Patent Publication Number: US-2006016708-A1

Title: Transparent autoclavable bag

Description:
FIELD OF THE INVENTION  
      The invention relates to a sterilization bag for medical applications, and to a composite film laminate suitable for producing such a bag.  
     BACKGROUND OF THE INVENTION  
      Many healthcare products, including medical devices and pharmaceutical solutions, are stored until ready for use inside of sealed sterilization bags. Typically, the bags are in the form of a pouch, open along one side for receiving the medical instrument or other medical supply. The bag is then sealed and subjected to sterilization by exposure to gamma irradiation, electron beam, ultraviolet radiation, ethylene oxide, autoclaving, or other sterilization procedures.  
      In order to withstand the severe conditions of sterilization while providing high moisture barrier properties and long shelf life, sterilization bags this type have traditionally used composite laminate films with a barrier layer of either a metal foil or a metallized film. A disadvantage this type of laminate structure is that the bag is not transparent and therefore does not reveal the contents of the bag. To address this problem, some sterilization bags have provided a small window formed of a transparent barrier material. However, in order to maintain high barrier properties for the bag, the transparent window is kept relatively small in size. It would be desirable for a sterilization bag to have at least one transparent side to more clearly reveal the contents of the bag.  
     SUMMARY OF THE INVENTION  
      The present invention provides a transparent high barrier laminate material that can be suitably fabricated into sterilization bags, providing the ability to see the contents of the bag. The high barrier properties are achieved by using as the barrier layer a molecularly oriented polychlorotrifluoroethylene (PCTFE) film layer.  
      The autoclavable sterilization bag of the present invention comprises first and second composite film laminates positioned in opposing relation and sealed to one another to form a pouch. At least the first laminate comprises a heat sealable transparent thermoplastic polymer inner layer forming an inner surface of the laminate and a transparent polymer film outer layer. A transparent barrier layer is located between the inner and outer layers and formed of molecularly oriented polychlorotrifluoroethylene (PCTFE). In advantageous specific embodiments of the invention, the heat sealable transparent thermoplastic polymer inner layer is a polyolefin film, polyolefin copolymer, or coextrusions of either, and the transparent polymer outer layer is a film selected from the group consisting of polyethylene terephthalate, nylon, polypropylene, polyethylene and cellophane.  
      Polychlorotrifluoroethylene (PCTFE) fluoropolymer films are manufactured and sold by Honeywell Inc. under the trademark Aclar®. Non-oriented PCTFE films are used extensively by pharmaceutical companies in manufacturing transparent vacuum-formed blister packages for pharmaceuticals and for other healthcare packaging. However, PCTFE films have seen limited success in non-forming barrier applications in the flexible packaging industry.  
      The present invention is based upon the discovery that molecularly oriented PCTFE films provide a clear structure with sufficient barrier properties to replace metal foil in even the most demanding barrier applications utilizing ethylene oxide, gamma sterilization, e-beam sterilization, and autoclave sterilization techniques, as well as in non-sterilized applications. Molecularly orienting the PCTFE film decreases the moisture permeation rate significantly as compared to standard non-oriented PCTFE film and provides a very durable barrier layer with superior flex crack resistance.  
      For most polymer films, the process of molecularly orienting the film results in the film having poor dimensional stability at elevated temperature. When the film is reheated, the molecular chains tend to try to revert to their original non-oriented state, resulting in a dimensional change in the film. When the film is a component of a composite laminate, the dimensional change can result in warping, curling or other unsightly and undesirable changes in the product. Molecularly oriented PCTFE film has surprisingly good thermal dimensional stability, and thus is well suited for use in applications involving exposure to high temperatures, such as in an autoclave sterilization process.  
      The present invention also provides a dimensionally stable autoclavable composite film laminate that can be used in the fabrication of sterilization bags or other articles. The laminate comprises a heat sealable transparent thermoplastic polymer inner layer forming an inner surface of the laminate, a transparent polymer film outer layer, and a transparent barrier layer between the inner and outer layers and formed of molecularly oriented polychlorotrifluoroethylene (PCTFE). In advantageous embodiments of the invention, the heat sealable transparent thermoplastic polymer inner layer is a film or coating of a polyolefin, polyolefin copolymers, or coextrusions of either, and the transparent polymer outer layer is a film selected from the group consisting of polyethylene terephthalate, nylon, polypropylene, polyethylene and cellophane. The laminate may suitably include a layer of adhesive adhering the polyolefin film inner layer to the transparent barrier layer. The laminate may further include a layer of adhesive adhering the transparent polymer outer film layer to the barrier layer. In one specific embodiment, the dimensionally stable autoclavable composite film laminate comprises a heat sealable transparent polypropylene inner layer forming an inner surface of the laminate, a transparent biaxially oriented polyethylene terephthalate film outer layer, and a transparent barrier layer between the inner and outer layers and formed of molecularly oriented polychlorotrifluoroethylene (PCTFE). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:  
       FIG. 1  is a top plan view of a sterilization bag in accordance with one embodiment of the present invention.  
       FIG. 2  is a cross-sectional view of a heat sealed edge portion of the bag taken substantially along the line  2 - 2  of  FIG. 1 .  
       FIG. 3  is a cross-sectional view showing one embodiment of a dimensionally stable composite film laminate useful in producing the sterilization bag of  FIG. 1 .  
       FIG. 4  is a cross-sectional view showing a second embodiment of a dimensionally stable composite film laminate in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS  
      The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.  
      In  FIG. 1 , the reference character  10  indicates an autoclavable sterilization bag in accordance with the present invention. The bag  10  is formed from first and second composite film laminates  11 ,  12  positioned in opposing face-to-face relation and sealed to one another along three sides to form a pouch-like structure, leaving an opening  14  along the remaining side suitable for receiving medical instruments or other articles for being sterilized. In the embodiment shown, the film laminates  11 ,  12  are generally rectangular in shape and they are sealed to one another along seal areas  15 , 16  adjacent opposite side edges of the bag, and along an angularly extending seal area  17  adjacent the top edge of the bag. After the bag  10  has been filled with its contents by the user, it may be sealed to close the opening  14 . Sealing of the film laminates  11 ,  12  to one another may be carried out using conventional heat or ultrasonic sealing equipment as is well known in the art.  
      As shown in greater detail in  FIG. 2 , the film laminate  11  includes three film layers, a heat sealable transparent thermoplastic polymer film inner layer  21  that forms an inner surface of the laminate, a transparent polymer film outer layer  22 , and a transparent barrier film layer  23  between the inner and outer film layers  21 ,  22 . The three film layers  21 ,  22 ,  23  are laminated to one another by adhesive. The thermoplastic polymer film outer layer  21  has an exposed surface that will soften and become adhesive upon exposure to heat or ultrasonic energy. The film layer  21  is preferably a polyolefin material, suitable examples of which include polypropylene, polyethylene, ethylene copolymers such as EAA, EMA, EVA and ionomer resins such as Surlyng from DuPont or Iotek™ from ExxonMobil. A particularly suitable film material for the inner film layer  21  is a cast polypropylene film made using a cast film extrusion process. The film layer  21  may suitably have a thickness of from about 0.5 mils to about 4.0 mils, more preferably about 1.5 to about 3.0 mils, and most preferably about 2 mils.  
      The transparent outer film layer  22  imparts strength, puncture resistance, dimensional stability and durability to the film laminate. The film layer  22  also assists in giving the laminate resistance to shrinkage when heated to elevated temperature. Suitable materials for the outer film  22  include polyethylene terephthalate (PET), nylon, polypropylene, polyethylene and cellophane. Particularly preferred are biaxially oriented films such as biaxially oriented PET and biaxially oriented nylon. The outer film layer  22  may have a thickness of from about 0.36 to 2.0 mils, more preferably from about 0.48 to 1.0 mils, and most preferably about 0.48 mils (48 ga).  
      The transparent barrier layer  23  imparts moisture barrier properties to the laminate. Barrier layer  23  is a molecularly oriented polychlorotrifluoroethylene (PCTFE) fluoropolymer film. The PCTFE film is transparent, biochemically inert, chemical resistant and free from plasticizers and stabilizers. Preferably the molecularly oriented PCTFE film is a monoaxially oriented film. The film may suitably have a thickness of from about 0.60 to 3 mils, more preferably from about 1 to 2 mils, and most preferably a thickness of about 1.5 mils. PCTFE fluoropolymer films are sold by Honeywell, Inc. under the Aclar® trademark.  
      The sealable inner film layer  21  may be laminated to the barrier layer  23  with an adhesive, using conventional lamination techniques. The adhesive may be applied using known processes such as spraying, roll coating, knife over roll coating, wire rod coating, or gravure coating. Suitable adhesives include solvent based, water based or solventless adhesives including acrylic adhesives, epoxy cured polyester urethanes, moisture cured polyester urethanes and isocyanate terminated polyester adhesives. Alternatively, the inner layer  21  can be formed directly on the barrier layer  23  by extrusion coating. The transparent outer layer  22  can be laminated directly to the barrier layer  23  using known adhesives and techniques as described above. If desired, the inner surface of the transparent outer layer  22  may be reverse printed prior to laminating to provide a layer of printing with graphics or other information. The outer layer may also be surface printed prior to or post lamination.  
      The film laminate  12  in the embodiment shown in  FIG. 2  includes a metal foil layer  24  with a sealable inner surface defined by a sealable film layer  25  of a thermoplastic polymer, such as a polyolefin. Alternatively, the sealable layer  25  can be a coating of a thermoplastic polymer such as a polyolefin. The foil layer  24  may comprise an aluminum foil having a thickness of from 0.275 mil to 1.50 mil. The sealable layer  25  may suitably have a thickness of about 0.5 mil to 4.0 mil. The foil layer  24  provides moisture barrier properties to the laminate. The coating layer  25  facilitates obtaining a strong seal with the heat sealable inner layer  21  of composite laminate  11 . The laminate  12  additionally includes a protective outer film layer  26  formed of biaxially oriented PET laminated by an adhesive to the surface of the foil layer  24 . The outer film layer  26  may be optionally reverse or surface printed with graphics or other information. In alternative embodiments, the metal layer may comprise a vacuum metallized moisture barrier layer deposited on a film layer such as PET.  
       FIG. 3  shows a cross-section of the composite film laminate  11  in greater detail. It will be seen that the inner layer  21  is laminated to the intermediate barrier layer  23  by an adhesive layer  27 . The outer layer  22  is laminated to the opposite surface of the intermediate barrier layer  23  by an adhesive layer  20 .  
       FIG. 4  shows an alternative construction for a transparent composite film laminate  11 ′ which is similar in many respects to the laminate  11  shown in  FIGS. 2 and 3 . To avoid repetitive description, corresponding reference numbers are used to identify corresponding elements wherever applicable. This embodiment differs over that of  FIG. 3  in that there is an additional intermediate film layer  30  located between the heat sealable inner layer  21  and the barrier layer  23 . This intermediate barrier layer may suitably comprise a biaxially oriented nylon film or a biaxially oriented PET film, or biaxially oriented polypropylene. It may suitably have a thickness of from 0.36 to 2.0 mils. It is laminated to the inner film layer  21  by an adhesive layer  27  and to the intermediate barrier layer  23  by an adhesive layer  32 .  
      In the embodiment shown and described, the autoclavable bag  10  has a transparent composite film laminate  11  on one side and an opaque metal layer-containing laminate  12  on the opposite side. The article contained within the bag is readily visible through the transparent film laminate  11 . However, bags in accordance with the present invention can also be produced using the transparent composites film laminate  11  for both the front and back side of the bag.  
     EXAMPLES  
     Example 1  
      A dimensionally stable composite film laminate was manufactured by first laminating a 0.48 mil biaxially oriented transparent polyethylene terephthalate (PET) film to a 1.5 mil thick monoaxially oriented transparent Aclar® polychlorotrifluoroethylene (PCTFE) film to form a two-layer composite. Rolls of the PET film and the Aclarg film were each mounted on unroll stands. The PET film was unrolled and directed across a gravure coating apparatus and a 1.5 lb/ream layer of urethane adhesive was applied to one surface. The Aclar® film was unrolled and then brought into contact with the adhesive-coated surface of the PET film, and the films were directed through a nip formed between two smooth surface rolls. A 2.0 mil polypropylene transparent film made using a cast film extrusion process was then laminated to the exposed surface of the Aclar® film by a similar laminating procedure. The resulting composite laminate exhibited high moisture barrier properties and excellent dimensional stability at elevated temperature. The 1.5 mil machine direction oriented Aclar® layer provided a moisture barrier of 0.0077 g/100 in 2 /24 hours at 100° F. and 100% relative humidity.  
     Example 2  
      A laminating procedure similar to that described in  FIG. 1  was used to produce the following metal laminate: 48 gauge biaxially oriented transparent PET film/adhesive/35 gauge aluminum foil/adhesive/2.0 mil cast polypropylene This tri-laminate was positioned opposite the laminate of Example 1, with the polypropylene surfaces facing one another and the two films were contacted with a heat sealing die to seal the two films together into a pouch of the configuration generally similar to that shown in  FIG. 1 .  
     Example 3  
      A metal laminate of the following structure can be produced by a procedure similar to example 2: 0.48 mil biaxially oriented transparent PET film with a coating of aluminum deposited on one surface by vacuum metallization to an optical density of 2.8/adhesive/2.0 mil cast polypropylene. A pouch is fabricated from this laminate and the laminate of Example 1.  
     Example 4  
      A pouch is produced by the procedure generally described Example 2, except that the following transparent laminate structure is substituted for the transparent laminate of example 1: 48 gauge biaxially oriented PET/adhesive/1.5 mil oriented Aclar® PCTFE film/adhesive/0.6 mil biaxially oriented nylon film/adhesive/2.0 mil cast polypropylene.  
     Example 5  
      A pouch is produced by the procedure generally described example 2, except that the following transparent laminate structure is substituted for the transparent laminate of Example 1: 48 gauge biaxially oriented PET/adhesive/1.5 mil oriented Aclar® PCTFE film/adhesive/0.48 mil biaxially oriented PET film/adhesive/2.0 mil cast polypropylene.  
      Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.