EP0737624B1 - Method for the manufacture of an easy open lid having an incision located in a sloping region - Google Patents

Description

FIELD OF THE INVENTION

The invention relates to the field of containers with opening easy and especially the metal covers to easy opening.

STATE OF THE ART

The easy-opening lids have a generally peripheral incision in the case of containers for food products, as shown in FIGS. 1a to 1c, FIGS. 1a and 1b corresponding to easy-opening lids with bowl, or have a localized incision at a small portion of the cover panel in the case of a cover for a beverage can.
The incisions are defined by their profile and the residual metal thickness under the incision which is also called the "residual".
A profile is defined by the angle alpha of the incision and by the calculated width P of the bottom of the incision. A typical incision is shown in Figure 2 where the angle alpha is 60 ° and the width P is 40 µm and is designated by "60P40".
Furthermore, US patent 4,132,328 is known in which the incision of an easy-opening cover is formed on a strip delimited between two zones formed by two punching stages, so as to increase the compression of said delimited strip and thus facilitate opening the cover.

PROBLEM

There is an ever-increasing demand for easy-opening covers which simultaneously present greater ease of opening and greater safety in manufacture and use. But these requirements are to date largely contradictory to the extent that the greatest ease of opening is generally obtained by reducing the residual, a decrease which results in a much lower manufacturing safety (greater precision of tools, greater safety margin low), and above all very significant risks of the appearance of cracks at the bottom of the incision, which lead to leaks, either directly, or by the action of pressure during conditioning, typically with sterilization, or after conditioning by the corrosive action of conditioned product.
In addition, the presence of cracks makes the covers more sensitive to impact punctures during handling of the packaged product, and this from the packaging of the product to its final use by the consumer.

Figure 7 shows in section an incision after crimping and sterilization, with cracks at the bottom of the incision characteristics that the present invention proposes otherwise delete entirely, at least reduce very strongly.

The problem is to find a way to manufacture, so reliable and economical, low residual COF whose bottom incisions is not cracked at the end of manufacture, nor after packaging of the product to be packaged.

DESCRIPTION OF THE INVENTION

This problem is solved by the method according to claim 1.

According to a first preferred embodiment of the invention, said strip is located on the periphery of the central panel and the skirt inside of the edge to be crimped, and forms an inclined plane between said central panel and said skirt, as illustrated in Figures 3a and 3b, having the shape of a corner cone portion at the top 180 ° -2.beta.

According to a second embodiment of the invention, said cover is a convercle with a peripheral counter-bowl, in which said strip is located at the periphery of the central panel and of said counter-bowl, and forms an inclined plane between said central panel and said counter-bowl, as illustrated in Figures 3c, 3f and 3g, having the shape of a portion of a cone angle at the top 180 ° -2.beta.

According to a third embodiment of the invention, said cover is a partially open lid, for example a lid for a beverage can in which said strip forms a non-zero beta angle inclined plane bordering the part of said panel intended to be opened, as illustrated in Figures 3d and 3rd. In this case, said strip does not close on itself, as in the previous cases.

The inclination of said incision strip can be oriented at an angle of +/- beta relative to said mean plane of the central panel, considered as a horizontal plane (see FIGS. 3a and 3b).
Said beta angle is generally between 5 ° and 45 °. Indeed, for a beta angle less than 5 °, the desired effect (reduction of cracks) obtained is relatively moderate. Furthermore, as the problem posed is solved with a beta angle less than 45 °, there is no technical interest in making an incision on an incision band having a slope greater than 45 °.
Said beta angle is preferably between 10 and 30 °.
As the embodiments and the comparative tests will demonstrate, the means of the invention effectively solve the problem posed.

DESCRIPTION OF THE FIGURES

Figures 1a to 1c show, in axial section, different shapes of covers with easy opening (1) of the prior art.
These covers include a central panel (3) on which there is an incision (2) on the incision strip (6) in a horizontal plane, parallel to the mean plane (17) of the panel (3), and a crimping edge ( 4).
The central panel is provided with a rivet (7) which fixes a ring (8), the spout (9) of which is located in line with the incision (2) so as to ensure the opening by tilting of the ring.
The crimping edge (4) comprises a skirt (5), strongly inclined, connecting to said central panel, possibly by a bowl (20).

Figures 1a to 1c are distinguished by the presence of a bowl (20) in the case of FIGS. 1a and 1b, and by the position of the incision (2) located in the plane of said panel central in the case of FIGS. 1a and 1c, and at the bottom of the bowl (20) in the case of FIG. 1b.

Figure 2 shows in axial section an incision (2). A incision (2) is defined, for a thickness E of the layer metallic, by an alpha angle, by a calculated value P of bottom (10) of the incision, by an R value of the thickness residual (11) (also called "residual"). The sides of the incision were designated by 16a and 16b.

Figures 3a, 3b and 3c show, in axial section similar to that of FIGS. 1a to 1c, portions of easy opening cover (1) according to the invention having a sloping incision band (6).

Figures 3a and 3b illustrate the position of the incision (2) on the incision strip (6) forming the bottom of the bowl (20). This strip (6) has a slope of angle beta with respect to the plane (17), corresponding to the horizontal mean plane of said central panel (3).
In Figure 3a, said strip (6) has a slope of an angle + beta, while the angle is -beta in Figure 3b.

Figure 3c illustrates the position of the incision (2) on the incision band (6) forming the periphery of the beach central (3), externally limited by the counter-bowl (18). This strip (6) has an angle slope + beta by relative to the plan (17).

Figures 3f and 3g relate to the cover of Figure 3c. FIG. 3f is a top view showing the incision strip (6) in the form of a hatched crown, the incision (2) passing through the center of this strip.
Figure 3f is an axial section along the axis BB of Figure 3f, showing that said strip (6) has the shape of a cone portion with an angle at the top equal to 180 ° - 2.beta.

Figures 3d and 3e relate to an opening cover partial beverage can. Figure 3d is a top view and Figure 3e is a section along the axis A-A of Figure 3d. With this type of cover, the incision strip (6) does not form not a band closed on itself, but has the form a horseshoe, the open part of which remains attached to the central panel (3) of the cover. The ring (8) is positioned on the side of this open part, and tilting forward just tear the incision (2) and fold inwards the box the tongue delimited by said incision (2).

• à la figure 4a, une limite de l'angle gamma est atteinte car le côté 14a du poinçon est vertical,
• à la figure 6a, l'autre limite de l'angle gamma est atteinte car l'autre côté 14b du poinçon est vertical,
• la figure 5a représente un cas intermédiaire où l'angle gamma vaut zero.

FIGS. 4a, 5a and 6a are partial axial sections of punches (13) intended to form incisions (2) according to the invention, the two sides (14a, 14b) of the punch forming an alpha angle and being connected by one end (15). The punches move in the vertical direction (19) to form the corresponding incisions (2) shown in Figures 4b, 5b and 6b.
These figures show the limits of the inclination of the punch at a gamma angle relative to the vertical:

• in FIG. 4a, a limit of the gamma angle is reached because the side 14a of the punch is vertical,
• in FIG. 6a, the other limit of the gamma angle is reached because the other side 14b of the punch is vertical,
• FIG. 5a represents an intermediate case where the gamma angle is zero.

Figure 7, similar to Figure 2, shows a section micrographic showing the presence of cracks (12) at the bottom incision (10).

DETAILED DESCRIPTION OF THE INVENTION

The invention applies more particularly to covers with easy opening (1) in steel or aluminum or alloy aluminum, alpha angle between 40 and 120 °, thickness between 0.12 and 0.30 mm (nominal thickness of the metal strip intended to form the metal layer of the lid with easy opening), and of residual thickness R at the bottom of an incision greater than 40 µm.

The residual thickness value R is generally understood between 60 and 140 µm, depending on the nature of the metal strip, and according to the value of said nominal thickness.

According to the invention, the angle alpha is preferably between 40 ° and 60 ° and the width P at the bottom of the incision is between 10 and 40 μm.
These preferential values are those which correspond to the best ease of opening.

The invention also includes a method of manufacturing easy opening covers (1) in which said incision is obtained by punching, using a corner punch alpha, an incision strip (6) of a blank cover, in a vertical direction (19) perpendicular to the plane by means of said central panel (3), said incision strip having a non-zero beta angle slope.

As already stated about the incision itself, the angle alpha can be between 40 and 120 °, and the beta angle is generally between 5 and 45 °.

Said incision strip (6) with a beta angle slope is formed by stamping metal strip in a manner known per se during the formation of the cover blank. Given the high precision of the tools used to manufacture covers, it suffices that said strip has a width of around 1 mm to be sure that said incision (2) will be always well positioned on said sloping strip (6) beta angle.

Said punch (13) can be oriented at a gamma angle by with respect to said perpendicular direction (19) between two extreme values such as one of these values corresponds to a punch having one of its vertical faces (16a), as shown in Figure 4a, the other value corresponding to a punch having the other of its faces (16b) vertical, as shown in Figure 6a.

In a manner known per se to form said incision (2) by action of said punch (13), the blank cover not incised is positioned on an appropriately shaped anvil so the incision band (6) is in abutment on said anvil during the action of said punch.

EXAMPLES OF REALIZATION

All of the easy-open lids were made to from 5182 alloy aluminum strip (designation according to Aluminum Association), nominal thickness of 270 µm, varnished on both sides, and in metallurgical condition H28 corresponding to a strongly hardened state, restored during opening).

Standard easy-opening covers (1) of 73 mm in diameter were manufactured, with a peripheral incision according to FIG. 3a, incision having a profile of the "60P40" type (alpha angle of 60 ° and a calculated value of dish at the bottom 40 µm incision).
The punch therefore made an alpha angle of 60 °, its bisector was oriented vertically (gamma angle = 0).

• un angle beta de 0° selon l'état de la technique,
• un angle beta de 15° selon l'invention.

The tests consisted in varying the residual thickness R on the one hand (residual 50 µm / 60 µm / 70 µm / 95 µm), and in varying the beta slope of the incision band (6) of the blank cover to be cut.
The results of two comparative tests, among the various tests carried out, are described in detail below, with:

• a beta angle of 0 ° according to the state of the art,
• a beta angle of 15 ° according to the invention.

For each pair of values of R and beta angle of the band incision (6), 200 easy-opening covers were manufactured.

The lids obtained were crimped onto boxes which were then sterilized in a standard manner (30 min at 125 ° C).
Cuts were made on the covers as manufactured, on the covers after crimping and on the covers after sterilization, so as to be able to carry out observations under the microscope by reflection and to assess the presence and extent of cracks at the bottom of the incision. .

a) présence de fissures :

Oui = plus de 1 cas sur 10
Rares = de 1 cas sur 10 à 1 sur 100
Non = moins de 1 cas sur 100

b) longueur des fissures:

< 2 µm-5µm (amorces)
fissures au-delà de 5 µm

La distinction entre amorce et fissure repose sur le fait que le risque d'endommagement n'apparaít pas linéaire avec la longueur des fissures et qu'il y a un seuil (2-5 µm) au-delà duquel il y a une grande probabilité pour que la fissuration s' aggrave au lieu de rester relativement stable comme dans le cas d'amorces de fissures.Rating of cracks by their frequency and their length:

a) presence of cracks:

Yes = more than 1 in 10 cases
Rare = 1 in 10 to 1 in 100
No = less than 1 in 100 cases

b) length of the cracks:

<2 µm-5µm (primers)
cracks beyond 5 µm

The distinction between primer and crack is based on the fact that the risk of damage does not appear linear with the length of the cracks and that there is a threshold (2-5 µm) beyond which there is a high probability. so that the cracking worsens instead of remaining relatively stable as in the case of crack initiators.

Results obtained on covers as manufactured: SETTINGS Beta angle 0 ° 15 ° Residual R 50 µm at) total rupture Rare b) <2 µm 60 µm at) Yes Rare b) > 10 µm <2 µm 70 µm at) Yes No b) 2 to 5 µm - 95 µm at) No No b) - -

The results obtained after crimping and after sterilization go in the same direction with a tendency to increase the number and / or the depth of the cracks.
In addition, the manual opening tests led to comparable results for the same residual value R.

These results clearly show the influence of the beta angle on the appearance of cracks at the bottom of the incision.

These results are of great practical importance.
In fact, according to the corrosion resistance studies carried out by the applicant, the residual metal layer under the incision is particularly sensitive to the action of corrosion due to the ingredients of the packaged products (possible presence of acids and / or salts), and the sensitivity to corrosion increases with the presence of cracks, or the presence of cracks of greater length.
According to a qualitative approach, there is therefore a correlation between the damage to the incision, which can be quantified by the presence of cracks and the length of the cracks, and the resistance to corrosion.

• d'une part, pour le fabricant de couvercles, il est important de disposer d'une plage de sécurité en ce qui concerne la valeur de l'épaisseur résiduelle de métal. Dans le cas présent, toutes les valeurs testées pour R, de 50 à 95 µm conviennent. En effet, une fabrication est d'autant plus coûteuse en outillage, en contrôle et en rebus qu'elle doit satisfaire à une plage étroite de valeurs pour un paramètre donné tel que l'épaisseur résiduelle de métal.
  Par ailleurs, l'amélioration de la tenue à la corrosion peut aussi permettre une diminution de l'épaisseur de la couche de vernis intérieur.
• d'autre part, l'amélioration de la tenue à la corrosion se traduit par une augmentation de la durée de vie des produits conditionnés, et par la diminution corrélative des risques de perforation des emballages, avec tous les risques de contamination et de salissures associés.

En outre, l'invention permet de positionner l'incision à la périphérie du couvercle, tout en bas de la jupe (5) du bord à sertir (4), de sorte que, moyennant un très léger épaulement du corps de boíte correspondant au couvercle, il n'y aura pas, après ouverture du couvercle, dépassement du bord restant du couvercle à l'aplomb du corps de boíte, ce qui peut être indispensable pour démouler un produit relativement solide sans le désagréger (pâté, foie, etc...).
Enfin, la possibilité de diminuer, dans une large plage de valeurs, la valeur de l'épaisseur résiduelle de métal permet de moduler et de diminuer comme souhaité l'effort d'ouverture des couvercles à ouverture facile, alors que les couvercles de l'art antérieur nécessitaient, pour une même tenue à la corrosion, une valeur d'épaisseur résiduelle nettement supérieure, et donc impliquaient un effort d'ouverture supérieur.
Ce sont là des avantages importants dans le métier de l'emballage utilisant des couvercles à ouverture facile.The positive consequences of an improvement in the corrosion resistance of easy-opening covers are of several types:

• on the one hand, for the manufacturer of covers, it is important to have a safety range with regard to the value of the residual thickness of metal. In the present case, all the values tested for R, from 50 to 95 μm are suitable. Indeed, a manufacturing is all the more expensive in tooling, in control and in scrap as it must satisfy a narrow range of values for a given parameter such as the residual thickness of metal.
  Furthermore, improving the corrosion resistance can also allow a reduction in the thickness of the interior varnish layer.
• on the other hand, the improvement in corrosion resistance results in an increase in the service life of the packaged products, and in the corresponding reduction in the risks of perforation of the packaging, with all the risks of contamination and associated soiling .

In addition, the invention makes it possible to position the incision at the periphery of the cover, at the very bottom of the skirt (5) of the crimping edge (4), so that, by means of a very slight shoulder of the box body corresponding to the cover, there will not be, after opening the cover, beyond the remaining edge of the cover directly above the body of the box, which may be essential to unmold a relatively solid product without breaking it up (pâté, liver, etc. ..).
Finally, the possibility of decreasing, over a wide range of values, the value of the residual thickness of metal makes it possible to modulate and decrease as desired the opening force of the lids with easy opening, while the lids of the prior art required, for the same corrosion resistance, a significantly higher residual thickness value, and therefore involved a greater opening force.
These are important advantages in the packaging business using easy-open lids.

Claims (9)

1. Manufacturing process for easy opening metal covers (1) with central panel (3) and crimping edge (4) comprising a sore line (2) on a score line strip (6), part of the said panel on which the said score line is formed, and a ring (8) for perforation of the said score line and the said opening, in which the said score line (2) is made by punching with a punch (13) with an angle alpha and along a vertical direction (19) perpendicular to the average plane of the said central panel (3), a cover blank with a score line strip (6) placed on an anvil, characterized in that:

   a) the said score line strip (6) with a constant thickness E has a non-zero slope with an angle beta with respect to the average plane (17) of the said panel (3),

   b) the said anvil is an appropriate shape such that the said score line strip (6) is supported on the said anvil during the said punching operation.
2. Process according to claim 1 in which the said punch (13) is oriented at an angle gamma with respect to the said perpendicular direction (19) between two extreme values such that one of these values corresponds to a punch with one of its faces vertical (16a), the other value corresponding to a punch with the other of its faces (16b) vertical.
3. Process according to claim 2, in which the said score line strip (6) is located at the periphery of the said central panel (3) and the internal skirt (5) of
4. Process according to claim 2 in which the said cover (1) has a peripheral counter-sink (18) and in which the said score line strip (6) is located at the periphery of the central panel (3) and the said counter-sink (18), and forms an inclined plane between the said central panel and the said counter-sink.
5. Process according to claim 2, in which the said cover (1) opens partially, and in which the said score line strip (6) forms an inclined plane at the edge of the part of the said panel designed to be opened.
6. Process according to any one of claims 1 to 5, in which the said angle beta is between 5° and 45°.
7. Process according to claim 6 in which the said angle beta is preferably between 10 and 30°.
8. Process according to any one of claims 1 to 7 in which the said cover (1) is made of steel or aluminum or aluminum alloy with a score line with angle alpha between 40 and 120° and between 0.12 and 0.30 mm thick, its thickness being the nominal thickness of the metal strip for the cover, and the score line having a thickness at the bottom of the score line exceeding 40 µm.
9. Process according to any one of claims 1 to 8, in which the angle alpha is preferably between 40° and 60°, and the width P at the bottom of this score line is between 10 and 40 µm.

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