Method and apparatus for guiding a fastener in a bag making machine

[0002] The present application is being filed concurrently with U.S. patent application Ser. No. 09/636,244 entitled “Injection-Molded End Stop for a Slider-Operated Fastener,” U.S. patent application Ser. No. 09/636,421 entitled “Slider-Operated Fastener With Spaced Notches and Associated Preseals,” U.S. patent application Ser. No. 09/637,037 entitled “Method of Applying a Slider to a Fastener-Carrying Plastic Web,” and U.S. patent application Ser. No. 09/637,038 entitled “Method and Apparatus for Making Reclosable Plastic Bags Using a Pre-Applied Slider-Operated Fastener,” all of which are incorporated herein by reference in their entireties.

[0003] The present invention generally relates to reclosable plastic bags and, more particularly, to a method and apparatus for guiding a fastener in a bag making machine. As used herein, the term “bag making machine” may refer to a form, fill, and seal machine or a machine that makes empty bags.

[0004] In one method for making reclosable bags, a continuous fastener is sealed to a moving web of thermoplastic film. The fastener-carrying web is subsequently processed into individual plastic bags. One type of fastener includes a pair of interlocking profiles and a pair of fins/flanges extending from the respective profiles. Sliders are preferably mounted to the fastener at bag-width intervals for engaging and disengaging its profiles in response to movement therealong.

[0005] In one technique for installing sliders on the fastener, notches are formed in the fastener at bag-width distances apart. To install a slider on the fastener via a respective notch, the slider is first positioned within the notch, and then the slider is threaded onto an end of the fastener in response to relative movement of the slider and fastener. This installation technique is disclosed in U.S. patent application Ser. No. 09/307,937 (PCOS015) entitled “Zipper and Zipper Arrangements and Methods of Manufacturing the Same”, filed May 10, 1999, and incorporated herein by reference in its entirety. To form a notch, a short segment of the interlocked profiles and an upper portion of the fins extending from that segment are cut away from the fastener, leaving only a lower portion of the fins bridging opposite sides of the notch. Due to the notches and the mounted sliders, the fastener can be difficult to guide and control when processed through a bag making machine. The fastener tends to twist and distort. For example, when sealing the fastener to the web of plastic film, any distortion in the fastener could cause an uneven seal between the fastener and the web. The uneven seal, in turn, could cause wrinkles in the web and a package that leaks due to unsealed or weakly sealed areas.

[0006] Furthermore, to seal the fastener to the web of plastic film, a sealer generates seals between the fastener's fins and the web. Unless precise operational control is maintained over such variables as the alignment, temperature, pressure, and dwell time of the sealer, the sealer could transfer excessive heat to the fins during the sealing process. Such excessive heat could deform the fins, cause the fins to stick to each other, or even accidentally seal the fins to each other. These fin-related problems are exacerbated if the fins are relatively thin and are composed of compatible materials that readily bond to each other. If the fastener is not located properly to the web, the sealer may miss the fastener or seal a skewed fastener to the web resulting in a nonfunctional fastener in the final package.

[0007] To overcome the aforementioned shortcomings, the present invention provides a method and apparatus for guiding a fastener in a bag making machine. The apparatus includes a stationary support, an elongated internal guide, and an slitting mechanism. The elongated internal guide is mounted to the support and positioned within an enclosed space defined by the fastener. The fastener is moved downstream with the internal guide within the enclosed space. The fastener is slit upstream from the support. While the fastener is guided, a sealer may seal the fastener to a moving web of plastic film along a seal adjacent to the internal guide.

[0008] As the name suggests, the internal guide helps to guide and control the fastener so that it does not twist or distort while moving downstream through the bag making machine. In addition, the internal guide serves as an effective insulator between fastener portions on opposite sides of the internal guide. While the sealer seals the fastener to the moving web, the sealer will not deform such fastener portions, cause the fastener portions to stick to each other, or accidentally seal the fastener portions to each other. In fact, the internal guide reduces the degree of operational control that must be maintained over such variables as the temperature, pressure, and dwell time of the sealer.

[0009] Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:

[0010] FIG. 1 is an isometric view of a method and apparatus for guiding and sealing a fastener in a bag making machine where the fastener is sealed to a web of plastic film shown in FIGS. 2aand 2b;

[0011] FIG. 2ais a section view taken generally along line 2—2 in FIG. 1 showing the fastener being sealed to a flat web of plastic film;

[0012] FIG. 2bis a section view taken generally along line 2—2 in FIG. 1 showing the fastener being sealed to a folded web of plastic film;

[0013] FIG. 3 is an isometric view of a modified method and apparatus for guiding and sealing a fastener in a bag making machine where the fastener is sealed to a web of plastic film shown in FIG. 4; and

[0014] FIG. 4 is a section view taken generally along line 4—4 in FIG. 3 showing the fastener being sealed to a flat web of plastic film.

[0015] While the invention is susceptible to various modifications and alternative forms, a specific embodiment thereof has been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

[0016] Turning to the drawings, FIG. 1 depicts a method and apparatus for guiding and sealing a fastener 10 in a bag making machine. The fastener 10 includes first and second opposing tracks 12 and 14. The first and second tracks 12 and 14 include respective first and second interlocking profiles 16 and 18 and respective first and second fins 20 and 22 extending from the respective first and second profiles 16 and 18. The fins 20 and 22 are initially joined to each other along a breakable juncture 24 to form an enclosed space. The enclosed space is bounded by the interlocking profiles, the breakable juncture, and the fins. The juncture 24 may be rendered breakable by virtue of a perforated line, scored line, thinned die line, plastic oriented to propagate a tear along the juncture, or plastic material that can be cut with a blade. Prior to reaching the apparatus in FIG. 1, the fastener 10 may already include notches 26, sliders 28, and pairs 30 of end stops spaced at approximately bag-width distances apart.

[0017] The stationary L-shaped apparatus includes a support 32, an elongated internal guide 34, and an slitting mechanism 36. In operation, the slitting mechanism 36 allows the internal guide 34 to be supported by the support 32 and prevents the fastener 10 from interfering with the support 32 while the fastener 10 is moved downstream through the bag making machine. The slitting mechanism 36 is preferably in the form of a razor-type cutting blade composed of metal or rigid plastic. The blade 36 is connected to an upstream end of the support 32 and extends between the internal guide 34 and the support 32. Alternatively, the blade 36 is connected only to the internal guide 34 or the bag making machine such that it is arranged to slit the fastener 10 upstream from support 32. In the embodiment illustrated in FIG. 1, the blade 36 is arranged to slit the fins 20 and 22 apart along the juncture 24. Alternatively, the slitting mechanism 36 may be wedge shaped to apply enough stress to breakable juncture 24 to fracture at the juncture.

[0018] The support 32 is composed of metal or rigid plastic and projects from the internal guide 34 to an exterior of the fastener 10 via the slit juncture 24 so that it can be secured to a fixed portion of the bag making machine. Although the support 32 is illustrated as being connected to a downstream end of the internal guide 34, the support 32 may alternatively be connected anywhere else along the length of the internal guide 34 including, for example, its center or upstream end. The elongated internal guide 34 is fixedly mounted to the support 32, composed of metal or rigid plastic, and positioned within the enclosed space defined by the fastener 10.

[0019] The fastener 10 is conveyed downstream in a direction D with the internal guide 34 within the enclosed space. In the embodiment illustrated in FIG. 1, the blade 36 slits the fastener fins 20 and 22 apart along the juncture 24 immediately upstream from the support 32. While the fastener 10 is guided, a sealer 38 may seal the fastener 10 to a moving web of plastic film along one or more longitudinal seals 40 spaced from the juncture 24. The seal(s) 40 are adjacent to the internal guide 34. As shown in FIGS. 2aand 2b, the moving web 42 may be flat or C-folded. The web 42 is not shown in FIG. 1 for the sake of clarity.

[0020] If the web 42 is flat (FIG. 2a), the sealer 38 preferably includes a single heated, reciprocating seal bar that directly contacts the web 42 adjacent the fin 20 while movement of the fastener 10 and the web 42 is temporarily stopped. The temperature, pressure, and dwell time of the seal bar are properly adjusted to allow the seal bar to generate a permanent longitudinal fin seal 40 (see FIG. 1) between the fin 20 and the web 42. Other continuous sealing devices known in the bag manufacturing art can be used to seal fin 20 to web 42. Because the flat web 42 in FIG. 2ais only sealed to the fin 20, the web 42 is folded and sealed to the other fin 22 later in the bag manufacturing process.

[0021] If the web 42 is C-folded (FIG. 2b), the sealer 38 preferably includes a pair of heated, reciprocating seal bars that directly contact the web 42 adjacent the fins 20 and 22 while movement of the fastener 10 and the web 42 is temporarily stopped. The temperature, pressure, and dwell time of the seal bars are properly adjusted to allow the seal bars to permanently seal the fins 20 and 22 to the folded web 42 along respective longitudinal fin seals 40 (see FIG. 1). Other continuous sealing devices known in the bag manufacturing art can be used to seal the fins 20 and 22 to the web 42.

[0022] After attaching the fastener 10 to the web 42, the fastener-carrying web 42 is conveyed through other sections of the bag making machine which process the web 42 into individual plastic bags. The plastic bags may be filled with a product and thereafter sealed.

[0023] The embodiment illustrated in FIGS. 1 and 2a-bis suitable for applications in which the ultimately formed bags do not require a tamper-evident feature of the type disclosed in U.S. Pat. No. 5,964,532 to St. Phillips et al., which is incorporated herein by reference in its entirety. The '532 patent teaches a reclosable plastic package in which the fins (e.g., fins 20 and 22 described above) are joined to each other along a one-time breakable preferential line of weakness (e.g., breakable juncture 24 described above) to prevent tampering with the package prior to being opened. If the line of weakness is intact, the consumer can be reasonably assured that his or her newly purchased package has never been opened before. Because the fins 20 and 22 are split apart along the breakable juncture 24 before the ultimately formed bags reach the consumer, the embodiment in FIGS. 1 and 2a-bis not suitable for applications requiring the tamper-evident feature disclosed in the '532 patent.

[0024] On the other hand, the embodiment illustrated in FIGS. 3 and 4 is suitable for applications requiring such a tamper-evident feature. FIG. 3 depicts a modified method and apparatus for guiding and sealing the fastener 10 in a bag making machine. Analogous parts are identified by the same reference numerals used above in connection with FIGS. 1 and 2a-b. While the support 32 in FIGS. 1 and 2a-bprojects through the slit juncture 24, the T-shaped support 32 in FIG. 3 projects through a longitudinal slit 44 in the fin 20. The longitudinal slit 44 is spaced from the breakable juncture 24 and is generated by the blade 36, which is connected to an upstream end of the support 32 and extends between the internal guide 34 and the support 32. The support 32 is illustrated in FIG. 3 as being centrally located along the length of the internal guide 34, but may alternatively be located near or at one of the ends of the internal guide 34.

[0025] The fastener 10 is conveyed downstream in a direction D with the internal guide 34 within the enclosed space defined by the fastener 10. In the embodiment illustrated in FIG. 3, the blade 36 slits the fastener fin 20 along the longitudinal slit 44 spaced from the juncture 24 immediately upstream from the support 32. While the fastener 10 is guided, a sealer 46 may seal the fastener 10 to a moving flat web 42 (see FIG. 4) of plastic film along first and second longitudinal seals 48 and 50 on opposite sides of the longitudinal slit 44. The web 42 is not shown in FIG. 3 for the sake of clarity. The seals 48 and 50 are adjacent to the internal guide 34. Following the generation of the seals 48 and 50, the fins 20 and 22 are intact and still joined to each along the breakable juncture 24. Therefore, the fastener in FIG. 3 can easily be used to manufacture plastic bags that use the condition of the breakable juncture 24 for tamper evidence.

[0026] The sealer 46 preferably includes a heated, reciprocating seal bar that directly contacts the web 42 adjacent the fin 20 while movement of the fastener 10 and the web 42 is temporarily stopped. The seal bar includes a pair of projecting elements 46aand 46bfor generating the respective seals 48 and 50 between the fin 20 and the web 42. The temperature, pressure, and dwell time of the seal bar are properly adjusted to allow the seal bar to generate these seals. Other continuous sealing devices known in the bag manufacturing art can be used to seal fin 20 to web 42. Because the flat web 42 is only sealed to the fin 20, the web 42 is folded and sealed to the other fin 22 later in the bag manufacturing process. In an alternative embodiment, the apparatus of FIG. 3 may be modified to include a second seal bar and then used to attach the fastener 10 to a folded web 42 like in FIG. 2b.

[0027] After attaching the fastener 10 in FIGS. 3 and 4 to the web 42, the fastener-carrying web 42 is conveyed through other sections of the bag making machine which process the web 42 into individual plastic bags. The plastic bags may be filled with a product and thereafter sealed.

[0028] The embodiments illustrated in FIGS. 1-4 are particularly suitable for applications in which the notches 26, sliders 28, and pairs 30 of end stops are applied to the fastener 10 prior to sealing the fastener 10 to the web 42. Due to the notches, sliders, and end stops, the support 32 in these embodiments can only connect to the internal guide 34 via a slit generated by the slitting mechanism 36.

[0029] While the present invention has been described with reference to one or more particular embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present invention. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the claimed invention, which is set forth in the following claims.