1. Field of the Invention
The present invention relates to a slide fastener, and more particularly to a woven fastener stringer having a coiled continuous plastic filament woven into a longitudinal edge of a woven tape simultaneously with the wearing of the tape.
2. Description of the Prior Art
There have been proposed a number of slide fasteners of the type in which a row of fastener elements is woven into one longitudinal edge of a woven stringer tape simultaneously with the wearing of the tape. Usually the fastener element row is in the form of a helically coiled continuous plastic filament having a succession of loops.
In production, when it is bent into such a helical shape, the filament which is thicker and harder than the warp and weft yarns of the tape tends to yield back under its own resilience, thus not only causing the fastener stringer to stretch longitudinally but also causing the individual filament loops to tilt away from a proper upright posture with respect to the plane of the tape. This would result in staggering pitch of the filament loops, i.e. the fastener elements, which would hinder smooth closing and opening operation of the slide fastener.
A solution is disclosed in U.S. Pat. No. 4,623,004 for making the fastener stringer stable in the loop-to-loop pitch of the filament. According to this prior art, as shown in FIG. 5, the outermost upper and lower binding warp threads A, B extend respectively over and under the loops E and are disposed substantially in registry with one another, and a gap-filling warp thread C is laid between the outermost upper binding warp thread A and the next upper binding warp thread Al and extends under the loops E and alternately over and under the picks of a foundation weft thread D so as to pull the portions of the foundation weft thread D between the outermost upper binding warp thread A and the next upper binding warp thread Al toward the opposite side of the tape substantially halfway between the upper and lower legs of the respective loops E. A problem with this prior art arrangement is that the positions at which the gap-filling warp thread C is interlaced with the foundation weft thread D can be easily changed as affected by possible small changes in tension of the warp and weft threads and/or in properties of the material of the filament. As a result, reliable and accurate shaping of the filament loops is difficult to achieve.