US20170137168A1

US20170137168A1 - Metal cover for a container body

Info

Publication number: US20170137168A1
Application number: US15/322,880
Authority: US
Inventors: Fabrice Leboucher
Original assignee: Ardagh MP West France SA
Current assignee: Trivium Packaging West France SAS
Priority date: 2014-06-30
Filing date: 2015-06-29
Publication date: 2017-05-18
Also published as: FR3022895B1; BR112016030868B1; JP2017520490A; EP3160857B1; BR112016030868A2; EP3160857A1; RU2017102697A; CN106573700B; RU2017102697A3; FR3022895A1; PL3160857T3; CN106573700A; AU2015282552A1; AU2015282552B2; ES2682748T3; WO2016001562A1; BR112016030868A8; HUE039498T2; RU2676661C2

Abstract

Disclosed is a metal cover for a container body, in particular for a container such as a metal can, the cover including a removable portion (4) which is defined by a scoreline (5) and which is provided with an opening member (6). The scoreline (5) includes two upstream portions (55) and one downstream portion (56), provided on either side of a virtual axis (10). Each upstream portion (55) of the scoreline (5) includes a second section (522) including a residual thickness (E2) greater than a residual thickness (E1) of a first section (551); and the second section (552) extends over at least 20% of the length (L) of the upstream portion (55), a downstream end (5522) being provided within the upstream portion (55).

Description

TECHNICAL FIELD TO WHICH THE INVENTION RELATES

The present invention relates to the general field of packaging, and in particular the field of metal covers for containers of the can type. More particularly, it relates to the metal covers of the type including a removable part that is delimited by a scoreline and that is equipped with an opening member.

TECHNOLOGICAL BACK-GROUND

Some metal containers, mainly the cans for the packaging of foodstuffs, are provided with a so-called “easy” opening system (or “EOE” for “Easy Open End”), avoiding the use of tools such as can-openers.
For that purpose, a commonly implemented solution consists in a single-piece metal cover including two parts, i.e.:

- a ring-shaped peripheral part, intended to be fastened to the container body, and
- a central closing panel comprising a removable part that is delimited by a scoreline.

For the separation of the removable part, the scoreline is torn by a handling of an opening member carried by the central panel, commonly known as the “opening ring”.
This type of opening member conventionally comprises three parts, arranged successively over its length, i.e.:

- a so-called “beak”, peripheral incision part,
- an intermediate part for the fastening to the removable part of the cover, conventionally of the rivet type, and
- a central grasping part, conventionally loop- or ring-shaped.

In practice, before the opening of the metal cover, the opening member is flatten against the upper surface of the central panel.
For the opening, the user is brought to operate the opening member in two successive and distinct steps.
First, in a first step of opening initiation, the user grasps the opening member, generally by its central grasping part, then he moves it apart from the central part.
The opening member then forms a lever, so that its beak-shaped, peripheral incision part causes a local breaking of the scoreline.
This rotational operation leads to the tearing of two upstream portions, on either side of the longitudinal axis of the opening member.
The removable part of the cover is then locally bent inwardly, about a virtual axis that is oriented perpendicularly, or approximately perpendicularly, to the longitudinal axis of the opening member.
In a second step of opening, the user exerts a traction on the opening member so as to continue the tearing of the scoreline and to dissociate all or part of the removable part from the cover.
The opening member hence allows the transmission of the force applied by the user, and of the energy generated, to the removable part of the metal cover, so as to ensure the tearing of the metal along the scoreline.
The easiness of opening is defined by the level of force and energy required to break this scoreline, which is in practice the most possible reduced.
However, these easy opening covers must also resist to phenomena of implosion by internal depression during the storage, due to their vacuum filling or due to the use of particular cooking techniques (such as steam cooking).
For example, this depression is of the order of 600 to 700 mbars for canned corn, and of the order of 850 to 900 mbars for the canned, steam-cooked vegetables.
Such an implosion phenomenon, with sagging of the removable part of the central closing panel, is also liable to occur at the opening.
Indeed, the breaking of the balance holding the removable part in place is liable to generate a propagation of the scoreline tearing, due to the tearing effort that is relatively low once an initiation of this scoreline tearing has occurred.
To prevent this last phenomenon of sagging at the opening, it is usual to control the tearing of the upstream portions of the scoreline by “stop” points that aim to prematurely block the movement of tearing of this scoreline.
For that purpose, it is common to provide one or two punctual variations of the residual thickness in each of the upstream portions of the scoreline, over a length of the order of the millimetre, conventionally called “arrester flat”.
The user continuing his movement to perform the opening, it then implies an increase of the force to be applied (until the force for breaking this “arrester flat” is reached).
This causes a “pause” in the opening of the cover, which then allows a balancing (or rebalancing) of the pressures with a cancelling of the risk of sagging.
From the point of view of the tearing propagation progress, the “arrester flats” have hence a role of stop for this propagation.
Such a structure then generates a punctual blocking of the opening during the tearing of the upstream portions of the scoreline.
This arrest then requires an increased effort to resume/continue the tearing of the scoreline.
Moreover, the hardness increase of the material, and/or the decrease of the thicknesses, used for the cover may give rise to an influence of the rolling direction.
The force required for breaking an “arrester flat”, and in particular the additional effort required for resuming the scoreline tearing, is then liable to cause an untimely breaking of the central closing panel.
Indeed, in this case, the tearing is liable not to propagate along the scoreline, as desired, but in the central closing panel.
Moreover, in practice, it is possible that the user operates abruptly the opening member, then cancelling the effect of punctual blocking of the tearing.
In this context, there exists a need for a metal cover allowing a control of the opening, on the one hand, to control the breaking of the differential of pressure, with no risk of sagging of the central closing panel, and on the other hand, to cancel the risk of breaking of the central closing panel due to its rolling direction.

OBJECT OF THE INVENTION

To remedy these drawbacks, the applicant has developed a new structure of easy opening metal cover, that makes it possible, no longer to punctually block the opening during the tearing of the upstream portions of the scoreline, but to progressively control the energy used for this tearing.
The metal cover according to the invention comprises:

- a central part forming a central closing panel, and
- a peripheral part adapted to be fastened to the container body.

The central part comprises a removable part that is delimited by a scoreline having a variable residual thickness and that is equipped with an opening member.
This opening member includes, on either side of a part for the fastening to the removable part, a peripheral incision part and a central grasping part.
The scoreline comprises:

- two upstream portions, intended to be torn by an initial operation of pivoting of said opening member, extending on either side of the longitudinal axis of the opening member, and
- one downstream portion, consisted by the remaining length of said scoreline and intended to be torn by a following operation of traction on the pivoted opening member.

The upstream and downstream portions are arranged on either side of a virtual axis extending perpendicularly to the longitudinal axis of the opening member, said virtual axis corresponding to the bend line generated on the removable part after a pivoting of said opening member and the tearing of said upstream portions.
And according to the invention, each upstream portion of the scoreline includes, successively in the tearing direction, at least two sections:

- a first section having a first residual thickness, and
- a second section having a residual thickness higher than said first residual thickness (and advantageously also higher than the majority residual thickness of said downstream portion).

The second section extends over at least 20%, preferably over at least 25%, still preferably between 25% and 60%, of the length of said upstream portion.
Said second section of each upstream portion of the scoreline includes:

- an upstream end, connected to the first section, and
- a downstream end, provided within said upstream portion.

The structure of the scoreline according to the invention hence allows entering the second sections whose tearing will continue progressively and at a higher level of effort.
According to other advantageous embodiment characteristics, which can be taken in combination or independently from each other:

- the downstream end of the second section is connected to the downstream portion (i) directly or (ii) through a third section whose residual thickness is lower than the residual thickness of said second section of the upstream portion;
- the upstream end and/or the downstream end of the second section of the upstream portion show: —an abrupt variation of the residual thickness, or—a continuous progressive variation of the residual thickness (for example over a length comprised between 0.3 and 0.7 mm) or—a discontinuous progressive variation of the residual thickness (for example, by steps);
- the upstream end and the downstream end of the second section of the upstream portion each show a progressive variation of the residual thickness, and the downstream end extends over a length that is higher than the length of the upstream end;
- the first section of the upstream portion of the scoreline has a constant residual thickness, and the second section of the upstream portion of the scoreline has a constant or variable residual thickness;
- the residual thickness difference between the first section and the second section of each upstream portion is comprised between 10 and 50 μm;
- the first section, and as the case may be the third section, of each upstream portion has a residual thickness that is identical, or at least approximately identical, to the majority residual thickness of the downstream portion;
- the scoreline is formed by a lower groove and/or by an upper groove that are formed in a lower face and/or an upper face, respectively, of the central part of the cover, and said upper groove and/or said lower groove have a variable depth at each upstream portion of the scoreline;
- the upstream portions of the scoreline extend symmetrically on either side of the longitudinal axis of the opening member.

The present invention also relates to a container, in particular of the metal can type, equipped with a metal cover as defined hereinabove.
The present invention also relates to a method for manufacturing a cover according to the invention, wherein the method comprises a step of incision of the scoreline into said cover, by means of an incision tool comprising an upper member (for example an incision block) and a lower member (for example an anvil) each carrying a profile.
Within the framework of the invention, during said step of incision, the profiles of said incision tool are arranged so as to generate said upstream portions of the scoreline, each upstream portion of the scoreline includes, successively in the tearing direction, at least two sections:

- a first section having a first residual thickness, and
- a second section having a residual thickness higher than said first residual thickness,

wherein the second section extends over at least 20% of the length of said upstream portion,
wherein the second section of each upstream portion of the scoreline includes:

- an upstream end, connected to a first section, and
- a downstream end, provided within said upstream portion.

The present invention also relates to the device for manufacturing a metal cover according to the invention, comprising an incision tool for forming the scoreline, wherein the incision tool comprises an upper member (for example, an incision block) and a lower member (for example, an anvil), each carrying an incision profile.
According to the invention, the profiles in incision position define, between each other, a space of variable width to generate the upstream portions of the scoreline according to the invention.
Each upstream portion of the scoreline includes, successively in the tearing direction, at least two sections:

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

The present invention will be further illustrated, without being limited thereby, by the following description of particular embodiments in relation with the appended drawings, in which:

FIG. 1 shows, in top view, a metal cover according to the invention;

FIG. 2 schematically shows a cross-section of the scoreline formed in the metal cover;

FIG. 3 schematically shows a development of the longitudinal section of one of the upstream portions of the scoreline formed in the metal cover, showing the evolution of its residual thickness over its length;

FIG. 4 schematically illustrates the tool for forming the scoreline according to the invention into the metal cover;

FIG. 5 schematically shows the profile of incision of the upper member of the incision tool according to FIG. 4, adapted to form a scoreline according to FIG. 3;

FIGS. 6 to 12 each schematically show a development of the longitudinal section of a variant of embodiment of an upstream portion of the scoreline formed in the metal cover, showing the variation of its residual thickness over its length.

The metal cover 1, shown in FIG. 1, is intended to be assembled to the upper edge of a metal container body (not shown).
This container body is generally consisted of a bottom associated with the lower edge of a belt of lateral walls (of circular, square, rectangular cross-section, etc.).
The linking between the metal cover 1 and the upper edge of this container body is made in the conventional way, for example by a seaming technique.
This metal cover 1 is of the “easy opening” (or “EOE” for “Easy Open End”) type, avoiding the use of tools such as can-openers.
For that purpose, this metal cover 1 is conventionally consisted of two parts:

- a central part 2 forming a central closing panel, and
- a peripheral part 3, adapted to be fastened to the container body.

This metal cover 1 is advantageously made single-piece by a drawing technique, from a metal sheet (advantageously made of aluminium, steel, etc.).
The peripheral part 3 is herein of annular shape or ring shape. It is adapted for the fastening of the metal cover 1, advantageously by seaming, to the upper edge of a container body having a cylindrical lateral wall.
As an alternative, the peripheral part 3 may have any other shape (for example, square, rectangular), which would be adapted to the section of the container body (as the case may be, parallelepipedal).
The central part 2 has two faces (FIG. 2):

- an upper face 21, intended to be oriented towards the outside of the container obtained, and
- a lower face 22, intended to be oriented towards the inside of the container, facing the bottom of this container.

The distance between these two faces 21, 22 corresponds to the nominal thickness N of the central part 2 (FIG. 2).
This nominal thickness N of the central part 2 is for example comprised between 0.14 and 0.28 mm, preferably between 0.16 and 0.25 mm.
The central part 2 comprises a removable part 4 intended to form the opening of access to the container content.
The removable part 4 is, on the one hand, delimited by a scoreline 5, also called “incision line”, and on the other hand, equipped with an opening member 6.
The opening member 6 is arranged at the upper face 21 of the central part 2, covering the removable part 4 (FIG. 1).
The handling of this opening member 6 by a user will allow an easy opening of the metal cover 1, i.e. an unfastening, total or partial, of the removable part 4 by tearing of the scoreline 5.
This well-known opening member 6 is also met under the name “opening ring”.
This opening member 6 conventionally includes three parts, successively arranged along a longitudinal axis 6′, i.e.:

- a peripheral part 7, commonly named “beak”, arranged at the scoreline 5 to perform the incision into the latter,
- an intermediate part 8, for its fastening to the removable part 4 of the metal cover 1, for example by means of a rivet-shaped structure, and
- a central part 9, forming a grasping loop, which is originally flattened against the upper face 21 of the central part 2 of the metal cover 1.

For its part, the scoreline 5 consists in a narrowing of material, forming a lower-strength structure.
This scoreline 5 is herein complete (closed), and advantageously of circular shape (FIG. 1). As an alternative, it could be partial (for example, in an arc of a circle) and/or have any other shape (square, rectangular, for example).
As shown in FIG. 2, this scoreline 5 has a residual thickness E that corresponds to the minimum distance measured between:

- un upper surface 51 of the scoreline 5, on the side of the upper face 21 of the central part 2, and
- a lower surface 52 of the scoreline 5, on the side of the lower face 22 of the central part 2.

As also shown in FIG. 2, the upper surface 51 of this scoreline 5 is formed by an upper grove 53 provided in the upper face 21 of the central part 2.
This scoreline 5 could also be formed, as an alternative or a complement, by a groove 54 that would be provided in the lower face 22 of the central part 2 (as schematically illustrated in FIG. 2 in discontinuous lines). As the case may be, this lower groove 54 also forms the lower surface 52 of the scoreline 5.
Taking into account the arrangement of the opening member 6 and of the operation thereof at the opening of the cover 1, the scoreline 5 comprises different portions, i.e.:

- two upstream portions 55, intended to be torn by the initial operation of pivoting of the opening member 6, and
- a downstream portion 56 consisted by the remaining length of the scoreline 5, intended to be torn by the following operation of traction on the pivoted opening member 6.

The two upstream portions 55 extend on either side of the longitudinal axis 6′ of the opening member 6.
Each upstream portion 55, on the one hand, and the downstream portion 56, on the other hand, are herein separated by a virtual axis 10 shown in FIG. 1.
The virtual axis 10 corresponds, at least approximately, to the bend line generated on the removable part 4 after the pivoting of the opening member 6.
In this case, this virtual axis 10 extends perpendicularly to the longitudinal axis 6′ of the opening member 6.
This virtual axis 10 advantageously passes, at least approximately, at the level of the fastening part 8.
By “approximately”, it is herein understood that the virtual axis 10 passes, for example:

- through the fastening part 8, or
- in front of the fastening part 8 (between the fastening part 8 and the “beak” peripheral part 7), or
- behind the fastening part 8 (remote from the “beak” peripheral part 7).

In other words, each upstream portion 55 extends between two points (FIG. 1):

- an initial point A located on the longitudinal axis 6′ of the opening member 6, and
- a terminal point B defined by the above-mentioned virtual axis 10.

According to the invention, to control the first phase of opening of the removable part 4 (corresponding to the pivoting of the opening member 6), each upstream portion 55 of the scoreline 5 includes, over its length, a specific progression of its residual thickness E.
In this case, as illustrated in FIG. 3, each upstream portion 55 of the scoreline 5 includes three successive sections, i.e. in the tearing direction (from the initial point A to the terminal point B):

- a first section 551, having a residual thickness E1 over a length L1,
- a second section 552, having a residual thickness E2 over a length L2, and
- a third section 553, having a residual thickness E3 over a length L3.

The upper groove 53 and/or the lower groove 54 have hence a variable depth at each upstream portion 55 of the scoreline 5 to define this variable residual thickness E.
In this case, the different sections 551, 552 and 553 of the upstream portion 55 each form a step. Each section 551, 552 and 553 of the upstream portion 55 hence has a residual thickness E1, E2, E3, respectively, constant over its length L1, L2, L3.
According to the invention, the residual thickness E2 of the second section 552 is higher than the residual thickness E1, E3 of the first section 551 and of the third section 553, respectively.
The first section 551 and the third section 553 of the upstream portion 55 have moreover mutually identical residual thickness E1, E3.
The residual thickness E1, E3 of these first section 551 and third section 553 is advantageously identical, or at least approximately identical, to the majority residual thickness E4 of the downstream portion 56.
By “majority residual thickness”, it is understood in particular the residual thickness E4 of the downstream portion 56 over its whole length or almost its whole length, except possible punctual sections having a variation of residual thickness E aiming to control its tearing.
For example, the first section 551 and the third section 553 of the upstream portion 55 have residual thickness E1, E3 comprised between 45 and 80 μm for metal cover made of steel.
The residual thickness E2 of the second section 552 has an additional residual thickness EZ, with respect to the residual thickness E1, E3 of the first section 551 and of the third section 553.
For example, this additional residual thickness EZ is comprised between 10 and 50 μm, preferably between 15 and 35 μm.
Furthermore, the second section 552 extends over a length L2 corresponding to at least 20%, preferably at least 25%, still preferably between 25 and 60%, of the length L of this upstream portion 55.
More precisely, the second section 552 of the upstream portion 55 is ended by:

- an upstream end 5521, on the side of the initial point A and connected to the first section 551, and
- a downstream 5522, of the side of the terminal point B and connected to the third section 553.

The upstream end 5521 is advantageously located remote from the initial point A.
The downstream end 5522 is herein provided within the upstream portion 55, remote from the terminal point B.
As an alternative, this downstream end 5522 of the second section 552 could be located at the terminal point B of the upstream portion 55, directly connected to an end of the downstream portion 56 of the scoreline 5.
The upstream end 5521 and the downstream end 5522 herein consist in an abrupt variation of the residual thickness.
These upstream 5521 and downstream 5522 ends hence extend perpendicularly with respect, on the one hand, to the second section 552, and on the other hand, to the associated first or third section 551 and 553.
Only by way of example, for a metal cover 1 provided with a scoreline 5 whose diameter is of about 77 mm:

- the length L of each upstream portion 55 is comprised between 15 mm and 35 mm, and
- the length L2 of the second section 552 is advantageously comprised between 6 and 20 mm.

Still for example, the upstream end 5521 of the second section 552 is advantageously located at a distance comprised between 3 and 8 mm with respect to the initial point A of the upstream portion 55 (corresponding to the length L1 of the first section 551).
Generally, the two upstream portions 55 of the scoreline 5 advantageously extend symmetrically on either side of the longitudinal axis 6′ of the opening member 6.
In practice, for the opening, the user operates the opening member 6 in two successive and distinct operations.
First, in a first step of opening initiation, the user grasps the opening member 6, generally by its central grasping part 9, then he moves it apart from the central part 2.
The opening member 6 then forms a lever, whose beak-shaped, peripheral incision part 7 caused a local breaking of the scoreline 5, within the first section 551 of the two upstream portions 55.
This tearing propagates along the two upstream portions 55, on either side of the longitudinal axis 6′ of the opening member 6, towards their respective terminal points B.
The tearing then continues within the two second sections 552 of the upstream portions 55, progressively and at a higher level of effort.
This mechanism allows a slowing down of the speed of opening, during which a balancing of the pressure is performed between the container inside and the environment, with no risk of sagging of the cover.
Such a slowing down avoids any phenomenon of stopping in the tearing of the scoreline 5. An additional effort liable to generate an untimely breaking outside the scoreline is hence avoided.
This slowing down is in particular allowed by a level of force and energy increasing progressively, over a significant length of the upstream portions 55, in order to break the second sections 552 thereof.
The pivoting of the opening member 6 is continued until the total or partial tearing of the upstream portions 55 of the scoreline 5, ideal up to the terminal point B.
The removable part 4 of the cover 1 is then locally bent inwardly, about the virtual axis 10.
In a second opening step, conventionally, the user exerts a traction on the opening member 6 so as to continue the tearing of the scoreline 5, in particular the downstream portion 56 thereof, and to dissociate all or part of the removable part 4 with respect to the cover 1.
A metal cover 1 according to the invention may be obtained by a method comprising a step of incision of the scoreline 5 into the cover 1, by means of an incision tool 12 as schematically shown in FIG. 4.
Such an incision tool 12 comprises an upper member 121, for example an incision block, and a lower member 122, for example an anvil.
The upper member 121 and the lower member 122 include mutually opposite profiles 1211 and 1221, to define the section of the scoreline 5.
The geometry of the profile 1211, 1221 of the incision block 121 and/or of the anvil 122 intervene on the residual thickness E of the scoreline 5.
In particular, the profile 1211 of the upper member 121 constitutes an incision profile, intended to conform the upper groove 53 of the scoreline 5.
In this case, as shown in FIG. 5, the incision profile 1211 of the upper member 121 has a profile complementary of that of each upstream portion 55, with, in particular, a recess 1212 intended to define the second section 552 of the scoreline 5.
In practice, the method for manufacturing a cover 1 according to the invention firstly comprises the providing of a cover to be incised.
Then, the step of incision of the scoreline 5 is performed by means of the incision tool 12 described hereinabove.
For that purpose, during this step of incision, the profiles 1211, 1221 of said incision tool 121 are moved closer together by a movement of translation, to generate the upper 53 and/or lower 54 grooves in the central part 2 of the cover 1.
In the incision position, the profiles 1211, 1221 hence define, between each other, a space of variable width over the length of said profiles, which is complementary of the residual thickness E of the scoreline 5, to generate in particular the sections 551, 552 and 553 of the upstream portions 55 of the scoreline 5.
FIGS. 6 to 12 illustrate variants of embodiment for the upstream portions 55 of the scoreline 5.
In each of these variants, we find the three successive sections 551, 552 and 553 of the upstream portion 55, with the second section 552 having a higher residual thickness E2 with respect to the other sections 551 and 553.
The variants of FIGS. 6 and 7 are different from the structure described hereinabove in relation with FIGS. 1 to 3 by the structure of the upstream 5521 and downstream 5522 ends of the second section 552.
In FIG. 6, these upstream 5521 and downstream 5522 ends constitute a continuous progressive variations of the residual thickness E.
In this case, these ends 5521, 5522 consist in respectively ascending and descending straight slops.
For example, this variation of thickness is made over a length comprised between 0.3 and 0.7 mm.
Preferably, the downstream end 5522 extends over a higher length with respect to the length of the upstream end 5521.
This structural characteristic has for advantage to smoothen the variation of effort felt by the consumer.
In FIG. 7, the upstream end 5521 includes a discontinuous progressive variation of the residual thickness E.
In this case, this upstream end 5521 has the shape of a staircase or a succession of steps.
This structural characteristic has also for advantage to smoothen the variation of effort felt by the consumer.
The variants of FIGS. 8 to 12 are different from the structure described hereinabove in relation with FIGS. 1 to 3 by a variable residual thickness E2 of the second section 552.
In this case, the additional residual thickness EZ corresponds to the maximal residual thickness of this section 552.
In FIG. 8, the second section 552 has a continuous progressive variation of the residual thickness E2, with an ascending linear slope higher than a decreasing linear slope.
In FIG. 9, the second section 552 has a continuous progressive variation of the residual thickness E2, with an ascending linear slope identical, or at least approximately identical, to the decreasing linear slope.
In FIG. 10, the second section 552 has a curved variation of thickness, for example in an arc of a circle.
In FIGS. 11 and 12, the second section 553 has a variation of thickness with a generally oscillating shape, broken in FIG. 11 and curved in FIG. 12.
In these embodiments according to FIGS. 11 and 12, the residual thickness E2 of the second section 552 oscillates between a minimum value E21 and a maximum value E22 that both remain higher than the residual thickness E1, E3 of the first and third sections 551, 553.
Generally, the cover structure according to the invention has for interest to preserve an easiness of opening, while offering an efficient solution to the risk of implosion at the opening and to the risk of tearing of the removable part due to its rolling direction.
The structure of the cover according to the invention allows, for a same cover and scoreline thickness, an increased resistance to implosion with respect to a system of the “arrester flat” type.

Claims

1-12. (canceled)

13. A metal cover for a container body, in particular for a container of the metal can type,

said metal cover (1) comprising:

a central part (2) forming a central closing panel, and

a peripheral part (3) adapted to be fastened to said container body,

wherein the central part (2) comprises a removable part (4) that is delimited by a scoreline (5) having a variable residual thickness and that is equipped with an opening member (6),

wherein the opening member (6) comprises, on either side of a part (8) for the fastening to the removable part (4), a peripheral incision part (7) and a central grasping part (9),

wherein said scoreline (5) comprises:

two upstream portions (55), extending on either side of the longitudinal axis (6′) of the opening member (6), and

a downstream portion (56), consisted by the remaining length of said scoreline (5),

wherein the portions (55, 56) are arranged on either side of a virtual axis (10) extending perpendicularly to the longitudinal axis (6′) of the opening member (6), said virtual axis (10) corresponding to the bend line generated on the removable part (4) after a pivoting of said opening member (6) and the tearing of said upstream portions (55),

wherein each upstream portion (55) of the scoreline (5) includes, successively in the tearing direction, at least two sections:

a first section (551) having a first residual thickness (E1), and

a second section (552) having a residual thickness (E2) higher than said first residual thickness (E1),

wherein the second section (552) extends over at least 20% of the length (L) of said upstream portion (55),

and wherein said second section (552) of each upstream portion (55) of the scoreline (5) includes:

an upstream end (5521), connected to the first section (551), and

a downstream end (5522), provided within said upstream portion (55).

14. The metal cover according to claim 13, wherein the downstream end (5522) of the second section (552) is connected to the downstream portion (56) (i) directly or (ii) through a third section (553) whose residual thickness (E3) is lower than the residual thickness (E2) of said second section (552) of the upstream portion (55).

15. The metal cover according to claim 13, wherein the upstream end (5521) and/or the downstream end (5522) of the second section (552) of the upstream portion (55) show:

an abrupt variation of the residual thickness, or

a continuous progressive variation of the residual thickness, or

a discontinuous progressive variation of the residual thickness.

16. The metal cover according to claim 15, wherein the upstream end (5521) and the downstream end (5522) of the second section (552) of the upstream portion (55) each show a progressive variation of the residual thickness (E), and wherein the downstream end (5522) extends over a length higher than the length of the upstream end (5521).

17. The metal cover according to claim 13, wherein the first section (551) of the upstream portion (55) of the scoreline (5) has a constant residual thickness (E1), and

wherein the second section (552) of the upstream portion (55) of the scoreline (5) has a constant or variable residual thickness (E2).

18. The metal cover according to claim 13, wherein the difference of residual thickness (E2′) between the first section (551) and the second section (552) of the upstream portion (55) is comprised between 10 and 50 μm.

19. The metal cover according to claim 13, wherein the first section (551), and as the case may be, the third section (553), of the upstream portion (55) has a residual thickness identical, or at least approximately identical, to the majority residual thickness (E4) of the downstream portion (56).

20. The metal cover according to claim 13, wherein the scoreline (5) is formed by a lower groove (54) and/or by an upper groove (53) that are arranged in a lower face (22) and/or an upper face (21), respectively, of the central part (4) of the cover (1), and

wherein said upper groove (53) and/or said lower groove (54) have a variable depth at the upstream portion (55) of the scoreline (5).

21. The metal cover according to claim 13, wherein the upstream portions (55) of the scoreline (5) extend symmetrically on either side of the longitudinal axis (6′) of the opening member (6).

22. A container, in particular of the metal can type, equipped with a metal cover (1) according to claim 13.

23. A method for manufacturing a cover (1) according to claim 13, wherein the method comprises a step of incision of the scoreline (5) in said cover (1), by means of an incision tool (12) comprising an upper member (121) and a lower member (122) each carrying a profile (1211, 1221),

wherein, during said step of incision, the profiles (1211, 1221) of said incision tool (121) are arranged so as to generate each of said upstream portions (55) of the scoreline (5),

each upstream portion (55) of the scoreline (5) includes, successively in the tearing direction, at least two sections:

a first section (551) having a first residual thickness (E1), and

wherein the second section (552) of each upstream portion (55) of the scoreline (5) includes:

an upstream end (5521), connected to a first section (551), and

a downstream end (5522), provided within said upstream portion (55).

24. A device for manufacturing a metal cover (1) according to claim 13, comprising an incision tool (12) for forming the scoreline (5), which incision tool (12) comprises an upper member (121) and a lower member (122), each carrying an incision profile (1211, 1221),

wherein the profiles (1211, 1221) in incision position define, between each other, a space of a variable width to generate the upstream portions (55) of the scoreline (5),

a first section (551) having a first residual thickness (E1), and

an upstream end (5521), connected to the first section (551), and

a downstream end (5522), provided within said upstream portion (55).

25. A container, in particular of the metal can type, equipped with a metal cover (1) according to claim 14.

26. A container, in particular of the metal can type, equipped with a metal cover (1) according to claim 15.

27. A container, in particular of the metal can type, equipped with a metal cover (1) according to claim 16.

28. A container, in particular of the metal can type, equipped with a metal cover (1) according to claim 17.

29. A method for manufacturing a cover (1) according to claim 14, wherein the method comprises a step of incision of the scoreline (5) in said cover (1), by means of an incision tool (12) comprising an upper member (121) and a lower member (122) each carrying a profile (1211, 1221),

a first section (551) having a first residual thickness (E1), and

an upstream end (5521), connected to a first section (551), and

a downstream end (5522), provided within said upstream portion (55).

30. A method for manufacturing a cover (1) according to claim 15, wherein the method comprises a step of incision of the scoreline (5) in said cover (1), by means of an incision tool (12) comprising an upper member (121) and a lower member (122) each carrying a profile (1211, 1221),

a first section (551) having a first residual thickness (E1), and

an upstream end (5521), connected to a first section (551), and

a downstream end (5522), provided within said upstream portion (55).

31. A device for manufacturing a metal cover (1) according to claim 14, comprising an incision tool (12) for forming the scoreline (5), which incision tool (12) comprises an upper member (121) and a lower member (122), each carrying an incision profile (1211, 1221),

a first section (551) having a first residual thickness (E1), and

an upstream end (5521), connected to the first section (551), and

a downstream end (5522), provided within said upstream portion (55).

32. A device for manufacturing a metal cover (1) according to claim 15, comprising an incision tool (12) for forming the scoreline (5), which incision tool (12) comprises an upper member (121) and a lower member (122), each carrying an incision profile (1211, 1221),

a first section (551) having a first residual thickness (E1), and

an upstream end (5521), connected to the first section (551), and

a downstream end (5522), provided within said upstream portion (55).