EP0007944B1 - Manufacturing process of a folded cardboard packing covered with an impervious sheet and blank for use in the process - Google Patents

Abstract

Packing comprising one part of cardboard and a film of thermoformed synthetic material. A cardboard blank is cut up in the desired shape and grooved to allow the folding of its elements. Between the bottom (1) and the walls (8), a grooving line (18) is formed in the opposite direction to that of the known method to favour the expulsion of air during the thermoforming of the film (20). Between the walls (8) and the edges (16), a cutting up half-way down the thickness (19) is formed on the same face of the blank. The film (20) covers the cutting up (19) and maintains the walls as well as the bottom (1) despite of the wrong direction of the grooving (18). Packaging of various products, including food products.

Description

The present invention relates to containers obtained from a flat cardboard blank, cut and marked with fold lines, this blank then being folded along these lines to be set in volume.

The purpose of the line marking operation is to weaken the cardboard in well-defined places, where it must be folded when it is placed in volume.

It is important to obtain markings as clear as possible both for the appearance of the container and for its ability to pass through an automatic packaging line for example.

The fold lines can be obtained by notching the cardboard, by perforating it or by providing "creasing" lines.

The creasing is obtained by means of a male member called "repressor" and a female counterpart called "gutter" so that the repressor produces a permanent deformation of the cardboard by forcing it to penetrate into the gutter.

A crease line therefore comprises a hollow part, or "female" formed by the repressor and a raised part called "bead".

A sheet of cardboard being put in place to be creased, it is equally possible to provide the bead on the lower face or on the upper face of the cardboard sheet. But, on the other hand, the subsequent folding must always be done in a given direction, that is to say that the female part corresponds to the outside of the fold and constitutes, in a way, the male edge of the object obtained by folding.

Indeed, when we start folding along a crease line, this permanent deformation causes a tension between the layers that we can observe when looking at the crease line in section. When this tension is greater than the cohesive force of the layers, the cardboard "delaminates" and causes the desired hinge effect.

If we tried to fold the cardboard in the opposite direction, that is to say by providing the bead outside of the folding, we would obtain an elastic effect which would tend to open the hinge and we could not obtain an object with a very flat surface and very straight edges. On the contrary, we would obtain more or less random deformations which tend to give the panels non-planar and, one might say, "swollen" surfaces, while the angle would tend to open instead of remaining exactly the same. we want to give him.

In addition, with certain qualities of cardboard whose modulus of elasticity is poor, there would be an outer edge not straight and sharp but as formed by several more or less inclined lines and which give the impression that the cardboard is as broken.

Furthermore, containers are known which consist of a suitably cut, creased and folded cardboard part and a part made of synthetic material applied to the entire internal surface of the container by thermoforming.

As is known, thermoforming consists in placing a plastic sheet above the cardboard part and then causing the plastic sheet to deform by heating it and applying air pressure to it so that this plastic sheet closely follows the shapes of the cardboard part and is applied as perfectly as possible along the concave as well as convex edges.

When the cardboard part that we want to cover with a thermoformed plastic sheet has a concave shape, such as a tray for example, we understand that when we start to deform the sheet synthetic material, this expels the air between it and the cardboard part and, of course, this air must be able to escape as completely as possible so that, often, a lower air intake is added at higher air pressure.

However, as the plastic sheet must stick to the entire surface of the cardboard part, it may happen that air remains occluded between this cardboard part and the plastic sheet and this occurs especially at neighborhood of concave edges.

The presence of these air bubbles is a serious disadvantage not only with regard to the external appearance of the container but also by the fact that if the air expands following a rise in temperature for example, it can cause tearing of the plastic sheet which seals against the cardboard, so that such containers must be discarded when they have air bubbles.

The present invention relates to a container of this type, that is to say comprising a cardboard part and a plastic part associated by thermoforming and which does not have the above drawbacks.

To illustrate the state of the art, we can cite the French patent application 2197776 which describes a cardboard container, among many others, which includes fold lines.

Naturally, the present application does not in itself claim the marking of a cardboard blank for its subsequent folding, this marking being mentioned only to locate the technical field to which reference is made.

French patent application 2294097 is also known, which relates to a particular container, in the sense that it is obtained from a blank of cardboard cut out and then sandwiched between two external films then, subsequently, folded to constitute a volume.

It is clear that the folding of a three-layer complex poses problems and this patent application proposes a solution which consists in nicking the cardboard blank before covering it with film in order to weaken the cardboard blank as much as possible.

As specified on page 2, lines 13 to 17 of this patent application, the notches or V-shaped folding grooves are hollowed out over approximately two thirds of the thickness of the cardboard and their shape is the one which causes the least constraints "during the erection of the blank, in the outer films subsequently applied to the blank".

It is thus clearly stated that the sole purpose of these notches is to promote folding.

On the contrary, according to the invention, the cardboard blank is folded along lines (marked in two different directions, moreover) before the establishment of a film on the marked face.

As will appear below, the prediction of these markings has the essential aim of allowing a perfect application of the film on the cardboard by allowing the evacuation of the air included between the cardboard and the film.

The present invention relates to a method of manufacturing a container from at least one blank cut out and provided with markings constituting fold lines, this blank having to be subsequently formed by folding along these lines in order to present a bottom, walls which extend at an angle to the plane of the bottom and at least one flange which extends at an angle to the plane of the wall to which it is attached (see FR-A-2197776), characterized in that all the markings are carried out on the face of the blank which must correspond to the interior of the container so that their female part is situated on this face, the fold lines between the bottom and the walls being crease lines , that is to say lines comprising on one side a hollow or female part and on the other side a raised part, then fold the blank along these lines outwards for the or the edges and inwards for the walls and that we maintain ent the container thus placed in volume, then that is applied to the entire marked face and which constitutes both the interior of the container and its rim, a continuous waterproof film which covers the fold lines and keeps the container in shape , the crease lines between the bottom and the walls being such that they allow the air between the blank and the film to escape laterally along the crease lines.

• La fig. 1 est une vue en plan d'un flan découpé et marqué conformément à l'invention;
• La fig. 2 est une vue en coupe faite selon la ligne II-II de la fig. 1;
• La fig. 3 est une vue partielle à plus grande échelle montrant un détail de la fig. 2;
• La fig. 4 est une vue partielle en coupe d'un contenant conforme à l'invention avant mise en place de la pellicule thermoplastique.
• La fig. 5 est une vue analogue à la fig. 4 après mise en place de la pellicule thermoplastique.

The invention will be better understood with the aid of the detailed description below made with reference to the accompanying drawings. Of course, the description and the drawings are given only by way of an indicative and non-limiting example.

• Fig. 1 is a plan view of a blank cut and marked in accordance with the invention;
• Fig. 2 is a sectional view taken along line II-II of FIG. 1;
• Fig. 3 is a partial view on a larger scale showing a detail of FIG. 2;
• Fig. 4 is a partial sectional view of a container according to the invention before fitting the thermoplastic film.
• Fig. 5 is a view similar to FIG. 4 after installation of the thermoplastic film.

Referring to the drawings, it can be seen that a container in accordance with the invention is obtained from a blank of cardboard cut out and provided with markings constituting fold lines to present a bottom 1, side walls 2 to 9 and upper edges to be located at the periphery of the finished container, 10 to 17.

The bottom is delimited with respect to the side walls by crease lines 18 and the side walls are delimited with respect to the edges by notches 19.

According to the invention, the crease lines 18 and the notches 19 are all formed on the face of the blank which will constitute the interior of the finished container, so that their female parts are located on this interior face.

When the blank is folded to be put into its final shape, as seen in figs. 4 and 5, the side walls will be straightened inwards while the edges will be folded outwards.

The notches 19 are therefore formed in the usual direction and the folding of the edges does not pose any problem, so that these edges will not only be sharp to have a rectilinear edge but also well planes since no constraint will tend to bend or deform these edges.

On the other hand, the creasing lines 18 are oriented in the opposite direction to that which is necessary to obtain a correct folding, since the folding of the side walls with respect to the bottom will be inward (i.e. towards the female part) instead of going outside.

In other words, it is the bead which will be located outside after folding, so that in principle, the disadvantages indicated above must be found here, that is to say a spring effect. which tends to open the "hinge".

However, the research conducted by the applicants has revealed an advantage..specific to this kind of container because the cardboard part to be covered with a plastic film 20 (fig. 5), it is this film in synthetic material which, when applied correctly over the entire surface of the container, keeps the side walls properly erected.

In addition, and this is a very important point, the air comprised between the inner face of the cardboard part and the plastic film 20 tends to be forced from the center towards the periphery of the bottom 1 and when the blank is marked. in accordance with the invention, this air can easily escape along the lines of grooves 18 towards the spaces which remain between the side walls, so that the film applies perfectly without creating any air bubble.

With a traditional creasing line, the opposite effect would be obtained because the delamination effect of the cardboard after folding amplifies the projection of the bead and in a way creates two longitudinal channels on either side of this bead, so that the the air remains blocked in at least the lower channel and causes air bubbles which prevent the perfect bonding of the plastic film on the cardboard part.

The lines 19 could be traditional creasing lines since their female parts being provided on the internal face of the container, the folding of the edges towards the outside would be in the right direction.

However, in accordance with the invention, it is important that the folding of the edges relative to the side walls is as clean as possible because this edge must have a precision function when one wants to close this container by means of a heat-sealed lid. on this ledge.

It is therefore necessary that the edges 10 to 16 covered with the plastic sheet 20 are perfectly flat, rigid and are not subject to any permanent stress.

This is why, instead of providing a creasing line 18 with a female part and a male part, a cut is provided over a depth x (fig. 3) which is of the order of half the thickness y cardboard blank.

It is clear that such a cut weakens the cardboard and removes any waterproofing in case it is coated with an outer layer.

However, as the plastic sheet is intended to cover both the edges and the side walls, this plastic sheet 20 closes the cutout 19 by restoring the seal (or by creating it) and keeps the edges perfectly horizontal.

It can be seen that the cutting of the lines 19 allows the air therein before the establishment of the plastic sheet 20 to escape laterally, which again avoids the formation of bubbles.

The important thing is to create an extremely sharp fold line between the edges and the side walls, instead of the cutout 19, shown in the drawing in the form of a continuous cut, provide aligned perforations which ensure both correct bending and air delivery to the outside.

Claims (3)

1. Method for marking a container from at least one blank cut out and provided with markings forming folding lines, this blank subsequently being intended to form a volumetric body by bending along these lines for the purpose of displaying a bottom (1), walls (2 to 9) which extend at an angle to the plane of the bottom (1), and at least one flange (10 to 17) which extends at an angle to the plane of the wall (2 to 9) with which it is integral, characterised in that all the markings (18 and 19) are produced on the surface of the blank intended to correspond to the inside of the container, in such manner that their female sections are situated on this surface, the folding lines between the bottom (1) and the walls (2 to 9) being grooved lines (18), that is to say lines which on one face comprise a hollow or female section and a raised section on the other face, that the blank is thereupon folded along these lines (18 and 19) towards the outside in the case of the flange or flanges (10 to 17) and towards the inside in the case of the walls (2 to 9) and that the container thus erected is held, whereupon the entire marked surface which forms both the inside of the container and its flange has applied on it a continuous hermetic film which covers the folding lines (18 and 19) and maintains the container in its shape, the grooved lines (18) between the bottom (1) and the walls (2 to 9) being such that they allow the air enclosed between the blank and the film to escape sideways along the grooved lines (18).

2. Method according to claim 1, characterised in that the markings corresponding to outward folds comprise an incision (19) which cuts the blank through a fraction (x) of its thickness (y).

3. A cardboard blank cut out and marked according to either of the above claims 1 and 2.

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