Preparing a heat-shrinkable laminate film

The invention of course includes articles, especially foodstuffs and more especially bone-in meat and cheese packaged with filirb\pf the invention which has been heat-shrunk.

The following Examples illustrate the invention.

*4 a 9e • 9ft ·**’ 10 ft ft ft * •«« ** ft * ft 0 Oft » 9 » ft ft ft ft ft « «ft ft ft 4ft ft ft ft » ft* ft ft * ft ft * ft ft ft· ftft-ft &

ftft ft ft » «

Oft ft

EXAMPLE 1

A laminated tape of width 4 inches (10.2 cm.) and consisting of the following layers was produced by the above-described co-extrusion process with concentric annular dies4 14 mils (356 microns) thick layer of ethylene-vinyl acetate copolymer/2.0 mils (51 microns) thick layer of HEVA/ 4.5 mils (114 microns) thick layer of ethylene-vinyl acetate copolymer. The first-mentioned layer is that which becomes the radially innermost layer of the extruded tubing, and the same notation applies to the other Examples hereinafter. The content of vinyl acetate-derived units in the (unhydrolysed) ethylene-vinyl acetate copolymer in this / laminate was from 3.5 to 5% by weight and its melt flow index was 0.5 as determin .d by'AETM Method D 1238, Condition E.

The HEVA was the product of a 99% hydrolysis of an ethylenevinyl acetate copolymer having 69 mole percent of vinyl acetate-derived units. It had a melt flow index of about

<img file="AU507033B2_D0001.tif" />

6.0 a© determined by ASTM Method D123B, Condition L. The temperature of all three extrudates as they left the die orifices was approximately 425°F. (218°C.). The tape was cooled and when flattened had a width of 4 inches (10 cm.),

<img file="AU507033B2_D0002.tif" />

*

This tape was passed twice through the scanned beam of a £5

0.5 MEV insulated core transformer electron accelerator where «33 ¢3¾ it received a total dosage of 6.5 MR. After irradiation, the OQ flattened tape was passed through boiling water, inflated into a bubble, and oriented to form tubing 16 inches (41 cm.) in diameter and 2.3 mil (5Θ microns) thick, which

Was laid flat. The bubble was extremely stable and the appearance of the film was good. The resulting film had a 22% free shrinkage in the longitudinal direction and a 32% free shrinkage in the transverse direction at 195°F. (91°C.).

Free shrinkage is determined by ASTM Method D2732. The

HEVA layer of the film was 0.20 mil (5.1 microns) thick.

The shrink tensions at the 195°F. (91°C.) temperature were 311 p.s.i. (22 Kg./sq.cm.) in the longitudinal direction and 629 p.s.i. (44 Kg./sq.cm.) in the transverse direction, as

<img file="AU507033B2_D0003.tif" />

<img file="AU507033B2_D0004.tif" />

<img file="AU507033B2_D0005.tif" />

measured by ASTM Method D2838.

Bags were made from the oriented tubing prepared in this Example by making a transverse heat seal across the width of the tubing and then severing the tubing parallel to and immediately behind the seal. Beef steaks were inserted into the bags, air was withdrawn from the packages, the bags

<img file="AU507033B2_D0006.tif" />

I were closed with, a metal clip, and then shrunk tightly around the water bath

210°F. (88 chilled to steaks by placing the package briefly in a hot maintained at a temperature of from 190°F. to to 99°C.). The package was then immediately

34°F. (1°C.) and stored at that temperature for four weeks. The colour of the steak was evaluated periodically. After storage, the colour retention and were removed to bloom for 30 minutes in air to steaks had an adequate from the package, allowed appearance, and next placed in trays and overwrapped, and then put into a display case. After four days in the display case, beef steaks still had acceptable colour. The colour retention‘of demonstrated film and its the steak at the end of the four week period the low oxygen permeability of the laminate usefulness as a shrinkable packaging material.

EXAMPLES 2 and 3 • 9ft ? » ft « ft *9 ·

® · ft 9 ft «ββ· » 9

6

<img file="AU507033B2_D0007.tif" />

Using extrusion conditions similar to those of

Example 1, a laminated tape of width 4¾¹¹ (11.4 cm.) and consisting of the following layerswas produced:

• 17 mils (4-32 microns) thick layer of ethylene-vinyl

HEVA/5.5 mils (140 microns) thick layer of ethylene-vinyl acetate copolymer. The content of vinyl acetate-derived units in the (unhydrolysed) ethylene-vinyl acetate copolymer in this laminate was 3.5% by weight and its melt flow index was 0.5 as determined by ASTM Method D1238. Condition E.

The same HEVA polymer was used as in Example 1. An unirradiated tape of this composition would not expand into a bubble without breaking. The flatten? tube was irradiated, passed through boiling water, oriented by the bubble technique and laid flat, all as described in Example 1. Bubbles could be produced with inflated tubing which had been irradiated to dosage levels in the 3 to 6 MR range and satisfactory continuous production could be maintained with tapes irradiated to dosages of 7.5 MR and 9.5 MR respectively. Increasing the dosage beyond the 9.5 MR level was not attempted since experience with other ethylene-vinyl acetate copolymer laminates has shown that in general at dosage levels much beyond 12 MR the material becomes too stiff and difficult to orient and seal.

The Table below summarises the characteristics of the film laminates of Examples 2 and 3, the irradiation dosages being as shown.

EXAMPLE 2

EXAMPLE 3

Irradiation Dosage (MR)

7.5

9.5

Total gauge thickness of laid-flat laminate, mils (microns)

2.3 (58) 2.3 (58)

Thickness of HEVA layer, mil ft ft ft « ft ft (microns)

0.225(5.7) 0.225 (5.7)

<img file="AU507033B2_D0008.tif" />

<img file="AU507033B2_D0009.tif" />

<img file="AU507033B2_D0010.tif" />

β ft

9' © ft O ft ft » e ft ft ft &lt;f ft « ft ft » · e e e ft • ft ft ft ft ft ft ft O ft e ft e ® o e c © a »

ft 0 ft 6 ft ft ft ft

<img file="AU507033B2_D0011.tif" />

<img file="AU507033B2_D0012.tif" />

<img file="AU507033B2_D0013.tif" />

<td></td><td> EXAMPLE 2</td><td> EXAMPLE 3</td>

<td> Shrink Energy at 195°F. (91°C.):</td><td></td><td></td>

<td> Transverse· p.s.i.(Kg./sg.cm.)</td><td> 274 (19)</td><td> 252 (18)</td>

<td> Longitudinal, p.s.i=(Kg./sq.cm.)</td><td> 510 (36)</td><td> 569 (40)</td>

<td> Shrink Percent at 195°F. (91°C.):</td><td></td><td></td>

<td> Transverse</td><td> 22</td><td> 23</td>

<td> Longitudinal</td><td> 34</td><td> 34</td>

<td> Oxygen Transmission at 73°F.(23°C.)</td><td></td><td></td>

<td> (cc/m .24 hrs.atm.)</td><td> 1.4</td><td> 1.6</td>

<td> Tear Resistance, grams</td><td></td><td></td>

<td> Longitudinal</td><td> 27.38</td><td> 20.38</td>

<td> Transverse</td><td> 11.75</td><td> 8.30</td>

<td> Impact Resistance, cm.Kg.</td><td> 25.8</td><td> 28.0</td>

<td> Packages of beef steak were</td><td> made using</td><td> the laminate</td>

<td> of Examples 2 and 3, as described in</td><td> Example 1.</td><td> In the</td>

test with the films of all three Examples, satisfactory colour retention and storage lifetime was achieved.

EXAMPLE 4

Using the above-described co-extrusion process and extrusion conditions similar to those of Example 1, a tape was prepared consisting of the following layers:

mils (406 -microns) thick layer of ethylene-vinyl acetate 2 mils copolymer>/( 51 microns) thick layer of HEVA/ 6 mils (152 microns) thick layer of ethylene-vinyl acetate copolymer. The (unhydrolysed) ethylene-vinyl acetate

<img file="AU507033B2_D0014.tif" />

copolymer used consisted of a blend of 75% by weight of an ethylene-vinyl acetate copolymer having 3¾% by weight of acetate-derived units and 25% by weight of an ethylene-vinyl acetate copolymer having 9% by weight of vinyl acetate5 derived units. The same HEVA polymer was used as in

Example 1. The width of the laid-flat tubing was 4 3/16“ (10.6 cm.) and the flattened tubing was irradiated to a dosage of approximately 7.5 MR. The tubing was oriented out of a boiling water bath, as“ described in Example 1, the resulting oriented tubing being 16 inches (41 cm.) in from 2.0 to 2.5 mils « 9

99

99 ft 9 9

9 9 9 •* a a 9 ft

9 (51 to 63 microns).

EXAMPLE 5

Using the above-described ft9

9

9ft ea ft

9ft ft &lt;· • Oft and extrusion conditions similar to those of Example l_f a • 6 9 9 9 a I ft tape was prepared consisting of the following layers:

mil (381 microns) thick layer of ethylene-vinyl acetate copolymer having 9% by weight of vinyl acetate-derived • Oft ft · ft ft « 9 9.

units/a 2.5 mil thick layer of HEVA/9 mil thick layer of ethylene-vinyl acetate copolymer having 3¾% by weight vinyl acetate-derived units.

The same

HEVA polymer was used as in Example 1 . The flattened tape was 4 3/8“ wide (11,1 cm.) and was irradiated to a dosage level of <> e « · e

ft ft 9 ft ft ft ft ft approximately 6.5 MR, after which the inflated tape was oriented by the trapped bubble technique from a hot water

I

L·-

<img file="AU507033B2_D0015.tif" />

2F

-X2:

bath maintained at 210°F. (99°C=)

The resulting laid-flat tubing had a width of 14 inches (36 cm.) but difficulty was •U*u — of ethylene-vinyl acetate copolymer having 9% by weight of vinyl acetatederived units had a tendency to stick and weld to itself.

EXAMPLES 6 and 7

Whereas in relatively low the HEVA had a by ASTM Method melt melt the foregoing Examples the flow index flow index

D1238 Condition due to increased ethylene unit

HEVA had a (of 6.0), in Examples 6 and 7 of about 19.0, as determined

L. The melt flow change is content in the copolymer

0 • « «

9 A

0 9 9

In Example 6 the content of vinyl acetate-derived • 0

0

0 • 0 « « units in the unhydrolysed was 3.5% by weight and in ethylene-vinyl acetate copolymer

Example 7 it co-extrusion conditions similar to those of Example prepared having the following layers:

thick, layer of ethylene-vinyl acetate was 9% by weight.

process and extrusion

1, a tape was mil (406 microns) copolymer/2 mil · e ο « ®

O000 • 0 tt 0

0 «> ® (51 microns) thick, layer of the HEVA/6 ethylene-vinyl acetate copolymer. The mil thick layer of flattened tape

0«· • ' « 0 • 0 · width was 4 3/16 (10.6 cm.) and this flattened tape was irradiated to a dosage level of approximately 7.5 MR. The tape was then preheated and oriented from boiling water in

ί.

i.

j i ft

<img file="AU507033B2_D0016.tif" />

by the trapped bubble technique. The laid-flat width of the thus obtained tubular film was 16% (42 cm.) and its thickness ranged from 1.8 to 2.5 mils (46 to 63 microns). No extrusion or orientation problems were encountered.

EXAMPLE 8

Using the above-described coextrusion process and extrusion conditions similar to those of Example 1, a tape was prepared having the following layers: a 12 mils (305 microns) thick layer of low density polyethylene/ a 1.5 mils (38 microns) thick layer of HEVA/a 10 mils 10 (250 microns) thick layer of low density polyethylene.

·

The ethylene-vinyl acetate copolymer and HEVA polymer employed were as described in Example 1. This flattened tape was 4 inches (10 cm.) wide and was subsequently irradiated to a dosage of approximately 8.5 MR. The irradiated tape was preheated and oriented from a boiling hot water bath. The final tubing gauge was in the range of 2.2 to 2.8 mils (56 to 71 microns) and the film had a free shrinkage of 26% in the longitudinal direction and 36% in the transverse direction at 195°F. (91°C.).

The foregoincf Examples demonstrate that a shrinkable laminate film having a HEVA layer can be successfully manufactured. All the films produced in the Examples had oxygen permeabilities of leas than 5.0 cc/m . 24 hrs.atm. at 73°F. (23°C.) and free heat shrinkage of more than 10% in at least one direction. -Tue-TL-amlna-tes*-e-f—the*

<img file="AU507033B2_D0017.tif" />

<img file="AU507033B2_D0018.tif" />

1«^

They were all prepared without the use of plasticisers and stabilisers which must be used for commercial • φ ft β β « t» » t © « a ft ft · α · « β ο* o

c « η · e ' a *··«>

ft a ft ft·©* • ' ·

-prior art heat shrinkable films with very low oxygen

<img file="AU507033B2_D0019.tif" />

<img file="AU507033B2_D0020.tif" />

i