The subject of the present invention is a tubular element for the formation of impermeable and heat- sealable bags for the vacuum packaging of products, in particular of perishable food products.

Pre-manufactured elements for the above-mentioned use are known and are formed by one or two walls of synthetic material, sealed along longitudinal sides to form a continuous tube which can be formed into bags by transverse cutting and closure of the respective openings by welding.

Since up to now there are no known synthetic materials which are impermeable to gases and at the same time also heat-sealable and suitable for contact with foods, the walls are formed by two superimposed and closely connected layers, of which the outer layer is impermeable to gases and the inner layer is suitable for contact with foods and heat-sealable.

To prevent the walls from collapsing around the product during the evacuation of the bag, with the subsequent formation of isolated non-evacuated regions, the internal surface of at least one of the walls has

projections or protuberances which define escape channels along which the air is drawn out of the isolated regions.

However, this solution requires a greater usage of material, since the walls have a non-uniform thickness and their strength is determined principally by the weakest regions.

In EP 0216327, a bag is described in which the escape channels are formed by projections and grooves produced by shaping of the two layers together, or by embossing of the inner layer and subsequent connection of the two layers throughout their surfaces.

Both the shaping of the two layers together and the connection of a smooth layer and an embossed layer throughout their surfaces constitute operations which are difficult and therefore expensive, during which air inclusions may form between the two layers. After the evacuation of the bag, the included air diffuses through the inner layer and promotes deterioration of the product.

In EP 0648688 an alternative solution is described in which a plurality of parallel thread-like elements are associated with the inner side of a double-layered wall, the air-escape channels being defined between the thread-like elements.

However, the advantage of the double-layered walls, which are initially smooth and therefore inexpensive, is cancelled out by difficulties in positioning and fixing the thread-like elements to the surface. A thread-like element erroneously positioned transversely may create a barrier to the suction which renders the bag unserviceable.

In EP 0749912 a bag is described in which the thread-like elements are replaced by a perforated sheet which divides the bag into two chambers, of which one contains the product and the other constitutes a suction chamber. During the creation of the vacuum, the air passes from the chamber containing the product, through the perforations of the sheet, into the second chamber, and from there to the exterior.

In addition to the high suction resistance constituted by the perforated sheet, the system in EP 0749912 has the further disadvantage that, during evacuation, a portion of the product packaged, for example, meat juices, passes through the perforations, preventing complete evacuation and giving the package a soiled appearance.

In addition to the specific disadvantages of each of the solutions of the prior art described above, all of the known bags for the vacuum packaging of perishable

products, particularly food products, have the disadvantage that they cannot hold several different products. In fact, during the creation of the vacuum, the different products packaged together would contaminate one another, or the labels and the illustrative sheets inside the packages would be soiled, for example, by substances leaking from the product, particularly meat juices.

Finally, because of their pliability, the walls tend to bend under the effect of the vacuum, consequently closing the escape channels. All of the existing systems seek to prevent this problem by limiting the distance between the protuberances and by reinforcing the walls and the protuberances, which leads to excessive usage of material, but without achieving satisfactory results.

The object of the present invention is therefore to provide a system for the vacuum packaging of products which has characteristics such as to overcome the disadvantages mentioned with reference to the prior art.

This and other objects are achieved by means of a tubular element for the formation of bags according to Claim 1, as well as by a bag-produced by means of the tubular element.

For a better understanding of the invention, an

embodiment thereof will be described below by way of non-limiting example, with reference to the appended drawings, in which: Figure 1 shows, in section, a tubular element for forming a bag according to the invention.

Figure 2 is an enlarged view of the detail II of Figure 1, Figure 3 is a sectioned partial view of an embodiment of the invention, Figures 4a to 4e show possible embodiments of a portion of the tubular element, from above and in section, Figures 5 and 6 show further embodiments of the invention, in section, Figure 7 shows a possible method of evacuating and closing a bag produced by means of the tubular element of Figure 1, Figure 8 is a schematic view of the structural behaviour of a bag according to the invention and of a bag of the prior art, under the effect of the vacuum, Figure 9 is a schematic view of the exchanges of air enclosed in a bag according to the invention.

A tubular element, generally indicated 1, for forming bags for the packaging of products, is formed by two continuous sheets or strips which form walls 2 and a

continuous sheet or strip which forms a dividing sheet 3 interposed between the walls 2, the walls 2 and the dividing sheet 3 being connected along longitudinal sides 4, for example, by welding, to form a tubular body with two chambers 5 and 5'. According to the invention, each of the chambers 5 and 5'is at least partially delimited by the dividing sheet 3.

As can be seen from Figure 2, each wall 2 is constituted by an outer layer 6 of a material impermeable to gases, preferably polyester or polyamide, and an inner layer 7 of a heat-sealable material suitable for contact with foods, preferably polyethylene or polypropylene. The outer and inner layers 6 and 7 have uniform thicknesses and are connected to one another closely to form the walls 2, of which the inner surfaces 10 facing the chambers 5,5'and the outer surfaces 11 facing outwardly relative to the tubular body are advantageously flat and substantially smooth.

The dividing sheet 3, which is also made of heat- salable material suitable for contact with foods, comprises a continuous, substantially liquid-tight, central layer 12 from which projections 8 extend into both of the chambers 5 and 5'. The projections 8 can adhere to packaged products 17 and, together with regions 13 of the surfaces of the central layer 12,

define a system of suction channels 9.

The projections 8 are preferably arranged in a manner such that the regions 13 of one surface of the central layer 12 at least partially overlap the regions 13 of its other surface.

Figure 3 shows a very advantageous embodiment in which the positions of the projections 8 on the front of the dividing layer 3 correspond precisely to those of the projections 8 on its rear.

The projections 8 may have various shapes and may be arranged regularly or irregularly on the two surfaces of the dividing sheet 3 so as to define one or more systems of channels 9 that are continuous longitudinally relative to the tubular element and preferably but not necessarily communicating. Figure 4 shows examples of shapes and arrangements of the projections 8 which are particularly advantageous for rapid and direct suction of the air during the evacuation of the bag. In Figures 4a to 4c, the projections 8 are formed by elongate protuberances which extend continuously or discontinuously substantially parallel to the longitudinal sides 4. Figures 4d and 4e show embodiments in which the projections 8 are wart-shaped.

Figures 5 and 6 show further embodiments of the tubular element 1 which are distinguished substantially

by the number of chambers 5,5'formed within the tubular body as well as by the number of sheets or strips used to form the walls 2 and the dividing sheets 3.

Figure 5 shows a tubular element 1 which is advantageously produced by means of a single sheet for the wall 2 and in which the sheet has been superimposed on the dividing sheet 3, folded together therewith and, after alignment of the longitudinal sides 4, heat-sealed along these sides to form the tubular body.

The tubular element 1 shown in Figure 6 has been produced in similar manner with the use of four sheets or strips to form the walls 2 and a corresponding number of sheets to form the dividing sheets 3. The prefabricated elements 1 constituted by several sheets or strips both for the walls 2 and for the dividing sheets 3 permit the packaging of products 17 containing more than two separate parts, as well as the production of vacuum packages with external shapes and appearances that can be adapted to requirements for storage, distribution, and use.

In order to form bags 14 for the vacuum packaging of products, the tubular element 1 is cut to the desired length and closed transversely at a first end 15, preferably by heat sealing.

The functioning of a bag 14 produced by means of the tubular element 1 is described below with reference to Figures 7,8 and 9.

After the products 17 and/or information sheets have been placed inside the chambers 5, 5', a suction nozzle 16 is inserted in the opening formed by a second end 15'of the bag 14 so as simultaneously to reach all of the chambers 5, 5'. During the suction of the air, the pressure inside the chambers 5,5'falls below the pressure outside the bag 14, leading to deformation of the walls 2 towards the interior of the chambers 5,5'.

In the systems of the prior art, this deformation leads to partial or, in extreme cases, even total closure of the suction channels, as can be seen, for example, from Figure 8a, resulting in incomplete evacuation of the bag. In the bag 14 according to the invention, both sides of the dividing sheet 3 are under vacuum and, by virtue of the shape and arrangement of the projections 8, a reduction in pressure on one side of the sheet 3 leads to a deformation of the regions 13 such that the channels 9 on the other side are opened further, and vice versa, as can be seen from Figure 8b. After the evacuation of the bag 14, it is closed, preferably by heat sealing along the second end 15'.

Figure 9 shows the situation in an evacuated and heat-sealed bag 14 according to the invention, in which only a first chamber 5 has been used to hold products 17. By virtue of the easy and direct evacuation of the second chamber 5', it tends to have a pressure even lower than the pressure of the first chamber 5, leading to an effect of secondary evacuation of the air residues in the first chamber 5 by diffusion through the dividing sheet 3.

The tubular element 1 and the bag 14 according to the invention have many advantages.

The bag 14 can hold several different products 17 without the risk of transfer of substances from one product to another. The external walls are flat and of uniform thickness and therefore have the maximum strength, for a given material used. The formation of escape channels is functionally separate from the function of containment and protection from the outside environment, with the result that both the materials and the shape of the walls 2 and of the dividing sheet 3 can be optimized. Collapse of the walls of the suction channels 9 during the evacuation of the bag 14 is prevented by the pneumatic stabilization of the regions 13 of the channels 9. If some of the chambers 5,5' adjacent a dividing sheet 3 are not used for holding

products 17, the empty chamber or chambers form secondary evacuation chambers during the period of storage of the vacuum package.

Naturally, in order to satisfy contingent and specific requirements, a person skilled in the art may apply to the structural element 1 according to the present invention further modifications and variations all of which, however, are included within the scope of protection of the invention as defined by the appended claims.