CAN END

Abstract: An easy open can end is formed of an aluminium alloy, having a thickness of 0.22 mm or less, and having a proof strength of 250 N/mm<2> or less. The can end may typically be formed of 5052 alloy heat treated to H44 temper, typically providing a proof strength of 205 N/mm<2>. The can end is suitable for non-carbonated products, particularly hot-fill products in which the can end is reformed after filling.

Description: CAN END This invention relates to ends for containers, and more specifically to easy open can ends. Conventional easy open can ends for carbonated beverages are formed from pre-lacquered 5182 aluminium alloys. This alloy is chosen as it is a relatively hard alloy and, together with other design features such as the formation of an annular countersink to strengthen the can end, the aim is to make the can end as rigid as possible. This allows successively thinner material to be used, in order to provide material savings and, as aluminium is a relatively expensive raw material, consequent cost savings . It is an objective of the present invention to provide an easy open can end having very different characteristics, for uses other than with carbonated beverages . Accordingly there is provided an easy open can end formed from an aluminium alloy and characterised in that the end is formed from a material of thickness 0.22mm or less, and having a proof strength of 250N/_tιιrr or less. The proof strength is the force at which the material yields to give a permanent deformation. A proof strength of 250N/mm 2 is well below the level of conventional beverage can ends formed from 5182 aluminium alloy. Can ends according to the present invention, whilst being too soft and pliable for use with carbonated beverages, are ideally suited to non-carbonated products, particularly those hot-fill products in which the can end is deliberately reformed after filling in order to reduce or eliminate the vacuum formed within the container. Examples of this type of can end are given in US 4836398 and EP 0521642A. Can ends according to the present invention are particularly suited to the manufacturing process described in our UK Patent Application (Agent's ref 4930) having the same filing date as this specification. This provides a method in which an end shell is formed, converted to an easy open can end with a score, rivet and a tab attached to the rivet, and is subsequently reshaped to raise the centre panel above the level of the seaming flange of the can end. This raised centre panel is subsequently depressed once the can end has been afixed to a filled container body, to reduce the headspace within the container. A can end with a relatively low proof strength facilitates this manufacturing process, which requires a first and second reshaping to move the centre panel relative to the rest of the can end. The proof strength of the easy open can end is conveniently 225N/mm 2 or less, and conveniently 190- 220N/mm 2 . The aluminium alloy is conveniently a 5000 series alloy, and preferably 5052 aluminium alloy. Alternatively the alloy is selected from the list of 5352, 5042, 5154, 5182 and 5082 aluminium alloys. The heat treatment of the alloy selected will help to determine its ultimate proof strength, and tempers of H44 or H42 (Euronorm Designation or equivalent) are typically required for coil lacquered material, or H24 or H22 for sheet lacquered material. Alternatively, the aluminium alloy is a 3000 series alloy, preferably selected from the list of 3004, 3104 and 3105 aluminium alloys. The alloys are typically only suitable for easy open can ends if they are laminated with a polymer coating in accordance with our Patent Application 093/17864. According to a further alternative the alloy is conceivably an 8000 series alloy. The easy open can end is preferably a "stay on tab" easy open end. Such ends were first proposed in UK Patent 1540229, and are in widespread use on cans for carbonated beverages, but not formed of aluminium alloys having a proof strength of 250N/mm 2 or less, as previously described. Examples and embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which; Figs.l and 2 are schematic sectional views of easy open can ends in accordance with the present invention, and Fig.3 is a plan view of the can end of Fig.2. The easy can ends shown in Figs.1-3 are formed of 5052 aluminium alloy which has the following composition; Table 1 The 5052 alloy of Table 1 above is subjected to a heat treatment to provide it with an H44 temper (Euronorm Designation or equivalent) , which produces an alloy with a proof strength of between 190-220N/mm 2 , typically 205N/mm 2 . The alloy is manufactured into an easy can end including a central panel 1, seaming flange 2 and annular countersink 3. The can end is a stay on tab type can end, with an operable portion 4 surrounded by a score 5, and having the tab 6 attached the centre panel by means of a raised rivet 7. The can end, being of less than 0.22mm in thickness, and manufactured from a relatively soft alloy having a proof strength of less than 250N/mm 2 , is able to withstand the reshaping of the centre panel 1 between the positions as shown in Figs.l and 2. The can end is first manufactured as shown in Fig.l, reshaped as shown in Fig.2, and then, once the end has been secured onto a container body, the centre panel 1 is depressed back into the position previously shown in Fig.l. This reduces the headspace in the container, and helps to reduce or eliminate any vacuum, caused by the cooling of hot filled products within the can. Other aluminium alloys which can used to manufacture can ends according to the invention are listed in Table 2 below, together with the appropriate temper treatment as recognised by the Euronorm Designation system, or equivalent. The 5000 series alloys may be either coil lacquered or sheet lacquered. The 3000 series are included as being suitable for polymer lamination, as opposed to PVC lacquered coatings. Table 2 It will be appreciated that equivalents or derivatives of the alloys mentioned herein may also be employed without departing from the scope of the present invention. In particular, different manufacturers of aluminium alloys may have broadly similar alloys which they refer to using different designations, and these skilled in this field will be aware of such equivalent alloys.

Claims: CLAIMS 1. An easy open can end formed from an aluminium alloy and characterised in that the end is formed from a material of thickness 0.22mm or less, and having a proof strength of 250N/mm 2 or less. 2. An easy open can end according to claim 1 characterised in that the proof strength is 225N/mm 2 or less . 3. An easy open can end according to claim 2 characterised in that the proof strength is in the range 190-220N/mm 2 . 4. An easy open can end according to any of claims 1 to 3 characterised in that the aluminium alloy is a 5000 series alloy. 5. An easy open can end according to claim 4 characterised in that the alloy is 5052 alloy. 6. An easy open can end according to claim 4 characterised in that the alloy is selected from the list of 5352, 5042, 5154, 5182 and 5082. 7. An easy open can end according to any of claims 1 to 3 characterised in that the alloy is a 3000 series alloy. 8. An easy open can end according to claim 7 characterised in that the alloy is selected from the list of 3004, 3104 and 3105 alloy. 9. An easy open can end according to any of claims 1 to 3 characterised in that the alloy is an 8000 series alloy. 10. An easy open can end characterised in that the end is formed is from 5052 aluminium alloy heat treated to an H44 temper (Euronorm Designation) such that it has a proof strength of 250N/mm 2 or less, and having a thickness of 0.22mm or less. 11. An easy open can end according to any of claims 1 to 10 characterised in that the can end is a stay on tab easy open end.

Inventors: BLOW ANDREW OSBORNE, PERIGO JOHN ALFRED, ROBERTS DAVID ANDREW, BLOW, ANDREW, OSBORNE, PERIGO, JOHN, ALFRED, ROBERTS, DAVID, ANDREW
Applicants: BLOW ANDREW OSBORNE, CROWN CORK & SEAL TECH CORP, METAL BOX PLC, PERIGO JOHN ALFRED, ROBERTS DAVID ANDREW, BLOW, ANDREW, OSBORNE, CARNAUDMETALBOX PLC, CROWN CORK & SEAL TECHNOLOGIES CORPORATION, PERIGO, JOHN, ALFRED, ROBERTS, DAVID, ANDREW
Application year: 1998
Main classification: B65D17
IPC codes: B65D17