Stretch blow-moulding thermoplastics articles

Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Including application of internal fluid pressure to hollow...

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Details

264535, 264540, 425526, 425529, 425531, 425532, 425534, B29C 4904, B29C 4914, B29C 4968

Patent

active

050009052

DESCRIPTION:

BRIEF SUMMARY
This invention relates to the stretch blow-moulding of thermoplastics articles, in particular (but not exclusively) packaging containers for food or beverage products.
In a known system for forming tubular parisons of a thermoplastics material (for example polypropylene) for a stretch blow-moulding operation, a tube of the material is extruded on a continuous basis and on emerging from the extruder passes through successive sizing and cooling stages. Whilst still in essentially continuous form it is subsequently passed at a constant speed through a multi-pass oven by which it is heated to orientation temperature, and on emerging from the oven it has its leading end cropped or severed at regular intervals to form a succession of equal length parisons. These parisons are individually stretch blow-moulded whilst still at orientation temperature, to form packaging containers having a substantial biaxial (i.e. longitudinal and circumferential) orientation of their polymer material.
Such an arrangement, however, suffers from various shortcomings which largely arise from the continuous nature of the tube being handled. In particular, the oven required is necessarily large and thermally inefficient, and the serial production of heated parisons leads unavoidably to wall thickness and other variations if for high manufacturing throughput the containers are moulded from the parisons two or more at a time; this latter inconsistency arises because of the different thermal histories of the parisons of each group being moulded.
In a further known system for forming thermoplastics parisons for stretch blow-moulding the parisons to be moulded are severed from the front of the extruded tube after it has been sized and cooled but in advance of the oven by which the thermoplastics material is heated to orientation temperature. The severed parisons are carried individually through the oven on spaced pegs of a chain conveyor which is circulated at a constant speed. The parisons emerge from the oven at orientation temperature and in succession, and they are subsequently stretch blow-moulded to form packaging containers.
This further system has various advantages over the system previously described, amongst which are that the oven can be made smaller and thermally more efficient. However, the requirement for the parisons to be handled individually between their severance from the extruded tube and the blow moulding station involves substantial complexity, particularly in the oven, and carries its own space penalty; moreover, the heated parisons are again produced from the oven one at a time, so leading to the above mentioned quality variations if the parisons are to be simultaneously moulded in groups of two or more parisons.
The present invention is concerned with the stretch blow-moulding of thermoplastics articles simultaneously in groups of a predetermined number greater than one, and in this context seeks to overcome or substantially avoid at least some of the shortcomings of the two prior art systems described above. In accordance with a first aspect thereof the invention therefore provides a method of stretch blow-moulding thermoplastics articles from heated parisons of a thermoplastics material, wherein the parisons are severed from thermoplastics sticks each of which comprises a predetermined integral multiple of parison lengths greater than one, the sticks being formed by severance from the leading end of a continuously extruded thermoplastics tube and being individually heated to orientation temperature, subsequent to heating the sticks being presented for severance as successive groups of two or more associated sticks which are advanced longitudinally while disposed in parallel, laterally aligned relation, the articles being formed by repeated multiple stretch blow-moulding operations performed upon parison groups each created by a simultaneous severance operation upon the leading ends of the sticks of a said presented group.
By use of a method as defined in the previous paragraph, the parisons of each group to be si

REFERENCES:
patent: 3149373 (1964-09-01), Marzillier
patent: 3324507 (1967-06-01), Arlo
patent: 3339230 (1967-09-01), Farrell
patent: 3449792 (1969-06-01), Plummer
patent: 3462582 (1969-08-01), Cines
patent: 3787170 (1974-01-01), Gilbert
patent: 4323337 (1982-04-01), Korff
patent: 4560340 (1985-12-01), Younkin et al.

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