Metal Box Public Limited Company

Terence A Benge

Cyril M Prince

Alan J Maskell

John Chapman

A multilayer plastics sheet destined to be formed into foodstuff containers by thermoforming has a barrier layer for low oxygen permeability, and incorporates reclaim material for providing desired mechanical properties to the sheet. The reclaim material represents 40-60% of the sheet by volume, and in order to incorporate these high reclaim levels without concomitant organoleptic problems the reclaim material is formed as a single layer adjacent what is to be the outside surface of the container. The sheet is accordingly highly asymmetric, but any substantial polymer melt instability during coextrusion tending to cause layer thickness variation and lack of visual appeal of the sheet is prevented by forming the sheet as two substantially symmetrical components which are individually and separately coextruded, and subsequently extrusion laminated together. Of the components one includes, and is symmetrical in relation to, the barrier layer, and the other likewise incorporates the reclaim layer.

Multi-layer plastics structures and apparatus and methods for their

A retortable, hydraulically solid, sealed package (10) containing a liquid or semi-liquid food product (24) comprises a thermoplastics container (12) formed by a thermo-forming process and a heat-shrinkable thermoplastics closure diaphragm (20). The closure diaphragm is heat-sealed to a rim (18) of the container after the headspace above the product has been evacuated, and is subsequently subjected to external pressure so as to be non-elastically stretched and made to lie wholly in contact with the enclosed product. When retorted (e.g. for sterilization) the package suffers no visible deformation of the container (12), despite the considerable volume shrinkage of the container which may occur. The loss of volume caused by this volume shrinkage is accommodated by a reduction in the concavity of the diaphragm (20) caused by a corresponding heat-induced shrinkage of the diaphragm material. The diaphragm continues to exhibit a pleasing, smooth or smoothly curving surface, and the retorted package has a consumer-acceptable appearance.

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Farringdon, United Kingdom

Terence A Benge