AU729565B2 - Base for PET bottle with improved stability - Google Patents

Description

-1-

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

S" Name of Applicant: COCA-COLA AMATIL (AUST) PTY LTD, ACN 076 594 119 Actual Inventor: lan William TWADDLE Address of Service: BALDWIN SHELSTON WATERS 60 MARGARET STREET SYDNEY NSW 2000 Invention Title: "BASE FOR PET BOTTLE WITH IMPROVED STABILITY" Details of Associated Provisional Application No. PO 9933 dated 22nd October 1997 The following statement is a full description of this invention, including the best method of performing it known to us:- -2- Field of the Invention The present invention relates to plastics bottles of the type typically used for the packaging of carbonated beverages.

Background of the Invention The invention has been developed primarily for use in relation to blow moulded PET bottles and will be described hereinafter with reference to this application. It will be appreciated, however, that the invention is not limited to this particular field of use.

•Blow moulded PET bottles have been widely used for many years, as a substitute for glass bottles and aluminium cans, in the packaging of soft drinks and carbonated beverages 10 including colas, flavoured mineral waters, cordials, juices, and the like. PET bottles offer a number of advantages over glass and aluminium. They are less expensive to manufacture, S"they weigh less which minimises handling and transportation costs, they are more impact resistant and therefore less prone to damage, and they are also less costly to recycle.

o .Primarily for these reasons, PET plastics have come into widespread use in the packaging S. 15 of numerous consumable products, including soft drinks in particular.

S°A major disadvantage associated with PET bottles, however, is the flexibility and ultimate lack of strength inherent in the plastic material itself. Early designs were prone to failure, particularly under the relatively high internal pressures required for the bottling of carbonated soft drinks. Such designs typically formed cracks in regions of stress concentration, particularly in the vicinity of the base. In an attempt to overcome this problem, some bottles were formed with a substantially hemispherical bottom with a flat base attached as a separate moulding by adhesive, to retain the bottle in the upright orientation. By forming the base of the bottle in a hemispherical shape, localised stress concentrations were minimised and the bottle itself was found to be better able to withstand -3the necessary internal pressures. A disadvantage, however, was that the need to mould a separate support element to stabilise the bottle added significantly to the amount of plastic material ultimately required, as well as the number of processed steps, both of which increased significantly the cost of production.

In an attempt to overcome the problems outlined above, it is also known to form PET bottles with a generally hemispherical base and integrally moulded downwardly projecting feet disposed circumferentially around the base to retain the bottle in the desired upright orientation. Typically, each foot defines a substantially flat contact region designed to rest directly on the horizontal surface on which the bottle stands. The outermost points of S. 10 contact of the feet together define the so-called contact diameter or contact radius of the base. This parameter of contact diameter is directly related to the inherent tilt stability of the bottle. Thus, as the size of the contact diameter increases, the bottle becomes more stable. Conversely, a reduced contact diameter leads to reduced tilt stability, all other factors being equal. It has been found, however, that when PET bottles are filled and o 15 pressurised, the bottle in general, and the base in particular, tends to bulge outwardly. This phenomenon is particularly pronounced in the case of carbonated beverages where sustained pressurisation is required to retain the carbonating gas in solution. As this occurs, the previously flat horizontal contact surface of each foot assumes an outwardly inclining or curved orientation. Consequently, the inner edge rather than the outer edge of each contact region tends to contact the supporting surface. As a result, the contact diameter is substantially reduced and the tilt stability of the bottle is correspondingly reduced. This adversely affects the manufacturing and bottling operations, since the bottles become less stable on the conveying equipment, which leads to downtime and additional manual labour in order to keep the production line moving. Bottles with poor stability also -4cause inconvenience to retailers and consumers, due to the tendency to tip over in refrigerators and on shelves.

It is an object of the present invention to overcome or substantially ameliorate at least some of these disadvantages of the prior art.

Disclosure of the Invention Accordingly, the invention provides a base for a plastics bottle, said base including a plurality of peripherally spaced downwardly projecting feet adapted to contact a horizontal surface to support the bottle in an upright orientation, wherein the outermost radial contact points of the feet define a contact diameter of the base, and wherein at least some of said 10 feet include generally concave dimple formations tending to resiliently deform toward a flattened configuration upon pressurisation of the bottle without substantially reducing the "contact diameter of the base.

Preferably, the bottle is generally circular in transverse cross sectional profile and the feet preferably project downwardly from a generally convex, substantially hemispherical 15 portion of the base. More preferably the dimple formations are generally circular. The bottle preferably includes four, five or six feet spaced uniformly around the periphery of the base. It will be appreciated, however, that any number of feet, greater than three, could be used.

In the preferred embodiment, the bottle and base are blow moulded integrally from a PET plastics material. The bottle and base are preferably blow moulded from a preform, which is also configured simultaneously to form an integral neck. The neck is preferably adapted to receive a closure for the bottle. The closure preferably takes the form of a threaded cap.

In the preferred embodiment, the bottle is adapted to contain carbonated beverages, at an internal pressure of between 200 and around 500 kpa.

Brief Description of the Drawings A preferred embodiment of the invention will now be described, by way of example only, with referenceto the accompanying drawings in which:- Figure 1 is a diagrammatic longitudinal cross sectional view showing one foot of a typical prior art PET bottle base in a non-pressurised configuration; Figure 2 shows the prior art base of Figure 1, in a typical configuration as distorted under internal pressure; Figure 3 is a longitudinal cross sectional view showing one foot of the base formed in accordance with the present invention, in a non-pressurised configuration; Figure 4 shows the base of Figure 3 when pressurised; •o Figure 5 is a perspective view showing the base in more detail; and 0 0 Figure 6 is an underside view of the base; So 15 Figure 7 is a diagrammatic wire frame perspective view of the base; Figure 8 is an inverted wire frame perspective view of one foot of the base of Figure 7; and *•**Figure 9 is a wire frame side view of the foot shown in Figure 8.

Preferred Embodiment of the Invention Referring to the drawings, Figure 1 shows a typical prior art base 1 for a blow moulded PET bottle 2 adapted to contain carbonated beverages under pressure. The base includes a generally hemispherical section 3 and a plurality of circumferentially spaced feet 4 projecting downwardly therefrom. Each foot defines a substantially flat contact region adapted to engage a horizontal support surface 6. In this way, the fee retain the bottle in a -6generally upright orientation, as shown. The outermost contact points 10 of the feet together define a contact radius R 0 of the base, which essentially dictates the tilt stability of the bottle.

When the bottle is pressurised, the contact region 5 of each foot tends to bulge outwardly, as shown in ghost in Figure 2. As a consequence, the contact region 5 is no longer flat, but it rather is concave. The geometry of the feet is such that in this configuration, the outermost contact points 10 define a new contact radius Rp, which is substantially less than the contact radius R o of the base in the non-pressurised configuration. Consequently, once filled and pressurised, the prior art base loses its design •10 stability to a significant extent. This adversely affects the production, packaging and handling processes, since the bottles are no longer stable on conveyor lines. Likewise, the S"lack of stability causes problems on supermarket shelves, in consumer's fridges, and in **many locations in between.

A preferred embodiment of the present invention is shown in Figure 3, wherein 15 corresponding features are denoted by like reference numerals. In this case, it will be seen that the contact region of each foot incorporates a generally concave dimple formation 11 extending upwardly from the base of the foot. The dimple formation is generally circular in shape when viewed in plan although other shapes could also be used. When the base of Figure 3 is pressurised, as shown in Figure 4, the convex dimple formation tends to bulge outwardly and as a consequence, tends to adopt a flattened configuration. Importantly, however, it will be noted that in the pressurised condition, the contact radius Rp is substantially the same as the contact radius R 0 of the base on the non-pressurised state.

Hence, it will be appreciated that the inherent design stability of the base is retained, irrespective of whether the bottle is pressurised. Although the dimple 11 in Figure 4 is -7shown to have assumed a substantially flattened configuration, it will be appreciated that in some embodiments, the dimple formations may be only partially flattened so that a modified dimple formation would remain evident, even in the pressurised configuration.

Irrespective of the extent of flattening, however, the outer contact radius would not substantially alter.

As best shown in Figures 5 to 8, the base preferably includes six feet. It will be appreciated, however, that any number of feet greater than three could be used. The base shown in Figures 5 and 6 is ideally blow moulded from a preform composed of PET plastics material such that the bottle, base and neck are integrally formed in a single blow 10 moulding operation. It will be appreciated, however, that any suitable plastics material could be used. It will also be appreciated that the base need not be necessarily be formed integrally with the bottle, but could be attached as a separate process step, for example by a suitable adhesive or thermoplastic welding. Whilst the feet are shown to project •downwardly from a generally hemispherical portion, it will also be appreciated that the hemispherical design is a preferred aspect of the invention only.

By providing a base which retains its inherent stability irrespective of internal pressurisation, it will be appreciated that the invention represents a practical and commercially significant improvement over the prior art.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims (10)

1. A base for a plastics bottle, said base including a plurality of peripherally spaced downwardly projecting feet adapted to contact a horizontal surface to support the bottle in an upright orientation, wherein the outermost radial contact points of the feet define a contact diameter of the base, and wherein at least some of said feet include generally concave dimple formations tending resiliently to deform toward a flattened configuration upon pressurisation of the bottle without substantially reducing the contact diameter of the base. S2. A base for a plastics bottle according to claim 1, wherein said dimple formations 10 are generally circular. *0*

3. A base for a plastics bottle according to claim 1 or claim 2 wherein the bottle is generally circular in transverse cross sectional profile and wherein the feet project downwardly from a generally convex, substantially hemispherical portion of said base.

4. A base for a plastics bottle according to any one of the preceding claims, including 15 four, five or six feet spaced generally uniformly around the periphery of the base. o@ o o A base for a plastics bottle according to any one of the preceding claims wherein the base is blow moulded integrally with the bottle from a PET plastics material.

6. A base for a plastics bottle according to claim 5 wherein the bottle and base are blow moulded from a preform, which is also configured simultaneously to form an integral neck.

7. A base for a plastics bottle according to claim 6 wherein said neck is adapted to receive a closure for the bottle. -9-

8. A base for a plastics bottle according to claim 7 wherein said closure takes the form of a threaded cap.

9. A bottle formed from plastics material and including a base as defined in any one of the preceding claims.

10. A plastics bottle according to claim 9 wherein the bottle is adapted to contain carbonated beverages, at an internal pressure of between 200 and around 500 kpa.

11. A base for a plastics bottle substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.

12. A bottle formed from plastics material and including a base substantially as herein :described with reference to any one of the embodiments of the invention illustrated in the Saccompanying drawings and/or examples. **DATED this 16th Day of June, 2000 S 15 COCA-COLA AMATIL (AUST) PTY LTD Attorney: RUSSELL J. DAVIES :Fellow Institute of Patent Attorneys of Australia of BALDWIN SHELSTON WATERS 4 6. T