Expanded cans

Details Expanded cans Expanded cans

2000-08-04

2001-04-24

Moy, Joseph M. (Department: 3727)

Receptacles

Sidewall structure

Contoured sidewall

C220S675000, C220S669000

Reexamination Certificate

active

06220475

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to expanded cans. In particular it relates to a can having a cylindrical side wall with a regular pattern of expanded elements. The cylindrical can side wall has either an integral base and a single can end (as in a so-called “two-piece” can) or is closed at both ends (as in a so-called “three-piece” or an aerosol can).
Cans having a patterned side wall have been produced in order to improve resistance against deformation by external pressure. These known cans have pattern elements which are pressed into the side wall of the can blank in order to provide improved axial load or panel performance. Since the elements are only provided for structural reasons, any “pattern” is often covered by a product label. In any case, these cans have only achieved limited shape definition, i.e. a shape which is clearly visible to a consumer, and reduce the capacity of the can of a particular aspect ratio.
EP-A-0 441 618 describes cans having patterned side walls which are typical of those referred to above. The pattern elements of EP-A-0 441 618 are formed entirely by pressing inwardly on the can side wall such that the pattern elements are externally concave with their sides being at the original side wall diameter.
U.S. Pat. No. 3,335,902 describes superimposed axial and circumferential beading rather than pattern elements.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a metal can formed from a can blank having at least a cylindrical side wall, the side wall of the can comprising a regular pattern of individual polygonal pattern elements, in which: the pattern elements are arranged in at least two circumferential rows and at least two longitudinal columns; and each polygon comprises between 3 and 10 sides; characterised in that: at least some of the pattern elements are formed by expanding the cylindrical side wall of the can blank so that the can side wall extends beyond its original radius, each such expanded pattern element having an externally concave radius around its edges and an externally convex radius adjacent the concave radius, towards the centre of the pattern element; in which the concave radius is substantially constant around the element; the size of the convex radius is directly proportional to its distance from the centre of the pattern element; and the expansion of any point on an expanded pattern element is inversely proportional to its distance from the centre of the pattern element.
The Applicant has found that cans according to the present invention have great visual impact without reducing the can capacity of a particular aspect ratio. Furthermore, by varying the convex radius according to its distance from the centre of the element, splitting of the can side wall, especially at any corners of the pattern element, due to expansion is substantially avoided whilst maintaining definition of the pattern element shape.
In a preferred embodiment, any of the pattern elements may include, in addition to one or more expanded regions, one or more parts which are formed by depressing the cylindrical side wall of the can blank. The sides of the pattern elements may be at the original can side wall diameter.
Alternatively, the pattern elements may be curved in outline, for example tear drop shaped, circular, etc.
In one embodiment, when the pattern element is viewed in plan, the sides of any of the pattern elements are linear, curved, or comprise a complex curve. The sides of any of the pattern elements may meet at a radius, the maximum size of which is preferably directly proportional to the size of the pattern element.
The individual pattern elements may touch or overlap each other, or may themselves be separated by spaces either longitudinally or circumferentially or both. One or more spaces between columns of pattern elements may be provided for a logo, print or label.
The patterned side wall may be expanded by anything from 2% to 20%, dependent on pattern element size. Where the can blank has an integral base and side wall, as in a so-called two-piece can, the expansion is preferably not greater than 10%. The maximum expansion for a two piece can is limited by the degree of work hardening of the can side wall. The can blank is usually formed from aluminium or steel or alloys of either of these. The can blank side wall may be between 0.075 mm and 0.15 mm in thickness if made of aluminium, typically about 0.1 mm. If the can blank is of steel, the thickness of the side wall may be between 0.06 mm and 0.18 mm, typically about 0.08 mm. The closed and pressurised can may withstand up to 7 bar without pattern reversal. By pattern reversal is meant that radially inwardly extending parts of the pattern are pushed outwardly by pressure inside the can. This at least diminishes pattern definition and at worst, over 7 bar internal pressure, may result in buckling and/or loss of any visual pattern at all.
In one embodiment, the rows of pattern elements are out of phase with each other such that elements of adjacent rows are displaced longitudinally.
The patterned elements may be positioned anywhere on the can side wall and it may be preferred to include a margin at either or both ends of the side wall. This margin may be the same diameter as the original can blank side wall or may be expanded in the same way as the pattern.
Can expansion may be achieved by any of a variety of known methods such as by using an expanding mandrel, fluid jets, a roller device which rolls around and/or up the inner side wall, or by fluid pressure in a closed can. This last is sometimes referred to as blow forming the fluid is air. In some cases, particularly blow forming, the can is expanded to the shape of a mould.
Preferred embodiments of the invention will now be described, by way of example only, with reference to the drawings, in which:


REFERENCES:
patent: 3335902 (1967-08-01), Javorik
patent: 4050605 (1977-09-01), Wakana et al.
patent: 5100017 (1992-03-01), Ishnabe et al.
patent: 5178289 (1993-01-01), Krishnakumar et al.
patent: 044618A (1991-08-01), None
patent: 9640457A (1996-12-01), None

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