GB2292905A

GB2292905A - Blow moulded plastics bottles

Info

Publication number: GB2292905A
Application number: GB9517714A
Authority: GB
Inventors: Charles Jonathan Britton
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-08-31
Filing date: 1995-08-31
Publication date: 1996-03-13
Also published as: GB9417516D0; GB9517714D0

Abstract

Plastics bottles (1) of oblong cross-section are blown in mould cavities (11) defined in blow mould halves (9, 10) such that the split line (12) of the cavities extends along wider sides of the formed bottles. The arrangement enables more bottles to be blown in a moulding operation in a given size of mould than would be possible were bottles of similar cross-section and size to be formed in the mould with the split line along the narrower sides of the formed bottles. Because of the higher production rate bottles may be produced from more expensive plastics materials, such as p.e.t., at prices competitive with glass bottles of similar sizes and shapes. Parisons may be formed with screw-threaded necks before stretch blow moulding to the final shapes of the bottles. <IMAGE>

Description

BLOW MOULDED PLASTICS BOTTLES This invention relates to blow moulded plastics bottles.

Blow moulded plastics bottles of oblong cross-section have hitherto been formed in a mould such that the split line between the mould halves extends along the narrower sides of the cross-section. This follows the long established practice in the production of glass bottles of oblong cross-section. A disadvantage of the arrangement is that the number of bottles that can be produced at a time in one mould is restricted which limits production rates and has made the use of some plastics materials not generally economically viable.

The present invention aims to enable such bottles to be made more economically.

According to the present invention a method of blow moulding plastics bottles of oblong cross-section is provided in which the bottles are blown in mould cavities so defined in halves of a blow mould that the split line of the cavities extends along wider sides of the bottles formed therein. The invention is particularly relevant to the moulding of bottles having their wider sides at least twice as wide as the narrower sides of their cross-sections.

The split line of the mould cavities produces a visible mark, which may also be felt, at the exteriors of the formed bottles. Bottles blow moulded by the present method therefore have a mark extending along the wider sides of their oblong cross-section. If labels are applied to the bottles at their wider sides the marks will be largely hidden from view. A person holding a labelled bottle to read the label will usually hold the bottle at the narrower sides and so there will be no split line mark to be felt where the bottle is held.

When, in accordance with usual practice, a number of bottles are to be blown in the blow mould in one moulding operation, it is possible for more mould cavities to be defined for that purpose within a given size of mould than could be defined when the split line extends along the narrower sides of bottles of the same shape and size. More bottles can thus be blown in one operation. For example, in the production of bottles of a conventional shape with a rectangular cross-section used for medicaments five mould cavities may be provided for the present method where previously only three might have been possible, a substantial increase in production rate being achieved in consequence. Although higher tooling cost may be involved in the manufacture of the mould the higher production rate can soon compensate for that.

Extrusion blow moulding may be used in the present method in known manner, but the method has particular advantage when a stretch blow moulding technique is used. In such a technique a parison is formed in an injection mould and is then quickly transferred while still hot and pliable to the blow mould to be blown to the final shape. For bottles having screw-threaded necks to be fitted with screw caps, the screw-threaded necks are formed on the parison and retain their form as the parisons are blown to the final forms of the bottles.

Bottles made by the method of the present invention may be made of any suitable plastics material. For example, they may be made of polyvinyl chloride, high density polythene or polypropylene, which may be blown in a clear form. Since the method enables a higher production rate to be achieved other more expensive plastics material can be considered. For example polyethylene terethylene (p.e.t) may be used in crystalline or amorphous forms. Bottles made of p.e.t.

may be used for holding medicines, for example, and disinfectants and screw-threaded necks can be accurately formed in the material so that locking, child resistant, caps may be fitted to the bottles.

Click lock type caps may be fitted.

By use of the present invention bottles blow moulded from p.e.t. may be produced at prices competitive with those of bottles made of glass of similar sizes and shapes.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figures 1 and 2 are plan and front views respectively of a plastics bottle made by the method according to the present invention; Figure 3 is an elevational view of a parison used in the method, and Figure 4 is a diagrammatic section through a blow mould used in the method.

This embodiment of the present invention is applied to the manufacture of bottles suitable, for example, for holding disinfectants. As shown in Figures 1 and 2, the bottles have a body 1 of substantially rectangular lateral cross-section, having wider sides 2 and narrower sides 3 and a neck 4 is formed with an external screw thread 5. In the illustrated example the wider sides 2 are approximately 2.5 times wider than the narrower sides. Bottles may be made, which have the wider sides appreciably wider still than the narrower sides, possibly at least 5 times wider.

For each bottle to be blown a parison 6, Figure 3, is initially formed in known manner in an injection mould. The parison 6 is formed with the neck of the bottle, including the external screw thread 5, and a rudimentary body 7 of circular cross-section, generally test tube, shape.

From the parison 6 each bottle is blown to its finished shape in a blow mould 8, Figure 4. The blow mould 8, as is conventional, comprises two mould halves 9, 10, between which several, in this instance five, mould cavities 11 are defined of identical forms corresponding to the required finished external shapes of the bodies 1 of the bottles to be blown. Each cavity 11 has an entry, not shown, in which the portion of the respective parison 6 forming the neck 4 of the bottle to be blown is received to locate the parison in the mould cavity. Pressurised air is supplied at the entry to be blown into the parison at the neck portion so as to stretch the body of the parison to the finished form of the body 1 of the fully blown bottle.

Immediately after the parisons 6 have been formed in the injection mould they are located in the blow mould so that the plastics material is soft and pliable for the blowing to be done.

The mould cavities 11 extend side-by-side in the mould, parallel to one another. Half of each mould cavity is defined in one mould half 9 and the other half is defined in the other mould half 10. The two halves of the mould cavity meet on a central plane which, unlike the conventional practice in blow moulding products of oblong lateral cross-section, is transverse to the wider sides of the lateral cross-section of the mould cavity, i.e. transverse to the wider sides 2 of the body of the bottle to be blown.

The arrangement enables a larger number of mould cavities to be accommodated within a given face area of the mould halves than is possible in the conventional arrangement having the mould cavities split on the narrower sides of an oblong lateral cross-section.

The bottles blown in the blow mould 8 each have a split line 12 extending longitudinally of the bottle centrally of the wider sides 2 of its cross-section.

With accurately formed registering halves of the mould cavity the split lines 12 may be hardly discernable.

If labels are subsequently applied to the bottles the split lines 12 are substantially hidden from view.

Since the screw thread 5 on the necks of the bottles is formed in the injection moulding of the parison it can take a strong and accurate form so that the bottles may, if required, be fitted with suitable locking caps.

Claims

1. A method of blow moulding plastics bottles of oblong cross-section in which the bottles are blown in mould cavities so defined in halves of a blow mould that the split line of the cavities extends along wider sides of the bottles formed therein.

2. A method of blow moulding according to claim 1 in which the bottles so blown have their wider sides at least twice as wide as narrower sides of their cross-sections.

3. A method of blow moulding according to claim 1 or claim 2 in which a plurality of bottles is blown in one moulding operation, the mould cavities extending side-by-side in the mould such that the wider sides of adjacent bottles blown therein are juxtaposed.

4. A method of blow moulding according to any preceding claim in which the bottles are formed by stretch blow moulding, parisons being formed in an injection mould and then transferred while still hot and pliable to the blow mould to be blown to the final shape of the bottles.

5. A method of blow moulding according to claim 4 in which the parisons are formed with screw-threaded necks and the screw-threaded necks are retained as the parisons are blown to the final shape of the bottles.

6. A method of blow moulding according to any preceding claim in which the bottles are made of polyethylene terethylene.

7. A method of blow moulding according to any preceding claim in which the bottles are of substantially rectangular lateral cross-section and the split line of the cavities extends longitudinally of the bottles centrally of the wider sides of the bottles.

8. A bottle made by a method of blow moulding as claimed in any preceding claim.

9. A method of blow moulding bottles of oblong cross-section substantially as described herein with reference to the accompanying drawings.