Dupont Canada Inc.

Brian L Hetherington

Peter Y Kelly

The present invention relates to an improvement in a method for thermoforming of containers from thermoplastic materials in which method the rim of the container is formed as an integral part of the pre-form from which the container is thermoformed. The pre-form is obtained by introducing thermoplastic material into a closed space and then mechanically compressing the material. The improvement of the present invention relates to improved uniformity of flow of the thermoplastic material into the closed space, the use of a closed space defined by surfaces having a surface roughness in the range of 50-125 .mu.m rms and to a modified sequence of steps for forming the pre-form in which the compression of the thermoplastic material is commenced prior to the completion of the introduction of the material into the closed space. The process may be used in the manufacture of containers, e.g., for the packaging of margarine, from polyethylene or polypropylene.

Manufacture of plastic containers

A continuous process for forming a longitudinal heat-weakened strip in a cross-lapped oriented polyolefin film is disclosed. The process comprises directing heat from two longitudinally aligned sources, to opposing sides of a travelling web of the cross-lapped oriented polyolefin film, to such an extent that the tensile breaking strength at the heat-weakened strip so formed is in the range of 20 to 100 Newtons per centimeter of length of film. The film so formed is particularly useful for packaging slurry explosives.

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Kingston, Canada

Brian L Hetherington