Bottles and jars – Ejecting – Siphon type
Patent
1990-09-05
1991-12-17
Weaver, Sue A.
Bottles and jars
Ejecting
Siphon type
220606, 220608, B29C 4912, B65D 102
Patent
active
050728415
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with plastics containers and particularly with blow-moulded plastic bottles made from oriented thermoplastic materials such as PET and intended for use as containers for carbonated beverages.
The use of blow-moulded bottles as containers for pressurized liquids such as carbonated soft drinks, beers, ciders etc. presents a number of problems. In particular, the internal pressure generated by such liquids tends to distort the thin, flexible walls which are characteristic of blow-moulded bottles. This applies particularly to the base portion of the bottle.
Previously, this problem has been obviated by the use of a hemispherical base which distributes the pressure as evenly as possible and thus prevents distortion. Such a base is, however, inherently unstable and some means is required to allow the bottle to be free-standing. One approach is to attach a basecup to the hemispherical base, but this obviously increases manufacturing costs. There are also problems with adhesion and inaccurate positioning of the basecup which may result in a bottle which does not stand vertically.
Accordingly attempts have been made to produce a one-piece, blow-moulded bottle which is usable with pressurized liquids.
There have been many proposals for designs of such bottles, generally including either bases having a central concave portion, or a generally convex base with a plurality of stabilizing feet blown out therefrom, however none of these have been totally satisfactory in use. Problems encountered include creep and distortion of the bottle material, stress cracking, and poor resistance to impact. A typical bottle base is shown in FIG. 1 of the accompanying drawings and comprises a generally hemispherical section 2 having stabilizing feet 4 blown out therefrom. Such bottles are blow-moulded from an injection moulded preform as follows: the preform is heated, enclosed within a mould corresponding to the desired shape of the bottle, stretched by a stretch-rod inserted through the neck of the preform, and then blown. The stretch-rod stretches the preform to the full length of the mould so that the bottom of the preform impinges upon the bottom of the mould. The material which contacts the bottom of the mould at this stage is "frozen" so that when the bottle is blown the material around the centre of the base remains unoriented and relatively weak. In a bottle such as that of FIG. 1 this area of unoriented material extends well into the feet 4 of the base so that the base structure is weakened and becomes subject to creep and distortion. Additionally, the transition from unoriented to oriented material is relatively abrupt, creating weak points where the transition occurs and reducing the resistance of the base to stress cracking or the like. These problems can obviously be overcome by making the base thicker; however this increases the amount of material required and hence the weight of the bottle. Thus, the advantages of a one piece bottle over a conventional base cupped bottle are substantially reduced.
It is an object of the present invention to obviate or mitigate these disadvantages.
Accordingly, the invention provides a container of blow-moulded oriented thermoplastic material which is formed by enclosing a heated moulded preform within a mould corresponding to the shape of the container, and stretching it to the full length of the mould so that its bottom surface impinges upon the bottom surface of the mould prior to blow-moulding, said container comprising a generally cylindrical body portion and a base portion closing the bottom end of said body portion wherein said base portion is a figure of rotation formed by rotating a generally convex curve extending from the bottom of said side wall to the central longitudinal axis of the container about said central axis so as to define an annular convex surface having a central re-entrant portion, and wherein said preform, when stretched prior to blow-moulding, impinges upon a projecting central portion of the bottom of the mould corresponding
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Norderney Investments Limited
Weaver Sue A.
LandOfFree
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