6 . The grease composition of  claim 1 , wherein said component (a) has a dynamic viscosity of 10 to 50 mm 2 /sec at 40° C.  
     
     
         7 . The grease composition of  claim 1 , wherein said formula (II) is  
       
         
           
           
               
               
           
         
       
     
     
         8 . The grease composition of  claim 1 , wherein said formula (II) is  
       
         
           
           
               
               
           
         
       
     
     
         9 . The grease composition of  claim 1 , wherein said formula (II) is  
       
         
           
           
               
               
           
         
       
     
     
         10 . The grease composition of  claim 4 , wherein said lubricant is selected from alkyl diphenyl ether and polyol ester oil.  
     
     
         11 . The grease composition of  claim 1 , wherein said spindle motor is for a hard disk drive.  
     
     
         12 . The grease composition of  claim 1 , wherein said component (a) is a carbonate represented by the following formula (VI):