CA1284708C

CA1284708C - Oxygen barrier oriented film

Info

Publication number: CA1284708C
Application number: CA 509212
Authority: CA
Inventors: Gautam P. Shah
Original assignee: WR Grace and Co Conn
Current assignee: Cryovac LLC
Priority date: 1985-09-17
Filing date: 1986-05-15
Publication date: 1991-06-11
Anticipated expiration: 2008-06-11
Also published as: ATE71583T1; US4724185A; EP0217596B1; EP0217596A2; NZ217466A; JPS6297840A; DE3683432D1; AU591521B2; ZA866692B; BR8604417A; JPH049671B2; AU6267486A; EP0217596A3

Abstract

ABSTRACT A coextruded multiple layer oriented film comprises a core layer of a blend of ethylene vinyl alcohol copolymer and polyamide, two intermediate adhesive layers, and two outer layers of a blend of linear low density polyethylene, linear medium density polyethylene, and ethylene vinyl acetate copolymer. A preferred embodiment of the multilayer film exhibits excellent optics and shrink properties while providing high oxygen barrier especially useful in food packaging applications.

Description

7~3~

OXYGEN BARRIER ORIENTED FILM

BACKGROUND OF THE INVENTION
:
j This invention relates to oriented thermoplastic films for packaging;
and more particularly, this lnvention relates to a coextruded, multilayer, oriented film having high oxygen barrier characteristics.

Thermoplastic film, and in particular polyolefin materials, have been used for some time in connection with packaging of various articles including food products which require protection from the environmentJ an attractive appearance, and resistance to abuse during the storage and distribut~on cycle. Suitable optical properties are also desirable in order to provide for lnspection of the packaged product after packaging, in the distribution chain, and ultimately at point of sale. Optical properties such as high gloss, high cla~ity, and low haze characteris~ics contribute to an aesthetically attractive packaging material and packaged product- to enhance the consumer appeal of the product. Various polymeric mate~rials have been used to provide lower gas permeabllity in order to reduce the transmission of oxygen through the packaging film and thereby retard the spoilage ant ex~end the shelf life of products such as food items which are sensitive to oxygen.
~I .
It ~s also desirable to include in a packaging film a shrink feature~
i.e., the propensity of the film upon exposure to heat to shrink or, if res~rained, create shrink tension within the packaging film. This property is imparted to the film by orientation of the film during its manufacture.
.~`

, 47~3 Typically, the manufactured film is stretched in either a longltudinal (machinP) direction, a transverse direction, or both, in varying degrees to impart a certain degree ~of shrinkability in the f ilm upon subsequent heating. After being so stretched, the film is rapidly cooled to provide this latent shrinkability to the resulting film. One advantage of shrinkable film is the tight, smooth appearance of the wrapped product that results, providing an aesthetic package as well as protecting the packaged product from ~nvironmental abuse. Varlous food and nan~food i~e~s may bè
and have been packaged in shrinkable films.

It is sometimes also desirable to orient the packaging film and thereafter heat set the film by bringing the film to a temperature near its orientation temperature. This produces a film with substantially less shrinkability, while retaining much of the advantages of orienta~ion, including improved modulus and optical properties.

Eehylene vlnyl alcohol copolymer (EVOH) is known as an oxygen barrier material and has been used in the past in conjunction with multilayer packaging films. EVOH also provides a good barrier to odors or fragrances.
- Orienting EVOH to produce a heat shrinkable film has proven to be difficult.
During the stretching or racking step for orienting such a film9 the EVOH
can sometimes develop voids. This phenomenon can result in some loss of oxygen barrier properties, which can affect, i.e. reduce the effective shelf life of food products packaged in EVOH film.

The presence of volds in the EVOH layer can also result in discoloration of a food product, such as processed meat, and therefore reduce the appearance and market value of a packaged food item.

U.S. Patent No. 4,064,296 issued to Bornstein et al discloses a film formed by the coextrusion of hydroly~ed ethylene vinyl acetate (HEVA) with outside layers of, for example, ethylene vinyl acetate copolymer (EVA).
.,~ .
Also of interest is ~.S. Patent No. 4,464~4h~ issued to Farrell et al showing the use of EVOH in a multilayer polymer structure, and including drying agents or desiccants such as sodium phosphate-di-basic and calcium chloride. EVOH, although a good barrier material, is moisture sensitive, and loses a great deal of its barrier properties at higher levels of relative humidity.

o~
`~
~ 3 - 6~536-578 Also of in-terest is U.S. Patent No. ~,~57,960 issued to Newsome which discloses -the use of EVOH and EV~H blends in a multiple layer film. The film may be made as shrinkable film, and may be melt extruded. The outside layer of the multiple layer film may be a blend of linear low density polyethylene (LLDPE) and EVA.
Also of interest is U.S. Paten-t No. 4,495,249 issue~ to ohya et al and disclosing a multilayer laminate film ~lith a core layer of a saponified copolymer of ethylene and vinyl acetate, and including two outer layers of a mixture of EVA and LLDPE. The multilayer laminate film of this reference can be made heat shrinkable and has gas barrier properties.
U.S. Patent No. 4,501,797 issued to Super e-t al dis-closes an unbalanced oriented multiple layer film including an intermediate layer of anhydride modified polypropylene and a barrier layer of a blend of ethylene vinyl alcohol and nylon, V.S. Patent No. 4/501,798 issued to Koschak et al also discloses the use of a blend of EVOH and nylon and an unbalanced multiple layer polymeric film also including LLDPE or EVA in a sealant layer. Adhesive layers of materials having carboxy moieties and preferably anhydride derivatives are present. The film of the reference is characterized by having high barrier to gaseous transmission, high gloss, transparency and stiffness.
U.S. Patent No. 4,347,332 issued to Odorzynski et al discloses a film having a blend of nylon and ethylene vinyl alcohol copolymer.
U.S. Patent No. 4,514,465 issued to Schoenberg discloses a five layered thermopLastic film, oriented and irradiated, having a three component blend of LLDPE, LMDPE, and EVA, and a four component surface layer having LL~PE, LMDPE, and EVA combined with a UV stabilizer.
U.S. Patent No. 4,643,943, assigned to a common assignee with the present application, discloses a five-layer thermoplastic film having two cross-linked surface layers of LLDPE/LMDPE/EVA.

~`~

~8470~3 It is an ob~ect of the present invention to provide a coextruded thermo-plastlc multilayer film characterized by good oxygen barrier proper~ies over a wide range of moisture conditions.

It is also an object of the present invention to provide a coextruded thermoplastic multilayer film which is substantially free o volds - in the barrier material of the film.

iB a further ob~ect o the present inven~lon to provide a thermoplastic multilayer film having an aesthetic appearance with good, clarity, and other desirable optical properties.

- It i8 another object of the present invention to provide a thin ther~o-plastic multilayer film having superior toughness and abrasion resistance.

It is still another ob~ect of the present invention to provide a coextruded thermoplastic multilayer film which may be totally coextruded, and oriented to provide a film with good shrink properties and good barrier properties over a wide range of moisture conditions.

It is a yet another ob~ect of the ,present invention to provide a coextruded thermoplastic film which is oriented yet substantially shrink free.

- S~ARY OF THE INVENTION

The present invention relates to an oriented multilayer film comprising a cross-linked core layer comprising a blend of an ethylene vinyl alcohol copolymer and a polyamide resin; two cross-linked interior layers each comprising an adhesive resin; and two cross-linked surface layers each comprising a three component blend of a linear low density polyethylene, a linear medium density polyethylene, and an ethylene vinyl acetate copolymer.

.

1~8~0~3 In another aspect of the invention, a method of making an orlent~d multilayer film comprises the steps of si~ultaneously coextruding a core layer of a blend of an ethylene vinyl alcohol copolymer and a polyamide resin, two intermediate layers of an adhesive material~ and two outer layer6 of a blend of a linear low density polyethylene, a linear medlum density polyethylene, and an ethylene vinyl acetate copolymer; rapidly coollng the coextruded film; collapsing the cooled film; heating the collapsed film to a temperature between about 105C and 115C; and stretching and orienting th~
heated film.

DEFINITIONS
.

"Intermediate layer", "interior laye,r", and the like is used herein to define a layer in a multilayer fllm enclosed on both sides by other layers.

The term "oriented" and the like is used herein to define a polymeric material in which the molecules have been aligned by a process such as racking or blown bubble process.

The term "ethylene ~inyl alcohol copolymer", "EVO~I", and the like is used herein to include saponified or hydrolyzed ethylene vinyl acetate copolymers.

The term "racking" i6 used herein to define a well-known process for stretching coextruded and reheated multilayer film by means of tenter framlng or blown bubble processes~

The term "linear low density polyethylene", "LLDPE", and the like are used herein to refer to copolymers of ethylene with one or more comonomers selected from C4 to C10 alpha oleofins such as butene-1, octene, etc. in which the molecules of the copolymers comprise long chains with few side chain branches or cross-linked structures. This molecular structure is to be contrasted with conventional low or medium density polyethylenes which are more highly branched than ~heir respective counterparts.

70~

"LLDPE" as defined herein has a density usually in the range of from about 0.916 grams per cubic centimeter to about 0.925 grams per cublc cen~lmeter.

.
The terms "linear medium density polyethylene", "LMDPE" and the like as used herein refers to copolymers as described above and having a density usually in a range of from about 0.926 grams per cubic centimeter to abou~
0.941 grams per cubic centimeter.

The terms "ethylene vinyl acetate copolymer", "EVA" and the like is used herein to refer to a copolymer formed from ethylene and vinyl acetate monomers wherein ~he ethylene derived units in the copolymer are present in ma~or amounts, preferably between about 60% and 98% by weight, and the vinyl acetate derived units in the copolymerj are present in minor amounts, preferably between about 2% and 40% by welght.

The term "oriented" and the like is used herein to define a material which, when heated to an appropriate temperature above room temperature (for example 96C), will have free shrink of 5% or greater in at least one linear direction.
.
.
-~" All compositional percentages used herein are calculated on a "by weight" basis.

The term "polyamide" and the like refers to hlgh molecular weight polymers having amide linkages along the molecular chain, and refers more speciflcally to synthetic polyamide such as various nylons.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Further details are given below with reference to the sole drawing figure where figure 1 is a schematic cross-section of a preferred embodiment of a multilayer film of the lnvention.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

Referring specifically to the drawings, ln figure 1, a schematic cross-section of the preferred embodiment of the coextruded multilayer oriented film of the invention is shown. Film structure is directed to a multilayer film having the generalized structure of A/B/C/B/A where A is ~n outer layer, B is an intermedlate adhesive layer, and C is a core layer containing a blend of a barrier material and a po~yamide. Pre~erably, the outer layers ~ each comprise about 35~ of the total mulr.ilayer film thickness; the intermedlate layers B each comprise about 10% of the fil~
thickness, and the barrier/polyamide lay&r C about 10% of the total film thickness. The total thickness of the ~ultllayer film is preferably between about 0.5 and 2.0 mils, and more preferably between about .75 and 1.5 mils.
Even more preferably9 the multilayer filmjof`the present lnvention is about 1 mil thick.

Preferably, core layer 10 is a blend of ethylene vinyl alcohol copolymer and a polyamide or copolymer comprising polyamide comonomers.
Core layer 10 preferably forms between about 5% and 25% of the total fllm thickness. Thicknesses less than about 5~ result in a very thin film with possible voids in the barrier material. Thicknesses greater than about 25%
make the film difficult to s~retch or rack, and also result in increased cost due to the expensive barrier component.

Tntermediate layers 12 and 14 are preferably acid or acid anhydride-modified polymeric material which can bond the core layer 10 to the outer layers 16 and 18. This material preferably includes a graft copolymer of a polyolefin, such as polyethylene, or ethylene-ester copolymer substrate and an unsaturated carboxylic acid or acid anhydride, blended with a polyolefin, such as polyethylene, or ethylene-ester copolymer.

Outer layers 16 and 18 are preferably a three component blend of LLDPE, LMDPE, and EV~. These outer layers preferably include from about 40% to about 60% by weight of LLDPE, from about 20% to about 30% by weight of LMDPE, and from about 20% to about 30% by weight of EVA. More preferably, the outer layers 16 and 18 include about 50%, by weight, of a LLDPEs abou~
25%, by weight, of LMDPE, and about 25%, by weight, of E~A.

404/850830/5l7 7()~

., The EVA has a vinyl acetate (VA) content of preferably between about 3.5 and 9% by weight and more preerably between about 3.5 and 5% by weight. At VA contents g~eater than about 9%, the multilayer film becomes too sticky or tacky for many applications, or requires the use of relatively large amounts of slip and anti-block additives.

The film is preferably irradiated with between about 3 and 13 megarads (M.R.) of irradiation, even more preferably between about 5 ~nd 10 M,R., prior to orientation of the film. Orientation is done by racking or stretching the film at a racking ratio of from between about 3.0 and about 5.0 times the original dimensions of the film in the longitudinal (machine) and transverse directions.

.~. ~
A sample film was prepared by blending 50% of LLDPE (Dowlex 2045), 25%
LMDPE (Dowlex 2037) and 15% EVA having a vinyl acetate of about 3.6%, blended with about 10% of a masterbatch concentrate containing slip and antiblock additives compounded with EVA of about 3~% vinyl acetate content by weight. This outside blend layer was coextruded with a core layer containing a blend of 90% EVOH (EVAL H) and 10% of a nylon 6/nylon 12 copolymer (Grillon CA-6), and an intermëdiate adhesive ~Norchem Plexar 3150), .
The Dowlex 2045 may be obtained from Dow Chemical Company. This is an especially preferred LLDPE for use in this invention, and is a copolymer of ethylene and octené and has a density at 23C of about 0.920 grams per cubic centimeter and a melt flow index of from about 0.7 to about 1.2 g~r~s per ten minutes (as measured by ASTM-D-1238, E-28). LLDPE adds toug~ness to the film.

A preferred LMDPE is Dowlex 2037, also obtainable from Dow Chemical Company. This resin is a copolymer of ethylene and octene and has a density at 23C of about 0.935 grams per cubic centlmeter and a melt flow index of about 2.55 grams per ten minutes (ASTM-D-1238, E-28). The LMDPE imparts stiffness, i.e. high modulus, to the film without significantly sacrificing ~ r~J~ a~

... . ..

7~
, .~ g toughness. The hlgh modulus characteristic of the ilm i8 especially desirable in form-fill-seal applications where the fllm i8 fed as a lay-flat film and then formed on a formln~ shoe into a tube.

The EVA of the outside blend layer is commercially available from El Paso P~lyolefins Company under the trade designation El Paso PE 204-CS95.
This material has a density at 23C of from about 0.9232 to about 0.9250 grams per cubic centimeter and a melt flow (ASTM-D-1238, E-28) of about 2.0 0.5 grams per ten ~10) minutes. The vinyl acetate content o~ this EVA ls about 3.6% by weight.
.
EVA improves the processability of the film, and also provides a sealing layer which can be adequately sealed at relatively low temperatures, or else provides a stronger seal at a given temperature, than many other polymeric resins.

The EVOH of the core blend layer was EVAL H, available from EVAL
Company of America and having an ethylene content of about 38% by weight and a melt index of about 1.5 grams/10 minutes. Other suitable EVOH resins include EVAL E, EVAL F, and EVAL K, as well as blends of the above, and preferably such resins or blends having a melt index of between about 1 to 4 grams per ten minutes (ASTM 1238). Griilon CA-6, available from Emser Industries, was blended with the EVOH. The Grillon CA-6 is a nylon copolymer hav~ about 60% nylon 6 and about 40% nylon 12 by weight.
' Although nylon 12 would be effective alone as a blending material in the core layer, this is a relatively expensive material. Nylon 6 alone would be effective as a blending material, but with some difficulty in processing. The particular blend employed proved to be very advantageous in providing an economical yet effective means for providing a core blend having the good barrier properties associated with EVOH, but with the processing and elongation advantages oE nylon. Another suitable nylon copolymer is Grillon CR-9, having 20-30% nylon 6 and 70-80% nylon 12 by weight.

.

8a~7V~3 The intermediate adhesive material, Norchem Plexar 3150, i6 a low density polyethylene-based anhydride-modified resin produced by Norchem.
Other anhydride-modified adhesives such as CXA-162 (duPont) can also be used ~as the intermediate adhesive.

The polymer melt from the coextrusion die was then cooled and cast into a solid tape which was irradiated with about 8 megarads of irradlation. The tape was then heated to about 110C in an oven and blown into a bubble. The bubble was expanded to about 3.5 times its original dimensions in both the machine (longitudinal) and transverse directions, and then deflated and ply separated into single wound film rolls. The final film had a thickness of about one mil, and in addition to the shrink properties imparted by orientation, exhibited excellent toughness, good optics, burn out resistance, resistance to tear propagation, and heat sealability. The film also exhibited good abuse r~sistance and the necessary stiffness and lower tack required for packaging applications and was substantially free of voids in the EVOH/polyamide blend layer.

Test results for the sample film are listed below in Table I.
TABLE I
Tensile at Brea~
2 and 73F (PSI) Avg. Longitudinal1151.0xlOO
Std. Dev382.3xlOO
95% C.L.130.9xlOO
Avg. Transverse887.5x100 Std. Dev.25.4x100 95% C.L.40.4x100 Elongation at Br4eak and 73F (%) Avg. Longitudinal 86.
Std. Dev.6.
95% C.L. 9.
Avg. Transverse151.
Std. Dev.21.
95~ C.L.33.

8~7~

Modulus a5 73F
(PSI) Avg. Longitudinal 89.7xlO00 Std. Dev. 3.2xlO00 95% C.L. 5.2x1000 Avg. Transverse 81.6xlO00 Std. Dev. 4.5xlO00 95% C.L. 7.2x1000 Tear Propagatio~
at 73F (grams) Avg. Longitudinal 13.44 Std. Dev. 1.45 95% C.L. 2.31 Avg. Transverse 19.25 Std. Dev. 3,30 -- 95% C.L. 5.26 Free Shri7k ~%) at 220 F
Avg. Longitudlnal 22.
Std. Dev. l.
95X C.L. 2.
Avg. Transverse 33.
Std. Dev. ~ 1.
95% C.L. 1.
Free Shrink at 240F

Avg. Longitudlnal 66.
-- - Std. Dev. l.
95% C.L. l.
Avg. Transverse 64.
Std. Dev. l.
95% C.L. 2.
~,`` , ' .
Free Shrink at 260F
Avg. Longitudinal 69.
Std. Dev. 0.
95% C.L. 0.
Avg. Long. 64.
Std. Dev. 1.
95% C.L. 1.

- Shrink Properties ~;
at 220F
Shrink Force (lbs) 8 Avg. Longitudinal 0.439 Std. Dev. 0.013 95% C.L. 0.021 Avg. Transverse 0.533 Std. Dev. 0.015 95% C.L. 0,024 Shrink Tension (PSI) Avg. Longitudinal 374.
Std. Dev. 22.
95% C.L. 35.
Avg. Transverse 434.
Std. Dev. 15.
95% C.L. 23.
- Shrink Properties at 240~F
Shrink Force (lbs.) Avg. Longitudinal 0.459 Std. Dev. 0.013 95% C.L. 0.021 Avg. Transverse 0.500 Std. Dèv. 0.014 95% C.L. 0.022 O -; Shrink Tension ~PSI) v'~
,; Avg. Longitudinal 389. _ I
Std. Dev. 11.
95% C.L. 18.
Avg. Transverse 414.
- Std. Dev. 14.
- ` 95% C.L. 22.
Shrink Properties at 260~F
Shrlnk Force (lbs) Avg. Longitudinal 0.383 Std. Dev. 0.034 - 95% C.L. 0.054 Avg. Transverse 0.509 Std. Dev. 0.037 95% C.L. 0.059 .
.~ .
.
.

~8~73{~

Shrink Tension (PSI) _~.
; Avg. Longitudinal 338.
Std. Dev. 31.
95X C.L. 49.
Avg. Transverse 457.
- Std. Dev. 29.
95% C.L. 46.
Optical Properties at (3)710 .
Avg. 2.9 , Std. Dev. 0.2 95% C.L. 0.4 Clarity (%) 11 Avg. 65.2 Std. Dev. i 3.6 , 95% C.L. 5.7 - Gloss (45o~ 12 , ' ~ Avg. 84.
Std. Dev. 1 2.
95% C.L. 4.
.
, Oxygen Transmiss~n at 73JF, 0% RH
t, Sample 1 7.3 Sample 2 7.6 Sample 3 7.8 i The follow~ng footno~es apply to Table I.

1. ASTM D882-81.

2. All values in Table I ,are averages obtained from four (4) replicate measurements.

3. C.L. is Confidence Limit - e.g., if th~ reported average value was 10 and the 95% C.L. was 2, then if one hundred replicate readings were made, 95 of them would have a value between B and 12, inclusive.

4. ASTM D-882-81.

404/8S0~30/5/13 . .

8~7~3 . . .
.... ;, .. -....- ,~ ..
~ 5. ASTM D-882-81.
. . . ~, . : , ~ 6. AS~M D-1938-7g.
... ... . . . .
;` ; - 7. ~S~M D-2732-70 (reapproved 1976).

- ~ 8~ ASTM D-2838-81 tshrink frae ~ hr~nk tenslon x ~ hlckne~ in ;~ :.:, .
- ; ~ils x 1000) - ~- - ~ : .
, . ~ .. ... ~ .
~ 9. ASTM D-2838-81 .;~ .: ; :., ... : .
: ;1~;. ' . ;:- . .
~ 10. AST~ D-1003-61 (reapproved 1977) :,-,,. : . .
. :,- . :
~ , - - 11. ASX~ D-174~-70 ..... . . .
.......... .
. :. ,.. ~..;,, ~ ...
~ 12. AST~ D-2457-70 (reapproved 1977) :~. r~
~ - EXAMPLE 2 ~. ~ .; ., ~ . . .
A sample film was prepared according to the same procedure and formulatio~ described in Example 1, having Pl&xar 158 as an intermedlate ~, ad~esl~e layer, but withou~ a polyamide ~in the core layer. Thi6 film xhiblted ~oids ln the EVOH layer. Processed mea~ ~bologna) packaged ln ehe ; film was fou~d to discolor at regio~s ad~acent ehe void areas of the EVOH
: .~.. ~ . . . .
- ; ; ~ ; core laye~.
.... ~... ,; . .
Obvious difications to the invention as descrlbed may be made by one ; s~illed in t~e art without departing from the spirit and scope of the clalms ;; as Presented below.

. . .

.
:' ' , .
.. . . .

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An oriented multilayer film comprising (a) a cross-linked core layer comprising a blend of an ethylene vinyl alcohol copolymer and a polyamide resin:
(b) two cross-linked interior layers each comprising an adhesive resin; and (c) two cross-linked surface layers each comprising a three-component blend of a linear low density polyethylene, a linear medium density polyethylene, and an ethylene vinyl acetate copolymer.

2. An oriented five-layer film comprising (a) a cross-linked core layer comprising a blend of (1) from about 80%, by weight, to about 99%, by weight, of an ethylene vinyl alcohol copolymer and (2) from about 1%, by weight, to about 20%, by weight of a polyamide resin;
(b) two cross-linked interior layers each comprising an adhesive resin; and (c) two cross-linked surface layers each comprising a blend of (1) from about 40%, by weight, to about 60%, by weight, of a linear low density polyethylene, (2) from about 20%, by weight, to about 30%, by weight, of a linear medium density polyethylene, and (3) from about 20%, by weight, to about 30%, by weight, of an ethylene vinyl acetate copolymer.

3. An oriented five-layer film comprising (a) a cross-linked core layer comprising a blend of (1) about 90%, by weight, of an ethylene vinyl alcohol copolymer, and (2) about 10%, by weight, of a polyamide resin;
(b) two cross-linked interior layers each comprising an acid or acid anhydride-modified polymeric material;
and (c) two cross-linked surface layers each comprising a blend of (1) about 50%, by weight, of a linear low density polyethylene, (2) about 25%, by weight, of a linear medium density polyethylene and (3) about 25%, by weight, of an ethylene vinyl acetate copolymer.

4. The film of claims 1, 2 or 3 wherein said ethylene vinyl acetate copolymer comprises from about 3.5%, by weight, to about 9%, by weight, of vinyl acetate derived units.

5. The film of claims 1, 2, or 3 wherein said ethylene vinyl acetate copolymer comprises from about 3.5%, by weight, to about 5%, by weight, of vinyl acetate derived units.

6. The film of claims 1, 2, or 3 wherein said ethylene vinyl acetate copolymer comprises from about 3.6%, by weight, of vinyl acetate derived units,

7. The film of claims 1, 2 or 3 which has been cross-linked with from about three megarads to about thirteen megarads of irradiation.

8. The film of claims 1, 2 or 3 which has been cross-linked with from about five megarads to about ten megarads of irradiation.

9. The film of claims 1, 2 or 3 which has been cross-linked with about eight megarads of irradiation.

10. The film of claims 1, 2 or 3 which has been oriented by racking at a racking ratio of from about 3,0 to about 5.0 in both the longitudinal and transverse directions.

11. The film of claims 1, 2 or 3 which has been oriented by racking at a racking ratio of about 3.5 in both the longitudinal and transverse directions.

12. A method of making an oriented multilayer film comprising (a) simultaneously coextruding a core layer of a blend of an ethylene vinyl alcohol copolymer and a polyamide resin, two intermediate layers of an adhesive material, and two outer layers of a blend of a linear low density polyethylene, a linear medium density polyethylene, and an ethylene vinyl acetate copolymer;

.16.

(b) rapidly cooling the coextruded film;

(c) Collapsing the cooled film;

(d) heating the collapsed film to a temperature between about 105°C
and 115°C; and (e) stretching and orienting the heated film.

13. The method of claim 12 wherein the coextruded film is cooled to about room temperature.

14. The method according to claim 12 wherein the heated film is oriented by racking at a racking ratio of from about 3.0 to about 5.0 in both the longitudinal and transverse directions.

15. The method according to claim 12 wherein the heated film is oriented by racking at a racking ratio of about 3.5 in both the longitudinal and transverse directions.

16. The method according to claim 12 further comprising the step of reheating the oriented film to a temperature near its orientation temperature to provide a substantially non-shrinkable film.