Abstract:
A zipper strip for a reclosable bag or package includes a male interlocking profile and a female interlocking profile. The male interlocking profile includes a male interlocking member and a male web coextruded therewith. In like manner, the female interlocking profile includes a female interlocking member and a female web. The male interlocking member snappingly engages into the female interlocking member to join the profiles to one another. One of the male and female webs is wider than the other in at least one of two directions from the male and female interlocking members, the greater width being represented by at least one flange extending widthwise beyond the other web. The zipper strip is designed to be attached to thermoplastic sheet material by sealing the at least one flange thereto without sealing the male and female webs to each other. Methods for securing the zipper strip to thermoplastic sheet material, and for making packages on a horizontal form-fill-and-seal machine, are also disclosed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. patent application Ser. No. 09/074,567 filed on May 7, 1998, now U.S. Pat. No. 6,044,621, which is a division of U.S. patent application Ser. No. 08/839,974 filed on Apr. 24, 1997, now abandoned, which application is a continuation-in-part (CIP) of U.S. patent application Ser. No. 08/651,977 filed on May 21, 1996. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to reclosable plastic bags of the type in which perishable food products and other goods are packaged for sale to consumers in retail outlets. More specifically, the present invention relates to reclosable plastic bags manufactured and concurrently filled on horizontal or vertical form-fill-and-seal (FFS) machines, wherein a plastic interlocking zipper for each bag is disposed transversely relative to the direction of motion of the thermoplastic sheet material used to form the reclosable bags on the FFS machine. 
   2. Description of the Prior Art 
   The present invention relates to improvements in the package-making art and may be practiced in the manufacture of thermoplastic bags and packages of the kind that may be used for various consumer products, but which are particularly useful for food products which must be kept in moisture- and air-tight packages, free from leakage until initially opened for access to the product contents, which packages are then reclosable by zipper means to protect any remainder of the product therein. 
   The indicated art is fairly well-developed, but nevertheless remains susceptible to improvement contributing to increased efficiency and cost effectiveness. 
   One problem that still hampers the production of packages from continuous zipper-equipped sheet material is the difficulty in attaining a satisfactory sealing of the bag or package against leakage, where the zipper and area of film engaged by the zipper extends through the side (cross) seal areas separating one bag or package from the next. This problem occurs where the zipper is longitudinal with respect to the direction of motion of the thermoplastic sheet material used to form the reclosable bags on the FFS machine, in which case the transverse, or side, sealing bars must flatten and seal the zipper at the same time as they are sealing the thermoplastic sheet material from which the packages are being made. The difficulty with which this is consistently and successfully achieved is reflected by the high occurrence of leaking packages. 
   Numerous attempts have been made to solve this problem. Among the approaches that have been taken is the substitution of a transverse zipper for the longitudinal zipper. Where such a zipper is provided the transverse sealing bars associated with the FFS machine do not flatten the zipper as they are making a side seal, although they may seal the zipper to the thermoplastic sheet material transversely thereacross without flattening it. 
   The present invention relates to the provision of a transverse zipper for reclosable plastic bags or packages being manufactured on either a horizontal or vertical FFS machine. More specifically, the present invention is both a zipper strip and a method for securing the zipper strip transversely across the thermoplastic sheet material from which reclosable bags are being produced on a FFS machine. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is a zipper strip for a reclosable bag or package manufactured and filled using a form-fill-and-seal machine. In particular, the zipper strip is designed to be disposed transversely with respect to the movement through the machine of the thermoplastic sheet material used to fashion the packages. 
   The zipper strip comprises a male interlocking profile, having a male interlocking member and a male web coextruded therewith; and a female interlocking profile, having a female interlocking member and a female web coextruded therewith. The male interlocking member is snappingly engagable within the female interlocking member to join the male and female interlocking profiles together. 
   One of the male and female webs is wider than the other of the male and female webs in at least one of two directions from the male and female interlocking members in the closed zipper strip. The greater width of the wider of the male and female webs means that it has a flange extending beyond the other web on one and possibly both sides. The zipper strip, as a consequence, may be attached transversely upon thermoplastic sheet material by sealing the flange of the male or female web or flanges thereto without sealing the male and female webs to each other. 
   The present invention also comprises a method for attaching this zipper strip transversely on a sheet of thermoplastic sheet material during the production of plastic bags or packages on an FFS machine. In this situation, a length of the zipper strip is attached to the thermoplastic sheet material, each time it is brought to rest as it advances (incrementally or continuously) on or to the FFS machine. 
   This method includes the step of providing a zipper strip of the above-described variety. The length of zipper strip is then disposed transversely upon the sheet of thermoplastic sheet material, with the wider of the male and female webs in contact with the sheet and with a flange, or the flange if there is only one, oriented in the direction of the motion of the sheet. The flange or flanges are then sealed to the sheet without sealing the male and female webs to each other. Several specific ways of disposing the length of zipper strip onto the sheet of thermoplastic sheet material will be described below. 
   Finally, the present invention comprises a method for manufacturing reclosable packages on a horizontal form-fill-and-seal machine. The method includes the step of providing a sheet of thermoplastic sheet material having a length of zipper strip attached thereto at regularly spaced intervals as described above. A product conveyor then deposits a product to be packaged at regular intervals onto the sheet of thermoplastic sheet material. The two lateral edges of the sheet are then folded toward one another and around the product, and sealed to one another to form a tube therefrom enclosing the product. 
   The tube is then sealed transversely to each length of zipper strip without the webs of the male and female interlocking profiles being sealed to each other. The tube is then cut transversely adjacent to each length of zipper strip to separate each completed package from the next. 
   The present inventions will now be described in more complete detail with frequent reference being made to the figures identified below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a first embodiment of the zipper strip of the present invention; 
       FIG. 2  is a cross-sectional view of a second embodiment of the zipper strip; 
       FIG. 3  is a perspective view of an apparatus used to attach the zipper strip to thermoplastic sheet material; 
       FIG. 4  is a perspective view of an alternate apparatus used for this purpose; 
       FIG. 5  is a perspective view of still another apparatus used for this purpose; 
       FIG. 6  is a schematic view of a horizontal FFS machine; 
       FIG. 7  is a plan view of the thermoplastic sheet material, with lengths of zipper strip attached thereto, used to produce packages on the horizontal FFS machine; and 
       FIG. 8  is a simplified cross-sectional view of a package formed in a horizontal FFS machine in accordance with the present invention. 
       FIG. 9  is a plan view of the thermoplastic sheet material of  FIG. 7 , shown with the edges joined together to form a fin seal. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring specifically to the figures identified above,  FIG. 1  is a cross-sectional view of a first embodiment of the zipper strip  10  of the present invention. The zipper strip  10  comprises a male interlocking profile  12  and a female interlocking profile  14 . The male interlocking profile  12  includes a male interlocking member  16  which may have an arrowhead-shaped cross section or, as is shown in  FIG. 1 , an asymmetrical arrowhead-shaped cross section, designed to make the zipper strip  10  easier to open from one side than from the other. The female interlocking profile  14  includes a female interlocking member  18  comprising two inwardly curving members forming a receptacle or channel into which male interlocking member  16  may be snappingly engaged. 
   Both the male and female interlocking profiles  12 ,  14  include webs coextruded with the male and female interlocking members  16 ,  18 . Web  20  of male interlocking profile  12 , it may be observed, is wider than web  22  of female interlocking profile  14 . As a consequence, web  20  has a leading flange  24  and a trailing flange  26 , which together make up the amount by which web  20  is wider than web  22 . As will become clear below, the leading and trailing flanges  24 ,  26  are so called because, when zipper strip  10  is attached to a thermoplastic sheet material being fed into an FFS machine, the leading flange  24  “leads” the transversely attached zipper strip  10  toward the machine, and the trailing flange  26  “trails” or is last. Ultimately, the leading flange  24  resides inward of the mouths of the plastic bags or packages being manufactured and concurrently filled with a consumer product on an FFS machine. While the male interlocking profile  12  is shown to have both the leading and trailing flanges  24 ,  26 , both flanges  24 ,  26  could alternatively be part of the female interlocking profile  14  instead. 
   The zipper strip  10  is disposed transversely across thermoplastic sheet material during the manufacture of plastic bags or packages on an FFS machine. The zipper strip  10  is dispensed with male and female interlocking profiles  12 ,  14  joined as shown in  FIG. 1  onto thermoplastic sheet material with the male interlocking profile  12  resting thereupon. Heat seal bars  28  or the like, applied against the leading and trailing flanges  24 ,  26  as suggested by the arrows in  FIG. 1 , seal the male interlocking profile  12  to the thermoplastic sheet material (not shown) without sealing web  22  of the female interlocking profile  14  to web  20  of the male interlocking profile  12 . 
   Heat seal materials  30  may be applied to the outside of web  20  of male interlocking profile  12 , including the outsides of the leading and trailing flanges  24 ,  26 , as well as to the inside of the trailing flange  26  and to the outside of web  22  of the female interlocking profile  14 , to facilitate their being sealed to thermoplastic sheet material. The trailing flange  26  may also be separable from the rest of web  20  by perforations. 
   The outsides of the leading and trailing flanges  24 ,  26  are attached to thermoplastic sheet material before the sheet material reaches the shoulder on a vertical FFS machine, or before the sheet material enters the FFS machine. Later, when the sheet material is folded over to form a tube with lateral edges sealed in a fin or overlap seal, the sheet material is sealed to the inside of trailing flange  26 , as well as to the outsides of both webs  20 ,  22 , without sealing the facing portions of webs  20 ,  22  to one another. 
     FIG. 2  is a cross-sectional view of a second embodiment of the zipper strip  40  of the present invention. Elements common to both zipper strip  40  and zipper strip  10  described above are identified in  FIG. 2  using the same reference numbers. A comparison between  FIGS. 1 and 2  indicates that zipper strip  40  lacks a trailing flange  26 , but is identical to zipper strip  10  in all other respects. As was the case with zipper strip  10 , zipper strip  40  is disposed transversely across thermoplastic sheet material during the manufacture of plastic bags or packages on an FFS machine. Male interlocking profile  42  rests upon the thermoplastic sheet material. Heat seal bars  28  or the like, applied against the leading flange  24 , as suggested by the arrows in  FIG. 2 , seal the male interlocking profile  42  to the thermoplastic sheet material (not shown) without sealing web  22  of the female interlocking profile  14  to web  44  of the male interlocking profile  42 . As before, while the male interlocking profile  42  is shown to have the leading flange  24 , leading flange  24  could alternatively be part of the female interlocking profile  14  instead. 
   Both zipper strips  10 ,  40  shown in  FIGS. 1 and 2 , respectively, may be extruded from a polymeric resin material, such as a low-density polyethylene (LDPE). Heat seal materials  30  may be applied as shown by coextrusion or by coating following the extrusion of zipper strips  10 ,  40 . Ethylene vinyl acetate (EVA) copolymers may be used as the heat seal materials  30 . 
     FIG. 3  is a perspective view of an apparatus used to attach zipper strip  10  to thermoplastic sheet material  50 , which is conveyed in the direction of the arrows thereon toward an FFS machine. Thermoplastic sheet material  50  is moved intermittently in increments equal in length to the length of the packages being produced. 
   Each time the thermoplastic sheet material  50  is momentarily brought to rest, a length of zipper strip  10  is sealed transversely across the upwardly facing side thereof. Zipper tape  10  is dispensed from a roll or other supply not shown in  FIG. 3 , and fed through a stationary clamp  52 , and through a reciprocating shuttle  54 , which includes a clamp  56  and a guillotine  58 , the latter of which is used to cut the zipper strip  10  when required. 
   Shuttle  54  reciprocates each time the thermoplastic sheet material  50  is momentarily brought to rest. When shuttle  54  moves outward over thermoplastic sheet material  50 , clamp  56  is closed onto zipper tape  10 , while stationary clamp  52  is open, so that shuttle  54  pulls a length of the zipper tape  10  from the roll. The outward end of shuttle  54  is a probe  60 , which allows the leading flange  24  and the trailing flange  26  of the zipper tape  10  to protrude from the sides thereof. 
   As shown in  FIG. 3 , the shuttle  54  is in its retracted position. When in its forward position, not shown, the probe  60  extends into the space between the top sealing jaw  62  and its corresponding bottom sealing jaw  64 , the latter of which is on the underside of the thermoplastic sheet material  50 . The leading and trailing flanges  24 ,  26  extend outward from between the top and bottom sealing jaws  62 ,  64 . When the jaws  62 ,  64  close, heat seal bars  28  seal the flanges  24 ,  26  to the thermoplastic sheet material  50 . Jaws  62 ,  64  then are opened; guillotine  58  cuts the next length of zipper strip  10 ; clamp  56  is opened; and clamp  52  is closed. Then shuttle  54  retracts to the position shown in  FIG. 3 , while thermoplastic sheet material  50  moves a length equal to the length of a package being manufactured to repeat the process. 
     FIG. 4  is a perspective view of an alternate apparatus used to attach zipper strip  10  to thermoplastic sheet material  50 . As before, thermoplastic sheet material  50  is conveyed in the direction of the arrow thereon toward an FFS machine, and is moved intermittently in increments equal in length to the length of the packages being produced. 
   Again, each time the thermoplastic sheet material  50  is momentarily brought to rest, a length of zipper strip  10  is sealed transversely across the upwardly facing side thereof. Zipper strip  10  is dispensed from a roll or other supply not shown in  FIG. 4 , being pulled therefrom by a first clamp  70 , which reciprocates back and forth along mechanism  74  in step with a second clamp  72 . First and second clamps  70 ,  72  grasp leading flange  24  of zipper strip  10  to pull the zipper strip  10  transversely across the thermoplastic sheet material. Second clamp  72  holds the zipper strip  10  in position while it is being sealed to the upwardly facing side of the thermoplastic sheet material  50 . A stationary guillotine  76  is used to cut the zipper strip  10  when required. 
   Each time the thermoplastic sheet material  50  is momentarily brought to rest, second clamp  72  brings a length of zipper strip  10  cut by stationary guillotine  76  transversely outward thereover to the position shown in  FIG. 4 . At the same time, first clamp  70 , moving in step with second clamp  72 , moves a length of zipper strip  10  through guillotine  76 . Top sealing jaw  62  and its corresponding bottom sealing jaw  64 , the latter of which is on the underside of the thermoplastic sheet material  50 , seal the leading flange  24  and the trailing flange  26  of the zipper strip  10  thereto, while the second clamp  72  holds onto the leading flange  24 . Then, first clamp  70  and second clamp  72  retract from the positions shown in  FIG. 4 , the first clamp  70  retracting to a position adjacent to guillotine  76 , and the second clamp  72  retracting upstream from the guillotine  76  along zipper strip  10 . Thermoplastic sheet material  50  then moves a length equal to the length of a package being manufactured to repeat the process. 
     FIG. 5  is a perspective view of another apparatus used to attach zipper strip  10  to thermoplastic sheet material  50 . Thermoplastic sheet material  50  is conveyed in the direction of the arrow thereon toward an FFS machine, and, as before, is moved intermittently in increments equal in length to the length of the packages being produced. 
   Again, each time the thermoplastic sheet material  50  is momentarily brought to rest, a length of zipper strip  10  is sealed transversely across the upwardly facing side thereof. Zipper strip  10  is dispensed from a roll or other supply not shown in  FIG. 5 , being pulled therefrom by a perforated belt  80  entrained about chambers  82 ,  84  attached to a vacuum or suction. Suction through the perforated belt  80  is used to transport the zipper strip  10 . A stationary guillotine  86 , through which the zipper strip  10  passes, is used to cut the zipper strip  10  when required. 
   Each time the thermoplastic sheet material  50  is momentarily brought to rest, perforated belt  80  draws a length of zipper strip  10  transversely across thermoplastic sheet material  50 . The leading flange  24  and the trailing flange  26  of the zipper strip  10  extend beyond the two sides of the perforated belt  80  and chamber  82 , which extend into the space between the top sealing jaw  62  and its corresponding bottom sealing jaw  64 , the latter of which is on the underside of the thermoplastic sheet material  50 . The leading and trailing flanges  24 ,  26  extend outward from between the top and bottom sealing jaws  62 ,  64 . The vacuum is turned off. When the jaws  62 ,  64  close, heat seal bars  28  seal the flanges  24 ,  26  to the thermoplastic sheet material. The jaws  62 ,  64  are then opened, the thermoplastic sheet material  50  is moved a length equal to the length of a package being manufactured. The vacuum is then turned on; guillotine  86  cuts the zipper strip  10 ; and the perforated belt  80  draws the portion of zipper strip  10  transversely across the thermoplastic sheet material  50  to repeat the process. 
   Any of these preceding apparatus for attaching a zipper strip  10  to thermoplastic sheet material  50  may be used in the manufacture of packages on a horizontal or vertical FFS machine. In this regard,  FIG. 6  is a schematic view of a horizontal apparatus. A roll  90  of thermoplastic sheet material  50  dispenses the sheet  50  intermittently in lengths equal to that of the packages being manufactured and filled. A length of zipper strip  10  is applied by the zipper applicator  92 , which may include any of the three apparatus described, to the center of the sheet material  50 , as shown in  FIG. 7 , leaving sufficient material along the two lateral edges  96  of the sheet material  50  to fold over toward another for joining in an overlap or fin seam  300  (see  FIG. 9 ). 
   An accumulator  94  is used to convert the intermittent motion of the thermoplastic sheet material  50  to a continuous motion. 
   A product conveyor  98  carries the product  99  to be packaged toward the wrapping machine  100 , which comprises a forming area  102 , a sealing area  104 , and a cross-seal area  106 . In the forming area  102 , the two lateral edges  96  of the sheet material  50  are folded upward and around the duct. In the sealing area  104 , the two lateral edges  96  are sealed to one another with a fin or lap seal to form a continuous film tube with the product and zipper strips  10  inside. In the cross-seal area, the webs of the zipper strip  10  are sealed to the sheet material  50 , without sealing the webs to each other, and the packages are separated from one another along lines  112 , and carried onward by the takeaway conveyor  108 . 
     FIG. 8  depicts a package  110  formed in accordance with the above and containing therein the product  99 . In this package the top (wide) flange  26  of one of the profiles is sealed to the portions of the film web forming the package bottom  114  as well as the package top  116 . The other wide flange  24  of that profile is secured to the portions of the film web forming the package bottom  114  while the narrow flange  22  of the other profile is secured only to the portions of the film web forming the package top  116 . 
   Modifications to the above would be obvious to those of ordinary skill in the art, but would not bring the invention so modified beyond the scope of the appended claims.