NZ234427A - Multilayer shrink film comprising six layers; vldpe and ethylene acrylate - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £34427 # 23 4 42 7 Priority Dstrjj.}: . ,.., Complete Sp'j.jificr/.ic', ch^.: mewU i pubiicxb:-, . 23 DEC 1993 ;; P.O. Journal, No: ,,. 1ST)S", MA ™ NEW ZEALAND PATENTS ACT, 1953 -» -\- r- mw ff» hi r**~\ • / •> No.: Date: 4 COMPLETE SPECIFICATION AT/^f 'A&Vj3 COOK-IN FILM WITH VERY LOW DENSITY foPf^^/L£M£.

We, W R GRACE & CO.-CONN, a corporation organized and existing under the laws of the State of Connecticut, of 1114 Avenue of the Americas, New York, N-Y 10036, USA hereby declare the invention for which jsf we pray that a patent may be granted to prffe/us, and the method by which it is to be performed, to be particularly described in and by the following statement: - (followed by page la) 234427 COOK-IN FILM WITH VERY LOW DENSITY POLYETHYLENE BACKGROUND OF THE INVENTION This invention relates generally to heat shrinkable, relatively gas impermeable, thermoplastic packaging film which can be heat sealed to itself to form a flexible package. The invention relates more particularly to bags of such film for food products in which the packaged product is submerged in. heated water, or exposed to steam or dry air heat or autoclaved for a substantial period of time for pasteurizing or cooking, the bag structure being shrinkable and nondegradable under such conditions.

There is a need in the food packaging industry for a packaging film from which bags can be made which are of improved structural soundness such that they may be fully characterized as pasteurizable and/or cook-in. Further, it is desirable to have a precooked food product which is attractively packaged inside the film within which it was precooked.

The term "pasteurizable" as used herein is intended to refer to packaging material structurally capable of withstanding exposure to pasteurizing conditions while containing a food product. Many food products require pasteurization after they have been hermetically packaged to destroy harmful microbes which grow in the absence of air. Specific pasteurization requirements tend to vary by country; however, limiting conditions probably are submersion of the hermetically sealed product in water at 95°C for 1 hour. Thus, for a bag to be characterized as pasteurizable, structural integrity of the bag must be maintained during pasteurization, i.e. the bag must have superior high temperature seal strength and must be delamination resistant under such time-temperature 4/890802.3A/TXTGM 234427 conditions. Additionally/ the packaging material should be heat shrinkable under pasteurizing conditions so as to provide an attractively packaged pasteurized food product.

The term "cook-in" as used herein is intended to refer to packaging material structurally capable of withstanding exposure to cook-in time-temperature conditions while containing a food product. Cook-in packaged foods are essentially prepackaged, precooked foods that go directly to the consumer in that configuration which may be consumed with or without warming. Cook-in time-temperature conditions typically refer to a long slow cook, for example submersion in water at 70-80°C for 4-6 hours. Such cook-in time-temperature requirements are representative of institutional cooking requirements. Submersion at 80°C for 12 hours probably represents the limiting case. Under such conditions, a packaging material properly characterized as cook-in will maintain seal integrity and will be delamination resistant. Additionally, the packaging film should be heat shrinkable under these conditions so as to form a tightly fitting package and preferably should have some tendency for product adhesion to prevent "cook-out" or collection of juices between the surface of the food product and the interior surface of the packaging material.

The term "ethylene alkyl aery late copolymer" (EAA) is used herein to define a copolymer formed of ethylene and alkyl acrvlate comonomers wherein the ethylene derived units in the copolymer are present in major amounts, and the alkyl groups may include e.g. ethyl, methyl and butyl groups.

The term "very low density polyethylene" is used herein to describe an ethylene alpha-olefin copolymer, linear in nature, with a density generally below about 0.915 grains per cubic centimeter (ASTM D 1505) and having a comonomer of C4 to C8 such as butene, hexene or octene. A preferred commercial example is Attane 4003 available from Dow and having a density of about 0.905 grams per cubic centimeter.

The term "linear low density polyethylene" is. used herein to describe an ethylene alpha-olefin linear copolymer having a density of between about 0.915 and 0.940 grams per cubic centimeter and having a 4/890802.3A/TXTGM 2 23 4 4 comonomer such as butene, hexene or octene. A preferred commercial resin is Dowlex 2045.03 available from Dow Chemical.

There are a number of preferred features for a pasteurizable, cook-in packaging material. It is the purpose of the present invention to provide a pasteurizable, cook-in packaging film having all of these features. First, bags made from such film should have seal integrity under such conditions, i.e. the heat sealed seams should resist being pulled apart during heat shrinking. As a corollary, the film should be heat sealable to itself. Alternatively, bags or casings made from film of the present invention made be closed by clips by means well known in the art. Second, such bags should be delamination resistant, i.e. the layers making up the film must not separate or blister. Third, the food contact layer of such film should qualify under the appropriate food laws and regulations for safe food contact in end uses involving food packaging. Fourth, the film should provide an oxygen barrier, i.e. a low permeability to maintain the freshness of the food contained therein. Fifth, the film should be heat shrinkable in hot water under cook-in conditions, i.e. the film must possess sufficient shrink energy such that when the packaged food product is submerged in hot water the packaging film will shrink snugly around the product contained therein. Preferred free shrink values for films of the present invention range from about 25% to about 40%, and more preferably from about 30% to about 35 % in the transverse direction. Free shrink values in the machine direction range from preferably about 15% to about 25%, and more preferably from about 18% to about 20%. These values are measured at 185°F. at eight seconds. Sixth, the film should normally possess optical clarity, i.e. the film should not become cloudy upon exposure to these time-temperature conditions. An exception is the use of pigments to produce a pigmented film, typically a white opaque material.

Another important feature of a pasteurizable, cook-in packaging material made into a bag or casing is its resistance to grease. Many food products, especially meat products, contain significant amounts of grease which can attack the packaging material particularly under high temperatures and humidities associated with pasteurizing and cook-in processes. 4/890802.3A/TXTGM 3 234427 The present invention is characterized by exceptionally good cold temperature and high temperature strength and grease resistance.

In general, such a multilayer film structure will have the minimal structure (sealing and food contact layer)/(second layer)/(barrier layer)/(abuse layer), a composite structure being preferred to achieve the desired composite properties of the packaging film.

A heat shrinkable, thermoplastic, barrier packaging film for making bags which has enjoyed considerable commercial success is described in U.S. Patent 3,741,253 issued on June 26, 1973 to Brax et al, which relates to a multilayer film comprising a first outside layer of an irradiated ethylene-vinyl acetate copolymer, a core layer of vinylidene chloride copolymer, and a second outside layer of an ethylene-vinyl acetate copolymer. In manufacturing this type of heat shrinkable film, a tubular orientation process is utilized wherein a primary tube of the film is biaxially oriented by stretching with internal pressure in the transverse direction and with the use of pinch rolls at different speeds in the machine direction. Then the bubble is collapsed, and the film is wound up as flattened, seamless, tubular film to be used later to make bags, e.g. either end-seal bags typically made by transversely heat sealing across the width of flattened tubing followed by severing the tubing so that the transverse seal forms the bottom of a bag, or side-seal bags in which the transverse seals form the bag sides and one edge of the tubing forms the bag bottom.

This type of bag is typically used by placing the food product in the bag, evacuating the bag, gathering and applying a metal clip around the gathered mouth of the bag to form a hermetic seal, and then immersing the bag in a hot water bath at approximately the same temperature at which the film was stretch-oriented, typically about 160° to 205°F, hot water immersion being one of the quickest and most economical means of transferring sufficient heat to the film to shrink it uniformly. Alternatively, the bag may serve as a liner of a cooking mold. One problem which has been encountered is the failure of the bag ^"ials at the bottom of the bags as the bag is shrunk around a product, the shrink forces tending to pull the seal apart. 4/890802.3A/TXTGM 4 234427 Of interest is U. S. Patent 4,469,742 (Oberle et al) directed to pasteurizable, cook-in shrink film having six layers, the second or shrink layer comprising a cross-linked ethylene homopolymer or copolymer, and having a sealant layer of polypropylene or ionomer.

Also of interest is U. S. Patent 4,762,748 (Oberle) directed to pasteurizable, cook-in shrink films with good interlaminar adhesion and characterized by the presence of ethylene alkyl acrylate copolymer in the shrink and abuse layers, in the adhesive layers, or both.

Also of interest is European Patent Application 269325 (Oberle) disclosing a multilayer cook-in film having the construction A/B/C/D/C/E in which layer A may include a blend of polyamide and ionomer or polyamide and polyethylene; B is a second or shrink layer having for example linear low density polyethylene, low density polyethylene, ethylene vinyl acetate copolymer, very low density polyethylene, ethylene butyl acrylate copolymer and mixtures thereof; a third or adhesive layer of a modified ethylene homopolymer or copolymer; a fourth or barrier layer of for example hydrolyzed ethylene vinyl acetate copolymer; a fifth or adhesive layer like that of the third layer; and a sixth or abuse layer having linear low density polyethylene, ethylene vinyl acetate copolymer, low density polyethylene, very low density polyethylene, ethylene butyl acrylate copolymer or mixtures thereof. Related to the '325 EPO patent application is corresponding U.S. Patent Application Serial No. 932,138 filed November 17, 1986.

Of general interest concerning the present invention, is the disclosure of U.S. Patent 4,352,702 for "Method of Making a Thermoplastic Receptacle Having Improved High Temperature Seal" issued October 5, 1982 to Bornstein, being directed to a pasteurizable shrink bag from tubular film having a layer of hydrolyzed ethylene-vinyl acetate copolymer and an interior surface layer of a polyolefin which is cross-linkable by ionizing radiation, with the layers being directly melt-joined without an adhesive disposed therebetween and the film being irradiatively cross-linked and oriented. A second irradiation treatment is carried out on receptacles made from the film to condition their heat seals for pasteurizing conditions. 4/890802.3A/TXTGM 234427 Also of interest is U. S. Patent No. 4,424,243 issued to Nishimoto et al and disclosing a multilayer film having outer surface layers of linear low density polyethylene or a blend of this linear polyethylene with alpha-olefin polymers such as ethylene alkyl acrylate copolymers. Thermoplastic resins used as adhesive layers include ethylene alkyl acrylates having 1 to 6 carbon atoms in the alkyl group.

Of general interest is the disclosure of U.S. Patent 4,064,296 for "Heat Shrinkable Multilayer Film of Hydrolyzed Ethylene-Vinyl Acetate and a Cross-linked Olefin Polymer" issued December 20, 1977 to Bornstein et al, being directed to a coextruded tubular film having a layer of hydrolyzed ethylene-vinyl acetate copolymer between two other polymeric layers at least one of which is irradiatively cross-linkable, the film being irradiated and oriented.

Of general interest is the disclosure of U.S. Patent 3,595,740 for "Hydrolyzed Ethylene-Vinyl Acetate Copolymer as Oxygen Barrier Layer" issued July 27, 1971 to Gerow, being directed to oxygen barrier films having an interior barrier layer of a melt extrudable hydrolyzed ethylene-vinyl acetate copolymer and a heat sealing layer of an ethylene polymer or copolymer.

Of general interest is the disclosure of U.S. Patent 4,233,367 for "Coextruded Multilayer Film" issued November 11, 1980 to Ticknor et al, being directed to a coextruded multilayer film having adhesive interlayers of a chemically modified polyolefin, such as Plexar™ adhesive, with functional groups selected for their strong affinity for nylon under heat and pressure conditions of coextrusion.

Of general interest is the disclosure of U.S. Patent 4,276,330 for "Trilaminate Film For Forming Sideweld Bags" issued June 30, 1981 to Stanley et al, being directed to sideweld bags made from trilaminate film having a core layer of propylene-ethylene block copolymer between surface layers of propylene-ethylene random copolymer. 4/890802.3A/TXTGM 6 & h f ■' ■ 23*427' SUMMARY OF THE INVENTION 3 0 S E |° 1/93 ' ■s * . ' * In accordance with the present invention, a multilayer shrink film comprises a first or sealing layer comprising a polymeric material selected from the group consisting of a propylene ethylene copolymer,an ionomer, an ethylene acrylic acid copolymer, a blend of a linear low density polyethylene and an ionomer, and a blend of a linear low density polyethylene and an ethylene acrylic acid copolymer; a second shrink layer, melt bonded to said first layer; a third adhesive layer, melt bonded to said second layer; a fourth or barrier layer, melt bonded to said third layer, comprising an ethylene vinyl alcohol copolymer; a fifth adhesive layer, melt bonded to said fourth layer; and a sixth or abuse layer, melt bonded to said fifth layer; wherein very low density polyethylene and ethylene alkyl acrylate copolymer are each present in either the shrink or abuse layers, or both the shrink and abuse layers.

Additionally, there is provided a method for making a multilayer shrink film comprising fully coextruding a tubular multilayer film having the foregoing composite structure; cooling tha film; raising the temperature of the film to its orientation temperature range; and orienting the film.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the invention is a composite tubular film having the multilayer structure (inside) A/B/C/D/C/E (outside) where A is primarily a heat sealing layer, B is primarily a shrink layer, C is primarily an adhesive layer, D is primarily a barrier layer, and E is primarily an abuse layer. A tubular film configuration is especially suited for bag making.

The sealing layer is preferably a propylene-ethylene random copolymer (EPC) having a minor amount of ethylene, preferably about 1-6%. As an alternative, the sealing material is for example an ionomer, representatively Surlyn™ from the Du Pont Ccmpany, or a blend of an 4/890802.3A/TXTGM 7 234427 ionomer with a linear low density polyethylene (LLDPE). Also suitable for layer A is an ethylene acrylic acid copolymer or a blend of this material with LLDPE.

The second layer is melt bonded to the first layer and is preferably composed of a blend of a very low density polyethylene or linear low density polyethylene with an ethylene alkyl acrylate copolymer (EAA), ethylene vinyl acetate copolymer (EVA), or low density polyethylene (LDPE). The second layer contributes significantly to the overall shrink properties as well as grease resistance of the cook-in film. Very low density polyethylene and ethylene alkyl acrylate copolymer are the preferred blending materials.

More preferably, the ethylene alkyl acrylate copolymer component of the blend layer is an ethylene n-butyl acrylate copolymer (EnBA) such as Quantum/USI NPE 4771. This material has an n-butyl acrylate content of about 6% by weight.

Another commercial material preferred for the present invention is the EnBA available from Quantum/USI and designated as NPE 4774, having an n-butyl acrylate content of about 18% by weight.

Barrier layer D comprises an ethylene vinyl alcohol copolymer (EVOH). A preferred commercial resin is Eval™ SC105A. This resin has an ethylene content of 44 mole percent. The oxygen barrier property of EVOH resins does not degrade during irradiative cross-linking of the tubular film.

Adhesive interlayers C are melt bonded adjacent the barrier layer to provide delamination resistance of the barrier layer in the tubular film under pasteurizing or cook-in conditions.

Both ethylene vinyl acetate copolymer-based chemically modified adhesives and ethylene alkyl acrylate copolymer-based adhesives, such as ethylene methyl acrylate copolymer (EMA) and ethylene ethyl acrylate copolymer (EEA) and particularly ethylene butyl acrylate copolymer (EBA), are suitable as the adhesive for layer C. Also suitable for layers C are LLDPE- and VLDPE- based adhesives. 4/890802.3A/TXTGM 8 23 44 2 7 Abuse layer E preferably is a blend of a very low density polyethylene (VLDPE) or linear low density polyethylene (LLDPE) and ethylene alkyl acrylate or ethylene vinyl acetate copolymer, more preferably an ethylene n-butyl acrylate copolymer.

Abuse layer E and second layer B thus both preferably comprise a blend of a very low density or linear low density polyethylene and an ethylene alkyl acrylate copolymer, low density polyethylene or ethylene vinyl acetate copolymer. In each layer, the preferable alkyl acrylate comonomer is n-butyl acrylate. More preferably, each of the blend components comprises between about 20% and about 80% by weight of the blend layer. Although the specific range of each blend component i.e. the specific amount by weight of the linear polyethylene and the ethylene homopolymer or copolymer in each of blend layers B and E may be the same, it is not necessary that the blend layers be identical. For example, shrink layer B may comprise 20% by weight linear low density polyethylene and 80% by weight ethylene copolymer, while, in the same structure, the abuse layer E comprises about 60% by weight very low density polyethylene and 40% by weight ethylene copolymer.

All layers within the film are melt bonded to their respective adjacent layers by virtue of full coextrusion after which the entire multi-layer film can be subjected to ionizing radiation treatment. Preferably, the film will have an overall thickness prior to orientation of about 10-30 mils, seal layer A will have a thickness of about 2-6 mils, shrink layer B about 4-8 mils, adhesive layers C about 0.25-1.5 mil each, barrier layer D about 0.75-2 mils, and abuse layer E about 3-8 mils.

The tubular film of the invention can be made by a process similar to that described for the Brax patent, cited above, further provided that the tubular film can be fully coextruded, i.e. all layers are simultaneously coextruded, using the conventional blown bubble technique.

After cooling, the coextruded tube is flattened and then may optionally be guided through an ionizing radiation field, for example through the beam of an electron accelerator to receive a radiation dosage in the range of about 3-12 megarads (MR). Irradiation by electrons to 4/890802.3A/TXTGM 9 234427 cross-link the molecules of polymeric material is conventional in the art. Radiation dosages are referred to herein in terms of the radiation unit "rad", with one million rads or a megarad being designated as "MR". The degree of molecular cross-linking is expressed in terms of the radiation dosage that induces the cross-linking. In general, irradiation should be sufficient to cross-link the irradiatively cross-linkable layers of the film to increase strength of the shrink layer without substantially diminishing elongation properties, and to provide delamination resistance of the film during pasteurizing or cook-in conditions. Cross-linking of the film by irradiation or other means such as chemical cross-linking is optional depending on the end uses of the multilayer film, but is necessary for film exposed to pasteurizing or cook-in conditions.

The tubular film is then cooled and collapsed after which it is fed into a hot water tank having water at about 190°-205°F to soften the film for orientation; then it passes through pinch rolls and is inflated into a bubble and stretched to a point where the film thickness is representatively 2 to 3 mils. Suitable thicknesses will range from about 1-4 mils with a preferred transverse direction orientation ratio of between about 2.5:1 and 3.5:1. Preferred machine direction orientation ratios are also between about 2.5:1 and 3.5:1. After the orientation step, the bubble cools rapidly in the air and then is collapsed and rolled up into flattened tubing. It is from this tubing of this final oriented thickness that bags can be made as discussed above.

Since the barrier property of the layer of EVOH is not degraded appreciably during radiation treatment of the entire multilayer film, the film may be fully coextruded. Full coextrusion is advantageous in that all layers of the multilayer film are directly melt joined for enhanced inter layer strength under pasteurizing or cook-in conditions. Inter layer strength is further enhanced by the use of chemically modified adhesives in the third and fifth adhesive layers of the film.

In use, bags can be made from the film of the invention in conventional manner, as discussed above,- to form either end-seal, contour seal or side-seal bags. Eventually, the bags can be loaded with a food product, vacuumized and sealed, and subjected to pasteurizing or cook-in treatment in near boiling water. During this food treatment, bags 4/890802.3A/TXTGM 234427 maintain good seal integrity, do not delaminate, and heat shrink to form a neatly packaged pretreated food product. Bags or casings made from the inventive film can also be closed by conventional clipping means.

In one preferred embodiment of the invention, the sealing layer is composed of a propylene-ethylene random copolymer (PER) also referred to as ethylene propylene copolymer (EPC).

In another mode, the material of the sealing layer is an ionomer. Such a material is available from Du Pont under the trademark Surlyn which refers to metal salt neutralized copolymers of ethylene and methacrylic acid. In certain applications, it is advantageous that a cook-in package adhere to the contained food product to prevent cook-out, i.e. exudation of fluids from the food product during cooking. By restricting exudation of fluids from a cook-in contained food product, the yield of the precooked food product is increased by fluid retention. The inclusion of Surlyn in the multilayer film may limit service use to cook-in conditions.

In still another mode, the material of the sealing layer is a blend of a linear low density polyethylene with either an ionomer such as Surlyn™, or an ethylene acrylic acid or methacrylic acid copolymer such as Primacor™ available from Dow Chemical Company or Nuctel™ available from Du Pont Company. Layer A may comprise an ethylene acrylic acid copolymer.

The barrier layer is composed of hydrolyzed ethylene-vinyl acetate copolymer, preferably hydrolyzed to at least about 50%, most preferably to greater than about 99%. The mole percent of vinyl acetate prior to hydrolysis should be at least about 29% since for lesser amounts the effectiveness of the hydrolyzed copolymer as a gas barrier is substantially diminished. It is further preferred that the EVOH copolymer have a melt flow being generally compatible with that of the other components of the multilayer film, preferably in the range of 3-20, more preferably in the range of about 3-10 (melt flow being determined generally in accordance with ASTM D1238). The gas of main concern is oxygen and transmission is considered to be sufficiently low, i.e, the material is relatively gas impermeable, when the transmission rate is below 100cc/m2/mil thickness/24 hrs./atms, as measured at 0% relative 4/890802.3A/TXTGM 11 234427 humidity according to the procedures of ASTM Method D-3985. The multilayer film of the present invention has a transmission rate below this value. EVOH is advantageously utilized in the film of the invention since irradiative treatment of the fully coextruded film does not appreciably degrade the barrier property, as would be the case for a vinylidene chloride - vinyl chloride copolymer (saran) barrier.

The present invention may be characterized, by the fact that very low density polyethylene is present in either the second (B) layer or the sixth (E) layer, and likewise ethylene alkyl acrylate copolymer is present in either of these layers. In addition, the VLDPE and ERA. may be present in both the B and E layers.

The present invention may be further understood by reference to specific actual examples described below.

EXAMPLE NO. 1 A six layer structure was coextruded in a tubular form. The first sealing layer was an ionomer (Surlyn A1650). The second layer comprised 60% VLDPE (Attane 4003) and 40% LDPE (NA 345-225) (Quantum/USI). The third and fifth layers were tie layers comprising chemically modified ethylene vinyl acetate copolymer adhesive (Bynel 3062)(du Pont). The fourth layer comprised an ethylene vinyl alcohol copolymer (Eval SC-105A) as oxygen barrier material. The sixth layer comprised 80% EnBA (NPE 4771) and 20% LLDPE(Dowlex 2045.03). Immediately after coextrusion, the tubular film was quenched with cold water. The tube was irradiated with ionizing radiation at a dosage of 4 MR to cross-link some or all of the six layers. The tube was then oriented using a hot water heating system to an orientation ratio of 3.1 to 1 in each of the transverse and. longitudinal directions. 4/890802.3A/TXTGM 12

Claims (8)

1. 234427 EXAMPLE NO. 2 A film similar to that of example 1 was produced, by similar methods, except that an ethylene n-butyl acrylate copolymer (NPE 4771) formed 80% by weight of the second layer, and this material was blended with 20% LLDPE (Dowlex 2045.03). The sixth layer comprised 60% VLDPE (Attane 4003) blended with 40% EnBA (NPE 4771). EXAMPLE NO. 3 A film similar to that of examples 1 and 2 was produced by similar methodology, and having ethylene propylene copolymer (Eltex P KS 409) (Solvay) as the sealant layer, and a blend of 50% VLDPE (Attane 4003) and 50% EnBA (NPE 4774) in the second layer. Layer E, the abuse layer, comprised 60% EnBA (NPE 4771) and 40% VLDPE (Attane 4003). The tube was irradiated with ionizing radiation at a dosage of about 7.5 MR. EXAMPLE NO. 4 A film similar to that of Examples 1 and 2, made by a similar method, had a sealant layer of ionomer, a second layer having a blend of 48% VLDPE, 17% EnBA, and 35% of a color additive. The sixth layer comprised 80% VLDPE (Attane 4002 having a density of about 0.912 grams/cubic centimeter) and 20% EnBA (NPE 4771). The color additive of the second layer was a blend of 50% low density polyethylene and 50% titanium dioxide pigment. Although the present invention has been described in conjunction with preferred embodiments, it to be understood that modifications and variations may be utilized without departing from the principles and scope of the invention , as those skilled in the art will readily understand. Accordingly, such modifications and variations may be practiced within the scope of the following claims: 4/890802.3A/TXTGM 13 ^ what/we claim is WIIMMO CLAMED IC: 1. A multilayer shrink film comprising: a) a first or sealing layer comprising a polymeric material selected from the group consisting of a propylene ethylene copolymer, an ionomer, an ethylene acrylic acid copolymer, a blend of a linear low density polyethylene and an ionomer, and a blend of linear low density polyethylene and an ethylene acrylic acid copolymer; b) a second shrink layer, melt bonded to said first layer; c) a third adhesive layer, melt bonded to said second layer; d) a fourth barrier layer, melt bonded to said third layer, which comprises an ethylene vinyl alcohol copolymer; e) a fifth adhesive layer , melt bonded to said fourth layer; and f) a sixth abuse layer, melt bonded to said fifth layer; wherein very low density polyethylene is present in either the shrink or abuse layers, or in both the shrink and abuse layers; and wherein ethylene alkyl acrylate copolymer is present in either the shrink or abuse layers, or in both the shrink and abuse layers.
2. 2. The film of claim 1 wherein the second and sixth layers comprise a polymeric material or blend of materials selected from the group consisting of very low density polyethylene, linear low density 234 A 27 >r 30 SEP 1993 1 A 4/890802.3A/TXTGM 14 234427. polyethylene, ionomer, ethylene alkyl acrylate copolymer, ethylene vinyl acetate copolymer, and blends thereof.
3. 3. The film of claim 2 wherein said ethylene alkyl acrylate copolymer comprises ethylene butyl acrylate copolymer.
4. 4. The film of claim 3 wherein said ethylene alkyl acrylate copolymer comprises ethylene n-butyl acrylate copolymer.
5. 5. The film of claim 1 wherein the film is cross-linked by irradiation at a dosage sufficient to render the film delamination resistant under cook-in conditions.
6. 6. The film of claim 1 where the film is cross-linked by irradiation at a dosage of between substantially 3 and substantially 12 megarads. 9. The film of claim 8 wherein, said film is oriented to a stretch ratio of between substantially 2.5 to 1 to substantially 3.5 to 1 in the transverse and machine directions. cross-linked. 11. The film of claim 1 wherein said first layer comprises a propylene-ethylene random copolymer having an ethylene content of substantially 1-6% by weight.
7. 7. The film of claim 1 wherein said second and sixth layers comprise between substantially 1% and 99% by weight of a very low density polyethylene, and between substantially 99% and 10% by weight of an ethylene alkyl acrylate copolymer.
8. 8. The film of claim 1 wherein said film is oriented. 10. The film of claim v 1 wherein the film is chemically 12. A bag made from the film of claim 1. ^30SEPI993 / 13. A casing made from the film of claim 1. 4/890802.3A/TXTGM 15 14. A film as claimed in any one of claims 1 to 11 substantially as hereinbefore described with reference to any example thereof. 15. A film as claimed in any one of claims 1 to 11 and 14 when made by a method substantially as hereinbefore described with or without reference , <-^-J 6rcca> Co.—Gbv-sr-v to any example thereof. By Mw/Her/Their Authorised Agents, A. J. PARK & SON Per ....<3$.' 16