Patent Application
20240109119
The field of the invention is that of food processing. The invention relates more particularly to containers intended for the conservation of foodstuffs over a long period of time, and in particular to tins.
The metal cans allow a long conservation of the food they contain. They are made of a metal body, and differ in the way they are closed.
Some cans (in particular those used for preserving ready meals or vegetables) are closed by two rigid metal bottoms which are generally joined to the body by crimping to make a tight container. Such a closing process allows subjecting the food products contained in these cans, once they are closed, to a heat treatment at high temperature, in particular at a temperature higher than 110° C. (sterilization), in order to guarantee a conservation of several months at room temperature. These cans can present difficulties of opening, because of the importance of the thickness of the metal bottom, in order to support the variations of internal pressure.
Other cans for sterilization are closed with flexible bottoms that are directly attached to the metal body, as described in WO2016139341. These cans are non-peelable, but the use of flexible bottoms improves the opening of the cans, which can be easily cut, especially when the flexible bottom has a partial incision (maintaining air impermeability in order to maintain the quality and integrity of the product contained in the can) creating embrittlement along a rupture line corresponding to the location of the pre-cut, and aiding in opening.
There are also cans with peelable bottoms, the cans being closed by a lid made of a flexible peelable sheet attached to a conventional metal bottom which is previously hollowed out. The assembly is then crimped around the upper part of the metal body. The peelability is in particular and preferably measured according to the method described in FR 2955844, peeling the lid at 90° at a speed of 300 mm/min), allowing to measure the initial, flow and final peeling forces.
Today, there are 3 principles of opening
It is important to limit the weight and the cost of raw material of cans. Thus, it is preferable to use flexible bottoms rather than rigid metal bottoms. However, the methods of sealing soft bottoms as described in WO2016139341 require preparation of the metal body prior to providing the soft bottom, and changes to the processes currently used in packaging plants, which induce process changes, and some additional costs.
As far as cans with peelable bottoms are concerned, one disadvantage of this technique lies in the relatively high manufacturing cost of such cans. Indeed, the manufacturing process requires steps of cutting (hollowing) the metal bottom and fixing the flexible sheet to the metal bottom. This solution also leads to important losses of material, caused during the cutting of the metal bottom to be hollowed. Indeed, this hollowed out material cannot be reused.
Furthermore, the implementation of such a solution is complex and presents risks of leakage, in particular for cans to be sterilized, since the flexible sheet is supposed to be both peelable (i.e. not too strongly attached to the hollowed out bottom so that it can be easily removed by applying a moderate force) and yet resistant to the strong variations in pressure that occur during the sterilization of the container. In other words, there is currently no can:
The processes of adding flexible bottoms according to WO2016139341 or of strong sterilization of peelable bottoms require indeed adaptations of processes, according to the destination of the can, whereas the most standard and fixed conditions are preferentially sought.
U.S. Pat. No. 2,386,312A1 describes methods for attaching bottoms to drums. These bottoms do not appear flexible: indeed, although they can be deformed, they do not return to their original shape after deformation (col. 2, lines 13-19 of U.S. Pat. No. 2,386,312A1).
GB159188A relates to barrel closures and describes a way to create a crimping element that can fit perfectly on the barrel. It is not stated that the bottoms used are flexible, which does not seem relevant in view of the field of application (large metal barrels (see p.1, col. 1, lines 8-9)).
WO03051725A1 describes a container such as a soft drink can, comprising an upwardly open metal body having a side wall with an annular top portion having a reduced diameter neck formed therein, and a metal top structure such as a lid having an annular portion integral with the annular top portion of the side wall along an annular seam extending outwardly and substantially horizontally or downwardly from the side wall. This document does not mention the use of a welded ring, or a flexible sheet forming the bottom (although the bottom of WO03051725A1 may include a flexible peelable portion).
GB286364A describes the application of bottoms to containers by crimping.
GB698957A describes methods for improving crimping on containers.
The present application proposes a solution making it possible to use the existing crimping tools, without introducing notable changes in the can closing practices. It also makes it possible to work on containers whose diameters or opening dimensions are not imposed by market standards linked to the manufacturing processes of the bottoms conventionally used. The methods used in the art impose the use of standard can formats, linked to the press tools used in the manufacture of the bottoms. In fact, the current methods of manufacturing backgrounds are constraining as for the size of the cans, or their shape.
The present application aims at presenting a system allowing to put a bottom on a can, ensuring the tightness if the can is to be sterilized, and reducing the material losses. This bottom is preferably a flexible bottom. It can be peelable or not.
It is recalled that the flexibility of a bottom or a sheet is understood by its capacity to deform in a reversible way (compared to a rigid bottom, that a traditional metal bottom). Thus, a flexible bottom is able to deform (bulge), passively, during sterilization (increase of the internal pressure), and to recover the initial shape, without showing cracks or deterioration, when the internal pressure decreases when the temperature of the can goes down after sterilization. Thus, the flexible bottom presents an absence of irreversible mechanical deformation contrary to a traditional metal bottom which can present an irreversible deformation according to the applied force. In general, this flexibility is accompanied by a lower overall strength of the flexible bottom.
The invention thus relates to a method of manufacturing a can, characterized in that it comprises the step of placing a bottom at one end of the body of the can, said bottom being attached to the body by means of a retaining (or crimping) ring crimped to the end of the can body, characterized in that the retaining ring is a welded ring.
The use of a ring, which can be made of any diameter or shape, and a bottom cut out of a flexible sheet allows the shape or size of large containers to be unconstrained. The top diameter of the cans can be increased beyond the largest diameter generally observed (153 mm). Furthermore, because it is easier to make small series of cans than small series of bottoms that fit the cans, special commercial operations can be scheduled with small runs of cans of different shapes or sizes. It is also easy to prepare cans with bottoms of different shapes and sizes.
The crimping ring is thus a welded ring, i.e. it has a weld line. This weld line maintains the shape of the ring. In the context of the present invention, the crimping ring is preferably obtained by welding the ends of a metal strip (having the length of the can perimeter) in order to close it. It is thus to be noted that, in the context of the envisaged use, the ring may be circular or of any other shape, depending on the shape of the can.
Thus, the crimping ring is not obtained by hollowing out a metal sheet.
In a preferred embodiment, a welded ring is used, obtained by welding a metal strip, as described above, and then folding said strip to form a groove. This groove is thus positioned opposite the end of the can body during the crimping step. The end of the can body is then inserted into the groove and the edges of the groove are then strongly pressed/tightened against the body to ensure a perfect fit.
Alternatively, a sheet of metal can be welded to form a cylinder of suitable diameter and then welded rings of desired width can be cut from this cylinder.
In one particular embodiment, the welded ring also has a flat spot directed inwardly of the ring. This flat spot (typically a few millimeters wide) thus creates a flat surface around the perimeter of the can. This flat surface can be used to attach a peelable bottom, or to stretch a flexible non-peelable bottom, attached between the can body and the welded ring with the flat.
It can also be noted that, compared to the peelable bottoms of the prior art, when the flexible bottom is wedged between the ring and the body of the can, the flat part is located above the flexible bottom and is therefore not in contact with the products (generally food) located inside the container. Thus, the risks of oxidation of the products observed for the peelable bottoms are avoided associated with the presence of this metallic flat located under the bottom for this mode of realization of the prior art.
Thus, in a particular and preferred embodiment, the bottom is formed by a flexible sheet.
The invention also relates to the use of a welded ring for securing a bottom to a container, in particular a can body, by crimping the welded ring onto one end of the container or the container body, said bottom becoming secured with the container after crimping.
In one embodiment of this aspect of the invention, the bottom is directly attached to the welded ring (this is the case, for example, when the bottom is peelable).
In another embodiment, the bottom is trapped/cornered between the container wall and the crimping ring and becomes secured when pressure applied to the hems of the ring crimps it to the container body.
In a first embodiment, this bottom is a peelable bottom. It is then a cover sealed on the flat on the crimping ring. This cover is formed with materials known in the art, in particular aluminium or thermoplastic polymers. This peelable bottom can be formed of one or more layers, identical or different. Methods for sealing the bottom onto the flat are known in the art. In particular, heat sealing can be mentioned. Preferably, a tab is fixed on the bottom, allowing the peel-off of the lid (bottom) from the flat.
It is preferred when this peelable bottom is attached to the crimping ring before the ring is positioned on the can body and the can is closed.
Thus, it appears that, in this embodiment, manufacturing processes similar or identical to those already existing in the art for peelable bottoms are used, the essential difference being the use of a welded crimping ring, rather than a ring obtained by hollowing out a metal sheet. Thus, the method according to the invention allows a substantial saving of material, insofar as only the material necessary for the manufacture of the ring (strip of metal foil) is used, rather than losing the material hollowed out by the methods of the prior art.
In a second embodiment, the bottom is not peelable. In this embodiment, the bottom is formed by a flexible sheet with an area slightly larger than the area determined by the end of the metal body of the can. In the same way that the crimping ring has the same shape as this end, this flexible sheet has the same shape as the end of the metal body, but slightly larger dimensions in each of the dimensions (a slightly larger radius if the end of the metal body is circular, a larger length and width if the end of the metal body is rectangular . . . ).
Thus, the flexible foil is clamped between the metal body and the crimping ring and is thus held tightly when the ring is crimped onto the metal body, which thus serves to secure the bottom to the container and close it.
The flattened area preferably present on the crimping ring serves to pull the flexible film closing the end of the can, as well as to protect this flexible film (forming a flexible bottom) during the transfer or stacking of the cans. The first fragility of the film is in fact at the edges of the can body.
In one particular embodiment, the film used to close the can is in the form of a roll, slightly wider than the width of the can. This allows the use of a traditional crimping machine (a crimping machine used to close cans with rigid bottoms). The sides of the roller are pulled at the seaming speed and the film is placed between the welded ring and the can body. The film is cut during the ring application phase (just before sealing) using conventional cutting tools.
When a non-peelable bottom is desired, it can also be attached to the flat, according to the methods described in WO2016139341, and then the attached non-peelable bottom-bearing ring can be crimped onto the container body.
In a particular embodiment, the flexible sheet has a precut portion useful for facilitating the opening of the can. This precut portion consists of a partial incision, forming a break line, of said flexible sheet (while maintaining air impermeability). Thus, this partial incision weakens the sheet along the break line.
In an embodiment, a tab or a small gripping ring can be glued on the flexible bottom, and close to the precut area, which can be pulled by the end user, in order to induce the rupture of the fragile area, and thus improve the opening of the can. In this embodiment, the bottom is not peelable, but the opening system (pulling a tab inducing the rupture of the bottom and the opening of the can) is similar to the system known by consumers for peelable bottoms.
Alternatively, the opening can be made, for example with the help of a knife or a spoon, by exerting pressure at the location of the break line.
It is preferable that this break line with the precutting is also associated with a visual marking. The pre-cut can be made on an ink pre-marking or the ink pre-marking can be added after the pre-cutting step. This allows the consumer to better visualize the precut with regards to the rest of the can bottom.
The use of flexible bottoms within the framework of the invention makes it possible to solve the problem of the opening of large diameter cans. Indeed, it is not really possible to set up easy-opening systems for cans and bottoms with a diameter greater than 153, without there being a risk that the user will cut himself during opening, due in particular to the force to be exerted in order to open these cans, to the memory effect of the steel forming the bottom, which tends to oppose opening, and to the fact that these openings lead to two sharp parts (edge and bottom). Moreover, in general (and in particular for large cans), the use of can openers is avoided, especially in collective environments where these cans are used. Indeed, the hygiene conditions linked to the use of the can opener are not always optimal, because this tool penetrates inside the container, with a risk of contact with the contents and contamination of the latter. In addition, the use of a can opener can lead to the introduction of iron filings into the contents. Finally, the lid opened with a can opener presents dangerous asperities.
The use of flexible bottoms as described above allows for easy opening, with the removed lid not being as dangerous as a rigid metal lid can be.
In a preferred embodiment, said flexible sheet comprises at least one gas-impermeable layer.
In a particular embodiment, said flexible sheet comprises at least one metal layer. In particular, this layer may be aluminum. In particular, this metallic layer is useful for serving as a gas-tight barrier.
In another embodiment, said flexible sheet comprises at least one layer of plastic material. This is particularly interesting in order to guarantee, for a reduced thickness, sufficient strength of the flexible sheet so as to resist the deformations that take place during the heat treatment of the can.
In a particular embodiment, said flexible sheet comprises at least one layer of plant-based plastic material.
In a particular embodiment, said flexible sheet is formed in a single layer.
In a particular embodiment, said flexible sheet is formed of multiple layers. Such multi-layer sheets are known in the art and can be obtained by known methods, such as lamination.
Thus, in a particular embodiment, the flexible sheet has a gas-impermeable layer (in particular a metallic layer) which is covered on at least one side by a plastic layer.
The flexible sheet thus contains at least one layer allowing the tightness to gases, and air in particular. Indeed, it is necessary to avoid the entry of oxygen which could to oxidize the products (in particular food) contained inside the can. As mentioned above, this layer can be metallic. Aluminum is a preferred metal, in that it is easily malleable and can be rolled into flexible sheets. Thus, a metallic layer (particularly aluminum) with a thickness of between 40 and 100 microns, preferably between 40 and 80 microns, more preferably between 60 and 80 microns, can be used. Thus, a layer with a thickness of about (or) 70 microns can be used. Synthetic polymers such as polyamide films can also be used as a gas barrier layer. The thicknesses of these polymer films are in the same range as those of the metal films mentioned above.
Preferably, as seen above, the flexible film has a gas-tight (in particular oxygen-tight) layer which is covered on at least one side by a plastic layer, and preferably on both sides.
The inner layer (the layer inside the can after the bottom has been fixed) is preferably formed with a polymer suitable for food contact. In fact, this inner layer will be in contact with the food contained in the can, in particular during sterilization and/or handling of the can. This layer should also preferably have good physical resistance, including to sterilization temperatures if such a step is envisaged. Any plastic or polymeric film suitable for food contact may be chosen, in particular polyethylene, but polypropylene having better physical resistance and temperature resistance than polyethylene is preferred for this application. Homo polypropylene (HPP) or copolymer polypropylene (CPP) can be used. The thickness of the inner layer is generally between 35 and 55 microns, in particular between 40 and 50 microns. For example, a layer thickness of about (or about) 45 microns can be used.
The outer layer is particularly resistant, especially to abrasion, to avoid the risk of tearing during handling. Preferably, polyethylene type polymers are used, such as low density polyethylene, high density polyethylene, or polyethylene terephthalate (PET). Other polymers (polyethylene oxide, polycarbonate, polymethylmethacrylate) could also be considered. The thickness of the outer layer, especially when it is made of polyethylene, is of the order of 17-25 microns.
The cover formed from a flexible sheet therefore has a thickness of between 100 and 150 microns, generally between 120 and 150 microns. However, the thicknesses indicated above can be doubled if an increase in properties is sought. The sterilization temperatures are generally in the range of 125 to 130° C.
The multi-layer flexible film is produced in a conventional manner by laminating or bonding the inner and outer layers to the core layer, or a gas-impermeable layer (in particular metal) to the outer layer (polyethylene), followed by the addition of the inner layer polymer.
In a particular embodiment, the body of the can is of the stamped or stamped-drawn type. The advantage of using stamping for the manufacture of the metal body is that it is formed in a single piece, and does not have any welds (unlike three-piece cans whose body is formed by welding a metal sidewall). This avoids the need to crimp two welded areas that could potentially be areas of leakage, loss of tightness and lead to potential contamination.
The interest of the proposed method is that the size and shape of the backgrounds (and thus of the cans) is free and is no longer imposed by the usual standards of backgrounds manufacturing. Thus, one can consider cans of any shape.
In one particular embodiment, the end of the can body is circular in shape.
In another embodiment, the end of the can body is rectangular or square in shape. It generally has rounded corners.
In another embodiment, the end of the can body is oval in shape.
In another embodiment, the can body is shaped like bowls. In this embodiment, the can bodies can be stacked before filling or after use.
In a preferred embodiment, the invention relates to a method of applying a bottom to the body of a can, comprising the steps of
As a result of the cut in step (c), the projected area of the flexible sheet is slightly larger than that of the end of the can body. In this embodiment, flexible sheets as described above are used. In particular, they may contain at least one gas-impermeable layer (especially metallic), and preferably at least one plastic layer on one side.
The above method is preferably performed continuously.
The process may also include one or more of the following steps, performed before or after the above step:
Thus, in one embodiment,
In another embodiment,
In another embodiment,
In another embodiment,
In another embodiment,
In this embodiment, the flexible bottom at (a) may be attached to the can body via a crimp ring, said ring being a welded ring, according to the methods described above, or by any other method known in the art such as that described in WO2016139341.
In order to close the ends of the body of the can with the flexible bottom, one can
Because of the cut in step (b), the projected area of the flexible sheet is somewhat larger than that of the end of the can body. If the can is of the deep-drawn (stamped) type, the filling of the metal body is carried out before the steps of closing the can by crimping, as described above.
Thus, in this embodiment,
In another embodiment, one can also perform
In another embodiment, one can also perform
In another embodiment, one can also perform
The above processes may also include a step of heat treatment (sterilization) of the can sealed at both ends.
According to another particular aspect of the invention, the manufacturing process also includes a step of pre-cutting the (preferably flexible) bottom attached to the can via the (welded) crimping ring in order to allow easy opening of the can.
This pre-cutting preferably takes place after the heat treatment since the latter causes strong pressure constraints and it is therefore preferable that the bottom (preferably flexible) is not weakened.
The invention also relates to a method of sterilizing a can as described above, comprising a step of placing said can under temperature and pressure conditions inducing an internal suppression (in said can) of at least 0.8 bar (or any other value as indicated above). Preferably, in this method of sterilization, said can is subjected to the overpressure for at least 2 minutes (or any other time as indicated above, a preferred time being greater than or equal to 6 minutes, or 7 minutes).
The invention thus relates to a method of manufacturing a can as previously described comprising:
According to another particular aspect of the invention, the manufacturing process comprises a step of pre-cutting at least one of the two flexible bottoms in order to allow easy opening of the can.
This pre-cutting preferably takes place after the heat treatment since the latter causes strong pressure stresses and it is therefore preferable that the flexible bottom is not weakened.
Such a manufacturing process can be efficiently implemented in an industrial way.
These processes are used to obtain cans as described below. They can also be used to close metal trays of ready meals.
In another aspect, the invention relates to a container having at least one bottom formed by a flexible sheet, said flexible sheet being attached to one end of the container by being crimped onto the body of the container by means of a welded ring. The invention thus relates to a container having a metal body and at least one end of the metal body closed by a bottom comprising a flexible sheet, the flexible sheet being held on the metal body by means of a ring crimped onto the metal body, characterized in that said ring is a welded ring.
As seen above, the flexible bottom can be attached to the crimping ring (e.g., to a flat of this ring), especially when the bottom is peelable. In another embodiment, the flexible bottom is wedged between the metal body and the crimping ring, a tight closure of the container being obtained when the ring is crimped onto the metal body of the container.
In a particular embodiment, the flexible bottom has a pre-cut portion.
In one embodiment, the container may comprise two flexible bottoms, at least one of which is attached via a welded crimp ring. Preferably, in this embodiment, the two flexible bottoms are attached via a crimping ring, at least one of which is welded. More preferably, the two crimping rings are welded rings.
In one embodiment, the container has an internal vacuum relative to atmospheric pressure.
In one embodiment, the container is of the can type. It is illustrated that cans (in Europe) are generally of the types as described in Table 1.
For cans for canned fish, other formats are used, based on the “4/4 fish” with a capacity of 750 ml. There are also rectangular cans.
It may be noted, however, that due to the use of flexible bottoms, and in particular due to the fact that the bottoms are applied by a continuous process using rollers (reels), as described above, the size and shape of the cans is no longer a constraint such as it might have been in the prior art. The cans described above are therefore illustrations of cans on which the process can be applied.
In a particular embodiment, the can is of the of the stamped (deep-drawn) or stamped-drawn type.
As seen above, one can use flexible films made of various materials, possibly containing several layers of different materials. For example, a metal layer and a plastic polymer layer can be used.
The plastic polymer layer can be printed, which avoids the use of labels on the body of the cans. Transparent films can also be used to show the ingredients contained in the containers.
The invention is particularly interesting in the case of fish canning (such as sardine cans). In this case, the cans are rectangular in shape, with the bodies and easy-open bottoms made of aluminum. Aluminum is generally more expensive than steel for the same can, but easy-open steel lids cannot be used on these fish cans because of their rectangular shape. This is because the force required to open the can (breaking the hard lid by pulling on the ring) is too great and the shape memory properties of steel (tendency to snap back when pulled) complicate the opening ability of a steel bottom for these cans. Aluminum is used for these types of cans because it is more flexible than steel and therefore has better openability. An aluminum can body must then also be used because the use of a steel body leads to the risk of galvanic corrosion.
The use of flexible lids as described allows the substitution of aluminum for steel for these fish cans, thus greatly reducing costs.
In fact, it is possible to form the body from stamped steel and the welded ring from steel, and to use a flexible film which can be easily opened, and which can contain polymer or plastic layers which eliminate the problems of galvanic corrosion.
The use of a crimping ring makes it possible to obtain a good seal, by a process that is simpler to implement than that described in WO2016139341. Indeed, crimping is well known, used and mastered in the art (method used to fix rigid bottoms) and is known to guarantee a good seal. In fact, crimping involves a clamping operation, which once performed on metal ensures a gas-tight and micro-organism-tight link between the bottom and the body of the can.
In addition, the mechanical strength will also be improved over WO2016139341, which may require rims protecting the sealing area of the flexible film on the mechanical body. By using the crimp, the cans have the same type of mechanical strength, as a whole, as the rigid bottom cans of the prior art. This allows a good protection during logistic operations (transfers and handling of the cans).
The examples below and figures describe an embodiment for cylindrical shaped cans. In these embodiments, the rings are circular. In the case of cans with a non-circular end (rectangular, oval or other), the shape of the ring is identical to that of the end.
A welded ring is made for crimping on a 4/4 can. This can has a diameter of 99 mm.
A strip is cut from a steel sheet with a width of about 9 to 11 mm and a length of 99-101 mm, with a thickness of 0.20 to 0.24, in particular 0.21 to 0.23 mm.
This steel strip is folded and its ends are welded. An industrial welding machine such as the one sold by Soudronic (Bergdietikon, Switzerland) can be used. The result is a welded ring, similar to the one described in
The ring is then shaped into the form shown in
The welded ring (1) is thus composed successively (from the outside to the inside) of a hem (121) (hemming zone), a cup (122) (hem return) and a flat (13). The hem (121) and the hem return (122) have a development of about 6 to 7 mm and form the groove (12). The flat has an effective width of about 3 to 4 mm. A steel strip with an effective width of approximately 9 to 11 mm will therefore form a welded ring for a can with a diameter of 99 mm.
The step of crimping a flexible bottom (2) onto a can body (3) is shown in
These steps can be carried out continuously using the same machines as those used to crimp conventional rigid bottoms.
A ring (1) as obtained according to example 1 is used. A peelable bottom is attached to this ring according to the methods known in the art for attaching peelable bottoms to rings obtained by cutting out material. The ring with the peelable bottom is then assembled on the body of a can by crimping according to the methods known in the art.
After crimping, the container can be sterilized and then a partial incision (described as (21) in
| Number | Date | Country | Kind |
|---|---|---|---|
| FR1911383 | Oct 2019 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/078705 | 10/13/2020 | WO |
