Abstract:
According to one aspect of the present invention, a method of preparing a film for use in forming a storage bag comprises the steps of: supplying a pre-extruded thermoplastic film, the film having opposite first and second edge portions; extruding a first base onto the first edge, wherein the first base partially overlaps the first edge; and extruding a first profile onto the first base.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates generally to reclosable pouches, and more particularly, to a method of and apparatus for manufacturing a thermoplastic storage bag.  
         BACKGROUND ART  
         [0002]    The use of reclosable thermoplastic bags for the storage of household items, such as food or other articles, is well known. An example of a reclosable thermoplastic bag is disclosed in Ausnit, U.S. Pat. No. 5,259,904. The plastic bag includes thermoplastic bag walls of consistent thickness throughout. A closure profile comprised of male and female closure profile portions are disposed on internal portions of the bag walls. Two opposing lips with grip strips are disposed directly above the closure profiles. A user may place an item in the bag, interlock the closure profiles to close the bag, and re-open the bag using the grip strips to disengage the closure profiles.  
           [0003]    There are several methods for manufacturing such reclosable thermoplastic bags. Known processes include the blown method, the cast integral method, and the cast post applied method. Bags manufactured by one of these methods may have characteristics that are different than bags made by another of these methods. Also, the production speeds are different and the costs associated with the methods vary widely.  
           [0004]    The blown method is a two-up process that extrudes a cylindrical bag web of a single thickness simultaneously and integrally with two male and two female closure profiles. The two male profiles are disposed adjacent one another on an inside surface of the cylindrical bag web and the two female profiles are disposed adjacent one another on the inside surface of the web diametrically opposite the male profiles. As the bag web is extruded, air is blown into the interior thereof so that the thermoplastic is cooled. Thereafter, the bag web is slit between adjacent male and female closure profiles to form two web portions. The profiles of each web portion are then interlocked and the web portions are simultaneously severed and sealed at spaced locations by a hot wire resulting in individual reclosable thermoplastic bags. The production speed of the blown method is relatively slow as compared to other bag-making processes owing to the fact that the blown method utilizes convective cooling as opposed to conductive cooling. A bag manufactured by this method includes a bag web with a relatively uniform thickness throughout and, typically, lips of equal lengths. Any variation in the lip length or lip offset can be difficult to control using this manufacturing method.  
           [0005]    The cast integral method includes the step of using a flat extrusion die to extrude the bag web and male and female closure profiles together in an integral fashion directly onto a temperature-controlled driven casting roll. The production speed of the cast integral process is approximately twice the speed of the blown method and the bag web extruded by the cast integral method is typically of a uniform thickness. However, because the profiles are extruded at the same time as the bag web and the profiles are located at the edges of the bag web, neck-in of the extrudate complicates the correct formation of the profiles.  
           [0006]    The cast post applied method includes the steps of using a first extrusion die to extrude the bag web onto a casting roll and using one or more additional extrusion dies or other apparatus to extrude or adhere the closure profiles onto the bag web when the bag web is disposed at a location substantially downstream of the casting roll. An example of this method is disclosed in Geiger et al., U.S. Pat. No. 4,755,248. This method has the advantage of being operable at a production speed that is higher than the other two methods. In addition, the method can be used to produce bags having readily controllable portion dimensions and thicknesses.  
           [0007]    It has been found that consumers prefer a bag having relatively thick top portions, even where a relatively high force is required to close the closure profiles of the bag, as compared with a bag having uniform wall thickness and a relatively lower required closing force. Also, it has been found that the cost required to change over a cast integral production line to a cast post applied production line (which is the typical manner in which a cast post applied line is implemented) is extremely high due to the implementation cost of the required additional hardware components. An example of thickened top portions is seen in Zieke et al, U.S. Pat. No. 4,471,789. The apparatus and method described in this patent include the use of a single base layer completely overlapping the bag film combined with the use of a rib for guiding the fingers of a user on either side of a closure profile extruded on the base.  
         SUMMARY OF THE INVENTION  
         [0008]    According to one aspect of the present invention, a method of preparing a film for use in forming a storage bag comprises the step of supplying a pre-extruded thermoplastic film, wherein the film includes opposite first and second edge portions. The method further includes the steps of extruding a first base onto the first edge, wherein the first base partially overlaps the first edge and extruding a first profile onto the first base.  
           [0009]    According to another aspect of the present invention, a method of preparing a film for use in forming a storage bag comprises the steps of supplying a film having opposite first and second edges onto a casting roll and extruding a first base member onto the film, wherein the first base member partially overlaps the first edge of the film. The method further includes the steps of extruding a second base member onto the film, wherein the second base member partially overlaps the second edge of the film, extruding a male closure profile onto the first base member, and extruding a female closure profile onto the second base member.  
           [0010]    According to yet another aspect of the present invention, a storage bag is produced by a method comprising the step of supplying a film onto a casting roll, wherein the film includes opposite first and second edges. The method further includes the step of forming first and second bases onto the casting roll while the film is in contact with the casting roll, wherein the first and second bases partially overlap the first and second edges, respectively. Still further, the method includes the steps of forming first and second closure profiles on the first and second bases, respectively, while the bases and film are in contact with the casting roll and converting the film into individual storage bags.  
           [0011]    In accordance with a still further aspect of the present invention, an apparatus for producing thermoplastic storage bags comprises a casting roll and feed assembly for supplying a bag film to the casting roll. The apparatus further includes an extrusion apparatus for extruding a pair of bases partially overlapping the film on the casting roll, wherein the extrusion apparatus further extrudes a closure profile onto the bases while the bases are on the casting roll.  
           [0012]    Still further in accordance with another aspect of the present invention, a method of producing zipper tape comprises the step of extruding first and second bases onto a casting roll, wherein the bases include a central thickened portion, a lip portion extending from one side of the central portion and being thinner than the central portion, and a gripping portion extending from the side of the central portion opposite the lip portion. The gripping portion includes a plurality of gripping ribs extending from a side of the gripping portion opposite the casting roll. The method further includes the step of extruding male and female closure profiles onto the central portions of the first and second bases respectively while the bases are in contact with the casting roll.  
           [0013]    Other aspects and advantages of the present invention will become apparent upon consideration of the following detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is an elevational view of a reclosable thermoplastic storage bag made by the process and apparatus of the present invention;  
         [0015]    [0015]FIG. 2 is an enlarged, fragmentary, sectional view taken generally along the lines  2 - 2  of FIG. 1;  
         [0016]    [0016]FIG. 3 is an isometric view of a first embodiment of the apparatus of the present invention;  
         [0017]    [0017]FIG. 4 is a side view of the embodiment of FIG. 3;  
         [0018]    [0018]FIG. 4 a  is a side view of an alternative embodiment of the present invention;  
         [0019]    [0019]FIG. 4 b  is a side view of another alternative embodiment of the present invention;  
         [0020]    [0020]FIG. 5 is an enlarged fragmentary view of the base die of FIG. 3;  
         [0021]    [0021]FIG. 6 is a bottom elevational view of an extrusion die profile plate used in the base die of the embodiments of FIGS. 3 and 7; and  
         [0022]    [0022]FIG. 7 is an isometric view of another embodiment of the apparatus of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    Referring to FIG. 1, a reclosable pouch in the form of a thermoplastic storage bag  20  comprises first and second body portions  22 ,  24  joined to one another to form first and second bag walls  26 ,  28 . The first and second bag walls  26 ,  28  are joined at first and second side portions  30 ,  32 , respectively, and at a bottom portion  34 . An opening  35  is disposed at a top portion  36  of the bag  20 . A closure mechanism  38  and two lips  40  are also disposed at the top portion  36  of the bag  20 .  
         [0024]    Referring to FIG. 2, female and male closure elements  44   a ,  44   b  of the closure mechanism  38  are disposed on opposing inside surfaces  46 ,  48  of the first and second base portions  49   a ,  49   b , respectively. First and second end portions  51   a ,  51   b  of the first and second base portions  49   a ,  49   b , respectively, are attached to and overlap first and second top portions  53   a ,  53   b  of the first and second bag walls  26 ,  28 , respectively. Each of the inside surfaces  46 ,  48  further includes a plurality of gripping ribs  37  located near the opening  35  of the bag  20 . However, the number of gripping ribs  37  may vary and can range from none to six or more on each first and second base portions  49   a ,  49   b.    
         [0025]    The male closure element  44   b  comprises a base  58  integral with flanking side members  54  and  56  and an arrow-shaped male engagement member  60  that extends from the base  58 . The female element  44   a  comprises a base  62  with a C-shaped female profile member  64  extending therefrom, wherein the female element  44   a  is adapted to receive the male element  44   b  when pressure is exerted on the closure elements by a user&#39;s finger(s) during closing of the bag. The side members  54  and  56  are of a sufficient size and proximity to the male engagement member  60  such that the side members  54  and  56  move together with the male engagement member  60  when the male engagement member  60  and female profile member  64  are engaged and disengaged. The side members  54  and  56  also have a height which is less than the height of the male engagement member  60 , and the members  54  and  56  extend beyond tips  68  of the female profile member  64  when the male engagement member  60  is engaged with the female profile member  64 . Thus, at such time, the tips  68  of the female profile member  64  reside between the side members  54  and  56  and the male engagement member  60 . However, this is simply one preferable design of a male/female profile pair, any design know in the art could be utilized and still be within the scope of this invention.  
         [0026]    Referring now to FIGS. 3 and 4, an apparatus  70  for producing thermoplastic bags at a high speed includes a rotating and preferably driven casting roller  72  preferably in contact with a rotating secondary rotating roller  74 . Alternatively, the casting roller  72  may be idle, in which case, the film  76  is pulled by another driven roller (not shown) further downstream. The film web or film  76  is preferably fed from a roll (not shown) into contact with the secondary roller  74 , the film  76  is wrapped around an outer surface  74   a  of the secondary roller  74 , and is thereafter drawn between the casting roller  72  and the secondary roller  74 , the driving rotation of the casting roller  72  pulling the film  76 . As the film  76  is drawn between the casting roller  72  and the secondary roller the casting roller  72  and secondary roller  74  may not contact each other; rather the casting roller  72  and secondary roller  74  are simply in close proximity with each other. In another alternative, shown in FIG. 4 a  the film  76  may come from a film extruder  77  disposed upstream from the casting roller  72 . In such an embodiment the film  76  is extruded onto a third roller  79  which helps to form the film  76  and direct the film  76  to the secondary roller  74 . As would be known by one of skill in the art this process may include further steps, such as cutting off the edges of the film  76  after extrusion but prior to contact with the secondary roller. Also, the film in such a process could be produced via a cast rather than extrusion process. In yet other alternative embodiments, the process may include another roller (not shown) further downstream from the casting roller  72  where chilling of the film  76 , bases  49   a ,  49   b  and profiles  44   a ,  44   b  occurs.  
         [0027]    The apparatus  70  further includes first and second base extrusion dies  78   a ,  78   b  disposed to extrude the bases  49   a ,  49   b  in a position that allows the bases  49   a ,  49   b  to overlap edges  76   a ,  76   b  of the film  76  by approximately 0.125 inch (3.175 mm). In an alterative embodiment (not shown), the apparatus  70 , may include only one extrusion base die  78   a  or  78   b . In such an embodiment, the apparatus would be used to prepare a film  76  that would be combined with another such film  76  to create a storage bag or used to create a storage bag with only one of the profiles disposed on a base. The apparatus  70  further includes pinning air knives  80   a ,  80   b  positioned to pin the bases  49   a ,  49   b  to the film  76  and blow a jet of air onto the freshly extruded bases  49   a ,  49   b , thus beginning the cooling process. In particular, the pinning air jets  80   a ,  80   b  are directed onto the portion of the bases  49   a ,  49   b  overlapping the film  76 . Alternatively, the air knives  80   a ,  80   b  could be replaced by water jets (not shown) to pin the bases  49   a ,  49   b  to the film  76  and begin the cooling process. In another alternative, the air knives  80   a ,  80   b  could be replaced by shaped rollers (not shown) that rotate and pin the bases  49   a ,  49   b  to the film  76 . The apparatus  70  further includes profile extrusion dies  82   a ,  82   b  disposed adjacent the air jets  80   a ,  80   b  to extrude the profiles  44   a ,  44   b  onto the bases  49   a ,  49   b , respectively. In an alternative configuration (not shown), each pair of base extrusion dies  49   a ,  49   b  and/or profile extrusion dies  44   a ,  44   b  could be combined into a single die wherein the bases and/or profiles could be extruded as one combined piece and then cut apart or could be extruded as two separate pieces from the same die.  
         [0028]    The method of operation of the apparatus  70  includes the steps of feeding molten polymer to the base extrusion dies  78   a ,  78   b  and profile extrusion dies  82   a ,  82   b  by way of an extruder or melt pump. As the casting roll  72  rotates, the film  76 , as shown in FIG. 5, is fed under the base extrusion dies  78   a ,  78   b  and the bases  49   a ,  49   b  are extruded onto the casting roller  72  and film  76  with an overlap of approximately 0.125 inch (3.175 mm) where the bases  49   a ,  49   b  are laid over the film  76 . The bases are preferably between about 0.25 inch (6.35 mm) and 2.00 inches (50.8 mm), and most preferably about 1.00 inch (25.4 mm). The overlap between the film  76  and the bases  49   a ,  49   b  is also variable in this invention, and can range, with, for example a 1.00 inch (25.4 mm) wide base, preferably between about 0.0625 inch (1.5875 mm) to 0.9375 inches (23.813 mm), and most preferably about 0.125 inch (3.175 mm). However also, it has been found that arranging the overlap so that the film  76  is under the portion of the bases  49   a ,  49   b  where the profiles  44   a ,  44   b  are attached, discussed below, also provides a bag with acceptable strength and bonding. The amount of overlap varies based upon the width of the bases  49   a ,  49   b , but the only controlling factors in the variation are that the overlap is only partial and not complete and that the overlap is enough to ensure a bond between the bases  49   a ,  49   b  and the film  76  during use as a storage bag.  
         [0029]    Referring again to FIGS. 3-5 the method thereafter includes the step of pinning the overlapping portion of the bases  49   a ,  49   b  to the film  76 . Since the bases  49   a ,  49   b  are extruded in a molten form the heat from the cooling of the base  49   a ,  49   b  will begin the bonding process between the base  49   a ,  49   b  and the film  76  once contact is made. In order to encourage the bonding process, the air jets  80   a ,  80   b  shoot a stream of air onto the bases  49   a ,  49   b  pushing them onto the film and increasing the bonding therebetween. Thereafter, the profiles  44   a ,  44   b  are extruded from the profile extrusion dies  82   a ,  82   b  onto the central portions  84  of the bases  49   a ,  49   b . Because of the molten nature of the profiles  44   a ,  44   b  when extruded, the profiles  44   a ,  44   b  are bonded with the still semi-molten bases  49   a ,  49   b  by contact therewith. The combined film  76 , bases  49   a ,  49   b , and profiles  44   a ,  44   b  are then cooled as they continue around the casting roller  72  and are thereafter removed and processed into bags by means known in the art. Alternatively, the casting roller  72  may be temperature controlled to allow further chilling after the extrusion of the profiles  44   a ,  44   b  and bases  49   a ,  49   b . Also alternatively, as noted above, such chilling or cooling of the film  76 , bases  49   a ,  49   b  and profiles  44   a ,  44   b  may take place on an additional roller (not shown).  
         [0030]    An alternative roller setup and method is shown in FIG. 4 b . This embodiment includes a first casting roller  72  and a second casting roller  73 . Preferably, the first casting roller is driven, however both or neither of the casting roller  72 ,  73  may be driven. This embodiment further includes first secondary roller  74  and second secondary roller  75  associated with the first casting roller  72  and second casting roller  73  respectively. The optional last roller in such an embodiment is a transfer roller  85  that is disposed downstream of the first casting roller  72  and upstream of the second casting roller  73  in order to direct the film  76  between the first and second casting rollers  72 ,  73 . The base extrusion dies  78   a ,  78   b  and pinning jets  80   a ,  80   b  are associated with the first casting roller  72  while the profile extrusion dies  82   a ,  82   b  are associated with the second casting roller  73 . Therefore, in use the bases  49   a ,  49   b  are applied to the film  76  on the first casting roller  72 , the film  76  and bases  49   a ,  49   b  combined are then transferred to the second casting roller  73  where the profiles  44   a ,  44   b  are applied.  
         [0031]    Referring now to FIG. 6, an enlarged view of an extrusion die profile plate  83  of one of the base dies  78   a  is shown. The extrusion die profile plate  83  defines three primary areas that correspond to three areas of the base  49   a : a thickened central portion  84 , an overlap portion  86  extending from a first end of the central portion  84 , and a gripping portion  88  extending from a second end of the central portion  84  opposite the overlap portion  86 . The three portions  84 ,  86 ,  88  are integral with each other and form a flat bottom side  90  and a top side  92 . The top side  92  of the gripping portion  88  includes a plurality of optional gripping ribs  37  extending outwardly from the top side  92 . The thickened central portion  86  is thicker than the other portions to accept the extruded profiles  44   a ,  44   b  thereon and the overlap portion  86  is thinner than the other portions to facilitate attachment of base  49   a  to the film  76 . This however, is simply one embodiment of the base die  78 . Other embodiments may include none or one of the gripping ribs  78 , and/or the central portion  84  may be the same thickness as other portions  86 ,  88  as seen in the base shown in FIG. 2, and/or the overlap portion  86  may be the same thickness as the other portions  84 ,  88 .  
         [0032]    Referring now to FIG. 7, an apparatus  270  for forming zipper tape is shown. The apparatus  270  is similar to the apparatus  70  described in relation to FIGS. 3-5, except that the secondary roller  74  and the film  76  are omitted. The bases  249   a ,  249   b  are extruded from the base extrusion dies  278   a ,  278   b  onto the casting roller  272 . The base extrusion dies  278   a ,  278   b  are identical to the extrusion base die pictured in FIG. 6. The air jets  280   a ,  280   b  are positioned to pin the bases  249   a ,  249   b  onto the casting roller  272  whereby the bases  249   a ,  249   b  are positioned to receive the profiles  244   a ,  244   b  from the profile extrusion dies  282   a ,  282   b . Once the profiles  244   a ,  244   b  are extruded onto the bases  249   a ,  249   b , the complete zipper tape sections  296   a ,  296   b  are cooled on the casting roller  272  and thereafter removed from the casting roller  272 . The zipper tape sections  296   a ,  296   b  may be utilized further downstream from the casting roller  272 , or stored, either separately or combined, for later use. In another embodiment of a zipper tape apparatus (not shown) the bases  249   a ,  249   b  could be extruded as a single piece that preferably includes opposing bases  249   a ,  249   b  and includes a connection piece between the overlap portions  286   a ,  286   b . However, other arrangements can be within the scope of the present invention.  
       Industrial Applicability  
       [0033]    The methods and apparatus described herein advantageously allow the user of this invention a simple and cost effective manner by which to produce bags having a thicker tops then bag walls. This type of bag is highly preferred by consumers and thus demand is high for this type of bag. This invention enables the user to convert production lines that had been producing a uniform thickness bag into a line producing bags with thickened top portions. Furthermore, this invention enables the user to produce zipper tape on those same lines without further modification, but by simply removing the film supply. One advantage of this invention is that it only requires the addition of two small base extrusion dies to upgrade a line compared to the much greater cost of an entire film with thicker top die that would be much larger. Also, this invention allows the use of a pre-extruded film thus allowing film to be produced on higher speed lines before hand. The partial overlap design also allows the inclusion of gripper ribs directly in the bases thus giving the user of a bag produced by these methods a firm gripping surface.  
         [0034]    Numerous modifications to the present invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is presented for the purpose of enabling those skilled in the art to make and use the invention and to teach the best mode of carrying out the same. The exclusive rights to all modifications that come within the scope of the appended claims are reserved.