Heat shrinkable nylon food casing with a polyolefin core layer
AssigneeViskase Corporation
InventorStephen J. Vicik
Life of this patent
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Abstract
Tubular, biaxially stretched, heat shrinkable multilayer film food casings comprising inner and outer polyamide layers on either side of a core layer predominantly of one or more polyolefins such as VLDPE or EVA and a coextrusion process for making the film.
Claims36
A tubular, biaxially stretched, heat shrinkable, multilayer film, food casing consisting essentially of three polymeric layers:
- (a) an inner layer comprising a polyamide;
- (b) a core layer comprising at least 60% by weight of at least one polyolefin selected from the group of copolymers of ethylene with at least one C.sub.3 -C.sub.10 .alpha.-olefin, VLDPE, LLDPE, copolymers of ethylene with an alkyl acrylate, LDPE, HDPE, and blends thereof;
- and
- (c) an outer layer comprising a polyamide;
- wherein said core layer (b) is disposed between and directly adhered to said inner layer (a) and said outer layer (c), and said multilayer film has a shrinkage value of at least 20% in at least one direction at 90.degree. C.
A tubular, biaxially stretched, heat shrinkable multilayer film food casing comprising:
- (a) an inner layer comprising a polyamide;
- (b) a core layer comprising at least 60% by weight of a very low density polyethylene (VLDPE) copolymer of ethylene and at least one C.sub.4 -C.sub.8 alpha-olefin, said copolymer having a density less than 0.915 g/cm.sup.3 and a melt index less than 2 dg/min.;
- and
- (c) an outer layer comprising a polyamide;
- wherein said core layer (b) is disposed between inner layer (a) and outer layer (c), and said film has a shrinkage value of at least 10% in at least one direction at 90.degree. C.
A continuous process for making a tubular, biaxially stretched, heat shrinkable multilayer thermoplastic food casing comprising:
- (a) coextruding a melt plastified multilayer thermoplastic tube having an exterior surface and an interior surface through an annular die wherein said tube comprises an inner polyamide layer and an outer polyamide layer with a core layer between said inner and outer layers of at least one polyolefin;
- (b) cooling said coextruded tube below the melting point of each layer by applying water to the exterior surface of said tube;
- (c) transferring said cooled tube to an orientation zone wherein said tube is reheated to a temperature below the melting point of each tube layer followed by cooling while a fluid mass is admitted to the interior of said tube as said tube is passed between first and second means for blocking fluid flow along the interior of said tube thereby causing said tube to stretch circumferentially about the entrapped fluid mass and simultaneous with said circumferential stretching, said tube is stretched in a direction perpendicular thereto to produce a biaxially stretched tubular film;
- and
- (d) annealing said biaxially stretched film at elevated temperature to dimensionally stabilize said film thereby producing a multilayer film having a shrinkage value at 90.degree. C. of at least 20% or higher in at least one direction.
A process, as defined in claim 37, wherein said coextruded tube after cooling step (b) and prior to said stretching step (c), has its exterior surface contacted with water under conditions sufficient to cause said outer polyamide layer to absorb water to a level greater than 0.1 and less than 1.0 weight percent based upon the weight of the outer polyamide layer.
Dependencies are inferred from the claim text.