Process and Means for the Manufacture of Zip Fasteners

This invention relates to a process for the manufacture of zip fastener textile supporting tapes with sets of injection molded locking members and means for implementing the process. A process and means of this kind are described in CH-A-635 026 which discloses as the principal component a transverse slide whereby both the locking members with the upper stopping members and the end members are manufactured in a single injection molding process using the same molding tool together with a center portion of any length. This process and means represented a technical advance over the prior art since previously the end members had to be injection molded separately and applied. However with the process and means according to this patent it is not possible to mold the box as well, and in accordance with CH-A-626 241 this is manufactured separately and connected to one of the end members of the previously mentioned patent using a connector. Separate manufacture of the box and its connection with the connector requires further process steps and is therefore cost intensive.

Also there are in the main two types of zip fasteners on the market, namely a type with staggered members in which each member consists of two teeth offsetting each other on the two sides of the textile tape, and a so-called slit-teeth type in which the member is of one piece and located on both sides of the textile tape and in which a slit is provided in the front side of the other member. According to the known state of the art this slit is milled subsequently using special tools with the result that the wear on precise and expensive tools is very great.

On the basis of this state of the art the object of this invention is to provide a process and means for the manufacture of zip fasteners whereby all the members of a zip fastener and its in particular the end parts, can be injection molded with one tool and in one operation regardless of the type of zip. Another object is in particular to injection molded a zip fastener completely with a single tool in a single operation.

The invention is more particularly described below with reference to a drawing of specimen embodiments.

FIG. 1 shows the lower part of an injection molding tool of the means according to the invention in plan view and in partly diagrammatical form,

FIG. 2 shows a longitudinal cross-section along the line II--II in FIG. 1,

FIG. 3 shows a view from the left hand side of FIG. 1,

FIG. 4 shows the central portion with the upper and lower end members of a zip fastener injection molded with the injection molding tool and

FIGS. 5+6 show cross-sections through the tools in the positions indicated by lines V--V and VI--VI.

Some parts of the injection molding tool and the base of the injection molding tool of the means in accordance with the invention are illustrated in FIGS. 1 and 2. These show the tool body 1 of the base, the lower transverse slide member 2, which is located approximately in the center, strips 3 screwed to tool body 1 and holes 5 and 6 in the body for ejector 4, see also FIG. 6. The ejector is operated by an ejector plate in a known way. Two screwed strips 7 and an end member 8 are located on transverse slide member 2 in the upper part of the drawing, with two depressions 9 for the upper stop members on the right side of the drawing and opposite to this on the left side of the drawing a recess 10 for forming the coupling and a mold 11 for forming the box. The strips 3 are screwed to tool body 1 by means of screws 12. Transverse slide member 2 is likewise screwed to the tool body using screws 13.

In addition to mold 11 for the box, which will be described in greater detail below, there is another major difference from the known state of the art in that recesses 31 for the interlocking members and the corresponding end pieces are not formed directly in the tool body but are formed in removable and exchangeable strips. This not only has the advantage that different types of members can be injection molded using the same and torsionally rigid strips can be used which can be oriented precisely on the tool body with the result that considerably longer tools can be manufactured with sufficient accuracy than is possible in the present state of the art. In fact tools of a length of 650 to 700 mm can be manufactured without any special measures being necessary in order to achieve the necessary precision. The two ends, on the right side of FIG. 1, of the strips have an end recess 14 on which the first member of the zip fastener member first molded to hand is looked. The mold zip fastener members or the upper stop member are then formed when the transverse slide is displaced into the other position which is not shown.

In addition to the two strips 3, FIG. 3 shows two longitudinal holes 15 which serve to maintain the tool at a particular temperature by means of a suitable medium, and longitudinal slot 22 which forms the main channel.

FIG. 4 shows the central part of a zip fastener caster, on a magnified scale, as it is briefly before the tool is removed. On the right side are located the two upper stop members 16 with the directly connecting members 17, wherein members of the slit type are shown here, in which slit 18 is formed. The stop members and the other members are secured on both sides of textile tape 19. The plastic is injection molded from the top, i.e. through the upper tool body 20 illustrated in FIG. 6 which also shows the main feed 21 which opens into longitudinal slot 22, (see FIG. 3) between the two strips, which forms the main length 23 from which channels 24 branch off to the separate members. FIG. 4 also shows that all four end members are cast together with the individual zip fastener member on the right side of the drawing.

Although injection molding of the upper stop member and coupling piece 25 offers no special problems, since only recesses in the tool, or the strips, are necessary, simultaneous molding of box 26 obviously raises such difficulties that this has hitherto not appeared to be possible, because the box requires a body (shown by means of dashed lines in FIG. 4) 27, which cannot be removed upwards or downwards like the parts of the tool. The solution to this problem can be seen in FIG. 1 and the cross-section in FIG. 5. Body 27 which forms the box is connected via an arm 28 with a quarter-circle-shaped rammer 30 which runs in a correspondingly curved groove 29 in slide member 2 and is mechanically operated from the back towards the front in FIG. 5. Rammer 30 is secured to arm 28 by means of a screw 32.

FIG. 5 also shows the other already described components such as textile tape 19, box 26, coupling piece 25, and it can also be seen that the textile tape has as usual a thickening 33 on its inner edges; and also upper tool body. It is also known and shown in FIG. 5 that upper tool portion is constructed in the same way as lower portion 2 with the exception of the ejector in the lower part and the channels for the plastic in the upper part. A further difference between the lower and upper parts lies in the upper part of the slide 20' which has no strips, only the corresponding hollows and recesses for the members and the end portions.

The parts, means and advantages so far described apply to all types of zip fasteners, i.e. the staggered or the slit types. As already mentioned in the introduction, it was not possible in the known state of the art to mold members of the slit type in one operation and it was in fact necessary to mold members without a slit in order that they could then be subsequently machined in a special machine, i.e. to cut out the slit. FIG. 6 also shows why the molding of slit members in a multiple tool gives rise to major difficulties, because as in the case of the box, the inserted piece which forms the slit cannot be removed from above or beneath, but only from the side. As will be seen from the following description the solution to this problem is achieved in that the recesses for the members are not located directly in the parts of the tool, but in strips. As mentioned the injection of slit members requires a lateral movement of inserts 34, which form slit 18 in member 17. Insert 34 is a short limb of a U-shaped insert 35 which is movably mounted in strip 3 wherein upper limb 34, i.e. the insert, and lower limb 36 guide the insert strip. At approximately the center or midway between upper limb 34 and lower limb 36 pressure is applied to the insert strip by means of a compression spring 37 which is housed in a recess or cutout 38 in the strip in such a way that this is pressed out against the center, i.e. out of the slit. The two long limbs 39 of the insert strip are inclined together and are supported on a trapezoidal longitudinal strip 40 which is formed in a single piece with lower tool body 1. In the closed position shown here shortly after molding of the members and before their ejection, this longitudinal strip supports insert strip 35 and thus insert 34.

In the known state of the art, the upper part of the mold is removed after molding and the molded zip fastener member is removed by ejector 4 as shown in FIG. 6. In the case of the tool construction as shown, the ejector does not only eject the molded zip fastener members upwards, but also lifts strips 3 by raising insert strip 35 while strip 35 is located in slit 18. While the upper strips 3' are fixed to upper tool body 20 by means of screws 41, strips 3 are attached to lower tool body 1 by means of screws 12 in such a way that strips 3 can move downwards and upwards. For this purpose sleeves 42 on which strips 3 are guided are placed around screws 12. When the zip fastener members are ejected together with insert strips 35 attached to them, the insert strips 35 are raised along trapezoidal longitudinal strip 40 which assists compression spring 37 to eject the insert strips and their insert 34 from the slit 18 of members 17 and thus release the zip fastener member. By this means strips 3 fall back into their original positions. As is known from the state of the art, the ejector is as a rule operated by an ejector plate, the ejector in the lower transverse slide member having to be of a different design from the ejector for the other parts, i.e. in two portions and with a return spring in the slide portion.

The above description shows that all types of zip fastener member and all their components can be molded in one operation with the tool described, whereas previously several operations were necessary for this, in particular time-consuming and cost-intensive operations in order to manufacture the slit for the zip fastener or to manufacture the box separately and fit it.

Further simplifications can be applied at the ends. In accordance with the state of the art it is usual, as shown at the top of FIG. 4, to mold so-called "butterflies" 43, i.e. lattices of plastic, in order to strengthen this region. Instead of this it is also possible to provide a reinforcing strip 44 which can be applied to appropriate places before the tape is placed in the tool in order to strengthen weak points. With this process it is also possible to apply narrow reinforcing strips 45 to the upper stop members. As textile tape 19 is fed continuously into the tool from a roll the reinforcing strips can be applied automatically in advance, preferably by means of ultrasonic welding.

In order to increase the economy and service life of the tool the strips can be manufactured from hard metal or hardened steel or be provided with a very hard coating of metal or steel by means of known coating processes so that they have both low friction and reduced adherence to plastic in order to aid removal of the molded zip fastener members.

The method of working can be seen in FIG. 4. Here the right zip fastener member is either an overmolding, i.e. the firs molding, or an already cast component with end members 25 and 26. After molding the upper part of the tool is removed, the zip fastener member is ejected and in this particular case transported to the right. After this, either the upper stop member 16 is molded or the transverse slide member is placed in the other position in order to mold only locking members, it being possible for this process to be repeated in the case of specially long zips or upper stop member 16 and the lower end pieces 25 and 26 to be molded subsequently with the corresponding members. The process operates fully automatically and is controlled by appropriate electronics which can be manufactured and designed by one skilled in the art. Because the strips are exchangeable it is possible to manufacture all zip fasteners known on the market, for example, with appropriate modification of the transverse slide, zip fasteners with an open or closed end, i.e. separable or useparable end members, or double open or continuous zip fasteners of the above-mentioned types or other types of fastener. For this only the corresponding parts of the transverse slide member need to be replaced.

In addition to this the injection molded tool constructed on the modular system offers the user not only the possibility of selecting and combining different zip types, but also convenient exchangeability, rapid insertion for different sizes of member and the rapid replacement of individual strips which have become damaged by wear or otherwise.

In addition to this spacing wedges may be inserted on one or both sides in order to determine the length.