This invention generally relates to methods and apparatus for manufacturing reclosable bags. In particular, the invention relates to methods and apparatus for making reclosable packages having slider-operated string zippers.
Reclosable bags are finding ever-growing acceptance as primary packaging, particularly as packaging for foodstuffs such as cereal, fresh fruit and vegetables, snacks and the like. Such bags provide the consumer with the ability to readily store, in a closed, if not sealed, package any unused portion of the packaged product even after the package is initially opened.
Reclosable bags comprise a receptacle having a mouth with a zipper for opening and closing. In recent years, many zippers have been designed to operate with a slider mounted thereon. As the slider is moved in an opening direction, the slider causes the zipper sections it passes over to open. Conversely, as the slider is moved in a closing direction, the slider causes the zipper sections it passes over to close. Typically, a zipper for a reclosable bag includes a pair of interlockable profiled closure strips that are joined at opposite ends of the bag mouth. The profiles of interlockable plastic zipper parts can take on various configurations, e.g. interlocking rib and groove elements having so-called male and female profiles, interlocking alternating hook-shaped closure elements, etc. Reclosable bags having slider-operated zippers are generally more desirable to consumers than bags having zippers without sliders because the slider eliminates the need for the consumer to align the interlockable zipper profiles before causing those profiles to engage. In one type of slider-operated zipper assembly, the slider straddles the zipper and has a separating finger at one end that is inserted between the profiles to force them apart as the slider is moved along the zipper in an opening direction. The other end of the slider is sufficiently narrow to force the profiles into engagement and close the zipper when the slider is moved along the zipper in a closing direction.
In the past, many interlocking closure strips were formed integrally with the bag making film, for example, by extruding the bag making film with the closure strips formed on the film. Such constructions, however, were limited by the conditions required to extrude both the film and zipper together. To avoid such limitations, many bag designs entail separate extrusion of the closure strips, which are subsequently joined to the bag making film, for example, by conduction heat sealing. These separate closure strips typically have flanges (also called fins) extending therefrom in such a way that the flanges can be joined to bag making film in order to attach the closure strips to the film. Previous slider-operated, separately extruded zippers used flange-type constructions.
An alternative zipper design is the so-called flangeless or string zipper, which has no flange portion above or below the interlockable closure profiles. In the case of a string zipper, the bag making film is joined to the backs of the bases of the closure strips. String zippers can be produced at much greater speeds, allow much greater footage to be wound on a spool, thereby requiring less set-up time, and use less material than flanged zippers, enabling a substantial reduction in the cost of manufacture and processing.
U.S. patent application Ser. No. 10/367,450, entitled “Reclosable Packaging Having Slider-Operated String Zipper”, discloses a reclosable bag in which respective marginal portions of the bag film are sealed to the backs of respective flangeless zipper strips and in which the resulting string zipper is actuated by means of a straddling-type slider having a plow that separates the zipper strips during opening.
U.S. patent application Ser. No. 10/436,433, entitled “Method and Apparatus for Inserting Sliders During Automated Manufacture of Reclosable Bags”, disclosing a method of manufacturing bags with slider-actuated string zippers. The method involves attaching string zipper at its bases to respective portions of the bag making film using a band or “drag” sealer and then pressing a slider clip across the zippered film. The band sealer welds the zipper to the film by conductive heat sealing in approximately respective central band-shaped zones on the bases of the respective zipper strips. Excess unsealed film on the consumer side of the zipper is then removed or trimmed in a downstream process.
A razor-sharp knife can be used to trim excess film after the string zipper and film have been joined. More specifically, a pair of stationary knives can be placed on opposing sides of the zippered film to slit the excess unsealed film on both sides concurrently as the web of film is advanced on the machine. The portion of the excess unsealed film severed from the zipper-film assembly is taken away. In theory, each knife could be placed so that the knife tip is as close to the zipper as one-half of the width of the knife blade. However, the zipper wanders during the manufacturing process so that the distance between the moving zipper and the tips of the stationary knifes is subject to variation during the manufacturing process. As the zipper wanders, a knife placed too close or pressed against the zipper could cut the zipper if the zipper tended to wander towards the knife, thereby causing sufficient pressure to cut the zipper. Thus, the tip of each knife can be set as close as one-half of the width of the knife tip away, but in practice, zipper wander will result in a knife position further away from the zipper than one-half width of the knife blade to provide a tolerance for zipper wandering.
After trimming, the resulting zipper-film assembly has respective “tails” or remnants of excess unsealed film on the consumer side of the zipper-film band-shaped zones of joinder. Even if the excess film could be cut closer to the zipper-film seal, instead of one-half of the knife blade width away, invariably some tail will remain. In some cases, these tails may extend beyond the tops of the zipper strips. If these tails are not removed, several problems can result. As the slider clips are pressed onto the zipper film, the unattached tail ends tend to gather or bunch up when the slider clip drags across the film. The gathered film can interfere with fully seating the slider clip around the zippered film. Also, the film can be pulled or peeled away from the zipper. During usage of the completed package, gathered film along the lip of the bag mouth may interfere with the function of the seated slider, which is to open and close the zipper during slider travel.
There is a need for a method and an apparatus for making slider-actuated string zipper bags having improved functionality and manufacturability.
The present invention is directed to methods and apparatus for low-cost manufacture of slider-actuated string zipper bags having improved functionality and manufacturability. In particular, the invention provides means for eliminating unattached remnants or tails of bag making film adjacent the string zipper. Gathered film tails may interfere with slider insertion or slider operation or may cause the film to be pulled off of or peeled away from the string zipper during slider operation. After trimming, the tails of the film are welded to the zipper by conductive heat sealing or equivalent means.
One aspect of the invention is a method of manufacture comprising the following steps: (a) joining a first portion of a length of film material to a back of a length of a first flangeless zipper strip having a first closure profile on its front; (b) joining a second portion of the length of film material to a back of a length of a second flangeless zipper strip having a second closure profile on its front, the first and second closure profiles of the respective lengths of the first and second zipper strips being interlockable to form a length of string zipper assembly; (c) after steps (a) and (b), removing an unattached marginal portion of the length of film material that extends beyond the joined first portion of the length of film material, leaving a first tail portion of the length of film material unattached to the first flangeless zipper strip; and (d) after step (c), joining the first tail portion of the length of film material to the first flangeless zipper strip. Optionally, steps analogous to steps (c) and (d) can be performed on the unattached marginal portion of film material that extends beyond the joined second portion of the film material.
Another aspect of the invention is a machine comprising: first joining means for joining a first portion of a length of film material to a back of a length of a first flangeless zipper strip; second joining means for joining a second portion of the length of film material to a back of a length of a second flangeless zipper strip; first trimming means for removing a first unattached marginal portion of the length of film material that extends beyond the joined first portion of the length of film material, leaving a first tail portion of the length of film material unattached to the first flangeless zipper strip; and third joining means for joining the first tail portion of the length of film material to the first flangeless zipper strip, wherein the first trimming means is disposed between the first and third joining means. Similar means can be provided for removing a second unattached marginal portion of film material that extends beyond the joined second portion of the film material and then joining the corresponding tail portion to the second flangeless zipper strip.
A further aspect of the invention is a method of manufacture comprising the following steps: (a) interlocking a first closure profile of a first flangeless zipper strip with a second closure profile of a second flangeless zipper strip; (b) joining a first band-shaped portion of an elongated film structure to a back of the first flangeless zipper strip; (c) joining a second band-shaped portion of the elongated film structure to a back of the second flangeless zipper strip; (d) removing a first unattached marginal portion of the elongated film structure that extends beyond the joined first band-shaped portion of the elongated film structure, leaving a first tail portion of the elongated film structure unattached to the first flangeless zipper strip; (e) joining the first tail portion of the elongated film structure to the first flangeless zipper strip; and (f) inserting a slider on the interlocked first and second zipper strips some time after completion of steps (a) through (e). Optionally, steps analogous to steps (d) and (e) can be performed on the unattached marginal portion of the elongated film structure that extends beyond the joined second band-shaped portion of the elongated film structure.
Yet another aspect of the invention is an automated production line comprising the following components: a zipper sealer for sealing a band-shaped portion of a section of a web of packaging film to the back of a section of a flangeless zipper strip; a knife arranged for trimming off an unsealed marginal portion of the section of the web downstream of the zipper sealer; and a lip sealer arranged for sealing, to the zipper strip, any unsealed tail portion that remains after the unsealed marginal portion has been trimmed.
Other aspects of the invention are disclosed and claimed below.
Reference will now be made to the drawings in which similar elements in different drawings bear the same reference numerals.
A reclosable package or bag comprising a receptacle 2 and a flexible plastic string zipper 4, operated by manipulation of a slider 10, is shown in
The present invention is directed to methods and apparatus for making reclosable bags of the type shown in
Referring to
The receptacle 2 comprises opposing walls (only the front wall 2a
is visible in
At its top end, the receptacle 2 has an openable mouth, on the inside of which is an extruded plastic string zipper 4. The string zipper 4 comprises a pair of interlockable zipper parts or closure strips 6 and 8 (best seen in
and 2b (see
The string zipper is operated by sliding the slider 10 along the zipper parts. As the slider moves across the zipper, the zipper is opened or closed. As shown in
The bag shown in
The zipper in this example is an extruded plastic structure comprising mutually interlockable profiles. Zipper part 8 comprises a base 14 and two generally arrow-shaped rib-like male closure elements or members 20 and 28, while zipper part 6 comprises two pairs of hook-shaped gripper jaws 16, 18 and 22, 24 connected by a sealing bridge 12. Jaws 16 and 18 receive and interlock with the male element 20, while jaws 22 and 24 receive and interlock with the male element 28. Alternatively, one zipper part could have one male profile and one female profile, while the other zipper part has one female profile and one male profile, or the respective zipper parts could each have more than two male or female profiles.
The sealing bridge 12 and the base 14 are resiliently flexible self-supporting structures having a thickness greater than the thickness of the bag film. The male closure elements are integrally formed with the base 14, while the female closure elements are integrally formed with the sealing bridge 12. The upper margins of the walls 2a and 2b of the bag are joined to the backs of the sealing bridge 12 and the base 14 respectively, as seen in
The end face of the upper edge of the base 14, which carries the male closure elements 20 and 28, is inclined at about a 45° angle to facilitate loading of the slider onto the zipper from above without snagging on a corner of the upper edge. The top edge 70 of wall 2b is sealed against this inclined end face. The bottom edge 8 of the base 14 cooperates with a retaining ledge on the slider (to be described later) to increase the slider-pull-off resistance. For the same purpose, a rib 26 is formed on zipper part 6, the rib 26 cooperating with a retaining ledge on the other side of the slider.
In the slider-zipper assembly shown in
The slider 10 also comprises a plow or divider 42 that depends downward from a central portion of the top wall 32 to an elevation below the lowermost portions of each side wall. The plow is disposed between opposing sections of the zipper parts that pass through the tunnel. The tip of the plow 42 is truncated and has rounded edges and flattened corners 46 at opposing ends for facilitating insertion of the plow between the zipper profiles without snagging during automated slider insertion. The plow 42 comprises a beam having a cross-sectional shape that is a rectangle with rounded corners. The axis of the beam is generally perpendicular to the top wall of the slider. As the slider is moved in the opening direction (i.e., with the closing end leading), the plow 42 pries the impinging sections of zipper parts 6 and 8 apart.
Although the slider in the disclosed embodiment has a plow, the string zipper, if suitably designed, could be actuated by a slider that has no plow or separating finger. The present invention is not limited in its application to string zipper bags having sliders with plows.
In the embodiment depicted in
The slider may be made in multiple parts and welded together or the parts may be constructed to be snapped together. The slider may also be of one-piece construction. The slider can be made using any desired method, such as injection molding. The slider can be molded from any suitable plastic, such as nylon, polypropylene, polystyrene, acetal, polyketone, polybutylene terephthalate, high-density polyethylene, polycarbonate, or ABS.
Improved slider designs are disclosed in U.S. patent application Ser. No. 10/412,438, entitled “Molded Sliders for Actuating Zippers of Reclosable Packages”. In one such design, the each retaining ledge on the interior surface of the slider side walls is replaced by a pair of retaining teeth spaced apart at opposite ends of the slider.
In the embodiment shown in
To avoid fusing the tops of the zipper strips together during lip sealing, the roof of the tunnel has a recess 142, thereby creating an open space that insulates the confronting portions of the zipper from the heat of the sealing bar 122. Also, the heat sealing of the film to the zipper is controlled to prevent seal-through of the zipper.
The operations depicted in
The drawn string zipper material is passed around guide rollers 112 and 114 and then through a zipper guide 116 that is situated between the opposing marginal portions of the film web. In its simplest form, the zipper guide may be a straight tube that maintains the zipper in the proper position and orientation relative to the opposing marginal portions of the film web, which in this case is parallel to the edges of the folded web. At a zipper sealing station, these marginal portions of the film are joined to the respective backs of the zipper strips by a pair of mutually opposing conventional heated sealing bars 80 and 82 (see
The zipper sealing station is conventional apparatus and is described hereinafter only briefly. As the folded web 2 with inserted string zipper 4 advances continuously between the opposing sets of sealing bars 80, 82, the respective zipper strips have their backs sealed to opposing marginal portions of the bag making film, thereby continuously attaching incoming sections of the moving string zipper to adjoining sections of the moving web. The sealing is accomplished by electrically heating the sealing bars, the heat being conducted through respective endless barrier strips (not shown) made of Teflon or similar material, which circulate on respective sets of rollers (not shown). Each Teflon barrier strips passes between a respective side of the folded web and a respective sealing bar in the gaps between the opposing sealing bars. The web and string zipper are sandwiched between and held together by the Teflon barrier strips, which move with the web and zipper and prevent the bag making film from sticking against the stationary heated sealing bars during conduction heat sealing. The Teflon barrier strips and intervening web and zipper pass through the nips of a series of guide rollers (not shown).
Downstream from the zipper sealing station, excess film that extends beyond the zipper is continuously trimmed by a pair of stationary knives 120 and 121 (see
As previously stated, the presence of unattached film tails could interfere with slider insertion during manufacture as well as with slider operation during use of the reclosable package by a consumer. Therefore an additional step is performed of sealing the tails to the respective zipper strips. The tails are sealed by the lip sealer 122, which was previously described in detail with reference to
The trimmed and lip-sealed zipper-film assembly then wends its way through a conventional dancer assembly (not shown), which converts the continuous advancement of the film into intermittent advancement of the film. In the intermittent advancement phase, the zipper-film assembly is moved one package increment and then stopped for a period of time, i.e., the dwell time. This cycle is repeated periodically.
In accordance with an alternative embodiment of the automated production line disclosed above, the web of film material and the string zippers could be moved intermittently through the zipper sealing and lip sealing stations. In this case respective lengths of the string zippers would be sealed to the film (e.g., by reciprocating sealing bars) during each dwell time, with the string zippers and film being advanced an equal length during each interval between successive dwell times. The trimming operation would be performed during advancement of the film.
Still referring to
During the same dwell time that a slider is being inserted, a slider end stop structure is being formed on the zipper at an ultrasonic stomping station downstream from the slider insertion zone. The stomping station comprises a horn 128 and an anvil (not shown). This slider end stop structure will be bisected later when the film and zipper are cut in the cross direction using a hot knife 118 that both severs and seals the film.
The respective sets of contact fingers have respective geometries that facilitate machining. {The curved contact surfaces shown in
While the invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for members thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation to the teachings of the invention without departing from the essential scope thereof. Therefore it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
As used in the claims, the verb “joined” means fused, bonded, sealed, adhered, etc., whether by application of heat and/or pressure, application of ultrasonic energy, application of a layer of adhesive material or bonding agent, interposition of an adhesive or bonding strip, etc.
Number | Name | Date | Kind |
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6212857 | Van Erden | Apr 2001 | B1 |
6553740 | Delisle | Apr 2003 | B1 |
6581358 | Buchman | Jun 2003 | B1 |
6662843 | Johnson | Dec 2003 | B1 |
Number | Date | Country | |
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20050054504 A1 | Mar 2005 | US |