EP3784581A1

EP3784581A1 - Tearable metal cover with convex central arched shield

Info

Publication number: EP3784581A1
Application number: EP19724934.5A
Authority: EP
Inventors: Romano RAVASIO
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-04-24
Filing date: 2019-04-18
Publication date: 2021-03-03
Also published as: MA52356A; IT201800004841A1; AR115347A1; WO2019207430A1

Abstract

A metal container with variable resistance cover for easy opening comprises a container body (12) and a cover (20) integral with the container body (12) along a perimeter edge (13), wherein the cover (20) is provided with a perimeter pre-cut (21) adjacent to the edge (13), as well as comprising a pull tab (14) provided, at one end, with a ring portion (14A) that the user grasps and, at the opposite end, with a pressure apex (14B), as well as between the two ends, with a rivet (15) for joining to the cover (20), the cover (20) having at least one surface shaping, wherein the container (10) comprises, in the portion inside the pre-cut (21), at least one permanently convex central shield (30, 30'), comprising at least one convex surface shaping (30, 130) and identifying a longitudinal convex arc (ill), which determines between its ends an opening straight line (11B) of the container (10).

Description

TEARABLE METAL COVER WITH CONVEX CENTRAL ARCHED SHIELD

The present invention relates to a metal container with variable resistance cover for easy opening.

The production of metal containers is known, such as, for example cans for foods made of aluminium or tin plate, provided with a cover seamed to the container body and provided with a perimeter pre-cut close to the seam. The cover comprises a pull tab provided at one end with a ring portion that the user grasps and, at the opposite end, with a pressure apex, as well as with a connecting rivet to the cover between the two ends.

The initial opening step is carried out by acting on the pull tab so as to use the rivet as a rotation pin to cause the lifting of the tab from the plane of the cover and the simultaneous breaking of the pre-cut due to the effect of the pressure apex acting close to the same. The opening continues by exerting a traction on the cover by means of the ring portion according to a line of force, which extends in the space above the container according to an arc of a circle and then continuing, substantially parallel to the plane of the container .

This operation requires the user to exert a considerable force both in the initial opening steps and in the subsequent step.

Additionally, the tendency of the cover to deform in a transverse direction to the direction of traction during the opening steps with a strong elastic component makes it all the more difficult to exert the traction in the final opening steps.

Moreover, users risk injuring themselves with the sharp edge of the cover portion, already separated from the container body, which tends to come close to their hand due to the "rolling" effect of the cover in a transverse direction to the direction of traction.

Especially in the case of containers containing liquids filled to the rim, such as, for example, fish products, when they are packed by filling with oil or brine, in the above described operations there is an elevated risk of spillage of some of the filling liquid over the edge or nonetheless splashing due to the uncontrolled movement of the cover.

Generally, known covers have, on the plane thereof, shapings distributed on the surface, to obtain a certain level of rigidity. Such rigidity satisfies the needs for stability of the container, for example during the autoclave sterilization process for food containers or during preservation, or storage, before consumption .

However, such shapings are not adapted to prevent the cover from folding transversely to the direction of traction during the opening of the cover, above all, nor do they overcome the difficulty of traction during the opening.

It is an object of the present invention to provide a metal container with variable resistance cover for easy opening, which overcomes the drawbacks of the described prior art.

It is another object of the present invention to provide a metal container with variable resistance cover for easy opening, which requires a reduced use of traction forces with respect to known covers, having the same geometry as the container. It is another object of the present invention to provide a metal container with variable resistance cover for easy opening, which is particularly simple and practical, with reduced costs.

These objects according to the present invention are achieved by providing a metal container with variable resistance cover for easy opening as outlined in claim 1.

Further features are comprised in the dependent claims .

The features and advantages of a metal container with variable resistance cover for easy opening according to the present invention will be more apparent from the following description, which is to be understood as exemplifying and not limiting, with reference to the attached schematic drawings, wherein: figure 1A is a plan view of a first embodiment of a metal container with variable resistance cover for easy opening, object of the present invention;

figure IB is a section of the container in figure 1 according to the trace plan IB-IB;

figure 2 is a plan view of a simplified version of the container in figure 1;

figures from 3 to 6 show further embodiments of the container according to the invention provided with a simple convex shield and with a coinciding opening and traction straight line;

figures from 7 to 9 show further embodiments of the container according to the invention provided with a complex convex shield and with a coinciding opening and traction straight line;

figure 10 shows an embodiment bearing two simple convex shields placed in longitudinal sequence;

figures 11 and 12 show two embodiments of the container according to the invention provided with a simple or complex convex shield and with a non coinciding opening and traction straight line respectively;

figure 13 shows a further embodiment of the container according to the invention having a simple convex shield extended to the portion bearing the tab; figures 14 and 15A and 15B show examples of convex shields progressively degrading until cancelling the height thereof;

figures 16 and 17 show two further embodiments of a container according to the invention wherein the load line is close to the rivet of the tab;

figures 18A and 18B show an embodiment, wherein a perimeter concavity is shown, by way of example, about the convex shield;

figures from 19A to 19C show the opening sequence of the container in figure 1.

With reference to the figures, a metal container is shown with variable resistance cover for easy opening globally indicated with 10. The container 10 comprises a container body 12 and a cover 20, integral with the container body 12 along a perimeter edge 13.

In the example shown in the figures, the cover 20 is integral with the container body 12 along the edge 13 by means of seaming.

The cover 20 is provided with a perimeter pre-cut 21 adjacent to the edge 13 for opening by means of a pull tab 14, joined to the cover 20 by means of a rivet 15 and provided at a first end with a ring portion 14A, that the user grasps and, at a second opposite end, with a pressure apex 14B. According to what is known, on opening the container, the tab 14, lifted by the user with the ring portion 14A, has a fulcrum effect at the rivet 15, starting the opening of the cover 20 by means of a first incision of the pre-cut 21 due to the effect of the pressure apex 14B acting close to the same. The pull tab 14, which can also have a different shape from the shape shown in the figures, was represented sketched. For example, the fulcrum could be in a different position from the rivet. In general, what is described with reference to the rivet as a fulcrum is understood to refer to the fulcrum of the tab, also when it doesn't coincide with the rivet.

The traction by the user is thus exerted with a component lying in the plane of the cover 20 according to a traction straight line 11A (shown dotted in the figures) and with a component outside the plane of the cover 20, schematized with the arrows Ti, T2 and T3 in the plan figures, which identify an angle bi, b₂, b3 with the plane of the cover.

A "traction straight line" 11A is understood to mean the straight line lying in the plane of the container 20 and passing through the median axis of the tab 14, where both the rivet 15 and the opposite ends of the tab 14A, 14B lie, along which the traction force is exerted by the user.

The cover 20 has one or more permanently convex surface shapings 30, 130, i.e. convex three-dimensional geometric figures with respect to the plane of the cover 20, identifying at least one permanently central convex shield 30, 30', which identifies a longitudinal convex arc 111, which is a real or virtual subtended arc, determining the opening straight line 11B.

The cover 20 according to the invention, as described above, is provided with variable resistance, in the sense that the specific three-dimensional geometry of the cover determines the presence of areas, each having own permanent features, which are different with respect to the adjoining areas.

Figures from 1 to 6 show a first embodiment of the convex shield 30, so-called "simple", according to the invention .

The convex shield 30, which will subsequently be called "simple", is made up of a single convex surface shaping, or of a single convex three-dimensional figure, shaped according to a convex profile whose geometry defines the longitudinal convex arc 111 and consequently the opening straight line 11B. In this case, the longitudinal convex arc 111 can exceptionally coincide with the geometric profile of the convex surface shaping 30 or it can be a virtual arc subtended to the same. The longitudinal convex arc 111, determined by the single convex surface shaping 30, can have any orientation with respect to the cover 20.

Figures from 7 to 9 show a second embodiment of the convex shield 30', so-called "complex", according to the invention.

The convex shield 30', which will subsequently be called "complex" is made up of a plurality of convex three-dimensional figures 130, for example punctiform or shaped according to another permanently convex profile, placed side by side longitudinally or in regular sequence or not and partially overlapping in a transverse direction at least in pairs. In fact, the convex surface shapings 130 identify the longitudinal convex arc 111 by interpolation of the upper outlines thereof. In this case, it is necessarily a virtual longitudinal convex arc 111 subtended to the complex shield 30'. In the case of a complex shield 30', the opening straight line 11B is made up of an average of the geometries of the single convex surface shapings 130.

By acting on the shape and position of the convex surface shapings 30, 130 it is possible to orient the convex longitudinal arc 111 of the simple shield 30 or complex shield 30' according to any direction on the plane of the cover 20, to direct the opening thereof, as well as obtain a positioning of the apex of the convex longitudinal arc 111, which is such as to determine the resistance to pressure, i.e. to the risk of breaking, determining the permanent convexity of the convex shield 30, 30'. Furthermore, the return of the traction forces is determined through the longitudinal arc 111, which is such as to convey them, multiply them and optimize them for opening.

The complex shield 30', indicated schematically in figures from 7 to 9 and circumscribed with a dotted outline, behaves like a simple shield 30 in all respects, during the opening.

Again according to the invention, the cover 20 can comprise two or more simple 30 or complex 30' convex shields, also in a mixed combination between one another, placed longitudinally in sequence without mutual overlapping.

According to what is shown in figure 10, the simple shields 30 are placed longitudinally in sequence on the opening straight line 11B.

According to a further variation, not shown, each of the simple and/or complex shields could have an own opening straight line, wherein the opening straight lines are mutually incident or not.

According to the invention, the traction straight line 11A can coincide with the opening straight line 11B, when the opening straight line passes through the rivet 15 of the tab 14. In this case, the longitudinal convex arc 111 is oriented according to the traction straight line 11A passing through the median axis of the tab 14. Alternatively, the two straight lines can be mutually incident with an obtuse angle a, as shown for example in figures 11 and 12. In this second case, the user exerts a first step of traction on opening the container 10 according to the traction straight line 11A, whereas, after reaching the shield 30, 30' the opening of the container is carried out in the direction of the opening straight line 11B defined by the longitudinal convex arc 111.

Each simple 30 or complex 30' convex shield defines, at opposite ends of the own opening straight line 11B, a leading end 31, which determines a load line 22 of the shield, shown in a sketched line, and a tail end 32, which determines an opening target point 23. The leading 31 and tail 32 ends comprise the opposite ends of the longitudinal convex arc 111 subtended by the convex shield 30, 30'.

Nonetheless, the load line 22 cannot be further upstream in the direction of traction with respect to the fulcrum of the tab 14, which constitutes the initial opening point of the container 10. Thus, in cases where the leading end 31 is placed between the rivet 15, generally constituting the fulcrum, and the pre-cut 21, i.e. upstream of the rivet 15, the load line 22 nonetheless passes through the rivet 15, as, for example, in figures 10 and 13.

In the case of a longitudinal sequence of two or more simple 30 or complex 30' shields, the transition between the leading end 31 and the tail end 32 of two shields 30, 30', which are adjacent in the opening direction, determines an intermediate target point 123, subject to folding in the opening step of the cover 20 (figure 10).

In a container according to the invention, advantageously, the tail end 32 can be placed close to the pre-cut 21, in particular upstream of the pre-cut 21, so that the cover 20 separates integrally from the container body 12.

The preferred maximum extension of a shield 30, 30' or of a succession in longitudinal sequence of shields 30, 30' goes from the fulcrum of the tab 14 to the pre-cut 21 on the opposite side of the container 10. According to the invention, at least one shield 30, 30' or the longitudinal succession of shields 30, 30' can also have a shorter length.

The convex shield 30, 30 ' can be longitudinal or oblique, of any shape, symmetric or not, have an elliptic shape, vaguely oval or other shapes, as long as the direction of thrust between the various forces in act is compensated and thus directed towards the target point 23.

The simple 30 or complex 30' shield can have a leading end 31 or tail end 32 with a rounded, square or acute tip, thus with any initial or end tip. Furthermore, the leading 31 or tail 32 ends can be symmetric or not, both with respect to the opening straight line 11B, and with respect to a straight line transverse thereto.

In the presence of pronounced leading 31 and/or tail 32 ends, the forces are conveyed with greater precision .

Along the perimeter thereof, the convex surface shapings can have a profile with a bending point with respect to the plane of the cover 20, identifying a so- called "closed" geometry or at least some of them can have a profile, which fades progressively in the plane of the cover 20 until cancelling the height thereof (figure 14), identifying a so-called "open" geometry.

According to a particular embodiment of the invention, for example shown in figures 15A and 15B, the profile of the convex surface shaping 30, which forms the central convex shield, is asymmetric and, in particular, it has a more pronounced curvature in the first section, i.e. at the end placed on the side of the tab 14, and progressively less pronounced in the second section along the traction straight line 11A in the direction of the target point 23 until cancelling the height thereof.

Despite having minimum convexity, the second section of the profile constitutes a line of weakness, which is amplified, at the time of opening the cover 20, forming a more accentuated convex profile than before the opening. In this case, the convex longitudinal arc 111 subtended by the shield is modified during the opening of the container 10.

This amplification effect is particularly pronounced, especially if the leading end 31 is close to the fulcrum 15 of the tab 14, in particular downstream of the fulcrum or at most coinciding therewith. In fact, in this case, the traction force exerted by the user on the tab 14 at the initial section of the shield 30, 30 ' is oriented outside the plane of the cover 20, in a direction substantially orthogonal to the same, according to the arrow T₃. Due to the orthogonal orientation of the traction force, (with b₃ greater than b₂₎ when starting traction, the shield 30, 30' amplifies the width thereof.

One shield 30, which completely occupies the cover 20, will cancel the target point 23, figures 15A and 15B. In this case, the travel will not stop and the cover 20 will tend to break off, unless the final part of the shield 30 is weakened, interrupting the convexity or inserting a depression, not shown in figures 15A and 15B.

A further embodiment of the container 10 is shown in figure 16, wherein the load line 22 is close to the rivet 15. As for the example in figure 15, the ring portion 14A of the tab 14 overlaps the first portion of shield 30 in this case and will preferably have to be shaped in a complementary manner thereto, to reduce the volume .

On wishing to insert a simple 30 or complex 30' shield, which goes from pre-cut 21 to pre-cut 21, but preferring not to intervene in the area of the ring 14A and the rivet 15, it is possible to avoid them, as shown in figure 17. According to a preferred embodiment of the invention, the cover 20 comprises a first non-shaped surface 24 situated at the side and about at least one shield 30, 30', preferably extended to the pre-cut 21. A non-shaped surface is understood to mean a surface devoid of moldings, ribbings or other convex three- dimensional geometric protrusions. Such non-shaped surface can be arranged in the horizontal plane of the cover, shown dotted, for example in figures IB, 15B and 18B.

If the load line 22 is downstream of the tab 14 along the traction straight line 11A, a further non- shaped surface 25 of the cover 20 is created, i.e. devoid of convex geometric protrusions, placed between the rivet 15 of the tab 14 and the load line 22.

Advantageously, in particular, but not exclusively in the configuration shown in figure 1A and IB, the cover 20 can comprise pressure protrusions 26 arranged between the rivet 15 of the tab 14 and the edge 13 of the container for a section of the perimeter, with the purpose of assisting the pressure of the tip, determining a wider initial opening and, above all, advantageously keeping the non-shaped load surface 25 flat .

According to the invention, the cover 20 can also comprise one or more concavities, or depressions, on the non-shaped side surface 24 and/or on the further non-shaped surface 25, which must always be compensated by the convexity of the shield 30, 30 ', so as not to alter the behavior thereof.

For example, it can comprise a perimeter concavity 27 about at least one shield 30, 30' to compensate the convexity in height of at least one shield 30, 30 ' (figures 18A and 18B) .

Furthermore, the cover 20 can comprise other concavities, not shown, for example at the load line.

These concavities can have the object, for example, of reducing the explosiveness of the convex shield, lowering the median plane of the cover in cases of excessive shield elevation, serving as a connection between the multiple or successive convex shields.

Advantageously, the cover 20 can also comprise a stiffening perimeter recess 29, external to the pre cut, shown by way of example in figures 1A and IB, which could be introduced into each of the embodiments shown, placed between the pre-cut 21 and the edge 13 of the container 20.

Containers 10 of different geometric shapes are shown by way of example in the figures, such as, for example containers having a round, smoothed rectangular or oval plan shape, as well as different measurements and proportions, bearing one or more simple 30 or complex 30' convex shields according to the invention. In principle, everything described and shown for each container can be applied in an equivalent manner to each of these containers, although there are some particularly advantageous specific shapes and types of shield for one container shape rather than for another different one.

Furthermore, the convexities described in the present invention can be realized by drawing or shaping of the laminated metal, or they can be the result of a mold or a die, or of a 3D print, or they can be obtained by overlapping and adhesion (bonding or welding) of other material having the required shape.

The opening of the container 10 is carried out by means of traction by the user on the ring end 14A of the tab 14 with a force component in the plane of the cover 20 according to the traction straight line 11A and a force component outside the plane of the cover 20.

For containers 10 having a non-shaped surface 25 at the tab 14, during the first steps of opening, this traditionally results in forces outside the plane arranged in an arched manner, identifying a quarter of a circle, as shown schematically by the arrows Ti in the illustrative plan figures. The non-shaped surface 25 allows the folding of the cover up to the load line ( figure 19A) .

On reaching the load line 22, a simple 30 or complex 30' convex shield is intercepted and compressed by the energy exerted by the user. Now the traction by the user is exerted with a force component outside the oblique plane, schematized in the plan figures with the arrows T₂. The convex shield 30, 30' doesn't yield to the pressure, but resists and is loaded, accumulating the forces until reaching the target point 23. In fact, the target point 23, which corresponds to the end of the complex shield 30, 30', represents the point where the rapid transfer of the accumulated forces suddenly stops. This results in an explosive opening (figure 19B) , until the target point 23 is reached (figure 19C) .

During the opening steps, the complex shield 30' behaves in a completely equivalent manner to the simple shield 30 and will subsequently be described jointly. For containers 10 not having the non-shaped surface 25 at the tab 14, i.e. in which the at least one convex shield 30, 30' is positioned with its leading end 31, which identifies the load line 22, close to the fulcrum of the tab 14, the shield 30, 30' is immediately compressed at the time of the first traction on the tab 14 by the user. In this case the traction is exerted with a force component outside the almost vertical plane, schematized in figure with the arrows T₃, which is advantageous with respect to the ergonomics of the traction gesture and has a greater explosiveness .

Whereas, if a less explosive opening of the container is desired, the leading end 31 of the convex shield 30, 30' is arranged in a point further from the fulcrum of the tab 14.

In both cases, the geometries described determine that from the moment the traction on the cover reaches the load line 22, the convex shield 30, 30' starts the step of compression and is deformed with a component of elastic deformation, gathering the energy that the user exerts in the initial step of traction, returning it in an explosive form, using it to open the can. After being loaded by compression without undergoing excessive deformations, the convex shield 30, 30' returns the energy accumulated, directing it towards the target point 23 in an oblique direction with respect to the traction, according to what is shown schematically by the arrows Fi in the figures.

In the presence of a non-shaped side surface 24, i.e. devoid of convexity, the forces are distributed on the same in the direction of the pre-cut 21 according to the arrows F2 in the figures, without meeting resistance. The non-shaped surface 24 must remain plastic and yield easily, assisting the breaking of the pre-cut 21. Whereas, concave surfaces are allowed, provided that they are made so as not to create resistance to the propagation of the forces.

Due to this distribution effect, the separation of the cover 20 from the container body 12, along the pre cut 21, occurs almost simultaneously, i.e. in an explosive manner, up to the tail end 32 of the convex shield 30, 30', which constitutes the target point 23, without the user having to apply traction on the tab 14. In fact, the opening follows the opening straight line 11B, determined by the geometry of the shield 30, 30' and not by the action of the user.

In the embodiments where the tail end 32 is at the pre-cut 21, the cover is completely removed from the container body 12 due to the effect of the explosion of forces .

In the embodiments where the tail end is at a determined distance from the pre-cut 21, which is significantly different from zero, the cover folds at the target point 23.

The presence of two or more simple 30 or complex 30' shields in longitudinal sequence determines an operation in sequence of the same and a consequent folding of the cover 20 between the single shields 30, 30'. Each of the single convex shields 30, 30 ' needs, as traction force, only the force intended for the separation of the corresponding section of cover from the container body. The distribution of tension makes the single steps of traction less hard, with particular benefit to the first step of traction, which normally requires greater force.

Advantageously, the container according to the invention allows the explosiveness of the opening and of the vertical traction angles to be controlled. This occurs by acting on the non-shaped side surface 24, when present .

In fact, the smaller is the portion of lateral space free from shapings, the more explosive the force will be: the forces will act immediately on the pre-cut area with minimum deformation of the side bands. The larger is the portion of free space, the smaller the explosiveness will be and the greater the deformation of the side bands, which, during the step of traction, will accentuate the convexity of the cover and release the energy into the pre-cut area with a delay.

The difference is also in the traction angles outside the plane of the cover. In the first case, i.e. in the presence of a reduced portion of side space free from shapings, since the convex shield 30, 30' gathers and returns the forces immediately, the traction angle b outside the plane of the cover, i.e. measured with respect to the horizontal plane of the cover, will be smaller than in the second case. In the second case, i.e. in the presence of a greater portion of side space free from shapings, the deformation suffered by the cover means that the angle b is greater than in the first case and increasing, i.e. the more vertical it is, the greater the deformation suffered by the cover. In this way it will be possible to choose whether to have a more explosive, but stiffer opening, or a less explosive but softer one with a greater upward traction angle b, which is thus more comfortable.

By further defining the convex shield, identifying a closed geometry, or leaving it more blurred (less reactive), identifying an open geometry, it will be further possible to control the two described options.

In case of an open geometry, during the opening steps, the deformation of the non-shaped side surface 24 leads to an amplification of the profile of the initial convex surface shapings. In this case, during the opening, the convex shield is deformed with a significant component of plastic deformation, which determines the accentuation of the arc with respect to the initial conditions when the container is closed, as well as having a component of elastic deformation for the return of the forces. The convex arc 111, which is only slightly pronounced in the initial steps of opening and which assumes a more pronounced appearance during the action of opening, is strengthened in its action during opening. The more open the geometry is and the more abundant and yielding the non-shaped bands are, the more the traction will deform the shield, accentuating the arc thereof.

Furthermore, the presence of a pronounced spine on a shield 30, 30 ' of any shape and with abundant side bands 24 optimizes the forces to a maximum, keeping them on the central axis of the longitudinal arc 111, promoting the maximum amplification possible of the profiles .

Some examples of containers according to the invention, which are able to optimize different types of use include:

- narrow shield, pronounced spine, abundant side bands: optimizes the forces and traction lines;

- wide shield: for design needs;

- succession of several consecutive shields: subdivides the effort;

- shield from pre-cut to pre-cut: a completely flat panel is obtained after breakage.

The container according to the invention allows the optimization of the cover lifting step (which occurs abruptly and with minimum effort) stopping the travel precisely in the predetermined target point. The achievement of the target is more precise the more pronounced the design of the final part of the shield, close to the target point, is. In this way, the forces are directed with precision and the arc exhausts its force in a precise manner.

In the lifting step, the cover 20 no longer folds towards the user's hands, but it tends to fold the sharp part in the opposite direction, reducing the risk of accidental injury.

Furthermore, the convexity of the cover limits potential dripping once the container is opened.

The particular conformation of the permanently convex shield stiffens the shaped part of the cover, making it highly resistant in both directions prior to opening. Whereas, after breaking, the cover will remain rigid only in one direction, while in the other, it will maintain the capacity to bend.

Advantageously, the container according to the invention allows the use of sheets having a small thickness, whose extreme plasticity best receives the deformations imposed by the rigid, shaped parts.

The main advantage of the container object of the present invention consists of making the opening easier by strengthening forces, which are gathered and multiplied by opportune geometries.

Advantageously, the cover according to the invention carries the forces to the sides with an optimal angle of incidence for the opening of the cover .

A further advantage lies in the fact that, after initiating the opening step, this necessarily terminates in the target point and does not depend on the action exerted by the user.

The metal container with variable resistance cover for easy opening, object of the present invention, also has the advantage of optimizing the direction of traction which the user exerts outside the plane of the cover .

Advantageously, the convex shield can be realized from any geometric shape, in compliance with the indicated rules, allowing it to be adapted to the graphic needs of the designer.

A further advantage, despite being secondary, consists of having stiffened the cover, overcoming the problem of discontinuous traction in the opening step and of the spring effect created by known covers, which fold in an arc towards the user's hand with the consequent risk of injury and splashing the filling liquid .

The metal container with variable resistance cover for easy opening thus conceived is susceptible to many modifications and variations, all falling within the invention; furthermore, all of the details are replaceable by technically equivalent elements. In practice, the materials used, as well as the dimensions, can be any according to the technical requirements .

Claims

1) A metal container with variable resistance cover for easy opening comprising a container body (12) and a cover (20) integral with the container body (12) along a perimeter edge (13), wherein the cover (20) is provided with a perimeter pre-cut (21) adjacent to the edge (13), as well as comprising a pull tab (14) provided, at one end, with a ring portion (14A) that the user grasps and, at the opposite end, with a pressure apex (14B), as well as between the two ends with a rivet (15) for joining to the cover (20), said cover (20) having at least one surface shaping, characterized in that it comprises, in the portion inside the pre-cut (21), at least one permanently convex central shield (30, 30'), each of said at least one permanently convex central shield (30, 30') comprising at least one permanently convex surface shaping (30, 130), said at least one permanently convex central shield (30, 30') identifying a longitudinal convex arc (111), which determines, between its ends, an opening straight line (11B) of the container (10) .

2) A container according to claim 1, characterized in that said at least one central convex shield (30) comprises one single convex surface shaping, which identifies said longitudinal convex arc (111) .

3) A container according to claim 1, characterized in that said at least one central convex shield (30') comprises a plurality of convex surface shapings (130) placed side by side longitudinally or in sequence and partially overlapping transversely at least in pairs, which identify a single longitudinal convex arc (111) .

4) A container according to any one of the preceding claims, characterized in that each convex shield (30, 30') defines, at opposite ends of the opening straight line (11B), a leading end (31), which determines a load line (22) of the shield, and a tail end (32), which determines an opening target point (23) .

5) A container according to any one of the preceding claims, characterized in that it comprises only one convex shield (30, 30') .

6) A container according to any one of the preceding claims from 1 to 4, characterized in that it comprises two or more convex shields (30, 30'), longitudinally in sequence without mutual transverse overlapping .

7) A container according to claim 5 when dependent on 4, characterized in that said tail end (32) is upstream of the pre-cut (21) with respect to the opening straight line (11B) and/or in that said leading end (31) is downstream of the fulcrum on a traction straight line (11A) of the tab (14) or, at most, coinciding therewith.

8) A container according to claim 6 when dependent on 4, characterized in that in a longitudinal sequence of shields (30, 30 ') said tail end (32) of the last shield in the opening direction is upstream of the pre cut (21) with respect to the opening straight line (11B) and/or in that said leading end (31) of the first shield (30, 30') in the opening direction is downstream of the fulcrum on a traction straight line (11A) of the tab (14) or, at most, coinciding therewith and in that the transition between the leading end (31) and the tail end (32) of two shields (30, 30 '), which are adjacent in the opening direction, determines an intermediate target point (123) .

9) A container according to any one of the preceding claims, characterized in that at least some of said convex surface shapings have bending points with respect to the plane of the cover (20) .

10) A container according to any one of the preceding claims, characterized in that at least some of said convex surface shapings fade progressively in the plane of the cover (20) .

11) A container according to any one of the preceding claims, characterized in that said cover (20) comprises a first non-shaped surface (24) laterally to the at least one convex shield (30, 30 '), said non- shaped surface extending to the pre-cut (21) .

12) A container according to claim 11, characterized in that said non-shaped surface (24) is also devoid of concavities.

13) A container according to claim 12, characterized in that said non-shaped surface (24) comprises one or more concavities.

14) A container according to claim 13, characterized in that said non-shaped surface (24) comprises a perimeter concavity (27) about the at least one shield (30, 30') .

15) A container according to claim 11, characterized in that said cover (20) comprises a further non-shaped surface (25), placed upstream of the load line (22) and downstream of the rivet (15) with respect to the traction straight line (11A) .