Mineral-oil base oil, lubricating oil composition, internal combustion engine, and lubricating method for internal combustion engine

Abstract

Disclosed herein is a mineral base oil satisfying the following requirements (I) to (V): (I): a kinematic viscosity at 100° C. is 2 mm2/s or more and less than 7 mm2/s; (II): a viscosity index is 100 or more; (III): a temperature gradient Δ|η*| of complex viscosity between two points of −10° C. and −25° C. is 60 Pa·s/° C. or less as measured with a rotary rheometer under conditions at an angular velocity of 6.3 rad/s and a strain amount of 0.1 to 100%; (IV): a content ratio [R1/R2] of a monocyclo paraffin component (R1) to a dicyclo to hexacyclo paraffin component (R2) is 0.70 or less by a volume ratio as measured in accordance with ASTM D2786; and (V): a % CA is less than 1.0.

1 . A mineral base oil satisfying the following requirements (I) to (V):
 Requirement (I): a kinematic viscosity at 100° C. is 2 mm 2 /s or more and less than 7 mm 2 /s;   Requirement (II): a viscosity index is 100 or more;   Requirement (III): a temperature gradient Δ|η*| of complex viscosity between two points of −10° C. and −25° C. is 60 Pa·s/° C. or less as measured with a rotary rheometer under conditions at an angular velocity of 6.3 rad/s and a strain amount of 0.1 to 100%;   Requirement (IV): a content ratio [R1/R2] of a monocyclo paraffin component (R1) to a dicyclo to hexacyclo paraffin component (R2) is 0.70 or less by a volume ratio as measured in accordance with ASTM D2786; and   Requirement (V): a % C A  is less than 1.0.   
     
     
         2 . The mineral base oil according to  claim 1 , wherein a total content of a monocyclo paraffin component (R1) and a dicyclo to hexacyclo paraffin component (R2) is 20 vol % or more based on 100 vol % of a total amount of paraffin components contained in the mineral base oil as measured in accordance with ASTM D2786. 
     
     
         3 . The mineral base oil according to  claim 1 , wherein a content of the dicyclo to hexacyclo paraffin component (R2) is from 15 to 70 vol % based on 100 vol % of the total amount of paraffin components contained in the mineral base oil as measured in accordance with ASTM D2786. 
     
     
         4 . The mineral base oil according to  claim 1 , wherein a complex viscosity η* at −35° C. is 60,000 Pa·s/° C. or less as measured with a rotary rheometer under conditions at an angular velocity of 6.3 rad/s and a strain amount of 0.1%. 
     
     
         5 . The mineral base oil according to  claim 1 , which has a naphthene content (% C N ) is 15 to 30. 
     
     
         6 . The mineral base oil according to  claim 1 , which has a viscosity index of 145 or less. 
     
     
         7 . The mineral base oil according to  claim 1 , wherein a content of a sulfur component is less than 100 ppm by mass based on the total amount of the mineral base oil. 
     
     
         8 . The mineral base oil according to  claim 1 , which has a weight average molecular weight of 450 or less. 
     
     
         9 . The mineral base oil according to  claim 1 , which is obtained by purifying a feedstock oil containing a wax. 
     
     
         10 . The mineral base oil according to  claim 1 , which is obtained by purifying a feedstock oil containing a wax and a bottom oil. 
     
     
         11 . The mineral base oil according to  claim 10 , wherein a content ratio [wax/bottom oil] of the wax and the bottom oil is from 30/70 to 95/5 by a mass ratio. 
     
     
         12 . A lubricating oil composition, comprising the mineral base oil according to  claim 1 . 
     
     
         13 . The lubricating oil composition according to  claim 12 , wherein a content of an additive for lubricating oil including a polymer component is 10 mass % or less based on a total amount of the lubricating oil composition. 
     
     
         14 . The lubricating oil composition according to  claim 12 , which has a kinematic viscosity at 100° C. of 4 mm 2 /s or more and less than 15 mm 2 /s, and a viscosity index of 140 or more. 
     
     
         15 . The lubricating oil composition according to  claim 1 , which has a kinematic viscosity at 100° C. of less than 12.5 mm 2 /s, and a high-temperature high shear viscosity (HTHS viscosity) at 150° C. of less than 3.5 mPa·s. 
     
     
         16 . An internal combustion engine comprising a sliding mechanism equipped with a piston ring and a liner; and the lubricating oil composition according to  claim 12 . 
     
     
         17 . A method of lubricating an internal combustion engine having a sliding mechanism equipped with a piston ring and a liner, the method comprising lubricating the piston ring and the liner with the lubricating oil composition according to  claim 12 .