Abstract:
A method for making a film/board laminate for use in pilfer resistant packaging includes providing a non-treated paperboard substrate, adhering a single ply of an oriented film to the substrate, the oriented film being applied at an orientation angle to the board between but not equal to zero degrees and 180 degrees such that a film to substrate adhesion is about 0.5 pli to 1.4 pli, and applying a heat seal layer to the film.

Description:
BACKGROUND 
       [0001]    Packaging materials are used in every manner of everyday life. Corrugated packaging materials were used as early as the 1870s to protect fragile and valuable objects during packing and handling. Many of the paper, paperboard and fiberboard materials used in the manufacture of early corrugated materials are still in use today in their basic form and/or with slight improvements. 
         [0002]    In present day use, packaging serves a number of purposes. Aside from traditional protection functions, in many instances, packaging must also serve a pilfer deterrent function. This is particularly so for smaller, more valuable items. 
         [0003]    Although traditional packaging, e.g., paperboard or corrugated board, with various coatings serve protection functions well, they do not provide a substantial level of pilfer resistance. As such, more rugged, tear resistant materials have been incorporated into packaging materials to meet today&#39;s requirements. 
         [0004]    One type of packaging material includes a tear resistant film, such as a cross-oriented, laminated film in a laminate with a paperboard substrate. One such film is a VALERON® film, which is a cross-oriented, laminated polyolefin film commercially available from VALERON® Strength Films, an Illinois Tool Works company, of Houston, Tex. One structure using such a film is disclosed in Amendt, U.S. Pat. No. 7,097,895, which patent is commonly assigned with the present application and is incorporated herein by reference. 
         [0005]    While such a laminate better serves both the protective and pilfer resistant requirements for merchandising, the two film layers increase the costs for such packaging. As such, a lower cost option is desirable. 
         [0006]    In addition, it has also been found that the level of adhesion of the film to the paperboard substrate can impact the tear resistance of the package. Specifically, it has been found that if the adhesion of the film to the paperboard substrate is too great, tear propagation resistance decreases. 
         [0007]    Accordingly, there is a need for a packaging material and a method for making the packaging material that provides protection for the packaged item, as well as a pilfer resistant structure. Desirably, such a material is provided at a low cost, and uses known material elements within the material structure. More desirably still, such a material can be manufactured using known techniques. 
       SUMMARY 
       [0008]    A method for making a film/board laminate for use in pilfer resistant packaging, includes providing a non-treated paperboard substrate and adhering a single ply of a monoaxially oriented film to the substrate. The film is applied at an orientation angle to the board between but not equal to zero degrees and 180 degrees, such that a film to substrate adhesion is about 0.5 pli to 1.4 pli, and preferably about 0.7 pli to about 1.1 pli. A heat seal layer is applied to the film. 
         [0009]    The adhesion strength pli is measured substantially immediately following the laminating step and is no more than about 1.6 pli, and preferably no more than about 1.4 pli four days following the adhering step. 
         [0010]    The film is preferably an oriented polyolefin film. A suitable film is a polyethylene film, more preferably a high density polyethylene (HDPE) film. The HDPE film is a spiral cut film cut an angle of about 37 degrees to 57 degrees relative to a machine direction, and preferably about 37 degrees to about 41 degrees relative to the machine direction. 
         [0011]    The method can include folding the film/board laminate over onto itself with the oriented film layers confronting one another. In this arrangement, when the film/board laminate is folded over onto itself, the heat seal layers contact one another, and the confronting oriented films are cross-oriented relative to one another at an angle of about 74 degrees to about 114 degrees. A packaged item can be contained within an opening in one or both of the film/board laminate layers enclosed within, for example, a clear portion that is sandwiched between the confronting film/board layers. 
         [0012]    These and other features and advantages of the present invention will be readily apparent from the following detailed description, in conjunction with the claims. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]    The benefits and advantages of the present invention will become more readily apparent to those of ordinary skill in the relevant art after reviewing the following detailed description and accompanying drawings, wherein: 
           [0014]      FIG. 1  is a cross-sectional view of a film/board laminate; 
           [0015]      FIG. 2  illustrates the orientation of the film on a board substrate; 
           [0016]      FIG. 3  is a view of the film/board laminate having formed for making a package in which the laminate has an opening therein to accommodate, for example, a (plastic) window covering; 
           [0017]      FIG. 4  illustrates the laminate of  FIG. 3  that has been folded over onto itself to establish the package; and 
           [0018]      FIG. 5  is a graphical representation the seal strength and tear resistance of various samples of board/film laminates made at various seal temperatures. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    While the present disclosure is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exemplification thereof and is not intended to be limited to the specific embodiment illustrated. 
         [0020]      FIG. 1  illustrates an exemplary film/board lamination  10 . The lamination  10  (or laminate) is formed from a base or substrate layer  12  and a film layer  14  that are adhered to one another. An extrudate or adhesive  16  is provided between the film  14  and the substrate  12 . Accordingly, the laminate  10  can be formed by extrusion, adhesive lamination or a combination of extrusion and adhesive lamination. The laminate  10  further includes a heat seal layer  18  on the film  14 , opposite of the extrudate  16 /substrate  12  layer. The heat seal layer  18  provides for folding the laminate  10  onto itself the for fabrication of a package (for example, as seen in  FIGS. 3 and 4 ). 
         [0021]    In an embodiment, the film  14  is high density polyethylene (HDPE) or a combination of HDPE and low density polyethylene (LDPE) such as that described in Barnes, U.S. Pat. No. 6,284,344, which is commonly assigned with the present application and is incorporated herein by reference. The film of Barnes is a multi-layer film in which at least two of the layers are cross-oriented. That is, at least two of the layers are oriented (each monoaxially oriented), relative to the machine direction, at an angle to one another. Other suitable materials include polypropylene or a variety of other polyolefin materials and blends, polyamides, polyethylene terephthalate and other thermoplastic materials capable of being oriented. A discussion of forming multi-layer, oriented or “bias-cut” plastic films is described in Barnes et al. 
         [0022]    In a present film/board laminate  10 , a single ply of the film  14  is used rather than the multi-ply cross-oriented film. The single ply film  14  is adhered or affixed to the substrate  12  in a direction such that the film orientation (as indicated at  20  in  FIG. 2 ) is at an angle a of about 37 degrees to about 57 degrees, and preferably about 37 degrees to about 41 degrees, relative to the machine direction of the laminate  10  (indicated at  22 ) or a longitudinal direction L of the package, as seen in  FIG. 3 . As such when the laminate  10  is folded along a fold line  24 , creating a sandwich construction, as seen in  FIG. 4 , the orientations of the two plies of film  14  (each mounted to the substrate  12 ) are at an angle β of about 74 degrees to about 114 degrees, and preferably about 74 degrees to about 82 degrees, to one another. This effectively results in a package P with film ply orientations that are at an angle β to one another which increases tear resistance. 
         [0023]    It has also been found that the level of adhesion between the film  14  and board  12  is important to produce an optimum product. Surprisingly, it has been found that the highest levels of adhesion do not produce the optimum laminate  10  construction. It has been observed that too great a level of adhesion results in a laminate construction in which the resistance to tear propagation is less than that in which lower levels of adhesion are established. Of course, too low of an adhesion level also negatively impacts the characteristics of the laminate. Bond strength can be controlled by lamination nip pressure, extrudate type and temperature, primers and the like. 
         [0024]    One way in which the level of adhesion is increased is by treatment, such as corona treatment, flame treatment, plasma treatment and the like, of the substrate prior to adhering to the film. It has however, been found that when the substrate is treated, the adhesion level increases with time following manufacture of the laminate. 
         [0025]    It will be understood that often, the substrate, such as a paperboard material, is treated during the manufacturing process. In the manufacture of laminates, often the surfaces of one or more of the plies or layers is treated to, for example, increase the adhesion between the layers. Surface treatments include corona treatment, flame treatment, plasma treatment and the like. Typically, surface treatment is carried out just prior to the lamination process. Accordingly it will be understood that for purposes of the present disclosure, the term untreated or non-treated means board or substrate that is not surface treated prior to lamination by any of the above-noted methods or other treatments intended to increase adhesion between the layers. 
         [0026]    Table 1 below shows the bond strength of a laminate with treated and untreated board immediately off of the manufacturing line and four days post manufacture. The values in Table 1, below are the force required to separate (pull) the film from the substrate in pounds per linear inch (pli). 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Bond Strength Results on 18 pt Board//4.0 mil VALERON ® Strength 
               
               
                 Film//Heat Seal Laminations 
               
             
          
           
               
                   
                 Avg. Bond Offline 
                 Avg. Bond After 4 days 
               
               
                   
                 (pli) 
                 (pli) 
               
               
                   
                   
               
             
          
           
               
                 Board Treated 
                 1.17 
                 2.16 
               
               
                 Board - No Treatment 
                 1.16 
                 1.39 
               
               
                   
               
             
          
         
       
     
         [0027]    While conventional thought has it that a stronger bond is more desirable, it has been found that to obtain a desirable tear strength, a target bond strength of about 0.5 to 1.4 pounds per linear inch (pli) and preferably about 0.7 to 1.1 pli provides better overall tear resistance with aging of the laminate post manufacture. The above exemplary characteristics are for oriented and cross-laminated films, however, similar results are anticipated for single ply films laminated to a board. 
         [0028]    It has also been found that the cut angle of the film, that is the angle at which the film is cut relative to the machine direction of the film (during manufacture), which can be the same as the angle a at which the film  14  is adhered to the substrate  12 , has an effect on tear performance. As noted in Table 2, below, spiral cut angles (as measured as shown in  FIG. 2 ) between about 46 degrees and 57 degrees provide good tear performance, while spiral cut narrow angles (e.g., about 39 degrees) provide the best observed tear resistance. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Hand Tear Results on Pilfer Coupons vs. Spiral Cut Film Angle 
               
             
          
           
               
                 Single Ply Film 
                   
                 # of Failures/# of Tests 
               
               
                 Spiral Cut Angle 
                 Tear Type 
                 (into center of coupon) 
               
               
                   
               
               
                 39° 
                 Un Notched 
                 0/32 
               
               
                   
                 Notched 
                 2/32 
               
               
                 45° 
                 Un Notched 
                 1/32 
               
               
                   
                 Notched 
                 5/32 
               
               
                 57° 
                 Un Notched 
                 0/32 
               
               
                   
                 Notched 
                 4/32 
               
               
                   
               
             
          
         
       
     
         [0029]    The tear results of Table 2 are shown for 4 inch by 4 inch sample boards, both notched and un-notched for spiral cut films of 39 degrees, 45 degrees and 57 degrees. While the laminates  10  all provided acceptable tear resistance, it was found that the narrower spiral cut angles (e.g., about 39 degrees) were observed to provide tear resistance superior to those of wider spiral cut angles. 
         [0030]    It has also been observed that when highly oriented films  14  are used, particularly those with orientation not parallel to the machine direction, there is a high likelihood of film  14  web tears and breaks. As such, it has been found that the tension on the oriented film is preferably below 0.3 pli. 
         [0031]    It has also been found that the heat seal layer  18  should contain a material that allows a low seal initiation temperature. When the laminate  10  is heat sealed to itself (for example, as shown in  FIG. 4 ), sealing temperatures over 250° F. reduce tear resistance, particularly uninitiated tear. Without being held to theory, this may be due to high interply adhesion (that is, between the confronting film  14  plies) or melting (or relaxation of the orientation) of the film  14  plies due to the higher sealing temperatures used.  FIG. 5  is a graphical representation of the seal strength and tear versus seal temperature. The measurements were taken using a substrate adhered to a 1.75 mil (1.75/1000 inch) single ply HDPE monoaxially oriented film with a low seal initiation temperature heat seal layer. The laminate was sealed at 60 psi for a period of three seconds. The graph shows hand tear results for both un-notched and notched samples in the right-hand and left hand columns, respectively, at varying temperatures, with the tear ratings being shown on the right-hand vertical axis. The seal strength, in pounds per inch, indicated by the line above the columns tear strength columns, exhibited the values as shown along the left-hand vertical axis, all as a function of seal temperature in degrees F., which is shown along the horizontal axis. In the graph, lower hand tear values indicate greater resistance to tearing (lesser depth of tear into the sample). 
         [0032]    One or both of the film/board laminate  10  layers can include an opening, such as the exemplary window W, and a packaged item can be contained within the opening in one or both of the layers. The item can be contained within a window (such as a suitable plastic material) that is sandwiched between the confronting film/board layers  10  that are sealed to one another with the heat seal layers  18  in contact with one another. 
         [0033]    In the disclosures, the words “a” or “an” are to be taken to include both the singular and the plural. Conversely, any reference to plural items shall, where appropriate, include the singular. 
         [0034]    From the foregoing it will be observed that numerous modification and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present invention. It is to be understood that no limitation with respect to the specific embodiments illustrated is intended or should be inferred. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.