Lubricating oil composition for hydraulic oil and method for producing the same

A lubricating oil composition for hydraulic oils, comprising 10 to 99% by mass of a lubricant base oil (A) having the properties of the below (A1) to (A3), 90 to 1% by mass of a liquid random copolymer of ethylene and α-olefin having the properties of the below (B1) to (B5), wherein the total amount of the lubricant base oil (A) and the copolymer is 100% by mass, the lubricating oil composition having the properties of the below (C1).

• (A1) The lubricant base oil has a kinematic viscosity at 100° C. of 1 to 14 mm2/s.
• (A2) The lubricant base oil has a viscosity index of 100 or more.
• (A3) The lubricant base oil has a pour point of 0° C. or lower.
• (B1) The liquid random copolymer comprises 40 to 60 mol % of ethylene units and 60 to 40 mol % of α-olefin units having 3 to 20 carbon atoms.
• (B2) The liquid random copolymer has a number average molecular weight (Mn) of 500 to 10,000 and a molecular weight distribution (Mw/Mn, Mw is the weight average molecular weight) of 3 or less, as measured by gel permeation chromatography (GPC).
• (B3) The liquid random copolymer has a kinematic viscosity at 100° C. of 30 to 5,000 mm2/s.
• (B4) The liquid random copolymer has a pour point of 30 to −45° C.
• (B5) The liquid random copolymer has a Bromine Number of 0.1 g/100 g or less.
• (C1) The lubricating oil composition for hydraulic oils has a kinematic viscosity at 40° C. of 10 to 300 mm2/s.

A method for producing a lubricating oil composition for hydraulic oils, comprising the steps of:

• preparing a liquid random copolymer (B) of ethylene and α-olefin by the following method (α);
• preparing a lubricating oil composition for hydraulic oils by a lubricant base oil (A) having the properties of the below (A1) to (A3) in an amount of 10 to 99% by mass in the lubricating oil composition with the liquid random copolymer (B) in an amount of 1 to 90% by mass in the lubricating oil composition, wherein the total amount of the lubricant base oil (A) and the copolymer (B) is 100% by mass, the composition having the properties of the below (C1).
• (A1) The lubricant base oil has a kinematic viscosity at 100° C. of 1 to 14 mm2/s.
• (A2) The lubricant base oil has a viscosity index of 100 or more.
• (A3) The lubricant base oil has a pour point of 0° C. or lower.
• (C1) The lubricating oil composition for hydraulic oils has a kinematic viscosity at 40° C. of 10 to 300 mm2/s.
• (Method (α))
• A method (α) for preparing a liquid random copolymer of ethylene and α-olefin, comprising a step of carrying out solution polymerization of ethylene and α-olefin having 3 to 20 carbon atoms, under a catalyst system comprising
• (a) a bridged metallocene compound represented by the following Formula 1, and
• (b) at least one compound selected from a group consisting of
• (i) an organoaluminum oxy-compound, and
• (ii) a compound which reacts with the bridged metallocene compound to form an ion pair.
• [In Formula 1, R1, R2, R3, R4, R5, R8, R9 and R12 are respectively and independently hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, and adjoining groups are optionally connected to each other to form a ring structure,
• R6 and R11, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group,
• R7 and R10, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group,
• R6 and R7 are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure,
• R11 and R10 are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure,
• R6, R7, R10 and R11 are not hydrogen atom at the same time;
• Y is a carbon atom or silicon atom;
• R13 and R14 are independently aryl group;
• M is Ti, Zr or Hf;
• Q is independently halogen, hydrocarbon group, an anionic ligand or a neutral ligand which can be coordinated to a lone pair of electrons;
• and
• j is an integer of 1 to 4.]