| 摘要 |
PROBLEM TO BE SOLVED: To obtain a water-soluble working oil improved in working performances, rust-preventive properties, antifoaming properties and workability by using an ester of a propylene oxide/ethylene oxide block copolymer with a specified carboxylic acid. SOLUTION: A propylene oxide/ethylene oxide block copolymer having an ethylene oxide content of 10-80wt.% and an average molecular weight of 1,000-30,000 and represented by any one of formulas I to IV (wherein a, b, c, d, e, f and h are each 1 or greater; and R is a 2-4C alkylene) and an aliphatic, aromatic and alicyclic saturated or unsaturated monocarboxylic acid which may have a 2-20C branch are subjected to a dehydration reaction at 100-250 deg.C in the presence of an acid catalyst or an alkali catalyst in a solvent or subjected to thermal dehydration in an inert gas to obtain an ester. A concentrated solution containing 1-80wt.%, desirably 5-60wt.%, based on the oil stock solution, above ester is formed. This is used after dilution with water five-fold to one- hundred-fold. The ester can not exhibit sufficient performances when its content of a diluted solutions is 0.1wt.% or below. |
