CA1113898A

CA1113898A - Coextruded laminar thermoplastic bags

Info

Publication number: CA1113898A
Application number: CA318,490A
Authority: CA
Inventors: Robert H. Olson
Original assignee: Mobil Oil Corp
Current assignee: Pactiv LLC
Priority date: 1977-12-27
Filing date: 1978-12-22
Publication date: 1981-12-08
Also published as: JPS54100475A; DE2855053A1; NL7812412A; IT7823615V0; BE873112A; GB2011317B; FR2413853A7; GB2011317A; JPS6151548B2

Abstract

ABSTRACT

A thermoplastic bag particularly adapted for the containment and storage of foods comprising a laminar bag structure having an interior layer of a high density polyethylene copolymer and an exterior layer of polypropylene. The layers are intimately and continu-ously bonded together at their interface. Such bag structures are suitable for the containment of food-stuffs while they are being heated or reheated following storage.

Description

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COEXTRUDED LA~INAR THE~MOPLASTIC BAGS

The present invention relates to thermoplastic bag structures which have been fabricated from a thermo-plastlc fllm lamlnate comprising two layers of fllm whlch are formed from dissimilar thermoplastic resins.

In the past, polyethylene bags have been used for food storage and, in particular, refrigerated food stora~e. Such food container bags are particularly con-venient for the storage of food left-overs which may be lntended for later reheating. The bulk of such food storage bags have been formed from low den~ity, i.e.
0.91 to 0.93 g/cc, polyethylene. For reheating pur-poses foodstuffs must be removed from such low density polyethylene bags be¢ause of their tendency to partlally melt and adhere to the surfaces Or ¢ooking ve3sels at temperature~ on the order of 212F and below.

To remedy this deficiency of low density poly-ethylene bags, attempts have been made to employ polyester bags, such as polyethylene terephthalate, for such elevated temperature appllcations as "boil" bags, however such rilms are difficult to seal and more importantly are prohibitively expensive for such dispos-able bag applicationq.

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-2-The present invention provides for an economi-cal thermoplastic bag which may be employed to contain roods during storage and, most importantly, may be used to contain such foods during reheating preparatory to serving. The bag structureq Or the present inventlon comprise a two layer laminar structure, the inner bag layer or that surrace layer in contact with the food-sturrs, being rormed from polyethylene and preferably a high density ethylene copolymer. The outer layer Or the bag laminate or that sur~ace Or the bag which comes into direct contact with the cooking vessel, comprises a ply Or relatively thin polypropylene film. The outer poly-propylene film layer maintainq the inner more thermally suscept~ble polyethylene layer out Or contact with the surraces Or the cooking vessel and hence improves the bag's ability to withstand higher temperaturea. The polypropylene layer, having a melting or sticking tem-perature on the order Or above 150C is stable and will not atick to the vesqel side walls while roodsturr~ are being reheated therein. Obviously the bag containing roodsturrs i~ intended to be immersed in a rluid such as water during the reheating operation. Accordingly, the present invention provide~ laminar bags for the optimum storage and containment of roodsturfs which may then be reheated without rirst removing them ~rom the bag. The bag ls oon~tru¢ted from a two-ply laminate comprislng an lnner rllm layer Or a high density ethylene/alpha-olefin copolymer and an outer layer Or polypropylene rilm. The hlgh density ethylene copolymer preferably comprises ethylene which has been copolymerized with a minor amount, on the order Or le~s than 10S, Or another alpha-olerin having rrom about 3 up to about 10 carbon atoms, for example octene-1.
~, , A tubular thermoplastic laminate waq prepared utilizing conventional blown tubular rilm coextrusion ~ . ~ ................. .
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techniques whereby the final inner-tube layer comprised a 1.0 mil thick layer of high density polyethylene copolymer and a 0.2 mil thick outer layer o~ polypro-pylene. me continuous laminar tube was subsequently converted lnto bag ~tructures utilizing techniques well known in the prior art. The high den~ity polyethylene copolymer inner layer was a copolymer of ethylene and about 3% by weight of octene-1. This re~in is identi-fied by the manufacturer as ~Alathon 78lO"* and has the following typical physical properties for a 1.25 mil ~ilm extruded at a 4.3/1 blow-up ratio:

Density .945 g/cc Melt Index .25 g/10 min.
Tensile Yield (MD) 3000 psi ~
tTD) 3100 psi ~-Elongation (MD) 660%
(2n/min) 7~0S
Secant Modulus (MD~ 80M psi (TD) 82M psi Elmendorf Tear (MD) 45 gm/mil ~-(TD) 247 gm/mil ~
Spencer Impact 2.8 in. lbs/mil Dart Drop (26") 115 gm/mil Tear Propagation (MD) 3.2 Kg force ASTM D-2582 (TD) 3.7 Kg ~orce The propylene outer layer was fabricated from resin identified by the manu~acturer as ~Tenite 612 F"**
which has the ~ollowing typical physical properties:

Density .902 g/cc Flow Rate 4.5 g/10 min Tensile, Yield 5000 psi Vicat So~tening Point 145C ~, Trademark ** Trademark , .. .

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The two ply laminated film comprising inte-grally adhered layers of the high density ethylene-octene-l copolymer and the polypropylene outer layer had the following physical properties:

Film Gauge 1.20 mil 91OW-Up Ratio 2.5/1 Tensile Yield (MD) 3200 psi (TD) 3400 psi Elongation (HD) 525S
(TD) 850S
Tear-Elmendorf(MD) 24 gms/mil (TD) 477 gms/mil Modulus (HD) 80M psi (TD) 105M psi For purposes of the present invention the : thicknes~ of the inner high density poiyethylene copoly-mer layer may vary from about 0.5 mils up to about 3.0 ` mils and is preferably 1.0 mils thick. The outer poly-propylene layer may vary from about 0.1 mil up to about

3.0 mil in thlckness and is preferably about 0.2 mil thick.

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Claims

1. A thermoplastic resin bag made of a two layer laminate, the outer layer of which comprises polypropylene and the inner layer a high density ethylene/alpha-olefin copolymer comprising ethylene copolymerized with less than 10% by weight of the alpha-olefin.

2. A thermoplastic resin bag as claimed in claim l in which the ethylene/alpha-olefin copolymer comprises ethylene copolymerized with less than 10% by weight of octene-1.

3. A thermoplastic resin bag as claimed in claim 2 in which the thickness of the inner layer is from 0.5 to 3.0 mils.

4. A thermoplastic resin bag as claimed in claim 3 in which the thickness of the outer layer is from 0.1 to 3.0 mils.