EP0333605A1 - Package made of a thin folded blank with reinforcing of the welds - Google Patents

Abstract

The package for an article of convex shape, made from a paper- plastic material compound is folded and then the folds are welded over the edges and reinforced either by the addition of a band of paper- plastic material compound, or by the folding and welding of the edge thus folded in such a way that the edge of the folding prevents the opening by delamination of the folds. The carrying out of welding whose spacing varies makes it possible to facilitate assembly of the package. <IMAGE>

Description

The present invention relates to a packaging for a convex shape obtained from a pleated thin sheet of the kind described in French patent application No. 86.03956 of March 17, 86, and it relates more particularly to the method of fixing the plies together. .

We know the way to make a packaging from a sheet of initial rectangular shape, which is first folded according to dimensional criteria defined according to the object to be packed, the folds being then fixed together on their edge, along a narrow strip perpendicular to the folds, by various fixing methods such as gluing, welding, adhesive bonding. It is thus known a number of means for fixing the plies together, in particular from lines of heat-activated glue previously deposited on the sheet before pleating in directions substantially parallel to each other. It turns out that in a certain number of applications, an extremely light kraft is used as the sheet, which does not support any coating of heat-activated adhesive, especially if the latter is in the form of an aqueous solution, because it disrupts the structure of the paper. This type of paper is generally used in combination with a layer of plastic material, which coats one of its faces, and which gives it a certain number of additional properties such as the solidity, the water and fat tightness. . The layer of plastic material can consist for example of polyethylene which is hot deposited by extrusion through a die, but the plastic material can also be brought in the form of a thin film which is fixed by gluing to the paper. When it is a polyethylene and paper complex and that it is pleated, as indicated in said patent application, there is between two successive plies on one side a paper side against a paper side, and the other side a coated side against a coated side. To fix the folds together, as indicated in said patent application, it suffices to apply a sufficiently hot electrode to the paper, along a line substantially perpendicular to the folds, so as to melt the plastic which is welded during cooling. to the one on the wall in front. Under these conditions, the fold is welded on the plastic coating side and free on the other side. The advantage of this type of welding is that the folds are fixed without having to add another product to the paper-plastic complex. But this way of proceeding has a drawback: When you pull on the folds as if you wanted to open them, you can see that the weld thus obtained works on the peel and that it is ultimately very fragile. Indeed the traction causes delamination between the paper and the plastic coating material, so that the fold opens relatively easily and we do not obtain the resistance that we would be entitled to expect from this type of fixing folds. Another drawback concerns the production of this weld, which is disturbed by the fact that on the coating side, the plastic coating material is in direct contact with either the electrode or the counter electrode, and it is necessary to interpose a "Teflon" fabric if you want to avoid sticking of the electrode or counter electrode on the coating of the paper. On the industrial level it is preferable to avoid having to resort to this kind of device because in the long term, the fabric of "Teflon" is impregnated with plastic material which tends to burn and which makes the fabric lose its protective function. It is then necessary to change the fabric which is a waste of time.

The invention consists in providing solutions to this welding problem in order either to reduce the forces which are supported by the welded part of the fold, or to transfer them partially elsewhere, or to make a combination of the two.

One way of reducing the forces supported by the welds (1) Fig. 1 of the folds (2) is to size the packaging, according to said patent, so that during assembly the tensions remain low. This is obtained by the shape of the folds (2) combined with the distance (3) between the welds (1). If the packaging is correctly adjusted according to the terms of the said patent, we note in particular that having deployed the pleating around the convex object to be packaged, we experience difficulties when, having made a complete revolution of the convex object , we proceed to overlapping of the first layer by the second because the volume has changed, it has increased in the thickness of the packaging itself. It is therefore necessary that the part (4) Fig. 2 of the packaging which is mounted last has a distance (5) between the welds (6) and (7) greater than the distance (8) between welds (6) and (7) of the part (9) which mounts first. One way to do this is to vary the spacing of the welds (6) and (7) between the start (9) and the end (4) of the package. When the welds are straight, a variation of 5 to 15% of the spacing allows an acceptable result to be obtained. It is desirable to identify the direction of assembly of the packaging, and therefore provide a tongue (10) which also serves as an application point for the fingers at the time of assembly.

One way to strengthen the welds is to add the plastic coating side (11) Fig. 3 a thin sheet (12) not pleated itself coated on one face (13) with a plastic material which can be welded to the plastics material of the pleated sheet, the coated part (13) obviously being turned towards the side of the folds (14). This technique obviously does not apply to flat folds whose folds are asymmetrical like those described in said patent. We can for example use the same type of support as that used to make the pleating. Under these conditions when the hot electrodes are applied to perform the welding (15), the plastic material is sandwiched between two layers of paper which is alone in contact with the hot electrodes and there is no longer any problem of sticking. with these at the time of welding. The attached sheet (12) is a strip projecting sufficiently on each side of the weld (15) so that the forces imparted to the weld (15) are not fully transmitted to the edge of the strip (12) which could cause it to tear . When pulling on the folds (2) Fig. 1 in the extension of the welds (1) as if we wanted to undo the folds, we see that it is the attached strip (16) which is stretched and which supports most of the effort. The welds (1) as well as the attached strip (16) then work in shear which is very favorable to good resistance of the assembly.

Finally, if we want to avoid having to add a strip which is a significant constraint, another way of reinforcing the weld consists in folding the edge (17) Fig. 4 of the folds (18) after pleating so that the uncoated part (19) of the paper is on the outside, and to weld this edge (17) thus folded taking care that the edge (20) of the folding is affected by the weld (21). The electrode as well as the counter-electrode being in contact with the paper support at the time of the welding and partially projecting beyond the edge (20), do not pose any bonding problem. We note that this way of proceeding creates, at the edge (20), an unfolding brake sufficient to block the extension of a possible delamination due to the fact that these are two pleats which are welded one on the 'other. In practical terms, the folding of the side edges (22) Fig. 5 is done after pleating and cutting to the desired width of the packaging. The problem is to keep the pleating in shape during the lateral folding. There are multiple ways to operate. The pleating can be pinched between two walls which move at the same speed as the latter during the folding and welding of the edges (22). It is also possible to pre-weld the folds (24), on their edge before folding, at a sufficiently low temperature so as not to disrupt the final weld (23) and not to integrate problems of bonding of electrodes. This presoldering can be done at the time of pressing the plies, insofar as the pressing cylinder has heated and temperature controlled zones. This type of fixing of the folds by folding the edges does not make it possible to have, beyond the weld (23) and the edge (25), a zone called "C" in the said patent application premising the recovery of the central surface of the convex body to be covered and delimited by the weld (23) of the folds (24). As distance "M" (26), between the welds (23), the value of which is determined, in said patent application, as a function of the main dimensions of the convex object to be packaged, the distance between the edges ( 25). It is thus admitted that there may be a slight delamination of the paper and the plastic material at the welds (23) due to the tearing stresses when the spacing of the folds (24) during assembly of the packaging. However, delamination is stopped when it comes into abutment against the edge (25). to limit the extent of surface delamination, it is necessary to fold and particularly the weld (21) Fig. 3 of a width (27) as small as possible. This procedure also prevents the weld zone (21) from forming in the form of a chimney when the packaging is in place on the convex body to be packaged. Finally to facilitate the assembly of the packaging Fig. 5 as described above, it is possible to fold the edges (28) FIG. 6 so as to increase the distance "M" (29) between the edges (30) from the start (31) to the end (32) of the pleated packaging. The folding of the edges (28) being substantially rectilinear, it is preferable that the cutting is made to give the pleated packaging before folding the edges and welding the shape of a trapezoid. Otherwise we would be left with an excess of paper, turned inside out, which could disturb the assembly. In the latter case, there is a crossover of folds at the time of welding, which is favorable to the solidity of the fixing.

Claims (3)

1 - Packaging for convex shape obtained from a thin pleated sheet, characterized in that the packaging being produced from a paper-plastic complex, the reinforcement of the weld at the edge of the folds is obtained by adding d '' a strip of uncreated paper-plastic complex which is welded simultaneously with the welding of the plies while making it possible to avoid direct contact of the welding electrodes with the plastic. 2 - Packaging for convex shape obtained from a pleated sheet, characterized in that the packaging being produced from a paper-plastic complex, the reinforcement of the fixing of the edge of the folds is obtained by folding a narrow strip which is then welded so that the edge of the fold is itself interested in the weld and constitutes a fold blocking element during assembly of the packaging. 3 - The packaging according to any one of the preceding claims is characterized in that the welds of the edge of the folds have a distance which increases by 5 to 15 percent between the beginning of the packaging and the end of the packaging, in order to facilitate its assembly.

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