FIELD OF THE INVENTION
The present invention relates to a film structure that is irradiated by a focused laser beam or other focused energy source to provide a score line on an internal layer of the film structure, or on both the internal layer of a film structure and an outer layer of the film structure. In addition, the present invention relates to a package that may be torn along the score line. More specifically, the package may have a score line provided on an internal layer of barrier material, such as ethylene vinyl alcohol copolymer, polyvinylidene chloride copolymer, nylon, blends thereof or any other laser scorable barrier polymeric material. In addition, the package may have a recloseable feature to open and then reclose the package, such as, for example, a zipper or an adhesive. The score line on an internal layer and/or on the surface of the film may allow the package to be more easily opened using pull-apart forces, thereby exposing a product within the package and allowing a user of the package to gain access to product that may be contained therein.
BACKGROUND OF THE INVENTION
It is generally known to provide a line of weakness on a surface of a film structure via a focused laser beam. The focused laser beam is typically applied to the film in a first direction, such as in the machine direction of the web after extrusion or after being unwound from a roll. As a web of polymeric film, made via conventional extrusion or extrusion laminating methods, moves in the machine direction, the focused laser beam vaporizes the outer layer of the web thereby leaving a very thin line of weakness in the web material. Typically, the focused laser beam may vaporize the polymeric material of a single layer of material, such as a surface layer of the material, so that the web may be torn using digital pull-apart forces.
Many conventional polymeric materials are known to be very receptive to absorbing focused laser energy, typically focused infrared radiation. These polymeric materials include, for example, biaxially oriented polyethylene terephthalate (PET), biaxially oriented nylon (BON), nylon, paper, cellophane, polyvinylidene chloride copolymer (PVdC), or ethylene vinyl alcohol copolymer (EVOH). However, certain other thermoplastic polymers are not as susceptible to infrared laser energy at the energy level exposure of the presently preferred embodiments, such as polyolefins like low density polyethylene (LDPE) and polypropylene.
Score lines are typically applied to a film structure in a first direction, as noted above, such as in the machine direction of a web of film. However, score lines may also be applied in two different directions, such as in the machine direction of the web and the transverse direction of the web.
Typically, score lines applied to film structures useful for packages allow a user to gain access to a recloseable feature disposed on the package. Recloseable features are utilized on flexible plastic packaging to allow an individual to gain access to a product contained therein, and to then seal the product within the packaging for later use. For example, a recloseable plastic zipper can be incorporated into the plastic packaging. The plastic zipper typically is attached on an end of the packaging and utilized to provide an opening in the end of the package. Alternatively, the plastic zipper is attached to inside surfaces of the package and is exposed when a portion of the plastic packaging is removed from the plastic packaging.
The flexible plastic packaging may be provided with a feature that allows the portion of the plastic packaging to be removed from the plastic packaging thereby exposing the recloseable feature. This feature is typically a score line that is used to allow the portion of the plastic packaging to be removed, thereby exposing the recloseable feature.
Packages are known that contain a product, such as, for example, a cheese product. A typical package consists of two flat multilayer films that are heat sealed on three sides to provide a compartment therein. For example, a single multilayer film is folded and sealed on its sides to provide the package. On the fourth side, a resealable feature is provided for opening and closing the package to add and/or remove the product from the package. The recloseable feature may be a zipper that opens or closes the package when the slider is moved laterally over the open end of the package. However, the open end of the package containing the recloseable feature must be initially hermetically sealed to keep and store the product that is contained therein. A typical hermetic seal is provided below the zipper, which is separated by pull-apart forces when the package is opened for the first time.
Alternatively, the zipper is provided on inside surfaces of the package. The outer surfaces of the package therefore extend over the zipper and are hermetically sealed at a position over the zipper thereby providing a sheath over the zipper. Not only does this configuration provide a hermetic seal for the package, but also the sheath further protects the zipper. To remove the sheath, straight line or patterned score lines (i.e. two dimensional, or provided in both the machine and transverse directions of the film) are provided so that the sheath can be torn and the zipper exposed.
FIG. 1 illustrates a prior art package 500 with a sheath 501 extending over a zipper 504 and having a one-dimensional score line 502 that extends horizontally across the sheath 501 at a position below the zipper 504. When the sheath 501 is torn at the score line 502, made easier by the use of a notch 506 in the side of the package 500, the zipper 504 is exposed, and the package 500 may be opened or closed by the zipper 504.
Typically, barrier materials are utilized in film structures and packages that contain products that can be damaged by oxygen, moisture or other gases. Typical barrier materials may include polyvinylidene chloride copolymer (PVdC) and ethylene vinyl alcohol copolymer (EVOH), nylon, blends thereof, or any other laser scorable barrier material known to one having ordinary skill in the art. Many of these materials have limitations, however. Polyvinylidene chloride copolymer is susceptible to yellowing during cross-linking of the films by irradiation, which also tends to break down the barrier properties of the polyvinylidene chloride. In addition, EVOH has a relatively low melting temperature, and may be damaged if extruded with polymers having relatively high temperature melting points.
A known process of coextruding and laminating heat sensitive materials is described in U.S. Pat. Nos. 5,106,562, 5,108,844, 5,190,711 and 5,236,642 and 6,500,514, which are hereby incorporated by reference in their entireties. Various methods are disclosed for reducing the impact of higher temperature polymeric meltstream elements on a lower temperature polymeric meltstream. The methods may include super-cooling the hotter meltstream element below the melting temperature but above the crystallization temperature, exposing one or more meltstream elements to an undesirable thermal condition for a limited period of time, and/or using one or more layers as a heat sink via encapsulation.
Specifically, these patents describe methods of encapsulating one film layer by another material. The '562 and '844 patents specifically relate to PVdC or, preferably, PVdC-MA core materials with ethylene vinyl acetate copolymer (“EVA”) or ethylene methyl acrylate copolymer (“EMA”) or blend's thereof encapsulating the core material. The encapsulated PVdC or PVdC-MA is, therefore, protected from the high temperatures of the coextrusion process. Generally, the encapsulation method uses an encapsulator having a crosshead mandrel with a central bore to receive a first meltstream element from an extruder. A second polymeric meltstream is fed through a sleeve via an inlet passage into the encapsulator. As the second meltstream enters the encapsulator, it splits and flows around the first meltstream. Consequently, the second meltstream completely surrounds the first meltstream, thereby forming a combined meltstream. The second meltstream forms a continuous layer about the circumference of the first meltstream completely surrounding the first meltstream. Thus, the first and second meltstreams maintain their individual identities while the first meltstream is completely surrounded by and encapsulated within the second meltstream. The combined meltstream may then be fed through a transport pipe to a feedblock for coextrusion with one or more other layers to produce a multilayer film.
In addition, other film structures containing barrier layers may be utilized in the present invention, such as those film structures described in U.S. Pat. Nos. 6,068,933 and 09/411,671 to Shepard et al., entitled “Thermoformable Multilayer Polymeric Films”, which are expressly incorporated herein by reference. These films may include alternating layers of nylon and adhesive, with one or more layers of EVOH as internal barrier layers.
Typically, film structures having barrier materials, such as polyvinylidene chloride, ethylene vinyl and alcohol, nylon, blends thereof, or any other laser scorable barrier material which are susceptible to being vaporized by a focused laser beam, are carefully scored via the laser beam so that the barrier layers are not damaged via the focused laser beam, such that the barrier characteristics of a package made from these film structures are not affected by the scoring of the film structure. However, it has been found that laser scoring one or more internal barrier layers does not appreciably decrease the barrier properties of packages made from the films because the area of scoring is so small. Typical laser score lines are 0.003-0.006 inches thick.
If only surface layers of a film structure are scored and internal layers of film structures are left intact, it may be difficult to tear a package made from the film structure cleanly, evenly or easily. When tearing forces are applied to tear a package along a laser scored tear line wherein the surface layer is the only layer that is scored, the tensile strength of the film structure may be relatively high making it difficult to tear the package cleanly.
A need exists, therefore, for a film structure having a plurality of layers wherein an internal layer of the film structure, or both the internal layer of the film structure and an outer surface layer of the film structure is scored via a focused laser beam so that the film structure may more easily be torn using tearing forces. A need further exists for internal scoring of a film structure via a focused laser beam or other focused energy source wherein the film structure is useful as a package so that the package retains or mostly retains its barrier properties and/or hermetic properties. Still further, a need exists for methods of making the film structures and packages made therefrom.
SUMMARY OF THE INVENTION
The present invention relates to flexible film structures having a plurality of layers wherein one or more of the internal layers, such as a layer of EVOH copolymer, PVdC copolymer, nylon, blends thereof, or other laser scorable barrier materials is scored via a focused laser beam or other focused energy source. Further, the present invention relates to flexible film structures having a plurality of layers wherein one or more of the internal layers and an outer surface layer of the film structure are scored via a focused laser beam or other focused energy source. In addition, the present invention relates to packages made therefrom, and methods of making the film structures.
In addition, the present invention relates to film structures containing one or more barrier layers of, preferably, ethylene vinyl alcohol copolymer, although other barrier layers are contemplated by the present invention. The film structures may be coextruded or extrusion laminated to other film layers, including an outer layer of a laser scorable polymeric material, such as PET or BON. A focused laser beam, or other focused energy source, can be applied to a film structure in a first direction, such as the machine direction, in a second direction, such as the transverse direction, or both the machine and transverse directions to provide a package having a score line on the internal barrier layer or both an internal layer and an outer layer of the film structure. Of course, film structures made with barrier layers may be made according to any method known in the art, via extrusion lamination or coextrusion, for example, such as via encapsulation as described in U.S. Pat. Nos. 5,106,562, 5,108,844, 5,190,711 and 5,236,642 and 6,500,514.
To this end, in an embodiment of the present invention, a film structure is provided having a plurality of layers wherein a first internal layer is a barrier material. The film structure has a score line on the internal layer of barrier material, and optionally includes a score line on both an internal layer of the film structure and an outer surface layer of the film structure. A preferred film structure includes a first layer of EVOH, and various other layers, in the following structure:
PET or BON/Ink/LDPE/PE/tie/EVOH/tie/heat sealant
The tie layers may be any polymeric material that may be useful to bond the EVOH layers to the heat sealant layer or the layer of polyethylene. The heat sealant layer is comprised of any polymeric material useful to provide a seal when heat is applied to the film structure. Typical materials include ethylene vinyl acetate copolymer and/or linear low density polyethylene, for example.
In an alternate embodiment of the present invention, a package is provided comprising a first side wall; a second side wall wherein the first side wall and the second side wall are bonded together on edges to form a pouch having a space therein for storing a product; a recloseable feature disposed on inside surfaces of the side walls wherein the side walls are sealed together on an end of the package; and a score line in at least one side wall from a first edge to a second edge of the at least one side wall. The package comprises an internal layer of a barrier material of EVOH copolymer. The score line may be a straight score line or may be a patterned score line, i.e., a score line disposed in both the machine and transverse directions of the film structure utilized as a package wall. The score line creates a line of weakness on the EVOH layer disposed as an internal layer in the package.
In an alternate embodiment of the present invention, a method of making a scored film wherein said score line is applied via a focused laser beam or other focused energy source on an internal layer is provided. The method includes providing a film structure having a plurality of layers wherein a first internal layer comprises a barrier material. The method further includes applying a focused laser beam or other focused energy source to the film structure wherein the focused laser beam or other focused energy source produces a line of weakness in the barrier layer. In addition, the film layer may comprise an outer layer of PET or BON that may be scored via the laser beam or other focused energy source as well.
In an alternate embodiment of the present invention, a method of making a package is provided comprising the steps of providing a first wall and a second wall; laser scoring a line of weakness in at least one side wall; providing a recloseable feature attached at a first end of the side walls; attaching the recloseable feature to inside surfaces of the side walls; and sealing the first wall and the second wall together on edges of the walls to form a pouch having a space therein for a product, wherein said score line is disposed above the recloseable feature at edges of the side walls and further wherein said score line is a straight line or traces a path to below the recloseable feature between the edges of the side walls. The package further comprises an internal layer of a barrier material. Further, the score line may create a line of weakness on the internal barrier layer.
It is, therefore, an advantage of the present invention to provide a film structure having a plurality of layers wherein one or more of the layers is an internal layer of laser scorable barrier material wherein a focused laser beam imparts a line of weakness in the internal barrier layer. The barrier properties of a package made from the film structure remain relatively unchanged after scoring the barrier layer with the focused laser beam.
In addition, it is an advantage of the present invention to provide a film structure having a plurality of layers wherein an outer layer of the film structure comprises a laser scorable polymer such as PET or BON, and further wherein an internal layer is made from a barrier material of ethylene vinyl alcohol copolymer. A focused laser or other focused energy source applied to the film structure creates a line of weakness in both the outer layer of laser scorable polymer and the internal layer of EVOH. The line of weakness aids in tearing the film structure when pulled apart by digital pull-apart forces.
It is further an advantage of the present invention to provide a package made from a film structure that may keep and store a product, such as a product that may have a limited shelf-life. For example, the product may be a food product, such as cheese. The package may be hermetically sealed on all sides and may further restrict the movement of moisture and/or oxygen through the walls of the package, thereby keeping the product contained therein fresh. The package may further have a score line in at least an internal layer of said film structure or on both an internal layer and an outer layer of said film structure.
Still further, it is an advantage of the present invention to provide a straight line or patterned score line on an internal layer of a film structure or on both an internal layer and an outer layer of a film structure thereby allowing a portion of the film structure to be removed by tearing forces. The removable portion may allow access to an internal space within a package made by the film structure or to expose a recloseable feature disposed on the package.
Additional features and advantages of the present invention are described in, and will be apparent from, the detailed description of the presently preferred embodiments and from the drawings.