Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2000-09-11
2003-04-01
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S034800, C428S034900, C428S035400, C428S036910, C428S474400
Reexamination Certificate
active
06541087
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a multilayer, biaxially stretched, polyamide-based, polyvinylidene chloride copolymer-free (PVDC-free), plastic skin which exhibits elevated oxygen and water vapour barrier properties and in particular avoids weight loss and greying phenomena of the contents during extended storage even outside cold storage conditions.
BACKGROUND OF THE INVENTION
As is known, the casings of boiled and boiling sausages must meet wide-ranging and specific requirements in order to comply with practical requirements.
These requirements substantially include:
elevated strength of the casing, such that permanent plastic deformation of the casing or even bursting of the casing due to the internal pressure arising during filling or boiling cannot occur
highly cylindrical shape of the finished sausages, such that, firstly, they exhibit an attractive appearance which appeals to potential purchasers and, secondly, that they may readily be packed in large packages, such as cartons etc.
tautness of the sausages, so ensuring that the casing encloses the contents without creases, imparting an appearance which appeals to potential purchasers
good sealability (clippability)
heat resistance up to sterilisation temperature
very good barrier properties towards water vapour to reduce weight loss, such that creasing of the product may be avoided.
very good barrier properties towards oxygen (reduction of greying of sausage mix)
elevated adhesion to the sausage mix to avoid the formation of jelly between the casing and the contents
good peelability, good slicing behaviour
good shirrability with regard to various shirring methods (axial shirring, helical shirring)
good thermal deformability to ensure that the casings may readily be shaped into conventionally shaped rings (A, B and C rings) and into natural shaped casings
compliance with foodstuffs legislation (EC Directives, Bundesamt fur gesundheitlichen Verbraucherschutz und Veterinärmedizin [German Federal Office for Consumer Health Protection and Veterinary Medicine] (BGVV), Food & Drug Administration (FDA)) and fulfilment of environmental requirements with regard to the avoidance of halogenated compounds and heavy metals.
reliable printing ink adhesion
low cost production process.
Single and multilayer casings have long been prior art. Casings which have hitherto been developed, however, have never been able to meet the entire range of requirements.
DE 28 50 181 describes a single layer, biaxially stretched casing of a polymer blend of aliphatic polyamide and an olefinic copolymer. While incorporation of the olefinic copolymer may indeed bring about a distinct reduction in water vapour permeation, in particular the water vapour barrier action which is achieved is far poorer than that of PVDC. The inadequate water vapour barrier properties means that weight losses occur due to evaporation of water over the course of the storage period. This not only reduces revenue from the sausage product, but also gives rise to creased, unattractive products.
Japanese application JP 10 14 032 describes a biaxially stretched, coextruded tubular film comprising three polymer layers for use as casing for boiled and boiling sausages, wherein the outer layer facing away from the contents, consists of aliphatic polyamide (PA) and the inner layer facing towards the contents consists of ethylene/acrylic acid copolymers. The ply arranged between the outer and inner layer of copolymers based on propylene or ethylene acts as coupling agent. The inner polymer layer of ethylene/aciylic acid copolymers here imparts adhesion to the sausage mix. According to a subsequent application, GB 22 05 273, the adhesive properties of the inner layer of linear low density polyethylene (LLDPE) facing towards sausage mix are improved by a complex corona treatment acting upon the inside of the tubular film. While good water vapour barrier properties may be achieved by this film structure, consumers in particular criticise properties, such as excessive tear propagation resistance, inadequate adhesion to the sausage mix and superficial greying of contents sensitive to oxygen and light during storage.
According to EP-A 02 16 094, improved oxygen barrier properties simultaneously accompanied by elevated permeability to smoke flavourings are achieved in single layer PA casings by blending aliphatic PA with ethylene/vinyl alcohol copolymers (EVOH). While the addition of EVOH may indeed bring about a distinct reduction in oxygen permeation, this is not enough effectively to suppress surface greying of the contents during storage. Moreover, inadequate thermal stability of the EVOH during coextrusion with PA at relatively high temperatures results in crosslinking of the EVOH, which disrupts the production process for this casing. The inadequate water vapour barrier properties result in sausage products becoming creased during storage.
DE-A 41 41 292 describes a single layer, biaxially oriented, tubular PA foodstuff casing which substantially consists of aliphatic polyamide, partially aromatic copolyamide, acid-modified polyolefin and ultrafine pigment. While the objective of this film formulation is in particular to ensure adequate light barrier properties, the barrier properties with regard to water vapour and oxygen permeation are inadequate.
DE-A 41 28 081 describes a multilayer, biaxially stretched tubular film which comprises as core layer at least one oxygen barrier ply of 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 and also exhibits good adhesion to the contents. However, during storage, moisture passes from the contents into the core layer, which acts as the oxygen barrier layer. Since th~e 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 30 486 describes a five-layer, coextruded, biaxially stretched tubular film which comprises at least three polyamide layers, which form the core, inner and outer layers. Layers of EVOH or coupling agents are located between these layers. In the proposed film structure, one or two coupling layers, consisting of functionally modified polyolefins, are intended to act as the water vapour barrier. Due to the functional groups, such modified polyolefins have higher water vapour permeability values than the corresponding unmodified polyolefins and thus, at an identical layer thickness, do not achieve the water vapour barrier properties thereof.
EP-A 04 67 039 A2 claims a multilayer, tubular packaging casing based on polyamide, which casing is characterised in that it is produced from an outer layer based on aliphatic polyamide, aliphatic copolyamide or a polymer blend of at least one of these compounds, a middle layer of polyolefin and coupling component together with an inner layer based on aliphatic and/or partially aromatic polyamides and/or aliphatic and/or partially aromatic copolyamides. The outer layer is the actual support layer of the multilayer casing and is also the thickest layer in comparison with the other two layers. If it is intended to improve the oxygen barrier properties of the casing, the inner layer is produced from a mixture of aliphatic polyamide and partially aromatic polyamide. However, since the inner layer is to be provided as a very thin layer, no particularly good oxygen barrier properties may be expected as a result. The middle layer, which is intended to provide water vapour barrier properties, consists of a mixture of polyolefin an
Pophusen Dirk
Schröder Nils
Franks James R.
Gil Joseph C.
Miggins Michael C.
Preis Aron
Pyon Harold
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