GB2093793A

GB2093793A - Plastics containers

Info

Publication number: GB2093793A
Application number: GB8205730A
Authority: GB
Original assignee: National Plastics Ltd
Current assignee: National Plastics Ltd
Priority date: 1981-02-27
Filing date: 1982-02-26
Publication date: 1982-09-08

Abstract

A moulded plastics container has a side wall (1), a base wall (2) and a peripheral flange (3), the base wall (2) having projections (6) depending from therefrom in spaced concentric closed figures around its centre, the thickness of the base wall being reduced in the region of the projections. When the container is filled, the base wall bulges downwardly, the projections contact the supporting surface on which the container is standing, and the thinner region of the base wall bends to maximise that contact and so provide additional frictional grip on the supporting surface. <IMAGE>

Description

SPECIFICATION Containers This invention relates to containers of plastics material in the form of a side wall or walls integral with or joined to a base wall. Such containers may be moulded in a single operation as an integral unit, for example by injection moulding, or the side wall or walls may be moulded separately from the base wall and joined to it in a separate operation, for example by friction welding. The top of the container may be open or closed or fitted with a lid or other closure.

In this specification, expressions such as 'top', 'lower', 'upper', 'base' and 'below' are used for convenience with reference to the container of the invention in its normal mode resting on its base, but are not meant to limit the invention to containers disposed in that mode alone.

It is usual in the production of a container by injection moulding of thermoplastic materials to form the base wall of the container with some kind of irregularity disposed in a circle or other closed figure around the centre of the base in order to reduce the stresses which are set up in the base wall by the moulding process. Without such an irregularity there is a risk of distortion or splitting of the base wall resulting from these stresses. One common form of irregularity, which is included in the container illustrated in our British Patent No.

1,602,818, is a projection of part-circular crosssection, depending below the base wall along a circular ring around the centre of the base wall, and defining a complementary depression in the upper surface of the base wall so that the thickness of the base wall is substantially uniform.

The container shown in that Patent has a peripheral base flange depending below the base wall and this normally holds the base wall clear of any supporting surface on which the container is standing. However, we have found that when the container is filled, the base wall may be bowed downwardly by the weight of the contents until the dependent projection contacts the supporting surface. By modification of the base wall this phenomenon can be put to advantage to increase the frictional engagement between the container and a supporting surface on which it stands. Good frictional engagement is desirable when the supporting surface is the surface of a conveyor or other moving part in container-filling or mechanical handling equipment.

According to this invention a container of plastics material comprises a side wall or walls integral with or joined to a base wall, a peripheral base flange depending below the base wall, and a plurality of projections depending from the base wall and extending along spaced concentric closed figures around its centre, said projections having a depth such that, when the container is empty and standing on a flat surface, the lower end of each projection is disposed above said flat surface, and the base wall having a reduced thickness in the region of the projections giving that region an increased flexibility compared with other regions of the base wall.

Preferably, when the container is empty and standing on a flat surface, the lower ends of all said projections lie in a plane above and substantially parallel to said flat surface.

When the container of the invention is filled and the base wall bows downwardly as described previously, then upon the innermost projection or projections engaging a surface on which the container is standing, local bending of the base wall occurs in the region of reduced thickness so that all of the projections make contact with the surface and enhance the frictional engagement between the container and the surface.

The projections may comprise continuous ribs extending along the closed figures, or spaced discontinuous rib sections or teeth extending along the closed figures. They may extend along closed figures which are concentric with the peripheral base flange. Preferably the projections extend along circular figures.

The flexibility of the base wall in the region from which the projections depend may be enhanced by having that region itself formed into a projection which depends below the other regions of the base wall and which defines a complementary depression in the upper surface of the base wall in that region. The projecting part of the base wall may be suitably downwardly-convex in cross-section.

The invention is illustrated by way of example by the accompanying drawing, in which: Figure 1 is an elevation, half in section, of the lower part of a container according to the invention, Figure 2 is an inverted plan of the container of Figure 1, and Figure 3 is a fragmental cross-sectional view on an enlarged scale, of part of the base of the container of Figure 1 when filled.

The container shown is circular in plan with a cylindrical side wall 1 and a circular base wall 2 surrounded by a peripheral base flange 3 the outer surface of which is continuous with the outer surface of the side wall. The side wall 1, base wall 2 and base flange 3 are integrally moulded in plastics material, for example polypropylene.

As shown, the base wall 2 of the container is formed with an annular projection 4, of downwardly-convex cross-section, which is disposed around the centre of the base wall. A complementary depression 5 is formed in the upper surface of the base wall. The thickness of the base wall at that region which defines the projection 4 and complementary depression 5 is slightly less than that of the other regions of the base wall. Extending downwardly from the projection 4 are three integrally-formed projections, in the form of concentric ribs 6, which, when the container is empty and standing on a flat surface, have their lower ends lying in a plane disposed above and substantially parallel to said flat surface.

When the container is filled, however, the weight of the contents causes the base wall 2 to bow downwardly. This bowing may be sufficient to depress the innermost of the ribs 6 to the level of the edge of the base flange 3 so that it would contact any flat surface on which the container was placed. It is intended that when the container is filled with the contents for which it is designed the downward bowing of the base wall 2 will be sufficient to cause substantial engagement between the ribs 6 and a flat surface on which the container stands.

Figure 3 shows such engagement. It will be understood that with ribs 6 of equal depth, the initial engagement between the ribs 6 and the supporting surface 7 on which the container stands will be at the inner edge 8 of the innermost rib 6. This will be line contact around the circular edge of the rib and would not provide significant frictional grip with the supporting surface 7.

However, due to the reduced thickness of the base wall in the region forming the projection 4, locaiised bending takes place in this region so that all three of the ribs 6 engage squarely with the supporting surface 7, thus providing an enhanced frictional grip to resist slipping of the container on the surface.

Instead of the circular ribs 6 a number of separate projections could be disposed in concentric rings and their shape and spacing could be designed to provide a mechanical as well as frictional grip with a suitably roughened surface.

Claims

1. A container of plastics material comprising a side wall or walls integral with or joined to a base wall, a peripheral base flange depending below the base wall, and a plurality of projections depending from the base wall and extending along spaced concentric closed figures around its centre, said projections having a depth such that, when the container is empty and standing on a flat surface, the lower end of each projection is disposed above said flat surface, and the base wall having a reduced thickness in the region of the projections giving that region an increased flexibility compared with other regions of the base wall.

2. A container as claimed in claim 1, in which, when the container is empty and standing on a flat surface, the lower ends of all said projections lie in a plane above and substantially parallel to said flat surface.

3. A container as claimed in claim 1 or claim 2, in which the projections comprise continuous ribs extending along said closed figures.

4. A container as claimed in claim 1 or claim 3, in which the projections comprise spaced discontinuous rib sections or teeth extending along said closed figures.

5. A container as claimed in any of claims 1 to 4, in which the projections extend along closed figures which are concentric with the peripheral base flange.

6. A container as claimed in any of claims 1 to 5, in which the projections extend along circular figures.

7. A container as claimed in any of claims 1 to 6, in which the region of the base wall from which the projections depend is itself formed into a projection depending below the other regions of the base wall and defining a complementary depression in the upper surface of the base wall in said region.

8. A container constructed and arranged substantially as herein described with reference to, and as illustrated in, the accompanying drawing.