Abstract:
Methods for forming a thermoplastic film with an attached closure strip are disclosed. The thermoplastic film can then be used to produce zippered reclosable plastic bags. The methods include providing a thermoplastic film web having a sealing surface and providing a closure strip having a binding surface, both being maintained in a non-melted condition at room temperature. A heated thermoplastic binder layer is then extruded and positioned between the sealing surface of the film web and the binding surface of the closure strip very quickly after extrusion. The hot freshly extruded binder layer transfers enough heat to the closure strip and to the film web to melt the binding surface of the closure strip and sealing surface of the film web. Pressure is then applied to the film web and the closure strip to seal the closure strip to the film web. An apparatus for practicing the method at high speed is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     The present invention relates to methods for attaching closure members, i.e., a zipper tape, to a plastic film web. It appears especially well suited for laminating zipper elements to plastic storage bags so as to form reclosable storage bags. 
     The prior art has developed reclosable plastic storage bags for use in protecting food items and for other storage purposes. A film of a plastic such as polyethylene is provided with a closure member (one half of a zipper) on its opposed ends. The film is then folded to bring the zipper halves adjacent to each other, with the sides of the bag then being heat sealed. The bag can then be opened or closed in the usual manner by interlocking the zipper elements. 
     One difficulty experienced by manufacturers of reclosable plastic storage bags involves the joining of the closure members to the bag film web portion. Care must be taken to ensure that the closure members are positioned properly on the bag film web. Further, there should be no wrinkles or creases in the area of the bag in which the fastener profiles and bag film web are joined. 
     A variety of methods are known for attaching closure members to a plastic film web prior to forming reclosable plastic storage bags. One approach has been to form the bag film web and the closure members in a single extrusion operation. See e.g. U.S. Pat. Nos. 3,338,284 and 3,852,386. The disclosure of these publications and of all other publications referred to herein are incorporated by reference as if fully set forth herein. 
     A second approach utilizes an adhesive, such as a strip of tape or glue, to join a closure member to a bag film web. For example, U.S. Pat. No. 4,101,355 discloses a reclosable bag film forming process wherein a web and closure member are joined by a liquid adhesive which is supplied by an applicator having a nozzle. After the adhesive is applied, the web and closure members are pressed together by a presser roll and a backing roll. See also U.S. Pat. Nos. 4,341,575 and 3,226,787. 
     A third approach involves the use of a pre-formed bag film web and a pre-formed closure member which are drawn from separate stock rolls. The bag film web and/or closure member are then heated and joined. For example, U.S. Pat. No. 3,846,209 discloses a method for producing a closure member-containing bag film wherein a pre-formed plastic film is fed from a stock roll into a sealing station. A separate closure strip from a second stock roll is also fed into the sealing station. In the sealing station, the closure strip and plastic film are welded together by a pair of heating bars. 
     A fourth approach uses a pre-formed bag film web drawn from a supply roll and then joined to a relatively freshly extruded closure member. For example, U.S. Pat. No. 3,904,468 discloses a method of making a reclosable bag film wherein a web of bag film material is unwound from a stock roll and then transferred to a heating station having a heating roll on which the film is heated to a desired temperature. The film is then transferred to a heated joining roll wherein the film is joined to the freshly extruded fastener profile strips. See also U.S. Pat. Nos. 4,279,677 and 4,582,549. 
     Another variation on this fourth approach is disclosed in U.S. Pat. No. 4,555,282 which discloses a method of bonding a closure member to a bag film web wherein a closure member having a base portion and a fastener profile portion is extruded shortly before being bonded to a bag film web. Intermediate the extrusion of the closure member and its joinder to the bag film web, the fastener profile portion of the closure member is cooled (and thereby solidified and stabilized) while the base portion is left heated (and thereby remains thermoplastic) when the closure member is joined to the film. 
     U.S. Pat. No. 4,306,924 discloses another variation on this fourth approach wherein the film web is extruded on to a casting roll to join an already formed closure member. 
     A fifth approach involves the.extrusion of a bag film web and a closure member in close proximity to each other, and the joinder of the bag film web and closure member to each other shortly after extrusion. For example, U.S. Pat. No. 4,428,788 discloses a method for forming a reclosable bag wherein a film, a tape, and a closure member are extruded by three separate dies. The film, tape and closure member dies are positioned so that the film, tape and closure members contact each other while still at a temperature of above 200° F. A chill roll is provided for cooling the film, tape and closure members. 
     U.S. Pat. No. 4,295,915 discloses an apparatus for forming a reclosable bag film wherein a fastener profile and its base strip are extruded integrally, and then joined to a film web. The die for extruding the bag film web is disposed adjacent to the fastener die block so that the fastener profile and bag film are joined shortly after both are extruded. See also U.S. Pat. Nos. 3,462,332 and 4,522,678. 
     A sixth approach involves the extrusion of a bag film web having a relatively thinner first portion and a relatively thicker second portion, and the separate extrusion of male and female fastener profiles that are joined to the thicker second portions before the thicker second portions have cooled. An example of this approach is found in U.S. Pat. No. 4,755,248. 
     A seventh approach involves attaching a closure member for a storage bag to the bag via an intermediate heat setting adhesive. See eg. U.S. Pat. Nos. 5,749,658 and 5,827,163. 
     However, to keep the costs of producing such bags to the minimum it is desirable to use high speed equipment to form these bags. Prior methods may not achieve a consistent seal between the closure members and the film web (and may introduce tension differences across the film web) when run at a very high speed. In addition, room for improvement exists in the fabrication of a reclosable bag which can be manufactured to consistently high quality standards. 
     There is therefore still a need for improved methods of attaching closure elements to plastic film such as that used in forming reclosable storage bags. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides methods for forming a thermoplastic film having a closure strip. In one method, one provides a thermoplastic film web having a sealing surface, the temperature of the film web being below a melting temperature of the film web. One also provides a thermoplastic closure strip having a binding surface, the temperature of the closure strip being below a melting temperature of the closure strip. 
     One extrudes a thermoplastic binder layer, and then positions the binder layer between the sealing surface of the film web and the binding surface of the closure strip. The binder layer contacts the sealing surface of the film web before the binder layer has cooled to a temperature below the melting temperature of the film web and the binder layer also contacts the binding surface of the closure strip before the binder layer has cooled to a temperature below the melting temperature of the closure strip. Pressure applied to the film web and the closure strip binds the closure strip and film web to the binder layer. 
     In preferred forms there can be multiple closure strips (such as interlockable male and female strips), multiple binder layers (one binding each of the strips to the web), and the invention can be practiced on a folded web at opposite ends of the web. 
     In another aspect there is a first cylindrical roller having a surface and an axis of rotation and a second cylindrical roller having a surface and an axis of rotation, the axis of the first roller and the axis of the second roller being substantially coplanar, the first roller and the second roller being aligned in spaced apart relationship such that a pinch area is formed between the surface of the first roller and the surface of the second roller. 
     One feeds a continuous length of a thermoplastic film web having a sealing surface, such that the film web wraps on the surface of the first roller, while the temperature of the film web is below a melting temperature of the film web; and feeds a continuous length of a thermoplastic closure strip having a binding surface such that the closure strip wraps on the surface of the second roller, while the temperature of the closure strip is below a melting temperature of the closure strip. 
     One extrudes a thermoplastic binder layer, positions the binder layer between the sealing surface of the film web and the binding surface of the closure strip, and feeds the film web, binder layer and closure strip through the pinch area such that the binder layer contacts the sealing surface of the film web before the binder layer has cooled to a temperature below the melting temperature of the film web. The binder layer contacts the binding surface of the closure strip before the binder layer has cooled to a temperature below the melting temperature of the closure strip. 
     In another method one forms a folded thermoplastic film having a female closure strip and a male closure strip at opposed ends of the film. One step is to provide a first cylindrical roller having a surface and an axis of rotation and a second cylindrical roller having a surface and an axis of rotation, the axis of the first roller and the axis of the second roller being substantially coplanar, the first roller and the second roller being aligned in spaced apart relationship such that a first pinch area is formed between the surface of the first roller and the surface of the second roller. 
     Another step is to provide a third cylindrical roller having a surface and an axis of rotation and a fourth cylindrical roller having a surface and an axis of rotation, the axis of the third roller and the axis of the fourth roller being substantially coplanar, the third roller and the fourth roller being aligned in spaced apart relationship such that a second pinch area is formed between the surface of the third roller and the surface of the fourth roller. 
     One then feeds a continuous length of a folded thermoplastic film web having a first sealing surface on a first edge spaced apart from a fold line of the film web and a second sealing surface on a second edge spaced apart from the fold line of the film web such that the first edge of the film web wraps on the surface of the first roller and the second edge of the film web wraps on the surface of the third roller, while the temperature of the film web is below a melting temperature of the film web. One also feeds a continuous length of a thermoplastic female closure strip having a binding surface, such that the female closure strip wraps on the surface of the second roller, while the temperature of the female closure strip is below a melting temperature of the female closure strip. 
     Another step is to extrude a first thermoplastic binder layer and then position the first binder layer between the first sealing surface of the film web and the binding surface of the female closure strip. One then feeds the film web and the female closure strip through the first pinch area such that the first binder layer contacts the first sealing surface of the film web before the first binder layer has cooled to a temperature below the melting temperature of the film web and the first binder layer contacts the binding surface of the female closure strip before the first binder layer has cooled to a temperature below the melting temperature of the female closure strip. 
     One also feeds a continuous length of a thermoplastic male closure strip having a binding surface, such that the male closure strip wraps on the surface of the fourth roller, while the temperature of the male closure strip is below a melting temperature of the male closure strip. 
     Another step is to extrude a second thermoplastic binder layer and position the second binder layer between the second sealing surface of the film web and the binding surface of the male closure strip. One then feeds the film web and the male closure strip through the second pinch area such that the second binder layer contacts the second sealing surface of the film web before the second binder layer has cooled to a temperature below the melting temperature of the film web and the second binder layer contacts the binding surface of the male closure strip before the second binder layer has cooled to a temperature below the melting temperature of the male closure strip. 
     In another aspect the invention provides an apparatus for forming a thermoplastic film having a closure strip. There is a cylindrical lamination roller having a surface and an axis of rotation. There is also a cylindrical lay-on roller having a surface and an axis of rotation. The axis of the lamination roller and the axis of the lay-on roller are substantially coplanar, and the lamination roller and the lay-on roller are aligned in spaced apart relationship such that a pinch area is formed between the surface of the lamination roller and the surface of the lay-on roller. 
     There is also a web feed roller for feeding a continuous length of a thermoplastic film web having a sealing surface, the web feed roller being positioned such that the film web can wrap on the surface of the lamination roller after leaving the web feed roller. Another element is a closure strip feed roller for feeding a continuous length of a thermoplastic closure strip having a binding surface, the closure strip feed roller being positioned such that a closure strip can wrap on the surface of the lay-on roller. 
     An extruder can extrude a heated thermoplastic binder layer, the extruder including a die block with an opening, and the extruder being positioned such that the opening in the die block is adjacent the pinch area so as to be suitable to direct a heated binder layer between a nonheated closure strip and a nonheated film web. 
     The above methods and equipment permit the production of film webs with closure members assembled thereon at very high speeds (e.g. about 200 linear feet per minute). When the methods are used to form bags, the seal between the bag and zipper will be highly reliable and consistently formed (thus permitting an airtight structure). 
     Particularly preferred thermoplastics for the film web are low or high density polyethylene, linear low density polyethylene, polypropylene, nylon, and interpolymers of ethylene and one or more monomers copolymerizable therewith. 
     It is particularly preferred to have the closure members formed from the same thermoplastic as the film web. However, this is not essential. It is also preferred that the binder layer be formed from the same thermoplastic as the film web. However, this is also not essential. 
     It is particularly important that the binder layer thickness be sufficiently great so as to carry enough heat to create a melted region adjacent the binder layer when the binder layer contacts the closure members and the film web. At the same time, the binder layer should be sufficiently thin so as to create a stable cooled structure in under a second after the binder layer is pressed between a closure member and the film web. 
     It is an advantage of the present invention to provide a rapid method for attaching prefabricated thermoplastic closure members to prefabricated thermoplastic film webs traveling at high speeds. 
     This and still other advantages of the present invention will be apparent from the description of the preferred embodiments which follow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a reclosable plastic bag made in accordance with the present invention; 
     FIG. 2 is a partial cross sectional view of the closure arrangement of FIG. 1, albeit when the bag is closed; 
     FIG. 3 is a perspective view of an apparatus in accordance with the invention; 
     FIG. 4 is a side view of the apparatus of FIG. 3; and 
     FIG. 5 is a side view of an alternative apparatus in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Flexible bag  10  is made of first and second opposed panel sections  12 ,  13  from a polymeric film. The sections are heat sealed together along a pair of side edges  15 ,  16 , and a bottom edge  17  in order to form a pocket  19  within the interior of the bag  10 . The pocket  19  may be used to hold a product  18 , such as a variety of “left over” edible food substances, or non-edible products. Access to the interior of the bag  10  is provided through an opening  14 . 
     Sections  12 , 13  may be made of any thermoplastic resin capable of forming a flexible film. Specific thermoplastic resinous films are chosen to provide adequate tensile strength, tear strength, pressure resistance, impact strength, and the like, for the end use desired, at minimal cost for the selected use. Low or high density polyethylene, linear low density polyethylene, polypropylene, nylon, and interpolymers of ethylene and one or more monomers copolymerizable therewith are typically preferred. Suitable thicknesses generally fall within the range of 0.025 mm to 0.254 mm, preferably from about 0.038 mm to about 0.114 mm. The film can be formed from a single layer of thermoplastic resin or it may be formed as a multilayer structure. 
     Flexible bag  10  includes a zipper type closure  21  extending from side edge  15  to side edge  16 . Female closure strip  20  includes an elongated inward profile  22  attached to or integrally formed with female closure strip  20 , and the male closure strip  30  includes an elongated projecting profile  32  attached to or integrally formed with male closure strip  30 . The inward profile  22  and the projecting profile  32  cooperate by snap interlocking to allow bag  10  to be opened and re-closed in the usual manner. 
     As illustrated in FIG. 2, the projecting profile  32  has a cross section which is generally tree-shaped including an expanded head portion  33   a  and a narrower trunk portion  33   b . The locking structure of the inward profile  22  includes first and second arcs  23   a  and  23   b  with a cross section which mechanically engage the head  33   a  of the male projecting  32  to re-close bag  10 . 
     The female closure strip  20  also includes a flange portion  24 , and the male closure strip  30  also includes a flange portion  34 . The inner surface  26  of the flange portion  24  is configured for attachment to the panel  12  of the bag  10 , and the inner surface  36  of the flange portion  34  is configured for attachment to the panel  13  of the bag  10 . The zipper  21  is permanently attached to bag  10  by adhering the inner surface  26  of the flange portion  24  of the female closure strip  20  to the panel  12  via binder layer  28   a , and adhering the inner surface  36  of the flange portion  34  of the male closure strip  30  to the panel  13  via binder layer  28   b.    
     The female closure strip  20  and the male closure strip  30  of the zipper  21  can be made of any thermoplastic resin suitable for forming a reclosable bag zipper. Thermoplastic resins preferred for use in forming the zipper of the present invention include low or high density polyethylene, linear low density polyethylene, polypropylene, nylon, and interpolymers of ethylene and one or more monomers copolymerizable therewith. 
     Suitable thicknesses for the flange portion  24  of the female closure strip  20  and for the flange portion  34  of the male closure strip  30  generally fall within the range of from about 0.076 mm to 0.305 mm, preferably from about 0.152 mm to 0.229 mm. Again, the female closure strip  20  and the male closure strip  30  can be formed from a single layer of thermoplastic resin or they may be formed as a multilayer structure having a plurality of layers. 
     The binder layer  28   a  and the binder layer  28   b  may comprise any thermoplastic resin suitable for bonding the male and female closure members and the film used to form the opposed panel sections  12 , 13 . Thermoplastic resins suitable for use in the binder layer  28   a  and the binder layer  28   b  of the present invention include low or high density polyethylene, linear low density polyethylene, polypropylene, nylon, and interpolymers of ethylene and one or more monomers copolymerizable therewith. 
     Suitable thicknesses for the binder layers  28   a / 28   b  generally fall within the range of about 0.025 mm to about 0.152 mm, preferably from about 0.025 mm to 0.102 mm. The binder layers can be formed from a single layer of thermoplastic resin or may be formed as a multilayer structure having a plurality of layers. 
     The width of the binder layer  28   a  and the binder layer  28   b  (as measured in a direction extending from the bottom edge  17  of the bag  10  toward the zipper  21 ) generally fall within the range of about 1.27 mm to 6.35 mm, preferably from about 3.175 mm to 4.445 mm. 
     FIGS. 3 and 4 show an apparatus that may be used to manufacture a bag film with closure members (one half of a zipper) on its opposed ends. The bag film can then be folded to bring the zipper halves adjacent to each other and heat sealed along the side edges to form a reclosable bag  10 . 
     Lamination apparatus  40  includes a bag film supply roll  42  for supplying a bag film web  41  wound into a roll, a female closure strip supply roll  47   a  for supplying the female closure strip  20 , a male closure strip supply roll  47   b  for supplying the male closure strip  30 , a binder layer extruder  45   a  for supplying the binder layer  28   a , a binder layer extruder  45   b  for supplying binder layer  28   b , and a lamination roller  44  and a lay-on roller  43  which cooperate to squeeze binder layer  28   a  between one edge of bag film web  41  and the inner surface  26  of the flange portion  24  of the female closure strip  20  and to squeeze binder layer  28   b  between an opposite edge of bag film web  41  and the inner surface  36  of the flange portion  34  of the male closure strip  30 . 
     The binder layer extruders  45   a  and  45   b  may include a hopper (not shown) for receiving plastic material, a body (not shown) which contains a heating means for heating the plastic material into a molten state, and a screw auger (not shown) for advancing the molten plastic material to and through die blocks  45   c  and  45   d . The die blocks  45   c  and  45   d  include a die slot (not shown) configured such that the binder layers  28   a  and  28   b  extruded from the extruders  45   a  and  45   b  have a cross-sectional shape similar to the cross-sectional shape of the die slot. 
     The bag film web  41  is prefabricated using known techniques such as extrusion and is rolled up for storage on the bag film supply roll  42 . The female closure strip  20  is also prefabricated using known techniques such as extrusion and is rolled up for storage on the female closure strip supply roll  47   a . The male closure strip  30  is likewise prefabricated using known techniques such as extrusion and is rolled up for storage on the male closure strip supply roll  47   b . The bag film web  41  is fed from the bag film supply roll  42  at a temperature that is below the melting temperature of the film web  41  (typically room temperature) and then wraps on the lamination roller  44  to stabilize the bag film web  41 . 
     At the same time, the female closure strip  20  is fed from the female closure strip supply roll  47   a  at a temperature that is below the melting temperature of the female closure strip  20  (preferably room temperature) and the male closure strip  30  is fed from the male closure strip supply roll  47   b  at a temperature that is below the melting temperature of the male closure strip  30  (preferably room temperature). The female closure strip  20  and the male closure strip  30  then wrap opposite ends of the lay-on roller  43 . 
     The binder layer extruders  45   a  and  45   b  are positioned in the apparatus  40  such that binder layers  28   a  and  28   b  are placed on the inner surface  26  of the flange portion  24  of the female closure strip  20  and the inner surface  36  of the flange portion  34  of the male closure strip  30  respectively just prior to the female closure strip  20  and the bag film web  41  being squeezed between the lay-on roller  43  and the lamination roller  44  and just prior to the male closure strip  30  and the bag film web  41  being squeezed between the lay on roller  43  and the lamination roller  44 . During operation of the binder layer extruders  45   a  and  45   b , the drawdown of the binder layers  28   a  and  28   b  is about 11.5 cm from a 1.9 cm width die. 
     The temperature of the binder layers  28   a  and  28   b  at the die blocks  45   c  and  45   d  is typically about 127° C. The binder layers  28   a  and  28   b  transfer enough heat to the flange portion  24  of the female closure strip  20  and the flange portion  34  of the male closure strip  30  respectively to melt a surface of flange portion  24  of the female closure strip  20  and a surface of flange portion  34  of the male closure strip  30 . The binder layers  28   a  and  28   b  also transfer enough heat to the edges of the bag film web  41  to melt the edges of the bag film web  41 . 
     It is particularly important that the binder layer thickness and width be sufficiently great so as to carry enough heat to create a melting surface adjacent the binding layers  28   a  and  28   b . At the same time, the binding layers  28   a  and  28   b  must be sufficiently thin so as to create a stable cooled structure in a short period of time (typically under one second after the binding layers  28   a  and  28   b  contact the edges of the bag film web  41 ). Likewise, the die blocks  45   c  and  45   d  of the binder layer extruders  45   a  and  45   b  must be located sufficiently near the female closure strip  20 , the male closure strip  30 , and the edges of the bag film web  41  so that the binder layers  28   a  and  28   b  retain enough heat after moving away from the die blocks  45   c  and  45   d  such that the binder layers  28   a  and  28   b  melt the female closure strip  20 , the male closure strip  30 , and the edges of the bag film web  41 . 
     The pressure applied by the lay-on roller  43  and the lamination roller  44  keeps the melted flange portion  24  of the female closure strip  20  in contact with the melted binder layer  28   a  and keeps the melted portion of the bag film web  41  in contact with the melted binder layer  28   a  at that point in the web path such that the female closure strip  20  is sealed to one longitudinal edge of the base film web  41  when the melted flange portion  24  of the female closure strip  20 , the melted binder layer  28   a  and the melted portion of the bag film web  41  cool. Likewise, the pressure applied by the lay on roller  43  and the lamination roller  44  keeps the melted flange portion  34  of the male closure strip  30  in contact with the melted binder layer  28   b  and keeps the melted portion of the bag film web  41  in contact with the melted binder layer  28   b  at that point in the web path such that the male closure strip  30  is sealed to the other longitudinal edge of the base film web  41  when the melted flange portion  34  of the male closure strip  30 , the melted binder layer  28   b  and the melted portion of the bag film web  41  cool. 
     For example, the apparatus  40  can seal a polyethylene female closure strip  20  having a flange portion  24  with a thickness of about 0.190 mm to a polyethylene bag film web  41  having a thickness of about 0.076 mm with a polyethylene binder layer  28   a  having a thickness of about 0.063 mm and a width (as measured in a direction extending from the bottom edge  17  of the bag  10  toward the zipper  21 ) of about 3.81 mm. Because the dimensions of the polyethylene binder layer  28   a  are small compared to the dimensions of the flange portion  24  of the female closure strip  20  and the dimensions of the melted portion of the bag film web  41 , the melted polyethylene binder layer  28   a  cools quickly. For instance, at bag film web speeds of 200 feet per minute, the melted polyethylene binder layer  28   a  drops below the melt temperature within 10 inches of the squeeze point between the lay on roller  43  and the lamination roller  44 . This corresponds to about 0.25 seconds. 
     The lamination apparatus  40  and associated lamination methods provide advantages over prior approaches to attaching closure members to a plastic film web prior to forming reclosable plastic storage bags. For example, the lamination apparatus  40  and methods introduce less tension differences across the film web compared to “hot shoe” lamination methods where the film web and closure members are pulled between two hot shoes. In addition, the lamination apparatus  40  and methods result in more consistent film web tracking thereby improving consistency of the seal between the closure members  20 , 30  and the film web  41 . 
     FIG. 5 shows an alternative lamination apparatus  50  to obtain a folded film  63  with a female closure strip  20  and a male closure strip  30  at opposite edges of a folded film web  51 , the lamination apparatus  50  includes: a folded film supply roll  52  for supplying a folded film web  51  wound in a roll; a zipper supply roll  57  for supplying a zipper  21  comprising joined female closure strip  20  and male closure strip  30 ; a separation shift  54  for separating the female closure strip  20  and the male closure strip  30  after the zipper  21  is fed from the zipper supply roll  57 ; a binder layer extruder  55   a  with a die block  55   c  for supplying binder layer  28   a ; a binder layer extruder  55   b  with a die block  55   d  for supplying binder layer  28   b ; a female closure strip lamination roller  53   a  and a female closure strip lay on roller  59  for squeezing binder layer  28   a  between one edge  51   a  of the folded film web  51  and the inner surface  26  of the flange portion  24  of the female closure strip  20 ; and a male closure strip lamination roller  53   b  and a male closure strip lay on roller  60  for squeezing binder layer  28   b  between an opposite edge  51   b  of the folded film web  51  and the inner surface  36  of the flange portion  34  of the male closure strip  30 . 
     The folded film web  51  is prefabricated using known techniques, such as extrusion and subsequent film folding, and is rolled up for storage on the folded film web supply roll  52 . The female closure strip  20  and the male closure strip  30  are also prefabricated using known techniques such as extrusion and are joined and rolled up for storage on the zipper supply roll  57 . 
     The folded film web  51  is then fed at a temperature that is below the melting temperature of the folded film web  51  (typically room temperature) from the folded film web supply roll  52  and at the same time, the zipper  21  is fed at a temperature that is below the melting temperature of the zipper  21  (typically room temperature) from the zipper supply roll  57 . The zipper  21  is fed around stabilizing guide roller  61   a  into the separation shaft  54  to uncouple the female closure strip  20  and the male closure strip  30 . After uncoupling, the female closure strip  20  and the male closure strip  30  are processed separately. 
     The female closure strip  20  wraps stabilizing guide rollers  61   b ,  61   d  and  61   f  and then wraps the female closure strip lay on roller  59 . The binder layer extruder  55   a  is positioned in the lamination apparatus  50  such that binder layer  28   a  is placed on the inner surface  26  of the flange portion  24  of the female closure strip  20  just prior to the female closure strip  20  and the edge  51   a  of the folded film web  51  being squeezed between the female closure strip lay on roller  59  and the female closure strip lamination roller  53   a , which also serves to open one end of the folded film web  51 . 
     The binder layer  28   a  transfers enough heat to the inner surface  26  of the flange portion  24  of the female closure strip  20  and the edge  51   a  of the folded film web  51  to melt the flange portion  24  of the female closure strip  20  and the edge  51   a  of the folded film web  51 . Pressure applied by the female closure strip lay on roller  59  and the female closure strip lamination roller  53   a  keeps the melted flange portion  24  of the female closure strip  20  in contact with the melted binder layer  28   a  and keeps the melted portion of the folded film web  51  in contact with the melted binder layer  28   a  at that point in the web path such that the female closure strip  20  is sealed to edge  51   a  of the folded film web  51  when the melted flange portion  24  of the female closure strip  20 , the melted binder layer  28   a  and the melted portion of the folded film web  51  cool. 
     The male closure strip  30  wraps stabilizing guide rollers  61   c ,  61   e ,  61   g  and then wraps the male closure strip lay on roller  60 . The binder layer extruder  55   b  is positioned in the lamination apparatus  50  such that binder layer  28   b  is placed on the inner surface  36  of the flange portion  34  of the male closure strip  30  just prior to the male closure strip  30  and the edge  51   b  of the folded film web  51  being squeezed between the male closure strip lay on roller  60  and the male closure strip lamination roller  53   b . The binder layer  28   b  transfers enough heat to the inner surface  36  of the flange portion  34  of the male closure strip  30  and the edge  51   b  of the folded film web  51  to melt the flange portion  34  of the male closure strip  30  and the edge  51   b  of the folded film web  51 . 
     Pressure applied by the male closure strip lay on roller  60  and the male closure strip lamination roller  53   b  keeps the melted flange portion  34  of the male closure strip  30  in contact with the melted binder layer  28   b  and keeps the melted portion of the folded film web  51  in contact with the melted binder layer  28   b  at that point in the web path such that the male closure strip  30  is sealed to edge  51   b  of the folded film web  51  when the melted flange portion  34  of the male closure strip  30 , the melted binder layer  28   b  and the melted portion of the folded film web  51  cool. At folded film web speeds of 100 feet/minute, the lamination apparatus  50  produces a folded film  63  with good lamination of the female closure strip  20  and the male closure strip  30  to the folded film web  51  and with no tack of the film layers. 
     In the version of the lamination apparatus  50  shown in FIG. 5, the female closure strip  20  is sealed to the folded film web  51  before the male closure strip  30  is sealed to the folded film web  51 . Of course, the lamination apparatus  50  also works well if configured such that the male closure strip  30  is sealed to the folded film web  51  before the female closure strip  20  is sealed to the folded film web  51 . After processing in the lamination apparatus  50 , the folded film web  51  exits as folded film  63  with female closure strip  20  and male closure strip  30  at opposite top edges and adjacent to each other. The side edges  15 , 16  and the bottom edge  17  of the reclosable bag  10  shown in FIG. 1 may then be formed by heat sealing as is well known in the art. 
     Thus, it can be seen that there is provided a method and apparatus for attaching prefabricated thermoplastic closure members to a prefabricated thermoplastic film web. The method and apparatus introduce less tension differences across the film web compared to “hot shoe” lamination, and improve the consistency of the seal between the closure members and the film web compared to prior methods. 
     The preceding description is merely of preferred embodiments of the invention. The claims should be looked to in order to understand the full scope of the invention. 
     INDUSTRIAL APPLICABILITY 
     Methods are disclosed for attaching closure elements such as zipper halves to thermoplastic film webs, particularly those used in forming reclosable plastic storage bags.