IMPROVEMENTS IN OR RELATING TO PLASTICS CONTAINERS

Abstract: A plastics container, such as a bottle, includes a generally convex base portion (72) having a plurality of stabilising feet (78) projecting downwardly therefrom and spaced around the circumference thereof. The fundamental radius (R1) of the base portion (72) is greater than the radius (R2) of the body of the container and its resistance to deformation by internal pressure is enhanced by the provision of spurs, formed by the bottom surfaces (79) of the feet (78), extending radially inwards towards the centre of the base portion and terminating at or adjacent to said centre and/or by one or more frusto-conical portions (74, 76) superimposed upon the base portion (78).

Description: IMPROVEMENTS IN OR RELATING TO PLASTICS CONTAINERS Desc rjgt i_on The present invention relates to improved plastics containers and particularly to improvements in blow moulded plastic bottles for use as containers for pres¬ surised liquids such a carbonated beverages. The use of blow moulded bottles as containers for pressurised liquids such as carbonated soft drinks, beers, ciders etc. presents a number of problems. The principal problem is that the internal pressure generated by such bottles tends to distort the thin, flexible walls of a blow moulded bottle. Th i s app I i es pa rt i cu la r ly to the base portion of the bottle. Previously, this problem has been obviated by the . use of a hemispherical base which allows the pressure to be distributed as evenly as possible. 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 the manufacturing costs. There are also problems with adhesion and inaccurate positioning of the basecup 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 pressurised liquids. One such bottle is shown in Fig. 1 and includes a hemispherical base 2 (ie. a base having its radius of curvature equal to the radius of the bottle) with a num- ber of stabi lising feet 4 blown out therefrom. This design also has a number of associated problems. Since the base is fully hemispherical, the feet have to be very deep to project below the bottom of the base, requiring a significant increase in the weight of the bottle and resulting in the effective base diameter d.. being very much less than the diameter of the bottle d^, leading to instabi lity. The bottle is also liable to stress crack¬ ing owing to the depth of the feet 4 and also to the fact that the area of relatively weak unoriented plastics material around the centre of the base extends approxi¬ mately half way along the lower surface of the feet 4. It is an object of the present invention to obviate or mitigate the aforesaid disadvantages. Accordingly, the present invention provides a plastics container comprising a generally cylindrical body portion and a generally convex base portion having a plurality of stabi lising feet projecting downwardly therefrom and spaced around the ci rcumference thereof, ' wherein the fundamental radius of curvature of said base portion is greater than the radius of said body portion, and further including means for .increasing the resistance of said base portion to deformation due to internal pressure, said means comprising spurs, formed by the bottom surfaces of said stabi lising feet, extending radially inwards towards the centre of said base portion and ter¬ minating at or adjacent to said centre and/or at least one f rus to-con i c a I portion superimposed upon said base portion. Preferably, the bottom surfaces of said spurs each comprise, in radial cross-section, a generally straight- line portion extending radially inwards and merging with said generally convex base portion adjacent the centre thereof . Preferably also, said base portion, in transverse cross-sec ion, comprises a generally convex wall and each of said frusto-conical portions comprises a pair of st ra i ght- I i ne portions, disposed symmetrically about the central axis of the container, superimposed upon said convex wall. Preferably also, said base portion, in transverse cross-section, is generally part-elliptical, having bottom arcuate portion of radius greater than the radius of said body portion and first and second peripheral arcuate portions of radius less than the radius of said body portion. Alternati ely, said base portion, in transverse cross-section, is generally part-circular, comprising an arc of radius greater than the radius of said body portion. Preferably also, the container further includes an upwardly concave portion located at the centre of said base portion. Preferably also, the stabi lising feet are generally U-shape.d in section perpendicular to their radial axis and radiused into the base portion. Preferably also, the number of said stabi lising feet is in the range 7 to 12. It is particularly preferred that the number of feet is an odd number. An embodiment of the invention wi ll now be described, by way of example only, with reference to the accompanying drawings, in hich : - Fig. 1 is a sectional view of a known blow moulded bott le; Fig. 2 is a plan view of the base of a container having an elliptical base; Fig. 3 is a section on line A-A of -Fig. 2; Fig. 4 is a sectional perspective view on line B-B-B of Fig. 2; Fig. 5 is a sectional view of a foot of the base; Figs. 6 and 7 are sections on lines C-C and D-D of Fig. 5 ; and Figs. 8 to 12 show various embodiments of the inven¬ tion. Referring now to Figs. 2 and 3 of the drawings, a container, such as a bottle comprises a substantially cylindrical body portion 6, a suitable neck (not shown) and a base portion 8. The base portion 8 is generally convex (ie. part-spherical or ellipsoid) and has a pluraltiy of stabi lisng feet 10 projecting downwardly therefrom and spaced around the circumference. As is best seen in Fig. 3 in section, the shape of the base 8 is described by a segment of an arc having a radius of curvature (the fundamental radius) greater than the radius of the cylindrical body 6 of the bottle. The radius and centre of curvature preferably vary towards the periphery of the bottle so that the wall of the base portion 8 is semi -e 11 i pt i ca I ; ie. it becomes vertical at the point 12 where the base portion 8 meets the body por¬ tion 10. Thus, the base portion 8 of the bottle is not a full hemisphere. This is advantageous since the feet 10 need not be so deep as with a hemispherical base (the broken line 1-4 shows the line of an equivalent hemispher- • ical base for comparison, see also Fig. 1), reducing the weight of the bottle and increasing the strength of the feet. The area of unoriented material around the centre o-f the base is also decreased. A further advantage associated with the relatively shallow feet 10 is that the point of contact of each foot 10 with a supporting surface may be made closer to the periphery of the base 8 so that the effective base dia¬ meter is increased. That, is the ratio d-,:d, (Fig. 3) is greater than d_. :d ? (Fig. 1), so that the stabi lity of the bottle is improved. Normally, when pressurised liquid is contained in a sealed container of flexible material, the internal pres¬ sure wi ll tend to cause the container to assume a spher- cal shape. In this case, the shape of the base need not be perfectly spherical since the pressure on the sidewalls equalises the pressure on the base to a certain extent, so tending to resist deformation by the internal pressure. Preferably, the ratio of the fundamental radius of curvature of the base to the radius of the bottle is in the range 1.2 to 2.0. The shape of the feet 10 themselves may vary but should generally be rounded to distribute the internal pressure as evenly as possible and, as explained above, it is desirable that the supporting point be as close as possible to the periphery of the base 8. A preferred form of the feet 10 which fulfi lls the above criteria is shown in the drawings and their overall shape is best seen in the perspective view of -Fig. 4, wherein the dashed and dotted lines 16 correspond to the line along which the right-hand foot 18 has been cut (ie. the radial axis) and dashed lines 20 correspond to the line through which the base has been cut at the left hand side (ie. the mid-point between adjacent feet) . These lines also correspond to lines 16 and 20 in Fig. 2. Fig. 5 shows a foot 10 in section along its radial axis. In this view, the foot 10 comprises a substantially straight portion 22 depending from point 12 and sloping slightly inwards from the vertical (angle E. , approxi¬ mately 5 ) . The straight portion 22 is tangent to an arc 24 (centre of curvature 26) which extends to the point of contact with a supporting surface. Thereafter, a second substantially straight portion 28 extends radially in¬ wardly and upwards from the horizontal (angle E ? , approxi¬ mately 6.5 ) . The second straight portion 28 is connected to the base 8 by a concave portion 30 (centre of curvature 32) . Figs. 6 and 7 are sectional views of the foot 10, perpendicular to the radial axis, on lines C-C and D-D respectively of Fig. 5. In these views, the foot is generally U-shaped, comprising an arc 34 (Fig. 6, 42 in Fig. 7) having centre of curvature 36 (44) which is radiused into the base by concave portions 38 (46) about centres of curvature 40 (48). As can be seen from the drawings, the radius of curvature of the arc 34 reduces from the periphery of the base 8 towards the centre. As has been described above, the use of a base portion which is less than sem i -c i rcu la r in section pro¬ vides advantages in relation to the stabi lity of the bottle and resistance to s ress-cracking around the feet, whi lst being reasonably resistan ' t to distortion. In many practical applications however, the internal pressure on the bottle is great enough to distort the base, causing the centre portion of the base to expand downwards, and pushing the feet outwards. Eventually the bottom of the base ill project below the feet so that the bottle wi ll rock on its base. The configuration of the base can however, be modified in a number of ways to increase its resistance to distortion thereby allowing it to be used with liquids of higher pressure, as is ' shown in Figs. 8,- 9 and 10. Fig. 8 shows a bottle base 50 which is generally elliptical in section as before, having a fundamental radius R1, which is greater than the radius R2 of the cylindrical body of the bottle, centred at 52, and- wherein the radius of the peripheral portions of the base 50, R3, is less than R2 and centred at points 54 and 56. Superimposed upon the elliptical base are fi rst and second straigh -line portions 58 and 60 symmetrically disposed opposite one another on either side of the long axis of the bottle. Thus, in section, the base 50 comprises a first short peripheral arcuate portion PQ of radius R3, a first straight line portion QR, a bottom arcuate portion RS of radius R1, a second st ra i gh t- I i ne portion ST and a sec¬ ond short peripheral arcuate portion TU, radius R3. The base portion 50 is therefore generally ellipsoidal with an upwardly diverging f rus to-coni ca I portion superimposed thereon. The introduction of the frusto-conical portion causes the forces exerted on the base by the internal pressure to be redistributed in such a way as to reduce the tendency of the bottom portion of the base to distort downwards. It is also possible to use more than one frus o-conical portion (ie. further pairs of straight- line portions disposed around the section of the base) and to vary thei r length and position on the base. In this case the shape of the feet is not critical. As i llustrated, the feet 62 are generally simi lar to that shown in Fig. 5 and the same broad principles apply. An alternative means of strengthening the base is shown in Fig. 9 wherein the base portion 64 is elliptical in section (ie. R1 greater than R2; R3 less than R2) and the radially extending lower portion 66 of the foot 68 is extended further inwards towards the centre of the base. In this way, the feet of the bottle form a series , if downwardly projecting "spurs" di ve rg i ng . rad i a I ly from the centre of the base, effectively bracing it against distortion. As shown, the bottom portion 66 of the foot 68 comprises a straight-line portion tangent to the ar¬ cuate portion 70 and extending inwardly to merge with the bottom portion of the elliptical base. This shape of foot can of course be varied provided that its inner- most termination is as close to the centre of the base as possi b le . Fig. 10 shows a particularly preferred embodiment of the invention wherein the generally elliptical base portion 72 is provided both with a f rusto-conc i a I por- tion (defined by s t ra i gh - I i ne portions 74 and 76) and "spurs" formed by the feet 78 as described above. Again, the size, position and number of the frusto- conical portions and the particular shape of the feet may be varied. Fig. 11 shows a further variation wherein the base portion 80 is part-spherical having radius R4 greater than R1 so that the base portion 80 comprises an arc which joins the vertical side walls 82 without the transitional arcuate portions of an elliptical base. Such a base has not hitherto been considered suitable for use with the pressurised liquids, but the provision of feet having inwardly extending "spurs" as described above enhances its resistance to deformation sufficiently for it to be of practical use for such applications. this base may also be provided with one or more frusto- conical sections as previously described (83. -Fig. 12 ) . A further modification which may be incorporated into any of the embodiments hereinbefore described is an upwardly concave arcuate portion (84, shown in dotted lines in Fig. 12) located at the centre of the base.. This provides further strengthening of the base. Fig. 2 of the drawings shows the base as having nine feet 10. The number of ' feet may be varied, but it is preferred to have a large number (ie. in the range seven to twelve) of relatively small, closely spaced feet, since this provides a stronger structure than fewer, larger feet. An odd number of feet is also preferred since this tends to improve the stabi lity of the bottle if there are slight variations in the size of feet. If the base includes a f rus to-conc i ca I portion, fewer feet are requi red since the basic structure is inherently stronger. If "spurs" alone are used, a larger number of feet is preferable since they contribute directly to the strength of the base. Preferred materials for the container are PET, PVC, polypropylene and polyethylene, including HDPE, LDPE and LLDPE.

Claims: C l a i s 1. A plastics container comprising a generally cylindrical body portion and a generally convex base por ¬ tion closing the bottom of said body portion, said base portion having a plurality of stabi lising feet projecting downwardly therefrom and spaced around the circumference thereof, wherein the fundamental radius of curvature of said base portion is greater than the radius of said body portion, and further including means for increasing the resistance of said base portion to deformation due to internal pressure, said means comprisng spurs, formed by the bottom surfaces of said stabi lising feet, extend¬ ing radially inwards towards the centre of said base portion and terminating at or adjacent to said centre and/or at least one frusto-conical portion superimposed upon said base portion. 2. A container as claimed in claim 1 comprising a generally cylindrical body portion and a generally convex base portion closing the bottom of said base por- tion, said base portion having a plurality of stabi lising feet projecting downwardly therefrom and spaced around the circumference thereof, wherein the fundamental radius of curvature of said base portion is greater than the radius of said body portion, and further including m-eans for increasing the resistance of said base portion to deformation due to internal pressure, said means compris¬ ing spurs, formed by the bottom surfaces of said stabi li¬ sing feet, extending radially inwards towards the centre of said base portion and terminating at or adjacent to said centre. 3. A container as claimed in claim 1 comprising a generally cylindrical body portion and a generally convex base portion, said base portion having a plurality of stabi lising feet projecting downwardly therefrom and spaced around the ci rcumference thereof, wherein the fundamental radius of curvature of said base portion is greater than the radius of said body portion, and further including means for increasing the resistance of said base portion to deformation due to internal pressure, said means comprising at least one frusto-conical portion superimposed upon said base portion. 4. A container as claimed in claim 1 or claim 2 wherein said bottom surfaces of said spurs each comprise, in radial cross-sec ion, a generally s raight-line por¬ tion extending radially inwards and merging with said generally convex base portion adjacent the centre thereof . 5. A container as claimed in claim 1 or claim 3 wherein said base portion, in transverse cross-section comprises a generally arcuate convex wall and each of said frusto-conical por ions comprises a pair of straight- line portions disposed symmetrically about the central axis of the container, superimposed upon said convex wall. 6. A container as claimed in any preceding claim wherein said base portion, in transverse cross-section, is generally part-elliptical, having a bottom arcuate portion of radius greater than the radius of said body portion and fi rst and second peripheral arcuate portions of radius less than the radius of said body portion. 7. A container as claimed in any of claims 1 to 5 wherein said base portion, in transverse cross-section, is generally part-circular, comprising an arc of radius greater than the radius of said body portion. 8. A container as claimed in any preceding claim fur¬ ther including ah upwardly concave portion located at the centre of said base portion. 9. A container as claimed in any preceding claim, wherein said stabi lising feet are generally U-shaped in section perpendicular to their radial axis and radiused into said base portion. 10. A container as claimed in any preceding claim wherein the number of said stabilising feet is in the range 7 to 12. 11. A container as claimed in claim 10 wherein the the number of said stabilising feet is an odd number.

Inventors: OKHAI AZIZ A, OKHAI, AZIZ, A.
Applicants: MERI MATE LTD, MERI-MATE LIMITED
Application year: 1986
Main classification: B65D1
IPC codes: B65D1