Polyester filament woven fabric for air bags

A non-coated and uncalendered polyester filament woven fabric for air bags produced by (A) weaving a plurality of polyester multifilament warp and weft yarns having respectively and independently from each other, a thermal shrinkage of 3 to 13% at a temperature of 150.degree. C., to provide a gray woven fabric having cover factors in the warp and weft directions of from 1,000 to 1,200 and a difference of 200 or less between the cover factor in the warp direction and that in the weft direction;

• and (B) dry-heat-setting the woven fabric under tension by at least two steps of roll surface-contact heat-setting procedures wherein in the first step thereof, the woven fabric is brought into contact with a low temperature roll having temperature of 130.degree. C. to 170.degree. C. and in the final step thereof, the woven fabric is brought into contact with a high temperature roll having a temperature of 160.degree. C. to 220.degree. C. and higher than the temperature of the low temperature roll, at a speed of 5 to 30 m/min. for a total heat-setting time of 10 to 180 seconds, to such an extent that the polyester multifilament warp and weft yarns in the resultant heat-set woven fabric exhibit:
• (1) a maximum thermal stress of 0.8 g/denier or less determined by heating a specimen yarn fixed to a length of 50 mm from room temperature to a melting temperature of the yarn, under an initial load of 0.08 g/denier at a heating rate of 150.degree. C./minute,
• (2) a maximum thermal shrinkage of 25% or less determined by heating a specimen yarn having a length of 50 mm from room temperature to the melting temperature of the yarn under an initial load of 0.08 g/denier at a heating rate of 150.degree. C./minute without restricting the thermal shrinkage of the specimen yarn,
• (3) a limiting viscosity number of from 0.80 to 0.95 dl/g determined in a concentration of 1.2 g/100 ml in o-chlorophenol at a temperature of 25.degree. C. and,
• (4) a content of thermal carboxyl groups of 5 to 35 equivalents per ton of the polyester yarns, and that the resultant heat-set woven fabric exhibits an air permeability of 0.5 ml/cm.sup.2 /sec/0.5 inch water or less.