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 bearing grease composition comprising: 
 (a) a carbonate compound represented by the following formula (I)                          wherein R and R′, which may be the same or different, each represent a branched alkyl group having 13 to 15 carbon atoms; and    (b) a group consisting of an alkali metal salt and/or an alkaline earth metal salt, synthesized from a hydroxide of an alkali metal or an alkaline earth metal and a higher hydroxyfatty acid having 10 or more carbon atoms or a higher hydroxyfatty acid having at least one hydroxyl group and having 10 or more carbon atoms.    
     
     
         2 . The bearing grease composition as claimed in  claim 1 , wherein the branched alkyl group R and R′ in the carbonate compound represented by the formula (I) is represented by the following formula (II):  
       
         
           
           
               
               
           
         
       
       wherein n is a number of 13 to 15 and m is a number of 0 to 6.  
     
     
         3 . The bearing grease composition as claimed in  claim 1 , which comprises 70 to 95 parts by weight of the component (a) and 5 to 30 parts by weight of the component (b).  
     
     
         4 . The bearing grease composition as claimed in  claim 1 ,  2  or  3 , wherein the component (a) includes a plurality of carbonate compounds.  
     
     
         5 . The bearing grease composition as claimed in claim  1 ,  2 ,  3  or  4 , which further comprises one or more thickening agents.  
     
     
         6 . The bearing grease composition as claimed in  claim 1 ,  2 ,  3 ,  4  or  5 , which further comprises lubricants and/or additives.