AU655221B2 - Protein adhesion film for packaging - Google Patents

Description

I

(555221

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S): W. R. Grace Co.-Conn.

ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

INVENTION TITLE: Protein adhesion film for pacaging Protein adhesion film for packaging The following statement is a full description of this invention, including the best method of performing it known to me/us:- 1A Field of the Invention In general, the instant invention relates to protein adhesion cook-in films having a sealing layer of polymer having carboxylic acid moieties and wherein the sealing layer does not require metal ionomer cross-linking of the polymer having carboxylic acid moieties in order to exhibit protein adhesion. The present invention provides a flexible thermoplastic film suitable for protein-adhesion, cook-in packaging comprising a thermosealing layer of a copolymer of an alpha-olefin having the formula RCH=CH 2 wherein R is H or C 1 1 o

C

20 alkyl, C, to C 20 alkoxy, or C 6 aryl, and (ii) an alpha,beta-ethylenically unsaturated carboxylic acid. In a preferred embodiment, it relates to a film comprising a thermosealing layer selected from ethylene-methacrylic acid copolymers (EMMA) having a Smethacrylic 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.

20 Surprisingly it has been found that after cook-in of a food product, the film has protein adhesion characteristics.

The protein adhesion characteristic of the thermosealing layer of the instant films cause them to stick, i.e.

bindingly adhere, to a food product cooked in a package of 25 the 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 films and to packages, particularly for food items, using such films and containers. The use of plastic films for packaging items in general, and foods in particular, is widespread nowadays. Depending on the perfor- 941011,p:\opcr\c, 10030gimaspc,1

S'I

mance to be achieved, the films typically comprise various plastic layers which, according 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 polyethylene VLDPE or ionomeric copolymers such as those available under the trademark Surlyn from E.I. duPont de Nemours Inc., Co. (USA). These latter ionomeric polymers generally consist of copolymers of ethylene and methacrylic acid or copolymers of ethylene and acrylic acid which copolymers are ionically cross-linked so as to convert them into metal salts, just designated as ionomers.

Notwithstanding the fact that such polymers used hereto- **e fore as thermosealing layers gave sufficiently satisfactory .performance, they still had disadvantages which limited their S use in certain applications. In particular, none of these polymers showed a sufficiently broad spectrum of properties comprising both a good sealability in the presence of contamination and t of creases or folds in the sealing area as well as a good seal strength together with a wide sealing range in terms of temperature or time, and also protein adhesion characteristics.

Blends of 80 to 90% 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), the disclosure of which is incorporated herein by reference.

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, for use in forming oriented multilayer films, the disclosures of all of which are incorporated herein by reference. None of these prior patents discloses, however, 5/900523.5A/TXTJLS 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 Grace; sealing layer is Surlyn), U.S. Patent 4,606,922 Grace; sealing layer is Surlyn), and U.S. Patent 4,855,183 Grace; sealing layer is nylon, optionally blended with Nucrel or Primacor). A perforated, heat-shrinkable bag containing 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). The disclosures of all of these are incorporated herein by reference. U.S. Patent 4,855,183 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 combination of properties such as to render it suitable for use in films, preferably multilayer films, for the packaging of various articles in various packaging and handling conditions. More Sparticularly, 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 packaging structures, like bags, et cetera from the films of the invention, which are suitable both for cold packaging and for cook-in with protein adhesion of the packaged food items.

5/900523.5A/TXTJLS 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 invention having a thermosealing layer comprising a copolymer of (i) an alpha-olefin having the formula RCH=CHa wherein R is H or C, to C 2 o alkyl, to C2o alkoxy, or C 6 aryl, and (ii) an alpha,beta-ethylenically unsaturated carboxylic acid.

Preferably, the thermosealing layer comprises a copolymer selected from ethylene-methacrylic acid EMAA copolymers, ethyleneacrylic acid EAA copolymers, or mixtures thereof. More preferably, the thermosealing layer comprises a copolymer 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 S 00 acid AA content of about 4 to about 22% by weight, or mixf* f tures thereof.

S

This invention is based on the discovery that a polymer containing carboxylic acid moieties, such as 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 Slayer does not require the presence of the related metal salt cross-linked ionomeric materials, many of which are Iold as Surlyn by du Pont, in order to give rise to the protein adhesion characteristic.

Most preferably, the thermosealing layer according to t t' this invention comprises said EMA 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 12% by weight, or a blend of such copolymers in any proportion.

According to further embodiments 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 5/900523.5A/TXTJLS I to about 1% by weight of a polyolefinic polymer or copolymer. Preferably, the thermosealing layer comprises a blend of about 30 to about 70% by weight of the polymer containing carboxylic acid moieties, such as the EMAA or EAA copolymer as defined above, with about 70 to about 30% 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-vinyl acetate modified with functional groups, and mixtures thereof.

These polymers are abbreviated herein as follows: ethylene-methacrylic acid EMAA ethylene-acrylic acid EAA linear low density polyethylene LLDPE linear very low density pclyethylene VLDPE eth ethylene-butyl acrylate EBA ethylene-ethyl acrylate EEA ethylene-methyl acrylate EMA ethylene-vinyl acetate EVA Statement of Invention Therefore, the present invention provides a flexible thermoplastic film suitable for protein-adhesion cook-in packaging comprising a thermosealing layer of a copolymer of an alpha-olefin having the formula RCH=CH 2 wherein R is H or Ca to C2o alkyl, C. to C 2 o alkoxy, or C, aryl, and (ii) an alpha,beta-ethylenically unsaturated carboxylic acid.

The present invention also provides 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 5/900523.5A/TXTJLS 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 thermosealing together at least two portions of the thermosealing layer facing each other, and subjecting the sealed package to cooking at high temperature, whereby the thermosealing layer adheres to the food product. The present invention also provides a cooked, proteinadhesion, cook-in package comprising a food product enveloped in the film described in the above paragraph, the film being eealed 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 temperature, 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 thermoseal 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 "polymers containing carboxylic acid moieties" as that term is used herein it is intended to mean copolymers of an alpha-olefin having the formula S RCH=CH, wherein R is H or Cx to Cao alkyl, C, to C 20 alkoxy, or C 6 aryl, and (ii) an alpha,beta-ethylenically unsat- S urated carboxylic acid. Preferably, when R is alkyl, it is C, S" to C, alkyl. Also, preferably, the alpha,beta-ethylenically unsaturated carboxylic acid is present in an amount by mol of about 50% or less, more preferably about 30% or less, most preferably about 20% or less. Furtner, by the term "polymers containing carboxylic acid moieties" it is 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 5/900523.5A/TXTJLS 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 combination 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 invention 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 hydrogen maleate/ethyl acrylate terpolymers, ethylene/methacrylic acid/vinyl acetate terpolymers, ethylene/acrylic acid/vinyl acetate terpolymers, ethylene/acrylic acid/vinyl alcohol terpolymers, ethylene/propylene/acrylic acid terpolymers, ethylene/styrene/acrylic acid terpolymers, ethylene/acrylic **Go acid/methyl methacrylate terpolymers, ethylene/methacrylic acid/ ethyl acrylate terpolymers, ethylene/itaconic acid/methyl methacrylate terpolymers, ethylene/methacrylic 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=CH

2 wherein R is H or Ca to Cao alkyl, C, to C2o alkoxy, or C 6 aryl, and an alpha,beta-ethylenically unsaturated carboxylic acid representatively may be produced by the copolymerization of ethylene and a carboxylic acid comonomer therefor such as acrylic acid or methacrylic acid. Preferably, when R is alkyl, it is C. to C 8 Suitable such acid copolymers are the Primacor (TM) polymers, supplied by Dow Chemical Company, Midland, Michigan. Primacor is produced by the copolymerization of ethylene and acrylic acid EAA A very suitable Primacor polymer is Primacor 1410 or Primacor 5981. Other suit- 5/900523.5A/TXTJLS 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 suitable Nucrel polymer is Nucrel 1202.

The instant thermosealing layer does not require the presence of ionomer in order to exhibit protein adhesion characteristics. 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=CH, wherein R is H or C. to C20 alkyl, CI to C 2 alkoxy, or C 6 aryl, and an alpha,beta-ethylenically unsaturated carboxylic acid which are partially neutralized with a suitable metal cation such as zinc cation or sodium cation. These metal salt *S09 0640.a neutralized copolymers containing carboxylic acid moieties are called ionomers. lonomers 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 a Surlyn sealing layer) are described in the above-mentioned U.S. 4,469,742 and U.S. 4,606,922.

polme 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. Other methods, such as "slot die" extrusion wherein the resultant extrudate is in planar, as opposed to tubular form are also well known. If heat shrinkab.e 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 impart the heat-shrinkable property to the film. For multilayer films, such as those made by coextrusion of multiple individual resins or blends, a suitable adhesive polymer layer may be employed to promote interlayer adhesion.

5/900523.5A/TXTJLS SI 1 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; 4,194,039; 4,188,443; 4,048,428; 3,555,604; 3,741,253; 3,821,182; and 3,022,543. The disclosures of these patents are generally representative 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 c The gas barrier layer can be made of materials conventionally 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.

a a The structural layer which, beyond conferring abuse resistance, also increases the heat-shrink percentage when heatshrinkable 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 EEA ethylene-methacrylic acid EMAA 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, 5/900523.5A/TXTJLS 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 12% by weight.

Among the possible blends of the above polymers for producing the structural layer, blends of LLDPE and EVA or of VLDPE and EVA in a weight ratio of 70:30 to 20:80 can be mentioned.

The preferred multilayer film of the invention can comprise, in addition to the above-mentioned layers, further *6 layers, such as adhesive layers, which improve the adhesion between the various functional layers. A structure of this type may comprise the following layers: 6* Sealing/Adhesive/Barrier/Adhesive/Structural fr 0 As adhesive layers, those commonly known for 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.

bi 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 15 MR (megarads). It has been found that such treatment notably increases the overall resistance 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 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 and 6 below.

5/900523.5A/TXTJLS According to a specific embodiment of this invention, a whole multilayer film can be irradiated to achieve cross-linking. 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 irradiation may take place on the collapsed tube, or on a slit open lay-flat 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-linking the substrate by electron beam irradiation, and finally extruding onto the irradiatively cross-linked substrate the further layers of the final film.

*0 o According to a still further embodiment of the inven- S tion, a multilayer film can be prepared by laminating various self-supporting preforned films accort.ing to the desired structure, by using intermediate adhesive layers. The above-mentioned adhesive materials can be used for this purpose. Also, in this embodiment part of the laminate, or alternatively the whole laminate may be subjected to electron beam irradiation treatment.

Since for 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-axial stretching in the longitudinal or transverse direction with respect t3 the direction of extrusion, but preferably through biaxial stretching, using techniques well-known in the field.

For example, .n the case when the film is prepared by coextrusion in tubular form, the bi-axial stretching can be performed by the "air bubble" blowing method, on-line or offline 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.

5/900523.5A/TXTJLS As used herein the term "extrusion" or the term "extruding" is intended to include coextrusion, extrusion coating, or combinations thereof, whether by tubular methods, planar methods, or combinations thereof.

An "oriented" or "heat-shrinkable" material is defined herein as a material which, when heated to an appropriate temperature above room temperature (for example 90°C), will have a free shriuk of about 5% or greater in at least one linear direction.

Melt index was measured in accordance with ASTM D 1238, Condition E.

oo* The term "cook-in package", as used herein, is intended to refer to packaging material structurally capable of withstanding exposure to cook-in time-temperature conditions while con- Staining a food product. Cook-in time-temperature conditions typically imply a long slow cook, for example by submersion in water at 70-80 0 C for 4-6 hours. Submersion at 80 0 C for 12 hours probably represents the limiting case. Under such conditions, a packaging material properly characterized as cook-in will maintain heat seal integrity and will be delamination resistant.

Typically, cooked "cook-in" packaged foods go directly to the consumer in that configuration and may be consumed with or without warming.

of g The term "protein adhesion", as used herein, is intended 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 demonstrated by the "Cook-In Protein Adhesion Test" described below.

TEST METHODS Seal Strength Test: 5/900523.5A/TXTJLS The bags were tested at about 73 0 F (about 23 0 C) (room temperature).

All bag samples were heat sealed at one end on conventional equipment well known in the art of heat sealing of tubing, 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 retained each inflated bag air at 23 0 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/cm 2 per second till the heat seal for that bag either S. leaked or burst open at the IOWP (inches of water pressure) designated below.

So* Cook-In Protein Adhesion Test (Binding Adherence to Food): Bags of the film samples were tested for binding adherence to a cooked-in meat product. Each bag was stuffed with turkey emulsion, vacuumized, heat-sealed, and cooked at 55°C for 30 minutes, and then at 60 0 C for 30 minutes, and then at 65 0

C

for 30 minutes, for a total of 90 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 instance turkey.

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 5/900523.5A/TXTJLS to pull the bag from the meat was measured at a constant crosshead speed. (Another machine commonly used for such measuring 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.

a obee S. 12 Hour Delamination Test: 0

S

Bags were filled with an oil-water emulsion and then 9 heat sealed closed. Then they were heated for 12 hours. Some were heated at 150°F (65.6 OC), some at 160 0 F (71.1 CC), and some at 170°F (76.7 OC). 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 failures of °the films was indicated by delamination of the films.

Materials employed in the Examples: 0 GENERIC NAME

FOLLOWED

BY TRADE NAME OF DESCRIPTIVE INFORMATION SUPPLIER POLYMER ABOUT THE POLYMER COMPANY

ADHESIVE

Bynel 3062 du Pont 5/900523.5A/TXTJLS

EVOH

EVAL LC-E1O5A EVALCA

EPC

KS400

DENSITY

0.90 q,'cc Solivay Zinc Methacrylate Tonomer Surlyn 1650 a 0 a a a 0 Type of copolymer Partially zinc neutralized ethylene methacrylic acid copo:lymer du Pont Exxon Us'

EVA

LD318 .92 NA-295-00

MI

2.6

COMONOMER

Vinyl Acetate Vinyl Acetate

VA

9 6

EBA

EA719 .009

MI

0.35 COMONOMER %BA Butyl acrylate 18.5%

DENSITY

0.926 Quantuin/usI LLDPE MI Dowlex 1.1 2045.03 5/900523.

COMONOMER

Octene

DENSITY

0.920 g/cc DOW Chemical By Weight Methacrylic Acid EMAA By Weight Ethylene 88 EMAA-1 Nucrel 1202 EMAA-2 Nucrel 0903 EMAA-3 Nucrel 0403 du Pont du Pont du Pont 004*

EAA

0 t 04'*0 PRIMACOR 1410 be*& 0: 0 4 By Weight Acrylic Acid By Weight Ethylene 1.5 9.5 90.5 Dow 0* -0 NPP8000gk 161°C Quantum/USI The following examples show, only for illustrative and not limiting purposes, various structures of films according to this invention.

Example 1 (manufacture of films) The following biaxially stretch oriented 12:1 films were prepared as described above. Percentages 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 ID, 1E, and IF, the sealing layer thickness was about 0.36 mils. In sample number 9A, the 5/900523.5A/TXTJLS 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 abuse layer (on the right). (Samples 3-8 AND 11 were a comparison films.) Table I SAMPLE NUMBER (MR IRRADIATION) COMPOSITION OF EACH LAYER 6 4 e 6 1A (3MR) 1B (5MR) 1C (7MR) 1D (3MR) 1E 1F (7MR) EMAA-1 /70% LLDPE /30% LLDPE EVA VA) /70% EVA (9"s VA)

SAME

SAME

EMAA-1 /70% LLDPE /30% LLDPE EVA VA) /70% EVA VA)

SAME

SAME

2 (5MR) 3 (1MR)

COMPARISON

4 (1MR)

COMPARISON

EMAA-1 70% LLDPE 30% EVA VA)

EPC

80% LLDPE /30% LLDPE /50% LLDPE 20% Surlyn 1650/70% EVA VA)/50% EVA(6% VA) 85% LLDPE /30% LLDPE /50% LLDPE 15% Surlyn 1650/70% EVA VA)/50% EVA(6% VA) 5/900523.SA/TXTJLS

(IMR)

COMPARI SON 6 (1MR) COMPARI SON 7 (4lMR) COMPARI SON 8A (2MR) 8B (4MR) 9A E (3MR) BDX 2875 9B ED (3MR) 90% LLDPE /30% LLDPE /50% LLDPE 10% Surlyn 1650/70% EVA VA)/50% EVA(6% VA) 83% LLDPE /30% LLDPE /50% LLDPvE 17% Surlyn 1650/70% EVA VA)/50% EVA(6%, VA) SurJlyn 1650 /30% LLDPE /50% LLDPE /70% EVA VA) /50% EVA(6% VA) EMAA-1 /30% LLDPE /50% LLDPE /70% EVA (9%VA)/50% EVA (6%VA)

SAME

1AA-1 /8n'sEVA(6%VA)/ ADH /EVOH- ADH /80%EVA(6%VA) /20%LLDPE met* 0 4AA-1/ 80%EVA(6%VA) /ADH /EVON ADH /80%EVA(6%VA) 20%LLDPE 80%EVA(6%VA) /ADHi EVOH /ADH /80%EVA(6%VA) 20%LLDPE *5 S S S

S.

S4 S~ 5* .5 4

S

050055 9C (5MR) 9D (3MR) 9E 5MR) EMAA EMAA-1 /80%EVA(6%VA) /ADH /EVOH /ADH /80%EVA(6%VA) /20%LLDPE 2"'%LLDPE EMAA-1 /80%EVA(6%VA)/ /20%LLDPE ADH/ EVOH /ADH/ 80%EVA( 6%VA) .00 as Surlyn/ 80%EVA(6%VA) /ADH /EVOH /ADH 80%EVA(6%'VA) (4MR.) 1650 /20%LLDPE COMPARI SON Example 2 (performance evaluation of films of Example 1) 5/900523. In order to evaluate the performance of a multilayer f ilm according to this invention comparative tests were run relating to the puncture impact, seal strength, delamination, and protein adhesion of the inventive f ilms 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 EMvAA thermosealing layer). The results are given in the following tables: Table 11(a)

SAMPLE

NUM~BER

6 0300 ~0 .0 9

S

e0* 0 0Ss* 0S*U 0

OOSS

0 00000S PUNl~CTURE IMPACT RESULTS-

FAILURES)

44.0 13.0 2.7 8.0 10.7 SEAL STRENGTHI 230C)

(IOWP)

183 .8 183 .8 206.8 158. 8 131.3 0.0 00 0

S

06 0* 55 0 29.0 41.0C 183.5 216.4 136.1 3 COMPARI SON 2-Maximum weight and potentialenergy used of 305.25 inch *:pounds.

Table I1(b) 12 HOUR DELAMINATION Cook-In Test Results Failures) HIGH HUMIDITY WATER COOK

SAMPLE

NUTMBER

I A 13 150OF 160"F 170OF 12 HRS 12 HiRS 12 HRS 150OF 160 0 F 170OF 12 HRS 12 HRS 12 HRS 0.0 0.0 0.0 0.0 0.0 0.0 0.0 50.0 60.0 0.0 0.0 0.0 30.0 27.3 0.0 75.0 50.0 0.0 5/900523. 0.0 0.0 0.0 0.0 0.0 12.5 0.0 0.0 0.0 20.0 50.0~ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.o0 33 .3 66.7 22.2 57.1 (delam) (delan) 100.0 100.0 (delam) (de).am) 3

COMPARISON

0.0 100.0 10.0 0.0 NOTE: delan is an abbreviation for delamination.

Table Ii (c) Protein Adhesion ADHESION (g/in)

MEAN

SAMPLE

NUMBER

NUMBER

OF TESTS doe 0 0*060: 0 0 3 COMPARISON 4 COMPARISON

COMPARISON

6 COMPARI SON 7 COMPARISON 141.5 92.5 80.6 128.0 147.7 154.1 178.2 S. *4 S0 0000 90 *0 S 55.000

S

dO 0 05 *0 From the above results it can be seen that the f ilm according to the invention had a seal strength and a protein adhesion which was notably improved, over that of the control f ilms that had a Surlyn thermosealing layer.

The multilayer, f ilm of the invention showed superior properties also with respect to other conventional materials used heretofore as thermosealing layers.

5/900523. 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).

Table III SAMPLE NUMBER (MR IRRADIATION) COMPOSITION OF EACH LAYER Surlyn/80%EVA(6%VA)/ ADH/EVOH/ADH /80%EVA(6%VA) 1650 /20%LLDPE 0 4 4b@ 4 4 9 (4MR)

COMPARISON

11 (4MR) 50% EMAA-1 50% LLDPE /70% LLDPE /30% LLDPE /30% EVA VA) /70% EVA VA) 12 (4MR) 44 4 9 @4 4 44 4 44 13 (4MR) 14 (4MR) 15 (4MR) 50% EMAA-1 70% LLDPE /30% LLDPE EVA (6%VA) 30% EVA (9%VA) /70% EVA (9%VA) 50% EMAA-1 70% LLDPE /30% LLDPE 50% EVA (9%VA) 30% EVA (9%VA) /70% EVA (9%VA) EMAA-2 /70% LLDPE /30% LLDPE EVA VA) /70% EVA VA) EMAA-3 /70% LLDPE /30% LLDPE /30% EVA VA) /70% EVA VA) Example 4 (performance evaluation of films 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 thermosealing layer) with respect to that of the comparative multilayer film recited in 5/900523.5A/TXTJLS Example 3 (which did not have an EMAA thermosealing layer).

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 extraneous fat and other connective tissue such as partial removal of the sinews were used. (The chunks wax-e 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 IV Protein Adhesion SAMPLE ADHESION INDEX* NU114BER MEAN STANDARD DEVIATION

S

.505 to 10 (4MR) 100.0

*COMPARISON

0e0 11 (4MR) 98.8 8.1 *gOO 12 (4MR) 84.0 21.1 13 (4MR) 88.2 19.6 14 (4MR) 95.5 11.2 15 (4MR) 60.4 26.7 •5• o nda -adhesion force o sample on Day n X LOO 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.

5/900523.5A/TXTJZ 1

S

Example 5 (manufacture of films) The following additional unoriented films wero( prepared by the tubular hot blown method as described above. Percentages designated were by weight. The films were monolayer and thus the entire film was the "thermosealing" layer. None of the monolayer films was electron beam irradiated. The composition of each is recited below.

Table V SAMPLE COMPOSITION

S

CISC

0* SC eq 0

C

0

SOS...

S.

rI EMAA-1 90% LLDPE 20% EMAA-1 80% LLDPE EMAA-1 70% LLDPE 10% EMAA-1 90% EVA (9%VA) EMAA-1 80% EVA (9%VA) 30% EMAA-1 70% EVA (9%VA) 10% EMAA-1 90% EBA EMAA-1 80% EBA 30% EMAA-1 70% EBA 100% EAA EAA 90% EBA EAA 80% EBA EAA 70% EBA 9 9 Q 5/900523.5A/TXTJLS

S.

S 3* I S *3*O SO SQ

S

5.4.

3 *500 *0*5 3055

S

S

*5 5 4 00

SO

SaOt S S S. S

S

00e55S 0 EAA 90% EVA (9%VA) EAA 80% EVA (9%VA) EAA 70% EVA (9%VA) EAA 90% LLDPE EAA 80% LLDPE EAA 70% LLDPE EI4AA-1 90% PP 20% EMAA-1 80% PP 30% EMAA-1 70% PP 10% 2AA 90% PP EAA 80% PP 30% EAA 4- 70% PP 100% EVA (9%VA) 100% EBA 100% LLDPE

(COMPARISON)

(COMPARISON)

(COMPARISON)

Example 6 (performance evalation of f ilms of Example 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 f ilms recited in Example 5 (which had EI4AA) with respect to that of the compar- 5/900523.5A/TXTJLS utive 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 extraneous fat and other connective tissue such as partial removal of the sinews were usea. (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

NUMBER MEAN ADHESION INDEX* STANDARD DEVIATION No adhesion Sao# 0

S

S

*000

S..

a 70.9 33.6 No adhesion 32.6 12.3 3 *0 *SSS No adhesion 41.1 119.4 104.3 No adhesion No adhesion No adhesion 9.4 21.1 28.0 26 (COMPARISON) 27 (COMPARISON) 28 (COMPARISON) *a.ea.ion inaex adhesion force of sample on Day n adhesion force of Comparison on Day n x 0oo 5/900523.5A/TXTJLS 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 protein adhesion ,aring cook-in, even though none was electronbeam irradiated.

While certain representative embodiments and details have been shown for the purpose of illustration, numerous modifications to the formulations described above can be made without departing from the invention disclosed.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

o*

S*

S

*go• *o i23.5A/TXTJLS

Claims (16)

1. A flexible thermoplastic film suitable for protein- adhesion, cook-in packaging comprising a thermosealing layer of a copolymer of an alpha-olefin having the formula RCH=CH, wherein R is H or Ci to C 2 o alkyl, Ca to C 2 o alkoxy, or C 6 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 EMAA copolymers, ethylene-acrylic acid EAA copolymers, or mixtures thereof.

3. The film of claim 2, wherein said copolymer of said S.l. 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, and said EAA copolymer is chosen from EAA copolymers with an AA content of about 6 to about 12% by weight.

5. The film of claim 1 comprisinq 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 claim 1, wherein said thermosealing layer is cross-linked by electron beam irradiation. 5/900523.5A/TXTJLS 6- .0 1 d

8. The film of c2aim 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 polyethyl- ene 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 claim 1 wherein said fi] is heat- shrinkable. 4 4se*

10. A cook-in structure for packaging made of said film of claim 1 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 claim 1, said film being sealed together by at least one thermoseal at two portions of said thermosealing layer facing each other. *4

14. A method for making a protein adhesion cook-in package comprising enveloping a food product i. said film of claim 1, 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. 5/900523.5A/TXTJLS A cooked, protein- adhe sionr, cook-in package com- prising a food product enveloped in said film of claim 1, 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 tempera- ture, whereby said thermosealing bindingly layer adheres to said food product. feel 4 4 a A 00 V9 5/900523.

16. A flexible thermoplastic film according to claims 1 to 9, or a cook-in structure/package according to claims to 13 and 15, and methods for making the same substantially as hereinbefore described with reference to the Examples.

17. The steps, features, compositions and comws disclosed herein or referred to or indi in the specification and/or claims oti s application, individually or O. :ively, and any and all combinations see* of any or more of said steps or features. 0 e go *e 9 *0 0 DATED this SECOND day of JANUARY 1992 W. R. Grace Co.-Conn. 0* a 0 S by DAVIES COLLISON CAVE Patent Attorneys for the applicant(s) So ABSTRACT OF THE INVENTION In general, the instant invention relates to protein adhesion cook-in films having a protein adhesion sealing layer of polymer haviin .arboxylic acid moieties and 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. *0S@ as *00** a *o S S S S