Method for manufacturing a plastic zipper with end stops

[0002] The present invention relates to reclosable packaging and, in particular to an improved zipper for use in the manufacture of such packaging.

[0003] Reclosable plastic bags are growing increasingly popular both for storage purposes and as primary packaging for food stuffs and other products. Such bags are formed with plastic zipper having profiles with mating interengageable elements. A problem that has been encountered with such zippers is that when the user opens the zipper, if too much force is exerted a run may develop down one or both side seams of the bag. To avoid this from happening, it has heretofore been proposed to crimp or crush the ends of the zipper. While such crimping works fine for sliderless packages, the result is not always satisfactory when a slider is provided to facilitate opening and closing the zipper elements. In such case, the slider may be pulled over the crimp and off the package if too much force is exerted.

[0004] In order to maintain the slider on the zipper profiles, it has heretofore been suggested to provide stops at the ends of the zipper. The prior art is replete with suggestions as to how the end stops may be formed. Thus, in U.S. Pat. No. 5,131,121 end stops are formed of the material at the ends of the zipper by deforming the material to extend outwardly from the sides of the bag. In U.S. Pat. No. 5,161,286, U.S. Pat. No. 5,448,807 and U.S. Pat. No. 5,833,791 a clip is provided at the ends of the zipper.

[0005] In accordance with the present invention a zipper is disclosed for use in the production of reclosable plastic bags of the type having said zipper extending across a top end of the bag. The zipper has a first profile member and a second profile member that is interengageable with the first profile member. The exact profile configuration may be one of many conventional shapes that are well known in the art. At bag length intervals of the zipper notches are formed by removing at least a portion of the first profile member and a portion of the second profile member. A mold is positioned about each of the notches and a molten thermoplastic material is introduced into the mold cavity filling the notch and extending beyond the notch and over the zipper top so that when the molten thermoplastic material is cooled, an end stop is formed in situ at each of the notches.

[0006] In the accompanying drawings:

[0007] FIG. 1 is a schematic perspective view of a line for producing zippers in accordance with the present invention;

[0008] FIG. 2 is a profile view of the line depicting the stamping area and interlocking members;

[0009] FIG. 3 is a top plan view of the line of FIG. 1;

[0010] FIG. 4 is a perspective view of a first embodiment of zipper notching in accordance with the present invention;

[0011] FIG. 5 is a perspective view of the zipper of FIG. 4 with end stops molded in situ;

[0012] FIG. 6 is a view with a slider in position and indicating the cut position for a length of zipper to be attached to a package.

[0013] Reference is now made to the drawings and to FIGS. 1 and 2 in particular wherein a length of zipper 10 is shown comprising a first elongated profile 12 and a second elongated profile 14. Each of the profiles 12, 14 consists of an interlocking element 16, 18 and an attachment flange 20. The configuration of the interlocking elements 16, 18 is such as to enable the elements to securely interlock with one another. Numerous such configurations are known to those skilled in the art. The attachment flanges 20 are provided to secure the zipper to a film of bag making material. The zipper 10 is conventionally formed of polyethylene but other thermoplastic materials may be used.

[0014] In accordance with the present invention, interlocking elements 16, 18 are joined together. Profiles 12 and 14 are stamped together to form a seal 21 in the area of the cutting of zipper 10. Stamping minimizes cavity 23 and stabilizes the profile of zipper 10 prior to cutting. Profiles 12, 14 are brought to a cutting station 22 at which a notch of plastic material is removed from the interlocking members of both profiles 16, 18. It should be noted that the flanges 20 remain intact so that the zipper segments on opposite sides of the notch 24 remain joined together.

[0015] The notching may be performed by die cutting, milling out the plastic material of the interlocking members with a milling machine 25 or with a punch or knife. As shown in FIG. 4, at notch 24 the material of the interlocking members is entirely removed with a “V” notch showing. The “V” notch is the result of cutting the end of the profile of zipper 10 at an angle. This style cutting increases holding power and allows for easy cavity filling for a complete leak-proof end-stop. Notches 24 are formed along the zipper at bag-length intervals so that the spacing between adjacent notches results in zipper segments that correspond to the length of a bag that is to be formed with the zipper 10.

[0016] As shown in FIG. 1, after the zipper 10 is notched, the notching device 25 is withdrawn and the zipper is advanced so that the notch is brought to a molding station 28, shown in FIG. 1. As shown in FIG. 3, at the molding station 28 mold halves 30aand 30bare closed and a thermoplastic material is simultaneously introduced into the mold cavities 33aand 33bthough line 32 to form end stops 34 in situ about the joined profiles 12 and 14, such that end stops 34 overlap the cut of the V notch to give a complete seal of the end stops. Each of the molds 30aand 30bincludes two cavities 33aand 33bwhich are mirror images of each other. The mold cavities 33aand 33bare configured to form an end stop 34aat a lagging end of one zipper segment 38 (at the leading side of the notch 24) and a segment 34bat the leading end of the next zipper segment 40 (at the lagging side of the notch 24). The end stops 34aand 34bare each provided with sides 36 abut the interlocking members 16 and 18 of the profiles and a cap 39 that goes over the top of the zipper and joins the sides 36. The end stops may be molded of polyethylene or a material such as EVA that may readily be sealed to polyethylene or the material from which the zipper is formed. Seal 21 provides increased holding pressure to prevent separation at the end of the end-stops.

[0017] After the end stops 34aand 34bare formed, a slider 42 is positioned on each leading zipper segment 38 as shown in FIG. 6. The zipper with attached sliders 42 and end caps 34aand 34bis then brought directly to bag making equipment (not shown) or spooled to be subsequently brought to such equipment. At the bag making equipment, flange 20 is cut between adjacent end caps 34aand 34b(along line 44) and the zipper is attached to the bag making film in the usual manner by sealing flanges 20 of the zipper to the film.

[0018] Thus, in accordance with the above an efficient method of forming zipper with end stops at predetermined lengths is disclosed.