Abstract:
This invention relates to a method for sealing film layers to form a sealed portion and a notch within the sealed portion, comprising: providing film layers between sealing jaws comprising a heat sealing element, with a sealing face having a length and a protrusion extending partly along the length of its sealing face; inducing a temperature gradient along the of sealing face length, wherein the temperature proximate to the protrusion is higher than at a distance from the protrusion; closing the jaws and simultaneously clamping the film at a location adjacent to the sealing face; holding the jaws closed for a period of time; and opening the jaws to release the layers of film.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is filed under the provisions of 35 U.S.C. §121 and claims priority to U.S. patent application Ser. No. 12/220,606, filed on Jul. 25, 2008, which in turn claims priority to the U.S. Provisional Patent Application No. 60/962,517, filed on Jul. 30, 2007. Both applications are incorporated herein in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to the production of packaging pouches and more specifically to a heat sealing jaw that is suitable for producing an easy-open feature on a packaging pouch. 
       BACKGROUND 
       [0003]    Packaging pouches are typically made on form, fill and seal machines. For example, using a vertical form, fill and seal machine, a flat web of synthetic thermoplastic film is unwound from a roll and formed into a continuous tube in a tube forming operation, by sealing the longitudinal edges of the film together to form a lap seal or a fin seal. The tube thus formed is pulled vertically downwards to a filling station. The tube is then collapsed across a transverse cross-section of the tube, the position of the cross-section being at a sealing device below the filling station. A transverse heat seal is made by the sealing device at the collapsed portion of the tube, thus making an airtight seal across the tube. The sealing device generally comprises a pair of jaws. 
         [0004]    After making the transverse seal, but before the jaws of the sealing device are opened, a quantity of material to be packaged, for example a liquid, is caused to enter the tube at the filling station, and to fill the tube upwardly from the aforementioned transverse seal. The tube is then caused to move downwardly a predetermined distance. This movement may be under the influence of the weight of the material in the tube, or it may be caused by pulling or mechanically driving the tube The jaws of the sealing device are closed again, thus collapsing the tube at a second transverse section. The second transverse section may be above, usually just above the air/material interface in the tube, or the second transverse section may be below the air/material interface. The sealing device seals and severs the tube transversely at the second transverse section. The material filled portion of the tube is now in the form of a pillow shaped pouch. Thus the sealing device has sealed the top of the filled pouch and sealed the bottom of the next pouch to be formed, all in one operation. The filling of the product may be conducted on a continuous or intermittent basis. One such vertical form, fill and seal machine of the type described above is sold under the trade-mark PREPAC. Other suitable machines are sold under the trade-marks INPACO and ELECSTER. 
         [0005]    A variety of flowable materials may be packaged in this manner, for example, milk, syrups, sauces, juices, water and the like. The term “flowable material” can include materials that are flowable under gravity or may be pumped. Such materials may include emulsions, pastes, peanut butter, preserves, dough, ground meat, powders, detergents, oils and granular solids. Such pouches can also be used to contain other flowable materials such as foods that are packaged under sterile, pasteurized or aseptic conditions. The packaging conditions will normally require modifications to the machine and also modifications to the methods of packaging. 
         [0006]    The pouches produced through this type of process can be manufactured to contain any volume of flowable material. In the situation where drinking fluids are packaged in this fashion, a typical size might be 250 mls or 500 mls. In such instance, it is possible to consume the fluid directly from the pouch. Thus, providing a pouch that includes an easy-open feature for this purpose is desirable especially when served in correctional facilities since it avoids the necessity to use an implement such as a knife or scissors. In addition, since these packages are meant for one-time use and are disposable, it is appropriate that the manner in which they are manufactured is as economical as possible, without sacrificing the basic packaging requirements for the materials in question. 
         [0007]    Many solutions have been proposed for producing packages of this type, and typically such packages have included a notch or tear line which allows the package to be opened. For example, French Patent No. 1 216 422 discloses liquid-filled polymer pouches that are produced by collapsing a tube and having an easy-open feature. The easy-open feature comprises a sealed area partially extending across the width of the pouch and a weakened line extending within the sealed area. The weakened line is formed using a set of jaws where one jaw comprises a piano wire. 
         [0008]    United Kingdom Patent No. 898,641 discloses a pouch having a line of weakness for easy opening that is produced by pressing the sheet between a solid plate and a ribbed die while heat is applied. The sheet is pinched between the plate and the rib of the die and reduced in thickness but not sheared, or otherwise punctured along the desired line. 
         [0009]    U.S. Pat. No. 5,038,550 and European Patent No. 0 372 886 both disclose pouches having a slit formed within a sealed portion. The slit is intended as a device for starting a tear and for directing the tear in a preferred direction. In both cases the sealed portion is formed first using a sealing element and then the slit is formed using a separate cutting operation using a knife. 
         [0010]    U.S. Patent Application Publication No. US 2006/0110081 A1 published on May 25, 2006, discloses a pouch for containing a flowable material, provided with an easy-open feature located adjacent to an upper closure or a lower closure of the pouch. The easy-open feature comprises a seal formed between two layers of film and provides a tear line for opening the pouch and tearing a corner off the pouch. 
         [0011]    One concern with easy-open features in packaging pouches is that during the production, filling, handling or any manipulation of the pouches, stresses are induced in the film that forms the walls of the pouch. Therefore, depending on the configuration of the easy-open feature, it may produce a stress concentration in the film and hence make the film more susceptible to tearing in specific areas. 
         [0012]    Thus there is a need for an improved heat sealing jaw that can be used to easily and economically produce an easy-open feature in a pouch that is sufficiently robust to withstand stresses induced on the pouch during manipulation and/or filling of the pouch. 
       SUMMARY OF THE INVENTION 
       [0013]    Accordingly, the present invention provides a heat sealing jaw which can be used to produce a packaging pouch with an easy-open feature, wherein the easy-open feature does not significantly compromise the integrity of the packaging pouch. 
         [0014]    According to one aspect, the present invention provides a heat sealing jaw for use in cooperation with an opposing backing jaw for sealing layers of film together to form a sealed portion and a notch within the sealed portion. The heat sealing jaw comprises a jaw body, a heat sealing element secured to the jaw body, a support surface associated with the heat sealing element for clamping the layers of film against the opposing backing jaw and a heat sink coupled to the heat sealing element. The heat sealing element has a sealing face for pressing the layers of film together against the opposing backing jaw and forming the sealed portion. The sealing face has a protrusion for forming the notch within the sealed portion. The heat sink is coupled to the heat sealing element at a location adjacent to the support surface, and during operation, the heat sink induces a temperature gradient along the sealing face of the heat sealing element. 
         [0015]    Advantageously, the heat sealing element may further comprise a clamping portion that is disposed at an orientation diverging from a plane along which the layers of film are sealed together. This tends to facilitate the securing of the heat sealing element to the jaw body which may also serve as the heat sink. 
         [0016]    According to another aspect, the present invention also provides a heat sealing jaw for use in cooperation with an opposing backing jaw for forming an easy open feature adjacent to an edge of a packaging pouch made from layers of film sealed together. The heat sealing jaw comprises a jaw body, a heat sealing element secured to the jaw body, a support surface associated with the heat sealing element and a heat sink coupled to the heat sealing element. The heat sealing element has a sealing face for forming a sealed portion extending inwardly from the edge of the pouch. Accordingly, the sealing face has an outboard end to be positioned outside of the edge of the pouch, an inboard end to be positioned inside the edge of the pouch and a protrusion for forming the notch within the sealed portion. The support surface is associated with the inboard end of the sealing face for clamping the layers of film against the opposing backing jaw. The heat sink is coupled to the heat sealing element at a location adjacent to the inboard end of the sealing face, and during operation, the heat sink induces a temperature gradient along the sealing face of the heat sealing element. 
         [0017]    According to another aspect, the present invention provides a heat sealing element for use in a heat sealing jaw in cooperation with an opposing backing jaw for sealing layers of film together to form a sealed portion and a notch within the sealed portion. The heat sealing element comprises a sealing face for pressing the layers of film together against the opposing backing jaw and forming the sealed portion, and, a clamping portion adjacent to the sealing face. The sealing face has a protrusion for forming the notch within the sealed portion. The clamping portion is disposed at an orientation diverging from a plane along which the layers of film are sealed together. 
         [0018]    According to a further aspect, the present invention provides a method of sealing layers of film together to form a sealed portion and a notch within the sealed portion comprising the steps of:
       a) providing layers of film to be sealed together between a heat sealing jaw and a cooperating backing jaw, the heat sealing jaw comprising a heat sealing element with a sealing face having a length and a protrusion extending partly along the length of the sealing face;   b) inducing a temperature gradient along the length of the sealing face of the heat sealing element, wherein a first temperature of the sealing face adjacent to the protrusion is higher than a second temperature of the sealing face at a distance from the protrusion;   c) closing the jaws to press the layers of film between the sealing face of the heat sealing element and the backing jaw, and, to simultaneously clamp the film at a location adjacent to the sealing face;   d) holding the jaws closed for a period of time required to form the sealed portion and the notch; and   e) opening the jaws to release the layers of film.       
 
         [0024]    The above method may be performed on a pouch forming and filling machine such as a vertical form, fill and seal packaging machine, in conjunction with additional steps that are required to form a packaging pouch having an easy-open feature and filled with flowable material. Accordingly, the layers of film may be provided between the heat sealing jaw and the cooperating backing jaw in the form of a film tube that is partially filled with flowable material. The temperature gradient along the length of the sealing face may be induced by extracting heat from the heat sealing element using, for example, a heat sink coupled to the heat sealing element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below, which are exemplary and included for illustrative purposes. Those skilled in the relevant art(s) will understand that the following description and drawings and are not intended to limit the scope of the teachings herein in any way. 
           [0026]    Reference is now made to the accompanying figures, in which like references are intended to refer to like or corresponding parts: 
           [0027]      FIG. 1  is an isometric view of a heat sealing jaw according to an embodiment of the present invention; 
           [0028]      FIG. 2  is an isometric view of the heat sealing jaw of  FIG. 1  with a clamp removed; 
           [0029]      FIG. 3  is an isometric view of a heat sealing element from the heat sealing jaw of  FIG. 1 ; 
           [0030]      FIG. 4  is a cross-sectional view of the heat sealing element of  FIG. 3  along line  4 - 4  in  FIG. 3 ; 
           [0031]      FIG. 5  is a front elevation view of a packaging pouch having an easy-open feature formed using the heat sealing jaw of  FIG. 1 ; 
           [0032]      FIG. 6  is an isometric view of the heat sealing jaw of  FIG. 1  positioned in relation to an opposing resilient backing member; 
           [0033]      FIG. 7  is a front elevation view of the heat sealing jaw of  FIG. 1  positioned in relation to a film tube used for producing the pouch of  FIG. 5 ; and 
           [0034]      FIG. 8  is an isometric view of the heat sealing jaw of  FIG. 1  positioned within the filling compartment of a vertical form, fill and seal packaging machine. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    Referring now to  FIG. 1 , a heat sealing jaw, generally shown at  10 , for use in cooperation with an opposing backing jaw (not shown) for sealing layers of film together is shown. The heat sealing jaw  10  can be used on a vertical form, fill and seal (VFFS) packaging machine for producing an easy-open feature on a pouch containing flowable material. 
         [0036]    Many types of films can be used to manufacture pouches in accordance with the present invention. Generally these films must be capable of self-sealing and processing through the VFFS equipment. They should be stiff enough and strong enough for the proposed packaging applications. The nature of the packaging application determines the film selection and the person skilled in the art would be capable of readily selecting a suitable film for the desired purpose. Examples of suitable films include any synthetic thermoplastic polymeric film which meets the above-mentioned criteria. The films may contain a barrier layer selected from nylon polymers, polyethylene terephthalate polymers, amorphous nylon or ethylene vinyl alcohol. An additional tie layer may be present and can be selected from ethylene vinyl acetate polymer, ethylene acid copolymers, ionomers or anhydride functionalized ethylene copolymers. All of these may be combined with at least one high pressure ethylene homopolymer. Other examples of suitable films are described in the following references: WO 98/34844, WO 98/29249, WO 97120693, WO 97/12755, WO 95/21743, WO 95/10566, WO 95/00587, the disclosures of which are incorporated herein by reference. These are merely representative examples of thermoplastic films and the invention is not to be limited in any way with respect to the film selected for manufacture of the pouch. 
         [0037]    As shown in  FIGS. 1-4 , the heat sealing jaw  10  comprises a jaw body  12  and a heat sealing element generally shown at  14  secured to the jaw body  12 . The heat sealing element  14  comprises a sealing face  16  having a first end  18  and a second end  20 , and, a back face  22 . The heat sealing element  14  also has a clamping portion  24  that is disposed at an orientation diverging from the sealing face  16 , which is also diverging from a plane along which the layers of film are sealed together during operation. The sealing face  16  has a rib-shaped protrusion  26  which is located at a distance from the second end  20 . 
         [0038]    The heat sealing element  14  is secured to the jaw body  12  by clamping the clamping portion  24  of the heat sealing element  14  to the jaw body  12  using a clamp  28 . The clamping portion  24  of the heat sealing element  14  is thermally and electrically connected to the jaw body  12  so that the jaw body  12  can also serve as an electrical terminal of the heat sealing element  14 . The heat sealing element  14  is also electrically connected to terminal  30  which is electrically isolated from the jaw body  12 . 
         [0039]    A thermal insulator  32  is also disposed on at least a portion of the back face  22  of the heat sealing element  14  so as to thermally insulate the heat sealing element  14  from the jaw body  12  in a region adjacent to the sealing face  16 . 
         [0040]    Referring now to  FIG. 5 , an exemplary packaging pouch generally shown at  34  and made in accordance with the present invention is shown. The pouch  34  is made by sealing layers of film together and comprises an upper transverse seal  36 , a lower transverse seal  38  and a longitudinal fin seal  40 . The pouch  34  also has an easy-open feature  42 , disposed along or adjacent to a side edge  44  of the pouch  30 . The easy-open feature  42  can be made using the heat sealing jaw  10  and comprises a sealed portion  46  and a notch  48  within the sealed portion  46 . 
         [0041]    In order to seal the layers of film together and produce the easy-open feature  42  on the pouch  34 , the heat sealing jaw  10  works in cooperation with an opposing conventional backing jaw which is not shown. However, a resilient backing member  50  which is part of the opposing backing jaw is shown in  FIG. 6 . The structure and configuration of such backing jaws are known to one skilled in the art. The heat sealing element  14  is heated by resistance heating and the layers of film are pressed together between the heat sealing jaw  10  and the resilient backing member  50 . 
         [0042]    The protrusion  26  on the sealing face  16  forms the notch  48  within the sealed portion  46  of the easy-open feature  42 . The geometry of the protrusion  26  may be selected based on the notch geometry desired. The notch  48  may comprise an indentation, a cut or any type of material weakness formed within the sealed portion  46  that can be used to initiate tearing of the layers of film and thereby facilitate the opening of the pouch  34 . For example, the protrusion  26  may be selected to produce a notch which extends completely through the layers of film that are sealed together or to produce a notch which only partially extends through the layers of film so as to form a weakened region of reduced thickness. Other shapes and configurations of protrusions to produce any variety of notches may also be used. In different embodiments, the weakened region may be made prior to or at the same time as the perimeter seal. 
         [0043]    As shown in  FIG. 6 , the resilient backing member  50  may extend beyond the area of the sealing face  16  of the heat sealing element  14  so that during the sealing process, the film layers are simultaneously clamped between the resilient backing member  50  and a support surface  51  associated with the heat sealing element  14 . The support surface  51  may be provided by at least a portion of at least one of the thermal insulator  32 , the jaw body  12 , and the clamp  28 . Depending on the process conditions, a portion of the sealing face  16  adjacent to the second end  20  may also provide some support for clamping the film layers. The support surface  51  serves to stabilize the film around the area where the sealed portion  46  is being formed. Providing adequate support or film clamping adjacent to or at the second end  20  of the sealing face  16  during the sealing process can be beneficial in producing a good quality seal. 
         [0044]    The difference in elevation between the heat sealing element  14  and the support surface  51  produces a pressure profile across the resilient backing member  50  during the sealing cycle and causes any flowable material in the pouch  34  to clear the location of the easy-open feature  42 . This ensures that the flowable material inside the pouch  34  does not contaminate the sealed portion  46  of the easy-open feature  42 . 
         [0045]      FIG. 7  shows the position of the heat sealing jaw  10  in relation to a film tube generally shown at  52 , during the process of producing pouches  34  filled with flowable material on a VFFS packaging machine. The pouches  34  are typically sealed and separated along a cut line  54  using another separate transverse heat sealing and cuffing element (not shown) in order to form the transverse seals  36  and  38  on the pouch  34 . The separate transverse heat sealing and cutting element, may be secured to a separate jaw or to the same jaw as the heat sealing element  14 . Therefore, the easy-open feature  42  may be formed at the same time or at a different time as when the pouches  34  are sealed and separated along the cut line  54 . 
         [0046]    Also seen in  FIG. 7 , in an embodiment second end  20  of heat sealing element  14  is seen to be within the film path of film tube  52  moving through the apparatus to form pouch  34 , while first end  18  of heat sealing element  14  is outside the film path. In this arrangement, the inboard terminal associated with heat sealing element  14  is within the film path, and thus extends a distance towards the interior of pouch  34 , while the outboard terminal associated with heat sealing element  14  is outside the film path. 
         [0047]      FIG. 8  shows the heat sealing jaw  10  installed within the filling compartment of an exemplary VFFS packaging machine. The filling compartment comprises transverse sealing jaws  58 , longitudinal sealing jaws (not shown), a fill tube  60  and driven feed rollers  62 . During the process of forming and filling pouches  34  in the VFFS machine, the transverse sealing jaws  58  form a first transverse seal ( 36  and  38 ) across the film tube  52  then the vertically extending film tube  52  is intermittently fed downwardly by the driven feed rollers  62  by a distance corresponding to a height of the pouch  34  while being simultaneously filled with flowable material via the fill tube  60 . When the film tube  52  stops, the heat sealing jaw  10  in cooperation with the opposing backing jaw, forms the easy-open feature  42  and the transverse sealing jaws  58  form the transverse seal  36  and  38  across the film tube  52 . The transverse sealing jaw may also simultaneously cut the film tube  52  in order to separate the pouches  34  or weaken the film tube  52  in order to form a string of separable pouches  34 . Alternatively, the film tube  52  may be cut via a separate operation using conventional means such as a knife or the like. The longitudinal sealing jaws form the fin seal  40  of the pouch  34 . In the present embodiment, the heat sealing jaw  10  is located above or upstream of the transverse sealing jaws  58  and actuated by a separate actuator  64 . Alternatively, the heat sealing jaw  10  could be disposed below the transverse sealing jaws  58  and/or be associated with the same actuator as the transverse sealing jaws  58 . 
         [0048]      FIG. 7  further shows that the first end  18  of the sealing face  16  is positioned on the outside of the side edge  44  or outboard of the film tube  52  and that the second end  20  of the sealing face  16  is positioned on the inside of the side edge  44  or inboard of the film tube  52 . Accordingly, the sealing face  16  of the heat sealing element  14  extends across the side edge  44  of the film tube  52  so as to produce the sealed portion  46  and the notch  48  which extend inwardly from the side edge  44  of the film tube  52 . 
         [0049]    The heat sealing jaw  10  may also be positioned so as to orient the notch  48  in the sealed portion  46  at an oblique angle from the side edge  44  as shown in  FIG. 7 . This provides the advantage that the easy-open feature  42  can be used to facilitate the opening of the pouch  34  by tearing off a corner of the pouch  34 . Advantageously, this may also reduce the stress concentration factor created by the easy-open feature  42  in the pouch  34 . During filling and handling of the pouches  34 , tensile stresses are induced in the walls of the pouch  34  and the oblique orientation of the notch  48  of the easy-open feature  42  may reduce the tendency of the easy-open feature  42  to initiate failure of the pouch  34  during filling and handling. 
         [0050]    The clamping portion  24  of the heat sealing element  14  is thermally coupled to the jaw body  12  via the clamp  28 . Hence, the jaw body  12  and potentially also the clamp  28  can serve as a heat sink to draw heat away from the heat sealing element  14 . This results in a temperature gradient being induced along the sealing face  16  wherein the temperature of second end  20  of the sealing face  16  is lower than the temperature of the first end  18  of the sealing face  16 . The higher temperature near the first end  18  of the sealing face  16  allows the protrusion  26  to form a notch which may extend completely through the film layers while the lower temperature of the second end  20  of the sealing face  16  is such that a seal is not formed between the film layers and therefore allows the seal to be terminated at this location. Such a temperature gradient is beneficial in forming a suitable transition between the sealed portion  46  and an unsealed portion of the pouch  34 , which does not significantly compromise the integrity of the pouch  34 . Depending on the process conditions, any portion of the sealing face  16  where the temperature is such that no seal is formed between the film layers, may effectively serve to clamp and stabilize the film layers against the backing jaw in addition and similar to the support surface  51 . 
         [0051]    A suitable temperature gradient along the sealing face  16  of the heat sealing element  14  may be achieved in a number of different ways. For example, depending on the process conditions (i.e. film material, configuration of easy-open feature, cycle time), it may be necessary to use a jaw body  12  that is actively cooled using liquid cooling or the like. It may also be necessary to thermally isolate at least a portion of the heat sealing element  14  from the jaw body  12  using the thermal insulator  32 . A suitable material for the thermal insulator  32  could be for example a reinforced fibre glass material. Other choices would be apparent to those skilled in the art. The clamp  28  may also be thermally coupled to the clamping portion  24  and contribute to the heat sink. Proper design and material selection and configuration of the jaw body  12 , clamp  28  and thermal insulator  32  for producing a suitable temperature gradient along the sealing face  16  of the heat sealing element  14  will depend on the process conditions and will be apparent to one skilled in the art. Accordingly, it is also apparent that the components which contribute to the heat sink do not necessarily have to be electrically coupled to the heat sealing element  14 . 
         [0052]    Depending on the process conditions, it may also be desirable to use a release medium  56  between the heat sealing element  14  and the layers of film so as to prevent the film from adhering to the heat sealing element  14  when releasing the film following the sealing operation. The release medium  56  disposed on the sealing face  16  of the heat sealing element  14  is illustrated in  FIG. 4 . Teflon® tape or film is suitable for this purpose. Similarly, a release medium may also be disposed on the resilient backing member  50 . 
         [0053]    Depending on the process conditions, it may also be desirable to use an electrical insulating medium between the back face  22  of the heat sealing element  14  so as to electrically insulate the heat sealing element  14  from the jaw body  12 . In one embodiment, the thermal insulator  32  may also be an electrical insulator. In another embodiment, the electrical insulating medium can be Teflon® tape or a film suitable to provide electrical insulation. The tape or film may also extend beyond the end of the thermal insulator  32  to provide electrical insulation as far as the clamping portion  24 . In some embodiments, the electrical insulating medium may further provide additional thermal insulation. 
         [0054]    The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without department from the scope of the invention disclosed. It is apparent that the heat sealing jaw  10  described above can be fabricated using conventional manufacturing procedures using suitable materials that would be apparent to a person skilled in the relevant art. It is also apparent that other heat sink configurations may also be used for producing a suitable temperature gradient along the sealing face  16  of the heat sealing element  14 . One skilled in the art would also recognize that an easy-open feature located at a distance from a free edge of the pouch may also be produced using a heat sealing element  14  wherein both the first section end  16  and the second section end  18  are coupled to a heat sink and the sealing face does not extend across an edge of the pouch. It is further apparent that the heat sealing jaw  10  is not limited to vertical form, fill and seal machines but could also be used on other types of packaging machines. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.