Working oil for hydraulic shock absorber, and hydraulic shock absorber

Abstract

According to the operating oil, in view of the fact that swelling properties of a rubber material, such as a seal material, etc., are reduced, conventionally used rubber materials can be used without being changed.

1 - 13 . (canceled) 
     
     
         14 . An operating oil for reducing swelling properties of a rubber material, comprising containing a polyalkylene glycol and at least one base oil selected from a fatty acid diester, a poly-alfa-olefin, and a lubricating oil classified as Gill in American Petroleum Institute (API), the operating oil having a density of 0.87 g/cm 3  or more at a temperature of 15° C. 
     
     
         15 . The operating oil according to  claim 14 , wherein the fatty acid diester is an ester of a fatty acid as a dibasic acid and an alcohol, or an ester of a polyhydric alcohol and a fatty acid. 
     
     
         16 . The operating oil according to  claim 14 , wherein the polyalkylene glycol has a carbon-chain oxyalkylene group having 1 to 7 carbon atoms. 
     
     
         17 . The operating oil according to  claim 14 , wherein the fatty acid diester is an ester of a fatty acid as a dibasic acid and an alcohol, or an ester of a polyhydric alcohol and a fatty acid, and the polyalkylene glycol has a carbon-chain oxyalkylene group having 1 to 7 carbon atoms. 
     
     
         18 . The operating oil according to  claim 14 , which is an operating oil for shock absorber. 
     
     
         19 . The operating oil according to  claim 18 , wherein a density of the operating oil is in a range of from 0.87 to 1.00 g/cm 3 . 
     
     
         20 . The operating oil according to  claim 18 , wherein a base oil of the operating oil is contained in an amount of 80 to 99.5% by weight. 
     
     
         21 . The operating oil according to  claim 18 , wherein a proportion of the polyalkylene glycol in the base oil is 17% by weight or more. 
     
     
         22 . The operating oil according to  claim 18 , which is an operating oil having a coefficient of friction in a range of 0.012 or less as measured under a condition of 0.06 m/s. 
     
     
         23 . The operating oil according to  claim 14 , which is an operating oil coming into contact with a rubber material. 
     
     
         24 . The operating oil according to  claim 23 , wherein at least one selected from the fatty acid diester, the poly-alfa-olefin, and the lubricating oil classified as Gill in American Petroleum Institute (API) is contained in an amount of 5 to 60% by weight in the base oil. 
     
     
         25 . The operating oil according to  claim 23 , the rubber material is any of a nitrile rubber, a hydrogenated nitrile rubber, and a fluorocarbon rubber. 
     
     
         26 . A shock absorber comprising using the operating oil as according to  claim 22  and the rubber material. 
     
     
         27 . A method for producing an operating oil for reducing swelling properties of a rubber material, comprising mixing a polyalkylene glycol with at least one base oil selected from a fatty acid diester, a poly-alfa-olefin, and a lubricating oil classified as Gill in American Petroleum Institute (API).