Tube skirt decorated with an attractive side seam

Abstract

The invention relates to a flat strip (1) for forming a flexible tube skirt, comprising a decorative film (15) arranged over a primary film (16), said primary film (16) consisting of a succession of layers of a polymer material and comprising a sealable inner layer (14) on the lower surface (20) of the strip (1), said decorative film (15) comprising a sealable outer layer (7) on the upper surface (19) of the strip (1) and a decorative layer (8, 9). The primary film (16) comprises means for stabilising the strip (1) and protecting the decorative layer (8, 9) from overheating.

Description

DECORATED TUBE SKIRT WITH AN AESTHETIC SIDE WELD Field of invention The invention concerns: - a flat multi-layer strip adapted to form a decorated tube skirt; - a decorated flexible tube skirt; - a flexible tube intended for storing and dispensing liquid to pasty products, and more particularly cosmetic and toiletry products; - a method of manufacturing a decorated flexible tube skirt; - a tool allowing the implementation of the manufacturing process of the decorated flexible tube skirt. The tape used in the context of the present invention conventionally comprises several layers of different materials, which combine the different functions that a tube skirt must fulfill, namely flexibility, the ability to retain its deformed shape, the barrier to diffusion (especially water vapor impermeability), the printing medium for decoration, etc. Indeed, the outer appearance and decoration are very important in the field of soft tubes, especially for cosmetics and toiletries. The tubes must have decorated outer surfaces, including metallic, holographic, shine effects, and with a large color palette. Soft tubes are made from a multi-layer flat strip that is rolled into a sleeve called a tube skirt. The rolling is carried out in such a way that the strip is shaped into a cylinder, the lateral edges of said strip being placed opposite one another and then welded together to form a lateral weld. A tube head, comprising a dispensing orifice, is then welded to one end of said skirt. The tube thus produced is delivered to the packager, upside down and its dispensing orifice being closed - for example by a cap screwed onto the neck. The conditioner fills the tube by pouring the product to be packaged through the open end of the tube. Once the tube is filled, its open end is flattened and then welded. The tube decoration is present on the flat strip, before its transformation into a tube skirt. The difficulty lies in obtaining a lateral weld that is as aesthetic as possible, that is to say the least visible and with a decoration going as close as possible to the weld on either side, while guaranteeing robustness in the weld in order to prevent the product contained in the tube from subsequently leaking or being polluted by humidity or the like. State of the art There are several techniques for making a side weld of a tube skirt. The first consists of positioning the two lateral ends of the strip edge to edge, then welding them: - either by having previously bevelled the edges so that they fit asymmetrically against each other either by adding a tape at the seam between the edges This technique requires high precision as to the edge-to-edge positioning, which is unfortunately rarely the case because the guidance of the tape is not obvious in the manufacturing devices of tube skirt. The second technique consists of covering one edge with the other edge: this is an overlapping process. In this case, the positioning accuracy is less important, which facilitates the process. The main disadvantage is that it is generally necessary to avoid any decoration in the overlapping area because of its lack of resistance to welding conditions. This results in a line of some undecorated width visible along the tube in the region of the weld. In addition, the weld bead is generally clearly visible from the outside, and unsightly. To solve this problem, it is known to place a decorative layer between a sealable upper layer and a lower support layer, so that it is practically not damaged during the lateral welding step. In this case, the decorative layer extends over the entire surface of the strip. This decorative layer can also be placed upside down under the lower support layer in order to be better protected, but this technique is expensive and therefore interesting only for large quantities of tube skirts to be produced. In all cases, such a decorative layer only makes it possible to insert a colored, and / or shiny and / or metallic “background” on the tube skirt. The next step is to make a print on the strip so that distributors can affix their brand and the various information relating to the product poured inside the tube. This step is performed before the sleeve forming step and the lateral welding step. It is therefore an additional layer added on top of the sealable top layer. However, this printing layer is fragile, and the ink tends to flow under the effect of the heat applied to the top of the overlapping zone during welding. It is therefore customary not to carry out printing on the two lateral edges of the strip which will form the zone of overlap of the tube skirt, especially since there are numerous inks which are not weldable. The same applies to the protective varnish applied to the inks, which cannot be welded. More specifically, it is customary to heat both the outer surface and the inner surface of the tube skirt at the level of the overlap zone, in order to melt material, not only at the surface of the overlap zone. , but also in the thickness of the overlap zone, which allows the production of a robust and durable weld over time. Conventionally, the heating temperature T1 applied to the outer surface of the tube skirt is higher than the heating temperature T2 applied to the inner surface of the tube skirt. The objective is to melt the outer surface before melting the inner surface, so that the layers close to the inner surface, including in particular a barrier layer sealing the tube skirt, do not have time to get mixed up and therefore create points of weakness in the overlap zone. Indeed, for a classic structure of a multilayer strip, if T2 were greater than T1, the internal layers would mix together while melting and would destructure the strip at the level of the overlap zone, thus creating points of weakness resulting for example in a poor sealing barrier no longer guaranteeing optimum preservation of the cosmetic product which will be poured inside the tube. The objective of the present invention therefore consists in proposing a strip structure for a tube skirt which allows the production of an aesthetic lateral weld from the outside, and sufficiently robust to maintain the desired barrier effect. This band structure must also allow the application of a wide range of inks in the overlap zone of the tube skirt. The invention also aims to provide a method for producing such an aesthetic and robust side weld, as well as a device for implementing this method. Summary of the invention The present invention goes against technical prejudices, by reversing the heating temperatures so as to heat the internal surface more than the external surface of the tube skirt in the overlap zone to form the lateral weld. In this case, the heating temperature T1 applied to the outer surface of the tube skirt is lower than the heating temperature T2 applied to the inner surface of the tube skirt. Since the heating temperature T2 applied to the internal surface of the tube skirt is higher than in the prior art, there is a risk of degradation of the layers, in particular the barrier and decorative layers, as well as a risk of significant deformation of the tube skirt at the level of the lateral weld zone. In order to avoid any deterioration of the layers, a specific structure has been developed for the production of the strip forming the tube skirt. Thus, the present invention relates to a flat strip, suitable for forming a flexible tube skirt, comprising a decorative film superimposed on a primary film, said primary film consisting of a succession of layers of polymeric material and comprising an internal layer that can be sealed at the level of the lower surface of the strip, said decorative film comprising a sealable outer layer at the upper surface of the strip and a decorative layer. This strip is mainly characterized in that the primary film comprises means for stabilizing the strip and for protecting the decorative layer against heating. Consequently, the film on which the heating temperature T2 is applied, that is to say the primary film, is consolidated in order to avoid deformation of the strip forming the tube skirt and to retain a decorative layer in a excellent condition even after the completion of the side weld. Said means of stabilization and protection consist of at least two stabilizing layers made of ethylene vinyl alcohol (EVOH). The mechanical behavior of EVOH differs from that of other layers because it is more rigid. Even in a softened state following heating for the realization of the side weld, the EVOH retains its structure and does not mix with the adjacent layers. It thus acts as a reinforcement or a reinforcement within the strip, and makes it possible to maintain stability throughout the thickness of the overlap zone. In addition, EVOH is a polymeric layer with a barrier effect vis-à-vis oxygen and aromas, which makes it possible to limit the loss of aroma or perfume of the packaged product. He therefore has a dual function within the band. Advantageously, the presence of two layers of EVOH guarantees the stability of the film. The distribution of these layers is also important. Indeed, they are arranged symmetrically with respect to the median plane of the primary film, and at a distance from each other, so as to be placed in the upper and lower halves of the primary film and not in the center in an adjacent manner. This arrangement allows an optimal distribution of the reinforcements in the thickness of the primary film. Preferably, the barrier stabilizing layers are each located at a relatively small distance from the upper and lower surfaces of the primary film, typically at 50-120 μηι. By reducing the cumulative thickness of the layers between, on the one hand, the upper surface and one of the proximal barrier stabilizing layers, and, on the other hand, the lower surface and the other proximal barrier stabilizing layer, the less at first, the losses in humidity (and in perfumes) of the product contained in the tube. Even if the stabilizing barrier layer closest to the inside of the tube ends up being degraded by the effect of humidity, it slows down the diffusion of humidity and perfumes to the other barrier layer which remains totally effective much longer. The primary film is a film composed of symmetrical layers and obtained by blowing. The primary film has a perfectly symmetrical structure with respect to its median plane, that is to say having symmetrical layers having substantially the same thickness and consisting substantially of the same material. All the layers forming the primary film are continuously bonded together. The idea is to try to limit the heterogeneities of behavior of the different layers by aiming for a symmetry with respect to the median plane of the film that is as perfect as possible, not only geometrically but also at the level of the constituent material, by not being satisfied with the identity of the chemical composition of the base monomer(s). Thus, the symmetrical layers have substantially the same thickness, that is to say different thicknesses between them of less than 2μηι for thicknesses less than 20 μηι and less than 10% for greater thicknesses. The symmetric layers consist of substantially the same material, i.e. polymers consisting not only of monomers of the same chemical composition but also of macromolecules of comparable lengths, resulting in molar masses (number average) n M substantially equal, ie differing from each other by less than 10%, preferably by less than 5%. The symmetry with respect to the median plane of the film makes it possible in particular to compensate for the shrinkages or differential deformations between layers occurring on one side of the film by the shrinkages or differential deformations between layers occurring on the other side of the film. It is important that the film has symmetry at the level of the EVOH layers, which are rigid layers, in order to avoid any risk of the formation of unbalanced residual stresses. In order to obtain symmetrical layers, it is customary to use a blown film. To obtain such a film, the process consists in co-extruding and inflating a cylindrical multilayer sheath using an annular co-extrusion die head. The sheath is inflated so that it forms a thin-walled bubble which is then pinched and flattened, with the inner layer of the sheath pressing against itself. The double internal layer thus obtained is produced using a material capable of adhering to itself under the effect of the flattening pressure of the bubble, at the typical temperature of the pinching of the bubble, namely between 40° C. and 80°C. It is for example a thermoplastic material such as a linear polyethylene, in particular chosen from polyethylene hexene copolymers, more particularly a linear low density polyethylene hexene copolymer (PEL-BD), a very low density polyethylene (PE -VLD density between 0.88 g / cm3 and 0.93 g / cm3), a polyethylene obtained with single-site metallocene catalysts, an EVA (ethylene-vinyl acetate copolymer), or even graft copolymers such as an EAA (Ethylene-acrylic acid copolymer or even ethylene-alkyl acrylate copolymer), in particular an EAA ionomer, for example a Surlyn (trademark registered by the company Dupont de Nemours) or else a copolymer (ethylene-acrylic ester) such as an EBA (ethylene-butyl acrylate copolymer) or an EMA (ethylene-methyl acrylate copolymer or even ethylene-maleic anhydride copolymer). Said sealable inner layer and said sealable outer layer are made of medium density polyethylene (MDPE). The fact of having two sealable layers in an identical material promotes the welding between the two layers since they tend to mix homogeneously when they are in contact with one another and softened by heating. In fact, the outer sealable layer comes into contact with the inner sealable layer in the overlap zone during the shaping of the strip into a sleeve. These two layers must therefore be able to be easily sealed together. In addition, these internal and external sealable layers are also found directly in contact with the internal and external heating means during the production of the lateral weld. Thus, the choice of the material making up these layers is all the more important since it must be adapted to the heating temperatures. Advantageously, the material chosen must therefore have a relatively high melting point to be lower than the heating temperature T1 applied to the outer surface of the tube skirt so as not to deteriorate during lateral welding and to maintain a Aesthetic and clean exterior appearance. Indeed, it is important to avoid the fusion of the sealable outer layer and the cracking of nearby inks. In particular, MDPE has a relatively high melting point, between 122°C and 125°C, which makes it possible to have a heating temperature T1 applied to the outer surface of the tube skirt which can go up to 120° C, without risk of deterioration of the sealable outer layer. The melt index of MDPE, for tests carried out at 190° C. with a loaded piston having a standard mass of 2.16 kg, is between 0.9 and 3.5 g / 10 minutes. Finally, the density of MDPE is between 0.930 and 0.935. The use of MDPE at the sealable inner layer is also advantageous during the last stage of the manufacture of the tube, where once it is filled with the product to be packaged, the open end of the tube is flattened, which means that the round-shaped sealable inner layer becomes flattened and forms a double layer of MDPE which can then be easily welded to close the filled tube. The decorative layer comprises polyethylene terephthalate (PET), and may have a metallic, or holographic, or other coating. The example of the metal will be taken in the remainder of the description. PET is particularly advantageous in the sense that it provides stability in the decorative film. Indeed, unlike PE or PP, PET is much more rigid, and has a high density, making it possible to stiffen the decorative film, like the layers of EVOH in the primary film. However, PET and metal are heat sensitive and brittle when heated. This constitutes an additional reason for limiting the heating temperature T1, since this decorative layer of metallized PET is located close to the upper surface of the strip, given that the objective is to be able to visualize the decoration from the outside of the bandaged. At the strip portion which is covered during the formation of the tube skirt, the two layers of EVOH located under the metallized PET layer make it possible to protect the latter against the heating temperature T2. In addition to the metallized PET layer, the decorative film comprises additional decoration means, such as an additional printed layer extending over part of the outer surface of the sealable outer layer. Indeed, the metallized PET layer can produce a uniform decorative background, while the printed layer makes it possible to affix a decoration based on drawings and writings which is superimposed and added to the uniform background. More specifically, the band comprises a central zone bordered by two side borders, said additional printed layer extending over the central zone as well as over one of the two side borders. Thus, the printed layer does not extend over the entire surface of the strip. As explained previously, the printed layer is not sealable, and therefore must not cover the portion of strip which will be covered during the production of the side weld of the tube skirt. The decorative film comprises an additional protective layer of the printed layer extending over the entire outer surface of the printed layer Just like the printed layer, the protective layer, of the varnish type, is not sealable, and therefore must not not cover the portion of tape that will be covered when making the side weld of the tube skirt. As previously announced, the invention also relates to a tube skirt formed by rolling a flat strip as described above, and comprising a side overlapping weld, a first of said side edges covering the second of said side edges. In this way : - the printed layer extends over the central zone as well as over the first lateral edge; - the sealable inner layer at the level of the first side edge is sealed to the sealable outer layer at the level of the second side edge and this directly, that is to say without interposing additional elements, such as a ribbon, a strip, a tab. By this is meant a band of small width interposed at the level of the overlap zone between the sealable inner layer and the sealable outer layer. The invention also relates to a flexible tube intended for storing and dispensing liquid to pasty products, and comprising a tube skirt as described above. The invention also relates to a method for producing a tube skirt for a flexible tube, said tube skirt being manufactured from a flat strip comprising a decorative film superimposed on a primary film, said primary film comprising an inner sealable layer at the lower surface of the strip and two stabilizing layers, said decorative film comprising an outer sealable layer at the upper surface of the strip, and a decorative layer. This process includes the following steps: winding the flat strip in the form of a sleeve to shape the tube skirt; superimposing a first side edge of the strip on a second side edge of the strip to form an overlap zone, the sealable inner layer of the primary film of the first side edge coming to cover the sealable outer layer of the decorative film of the second side edge; - apply a heating temperature T2 inside the tube skirt at the level of the internal face of the overlap zone to produce the lateral weld of the tube skirt; simultaneously with the application of the heating temperature T2, apply compression between the outer and inner faces of the overlap zone in order to finalize the lateral welding of the tube skirt. Advantageously, the heating temperature T2 is higher than the melting temperature of the sealable inner layer of the primary film and of the sealable outer layer of the decorative film, and lower than the melting temperature of the decorative layer of the decorative film and the two stabilizing layers of the primary film. Hence the choice of the structure detailed above, with: the sealable inner layer of the primary film and the sealable outer layer of the decorative film made of MDPE whose melting temperature is around 122 to 125°C - the decorative layer of the decorative film made of PET whose melting temperature is around 250°C - the two stabilizing layers of the primary film composed of EVOH whose melting temperature is around 183°C - the intermediate layers of the primary film (apart from the EVOH layers) whose melting temperature is between 87°C and 123°C. Thus, the temperature T2 must at least reach 125°C in order to melt the sealable layers and the intermediate layers which will mix and form the core of the lateral weld. However, the temperature T2 must not reach 183° C. so as not to melt the stabilizing layers and the decorative layer, which allow the tube skirt to retain stability and a certain rigidity in the overlap zone. In summary, the temperature T2 will preferably be between 125°C and 180°C. Other features, optional and non-limiting, are set out below: - a heating temperature T1 is applied, simultaneously with the heating temperature T2, on the outer face of the overlap zone: the fact of slightly softening the outer face of the tube skirt makes it possible to obtain a weld line which is more melted and less clear, and therefore less visible to the naked eye. - the heating temperature T1 is lower than the heating temperature T2, in other words when a compression is applied between the outer and inner faces of the overlap zone, the heating temperature T1 to which the outer surface is brought is lower than the heating temperature T2 to which the internal surface is brought. The objective is for the heat to come approximately 80% from T2, and only 20% from T1, since the main heating allowing the realization of the side weld must come from inside the tube skirt, and not from the outside, in order to have a weld bead located inside the tube skirt, and therefore not visible from the outside. - the heating temperature T1 is lower than the melting temperature of the material which constitutes the sealable outer layer of the primary film: in fact, the sealable outer layer must not melt in order to remain uniform and to retain an aesthetic appearance from the outside the tube - the sealable outer layer of the primary film is made of polyethylene, the melting temperature of which is greater than 120°C, the heating temperature T1 being less than 120°C: this temperature limitation makes it possible to add prints (for decoration ) on the sealable outer layer of the decorative film without the ink flowing and cracking when heated. - the heating temperature T1 is preferably less than 100° C.: this makes it possible to use a wider range of inks. - Instead of applying a heating temperature T1, it is possible to carry out a step of preheating the overlap zone before the superposition of the side edges. - The preheating consists of blowing hot air into the gap separating the first side edge from the second side edge before they are superimposed. - It is also possible not to apply a heating temperature T1, nor preheating, and to heat the overlap zone only from the inside of the tube skirt with T2; - A cooling step of the overlap zone is carried out after said compression step. - Said cooling step consists of cooling the internal face of the covering zone. - The overlap zone has a width preferably between 1.5 and 2.5 mm. In order to set up the process for producing the tube skirt, and in particular the side weld, a specific manufacturing device has been set up. Indeed, since the internal heating temperature T2 now constitutes the main heating for the realization of the lateral weld, it is then necessary to cool the internal face of the overlap zone and not the external face of the overlap zone as it was of use to do. Adaptations have therefore had to be made to the conventional systems. Conventionally, since T1 is greater than T2, the cooling is carried out mainly on the external face of the covering zone of the tube skirt by means of a mobile cooling strip which also ensures the compression of the covering zone. , and driving the tube skirt within the device. This moving strip can provide only the external cooling, or can also provide the external heating upstream of the external cooling. It is a mobile strip closed on itself, driven via pulleys, and developing in parallel with a mandrel around which the flexible strip forming the tube skirt is wound. The main drawback with the use of strips for heating and cooling is that it is difficult to control the temperature of the strip, due to its mobility, its thickness, and the material of which it is made. Moreover, it is a complex system of implementation with the pulleys. There are also devices where a cooling system is arranged within the mandrel, on the inside of the tube skirt, as disclosed in the document FR1571778. However, it is a system used to cool the mandrel itself, and the overlap zone indirectly. This cooling system is therefore not very efficient. The manufacturing device of the invention comprises a frame, an elongated cylindrical mandrel, a means for advancing and guiding the flexible strip to put it in the form of a sleeve around the mandrel, one of the side edges of this strip coming to cover the other lateral edge to form an overlap zone to be welded, an internal heating means located in the mandrel to heat the internal face of the overlap zone, an internal cooling means located in the mandrel to cool the face inside the covering zone and downstream of the interior heating means. This device is mainly characterized in that said cooling means is arranged facing the overlap zone and configured to be in direct contact with the overlap zone. Thus, the cooling means acts directly on the covering zone of the tube skirt, and does not have the function of cooling the mandrel. The latter only serves as a support for the cooling means. Other features, optional and non-limiting, are set out below: - Said cooling means is fixed in the device. - The cooling means consists of a cooling strip inserted into a corresponding groove made in the chuck. - Said cooling bar comprises a channel inside which circulates a cooling fluid. - the cooling bar comprises a flat wall closing the channel in the upper part and being in direct contact with the internal face of the covering zone. - Said channel defines a crenellated inner path. - Said channel comprises a staggered arrangement of cooling fluid guide fins, defining said internal crenellated path. - Said fins extend orthogonally from the flat wall in the direction of the central axis of the mandrel. - Said fins form two staggered rows oriented in a longitudinal direction parallel to the central axis of the mandrel. - Said fins correspond to tabs of rectangular appearance. - Said groove defines a parallelepipedal hollow space. - The cooling bar has a generally parallelepipedal outer shape matching the shape of the walls of said groove. Presentation of figures The invention will be better understood, and other aims, details, characteristics and advantages thereof will appear more clearly during the detailed explanatory description which follows, of at least one embodiment of the invention given in By way of purely illustrative and non-limiting example, with reference to the appended schematic drawings. In these drawings: - Figure 1 is a top view of a strip according to the invention; - Figure 2 is a cross-sectional view of the strip of Figure 1; - Figure 3 is a cross-sectional view of a tube skirt formed from the strip of Figure 1; - Figure 4 lists the different layers at the level of the overlap zone of the tube skirt of Figure 3; - Figure 5 shows the overlap zone of the tube skirt of Figure 3 before making the side weld, according to a first embodiment; - Figure 6 shows the overlap zone of the tube skirt of Figure 3 before the realization of the side weld, according to a second embodiment; - Figure 7 shows the overlap zone of the tube skirt of Figure 3 after the completion of the side weld, for the first and second embodiments; - Figure 8 is a perspective view of part of the tools necessary for making the side weld of the tube skirt of Figure 3; - Figure 9 is an exploded view of the cooling device belonging to the tool of Figure 8; - Figure 10 shows in detail the cooling strip of the cooling device of Figure 9; - Figure 1 1 shows in detail the heating device belonging to the tool of Figure 8. detailed description The terms "external" and "exterior" are used to indicate that a layer faces the exterior of the tube skirt thus formed. Likewise, the terms "inner" and "inner" are used to indicate that a layer faces the inside of the tube skirt thus formed. Referring to Figures 1 and 2, there is shown a section of a flat strip 1 according to the invention, which will then be rolled up to form a tube skirt. This strip 1 comprises a central zone 4 bordered by a first 2 and a second 2′ side edges. It is known to obtain such a strip 1 by using multilayer films obtained by extrusion or by lamination-bonding. The flat strip 1 according to the invention comprises a succession of layers. Concretely, it is composed of a decorative film 15 surmounting a primary film 16. In each embodiment, the decorative film 15 comprises a sealable outer layer 7 located at the level of the upper surface 19 of the strip 1, and a decorative layer 8,9 consisting of a PET base 9 located under the outer layer sealable 7. The decorative layer 8.9 is applied over the entire surface of the decorative film 15 and is located under the sealable outer layer 7. In other words, there are no areas belonging to the decorative film 15 which are not covered by both the decorative layer 8.9 and the sealable outer layer 7. This decorative layer 8.9 may contain a metallic or holographic film 8, or other, depending on the type of decoration chosen. It constitutes the background of the decoration of the tube which will subsequently be formed. Preferably, this film 8 is applied on top of the PET base 9, so that it is oriented in the direction of the upper surface 19 of the strip 1 . In another possible configuration, this film 8 could be applied to the underside of the PET base 9. The PET base consists of a high-density layer, which has a reinforcement role during the formation of the tube skirt. This layer 9 is hatched in figure 2. The decorative layer 8.9 of the decorative film 15 has a thickness of between 5 and 50 μηι, preferably between 10 and 30 μηι. In all cases, the sealable outer layer 7 is located above the decorative layer 8.9 and therefore protects the latter against impacts / scratches associated with future handling of the tube skirt thus formed. The sealable outer layer 7 is preferably transparent so that the decoration can be clearly visible from the outside of the tube which will be formed. This sealable outer layer 7 is made of PE, and can also be multilayered. Preferably, the sealable outer layer 7 consists of three PE layers. Preferably, the material chosen for the three layers will be MDPE for its technical characteristics. In general, the sealable outer layer 7 of the decorative film 15 has a thickness of between 5 and 90 μηι, preferably between 5 and 80 μηι. Optionally, in addition to the decorative layer 8.9, the decorative film 15 can be printed directly on the sealable outer layer 7, in order to add decoration. Thus, an additional printed layer 6, as well as a protective layer 5 (varnish type) can extend over part of the outer surface of the decorative film 8.9. More precisely, these two printed 6 and protective 5 layers extend over the central zone 4 and the first lateral edge 2 of the strip 1 . In other words, the two printed 6 and protective 5 layers extend over the entire surface of the strip 1, apart from the second lateral edge 2' (see hatched area in FIG. 1). This is the side edge 2' which will be covered by the first side edge 2 during the formation of the tube skirt. Since the ink and the varnish are not sealable, it is imperative not to put any on the second edge 2' which will be overlapped for the realization of the lateral weld. The primary film 16 is a multilayer film which comprises a sealable inner layer 14 located at the level of the lower surface 20 of the strip 1, as well as two stabilizing layers 11,13 distributed symmetrically in the primary film 16 with respect to its plane median X and hatched in Figure 2 to show their reinforcing role. The primary film 16 can comprise up to 22 layers. At least one layer consists of a barrier layer making it possible to seal against moisture and preserve the aromas with respect to the product which will be poured inside the tube thus formed by the rolled-up strip 1. The other layers can be chosen from polyethylenes, such as for example a low density polyethylene (LDPE), a linear low density polyethylene (LLDPE), a medium density polyethylene (MDPE), a high density polyethylene (HDPE), or a mixture of these polyethylene, or ethylene-vinyl acetate (EVA). Between these different layers, a tie layer and / or an adhesive coating can be applied in order to improve the adhesion between the layers. The primary film 16 has a thickness between 100 and 500 μηι, preferably between 200 and 350 μηι. The primary film 16 can be a blown film, in order to present a symmetry between its different layers. In this case, the central double layer 12 will preferably be composed of EVA which has good abilities to stick to itself when the blown sheath is flattened. The two stabilizing layers 11.13 are distributed symmetrically on either side of the median plane X of the film 16 produced by the double layer of EVA 12. These stabilizing layers 11.13 consist of EVOH. It turns out that EVOH is also a material capable of performing the barrier function for waterproofing. Consequently, the two layers of EVOH 1 1 , 13 fulfill the double function of reinforcement and sealing within the primary film 16. Finally, the sealable internal layer 14 also has its double, located symmetrically in the primary film 16, corresponding to a sealable outer layer 10 of the primary film 16, and which is therefore in contact with the lower layer of the decorative film 15. The two sealable layers 10,14 of the primary film 16 are made of MDPE, in order to correspond to the outer layer sealant 7 of decorative film 15. Here are examples of detailed structure forming the strip 1 according to the invention. Example 1: Example 2 Thickness Material layer Correspondence with figures 1 and 2 (μπι) 1 MDPE 15 2 MDPE 22 Sealable outer layer 7 3 MDPE 13 4 Coating Adhesive layer adhesive 5 foil Decorative foil 15 metallic (around 12 Decorative layer 8.9 the top) + PET 6 Coating Adhesive layer adhesive 7 MDPE 72 Sealable outer layer 10 8 Resin 7 Adhesive layer 9 EVOH 7 Stabilizing layer 1 1 10 Resin 7 Adhesive layer 1 1 MDPE 40 12 EVA 17.3 x 2 Core layer 12 Primer film 16 13 MDPE 40 14 Resin 7 Adhesive layer 15 EVOH 7 Stabilizing layer 13 16 Resin 7 Adhesive layer 17 MDPE 72 Sealable inner layer 14 During the formation of the tube skirt, by rolling up the strip 1, the first lateral border 2 comes to cover the second lateral border 2 ', as illustrated in figure 3. Figure 4 shows the succession of layers in the overlap zone 3. For greater clarity, the layers located at the level of the second side border 2 'have a numbering corresponding to the layers located at the level of the first side border 2 since they are the same layers, but are numbered with a 'prime' additional to differentiate them. We find in order, from the outside of the tube skirt to the inside of the tube skirt: - 5: the protective layer of the first side border - 6: the printed layer of the first side border - 7: the sealable outer layer of the decorative film of the first side border - 8: the metallic coating of the decorative film of the first side border - 9: the PET layer supporting the metallized coating of the decorative film of the first side border 10: the sealable outer layer of the primary film of the first side border 1 1: the stabilizing layer of EVOH of the primary film of the first side edge 12: the central layer of the primary film of the first side border 13: the stabilizing layer of EVOH of the primary film of the first side border 14: the sealable inner layer of the primary film of the first side border - 7': the sealable outer layer of the decorative film of the second side border - 8': the metallic coating of the decorative film of the second side border - 9': the PET layer supporting the metallized coating of the decorative film on the second side border 10': the sealable outer layer of the primary film of the second side edge 1 1': the stabilizing layer of EVOH of the primary film of the second side edge 12': the central layer of the primary film of the second side border 13': the stabilizing layer of EVOH of the primary film of the second side edge 14': the sealable inner layer of the primary film of the second lateral edge. The adhesive intermediate layers are not represented for greater clarity. It should be noted that the sealable inner layer 14 of the primary film 16 of the first lateral border 2 is located directly on the sealable outer layer 7' of the decorative film 15' of the second lateral border 2'. These two sealable layers 14.7' in MDPE will melt and fuse together during the lateral welding, thus allowing the two lateral edges 2.2' to be welded together. In other words, an additional element interposing at the level of the overlap zone between the sealable inner layer and the sealable outer layer is not necessary to produce the side weld of the skirt. FIG. 5 precisely shows the covering produced for the formation of the tube skirt, before the production of the lateral weld, and according to a first embodiment. In this case, a heating temperature T2 of between 125°C and 180°C is applied to the inner surface 22 of the tube skirt, more precisely to the sealable inner layer 14' of the primary film 16' of the second lateral border 2' in MDPE. Simultaneously, a heating temperature T1, much lower than the heating temperature T2, and lower than 120° C. is applied to the outer surface 21 of the tube skirt, more precisely to the sealable outer layer 7 of the decorative film 15 of the first side border 2 in MDPE. Simultaneously with the heating, the covering zone 3 is compressed at the level of its two external 21 and internal 22 faces in order to help the molten layers to mix well and to adhere to each other in order to produce the lateral welding of the tube skirt. Concretely, the following layers will merge thanks to the heating temperature T2: 14: the sealable inner layer of the primary film of the first side edge - 7': the outer sealable layer of the decorative film of the second side edge - 10': the outer sealable layer of the primary film of the second side edge 12': the central layer of the primary film of the second lateral edge 14': the sealable internal layer of the primary film of the second lateral edge The intermediate bonding layers will also be in fusion. The stabilizing layers 11, 11′, 13, 13′, and the decorative layers in metallized PET 8,9, 8′, 9′ will not melt and will not mix with the other layers, thus making it possible to maintain a order in the layers at the time of welding and after welding, and to maintain stability in the heated structure. The two stabilizing layers of EVOH 11,13 of the primary film 16 of the first lateral edge 2 also make it possible to protect the decorative layer of metallized PET 8.9 against heating from the heating temperature T2, since the layer of PET metallized is sensitive to heating and becomes brittle. This is particularly visible in FIG. 7 where the deformations of the various layers are shown after the completion of the lateral weld. It is clearly visible that the stabilizing layers 11,11′, 13, 13′ and the decorative layers in metallized PET 8, 9, 8′, 9′ are not mixed with the other layers and have simply been deformed under the action of compression. The layers upstream, downstream, and between the stabilizing layers have in turn been mixed and merged. The weld bead is well located inside the tube skirt. It should be noted that the layer of metallized PET 8', 9' of the second side edge 2' has also been protected against heating by the two stabilizing layers of EVOH 11', 13' of the second side edge 2' , in particular in the new junction zone 17 between the two side edges 2,2' in area of ​​the tube skirt. This junction zone 17 is very narrow, the two edges 2.2' being very close, and the discontinuity of the printed layer 6 on the tube skirt is thus minimal. The tube skirt thus formed is aesthetic, and has a robust weld. In a second embodiment, instead of applying a heating temperature T1 to the outer surface 21 of the tube skirt, it is possible to preheat the covering zone 3 by blowing hot air 18 into the interstice. separating the first lateral border 2 from the second lateral border 2' before their superposition, as illustrated in figure 6. The objective being to soften beforehand the layers supposed to melt during the lateral weld, in particular the layers facing the outside of the tube skirt, in order to obtain a weld having a uniform appearance from the outside of the skirt. of tubing. The final result is similar to that of the first embodiment, and corresponds to that presented in figure 7. Figure 8 shows a tool suitable for implementing the manufacturing method as described above. This tool mainly relates to a cylindrical mandrel 30 extending longitudinally along an axis Y, and able to be fixed on a frame (not shown). This mandrel 30 consists of a first end section 31, an interior heating section 32, an interior cooling section 33, and a second end section 34. The flexible strip (not shown) is guided so as to wrap around the mandrel 30, and so that a first lateral edge of the strip comes to cover a second lateral edge of the strip, thus forming a zone of covering located in the upper part of the mandrel 30. The part of the device allowing the winding of the strip will not be described since it has been known and widely used for years. The zone of overlap of the tube skirt thus formed arrives first of all at the level of the interior heating section 32 of the mandrel 30, illustrated more precisely in FIG. 11. This section 32 comprises a groove 35 made in the upper part of the mandrel 30, in which is housed an insulating part 36 adapted to accommodate a heating part 37 which will be in contact with the internal face of the overlapping zone for the realization of the welding. lateral. The groove 35 has a parallelepipedal shape. The insulating piece 36 has a U-shape with its angular outer walls matching the shape of the groove 35 of the mandrel 30. The heating part 37 consists of a cylinder whose lower 38 and upper 39 parts include a flat allowing it respectively to be positioned correctly at the bottom of the insulating part 36 with a flat contact, and to present an upper flat surface 39 whose width L1 corresponds at least to that of the overlap zone. This heating part 37 thus positioned can heat the inner face of the overlap zone to the heating temperature T2, in order to produce the lateral weld. In parallel, a moving metal band (not shown) presses against the outer face of the overlap zone in order to compress the overlap zone and help the different layers that melt to mix and ensure that there is no longer any offset at the level of the overlap zone, that is to say that the outer surface of the tube skirt is linear over its entire circumference. This compression also makes it possible to ultimately reduce the thickness of the lateral weld. Optionally, an external heating means (not shown) located opposite the mandrel 30 can be provided on the device to heat the external face of the covering zone to the heating temperature T1. This heating means can be associated with the moving strip. When the lateral weld is made, the tube skirt, driven in particular via the movable metal strip, reaches the level of the central part of the mandrel 30 where rollers 40 are arranged having a conventional function of compression and forming of the tube skirt. at the overlapping area. Then the tube skirt reaches the cooling section 33 of the mandrel 30, shown in more detail in Figure 9. This section 33 also includes a groove 41 made at the level of the upper surface of the mandrel 30. This groove 41 forms a space parallelepiped hollow. Within this groove 41 is housed a cooling strip 42, also parallelepipedic in shape. The dimensions of the bar 42 and of the groove 41 coincide in order to ensure optimum positioning of one inside the other. The bar 42 is therefore fixed within the mandrel 30. This strip 42 comprises a flat upper wall 43 which is arranged and able to come directly into contact with the internal face of the overlap zone. The latter will therefore be cooled via this flat contact with the flat wall 43 of the strip 42. The cooling temperature is therefore regulated from the temperature measured on the surface of the flat wall 43. This upper wall 43 has a width L2 at the less as large as that of the overlap area in order to cool the entire side weld well. Under this flat wall 43, there is a channel 44 inside which a cooling fluid circulates. In the present example, this channel 44 has a crenellated shape, as illustrated in FIG. 10. Indeed, a plurality of fins 45 extend perpendicularly from the flat wall 43 of the bar 42 in the direction of the central axis Y of the mandrel. 30. These fins 45 form two longitudinal rows 46,47 developing along an axis parallel to the Y axis of the mandrel 30, and are staggered so as to form the castellation. The cooling fluid thus circulates between the fins 45, taking the crenellated path 44, as illustrated by the arrows. This path 44 forces the fluid to crisscross, and thus spend more time within the bar 42 in order to promote heat exchange. The fins 45 make it possible to increase the heat exchange surface between, on the one hand, the covering zone which is still hot following the welding, and, on the other hand, the cold coolant. By increasing the exchange surface in this way, the cooling performance is also increased. Thus, the length of the cooling section 33 of the mandrel 30 according to the invention can be greatly reduced while obtaining optimum cooling results compared to a cooling device without fins 45, and / or having a rectilinear cooling channel 44 . The mandrel 30 according to the invention therefore has the advantage of being compact. Preferably, the fins 45 consist of rectangular tabs. However, they could have other advantageous shapes. It is the same for the cooling channel 44 which can take other advantageous forms. During the cooling step, the overlap zone preferably continues to be compressed via the moving band.

Claims

Demands Flat strip 1, adapted to form a flexible tube skirt, comprising a decorative film 15 superimposed on a primary film 16, said primary film 16 consisting of a succession of layers of polymer material and comprising a sealable inner layer 14 at the lower surface 20 of the strip 1, said decorative film 15 comprising a sealable outer layer 7 at the upper surface 19 of the strip 1 and a decorative layer 8, 9, characterized in that the primary film 16 includes means for stabilizing the strip 1 and protecting the decorative layer 8,9 against heating. Flat strip 1 according to the preceding claim, characterized in that said stabilization and protection means consist of at least two stabilizing layers 1 1 13 made of ethylene vinyl alcohol (EVOH). Planar strip 1 according to the preceding claim, characterized in that the two stabilizing layers 11, 13 are arranged symmetrically with respect to the median plane X of the primary film 16 and at a distance from each other. Planar strip 1 according to one of the preceding claims, characterized in that the primary film 16 is a film composed of symmetrical layers and obtained by blowing. Flat strip 1 according to any one of the preceding claims, characterized in that said inner sealable layer 14 and said outer sealable layer 7 are made of medium-density polyethylene (MDPE). Flat strip 1 according to any one of the preceding claims, characterized in that the decorative layer 8,9 comprises polyethylene terephthalate (PET). Flat strip 1 according to one of the preceding claims, characterized in that the decorative layer 8,9 is provided with a metallized coating 8.

8. Flat strip 1 according to any one of the preceding claims, characterized in that the decorative layer 8,9 is located near the upper surface 19 of the strip 1.

9. Flat strip 1 according to any one of the preceding claims, characterized in that the decorative film 15 comprises an additional printed layer 6 extending over a part of the outer surface of the sealable outer layer 7.

10. Flat strip 1 according to the preceding claim, characterized in that it comprises a central zone 4 bordered by two lateral borders 2, 2', said additional printed layer 6 extending over the central zone 4 as well as over one of the two lateral borders 2, 2'.

1. A flat strip 1 according to the preceding claim, characterized in that the decorative film 15 comprises an additional protective layer 5 of the printed layer 6 extending over the entire outer surface of the printed layer 6.

12. A flexible tube skirt formed by rolling a flat strip 1 as described in the preceding claims and comprising an overlapping lateral weld, a first of said lateral edges 2 overlapping the second of said lateral edges 2'.

13. A flexible tube skirt according to the preceding claim, characterized in that the printed layer 6 extends over the central area 4 as well as over the first lateral edge 2.

14. Flexible tube skirt according to any one of claims 12 and 13, characterized in that the sealable inner layer 14 at the level of the first lateral border 2 is sealed to the sealable outer layer 14' at the level of the second lateral border 2'.

15. Flexible tube for storing and distributing liquid to pasty products characterized in that it is provided with a skirt according to any one of claims 12 to 14.