Can end
A pressurised can (1) having a body (2) with an open end, through which a product (5) is inserted into the can, and a cover (3) arranged to cover and seal the open end of the body (2). The can is filled to a predetermined height such that the cover (3) is spaced from the product surface (55) to leave a headspace (7). The can (1) is adapted to minimise the volume of the headspace (7), whilst maximising the height (h) of the headspace (7) at the point at which the can (1) is first opened.
The present invention relates to a pressurised can and in particular, to an end suitable for use on a pressurised food can. In a pressurised food can, the food product is inserted into the can and stored therein under pressure. The increased pressure in the can is achieved by pressuring the headspace above the food product.
BACKGROUND ARTPressurisation of the headspace may be achieved in a number of different ways. For example, a droplet of liquid, inert gas may be inserted into the can prior to sealing with the end, as described in US 289844 PABST BREWING COMPANY) The liquid then evaporates and the resultant gas pressurises the headspace. Alternatively, after sealing, a portion of the can may be irreversible pushed inwardly to similarly pressurise the headspace gases by forced reduction of the volume of the headspace. This technique is described in EP 0521642 B (CMB FOODCAN)
DISCLOSURE OF INVENTIONThe advantage of pressuring a can is that the can may be made of substantially thinner gauge metal, which is deformable under normal conditions. The internal pressure in the pressurised can supports the walls of the can, providing the rigidity required for handling and transport.
However, a can whose contents are held under pressure has the disadvantage that upon first opening, the pressure inside the can is rapidly released to the atmosphere and the stream of released gases may carry a quantity of product. This problem is referred to as “spurting” and is highly undesirable for the consumer. In extreme circumstances, such “spurting” may have explosive force making the can dangerous. The present invention is concerned with mitigating or even eradicating “spurting”, upon first opening of a pressurised can.
Preferably, the volume of the headspace (the fee space between the surface of the product and the can) is minimised. This reduces the volume of pressurised gas released from the can upon first opening. However, the inventors have found that the height of the headspace at the point of first opening (i.e. the point at which the can is exposed to atmospheric pressure) needs to be maximised. The height of the headspace at the point of first opening has been found to be critical in determining whether the can will “spurt” when opened by a user.
Conventional food cans comprise a hollow body, in which the product is stored, and at least one end, which is connected to the free edge of the body, conventionally by seaming and in particular by a technique known as double seaming. Conventional ends comprise a flat plate-like centre panel connected to a seaming portion (often referred to as the “cover hook”) via a chuck wall, which-supports a seaming chuck during the double seaming process. At the base of the chuck wall a concave reinforcing bead (looking from the outside of the can) is normally provided, to strengthen the end and support the seam. Conventional can openers first pierce the can at a point adjacent to or lying within the reinforcing bead. Further shallow beads may also be provided on the wall of the can body and/or on the end, to strengthen the can.
Accordingly the invention provides a pressurised can comprising a sealed vessel having an access region at which the sealed vessel is first opened, and a product defining o product surface and a head space, the product confined within the sealed vessel with the headspace arranged in fluid communication with the access region, characterised in that the sealed vessel is adapted to minimise the volume of the headspace, whilst maximising the height of the headspace above the product surface at the access region.
Conventionally, the volume of the headspace in a can is minimised because any volume in the can not used for product is wasteful of space and poorly perceived by consumers. In a pressurised can, the volume of the headspace is particularly important, because this “space” contains the pressurised gas, which pressurises the can and has to be released into the atmosphere on first opening of the can. The inventors have found that the height of the headspace at the point of first opening is particularly important to the spurting properties of the can and should be maximised to reduce the risk of unacceptable spurting. Thus, the design of the can will involve a trade-off between minimising the volume of the headspace for the reasons discussed above and maximising the distance between the surface of the product and the point of first opening of the can, to reduce the chances/level of spurting. This may be achieved by increasing the height of the headspace within an access region, whilst reducing the height/volume of the headspace outside the access region.
Where a can is opened using a conventional can opener or where the can end is a so-called “easy-open end” (i.e. EOLE®), the can is conventionally opened towards the peripheral edge of the can end. In this situation, the central portion of the end may be indented so that it lies closely adjacent to or even touching the surface of the product. This allows the headspace volume to be minimised whilst ensuring that the height of the headspace at the point of first opening is sufficiently large to prevent or at least significantly reduce the level of spurting.
The inventors carried out a number of tests using conventional cans having two different types of end (EOLE®—Easy Open End and NEO—Non-easy Open End), different levels of headspace pressurisation and a height of headspace at the point of first opening of 8 mm. A headspace height of 8 mm was chosen as a good average of the headspace height provided in most conventional food cans. All tests were carried at an ambient temperature of 25° C.; the filled cans were allowed to stand for at least ½ hour before opening and NEO samples were opened using a Standard Butterfly can opener. The level of spurting from the can upon first opening was recorded by holding a sheet of white paper above the end of the can to catch any splatter of product, which was ejected. This test is referred to as the white glove test (WGT). The test is intended to represent the degree of “spurting” that a user would experience, if opening the can whilst wearing white gloves. The test is considered successful, if the user could open the can, with no marks damaging the gloves. The results of the tests are shown in Table 1 (below).
As shown by these results, even at the lowest level of pressurisation of 5 psi (0.34 bar) “spurting” is problematic, for both types of ends. At higher levels of pressurisation, “spurting” becomes unacceptable.
The same series of tests were then carried out for a headspace height at point of first opening of 12 mm and headspace pressurisation of 10 psi (0.69 bar) and 15 psi (1.03 bar), again using the same type of conventional cans and ends. The results of these tests are shown in Table 2.
By comparison of the results from Tables 1 and 2 above, it can be seen that a headspace height of 12 mm at the access region/point of first opening significantly reduces the level of spurting for both EOLE and NEO ends. As expected, lower pressurisation of the headspace results in lower levels of spurting.
This theory works well for liquid products (i.e. water) or products held in a liquid (vegetables in brine, for example), but further problems have been identified with more viscous products (chilli con carne and pet food, for example). When these products are agitated during transport, handling etc. or stored in an inverted position, it takes longer for the product to settle with the headspace in communication with the access region and in some cases this may never occur. In these circumstances, it is likely that at least some product will be retained within the access region, having the larger headspace height at the point of first opening. Consequently containers filled with such viscous products, have been found to spurt upon first opening of the container, despite the can having a maximised headspace height at this point.
In order to gain a better understanding of this phenomenon, a transparent can was filled with various products, to observe the effect of the product on opening of the can. The surface tension of thicker products was observed to cause the product surface to creep up the sidewall of the can, reducing the overall headspace height at the point of first opening.
However, the same surface tension forces of these thicker products can also be used to mitigate this problem, by the careful placement of attraction features within the headspace but outside the access region. If an indentation is provided extending into the headspace of the can, so that it touches or approaches close to the surface of the product, such viscous products will tend to be attracted to the indentation, which acts as an “attraction feature” and draws the product away from the access region, leaving the height of the headspace at the point of first opening largely unobstructed.
Furthermore, the meniscus formed on the surface of a the product has been found to make a “meniscus jump” toward such attraction features, even when they are not in contact with the product surface. Thus, the attraction feature will still draw product away from the access region, increasing the headspace height in this region, providing that it extends far enough towards the product surface to allow the meniscus to make a “meniscus jump” towards it The viscosity and composition of the product will determine the size of gap between the product surface and the attraction feature and therefore the size of “meniscus jump” that the product surface will make.
In an alternative embodiment the can/end are adapted, so that upon first opening (regardless of the headspace height/volume when the can was filled) the can/end accommodates a volume increase of the headspace and the can does not vent to the atmosphere until the end is lifted a predetermined height above the surface of the product. This may be achieved by providing a threaded can/end, in which the thread profile is modified to allow the end to be lifted relative to the can body before finally being unscrewed and the headspace vented to the atmosphere.
This arrangement has several advantages. The can may be filled to conventional fill heights leaving a headspace, which is pressurised. During opening, a user simply unscrews the end. The thread profile is modified so that during unscrewing, the end is first raised relative to the can body without venting to atmosphere. This increases the volume of the headspace, thereby relieving some of the internal pressure in the can. Also, the height of the headspace is increased before the can is first opened (i.e. when the headspace gases vent to atmosphere) is raised. Both these effects minimise “spurting”.
BRIEF DESCRIPTIONS OF THE DRAWINGS
For ease of reference, like features are designated using the same reference numerals throughout the drawings.
Referring to
The body 2 (comprising the sidewall and base) is filled with a product 5 to a predetermined fill height. Where the product 5 is liquid, the product surface 55 win form a meniscus, which is substantially flat. Due to surface tension effects, the product surface 55 will tend to creep up the sidewall of the body 2 to a point 52, where the product surface 55 adjoins the sidewall of the body 2. The free space between the product surface 55 and the end 3 is referred to as the headspace 7 and is filled with gas (normally air or an inert gas). In a pressurised food can, it is this headspace 7, which is pressurised.
Now concentrating on the top end 3 of the can, the periphery of which is wrapped into the double seam 4 together with the open end of the body 2. Positioned radially inwardly of the seam 4, the end 3 has an inwardly concave reinforcing bead 6, which strengthens the end 3. Conventional tin openers pierce the can 1 either at the base of the reinforcing bead 6 or through the sidewall of the body 2, at the base of the seam 4.
Considering a conventional tin opener which first pierces the can at the base of the reinforcing bead 6, the invention teaches that the headspace height h between the point of first opening (i.e. the point at which the tin opener first pierces the can) and the product surface 55 needs to be as large as possible, if “spurting” is to be avoided. However, it is also known that a large headspace volume is undesirable in a pressurised food can because a large headspace volume necessitates venting of a larger volume of gas before the pressure in the can reaches atmospheric pressure. A large headspace 7 is also perceived badly by consumers, who feel cheated by the fact that the can 1 is not as full as originally perceived. Thus, a compromise has to be reached between maximising the height h of the headspace 7, whilst controlling the overall volume of the headspace 7 in the can 1.
Referring now to
FIGS. 5 to 8 show a further embodiment of the invention, which is adapted to mitigate the effect of “spurting” when the can 1 is first opened. In this embodiment, the product fill height is less critical because the opening arrangement is designed to lift the end 3 relative to the body 2 before the can is allowed to vent for the first time. By lifting the end 3 on the body 2 during opening, the internal volume of the can 1 is increased and thereby, the internal pressure is reduced (as shown in
The can 1 may comprise a body 2 and a lid 3 connected together by a screw thread arrangement. The screw thread arrangement is modified, such that the lid 3 can lift a specified distance during unscrewing. This increases the internal volume of the can and thereby reduces the internal pressure thereof, without venting the gases in the headspace 7.
Referring to
Referring to
It can also be seen from
As shown in
Although the screw thread/lug arrangement shown in FIGS. 5 to 12 allows the internal volume of the can to expand and thus some of the internal pressure to be relieved, it is still important that any residual overpressure in the can is allowed to vent safely to atmosphere, before the can is opened. Furthermore, although FIGS. 5 to 12 illustrate examples in which the thread arrangement comprises a thread 42 and a lug 43, arranged to ride along the thread 42, it will be appreciated by those skilled in the art that this could be replaced by a mutually co-operating screw thread arrangement or by some other system, which allows controlled increase in the volume/headspace of the container, whilst preventing uncontrolled venting.
Finally, the lid (3) in the arrangements shown in FIGS. 9 to 12 is described as having a flared portion 35. However, the man skilled in the art will understand that the flared portion on the lid may be replaced by a tapered section of the open end of the body. Alternatively, the thread arrangement may comprise an internal thread on the can body and the lid may take the form of a stopper. In this case, the flared section may be provided at the open end of the body, rather than on the cover.
Claims
1. A pressurised can (1) comprising a sealed vessel (2, 3) having an access region (6) at which the sealed vessel (2, 3) is first opened, and a product (5) defining a product surface (55) adjacent to a headspace (7), the product (5) confined within the sealed vessel (2,3) with the headspace 7 arranged in fluid communication with the access region (6),
- characterised in that
- the sealed vessel (2,3) is adapted to minimise the volume of the headspace (7), whilst maximising the height (h, h′) of the headspace above the product surface (55) at the access region (6).
2. The pressurised can (1) according to claim 1, wherein the sealed vessel (2, 3) has at least one attraction feature (11), which extends into the headspace (7) to a point approaching or in contact with the product surface (55), wherein the attraction feature (11) lies outside the access region (6).
3. The pressurised can (1) according to claim 2, wherein an inwardly concave portion of the sealed vessel (2, 3) provides the attraction feature (11).
4. The pressurised can (1) according to claim 3, wherein the attraction feature (11) is defined by a series of progressively deepening beads, which are arranged to follow the form of a dome extending towards the inside of the sealed vessel (2, 3).
5. The pressurised can (1) according to claim 1, wherein the sealed vessel (2, 3) comprises a body (2) having an opening for inserting the product (5) and a cover (3) arranged to cover and seal the opening after the product (5) is inserted.
6. The pressurised can (1) according to claim 5, wherein the body (2) and cover (3) are connected together by a screw thread arrangement (42, 43) and the screw thread arrangement (42, 43) is adapted to allow the cover (3) to be lifted relative to the body (2) before the can (1) is allowed to vent to atmospheric pressure.
7. A can body (2) and a cover (3) connectable together by a screw thread arrangement (42, 43), wherein the screw thread arrangement (42, 43) is adapted to lift the cover (3) relative to the body (3) by a pre-defined distance during unscrewing of the cover (3) from the body (2).
8. The can body (2) and cover (3) according to claim 7, wherein the periphery of the body (2) and cover (3) are arranged to provide a clearance section at the end of the lifting movement of the cover (3) relative to the body (2).
9. A method of manufacture of a pressurised can (1) comprising the steps of
- taking a body (2) having an opening,
- filling the body (2) with a product (5) through the opening, to define a product surface (55)
- taking a cover (3) adapted to seal the body (2), whilst defining a headspace (7) above the product surface (55)
- pressuring the headspace (7) and sealing the opening of the body (2) with the cover (3),
- wherein the sealed body (2) and cover (3) is designed to maximise the height of the headspace (7) at the point of first opening the cover (3).
10. The pressurised can (1) according to claim 2, wherein the sealed vessel (2, 3) comprises a body (2) having an opening for inserting the product (5) and a cover (3) arranged to cover and seal the opening after the product (5) is inserted.
11. The pressurised can (1) according to claim 3, wherein the sealed vessel (2, 3) comprises a body (2) having an opening for inserting the product (5) and a cover (3) arranged to cover and seal the opening after the product (5) is inserted.
12. The pressurised can (1) according to claim 4, wherein the sealed vessel (2, 3) comprises a body (2) having an opening for inserting the product (5) and a cover (3) arranged to cover and seal the opening after the product (5) is inserted.
Type: Application
Filed: Oct 22, 2004
Publication Date: Mar 29, 2007
Inventors: Terence Benge (Southmoor), Gary Mills (Wantage)
Application Number: 10/576,538
International Classification: B65D 81/20 (20060101);