Grease compositions for a hard disk drive and a process for production thereof

Abstract

To provide a grease composition for HDD which is excellent in low outgas generation and acoustic properties and a process for production thereof. In a grease composition used in the bearing for a hard disk drive, a basal oil comprising a paraffin-base hydrocarbon and a polyurea as a thickener are contained.

What is claimed is:  
     
         1 . A grease composition for a hard disk drive which comprises a basal oil comprising a paraffin-base hydrocarbon and a polyurea as a thickener, which is used in the bearing for the hard disk drive.  
     
     
         2 . A grease composition for a hard disk drive according to  claim 1 , wherein the paraffin-base hydrocarbon comprises a polyolefin represented by the following general formula: 
       H—[R 1 ] n  —H 
       (wherein R 1 , is a saturated hydrocarbon group of which the carbon number is 8-12; and n is a real number of 3-5) alone or as a mixture of the olefins as a main component.  
     
     
         3 . A grease composition for a hard disk drive according to  claim 1 , wherein the paraffin-base hydrocarbon comprises components of which the carbon number is 30 or more as main components.  
     
     
         4 . A grease composition for a hard disk drive according to  claim 3 , wherein the paraffin-base hydrocarbon comprises components from which volatile components of which the carbon number is less than 30 have been eliminated in advance.  
     
     
         5 . A grease composition for a hard disk drive according to  claim 3 , wherein the content of the volatile components of which the carbon number is less than 30 is 30 ppm or less.  
     
     
         6 . A grease composition for a hard disk drive according to  claim 1 , wherein the polyurea is formed by reacting a polyisocyanate readily soluble in the paraffin-base hydrocarbon with a primary or secondary (poly)amine in the paraffin-base hydrocarbon.  
     
     
         7 . A grease composition for a hard disk drive according to  claim 6 , wherein the polyisocyante is an aliphatic isocyanate.  
     
     
         8 . A grease composition for a hard disk drive according to  claim 6 , wherein the (poly)amine has a molecular weight of 400 or less.  
     
     
         9 . A grease composition for a hard disk drive according to  claim 6 , wherein the residual amount of the starting material contained in the polyurea is 30 ppm or less.  
     
     
         10 . A grease composition for a hard disk drive according to  claim 1 , wherein the polyurea is contained as particles of 1 ma or less in average size.  
     
     
         11 . A process for producing a grease composition used in the bearing for a hard disk drive, which comprises a step for producing a polyurea as a thickener by adding a polyisocyanate readily soluble in a paraffin-base hydrocarbon and a primary or secondary (poly)amine into a basal oil comprising the paraffin-base hydrocarbon.  
     
     
         12 . A process for producing a grease composition for a hard disk drive according to  claim 1  wherein the paraffin-base hydrocarbon comprises a polyolefin of the following general formula: 
 (wherein R 1  is a saturated hydrocarbon group of which the carbon number is 8-12; and n is a real number of 3-5) alone or a mixture of the polyolefins as main components.  
 
     
     
         13 . A process for producing a grease composition for a hard disk drive according to  claim 11 , wherein the polyisocyante is an aliphatic isocyanate.  
     
     
         14 . A process for producing a grease composition for a hard disk drive according to  claim 11 , wherein the (poly)amine has a molecular weight of 400 or less.  
     
     
         15 . A process for producing a grease composition for a hard disk drive as described in  claim 11 , which comprises a step for treating at least the basal oil under reduced pressure.  
     
     
         16 . A process for producing a grease composition for a hard disk drive as described in  claim 11 , which comprises a step of adding an excess amount of the (poly)amine to the polyisocyanate and eliminating the residual (poly)amine after the reaction.  
     
     
         17 . A process for producing a grease composition for a hard disk drive according to  claim 11 , wherein the residual amount of the starting material is 30 ppm or less.