Oxygen impermeable leak free container
BACKGROUND OF THE INVENTION 
     The invention relates to a heat-sealable barrier laminate structure which produces an oxygen impermeable, leak free container. More particularly, this invention relates to barrier laminate structures which are comprised of specific high strength polymer resin layers which effectively prevent heat activation pinholes, cuts or cracking of oxygen barrier layers caused during scoring and especially during folding and heat sealing of the laminate in package formation. 
     The invention as disclosed and claimed herein is related to pending application Ser. Nos. 191,987; 191,988 now U.S. Pat. No. 4,888,822; 191,989 now U.S. Pat. No. 4,880,701; and 191,337 now U.S. Pat. No. 4,859,513, all owned by the Assignee and filed concurrently herewith. In addition, structures for paperboard containers using heat-sealable polymer resins and containing various oxygen barrier materials are disclosed in U.S. Pat. Nos. 3,972,467; 4,698,246; 4,701,360; 4,789,575; and 4,806,399, all owned by the Assignee. 
     Heat-sealable low density polyethylenes are well known to be components of current paperboard food and/or non-food packages which provide little barrier to the transmission of oxygen. Pinholes, cuts, score lines or channels, existent in conventional packaging and cartons, create additional leakage sites. It is well known that impermeable materials such as aluminum foil, polar brittle materials such as: polyacrylonitriles, polyvinylidene chlorides, polyvinyl chlorides, etc., provide varying degrees of barrier to the transfer of oxygen. However, all these materials lack the requisite strength at high rates of deformation, namely stress cracking resistance during scoring, package formation and distribution abuse to provide a resultant oxygen impermeable and airtight structure. In addition, leakage through the uncaulked channels of the carton in the top, bottom and side seam have likewise resulted in poor whole carton oxygen barrier properties. 
     The existing commercial structures for a paperboard carton for liquid and solid, food and non-food, products have utilized an easily heat-sealable barrier laminate composed of a paperboard substrate and a foil oxygen barrier layer, both being sandwiched between two thick layers of low density polyethylene (LDPE). The LDPE is a relatively inexpensive heat-sealable moisture barrier material. The conventional structure falters in that the foil layer which acts as the barrier to the transmission of oxygen in and out of the carton cracks during blank conversion, carton formation, and package distribution stages. 
     Bending and folding occurring during the formation of a gable &#34;type&#34; top, flat &#34;type&#34; top, or other folded, heat-sealed top closure, and a fin-sealed, or other conventional folded bottom puts excessive amounts of local stress on the thin foil and/or other oxygen barrier layer and, as typically results, cracks and pinholes appear. 
     To date, there have been no economically attractive commercially available paperboard packages which consistently approach the oxygen impermeability of glass or metal containers. The object of the present invention is to produce an oxygen impermeable, leak free container and/or laminate structure such as a paperboard based package or carton that prevents the transmission of gases therethrough, and in addition, prevents the escape of flavor components or the ingress of contaminates. A further object of the present invention is to produce such a package that is economical on a per-package cost basis, is fundamentally compatible with existing converting machinery and can be formed, filled and sealed at economically high speeds using conventional packaging machine temperatures, pressures and dwell times. 
     Another object of the present invention is to provide this oxygen impermeable package in a variety of applications including four-ounce to 128-ounce containers, or larger, as required by the packager. 
     A further object of this invention is to incorporate a functional polymer layer which exhibits high strength, abuse resistance and toughness during converting and carton forming in combination with aluminum foil or other oxygen barrier layers and paper, paperboard or other mechanically stable structural material such that the high-strength layer reduces the stresses incurred by the barrier layers during blank conversion, package formation, and distribution. Additionally, should a penetration of the barrier layer or layers occur, the high-strength layer serves to maintain package integrity at the failure site. The high-strength, heat-resistant layer effectively prevents heat activation pinholes through the product contact layer, even when non-foil barrier layers are used. 
     SUMMARY OF THE INVENTION 
     A preferred embodiment of the invention reveals an oxygen impermeable leak free barrier laminate, side-seamed blank and/or container providing a total barrier to the loss of essential food flavor oils or non-food components over an extended product shelf-life as well as an absolute barrier to the transmission of oxygen during the same extended shelf-life period. A preferred embodiment of the laminate structure comprises, from the outer surface to the inner surface, contacting the essential oils, flavors and/or components of food or non-food products: an exterior layer of a low density polyethylene, a mechanically stable structural substrate, such as a paper or paperboard material, a corrugated board, or a stiff polymer resin material such as high density polyethylene, polypropylene or the like, a co-extruded interior layer of an abuse resistant polymer such as a polyamide type polymer (nylon 6) and a caulking polymer resin such as an ionomer type resin (Surlyn® 1652), an oxygen barrier layer such as an aluminum foil layer, a second layer of a caulking polymer resin such as an ionomer type polymer (Surlyn® 1652), and a layer of low density polyethylene in contact with the food o non-food product rendering the laminate structure heat-sealable. 
     The cartons, side-seamed blanks, or containers constructed of the laminate of the present invention enable significant containment of gases in the container as well as preventing any migration of oxygen or contaminants into the structure. The present invention has produced a suitable container which has the ultimate barrier properties. It utilizes a laminate which can be heat-sealed easily with its exterior and interior layers being like, non-polar constituents. During the heat-seal processes, the scoring processes, the side-seaming processes, and the folding, forming and filling steps, the particular caulking polymer resins, namely ionomer type resins, ethylene acrylic acid copolymers, ethylene methacrylic acid copolymers, ethylene vinyl acetate copolymers, ethylene methylacrylate copolymers and the like have melt indexes which allow them to flow during the heat-sealing processes (temperatures ranging from 250° F.-500° F.).The particular selected resins act as a caulking agent to fill the channels produced during formation of the gable, or other type flat top, the fin-sealed, or other conventional type bottom and the skived side seam. Consequently, each of those gap areas is caulked to prevent the transmission of oxygen therethrough. In addition, the selection of the particular abuse resistant polymer, namely polyamide type polymers, polyester type polymers and ethylene vinyl alcohol copolymers or the like acts to prevent any type of significant deformation damage to the foil or other oxygen barrier layer which would result in a crack or pinhole allowing for the seepage of oxygen therethrough. 
     The preferred package structures formed from the preferred novel laminates of the present invention not only exhibit these novel oxygen impermeable and/or other high barrier properties, but the novel laminate structures are produced using conventional coextrusion coating equipment. 
     The novel laminate structure and materials selected therefor, namely the particular caulking polymer resins and abuse resistant polymer resins contemplated by the present invention, coupled with oxygen impermeable or high oxygen barrier materials, in various combinations, can be utilized in a variety of food or non-food packaging applications. 
     In one application, the preferred laminate structure is produced using conventional coextrusion coating equipment. 
     Secondly, this laminate is printed and forwarded through scoring dies and cutting dies to create flat blanks which are placed on conventional machinery for further preparation. 
     Thirdly, these flat blanks are skived and folded and side-seamed to create the side-seamed blanks. During the heat-sealing step of the side-seam operation, the resins which have been selected for their particular melt flow characteristics, caulk and seal along the seam. Resins which have melt flow indexes ranging from 4.5-14.0 are preferred. These side-seamed blanks are then forwarded to the particular customer for further assemblage. 
     Fourth, these side-seamed blanks are magazine fed into a machine wherein they are opened and placed on a mandrel, wherein sealing of the bottom takes place. 
     Typically, the bottom folding and sealing is where most of the damage to the interior thin barrier foil layer occurs in conventional cartons. Utilization of a particular strong polymer resin, comprising an abuse resistant polymer, such as a polyamide type polymer, prevents cracking of the foil layer during the bottom sealing process. The bottom is fully heat-sealed into a flat configuration at which time caulking polymer resins, such as ionomer resins, flow in a caulking manner to seal the bottom. The container or package is then forwarded to the filling step. Next, the top is &#34;prebroken&#34; and filled with the particular product and then top-sealed. Again, much damage is done to the foil or other barrier layer during this top-sealing process of conventional cartons. The utilization of the novel abuse resistant and caulking polymer resin constituents in the barrier laminate acts to prevent any damage to the foil or non-foil barrier layer and produce a top closure which has been caulked to doubly prevent any transport of oxygen. 
     The novel barrier laminate produced by the present invention not only exhibits excellent oxygen barrier properties and can be easily constructed, but also meets FDA approval for use in food packaging. The resins heat seal at low temperatures (250° F. to 500° F.) and the structures can be converted and cut on conventional machinery. 
     Thus, until the advent of the present invention, no suitable oxygen impermeable, leak free containers or packages have been developed which retain the advantages of using mechanically stable structural substrates such as paperboard or the like as the base material and FDA approved heat-sealable barrier layers which are economical and can be produced using conventional coextrusion coating equipment. 
     The present invention described herein is particularly useful as a coated paperboard structure employed in the packaging of food and non-food products. These types of containers make use of a heat-seal for seaming and closing, and are utilized in the formation of folding boxes, square rectangular cartons or containers, or even cylindrical tubes. 
     In addition, the novel combinations of caulking polymer resins, abuse resistant polymers and oxygen impermeable and/or high oxygen barrier materials have other applications as well. 
     Namely, the combination of high oxygen barrier materials such as ethylene vinyl alcohol copolymers o other brittle oxygen barrier materials coupled with abuse resistant type polymer resins such as polyamide type polymers or the like, have applications in combination with almost any mechanically stable structural substrate. Particularly, multilayer blow-molded containers incorporating abuse resistant polymer resins in combination with high oxygen barrier materials is one of the novel applications of this invention. 
     One specific example of such an application is the utilization of ethylene vinyl alcohol copolymer in combination with a polyamide type polymer mounted on a high density polyethylene structural substrate. The polyamide type polymer acts to protect the brittle ethylene vinyl alcohol copolymer oxygen barrier layer from abuse during shipping and transport of the overall container structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional elevation of the preferred embodiment of the laminate of the present invention; 
     FIG. 2 is a cross-sectional elevation of an alternate embodiment of the laminate of the present invention; 
     FIG. 3 is a cross-sectional elevation of an alternate embodiment of the laminate; 
     FIG. 4 is a cross-sectional elevation of an alternate embodiment of the laminate; and 
     FIG. 5 is a cross-sectional elevation of an alternate embodiment of the laminate. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The preferred embodiment of the invention is for an hermetic, oxygen impermeable leak free and/or high oxygen barrier leak free package incorporating a laminate structure as disclosed in FIG. 1. All weights given for particular laminate layers are expressed in pounds per 3,000 square feet. Disclosed is a mechanically stable structural substrate 12 which is most suitably high grade paperboard stock, for example, 200-300 lbs. or higher sized carton board, to which is applied on one side a coating of a low density polyethylene polymer 10 in a coating weight of about 20 lbs. Layer 10 is the &#34;gloss&#34; layer which contacts the outer atmosphere. An extrusion coating grade LDPE having a melt flow index ranging from 4.0 to 7.0 is suitable for use herein. On the underside or interior portion of the paperboard substrate 12 is coextruded thereon a combined layer of an abuse resistant polymer resin such as a polyamide type polymer (nylon 6), 14, in a coating weight of about 7.5 lbs., with a caulking polymer resin such as an ionomer type resin (Surlyn® 1652), 16, in a coating weight of about 5.5 lbs. Laminated thereon is an absolute oxygen impermeable material or a high oxygen barrier material, such as a 0.000285-0.0005 inch layer of aluminum foil 18. Coated on the outer layer of the foil is a second layer of a caulking polymer resin such as an ionomer type resin (Surlyn® 1652), 20, in a coating weight of about 5 lbs., and lastly coated thereon is a second layer of a low density polyethylene polymer 22, in a coating weight of about 20 lbs. rendering the entire laminate structure heat sealable on conventional heat-seal equipment at conventional heat seal temperatures (250° F.-500° F.). 
     Referring to FIG. 2, an alternate preferred embodiment of the laminate of the present invention is shown. The embodiment adds additional layers of low density polyethylene (LDPE) as well as a layer of ethylene vinyl alcohol copolymer (EVOH) which provides additional barrier protection to the overall container structure. In this alternate preferred embodiment, the mechanically stable structural substrate 26, such as a paperboard substrate, having a weight of 200-300 lbs. or higher for a quart, half-gallon, gallon or larger structures, has extrusion coated on its external surface a 24 lb. layer of a low density polyethylene polymer 24. On the internal surface of the mechanically stable structural substrate 26, is applied a 12 lb. coating of a caulking polymer resin such as an ionomer type resin (Surlyn® 1652), 28. Laminated thereon is a 0.000285-0.0005 inch layer of an oxygen barrier material (aluminum foil) 30. Coextruded onto the exposed surface of the foil 30 is a sandwich 33 comprising a 9 lb. layer of a caulking polymer resin such as an ionomer type resin (Surlyn® 1652), 32, and a 3 lb. layer of a low density polyethylene polymer 34. Coated onto the first coextruded sandwich layer 33 is a second coextruded layer 39 comprising from interior contacting layer 33 to exterior, a 10 lb. layer of a low density polyethylene polymer 36, a 2 lb. adhesive tie layer, such as a Plexar 177®, 38, a 12 lb. layer of an ethylene vinyl alcohol copolymer, such as EVAL SCLE 105B, 40, a second 2 lb. adhesive tie layer, such as a Plexar 177®, 42, and an exterior 10 lb. layer of a low density polyethylene polymer 44. Finally, coated thereon, is a 22 lb. layer of a low density polyethylene polymer 46 which in combination with layer 24 renders the entire laminate structure heat sealable. 
     FIG. 3 is a modified version of the alternate preferred embodiment outlined in FIG. 2 dropping various interior layers of low density polyethylene. The structure is described as follows: a mechanically stable structural substrate such as a paperboard layer having a weight of 200-300 lbs., or higher, 50 is coated on its exterior with a layer of 20 lbs. of a low density polyethylene polymer 48. On the interior side of the mechanically stable structural substrate 50 is a coextruded sandwich 53 comprised of a 7 lb. layer of an abuse resistant polymer such as a polyamide type polymer (nylon 6), 52, and a 4 lb. layer of a caulking polymer resin such as an ionomer resin (Surlyn® 1652), 54. An adhesive tie layer, such as Plexar 177®, 56, having a weight of 3.5 lbs., an oxygen barrier layer, such as an aluminum foil having a thickness of 0.000285-0.0005 inches, 58, which acts as an absolute barrier to the transmission of oxygen and a second adhesive tie layer, such as a Plexar 177®, 60, in a weight of 3.5 lbs. are all coextruded onto said coextruded sandwich 53. Finally, a 25 lb. layer of a caulking polymer resin such as an ionomer resin (Surlyn® 1652), 62, is coated onto the second coextruded sandwich 57 and an interior food contact layer of low density polyethylene 64 having a weight of 2 lbs. is placed thereon. The addition of layer 64 in combination with layer 48 allows for a better heat seal between the outer and inner layers. 
     Referring to FIG. 4, another preferred embodiment of the invention is disclosed. A mechanically stable structural substrate such as a paperboard substrate having a weight of 200-300 lbs., or higher, 68 is coated with a 24 lb. layer of a low density polyethylene polymer on its exterior 66. On the interior layer of the substrate 68 is coextruded the following laminate structure 75: a 10 lb. layer of low density polyethylene 70, a 12 lb. layer of an abuse resistant polymer resin such as a polyamide type polymer (nylon 6), 71, a 2 lb. adhesive tie layer, such as a Plexar 177®, 72, an oxygen impermeable layer such as an aluminum foil layer having a thickness of 0.000285-0.005 inches, 74, a second 2 lb. adhesive tie layer such as Plexar 177®, 76 and a 10 lb. layer of a caulking polymer resin, such as (Surlyn® 1652), 78. Finally coated onto the coextruded layer is a 22 lb layer of low density polyethylene 80 which in combination with layer 66 allows for the final heat-sealable uniform homogeneous laminate structure. 
     Referring to FIG. 5, an alternate preferred embodiment of the invention is depicted as follows: a mechanically stable structural substrate such as a paperboard substrate having a weight of 200-300 lbs., or higher, 84 has coated on its exterior a 24 lb. layer of a low density polyethylene polymer 82. On its interior, a 12 lb. layer of a caulking polymer such as an ionomer type resin (Surlyn® 1652), 86, is coated thereon. Laminated onto said caulking polymer layer, 86, is a 0.000285-0.0005 inch oxygen barrier layer (aluminum foil) 88. Coextruded on the interior portion of the aluminum foil layer 88 is a sandwich 93 of 4 lbs., an adhesive tie layer, such as Plexar® 177, 90, 7 lbs. of an abuse resistant polymer such as a polyamide type resin (nylon 6), 92, and 4 lbs. of a second adhesive tie layer such as Plexar® 177, 94. Lastly, coated on the interior portion of the laminate sandwich 93 is a 25 lb. layer of a low density polyethylene polymer 96, to render the laminate structure heat sealable. 
     Although specific coating techniques have been described, any appropriate technique for applying the layers onto the mechanically stable structural substrate can be suitably employed, such as extrusion, coextrusion or adhesive lamination of single layer and/or multilayer films t the mechanically stable structural substrate to achieve the stated inventions of this patent. The unique effect provided by the oxygen impermeable, leak free packages made from the laminate of the present invention is clearly demonstrated by the following Examples outlined in Table I. The preferred embodiment of the present invention is listed as the &#34;International Paper oxygen impermeable half-gallon&#34; and it utilizes as its mechanically stable structural substrate a 282 lb. layer of paperboard. The preferred structure is compared in Table I to a variety of commercial paperboard based and non-paperboard based containers currently available in the market place and recommended for extended shelf-life applications. 
     
                                           TABLE I                                 
__________________________________________________________________________
Average Whole Container Oxygen Transmission Rates (OTR)                   
                              OTR (CC/M.sup.2 /Day)                       
                  Avg., CC O.sub.2 /Pkg./Day                              
                              To Fill -                                   
Container         (75° F., 50% RH, in Air)                         
                              Volume (ml) Ratio*                          
__________________________________________________________________________
INTERNATIONAL PAPER                                                       
                   0.000       0.000                                      
(OXYGEN IMPERMEABLE                                                       
HALF-GALLON)                                                              
TOPPAN, EP-PAK (1500 ml)                                                  
                   0.005       0.004                                      
WITH PLASTIC FITMENT                                                      
INTERNATIONAL PAPER                                                       
                   0.016      0.2                                         
ASEPTIC (250 ml.)                                                         
TETRA BRIK-PAK (250 ml.)                                                  
                   0.013      0.2                                         
CAPRI-SUN POUCH   0.01        0.3                                         
(200 ml.)                                                                 
TREESWEET COMPOSITE                                                       
                  0.29        0.4                                         
FIBER CAN (1360 ml.)                                                      
CONOFFAST CUP      0.022      0.4                                         
(250 ml.)                                                                 
INTERNATIONAL PAPER                                                       
                  1.11        0.5                                         
HOT FILL (2000 ml.)                                                       
GALLON HDPE       2.75        0.5                                         
(BLOW MOLDED BOTTLE)                                                      
HALF-GALLON HDPE  1.98        1.1                                         
(BLOW MOLDED BOTTLE)                                                      
HYPAPAK (700 ml.) 0.52        1.7                                         
HAWAIAN PUNCH COMPOSITE                                                   
                  0.09        2.0                                         
CAN (236 ml.)                                                             
COMBIBLOCK (250 ml.)                                                      
                  0.21        3.2                                         
JUICE BOWL COMPOSITE                                                      
                  0.34        4.1                                         
CAN (355 ml.)                                                             
__________________________________________________________________________
 *All numbers should be multiplied by 10.sup.-2                           
 
    
     It can be seen that the container prepared from a laminate of the present invention provides a complete hermetic barrier to the transport of oxygen. 
     The specially selected abuse resistant polymer constituents such as the polyamide type polymers which make up the container are resilient enough to prevent any type of cutting, pinholing, or other damage caused during the converting, carton formation and distribution steps. In addition, the container utilizes ionomer type resins as caulking material for the channels and seams. 
     The mechanically stable structural substrate may consist of a paper or paperboard material, a corrugated type board material or a stiff polymer resin material such as high density polyethylene, polypropylene or the like. 
     The barrier layer may consist of an aluminum foil, an ethylene vinyl alcohol copolymer, a polyvinyl alcohol polymer, a polyethylene terephthalate, a polybutylene terephthalate, a glycol-modified polyethylene terephthalate, an acid-modified polyethylene terephthalate, a vinylidene chloride copolymer, a polyvinyl chloride polymer, a vinyl chloride copolymer, a polyamide polymer or a polyamide copolymer, or combinations of these materials. 
     The preferred embodiments of the present invention utilize an aluminum foil layer as the primary absolute oxygen and flavor oil barrier material. All of the above-identified materials could be utilized in all alternate embodiments in place of the foil layer as well as in the preferred embodiment of the invention. The barrier and high strength layers may be applied as film laminations and/or as extrusion coatings. 
     The invention may be used in materials for all types of blank fed or web fed package forming equipment. The effectiveness of the laminate of the present invention as an oxygen impermeable package structure permits significant extension of shelf-life of the products packaged in the containers. 
     The tough, high strength, abuse resistant type materials can be selected from the following group of polymers: polyamide type polymers such as the preferred Nylon 6, or Nylon 6/66, Nylon 6/12, Nylon 6/9, Nylon 6/10, Nylon 11, Nylon 12; polyethylene terephthalate; polybutylene terephthalate; and ethylene vinyl alcohol copolymers; or other similar tough, high strength polymeric materials which have tensile strengths of 10,000 psi or greater at conventional heat-seal temperatures (250° F.-500° F.). 
     In addition, the high strength, low viscosity caulking resins preferred are selected from the following group of polymers: ionomer type resins, such as the preferred zinc or sodium salts of ethylene methacrylic acid (Surlyn® 1652 or the like); ethylene acrylic acid copolymers; ethylene methacrylic acid copolymers; ethylene vinyl acetate copolymers; ethylene methylacrylate copolymers; and the like, all exhibiting melt flow indexes ranging from 4.5-14.0. 
     Adhesive tie layers preferred are selected from the following: Plexars® from Quantum Chemical Co.; CXA&#39;s® from Dupont; Admer&#39;s® from Mitsui, and similar performing tie resins. 
     The common generic name for the preferred adhesives are: Plexars® are ethylene based copolymers with grafted functional groups; CXA&#39;s® are modified polyethylene resin containing vinyl acetate acrylate; and Admers® are polyethylene copolymer based materials with grafted functional groups. 
     Additional abuse resistant polymers, caulking polymer resins, mechanically stable structural substrates, oxygen barrier materials, and adhesive tie layers which meet the specifications and requirements outlined above could also be utilized to practice the present invention. 
     This invention provides a means of transforming the economical, high volume, gable top or flat top paperboard or non-paperboard food/non-food carton into an oxygen impermeable, leak free package that can be produced, sold, and filled economically at high production speeds, offering a low-cost hermetic packaging alternative to glass and metal, with the bulk of one embodiment of the package being biodegradable paperboard from a renewable resource.