Polyester fiber treated with anionic polyalkylene oxide emulsified polyester polyether finish

A method for modifying polyester synthetic fiber products, comprising the steps of dipping said fiber products in a treating liquor having an aggregation initiating temperature in the range of 65.degree.-125.degree. C and then heating said treating liquor to 100.degree. C to 140.degree. C and to temperatures at least 1.degree. C higher than its aggregation initiating temperature to thereby heat said fiber products, said treating liquor being prepared by adding to an aqueous dispersed liquid of a polyester polyether block copolymer, which is prepared from an aromatic dicarboxylic acid or a lower alkyl ester thereof, a lower alkylene glycol and a polyalkylene glycol, (a) an emulsifying amount of a surface active agent as expressed by the following general formula (I):

• ##STR20## where;
• R is an alkyl, alkenyl or alkylaryl group;
• R.sub.1 is a hydrogen atom or a methyl group;
• A is a --SO.sub.3, --(CH.sub.2).sub.m SO.sub.3 or PO.sub.3, m is an integer of 2 or 3;
• M is a hydrogen atom or an ammonium, substituted ammonium or lower alkyl group or an alkali metal;
• n is an integer in the range of 4-20 and (b) a member selected from the group consisting of at least one acid or latent acid which forms an acid upon being hydrolyzed, at least one water-soluble salt and mixtures thereof, said salt being made up of cations selected from the group consisting of NH.sub.4 .sup.+, Na.sup.+, Li.sup.+, K.sup.+ and Mg.sup.+.sup.+ and anions selected from the group consisting of SO.sub.4 .sup.-.sup.-, CH.sub.3 COO.sup.-, Cl.sup.- and Br.sup.-, said member being used in an amount to increase the affinity and sorption power of said block copolymer to the polyester synthetic fiber products, and in cases wherein a water-soluble salt is used, said salt being also used in salting out proportions.