Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Patent
1991-06-18
1992-12-29
Buffalow, Edith
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
428349, 428523, 428516, B29D 2200
Patent
active
051750350
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention pertains to a plastic multilayer sheet for making containers meant to be closed by means of a sealed lid.
The present invention also pertains to the production of containers made from this sheet, to be used for foodstuff for instance, and meant to be closed by a lid sealed to their open upper side. These containers are, for example, the boats or pots into which are sold foodstuff such as deserts.
These containers are usually thermoformed from a plastic in sheet form often presenting several layers of different materials such as polystyrene, ethylvinyl alcohol (EVOH) and polyethylene, bound by adhesives.
At present, the lids come in the form of a thin multilayer sheet comprised, for instance, of a sheet of aluminium or of polyester onto which the information meant for the customers is printed, and which is coated, on its side in contact with the container, with a thin layer of polyethylene.
It is by means of this thin layer of polyethylene that sealing of the lid to the lip presented by the container around its open side, is ensured.
When analysing the opening of a container so sealed, it is found that in many cases, this opening is difficult to perform.
Indeed, the lower layer of the lid and the upper layer of the container are both made of polyethylene and are sealed together. For the container to open, it must be possible to break the bond between the two sealed layers.
In some cases, the seal is very difficult to break, and the force that one is brought to excert on the lid often results in the tearing of the lid, hence making it necessary to take hold of the latter by small fragments.
In other cases, the thin polyethylene layer remains sealed to the container while having removed the upper layer(s) of the lid.
This problem of sealed containers has not yet been suitably and definitely resolved. For this reason, the objective of the present invention is to propose a novel solution permitting the production of a seal of the lid that is impervious and sufficiently resistant to the various demands to which it may be subjected during the commercialization of the containers, while permitting the easy removal of the lid without tearing it.
BRIEF DESCRIPTION OF THE INVENTION
The object of the invention is a plastic multilayer sheet for making containers, meant to be closed by a sealed lid, itself comprised of a multilayer sheet presenting a lower layer meant to be sealed to the upper layer of the said sheet, characterised in that the said upper layer is a composite layer, comprised of an heterogeneous mixture of two products of perceptibly different viscosities, the most viscous one of which is distributed in the middle of the layer and the most fluid one on the surface of the layer, the said fluid product being sealable onto the lower layer of the lid in such a way that, upon removal of the lid, the upper composite layer of the sheet is torn throughout its thickness by decohesion.
According to other characteristics of the invention:
the composite layer is comprised of a mixture of polyolefin and polystyrene.
when the lower layer of the lid is made of polyethylene, the composite layer contains a polyethylene that is more fluid than the polystyrene.
The invention also pertains to a plastic container made from a sheet, characterised in that the composite upper layer of the sheet is comprised of an heterogeneous mixture of two products, the most fluid one of which is compatible with the lower layer of the lid so as to ensure the seal of the lid.
According to other characteristics of the invention:
The composite layer is comprised of a mixture of polyolefin and polystyrene having different coefficients of viscosity.
The mixture includes a polyolefin and polystyrene or a styrene co-polymer in proportions included, for each compound, between 10% and 90%.
BRIEF DESCRIPTION OF THE DRAWINGS
Other characteristics will come out of the description that follows, made in reference to the attached figure, where the following can be seen:
FIG. 1: a view, in section, of the ensem
REFERENCES:
patent: 4803102 (1989-02-01), Rainere et al.
patent: 4842187 (1989-06-01), Janocha et al.
European Space Agency File: Chemical Abstracts: Z. Funke et al.: Structure of heterogeneous blends of thermoplastics.
Notice of Rejection dated May 16, 1991 from Taiwan Patent Office No. 79109650.
Chaupin Vincent
Pinsolle Francis
Buffalow Edith
Siamp-Cedap
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