Hydraulic oil for use in construction machinery

Abstract

Hydraulic oil for use in construction machinery, wherein the hydraulic oil comprises a poly(meth)acrylate of weight average molecular weight in the range of from 30,000 to 100,000 in a highly refined base oil but does not incorporate an oiliness agent, and wherein the kinetic viscosity at 60° C. is in the range of from 25 to 60 mm{hacek over ( )}/s, the kinetic viscosity at 80° C. is in the range of from 15 to 34 mm{hacek over ( )}/s, the viscosity index is in the range of from 200 to 220, and the low temperature cranking viscosity at 25° C. is in the range of from 1000 to 8000 mPa·s. The hydraulic oil of the present invention not only has a high kinetic viscosity in the high-temperature domain even though the incorporation of an oiliness agent is omitted, and can thereby effect satisfactory operation efficiently and which has excellent braking characteristics, but which also has a low viscosity in the low-temperature domain and so has excellent low-temperature performance.

1 . An hydraulic oil for use in construction machinery, wherein the hydraulic oil, comprising: a poly(meth)acrylate of weight average molecular weight in the range of from 30,000 to 100,000 in a highly refined base oil but does not incorporate an oiliness agent, and wherein the kinetic viscosity at 60° C. is in the range of from 25 to 60 mm 2 /s, the kinetic viscosity at 80° C. is in the range of from 15 to 34 mm 2 /s, the viscosity index is in the range of from 200 to 220, and the low temperature cranking viscosity at −25° C. is in the range of from 1000 to 8000 mPa·s. 
     
     
         2 . An hydraulic oil according to  claim 1  wherein the poly(meth)acrylate has a weight average molecular weight in the range of from 30,000 to 70,000. 
     
     
         3 . An hydraulic oil according to  claim 2  wherein the kinetic viscosity at 60° C. is in the range of from 28 to 50 mm 2 /s. 
     
     
         4 . An hydraulic oil according to  claim 3  wherein the kinetic viscosity at 80° C. is in the range of from 17 to 30 mm 2 /s. 
     
     
         5 . An hydraulic oil according to  claim 4  wherein the viscosity index is in the range of from 205 to 215. 
     
     
         6 . An hydraulic oil according to  claim 5  wherein the low temperature cranking viscosity at −25° C. is in the range of from 1000 to 5000 mPa·s. 
     
     
         7 . An hydraulic oil according to  claim 6  wherein the kinetic viscosity at 40° C. is in the range of from 45 to 150 mm 2 /s. 
     
     
         8 . An hydraulic oil according to  claim 7  wherein the amount of poly(meth)acrylate, including diluent, is in the range of from 15 to 25% by mass, based on the total amount of the hydraulic oil. 
     
     
         9 . An hydraulic oil according to  claim 8  wherein the amount of pure poly(meth)acrylate is in the range of from 1 to 24% by mass, based on the total amount of the hydraulic oil. 
     
     
         10 . An hydraulic oil according to  claim 9  wherein the poly(meth)acrylate is selected from polymer having one kind or two or more kinds of the constituent units represented by general formula (1) below or polymers having those constituent units together with other constituent units together with other constituent units 
       
         
           
           
               
               
           
         
       
       wherein R 1  denotes hydrogen or a methyl group, R 2  denotes an alkyl group having from 1 to 30 carbons or a group represented by —(R) a -E where R is an alkylene group having from 1 to 30 carbons, E denotes either an amine residual group containing 1 to 2 nitrogen atoms and 0 to 2 oxygen atoms or a heterocyclic residual group, and a denotes an integer of 0 or 1.