Abstract:
An improved sealing method allows the ends of pouch closure to be joined while at the same time forming dome-shaped slider end stops at respective joined ends of the closure. The closure may comprise two zippers. In addition, the ends of the zipper profiles are terminated by means of dies that form uniform and consistent terminations in the zone where the ends of the zipper strips are joined. The dome-shaped slider end stops and the zipper profile terminations are produced by heat sealing, either ultrasonically or through resistance heating, of the closure material. After the closure material has been softened by ultrasonic energy or resistance heating, dies are used to form the dome structures and terminations of the zipper profiles.

Description:
RELATED PATENT APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application Ser. No. 61/407,351 filed on Oct. 27, 2010. 
     
    
     BACKGROUND 
       [0002]    This invention generally relates to reclosable flexible bags whose interior volume is hermetically sealed when the bag is closed. In particular, the invention relates to, but is not limited to, evacuable reclosable storage bags having a zipper that is closed (but not opened) by operation of a slider or clip mounted on the zipper. 
         [0003]    Collapsible, evacuable storage containers typically include a flexible, airtight bag, an opening through which a compressible article is inserted inside the bag, a zipper for closing the opening and hermetically sealing the bag, a U-shaped slider for closing the zipper, and one or more one-way valves or vents through which excess air is evacuated from the bag. A user places an article into the bag through the opening, seals the opening, and then removes air from the bag through the one-way valve or valves. As air is removed, the compressible article contained therein may be significantly compressed so that it is easier to transport and requires substantially less storage space. 
         [0004]    Collapsible, evacuable storage containers are beneficial for reasons in addition to those associated with compression of the stored article. For example, removal of the air from the storage container inhibits the growth of destructive organisms, such as moths, silverfish, and bacteria, which require oxygen to survive and propagate. Moreover, such containers, being impervious to moisture, inhibit the growth of mildew. 
         [0005]    Not only large, compressible items such as clothing may be stored in a collapsible, evacuable storage container. For example, it may be desirable to store bulk items made of small particles, such as powders or granulated resins, in an evacuated container. One situation that commonly occurs is that a particular bulk item is shipped in a large, rigid container such as a drum. Bulk items may be moisture sensitive and are sealed against moisture during shipment. But many times a user does not need to use the entire contents of the large container, and so once exposed to air the remaining bulk contents quickly become unusable and are thus wasted. 
         [0006]    Many commercially available evacuable storage bags are provided with an inverted U-shaped slider or clip mounted to the plastic zipper. This slider is capable of closing an open zipper, i.e., by camming the opposing zipper strips into engagement during slider travel in either direction, but cannot be used to open a closed zipper. The slider does not have means for opening the zipper because typically such means would leave a gap in the zipper, thereby preventing formation of a hermetic seal. 
         [0007]    In known reclosable bags, the zipper comprises a pair of mutually interlockable zipper strips, each zipper strip having one or more generally constant profiles extending across the mouth of the bag. For example, it is known to provide a reclosable bag having dual zippers which extend in parallel across the mouth of the bag. The ends of the zipper strips are joined together at the sides of the bag. For example, it is known to fuse the ends of the zipper strips together, at the same time that the bag side seals are formed, by the application of heat and pressure. This “thermal crushing” of the plastic zipper creates a transition between “as is” zipper and crushed zipper that is susceptible to the presence of leaks through which air can enter an evacuated bag. In addition, such crushing leaves the surface material flat at either end where the zipper ends are joined to each other and to the webs of film that form the front and rear walls of the bag. 
         [0008]    There is a continuing need for improvements in the construction of flexible storage containers that need to be hermetically sealed. In particular, there is a need for an improved evacuable storage container wherein leakage is eliminated in the areas where the bag side seals overlap the joined ends of the zipper strips. There is also a need for a leakproof construction that provides means for stopping a U-shaped slider at either end of the bag mouth as it travels along the closure. 
       SUMMARY 
       [0009]    The improved sealing method disclosed herein allows the ends of the closure to be joined while at the same time forming a dome-shaped projection at respective joined ends of the closure. In one embodiment the closure comprises a double zipper. The purpose of the dome structure is to prevent the slider or clip from coming off the bag when the consumer closes the double zippers. The ability of the clip to stay on the closure is a desirable benefit to the consumer. A bag without a zipper clip is difficult to close. 
         [0010]    In addition, known methods leave the zipper profile(s) (i.e., the interlockable elements of the closure) to be randomly terminated. In accordance with the teaching herein, the ends of the zipper profiles are terminated using dies that allow the formation of uniform and consistent terminations in the zone where the ends of the zipper strips are joined. 
         [0011]    The dome-shaped slider end stops and the zipper profile terminations are produced by heat sealing, either ultrasonically or through resistance heating, of the closure material. After the closure material has been softened by ultrasonic energy or resistance heating, dies are used to form the dome structures and terminations of the zipper profiles. In order to cause the soft material to harden in a short period of time, a cooling process is used to shorten the time required for the material to harden. 
         [0012]    One aspect of the invention is a method of joining mutually interlocked first and second zipper strips made of thermoplastic material, wherein the first zipper strip comprises a first flange and first and second closure elements projecting from the first flange, and the second zipper strip comprises a second flange and third and fourth closure elements projecting from the second flange, the third and fourth closure elements being interlocked with the first and second closure elements respectively. The method comprising the following steps: (a) joining the first flange of the first zipper strip to a corresponding band-shaped zone of a first panel made of web material; (b) joining the second flange of the second zipper strip to a corresponding band-shaped zone of a second panel made of web material; (c) supplying heat and pressure in sufficient amounts in an area overlapping respective lengths of the interlocked first and third closure elements and the interlocked second and fourth closure elements to cause the closure elements to be at least partially crushed along the respective lengths; (d) applying heat and pressure in sufficient amounts in the area to cause thermoplastic material of the zipper strips to flow into first and second pairs of mutually opposed depressions located adjacent to and on opposite sides of the area; (e) advancing the first and second zipper strips to a position whereat the thermoplastic material formed by the first and second pairs of depressions is aligned with and received by third and fourth pairs of mutually opposed depressions located adjacent to and on opposite sides of the area, with empty space between each formed thermoplastic material and the respective depression that receives it; (f) applying sufficient pressure in the area to cause additional thermoplastic material of the zipper strips to flow into the third and fourth pairs of depressions; and (g) cooling the zipper strip thermoplastic material in the area. 
         [0013]    Another aspect of the invention is a reclosable pouch comprising: a receptacle having a storage chamber and a mouth in communication with the storage chamber, a hermetically sealable closure installed in the mouth, and a slider mounted to the closure, which components have the following features. The receptacle comprises first and second walls made of thermoplastic web material, a first side seal that includes respective first marginal portions of the first and second walls, and a second side seal that includes respective second marginal portions of the first and second walls. The closure comprises first and second zipper strips made of thermoplastic material, the first and second zipper strips being fused together in first and second zones situated at respective ends of the closure and being unfused between the respective ends of the closure, an unfused portion of the first zipper strip comprising a first flange and first and second closure elements projecting from the first flange, and an unfused portion of the second zipper strip comprising a second flange and third and fourth closure elements projecting from the second flange, the closure elements spanning the space between the first and second zones. The slider comprises first and second sidewalls which force the closure elements of incoming unfused portions of the first and second zipper strips into mutual engagement as the slider travels along a portion of the closure where the closure elements of the first and second zipper strips are not mutually engaged. Each of the first and second zones comprises a respective pair of round projections arranged back to back to form respective obstacles to further travel of the slider at opposing ends of the closure, each round projection comprising thermoplastic material from portions of the first or second zipper strips other than the unfused portions. 
         [0014]    A further aspect of the invention is a roll comprising a chain of reclosable pouch precursors connected by a multiplicity of transverse seals spaced at equals intervals along a lengthwise direction and having the following features. Each pouch precursor comprises a respective receptacle having a storage chamber and a mouth in communication with the storage chamber, and an airtight closure for closing the mouth, the storage chambers being disposed between respective pairs of the transverse seals. Each receptacle comprises respective confronting sections of first and second webs of thermoplastic material. Each closure comprises respective confronting sections of first and second zipper strips. Each transverse seal comprises a first zone where the first and second webs are fused together and a second zone where the first and second zipper strips are fused together. Each of the second zones comprises first and second pairs of round projections, the round projections of each pair being arranged back to back, and each round projection comprising thermoplastic material from portions of the first or second zipper strips in said second zone. 
         [0015]    Other aspects of the invention are disclosed and claimed below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a diagram showing an isometric view of a reclosable pouch. 
           [0017]      FIG. 2  is a diagram showing a sectional view of a double zipper attached to the walls of a reclosable pouch. 
           [0018]      FIG. 3  is a drawing showing an isometric view of a corner at one end of the mouth of a reclosable pouch, which corner has dome-shaped structures for stopping a slider and leakproof zipper terminations in accordance with one embodiment. 
           [0019]      FIG. 4  is a drawing showing a plan view of a portion of two connected pouch precursors in process, the depicted portion including an area where the interlockable closure elements have been crushed and then the plastic material in the crush area has been deformed to make slider end stops and zipper terminations of the types depicted in  FIG. 3 . 
           [0020]      FIG. 5  is a drawing showing a top view of the zipper crush area depicted in  FIG. 4 . 
           [0021]      FIGS. 6 through 11  show four different tools which are employed in pairs at successive stations of an automated production line for making reclosable pouches, which tools are utilized to form the structures depicted in  FIGS. 3 and 4 . 
           [0022]      FIG. 6  is an isometric view of a tool which is one of two opposing tools used at a first crush station for crushing intervening plastic material of a work in process after each indexed advance thereof. 
           [0023]      FIG. 7  is an isometric view of a stepped tool which is one of two opposing tools used at a second crushing station to further crush the plastic material previously crushed at the first crush station after each indexed advance. 
           [0024]      FIG. 8  is a diagram showing an isometric view of one end of the stepped portion of the tool depicted in  FIG. 7 . 
           [0025]      FIG. 9  is a diagram showing an isometric view of a tool having two dimples which is one of two opposing tools used at a pre-forming station for forming crushed plastic material into respective dome shapes that project on both sides of the work in process. 
           [0026]      FIG. 10  is a diagram showing a sectional view of the tool depicted in  FIG. 9 , the section being taken along a plane that bisects the two dimples. 
           [0027]      FIG. 11  is a diagram showing an isometric view of a tool having two hemispherical dimples and four zipper termination channels, which tool is one of two opposing tools used at a post-forming station for forming crushed plastic material into respective hemispherical dome shapes which are larger than the pre-formed dome shapes and also forming zipper terminations in the crush area. 
           [0028]      FIG. 12  is a diagram showing an isometric view of two mutually opposing tools of the type depicted in  FIG. 11 , with a post-formed section of a zippered portion of work in process therebetween. 
           [0029]      FIG. 13  is a diagram showing an isometric view of a tool having two oval-shaped dimples and four zipper termination channels, which tool is one of two opposing tools used at a post-forming station for forming crushed plastic material into respective oval-shaped domes of sufficient height to stop the slider at the ends of the double zipper. 
           [0030]      FIG. 14  is a diagram showing an isometric view of a corner at one end of the mouth of a reclosable pouch made using dies of the type depicted in  FIG. 13 . 
           [0031]      FIG. 15  is a diagram showing an isometric view of a corner at one end of the mouth of a reclosable pouch having oval-shaped slider end stops and oval-shaped zipper terminations in accordance with an alternative embodiment. 
       
    
    
     Reference will now be made to the drawings in which similar elements in different drawings bear the same reference numerals. 
     DETAILED DESCRIPTION 
       [0032]      FIG. 1  shows a collapsible reclosable storage pouch  2  in accordance with one embodiment. The storage pouch  2  comprises a receptacle  4  consisting of a front wall or panel  6  and a rear wall or panel (not shown in  FIG. 1 , but see item  12  in  FIG. 2 ), which are sealed together in left and right marginal regions along their side edges. Although not shown in  FIG. 1 , the bottom of the receptacle  4  has a one-way vent, comprising multiple collapsible channels, that extends from one side seal to the other. The front and rear walls are heat sealed together at multiple locations across the pouch bottom to form multiple collapsible channels that allow escape of air from the interior volume when the contents (not shown) of the receptacle are compressed, but prevent the entry of air into the receptacle when the external pressure is released. The walls of the receptacle may be formed of various types of gas-impermeable thermoplastic web material. The preferred gas-impermeable thermoplastics are nylon, polyester, polyvinyl dichloride and ethylene vinyl alcohol. 
         [0033]    The upper marginal portions of the front and rear walls of the pouch  2  form a mouth in which a plastic closure  8  comprising double zippers  8   a  and  8   b  is installed. To maintain a vacuum inside the storage pouch, the closure  8  when closed must provide a hermetic seal at the mouth of the pouch. The closure is made from a plastic material that is less flexible than the plastic material of the pouch walls. The front and rear wall panels of the receptacle  4  are respectively sealed to the closure by lengthwise conduction heat sealing in conventional manner. Alternatively, the closure  8  can be attached to the wall panels by adhesive or bonding strips. 
         [0034]    Still referring to  FIG. 1 , the zippers  8   a  and  8   b  can be closed using a device  10  commonly referred to as a “slider” or “clip”, which straddles the closure  8 . During use, one or more discrete compressible articles (not shown) may be placed inside the receptacle  4  while the closure  8  is open, i.e., while the interlockable closure elements of zippers  8   a  and  8   b  are disengaged from each other. After the article to be stored has been placed inside the receptacle, the closure  8  is closed by moving the slider  10  in either direction, from one end of the closure to the other, thereby pressing the closure elements of zippers  8   a  and  8   b  into interlocking relationship. Although the interlockable closure elements may have many different designs, the design must be one that ensures formation of an airtight seal at the receptacle mouth. 
         [0035]    The pouch described above is designed for storing compressible articles. When the contents of the pouch with closed mouth are compressed by a user pushing down on the pouch, air inside the pouch is forced through the one-way vent at the pouch bottom, thereby forcing some or all of its collapsed channels open. When those channels have been fully opened, continued pushing down on the pouch causes the air that was forced into those channels to escape via respective air outlets (not shown). This procedure can be continued until the desired amount of air has been removed from the pouch  2 . When the pressure exerted on the pouch by the user is removed, the opened channels collapse, thereby blocking the re-entry of ambient air into the pouch via those channels. 
         [0036]    The present invention is not directed to any particular zipper construction. A suitable exemplary zipper construction is shown in  FIG. 2 . The closure  8  comprises a pair of extruded zipper strips  20  and  22  that are joined to each other in respective zipper crush areas at opposing ends of the closure. Zipper strip  20  comprises a web or flange  24  and a pair of mutually parallel male closure elements  26  and  28 ; zipper strip  22  comprises a web or flange  30  and a pair of mutually parallel female closure elements  32  and  34  which receive and grasp male closure elements  26  and  28  respectively. The closure elements  26  and  32  are designed to form an airtight zipper  8   a  when male closure element  26  is seated in female closure element  32  along the entire length of the pouch mouth. Likewise the closure elements  28  and  34  are designed to form an airtight zipper  8   b  when male closure element  28  is seated in female closure element  34  along the entire length of the pouch mouth. 
         [0037]    As previously noted, the zipper flanges  24  and  30  are more rigid than the adjoining pouch walls  6  and  12 . In accordance with one embodiment, only an uppermost portion of zipper flange  24  is attached to an uppermost marginal portion of pouch wall  6  by means of a heat seal  36 , which heat seal does not extend to the elevation of male closure element  26 . Thus, as seen in 
         [0038]      FIG. 2 , a major portion of zipper flange  24  is not attached to the pouch. Meanwhile the entirety of zipper flange  30  is attached to an uppermost marginal portion of pouch wall  12  by means of a heat seal  38 . This configuration prevents the zippers  8   a  and  8   b  from being forced open when the user compresses the pouch contents because a pressure is exerted on the unattached portion of zipper flange  24  which urges the zippers  8   a  and  8   b  to stay engaged rather than forcing the zipper flanges apart, as would be case if the entireties of both flanges were attached to the pouch walls. 
         [0039]      FIG. 2  shows the zippers  8   a  and  8   b  in respective closed states. The uppermost marginal portions of the pouch mouth (including the uppermost marginal portions of the zipper flanges  24  and  30 ) can be gripped by the user and pulled apart to open the closed zippers. The opened zipper can be reclosed by pressing the closure elements together along the entire length of pouch mouth, using a slider. Typically, such a slider takes the form of a U-shaped clip that fits over the zipper with clearance for the upper flanges, while the legs of the clip cam the closure elements of the incoming zipper section into engagement when the slider is moved along the zippers in either direction. In each pouch, opposing ends of the zipper strips  24  and  30  are typically fused together in the regions of the pouch side seals. 
         [0040]    In a known method for making hermetically sealed zipper joints, the closure elements are crushed in respective areas at opposite ends of the pouch mouth. This known method produces flattened material in crush zones at opposite corners of the pouch. However, it would be desirable to provide structure in the crush zones for preventing the slider from coming off a pouch corner when the consumer closes the double zipper. A pouch without a slider is difficult to close. 
         [0041]    In accordance with one embodiment, a method of manufacture is provided whereby a slider end stop  14  is formed in the each upper corner  50  of the pouch to prevent a slider  10  from coming off. In addition, the crushed zipper material adjacent the uncrushed ends of the closure elements is formed into respective zipper terminations  16  and  18  that form leakproof seals at the ends of the closure elements. 
         [0042]    The slider  10  shown in  FIG. 3  has a generally U-shaped profile, with respective legs disposed on opposing sides of the two-zipper closure. The gap between the slider legs is small enough that the zippers  8   a  and  8   b  can pass through respective slider gaps only if each zipper is in a closed state. Thus when the slider  10  is moved along an open closure, this has the effect of pressing the incoming sections of the closure elements together to close the mouth. A suitable slider is disclosed in U.S. Pat. No. 7,490,989. The slider  10  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. 
         [0043]    In accordance with the embodiment depicted in  FIG. 3 , each of the pouch corners at opposing ends of the closure has respective dome-shaped structures  44  on opposing sides of the pouch (only one dome is visible in  FIG. 3 ), the distance between the peaks of the oppositely extending domes being sufficiently greater than the width of the gap between those contacting portions of the slider legs that the slider is stopped and cannot pass over the domes (as depicted in  FIG. 3 ). Thus,  FIG. 3  shows the slider  10  at the limit of its travel along the closure. The slider can travel no further in the direction of the dome due to the dome-shaped obstacles  44  in its path and thus is prevented from falling off the pouch. 
         [0044]    As seen in  FIG. 3 , the slider  10  is generally U-shaped and comprises mutually opposing sidewalls  52  and  54 , a bridge  56  connecting the sidewalls  52  and  54 , and a generally U-shaped stiffening rib  58  projecting outward from sidewalls  52 ,  54  and bridge  56 . The sidewalls  52  and  54  are separated by a gap of varying width. In  FIG. 3 , the gap is not visible due to the presence of the pouch corner  50  therein. Preferably the slider is made by injection molding, so that the stiffening rib is integral with the sidewalls and bridge. On one side of the stiffening rib  58 , the sidewalls and bridge form a first generally clip-shaped structure  60  having undulating external surfaces. On the other side of the stiffening rib  58 , the sidewalls and bridge form a second generally clip-shaped structure  62  that is the same as structure  60 . 
         [0045]    Each sidewall  52 ,  54  of the slider has a pair of mutually parallel linear grooves  64  and  66  (only the grooves of sidewall  52  are visible in  FIG. 3 ). The grooves  64  and  66  of sidewall  52  respectively oppose identical grooves on the other sidewall. These grooves ride on the tracks formed by the interlocked closure elements of zippers  8   a  and  8   b  as the slider travels from one pair of dome-shaped slider end stops at one end of the zipper to the other pair of dome-shaped slider end stops at the other end of the zipper. These grooves cam the closure elements of the incoming zipper section into engagement when the slider is moved along the zippers in either direction, thereby hermetically sealing the pouch mouth. 
         [0046]    The grooves  64  and  66  define a plateau or ridge  68  therebetween, as seen in  FIG. 3 . An identical plateau on the other sidewall is not visible in  FIG. 3 . The opposing plateaus  68  form a gap that is less than the combined height of the oppositely projecting back-to-back domes  44 . The domes  44  are placed so that they lie in the path of plateaus  68  as the slider approaches the domes. Thus, the ends of the plateaus  68  will abut the domes  44  on respective sides of the pouch corner  50  when the consumer pulls the slider toward the pouch side edge  70 . The slider  10  and the domes  44  are sufficiently rigid and the difference between the plateau gap and the dome combined height is sufficiently great that the opposing plateaus  68  cannot easily pass over the domes  44  after they come into contact. 
         [0047]    In accordance with the embodiment depicted in  FIG. 3 , each of the pouch corners at opposing ends of the closure also has respective pairs of half dome-shaped projections  46  and  48  arranged back to back on opposing sides of the pouch (only one pair of these projections is visible in  FIG. 3 ). Alternatively, projections  46  and  48  may be dome-shaped or having any shape intermediate a half dome and a full dome. The distance between the peaks of back-to-back projections  46  and  48  is sufficiently greater than the width of the gap between the plateaus  68  that, when the slider has been stopped by domes  44  as depicted in  FIG. 3 , the back-to-back projections  46  and  48  pose respective obstacles to upward and downward movement of the plateaus  68  while they are in contact with domes  44 . In the embodiment depicted in  FIG. 3 , at least part of each projection  46  or  48  has the shape of a half-dome with a rounded half-circumference facing away from the respective uncrushed closure element, the back side of each pair of back-to-back half dome-shaped projections being integrally connected and hermetically sealed to respective uncrushed closure elements, thereby providing leakproof transitions from uncrushed closure element to crushed closure element at the ends of the zippers over an angle of at least 180 degrees relative to the end of the uncrushed closure element. 
         [0048]      FIG. 4  is plan view showing one side of a portion of two connected pouch precursors in process, the depicted portion including a transverse rectangular area  40  where two sheets of bag making film have been heat sealed together and an area  42  where the closure elements have been crushed and then the plastic material in the crush area has been formed into a pair of slider end stops  14  and respective pairs of zipper terminations  16  and  18 . The dashed line  45  in  FIG. 4  indicates where the transverse heat seal  40  and the crush area  42  will be cut, thereby severing a completed pouch on one side of cut line  45  from the chain of pouch precursors on the other side of cut line  45 . 
         [0049]    Each transverse heat seal  40  is made wide enough so that respective halves of the heat sealed area can be incorporated into separate pouches. More specifically, the cross-sealed area  40  is bisected by cutting along a line  45  transverse to the closure  8 . The area to the right of the cut line  45  forms the trailing side seal of the leading pouch precursor  2 A (assuming advancement of the chain of pouch precursors from left to right in  FIG. 4 ), while the area to the left of the cut line  45  forms the leading side seal of the trailing pouch precursor  2 B. 
         [0050]    As seen in  FIG. 4 , the centers of the round slider end stops  14  are located along a line which is parallel to and, if extended, would be located midway between the closure elements of zippers  8   a  and  8   b.  Although the slider end stops  14  and the zipper terminations  16  and  18  shown in  FIG. 4  appear to share a common tangent T that is parallel to the transverse cut line  45 , the tangent common to zipper terminations  16  and  18  may be separated from the nearest parallel line that would be tangent to dome  14   a  by a small distance (e.g., a few hundredths of an inch in some implementations). The centerlines of zipper terminations  16  and  18  are separated by a distance equal to the distance between the centerlines of the male closure elements of zippers  8   a  and  8   b.    
         [0051]      FIG. 5  shows a top view of the zipper crush area  42  depicted in  FIG. 4 . As can be seen in  FIG. 5 , the zipper crush area  42  has two pairs of back-to-back domes  44  and two upper pairs of back-to-back half dome-shaped projections  46  on both sides (i.e., front and back) of the pouch. The two lower pairs of back-to-back half dome-shaped projections (items  48  in  FIG. 4 ) on both sides (i.e., front and back) of the pouch are not visible in  FIG. 5 . Each pair of domes  44  are disposed back to back to form a respective slider end stop  14 . The half dome-shaped projections (items  46  and  48  in  FIGS. 4 and 5 ) are similarly disposed back to back to form zipper terminations  16  and  18 , which serves as leakproof transitions from uncrushed portions  72  of the interlocked closure elements to adjacent areas where portions of the same interlocked closure elements have been crushed. 
         [0052]    The pouch described above can be manufactured on an automated production line. For example, two webs of thermoplastic material, having the same width, can be paid out from respective rolls. Downstream respective sets of pull rollers are provided for pulling the webs through the pouch making machine. At the same time continuous lengths of the zipper strips depicted in  FIG. 2  are paid off respective spools and advanced to respective stations whereat the backs of the zipper strips are positioned in overlying relationship with the marginal portions of the respective webs of bag making film. Typically the webs and the zipper strips are advanced intermittently and all manufacturing operations are performed during dwell times. At a pair of parallel sealing stations, the zipper strips are joined to the respective webs in well-known manner, for example, by conductive heat sealing (see heat seals  36  and  38  in  FIG. 2 ). Then the webs with attached zipper strips are brought together in a manner that causes the respective webs to overlap and the closure elements of the respective zipper strips to interlock. (Alternatively, the interlocked zipper strips could be placed between the overlapping webs of bag making film and joined to webs in one operation.) At the next station, the marginal web portions on the side opposite the zippers (which portions will become the bottom of the pouches) are heat sealed to form collapsible channels for venting air when the pouch contents are compressed. A teaching of this operation can be found in International Patent Application No. PCT/US11/57389 filed on Oct. 21, 2011. At the next station, transverse heat seals are formed across the two webs, which seals will become the pouch side seals after being bisected during a cutting operation. Between each transverse heat sealing operation, the webs are advanced by a distance equal to one pouch width. In accordance with one implementation, the work in process then advances in succession through four stations where the crush area  42  with dome-shaped slider end stops and zipper terminations (see  FIG. 4 ) is formed in stages. Within the crush zone  42 , the closure elements are thermally crushed, i.e., flattened, and then the crushed zipper material is deformed into the protruding shapes depicted in  FIG. 5 . 
         [0053]      FIGS. 6 through 11  show four different tools which are employed in pairs at four successive stations of an automated production line for making reclosable pouches, which tools are utilized to form the structures depicted in  FIGS. 4 and 5 . These successive stations will hereinafter be respectively referred to (in order) as the zipper crush station, the zipper stepped crush station, the slider end stop pre-forming station and the slider end stop post-forming station. Each of these stations comprises a stationary tool and a reciprocating tool which are arranged in mutually confronting relationship. The reciprocating tool alternately extends and retracts toward and away from the stationary tool, with the work in process therebetween. When the reciprocating tool is fully extended, the work surfaces of the opposing tools at each station shape the plastic zipper material in contact therewith. However, the work surfaces of the opposing tools, which are the same for each pair, have a different geometry for each station, as explained in detail hereinafter. Each tool can be made from heat-treated A-2 tool steel or other suitable metal alloy. 
         [0054]    The zipper crush station comprises two mutually confronting tools of the type  74  depicted in  FIG. 6 . Each tool  74  (only one of which is shown in  FIG. 6 ) comprises a heated rectangular metal block having a rectangular planar contact surface  76  and rounded edges along the perimeter of planar surface  76 . The planar contact surfaces  76  of opposing tools  74  are pressed together with a section of the interlocked plastic zipper strips (with attached bag film) therebetween. The temperature between the contacting surfaces and the resulting pressure applied are controlled to at least partially crush the male and female closure elements. After each crushing cycle, the work in process is advanced one pouch width and then the crushing operation is repeated on a different section of the interlocked plastic zipper strips. 
         [0055]    The second (stepped) zipper crush station comprises two mutually confronting tools of the type  78  depicted in  FIGS. 7 and 8 . Each tool  78  (only one of which is shown in  FIG. 7 ) comprises a heated rectangular metal block having a rectangular stepped face and rounded edges along the perimeter of the stepped face. The stepped face comprises a rectangular planar surface  80 , a stepped rectangular planar surface  82  and a beveled surface  84  (e.g., with a bevel angle of 45 degrees) that connects to planar surfaces  80  and  82 . As seen in  FIG. 8 , there is a triangular facet  86  at each end of beveled surface  84  instead of a rectilinear corner. 
         [0056]    The stepped planar surfaces  82  of opposing tools  78  are pressed together with a minor portion of the zipper crush zone therebetween. The temperature between the contacting surfaces and the resulting pressure applied are controlled to cause some of the plastic zipper material to flow in the compressed zone to flow toward the lower portion of the closure. This downward displacement of plastic material provides additional material for the formation of slider end stops and zipper terminations in the central portion of the closure during subsequent operations. After each stepped crushing cycle, the work in process is advanced one pouch width and then the stepped crushing operation is repeated on a different crushed section of the work in process. 
         [0057]    The slider end stop pre-forming station comprises two mutually confronting dies of the type  88  depicted in  FIGS. 9 and 10 . Each die  88  comprises a heated rectangular metal block having a dimpled face and rounded edges along the perimeter of the dimpled face. The dimpled face comprises a rectangular planar surface  90  and a pair of preferably identical hemispherical depressions  92  (hereinafter “dimples”) positioned as shown. The dimples  92  are shown in mid-cross section in  FIG. 10 . 
         [0058]    The dimpled faces of opposing dies  88  are pressed together with the crush zone therebetween. The temperature between the contacting planar surfaces  90  and the resulting pressure applied are controlled to cause some of the plastic zipper material to flow into and fully occupy dimples  92 . The displaced material in dimples  92  forms respective domes that are precursors of the final slider end stops. After this pre-forming operation, the diameter of these dome-shaped slider end stop precursors will be less than the diameter of the dome-shaped projections on completed pouches. The distance between the centers of dimples  92  is equal to two times the desired distance of the center of each slider end stop to the nearest edge of each completed pouch. After each pre-forming cycle, the work in process is advanced one pouch width and then the pre-forming operation is repeated on a different crushed section of the work in process. 
         [0059]    The slider end stop post-forming station comprises two mutually confronting dies of the type  94  depicted in  FIGS. 11 and 12 . Each die  94  comprises a cold rectangular metal block having a rectangular contact face surrounded by rounded edges. The dies  94  can be cooled by a cold air gun directed at the dies or by coolant from a chiller that circulates in channels formed in the dies. The rectangular contact face of each die  94  comprises a rectangular planar surface  96 , a pair of preferably identical hemispherical depressions  98  (hereinafter “dimples”) positioned as shown, and two pairs of zipper termination channels, each pair including an upper channel  100  and a lower channel  102 . The zipper termination channels of each pair are mutually parallel to a hypothetical line connected the centers of dimples  98  and extend from a respective one of opposing sides of the die  94 . In accordance with the embodiment shown in  FIG. 11 . each zipper termination channel comprises a channel wall  104  that is semicircular at the closed end of the channel and a flat bottom  106  that extends to an open end of the channel. The channels  100  and  102  provide clearance for the zipper profiles during formation of the slider end stops. During this operation, zipper material tends to flow into these channels at their closed ends. The surface tension of the molten zipper material tends to cause the material in channels  100  and  102  to form round projections, such as the dome-shaped projections  46  and  48  seen in  FIG. 4 . The centerlines of channels  100  and  102  are separated by a distance equal to the distance between the midpoints of the male closure elements on the closure. 
         [0060]    The faces of opposing dies  94  are pressed together with the crush zone, now with slider end stop precursors, therebetween. The dimples  98  on dies  94  are aligned with the slider end stop precursors (not shown in  FIG. 11 ) so that the latter are received in the former, but with empty space between the slider end stop precursor surfaces and the surfaces of depressions  98 . The pressure exerted by the contacting planar surfaces  96  is sufficient to cause some of the plastic zipper material to flow into and fully occupy the empty spaces inside dimples  98 . The additional displaced material fills dimples  98  to form respective domes that will serve as slider end stops in the completed pouch after the plastic has cooled. In addition, plastic zipper material flows into the rounded ends of channels  102  and  104  and, upon cooling, will form zipper terminations having rounded or partially rounded shapes. 
         [0061]      FIG. 12  shows the separated dies  94  after the slider end stops  14  and zipper terminations  16 ,  18  have been formed on closure  8 . To avoid clutter in the drawing,  FIG. 12  does not show the pouch walls which are sealed to the backs of respective zipper flanges of closure  8 , as seen in  FIG. 2 . As seen in  FIG. 12 , each die  94  has a pair of threaded bores  108  spaced apart in a central section and a pair of unthreaded bores  110  at diagonally opposed corners. The unthreaded bores  110  of each die  94  receive respective alignment pins projecting from a respective die support plate (not shown) installed at the post-forming station, while each die  94  is affixed to the respective die support plate by means of threaded bolts received in threaded bores  108 . 
         [0062]    After each post-forming cycle, the work in process is advanced one pouch width and then the post-forming operation is repeated on a different crushed section of the work in process. At the next station (see  FIG. 4 ), the distal pouch precursor  2 A is severed from the adjacent pouch precursor  2 B by cutting along line  45 . 
         [0063]    Alternatively, the chain of pouch precursors (each pouch precursor having slider end stops and zipper terminations as described above) could be wound on a roll (i.e., without cutting) for transport to a cutting station. Thus, it is within the scope of this invention to not sever each completed pouch at the leading end of the chain of pouch precursors and instead to wind the chain of pouch precursors on a roll for transport to another location. At such other location, the connected pouch precursors can be unwound from the roll and severed to form individual pouches. 
         [0064]    In accordance with an alternative embodiment, the dome-shaped slider end stops may be oval, not circular.  FIG. 13  shows a die  108  having two oval-shaped dimples  110  and two pairs of zipper termination channels  100  and  102 , which die is one of two opposing dies used at a post-forming station for forming crushed plastic material into respective oval-shaped domes of sufficient height to stop the slider at the ends of the double zipper. The result crush zone structure is shown in  FIG. 14 . Each upper corner of the pouch has an oval-shaped rounded projection  112  on both sides of the closure  8  and a pair of dome-shaped zipper terminations  114  and  116 .  FIG. 15  shows a further alternative embodiment in which the zipper terminations  118  and  120  are oval-shaped, not circular as in  FIG. 14 . 
         [0065]    While the invention has been described with reference to various embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements 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. 
         [0066]    The method claims set forth hereinafter should not be construed to require that all operations of the method be performed in alphabetical order or in the order in which they are recited.