EP3604155A1 - Tin can with flexible bottom and corresponding manufacturing method - Google Patents

Abstract

The invention relates to a can (1) comprising a metal body (2) having at least one end hermetically closed by a bottom (3) formed by a flexible sheet, directly welded to the metal body so as to resist the stresses of pressure during heat treatment (sterilization) of the can.

Description

1. Field of the invention

The field of the invention is that of the food industry.

The invention relates more particularly to containers intended for the preservation of food for a long period.

The invention also relates to the bottoms and the method of manufacturing such containers.

2. Prior art

Metal cans allow long-term storage of the food they contain. They consist of a metallic body and two rigid metallic bottoms which are generally joined to the body by crimping to make it a sealed container.

The food products contained in these boxes, once they are closed, undergo a heat treatment at high temperature, in particular at a temperature above 110 ° C. (sterilization). In this way, these food products can be stored for several months at room temperature.

During the heat treatment, the body of the box is generally subjected to positive and / or negative pressure constraints depending on the process used, which can cause deformation of the packaging and cause a variation in the internal volume of the box. These mechanical stresses are exerted on the entire box and require a relatively large thickness of the body and of the two metal bottoms to avoid irreversible deformation of the box.

The weight and raw material costs of such a box are, therefore, relatively large.

Another drawback of this type of box lies in the difficulty of opening the packaging. Indeed, the thickness of the metal bottom being relatively large so as to withstand the variations in internal pressure, the opening can prove to be difficult.

• l'ouverture avec un ouvre-boîte : le couvercle n'offre aucun système d'ouverture.
• l'ouverture totale à anneau (voir ci-après) : on soulève puis on tire un anneau solidaire du couvercle préalablement incisé. C'est de loin le système le plus répandu et toujours en constante progression. En 2007, 86% des boîtes de conserve sont équipées d'ouverture facile (le taux était de 77% en 2002).
• L'ouverture pelable : en tirant sur la languette, un opercule en aluminium thermoscellé se décolle de la boîte pour offrir une ouverture totale. Ce nouveau système est principalement utilisé pour les produits nomades (salades, desserts.), mais n'est pas adapté aux boîtes devant subir une stérilisation, car la force demandée (l'effort d'ouverture (force d'arrachement initiale) est généralement de l'ordre de 20 N, mais généralement inférieure à 28 N) pour décoller l'opercule est plus faible que celle exercée par la surpression interne observée lors de la stérilisation.

There are indeed 3 opening principles today

• opening with a can opener: the lid offers no opening system.
• total ring opening (see below): lift and then pull a ring secured to the previously incised cover. It is by far the most widespread system and is constantly growing. In 2007, 86% of cans were equipped with easy opening (the rate was 77% in 2002).
• The peelable opening: by pulling on the tab, a heat-sealed aluminum cover peels off the box to offer a total opening. This new system is mainly used for nomadic products (salads, desserts.), But is not suitable for boxes that have to undergo sterilization, since the force required (the opening force (initial pulling force) is generally of the order of 20 N, but generally less than 28 N) to peel off the seal is weaker than that exerted by the internal overpressure observed during sterilization.

The ring system aims to make it possible to easily open the boxes having a relatively large thickness of the metal bottom, making it possible to withstand variations in internal pressure. This system implements, on one of the two metallic bottoms, a gripping ring allowing the opening of a part of the metallic bottom, previously weakened (by an incision, for example).

Such a solution proves impractical since a relatively large effort is still necessary for the user to lift the ring and remove the cover by pulling on the ring. In addition, this solution does not limit the weight of such packaging (on the contrary, it requires an additional element, namely a gripping ring).

The peelable system implements a metal body and bottom, the box being closed by a cover consisting of a flexible peelable sheet secured to a conventional metallic bottom which is previously hollowed out. The assembly is then crimped on the periphery of the upper part of the metal body. The peelability is in particular and preferably measured according to the method described in FR 2955844 , peeling of the cover at 90 ° at a speed of 300 mm / min), making it possible to measure the initial tearing, flow and final tearing forces.

A drawback of this technique lies in the relatively high manufacturing cost of such a box. In fact, the manufacturing process is substantially identical to that making it possible to obtain a conventional can but requires, in addition, steps for cutting the metal base and securing the flexible sheet to the metal base.

Another drawback of this solution lies in the material losses caused during the cutting of the metal bottom to be hollowed out. Indeed, this hollow material cannot be reused.

In addition, the implementation of such a solution proves to be complex and presents risks of leakage, in particular for boxes having to be sterilized, since the flexible sheet is supposed to be both peelable (this is that is to say, not be attached too strongly to the hollowed-out bottom to be able to be easily removed by applying a moderate force) and still resist the large variations in pressure which occur during sterilization of the container.

• qui présente une ouverture facile,
• qui permette de réduire les besoins et les coûts en matière première,
• qui garantisse une bonne résistance aux variations de pressions lors de la stérilisation et une étanchéité optimale de la boîte, et
• qui permette une fabrication simple et peu coûteuse.

In other words, there is currently no tin can:

• which has an easy opening,
• which makes it possible to reduce the needs and costs of raw materials,
• which guarantees good resistance to pressure variations during sterilization and optimal sealing of the box, and
• which allows simple and inexpensive manufacturing.

3. Statement of the invention

The present invention aims to solve the weaknesses of the solutions of the prior art and therefore provides a can comprising a metal body having an upper part hermetically closed by a first bottom formed by a flexible sheet.

In a particular embodiment, said tin can comprises a metal body having an upper part hermetically closed by a first bottom and a lower part hermetically closed by a second bottom. According to this embodiment of the invention, said first and second bottoms are each formed by a flexible sheet.

It is therefore proposed a tin can having, at one of its ends or at each of its ends, a bottom in the form of a film or a flexible sheet ("foil" in English).

When the can has only one flexible bottom at one of its ends, the other bottom can in particular be a “classic” bottom, that is to say crimped to the metal body of the box according to the methods known in the prior art. It is also conceivable that the second bottom of the box is in fact in the same mass as the metal body, which is observed when the can is produced by stamping and / or drawing a metal sheet.

These boxes are in particular of great interest for sterilization operations: the flexibility of the flexible bottom or of the two bottoms and their greater capacity to deform in a reversible manner (compared to conventional metallic bottoms) during pressure constraints, varies the interior volume of the box, thus absorbing part of the pressure stresses experienced by the entire container.

The body of such a box therefore undergoes less pressure constraints than a box body using conventional metallic bottoms, under industrial sterilization conditions.

In other words, the flexible bottom (s) contribute more to the variation in volume of the interior of the box than the rigid metallic bottoms.

Such an approach allows an overall reduction in the mass of materials necessary for the manufacture of such a can compared to a conventional metal can with two rigid metal bottoms.

Indeed, in addition to the implementation of flexible bottoms, the reduction of stresses on the body of the box makes it possible to reduce the thickness of the body.

It should be noted that the flexible bottom (s) used to close the boxes are not peelable bottoms, and that they must be fixed to the box in such a way that they can withstand the internal pressure of the box during the sterilization, if necessary.

The description below presents various technical aspects which are implemented for the realization of the invention in its various aspects.

It is recalled that the invention is based on the use of a flexible film for sealing at least one end of a can type can, without said film being peelable.

In a first aspect, the invention relates to a tin can comprising a metal body having one end hermetically closed by a first bottom formed by a flexible sheet. In this aspect of the invention, it is particularly preferred when said bottom is fixed to the box to resist sterilization. The internal pressure of the hermetically sealed box is equal to atmospheric pressure or may be slightly lower than the pressure atmospheric. This aspect of the invention aims to solve the problem of the quantity of material used for the manufacture of cans, by reducing the material used, both for the bottom and possibly for the body of the can, while maintaining the capacity to sterilization of the box for the preservation of the food contained therein.

• les fonds peuvent optionnellement (bien que ceci soit préféré) être fixés de telle façon à ce que la boîte remplie avec un pu plusieurs produits alimentaires (ou non-alimentaires) résistent aux conditions de stérilisation desdits produits. Toutefois, on envisage également des boîtes de conserve qui présentent des films souples fixés sur le corps métallique, à leurs deux extrémités, sans que ces boîtes ne soient destinées à stérilisation (en particulier, on envisage les boîtes contenant du lait en poudre, tel que le lait infantile). Dans ce mode de réalisation (présence de deux films souples aux extrémités dans la boîte non-destinée à la stérilisation), la fixation d'au moins un film peut être moins forte que pour les boîtes destinées à la stérilisation. En conséquence, au moins un des deux films (préférentiellement un seul des deux) peut être pelable. Si, dans ce mode de réalisation, l'on envisage également la présence de deux films pelables, ceci n'est pas préféré, pour éviter que le consommateur n'ouvre aisément la boîte par les deux extrémités.
• on envisage également le mode de réalisation dans lequel la pression interne de la boîte (après stérilisation, et dans les conditions usuelles de stockage (température ambiante, pression atmosphérique)) est légèrement inférieure (jusqu'à 0,4 bars) à la pression atmosphérique. En d'autres termes, l'intérieur de la boîte est en dépression par rapport à l'extérieur de la boîte (pression atmosphérique).

In a second aspect, the invention relates to a tin can which comprises a metal body having an upper part hermetically closed by a first bottom and a lower part hermetically closed by a second bottom, said first and second bottoms are each formed by a flexible sheet. In this aspect of the invention,

• the bottoms can optionally (although this is preferred) be fixed in such a way that the box filled with one or more food (or non-food) products withstand the conditions of sterilization of said products. However, it is also envisaged cans which have flexible films fixed to the metal body, at their two ends, without these cans being intended for sterilization (in particular, cans containing milk powder, such as infant milk). In this embodiment (presence of two flexible films at the ends in the box not intended for sterilization), the fixing of at least one film may be less strong than for the boxes intended for sterilization. Consequently, at least one of the two films (preferably only one of the two) can be peelable. If, in this embodiment, it is also envisaged the presence of two peelable films, this is not preferred, to avoid that the consumer does not easily open the box by the two ends.
• the embodiment is also envisaged in which the internal pressure of the box (after sterilization, and under the usual storage conditions (ambient temperature, atmospheric pressure)) is slightly lower (up to 0.4 bar) than atmospheric pressure . In other words, the inside of the box is in depression relative to the outside of the box (atmospheric pressure).

This aspect of the invention aims in particular to solve the problem of the deformation of the “lower” bottom of the box after filling (the internal depression makes it possible to compensate for the weight of the contents of the box and to avoid a convex deformation of the flexible bottom, ie towards the outside of the box). This aspect of the invention aims in particular to ensure, on the one hand, maximum protection of the flexible bottom in the stages of logistics, handling, conveying and storage of the can, possibly also allowing slight deformation of the flexible bottom towards the inside the package (concave deformation). The fact of avoiding the convex deformation, and even of generating a concave deformation of the flexible bottom also makes it possible to ensure a better guarantee of acceptability of the product by the consumer. Indeed, the presence of a convex bottom (curved towards the outside of the packaging) could make one think of a product that is not stable or unfit for consumption (curved).

In another aspect, the invention relates to a tin can comprising a metal body having at least one end hermetically closed by a bottom formed by a flexible sheet, welded on the upper part of said metal body, and such that the upper part welded from said metallic body of the box is folded / rolled so as to form a peripheral hem at said end of the box. As will be seen below, we also consider the case where each of the two ends of the box is closed by a flexible film. In this aspect of the invention, at least one film may or may not be peelable, or the films are fixed so that the box will withstand the sterilization conditions. In these aspects of the invention, it is also possible (or not) that the interior of the box after filling and closing, is in depression relative to the exterior. This aspect of the invention aims in particular to solve the technical problem of handling and storing boxes having one or more flexible bottoms, said hem allowing protection of the flexible bottom (s) in particular on industrial chains or during placement. on the shelves at the point of sale. Depending on the shape of the hem, it will also optimize the storage and storage of boxes.

In another aspect, the invention relates to a tin can having at least one bottom formed by a flexible sheet, said flexible sheet having a precut part. In this aspect of the invention, the box can comprise two flexible bottoms, present (or not) an internal depression relative to atmospheric pressure and / or present (or not) peripheral hems formed by the rolling / folding of the end of the metal body. This aspect of the invention aims to solve the technical problem of opening the box, by providing a technical solution (precut area) aimed at allowing easy opening of the box by facilitating the rupture of the flexible bottom.

In another aspect, the invention relates to a tin can (preferably filled with food products), having at least one bottom formed by a flexible sheet, the internal pressure in said tin being less than atmospheric pressure under the conditions ambient.

The description below provides additional elements relating to the implementation of the invention, in its various aspects. Some of these technical elements will be optionally applied to certain aspects of the invention.

In this description, reference is made to atmospheric pressure (under ambient conditions), which corresponds to a pressure of 1.01325 bar ± 2%. The ambient temperature is 20 ° C.

Structure of flexible funds

According to a particular aspect of the invention, said flexible sheet comprises at least one metallic layer, such as an aluminum layer.

This makes it possible to guarantee, for a reduced thickness, sufficient solidity of the flexible sheet so as to resist the deformations which take place during the heat treatment of the can. Furthermore, this metal layer is also useful for serving as a gas-tight barrier.

The flexible bottoms which can be used to close one or both ends of the can can thus be formed from several layers, and are known in the art and therefore obtained by known methods, such as lamination. However, one of its layers should allow the welding with the body of the box.

Heat treatment of cans / Induced pressure resistance

In a particular embodiment, the cans according to the invention must be able to withstand the sterilization conditions necessary to ensure the preservation of the products.

In general, sterilization is a heat treatment of a foodstuff aimed at the destruction of microorganisms even spore-forming, and the enzymes which are sources of spoilage of the products (core temperature of the product above 105 ° C), and cook the product.

We can define the sterilizing value (Fo) of a heat treatment, which expresses the efficiency of a heat treatment. Fo is established in relation to the most heat-resistant spores ( Clostridium botulinum spores) . The more the heat treatment is carried out at a high temperature and the longer its duration, the higher the Fo. The Fo is expressed in equivalent time spent at 121.1 ° C to obtain a destruction of the spore.

It is thus possible to define time-temperature couples which are applied to foodstuffs in order to sterilize them while maintaining a satisfactory organoleptic quality.

It should also be noted that the sterilization conditions are established according to the characteristics of the product (initial contamination, pH, texture and initial temperature), the nature and format of the packaging (in particular the size of the cans) as well as the characteristics from the autoclave

Thus, and by way of illustration, the products to be sterilized can have various consistencies ranging from liquids such as fish soups, sauces, ...), to solids (foie gras, pâté, ...) while some products include liquids and solids (canned vegetables, meat in sauce). The consistency of the product influences the distribution of heat in the product: the more liquid a product, the faster the heat diffuses.

It is therefore understood that the sterilization conditions depend on the nature of the products (vegetables or fruit, or other products) to be sterilized. Thus the temperature curves and durations of application of these temperatures to the boxes will depend on the products contained in these boxes.

• montée en température de l'élément à stériliser : on place cet élément dans un stérilisateur / autoclave hermétiquement fermé
• barème de stérilisation : la température de régime, est atteinte et reste stable pendant une durée définie, afin de permettre la stérilisation du produit. Le barème est ajusté de façon à permettre à la fois le traitement thermique du produit tout en préservant ses qualités organoleptiques.
• refroidissement : lorsque la durée du barème est atteinte, on refroidit le produit, soit en remplaçant le fluide chauffant par de l'eau froide, soit en plongeant l'élément dans un bain d'eau froide. L'objectif est de permettre le refroidissement rapide des denrées, afin notamment de stopper la cuisson et d'éviter les sur-cuissons.

In fact, the sterilization treatment takes place in three distinct phases:

• temperature rise of the element to be sterilized: this element is placed in a hermetically sealed sterilizer / autoclave
• sterilization scale: the operating temperature is reached and remains stable for a defined period, in order to allow the product to be sterilized. The scale is adjusted so as to allow both the heat treatment of the product while preserving its organoleptic qualities.
• cooling: when the scale duration is reached, the product is cooled, either by replacing the heating fluid with cold water, or by immersing the element in a cold water bath. The objective is to allow the rapid cooling of the foodstuffs, in particular in order to stop the cooking and to avoid overcooking.

In certain embodiments, the temperature rise is carried out by placing the box in the sterilizer and then raising the temperature of the sterilizer. In this embodiment, the rise in temperature within the box follows that of the sterilizer.

In other embodiments, the box is placed in a sterilizer for which the temperature rise has already been carried out, which induces a thermal and pressure "shock" on the box. The following conditions (entry of the box into an enclosure at a pressure of 2.5-2.8 bar (in absolute pressure, that is to say an overpressure of 1.5-1.8 bar relative to the atmospheric pressure) and a temperature of approximately 130 ° C., which induces a very high external overpressure before the box warms up) illustrate this embodiment.

The following conditions are observed conditions, depending on the sterilizers used.

• introduction de boîtes dans une enceinte à environ 2,8 bars et environ 130°C (soit une surpression externe d'environ 1,6-1,7 bar)
• maintien des boîtes dans cette enceinte pendant environ 11-12 minutes (la température intérieure des boîtes monte jusqu'à 130 °C, la pression interne des boîtes monte jusqu'à environ 4 bars, soit une surpression interne d'environ 1,2-1,3 bars)
• refroidissement par passage brutal des boîtes à une température d'environ 50 °C (qui descend jusqu'à 25 °C en environ 3 minutes) et pression atmosphérique (1 bar).

A sterilization treatment is as follows:

• introduction of boxes into an enclosure at approximately 2.8 bars and approximately 130 ° C. (i.e. an external overpressure of approximately 1.6-1.7 bars)
• holding boxes in this enclosure for about 11-12 minutes (the inside temperature of the boxes goes up to 130 ° C, the internal pressure of the boxes goes up to about 4 bars, i.e. an internal overpressure of about 1.2- 1.3 bars)
• cooling by sudden passage of the boxes at a temperature of around 50 ° C (which drops to 25 ° C in about 3 minutes) and atmospheric pressure (1 bar).

In this embodiment, (and depending on the content of the boxes), the boxes can undergo an internal overpressure of between -1.7 and 1.3 bar.

• introduction de boîtes dans une enceinte à environ 2,5 bars et environ 126°C (on observe une surpression externe maximum d'environ 0,4-0,5 bar)
• maintien des boîtes dans cette enceinte pendant environ 15 minutes (la température intérieure des boîtes monte jusqu'à 126 °C, la pression interne des boîtes monte jusqu'à environ 3,5 bars, soit une surpression interne d'environ 1,1 bars)
• refroidissement par passage brutal des boîtes à une température d'environ 50 °C (qui descend jusqu'à 25 °C en environ 3 minutes) et pression atmosphérique (1 bar).

In another mode of implementation, the following conditions can be applied:

• introduction of boxes into an enclosure at approximately 2.5 bars and approximately 126 ° C. (a maximum external overpressure of approximately 0.4-0.5 bars is observed)
• holding boxes in this enclosure for about 15 minutes (the inside temperature of the boxes goes up to 126 ° C, the pressure internal of the boxes increases to approximately 3.5 bars, i.e. an internal overpressure of approximately 1.1 bars)
• cooling by sudden passage of the boxes at a temperature of around 50 ° C (which drops to 25 ° C in about 3 minutes) and atmospheric pressure (1 bar).

In this embodiment, (suitable for canned flageolet beans), the boxes can undergo an internal overpressure of between approximately -0.5 and approximately 1.1 bar (the term approximately signifying the specified value +/- 10%).

• introduction de boîtes dans une enceinte à environ 2,6 bars et environ 127°C (on observe une surpression externe maximum d'environ 1,4-1,5 bar)
• maintien des boîtes dans cette enceinte pendant environ 11 minutes (la température intérieure des boîtes monte jusqu'à 127 °C, la pression interne des boîtes monte jusqu'à environ 3,6-3,8 bars, soit une surpression interne d'environ 1,3 bars)
  refroidissement par passage brutal des boîtes à une température d'environ 50 °C (qui descend jusqu'à 25 °C en environ 3 minutes) et pression atmosphérique (1 bar).

In another mode of implementation, the following conditions can be applied:

• introduction of boxes into an enclosure at approximately 2.6 bars and approximately 127 ° C. (a maximum external overpressure of approximately 1.4-1.5 bar is observed)
• holding boxes in this enclosure for about 11 minutes (the inside temperature of the boxes goes up to 127 ° C, the internal pressure of the boxes goes up to about 3.6-3.8 bars, i.e. an internal overpressure of about 1.3 bars)
  cooling by sudden passage of the boxes at a temperature of around 50 ° C (which drops to 25 ° C in about 3 minutes) and atmospheric pressure (1 bar).

In this embodiment, (suitable for canned beans), the cans can undergo an internal overpressure of between approximately -1.4 and approximately 1.3 bar (the term approximately signifying the specified value +/- 10%).

• introduction de boîtes dans une enceinte à environ 2,6 bars et environ 127°C (on observe une surpression externe maximum d'environ 1,4-1,5 bar)
• maintien des boîtes dans cette enceinte pendant environ 11 minutes (la température intérieure des boîtes monte jusqu'à 127 °C, la pression interne des boîtes monte jusqu'à environ 3,6-3,9 bars, soit une surpression interne observée entre environ 1,1 et 1,5 bars) refroidissement par passage brutal des boîtes à une température d'environ 50 °C (qui descend jusqu'à 25 °C en environ 3 minutes) et pression atmosphérique (1 bar).

In another mode of implementation, the following conditions can be applied:

• introduction of boxes into an enclosure at approximately 2.6 bars and approximately 127 ° C. (a maximum external overpressure of approximately 1.4-1.5 bar is observed)
• holding the boxes in this enclosure for about 11 minutes (the inside temperature of the boxes goes up to 127 ° C, the internal pressure of the boxes goes up to about 3.6-3.9 bars, i.e. an internal overpressure observed between about 1.1 and 1.5 bars) cooling by sudden passage of the boxes at a temperature of around 50 ° C (which drops to 25 ° C in about 3 minutes) and atmospheric pressure (1 bar).

In this embodiment, (suitable for canned beans), the cans can undergo an internal overpressure of between approximately -1.4 and approximately 1.5 bar (the term approximately signifying the specified value +/- 10%).

• de la nature du produit alimentaire présent dans la boîte (on adaptera les conditions afin de ne pas altérer les qualités organoleptiques)
• de la nature du stérilisateur / autoclave utilisé (eau, vapeur...)
• de la taille des boîtes à stériliser
• de la nature (notamment la température initiale) des boîtes au début de la stérilisation
• des contraintes industrielles liées à la production dans l'usine (vitesse des lignes de production, qui peut induire des contraintes de durée de l'étape de stérilisation)

It can therefore be seen that the sterilization conditions are very variable and will depend in particular

• the nature of the food product present in the box (we will adapt the conditions so as not to alter the organoleptic qualities)
• the nature of the sterilizer / autoclave used (water, steam, etc.)
• the size of the boxes to be sterilized
• the nature (especially the initial temperature) of the boxes at the start of sterilization
• industrial constraints linked to production in the factory (speed of the production lines, which can induce constraints on the duration of the sterilization stage)

In general, the boxes according to the invention resist internal overpressure (corresponding to the difference between the internal pressure in the box and the external pressure) greater than or equal to 0.7 bar, 0.8 bar, preferably greater than or equal to 0.9 bar, preferably greater than or equal to 1 bar, preferably greater than or equal to 1.05 bar, preferably greater than or equal to 1.1 bar, preferably greater than or equal to 1.15 bar , preferably greater than or equal to 1.2 bar. In some embodiments, the boxes resist internal overpressure of up to 1.5 bar.

The boxes must resist this internal overpressure for at least 2 minutes, preferably for at least 3 minutes, preferably for at least 4 minutes preferably for at least 5 minutes, preferably for at least 6 minutes, preferably for at least 7 minutes, preferably for at least 8 minutes, preferably for at least 9 minutes.

Such internal overpressure is obtained by any method known to those skilled in the art, using sterilizers / autoclaves known in the art. Internal and external pressures are measured by sensors placed respectively in the box and in the autoclave, the internal overpressure being the difference between the internal pressure and the external pressure.

The cans are considered to resist internal overpressure when their integrity is maintained after application of the internal overpressure for the time mentioned above. This means that the boxes do not “explode” under the effect of the overpressure, and that the flexible bottom is not torn off or destroyed under the effect of this overpressure.

It is also noted that, under certain sterilization conditions, the cans can undergo an external overpressure (that is to say that the external pressure will be greater than the internal pressure). This is particularly the case when the boxes are introduced into an enclosure already under the temperature and pressure conditions used for sterilization. The boxes (whose internal pressure is atmospheric pressure) then undergo an external overpressure of up to 2 bars. The boxes must therefore also resist this external overpressure. If we consider an internal depression in the box under ambient conditions (to play on the concavity of the flexible bottom), we will then preferentially choose to sterilize the boxes immediately after hot filling (i.e. when the temperature of the box is of the order of 35-40 ° C.), the internal pressure of the boxes then being close to atmospheric pressure.

Thus, the boxes according to the invention resist an external overpressure (corresponding to the difference between the pressure outside the box and the internal pressure) greater than or equal to 0.4 bar, preferably greater than or equal to 0.5 bar, preferably greater than or equal to 0.6 bar, preferably greater than or equal to 0.7 bar, preferably greater than or equal to 0.8 bar, preferably greater than or equal to 0.9 bar, preferably greater than or equal to 1 bar, preferably greater than or equal to 1.1 bar, preferably greater than or equal to 1.2 bar, preferably greater than or equal to 1.3 bar, preferably greater than or equal to 1.4 bar, preferably greater or equal to 1.5 bar, preferably greater than or equal to 1.6 bar, preferably greater than or equal to 1.7 bar. In some embodiments, the boxes resist internal overpressure of up to 2 bar. This means that the boxes do not “implode” under the effect of the external overpressure, and that the flexible bottom is not torn off or destroyed under the effect of this overpressure. This external overpressure is generally observed for a duration generally less than 2 minutes, or even less than one minute.

It is also preferred when the physical appearance of the boxes is not altered after sterilization, that is to say when the boxes retain their appearance (for example cylindrical if the metal body has been prepared in this form). Thus, if it is envisaged that the boxes can deform (both outward and inward) during sterilization operations, it is preferred that these deformations are not irreversible, that is to say that the boxes return to their initial shape (ie the shape they had before entering the sterilizer) after the sterilization operations. In fact, it is desired to prevent the internal overpressure from inducing an irreversible deformation of the metallic body, which would lead, for example, to "domed" boxes which might not be accepted by consumers. It will be recalled that this problem of non-irreversible deformation is already known to those skilled in the art for the sterilizations carried out with the models of cans of the prior art: these cans also undergo internal and external overpressures leading to slight deformations. of the metal body, reversible at the end of the sterilization phase, when the boxes are again subjected to the ambient conditions of temperature and pressure. Those skilled in the art are therefore used to evaluating this parameter.

In conclusion, the boxes must resist an internal overpressure between -0.4 bar and 0.8 bar or any other value mentioned above, preferably without undergoing irreversible deformation (i.e. deformation of the metallic body which is maintained) after return to ambient conditions. The negative internal overpressure corresponds to the external overpressure applied to the box.

Mass of cans

According to a particular aspect of the invention, for a standard format "4/4" can with a capacity of 850 ml, the mass of the metal body is less than 50g (a conventional metal body of the prior art for this box format has a mass equal to 51g).

Preferably, the mass of said metal body is less than 40g.

The thickness of the metal body of the box according to the invention is significantly reduced insofar as the metal body undergoes less stress than the metal body of a conventional tin can.

According to a particular aspect of the invention, the mass of said flexible bottom is less than 10 g.

Preferably, the mass of said flexible bottom is less than 5 g.

The mass of the flexible bottoms of the invention is significantly less than that of known box bottoms.

It should be noted that the mass of a classic rigid box bottom is equal to 16g, the mass of an easy opening bottom by grip ring is 22g, while the mass of a peelable bottom is 10g.

According to a particular aspect of the invention, the mass of said tin can according to the invention is less than 56g.

The use of two flexible bottoms makes it possible to reduce the mass of the bottoms and of the body forming the can.

The mass of the can according to the invention is therefore reduced compared to cans of the prior art whose mass is generally between 77g and 89g.

The reduction in the thickness of the bottoms and the body of the can therefore allows a relatively large gain in mass, and therefore a reduction in the cost of the can.

Welding of the bottom (s) on the body of the box

According to a particular aspect of the invention, said first and possibly second bottoms are welded to the upper part and the lower part respectively of said metallic body (in particular by heat-sealing).

The flexible bottoms are directly welded to the box, and more precisely to the flat metal of the body of the box, at the ends of the body. The bottom (s) are welded on the inside face of the body of the box, on flat annular edges at the end of the body.

Soft bottoms are not peelable. This means that it is not possible to break the bottom weld on the box by applying a reasonable force (ie of the order of 20 N, force applied for peelable bottoms). The initial breakout force to be applied in order to “peel” the bottoms of the metal body is therefore preferably greater than 25 N, more preferably greater than 28 N, or more than 30 N, even more preferably greater than 35 N.

In addition, the flexible bottoms of the box are in one piece, unlike the peelable bottoms developed under the EASIP® brand. These Easip® peelable bases are constructed by placing a complex film based on aluminum on a steel or a steel or aluminum ring crimped on the body of the can (see for example WO 2012/072383 ), while the flexible bases described in the present application are directly welded to the body of the box.

As indicated above, the welding of the flexible bottoms is sufficiently robust to withstand the pressure constraints which arise during a heat treatment (sterilization) of the food content, and which are exerted, as previously emphasized, in part on the flexible bottoms.

Such an approach (soldering or heat sealing directly on the body of the box rather than on a ring crimped on the body of the box) allows the flexible bottoms better resistance to sterilization compared to the flexible peelable bottoms of the prior art, which does not not withstand the above-mentioned overpressures observed during sterilization. They are therefore more suitable for heat treatment systems causing high pressure constraints.

The welding of the film on the body of the box is carried out by any method known in the art.

In particular, the edge of the box can be locally coated with a material capable of making heat sealing possible (organic and / or mineral material in which mineral and / or organic fillers can be incorporated, in particular polypropylene (PP)). This material will melt at the time of heat sealing, then cool down producing a solid seal, which allows the flexible fixing of the flexible sheet serving as a bottom. The exact conditions (type of material, welding conditions) can easily be determined by a person skilled in the art by checking that the conditions meet the specifications (pressure resistance conditions) defined above. These conditions are known in the art, the heat sealing of a film on a material, using, for example a flexible head heat sealer).

If you cover the aluminum or steel of the body of the box with a varnish of polypropylene type (or loaded with polypropylene particles), and the film also contains polypropylene, you can heat seal (weld) applying a pressure between 20 and 70 kPa, for 0.25 to 4 seconds, with a temperature between 160 ° C to 220 ° C. The exact conditions of pressure and duration of pressure application depend on the temperature applied. You can even go up to durations greater than 4 seconds if you use manual equipment (manual heating clamp type).

One can in particular use the films of the brand Fastelfoil ™ (Fastel Adhesive Products, San Clemente, CA, United States), in particular the reference film PP320, for which the manufacturer is considering applying pressure between 3 and 10 psi (20 to 70 kPa) for 0.25 to 1 second at a temperature of 165 to 175 ° C.

A seal (welding) for 2 sec at 200 ° C with a flexible bottom, the lower membrane (in contact with the body of the box) is made of polypropylene, the varnish of the body of the box being loaded with the same material, is perfectly suited to the implementation for the desired application, and obtaining a weld allowing the bottom to resist the temperature and pressure conditions specified above.

Metallic body ends

According to a particular aspect of the invention, the upper and / or lower welded parts of said metallic body of the box are respectively folded / rolled up so as to form a peripheral hem at each end of the box.

The invention thus relates to a tin can comprising a metal body having an upper part hermetically closed by a first bottom, characterized in that said first bottom is formed by a flexible sheet, and is welded to the upper part of said metal body , the welded upper part of said metallic body of the box being further folded / rolled so as to form a peripheral hem at the upper end of the box. It is clear that the term "superior" is relative and means at one end of the box.

In this aspect of the invention, the welding of the flexible bottoms on the box body is protected by a roll of the flat metal of the box body. This roll, or hem, is prominent and protects the flexible bottoms (and the welding) during sterilization, transport, handling and storage of the box.

This mode of implementation is particularly suitable when the two bottoms of the box are made of flexible sheets.

Thus, in another embodiment the invention relates to a tin can comprising a metal body having an upper part hermetically closed by a first bottom and a lower part hermetically closed by a second bottom, characterized in that said first and second bottoms are each formed by a flexible sheet, said first and second bottoms being welded on the upper part and the lower part respectively of said metallic body, said upper and lower welded parts of said metallic body of the box being respectively folded / rolled so as to each form a peripheral hem at each end of the box. It should be noted that, according to this aspect of the invention, it is not mandatory that the box or boxes thus obtained withstand the pressure conditions indicated above, even if this is preferred. One or both flexible bottoms may therefore be peelable.

According to a particular aspect of the invention, said hems are of different shapes.

The shape of the top bottom roll may be different from the shape of the bottom bottom roll and thus allow optimized stacking of such cans while protecting the flexible bottoms.

• une étape de fixation d'un fond souple à une extrémité d'un corps métallique, (notamment par soudure dudit fond sur un rebord annulaire plat à ladite extrémité du corps) suivie par
• une étape de roulé du métal dudit rebord annulaire plat du corps de boîte de façon à former un roulé, ou ourlet, proéminent (c'est-à-dire supérieur au plan dans lequel est situé ledit fond souple).

The invention also relates to a method of manufacturing a can comprising

• a step of fixing a flexible bottom at one end of a metal body, (in particular by welding said bottom to a flat annular rim at said end of the body) followed by
• a step of rolling the metal of said flat annular rim of the box body so as to form a roll, or hem, prominent (that is to say greater than the plane in which said flexible bottom is located).

Pre-cut / open the box

As indicated above, the funds described in the present application are not peelable funds as described in the prior art. They cannot therefore be detached from the body of the box by exerting a "reasonable" traction that a user would exert to open a flexible peelable bottom (ie of the order of 20 N).

These funds must however be able to be easily opened by the users, which is possible by breaking them with any suitable instrument, such as a knife blade. However, technical elements can be added to these funds, in order to further improve the opening of the boxes.

Thus, and according to another particular aspect of the invention, said first bottom and / or said second bottom has (s) a precut part.

Consequently, a tin can with one or two bottoms formed by a flexible sheet, and in which one and possibly the other flexible sheet has a precut part is an object of the invention. It should be noted that the subject of the invention also includes any tin can thus defined, whether one or the other bottom is peelable, as long as at least one of the two funds has a pre-cut part as described above. Thus, according to this aspect of the invention, it is not mandatory that the box or boxes thus obtained withstand the pressure conditions indicated above, even if this is preferred.

A precut, in particular by laser or other technology, is implemented on at least one of the two flexible bottoms. This allows the consumer to easily perforate the flexible base and thus open the can to access the food content. This precut is carried out once the heat treatment of the food content has been finalized, when the flexible base is no longer required to undergo strong pressure constraints so as not to degrade the latter. It is noted that this laser precut, common in the art, allows a partial incision of the flexible sheet, while maintaining air impermeability in order to maintain the quality and integrity of the product contained in the can. The flexible sheet is thus weakened along a breaking line corresponding to the location of the precut, which helps to open it.

According to yet another particular aspect of the invention, the said precut part (s) is / are associated with visual marking.

The precut can be done on an ink pre-marking or the ink pre-marking can be done once the precut is finalized which will allow the consumer to better visualize the precut compared to the rest of the bottom of the box.

In another embodiment, a tongue or a small gripping ring is glued, on the flexible bottom, and close to the pre-cut zone, which can be pulled by the end user, in order to induce the rupture of the zone. fragility, and thus improve the opening of the box.

The invention also relates to a method comprising a step of precutting a flexible bottom closing off one end of a can, said precut consisting of a partial incision of said flexible sheet, while maintaining the air impermeability of said background.

Box shape

According to a particular aspect of the invention, said metal body has the shape of a truncated cone.

The use of flexible bottoms at each end of a can makes it possible to dispense with the standards of production of conventional rigid bottoms, and therefore of associated metal body shapes.

A metal body in the shape of a truncated cone allowing the boxes to be stacked one inside the other once empty.

This aspect makes it possible to limit the storage volume of boxes when the latter are empty, that is to say before filling or after use of the box in particular.

The invention also relates to a can bottom formed by a flexible sheet intended to be used in a can as described above.

According to a particular aspect of the invention, the flexible sheet comprises a metallic layer (made of aluminum, for example) covered on at least one face by a plastic layer.

A flexible sheet made up of such a succession of layers of different materials makes it possible to ensure a strong solidity of the sheet so as to resist the pressure variations which take place during the heat treatment, for example.

Manufacturing process

• une étape de soudure d'un fond souple à une extrémité d'un corps métallique ;

The invention also relates to a method for manufacturing a can as described above, comprising:

• a step of welding a flexible bottom to one end of a metal body;

• une étape de remplissage du corps métallique avec un ou plusieurs produits alimentaires ;
• une étape de sertissage d'un fond rigide sur l'autre extrémité du corps métallique de manière à fermer hermétiquement la boîte ;

The method can also include one or more of the following steps, carried out before or after the step indicated above:

• a step of filling the metallic body with one or more food products;
• a step of crimping a rigid bottom on the other end of the metal body so as to hermetically close the box;

If the box is of the stamped type, the metal body is filled before the welding step above.

1. 1) une étape de sertissage (ou équivalent) d'un fond rigide à une extrémité de la boîte
2. 2) une étape de remplissage du corps métallique avec un ou plusieurs produits alimentaires
3. 3) l'étape indiquée ci-dessus de soudure d'un fond souple à l'autre extrémité d'un corps métallique.

In another embodiment, one can also perform

1. 1) a crimping step (or equivalent) of a rigid bottom at one end of the box
2. 2) a step of filling the metallic body with one or more food products
3. 3) the step indicated above of welding a flexible bottom at the other end of a metal body.

1. 1) l'étape indiquée ci-dessus de soudure d'un fond souple à une extrémité d'un corps métallique
2. 2) une étape de remplissage du corps métallique avec un ou plusieurs produits alimentaires
3. 3) une étape de sertissage d'un fond rigide à l'autre extrémité de la boîte.

In another embodiment, one can also perform

1. 1) the step indicated above of welding a flexible bottom to one end of a metal body
2. 2) a step of filling the metallic body with one or more food products
3. 3) a step of crimping a rigid bottom at the other end of the box.

According to a particular aspect of the invention, the manufacturing process further comprises a metal working step consisting in folding or rolling the welded part (before or after filling as the case may be) of said body of the box so as to form a peripheral hem at the end of the box, thus acting in particular as a protection of the flexible bottom.

The above process can also include a heat treatment step (sterilization) of the hermetically sealed can at both ends.

According to another particular aspect of the invention, the manufacturing process also includes a step of precutting the flexible bottom in order to allow easy opening of the box.

This precut occurs preferably after the heat treatment since the latter causes high pressure constraints and it is therefore preferable that the flexible bottom is not weakened.

The invention also relates to a method for sterilizing a can as described above (comprising a metal body and hermetically closed by one or two flexible bottoms at (respectively) one or both ends of said metal body) , comprising a step of placing said box under conditions of temperature and pressure inducing an internal suppression (in said box) of at least 0.8 bar (or any other value as indicated above). Preferably, in this sterilization method, said box undergoes overpressure for at least 2 minutes (or any other duration indicated above, a preferred duration being greater than or equal to 6 minutes, or 7 minutes).

• une étape de soudure d'un premier fond souple sur la partie inférieure du corps métallique ;
• une étape de remplissage du corps métallique avec un ou plusieurs produits alimentaires ;
• une étape de soudure d'un deuxième fond souple sur la partie supérieure du corps métallique de manière à fermer hermétiquement la boîte ;
• éventuellement une étape de traitement thermique (stérilisation) de la boîte de conserve.

The invention also relates to a method for manufacturing a can as described above, comprising:

• a step of welding a first flexible bottom onto the lower part of the metal body;
• a step of filling the metallic body with one or more food products;
• a step of welding a second flexible bottom on the upper part of the metal body so as to hermetically seal the box;
• possibly a heat treatment step (sterilization) of the can.

According to a particular aspect of the invention, the manufacturing process further comprises a metal working step consisting in bending or rolling the lower welded part (before filling) then the upper welded part (after filling) of said body of the box so as to form a peripheral hem at each end of the box, thus acting as a protection of the flexible bottom.

According to another particular aspect of the invention, the manufacturing process comprises a step of precut of at least one of the two flexible bottoms in order to allow easy opening of the box.

This precut occurs preferably after the heat treatment since the latter causes high pressure constraints and it is therefore preferable that the flexible bottom is not weakened.

Such a manufacturing process can be implemented efficiently, industrially.

Filling boxes

When the box has a flexible bottom at each of its ends, the weight of the contents is likely to deform the lower flexible bottom. The hem which can be placed at the lower end can protect the flexible bottom and prevent it from touching the plane on which the box is placed, including when it is deformed by the weight of the contents of the box ( due to sufficient space between (a) the point of contact of the hem and the storage plane and (b) the flexible bottom); the hem making conditions, and the space between the end of the hem and the flexible bottom are therefore adapted to the mass which the flexible bottom will have to undergo, as well as its resistance and its deformability).

However, the box can also be closed (setting up of the second base) under conditions such that the box will have a slight internal depression (of the order of 0.1 to 0.4 bar) relative to atmospheric pressure. In this embodiment, the external overpressure will exert a force opposite to the force exerted by the food (weight) on the external bottom, which will therefore not deform, or only marginally.

This internal depression (relative to atmospheric pressure) can be obtained by conducting the step of hermetically closing the box in an enclosure under vacuum. The filling step which precedes this step of closing the box can also be carried out in this vacuum enclosure. These operating conditions are particularly suitable when the content of the can is content at room temperature, in particular milk powder (in particular infant milk), chocolate powder, ground coffee, or the like.

When the food products are hot products (such as cooked dishes or cooked vegetables), this depression can be obtained under ambient conditions by closing the box when the products have been put hot in the box, and keeping a certain amount of air in the box. The trapped air is then at the temperature of the products. When the box is cooled, the cooling of the air will therefore induce the internal vacuum in the box. In this embodiment, it will preferably be chosen to introduce the box into the sterilization chamber before the latter cools down (that is to say when the temperature of the box is still greater than approximately 35 ° VS).

A tin can, closed by at least one flexible bottom at one of its ends (preferably closed by flexible bottoms at both ends), and which is in slight internal depression compared to atmospheric pressure, is also an object of the invention.

4. List of figures

• la figure 1 est une vue en perspective d'une boîte de conserve conforme à l'invention, comprenant deux fonds souples ;
• la figure 2 est une vue schématique, en coupe, du corps métallique de la boîte de la figure 1 au cours de sa fabrication ;
• la figure 3 illustre un exemple de feuille utilisable sur une boîte conforme à l'invention montrant la partie prédécoupée destinée à faciliter l'ouverture de la boîte ;
• la figure 4 est une vue éclatée des différentes couches constituant une feuille souple conforme à l'invention ;
• la figure 5 est une représentation schématique partielle, en coupe, des jonctions supérieure et inférieure entre le corps métallique et la feuille souple de la boîte de la figure 1;
• la figure 6 illustre un exemple de stockage de deux boîtes de conserve conformes à l'invention, notamment lorsqu'elles présentent deux fonds souples ;
• la figure 7 illustre les principales étapes du procédé de fabrication d'une boîte de conserve selon l'invention, comprenant deux fonds souples, tel que décrit dans les exemples ; et
• la figure 8 est une vue en perspective d'une autre forme de boîte de conserve conforme à l'invention.

Other characteristics and advantages of the invention will appear more clearly on reading the following description of an exemplary embodiment, given by way of simple illustrative and nonlimiting example, and of the appended drawings, among which:

• the figure 1 is a perspective view of a tin can according to the invention, comprising two flexible bottoms;
• the figure 2 is a schematic view, in section, of the metal body of the box of the figure 1 during its manufacture;
• the figure 3 illustrates an example of sheet usable on a box according to the invention showing the precut part intended to facilitate the opening of the box;
• the figure 4 is an exploded view of the different layers constituting a flexible sheet according to the invention;
• the figure 5 is a partial schematic representation, in section, of the upper and lower junctions between the metal body and the flexible sheet of the box of the figure 1 ;
• the figure 6 illustrates an example of storage of two cans in accordance with the invention, in particular when they have two flexible bottoms;
• the figure 7 illustrates the main steps of the manufacturing process of a can according to the invention, comprising two flexible bottoms, as described in the examples; and
• the figure 8 is a perspective view of another form of can according to the invention.

5. Detailed description of the invention 5.1 General principle

The invention therefore relates to a new type of tin can comprising one or two bottoms, or lids, in the form of a flexible sheet ("foil" in English). Such a tin can differs from known tin cans which use rigid metallic bottoms (relatively thick) at each of their ends.

These flexible bottoms are intended to absorb the pressure constraints to which the can is subjected when the latter undergoes a heat treatment (sterilization) intended to preserve the food products which it contains. The thickness of the body of the can can thus be reduced.

Consequently, the particular structure of the can according to the invention makes it possible to reduce the metal requirements compared to the current cans and reduces the manufacturing costs.

5.2 Structure of the can

An embodiment of a can according to the invention, comprising two flexible bottoms is described below in relation to the Figures 1 to 6 . These figures and the teaching below are also applicable when the box contains only one flexible bottom.

As illustrated in the figure 1 , the can 1 comprises a metal body 2 of cylindrical section. The metal body 2 is secured at its two ends to a flexible bottom 3 for hermetically closing the can 1.

The metal body 2, which is preferably made of steel or aluminum, has, in longitudinal section, a substantially parallelepiped profile, as illustrated in the figure 2 .

The profile has two rectilinear and parallel walls 21 ending at each of their ends by annular flat parts 22, 23 which extend perpendicular to the walls 21, around the periphery of the opening (these flat parts 22, 23 are deliberately oversized on the figure 2 for clarity).

The flat parts 22, 23 are each intended to receive a flexible bottom.

To do this, flexible bottoms 3, taking the form of a flexible sheet (or "foll") 31, are affixed respectively to the upper 22 and lower 23 before being secured to the latter by welding (induction welding or by Joule effect, for example). The weld must be strong enough / resistant to ensure optimal hold of the flexible bottoms 3 during the heat treatment (sterilization) of the can 1.

The peripheral part or periphery 311 of the flexible sheet 31 is therefore directly welded to the flat annular parts 22, 23 of the metallic body 2.

Once the flexible sheets 31 are secured to the metal body 2, the upper 22 and lower 23 parts are rolled up on themselves, as illustrated in the figure 5 .

This winding, in double stapling ply for example, forms an upper hem 24 and a lower hem 25 respectively encompassing the upper part 22 and the lower part 23 of the metal body 2 and the peripheral part 311 of the corresponding flexible sheet 31.

Such a hem makes it possible to protect the flexible sheets 31 from shocks and friction which could possibly degrade the sealing of the box. can 1, especially when handling and transporting can 1 (in automatic conveyor systems, for example).

Note that the upper hem 24 is oriented towards the inside of the can 1 and that the lower hem 25 is oriented towards the outside of the can 1. This allows stable stacking and optimized storage of the cans 1 on top of each other, as shown in the figure 6 . However, it is also possible to envisage an upper hem 24 oriented towards the outside of the can 1 and a lower hem 25 oriented towards the inside of the can 1.

5.3 Structure of the flexible bottom

The flexible base 3 of the invention is formed by a flexible sheet 31 consisting of one or more layers. The layers can be made of different materials, such as polypropylene, aluminum or polyethylene.

In the example illustrated on the figure 4 , the flexible sheet 31 of the flexible bottom 3 comprises two layers of plastic 310a and 310c between which is interposed a metal sheet, an aluminum sheet 310b in this example.

Such a combination of materials allows optimal resistance while guaranteeing a high flexibility of the flexible base 3, that is to say that the flexible sheet is capable of stretching without breaking.

The use of an aluminum sheet 310b in such a flexible bottom 3 makes it possible to provide a reliable oxygen barrier. This aspect contributes to the long conservation of sterilized foodstuffs which then allows long-term ambient storage.

The plastic layer 310c located between the aluminum foil 310b and the flat parts 22, 23 ensures optimal sealing of the flexible bottoms 3 on the metal body 2 of the box.

Such a flexible bottom 3 also has a small thickness and a reduced weight.

Indeed, for a standard format tin can said 4/4, the flexible bottom 3 has a mass less than 10g, and more precisely less than 5g.

Preferably, the mass of the flexible bottom 3 is equal to 3 g.

If we compare these values with those of the bottoms of the boxes of the prior art, namely 16g for a standard rigid bottom, 22g for a rigid bottom with opening easy by a grip ring and 10g for a peelable bottom, we see that the gain in mass, and therefore in material, is relatively large.

The use of a flexible bottom 3 at each of the ends of the metal body 2 makes it possible to relieve the body of the box from the constraints linked to pressure variations between the inside and the outside of the box 1, during sterilization especially.

In fact, the flexible bottoms 3 are capable of deforming in a reversible manner, so as to vary the interior volume of the box, thereby allowing pressure variations to be absorbed.

In other words, the flexible bottoms 3 allow the box 1 to inflate and retract during pressure variations occurring during the heat treatment.

The metal body 2 being less stressed during the heat treatment, its thickness, and therefore its mass, are reduced compared to a conventional can body.

Still for a standard size 4/4 can, a classic metal body has a mass of around 51g.

The use of two flexible bottoms according to the invention allows the use of a metallic body 2 of reduced thickness and having a mass of less than 50 g.

Preferably, the mass of the metal body 2 is less than 40g.

Consequently, a can 1 in accordance with the invention, using two flexible bottoms of 3 g each and a conventional can body (50 g) has a total mass of maximum 56 g. The boxes of the prior art which have a conventional body of 51g, a conventional rigid bottom of 16g and a peelable bottom of 10g have a mass of 77g, which is much higher.

The gain in mass of the can 1 of the invention is therefore at least 15g.

5.4 Easy opening of the can

One of the flexible sheets 31 of the can 1 has a precut 313 which is intended to weaken the flexible bottom 3 and allow easy opening of the can 1.

The precut 313 of the flexible bottom 3 is implemented in a conventional manner, preferably by a laser cutting technique.

This operation is carried out after sterilization of the can 1 so as not to weaken the flexible bottom 3 which must guarantee optimal sealing of the can 1. In fact, as underlined before, during sterilization, the flexible bottom 3 undergoes significant stresses due to variations in pressure internal to the can 1.

This precut 313 is indicated to the user by means of an ink trace, for example in dotted lines.

When the user wishes to open the can 1, he need only apply a relatively low pressure on the part 312 of the flexible sheet 31 situated inside the precut 313, near the latter. This pressure, which can be carried out using a spoon for example, causes the part 312 of the flexible bottom 3 located inside the pre-cut 313 to rupture and allows the user to access the content at inside the box.

Thus, the opening of the can 1 of the invention does not require any particular tool and does not require significant effort on the part of the user. This approach allows for easy opening (opening requires little effort and no special tools) and guarantees optimal sealing of the can 1.

5.5 Method of manufacturing the can

The tin can of the invention is obtained by a different manufacturing process compared to that of tin cans of the prior art.

• une étape de soudure E1 d'un premier fond souple 3 sur une première partie plate 23 (partie inférieure) du corps métallique 2 ;
• préférentiellement une étape de pliage/roulage E2 de la partie inférieure 23 sur elle-même pour former un ourlet 25 ;
• une étape de remplissage E3 du corps métallique 2 avec un ou plusieurs produits alimentaires ;
• une étape de soudure E4 d'un deuxième fond souple 3 sur la seconde partie plate 22 (partie supérieure) du corps métallique de manière à fermer hermétiquement l'ensemble ;
• préférentiellement une étape de pliage/roulage E5 de la partie supérieure 22 sur elle-même pour former un ourlet 24;
• préférentiellement une étape de traitement thermique (stérilisation) E6 de la boîte de conserve 1;
• préférentiellemen une étape de prédécoupe E7 d'au moins un des deux fonds souples 3 afin de permettre une ouverture facile de la boîte 1.

When the box has two flexible bottoms, such a manufacturing process comprises:

• a step of welding E1 of a first flexible bottom 3 on a first flat part 23 (lower part) of the metal body 2;
• preferably a step of folding / rolling E2 of the lower part 23 on itself to form a hem 25;
• a step E3 of filling the metallic body 2 with one or more food products;
• a step E4 of welding a second flexible bottom 3 on the second flat part 22 (upper part) of the metal body so as to hermetically seal the assembly;
• preferably a folding / rolling step E5 of the upper part 22 on itself to form a hem 24;
• preferably a heat treatment step (sterilization) E6 of the can 1;
• preferably a precut step E7 of at least one of the two flexible bottoms 3 in order to allow easy opening of the box 1.

Note that the method of manufacturing such a can according to the invention does not require the implementation of a crimping operation.

5.6 Other aspects and variants

The structure of the can according to the invention offers optimal resistance to the pressures undergone during the sterilization of the food content.

The can according to the invention has an easy opening for the user and guarantees a perfect seal.

Such a box is also light, robust, simple and inexpensive to manufacture.

Furthermore, the precut can have other shapes than a circular shape.

The use of a flexible bottom in accordance with the invention makes it possible to overcome the standards of production of conventional metallic bottoms and therefore to envisage the production of cans of various shapes.

The figure 8 has a can 1 having a can body 2 in the form of a truncated cone, the diameter of the lower flexible bottom (not visible) being less than that of the upper flexible bottom 3.

This particular shape makes it possible to stack the conical cans one on top of the other in a stable manner, but also one inside the other, in a compact manner, once the cans are empty.

The boxes can be stacked one inside the other before filling the can and / or after consumption of the contents of the can.

Claims (15)

Tin can (1) comprising a metal body (2) having an upper part (22) hermetically closed by a first bottom (3) and a lower part (23) hermetically closed by a second bottom (3), characterized in that the first base is formed by a flexible sheet (31) forming a flexible base, directly welded to the metal body (2) so as to withstand the pressure constraints during a heat treatment (sterilization) of the can (1) . Tin can (1) according to claim 1, characterized in that said first bottom (3) has a pre-cut part (313), consisting of a partial incision of the flexible sheet, maintaining the impermeability of the sheet against air. Can (1) according to claim 2 characterized in that the pre-cut part (313) is associated with a visual marking. Can according to any one of claims 1 to 3, characterized in that the second base (3) is also formed by a flexible sheet (31). Can (1) according to any one of claims 1 to 4, characterized in that said flexible sheet (31) comprises at least one metallic layer (310b). Can (1) according to any one of claims 1 to 5, characterized in that , for a standard can in 4/4 format, the mass of the metal body (2) is less than 50g. Tin can (1) according to claim 4, characterized in that said first and second bottoms (3) are welded on the upper part (22) and the lower part (23) respectively of said metallic body (2). Can (1) according to any one of claims 1 to 7, characterized in that said metal body (2) has the shape of a truncated cone. Method of manufacturing a can (1) according to one of claims 1 to 8, characterized in that it comprises a step of welding a flexible bottom at one end of the metal body, under conditions allowing said audit flexible bottom to withstand the pressure stresses which arise during a heat treatment of the can (1). Method according to claim 9, characterized in that the welding of the flexible bottom to the end of the metal body is carried out by heat sealing. A method according to claim 10, characterized in that said flexible bottom has a lower polypropylene membrane, which is heat sealed on the end of the metal body covered with a varnish loaded with polypropylene. Method according to any one of Claims 9 to 11, characterized in that it also comprises one or more of the following steps, carried out before or after the step indicated in Claim 11: a step of filling the metallic body with one or more food products; - A step of crimping a rigid bottom on the other end of the metal body so as to hermetically close the box. A method according to any one of claims 9 to 12, characterized in that the box is of the stamped type, and that the metal body is filled with one or more food products before the welding step of claim 9 . Method for manufacturing a can according to any one of Claims 9 to 13, characterized in that it comprises a step of heat treatment (sterilization) of the can closed hermetically at both ends. Method for manufacturing a can according to any one of Claims 9 to 14, characterized in that it further comprises a step of precutting the flexible bottom, consisting of a partial incision of the flexible sheet, maintaining the impermeability of the sheet in air, preferably after heat treatment.

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