CA1274961A - Biaxially oriented oxygen and moisture barrier film - Google Patents

Abstract

A biaxially oriented oxygen and moisture barrier film and a method of producing such a film which comprises co-extruding at least one polyolefin core layer, at least one layer of an ethylene vinyl alcohol copolymer with a melt flow rate of at least about 8 grams per 10 minutes, and an adhesive layer wherein the layers are combined into a composite sheet with the adhesive interposed between the core layer and ethylene vinyl alcohol copolymer layers. Next, the composite sheet is immediately cooled so that the crystallinity of the ethylene vinyl alcohol copolymer is no more than about 25 percent. Finally, the composite sheet is biaxially oriented in the longitudinal direction to a degree of about 2:1 to about 4:1 and in the transverse direction to a degree of about 3:1 to about 7:1.

Description

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BIAXIALLY ORIENTED XYGEN AND MOISTURE B~RRIER E'~LM
The present invention relates to a method for proclucing a biaxially oriented oxygen and moisture barrier film which is comprised of a core layer and an ethylene vinyl alcohol copolymer barrier layer. More particularly, the invention relates ~o a simple continuous method whereby the two layers are combined by co-extrusion and biaxially oriented at the same time.
Ethylene vinyl alcohol copolymer resins offer excellent barrier properties with respect to such gases as oxygen, carbon dioxide and nitrogen~ In addition, they are also effective barriers against odors and the loss of flavor. Such resins, hereinafter referred to as EVOH resins, are moisture sensitive and the barrier properties are reduced in the presence of high humidity. Polypropylene offers excellent barrier properties with respect to moisture together wi~h good strength properties and a high heat use temperature. When EVOH resins are encapsulated by layers of polypropylene, they are protected from moisture and therefore retain their barrier characteristics.
The biaxial orientation of ~VOH resins enhances their barrier properties as well as reduces their susceptibility to moisture. The biaxial orientation of polypropylene increases its stiffness and enhances both its optical and other physical propertie~ such as tensile strength, tear strength, and other mechanical properties.
In the past, others have attempted to produce biaxially oriented composite structures containing both polypropylene and EVOH resins by first producing a polypropylene sheet and orienting the sheet in the longitudinal direction. Then a layer of EVOH resin was either laminated or extrusion coated onto the 7i polypropylene and the composite was then orientecl in the transverse direction. This methocl of production is costly and only results in the orientation of the EVO~I resin in one directionr thus not achieving the full benefit of biaxial orientation.
U.S. Patent No. 4,239,326, issued December 16, 1980, discloses a multl-layered barrier film comprising a barrier layer of substantially pure ethylene vinyl alcohol copolymer adhered between adjacent adherent layers consisting essentially lO of a partially hydrolyzed vinyl acetate polymer or copolymer. A
layer of another material such as polypropylene can overlie the partially hydrolyzed vinyl acetate layers. The patent discloses co-extrusion of the EVOH and the partially hydrolyzed vinyl acetate polymer to form the multi-layer structure and then subsequent co-extrusion of ~he overlying material onto this structure. The patent do~s not suggest that this construction could be biaxially oriented and is otherwise distinguishable from the present invention because the adhesive is different, it does not mention controlling crystallinity of the EVOH, the 20 percent ethylene of the products mentioned is too low for flexibility for biaxially oriented film, and, even if this film was to be biaxially oriented, the operation would be a two step operation whereas the operation of the present invention is a one-step operation.
The present invention relates to a method of producing a biaxially oriented oxygen and moisture barrier film which comprises a first co-extruding at least one core layer of a polyolefin selected from one group consisting of polyethylene, polypropylene and copolymers of ethylene with o~her olefin 30 monomers, at least one layer of an ethylene vinyl alcohol copolymer wi~h a melt flow rate oE at least about 8 yrams p~r 10 minutes, and at least one adhesive layer wherein t}lese layers are combined into a composite sheet with the adhesive interposed between the core layer and the ~VOH. Next, the composite sheet is immediately cooled so that the crystallinity of the EVOH i5 no more than about 25~. Finally, the composite sheet is biaxially oriented in the longitudinal direction to a degree of about 2:1 to about 4:1 and in the transverse direction to a degree of about 3:1 to about 7:1. In a preferred embodiment of the invention, the ratio of the thickness of the adhesive to the thickness of the core layer is about 1:8 to about 1:15~ The invention also relates to a biaxially oriented oxygen and moisture barrier film formed by the above method.
The ethylene vinyl alcohol (EVOH) copolymers used in the present invention are the saponified or hydrolyzed produc~ of an ethylene-vinyl acetate copolymer having, generally~ an ethylene content of 25 to 75 mole percentO It is hlghly preferred that the percent ethylene in the EVOH be at least 45 percent so that the EVOH is flexible enough to be stretched during the orientation process. The degree of hydrolysis should reach at least ~6 percent, preferably at least 99 percent. It is highly preferred that the degree of hydrolysis be greater than 96 percent because below that the barrier properties are less than optimum. It is extremely important to the performance of the present invention that the melt flow rate of the EVOH be at least 8 grams per 10 minutes at 190C and a load of 2,160 grams.
If the melt flow rate is less than 8 grams per 10 minutes then the viscosities of the EVOH, adhesive, and core layer cannot be matched. It is important to match the viscosities of these materials to avoid interfacial instability which causes waviness _~_ of the melt and uneven distribution Oe the layers, otherwise known as melt fracture. The visc091ty of these materials is most easily and effectively matched by monitoring the melt 10w rate o the materials. At EVOH melt Elow rates below 8 grams per 10 minutes, melt fracture occurs. It does not occur if the melt 10w rate is higher.
The core layer used in the present invention can be of a polyolefin selected from the group consisting of polyethylene, including low density polyethylene, high density polyethylene, and linear low density polyethylene, polypropylene, and copolymers of ethylene with other olefins. The preEerred polymers for use as the core layer are polypropylene and ethylene propylene copolymers containing predominately propylene. The melt flow rate of the core layer must not be so low that it is too stiEf and thus unorientable. For propylene ethylene copolymers, it is preferred that the melt flow rate be from about 2.5 to about 6.0 grams per 10 minutes at 230C and a load of 2,160 grams. For polypropylene, it is preferred that the melt flow rate be from about 2.5 to about 4.5. In this range, the viscosities of the copolymer and the polypropylene are most compatible with EVOH and the adhesive. Also, in this range, orientation of the copolymer or the polypropylene results in the best properties.
The adhesive used in the present invention should be selected from the group consisting of maleic anhydride-modified polymers and polymers similar thereto. Such polymers are effective adhesives for adhering the core layer to the EVOH
layer and also have a viscosity similar to the above-described EVOH and core layers. The preferred adhesives for use in this inven~ion are maleic anhydride-modified polyolefins~ Examples _5_ 36~

of such polymers are the Admer~ QF-500 series manuactured by Mitsui Petrochemical Company, the Modic~ P-300 series manufactured by Mistubishi Petrochemical Comparly, and Plexar~
adhesives manufactured by Chemplex.
The pxocess for the manufacture of a biaxially oriented three or more layer composite barrier sheet consists of four distinct steps which together comprise a rela~ively simple continuous operation. First, the composite sheet, consistiny of polypropylene, for example, an adhesive layer, and an EVOH
barrier layer, is formed by co-extrusion of the above components. One way of accomplishing this is to use three extruders and have the materials fed into a combinin~ feed block. Within the feed block, the materials are layered to form tbe multi-layer melt stream wherein the adhesive is interposed between the polypropylene and the EVO8. The melt stream is fed into a slot cast sheet die or other type of die to form the multi-layer sheet~ As ~he sheet exits the die, it is immediately cooled by use of a cooling drum or a water bath to a temperature satisfactory to maintain a 25 percent crystallinity rate in the EVOH material.

The 25 percent crystallinity rate can be obtained by maintaining the temperature of the cooling medium at 30 to 40C.
If the crys~allinity of the EVOH is higher than 25 percent at this point in the process, the EVOH becomes ~oo stiff ~o stretch properly in the orientation process and it will merely break apart. It is preferable that the crystallini~y of the EVOH
should be at least about 20 percent in order to obtain sufficient crystallinity in the final pro~uctr Immediately after cooling, the composite sheet is fed into an apparatus adapted for biaxial orientation of plastic ~L~t7~

mater ial. Any such apparatus can be used in the present invention. One example would be to feed the composlte sheet .into a set of differentlal speed heated rollers to stretch the sheet in the longitudinal direction to a degree of about 2:1 to about 4:1~ Next, the sheet can be fed to a tenter frame where it is stretched in the transverse direction ~o a degree of about 3:1 ~o àbout 7:1.
If the degree of longitudinal orientation i~ less than about 2:1, then uneven orientation occurs, and if it is more than about 4 1, then fracture oE the sheet occurs. If the degree of orientation in the transverse direction is less than abou~ 3nl. then uneven orientation occurs, and more than about 7:1, then fracture of the sheet occurs. If polypropylene is used as the core layer, then it is preferred that the machine direction orientation rollers be at a temperature of from abou~
130 to about 140C and that the tenter frame for transverse orientation be at about 150 to about 160C. If the propylene ethylene copolymers are used in the core layer, then the machine direction roller temperature should be about 125 to about 130C and the tenter frame temperature should be about 130 ts about 135C.
After the sheet has been biaxially oriented, it is subjectged to a heat setting treatment which allows the ~VOH to crystallize. The crystallizing of the EVO~ impart~ high barrier properties to the EVOEI layer and thus to the composite film.
Any known heat setting method can be used, but one example of such a method is to pass the biaxially stretched sheet over a series of heated rollsn I is highly preferred that the ratio of the thickness of the adhesive to ~he thickness of the core layer be about 1:8 to 49~i~

about 1:15. If the ratio is less than about 1:~. then poor adhesion between the EVOH and adhesive occur~, preventlng satisfactory orientation. If the ratio is more than ahout 1:15, then uneven flow dis~ribution of the adhesive occur~ and the adhesion is poor.
EXAMPLES
The materials used in all of the following examples are:

Polypropylene: Homopolymer - Solvay Eltex HP405 318 melt flow rate Copolymer - Solvay KS400, 5.7 mel~ flow rate (4~ ethylene, 96~ propylene) Ethylene Vinyl Alcohol Copolymer:

EV~D~ "F" Grade resin mada by Kuraray Co., Ltd. - 1.5 melt index EVAL~ "E" Grade resin made by Kuraray Co., Ltd. - 5.6 melt index EVAL~ "G" Grade resin made by Kuraray Co., Ltd. - 15~1 melt index Adhesive: Admer~ QF500~ - 4.2 melt flow rate (a maleic anhydride-modified poly-propylene~
All of the following examples attempted to produce a biaxially oriented five layer composite barrier sheet of ABCBA
construction according to the same general process consistin~ o the following four distinct steps:
1. A five layer composite sheet was co-extruded by the use of three extruders. The sheet considered of a polyolefin (A
layer), an adhesive layer tB layer), an EVOH layer (C layer), another adhesive layer (B layer), and another polyolefin layer (A layer). The materials were fed into a combining feed block where they were layered to form the five layer melt stream of ABCBA construction. This melt stream was then fed into a slot cast sheet die ~o form the five layer sheet. As the sheet exited the die, it was immediately cooled by the use of a cooling drum, or in some cases a water bath, to a temperature 9~;~

which maintained a 25 percent crystallinity rate ln the EVO}I
material.

2. Immediately after cooling, the composite sh~et was fed into a set of diferential speed heatecl rolls (MDO) which stre~ched the sheet in the longitudinal direction.

3. A~ter exiting the differential speed heated rollers (MDO), the sheet was fed to a tenter frame. In the tenter frame, the sheet was stretched in the transverse direc~ion.

4. After the sheet was biaxially stretched, it was passed over a series of heated rolls which imparted a hea~ setting to the composite sheet and allowed the EVOH layer to crystallize.
The crystallizing of the ~VO~ imparted high barrier properties to the composite sheet.
The following examples specify which materials were used~
The orientation of the extruders was as follows in all cases:
Extruder #1: Always polypropylene Extruder #2: Always EVOH
Extruder #3: Always Adhesive Examples In all cases in the following examples, the crystallinity of the EVOH material as it exited the Aie was maintained below 25%. The crystallinity ranged from 18 to 22% in the examples.
The method of determination of the percent crystallinity is based upon the linear relationship between the percent crystallinity and the density of the filmO The percen~
crystallinity is empirically determinecl by measuring the density of the total amorphous portion and the total crystalline portio~
of a par~icular grade of EVO~ film and using this information in the formula set out below.

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The density is first measured by any accep~able method such as ASTM D1505-68. Next, the total amorphous arld total crystalline portions oE the EVOH are separated and their densities measured according to the same procedure. For the three grades of EVOH used in the following examples, the densities of the amorphous and crystalline portions are as follows:
Table Density of Density of Amorphous Crystalline Grade Portion Portion E Grade 1.110 1.148 F Grade 1.163 1.200 G Grade 1.094 1.130 The above densities are considered constants because they do not change. The film density will change depending upon the degree of the quenching treatment. In the following formula FD
is the film density, AD is the amorphous density constant, and CD is the crystalline density constant. The percent crystallinity of a film is determined by:
% Crystallinity = FD - AD X 100 CD - AD
Thus, it is clear that the percent crystallinity increases linearly as the density of the film increases. The crystallinity of the film can be controlled by controlling the density of the film. This is what takes place in the quenching step.
EXAMPLE I
Materials: Homopolypropylene EVOH "E" Grade Adhesive ~7~1'3~i1 ~xtruder #1: Melt Temp. 260C, RPM (revolutions per minute~ 117.5 Extruder ~2: Melt Temp. 190C, RPM 25 Extruder # : Melt Temp. 185~C, RPM 29.5 Feedblock Temperature: 200C
MDO Rolls Temperature: 120C
Tenter Temperature: 165C
MDO OrientationO 2.0:1 Transverse Orientation: 3.0:1 The stretched film exhibited a fishnet effect due to the fibrillation of the EVOH layer.
EXAMPLE II
Using the same conditions and materials as in Example I, except that the RP~ of the Extruder #2 (EVO~) was reduced to 15 and the machine direction (MD) orientation was increased to 3.0:1, the same fishnet appearance was evident.
EXAMPLE III
Starting with the conditions and materials in Example II, the degree of MD orientation was varied while the transverse direction (TD) orientation was held constant. As the MD
orientation was decreased from 3.0:1 to 2.0:1, the fishnet appearance decreased. At a 1.0:1 MD orientation and a 3.0:1 TD
orientation, the fishnet appearance disappeared. This, however, only result2d in a uniaxially (transverse direction) oriented sheet which exhibited non-uniform thickness and poor optical proper~ies.
EXAMPLE IV
In observing the samples from Examples I through III, it was noted that the reason for the fibrillation of the EVOH layer might have been due to the lack of adhesion between the PP and EVOH layers. To investigate this, the conditions and materials used in Example I were selected as a base point. The melt ~4916~

temperature of the adhesive layer was increased in increments of

5~C until the melt temperature was the same as that of the polypropylene. It was noted that the adhesion became better a~
the temperature was increased. However, fibrillation of the EVOH layer was still present.
EXAMPLE _ Materials: Copolymer Polypropylene EVOH "E" Grade Adhesive Extruder #1: Melt Temp. 240C, ~PM 95 Extruder $2: Melt TempO 190C, RPM 15 Extruder #3: Melt Temp. 2~0C, RPM 50 Feedblock Temperature: 180C
MDO Rolls Temperature: 120C
Tenter Temperature: 165C
MDO Orientation: 2~4:1 Transverse Orienta~ion: 4Ø1 The initial trials exhibited minor fibrillation of the EVOH layer and uneven orientation of the polypropylene layer.
The RPM of the EVOH layer were increased to 30 to increase the thickness. Fibrillation still resulted. The thicknesses of the various layers were increased in increments of 0.5 times the original up to two times the original. There was no appreciable effect on fibrillation. Orientation temperatures were varied until a limit on the low end was reached where transverse stretching would not occur and on the high end until the polypropylene would stick to the tenter frame clips.
Fibrillation still was evident. The conclusion reached from the first five examples was that EVOH "E" grade could not be satisfactorily biaxially oriented.
EXAMPLE VI

Materials: Copolymer Polypropylene EVOH "G" Grade Adhesive ~L~'7~g~L

Extruder #1: Melt Temp. 240C, RPM as ~xtruder #2: Melt Temp. 185C, RMP ~0 Extruder ~3: Melt Temp. 250C, RMP 75 Feedblock Temperature: 185C
MDO Rolls Temperature: 120C
Tenter Temperature : 140C
MDO Orientation : 2.8:1 Transverse Orientation: 3.0:1 The above conditions were the starting conditions. The composite sheet exhibi~ed extreme melt fracture upon exit from the die. This melt fracture was occurrin~ in the EVOH layer and was due to the difference in viscosities of the various components. The difference in viscosities in turn affected the flow properties through the feedblock and die. Various combinations of heat and speed were investigated until the following parameters were reached which in turn resulted in a satisfactory biaxially oriented composite sheet.
Extruder #1: Melt Temp. 240C, RMP 95 Extruder #2: Melt Temp. 200C, RMP 20 Extruder #3: Melt Temp. 250C, R~IP 50 Feedblock Temperature: 200~
MDO Rolls Temperature: 129C
Tenter Temperature : 130C
~DO Orientation : 2.0:1 Transverse Orientation: 3.0:1 EXAMPLE VII

Materials: Homopolypropylene EVOH "G" Grade Adhesive Extruder #1: Melt Temp. 260C, RPM 115 Extruder ~2: Mel~ Temp. 1~0C, RPM 20 Extruder #3: Melt Temp. 250C, RPM 80 Feedblock Temperature: 200C
MDO Rolls Temperature: 140C
Tenter Temperature : 150C
MDO Orien~ation : 4.4:1 Transverse Orientation: 3.0:1 ~.~749~L

Again, the above condi~ions were the starting conditions.
Althouyh the sheet going into ~he tenter frame looked good, holes were torn in the sheet during transverse orientation.
This indicates either the sheet is too cold or the orientatlon is too high. Various orientation ratios were investigated Erom MDO ~.0:1 to 4.0:1 and transverse from 3.0:1 to 5.4:1. It was noted that as the M~O ratio was increased from 2.0:1, the EVOH
started to fibrillate. At 4.0:1 MDO ratio, the EVO~ was totally fibrillated. Increasing the trans~erse ratio and holding the MDO at 2.0:1 did not have the same effect.
EXAMPLE VIII
In an attempt to match viscosities and 10w rates of the various materials, the following changes were made in the conditions used in Example VII.
Extruder #l: RPM 35 Extruder #2: ~PM 25 Extruder ~3: RPM 25 Tenter Temperature: 160C
MDO Orientation: 3.0:1 Transverse Orientation: 4.2:1 Using these conditions, an excellent biaxially oriented sheeet was produced. The properties of this sheet are shown in the Table. Orientation ranges from MDO 2.0:1 to MDO 4.0:1 and transverse 3.0:1 to 7.0:1 were studied and satisfactory sheets were produced. The properties of two different films made hereunder are shown in the Table.
EXAMPLE IX
To further investigate the effects of parameters on the ability to orient the sheet, the following was studied:
To determine the effect of Adhesive thickness: The PP RPM

was held constant. The adhesive RPM was decreased in 5 RPM

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increments to 25 RPM. At 25 RPM, fib~illation occurs.
To determine the eefect of PP thickness: The adhesive RPM
was held constant. The PP RPM was decreased to 7~ RPM. Uneven flow distribution occurred. The adhesive RPM was set at 25 RPM.
The PP RPM was 70. Uneven flow distribution occurred.
EX~MPLE X

Materials: Homopolypropylene EVOH "F" Grade Adhesive Extruder #1: Melt Temp. 260C, ~PM 35 Extruder ~20 Melt Temp. 210C, RPM 25 Extruder #3: Melt Temp. 250C, RPM 50 Feedblock Temperature: 210C
MDO Rolls Temperature: 140C
Tenter Temperature : 160C
~ DO orientation from 2.0:1 to 3.0:1 and transverse orientation at 3.0:1 ~ere attempted and fibrillated film resulted. Changes in Extruder #1 RPM to 80 and Extruder #2 RPM
to 40 did not have any effect. Various temperature conditions did not have any effect. The conclusion was that the EVOH "F"
grade could not be satisfactorily biaxially oriented.
Final Thickness This is a determination of the thickness of each layer in the five layer composite sheet. The film was characterized by both ligh~ microscopy and scanning electron microscopy (SEM) techniques. For the SEM technique, the samples were notched and fractured. Light microscopy samples were embedded in LDPE and microtomed in thin sections. By using the thickness of the individual layers, comparisons can be made between the properties of oriented and unoriented films of the same thickness.

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2 Transmls _on It is known that the presence of oxygen callse~ ~oods to degrade. The 2 transmission of a s~ructure is a measure of its barrier to the penetration of oxygen to the materials packaged with the film s~ructure~ This determination was carried out according to ASTM Standard D3985-81.
MVTR
The Moisture Vapor Transmission is an indication of the amount o H2O that will permeate to the packaged goods or conversely the amount o~ moisture that can escape from a packaged liquid product. Also the barrier properties of a barrier material are deteriorated by the presence of moisture.
Therefore, it is desirable ~u prevent as much moisture as possible Erom reaching the barrier layer. This test was carried out according to ASTM Test Methods E398-70.
Ultimate Tens i le The ultimate tensile strength is a measure of the strength of the material. It is the amount of force per square inch of material required to pull it apart. This test was carried out according to ASTM D-882-73, Method Ao Secant Modulus The secant modulus is a measure of the stiffness of the materialO A stiff material is required to provide good machineability and handling in subsequent packaging operations, and also to provide a crisp feel to packaged products. This method was carried out according to ASTM D-618.

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TABLE
2 Tran~-mission Ultimate Secant Tenslle Modulus Final cc/m2/24 Thick- hrs. @ 20C MVT~ MD TD MD TD
Example ness 0~ RH g/m Mpa Mpa ~ Mpa Homopolymer12 12 3.0 30 250 18~8 5143 PP
Adhesive 1.3 EVOH G 3.5 Adhesive 1.3 ~Iomopolymer 12 PP

~omopolymer13 13 3.3 91 233 1575 4089 PP
Adhesive Adhesive Homopolymer 13 PP

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of producing a biaxially oriented oxygen and moisture barrier film which comprises:
(a) co-extruding (1) at least one layer of a core material selected from the group consisting of polyethylene, poly-propylene, and copolymers of ethylene with other olefins, (2) at least one layer of an ethylene vinyl alcohol copolymer with A melt flow rate of at least about 8 grams per 10 minutes, and (3) at least one adhesive layer and combining these layers into a composite sheet wherein the adhesive is interposed between the core layer and the ethylene vinyl alcohol copolymer layers, (b) immediately cooling the composite sheet so that the crystallinity of the ethylene vinyl alcohol copolymer is no more than about 25 percent, and (c) biaxially orienting the composite sheet in the longi-tudinal direction to a degree of about 2:1 to about 4:1 and in the transverse direction to a degree of about 3:1 to about 7:1.

2. The method of claim 1 wherein the ratio of the thickness of the adhesive to the thickness of the core layer is about 1:8 to about 1:15.

3. The method of claim 1 wherein the composite sheet is cooled in a cooling medium at a temperature of 30 to 40°C in step (b).

4. The method of claim 1 wherein the longitudinal orientation is carried out at a temperature of from about 130 to about 140°C and the transverse orientation is carried out at a temperature of from about 150 to 160°C when polypropylene is the core layer.

5. The method of claim 1 wherein the longitudinal orientation is carried out at a temperature of from about 125 to 130°C and the transverse orientation is carried out at a temperature of from about 130 to 135°C when the core layer is a copolymer of propylene and ethylene.

6. The method of claim 1 wherein the core layer is selected from the group consisting of polypropylene and copolymers of propylene and ethylene.

7. The method of claim 1 wherein a five layer film is produced comprising two outer core layers, an inner ethylene vinyl alcohol copolymer layer and two adhesive layers disposed between the core layers and the ethylene vinyl alcohol copolymer layer.

8. A biaxially oriented oxygen and moisture barrier film, formed by:
(a) co-extruding (1) at least one layer of a core material selected from the group consisting of polyethylene, poly-propylene, and copolymers of ethylene with other olefins, (2) at least one layer of an ethylene vinyl alcohol copolymer with a melt flow rate of at least about 8 grams per 10 minutes, and (3) an adhesive layer and combining these layers into a composite sheet wherein the adhesive is interposed between the core layer and the ethylene vinyl alcohol copolymer layers, (b) immediately cooling the composite sheet so that the crystallinity of the ethylene vinyl alcohol copolymer is no more than about 25 percent, and (c) biaxially orienting the composite sheet in the longi-tudinal direction to a degree of about 2:1 to about 4:1 and in the transverse direction to a degree of about 3:1 to about 7:1.

9. The film of claim 8 wherein the ratio of the thickness of the adhesive to the thickness of the core layer is about 1:8 to about 1:15.

10. The film of claim 8 wherein there are five layers which are comprised of two outer core layers, an inner ethylene vinyl alcohol copolymer layer, and two adhesive layers disposed between the core layers and the ethylene vinyl alcohol copolymer layer.

11. The film of claim 8 wherein the core layer is selected from the group consisting of polypropylene and copolymers of propylene and ethylene.