CA2038757C - Protein adhesion film for packaging - Google Patents

Abstract

In general, the instant invention relates to protein adhesion cook-in films (1) having a protein adhesion sealing layer of polymer having carboxylic acid moieties and (2) wherein said sealing layer does not require metal ionomer cross-linking in order to exhibit protein adhesion. More particularly, it relates to a thermoplastic film comprising a thermosealing layer selected from ethylene-methacrylic acid copolymers ( EMAA ) having a methacrylic acid content of about 4 to about 18% by weight, and ethylene-acrylic acid copolymers ( EAA ) having an acrylic acid content of about 4 to about 22% by weight. The sealing layer has improved sealing and strength properties, as well as protein adhesion characteristics.

Description

PROTEIN ADHESION FILM FOR PACKAGING
Field of the Invention In general, the instant invent~_an relates to protein adhesion cook-in films (1) having a sealing layer of polymer having carboxylic acid moieties and (2) wherein the sealing layer does not require metal ionomer cro:5s-linking of the poly-mer having carboxylic acid moieties in order to exhibit protein adhesion. More particularly, it relates to a film comprising a thermosealing layer selected from ethylene-methacrylic acid copolymers ( EMAA ) having a methacrylic acid content of about 4 to about 18% by weight, and ethylene-acrylic acid copolymers ( EAA ) having a.n acrylic acid content of about 4 to about 22 %
by weight. Surprisingly it has been found that after cook-in of a food product, the film has protein adhesion characteristics.
The protein adhesion characteristic of t:he thermosealing layer of the instant films cause them to stick, i.e. bindingly adhere, to a food product cooked in a package of t:he film.
Background of the Invention This invention relates to the field of flexible plastic films for packaging, and more specifically to such films which are thermosealing, whether heat-shrinkable or not, as well as to container structures made from such filma and to packages, par-ticularly for food items, using such filnns and containers. The 5/900523.5A/TXTJLS

use of plastic films for packaging items in general, and foods in particular, is widespread nowadays. Depending on the perfor-mance to be achieved, they films typically comprise various plas-tic layers which, accarding to their chemical composition and the consequent properties, do perform the required function.
As thermosealing layers various polymeric materials have been used heretofore, among which the most widely used have been, for example, ethylene-vinyl acetate ( EVA ) copolymers, various ethylene polymers such as very low density linear poly-ethylene ( VLDPE ), or ionomeric copolymers such as those avail-able under the trademark Surlyn (R) from E.I. duPont de Nemours Inc., Co. (USA). There latter ionomeric polymers generally consist of copolymers of ethylene and methacrylic acid or copolymers of ethylene and acrylic acid which copolymers are sonically cross-linked s;o as to convert them into metal salts, just designated as ionomers.
Notwithstanding the fact that such polymers used hereto-fore as thermosealing layers gave sufficiently satisfactory performance, they still had disadvantages which limited their use in certain applications. In particular, none of these poly-mers showed a sufficiently broad spectrum of properties compris-ing both a good sealability in the presence of contamination and of creases or folds in the sealing area as well as a good seal strength together with a wide sealing range in terms of tempera-ture or time, and also protein adhesion characteristics.
Blends of 80 to 90o ethylene/acrylic acid copolymer ( EAA ) with the remainder being linear low density polyethylene ( LLDPE ) are shown in U.S. Patent 4,678,836 (Dow Chemical).
From U.S. Patent 3,365,520 (duPont), U.S. Patent 4,399,181, (Asahi-Dow), or U.S. Patent 4,414,053 (Gulf) films are known that comprise blends of ethylene-methacrylic acid ( EMAA ) with Surlyn, with ethylene methyl acrylate ( EMA ) or with other polymers, f or use in forming oriented multilayer films, the disclosures of all of which are incorporated herein by reference. None of these prior patents discloses, however, an improved thermosealing layer as that which forms the subject matter of this invention..
Cook-in films are disclosed in U.S. Patent 4,469,742 (W. R. Grace; sealing layer is Surlyn), U.S. Patent 4,606,922 (W. R. Grace; sealing layer is Surlyn), and U.S. Patent 4,855,183 (W. R. Grace; sealing layer is nylon, optionally blended with Nucrel or Primacor). A perforated, heat-shrinkable bag contain-ing a meat product to be cooked therein is shown in U. S . Patent 4,879,124 (Oberle, assignor to W.R. Grace). Cook-in films with a VLDPE abuse layer are shown in U.S.S.N. 392,810, filed August 11, 1989 (Friedrich and Oberle, assignors to W.R. Grace).
U . S . Patent 4 , 8 5.'i ,183 requires the sealing layer to have nylon for the protein adhesion characteristic, and does not recognize that the Nucrel ( EMAA ) or the Primacor ( EAA ) will, without the nylon, give protein adhesion characteristics.
Objects and Features of the Invention The main object of this invention is to provide a thermosealing protein adhesion film having an optimum combina-tion of properties such as to render it suitable for use in f films , preferably multilayer f films , f or the packaging of various articles in various packaging and handling conditions» More particularly, the object: of this invention is to provide a thermosealing protein adhesion layer and a film incorporating it, wherein the thermosealing layer has a good sealability in the presence of contamination or folds in the sealing area, an improved cold and hot seal strength, and a wide sealing range in terms of temperatures and times.
A further object of the invention is to provide packag-ing structures, like baga, et cetera from the films of the inven-tion, which are suitable both for cold packaging and for cook-in with protein adhesion of the packaged food items.
These and other objects which will appear more clearly from the following disclosure are achieved by a flexible, thermoplastic film for cook-in packaging according to this inven-tion having a thermosealing layer comprising a copolymer of (i) an alpha-olefin having the formula RCH=CH2 wherein R is H or C1 to G2o alkyl, G1 to CZO alkoxy, or C6 aryl, and (ii) an alpha, beta-ethylenically unsaturated carboxylic acid.
Preferably, the thermosealing layer comprises a copolymer select-ed from ethylene-methacrylic acid ( EMAA ) copolymers, ethylene-acrylic acid ( EAA ) copolymers, or mixtures thereof. More preferably, the thermosealing layer comprises a copolymer select-ed from ethylene-methacrylic acid ( EMAA ) copolymers with a methacrylic acid ( MAA ) content of about 4 to about 18% by weight, ethylene-acrylic acid ( EAA ) copolymers with an acrylic acid ( AA ) content of about 4 to about 22 % by weight, or mix-tures thereof .
This invention is based on the discovery that a polymer containing carboxylic acid moieties, such as an EMAA or EAA
copolymer as defined above, gives rise to a film for use as thermosealing layer, particularly in multilayer films, which has an excellent combination of properties, surprisingly including protein adhesion from cook-in of a food product. The sealing layer does not require the presence of the related metal salt cross-linked ionomeric materials, many of which are sold as Surlyn by du Pont, in order to give rise to the protein adhesion characteristic.
Most preferably, the thermosealing layer according to this invention comprises said EMAA copolymer with a MAA content of about 4 to about 15% by weight, e.g. of about 12 % by weight, or said EAA copolymer with an AA content of about 6 to about 120 by weight, or a blend of such copolymers in any proportion.
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23~~~'~
According to further embodiment; of the invention the thermosealing layer comprises a blend of about 10 to about 99%
by weight of the polymer containing carboxylic acid moieties, such as the EMAA or EAA copolymer as defined above, with about 90 to about to by weight of a po:Lyolefinic polymer or copolymer. Preferably, the thermosealing layer comprises a blend of about 30 to about 70~ by weight ~~f the polymer contain-ing carboxylic acid moieties, such as them EMAA or EAA copolymer as defined above, with about 70 to about 30o by weight of a polyolefinic polymer or copolymer. Polyolefin includes but is not limited to, linear low density polyethylene, linear very low density polyethylene, ethylene alkyl acrylate copolymers (such as ethylene-butyl acrylate, ethylene:-ethyl acrylate, or ethylene-methyl acrylate), ethylene-vinyl. acetate, ethylene-vi-nyl acetate modified with functional groups, and mixtures there-of.
These polymers are abbreviated herein as follows:
ethylene-methacrylic acid EMAA

ethylene-acrylic acid EAA

linear low density polyEahylene LLDPE

linear very low density polyethylene VLDPE

ethylene-butyl acrylate EBA

ethylene-ethyl acrylate EEA

ethylene-methyl acrylate: EMA

ethylene-vinyl acetate EVA

S atement of Invention Therefore, the present invention provides a flexible thermoplastic film suitable for protein-adhesion cook-in packag-ing comprising a thermosealing layer of a copolymer of (i) an alpha-olefin having the formula RCH=CHz wherein R is H or C1 to CZO alkyl; C1 to Czo alkoxy, or C6 aryl, and (ii) an alpha, beta-ethylenically unsaturated carboxylic acid.

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The present invention also provi<ies a cook-in structure for packaging made of the film described :in the above paragraph, which is sealed together at two portions of said thermosealing layer arranged adjacent and facing each other. The present invention also provides a method for making a protein adhesion cook-in package comprising enveloping a food product in the film described in the above paragraph , removing air from inside the thus obtained package, sealing the package by thermasealing together at least twa portions of the thermosealing layer facing each other, and subjecting the sealed pae:kage to cooking at high temperature, whereby the thermosealing lawyer adheres to the food product. The present invention also provides a cooked, protein-adhesion, cook-in package comprising a food product enveloped in the film described in the above paragraph; the film being sealed together by at least one thermoseal at two portions of said thermosealing layer facing each other, the sealed package having been subjected to cooking at high ternperature, whereby the thermosealing layer bindingly adheres to the food product.
These cook-in structures or packages are bags, casings, pouches, and the like. As mentioned, there is a thermoseal. The food product is then put inside the bag; casing, pouch, et cetera, and prior to cook-in, the other end may be simply folded over, or may be sealed such as by another thE~rmoseal or by a clip:
Then the package of food is cooked.
Detailed Description of the Invention The thermosealing layer comprises a polymer containing carboxylic acid moieties. By "polymer's containing carboxylic acid moieties" as that term is used herein it is intended to mean copolymers of (i) an alpha-olefin having the formula RCH=CH2 wherein R is H or Cz to C2o alkyl, C1 to CZo alkoxy, or C6 aryl, and (ii) an alpha,be.ta-ethylenically unsat-urated carboxylic acid. Preferably, when R is alkyl, it is C
to C8 alkyl. Also, preferably, the alpha, beta-ethylenically unsaturated carboxylic acid is present in an amount by mol o of about 500 or less, more preferably about 300 or less, most pref-5/900523.5A/TXTJLS

erably about 200 or less. Further, by t:he term "polymers con-taining carboxylic acid moieties" it ins intended to include carboxylic acid-forming moieties such as anhydrides.
The acid copolymer need not necessarily comprises a two component polymer. Thus, although the olefin content of the acid copolymer preferably is at least 50 mol percent, more than one olefin may be employed. Also, other copolymerizable monoethylenically unsaturated monomers may be employed in combi-nation with the olefin and the carboxylic acid comonomer. It is intended also to include terpolymers. Accordingly, acid copolymers or terpolymers suitable for use in the present inven-tion include, but are not limited to, ethylene/acrylic acid copolymers, ethylene/methacrylic acid copolymers, ethylene/itaconic acid copolymers, ethylene/methyl hydrogen maleate copolymers, ethylene/maleic acid copolymers, styrene/maleic acid copolymers, styrene/maleic half ester copolymers, alkyl vinyl ether/maleic acid copolymers, alkyl vinyl ether/maleic half ester copolymers, ethylene/methyl hydro-gen maleate/ethyl acrylate terpolymers, ethylene/methacrylic acid/vinyl acetate terpolymers, ethyl~ene/acrylic acid/vinyl acetate terpolymers, ethylene/acrylic acid/vinyl alcohol terpolymers, ethylene/propylene/acrylic acid terpolymers, ethylene/styrene/acrylic acid terpolyr~ters, ethylene/acrylic acid/methyl methacrylate terpolymers, eth.ylene/methacrylic acid/
ethyl acrylate terpolymers, ethylene/itaconic acid/methyl methac-rylatb terpolymers, ethylene/methaery7_ic acid/acrylonitrile terpolymers, ethylene/fumaric acid/vinyl methyl ether terpolymers, ethylene/vinyl chloride/acrylic acid terpolymers, ethylene/vinylidene chloride/acrylic acid terpolymers, ethylene/vinyl fluoride/methacrylic acid terpolymers, and ethylene/chlorotrifluoethylene/methacrylic: acid terpolymers.
The copolymer of an alpha-olefin having the formula RCH=CHZ Wherein R is H or C, to CZO alkyl, C1 to C2o alkoxy, or C6 aryl, and an alpha, beta-ethylenically unsaturat-ed carboxylic acid representatively may b~e produced by the copo-lymerization of ethylene and a carboxylic acid comonamer there-5/300523.5A/TXTJLS

for such as acrylic acid or methacrylic acid. Preferably, when R is alkyl, it is C~ to C8. SuitablE: such acid copolymers are the Primacor (TM) polymers, supplied by Dow Chemical Compa-ny, Midland, Michigan. Primacor is produC:ed by the copolymeriza-tion of ethylene and acrylic acid ( EAA ). A very suitable Primacor polymer i_s Primacor 1410 or Primacor 5981. ~ther suit-able such acid copolymers are sold under the trade name Nucrel by duPont; they are produced by the copolymerization of ethylene and methacrylic acid ( EMAA ). A very ;sui.table N.ucrel polymer is Nucrel 1202.
The instant thermosealing layer does not require the presence of ionomer in order to exhibit protein adhesion charac-teristics. Thus, the "polymers containing carboxylic acid moieties" are to be distinguished from ionomers, namely from the copolymer of an alpha-olefin having the formula RHC=CH2 where-in R is H or C~ to CZO alkyl, C1 to Coo alkoxy, or aryl, and an alpha, beta-ethylenically unsaturated carboxylic acid which are partially neutralized with a suitable metal cat-ion such as zinc cation or sodium cati.on. These metal salt neutralized copolymers containing carboxylic acid moieties are called ionomers. Ionamers are commercially available as Surlyn(R) from the E.I, duPont de Nemours Company of Wilmington, Delaware, and are described in detail in U.S. Patents 3,355,319 and 3,845,163. Protein adhesion cook-in films having an ionomer sealing layer (i.e. a Surlyn sealing layer) are described in the above-mentioned U.S. 4,469,742 and U.S. 4,.606,922.
Typically, in the manufacture of films, a suitable polymer usually in the form of pellets or the like, is brought into a heated area where the polymer feed is melted and heated to its extrusion temperature and extruded as a tubular hot "blown bubble" through an annular die. Qther methods, such as "slot die" extrusion wherein the resultant extrudate is in planar, as opposed to tubular form are also well known. If heat shrinkable film is desired, then after extrusion, the film is typically cooled and then reheated and stretched, i.e. oriented by '"tenter framing" or by inflating with a "trapped bubble" , to 5/900523.5A/TXTJLS

impart the heat-shrinkable property to the film. For multi-layer films, such as those made by coextrusion of multiple indi-vidual resins or blends, a suitable adhesive polymer layer may be employed to promote interlayer adhesion.
The above general outline for manufacturing of films is not meant to be all inclusive since such processes are well known to those in the art. For example, see U.S. Patent Nos.
4,274,900; 4,229,241; 4,294,039; 4,188,443; 4,048,428;
3,555,604; 3,741,253; 3,821,182; , 3,022,543. The disclosures of these patents are generally represen~.ative of such processes and are hereby incorporated by reference.
The thermosealing layer of the invention is preferably used in multilayer films comprising at least a second structural layer conferring upon the film mechanical or abuse resistance.
Preferably the film of the invention comprises at least the multi-layer structure as follows:
Sealing/Structural/Structural or Sealing/Barrier/Structural The gas barrier layer can be made of materials conven-tionally used for such purpose, for example of copolymers of vinylidene chloride with vinyl chloride or with methyl acrylate or with both, ethylene-vinyl alcohol (EVOH) copolymers, for example having an ethylene content of 30 to 47%, polyamides or copolyamides or blends thereof with EVOH.
The structural layer which, beyond conferring abuse resistance, also increases the heat-shrink percentage when heat-shrinkable films are prepared, can be selected from polymers including, but not limited to, very low density polyethylene ( VLDPE ) , high density ( HDPE ) , linear low density ( LLDPE ) , ethylene copolymers with vinyl or acrylic comonomers such as ethylene-vinyl acetate ( EVA ), ethylene-butyl acrylate (EBA), ethylene-methyl acrylate ( EMA ), ethylene-ethyl acrylate r ( EEA ), ethylene-methacrylic acid ( EPZAA ), ethylene-acrylic acid ( EAA ), ionomers, ethylene-propylene random copolymers ( EPC ), polyethylene ( PE ), polypropylene ( PP ) optionally modified with functional groups, polyamides such as Nylon 6, Nylon 6-66, Nylon 6-12, or Nylon 6-69; polyesters, copolyesters, and mixtures thereof. These may also be blended with the thermosealing layer.
Among the ethylene copolymers a preferred copolymer is EVA having a VA content of from 2 to 20'~ by weight, preferably of from 5 to 12o by weight.
Among the possible blends of the above polymers for producing the structural layer, blends c>f LLDPE and EVA or of VLDPE and EVA in a weight ratio of 70:30 to 20:80 can be men-tioned.
The preferred multilayer film of the invention can comprise, in addition to the above-mentioned layers, further layers, such as adhesive layers, which. improve the adhesion between the various functional layers. A. structure of this type may comprise the fallowing layers:
Sealing/Adhesive/Barrier/Adhes.i.ve/Structural As adhesive layers, those commonly known far such use can be employed, e.g. EVA copolymers or EVA copolymers modified with acid functional groups. The EVA copolymers useful as adhesives have a high VA content.
Preferably at least the thermosealing layer of a film according to the invention is electron beam cross-linked by irradiation at about 1 to about l5 MR (nnegarads). It has been found that such treatment notably increases the overall resis-tance of the obtainable seal, whether cold or hot.
However, it is not necessary to electron-beam irradiate the films of the invention; suitable films may be obtained 5/900523.5A/TXTJLS

often absent any electron beam irradiation. From cook-in, the thermosealing layer, even though it has not been electron beam irradiated, often adheres to the food product. See Examples 5 and 6 below.
According to a specific embodirne:nt of this invention, a whole multilayer film can be irradiated to achieve cross-link-ing. In this case, the film can be prepared by simultaneous extrusion of all the layers; for example in tubular form, and their subsequent electron beam irradiation treatment. The irra-diation may take place on the collapsed tube, or on a slit open lay-f lot structure.
According to an alternative embodiment, a multilayer film of the invention is produced by first extruding a substrate comprising the EMAA or EAA thermosealing layer and possible further layers, in particular structural layers, then cross-link-ing the substrate by electron beam irradiation, and finally extruding onto the irradiatively cross-linked substrate the further layers of the final film.
According to a still further embodiment of the inven-tion, a multilayer film can be prepared by laminating various self-supporting preformed films according to the desired struc-ture, by using intermediate adhesive layers. The above-men-tioned adhesive materials can be used fcrr this purpose. Also, in this embodiment part of the laminate, or alternatively the whole laminate may be subjected to electron beam irradiation treatment.
Since far packaging food products it is advantageous to have heat-shrinkable films, the film of: the invention may be made heat-shrinkable by orientation through at least a mono-axi-al stretching in the longitudinal or transverse direction with respect to the direction of extrusion, but preferably through biaxial stretching, using techniques well-known in the field.
For example, in the case when the film is prepared by coextrusion in tubular form, the bi-ax:ial stretching can be 5/900523.5A/TXTJLS

t performed by the "air bubble" blowing method, on-line or off-line of the extrusion process. The film of this invention, either irradiated or not, has a thickness that depends on the number of layers, for example, typically from about 15 to about 250 microns, preferably from about 40 to about 150 microns.
As used herein the term "extrusia~n" ar the term "extrud-ing" is intended to include coextrusion, extrusion coating, or combinations thereof, whether by tubular methods, planar meth-ods, or combinations thereof.
An "oriented" or "heat-shrinkable" material is defined herein as a material which, when heated tcnan appropriate temper-ature above room temperature (for example 90°C), will have a free shrink of about 5% or greater in at least one linear direc-tion.
Melt index was measured in accordance with ASTM D 1238, Condition E.
The term "cook-in package", as used herein, is intended to refer to packaging material structurally capable of withstand-ing exposure to cook-in time-temperature conditions while con-taining a food product. Cook-in time-temperature conditions typically imply a long slow cook, for e:~ample by submersion in water at 70-80°C for 4-6 hours. Submersion at 80°C for 12 hours probably represents the limiting case. Under such conditions, a packaging material properly characterized as cook-in will main-tain heat seal integrity and will be delami:natian resistant.
Typically, cooked "cook-i.n" packaged foods go directly to the consumer in that configuration and may be consumed with or with-out warming.
The term "protein adhesion", as used herein, is intend-ed to refer to packaging material which has a sealing layer, that from cook-in exhibits binding adherence to the food product cooked in the packaging material. Binding adherence is demon-strated by the "Cook-In Protein Adhesion Test" described below.
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Seal Strength Test:
TEST METHODS
The bags were tested at about T3°F (about 23°C) (room temperature).
All bag samples were heat sealed at one end on conven-tional equipment well known in the art of heat sealing of tub-ing, and a mouth end of each bag was left open.
Each bag was then clamped in a fixture provided with a hose. The open mouth end of each bag was clamped around the hose. Air was pumped through each hose whereby each bag was inflated to the same initial pressure. Then, each fixture re-tained each inflated bag in air at 23°C, and two sides of each bag were respectively restrained by two metal plates spaced about 10 cm apart. For each bag, the pressure was increased via the hose at the rate of 1 inch of water pressure (2491 dynes/cm2) per second till the heat seal for that bag either leaked or burst open at the IOWP (inches of water pressure) designated below.
Cook-In Protein Adhesion Test (Binding Adherence to Food):
Bags of the film samples were teated for binding adher-ence to a cooked-in meat product. Eaclh bag was stuffed with turkey emulsion, vacuumized, heat-sealed, and cooked at 55°C for 30 minutes, and then at 60°C for 30 minutes, and then at 65°C
for 30 minutes, for a total of 9a minutes. cooking time, followed by cooling in an ice bath.
The protein adhesion characteristic of the thermosealing layer of the instant films cause them to stick, i.e. bindingly adhere, to the cooked food product, in this in-stance turkey.
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A quantitative comparison of the adherence level of several of the samples in relation to that of control samples (samples wherein the food contact layer contained Surlyn) was determined as follows. After cook-in and cooling, each sample was placed in the jaws of a Scott tester CRE 1000, and the force to pull the bag from the meat was measured at a constant crosshead speed. (Another machine cammonl.y used for such measur-ing is the Instron model 1122 tester.) Puncture "Impact" Test:
This was performed in accordance with a variation of ASTM-D 3763-84. The impact test was a~ measure of cold seal strength. A weighted mandrel was allowed to fall into an open bag, impacting the heat seal. The amount of weight needed to break the seal times the height from which the weight was dropped constituted the amount of energy needed to break the seal. The percentage of seals that broke at a specified energy in inch-pounds was recorded.
12 Hour Delamination Test:
Bags were filled with an oil-water emulsion and then heat sealed closed. Then they were heated for 12 hours. Some were heated at 150°F (65.6 °C), some at 160°F (?1.1 °C), and some at 170°F (76.7 °C) . Some of these were in a high humidity environment at the designated temperature, and some of these were in water at the designated temperature. The °s failures of the films was indicated by delamination of the films.
Materials employed in the Examples:
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GENERIC NAME
FOLLOWED
BY TRADE
NAME OF DESCRIPTIVE INFORMATION SUPPLIER
POLYMER ABOUT THE POLYMER COMPANY
ADHESIVE
Bynel 3062 du Pont EVOH

EPC DENSITY
KS400 0.90 g/cc Solway Zinc Methacrylate Ionomer Type of copolymer Surlyn 1650 Partially zinc neutra7Lized du Pont ethylene methacrylic acid copolymer EVA MI COMONOMER o VA

LD318.92 2.0 Vinyl Acetate 9 Exxon 5/900523:5A/TXTJLS

NA-295-00 2.6 Vinyl Acetate 6 USI
EBA MI COMONOMER %BA, DENSITY
EA719.009 0.35 Butyl acrylate 18.5~°s 0.926 Quantum/USI
LLDPE MI COMONOMER DENSITY
Dowlex 1.1 Octene 0.920 g/cc Dow 2045.03 Chemical By Weight o By Weight EMAA MI Methacrylic Acid Ethylene EMAA-l Nucrel 1202 2 12 88 du Pont Nucrel 0903 3 9 91 du Pant Nucrel 0403 3 4 96 du Pont By Weight ~ By Weight EAA MI Acrylic Acid Ethylene PRIMACOR 1410 1.5 9.5 90.5 Daw 5/900523.5A/TXTJLS

PP MI MP
NPP8000gk 5 161°C Quantum/USI
The following examples show, only for illustrative and not limiting purposes, various struetures~ of films according to this invention.
Example 1 (manufacture of films) The following biaxially stretclh oriented 12:1 films were prepared as described above. PercE~ntages designated were by weight. Samples vary in megarads of irradiation. Thickness of the multi-layer films was about 2.3 to 2.4 mils. In sample numbers 1A, 1B, and 1C, the sealing layer thickness was about 0.54 mils, and in sample number 1D, 1E:, and 1F, the sealing layer thickness was about 0.36 mils. In samp7:e number 9A, the sealing layer thickness was about 0.45 mils; in 9B and 9C, it was about 0.35 mils; and in 9D and 9E, it was .about 0.55 mils.
The composition of each layer is recited below from the sealing layer (on the left) to the abu a layer (on the right). (Samples 3-8 AND 11 were a comparison films.) Table I
SAMPLE NUMBER
(MR IRRADIATION) COMPOSITION OF EACH LAYER
1A (3MR) EMAA-1 /70o LLDPE /30o LLDPE
/30o EVA (9o VA) /70% EVA (9% VA) 1B (5MR) SAME
5/900523.5A/TXTJLS

1C (7MR) SAME
1D (3MR) EMAA-1 /70% LLDPE /30% LLDPE
/30 % EVA ( 9 % VA) /70 % EVA ( 9 % VA) (5MR) 2 EMAA-1 / 70% LLDPE / EPC
( 5MR ) / 3 0 % EVA ( 9 % VP~ ) /
3 80% LLDPE /30% LLDF'E /50% LLDPE

(1MR) 20% Surlyn 1650/70%EVA (9% VA)/50% EVA(6% VA) COMPARISON

4 85% LLDPE /30% LLDPE /50% LLDPE

(1MR) I5% Surlyn 1650/70%EVA (9% VA)/50% EVA(6% VA) COMPARISON

% % %

(1MR) 10% Surlyn 1650/70%EVA (g% VA)/50% EVA(6% VA) COMPARISON

6 83% LLDPE /30% LLDPE /50% LLDPE

(1MR) 17% Surlyn 1650/70%EVA (9% VA)/50% EVA(6% VA) COMPARISON

7 Surlyn LLDPE /50% LLDPE

/30%

(4MR) /70% EVA (9% EVA(6% VA) VA) /50%

COMPARISON

8A EMAA-1 x'50% LLDPE
/30%
LLDPE

( 2MR) /70 % %VA) x'50%EVA ( EVA 6%VA) ( 9 (4MR) 5/900523.5A/TXTJLS

9A EMAA-1 / 80%EVA( 6%VA) / ADH / EVOH: / ADH / 80%EVA( 6%VA) (3MR) / 20%LLDPE / / / / 20%LLDPE

9B EMAA-1 / 80%EVA(C%VA) / ADH / EVCEH / ADH / 80%EVA(6%VA) (3MR) / 20%LLDPE / / / / 20%LLDPE
9C EMAA-1 / 80%EVA(6%VA) / ADH / EVOH / ADH / 80%EVA(6%VA}
(5MR) / 20%LLDPE / / / / 20%LLDPE
9D EMAA-1 / 80%EVA(6%VA) / ADH / EVOH / ADH / $0%EVA(6%VA) (3MR) / 20%LLDPE / / / / 20%LLDPE
9E EMAA-1 / 80%EVA(6%VA) / ADH / EVC>H / ADH / 80%EVA(6%VA}
(5MR) / 20%LLDPE / / / / 20%LLDPE
Surlyn/ 80%EVA(6%VA) / ADH / EVOH / ADH / 80%EVA(6%VA}
(4MR) 1650 / 20%LLDPE / / / / 20%LLDPE
COMPARISON
Example 2 (performance evaluation of filmy of Example 1) In order to evaluate the performance of a multilayer film according to this invention comparative tests were run relating to the puncture impact, seal strength, delamination, and protein adhesion of the inventive films recited in Example 1 (which had an EMAA thermosealing layer) with respect to that of the comparative multilayer films recited in Example 1 (which did not have an EMAA thermasealing layer). T'he results are given in the following tables:
Table II(a) PUNCTURE SEAL STRENGTH
SAMPLE IMPACT RESULTS1 (23°C) NUMBER (% FAILURES) (IOWP) 1A 44.0 183.8 1B 13.0 183.8 5/900523.5A/TXTJLS

lc 2.7 2a6.s 1D 8.0 158.8 1E 10:7 131.3 1F 0.0 183.5 2 29.0 216.4 3 41.0 136.1 COMPARISON

'- Maximum weight and potentia:lenergy used of 305.25 inch pounds.
Table II(b) 12 HOUR DELAMINATIC)N
Cook-In Test Results (o Failures) HIGH HUMIDITY WATER COOK

1A 0.0 0.0 0.0 0.0 30.0 75.0 1B 0.0 0.0 50.0 0.0 27.3 50.0 1C 0.0 0.0 60.0 0:0 0.0 0.0 1D 0.0 12.5 0.0 0.0 0.0 0.0 1E 0.0 0.0 20.0 0.0 0:0 33.3 1F 0.0 0.0 50.0 0.0 0.0 66.7 2 0.0 22.2 57.1 0.0 100.0 100.0 (delam) (delam) (delam) (delam) 3 0.0 0.0 I:00.0 0.0 10.0 0.0 COMPARISON
NOTE: delam is an abbreviation for delamination.
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~o~~~~~
Table II(c) Protein Adhesion SAMPLE NUMBER ADHESION (g/in) NUMBER OF TESTS MEAN

3 COMPARISON 6 141.5 4 COMPARISON 8 92.5 COMPARISON 8 80.6.

6 COMPARISON 8 128.0 7 COMPARISON $ 147.7 8A 6 154 .1.

8B 5 178. 2;

From the above results it can be seen that the film according to the invention had a seal .strength and a protein adhesion which was notably improved, over that of the control films that had a Surlyn (R) thermosealing layer.
The multilayer film of the invention showed superior properties also with respect to other conventional materials used heretofore as thermosealing layers.
Example 3 (manufacture of films) The following additional biaxially stretch oriented 12:1 films were prepared as described in Example 1. Percentages designated were by weight. Samples vary in the sealing layer.
The composition of each layer is recited below from the sealing layer (on the left) to the abuse layer (on the right).
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Table III
SAMPLE NUMBER
(MR IRRADIATION) COMPOSITION OF EACH LAYER
Surlyn/80 oEVA( 6 OVA) / ADH:/EVOH/ADH /80°sEVA( 6 oVA) ( 4MR) 1650 /20 oLLDPE / / / / 20 oLLDPE
COMPARISON
I1 (4MR) 50a EMAA-1 /70°s LLDPE /30$ LLDPE
SOo LLDPE /30o EVA (9~o VA) /70o EVA (9o VA) 12 (4MR) 50o EMAA-1 / 700 LL~DPE /30o LLDPE
50% EVA ( 6 oVA) / 30 o EVP; ( 9 oVA) /70 a EVA ( 9 oVA) 13 (4MR) 50o EMAA-2 / 70o LLDPE /30o LLDPE
50 o EVA ( 9 oVA) / 30% EVA ( 9 oVA) /70 a EVA ( 9 oVA) 14 (4MR) EMAA-2 /70°s LLDPE /30a LLDPE
/30a EVA (9o VA) /70o EVA (9o VA) (4MR) EMAA-3 /70o LLDPE /30a LLDPE
/30 o EVA ( 9 o VA) /70% EVA ( 9°s VA) Example 4 (performance evaluation of film:i of Example 3) In order to evaluate the performance of a multilayer film according to this invention comparative tests were run relating to the protein adhesion of the inventive films recited in Example 3 (which had an EMAA thermosoealing layer) with re-spect to that of the comparative multilayer film recited in Example 3 (which did not have an EMAA, thermosealing layer).
This test differed from the protein adhesion test method de-scribed above in that instead of using turkey emulsion, chunks of turkey which had been cleaned up by removing the extraneous fat and other connective tissue such as partial removal of the sinews were used. (The chunks were cubes about 3 inches on a 5/900523.5A/TXTJLS

,., side, which is about 7.6 cm on a side.) The results are given in the following table:
Table IV
Protein Adhesion SAMPLE ADHESION INDEX*
NUMBER MEAN STANDARD DEVIATION
(4MR) 100.0 + 4.5 COMPARISON
11 (4MR) 98.8 + 8.1 12 (4MR) 84.0 + 21.1 13 (4MR) 88.2 + 19.6 14 (4MR) 95.5 + 11.2 (4MR) 60.4 + 26.7 Adhesion ~n~ex ~ adhesion force of samp7.e on Day n X goo adhesion force of Comparison 10 on Day n where the Comparison sample 10 was ambient.
It is noted that sample number 15 worked, but not as well as the others. This sample had a sealing layer of EMAA-3, which, as can be seen from the description above of materials used in the Examples, is an EMAA with only 4% MAA.
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Example 5 (manufacture of films) The following additional unorieni~ed films were prepared by the tubular hot blown method as deseri:bed above. Percentages designated were by weight. The films were monalayer and thus the entire film was the "thermosealing"' layer. done of the manolayer films was electron beam irradiated. The composition of each is recited below.
Table V
SAMPLE COMPOSITION
1 10% EMAA-1 + 30% LLDPF:

2 20% EMAA-1 + 80% LLDPE

3 3 0 % EMAA-1 + 7 LLDPf's %

4 10 % EMAA-1 + 90 EVA (:
% 9%VA) 20 % EMAA-1 + 80 EVA (, % 9%VA) 6 30 % EMAA-1 + 70 EVA (;
% 9%VA) 7 10% EMAA-1 + 90% EBA

8 20% EMAA-1 + 80% EBA

9 30% EMAA-1 + 70% EBA

100 % EAA

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2~~~5~
11 10% EAA + 90% EBA

12 2 0 % EAA + 8 EBA

%

13 3 0 % EAA + 7 EBA

%

14 10 % EAA + 9 EVA ( 9 0 %~i'A
% ) 15 2 0 % EAA + 8 EVA ( 9 0 %V~A ) %

16 3 0 % EAA + 7 EVA ( 9 0 %~i'A
% ) 17 10% EAA + 90% LLDPE

18 20% EAA + 80% LLDPE

19 30% EAA + 70% LLDPE

20 10% EMAA-1 90% PP
+

21 20% EMAA-1 80% PP
+

22 30% EMAA-1 70% PP
+

23 10% EAA + 90% PP

24 20-s EAA + 80 PP
%

25 30% EAA + 70% PP

26 (COMPARISON) 100% EVA (9%VA) 27 (COMPARISON) 100% EBA
28 (COMPARISON) 100% LLDPE
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Example 6 (performance evaluation of films of Example 5) In order to evaluate the performance of a mono-layer film according to this invention comparative tests were run relating to the protein adhesion of the inventive films recited in Example 5 (which had EMAA) with respect: to that of the compar-ative mono-layer films recited in ExamplE. 5 (which did not have any EMAA). This test differed from the: protein adhesion test method described above in that instead of using turkey emulsion, chunks of turkey which had been cleaned up by removing the extra-neous fat and other connective tissue such as partial removal of the sinews were used. (The chunks were cubes about 3 inches on a side, which is about 7.6 cm on a side.) The results are given in the following table:
Table VI
Protein Adhesion SAMPLE ADHESION INDEX*
NUMBER MEAN STANDARD DEVIATION
1 No adhesion 3 70.9 + 33.6 4 No adhesion 6 32.6 + 12.3 7 No adhesion 9 41.1 + 9.4 119.4 + 21.1 104.3 + 28.0 5/900523.5A/TXTJLS

26 (COMPARISON) No adhesion 27 (COMPARISON) No ad.hesian 28 (COMPARISON) No adhesion *Adhasioxi ~ndgx ~ adhesion forceof sample on Day n x 100 adhesion force of Comparison on Day n where the Comparison sample was ambient.
It is surprising that many of the above mono-layer films of the invention, as recited in Example 5, exhibited pro-tein adhesion during cook-in, even though none was electron-beam irradiated.
While certain representative embodiments and details have been shown for the purpose of illustration, numerous modifi-cations to the formulations described above can be made without departing from the invention disclosed.
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Claims (16)

1. A flexible thermoplastic film suitable for protein-adhesion, cook-in packaging comprising a thermosealing layer of a copolymer of (i) an alpha-olefin having the formula RCH=CH2 wherein R is H or C1 to C20 alkyl, C1 to C20 alkoxy, or C6 aryl, and (ii) an alpha, beta-ethylenically unsaturated carboxylic acid.

2. The film of claim 1, wherein said copolymer of said thermosealing layer is selected from ethylene-methacrylic acid (EMMA) copolymers, ethylene-acrylic acid (EAA) copolymers, or mixtures thereof.

3. The film of claim 2, wherein said copolymer of said thermosealing layer is selected from ethylene-methacrylic acid (EMAA) copolymers with a methacrylic acid (MAA) content of about 4 to about 18% by weight, ethylene-acrylic acid (EAA) copolymers with an acrylic acid (AA) content of about 4 to about 22% by weight, or mixtures thereof.

4. The film of claim 2 wherein said EMAA copolymer is chosen from EMAA copolymers with an MAA content of about 9 to about 15% by weight, ano. said EAA copolymer is chosen from EAA
copolymers with an AA content of about 6 to about 12% by weight.

5. The film of any one of claims 1 to 4 comprising at least one said thermosealing layer, a gas barrier layer and a structural layer.

6. The film of claim 5 wherein said gas barrier layer is selected from copolymers of vinylidene chloride with vinyl chloride or methyl acrylate or mixtures of the two, ethylene vinyl alcohol (EVOH) copolymers, polyamides or copolyamides or blends thereof with each other or with EVOH.

7. The film of an y one of claims 1 to 6, wherein said thermosealing layer is cross-linked by electron beam irradiation.

8. The film of claim 7 wherein said thermosealing layer comprises a blend of about 10 to about 99% of said copolymer with about 90 to about 1% of one or more additional polymers and copolymers selected from ethylene-butyl acrylate (EBA), ethylene-methyl acrylate (EMA), ethylene-ethyl acrylate (EEA), very low density linear low density polyethylene (VLDPE), linear low density polyethylene (LLDPE), ionomers, ethylene-vinyl acetate (EVA), EVA modified with acid functional groups, ethylene-propylene random copolymers (EPC), and polypropylene (PP) optionally modified with functional groups.

9. The film of any one of claims 1 to 8 wherein said film is heat-shrinkable.

10. A cook-in structure for packaging made of said film of any one of claims 1 to 9 which is sealed together at two portions of said thermosealing layer arranged adjacent and facing each other.

11. Structure according to claim 10 in the form of a bag having a bottom seal.

12. Structure according to claim 10 in the form of a bag having two lateral seals.

13. A cook-in package comprising an enveloped food product in said film of any one of claims 1 to 9, said film being sealed together by at least one thermoseal at two portions of said thermosealing layer facing each other.

14. A method for making a protein adhesion cook-in package comprising enveloping a food product in said film of any one of claims 1 to 9, removing air from inside the thus obtained package, sealing said package by sealing together at least two portions of said thermosealing layer facing each other and subjecting said sealed package to cooking at high temperature, whereby said thermosealing layer adheres to said food product.

15. A cooked, protein-adhesion, cook-in package comprising a food product enveloped in said film of any one of claims 1 to 9, said film being sealed together by at least one thermoseal at two portions of said thermosealing layer facing each other, said sealed package having been subjected to cooking at high temperature, whereby said thermosealing layer adheres to said food product.

16. Use of said film of any one of claims 1 to 9 for making a protein adhesion cook-in package.