Plastic and nonmetallic article shaping or treating: processes – Utilizing heat releasable stress to reshape solid workpiece
Patent
1992-11-02
1994-12-06
Timm, Catherine
Plastic and nonmetallic article shaping or treating: processes
Utilizing heat releasable stress to reshape solid workpiece
264294, 264534, 425384, 4253871, 425403, 425526, B29C 6102, B29C 4902
Patent
active
053708342
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and an apparatus for producing a
container in accordance with the preamble of the appended independent claims.
There are needs in the art for a container of thermoplastic possessing superior configurational stability also at elevated temperatures. In addition, it is generally required that the container has at least one substantially planar side surface and, in particular, there is a need for a container with, for example, substantially triangular, quadratic, rectangular or other substantially polygonal cross section. Finally, it is necessary that the container possess a superior capability to withstand both partial vacuum and excess pressure within the sealed container, without any resultant troublesome change in shape.
A container possessing the properties disclosed in the foregoing paragraph is eminently suited for a multiplicity of fields of use, for instance for the storage of foods. In particular in practical applications in which pasteurization, hot-filling or sterilization occur, it is necessary that the container, without changing shape, withstand the elevated temperatures involved. It will also be obvious to the skilled reader that, in practical applications in which the container has been filled with, for example, beverages containing, for instance, carbon dioxide or nitrogen gas, high pressures occur in the sealed container both in connection with the filling operation and during subsequent storage. It should particularly be observed that very high pressures occur within a container which is filled with carbonated beverages when such a container is exposed to heating.
As one non-restrictive example of a thermoplastic material for the production of a container for the above-outlined purposes, mention might be made of polyethylene terephthal ate, hereinafter generally abbreviated to PET. Like most other thermoplastic materials, PET is characterized int. al. in that it obtains, by mono and/or biaxial orientation, superior mechanical strength properties, that the material is thermocrystallizable and that its barrier properties are generally sufficient for many practical applications within the food sector.
As has already been briefly disclosed above, the mono and/or biaxial orientation of the thermoplastic material entails that the material obtains the contemplated superior mechanical strength properties, by which is primarily taken to mean a capacity to withstand, without appreciable configurational change, increased internal pressure in those parts of the container in which are included oriented material. In the production of the container, the point of departure is, as a rule, a blank of substantially amorphous material, the blank being expanded in connection with production of the container. On the expansion, the thickness of the material is reduced at the same time as the material is oriented. Normally, only material in the walls of the container body is expanded, the material being, as a rule, given a biaxial orientation. However, in certain practical applications, the material in the mouth or opening portion of the container is also expanded/oriented. On the other hand, in most practical applications, the material in the bottom portion of the container is not expanded/ oriented, at least not in the central region of the bottom portion.
As a rule, the non-oriented material portions are thermally crystallized so as to increase configurational stability at both low temperatures and elevated temperatures. In certain practical applications, the non-oriented material portions are, in connection with the thermal crystallization, exposed to external pressure forces (generally mechanical forces) in order to control the crystallization speed. In such instance, a combination of compression forces and temperatures is generally selected which entails that the material thickness undergoes a certain reduction, at least a reduction of a minimum of 1%. This will ensure, on thermal crystallization by abutment against mechanical devices, also good contact between the
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A/S Plm Haustrup Holding
Timm Catherine
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