Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2000-09-11
2003-02-11
Nolan, Sandra M. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C426S105000, C426S129000, C426S135000, C426S278000, C428S475800, C428S476100
Reexamination Certificate
active
06517920
ABSTRACT:
CROSS REFERENCE TO RELATED PATENT APPLICATION
The present patent application claims the right of priority under 35 U.S.C. §119 (a)-(d) of German Patent Application No. 199 43 909.5, filed Sep. 14, 1999.
FIELD OF THE INVENTION
This invention relates to tubular, seamless, at least five-layer, biaxially stretched, shrinkable casing for wrapping pasty or liquid products, in particular foodstuffs, in a durable and wrinkle-free manner, which casing is characterised by extraordinarily high water vapour and oxygen barrier properties and exhibits low adhesion to the contents.
BACKGROUND OF THE INVENTION
Seamless plastic casings are frequently used for wrapping pasty or liquid products for manufacturing or packaging purposes. Typical applications are the use of such casings for the production and/or packaging of boiled and boiling sausages, processed cheese, soups or pastes having a high fat content. Depending upon the product to be produced or packaged, however, wide-ranging and specific requirements must be met in order to comply with practical requirements.
In relation to sausage production, these requirements may, for example, include:
good barrier properties
heat resistance up to sterilisation temperature
good adhesion to the contents
elevated shrinkage
elevated strength, dimensional stability, tautness
good peeling behaviour, easy peelability, good slicing behaviour
good conversion properties, in particular gatherability
good colouring properties
good printability and reliable printing ink adhesion
compliance with foodstuffs legislation (EC Directives, Bundesamt für gesundheitlichen Verbraucherschutz und Veterinärmedizin [German Federal Office for Consumer Health Protection and Veterinary Medicine] (BGVV), Food & Drug Administration (FDA))
environmental compatibility of the materials used.
Hitherto known, commercially available multilayer, biaxially stretched, seamless casings are specifically tailored for the production and/or packaging of meat products, in particular sausage, and, to a greater or lesser extent, meet the above-stated requirements. There are, however, certain applications in which in particular the barrier properties of commercially available casings are inadequate and where moreover elevated adhesion of the casing to the contents is not necessary or is even disadvantageous. Such applications include, for example, the production of animal food having a desired storage life without refrigeration of several months or the packaging of contents which react particularly sensitively to loss of moisture and have a tendency to dry out, such as marzipan. If contents of the stated type are packaged in conventional commercial multilayer, biaxially stretched, seamless plastic casings and stored for an extended period, the contents undergo a distinct loss in weight, which is usually accompanied by creasing of the casing, over a period of a few weeks to months due to permeation of water vapour originating from the contents outwards through the casing as a result of inadequate water vapour barrier properties of the casing, and/or oxidation processes occur on the surface of the contents, which may impair visual and/or sensory properties, due to permeation of atmospheric oxygen inwards through the casing as a result of inadequate oxygen barrier properties. Any obvious discrepancy between the weight of the contents and the weight printed by the manufacturer, creased appearance of the casing and/or surface discolouration of the contents give the consumer an impression that the product is old and stale, so that it is rejected by the consumer.
Another disadvantage of commercially available plastic casings for use as a casing for animal food is the elevated adhesion which such casings develop towards contents containing protein, such as for example meat products. While for sausage products for human consumption adhesion must be sufficiently high in order to avoid the formation of a coating of jelly which is considered unappetising, consumers desire low adhesion for casings for animal food, for example dog sausage, so that, once the casing has been cut, the contents slide out easily and, if possible, without any necessity to touch the contents, which is considered unpleasant.
A casing suitable for the stated applications is accordingly characterised by the following core properties which are in addition to or at variance with the range of requirements for sausage casings described above:
extraordinarily good barrier properties towards oxygen (oxygen permeability <5 ml/m
2
·d·bar at 23° C. and 75% relative humidity to avoid oxidation processes) and water vapour (water vapour permeability <2 g/m
2
·d at 23° C. and 85% relative humidity to avoid weight loss on extended storage without refrigeration),
low adhesion to the contents.
European application EP-A-0 107 854 describes a tubular, five-layer laminate consisting of an inner layer of thermoplastic resin, a middle layer of vinylidene chloride copolymer (PVDC), an outer layer of olefin resin and two adhesive layers between the main layers. Having an oxygen permeability of 50 ml/m
2
·d·atm (30° C., 100% relative humidity) and a water vapour permeability of 5 g/m
2
·d (40° C., 95% relative humidity), the casing exhibits inadequate barrier properties towards oxygen and water vapour and moreover contains PVDC, which contains halogen, as the water vapour barrier component, use of which is environmentally questionable and is thus now increasingly unacceptable.
DE-A-40 01 612 discloses a tubular, three-layer coextruded, biaxially stretched casing having an inner and outer layer of polyamide or a polymer blend containing polyamide and a middle oxygen barrier layer of aromatic polyamide or copolyamide. While this composite does indeed provide elevated oxygen barrier properties, it provides only a low to moderate water vapour barrier which is not adequate for several months' storage without refrigeration. Moreover, due to the polyamide-based inner layer, the inside of the casing adheres undesirably strongly to contents containing fat and protein.
DE-A-41 28 081 describes a multilayer, biaxially stretched tubular film which comprises as core layer at least one oxygen barrier ply of ethylene/vinyl alcohol copolymer (EVOH), aromatic or aliphatic (co)polyamide and, as inner layer, at least one water vapour barrier ply of aliphatic (co)polyamide. This casing meets the requirements for good water vapour barrier properties. However, during storage, moisture passes from the contents into the core layer, which acts as the oxygen barrier layer. Since the moisture accumulates in the core layer and cannot be released through the outer polyolefin layer, which acts as the water vapour barrier layer, oxygen barrier properties become ever poorer during storage. This casing is accordingly unsuitable for extended periods of storage, in particular for storage without refrigeration. An outer polyolefin layer furthermore has the disadvantage that, before being printed, the film must be subjected to an additional step, for example corona discharge, in order to ensure sufficient adhesion of the printing inks.
DE-A 41 28 082 describes an at least three-layer, biaxially stretched tubular film, which comprises an outer layer of aliphatic polyamide, an oxygen barrier core layer of EVOH, aromatic and/or aliphatic (co)polyamide and an inner polyolefinic water vapour barrier layer, preferably an ionomer polymer, which exhibits adhesion to the contents. The disadvantage of this casing is the adhesion of the inner layer to the contents and the elevated water vapour permeability of ionomer polymers in comparison with other polyolefins.
EP-A-0 530 538 describes a tubular, five-layer coextruded, biaxially stretched casing, which consists of an outer layer of polyamide, a secondary outer layer of coupling polyolefin or EVOH, which optionally has oxygen barrier properties, a middle layer of polyamide, a secondary inner layer of coupling polyolefin which has water vapour barrier properties and an inner layer of polyamide. Although this casing has proven water vapo
Schröder Nils
Wolf Detlef
Akorli Godfried R.
Franks James R.
Gil Joseph C.
Nolan Sandra M.
Wolff Walsrode AG
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