EASY OPEN CAN ENDS

Abstract: A can end (1) is formed with a score (3) by pressing the end between a score die (2) and an anvil (13). The score die comprises a truncated "V"-shaped projection (9) having a first score sidewall (10) typically at about 55 DEG to the longitudinal axis of the projection, and a second score sidewall (11) typically at about 15 DEG to the longitudinal axis. The score die has a horizontal land portion (12) between the first and second sidewalls. The score die produces a score (3) having sidewalls (16 and 17) which are at different angles to the longitudinal, and this helps to prevent the formation of "angel hairs", i.e. thin slivers of the film (23) coating the base of the score which can otherwise become detached on operation of the tear panel (15).

Description: "EASY OPEN CAN ENDS" This invention relates to easy open can ends and to score dies for manufacturing such easy open ends. Easy open ends have a score track defining an operable portion or panel, which can be operated by a tab or other opening mechanism. This principle is the same whether the can end is a full aperture easy open end (normally used for foodstuffs), a pull tab beverage end, or the more modern stay-on tab commonly used for drinks cans. Easy open ends are conventionally manufactured using score dies, which are a truncated "V" shape and which cooperate with an anvil to form a score track in the can end. Examples of such score dies are given in UK patents 1261315, 1329583 and 1474496. Problems have been encountered in using such score dies, particularly with can ends manufactured from polymer film coated materials. On opening of the can end, thin slivers of the polymer material used to coat the metal substrate can be formed in the region of the score. The slivers, known as "angel hairs", are visually unattractive and can become detached or otherwise interfere with the product within the container. When the polymer material is coloured or printed, the angel hairs can be particularly noticeable. It is an object of the present invention to produce score dies for easy open can ends which reduce or alleviate this particular problem. Accordingly there is provided a method of producing an operable portion in an easy open can end formed of a metallic substrate coated with a polymer film material, the method comprising the steps of contacting the can end with a score die and an anvil die, the score die comprising a truncated "V" shaped projection having a planar inner sidewall adapted to produce a planar score sidewall adjacent the operable portion, a planar outer sidewall adapted to produce a planar score sidewall adjacent the remainder of the can end, and a generally horizontal flat land portion adapted to form the base of the score, characterised in that each of the inner and outer sidewalls is at an angle of between 15° and 60° to the longitudinal axis of the projection, there being a difference of at least 15° between the angles of the inner and outer sidewalls. Our research has shown that when the tear panel of an easy open can end is caused to operate, the score residual will fracture adjacent either the inner or outer score sidewall, i.e. at either the inner or outer extremity of the land portion. Occasionally, the fracture will switch from one extremity to the other as it progresses around the score track, and this switching is implicated in the formation of angel hairs. The switching can vary from one design of can end to another, and it is believed that this is due to the different strains inherent in different diameter/designs of can ends. By varying the angles of the inner and outer score sidewalls, the fracture is urged to remain on either the inner or outer extremities of the score, and the incidence of angel hairs is reduced. The steeper of the inner or outer sidewalls preferably lies at an angle of between 15° and 25° to the longitudinal axis, and the shallower of the inner or outer sidewalls at an angle of between 45° and 60° to the longitudinal axis. Conveniently the included angle between the inner and outer sidewalls is at least 60°. Most preferably the steeper of the inner or outer sidewalls lies at an angle of about 15° to the longitudinal axis, and the shallower of the inner or outer sidewalls at an angle of about 50° to the longitudinal axis. Preferably the outer sidewall lies at a steeper angle than the inner sidewall, although this may vary depending on individual end presses or different sizes of easy open end. The invention further resides in a score die for producing an operable portion in an easy open can end, the score die comprising a truncated "V" shape projection having a planar inner sidewall adapted to produce a planar score sidewall adjacent the operable portion, a planar outer sidewall adapted to produce a planar score sidewall adjacent the remainder of the can end, and a generally horizontal flat land portion adapted to form the base of the score, characterised in that each of the inner and outer sidewalls is at an angle of between 15° and 60° to the longitudinal axis of the projection, there being a difference of at least 15° between the angles of the inner and outer sidewalls. According to a further aspect of the invention there is provided an easy open can end formed of a metallic substrate coated with a polymer film material, and including a panel portion having an operable portion defined by a score line, the score line comprising a planar inner score sidewall adjacent the operable portion, a planar outer score sidewall adjacent the remainder of the panel portion, and a generally horizontal flat land portion therebetween forming the base of the score, characterised in that each of the inner and outer sidewalls is at an angle of between 15° and 60° to an axis perpendicular to the can end, there being a difference of at least 15° between the angles of inner and outer sidewalls. Preferably the metallic substrate is an aluminium alloy. The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: - Fig.l is a schematic sectional view of a conventional score die producing a score track on an easy open can end, Figs. 2 and 3 are schematic sectional views of score dies according to the present invention, and Fig.4 is a graph showing the incidence of angel hairs obtained from the score dies of Figs. 1 to 3. Referring to Fig.l there is shown a can end 1, and a score die 2 which has formed a score 3 in the can end. The can end 1 comprises a metallic substrate 4, typically of aluminium, with a film 5, typically of polyester, laminated to the upper surface 6 thereof. A similar film 7 is laminated to the lower surface 8 of the can end. The can end is typically as described in our PCT application No. W093/17864. The score die comprises a "V" shaped projection 9 having a first sidewall 10, a second sidewall 11, and a horizontal land portion 12 therebetween. The first and second sidewalls are each inclined at an angle of approximately 25° to the longitunal axis of the projection 9. The "included angle" of the score die is therefore approximately 50°. Score dies such as these are frequently given a surface coating (not shown) in order to increase the wear resistance of the score die. In use the can end 1 is pressed between the score die 2 and an anvil 13 to form the score 3, defining a tear panel 14 within the remainder of the central panel 15 of the can end. The score 3 comprises an inner sidewall 16 adjacent the tear panel and formed by the first sidewall 10 score die, and an outer sidewall 17 adjacent the panel 15 and formed by the second sidewall 11 of the score die. The inner and outer sidewalls 16 and 17 are formed at substantially the same angles as the first and second sidewalls 10 and 11 of the score die. The base 18 of the score extends between the sidewalls 16 and 17, and the portion 19 between the base 18 and the lower surface 8 of the can end is known as the "score residual". When the opening mechanism (not shown) of the can end is operated, the tear panel 15 is pressed down with respect to the panel 15, to cause the score 3 to break. The score will tend to separate along a line extending through the score residual from either a point 20 at the intersection of the base 18 and inner sidewall 16, or a point 21 at the intersection of the base 18 and outer sidewall 17. As the tear panel separates from the panel 15 along the length of the score, the fracture (shown schematically at 22) may switch one or more times between points 20 and 21. This may cause the film 23 in the base of the score to become detached, forming a sliver of film known as an "angel hair". Fig.2 shows how the score die 2 and hence the score 3 is adapted to reduce this problem. The first sidewall 10 of the score die, and hence the inner sidewall 16 of the score, is at a first angle A to the longitudinal axis of the projection 9. In Fig.2 the angle A is approximately 45°. Conversely the second sidewall 11, and hence the outer sidewall 17 of the score, is at a second angle B to the longitudinal axis. In Fig.2 this angle B is only 25°. The difference in angles urges the fracture 22 to stay associated with the point 21 (i.e. adjacent the steeper score sidewall) throughout the length of the score. Thus the incidence of angel hairs is reduced or even eliminated. Fig.3 shows the opposite arrangement in which the inner sidewall 16 of the score is at the relatively steep angle (i.e. 25°) and the outer sidewall 17 is at the relatively shallow angle (i.e. 45°). This arrangement will tend to be appropriate where it is preferable to try to associate the fracture 22 with the point 20, i.e. adjacent the inner sidewall 16. Table 1 below shows how a range of score dies, with different angles A and B, have been tested. The samples were all subjected to a corner treatment, such as a tumbling process which rounds the sharp edges of the score dies prior to use. Samples A to C were prior art designs in accordance with Fig.l, samples D to G and J to M were similar to that of Fig.2, whilst sample H was generally in accordance with Fig.3. TABLE 1 The graph of Fig. shows how these samples behaved in producing angel hairs, with the number of angel hairs observed being shown as a percentage. As can be clearly seen, the asymmetric score tracks of samples D, E, F, G, J, K, L and M showed a marked reduction in angel hairs over the conventional score track of samples A to C. Sample H showed an actual increase in angel hair percentage, but this is believed to be because the natural inclination of the easy open ends being tested was to fracture around the edge of the panel 15 rather than the tear panel 14. It is believed that other easy open ends of a different diameter or design, or manufactured with different equipment, may have a natural predisposition to fracture adjacent the panel 15 and hence the design of Fig.3 may offer improvements in such cases. Simple tests will be able to demonstrate whether, for any particular type of can end, the design of Fig.2 or that of Fig.3 will give better results. Can ends produced from a prior art score die such as sample A, were compared with those from a score die in accordance with the invention, such as sample K, in respect of break and tear force, and coating integrity. Score break and score tear performance is shown in Table 2 below with the figures being shown in lbf (kgf) . The break and tear force figures for the ends made in accordance with the invention were well within the accepted specification of 2.5 to 4.5 lbf (1.14 to 2.05 kgf) for score break, and 3 to 5 lbf (1.36 to 2.27 kgf) for score tear force. TABLE 2 Coating integrity performance is shown in Table 3, with the figures being the mA readings from the industry standard enamel rater test. The figures were well within the accepted specification of <5mA (mean) / <10mA (max) . TABLE 3 Finally a can end according to sample K was tested for metal exposure using the standard enamel rater test. The mean enamel rater reading of 3.6mA is well below the accepted specification of <5mA. Thus break and tear force, coating integrity and metal exposure are all within specification, in addition to the significant reduction in angel hairs described previously.

Claims: CLAIMS : 1. A method of producing an operable portion in an easy open can end formed of a metallic substrate coated with a polymer film material, the method comprising the steps of contacting the can end with a score die and an anvil die, the score die comprising a truncated "V" shaped projection having a planar inner sidewall adapted to produce a planar score sidewall adjacent the operable portion, a planar outer sidewall adapted to produce a planar score sidewall adjacent the remainder of the can end, and a generally horizontal flat land portion adapted to form the base of the score, characterised in that each of the inner and outer sidewalls is at an angle of between 15° and 60° to the longitudinal axis of the projection, there being a difference of at least 15° between the angles of the inner and outer sidewalls. 2. A method according to claim 1, characterised in that the steeper of the inner or outer sidewalls lies at an angle of between 15° and 25° to the longitudinal axis. 3. A method according to claim 1 or claim 2, characterised in that the shallower of the inner or outer sidewalls lies at an angle of between 45° and 60° to the longitudinal axis. 4. A method according to any of claims 1 to 3, characterised in that the included angle between the inner and outer sidewalls is at least 60°. 5. A method according to any of claims 1 to 4 characterised in that the steeper of the inner or outer sidewalls lies at an angle of about 15° to the longitudinal axis, and the shallower of the inner or outer sidewalls lies at an angle of about 50° to the longitudinal axis. 6. A method according to any of claims 1 to 5, characterised in that the outer sidewall lies at a steeper angle than the inner sidewall. 7. A score die for producing an operable portion in an easy open can end, the score die comprising a truncated "V" shaped projection having a planar inner sidewall adapted to produce a planar score sidewall adjacent the operable portion, a planar outer sidewall adapted to produce a planar score sidewall adjacent the remainder of the can end, and a generally horizontal flat land portion adapted to form the base of the score, characterised in that each of the inner and outer sidewalls is at an angle of between 15° and 60° to the longitudinal axis of the projection, there being a difference of at least 15° between the angles of the inner and outer sidewalls. 8. An easy open can end formed of a metallic substrate coated with a polymer film material, and including a panel portion having an operable portion defined by a score line, the score line comprising a planar inner score sidewall adjacent the operable portion, a planar outer score sidewall adjacent the remainder of the panel portion, and a generally horizontal flat land portion therebetween forming the base of the score, characterised in that each of the inner and outer sidewalls is at an angle of between 15° and 60° to an axis perpendicular to the can end, there being a difference of at least 15° between the angles of inner and outer sidewalls. 9. An easy open can end according to claim 8, characterised in that the metallic substrate is an aluminium alloy. 10. An easy open can end according to claim 8 or claim 9 characterised in that the polymer film material is a PET film.

Inventors: BUCKLOW JOHN IAN, HEYES PETER JOHN, MOGER MICHAEL ALAN, BUCKLOW, JOHN, IAN, HEYES, PETER, JOHN, MOGER, MICHAEL, ALAN
Applicants: BUCKLOW JOHN IAN, CROWN CORK & SEAL TECH CORP, HEYES PETER JOHN, METAL BOX PLC, MOGER MICHAEL ALAN, BUCKLOW, JOHN, IAN, CARNAUDMETALBOX PLC, CROWN CORK & SEAL TECHNOLOGIES CORPORATION, HEYES, PETER, JOHN, MOGER, MICHAEL, ALAN
Application year: 1998
Main classification: B21D51
IPC codes: B21D51, B65D17