Packaging can and method and apparatus for its manufacture

Abstract

A can for packaging food, comprising a metal can body and a diaphragm lid (16) formed of lidding material which comprises a multilayer structure with at least an aluminum layer of from 6 to 90 microns thickness and a bond layer for fixing the lid (16) directly to the can body. One method for forming the can forms the lidding material by using an outwardly extending curl (20) at one end of the metal can body as the draw die. Lidding material which is carried by the body maker punch is drawn around the curl of the can body draw die so as to form the lidding material into a cup shape.

Claims

1. A method for manufacturing a can for food packaging, the method comprising: supporting a lidding material on a punch, the lidding material defining a tab, the tab configured to be grasped by the user to remove the lidding material from a metal can body; positioning the metal can body having an open end, an outwardly extending curl disposed about the open end, a sidewall, and a sealing surface adjacent the curl, the sealing surface being inclined upwards and outwards with respect to a can body center axis at an angle between 20 and 60; supporting the can body on a base support; moving the can body and punch relative to each other; drawing the lidding material that is carried by the punch, along the sealing surface of the can body; and sealing the lidding material directly to the sealing surface of the can body.

2. A method according to claim 1, wherein the sealing step comprises induction heating at least one of the lidding material and the can body so as to bond the lidding material directly to the can body.

3. A method according to claim 1, wherein the step of moving the can body and punch relative to each other comprises 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.

4. An apparatus for forming a sealed food can, the apparatus comprising: a metal can body having an open end, an outwardly extending curl, a sidewall, and a sealing surface adjacent the curl, the sealing surface being inclined upwards and outwards with respect to a can body center axis at an angle between 20 and 60; a base support for supporting the can body; and a punch configured to carry a lidding material that defines a tab, the tab configured to be grasped by the user to remove the lidding material from the metal can body; wherein the can body acts as a forming die such that, in use, the lidding material is adapted to be drawn along the sealing surface of the can body and is held directly against the sealing surface for bonding.

5. An apparatus according to claim 4, in which the punch has an end portion which has a diameter which is less than that of the can body inner wall and which extends axially at least 2 mm.

6. An apparatus according to claim 4, further including an induction heater coil that surrounds the can body either externally or radially-inboard of the can body and lidding material.

7. An apparatus according to claim 4, wherein the can body is formed from a metal sheet into a cylinder and a side seam formed from the metal sheet is coated with an internal lacquer or with a polypropylene powder.

8. An apparatus according to claim 4, wherein the base support comprises a plate that is coated with a conventional lacquer and a lacquer which includes a dispersion lacquer is used only for coating that part of the can and side seam which is to contact the lidding material.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Preferred embodiments of the invention will now be described, by way of example only, with reference to the drawings, in which:

(2) FIG. 1 is a perspective view of a food can according to a first embodiment of the invention;

(3) FIG. 2 is a side view of the can of FIG. 1;

(4) FIGS. 3 and 4 are side views of the can body and lid of FIGS. 1 and 2 during manufacture;

(5) FIGS. 5, 6, 7 and 8 are views analogous to those of FIGS. 1 to 4, according to a second embodiment of the invention;

(6) FIG. 9 is a side sectional view of a third embodiment of the inventiona food canwhich has an angled sealing surface;

(7) FIGS. 10 and 11 are side views of the can of FIG. 9, showing an apparatus for forming the lidding material before and after forming;

(8) FIG. 12 is a schematic side section of another apparatus for forming the lidding material into a cup;

(9) FIG. 13 is a schematic side section of the apparatus of FIG. 12, after forming the cup of lidding material;

(10) FIGS. 14 and 15 are views analogous to FIGS. 1 and 2, showing a fourth embodiment of the invention; and

(11) FIG. 16 is a side view of a further embodiment of can which has a barometric lid.

DETAILED DESCRIPTION

(12) FIG. 1 shows a can for packaging foodstuffs, designated by the general reference 10. The food can 10 comprises a metal can body 12 having an access opening 14, a lid 16 (also referred to as foil or lidding material) for closing the access opening 14 and an opening tab 18. The tab 18 shown in FIG. 1 is integral (a single piece) with the lid 16 and projects over the edge of the latter and is folded back onto this lid. Optionally, of course, the tab 18 could be made from a separate piece of material and fixed to the lid 16 in any desired position.

(13) The metal can body 12 is generally cylindrical, having a circular cross-section. The can body 12 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. The other extremity has a flare 22, on a level with the second extremity, designed to receive a conventional can end (not shown).

(14) The lid 16 is sealed directly onto the can body 12, to an upper part 24A of an inner surface of the can body, adjacent the curl 20. This inner surface 24A delimits the access opening 14 and, in this embodiment, is substantially perpendicular to the plane of the 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.

(15) 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 the lid. The base 18A of the tab 18 corresponds to the part of the tab extending from the junction with the lid 16 along the sealed part of the lid.

(16) The tab 18 is sealed to the lid 16 by fusion of material. More precisely, in the example shown in FIGS. 1 and 2, the outer face of the lid 16 in relation to the can body 12, as well as the face of the tab 18 opposite the lid in folded-back position, are covered by a film which is heat-sealable onto itself, for example of the polyethylene terephthalate (PET) type. The lid 16 and the tab 18 can comprise a non-preformable material; for example, mainly based on polypropylene (pp). This material may in particular have the following composition: 9 microns aluminum, 12 microns nylon (OPA) and 50 to 80 microns polypropylene. As a variant, the lid 16 and tab 18 comprise a pre-formable material; for example, based on aluminum.

(17) A process for manufacturing the can 10 of FIGS. 1 and 2 will now be described. With reference to FIG. 3, after having folded back the tab 18 onto the lid 16, the lid is positioned so that the tab is under the lid and the lid rests on a support 28. The support comprises a fixed disc 30 surrounded by a cylinder 32 which is slidable coaxially relative to the disc 30 and returnable elastically upwards to a position in which its upper annular face 33 is coplanar with that of the disc 30.

(18) The can body 12 is then brought close to the lid 16 so as to apply the peripheral curl 20 against a part of this lid 16. The relative centering of the can body 12 with the lid 16 is ensured by a sleeve 34 for centering the can body relative to the lid's support 28. The periphery of the lid 16 is thus pinched between the curl 20 and the upper annular face 33 of the sliding cylinder 32.

(19) 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, the lid 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 a flat bottom 16A and substantially cylindrical sidewall 16B.

(20) One thus obtains the drawn configuration represented in FIG. 4. While keeping this configuration, the parts of the lid 16 in contact with the upper part 24A of the inner surface 24 are then heated, typically by induction heating either externally to the can upper sidewall or within the dish of the foil lid, so as to seal this lid onto the can body 12 by fusion of its material. The residual heat being diffused in the lid 16 at the same time may be used to seal the tab 18 onto the lid 16 so that two bonds are realized in a single operation. However, it is not always necessary or even desirable to seal the tab onto the can body.

(21) In the following figures, the elements analogous to those of the first embodiment are designated by identical references.

(22) FIGS. 5 and 6 represent a second embodiment of the invention. This embodiment differs from the previous one in that the tab 18 extends over the outside of the can body 12. The manufacturing process of this embodiment is represented in FIGS. 7 and 8. Unlike the process of FIGS. 3 and 4, the lid 16 is centered on the support 28 with the tab folded back. During the stage of drawing the lid 16, the centering sleeve 34 allows the tab 18 to be guided in such a way that it extends along the can body 12.

(23) FIG. 9 shows a third embodiment of the invention, in which the sealing surface 24A is inclined at an angle of 45. The tab 18 in its folded and unfolded positions corresponds to that shown in FIGS. 1 and 5 respectively. The tab 18 could be pre-folded and then the lidding material placed on the punch 30 (see FIGS. 10 and 11). Alternatively, the punch 30 could be allowed to fold the tab, although care is then required to avoid the tab 18 bonding to the top of the curl of the can body.

(24) In a small scale trial, the embodiments of FIG. 2 (vertical seal) and FIG. 9 were tested by a random group for openability. The vertical sealing surface 24A of the cans of FIG. 2 was considered by many of the group to be unconventional and so individuals had to decide on a new opening technique. Two separate sample batches of cans according to FIG. 2 were tested by the group. In the first batch, 61% of the tabs stayed attached and 31% of the ends were removed completely. In the second batch, only 17% of tabs stayed attached and 8% of the ends were removed completely. The main problem with the FIG. 2 cans appeared to be that the tab was too tight so that it was hard to pull out and to break the seal with the can body. Careful pulling of the tab at the beginning and end of the opening process was required in order to peel open the whole of lid without risk of tearing.

(25) The embodiment of FIG. 9 was also tested for a variety of taper angles, the taper being present on both the sealing surface 24A of the can (FIG. 9) and punch 30A (FIGS. 10 and 11). Cans and punches having tapers of 30, 40 and 60 were tested. The tab 16 could be pulled and the lidding removed in 100% of the can batches and for all angles tested. Openability was clearly improved with the sealing surface angled outwards as in FIG. 9. It is believed that reducing the angle between the sealing surface 24A and the vertical (direction of tab pull) led to successful opening, even when pulling the tab 18 vertically.

(26) The foil 16 for all embodiments was fixed to the can body 12 by heat sealing. When heating the can using an external induction heater to seal the foil 16 in place, a long delay is necessary to cool the can before the punch 30 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 16 and can sidewall 24 so that the can sidewall is not directly adjacent the heater. The foil 16 which is adjacent the heater reduces direct heating of the can body curl 20 which, in turn, may lead to lacquer damage and subsequent rusting of the can body. Furthermore, the tapered can and punch 30 allows the punch to be withdrawn sooner as the foil 16 is not gripped by the punch when tapered.

(27) The rigidity of cans having a taper in the top of the can and top double seam curl and increased can gauge (FIG. 9) was also compared with the straight walled cans (FIG. 2). The straight walled cans 10 of FIG. 2 did not have enough hoop strength to withstand impact before collapsing at a very low height. Gripping of the straight walled cans 10 to open or peel back the foil 16 and transporting on conveyor belts could cause the can to flex inwardly and for product to be forced outwards and spill. The tapered cans of FIG. 9 enabled the cans to be dropped at 0.8 m for a 30 taper, 1.08 m for a 45 taper and 1.23 m for a 60 taper before the foil bursts. When opened by a consumer, tapered wall cans no longer flex inwards.

(28) 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 10 of FIG. 2 which had to be necked for stacking caused problems when forming the top curl 20, as the necked-in part requires extra support. Also when induction heating the straight walled can 10, when the clamp pressure is too high the can may crumple if it is slightly out of height specification. This would lead to unacceptable downtime in production lines. The increased top diameter due to the taper in the cans of FIG. 9 allows the bottom of one can to fit snugly into the top of the next can. A 30 taper is a little tight in stacking, 60 is a little loose and around 45 is about ideal.

(29) When the foil 16 is sealed to the can body, the lower the sealing surface 24A 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.

(30) The apparatus of FIG. 12 shows a base support 110 of polymeric, glass or ceramic material which includes a mandrel portion 112 which enters a can body 120. The can body 120 has been formed in conventional manner for a so-called three piece can, by welding a sheet of lacquered tinplate into a cylinder. A further lacquer layer (side stripe) is painted, roller coated or sprayed over the welded side seam. Can body 120 is shown in diagrammatic form only and not in any way to scale. The can body 120 is flanged at one end, this end being known as the filler's end, being the end through which the can body is filled with product. The flange 122 contacts plate 114 of the base support 110. This end may also be necked to reduce the sidewall diameter by typically 1 to 4 mm for improved stackability of the filled and closed container.

(31) At the opposite end, the can body 120 has a curl 126. The lidding material 160 will be fixed to this end prior to filling, as is described in more detail below. A punch 130 surrounded by ejector 140 and foil locator 150 supports lidding material 160 in the start position shown in FIG. 12. The base support 110 is pushed into the open end of the can body 120 with the piston and ejector biased against the curl 126.

(32) The lidding material 160 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 aluminum 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 aluminum 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 aluminum layer, and about 18 microns of polypropylene modified with polyethylene and/or other materials which is peelable when sealed against polypropylene.

(33) 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 aluminum, and 12 to 25 microns of polyethylene terephthalate (PET).

(34) Another example is to use the same lidding material, but with 15 to 30 microns of a nylon between the polypropylene and the aluminum.

(35) In the position shown in FIG. 13, the punch 130 has entered the curled end of the can body 120, carrying the lidding material 160 with it. The lidding material 160 is drawn around the curl 126 until the sidewall of the lidding material cup 160 contacts the can body sidewall by at least 2 mm (typically between 2 and 5 mm).

(36) In FIG. 13, the lidding material cup 160 extends into an integral tab 162 for ease of opening the can. This tab 162 could be folded over before, during or after forming, or alternatively could be a discrete tab which is positioned elsewhere on the lidding material, for example in the center of the cup. In this case, the tab could be fixed to the cup after forming, or to the lidding material prior to the drawing operation.

(37) After the lidding material cup 160 has been formed, the apparatus is passed through an induction coil with at least the base support 110, can body 120 and punch 130 remaining in position. Heat is induced in the can body 120 and lidding material 160 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 130 and base support 110 are of polymeric, glass or ceramic material, no heat is induced in these components and the polypropylene will not adhere to them.

(38) When the lidding material cup 160 has been bonded to the can sidewall, the punch 130 is withdrawn whilst the ejector 140 is held against the curl 126. A taper provided on the can and punch improves this removal; a taper of up to 90 or as in the specific examples of FIG. 9 will improve release of the can. The can body 120 which is closed by the cup 160 is then removed from the base support mandrel 112 for filling. In contrast with can bodies of the prior art, the can body 120 of the present invention is closed by the peelable membrane by the can manufacturer, and the filler can fill and close the base of the can with conventional machinery without the requirement to be able to fix a peelable membrane closure. This is clearly of great benefit to the filler.

(39) 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.

(40) Although the embodiment of FIGS. 12 and 13 has been described with the can body being used as the forming die and avoiding the need for an intermediate ring to which the membrane is fixed, it would clearly be possible (although not as economic) to use an intermediate ring as the forming die.

(41) The fourth embodiment of FIGS. 14 and 15 differs from the previous ones in that the lid is sealed directly onto an outer surface of the can body 12. More precisely, it is sealed onto the toric curl 20 and, in particular, onto the outermost surface 36 of the latter, which is more or less perpendicular to the plane of the access opening 14.

(42) The final embodiment of FIG. 16 shows a container for a barometric lid,

(43) in which the sealing surface 24A angle is 115 to the vertical. Although this extends the sealing surface significantly beyond the can body diameter, this enables in-can pressure during processing of a food product in the container to be controlled. The bond of the sealing surface 24A of FIG. 16 only undergoes shear loading and thereby improves burst pressure performance significantly. The container of FIG. 16 can thus be used for processing of products in non-overpressure processes, such as using hydrostatic or reel and spiral retorts.

(44) 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.