Abstract:
A seal laminate for closing a mouth of a container is provided. The seal laminate includes a heat seal layer, a structural base support layer and upper and lower dimensional stable layers. The heat seal layer bonds the laminate to a rim surrounding the container&#39;s mouth. The structural base support layer may be comprised of a pulp, paper, cardboard, chipboard, paperboard, or cellulose based material having a moisture content of about 3 to about 6 percent and is positioned above the heat seal layer. The upper and lower dimensionally stable layers are disposed above and below the structural base support layer and are sized to balance the vertical forces on the structural base support layer upon exposure to about 60 percent or greater relative humidity. The upper and lower dimensionally stable layers have a water vapor transmission rate of about 1.5 g/100 in 2 /24 hours or below.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims benefit of U.S. Provisional Application No. 61/468,257, filed Mar. 28, 2011, which is hereby incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    This disclosure relates to a laminate sealing member for the mouth of a container, and more particularly, to a laminate sealing member including a dimensionally unstable layer combined with one or more stabilizing layers. 
       BACKGROUND 
       [0003]    One-piece induction seals typically include a membrane or foil layer combined with a heat seal layer for adhering the seal to an upper rim of a bottle or container. To support the foil and heat seal, such one-piece induction seals often include a top structural support or backing layer. The structural support is often a pulp, paper, paperboard, cardboard, chipboard, or other cellulose-type materials. This top backing layer provides a structural support for the barrier and heat seal layers of the induction seal. 
         [0004]    In use, the one-piece induction seals are generally die-cut from sheets into a disk shape and, then, inserted into a container or bottle cap at a closure manufacture. The cap generally includes internal threading or other internal retention projections that hold the seal against the upper surface of the cap by friction or interference. The cap and seal combination may then be provided to an end user where the seal is induction sealed to the upper rim of a bottle or container when the cap is placed thereon after the container is filled with a product. 
         [0005]    During periods of higher humidity, such as in the spring and summer months, the paper or pulp-based materials commonly used for the support layer tend to be susceptible to changes in the environment. When exposed to higher humidity levels, the paper or pulp-based materials tend to absorb moisture, swell, and then may deform or curl into a potato-chip like shape. If this backing curl is significant and occurs while the seal is in the cap or closure before being combined with the bottle or container, the threading or internal retention projections of the cap may not retain the seal within the cap. Due to the curling, the seal may actually fall out of the cap. In other cases, the curled seal may shift within the cap so that it can not be effectively induction sealed to the bottle during the bottle or container closing operations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a cross-sectional view of an exemplary sealing member; and 
           [0007]      FIG. 2  is a graph showing the dimensional stability of the laminates herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    A one-piece, peelable sealing member or induction seal for a container is described herein. The sealing member is generally constructed from a flexible sheet or laminate and includes, in an upper portion thereof, at least one dimensionally unstable support layer that is susceptible to dimensional changes due to variations in environmental conditions. In one aspect, the sealing member includes relatively thin dimensionally stable layers bonded to upper and lower surfaces of the dimensionally unstable layer to provide enhanced dimensional stability to the seal in the presence of higher humidity. In some approaches, the combination of dimensionally stable layers above and below the unstable layers may, in some instances, provide balanced internal forces within the seal laminate structure to help retain the unstable layer in a flat configuration when exposed to higher humidity. In other approaches, the dimensionally stable layers may also exhibit a low water vapor transmission rate and/or a low oxygen transmission rate to hinder and, in some cases, prevent moisture and humidity to reach the dimensionally unstable stable layer that is sandwiched between the two stable layers above and below it. In yet other approaches, the seals described herein exhibit less than about 9.5 mm of curl, which is discussed more below, in the presence of higher humidity, which is sufficient so that the seal may be retained in a common closure or cap prior to capping operations. 
         [0009]    As used herein, higher humidity generally refers to greater than about 60 percent relative humidity, and in some cases, about 60 percent to about 85 percent relative humidity at temperatures ranging from about 35° C. to about 50° C. As also used herein, dimensionally stable generally refers to materials that do not exhibit significant deformation or are otherwise not affected in size, shape, or thickness by variations in temperature, humidity, moisture, and the like. By one approach, as mentioned above, dimensionally stable is about 9.5 mm or less of curl. Dimensionally unstable generally refers to materials that tend to be negatively affected by environmental conditions, such as humidity and moisture, and may exhibit one or more of swelling, deformation, curling, expansion, shrinkage, and the like upon exposure to variations in environmental conditions, such as variations in humidity and moisture. 
         [0010]    Turning to more of the specifics,  FIG. 1  illustrates one example of a seal  10  showing enhanced levels of dimensional stability in the presence of variations in environmental conditions, such as exposure to higher relative humidity. Seal  10  includes a lower bonding layer  12  for bonding to the rim of a container. The lower bonding layer  12  may include a hot melt adhesive or heat seal layer for bonding or securing the liner to the container rim by a heat seal or induction sealing apparatus. Suitable heat-activated adhesives or sealants include, but are not limited to, ethylene vinyl acetate, ethylene-acrylic acid copolymers, surlyn and other suitable materials. In one approach, the lower bonding layer may be 0.5 to about 2 mils thick, and in other approaches, about 1.5 mils thick. On top of the lower bonding layer  12 , the seal includes a first dimensionally stable layer  14 . In this case, the first dimensionally stable layer  14  may be a metal layer or a foil layer. In one approach, the foil layer may be relatively thin, such as about 0.5 mil to about 1.5 mils thick, and in other approaches, about 1 mil thick. 
         [0011]    Above the first dimensionally stable layer  14 , the seal  10  include a dimensionally unstable structural or base layer  16 . In one approach, this dimensionally unstable structural layer may be a pulp, paper, cardboard, chipboard, paperboard, or other cellulose-type layer. Base layer  16  may also include fibers or filaments. This base layer is about 5 to about 10 mils thick in one approach, and in other approaches, about 8 mils thick. By one approach, the base layer  16  is a blend of softwood and hardwood paper fibers having a moisture content of about 3 to about 6 percent that tends to be dimensionally stable at about 50 to about 55 percent relative humidity. When exposed to higher humidity as defined herein, these materials of layer  14  tend to absorb moisture. In prior seals, the paper or cardboard layer tended to exhibit undesirably high levels of deformation of about 10 mm to about 38 mm of curl in the presence of higher humidity. 
         [0012]    To enhance the stability of seal laminates using the dimensionally unstable structural layer  16 , the seal  10  also includes a second dimensionally stable layer  18  above the dimensionally unstable structural layer  16 . In one approach, the second dimensionally stable layer  18  is a relatively thin layer of PET or other polymer layer having a relatively high resistance to moisture, water, and/or oxygen transmission. In another approach, the second dimensionally stable layer may be a coating of one or more polymers applied to the upper surface of the unstable layer  16  in an effective coating weight. The second dimensionally stable layer  18  may be about 0.5 to about 1.0 mils thick or a coating applied at about 6 to about 30 pounds per about 3000 square feet. By another approach, the layer  18  may be a thin and effective layer (coated or film layer) of PET (Polyethylene terephthalate), PEN (Polyethylene naphthalate), polyethylene, polypropylene, ethylene-acrylic acid copolymers, ethylene methacrylate copolymers, blends thereof, or the like materials so long as the materials are constructed in a manner and in a thickness to provide dimensional stability to the structural layer  16  as described herein when combined with the lower dimensionally stable layer  14 . 
         [0013]    In one approach, the seal  10  may also define a ratio of the thicknesses of the first and second dimensionally stable layers  14  and  18  relative to a thickness of the dimensionally unstable support layer  16  effective so that deformation of the dimensionally unstable support layer is less than about 9.5 mm of curl when exposed to about 60 to about 85 percent relative humidity. Effective ratios may be, in some cases, expressed as a thickness ratio of layer  14  to layer  16  to layer  18  of about 1:6:0.6 (thickest foil and layer  18  with thinnest backing) to about 1:20:1 (thinnest foil and layer  18  with thickest backing). Effective ratios may also be, in other approaches, expressed as a thickness of the sum of layer  14  and  18  relative to the thickness of layer  16  and range from about 1:2 to about 1:10. So constructed, the seal  10  exhibits about 0 to about 9.5 mm of curl when exposed to the higher humidity levels as defined herein, and in some cases, about 4 to about 9.5 mm of curl, and in other cases, no deformation or curling at all in the presence of higher humidity. 
         [0014]    While not wishing to be limited by theory, it is believed that the combination of the dimensionally stable layers  14  and  18  above and below the dimensionally unstable layer  16  may have a thickness and/or composition effective to balance any vertical and/or transverse forces in the seal due to moisture absorption and swelling of the backing layer  16 . This may be, in some cases, due to the layers  14  and  18  forming a sufficiently stable interface at the upper and lower perimeter edges of the backing layer  16  such that the swelling forces are balanced within the seal. The stable layers  14  and  18  also, in some cases, have water vapor transmission rates sufficient low (such as, in some cases, about 1.5 g/100 in 2 /24 hour at 100° F. at 90% or below and, in other cases, about 1 to about 1.5) so that the stable layers  14  and  18  hinder and, in some cases, prevent moisture and humidity from reaching the unstable layer  16 . The advantage of the seal constructions herein is that they provide a dimensionally stable seal while minimizing the overall seal thickness at the same time. In some approaches, the overall thickness of seal  10  is about 12 to 15 mils or less. Any thicker, the seal is cost prohibitive and undesired from a structural standpoint when used in a bottle or container closure/cap. Thus, the enhanced dimensional stability is achieved with a minimum about of materials. 
         [0015]    In another approach, the unstable structural base layer  16  is stabilized at an interface of its upper and lower surfaces by being bonded to the upper and lower structurally stable support layers  14  and  18 . Thus, the upper and lower interface and surfaces of the base layer  16 , upon exposure to higher humidity (as defined herein) are stabilized and hindered from expanding in a horizontal or transverse direction. 
         [0016]    If desired, the seal  10  may also include a pull-tab or pull-tab portion. Many types of pull-tab portions may be used. Examples of pull-tabs suitable for the seal  10  include those as described in U.S. Pat. No. 5,433,992; U.S. Pat. No. 5,514,442; U.S. Pat. No. 5,004,111; U.S. Pat. No. 6,866,926; U.S. Pat. No. 6,902,075; U.S. Pat. No. 7,217,454; US 2006/0151415; and US 2008/0233339. Each of these patents and publications are incorporated herein by reference in their entirety. In general, the pull-tab may be defined wholly within a perimeter of the sealing member or laminate. 
         [0017]    Advantages and embodiments of the seal and the dimensional stability described herein are further illustrated by the following example; however, the particular conditions, processing schemes, materials, and amounts thereof recited in this example, as well as other conditions and details, should not be construed to unduly limit the seals as described herein. All percentages are by weight unless otherwise indicated. 
       EXAMPLES 
     Example 1 
       [0018]    A dimensionally stable seal having a 0.5 mil PET layer bonded to a 8 mil backing with a 1 mil foil and 1.5 mil heat seal layer under the backing was evaluated for curl (identified as TR seal below). A comparative or base seal having the same 8 mil backing, 1 mil foil, and 1.5 mil heat seal, but no upper PET layer was also evaluated for curl (identified as BR seal below). 
         [0019]    Curl was determined by cutting an 89 mm disk of the material and placing it on a flat surface in a humidity chamber. Curl was determined by measuring the distance an outer perimeter of the disk raised above the flat surface in the chamber. The degree of curl is shown in Tables 1 and 2 below. Table 1 shows the results of 6 different trials of the same dimensionally stable inner seal (labeled as TR 1-6 in the Table and Figure). Table 2 shows the results of 6 different comparative seals that do not demonstrate dimensional stability in the presence of higher humidity (Labeled as BR 1-6 in the Table and Figure).  FIG. 2  shows the results of this study graphically. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Dimensionally stable inner seals 
               
             
          
           
               
                   
                 Level of Curl, Inches 
               
             
          
           
               
                 Temp 
                 Humidity 
                 TR1 
                 TR2 
                 TR3 
                 TR4 
                 TR5 
                 TR6 
               
               
                   
               
               
                 35° C. 
                 60% 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 38° C. 
                 70% 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 38° C. 
                 80% 
                 0 
                 4/16 
                 3/16 
                 5/16 
                 3/16 
                 0 
               
               
                 48° C. 
                 85% 
                 0 
                 5/16 
                 0 
                 6/16 
                 4/16 
                 0 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Comparison dimensionally unstable inner seals 
               
             
          
           
               
                   
                 Level of Curl, Inches 
               
             
          
           
               
                 Temp 
                 Humidity 
                 BR1 
                 BR2 
                 BR3 
                 BR4 
                 BR5 
                 BR6 
               
               
                   
               
               
                 35° C. 
                 60% 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 38° C. 
                 70% 
                 0 
                 6/16 
                 0 
                 10/16 
                  5/16 
                  6/16 
               
               
                 38° C. 
                 80% 
                  5/16 
                 9/16 
                 6/16 
                 12/16 
                 12/16 
                 10/16 
               
               
                 48° C. 
                 85% 
                 14/16 
                 14/16  
                 15/16 
                 18/16 
                 1 
                 15/16 
               
               
                   
               
             
          
         
       
     
         [0020]    It will be understood that various changes in the details, materials, and arrangements of the seal laminate, which have been herein described and illustrated in order to explain the nature of the seals described herein, may be made by those skilled in the art within the principle and scope of the embodied description.