Refrigerator oil and working fluid composition for refrigerator

A method for improving a compatibility of a working fluid composition for a refrigerating machine comprising,

• (a) preparing a refrigerating machine oil comprising a base oil consisting of a poly(meth)acrylate, and
• (b) mixing a refrigerant and the refrigerating machine oil, wherein the poly(meth)acrylate has a structural unit represented by the following formula
• wherein R1 and R2 each are a hydrogen atom and R3 be a hydrogen atom or a methyl group, and R4 is an alkyl group having 1 to 10 carbons, and
• a content of a unit having a carbon-carbon double bond present at a terminal in the poly(meth)acrylate is 6% by mole or less relative to total units constituting the poly(meth)acrylate;
• an amount of the hydrogenated poly(meth)acrylate is 30% by mass or less based on the total amount of the poly(meth)acrylate;
• and
• the refrigerant comprises at least one refrigerant selected from the group consisting of a mixture of difluoromethane, pentafluoroethane, and 1,1,1,2-tetrafluoroethane, a mixture of pentafluoroethane, 1,1,1,2-tetrafluoroethane, and 1,1,1-trifluoroethane, an unsaturated hydrofluorocarbon, and a hydrocarbon.

A working fluid composition for a refrigerating machine, comprising

• a refrigerant;
• and
• a refrigerating machine oil comprising a base oil consisting of a poly(meth)acrylate,
• wherein the refrigerant comprising a refrigerant selected from the group consisting of
• a mixture of difluoromethane, pentafluoroethane, and 1,1,1,2-tetrafluoroethane,
• an unsaturated hydrofluorocarbon, and
• a hydrocarbon,
• the unsaturated hydrofluorocarbon is selected from the group consisting of 1,3,3,3-tetrafluoropropene (HFO-1234ze), and 2,3,3,3-tetrafluoropropene (HFO-1234yf), 1,2,3,3-tetrafluoropropene (HFO-1234ye), and
• the hydrocarbon is selected from the group consisting of propane (R290), normal butane, isobutane, and 2-methylbutane,
• a mass ratio of the refrigerating machine oil/the refrigerant is from 2/100 to 400/100;
• and the poly(meth)acrylate has a structural unit represented by the following formula (1):
• wherein R1 and R2 each are a hydrogen atom and R3 be a hydrogen atom or a methyl group, and R4 is an alkyl group having 1 to 10 carbons,
• the poly(meth)acrylate contains a hydrogenated poly(meth)acrylate, and
• a content of a unit having a carbon-carbon double bond present at a terminal in the poly(meth)acrylate is greater than 1% by mole and 6% by mole or less relative to total units constituting the poly(meth)acrylate.