Polyester fiber for industrial use and process for preparation thereof
 Disclosed is a polyethylene terephthalate untwisted multifilament which satisfies the following requirements (A), (B), (C) and (D); PA1 (A) the intrinsic viscosity [IV] is 0.97 to 1.15; PA1 (B) the amorphous orientation function [fa] is not larger than 0.55; PA1 (C) the tenacity [T] (g/d), the shrinkage [.DELTA.S] (%) as measured after standing in dry air at 150.degree. C. for 30 minutes, the medium elongation [ME] (%) under a load of 4.5 g/d, and the dimensional stability index [Y] expressed by the formula: Y=ME.sup.0.81 +.DELTA.S+1.32 are within ranges defined by the following formulae (a), (b), (c), (d) and (e): EQU 0.33Y+5.55.ltoreq.T.ltoreq.0.33Y+6.50 (a), EQU 8.0.ltoreq.T.ltoreq.9.5 (b), EQU 8.5.ltoreq.Y.ltoreq.10.5 (c), EQU 5.ltoreq.ME.ltoreq.10 (d), PA1 and EQU 2.ltoreq..DELTA.S.ltoreq.g (e); PA1 and (d) the elongation at break is at least 11% and the product of the tenacity and elongation, which is defined by: ##EQU1## is 30 to 36. 
Toray Industries, Inc.
Y Y D Y Y D Y
Y10T Y10T D01F Y10T Y10T D01D Y10S
additional additional inventional additional additional inventional additional
Ken-ichiro Masuki Takeshi
Oka Sano Shindo