Abstract: Thermoplastic elastomer composition comprising 100 parts by weight of a polyester block copolymer and 0.05 to 20 parts by weight of a liquid diphenylmethane diisocyanate, which has a stable high melt viscosity with less variation of viscosity in the production lots and has also excellent flexural fatigue resistance and water resistance and is useful for the production of hollow shaped products such as bellows and section profiles such as moldings by blow molding or extrusion molding.

Abstract: An oriented polyester film comprising ethylene terephthalate as the major repeating unit, which comprises particles of kaolinite and calcium carbonate uniformly dispersed therein, said kaolinite and said calcium carbonate having each an average particle size of 0.05 to 0.8 micron and being contained in such amounts as satisfying the following equations:70.ltoreq.D.times.A.ltoreq.1000 (I)1000.ltoreq.A+B.ltoreq.10000 (II)0.1.ltoreq.B/A.ltoreq.25 (III)wherein D is an average particle size (micron) of calcium carbonate, A is a content (ppm) of calcium carbonate and B is a content (ppm) of kaolinite, said oriented polyester film being excellent in flatness, slipperiness, abrasion resistance, etc. with a small number of coarse particles.