Abstract:
Multilayer films and packaging structures having a delamination seal and an oxygen barrier layer are disclosed. The delamination structure adjacent to the EVOH oxygen barrier layer binds well to the EVOH layer and also retains its ability to delaminate. The multilayer films, and packages in which they are utilized, have several layers including a first, external layer; a second, tie layer comprising a mixture of polybutylene and an anhydride modified polyethylene such that a peelable bond is formed between said first, external layer and said second, tie layer; a third, core layer comprising ethylene vinyl alcohol which functions as an oxygen barrier layer; a fourth, tie layer comprising an anhydride modified polyethylene and a fifth, external layer.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the packaging industry. More particularly, the invention relates to multilayer films and packages which incorporate a delamination seal feature and also have oxygen barrier properties. 
     BACKGROUND OF THE INVENTION 
     In many commercial packaging applications it is desirable to provide multilayer packaging materials in order to produce a package having multiple attributes. For instance, in the food packaging area, it is especially desirable to make consumer packages which are readily opened by digital pull-apart force. Delamination seals are particularly useful for this purpose. These seals include two or more layers and in which delamination occurs between two of the layers. Such a delamination system works on the principal that a bond is formed between structural package layers and one of the layers making up the delamination structure which has a greater bond strength than the peelable bond between the two film layers which delaminate from each other with manual force. Choice of materials determines which layers will delaminate from each other. 
     It is also important to place perishable foods such as meats and cheeses into packages which allow for the preservation of these foods for as long as possible. Maximizing the time in which the food remains preserved, especially between initial packaging and arrival at the retail store is especially important. Atmospheric oxygen is a common culprit in promoting food spoilage. Oxygen is reduced to a variety of free radical species which oxidize carbon-carbon double bonds in food and other perishable products. Such oxidation by free radicals adversely affects the odor and flavor of certain foods and can affect the stability of non-food products. Thus, it is desirable to incorporate oxygen barrier film layers into packaging materials. A particularly effective oxygen barrier material is ethylene vinyl alcohol (EVOH). 
     Providing packages having multiple attributes such as an easy opening delamination seal and oxygen barrier properties frequently necessitates bonding multiple layers of film having different properties together. Unfortunately, many film materials are not compatible with and thus, do not adequately seal to other packaging materials. It has been especially difficult to directly seal oxygen barrier film layers containing EVOH to film layers typically used in delamination seal technology. One approach to the problem is to interpose extra layers in between the EVOH layer and the layers making up the delamination seal. However, this approach does not always prove expedient or convenient. 
     A need therefore exists for a multilayer packaging material having an oxygen barrier layer as well as delamination layers. Furthermore, it is desirable to achieve this structure with a minimal number of film layers. It is therefore necessary to find film layer materials which bind together well and also retain their independent attributes of ease of delamination and oxygen barrier properties. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to multilayer films and packaging structures having a delamination seal and an oxygen barrier layer. The delamination structure adjacent to the EVOH oxygen barrier layer binds well to the EVOH layer and also retains its ability to delaminate. 
     In one embodiment, the invention provides an easy open package adapted to be heat sealed closed in order to contain a product within the package. The package is easily opened by manual force. The package includes a first package wall having a multilayer film construction. The multilayer film construction includes the following layers: a first, external layer; a second, tie layer comprising a blend of an anhydride modified polyethylene and one or a mixture of polybutylene, polypropylene or a styrene-butadiene copolymer so that a peelable bond is formed between the first, external layer and the second, tie layer; a third, core layer comprising ethylene vinyl alcohol; a fourth, tie layer comprising an anhydride modified polyethylene; and a fifth, external layer. The package also includes a second package wall joined at a portion of its perimeter to the first package wall. The first, external layer of the first package wall is heat sealed to the second package wall to create a sealed pouch or package, The bond formed between the first, external layer of the first package wall and the second package wall has a greater bond strength compared to the peelable bond so that upon application of manual force, the first and second package walls will remain bonded together and delamination will occur between the peelably bonded layers. 
     In a preferred embodiment, the first package wall has a multilayer film construction specifically including the following layers: a first, external layer comprising an ethylene vinyl acetate copolymer; a second, tie layer comprising a blend of an anhydride modified polyethylene and a compound selected from the group consisting of polybutylene, polypropylene and a styrene-butadiene copolymer such that a peelable bond is formed between the first, external layer and said second, tie layer; a third, core layer comprising ethylene vinyl alcohol; a fourth, tie layer comprising an anhydride modified polyethylene and a fifth, external layer comprising an ethylene vinyl acetate copolymer. The package also includes a second package wall joined at a portion of its perimeter to the first package wall. The first, external layer of the first package wall is heat sealed to the second package wall to create a sealed pouch or package. The bond formed between the first, external layer of the first package wall and the second package wall has a greater bond strength compared to the peelable bond so that upon application of manual force, the first and second package walls will remain bonded together and delamination will occur between the peelably bonded layers. 
     In yet another preferred embodiment, the second package wall comprises a polymer which is identical to or, at least, heat seal compatible to, the first package wall. 
     In an especially preferred embodiment, the second, tie layer of the first package wall comprises approximately ten to thirty-five percent polybutylene by weight and between about sixty-five to ninety percent of an anhydride modified polyethylene by weight. 
     In a second embodiment, the present invention provides a multilayer film construction which includes the following layers: a first, external layer; a second, tie layer comprising a blend of an anhydride modified polyethylene and a compound selected from the group consisting of polybutylene, and a styrene-butadiene copolymer so that a peelable bond is formed between the first, external layer and the second, tie layer; a third, core layer comprising ethylene vinyl alcohol; a fourth, tie layer comprising an anhydride modified polyethylene and a fifth, external layer. 
     In a preferred embodiment, the multilayer film construction specifically includes the following layers: a first, external layer comprising an ethylene vinyl acetate copolymer; a second, tie layer comprising a blend of an anhydride modified polyethylene and a compound selected from the group consisting of polybutylene, polypropylene and a styrene-butadiene copolymer such that a peelable bond is formed between the first, external layer and said second, tie layer; a third, core layer comprising ethylene vinyl alcohol; a fourth, tie layer comprising an anhydride modified polyethylene and a fifth, external layer comprising an ethylene vinyl acetate copolymer. 
     In an especially preferred embodiment, the second, tie layer of the multilayer film construction comprises approximately ten to thirty-five percent polybutylene by weight and between about seventy to ninety percent of an anhydride modified polyethylene by weight. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which: 
     FIG. 1 is a side sectional view of the multilayer film of the instant invention. 
     FIG. 2 is a side sectional view of the multilayer film shown in FIG. 1 heat sealed to an opposing package film. 
     FIG. 3 is a view of a closed, heat sealed package which incorporates the multilayer film of the instant invention. 
     FIG. 3 a  is a magnified view of a portion of the package depicted in FIG.  3 . 
     FIG. 4 is a view of the heat sealed package depicted in FIG. 3 being opened by a consumer. 
     FIG. 5 is a view of a lidded cup showing delamination occurring between the peelably sealed layers. 
    
    
     While the invention will be described in connection with certain preferred embodiments, it is not intended to limit the invention to the specific exemplary embodiments. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to the drawings, FIG. 1 depicts the multilayer film  12  of the instant invention. The multilayer film  12  is composed of five distinct layers of resins and/or resin combinations. The inside, or first external layer  2  is preferably made of an ethylene vinyl acetate (EVA) resin. Slip/antiblock additives may be added to improve the surface characteristics of various film layers. An example of an antiblock additive is silica. An example of a slip additive is erucamide, a fatty acid amide. Other suitable resins for the first, external layer  2  include an ethylene vinyl acetate copolymer, linear low density polyethylene, an ethylene ethyl acrylate copolymer, an ethylene methyl acrylate copolymer, a neutralized ethylene acid copolymer, and low density polyethylene and certain mixtures and blends of these resins. As shown in FIG. 2, it is this first, external layer  2  which is heat sealed to a second package film  14  to form a package. Most preferably, the second package film is a single layer film which is heat seal compatible to the portion of the first package wall to which it is heat sealed. Most preferably, these two heat sealable surfaces are made of identical materials. The heat seal area is indicated by cross-hatching. 
     The first external layer  2  is a thin layer, preferably measuring only approximately ten percent of the total thickness of the multilayer film  12  of the instant invention. The second, tie layer  4  is the layer containing the resin combinations giving this film structure the ability to perform as a delamination peelable sealant. Specifically, the second, tie layer  4  is comprised of a combination of an anhydride modified polyethylene and polybutylene, polypropylene and/or styrene-butadiene copolymer resins. Most preferably, the anhydride modified polyethylene component of the tie layer  4  is made of a combination of Bynel® resins from E.I. DuPont De Nemours &amp; Company, Wilmington, Del. Specifically, it is most preferable to utilize a blend of a Bynel® resin which is an anhydride modified linear low density polyethylene (LLDPE) with a Bynel® resin which an anhydride modified low density polyethylene (LDPE) and combine this blend with polybutylene. This combination of Bynel® adhesives and polybutylene allows the first, external layer  2  and the second, tie layer  4  to separate while maintaining adhesion between the second, tie layer  4  and the third oxygen barrier layer  6 . The second, tie layer  4  preferably comprises between about ten to thirty-five percent polybutylene by weight and between about sixty-five to ninety percent of Bynel® resins by weight. Most preferably, the second, tie layer  4  is made up of approximately 20% polybutylene by weight and about 80% of Bynel® resins by weight. The second, tie layer  4  measures approximately fifteen percent of the total thickness of the multilayer film  12 . 
     The center core layer  6  contains an ethylene vinyl alcohol (EVOH) barrier resin. This layer is primarily responsible for the oxygen barrier properties of the multilayer film of the instant invention. This core layer  6  measures approximately ten percent of the total thickness of the multilayer film  12 . 
     The fourth, tie layer  8  is comprised of an anhydride modified polyethylene such as Bynel® or a combination of Bynel® resins and an ethylene vinyl acetate (EVA) resin. This fourth, tie layer  8  measures approximately thirty-five percent of the total thickness of the multilayer film  12 . 
     The fifth, external layer  10  comprises EVA, preferably having a low vinyl acetate content. Other suitable resins for the fifth layer include an ethylene vinyl acetate copolymer, linear low density polyethylene, an ethylene ethyl acrylate copolymer, an ethylene methyl acrylate copolymer, a neutralized ethylene acid copolymer, and low density polyethylene and certain mixtures and blends of these resins. This fifth, external layer  10  is the side of the multilayer film that may be laminated to other layers including forming webs and non-forming webs, both printed and unprinted. This fifth, external layer  10  measures approximately thirty percent of the total thickness of the multilayer film  12 . The total thickness of the multi-layer film is approximately 2.0 mils. 
     Provided below is a simple illustration of the preferred five layer multilayer film of the instant invention: 
     
       
         
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 5-Layer EVA-EVOH Delamination Structure: 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 EVA + 
                 Bynel Adhesive Resin + 
                   
                 Adhesive 
                 EVA 
               
               
                 Slip/AB 
                 Polybutylene Resin 
                 EVOH Resin 
                 Tie 
                 Resin 
               
               
                 Inside 
                 Peelable Tie 
                 Core 
                 Outside 
                 Outside 
               
               
                   
                   
                   
                 Tie 
               
               
                 Layer 1 
                 Layer 2 
                 Layer 3 
                 Layer 4 
                 Layer 5 
               
               
                   
               
             
          
         
       
     
     FIG. 2 shows the multilayer film  12  shown in FIG. 1 heat sealed to an opposing package film  14 . In order to insure adequate heat sealing between the two multilayer packaging films,  12  and  14 , the first, external layer  2  of the first multilayer package film  12  should be of the same or a similar composition to the second packaging film  14 . Films with similar properties heat seal best to each other. If the second packaging film  14  is a multilayered film, the layer which contacts the first external layer of the first multilayered film  12  should be of the same or a similar composition. Thus, if the first, external layer  2  of the first multilayer package film  12  is made up of EVA, the second package film  14  or if multilayered, the layer of package film  14  which is heat sealed to the first multilayer film  12 , should also be made of EVA or a composition with properties similar to that of EVA. 
     FIG. 3 shows a package  18  having first and second package walls  20 ,  30  having multilayer film construction. The first package wall  20  is joined at a portion of its perimeter  21  to the second package wall  30 . Again, the two package walls need not be identical as long as the film layer of one package wall that is to be heat sealed to the film layer of the second package wall are heat seat compatible. 
     FIG. 3 a  is a magnified view of the area of FIG. 3 identified by the dotted circle. The bond formed between the first, external layer  22  of the first package wall  20  and the first external layer  32  of the second package wall  30  has a greater bond strength than the peelable bond between the first external layer  22  of the first package wall  20  and the second tie layer  24  of the first package wall  20  such that upon application of digital pull-apart force, the first and second package walls  20 ,  30  will remain bonded together and delamination will occur at the peelable bond between the first, external layer  22  and the second, tie layer  24  of the first package wall  20 . It is preferable that the second package wall not include a delamination seal such that a clean delamination occurs. 
     FIG. 4 shows the multilayer package  18  depicted in FIG. 3 being opened by a consumer. The consumer must simply grasp the two opposing package walls  20 ,  30  and pull to start the delamination or peeling process. One can pull from below the heat sealed top portion of the package or, if one package wall extends above the opposing package wall, one can pull apart the delamination layers from the top portion of the package. Preferably, the uppermost portions of the first and second package walls are not heat sealed together at their uppermost perimeters, creating tabs on flanges to grab and pull apart. 
     As discussed, the resin combinations in the second tie layer  24  allow the film structure constituting the first package wall  20  to separate at the interface of the first external layer  22  and the second, tie layer  24  when the consumer peels apart a package which is heat sealed at the first and second package wall interface  25 . When the first and second layers  22  and  24 , respectively separate, the first, external layer  22  stays with the second package wall  30  to which it was heat sealed and the new surface of the original five layer film making up the first package wall  20  becomes the second, tie layer  24 . A by-product of the delamination process provides a tamper-evident feature to alert the consumer if the package has been partially or completely opened prior to purchase or use of the product contained within the package by the consumer. Specifically, as the peelable layers delaminate from each other, a whitening occurs on the surface of the delaminated layers. 
     Provided below is a simple illustration depicting delamination: 
     
       
         
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 Package Opened and Delamination Occurs: 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Heat 
                   
                   
                   
               
               
                 Second 
                 ////////// 
                   
                 Delamination 
               
               
                 Package 
                 ///////// 
                   
                 Occurs 
               
               
                 Wall 
                 Seal 
                 EVA 
                 HERE 
                 Peelable Tie 
               
               
                 LAYER 1 
                   
                 LAYER 2 
               
               
                   
               
             
          
         
       
     
     FIG. 5 depicts an alternate embodiment of the instant invention. A multilayer film construction as shown in FIG. 1 can be incorporated into the lid  36  of a package constituting a polymeric pre-formed cup or receptacle  38 . The lid  36  can be hermetically heat sealed to the exposed lip  40  of the receptacle and constitute a multilayered construction including a delamination peelable seal such that a consumer can easily open the package. The five layers (not shown in FIG. 5) of the lid  36  are of the same composition as the layers of the multilayer film shown in FIG.  1 . Specifically, the film structure of the lid constitutes a first external layer  2  preferably made of an ethylene vinyl acetate (EVA) resin. Slip/antiblock additives may be added to achieve desired surface characteristics. Other suitable resins for the first, external layer  2  include an ethylene vinyl acetate copolymer, linear low density polyethylene, an ethylene ethyl acrylate copolymer, an ethylene methyl acrylate copolymer, a neutralized ethylene acid copolymer, and low density polyethylene and certain mixtures and blends of these resins. This first, external layer  2  is heat sealed to the receptacle. The second, tie layer  4  is the layer containing the resin combinations giving the layers of the lid the ability to perform as a delamination peelable seal. Specifically, the second, tie layer  4  is comprised of a combination of an anhydride modified polyethylene and polybutylene, polypropylene and/or styrene-butadiene copolymer resins. Most preferably, the anhydride modified polyethylene component of the tie layer  4  is made of a combination of Bynel® resins from E.I. DuPont De Nemours &amp; Company, Wilmington, Del. Specifically, it is most preferable to utilize a blend of a Bynel® resin which is an anhydride modified linear low density polyethylene (LLDPE) with a Bynel® resin which an anhydride modified low density polyethylene (LDPE) and combine this blend with polybutylene. This combination of Bynel® adhesives and polybutylene allows the first, external layer  2  and the second, tie layer  4  to separate while maintaining adhesion between the second, tie layer  4  and the third oxygen barrier layer  6 . The second, tie layer  4  preferably comprises between about ten to thirty-five percent polybutylene by weight and between about sixty-five to ninety percent of an anhydride modified polyethylene by weight. Most preferably, the second, tie layer  4  is made up of approximately twenty percent polybutylene by weight and about eighty percent of an anhydride modified polyethylene by weight. 
     The center core layer  6  contains an ethylene vinyl alcohol (EVOH) barrier resin. This layer is primarily responsible for the oxygen barrier properties of the multilayer film of the instant invention. 
     The fourth, tie layer  8  is comprised of an anhydride modified polyethylene such as Bynel® or a combination of Bynel resins and an ethylene vinyl acetate (EVA) resin. 
     The fifth, external layer  10  comprises EVA, preferably having a low vinyl acetate content. Other suitable resins for the fifth layer include ethylene vinyl acetate copolymer, linear low density polyethylene, ethylene ethyl acrylate copolymer, ethylene methyl acrylate copolymer, neutralized ethylene acid copolymer, and low density polyethylene and certain mixtures and blends of these resins. Preferably, the material making up the lip  40  of the receptacle is made of the same of similar material to the first external layer  2  of the multilayer film of the lid  36 . Of course, the lip  40 , and entire receptacle  38  for that matter, may also be multilayered. 
     As is true of all of the packages incorporating the multilayer film  12  of the instant invention, additional layers (not shown) of polymeric or non-polymeric material such a paper or foil may be bonded to the fifth, external layer  10  of the multilayer film  12 . 
     Multilayer films of the instant invention can be formed by any of the conventional processes for making films and multilayer films including laminations, extrusions, coextrusion, blown extrusion, tubular water quench extrusion, extrusion coating and the like. Coextrusion utilizing a tubular water quench process is presently preferred for forming the multilayer films of the instant invention. These multilayer films can be formed into usefull articles such as packages, e.g. pouches, containers, and the like by conventional processes for making such articles including blow molding, stretch blow molding, and similar processes. 
     While the present invention has been described with reference to one or more particular embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present invention. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the claimed invention, which is set forth in the following claims.