Abstract: There is provided by the present invention a polyester resin composition containing a copolyester having hydroxy carboxylic acid units as constituent units or a polyoxycarboxylic acid, wherein hydroxy carboxylic acid units of 5 or less carbon atoms are contained in amounts of 2 to 75% by mol based on 100% by mol of all the constituent units contained in the composition, and a molar ratio SAA of hydroxy carboxylic acid units both of whose neighboring units are hydroxy carboxylic acid units to all the hydroxy carboxylic acid units contained and a molar ratio SBB of hydroxy carboxylic acid units neither of whose neighboring units is a hydroxy carboxylic acid unit to all the hydroxy carboxylic acid units contained satisfy the following formula: 0.03<SAA/SBB<30.

Abstract: The present invention provides a polyester resin which comprises (a-1) 45 to 99% by mole of an oxycarboxylic acid unit having 5 carbon atoms or less, (a-2) 0.5 to 27.5% by mole of an aromatic dicarboxylic acid unit, and (a-3) 0.5 to 27.5% by mole of an aliphatic diol unit having 4 carbon atoms or less, and containing (a-1) to (a-3) in a total amount of 95% by mole or greater, wherein the relationship between the content of the oxycarboxylic acid, expressed as M % by mole, and the density ? (kg/m3) of the polyester resin, satisfies the formula ??1349+M×0.85.

Abstract: There is provided by the present invention a polyester resin composition containing a copolyester having hydroxy carboxylic acid units as constituent units or a polyoxycarboxylic acid, wherein hydroxy carboxylic acid units of 5 or less carbon atoms are contained in amounts of 2 to 75% by mol based on 100% by mol of all the constituent units contained in the composition, and a molar ratio SAA of hydroxy carboxylic acid units both of whose neighboring units are hydroxy carboxylic acid units to all the hydroxy carboxylic acid units contained and a molar ratio SBB of hydroxy carboxylic acid units neither of whose neighboring units is a hydroxy carboxylic acid unit to all the hydroxy carboxylic acid units contained satisfy the following formula: 0.

Abstract: The present invention provides a polyester resin which comprises (a-1) 45 to 99% by mole of an oxycarboxylic acid unit having 5 carbon atoms or less, (a-2) 0.5 to 27.5% by mole of an aromatic dicarboxylic acid unit, and (a-3) 0.5 to 27.5% by mole of an aliphatic diol unit having 4 carbon atoms or less, and containing (a-1) to (a-3) in a total amount of 95% by mole or greater, wherein the relationship between the content of the oxycarboxylic acid, expressed as M % by mole, and the density ? (kg/m3) of the polyester resin, satisfies the formula ??1349+M×0.85.