PLASTICS BOTTLE

Abstract: A plastics bottle (1) having a base (5) comprising circumferentially spaced feet (10) separated by valleys (20). The bottle has improved stability which makes it suitable for standing on a variety of surfaces and also maintains ease of blow moulding and good stress crack resistance. The base design combines narrow valleys, which have side walls at an angle of 25 DEG or less to each other, with wide feet. The foot width is at least 35 % of the circumference of the standing surface, significantly larger than the more typical 20 to 25 % of comparable prior art designs.

Description: PLASTICS BOTTLE This invention relates to a plastics bottle for carbonated beverages which has a so-called "petaloid" or "footed" base. The use of lightweight plastics bottles is well known for a multitude of products. Since the development of blow-moulding techniques, clear biaxially-oriented PET bottles have become widely used for carbonated soft drinks, particularly of 1 and 2 litre capacity but also of 500 cl capacity which are sold in direct competition to canned drinks. Originally, the base was formed in a domed shape and a separate base cup was used to provide stability to the bottle. In order to reduce the cost of using a separate cup, the base design evolved into a so-called "champagne" base and the now popular petaloid base which typically has up to 7 feet separated by ribs. It is known that such footed bases must meet a number of criteria which in some situations may be at odds with each other. For example, it is essential to minimise stress concentrations so as avoid failure of the base which arises when stress cracks are initiated, particularly when the bottle is filled with a carbonated beverage. On the other hand, the base must also be readily blow moulded and should be stable when filled, even when internal pressure changes due to temperature variations for example. US-4785949 (Krishnakumar et al) proposes a design which is said to limit stress levels by maximising the cross sectional areas of the ribs and avoiding sharp transitions between the ribs and feet. This design has a maximum of five feet separated by wide ribs. Another plastics bottle for carbonated drinks is described in US-5024339 (Rie er) . This design has seven feet which the patent recommends for small bottle sizes. Small half litre bottles may comprise plastics material which has not been fully stretched during blow moulding and is therefore not completely biaxially oriented. This patent recommends that the ribs be sufficiently wide to provide pressure resistance but narrow enough to ensure optimum stretching and biaxial orientation. A suitable compromise is said to be provided by a seven-footed base with the feet being separated by parallel sided ribs. The present invention seeks to provide a container having a base which provides improved stability whilst still ensuring efficient and easy blow moulding of the container . According to the present invention, there is provided a plastics bottle for carbonated drinks, the bottle including an integral base, the base comprising: a plurality of circumferentially spaced feet separated by valleys which are substantially inverted U shaped and have side walls which are at an angle of 25° or less to each other; and in which each foot has a flat pad, the radially outer edge of which is substantially arcuate, the foot pads together making up a standing surface for the bottle; and the total length of the outer edges of the foot pads is at least 35% of the circumference of the outer edge of the standing surface. The base of the bottle of the present invention thus has relatively sharp angled valley side walls in comparison with known bottle base designs and proportionately wide feet. It should be appreciated that for assessment of stability the important part of the feet is the flat pad which will contact the surface on which a bottle will be standing. The base of the present invention has been found to give excellent stability but also, surprisingly given the large foot pad size, the base is easily moulded and has good stress crack resistance . The size of the foot pads will clearly vary according to the number of feet used for a specific base. In order to maintain ease of mouldability, however, it is preferred that the total length of the outer edges of the foot pads is less than 65% of the circumference of the outer edge of the standing surface. Similarly, in order that the bottle maintains good stability irrespective of bottle size, the length of the outer edge of a foot pad should preferably be between 2 and 4.25 times the width of the narrowest part of a valley, at the base of the inverted U. The valleys may be ideally positioned around a substantially hemispherical dome having a central region which comprises an externally convex region surrounded by an externally concave first annulus and an externally convex second annulus which tapers into a foot on one side and blends into the hemispherical valley on the opposite side. A blow forming mould has a mould wall which is complementary in shape to the bottle to be formed so that the central convex region of a mould designed to form the bottle of the present invention will receive a preform gate. The annuli increase initial stretching of the preform away from its centre, thus keeping the preform away from the mould for as long as possible and limiting stress concentrations in the centre of the final bottle base . In one embodiment, the bottle base includes five feet. In this embodiment, the angular extent of a foot pad, i.e. the angle which the foot pads subtend at the longitudinal axis of the bottle, may be at least 25°. For ease of blowing, the foot pad is blended into the side wall of the adjacent valley by a radius which, for a five footed base, may be at least 3 mm, but is preferably at least 5 mm. An advantage of the present invention is that the excellent stability of the bottle makes it suitable for transporting on slat conveyors, standing on uneven surfaces, storage in domestic refrigerators or retail from chiller cabinets. Refrigerators and chiller cabinets typically have shelves made from small gauge wires with a spacing of up to 15 mm on which bottles must stand without tilting. A preferred embodiment of the present invention will now be described, with reference to the drawings, in which: Figure 1 is a side view of a bottle according to the invention; Figure 2 is a schematic underplan view of the bottle of figure 1; Figure 3 is a longitudinal section through the line III-III showing a foot and opposing valley; Figure 4 is a developed side section through the section IV-IV which is the standing circumference of the bottle of figures 1 to 3 and shows the foot and valley profile; and Figure 5 is a similar profile to that of figure 4 for a prior art bottle. Figure 1 shows a bottle 1 comprising a neck 2, cylindrical body having side wall 3 and base 5. The neck and cylindrical side wall are typical of known PET bottles designed for carbonated soft drinks. The novel base 5 of this invention is shown in more detail in figures 2 to 4. A preferred embodiment of the invention which is particularly suitable for half litre bottles comprises five feet 10 having a "petaloid" configuration as can be clearly seen in figure 2. The feet are equispaced around the base and are separated from each other by valleys 20. The base of each foot 10 includes a flat pad 12 such that when the bottle is standing upright the five pads 12 will be in contact with a shelf or table. The five pads thus make up a standing or support surface for the bottle. The outer edge 14 of each pad 12 is arcuate in shape so each pad comprises a segment of the support surface. In order to ensure optimum stability, we have found that the sum of the lengths l f of the outer arcuate edges 14 should always be at least 35% of the outer circumference of the standing surface. This is readily determined from the standing diameter D=. as shown in figure 3. Although the width of the pads themselves may not seem large when compared with the circumference of the standing surface, the side walls 22 of the valleys are sharply inclined, the angle θ between the side walls being less than 25°. As a result, the foot pads 12 are much wider than the bases 24 of the inverted U shaped valleys . The angle θ is the angle for the profile of the base which results from a developed (i.e. opened out) section through IV-IV, i.e. the standing circumference of the bottle as shown in figure 3. The value of θ is maintained more or less constant radially inwards of the section shown in figure 4 but may open out as the valley blends into the bottle side wall 3 where stiffness is not so critical . The width of foot pads 12 is determined by the length of their arcuate outer edges, i.e. If. Although the base 24 of each valley 20 is curved, by treating radius R v as a fillet radius, the width w v of the narrowest part of the valley can be determined. In accordance with the teaching of the present invention, the width of the foot pad w f is ideally between 2 and 4.25 times the valley width w v . The foot pads 12 are blended into the valley side walls 22 by a radius Rf which is selected to ensure ease of blowing in spite of the large foot size and narrow valleys . Figure 3 shows the configuration at the centre of a five footed bottle base 5. The section III-III passes through a hemispherical valley 20 and foot 10. In the centre 30 of the base there is an externally convex protrusion 32, surrounded by concave and convex annuli 34 and 36 respectively. This shape is selected so that the gate of a preform 4 (shown in dotted lines in figure 1) will not contact the mould until late in the blowing process. This ensures that stress concentrations at the gate region are kept to a minimum. The concentric annuli 34, 36 serve to protect the gate region further. The bottle shown in figure 1 to 4 has five feet which is suitable for bottles of half and one litre capacity. However, in order to maintain the valley shape and wide feet which have been found to be essential to this invention, the number of feet may be varied according to the bottle diameter and/or capacity. Thus whilst a half litre capacity bottle could conceivably have only four feet, it may be necessary to increase the number of feet to, say, seven for larger bottles. It will be appreciated that the number of feet is therefore not essential to the present invention since it may need to be varied if the criteria which we have found to be critical for combining stability with ease of blowing and minimum stress concentrations are to be met. When varying the number of feet, the angular extent α of each foot pad will also change. For a five footed bottle, this angle α should be at least 25° for optimum stability. On the other hand, for ease of blowing a five footed bottle, the radius R f should be at least 3 mm, preferably at least 5 mm. There is a compromise to be made between stability and ease of blowing since although tighter radii would enable angle α to be increased and thereby the foot pad width, as the radii are reduced the bottle becomes increasingly difficult to blow. The standing diameter D s of the bottle of figures 1 to 4 is at least 70% of the bottle side wall diameter D b . Example 1 A five footed bottle similar to that shown in figures 1 to 4 and having a half litre capacity, was blow moulded. The critical parameters according to the present invention were as follows: Foot pad width l f 12 mm Valley angle θ 20° Valley radius R v 2.8 mm Valley width w v 4.7 mm Foot/valley radius R f 5.86 mm Standing diameter D = 49 mm Bottle diameter 68 mm Foot pad angle α 28° Foot-foot spacing F s 30.79 mm From these values it can be seen that the total length of the outer edges of the foot pads is 60 mm which is 39% of the circumference of the standing surface (154 mm) . Comparative Example 1 Figure 5 shows a fifth part of a prior art half litre bottle base having five feet. Comparable parameters with those shown in figure 4 have been given like references and differentiated by a dash. A and E are the centres of adjacent feet. Thus the distance AE corresponds to the foot spacing F s ' . B and D are the radial edges of the flat pads so that AB and DE represent half the width of the pad outer edges. C is the centre of the valley. The prior art bottle design thus has the following parameters which can be compared with those of the bottle of example 1: Foot pad width l f ' 7.32 mm Valley angle θ' 58° Valley radius R v ' 2.28 mm Foot/valley radius R f ' 5.75 mm Standing diameter 50.2 mm Bottle diameter 68 mm Foot-foot spacing F, ' 31.55 mm The total length of the outer edges of the foot pads for the prior art bottle is therefore 36.6 mm which is only 23.2% of the circumference of the standing surface (157.75 mm), significantly less than the 39% of example 1. There is also a clear difference between the valley angle θ' of 58° and that of example 1 where θ is only 20°. The values given for the bottle of comparative example 1 are typical of prior art five footed bases. The angle θ' would typically be between 50° and 70° and the proportion of foot pad width to standing circumference would generally be between 20 and 25%. The bottles of the present invention have been found to provide excellent stability in a wide range of environmental conditions. Furthermore, the bases exhibit fully acceptable stress crack resistance and blowability as required by manufacturers and fillers.

Claims: CLAIMS : 1. A plastics bottle for carbonated drinks, the bottle including an integral base, the base comprising: a plurality of circumferentially spaced feet separated by valleys which are substantially inverted U shaped and have side walls which are at an angle of 25° or less to each other; and in which each foot has a flat pad, the radially outer edge of which is substantially arcuate, the foot pads together making up a standing surface for the bottle; and the total length of the outer edges of the foot pads is at least 35% of the circumference of the outer edge of the standing surface. 2. A plastics bottle according to claim 1, in which the total length of the outer edges of the foot pads is less than 65% of the circumference of the outer edge of the standing surface. 3. A plastics bottle according to claim 1 or claim 2, in which the length of the outer edge of a foot pad is between 2 and 4.25 times the width of the narrowest part of a valley, at the base of the inverted U. 4. A plastics bottle according to any one of claims 1 to 3, in which the valleys are positioned around a hemispherical dome having a central region which comprises : an externally convex region surrounded by an externally concave first annulus and an externally convex second annulus which tapers into a foot on one side and blends into the hemispherical valley on the opposite side. 5. A plastics bottle according to any one of claims 1 to 4, in which the base includes five feet. 6. A plastics bottle according to claim 5, in which the angular extent of a foot pad is at least 25°. 7. A plastics bottle according to claim 5 or claim 6, in which the radius between the foot pad and the valley side wall is at least 3 mm. 8. A plastics bottle according to claim 7, in which the radius between the foot pad and the valley side wall is at least 5 mm. 9. A plastics bottle according to any one of claims 1 to 8, in which the standing diameter is at least 70% of the diameter of the bottle side wall. 10. A plastics bottle according to any one of claims 1 to 9, in which the bottle has a capacity of 1 litre or less .

Inventors: WHEELWRIGHT DAVID, WHEELWRIGHT, DAVID
Applicants: CROWN CORK & SEAL TECH CORP, METAL BOX PLC, WHEELWRIGHT DAVID, CARNAUDMETALBOX PLC, CROWN CORK & SEAL TECHNOLOGIES CORPORATION, WHEELWRIGHT, DAVID
Application year: 1998
Main classification: B65D1
IPC codes: B65D1