A liquid anti-friction composition includes an ester product having a number average molecular weight that is greater than 3800 g/mol, and obtained by subjecting a mixture that includes diglycerol, a monobasic acid component, and a dibasic acid component to an esterification reaction. The monobasic acid component includes at least one C.sub.14-C.sub.24 branched chain fatty acid.

The present invention provides a working fluid composition for a refrigerating machine containing: a refrigerating machine oil containing: a first ester that is a polyol ester of dipentaerythritol and at least one fatty acid selected from fatty acids having 4 to 10 carbon atoms, and has a kinematic viscosity at 100 C. of 7.0 mm.sup.2/s or more; and a second ester that is a complex ester of a polyhydric alcohol containing at least one selected from neopentyl glycol, trimethylolpropane and pentaerythritol, a polybasic acid having 6 to 12 carbon atoms, and a monohydric alcohol having 4 to 18 carbon atoms or a fatty acid having 4 to 18 carbon atoms; and a refrigerant containing difluoromethane.

An aspect of the present invention provides a refrigerating machine oil containing an ester-based base oil, at least one epoxy compound selected from an alkyl glycidyl ether and an aryl glycidyl ether, and a phenol-based antioxidant, wherein a content of the epoxy compound is 0.7% by mass or more based on a total amount of the refrigerating machine oil, and the refrigerating machine oil is used with a refrigerant containing trifluoroiodomethane.

The present invention provides a working fluid composition for a refrigerating machine containing: a refrigerating machine oil containing: a first ester that is a polyol ester of dipentaerythritol and at least one fatty acid selected from fatty acids having 4 to 10 carbon atoms, and has a kinematic viscosity at 100 C. of 7.0 mm.sup.2/s or more; and a second ester that is a complex ester of a polyhydric alcohol containing at least one selected from neopentyl glycol, trimethylolpropane and pentaerythritol, a polybasic acid having 6 to 12 carbon atoms, and a monohydric alcohol having 4 to 18 carbon atoms or a fatty acid having 4 to 18 carbon atoms; and a refrigerant containing difluoromethane.

The instant invention involves the use of simple and complex carboxyl esters, or mixtures thereof, of carboxyl end-capped-polytetramethylene glycols of specific structure to minimize the elastohydrodynamic shear strength of these types of fluids.

The present invention provides a working fluid composition for a refrigerating machine containing: a refrigerating machine oil containing, as a base oil, a mixed ester of (A) a complex ester synthesized from a polyhydric alcohol such as neopentyl glycol, a polybasic acid having 6 to 12 carbon atoms, a monohydric alcohol having 4 to 18 carbon atoms and the like, and (B) a polyol ester synthesized from a polyhydric alcohol such as neopentyl glycol and a monocarboxylic fatty acid having 4 to 18 carbon atoms, in a mass ratio of (A) the complex ester/(B) the polyol ester of 5/95 to 95/5; and a refrigerant such as carbon dioxide.

The lubricating base oil of the present invention comprises an ester synthesized from: a first component that is at least one selected from polyhydric alcohols having 2 to 4 hydroxyl groups; a second component that is at least one selected from polybasic acids having 6 to 12 carbon atoms; and a third component that is at least one selected from monohydric alcohols having 4 to 18 carbon atoms and monocarboxylic acids having 2 to 12 carbon atoms. In addition, the refrigerating machine oil and the working fluid composition for a refrigerating machine of the present invention each comprise the above lubricating base oil.

The present invention provides a working fluid composition for a refrigerating machine, comprising: a refrigerating machine oil comprising, as a base oil, a mixed ester of (A) a complex ester and (B) a polyol ester, wherein (A) is obtainable by synthesis from a specific polyhydric alcohol, a polybasic acid having 6 to 12 carbon atoms, and a monohydric alcohol having 4 to 18 carbon atoms or a monocarboxylic acid having 4 to 18 carbon atoms, wherein (B) is obtainable by synthesis from a specific polyhydric alcohol and a monocarboxylic acid having 4 to 18 carbon atoms, and wherein a mass ratio of (A)/(B) is 5/95 to 95/5; and difluoromethane used as a refrigerant, and the working fluid composition having a refrigerant dissolved viscosity of 5.5 mm.sup.2/s or more, at a temperature of 80 C. and an absolute pressure of 2.1 MPa.

The instant invention involves the use of simple and complex carboxyl esters, or mixtures thereof, of carboxyl end-capped-polytetramethylene glycols of specific structure to minimize the elastohydrodynamic shear strength of these types of fluids.

The present invention provides a working fluid composition for a refrigerating machine containing: a refrigerating machine oil containing, as a base oil, a mixed ester of (A) a complex ester synthesized from a polyhydric alcohol such as neopentyl glycol, a polybasic acid having 6 to 12 carbon atoms, a monohydric alcohol having 4 to 18 carbon atoms and the like, and (B) a polyol ester synthesized from a polyhydric alcohol such as neopentyl glycol and a monocarboxylic fatty acid having 4 to 18 carbon atoms, in a mass ratio of (A) the complex ester/(B) the polyol ester of 5/95 to 95/5; and a refrigerant such as carbon dioxide.