This invention relates generally to reclosable plastic bags and in particular to tape used in the manufacture of reclosable plastic bags, the web that the bags are made from, methods related to their manufacture, and an apparatus for manufacturing reclosable bags that is more efficient and economical than conventional methods and devices.
While most packaging is done with polyethylene sheeting, or a polyethylene sealant layer if barrier sheeting is used, there are problems of sealing the intended sealant layer of the bag wall to reclosable profiles due to profile thicknesses, or due to the thicknesses of flange material that may be integral with the profile, even if the surfaces to be sealed are both polyethylene and compatible.
There are even more complex problems when the sealant layer of the bag walls is something other than polyethylene, as the inside bag wall layer of oriented polypropylene sealant layer of potato chip bags. Sealing reclosable materials to this wall means using materials that are compatible. This invention gives a practical means to accomplish these results.
U.S. Pat. No. 4,909,017, McMahon discloses the delivery of a pair of interlocked, profiled fasteners transversely across a web of film used in forming a plurality of bags. However, the system of McMahon is non-enabling in that fastener strips cannot be delivered as described therein.
There is no attempt in the written description to describe how the narrow fastener strip can be fed, held and sealed onto the base web. The strip material would be unstable for sealing due to the rib and groove design, which would rock on center. The strip material is naturally curled from extrusion and distorted from being wound onto a spool. The difficulty of feeding this unstable strip cross web, remove curls and twists, stretch straight and hold for heat and pressure application between a seal bar and anvil makes this method chaotic and impractical.
There are at least two other major shortcomings of the McMahon '017 patent. The first shortcoming involves the impossibility of making commercially acceptable seals of the bag walls to the backside of each fastener half in the bagger sealing jaws. The second shortcoming involves the window of registration required to seal the backside of the fastener to a finished bag wall during bagger cross sealing and the inability of known form fill seal and equipment to repeat the bagger film draw with the required accuracy.
Specifically, the McMahon '017 patent describes a pressure bar seal in the bagger sealing jaws that seals the outer bag material precisely to the backside of the fastener profile. Yet, it has been discovered, as described in Applicant's specification, that a pressure bar seal requires a stable and flat surface to properly seal. The irregular shape of the fastener profile makes this impossible. One requires heat, dwell time, and pressure to effect a commercially acceptable seal and due to the irregular shape of the profile, it is impossible to get enough stable pressure to accomplish a commercially acceptable seal. The surface moves and gives unpredictably. If enough heat and pressure are applied for a sufficient dwell time to mash the base of the profile flat enough to seal, the profile hooks are softened and deformed, making it impossible to repeatedly use the completed bag for opening and reclosing.
The McMahon '017 patent has an additional shortcoming related to sealing the seamed side of the bag to the opposite side of the fastener. Based on Applicant's knowledge and experience, this cannot be done to produce a commercially acceptable product. The fact is that no bagger can draw with the accuracy the McMahon '017 patent requires, to place the second seal, in register, on the back side of the fastener profiles.
Another illustrative patent is U.S. Pat. No. 5,461,845 to Yeager. There are at least two definitive shortcomings therein. The first shortcoming relates to the problem of having to open the zipper completely from the front panel of the finished bag. Users of reclosable bags and packaging are accustomed to opening the profiled fastener from the "top" of the package, and not from the front panel of the package. Hence, the user will have to become accustomed to a method with which he may not be familiar or comfortable.
The second shortcoming is more serious, and relates to the requirement of opening the package from the front panel thereof. If the package is to be opened from the front panel, a cut or perforation must be made before the fastener is applied. This cut, or perforation, is generally shaped like an "oval" with opening "tabs" for gaining access to the fastener. Since the fastener, most likely, is not closed at the ends of the fastener, the possibility of contamination exists.
The most expedient and economical way to make the package is to create the cut, or perforation, in one operation, just upstream of the fastener strip application. This operation, in its simplest form, will leave openings for potential contamination to pass through the cut or perforated, front panel opening. To overcome this contamination potential, users of this method add a great deal more cost and complexity to create a sealed, sealable "patch", or some other means of eliminating this contamination risk. The same problem occurs, if the package must be hermetically sealed.
There is also a serious drawback of coextroding a flanged zipper having ribs on the inside of the flanges so that it is unsealable, when heat is applied to each bag wall side. The drawback is that a unitary extruded flanged zipper has a limitation as to thinness of the flanges that can be integrally extruded with reclosable profile. Further, use of co-extruded ribs to make the inside of the flanges not seal together increases the thickness of the flange area even more.
This contrast in thickness of the 4 layers of material which includes the 2 bag walls and the 2 zipper flanges will make it virtually impossible to blend the cross seals through the 4 thickness area and into the 2 thickness area of the bag walls only. For example, if a 3 millimeter: i.e., "mils" wall bag is being made, the coextruded flange with ribs, will be 16 mils per side or 32 mils total. This would require a blending of 38 mils to 6 mils and would most likely eliminate the possibility of closing off openings in the folds of any bag made on a vertical FFS machine.
Thus, there exists a need to solve the problems in the art that are articulated above.