Patent Publication Number: US-2012033901-A1

Title: Bag comprising machine direction oriented film

Description:
CROSS REFERENCE TO RELATED APPLICATIONS: This application claims the benefit of provisional patent application Ser. No. 61/400,886, filed 2010 Aug. 4 by the present inventor. 
    
    
     FEDERALLY SPONSORED RESEARCH 
     None 
     BACKGROUND  
       1 . Field 
     This invention relates to flexible bags having a polyethylene, machine direction oriented polyethylene wall structure. 
       2 . Prior Art 
     Flexible packaging has played an increasing role in containing a wide variety of products ranging from liquid and dry chemicals to food products. Due to this wide variety of products, the flexible packaging industry is constantly changing the characteristics of the bag structures to meet the changing needs of the packers and consumers. Desired bag characteristics include optical clarity, rigidity, toughness, heat resistance, and recyclability. 
     Free standing, or stand-up pouches, offer better retail presentation since the printed front panel of the pouch is directly in front of the consumer when either hanging from a store rack or sitting on a store shelf. Stand-up pouches, like the one disclosed in U.S. Pat. No. 3,738,565 to Ackley (1973) demonstrate the need for free standing bags. Stand-up pouches often rely on a lamination of polyester, nylon, or polypropylene to polyethylene. The polyester, nylon, or polypropylene offer good clarity, rigidity, and heat resistance while the polyethylene offers a sealant layer to seal the bag closed using heat and pressure. The heat resistance on the outer layer is used to resist sticking to the high temperature sealing jaws of the packer machine. A sealant layer of polyethylene, although needed to seal the bag closed, does not have the rigidity desired in many packaging applications to stand up on a display shelf. A polyethylene to non-polyethylene lamination, however, is problematic for recycling due to the incompatible materials found in the bag. 
     Other modifications to the bag film structure have been made in the past to achieve different bag characteristics. U.S. Pat. No. 5,827,586 to Yamashita (1998) and U.S. Pat. No. 6,306,472 to Buelow (2001) are examples of film modifications that were needed. Neither of these address the rigidity and recyclability concerns of today&#39;s stand-up pouches. 
     Machine Direction Oriented film or MDO is polyethylene having more heat resistance and rigidity than standard polyethylene film. MDO film is sometimes sold as a sealant layer to packaging facilities to laminate to more rigid plastic films such as the previously mentioned polyester or polypropylene. By laminating MDO film to polyethylene, the entire package can be made of compatible plastics for recycling and still have the desired rigidity and heat resistance of other commonly used laminations. 
     The preferred embodiment of this invention uses MDO film on the outer wall and a standard polyethylene film on the inside wall of the flexible package. 
    
    
     
       DRAWINGS 
         FIG. 1  is an enlarged cross sectional view of the laminate components of the preferred embodiment. 
         FIG. 2  is a view of a stand-up pouch. 
         FIG. 3  is an enlarged view of the top of a stand-up pouch in accordance with one embodiment. 
         FIG. 4  is an enlarged view of the top of a stand-up pouch showing the polyethylene sealant layer heat sealed closed in accordance with one embodiment. 
     
    
    
     DRAWINGS—REFERENCE NUMERALS 
       1  Machine direction oriented polyethylene layer 
       2  Polyethylene sealant layer 
       3  Adhesive layer 
       4  Stand-up pouch 
     DETAILED DESCRIPTION 
     The laminated film of the preferred embodiment of the present invention is shown in  FIG. 1 . Machine direction oriented polyethylene film ( 1 ) is laminated with a substantially thin layer of adhesive ( 3 ) or tie layer to a polyethylene sealant layer ( 2 ). When the laminated film is formed to make a stand-up pouch ( 4 ) or flat bag, the machine direction oriented polyethylene ( 1 ) serves to stiffen the package, a trait desired in stand-up pouches. The machine direction oriented polyethylene ( 1 ) also has a slightly higher melt temperature and therefore provides heat resistance when the inner sealant layers of polyethylene ( 2 ) are heat sealed together. A stand-up pouch ( 4 ) is shown in  FIG. 2 . 
       FIG. 3  illustrates the desired MDO ( 1 ) and polyethylene ( 2 ) films of the stand-up pouch ( 4 ) in  FIG. 2 . Although the adhesive ( 3 ) or tie layer may be used, this illustration is not meant to limit the scope of the invention. The polyethylene layer ( 2 ) may be co-extruded with the MDO layer ( 1 ) and thus eliminate the adhesive layer ( 3 ). One disadvantage of co-extruding MDO ( 1 ) and polyethylene ( 2 ) is the ability to print on the inside of the structure. If the film is laminated instead of co-extruded, the MDO ( 1 ) can be printed and the ink can be sandwiched between the MDO ( 1 ) and polyethylene ( 2 ) layers in the laminating process. This helps protect the printed graphics and also keeps the ink from coming into contact with the contents of the package. 
       FIG. 4  shows an enlarged view of the stand-up pouch ( 4 ) with the polyethylene sealant layers ( 2 ) fused together following the application of heat and pressure with the sealing jaws of a typical bag making machine. 
     The resulting package simplifies recycling due to the substantial polyethylene ( 2 ) and machine direction oriented polyethylene ( 1 ) composition. Further, additions of degradable additive may be combined with the machine direction oriented polyethylene ( 1 ) and polyethylene ( 2 ) to enhance degradation.