Method of preventing lubricant from deteriorating, lubricant, and dynamic-pressure bearing device

Abstract

Disclosed are a lubricant whose oxidation degradation is inhibited, and a dynamic pressure bearing device which has a long lifespan by prolonging the period of time of depression of a lubricating function of the lubricant occurring as a result of oxidation degradation. Ester-based lubricating oil serving as the lubricant is brought into continuous or intermittent contact with an ionic compound or an ionic compound solution obtained by dissolving the ionic compound in a solvent. In the dynamic pressure bearing device, the ionic compound is provided in a portion of a bearing or a shaft member and is thus brought into contact with the lubricating oil, in which the ionic compound or ionic compound solution is substantially insoluble in the ester-based lubricating oil.

1 . A method of preventing degradation of a lubricant, comprising:
 bringing an ester-based lubricating oil serving as the lubricant into contact with an ionic compound continuously or intermittently, in which the ester-based lubricating oil contains mainly an ester, and the ionic compound includes a cation and an anion bonded to each other mainly through an ionic bond thus forming a molecule or crystal,   wherein the ionic compound is substantially insoluble in the ester-based lubricating oil.   
   
   
       2 . A method of preventing degradation of a lubricant, comprising:
 bringing an ester-based lubricating oil serving as the lubricant into contact with an ionic compound solution continuously or intermittently, in which the ester-based lubricating oil contains mainly an ester, and the ionic compound solution is obtained by dissolving an ionic compound, including a cation and an anion bonded to each other mainly through an ionic bond thus forming a molecule or crystal, in a solvent,   wherein the ionic compound and the solvent are substantially insoluble in the ester-based lubricating oil.   
   
   
       3 . The method as set forth in  claim 1  or  2 , wherein the ionic compound is a salt in which a hydrogen atom of an acid is substituted with a metal ion. 
   
   
       4 . The method as set forth in  claim 3 , wherein the salt has an acid dissociation constant (pKa) ranging from 9 to 11. 
   
   
       5 . The method as set forth in  claim 3 , wherein the salt is a bicarbonate of an alkali metal other than lithium. 
   
   
       6 . The method as set forth in  claim 3 , wherein the salt is a carbonate of an alkali metal other than lithium. 
   
   
       7 . The method as set forth in  claim 3 , wherein the salt is a carboxylate of an alkali metal other than lithium. 
   
   
       8 . A lubricant comprising:
 an ester-based lubricating oil containing mainly an ester; and   an ionic compound including a cation and an anion bonded to each other through an ionic bond thus forming a molecule or crystal,   wherein the ionic compound is substantially insoluble in the ester-based lubricating oil and an interface is formed between the ester-based lubricating oil and the ionic compound.   
   
   
       9 . A lubricant comprising:
 an ester-based lubricating oil containing mainly an ester; and   an ionic compound solution obtained by dissolving an ionic compound, including a cation and an anion bonded to each other through an ionic bond thus forming a molecule or crystal, in a solvent, wherein the ionic compound is insoluble in the ester-based lubricating oil and an interface is formed between the ester-based lubricating oil and the ionic compound solution.   
   
   
       10 . The lubricant as set forth in  claim 8  or  9 , wherein the ionic compound is a salt in which a hydrogen atom of an acid is substituted with a metal ion. 
   
   
       11 . The lubricant as set forth in  claim 10 , wherein the salt has an acid dissociation constant (pKa) ranging from 9 to 11. 
   
   
       12 . The lubricant as set forth in  claim 10 , wherein the salt is a bicarbonate of an alkali metal other than lithium. 
   
   
       13 . The lubricant as set forth in  claim 10 , wherein the salt is a carbonate of an alkali metal other than lithium. 
   
   
       14 . The lubricant as set forth in  claim 10 , wherein the salt is a carboxylate of an alkali metal other than lithium. 
   
   
       15 . A dynamic pressure bearing device comprising:
 an ester-based lubricating oil containing mainly an ester;   a first member having a first bearing surface; and   a second member rotatably disposed with respect to the first member and having a second bearing surface facing the first bearing surface through a fine gap in which the lubricating oil is retained,   wherein a salt in which a hydrogen atom of the acid is substituted with a metal ion is disposed in at least one of a portion of a surface of the first member coming into contact with the lubricating oil and a portion of a surface of the second member coming into contact with the lubricating oil, and the salt is substantially insoluble in the ester-based lubricating oil.   
   
   
       16 . A dynamic pressure bearing device comprising:
 an ester-based lubricating oil containing mainly an ester;   a first member having a first bearing surface; and   a second member rotatably disposed with respect to the first member and having a second bearing surface facing the first bearing surface through a fine gap in which the lubricating oil is retained,   wherein a salt solution obtained by dissolving a salt in which a hydrogen atom of the acid is substituted with a metal ion in a solvent is retained in a portion of a surface of the first member coming into contact with the lubricating oil or a portion of a surface of the second member coming into contact with the lubricating oil, and the salt is substantially insoluble in the ester-based lubricating oil.   
   
   
       17 . The device as set forth in  claim 15 , wherein at least a portion of the first member or the second member is made of a porous material, and pores of the porous material are filled with the salt. 
   
   
       18 . The device as set forth in  claim 16 , wherein at least a portion of the first member or the second member is made of a porous material, and pores of the porous material are filled with the salt solution. 
   
   
       19 . The device as set forth in any one of  claims 15  to  18 , wherein the salt has an acid dissociation constant (pKa) ranging from 9 to 11. 
   
   
       20 . The device as set forth in any one of  claims 15  to  18 , wherein the salt is a bicarbonate of an alkali metal other than lithium. 
   
   
       21 . The device as set forth in any one of  claims 15  to  18 , wherein the salt is a carbonate of an alkali metal other than lithium. 
   
   
       22 . The device as set forth in any one of  claims 15  to  18 , wherein the salt is a carboxylate of an alkali metal other than lithium.