This invention relates to a can for packaging foodstuffs and a method and apparatus for forming such a can. The invention also relates to the forming of lidding materials for fixing to metal packaging such as metal cans.
In particular, but not exclusively, it relates to the packaging of solid food, for people or pets. Such cans will also be referred to hereinafter as “food cans”.
Metal packaging is known in which a can body having a metal ring seamed to one end of the can body supports a peelable lid which comprises a multi-layer membrane having typically a peelable polypropylene layer, a layer of aluminium, and an outer layer of print, lacquer, PET or other coating. The material of the lidding material is generally chosen according to the requirements dictated by the product with which the can body is filled. For example, there is a need for maintaining seal integrity during processing, sterilisation etc. of food products but the lid must also be capable of being readily opened for access to the food for consumption.
The use of an intermediate metal ring to support the lidding material is usual for optimum seal integrity. However, the production of this ring leads to substantial wastage of material since the central part of the ring cannot economically be re-used for conventional can component sizes. In addition, the ring may reduce access to the can contents. Manufacturing time using separate stages for manufacturing the ring and fixing the lidding material to this ring is also long. There is therefore a need to provide a container in which the lid is bonded directly to the can body, thereby obviating the need for an intermediate component. Manufacture of the packaging can of the invention is also simplified so as to reduce manufacturing costs, whilst facilitating access to the contents of the finished can.
EP-0819086 describes a process for manufacturing a can with a foil membrane, in which the membrane is preformed with a raised edge and is inserted into the can so that the outside edge region is raised in the direction of the can axis. The edge is then connected to the inside of the can wall by an adhesive bond or heat seal. This process is inherently slow because not only does the foil membrane require preforming but careful handling is needed for location in the can body. The can body also has to be removed from the can making line or pass through one or more separate stations for pressing the membrane onto can body wall.
According to the present invention, there is provided a can for packaging food, comprising: a metal can body having an access opening; and a lid for closing the access opening, the lid being fixed directly to the can body; characterised in that the lid is formed of lidding material which comprises a multilayer structure with at least an aluminium layer of from 6 to 90 microns thickness and a bond layer.
Typically, the bond layer of the lidding material is of polypropylene or a modified polypropylene. The can body may be formed from a metal sheet which is coated with a lacquer having polypropylene dispersed in the lacquer. The sheet may then be formed by welding, for example, into a cylinder to provide the can body. The side seam thus formed is generally separately coated with a similar internal lacquer or with a polypropylene powder. Alternatively, the plate could be coated with a conventional lacquer and a specific lacquer, such as one including a dispersion lacquer, used only for coating that part of the can wall and weld which is to contact the foil lidding material.
In one embodiment, the lid may also include an integral tab which may be folded back onto the lid and, optionally, at least partly fixed to the lid, for example by heat sealing or fusion of material so as to keep the tab folded back onto the lid.
The lid may be fixed by tightly heat sealing for fusion of the lidding material directly onto the can body sidewall. This “sealing surface” may be substantially perpendicular to the plane of the access opening. In preferred embodiments of the invention, however, the sealing surface may be inclined at an angle so that opening of the closed container is not entirely in shear mode as would happen when the seam surface is vertical and the pull is vertical. By increasing the sealing surface angle, the container has been found to be easier to open without risking tearing off the tab, even if the customer pulls vertically.
A further advantage of the inclined sealing surface is that the incidence of wrinkles in the lidding material is reduced adjacent the can sidewall and localised peel from the can sidewall is eliminated.
In one embodiment of the invention, the sealing surface may be inclined at angles ranging from 20° to 150° to the vertical. Angles of above 90° are preferred for containers in which the lidding material is deflected in order to control in-can pressure during processing of the food product in the container. So-called barometric ends can be used for processes such as reel and spiral retorts. By increasing the wall angle above 90°, this angle becomes greater than the angle subtended by the extremity of the lidding material in it outwardly domed position. As a result, the bond only undergoes shear loading which effectively doubles burst pressure performance from that of standard cans which are loaded in peel mode.
Although trials have shown that ease of opening increases as the angle increases, the edge of the sidewall protrudes beyond the main sidewall diameter as the sealing surface is inclined. This can cause problems for handling and stacking. For this reason, 90° angles are avoided and for non-barometric ends, preferred sealing surface angles are from 20° to 60° to the vertical, ideally from 30° to 50°. For barometric ends, preferred sealing surface angles are up to 135° to give sufficient dome size. Thus for ease of opening, angles of from 30° to 135° are preferred but for handling, angles of substantially 90° tend to be avoided.
Preferably, the sealing surface is an inner surface of the can body which delimits the access opening. In this embodiment, the lid is substantially dish-shaped with vertical or inclined sidewall according to the sealing surface angle. Alternatively, the sealing surface may be an “outer” surface of the can body which forms part of a peripheral curl bordering the access opening.
Optionally, the tab may extend over the outside of the can body. The lid and tab may comprise non-preformable material.
According to another aspect of the present invention, there is provided a method of manufacturing the above can by directly fixing the lid to the can body, for example by heat sealing or fusion of the lidding material. This method may typically comprise the steps of drawing the lid along a surface which is parallel or inclined at angle to the can body centre axis; and sealing the lid directly to this surface. Alternatively, the method may comprise applying a part of the lid against a peripheral curl of the can body, bordering the access opening; and drawing the lid along the surface while moving the lid in support sliding on the curl.
When the lid includes an integral tab, the method may include folding back the tab onto the lid either prior to or simultaneously with or after fixing the lid to the can body.
According to a still further aspect of the present invention, there is provided a method for forming a lidding material, the method comprising:
supporting a lidding material on a punch;
forming a metal can body having an outwardly extending curl at one end;
supporting the opposite end of the can body on a base support;
moving the can body and punch relative to each other; and
drawing the lidding material which is carried by the punch around the curl of the can body so as to form the lidding material into a cup shape.
By drawing the lidding material around the can body and using the can body as a forming die, the lidding material can be both formed and held within the can body at a single station for fixing to the inner sidewall of the can body.
The step of moving the can body and punch relative to each other may be achieved by pushing the can body with the base support while the punch is moved into the can body, or holding the punch stationary while the can body is moved axially over the punch, or a combination of these.
According to a further aspect of the present invention, there is provided an apparatus for forming a lidding material, the apparatus comprising:
a metal can body having an outwardly extending curl at one end;
a base support for supporting the opposite end of the can body; and
a punch; in which the can body acts as a forming die so that lidding material which is carried by the punch is formed into a cup shape by drawing around the curl of the can body.
The apparatus may also include an ejector die surrounding the punch so that relative movement between the ejector die and the can body releases the punch from the can body after forming of the lidding material. The ejector die may be surrounded by a locator die for holding the lidding material in position on the punch, prior to and during forming.
Preferably, the base support acts as a pusher but in an alternative embodiment the punch could act as a pusher if the can is held stationary. Clearly it is also possible for both the base support and the punch to act as pushers, although this is less practical.
The base support may comprise a plate with a central mandrel extending from the plate into the can body. If the can body is flanged, then this flange may be located against the base support plate. The diameter of the central mandrel is selected for ease of sliding into the can body with a small clearance.
Ideally, the punch has an end portion which extends axially at least 2 mm. This end portion carries the lidding material as it forms around the can body so that the diameter of the punch end portion needs to be an interference fit or only sufficiently less than the can body inner wall and the thickness of the lidding material that the cup shape formed by the lidding material is held for bonding against the can body sidewall without damaging the lidding material or base flange. The seal length may be greater than 2 mm, for example around 2.5 mm. The punch internal diameter may be slightly greater than the can internal diameter so as to stretch the can body in an interference fit to assist in providing pressure across the seal and create a good bond.
The apparatus preferably further includes an induction heater coil which surrounds the can body or is within the punch when the punch is holding the cup of lidding material against the can body inner wall. The base support, punch and other apparatus components other than the can body may be made of metals with low electrical conductivity, polymeric, glass or ceramic material so that the induction heater only induces heat in the can body and lidding material for bonding the lidding material to the can body inner wall.
Preferred embodiments of the invention will now be described, by way of example only, with reference to the drawings, in which:
The metal can body is generally cylindrical, having a circular cross-section. The can body thus comprises two extremities. A first extremity forms a peripheral curl 20 which is shaped like a tubular ring (“toric” shape) and borders the access opening 14, while the other extremity has a flare 22, on a level with the second extremity, designed to receive a conventional can end (not shown).
The lid 16 is sealed directly onto the can body, to an upper part 24A of an inner surface of the can body, adjacent the curl 20. This inner surface 24 delimits the access opening 14 and, in this embodiment, is substantially perpendicular to the plane of this access opening 14. The lid 16 is sealed onto the can body 12 by a tight circumferential seam 26, obtained by fusion (heat sealing) of its material.
The tab 18 of this example is sealed at its base 18A onto the lid 16 in such a way as to keep it folded back onto this lid 16. The base 18A of the tab 18 corresponds to the part of the tab 18 extending from the junction with the lid 16 along the sealed part of the lid.
The tab 18 is sealed to the lid 16 by fusion of material. More precisely, in the example shown in
A process for manufacturing the can 10 of
The can body 12 is then brought close to the lid 16 so as to apply the peripheral flange 20 against a part of this lid 16. The relative centring of the can body 12 with the lid 16 is ensured by a sleeve 34 for centring the can body relative to its support 28. The periphery of the lid 16 is thus pinched between the curl 20 and the face 33 of the sliding cylinder 32.
The descent of the can body 12 then brings about the downward sliding of the cylinder 32. The disc 30 then draws the lid 16 along the inner surface 24, this lid 16 being moved in sliding support between the curl 20 and the face 33 of the sliding cylinder 32. At the end of the drawing process, the lid is released from this sliding support and takes the form of a dish with flat bottom 16A and substantially cylindrical sidewall 16B.
One thus obtains the drawn configuration represented in
In the following figures, the elements analogous to those of the first embodiment are designated by identical references.
In a small scale trial, the embodiments of
The embodiment of
The foil for all embodiments was fixed to the can body by heat sealing. When heating the can using an external induction heater to seal the foil in place, a long delay is necessary to cool the can before the punch can be successfully removed, without dragging the foil out with the punch and degrading the quality of the seal. This can also be improved by using an internal heater radially inboard of the foil and can sidewall so that the can is not directly adjacent the heater. The foil which is adjacent the heater reduces direct heating of the can body curl which, in turn, may lead to lacquer damage and subsequent rusting of the can body. Furthermore, the tapered can and punch allows the punch to be withdrawn sooner as the foil is not gripped by the punch when tapered.
The rigidity of cans having a taper in the top of the can and top double seam curl and increased can gauge (
Cans with a top taper can be stacked without the need for inward necking of the can bottom. The elimination of the neck creates improved axial strength as well as providing more flat surface area for paper labelling. Straight walled cans of
When the foil is sealed to the can body, the lower the sealing surface angle, the greater the tendency for the foil to wrinkle when sealed and processed with a vacuum (low pressure). A taper of 30° or more reduces this wrinkling to the point of acceptability.
The apparatus of
At the opposite end, the can body has a curl 126. The lidding material will be fixed to this end prior to filling as is described in more detail below. A punch surrounded by ejector 140 and foil locator 150 supports lidding material 160 in the start position shown in
The lidding material of the example shown in the figures may be a foil type of lidding or a flexible lidding. One example of a foil lidding material comprises a base layer of peelable polypropylene of about 25 microns thickness, a layer of aluminium of from 40 to 90 microns thickness, typically around 70 microns, and a print, lacquer, PET layer or other coating. Optionally, a thin layer of corrosion resistant lacquer may be provided between the polypropylene layer and the aluminium layer. The polypropylene layer is generally a single layer having about 7 microns of polypropylene which has been modified so as to adhere to the aluminium layer, and about 18 microns of polypropylene modified with polyethylene and/or other materials which is peelable when sealed against polypropylene.
One example of a flexible lidding material comprises a base layer of 25 to 100 microns or more of polypropylene, which has been modified to be peelable, 6 to 40 microns of aluminium and 12 to 25 microns of polyethylene terephthalate (PET).
Another example is to use the same lidding material but with 15 to 30 microns of a nylon between the polypropylene and the aluminium.
In the position shown in
In
After the lidding material cup has been formed, the apparatus is passed through an induction coil with at least the base support, can body and punch remaining in position. Heat is induced in the can body and lidding material so that the polypropylene layer of the lidding material bonds to polypropylene in the lacquer to fix the lidding cup to the can body. Because the punch and base support are of polymeric, glass or ceramic material, no heat is induced in these components and the polypropylene will not adhere to them.
When the lidding material cup 160′ has been bonded to the can sidewall, the punch 130 is withdrawn whilst ejector 140 is held against the curl 126. A taper provided on the can and punch to improve this removal. A taper of up to 90° or as in the specific examples of
The punch could be profiled and/or biased radially to ensure good contact over the bond region, particularly over the welded side seam. Alternative methods of biasing such as use of a conformed tool, springs, pneumatic or separate punch segments are possible.
Although the embodiment of
The fourth embodiment of
The final embodiment of
Thus in each embodiment, the lid is tightly sealed directly onto a surface of the can body. Where the sealing surface is parallel to the central axis of the can 10, the seal is broken by shearing which ensures a firm hold of the lid 16 on the can body. Where the sealing surface is inclined, opening forces are substantially reduced and opening is achieved without risk of tearing of the tab.
Number | Date | Country | Kind |
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05101552.7 | Mar 2005 | EP | regional |
0504741 | May 2005 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2006/060094 | 2/20/2006 | WO | 00 | 6/9/2008 |