Abstract:
An automated reclosable packaging manufacturing equipment for applying zipper tape to bag making film, especially as part of a form-fill-seal process, and a method of joining a zipper flange of a zipper assembly to bag making film without “seal-through” of the zipper flanges. The method comprises the steps of: (a) pressing a web of bag making film and first and second zipper flanges of a zipper assembly together along the length of the latter, with the first zipper flange sandwiched between and in contact with the web of bag making film and the second zipper flange; and (b) during step (a), causing heat to be conducted through the web of bag making film into the first zipper flange. The amount of heat conducted through the web of bag making film must be sufficient to seal the web of bag making film to the first zipper flange without sealing the first zipper flange to the second zipper flange.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to methods and apparatuses for automated manufacture of reclosable plastic packages having a resealable closure, especially as part of a form, fill and seal process.  
         [0002]     In the use of plastic bags and packages, particularly for foodstuffs, it is important that the bag be hermetically sealed until the purchaser acquires the product, takes it home, and opens the bag or package for the first time. It is then commercially attractive and useful for the consumer that the bag or package be reclosable so that its contents may be protected. Flexible plastic zippers have proven to be excellent for reclosable bags, because they may be manufactured with high-speed equipment and are reliable for repeated reuse.  
         [0003]     A typical zipper comprises one fastener strip or closure member having a groove and attached to one side of the bag mouth, and another fastener strip or closure member having a rib and attached to the other side of the bag mouth, which rib may interlock into the groove when the sides of the mouth of the bag are pressed together. Alternatively, a fastener strip having a plurality of ribs may be on one side of the bag mouth, while a fastener strip having a plurality of grooves or channels may be on the other side, the ribs locking into the channels when the sides of the mouth of the bag are pressed together. In the latter case, there may be no difference in appearance between the two fastener strips, as the ribs may simply be the intervals between channels on a strip that lock into another of the same kind. In general, some form of male/female interengagement is used to seal the two sides of the bag mouth together. The fastener strips or closure members are bonded in some manner to the material from which the bags themselves are manufactured.  
         [0004]     In the automated manufacture of plastic reclosable packages or bags, it is known to feed a zipper assembly to a position adjacent a sheet of thermoplastic film and then attach the zipper assembly to the bag by means of heat sealing. The zipper assemblies are attached at spaced intervals along the thermoplastic sheet, one zipper assembly being attached to each section of film respectively corresponding to an individual package or bag. The zipper assembly consists of two interlocking fastener strips that typically lie inside the mouth of the package. Each fastener strip preferably has a zipper flange that extends toward the product side of the package in a direction transverse to the line of the zipper. In accordance with one known method of feeding zipper assemblies to an automated form, fill and seal machine, the zipper assembly is in the form of a tape that is unwound from a spool for automated feeding. The tape comprises a continuous length of interlocked fastener strips. The continuous tape is fed to a cutting device that cuts the tape at regular lengths to form an individual zipper. Each individual zipper is then attached to the thermoplastic bag making film by heat sealing or other suitable means. Then the package is formed, filled and sealed on a form-fill-seal (FFS) machine.  
         [0005]     Other types of reclosable plastic bags, however, contain a slider that facilitates a consumer opening and re-closing the package by disengaging and re-engaging the two sides of the zipper together. Slide-zipper assemblies are well known in the reclosable packaging art. Conventional slider-operated zipper assemblies typically comprise a plastic zipper having two interlocking profiles and a slider for opening and closing the zipper. 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. Other types of slider-operated zipper assemblies avoid the use of a separating finger. For example, U.S. Pat. No. 6,047,450 discloses a zipper comprising a pair of mutually interlockable profiled structures and having an A-shaped profile. Portions of the two profiled structures form a fulcrum about which the profiled structures may be pivoted when the slider forces lower edges of the bases towards each other. Above the fulcrum point, the interlocked male and female profiles disengage, thereby opening the zipper. The path of the slider as blocked at opposing sealed ends of the zipper halves by slider end stops, which are typically formed by ultrasonically stomping.  
         [0006]     Whether or not the zipper assembly is opened and closed by a slider, the zipper flanges of the zipper assembly, when sealed to the bag making film, must not be sealed to each other. Such “seal-through” of the zipper flanges makes the bag difficult to open and susceptible to losing its reclosability, for example, if the bag film were to be tom during pulling apart of the sealed flanges.  
         [0007]     Some techniques for avoiding “seal-through” of the zipper flanges include: inserting an insulating separator plate between the zipper flanges prior to heat sealing the flanges to the bag making film; and constructing the zipper flanges to have confronting layers of high-melting-point thermoplastic material that does not soften during sealing. The use of separator plates is suited more to instances where the zipper assembly is applied to the bag making film in the machine direction, since transverse application would require that the separator plate be repeatedly inserted between the zipper flanges and then retracted. The manufacture of zipper assemblies in which each flange comprises a layer of high-melting-point thermoplastic material laminated to a layer of low-melting-point thermoplastic sealant material is more costly than the manufacture of zipper assemblies without laminated flanges.  
         [0008]     U.S. Pat. No. 6,327,837 discloses a zipper assembly having one flange longer than the other. In this case the zipper assembly is initially attached to the bag making film by sealing the portion of the long flange that extends beyond the short flange to the bag making film.  
         [0009]     There is a need for an alternative method for automated application of zipper assemblies to bag making film without flange “seal-through”.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0010]     The present invention is directed to automated reclosable packaging manufacturing equipment for applying zipper tape to bag making film, especially as part of a form-fill-seal process. The invention is also directed to a method of joining a zipper flange of a zipper assembly to bag making film without “seal-through” of the zipper flanges.  
         [0011]     One aspect of the invention is a method of making a zippered bag, comprising the following steps: (a) pressing a web of bag making film and first and second zipper flanges of a zipper assembly together along the length of the zipper assembly, with the first zipper flange sandwiched between and in contact with the web of bag making film and the second zipper flange; (b) during step (a), causing heat to be conducted through the web of bag making film into the first zipper flange, the amount of heat conducted through the web of bag making film being sufficient to seal the web of bag making film to the first zipper flange in a first seal without sealing the first zipper flange to the second zipper flange; (c) subsequent to step (b), folding the web of bag making film and sealing the folded web to form a bag having a mouth with the first seal disposed on and running the length of one side of the mouth; (d) pressing opposing walls of the bag and the first and second zipper flanges together along the length of the zipper assembly, with the second zipper flange sandwiched between and in contact with a folded-over portion of the web of bag making film and the first zipper flange; and (e) during step (d), causing heat to be conducted through the folded-over portion of the web of bag making film into the second zipper flange, the amount of heat conducted through the folded-over portion of the web of bag making film being sufficient to seal the folded-over portion of the web of bag making film to the second zipper flange in a second seal without sealing the first zipper flange to the second zipper flange. The second seal is disposed on and runs the length of the other side of the mouth of the bag.  
         [0012]     Another aspect of the invention is a system for making a zippered bag comprising: first means for pressing a web of bag making film and first and second zipper flanges of a zipper assembly together along the length of the zipper assembly, with the first zipper flange sandwiched between and in contact with the web of bag making film and the second zipper flange; first means for causing heat to be conducted through the web of bag making film into the first zipper flange during pressing, the amount of heat conducted through the web of bag making film being sufficient to seal the web of bag making film to the first zipper flange in a first seal without sealing the first zipper flange to the second zipper flange; means for folding and sealing the web of bag making film with attached zipper assembly to form a bag having a mouth with the first seal disposed on and running the length of one side of the mouth; second means for pressing opposing walls of the bag and the first and second zipper flanges together along the length of the zipper assembly, with the second zipper flange sandwiched between and in contact with a folded-over portion of the web of bag making film and the first zipper flange; and second means for causing heat to be conducted through the folded-over portion of the web of bag making film into the second zipper flange, the amount of heat conducted through the folded-over portion of the web of bag making film being sufficient to seal the folded-over portion of the web of bag making film to the second zipper flange in a second seal without sealing the first zipper flange to the second zipper flange. The second seal is disposed on and runs the length of the other side of the mouth of the bag.  
         [0013]     A further aspect of the invention is a method of making reclosable bags having a zipper assembly comprising first and second profiled closure members, and first and second zipper flanges respectively connected to the first and second closure members and extending generally parallel therefrom. The method comprises the following steps: (a) placing one side of the zipper assembly in contact with a length of bag making film, a first portion of the first zipper flange having one side confronting a first portion of the length of bag making film and the other side confronting a first portion of the second zipper flange; (b) sealing the first portion of the first zipper flange to the first portion of the length of bag making film while the first portion of the first zipper flange and a first portion of the second zipper flange are in contact, thereby forming a first seal without sealing the second zipper flange to the first zipper flange; (c) making the length of bag making film into a receptacle having a mouth, wherein the first portion of the length of bag making film forms one half of the mouth and a second portion of the length of bag making film, generally opposite to the first portion, forms the other half of the mouth; and (d) sealing a second portion of the second zipper flange to the second portion of the length of bag making film while the second portion of the second zipper flange is in contact with a second portion of the first zipper flange, thereby forming a second seal without sealing the second zipper flange to the first zipper flange. The first seal is produced by heat that is conducted through the first portion of the length of bag making film and then into the first zipper flange, and the second seal is produced by heat that is conducted through the second portion of the length of bag making film and then into the second zipper flange.  
         [0014]     Another aspect of the invention is a system for manufacturing reclosable bags comprising: a vertical form-fill-seal (VFFS) machine for forming, filling and sealing a reclosable bag, comprising a forming collar, a fill tube and sealing means; a roll of bag making film comprising a wound portion and an unwound portion, the unwound bag making film extending from the wound portion of the roll to the forming collar and through the vertical FFS machine; opposing grooved elements comprising grooves designed to hold interlocked first and second closure members of a zipper assembly while first and second zipper flanges of the zipper assembly project in a forward machine direction, the first zipper flange being disposed between unwound bag making film and the second zipper flange; first and second sealing bars arranged in opposition at a first sealing station with the first sealing bar above the second zipper flange and the second sealing bar below the unwound bag making film; means for moving the first and second sealing bars between respective extended positions and respective retracted positions, the first and second zipper flanges and a first portion of unwound bag making film being pressed between the first and second sealing bars in their respective extended positions; first control means for heating the second sealing bar while in its extended position, the first sealing bar being unheated while in its extended position, and the second sealing bar being heated to a degree that the first zipper flange is sealed to the first portion of unwound bag making film without the first zipper flange being sealed to the second zipper flange; and means for advancing the bag making film with the zipper assembly attached thereto from the first sealing station to the sealing means of the VFFS machine.  
         [0015]     Yet another aspect of the invention is a method of sealing a zipper assembly to bag making film, the zipper assembly comprising first and second profiled closure members that are mutually interlockable, and first and second zipper flanges respectively connected to the first and second profiled closure members and projecting generally parallel to each other when the first and second profiled closure members are interlocked. The method comprises the following steps: (a) pressing a web of bag making film and the first and second zipper flanges of the zipper assembly together along the length of the latter, with the first zipper flange sandwiched between and in contact with the web of bag making film and the second zipper flange; and (b) during step (a), causing heat to be conducted through the web of bag making film into the first zipper flange, the amount of heat conducted through the web of bag making film being sufficient to seal the web of bag making film to the first zipper flange without sealing the first zipper flange to the second zipper flange.  
         [0016]     Other aspects of the invention are disclosed and claimed below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a drawing showing a front view of a conventional reclosable package having a slider-zipper assembly installed in the mouth of the package.  
         [0018]      FIG. 2  is a drawing showing a fragmentary top view of a slide-zipper assembly attached to a tensioned bag making film and oriented in a transverse direction.  
         [0019]      FIG. 3  is a drawing showing a side view of the first sealing operation in accordance with one embodiment of the invention, whereby one flange of a slider-zipper assembly is sealed to a web of bag making film.  
         [0020]      FIG. 4  is a drawing showing a front view (partially sectioned) of a zipper tape transfer assembly with a slider-zipper assembly in accordance with one embodiment of the invention.  
         [0021]      FIG. 5  is a drawing showing a side view of the zipper tape transfer assembly shown in  FIG. 4  (without the slider-zipper assembly) and the first sealing station in accordance with the disclosed embodiment.  
         [0022]      FIG. 6  is a drawing showing a sectional view of the zipper tape transfer assembly shown in  FIG. 4 , the section being taken along line  6 — 6  indicated in  FIG. 4 .  
         [0023]      FIG. 7  is a drawing showing another sectional view of the zipper tape transfer assembly shown in  FIG. 4 , this section being taken along line  7 — 7  indicated in  FIG. 4 .  
         [0024]      FIG. 8  is a drawing showing a sectional view of the lower seal bar assembly at the first sealing station.  
         [0025]      FIG. 9  is a drawing showing an isometric view of a form-fill-seal machine with a second sealing station installed below the fill tube in accordance with the disclosed embodiment.  
         [0026]      FIG. 10  is a drawing showing a side view of the second sealing station with the other flange of the slider-zipper assembly sealed to the opposing bag wall in accordance with the disclosed embodiment.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     The present invention can be utilized in conjunction with many different methods of packaging product in a reclosable plastic bag. In particular, the invention has application in automated lines or machines which form a package, fill it with product, and then seal the product inside the package using any one of the known form-fill-seal (FFS) methods, such as HFFS (horizontal form-fill-seal), VFFS (vertical form-fill-seal) with the zipper applied in either the machine or transverse direction, or HFVFS (horizontal form/vertical fill-seal). In general, the conventional methods of packaging product in reclosable packaging using a form, fill and seal automated process comprise the following steps: attaching one zipper assembly to the bag making film for each package length interval; forming the bag making film into successive packages, each package having a respective zipper assembly; filling each package with product; sealing each filled package, and then separating the filled package from the bag making film. The zipper assembly can be oriented in either a machine direction or a transverse (cross) direction when attached to the bag making film. The present invention is directed to a method and an apparatus for sealing the zipper flanges of a zipper assembly, with or without a slider, to bag making film in the course of an automated reclosable packaging operation.  
         [0028]     In a typical form-fill-seal operation, a continuous supply of thin bag-making film is paid off of a supply reel by a suitable mechanism. For example, the FFS machine may be provided with feed drive rollers for pulling the film through the FFS machine. For each length of bag making film corresponding to an individual package, a zipper assembly is attached to the film. The zipper may be laid directly on the film, but preferably is fed laterally across the upper surface of the film at right angles to the longitudinal edges of the film, or in other words at right angles to the longitudinal formation axis of the film. The zipper assembly is cut off from the end of a zipper tape that is paid out from a zipper tape supply reel and guided to a sealing and cutting station, where an individual zipper is cut and sealed to the bag making film. The length of the zipper strip will be less than one-half of the film width. The lateral portions of the film beyond the ends of the attached zipper are sufficiently long so that they can eventually be folded over and sealed to the other zipper flange.  
         [0029]     The foregoing automated process becomes more complex when zipper assemblies with sliders are used as the reclosable plastic fastening means. The machinery for feeding the slider-zipper assemblies to the desired position overlying the thermoplastic film must take account of the different profile and larger dimensions of the slider as compared to the profile and dimensions of the interlocked fastening members of the zipper.  
         [0030]     Reference will now be made to the drawings in which similar elements in different drawings bear the same reference numerals.  FIG. 1  depicts a reclosable package  10  comprising a receptacle with a mouth at the top, the receptacle being formed by a front wall  12  and a rear wall (not shown) that is opposite to the front wall. The front and rear walls are typically formed from clear thermoplastic film heat sealed as necessary to form hermetically sealed junctures for the various portions of the package, e.g., along the sides if folded along the bottom or along a central seam and along the bottom if folded along the sides. A zipper  22  comprising a pair of fastener strips having respective interlockable profiled closure members is provided in the mouth of the receptacle, attached to the front wall  12  and the rear wall (not visible in  FIG. 1 ). A slider  20  is provided on the zipper to facilitate its opening and closing.  FIG. 1  shows the slider  20  in a position corresponding to closure of the zipper  22 . Moving the slider  20  toward the right-hand side would disengage the interlockable closure members of the zipper and moving the slider back to the closed position shown in  FIG. 1  would bring the interlockable closure members of the zipper into full engagement once again. For proper functioning, the interlockable members have spot seals or ultrasonic stomps  28  at the ends of the zipper strips. These seals ensure the zipper strips will not come apart during use and provide end stops for stopping the slider  20 .  
         [0031]     Prior to opening of the package by the consumer, the slider-zipper assembly may be covered on the consumer side by an enclosed header  16  that is hermetically sealed. The sealed header  16 , which provides a tamper-evident feature, comprises front and rear panels that may be integrally formed with or heat sealed to the front and rear walls, respectively, of the receptacle. The numeral  26  in  FIG. 1  designates a hard seal, i.e., a seal that is not intended to be broken, at the top of the header. Alternatively, the opposed header panels may be formed by folding a piece of film and attaching the ends to the walls of the receptacle. The sealed header  16  preferably has respective tear notches  18  formed on each side edge of the header, where the consumer can initiate tearing off of the sealed header from the package.  
         [0032]     It should be appreciated that the front wall of the header  16  and the front wall  12  of the receptacle are shown in  FIG. 1  as being made of relatively transparent thermoplastic material. Therefore, the slider-zipper assembly is visible through the clear walls and has not been depicted as hidden.  
         [0033]      FIG. 2  depicts thermoplastic bag making film  4  with a slider-zipper assembly  2  applied transverse to the machine direction. The slider-zipper assembly  2  comprises a slider  20  and a zipper assembly  22 . Preferably the slider-zipper assembly is cut off from the end of a tape or chain of such assemblies, fed transversely to the position shown in  FIG. 2 , and then heat sealed to the thermoplastic film by the apparatus depicted in  FIG. 2 .  
         [0034]     As best seen in  FIG. 3 , the zipper assembly comprises a closure member  40  having a female profile and a zipper flange  44  having one end connected to the closure member  40 ; and a closure member  42  having a male profile and a zipper flange  46  having one end connected to the closure member  42 . The zipper flanges  44  and  46  extend in the machine direction when laid on the bag making film  4 , generally parallel to each other. The zipper flange  44  is attached to the stationary film  4  at the first sealing station depicted in  FIG. 7 . The arrow in  FIGS. 2 and 7  indicates the direction of film advancement after the zipper assembly has been attached to the film. The first sealing station comprises a heated lower sealing bar  48  and an unheated upper sealing bar or bed  50 , both of which move in opposite directions between extended and retracted positions. In the extended positions, the lower sealing bar  48  and upper sealing bed  50  press the zipper flanges  44  and  46  together and heat from the heated lower sealing bar  48  is conducted through the film  4  and into the zipper flange  44 , forming a permanent seal  52  therebetween. The temperature of the lower sealing bar  48  is controlled by a programmable heat controller (not shown). The dwell time of the lower sealing bar in the extended position is controlled by a programmable controller (not shown). Both controllers are programmed to produce conditions at the first sealing station such that zipper flange  44  is sealed to film  4  without sealing zipper flange  44  to zipper flange  46 .  
         [0035]     A tape transfer assembly guides the zipper assembly into the position shown in  FIG. 2  and holds the zipper assembly in place while the sealing operation depicted in  FIG. 3  is performed. The tape transfer assembly is shown in detail in  FIGS. 4-7 . The zipper tape with sliders is fed from a tape drive assembly (not shown) to the tape transfer assembly. In the front view of  FIG. 4 , the terminal section of the zipper tape is shown in a position between a bank of drive roller assemblies  76 ,  78 ,  80  and a fixed shelf  75 . The slider  20  of the terminal zipper length sits atop the shelf  75  at a position to the right of the large drive roller  76 . The slider cannot not pass under the drive rollers. It should be appreciated that the zipper tape extends in the right-hand direction, where it passes through the tape drive assembly. The zipper tape enters the tape transfer assembly from right to left in  FIG. 4 . In the position shown in  FIG. 8 , the zipper tape is cut and the cut zipper length is sealed to bag making film that extends in a plane perpendicular to the sheet and passes directly below the shelf  75 . The cutting mechanism is not shown.  
         [0036]     As seen in  FIG. 6 , the shelf has a V-shaped longitudinal groove  79 , while the large drive roller assembly  76  has a circumferential groove  77  with a generally trapezoidal profile. Each of small drive rollers  78  has a similar circumferential groove. These circumferential grooves on the drive roller assemblies are generally aligned with the longitudinal groove  79  of the shelf  75 . At the nip where each drive roller nearly contacts the shelf  75 , the peripheral grooves  77  and the longitudinal groove  79  form respective passageways for the A-shaped zipper profile. Although not shown in  FIG. 6 , the zipper flanges of the zipper assembly extend rightward, through the gap between the shelf  75  and roller  76  and beyond the edge of the shelf, where the bottom flange will be sealed to the bag making film.  
         [0037]     Still referring to  FIG. 6 , the drive roller assembly  76  comprises a metal core surrounded by an annular ring made of silicone. The circumferential groove is formed in the annular ring of silicone. The other drive roller assemblies (i.e., items  78  and  80 ) have a similar construction. The metal core of the drive roller  76  is mounted to one end of a horizontal shaft  86 . The shaft  86  is rotatably supported by a pair of bearings  88 . The bearings  88  are mounted in a pulley mounting plate  82 . The other drive assemblies are also mounted to the end of respective horizontal shafts rotatably supported by respective sets of bearings mounted in the pulley mounting plate  82 . Shaft  86 , however, differs from the other shafts in that shaft  86  is longer and carries, on its opposite end, a gearbelt pulley  96  that is coupled to a servomotor by a gearbelt  98  and a gearbelt pulley  100  that is coupled to a gearbelt pulley of the tape drive assembly (not shown) by a gearbelt  46 . Thus, the servomotor ( 152  in  FIG. 5 ) drives the rotation of shaft  86  and drive roller assembly  76  mounted thereon. Referring to  FIG. 5 , the motor  152  is attached to the fixed support frame by means of a motor mounting plate  150  and motor space  154 .  
         [0038]     The rotation of shaft  86  also drives the rotation of the other drive roller assemblies  78  and  80  of the tape transfer assembly. As seen in  FIG. 6 , a gearbelt pulley  90  is mounted on shaft  86 . The gearbelt pulley  90  and the drive roller assembly  76  are mounted on shaft  86  on opposite sides of the pulley mounting plate  82 . Similarly, the other shafts, on which the other drive roller assemblies  78  and  80  are mounted, also have gearbelt pulleys aligned with gearbelt pulley  90  and coupled to gearbelt pulley  90  by means of a gearbelt  92 . The gearbelt  92  is retained against the gearbelt pulley  90  by a drive belt retainer  94 . Moreover, each gearbelt pulley driven by gearbelt  92  also has a respective drive belt retainer (not shown).  
         [0039]      FIG. 7  shows a similar arrangement for drive roller assembly  80 , which is mounted to one end of a shaft  114  rotatably supported by bearings  116 . A gearbelt pulley  118  is mounted to the other end of the shaft  114 . Pulley  118  is coupled to pulley  90  (shown in  FIG. 6 ) by the gearbelt  92 , which is held against pulley  118  by a drive belt retainer  121 . As seen in  FIG. 7 , the shelf  75  is fastened to a shelf mounting plate  120  and extends in cantilevered fashion to a location underneath the bank of drive roller assemblies. Although not shown in  FIG. 7 , the shelf mounting plate  120  is a vertical plate that overlaps and is fastened to a vertical bearing plate  101   a  (best seen in  FIG. 5 ).  
         [0040]     Referring again to  FIG. 4 , the position of drive roller assembly  80  is adjustable along the axis of a screw  81 . More specifically, the drive roller assembly  80  is rotatably mounted to adjustment pulley mount  84 , which translates along the screw axis as screw  81  is turned. This facilitates the installation and tightening of gearbelt  92 . The gearbelt  92  ensures that the peripheral points of contact with the zipper of all drive roller assemblies move at the same tangential velocity.  
         [0041]     As previously mentioned, the peripheral surface of each drive roller is made of silicone to prevent slippage of the plastic zipper tape during transfer of the zipper tape in a direction transverse to the running direction of the bag making film. The non-slipping contact of the periphery and groove of the drive rollers with the zipper tape during roller rotation in a clockwise direction (as seen in  FIG. 4 ) pulls the zipper tape from right to left in  FIG. 4 . Transverse transfer of the zipper tape is stopped before the slider  20  contacts drive roller assembly  76 . In this position, the zipper tape is cut and sealed to the bag making film. More specifically, while the drive rollers and shelf  75  restrain the closure members of the zipper assembly, the zipper flanges extend between the confronting faces of the sealing bar  48  and sealing bed  50 , which are shown in confronting relationship without the zipper assembly in  FIG. 5 .  
         [0042]     The sealing bar  48  is located below the tensioned bag making film while the sealing bed  50  is located above the tensioned film. They move in opposite directions between respective extended and retracted positions. The zipper flange  44  is sealed to the film  4  when the bar  48  and bed  50  are in their respective extended positions.  
         [0043]     Referring now to  FIG. 5 , two bearing plates  101   a  and  101   b , a horizontal mounting plate  102  fastened therebetween, and the shelf mounting plate  120  fastened to plate  101   a  form parts of a fixed support structure. A retractable sealing bed  50  is mounted to the horizontal mounting plate  102  in the following manner. The sealing bed  50  is suspended from a vertically displaceable seal bar mounting plate  132  via a pair of threaded rods  134 , only one of which is visible in  FIG. 5 . The seal bar mounting plate  132  is in turn fastened to the ends of a pair of guide shafts  124  (only one of which is visible in  FIGS. 5 and 6 ), which are in turn respectively supported for vertical displacement by a pair of flanged mount bearings  122  (only one of which is visible in  FIG. 5 ). The flanged mount bearings  122  sit atop and are fastened to a horizontal cylinder mounting plate  126 , which sits on and is fastened to horizontal mounting plate  102 . The force for lifting the sealing bed  50  is provided by an air cylinder  128  having a piston  130 , the end of which is fastened to the middle of the seal bar mounting plate  132 .  
         [0044]     Referring to  FIG. 6 , the retractable bed in turn comprises the following stack of elements: a seal bar cap  136 ; a heat insulator  138 ; a platen bar  140 ; a ¼-inch-thick layer of silicone rubber  142 ; and a ⅛-inch-thick layer of silicone rubber  144  covered with Teflon glass cloth, which contacts the zipper flange during sealing. The silicone rubber conforms to the shape of the compressed zipper flange  44  in contact therewith and facilitates the formation of a uniform permanent seal between the film  4  and the zipper flange  46 .  
         [0045]     The sealing bar  48  is a part of a lower sealing bar assembly shown in detail in  FIG. 8 . This assembly is supported by a series of connector plates (not shown) to a support frame. More specifically, a slider plate  164  is mounted to the distal portion of the last connector plate (not shown). A cylinder mounting plate  166  is in turn mounted to the slider plate  164 . Item  168  in  FIG. 8  is a curtain mount, while item  174  represents a portion of one of the aforementioned connector plates. Item  170  is one of two film support arms, the bottom ends of which are fastened to opposing ends of the sealing bar mounting plate  164 . A horizontal film support member  172  extends transversely underneath the bag making film and is fastened to the top ends of the film support arms  170 . When the lower sealing bar  48  retracts, the stationary horizontal member  172  engages the bag making film and supports it vertically, thereby disengaging the film from the sealing bar in the event that the film sticks to the heated surface of the bar.  
         [0046]     The sealing bar  48  is mounted to vertically displaceable seal bar mounting plate  176  via a pair of threaded rods  178 , only one of which is visible in  FIG. 8 . The seal bar mounting plate  176  is in turn fastened to the ends of a pair of guide shafts  180  (only one of which is visible in  FIG. 8 ), which are in turn respectively supported for vertical displacement by a pair of flanged mount bearings  182  (only one of which is visible in  FIG. 5 ). The flanged mount bearings  182  sit atop and are fastened to cylinder mounting plate  166 , which sits on and is fastened to slide plate  164 . The force for lifting the sealing bar  48  is provided by an air cylinder  184  having a piston (not visible in  FIG. 8 ) the end of which is fastened to the middle of the seal bar mounting plate  164 .  
         [0047]     The sealing bar  48  is an assembly comprising a seal bar core  186 , a seal bar cap  188  having a sealing bar  194  projecting therefrom, a seal bar cap  190 , and an insulator  192 . The seal bar cap  188  caps the seal bar core  186 . The insulator  192  is sandwiched between the seal bar core  186  and the seal bar cap  190 . The seal bar cap  190  is fastened to the ends of the threaded rods  178 . The seal bar core  186  has a pair of longitudinal channels that respectively house a thermocouple  196  and an electric heater  198 , both of which are electrically connected to a programmable heat controller (not shown) by electrical wiring (not shown). The thermocouple produces electrical signals representing the temperature of the seal bar core  186 , which signals are received by the heat controller. The heat controller controls the level of electrical current supplied to the heater  198  in accordance with a heat control program that is designed to maintain the sealing bar temperature within limits preset by the system operator. In particular, the temperature of the sealing bar must be selected such that the amount of heat conducted through the bag making film and into the adjoining zipper flange, during the time that the zipper flanges and film are pressed between the extended sealing bar and sealing bed, will achieve the desired result, namely, sealing of one zipper flange to the bag making film without “seal-through” of the zipper flanges.  
         [0048]     After each slider-zipper assembly has been attached to the bag making film along a band (i.e., permanent seal  52 ) transverse to the running direction of the film, the film with slider-zipper assembly must be advanced by one package length. With reference to the drawings, the bag making film will be advanced in a direction directed out of the page in  FIG. 4  and from left to right in  FIG. 5 . However, as seen in  FIG. 6 , the opposing grooves  77  and  79  form a passageway for receiving the A-shaped zipper profile while the gap to the right, through which the zipper flanges project, is too narrow to allow the A-shaped zipper profile to pass through during bag making film advancement. This problem is solved by providing means for lifting the drive roller assemblies upward and away from the stationary shelf  75 .  
         [0049]     Referring to  FIG. 4 , the drive roller assemblies are rendered vertically retractable by mounting them to a vertically displaceable mounting plate  85 . More specifically, the pulley mounting plate  82 , which supports the drive roller assemblies  76  and  78  directly and the drive roller assembly  80  indirectly (via screw  81 ), is fastened to the mounting plate  85 . The mounting plate  85  is fastened to the ends of a pair of guide shafts  106 , which are in turn respectively supported for vertical displacement by a pair of flanged mount bearings  104 . The flanged mount bearings  104  are fastened to a horizontal mounting plate  103 , which sits on and is fastened to another horizontal mounting plate  102 . The mounting plates  102 ,  103  also form part of the aforementioned fixed support structure. The horizontal mounting plate  102  spans and is supported by a pair of vertical bearing plates  101   a  and  101   b , shown in  FIG. 5 . The bearing plate  101   a  depicted in  FIG. 5  has the previously mentioned shelf mounting plate  120  fastened thereto. The flanged mount bearings  104  extend downward through respective sets of aligned apertures in the mounting plates  102  and  103 . The axes of the guide shafts  106  are mutually parallel and directed vertically. This arrangement allows the entire carriage comprising the mounting plate  85 , the pulley mounting plate  82 , the drive roller assemblies  76 ,  78 ,  80 , the gearbelt pulleys, and associated shafts, bearings, and belt retainers to be displaced vertically. Each of the drive rollers is separated from the shelf by a respective first gap when the carriage is in a fully extended position, this first gap being less than the width of the zipper profile, e.g., 0.020 inch. Each drive roller is separated from the shelf by a respective second gap when the carriage is in a fully retracted position, this second gap being greater than the zipper profile width, thereby providing sufficient clearance for the zipper profile to exit the tape transfer assembly when the bag making film, to which the zipper is now sealed, is advanced.  
         [0050]     The force for lifting the carriage is provided by an air cylinder  112  having a piston  113 , the end of which is fastened to a pressure plate  108 . Alternatively, a hydraulic cylinder could be used. The pressure plate  108  is fastened to the mounting plate  85 , the distance between plates  85  and  108  being determined by a plurality of stand-offs  110 . The air cylinder  112  is mounted to the mounting plate  103 . Aligned apertures in the mounting plates  102  and  103  allow passage of the piston  113 . Actuation of the air cylinder is controlled by the same programmable controller that controls the servomotor  152 . The programmable controller causes the drive roller assemblies to be lifted just prior to advancement of the bag making film, which is typically under the control of a separate programmable controller.  
         [0051]     Although  FIG. 6  does not show the zipper, the person skilled in the art will readily understand that the zipper profile will be captured between grooves  77  and  79  and the zipper flanges will extend to the right, through the gap between drive roller assembly  76  and shelf  75 . After the bottom zipper flange has been sealed to the top of the bag making film, which passes under shelf  75 , the carriage is lifted and then the bag making film is advanced. A tensioner arm  158  (see  FIG. 5 ) maintains tension in the drive belt when the carriage is lifted. Item  156  is a spacer; item  162  is a needle roller bearing; and item  159  is a shoulder screw. Extension spring  160  is coupled to the tensioner arm  158 . When the drive roller assembly  76  is raised, groove  77  no longer interferes with rightward movement of the zipper profile as the bag making film (which the zipper is now attached to) moves to the right. Also, the groove  79  in shelf  75  is formed with a surface that is inclined to facilitate the zipper profile leaving groove  79  without the lower lip of the zipper profile catching in the groove. After the bag making film has been advanced one package length, the carriage is lowered and the next zipper length is pulled into the flange sealing position by the drive roller assemblies.  
         [0052]     In accordance with one embodiment of the invention, the bag making film  4  with slider-zipper assemblies  2  attached at intervals therealong is fed to a VFFS machine  62  (shown in  FIG. 9 ). The thermoplastic film  4  is fed downwardly over a forming collar  64  and is folded around a filling tube  66 . The edges of the film are brought together and pressed by a pair of rollers  68 . These edges of the film are then sealed together by a pair of opposing longitudinal sealing bars  70   a  and  70   b  to form a longitudinal fin seal  30 . Contents are then dropped through the tube  66  into the bag  32  that is currently being made. At the time of filling, bag  32  has a bottom seal  56  that was formed when the immediately preceding bag  36  was completed by making a top seal  58 . After filling, the top of the instant bag  32  and the bottom of the next succeeding bag  38  are sealed by the action of cross sealing jaws  72   a  and  72   b . At the same or about the same time, the second zipper flange is sealed to the adjoining wall of the bag  32  by a pair of opposing cross sealing bars  74   a  and  74   b , which are respectively mechanically linked to the cross sealing jaws  72   a  and  72   b . The mechanically linked jaws  72  and bars  74  perform four functions concurrently or nearly concurrently, which will now be described with reference to  FIG. 10 .  
         [0053]      FIG. 10  shows the second sealing station, comprising cross sealing jaws  72  and cross sealing bars  74 , in more detail. The mechanical linkages between jaws  72  and bars  74  are not shown. Each cross sealing jaw  72   a  and  72   b  comprises a respective pair of mutually parallel sealing bars, the sealing bars of jaw  72   a  being aligned with and opposed to the respective sealing bars of jaw  72   b . Both cross sealing jaws  72   a  and  72   b  are heated to a temperature that causes the opposing walls  10  and  12  of the bag making film to seal together during a preset dwell time (controlled by a programmable controller not shown) in their extended positions, thereby forming a top seal  58  of the just-filled bag and a bottom seal  56  of the immediately preceding unfilled package. The temperature of sealing bar  74   a  is controlled by a programmable heat controller  6 .  
         [0054]     A knife  73  is incorporated in cross sealing jaw  72   a , while a backing member for supporting the film during cutting is incorporated in cross sealing jaw  72   b . When the cross sealing jaws are in their respective extended position, the opposing walls  10  and  12  of the film are cut as the cutting edge of knife  73  bears against the backing member with the film therebetween.  
         [0055]     Substantially concurrently with formation of the bottom seal  56  and the top seal  58 , the unsealed zipper flange  46  is attached to wall  12  of the formed bag by the sealing bar  74   a , which is heated. The opposing sealing bar  74   b  is not heated. In the extended positions, the sealing bars  74   a  and  74   b  press the zipper flanges  44  and  46  together, and heat from the heated sealing bar  74   a  is conducted through the film wall  12  and into the zipper flange  46 , forming a permanent seal  54  therebetween. The other zipper flange  44  has already been joined to film wall  10  by a permanent seal  52  formed at the first sealing station. The temperature of sealing bar  74   a  is controlled by a programmable heat controller  8 .  
         [0056]     Although the mechanical linkages are not shown, the sealing bar  74   a  is mechanically linked to the sealing jaw  72   a , while the sealing bar  74   b  is mechanically linked to the sealing jaw  72   b . Thus the dwell time of sealing bars  74   a  and  74   b  in their extended positions is the same as that for sealing jaws  72   a  and  72   b  However, the separate heat controllers  6  and  8  enable independent control of the temperature of the sealing jaws  72   a  and  72   b  as compared to the temperature of the sealing bar  74   a . The heat controller  8  controls the temperature of the sealing bar such that the zipper flange  46  is sealed to wall  12  without sealing zipper flange  46  to zipper flange  44 . Each of the heat controllers  6  and  8  operates in substantially the same manner as the heat controller, previously described, that controls the heating of sealing bar  50  at the first sealing station, to wit, each heated sealing bar incorporates a thermocouple and an electric heater, the heat controller controlling the electrical current supplied to the heater as a function of, at a minimum, the temperature reading supplied by the thermocouple and a preset temperature limit set by the system operator.  
         [0057]     Thus, due to the mechanical linkages at the second sealing station, four operations are performed substantially concurrently: (a) the completed bag is severed from the remainder of the tubular film by the knife  73 ; (b) the top seal  58  is formed in the completed bag; (c) the bottom seal  56  is formed for the next bag to be completed; and (d) the zipper flange  46  is sealed to the wall  12  of the completed bag. When the sealing jaws  72   a  and  72   b  and the sealing bars  74   a  and  74   b  are retracted, the severed completed bag will proceed to the next stage.  
         [0058]     The linked jaws  72  and bars  74  can be displaced by means of the same type of apparatus described in connection with sealing bar displacement at the first sealing station, namely, mounting the bar to a mounting plate supported by a pair of guide shafts slidable in respective bearings and then using an air cylinder to displace the mounting plate. Hydraulic cylinders can be employed in place of air, i.e., pneumatic, cylinders. A person skilled in the art of machinery design will readily appreciate that displacing means other than a cylinder can be used to vertically displace the sealing bars/jaws and the drive roller carriage. Any other known mechanical displacement means can be used. For the sake of illustration, such mechanical displacement devices include rack and pinion arrangements, rotation of the pinion being driven by an electric motor.  
         [0059]     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. For example, it should be obvious that the slider guide may be formed as a monolithic piece or may be an assembly having two or more parts. 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.  
         [0060]     As used in the claims the terms “first portion”, “second portion”, and so forth (e.g., of a zipper flange or of bag making film) refer to non-identical portions, but do not exclude portions that share a common area.