Slide Fastener Stringer With Stitched Coupling Element

Abstract

A slide-fastener stringer has its turns (of continuous coil or meander coupling element) secured to its fabric support tapes by means of single-needle or double-needle double chain-stitch or lockstitch wherein bights of the needle thread straddle the coil turns and pass through the filler cords. The U-shaped bights of the needle-thread loops of each stringer half snugly embrace the individual turns and this thread is so tensioned that the looper or gripper thread lies completely along the opposite face of the support tape. The support tape is formed parallel to at least one of its longitudinal edges with a longitudinally extending valley or channel in which the looper, locking or gripper thread lies. In addition the upper side of the coil is formed with a longitudinally extending groove (formed by notches in the shanks of the turns) in which the needle thread lies. After stitching of the interleaved coils to the tapes the thermoplastic monofilament needle thread which has been stretched, is heated to thermally fix and shrink it.

Description

FIELD OF THE INVENTION

The present invention relates to a slide-fastener stringer comprising a pair of parallel support tapes carrying on their facing longitudinal edges interleavable continuous coupling elements and also to a method of assembling such a stringer.

BACKGROUND OF THE INVENTION

It is important in a slide fastener that each coupling element be firmly attached to the edge of the respective support tape. In newer types of slide fasteners having continuous coupling elements formed of a generally helical or helicoidal coil or of a meander with the coupling heads interconnected by rearwardly extending shanks joined together by bights, the head, shanks and bight forming a "turn," difficulties may be encountered. Such coils are formed of a smooth synthetic-resin monofilament that deforms readily and therefore cannot be readily secured to the tapes.

Although it is known to weave or knit the coupling element into the edge of the support tape, by far the most common method of attachment is to stitch each element to the edge of its support tape to form a stringer half. The usual chainstitching or lockstitching has proven almost totally useless on slide fasteners in which the gripper or looper thread overlies the coupling-element turns since the constant rubbing of the slider tends to fray and chain stitches may simply be pulled out. In the lockstitching method, the coils are usually provided with an axial filler cord, and the needle thread or threads lie on the tape. In order to sew a stringer half in such a manner it is necessary to align the gaps between the turns with the needle with great care to prevent the needle from striking the coil and damaging it or the thread. This requires, of course, that the sewing operation be carried out slowly. With increased speed the chance that the tape deflects the needle into the coil is increased. A high sewing speed also increases the possibility that the needle will miss the filler cord.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide an improved slide-fastener stringer and method of making such a stringer.

Another object is the provision of a slide-fastener stringer wherein each coupling element (meander or coil) is securely attached to the edge of its tape.

A further object is to provide a method of rapidly stitching a coupling element (meander or coil) to the edge of a support tape wherein the possibility of the needle damaging the coil is eliminated.

SUMMARY OF THE INVENTION

The above objects are attained according to the present invention in a slide-fastener stringer wherein the coupling element (meander or coil) is secured to its support tape by lock-stitching with the needle thread of the row stitching overlying the coil or meander turns and the looper, locking or gripper thread lying on the tape. The looper thread thus lies in substantially one plane on the side of the tape opposite that on which the coupling element is provided, with the needle thread extending sinuously over the individual coil or meander turns. This is achieved by adjusting the tension of the needle thread to be substantially less than that of the looper thread.

Thus the method according to the present invention resides in lockstitching the coil or meander to the tape with the needle piercing the stringer tape from the coil or meander side or the face of the eventual slide fastener. The tension of the threads is so adjusted that the needle thread surrounds each coil or meander turn on three sides and the looper thread lies virtually entirely upon the support tape at the back of the fastener.

In accordance with yet another feature of the present invention the needle thread, at least, is a thermoplastic synthetic-resin monofilament with so-called plastic memory and is stretched before or during sewing, and the stringer is subjected to a heat treatment (which may consist simply of heating the monofilament) to shrink the needle thread for best securing of the coil to the tape.

The coil according to the present invention has turns each formed with two shanks which lie parallel to each other in a plane perpendicular to the plane of the support tape (i.e. have a common projection on a plane parallel to the support tape), and which are connected together at one end by a bight formed as a coupling head adapted to be interleaved with two similar heads of the facing coil. The lower shank of each turn is connected by a further bight to the upper shank of the neighboring turn. In this manner, according to yet another feature of the present invention, each loop or bight of the needle thread forms a U snugly engaged over the two shanks of a turn of the coil, holding this turn tightly in place.

In such a manner the sewing needle is guided by the sides of the turns of the coupling coil so that the chances of striking this coil are small. Thus it is possible to stitch at very high speed, thereby making production faster and cheaper.

According to another feature of the present invention the support tape is formed near one longitudinal edge with a longitudinally extending groove, channel or valley. This groove serves as a seat for the looper thread and can be formed easily in a warp-knit support tape in which one of the knitting needles is not threaded.

DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a top view of a portion of a slide-fastener stringer according to the present invention;

FIGS. 2 and 3 are sections taken along lines II--II and III--III, respectively, of FIG. 1;

FIG. 4 is a bottom view of the stringer portion shown in FIG. 1;

FIG. 5 is a view similar to FIG. 3 showing an alternative embodiment of the present invention;

FIG. 6 is a schematic diagram of a stringer assembling apparatus according to the present invention; and

FIG. 7 is a cross section through an element of FIG. 6, in enlarged scale.

SPECIFIC DESCRIPTION

FIGS. 1-4 show a pair of warp-knit support tapes 1 made, for example, according to principles discussed in the now allowed commonly assigned and copending patent application, Ser. No. 82,326 filed on 20 Oct. 1970 by myself jointly with M.L. Cappel and E. Stubiger. Secured to these tapes 1 are a pair of coupling coils 2 of a Nylon-type polyamide. Each coil 2 has a plurality of turns 6 each connected to the neighboring turn by a connecting bight 7 and each formed with a spread coupling head 5. Each turn comprises parallel and spaced upper and lower shanks 6a and 6b lying in a common plane as shown at P which is orthogonal to the plane E of the tapes 1. The head 5 interconnecting the upper and lower shanks 6a of each turn 6 is connected in one direction via a connecting bight 7 to the next lower shank 6b and the lower shank 6b of the same turn is connected in the opposite direction to the neighboring upper shank 6a. Thus the connecting bight 7 lies at an angle to the plane P.

Extending longitudinally through the center of each coil 2 is a natural fiber multifilament filler cord 8 that lies against the bight portion 7. Lockstitching 3, 4 passes through this cord 8 and over the upper shanks 6a to hold the elements against the tapes.

As best seen in FIGS. 2-4 the stitching 3, 4 comprises a needle thread 3 that is here advantageously a synthetic-resin monofilament, and a looper thread 4 sewn in a Type 401 single-needle double-locked stitch (Federal Standard number 751 A). The needle thread 3 is sinuous, running in a plurality of U-shaped bights 3a which snugly straddle the upper shanks 6a and which have legs extending substantially parallel to the planes P of the shanks 6a and 6b. The looper thread 4 lies on the back of the tape 1 in a longitudinally extending valley 10 formed between the wales of the warp-knit tape 1. In addition each upper shank 6a is formed with an indentation or notch 9 in which the extreme upper portion of each bight 3a lies. Thus the threads 3 and 4 hardly project from the faces of the stringer so that the slider is not likely to wear them out.

FIG. 5 shows an embodiment substantially identical to that of FIGS. 1-4 except that square-backed coil turns 6 of coils 21 are used. In addition tapes 1' are used which are folded over at 1b to have flaps 1a to which the elements 2' are secured via a single looper thread 4' and a pair of parallel needle threads 3'. Due to the wide transverse lay of the looper threads 4' the crease is maintained at 1b to allow use of the stringer of FIG. 5 in a so-called invisible slide fastener. In this embodiment a Type 402 double-needle double locked stitch is employed.

Double-locked stitches are extremely stable since at each stitch the needle thread locks the looper thread twice and vice versa. Thus, assuming that the stitching is cut at any point, raveling is virtually impossible. This is extremely important since the coupling coil of a slide fastener must not come loose from its tape at any point; the slightest disattachment suffices to make the fastener useless.

FIGS. 6 and 7 illustrate how the stringer of FIGS. 1-4 is made. First a pair of tapes 1 are fed from supply rolls 15 in a transport direction D towards a sewing station 11. Also upstream of the station 11 a pair of interleaved coupling coils 2 are provided with filler cords 8 are pulled off a spool 16 and laid on the juxtaposed longitudianl edges of the advancing parallel tapes 1.

In the sewing station 11 shown in FIG. 7 in detail the tapes 1 and elements 2 are advanced between two guide plates 13a and 13b, the former of which is formed with a T-shaped notch 19 extending in the transport direction. The tapes 1 and coils 2 are aligned perfectly by the notch 19 and when they pass between in-line holes 14 needles 12 and loopers 18 serve to execute the necessary stitching operation. Since the needles 12 pierce the stringer from the coil side there is no change that they be deflected by the textile tapes 1 to strike the coils 2.

The threads 3 and the threads 4 come from respective supplies 20 and 21 but pass through identical tensioners 22 formed of a threaded rod 23 screwed at one end into a disk 24 and carrying two more slidable annular disks 25 and 26. A nut 27 is threaded onto the end of the rod 23 and compresses a spring 28 against the ring 26. The threads to be tensioned passto either side of the disk 25 and are wrapped around the rod 23 so that the extent of compression of the spring 28 determines the thread tension. The tension of the looper threads 4 is made substantially greater than that of the needle threads 3 in order that these threads 3 rather than the threads 4 be pulled through the tapes.

Upstream of the sewing station 11 the assembled stringer S is passed in the transport direction between two heated rollers 29 at a heat-treatment station 30. These rollers 29 serve to shrink the stretched monofilamentary needle threads 3 in order that the coils 2 be held very securely on the tapes 1. The pressure exerted by these rollers 29 also serves to flatten the stringer S somewhat and to thermally fix the shapes of the coils 2 and threads 3.

Claims

I claim:

1. A slide-fastener stringer having a pair of slide-fastener stringer halves each comprising:

an elongated textile support tape having a front face, a back face and a longitudinal edge;

a thermoplastic generally helical synthetic resin coil composed of coil turns each having a pair of parallel shanks, one of the shanks of each turn lying on the front face of a respective tape, said coils extending parallel to the respective longitudinal edges of said tapes and being adapted to interdigitate with one another upon movement of a slider along said coils;

a filler cord extending through the turns of each of said coils; and

lockstitching securing each coil to the respective tape and formed of at least one needle thread and a looper thread, said needle thread having a plurality of U-shaped bights straddling said turns and passing through the respective tape with each bite straddling both shanks of each turn, said looper thread engaging the needle thread and lying along the back face of each tape, each turn having a connecting portion turned away from the respective said edge of its tape and connecting one shank of each turn to a shank of a neighboring turn, said cord being received between the shanks of each turn and lying against the connecting portions thereof, each of said tapes being folded back adjacent its respective longitudinal edge with the respective back face lying within the fold.

2. The stringer defined in claim 1 where at least one of said shanks of each turn is formed with a notch receiving the respective U-shaped bight of the needle thread.

3. The stringer defined in claim 1 wherein said tapes are formed on said back face adjacent said longitudinal edges with longitudinal grooves receiving said looper thread.

4. A slider-fastener stringer having a pair of stringer halves each comprising:

an elongated textile support tape having a front face, a back face and a longitudinal edge;

a continuous coupling element lying on said front face and extending along said longitudinal edge while having a plurality of spaced apart turns; and

lockstitching securing said element to said tape and formed of at least one needle thread and a looper thread, said needle thread having a plurality of U-shaped bites straddling said turns, said looper thread lying substantially against said back face of said tape, each of said tapes being folded back adjacent its longitudinal edge with its back face within the fold.

5. A slide-fastener stringer comprising a pair of slide fastener halves adapted to be interconnected upon movement of a slider therealong, each of said slide fastener halves comprising a longitudinally extending support tape, a continuous coupling element lying along one face of said support tape and having a plurality of turns defining a row of coupling head engageable with a similar coupling element and respective shanks extending generally transversely to the direction of displacement of the slider, said tape being formed along its opposite face with a longitudinal channel in line with said coupling element, and a row of stitching securing said coupling element to the tape, said row of stitching comprising a needle thread passing in loops around the turns of the coupling element and penetrating to said opposite face of said tape and a further thread engaging said needle thread along said opposite side of said face and lying wholly within said channel, said loops of said needle threads each consisting of a bight engaging a shank of one of said turns and a pair of strands leading from said bite and laterally hugging such shank.

6. The stringer defined in claim 5 wherein each of said turns has a pair of shanks disposed in a common plane perpendicular to the respective tape and said strands of each bite straddling both shanks of the respective turns, said stringer further comprising a filler cord extending through each of said coupling elements and through each turn thereof between the shank of the respective turn, said strands passing through said filler cords.