Abstract:
A heat shrinkable film package and a method for packaging food and non-food products is disclosed which includes a valve through which the package is evacuated during the heat shrinking step of the packaging process. Employing the valve of the present invention precludes the need for puncturing the film prior to heat shrinking. Thus, a wide variety of food products may be packaged in a manner more typically reserved for non-food products.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to heat shrinkable film packages, and specifically to a one-way valve for evacuating such packages during the heat shrinking step of the packaging operation. 
     BACKGROUND OF THE INVENTION 
     Heat shrinkable films are employed in packaging a wide variety of food and non-food items. Generally, most food products require a package which completely encloses the product. While some foods require packaging materials having oxygen barrier properties, nearly all foods require a complete, coherent covering which protects the underlying product from environmental contaminants. 
     Conversely, many non-food products are not particularly sensitive to exterior contamination. For non-food products such as games, compact discs, textiles, etc., the outer film overwrap merely serves as a dust cover or, as is particularly the case for software, evidence that the package has not yet been opened. In non-food products packaged in a heat shrinkable film, a hole or perforation is often provided in the film. The hole is formed in the film either prior to or during the packaging process to allow air trapped within the sealed film to escape during the heat shrinking step. 
     With a few minor exceptions, the presence of such perforation in food packages is not acceptable. Thus, food products must be packaged in a more complex shrink film packaging operation than that employed for packaging non-food products. Typically, food products require that the heat shrinkable packaging film is first formed into a pouch or bag into which the product is placed. The bag or pouch is then evacuated prior to sealing and heat shrinking. In addition to increased expense, such additional packaging steps provide an increased opportunity for film waste and packaging failure. 
     Accordingly, there is a need in the art for an apparatus and method which will allow for the packaging of food products in a simplified manner, similar to that employed in the packaging of non-food products, without leaving an opening which may result in contamination of the food and without leaving any void or opening that exposes the underlying portions of the food product to the atmosphere. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a shrink film package which includes a product, at least one web of a shrink film wrapped about the product, at least one seal defined in the shrink film enclosing the product, and a polymeric valve sealed to the film at the seal. The valve is comprised of a tube of film having a first end extending into the package, a second end extending out of the package, and an intermediate portion within the seal. The valve further includes an exterior surface and an interior surface, wherein the exterior surface comprises a sealable polymeric material whereby the intermediate portion of the exterior surface is sealed to the shrink film at the at least one seal and wherein the interior surface comprises a nonsealable material at least at the first end and the intermediate portion thereof. 
     The present invention is also directed to a method for packaging a product which includes the steps of 
     a) wrapping the product in at least one web of a heat shrinkable film; 
     b) subsequently sealing the heat shrinkable film thereby enclosing the product; 
     c) providing a polymeric valve comprising a tube of film sealed to the heat shrinkable film at a sealed portion of the heat shrinkable film such that a first end of the valve extends into the area enclosing the product, a second end extends out from the heat shrinkable film, and an intermediate portion is contained within the sealed portion of the heat shrinkable film, the valve further comprising an exterior surface and an interior surface, the valve being sealed to the heat shrinkable film at the intermediate portion of the exterior surface thereof and the interior surface comprising a nonsealable material at least at the first end and the intermediate portion thereof; and 
     d) heating the heat shrinkable film thereby shrinking the film about the product, 
     whereby simultaneously with the heat shrinking step, air surrounding the product is vented through the polymeric valve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the present invention can be obtained when the following detailed description of the preferred embodiment is considered in conjunction with the following drawings, in which, 
     FIG. 1 is a perspective view of a loading and sealing station employed in a packaging operation in accordance with the present invention; 
     FIG. 2A is a perspective, partial cut-away view of the valve of the present invention; 
     FIG. 2B is a cross-section of the portion of the valve which extends out of the package; 
     FIG. 2C is a cross-section of the portion of the valve which is sealed into an edge seal of the package; 
     FIG. 2D is a cross-section of the portion of the valve which extends into the package; 
     FIG. 3 is a perspective, partial cut-away view of a shrink tunnel employed in a packaging operation in accordance with the present invention; and 
     FIG. 4 is a perspective view of a shrink film package in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is directed to a shrink film package of the type typically employed for products such as board games and software. However, the present package lacks the perforation or perforations commonly found in such shrink film packages. Instead, the present package and packaging method employ a polymeric valve which serves the function of the perforation, i.e., providing a passage for trapped air to vent from the package during heat shrinking, without leaving a portion of the underlying product exposed. The present invention may best be understood from a review of the drawings which depict the preferred embodiment of the present packaging method and resultant package. 
     FIG. 1 illustrates a loading station  100  and a sealing station  200  of a typical shrink film packaging operation. Film roll  10  is positioned adjacent to the loading station  100  and includes lower web  12  and upper web  14 . Each of the lower and upper webs is a heat shrinkable film. Preferably the two webs are substantially identical films, most preferably separate portions of the same film. Examples of heat shrinkable films appropriate for use in accordance with the present invention include heat shrinkable films supplied by Cryovac, Inc., including D-955™, MPD-2055™, BDF-2001™, and other bag and film products. 
     In a typical packaging process, edge  16  of the film would be a fold such that lower web  12  and upper web  14  would be two halves of a single, folded web of film. For purposes of the present invention it is preferred that edge  16  is a previously formed seal  17 . As such, valve  20  is trapped within the seal, being sealed to webs  12  and  14 , as is shown more clearly in FIGS. 2A and 2C. However, it is also within the scope of the present invention for edge  16  to be a fold and for valve  20  to be sealed to film webs  12  and  14  at a seal to be subsequently formed at sealing station  200 . Such may be preferred when specific, selective placement of the valve or valves is desirable in order to accommodate the relative configuration of the product. However, it is more generally preferred that valves  20  (at least one for each package to be formed) have been positioned and sealed within seal  17  such that the operator at sealing station  200  need not position and seal the valves in place during the packaging operation. 
     Looking more closely at the valve  20  as shown in FIG.  2 A and in cross-sectional views in FIGS. 2B-D, it is seen that valve  20  is tubular in cross-section and includes a first end  22  (shown in cross-section in FIG. 2D) which extends into the package being formed, a second end  24  (shown in cross-section in FIG. 2B) which extends out of the package being formed, and an intermediate portion  26  (shown in cross-section in FIG. 2C) which is sealed to webs  12  and  14  within seal  17 . The tubular valve also includes an exterior surface  28  and an interior surface  30 . Exterior surface  28  is sealable to webs  12  and  14  and is sealed to such webs at intermediate valve portion  26  as is shown in FIG.  2 C. It is required, however, that interior surface  30  is not sealable to itself at the intermediate portion  26  of the valve. 
     Looking at FIGS. 2A-D it is seen that preferred valve  20  is formed of two film webs  32  and  34  which are sealed together at longitudinal seals  36  and  38 . For such preferred valve the interior surface comprises surfaces  30  and  30 ′ and the exterior surface comprises surfaces  28  and  28 ′. Surfaces  28  and  28 ′ may be of identical or differing compositions but must be sealable to webs  12  and  14 . Preferably surfaces  28  and  28 ′ are essentially identical in composition. Similarly, interior surfaces  30  and  30 ′ may be of identical or differing compositions but should be capable of forming longitudinal seals  36  and  38 . Preferably, seals  36  and  38  are formed by heat sealing surfaces  30  and  30 ′ to each other, although in an alternative embodiment seals  36  and  38  may be formed using an adhesive. In a most preferred embodiment film webs  32  and  34  are substantially identical monolayer webs of a blend of low density polyethylene and a metallocene catalyzed ethylene/α-olefin copolymer, although multilayer webs and webs of differing chemical compositions may be employed as long as the general requirements of sealability set forth herein are met. 
     It is preferred that a coating  31  which prevents sealing or adhesion between surfaces  30  and  30 ′ is applied to surface  30 , surface  30 ′ or both at intermediate portion  26  in-board of seals  36  and  38 . In a preferred embodiment the coating is a thermally resistive ink. A preferred ink for use as coating  31  in accordance with the present invention is Aqua-Tech 310 Pantone® 300C Blue sold by INX International Ink Company of Kansas City, Kans. Regardless of its composition, such coating preferably extends onto the interior surface of first end  22  in order to preclude undesirable tacking of that portion of the valve which extends into the package as is shown in FIG.  2 D. Such coating also is preferred for a valve formed from a single, folded web having only one longitudinal seal. 
     Similarly, such coating may be employed for a valve which is a unitary, tubularly extruded tube, although as an alternative option the interior surface ( 30 ) of such valve may comprise a polymeric composition which is not self-sealable, or at least such a composition which is not self-sealable under the conditions employed for sealing the exterior surface to webs  12  and  14  at seal  17 . Since the exterior surface is necessarily sealable to webs  12  and  14 , providing such a non-self-sealable interior surface would require an at least two layer coextruded structure for such valve embodiment. 
     However, for a valve having at least one longitudinal seal, a seal-resistant coating disposed in-board of the longitudinal seal or seals is the preferred means for maintaining an opened, unsealed valve at the intermediate portion as shown in FIG. 2C; although other means are also within the scope of the present invention. For example, the longitudinal seal or seals may be formed under time, temperature, and/or pressure conditions which are more severe than those employed to form seal  17  such that a composition or compositions which is sealable under those extreme conditions but not under the conditions employed to form seal  17  is employed. Alternatively, for a folded valve with a single longitudinal seal, an at least two layer film web having an interior surface ( 30 ) which is not self-sealing under the conditions employed for forming seal  17  and an exterior surface ( 28 ) which is sealable to webs  12  and  14  and is also sealable to the material of interior surface  30  may be formed into a tube by means of a lap seal (inside to outside) rather than a fin seal (inside to inside). 
     An important consideration in determining the desirable means for rendering at least a portion of the interior surface of the valve non-self-sealing is the desirability of sealing the valve at end  24  which extends out of the package either during or after package formation. For many end-use applications it is acceptable that the entire interior surface of the valve is non-self-sealing. Depending on its polymeric composition, the valve generally will deform to at least some degree from the heat of the shrink tunnel. Thus, if the entire interior surface of the valve is non-self-sealing, the valve will be tightly closed but not sealed. For certain end-use applications, such as certain high gassing cheeses, it is desirable that the valve remains open after shrinking of the film webs in order to allow for post-packaging outgassing of the product. For such embodiment, the valve must be formed of a polymeric composition which can withstand the time and temperature conditions of the shrink tunnel without significant deformation. If the end-use application requires that end  24  of the valve is sealed, then preferably a non-sealing coating is applied to those portions which must remain non-sealed. For such applications the interior surface or surfaces of the valve at end  24  may comprise a polymeric material which can be sealed in a separate sealing step (for a valve formed from one or two webs), two distinct polymeric materials which can be sealed to each other in a separate sealing step (for a valve formed from two webs), or a polymeric material or materials which will self-weld during the heat shrinking step. The latter option is an acceptable alternative when a seal, but not necessarily a hermetic seal, is desired for the protruding portion of the valve. 
     Returning to FIG. 1, product  50  is loaded between webs  12  and  14  at loading station  100 . The film and product are then indexed to sealing station  200 . Seal bars  210  and  220  are impulse or heat sealing bars, both of which are well known in the art. Seal bar  210  forms seal  230  opposite and parallel to previously formed seal  17 . Concurrently with forming seal  230 , seal bar  210  also trims the excess film. Seal bar  220  forms a seal  240  and a seal  240 ′ immediately adjacent to seal  240  and simultaneously cuts the film between the two seals such that the leading sealed edge of one package is being formed simultaneously with the formation of the trailing seal of the package ahead of it. 
     The product  50  enclosed within film webs  12  and  14  by seals  17 ,  230 ,  240  and  240 ′ is then placed on conveyor  310  of shrinking station  300  as is shown in FIG.  3 . Within hot air shrink tunnel  320  the film is generally subjected to hot air at temperatures ranging from 200°F. to 400°F. for 0.5 to 20 seconds. The shrinking film forces the air trapped within the sealed webs out through valve  20  as is illustrated in the cut-away view of the shrink tunnel  320  in FIG.  3 . 
     After indexing out of the shrink tunnel, the package  400  is essentially complete, as is shown in FIG.  4 . Optionally, the end  24  of valve  20  which extends out of the package may be sealed in a separate sealing step. As a further option, depending on the relative tearability of webs  12  or  14 , outwardly extending valve portion  24  may serve as an easy-open pull-tab for opening the package. 
     Although the above-described packaging equipment is preferred for use in executing the present claimed method and producing the present claimed package, other types of packaging equipment and systems may be employed in accordance with the present invention. For example, curved seal bars forming packages which conform to the shapes of certain products may be employed. For such shaped packages it may be desirable to selectively place the valve or valves for evacuation of product cavities which might otherwise fail to vent. Such selective placement may be in a preliminarily formed seal or may be performed on-site during the packaging operation, substantially as described above. Alternatively, form-fill-seal equipment may be employed in the production of the initial sealed package prior to shrinkage. In addition to allowing for the packaging of flowable products, the use of form-fill-seal equipment would allow for the introduction of a desired treating gas to the product environment prior to venting during the shrink step. 
     Although the invention has been described with reference to its preferred embodiments, those of ordinary skill in the art may, upon reading this disclosure, appreciate changes and modifications which may be made and which do not depart from the scope and spirit of the invention as described above and claimed below.