IE57896B1 - Containers - Google Patents

Description

This invention relates to containers comprising laminated thermoplastic sheet material.

Containers such as tubs for margarine, ice-cream and other products of the food and other industries, are commonly made from thermoplastic sheet material by thermoforming methods in which part of the sheet is heated and drawn by pressure or vacuum into a mould, the formed container then being cut from the web of sheet material. The sheet material is selected to provide a mechanically IQ robust container from an economically thin web and it may also be required to accept printing and meet other requirements, including in particular avoiding interaction between the container material and its contents. For this reason such containers may be made from laminated sheet material, each lamination being selected to contribute special properties appropriate to its position in the laminate. Thus the inner lamina may be selected for resistance to contamination of the contents and the outer for mechanical strength.

The present invention provides a container comprising two or more fused layers free from added adhesives, of olefine polymer with polyethylene terephthalate esters of glycol or polyethylene glycol.

The containers of the present invention may be provided by thermoforming under pressure or vacuum from a blank comprising two or more superimposed layers of thermoplastic polymer sheet material and parting surplus material from the formed container, wherein the superimposed sheets are brought into contact, substantially in the area of each container blank and in the absence of added adhesive, with contact plate means heated to fuse the layers together before thermoforming the container and wherein the contact plate means is contoured to exclude air between the layers. Such a process is described in Patent Specification No. / from which this specification is divided out.

Heating to fuse the superimposed layers is done before thermoforming by using contact plates only at those areas which are to be thermoformed i.e. in the area of each blank, to facilitate separation of each layer for recycling from the skeletal remnants of the sheet left after removing the formed containers. Similarly, since the extent of fusion between the layers may be controlled by the pressure, temperature and time applied, the thermoformed blank area may be used to a sufficiently limited extent to permit the constituent layers of the containers themselves to be separated for recycling after usage.

A particular advantage of the invention is that in the absence of adhesive between the layers, the rim of containers made in accordance with the invention may be rolled without contamination of the edges by adhesive.

Preferably the containers of the invention are printed on one layer only, the speed of the printing process for which is therefore higher in comparison with printing a single sheet of the full container thickness. Printing may be distorted intentionally in such a manner that the thermoforming process yields the required print design on the finished formed container. In another printed embodiment of the invention, the outer layer is transparent and reverse printed on its inner surface to protect the print from wear and the contents of the container from contamination with the print.

Different combinations of film material selected from the polyolefins, in particular polyethylene, polypropylene and polystyrene, with polyethylene terephthalate esters of glycol and polyethylene glycol are suitable for containers intended for use in the edible fats industry, for example for ice-cream and margarine.

The containers of the present invention may comprise two or more sheets or films of different thickness and three or four layers of laminates may, for example be used.

The containers may be formed by thermo-pressure or vacuum-forming in which the sheet material is pressed or sucked into a mould. The conventional methods of thermoforming are usually appropriate, provided the J temperature and contact pressure, by contact plates achieves the desired effect of fusing the thermoplastic film material and the necessary conditions for the thermoforming process can be applied.

Separate sheets, coming from different take-off rolls, may be combined and fed intermittently in a controlled manner via a system of feed rolls to a heating and pressing station where contact is made with a contact plate means at each of predeterminate succession of container blank zones on the web. The resulting partly fused film combination is then transferred from this station to a thermoforming station and after forming the containers are cut from the sheet and the waste can be collected and separated into its constituent layers.

Claims (3)

1. A container comprising two or more fused layers free from added adhesive, of olefine polymer with polyethylene terephthalate esters of glycol or polyethylene glycol. 5

2. A container according to claim 1 wherein print is applied in reverse to the inner face of an outer transparent layer.

3. A container according to Claim 1, substantially as hereinbefore described.