GB915779A - Amorphous linear copolyesters - Google Patents

Abstract

An amorphous film, which may be readily heat-sealed to itself or laminated to another substrate (see Group VIII), is made from a copolyester of (a) terephthalic acid, (b) an alkylene glycol of formula HO(CH2)nOH, where n=2-10, and (c) a branched-chain glycol of formula HO-CH2-C(R)2-CH2-OH, where R is an alkyl group containing 1-4 carbon atoms, the alkylene terephthalate recurring units constituting from 20-75% of the recurring terephthalate units in the copolyester. The films may be made by extruding the copolyester through a plate die on to quench drum. In Example 15, the polyester and polyethylene terephthalate are extruded on to the same quench drum and the resulting film laminate stretched in two directions and heat set. In Example 17, the copolyester is extruded through an annular die and the resulting tubing expanded with air which is sealed in the tubing between the die and the nip of a draw roll; the tubing is then drawn through a cooling zone where molecular orientation is effected by orientation and the film expanded to its final diameter. Finally, the tube is flattened by passage through draw rolls and the film is split. The copolyester may be made by (a) reacting terephthalic acid or an alkyl ester thereof with a mixture of the glycols to form a mixed ester which is thereafter polymerized, or (b) conducting two separate ester-forming reactions between terephthalic acid or an alkyl ester thereof and the alkylene glycol and terephthalic acid or an alkyl ester thereof and the branched-chain glycol, and thereafter mixing the two resulting esters and copolymerizing them. The usual esterification or ester-interchange catalysts may be used. Examples describe the manufacture of copolyesters by reacting dimethyl terephthalate, ethylene glycol and either 2:2-dimethyl-1:3-propane diol or 2-methyl-2-ethyl-1:3-propane diol. Specifications 578,079, 729,803, 731,023 and 773,778 are referred to.