Grease composition and bearing

Abstract

The present invention provides a grease composition which comprises a base oil and a thickening agent and in which the base oil comprises an ester oil represented by the following general formula (1) and composed of pentaerythritol and a fatty acid, the composition being characterized in that it comprises a pentaerythritol tetra-ester oil in which the fatty acid used for forming the ester, at least, comprises 2-ethyl hexanoic acid in an amount ranging from 51 to 55% by mass and caprylic acid and capric acid in a total amount ranging from 39 to 49% by mass wherein the content of caprylic acid is not less than 30% by mass and that of capric acid ranges from 5 to 10% by mass: C(CH 2 OCOR 1 ) 4 , wherein R 1 represents a linear and/or branched fatty acid residue having 6 to 12 carbon atoms as well as a bearing comprising the grease composition, filled therein. The grease composition of the present invention is suitably used in the rolling bearing under low temperature conditions and can show stable lubricating performance over a long period of time.

1 . A grease composition which comprises a base oil and a thickening agent and in which the base oil comprises an ester oil represented by the following general formula (1) and composed of pentaerythritol and a fatty acid, the composition being characterized in that it comprises a pentaerythritol tetra-ester oil in which the fatty acid used for forming the ester, at least, comprises 2-ethyl hexanoic acid in an amount ranging from 51 to 55% by mass and caprylic acid and capric acid in a total amount ranging from 39 to 49% by mass wherein the content of caprylic acid is not less than 30% by mass and that of capric acid ranges from 5 to 10% by mass:
   C(CH 2 OCOR 1 ) 4   (1)
   wherein R 1  represents a linear and/or branched fatty acid residue having 6 to 12 carbon atoms.   
     
     
         2 . The grease composition as set forth in  claim 1 , wherein the composition of the fatty acid is as follows: 38 to 41% by mass of caprylic acid; 6 to 8% by mass of capric acid; and 52 to 54% by mass of 2-ethyl hexanoic acid. 
     
     
         3 . The grease composition as set forth in  claim 1 , wherein the pentaerythritol tetra-ester oil has a kinetic viscosity of not more than 40 mm 2 /s as determined at 40° C.; a viscosity index of not less than 100; and a flow point of not higher than −45° C. 
     
     
         4 . The grease composition as set forth in  claim 1 , wherein the composition comprises the base oil in an amount of not less than 50% by mass and the thickening agent in an amount ranging from 5 to 30% by mass on the basis of the total mass of the grease composition and wherein the base oil comprises the pentaerythritol tetra-ester oil alone or a mixture of the pentaerythritol tetra-ester oil and a synthetic oil other than the tetra-ester oil and/or a mineral oil. 
     
     
         5 . The grease composition as set forth in  claim 1 , wherein the consistency of the grease composition ranges from 200 to 350. 
     
     
         6 . A bearing comprising the grease composition, filled therein, as set forth in  claim 1 .