Flexible multiple layer packaging film and packages made from such film.

This invention pertains to packaging, and more particularly to flexible multiple layer packaging films suitable for forming heat sealable packages. The invention also relates to a package openable by ply separation.

More specifically, the invention addresses packaging applications having a need for strong closure seals, and particularly those applications in which the product is sensitive to infusion of air or other gases into the package through the seals which are formed during closing a package.

In the design of flexible packaging films and packages formed from them, the designer has to grapple with the dual objectives of providing for strong package closures coupled with ease of opening to gain access to products contained in the packages. Various design features are available to ease the opening of packages. These often take the form of weakness lines, scores, cuts, perforations and so on. Many of these features require a separate operation on either the film or the package to ensure proper opening of the packages. Some opening facilities may penetrate the package, thus violating any gas barrier property which the film itself may possess. Separate manufacturing operations, of course, have a cost and impute an economic penalty to the films so made.

A highly desirable and economical method of providing for opening of the package involves making the closure seals such that they can be pulled apart. While a peelable seal is highly desirable in that it is economical to manufacture and easy to use, packages having peelable seals have not heretofore offered, in combination, the properties of hermetic, or gas-tight, seals, or inseparable seals.

In the packaging of products that are sensitive to certain gases in the air, it is imperative that the infusion of those gases be prevented. Gas barrier properties of various of the commercially available polymers commonly used in packaging films are known. These gas barrier properties are useful for preventing gaseous infusion into a package through the packaging film. Even so, there is still some possibility of gaseous infusion through the seal area of a package. The seal area can comprise heat seals which, for example, may be about the periphery of a pouch. Such seals do not provide an impervious barrier, whether by chemical composition or physical assemblage.

While the actual polymers commonly used to form heat seals are not normally considered to be particularly good gas barriers, they may function as such by virtue of the thickness of the seal measured from inside the package to its exterior, provided a physically gas-tight, normally hermetic, seal is made. This quasi-barrier property is usually associated with an inseparable seal.

In the formation of heat seals, two polymer layers, typically of identical composition, are brought together with heat and pressure, such that the layers are softened and somewhat fused together. To the extent softening and fusing is accomplished, the seal strength is enhanced. Seal strength is also enhanced by the homogeneity and internal cohesiveness of the layers so sealed.

It is known that inseparable seals may be formed by polymers that exhibit good softening and fusing properties. A polymer such as surlyn ionomer, for example may form inseparable heat seals and provide an hermetically sealed, gas-tight package. In a well-formed surlyn seal, the interface between the two layers so sealed essentially disappears, and the surlyn layers in the seal area appear to function as a single layer joining the two films which form the sides of the package.

While such a strong seal is highly desirable because it provides excellent package integrity at the seals and typically prevents gaseous infusion through the seals, a package so well sealed as this may be difficult to open to obtain access to the contained product. While access to the package contents may be achieved such as by the package having a special mechanical design, or by using a sharp tool, it would be highly desirable to simply peel the package open. Because hermetically sealed packages normally have inseparable seals, hermetically sealed packages have not heretofore been available with peelable opening features to gain access to the package contents.

Generally, this-invention aims to provide a package having strong seals in combination with a ply-separating peel capability, and desirably good oxygen and moisture barrier properties.

This invention provides, inter alia, an hermetically sealed package which can be readily peeled open, such a package preferably having film layers which offer excellent resistance to the transmission of oxygen and water vapors therethrough, in particular.

The invention also aims to provide a method of opening a sealed package, wherein the seals of the facing, innermost, layers of the package are not conducive to separation. Thus, the invention seeks to provide a package made from a multiple layer film and closable by means of inseparable heat seals, opening of the package being contrived by a partial tearing through of the packaging film and ply separation.

According to the present invention, there is provided a flexible, multiple layer packaging film having interfacial adhesion between the confronting pairs of adjacent layers, the film comprising, in order: <ul id="ul0001" list-style="none"><li>(a) a first layer of a heat sealable polymer capable of forming strong seals;</li><li>(b) a second layer of an olefin-based adhesive polymer having good adhesion to said first layer;</li><li>(c) a third layer whose composition is selected from ethylene vinyl alcohol copolymer, a polyamide-based polymer, and blends of ethylene vinyl alcohol copolymer with a polyamide-based polymer such as nylon;</li><li>(d) a fourth layer of an olefin-based adhesive polymer; and</li><li>(e) a fifth layer of an olefinic polymer selected from polypropylene, polyethylene, and ethylene vinyl acetate copolymer having less than about 5% by weight vinyl acetate,</li></ul> said film being susceptible to being made into a flexible, sealed package having good oxygen and moisture barrier properties, and strong seals between confronting layers of the heat sealable polymer, the force required to peel apart a seal between the heat sealable layers being greater than the force required to tear partially through the film to an interface between a given two of said layers and to separate the said two layers by ply separation.

Such a film can comprise, in order: <ul id="ul0002" list-style="none"><li>(a) a first layer comprising ionomer;</li><li>(b) a second layer comprising an olefin-based adhesive polymer having good adhesion to said first layer, said olefin base being selected from ethylene vinyl acetate and low density polyethylene;</li><li>(c) a third layer whose composition is selected from nylon, ethylene vinyl alcohol copolymer, and a blend of nylon and said polymer,</li><li>(d) a fourth layer comprising an olefin-based adhesive polymer, said olefin base being chosen from ethylene vinyl acetate and low density polyethylene; and</li><li>(e) a fifth layer comprising an olefinic polymer selected from low density polyethylene, linear low density polyethylene copolymer, and high density polyethylene,</li></ul> said film being susceptible to being made into a flexible package having hermetic seals, peelable opening without tearing across the entire thickness of said film, and good oxygen and moisture barrier properties.

The layers are all juxtaposed respectively in face-to-face contact with their adjacent layers bonded to each other with adhesion adequate for the integrity of the multiple layer film, and for a package formed therefrom. The film can be made into a flexible package, for example a pouch having hermetic sealability and peelable opening without tearing through the entire thickness of the film.

In some cases it is specifically desired that the third layer be a polyamide. In other cases, the use of EVOH for this layer is preferred.

The second layer adheres the first layer to the third layer, and in some cases a preferred composition for the second layer is an anhydride modified form of ethylene vinyl acetate copolymer (EVA). Another preferred composition for the second layer is anhydride modified polyethylene, particularly low density polyethylene (LDPE).

The fifth layer desirably functions as a barrier to transmission of water vapors, and preferred compositions therefor are low density polyethylene (LDPE), linear low density polyethylene copolymer (LLDPE), high density polyethylene (HDPE), and EVA having no more than 5% vinyl acetate (VA) by weight.

The composition of the fourth layer, e.g. EVA or LDPE, is selected for its adhesion to the third and fifth layers. The preferred olefin base for the fourth layer is either EVA or LDPE.

In a particularly preferred film structure, the compositions of the second and fourth layers are both based on EVA, and the most preferred composition for the fifth layer is LDPE.

A more complex structure for a film according to this invention is represented by one wherein an abuse resistant layer is adhered to the fifth layer by an adhesive layer. For example, a layer of oriented polypropylene (OPP) can be adhered to the fifth layer by an adhesive layer of LDPE.

A still more complex structure for a film according to the invention is represented by one having a sixth layer of polyethylene adhesive, a seventh layer of metal foil, an eighth layer of ethylene acrylic acid copolymer (EAA) adhesive and a ninth layer of OPP.

Also according to the present invention, there is provided a closed and sealed package made with packaging materials including multiple layer packaging film, said package having been closed by seals e.g. hermetic seals between surface layers of portions of the said packaging materials, the seals-having sufficient strength to discourage or prevent opening of the package by separation of the seals, and the package being susceptible of being opened, by a combination of tearing partially through the thickness of the said film and by ply separation peeling. Such an hermetically sealed package can be opened by a combination of partially tearing through the film, from the inside of the package outwardly, and by ply separation peeling.

In a preferred embodiment, the hermetically sealed package has a first layer of ionomer, a second layer of olefin-based adhesive polymer having good adhesion to the first layer, a third layer based on a polyamide or an EVOH, a fourth layer of an adhesive based on an olefin polymer and a fifth layer of polyethylene or polypropylene.

The package may, optionally, have a layer of an abuse resistant polymer, such as OPP, adhered to the fifth layer by an adhesive layer such as LDPE.

Packages according to the invention can feature the still more complex nine-layer structure mentioned hereinbefore.

The invention will now be explained in more detail in the following non-limitative description of preferred embodiments of the invention. This description is to be read in conjunction with the accompanying drawings, in which: <ul id="ul0003" list-style="none"><li>FIGURE 1 is a cross-section through a film according to this invention,</li><li>FIGURE 2 shows an external view of a flexible package made from films according to this invention,</li><li>FIGURE 3 illustrates a cut-away view of a portion of a pouch representing a first prior art structure having a potentially peelable seal,</li><li>FIGURE 4 illustrates a cut-away view of a portion of a pouch representing a second prior art package structure having a potentially peelable seal,</li><li>FIGURE 5 illustrates a cut-away view of a portion of a pouch representing a third prior art package structure having an inseparable sealing bond, and which has no means for functioning in a peel-open mode.</li><li>FIGURE 6 is a cut-away view of a portion of a pouch according to this invention which has an inseparable seal and a peel-open feature,</li><li>FIGURE 7 is a cut-away view similar to FIGURE 6, showing the opening of the pouch in progress,</li><li>FIGURE 8 is a cut-away view similar to FIGURE 7, showing the pouch fully opened for access to the contents therein.</li><li>FIGURE 9 shows a cross-section through a more complex 7-layer film according to the invention,</li><li>FIGURE 10 shows a cross-section of a still more complex 9-layer film according to the invention, and</li><li>FIGURE 11 is a cut-away view of a portion of a pouch as in FIGURE 6, but with loose pouch edges which have been pulled apart in attempting to open the package using an improper opening method.</li></ul>

Referring now to the drawings, FIGURE 1 represents a five layer film structure embodying this invention. The overall film is designated 10. Layer 12 is a heat seal layer, e.g. surlyn ionomer. Layer 16 is EVOH or polyamide or a blend of EVOH and polyamide. Layer 20 is a polymer based on polyethylene or polypropylene. Layers 14 and 18 are adhesives based on olefin polymers.

The sealant layer 12 is typically surlyn ionomer because of its ability reliably to form hermetic heat seals. The term "hermetic" as used herein refers generally to gas-tight seals where passage of, for example, atmospheric gases is minimized. For purposes of this invention, the composition of layer 12 is not so important as is its capability to form seals which have strength sufficient for hindering attempts to open the package by peeling apart of the seals.

In the construction of sealed film packages, such as that shown in FIGURE 2, there are known two general types of seal structure. In the first known type, the seal extends to the outer edge of the package as in FIGURE 3. In this FIGURE, and FIGURE 4 also, each of the outer unnumbered layers is in practice constituted by a plurality of layers while the layers bearing references 312 and 412 are each a single layer. As seen in FIGURE 3, the sealed area of sealant layers 312 extends from a location 322 inwardly of the edge 313 of the film to the edge 313 thereof, such that the edge of the package functions as a single film. In the second known type, as seen in FIGURE 4, the seal extends from a lcoation 422 which is inward of the edge 413 of the film, outwardly to another location 424 short of the edges 413, such that the edges 413 of the film are not sealed together. The unsealed portion of the film between edges 413 and locations 424 can be grasped for peeling open the package where the seal layers provide peelable seals and can be peeled apart. In cases where the seals are strong, the interfacial boundary between the sealant layers as at 326 in FIGURE 3 may disappear when the two layers function as one layer. Such a construction is seen in FIGURE 5, where the sealant layers 512 have been shown joined into one layer in the seal area. In structure of FIGURE 5, the seal area may be so strongly sealed as to form an inseparable bond and, thereby, resist separation into two layers in the seal area, such that the film will fail by tearing thereof as at 528A when sufficient pulling force is used in attempting to pull apart the two sides 510A and 510B of the package by pulling on it near the the edges 513. Such efforts fail to open the package to make the contents available.

The package may be opened, however, by grasping it on both sides, inwardly of the seal area, and pulling the two sides 510A and 510B apart. This opening is by tearing through the entire thickness of the package sidewall as at 528B. While the package may thus be opened, tearing through the entire thickness of the packaging film may be sudden, and is typically accompanied by an uncontrolled and jerky motion, with spillage of contents, as well as other undesirable results.

The packages of FIGURES 3 and 4, having weaker seals shown by the interfaces 326 and 426, may conceivably be opened along the seal interfaces and thus are of little consequence to the invention beyond their use as background information on conventional peelable seals which are undesirably weak. While the packages illustrated as FIGURE 5 have sufficient seal strength, they do not have a peel-open capability. The packages of this invention do have peel-open capability in combination with strong seals and excellent barrier properties, effected by the use of the multiple layer films disclosed herein.

Turning back now to FIGURE 1, layer 14 is an adhesive tie layer whose composition is selected for good adhesion to its adjacent layers. Typical adhesive materials for use in layer 14 are the anhydride modified polyolefins. These are available commercially, for example, Plexar 3 or Plexar 158 from Chemplex Company and AP220L from Novatec Company. It is common, and satisfactory, for layer 14 to form an inseparable bond with layer 12. It is also desirable that layer 14 form a good, but separable bond with layer 16.

Layer 16 provides the package with a barrier to transmission of oxygen through the package wall. The composition of layer 16 is EVOH, a polyamide-based polymer or a blend of EVOH with a polyamide-based polymer. As referred to herein, a polyamide-based polymer is one having a substantial recurrence of amide type molecular subgroupings. Among the preferred polyamide-based polymers are the various nylon polymers and polyetheramide copolymers. Significantly, layer 16 has moderate adhesion to layer 14 so that the package is structurally sound, but the adhesion between layers 14 and 16 is not so strong as to preclude the peeling apart of those layers.

Layer 18 is an adhesive tie layer whose composition is selected for good adhesion to its adjacent layers 16 and 20. Adhesive materials used in layer 18 are similar to those used in layer 14, as the functional requirements of adhesion are similar. Thus, the anhydride modified polyolefins are exemplary of satisfactory adhesive materials for use in layer 18. In some cases, it is acceptable, and for economic reasons may be desirable, to use the same material composition for both layers 14 and 18.

Layer 20 has, as its primary purpose, the protection of layers 12, 14, 16 and 18 and the package interior against intrusions from the external environment. Common intrusions of concern are those of oxygen and moisture. The intrusion of oxygen into the interior is prevented primarily by the oxygen barrier layer 16. In the usual case where layer 16 is or contains EVOH, the effectiveness of the EVOH depends on its being dry, its effectiveness as an oxygen barrier being reduced according to the extent moisture reaches the EVOH. Thus it is important that layer 20 should not only prevent moisture from getting into the package but should also prevent moisture from reaching any EVOH which may be in layer 16. The functional requirements of layer 20 are fulfilled by polyethylene, polypropylene, propylene ethylene copolymers, or ethylene vinyl acetate having less than 5% by weight vinyl acetate. Particularly desirable compositions for layer 20 are low density polyethylene, linear low density polyethylene and high density polyethylene.

Packages of the invention may be made entirely from films of the invention. In making these packages, portions of the films are positioned face-to-face with the sealant layers facing each other. The packaging materials thus positioned for formation of heat seals are in closure relationship. The package such as is seen in FIGURE 2 is formed and sealed closed by forming heat seals generally about a contiguous enclosure defined by the film portions.

Packages of the invention may also be made by sealing a first film of the invention to a second packaging material not of the invention. In these cases, both the overall cohesive strength of the second packaging material and the seal strength of the package closure seals must be stronger than the strength required to peel open the package.

The closed and sealed packages of this invention are represented by the illustration of FIGURE 6. They may also have unsealed edge portions such as those seen in FIGURES 4 and 5. The joining of the seal layers 612 in FIGURE 6 is represented as being inseparable by the absence of any line representing an interfacial surface between the two layers 612 in the seal area.

For opening packages of the invention, the package sidewalls, as at 610A and 610B FIGURE 6, are grasped at locations inwardly of the package from the seal area and pulled apart, as shown by arrows adjacent the sides of the package in FIGURE 7. The inseparable seal between the sealant layers 612, 712 remains intact, but the packaging film tears partially through its thickness, tearing the sealant layer 12 and the adjacent adhesive layer 14. Layers 712 and 714 in FIGURE 7 have been torn through. The adhesion between layers 714 and 716 is strong enough to allow for package integrity while being weak enough to be separated with moderate-amounts of force. As seen in FIGURE 7, layers 712 and 714 have been torn through, and the opening has progressed along the interface of layers 714 and 716 by ply separation, toward the edge 713 of the package.

FIGURE 8 shows the package fully opened for access to its contents through the opening shown by the double headed arrow.

Attempts to open the package by other conventional means may not be successful. Thus the method of opening the package is not obvious. For example, in a package of the invention wherein the seal does not extend to the edge of the film, one may grasp the loose edges and pull them apart, expecting to open the package. Such a package is illustrated in FIGURE 11. It is seen that the same combination of tear and peel opening which functions to open the package as in the method illustrated by FIGURES 7 and 8, does not function to open the package when done by the method illustrated in FIGURE 11. While a plurality of layers of the packaging material may be removed by that method, the package is not opened for access to the contents.

Thus it is seen that the packages of this invention have strong seals, and function with a special peelable opening feature,the seals being preferably made by heat sealing.

The packaging films according to this invention are preferably made by coextrusion processes, though other processes are acceptable so long as the resulting film has functional integrity for the life of the package and provides a peelable interface between the two layers other than the heat seal layers. For those purposes the interfacial adhesion between the two layers should be between 50 grams per inch width (19.7 g/cm) and 400 grams per inch (157 g/cm), preferably between 100 and 300 grams per inch (39.4 to 118 g/cm), as determined by ASTM d-903.

Films of this invention are generally thin, usually in the range of 1.25 mil to 3.5 mils (0.032 to 0.089 mm) in overall thickness. Thinner films in this range are preferred for purposes of driving heat through them in the heat sealing process, and are economical in use of materials. Thicker films are stronger and more durable, however.

EXAMPLE 1

A highly desirable film is 1.5 mils (0.038 mm) thick, and may be made by a conventional coextrusion process. The sealant layer as at 12, is surlyn ionomer at 33% of the film thickness. The two tie layers, as at 14 and 18, are each 7.5% of the overall film thickness and are composed of Plexar 3 anhydride modified ethylene vinyl acetate copolymer. The oxygen barrier layer, as at 16, is 10% of the overall thickness and is Soarnol-ET EVOH from Nippon Gohsei Company, Japan. The outer layer 20 is 42% of the overall film thickness and is Norchem 963 low density polyethylene. In opening tests of pouch-type packages, the film peeled to open the package between layers 14 and 16.

EXAMPLE 2

Another desirable film which may also be made by coextrusion is also 1.5 mils (0.038 mm) thick. The sealant layer is surlyn ionomer at 15% of the film thickness. The two tie layers are each 7.5% of the overall film thickness and are composed of Plexar 3 anhydride modified ethylene vinyl acetate copolymer. The oxygen barrier layer is 10% of the overall thickness and is nylon 6. The outer layer is 60% of the overall film thickness and is high density polyethylene. Packages made from this film could be peeled open in the same say as those in EXAMPLE 1.

The minimum thickness of the overall film is somewhat based on the functional performances of the individual layers. Minimum thickness of the oxygen barrier layer and the tie layers is about 0.1 mil (0.0025 mm) each, as that represents the approximate state of the art minimum thickness for fabrication of film layers by coextrusion. Minimum thickness of the outer layer 20 is about 0.5 mil (0.013 mm) to ensure a good moisture barrier property and at least a moderate amount of abuse resistance. Minimum thickness of the sealant layer 12 is that necessary to achieve the required seal strength.

While layers 14 and 16 have been chosen for ply separation in the foregoing illustration of the invention, other layer pairs could be selected so long as the functional affect is the same. It should be noted that, in the package structure, there is a substantial fraction of the film thickness between the peelable interface and the exterior surface of the package. In the film illustrated in EXAMPLE 1, about 60% of the film thickness is between the peelable interface and the exterior surface. In the film in EXAMPLE 2, about 87% of the film thickness is between the peelable interface and the exterior surface. Other percentages will be functional so long as the required peel force is less than the force required to tear through the remaining thickness of the film.

In some cases, additional protective properties are desired of films of this invention, whereby more complex structures are needed. In one such structure, having 7 layers, an additional adhesive tie layer 21 is used to adhere a special abuse-resistant layer 23 to the moisture barrier layer 20, as seen in FIGURE 9. Acceptable materials for abuse resistant layer 23 are paper, cellophane, biaxially oriented polyester, biaxially oriented polypropylene or biaxially oriented nylon. Suitable adhesive materials for tie layer 21 are the anhydride modified polyolefins as well as the unmodified polyolefins, depending on the specific compositions chosen for layers 20 and 23. Those skilled in the art will be able to make appropriate selections of adhesive compositions for these layers.

In another complex structure illustrated by FIGURE 10, a layer 25 having a metal composition is adhered to layer 20 by an adhesive layer 27 and an abuse resistant layer 23 is adhered to layer 25 by an adhesive layer 21. Layer 25 may be metal foil or a metallized plastic film such as metallized polyester or polypropylene. A suitable adhesive material for layer 27 is typically the same as for adhesive layers 14 and 18. Layer 23 is the abuse resistant layer as in the 7-layer structure described in the last preceding paragraph. In the 9-layer structure, adhesive layer 21 is preferably ethylene acrylic acid copolymer for good adhesion to a metal surface or may be other of the known adhesive polymers, such as low density polyethylene.

Where layer 23 is a generally transparent layer on an outside surface of the film, it is sometimes desirable to print artwork, graphics, and other indicia on the surface of the film which is disposed toward the adjacent layer in the film. This process is known as reverse printing and is completed before the abuse resistant layer 23 is incorporated in the multiple layer film.

The films according to this invention provide a combination of properties never before achieved in a single film. By using such films to make packages, e.g. for foodstuffs, strong seals are attainable coupled with an easy open facility provided by an ability to separate or peel apart two layers of the film, said two layers not including a layer which has a seal-forming function. Preferred films of this invention have good oxygen and moisture barriers; some such films may incorporate a light barrier, abuse resistant layer and a further enhanced gas barrier provided by a metal foil layer.