High slip polyester films containing siloxane units

Claim 1

A polyester film which has excellent slip characteristics and excellent haze values which is comprised of a random, linear, thermoplastic block copolyester consisting essentially of the polymeric reaction product of a mixture of reactants comprising (A) at least one reactant selected from the groups of reactants consisting of (1) aromatic dicarboxylic acids or the C 1 to C 4 dialkyl esters thereof and (2) aliphatic dicarboxylic acids or the C 1 to C 4 dialkyl esters thereof wherein the reactant selected from group (1) constitutes from 100 to 50 mol percent of the total mols of reactant (A) and the reactant selected from group (2) constitutes from 0 to 50 mol percent of the total mols of reactant (A); (B) from about 100 to about 300 mol percent, based on the total mols of reactant (A) of at least one reactant selected from the group consisting of alkylene glycols containing from 2 to 10 carbon atoms; and (C) from about 5.00 to about 12.0 weight percent, based on the weight of the polymeric reaction product, of a dihydroxy terminated polydimethylsiloxane block copolymer of the general formula ##STR2## wherein n is an integer ranging from about 8 to about 15 and R and R' are divalent polymethylene oxide radicals corresponding to the formulae --CH.sub.2).sub.x O--CH.sub.2).sub.x O].sub.y (CH.sub.2).sub.x (II) and --CH.sub.2).sub.x [O--CH.sub.2).sub.x ].sub.y O--CH.sub.2).sub.x (III) respectively and wherein x is an integer ranging from about 2 to about 8 and y is an integer ranging from about 8 to about 15 to provide said block copolymer with a molecular weight ranging from about 1600 to about 5500; wherein said polyester film has been biaxially oriented and has a kinetic coefficient of friction of less than 0.55 and a haze value of from 3.5% to 14% as determined by ASTM Test D-1003.