EP0425401B1 - Easy-open metal cover for a container - Google Patents

Abstract

The invention relates to a cover for a leaktight container which can be opened along a line of least resistance, by simple pulling, of the type comprising a fold (4) forming an angle which is substantially a right angle and constituting the said line of least resistance, characterised in that it is produced by stamping a sheet of steel of a thickness less than or equal to 0.16 mm. The line of least resistance permits the total or partial opening of the container. <??>The cover is preferably made from steel of a thickness of 0.10 to 0.16 mm and, at the level of the fold (4), the inner radius of curvature of the cover is from 10 to 50 mu m and the outer radius of curvature of the cover is from 100 to 200 mu m. <??>The invention applies to leaktight metal containers, such as ''beverage'' foodstuff cans or tray-type containers for precooked dishes. <IMAGE>

Description

The present invention relates to a metal cover intended to be mounted on tight containers called "easy opening" open by simple traction exerted on the cover which then tears along a line of least resistance.

Usually, watertight metal containers with easy opening, such as food "drink" boxes or trays for precooked dishes, have a metal cover made integral with the upper edge of the body of the box after filling. An incision is previously made on the lid and defines a line of least resistance along which the lid is torn when the box is opened. This opening operation is carried out manually by pulling from a tongue fixed to the cover, after having pierced the incision locally by exerting a pressure or a punctual pull in its vicinity, by means of the front part of the tongue. Such an opening device is described, for example, in documents FR-A-2034997 and FR-A-2043618.

Such a device is used on covers made either of aluminum or of coated steel (tin or chrome). Steel has a number of advantages, in particular its low cost, the good service properties of the containers thus produced, and the ease of recycling empty packaging. However, the mechanical characteristics of the thin irons usually used, which are thick from 0.20 mm to 0.25 mm, require that the user provide a relatively large tensile force to open the box which can in particular result in small well-known drawbacks during the sudden transfer of the resistance from the tearing off of the cover. In addition, the operation of sparing the incision, called "indentation", is costly because of the wear and the high price of the tools necessary for its production, and the loss of productivity which it causes. On the other hand, the indentation, which corresponds to a local reduction in the thickness of the cover, can lead to deterioration of the protective coating on both sides of the cover. The external coating must be repaired in order to avoid corrosion of the cover at the level of the incision, and repair of the internal coating is also recommended for reasons of food hygiene.

The document FR-A-1579365 describes a cover in which the cover and its line of least resistance are produced by stamping. However, the choice of material is limited to aluminum or similar materials.

The object of the invention is to reduce the manufacturing cost of easy-opening steel box lids, while facilitating the opening operation and allowing the use of steel.

To this end, the subject of the invention is a lid for a sealed container which can be opened along a line of least resistance by simple pull, as defined in claim 1.

Preferably, this cover is made of steel with a thickness of 0.10 to 0.16 mm, and at the fold, the internal radius of curvature of the cover is from 10 to 50 μm, and the external radius of curvature of the cover is 100 to 200 ”m

In an exemplary embodiment, this fold forms a closed line located in the vicinity of the periphery of the cover so as to allow total opening of the box.

As will be understood, the invention consists in materializing the line of least resistance along which the opening of the lid is carried out no longer by a pre-incision, but by a well-marked fold obtained by stamping a thin sheet of steel . This stamping operation results in a local reduction in thickness of the cover without removal of material. This reduction in thickness is therefore obtained without using consumable tools and without damaging the coatings on the two faces of the cover.

• la figure 1 représente schématiquement une boîte munie d'un couvercle selon l'invention, vue en coupe et en perspective ;
• la figure 2 représente un détail agrandi de la figure 1 ;
• la figure 3 représente une section partielle de la partie supérieure d'une boîte munie d'un couvercle selon une autre variante de l'invention.

The invention will be better understood in the light of the description which follows, referring to the single plate of drawings, in which:

• FIG. 1 schematically represents a box provided with a cover according to the invention, seen in section and in perspective;
• Figure 2 shows an enlarged detail of Figure 1;
• 3 shows a partial section of the upper part of a box provided with a cover according to another variant of the invention.

Figure 1 shows the body 1 of the box and the cover 2. Prior to its installation on the body of the box, the cover 2 is cut and then shaped by stamping. This stamping operation can optionally include in known manner a "paneling" of the cover, that is to say the provision of rectilinear folds 3 forming relief engravings facing the outside or inside of the box. These folds are intended to promote the winding of the cover on itself during the opening operation, and also to allow the cover to expand and contract during treatments involving a rise in temperature, such as sterilization or pasteurization, which the box may undergo once filled. These folds can also be in the form of circular steps. It is also during stamping that the cover is pleated so as to define, according to the invention, a line 4 of least resistance along which the opening of the cover will take place. In order to effectively allow the lid to break according to the fold 4, it must be very marked the horizontal pan 5 and the vertical pan 6 which define it form a substantially right angle, and at its level, the radius of curvature of the lid is very weak. FIG. 2 details the zone II of FIG. 1, that is to say the fold 4 of the cover 2. It shows that the cover 2 has a nominal thickness e, but that at the level of the fold 4, this thickness is reduced under the effect of the deformations inherent in the stamping forming operation, and takes a minimum value e ′. It is this reduction in thickness Δ e equal to (ee ′) which means that, after a local drilling of the cover made at any point of the fold 4, the tearing of the cover is carried out according to this fold when a pull is exerted on the cover. The drilling and this pulling are carried out by means of a tongue provided with a ring, not shown, fixed on the cover by riveting, welding or bonding, identical in principle to those which are commonly used on pre-incised covers. An action exerted on the tongue by means of the ring makes it possible to apply a high pressure at a point of the fold 4 so as to pierce the cover at this point then a traction on the ring makes it possible to complete the rupture of the cover that has just been primed.

The cover must be thin enough to allow easy tearing according to the fold, taking into account the mechanical properties of the base material used. But this material must be stiff enough for the tear to take place according to the fold, and not in any direction that the user could not control. Preferably, a steel with a low or very low carbon content is used, of thickness 0.10 to 0.16 mm and with an elastic limit between 500 and 600 MPa. The radii of curvature of the cover at the fold are, for the internal radius of curvature, from 10 to 50 "m, and for the external radius of curvature, from 100 to 200" m. The local thinning Δe resulting from the maintenance of the fold is from 70 to 100 »m.

The use of a steel of thickness thinner than those usually used advantageously provides a significant weight gain, as well as a reduction in the effort that the consumer must exert for the winding of the cover on itself during opening the box.

In the variant shown in Figures 1 and 2, the horizontal panel 5 of the fold 4, which forms the removable part of the cover, is located above the vertical panel 6 which remains attached to the box after opening. FIG. 3 illustrates another variant of the invention, in which the vertical panel 6 overhangs the horizontal pan 5. An advantage of this configuration is that the cutting edge which remains attached to the box after opening is oriented towards the inside of the box, and does not risk injuring the user.

The fixing of the cover 2 on the body of the box 1 is ensured by folding one on the other (crimping) of their outer edges, as shown schematically in Figures 1 and 3, or by gluing, or by any other known means .

In an exemplary embodiment of the invention, the fold constituting the line of least resistance forms a closed line located in the vicinity of the periphery of the cover, so as to allow a total opening of the box.

Of course, the invention is not limited to the example which has just been described and shown. The main thing is that the cover has a tear capacity and a sufficient stiffness to make possible the implementation of the proposed solution. On the other hand, the fold forming the line of least resistance may limit only a portion substantially less than the entire cover, so as to achieve only a partial opening of the box. It is thus possible to form an opening in the form of a pouring spout, of the type usually encountered on "drink" cans.

Claims (5)

1. Lid (2) for a sealed container which can be opened along a line of least resistance just by pulling, of the type comprising a substantially right-angled fold (4) which constitutes the said line of reduced strength the lid and the line of reduced strength being produced by drawing a steel sheet the thickness of which is less than or equal to 0.16 mm and the thickness at the fold being reduced under the effect of the deformations inherent in the drawing forming operation.
2. Lid according to Claim 1, characterized in that the said steel sheet has a thickness of between 0.10 and 0.16 mm.
3. Lid according to either of Claims 1 and 2, characterized in that the internal radius of curvature of the lid at the fold (4) is between 10 and 50 »m, and in that the external radius of curvature of the lid is between 100 and 200 »m.
4. Lid according to Claim 1, characterized in that the said fold forms a continuous line situated close to the periphery of the lid so as to enable the container to be opened completely.
5. Lid according to Claim 1, characterized in that the said fold forms a continuous line defining a portion substantially smaller than the whole lid so as to enable the container to be opened partially.

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