Fluid dynamic bearing, spindle motor, and disk drive device

Abstract

[Object] To provide a fluid dynamic bearing filled with a lubricating oil composition containing a base oil and an ionic liquid, and to provide a spindle motor with evaporation being suppressed in the lubricating oil composition provided in the fluid dynamic bearing by incorporating the fluid dynamic bearing in the spindle motor, and thus occurrence of a read-write error in an HDD can be suppressed, and a disk drive device including the spindle motor. [Solution means] A fluid dynamic bearing filled with a lubricating oil composition containing a base oil and an ionic liquid, the ionic liquid including at least one cation selected from the group consisting of tetraalkylammonium cations and at least one anion selected from the group consisting of borate anions represented by Formulas (C-1) to (C-3): (where in the formula, R 9 to R 12 each independently represent a linear or branched alkyl group.)

What is claimed is: 
     
         1 . A fluid dynamic bearing for a hard disk drive device, the fluid dynamic bearing filled with a lubricating oil composition comprising a base oil and an ionic liquid,
 the ionic liquid being an ionic liquid comprising:   at least one cation selected from the group consisting of tetraalkylammonium cations represented by Formula (B) described below; and   at least one anion selected from the group consisting of a borate anion represented by Formula (C-1), a borate anion represented by Formula (C-2), and a borate anion represented by Formula (C-3):   
       
         
           
           
               
               
           
         
       
       where in Formula (B), R 5 , R 6 , R 7 , and R 8  each independently represent a linear or branched alkyl group having from 1 to 18 carbon atoms, 
       
         
           
           
               
               
           
         
       
       where in Formula (C-1), R 9 , R 10 , R 11 , and R 12  each independently represent a linear or branched alkyl group having from 1 to 22 carbon atoms. 
     
     
         2 . The fluid dynamic bearing for a hard disk drive device according to  claim 1 , wherein the base oil comprises at least one compound selected from the group consisting of a monoester compound represented by Formula (1) and a diester compound represented by Formula (2): 
       
         
           
           
               
               
           
         
         where in Formula (1),
 R 21  is a linear or branched alkyl group having 10 or more carbon atoms in total, and when R 21  is a branched alkyl group, a number of carbon atoms in a side chain is 10 or more, 
 R 22  is a linear or branched alkyl group having 9 or more carbon atoms in total, and when R 22  is a branched alkyl group, a number of carbon atoms in a side chain is 7 or more; 
 
       
       
         
           
           
               
               
           
         
         where in Formula (2),
 R 23  and R 25  are each independently a linear or branched alkyl group having 8 or more carbon atoms in total, and when R 23  and R 25  are branched alkyl groups, a number of carbon atoms in the longest carbon chain counted from a carbon atom bonded to E 1  or E 2  is 9 or more, 
 R 24  is a linear or branched alkylene group having 4 or more carbon atoms in total, and 
 E 1  and E 2  each independently represent —C(═O)O— or —OC(═O)—. 
 
       
     
     
         3 . A spindle motor comprising the fluid dynamic bearing according to  claim 1 . 
     
     
         4 . A disk drive device comprising the spindle motor according to  claim 3 . 
     
     
         5 . A spindle motor comprising the fluid dynamic bearing according to  claim 2 . 
     
     
         6 . A disk drive device comprising the spindle motor according to  claim 5 .