EP0251877A1 - Process for obtaining food products hermetically packaged in containers, installation for carrying out this process, container especially suited for this process - Google Patents

Abstract

A deformable part (4) of the container (3) is maintained in a non- deformed state during the filling and closing stages so as to maintain a substantially constant volume inside the container (3), and, after hermetic closure of the container, the action maintaining the deformable part is released so as to create an increase in the internal volume of the sealed container, resulting from the deformation of the deformable part under the effect of the weight of the food products. The invention applies particularly to the packing of food products. <IMAGE>

Description

The present invention generally relates to a process for obtaining food products packaged in a leaktight manner in containers such as trays made of plastic material.

Such a method is already known, which consists essentially in supporting said container, filling said container with food products, and closing said container in a leaktight manner when it is filled, in particular by heat-sealing or self-sealing a lid or a film of deformable plastic material on the opening edge of said container.

In the implementation of such a known method, hitherto substantially non-deformable trays have been used.

This use has resulted in a number of drawbacks. Indeed, during the stacking of closed containers, there is a significant risk of the lid or lid taking off. This risk of take-off results from an increase in pressure occurring inside the container, due to the quantity of air trapped at the time of closing, and the subsequent degassing of the packaged food products.

Taking off the cover obviously results in a loss of tightness and a concomitant reduction in the good conservation of the packaged products.

The object of the present invention is to solve the aforementioned problems by proposing a method of the type mentioned above which makes it possible to obtain food products packaged in a leaktight manner in containers which can be stacked without the risk of their lid or lid taking off.

The solution according to the present invention, to solve this technical problem consists of a process of the type mentioned above, characterized in that it consists in maintaining in a non-deformed state a deformable part of the container, during the filling and closing stages. so as to maintain a substantially constant volume inside the container, and to release, after the sealed closure of said container, the action of maintaining said deformable part so as to create an increase in internal volume of the closed container, resulting from the deformation of said deformable part under the effect of the weight of said food products. Thus, a reduction in the internal pressure of the container responsible is obtained, when stacking them, when the cover or lid takes off.

The process of the present invention is very particularly advantageous in the case where the container is made of a thermoplastic material excluding polyolefins, and in particular of polystyrene.

In fact, for such materials, due to the reactions of the oils and oil vapors contained in certain food products, a phenomenon known as “stress-cracking” is observed when the containers are closed by heat sealing, which results in cracks in the container appearing either on its upper rim after a few hours or on its bottom in the thinnest places after a few days. This phenomenon can be interpreted by the combination of three effects, namely the presence of oils or fats, the heating of these during heat sealing, and the resulting increase in pressure inside the container.

Until now, to solve this problem, we used perforated covers or lids allowing gas evolution. This solution is unusable for products intended to be preserved.

Another solution is to work under vacuum, but requires a complex and expensive installation.

The method according to the invention therefore also makes it possible to solve this particular problem, in a completely advantageous manner, relative to the solutions proposed so far.

The invention also relates to an installation for implementing the method which has just been described.

Already known, in particular from French patent application No. 76 34 463, an installation making it possible to seal containers of plastic material, in particular by heat-sealing comprising a chamber or cavity intended to receive a container, and the upper edges of which form a bearing surface of the opening rim of said container; and a movable plate coming to apply on said opening rim of the container in order to tightly fix the corresponding edge of the cover or film of deformable plastic material therein.

This structure constitutes the basic structure of the installation according to the invention, which is characterized in that it further comprises means ensuring the maintenance of a deformable part of the container in an undeformed state, and means of suppression of the action of said means ensuring the maintenance to allow free deformation of said deformable part under the effect of the weight of food products.

According to a particular characteristic of the invention, the means ensuring the maintenance comprise a member maintaining the above-mentioned deformable part in a non-deformed state by direct contact, and of shape combined with that of said deformable part not deformed.

In addition, the abovementioned removal means comprise in this case means for relative movement of the container relative to the member ensuring the maintenance.

Finally, the present invention relates to a container intended in particular for the sealed packaging of food products after addition of a cover or film of plastic material, characterized in that it comprises a preformed deformable part, capable of being deformed under the effect of the weight of the food products contained in said container. he It appears that this container constitutes the inventive basis of the present invention, insofar as it has enabled in particular the development of the particularly advantageous process described above.

• - la figure 1 est une vue en coupe transversale d'une partie de l'installation permettant la mise en oeuvre du procédé selon l'invention;
• - la figure 2 est une vue en coupe transversale d'un récipient clos obtenu par la mise en oeuvre du procédé de l'invention, les traits mixtes représentant les positions respectives de l'opercule ou couvercle et de la partie déformable du récipient, après libération de l'action de maintien de la partie déformable.

The invention will be better understood, and other objects, characteristics and details thereof will appear more clearly on reading the explanatory description which follows, made with reference to the appended schematic drawings given solely by way of nonlimiting example illustrating a currently preferred embodiment of the invention and in which:

• - Figure 1 is a cross-sectional view of a part of the installation allowing the implementation of the method according to the invention;
• - Figure 2 is a cross-sectional view of a closed container obtained by implementing the method of the invention, the dashed lines representing the respective positions of the lid or cover and of the deformable part of the container, after release of the action to maintain the deformable part.

Referring to Figure 1, there is shown schematically an embodiment of an installation according to the invention, for sealingly closing, by heat-sealing or sticker of a cover or film of plastic material 1 deformable on the edge d opening 2 of a container such as a tray 3 shown in FIG. 2.

This tray 3 includes a preformed deformable part 4 capable of being deformed under the effect of the weight of the food products, not shown, contained in the container 3.

The machine according to the invention generally comprises a chassis defining an internal chamber or cavity 5 with a substantially rectangular section open on its upper horizontal face. A cover 6, for example forming a heat-sealing heating plate, is hinged mounted on one side of the chassis so as to close the upper face of the chamber 5 to obtain the sealing of the lid or cover 1 on the container 3.

This installation further comprises a member 7 intended to maintain the deformable part 4 of the container 3 in a non-deformed state shown in FIG. 1. This maintenance is ensured by direct contact between the member 7 and the deformable part 4, the member 7 being produced in a form conjugated with that which is not deformed of the deformable part 4.

Advantageously, the part 4 is a convex curved wall in the non-deformed state, constituted by the bottom of the container 3.

According to a particular characteristic of the invention, the holding member 7 is an axially displaceable element, such as for example a piston with head 8 in the form of a spherical cap.

Of course, the holding member 7 can also be fixed, in which case means will be provided allowing the upward movement of the container thus releasing it from the member ensuring the aforementioned holding.

The process for obtaining food products in accordance with the present invention consists in placing the container 3 in the cavity 5, so as to support the latter by its edges, then filling the container 3 with food products. The latter is then closed in a sealed manner.

During the filling and closing stages, the deformable part 4 is maintained using an organ 7 in an undeformed state, so as to maintain a substantially constant volume inside the container 3.

After sealing the container tightly, the action of retaining the deformable part 4 is released. Under the effect of the weight of the food products contained in the container, an internal volume thereof is created, and therefore a decrease. internal pressure. This reduction in pressure causes, as shown in FIG. 2, a deformation of the cover or cover 1.

The deformable part 4 of convex shape in the non-deformed state is of concave shape after release of the holding action (FIG. 2).

To allow the deformation of part 4, the bottom of the container has on its periphery a part forming a continuous groove 9. In other words the deformation of part 4 does not result from the elasticity of the material used but from the conformation specific from the bottom of the container.

The container can be made of any thermoplastic material, and as mentioned above the process according to the invention finds particular application when the container is made of polystyrene, since this avoids the phenomenon of "stress-cracking".

The process which has just been described makes it possible, in particular, to stack closed containers without the risk of the lid or lidding peeling off or of deterioration of the food qualities of the products contained in the container.

Claims (10)

1. Method for obtaining food products packaged tightly in containers such as plastic trays, of the type consisting in:
- support said container,
- fill said container with food products, - close said container tightly when it is filled, in particular by heat-sealing or sticker of a cover or of a film of deformable plastic material on the opening edge of said container, characterized in what it consists in maintaining in a non-deformed state a deformable part (4) of the container, during the aforementioned filling and closing steps, so as to maintain inside the container a substantially constant volume, and to release, after the sealed closure of said container, the action of maintaining said deformable part (4) so as to create an increase in the internal volume of the closed container, resulting from the deformation of said deformable part under the effect of the weight of said food products. 2. Method according to claim 1, characterized in that the above-mentioned deformable part (4) is a curved wall, of convex shape in the non-deformed state. 3. Method according to claim 1 or 2, characterized in that the above-mentioned deformable part (4) consists of the bottom of the aforementioned container. 4. Method according to one of claims 1 to 3, characterized in that the aforementioned container is made of a thermoplastic material excluding polyolefins, and in particular of polystyrene. 5. Installation for the implementation of the method according to one of claims 1 to 4, of the type comprising a chamber or cavity intended to receive a container, and whose upper edges form a bearing surface of the opening edge of said receptacle and a movable plate coming to apply on said opening rim of the receptacle in order to seal therein the corresponding edge of the cover or film of deformable plastic material, characterized in that it comprises means ensuring the maintenance of a deformable part (4) of said container (3) in a non-deformed state, and means for suppressing the action of said means ensuring maintenance to allow free deformation of said deformable part under the effect of the weight of said food products. 6. Installation according to claim 5, characterized in that the means ensuring the aforementioned maintenance comprise a member (7) maintaining the deformable part (4) above in a non-deformed state by direct contact, and of shape conjugated to that not deformed of said deformable part. 7. Installation according to claim 6, characterized in that the aforementioned removal means comprise means for relative displacement of the container relative to the member ensuring the aforementioned maintenance (7). 8. Installation according to claim 6 or 7, characterized in that the deformable part (4) above is a curved wall formed by the bottom of the container, and in that the holding member (7) above is an axially displaceable element , such as for example a piston, with a head (8) in the form of a spherical cap. 9. Container intended in particular for the sealed packaging of food products, after addition of a cover or film of plastic material, characterized in that it comprises a deformable part (4) preformed, capable of being deformed under the effect of the weight of the food products contained in said container. 10. Container according to claim 9, characterized in that the deformable part (4) above is a curved wall, formed by the bottom of said container.

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